CN111611671B - Calibration method, device and system for CFD model in cylinder of vehicle engine and readable storage medium - Google Patents
Calibration method, device and system for CFD model in cylinder of vehicle engine and readable storage medium Download PDFInfo
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- CN111611671B CN111611671B CN201910136591.8A CN201910136591A CN111611671B CN 111611671 B CN111611671 B CN 111611671B CN 201910136591 A CN201910136591 A CN 201910136591A CN 111611671 B CN111611671 B CN 111611671B
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Abstract
The invention discloses a method, a device and a system for calibrating a CFD model in a cylinder of a vehicle engine and a readable storage medium, wherein the calibration method comprises the following steps: determining the tumble center of a planar flow field of a plurality of different in-cylinder characteristic planes of the vehicle optical engine under at least one preset crank angle; correspondingly calculating the tumble ratio of each planar flow field under each preset crank angle according to the tumble center of each planar flow field under at least one preset crank angle; averaging the tumble ratios of all the plane flow fields under each preset crank angle to obtain the average tumble ratio under each preset crank angle; and adjusting model parameters of the in-cylinder CFD model according to the average tumble ratio under each preset crank angle and the pre-calculated model tumble ratio under at least one preset crank angle after the in-cylinder CFD model of the vehicle engine is set as the first experimental working condition. The method can improve the accuracy of the CFD model in the cylinder.
Description
Technical Field
The invention relates to the technical field of engines, in particular to a method, a device and a system for calibrating a CFD (computational fluid dynamics) model in a cylinder of a vehicle engine and a readable storage medium.
Background
The tumble ratio of a vehicle engine (such as a gasoline engine or a diesel engine and the like) plays a crucial role in the airflow movement, the oil-gas mixing and the combustion emission of a vehicle engine cylinder, and under the premise of ensuring a sufficient flow coefficient, the tumble strength is increased as much as possible, so that the combustion stability and the economy of the vehicle engine can be greatly improved. Therefore, when designing the engine of the vehicle, the tumble ratio is an important design index.
At present, when a vehicle engine is designed, a Computational Fluid Dynamics (CFD) software is generally used for constructing an in-cylinder CFD model of the engine, then the in-cylinder CFD model is used for simulation, working conditions such as a flow field and the like of the vehicle engine during working are simulated and analyzed, and finally the design of the cylinder of the vehicle engine is guided by using an analyzed result and various model working parameters (such as turbulent flow dissipation or initial turbulent kinetic energy and the like) of the in-cylinder CFD model, so that the designed vehicle engine is ensured to have good working performance. However, when the in-cylinder CFD model of the vehicle engine is constructed at present, it cannot be well ensured that the tumble ratio of the in-cylinder CFD model can actually reflect the actual tumble ratio of the vehicle engine, so that the in-cylinder CFD model is not accurate enough, and the combustion stability and the economy of the vehicle engine designed according to the in-cylinder CFD model are affected.
Disclosure of Invention
In view of this, embodiments of the present invention provide a calibration method, device, system and readable storage medium for a CFD model in a cylinder of a vehicle engine, which can ensure that a roll flow ratio of the CFD model in the cylinder of the vehicle engine can actually reflect an actual roll flow ratio of the vehicle engine, and provide accuracy of the CFD model in the cylinder of the vehicle engine, so as to improve combustion stability and economy of the designed vehicle engine.
An embodiment of the invention provides a calibration method for a vehicle engine in-cylinder CFD model, which comprises the following steps:
determining the tumble center of a plane flow field of a plurality of different in-cylinder characteristic planes of the vehicle optical engine under at least one preset crank angle; the plane flow field is obtained by pre-measuring under a preset first experiment working condition;
correspondingly calculating the tumble ratio of each planar flow field under each preset crank angle according to the tumble center of each planar flow field under at least one preset crank angle;
averaging the tumble ratios of all the planar flow fields under each preset crank angle to obtain an average tumble ratio under each preset crank angle;
adjusting model parameters of the in-cylinder CFD model according to the average tumble ratio under each preset crank angle and a model tumble ratio pre-calculated by the in-cylinder CFD model of the vehicle engine under at least one preset crank angle after being set as the first experimental working condition so that the adjusted in-cylinder CFD model meets a preset condition:
and the absolute value of the difference value between the model tumble ratio recalculated under the preset second experiment working condition and the average tumble ratio calculated under the same experiment working condition and the same crank angle is smaller than a preset threshold value.
As an improvement of the above solution, the determining a tumble center of a planar flow field of each of a plurality of different in-cylinder feature planes of the vehicle optical engine at least one preset crank angle specifically includes:
determining in-cylinder airflow simulation centroid coordinates of an in-cylinder CFD model of a vehicle engine at least one preset crank angle after being set to the first experimental operating condition;
and correspondingly determining the tumble centers of the plane flow fields of a plurality of different in-cylinder characteristic planes of the vehicle optical engine under at least one preset crank angle according to the in-cylinder airflow simulation mass center coordinates under at least one preset crank angle.
As an improvement of the above solution, the model parameters include at least one of: turbulence dissipation, initial turbulence energy, and cylinder wall temperature.
As an improvement of the above, the vehicle optical engine includes a cylinder which is a transparent cylinder block; then, a plurality of the in-cylinder feature planes includes at least: an in-cylinder plane passing through a center of a cylinder of the cylinder and an in-cylinder plane passing through a center of an intake valve of the cylinder.
As an improvement of the above scheme, the top of the cylinder is provided with two air inlet valves, namely a first air inlet valve and a second air inlet valve, and the plurality of in-cylinder characteristic planes comprise: the cylinder inner plane of the center of the first air inlet valve, the cylinder inner plane of the cylinder between the side wall of the cylinder close to the first air inlet valve and the first air inlet valve, the cylinder inner plane of the center of the first air inlet valve and the cylinder, the cylinder inner plane of the center of the second air inlet valve, the cylinder inner plane of the cylinder between the side wall of the cylinder close to the second air inlet valve and the second air inlet valve, and the cylinder inner plane of the center of the second air inlet valve and the cylinder;
and the cylinder inner plane passing through the center of the cylinder is positioned between the cylinder inner plane passing through the center of the first air inlet valve and the cylinder inner plane passing through the center of the second air inlet valve.
The invention correspondingly provides a calibration device of a CFD model in a vehicle engine cylinder, which comprises:
the system comprises a tumble center determining module, a tumble center determining module and a control module, wherein the tumble center determining module is used for determining the tumble centers of plane flow fields of a plurality of different in-cylinder characteristic planes of the vehicle optical engine under at least one preset crank angle; the plane flow field is obtained by pre-measuring under a preset first experiment working condition;
the tumble ratio calculation module is used for correspondingly calculating the tumble ratio of each planar flow field under each preset crank angle according to the tumble center of each planar flow field under at least one preset crank angle;
the average tumble ratio calculation module is used for averaging the tumble ratios of all the planar flow fields under each preset crank angle to obtain the average tumble ratio under each preset crank angle;
a model adjustment module to: adjusting model parameters of the in-cylinder CFD model according to the average tumble ratio under each preset crank angle and a model tumble ratio pre-calculated by the in-cylinder CFD model of the vehicle engine under at least one preset crank angle after being set as the first experimental working condition so that the adjusted in-cylinder CFD model meets a preset condition:
and the absolute value of the difference value between the model tumble ratio recalculated under the second preset experimental working condition and the average tumble ratio calculated under the same experimental working condition and the same crank angle is smaller than a preset threshold value.
As an improvement of the above, the tumble center determining module includes:
the first determining unit is used for determining in-cylinder airflow simulation mass center coordinates of an in-cylinder CFD model of a vehicle engine under at least one preset crank angle after the in-cylinder CFD model is set to be under the first experimental working condition;
and the second determining unit is used for correspondingly determining the tumble centers of the plane flow fields of a plurality of different in-cylinder characteristic planes of the vehicle optical engine under at least one preset crank angle according to the in-cylinder airflow simulation mass center coordinate under at least one preset crank angle.
Another embodiment of the invention provides a calibration system for a vehicle engine in-cylinder CFD model, comprising an optical engine system with a vehicle optical engine, a PIV test system and a calibration device;
the PIV testing system is used for testing and obtaining a plane flow field image of each of a plurality of different in-cylinder characteristic planes of the vehicle optical engine under at least one preset crank angle, and sending the plane flow field image to the calibration equipment so that the calibration equipment can obtain a corresponding plane flow field according to the plane flow field image;
the calibration apparatus includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, and the processor, when executing the computer program, implements the calibration method of the CFD model in the cylinder of the vehicle engine according to the embodiment of the invention.
As an improvement of the above solution, the PIV test system includes:
the laser emitter is used for emitting a sheet-shaped laser beam into a cylinder of the vehicle optical engine so as to form a laser beam plane in the cylinder of the vehicle optical engine;
the particle generator is used for generating trace particles and inputting the trace particles into a cylinder of the vehicle optical engine;
the CMOS camera is used for imaging the area in the cylinder where the laser beam plane is located, imaging the area into a plane flow field image and sending the plane flow field image to the calibration equipment; and a process for the preparation of a coating,
and the synchronizer is used for synchronizing the work of the laser transmitter, the particle generator and the CMOS camera.
Another embodiment of the present invention provides a storage medium, which includes a stored computer program, where when the computer program runs, the apparatus in the computer readable storage medium is controlled to execute the method for calibrating the CFD model in the cylinder of the vehicle engine according to the embodiment of the present invention.
Compared with the prior art, in some embodiments provided by the invention, the optical engine technology is introduced to analyze the actual flow field of the vehicle engine during working, wherein the vehicle optical engine and the in-cylinder CFD model of the vehicle engine are set as a first experimental working condition, and the planar flow field of each of a plurality of different in-cylinder feature planes of the vehicle optical engine under at least one preset crank angle is measured, and the planar flow field of the plurality of different in-cylinder feature planes can accurately reflect the actual flow field of the vehicle optical engine during working (i.e. can accurately reflect the actual flow field of the vehicle engine during working); then, determining the rolling flow centers of the planar flow fields, and correspondingly calculating the rolling flow ratios of the planar flow fields according to the rolling flow centers of the planar flow fields; then, averaging the tumble ratios of all the planar flow fields under each preset crank angle to obtain an average tumble ratio under each preset crank angle, wherein the average tumble ratio can accurately reflect the actual tumble ratio of the actual flow field when the vehicle optical engine works; finally, according to the average tumble ratio under each preset crank angle and the model tumble ratio calculated by the CFD model under at least one preset crank angle, adjusting the model parameters of the in-cylinder CFD model so that the adjusted in-cylinder CFD model meets the following requirements: and the absolute value of the difference value between the recalculated model tumble ratio and the calculated average tumble ratio under the same experiment working condition and the same crank angle is smaller than a preset threshold value. From the above analysis, it can be seen that in some embodiments provided by the present invention, the roll flow ratio of the in-cylinder CFD model is calibrated by using the roll flow ratio of the in-cylinder flow field of the optical engine of the vehicle, so that the roll flow ratio of the in-cylinder CFD model can actually reflect the actual roll flow ratio of the engine of the vehicle, and thus the accuracy of the in-cylinder CFD model of the engine of the vehicle is improved, and therefore the design of the engine of the vehicle can be better guided, so that the combustion stability and the economy of the designed engine of the vehicle can be finally improved.
Drawings
FIG. 1 is a schematic flow chart of a method for calibrating a CFD model in a cylinder of a vehicle engine according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a method for calibrating a CFD model in a cylinder of a vehicle engine according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a calibration system for a CFD model in a cylinder of a vehicle engine according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a test of an optical engine system provided by one embodiment of the present invention;
FIG. 5 is a top schematic view of a cylinder of a vehicle optical engine provided in accordance with an embodiment of the present invention;
FIG. 6 is a schematic plan flow field of a tested in-cylinder feature plane provided by one embodiment of the present invention;
FIG. 7 is a comparison test chart of a tumble ratio simulation value and an actual measurement value of an in-cylinder CFD model provided by an embodiment of the present invention;
fig. 8 is a schematic structural diagram of a calibration apparatus for a CFD model in a cylinder of a vehicle engine according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive step based on the embodiments of the present invention, are within the scope of protection of the present invention.
Referring to fig. 1, a flowchart of a calibration method for a CFD model in a cylinder of a vehicle engine according to an embodiment of the present invention is shown.
In the embodiment of the present invention, the calibration method may be automatically performed by a calibration device 4, so as to automate the working process of the whole calibration method. In this embodiment, the calibration device 4 may be a computer, a mobile phone, a tablet, or even a cloud server. The calibration device 4 may be implemented by software and/or hardware, and the calibration device 4 may be formed by two or more physical entities or may be formed by one physical entity. In this embodiment, the calibration device 4 is preferably a computer.
Preferably, with reference to fig. 3, the calibration device 4 is part of a calibration system of a CFD model in a cylinder of a vehicle engine, which may comprise: an optical engine system 3 with a vehicle optical engine 30, a PIV test system 2 and a calibration device 4; the PIV testing system 2 is configured to obtain a planar flow field image of each of a plurality of different in-cylinder feature planes of the vehicle optical engine 30 at least one preset crank angle through testing, and send the planar flow field image to the calibration device 4, so that the calibration device 4 obtains a corresponding planar flow field according to the planar flow field image. Of course, the PIV testing system 2 may also send the planar flow field pattern to another image processing apparatus (e.g., an image server, etc.) to be processed into the planar flow field, and then the planar flow field pattern is sent to the calibration device 4 by the image processing apparatus.
The optical engine is widely applied to the field of design of vehicle engines (such as gasoline engines or diesel engines), can cover all working processes of air intake, spraying, mixing, combustion and the like, and can research the in-cylinder airflow movement, spray droplet velocity field, droplet diameter distribution, mixed gas concentration distribution, flame propagation, in-cylinder combustible gas temperature field distribution and harmful emission generation of the vehicle engines by means of various non-contact optical methods with high space-time resolution and high accuracy. The combination of optical engines with PIV technology provides a good tool for observing in-cylinder flow fields of vehicle engines. In the embodiment, by introducing the optical engine technology, the working parameters such as the actual flow field and the like of the vehicle engine during working can be accurately analyzed, so that the method has important reference value for guiding the design of the vehicle engine.
Illustratively, referring to fig. 3 and 4, the PIV testing system 2 includes: a laser emitter 20, a particle generator 21, a CMOS camera 22, and a synchronizer 23; wherein a laser transmitter 20, preferably a high frequency dual chamber laser transmitter 20, is used to emit a sheet-like laser beam 24 into the cylinder of the vehicle optical engine 30 to form a laser beam plane in the cylinder of the optical engine; a particle generator 21 for generating trace particles and inputting them into a cylinder of the vehicle optical engine 30; the CMOS camera 22 is used for imaging the area in the cylinder where the laser beam plane is located, imaging the area into a plane flow field image and sending the plane flow field image to the calibration equipment 4; a synchronizer 23 for synchronizing operations of the laser emitter 20, the particle generator 21 and the CMOS camera 22.
Referring to fig. 4, the vehicle optical engine 30 has an air inlet pipe 306, an air outlet pipe 307, an upper cylinder 301, a lower cylinder 302, and a cylinder 300 that is a transparent cylinder (of course, the cylinder 300 may also be opaque as long as it can let laser light pass through and its interior can be photographed by a camera, for example, infrared light can pass through and its interior can be photographed by an infrared camera), when an in-cylinder CFD model of the vehicle engine needs to be calibrated, a planar flow field image of each of a plurality of different in-cylinder characteristic planes of the vehicle optical engine 30 at least one preset crank angle is firstly measured by the PIV system, specifically: when the crankshaft of the vehicle optical engine 30 is detected to be rotated to a preset crank angle, the laser generator emits a sheet-shaped laser beam 24 into the cylinder of the transparent cylinder body of the vehicle optical engine 30 to form a laser beam plane in the cylinder of the vehicle optical engine 30 (the laser beam plane is emitted in a direction marked in advance in the cylinder, so that the laser beam plane formed in the cylinder can be regarded as an in-cylinder characteristic plane described below); in this process, the particle generator generates trace particles and inputs the trace particles into the cylinder of the vehicle optical engine 30, so that when the vehicle optical engine 30 is in operation, the flow field of the air flow in the cylinder can be displayed through the motion track of the trace particles in the laser beam plane; in the process, the CMOS camera 22 will image the in-cylinder area where the laser beam plane is located, so as to form the planar flow field image and send the planar flow field image to the calibration device 4; specifically, the shooting direction of the CMOS camera 22 will be perpendicular to the laser beam plane.
Preferably, the laser energy of the laser transmitter 20 is not less than 22.5mJ, the transmitting frequency is not less than 1000Hz, the pixel of the CMOS camera 22 is not less than 100 ten thousand, and the shooting frequency is not less than 20Hz.
It should be noted that the PIV testing system 2 may also be other schemes, for example, the PIV testing system 2 may include a laser emitter 20, a particle generator 21, a CCD camera (not shown), a synchronizer 23, and the like. The PIV test system 2 may be controlled by the calibration device 4, or may be controlled by another control system, which is not limited in this regard.
It will be appreciated that the calibration system may also include a companion system 31 for the vehicle optical engine 30, and that the companion system 31 may include, for example: an ac electric dynamometer (not shown) for measuring the power of the vehicle optical engine 30, a simulated supercharging system (not shown) for supercharging the vehicle optical engine 30, a goniometer kit (not shown) for measuring the rotation angle of the crankshaft of the vehicle optical engine 30, a test stand automatic control system (not shown) for controlling the experimental work of the entire supporting system, and the like.
Referring to fig. 1, specifically, the calibration method of the CFD model in the cylinder of the vehicle engine includes steps S10 to S13:
s10, determining the tumble center of a plane flow field of a plurality of different in-cylinder characteristic planes of the vehicle optical engine 30 under at least one preset crank angle;
before this step, referring to fig. 2, the model of the vehicle engine is determined, the vehicle optical engine 30 is then allowed to operate under a first preset experimental condition, and then a plurality of different in-cylinder feature planes of the vehicle optical engine 30 are marked or set in advance, the in-cylinder feature planes are distributed at different positions in a transparent cylinder body of the vehicle optical engine 30, and preferably, the edges of the in-cylinder feature planes are in contact with the inner wall surface of the transparent cylinder 300, so that the areas of the in-cylinder feature planes are as large as possible, that is: these in-cylinder feature planes can be visually considered as a profile or cross-section of the cylinder 300. Then, when the crankshaft of the vehicle optical engine 30 is operated to a preset crankshaft angle, the above-mentioned PIV system test is used to obtain a planar flow field image of each in-cylinder feature plane, and then the planar flow field image is sent to the calibration device 4; and the calibration device 4 calculates and analyzes the planar flow field image according to the planar flow field image and flow field analysis algorithms such as autocorrelation or cross correlation to obtain the planar flow field of each in-cylinder feature plane under the current preset crank angle. Moreover, the planar flow fields of the plurality of different in-cylinder feature planes can more accurately reflect the actual flow field of the vehicle optical engine 30 during operation (i.e., can more accurately reflect the actual flow field of the vehicle engine during operation). In the present embodiment, the planar flow field of the above-described in-cylinder feature plane is exemplarily tested every crank angle of 5 ° CA. Preferably, the number of tests of the planar flow field of each in-cylinder feature plane may be multiple times (for example, not less than 10 times), and then the average value is taken as the planar flow field of the in-cylinder feature plane.
Preferably, in order to enable the planar flow field of a plurality of different in-cylinder feature planes to more accurately reflect the actual flow field of the vehicle optical engine 30 during operation, a plurality of the in-cylinder feature planes may at least include: a cylinder inner plane passing through the center of the cylinder (i.e., the cylinder inner plane passes through the center of the cylinder and is located at the center in the cylinder) and a cylinder inner plane passing through the center of the intake valve of the cylinder (i.e., the cylinder inner plane passes through the center of the intake valve and may be parallel to the cylinder inner plane passing through the center of the cylinder). Because, for the cylinder 300, the flow field of the in-cylinder plane passing through the center of the cylinder 300 is relatively regular, it has representativeness and typicalness of the in-cylinder flow field; the maximum airflow velocity at the position of the inlet valve in the cylinder has obvious influence on the airflow field in the cylinder, so that the airflow field in the area near the inlet valve in the cylinder needs to be analyzed, and the planar flow fields of the two planes in the cylinder can be selected for analysis. Therefore, the planar flow field of the two in-cylinder planes is selected, so that the actual flow field of the vehicle optical engine 30 during operation can be reflected more accurately.
More preferably, referring to fig. 5, when the cylinder 300 has two intake valves at the top, a first intake valve 303 and a second intake valve 304, then the plurality of in-cylinder characteristic planes include: cylinder inner plane 91 of the center of the first intake valve, cylinder inner plane 90 between the side wall of the cylinder close to the first intake valve and the first intake valve, cylinder inner plane 92 between the first intake valve and the center of the cylinder, cylinder inner plane 93 through the center of the cylinder, cylinder inner plane 95 of the center of the second intake valve, cylinder inner plane 96 between the side wall of the cylinder close to the second intake valve and the second intake valve, and cylinder inner plane 94 between the second intake valve and the center of the cylinder; the cylinder inner plane 93 passing through the center of the cylinder is located between the cylinder inner plane 91 passing through the center of the first intake valve and the cylinder inner plane 95 passing through the center of the second intake valve, and the cylinder inner characteristic planes are parallel to each other. Wherein, the seven dotted lines denoted by reference numerals 90-96 in fig. 5 can be approximately seen as: the seven hatching lines of the cylinder 300, and the cylinder area of the cylinder cross section cut by the seven hatching lines can be seen as the seven characteristic planes. By selecting the seven in-cylinder characteristic planes, the actual flow field of the vehicle optical engine 30 during operation can be reflected more accurately, and the measurement time is not too long. It should be noted that the number of in-cylinder feature planes may also be greater, and in general, a greater number will result in more accurate measurement results, but will also result in longer measurement times.
Referring to fig. 6, when the planar flow field of the in-cylinder feature planes is obtained through testing, the calibration device 4 may determine the tumble centers of the planar flow fields of the in-cylinder feature planes at least at a predetermined crank angle.
S11, correspondingly calculating the tumble ratio of each planar flow field under each preset crank angle according to the tumble center of each planar flow field under at least one preset crank angle;
when the tumble center of each planar flow field under each preset crank angle is obtained, the tumble ratio of each planar flow field under each preset crank angle is correspondingly calculated. For example, the formula for calculating the tumble ratio of the planar flow field may be:
wherein, ω is crankshaft Expressed as the angular velocity of rotation, ω, of the crankshaft of the vehicle optical engine 30 FK Expressed as the angular velocity of the planar flow field about the axis of rotation. Omega FK The calculation formula of (c) may be:
wherein, ω is i Is the rotation angular velocity r of the ith in-cylinder grid in the plane flow field relative to the tumble center of the plane flow field i Is the distance between the ith in-cylinder grid in the planar flow field and the tumble center of the planar flow field, f i Is the area of the i-th in-cylinder grid in the planar flow field. The cylinder of the cylinder 300 is artificially divided into a plurality of in-cylinder grids with the same size in advance, the in-cylinder feature plane where the planar flow field is located may also be divided into a plurality of in-cylinder grids with the same size, and the size of the in-cylinder grids may be preferably set to 1 × 1mm.
It should be noted that, the calculation of the tumble ratio of the planar flow field may also refer to other existing calculation methods, and is not limited herein.
S12, averaging the tumble ratios of all the planar flow fields under each preset crank angle to obtain an average tumble ratio under each preset crank angle;
the average tumble ratio may relatively accurately reflect the tumble ratio of the in-cylinder flow field of the vehicle optical engine 30.
S13, according to the average tumble ratio under each preset crank angle and according to a model tumble ratio which is pre-calculated by an in-cylinder CFD model of a vehicle engine under at least one preset crank angle after being set as the first experiment working condition, adjusting model parameters of the in-cylinder CFD model so that the adjusted in-cylinder CFD model meets a preset condition: and the absolute value of the difference value between the model tumble ratio recalculated under the second preset experimental working condition and the average tumble ratio calculated under the same experimental working condition and the same crank angle is smaller than a preset threshold value.
Specifically, referring to fig. 2, when the average tumble ratio at each preset crank angle is obtained and the model tumble ratio of the in-cylinder CFD model at least one preset crank angle is obtained, the average tumble ratio and the model tumble ratio may be compared and verified, referring to fig. 7, if the absolute value of the difference between the two values is smaller than a preset threshold (i.e. the difference between the two values is not large) at each preset crank angle, the model tumble ratio representing the in-cylinder CFD model may actually reflect the actual tumble ratio of the vehicle engine, and the CFD model is relatively accurate. And if the absolute value of the difference between the two values is larger than the preset threshold value (namely, the two values are greatly different) at each preset crank angle, the model tumble ratio of the in-cylinder CFD model does not actually reflect the actual tumble ratio of the vehicle engine, and the CFD model is inaccurate. At this time, the model parameters of the in-cylinder CFD model are adjusted according to the two tumble ratios, so that the adjusted in-cylinder CFD model meets the preset condition.
Illustratively, the model parameters include at least one of: turbulent dissipation, initial turbulent energy, and cylinder 300 wall temperature.
For example, the calculation formula of the model tumble ratio may be:
wherein, ω is 1 Expressed as angular velocity, ω, of the in-cylinder air flow rotating about the in-cylinder X-axis crankshaft Represented as the rotational angular velocity of the crankshaft of the vehicle optical engine 30. The in-cylinder X-axis is defined as: a straight line perpendicular to the in-cylinder plane passing through the center of the intake valve of the cylinder 300 and passing through the center of mass in the cylinder.
It should be noted that the operating condition parameters (such as the rotation speed, the intake pressure, the intake temperature, the intake flow rate, the intake/exhaust VVT, and the like) of the second experimental operating condition and the first experimental operating condition may be the same or different. In addition, the process of adjusting the in-cylinder CFD model may be one-step, or may be adjusted and optimized repeatedly for multiple times, which is not limited herein.
To sum up, in the embodiment of the present invention, the optical engine technology is introduced to analyze the actual flow field of the vehicle engine during operation, wherein the vehicle optical engine 30 and the in-cylinder CFD model of the vehicle engine are first set as the first experimental operating condition, and the planar flow field of each of the plurality of different in-cylinder feature planes of the vehicle optical engine 30 under at least one preset crank angle is measured, and the planar flow field of the plurality of different in-cylinder feature planes can more accurately reflect the actual flow field of the vehicle optical engine 30 during operation (i.e. can more accurately reflect the actual flow field of the vehicle engine during operation); then, determining the rolling flow centers of the planar flow fields, and correspondingly calculating the rolling flow ratios of the planar flow fields according to the rolling flow centers of the planar flow fields; then, averaging the tumble ratios of all the planar flow fields at each preset crank angle to obtain an average tumble ratio at each preset crank angle, wherein the average tumble ratio can more accurately reflect the actual tumble ratio of the actual flow field when the vehicle optical engine 30 works; finally, according to the average tumble ratio under each preset crank angle and the model tumble ratio calculated by the CFD model under at least one preset crank angle, adjusting the model parameters of the in-cylinder CFD model so that the adjusted in-cylinder CFD model meets the following requirements: and the absolute value of the difference value between the recalculated model tumble ratio and the calculated average tumble ratio under the same experimental working condition and the same crank angle is smaller than a preset threshold value. From the above analysis, it can be known that, by calibrating the model tumble ratio of the in-cylinder CFD model by using the tumble ratio of the in-cylinder flow field of the vehicle optical engine 30, it can be ensured that the tumble ratio of the in-cylinder CFD model can actually reflect the actual tumble ratio of the vehicle engine, so that the accuracy of the in-cylinder CFD model of the vehicle engine is improved, and therefore the design of the vehicle engine can be better guided, and finally the combustion stability and economy of the designed vehicle engine can be improved.
The turbulence dissipation, initial turbulence energy and wall temperature of the in-cylinder CFD model obtained by using the above calibration method may be: 200m2/s3, 0.8m2/s2, 900K. The turbulence dissipation, initial turbulence energy, and wall temperature of the CFD model in the cylinder without calibration are: 120m2/s3, 1m2/s2, 800K. Therefore, the engine in-cylinder simulation flow and combustion results of the calibrated in-cylinder CFD model are more accurate.
As another modified solution of the present invention, exemplarily, the step S10 specifically includes the steps S100 to S101:
s100, determining in-cylinder airflow simulation mass center coordinates of a vehicle engine under at least one preset crank angle after an in-cylinder CFD model is set as the first experimental working condition;
for example, the in-cylinder air flow simulation centroid (equivalent to the CFD simulation centroid in fig. 6) coordinate determination process may be:
the in-cylinder airflow particles of the in-cylinder CFD model are composed of n airflow particles, wherein the n airflow particles are respectively the geometric centers of CFD computational grids (namely the in-cylinder of the in-cylinder CFD model is divided into n grids), and the mass of each airflow particle is m 1 ，m 2 ，…，m n . If use r 1 ，r 2 ，…，r n The radial diameters of the airflow particles in the airflow particle system relative to a certain set fixed point O (x, y, z) are respectively expressed
And (4) showing. Radius of the center of mass:
If it is
The in-cylinder air flow simulation centroid coordinate is (x) cm ，y cm ，z cm )，
Wherein x is cm ＝x+x σ ，y m ＝y+y σ ，z cm ＝z+z σ 。
S101, correspondingly determining a tumble center of a planar flow field of each of a plurality of different in-cylinder feature planes of the vehicle optical engine 30 at least one preset crank angle according to the in-cylinder airflow simulation centroid coordinate at the at least one preset crank angle.
When the in-cylinder airflow simulation centroid coordinate under each preset crank angle is determined, the in-cylinder airflow simulation centroid coordinate is converted into the corresponding plane flow field, so that the tumble flow center (corresponding to the CFD simulation centroid corresponding point in fig. 6) of the plane flow field of each in-cylinder feature plane under at least one preset crank angle is obtained.
It should be noted that the determination of the tumble center of the planar flow field may also be in other manners, for example, may be in the existing determination manner: when determining the tumble center of the planar flow field, the velocity field of the planar flow field without the obvious vortex center needs to be removed, the instantaneous flow field with the obvious vortex center is subjected to low-pass filtering, the preliminary judgment and vortex matching processing are carried out on the area with the vortex center in a 'prejudgment-correction' mode, and the minimum velocity is selected from the screened grid points to serve as the tumble center. However, the existing determination method is troublesome in operation, the result randomness is high, and the measurement result is unstable.
Referring to fig. 8, a schematic structural diagram of a calibration apparatus for a CFD model in a cylinder of a vehicle engine according to an embodiment of the present invention is shown, including:
the tumble center determining module 10 is configured to determine a tumble center of a planar flow field of a plurality of different in-cylinder feature planes of the vehicle optical engine 30 at least one preset crank angle; the plane flow field is obtained by pre-measuring under a preset first experiment working condition;
a tumble ratio calculation module 11, configured to correspondingly calculate a tumble ratio of each planar flow field under each preset crank angle according to the tumble center of each planar flow field under at least one preset crank angle;
the average tumble ratio calculation module 12 is configured to average the tumble ratios of all the planar flow fields at each preset crank angle to obtain an average tumble ratio at each preset crank angle;
a model adjustment module 13 for: adjusting model parameters of the in-cylinder CFD model according to the average tumble ratio under each preset crank angle and a model tumble ratio pre-calculated by the in-cylinder CFD model of the vehicle engine under at least one preset crank angle after being set as the first experimental working condition so that the adjusted in-cylinder CFD model meets a preset condition:
and the absolute value of the difference value between the model tumble ratio recalculated under the preset second experiment working condition and the average tumble ratio calculated under the same experiment working condition and the same crank angle is smaller than a preset threshold value.
As an improvement of the above, the tumble center determining module 10 includes:
the first determining unit is used for determining in-cylinder airflow simulation mass center coordinates of an in-cylinder CFD model of a vehicle engine under at least one preset crank angle after the in-cylinder CFD model is set to be under the first experimental working condition;
and a second determining unit, configured to correspondingly determine, according to the in-cylinder airflow simulation centroid coordinate at least one preset crank angle, a tumble center of a planar flow field of each of a plurality of different in-cylinder feature planes of the vehicle optical engine 30 at the at least one preset crank angle.
In the embodiment of the present invention, the optical engine technology is introduced to analyze the actual flow field of the vehicle engine during operation, wherein the vehicle optical engine 30 and the in-cylinder CFD model of the vehicle engine are first set as a first experimental condition, and a planar flow field of each of a plurality of different in-cylinder feature planes of the vehicle optical engine 30 under at least one preset crank angle is measured, and the planar flow field of the plurality of different in-cylinder feature planes can more accurately reflect the actual flow field of the vehicle optical engine 30 during operation (i.e., can more accurately reflect the actual flow field of the vehicle engine during operation); then, determining the rolling flow centers of the planar flow fields, and correspondingly calculating the rolling flow ratios of the planar flow fields according to the rolling flow centers of the planar flow fields; then, averaging the tumble ratios of all the planar flow fields at each preset crank angle to obtain an average tumble ratio at each preset crank angle, wherein the average tumble ratio can more accurately reflect the actual tumble ratio of the actual flow field when the vehicle optical engine 30 works; finally, according to the average tumble ratio under each preset crank angle and the model tumble ratio calculated by the CFD model under at least one preset crank angle, adjusting the model parameters of the in-cylinder CFD model so that the adjusted in-cylinder CFD model meets the following requirements: and the absolute value of the difference value between the recalculated model tumble ratio and the calculated average tumble ratio under the same experimental working condition and the same crank angle is smaller than a preset threshold value. From the above analysis, it can be known that, by calibrating the model tumble ratio of the in-cylinder CFD model by using the tumble ratio of the in-cylinder flow field of the vehicle optical engine 30, it can be ensured that the tumble ratio of the in-cylinder CFD model can actually reflect the actual tumble ratio of the vehicle engine, so that the accuracy of the in-cylinder CFD model of the vehicle engine is improved, and therefore the design of the vehicle engine can be better guided, and finally the combustion stability and economy of the designed vehicle engine can be improved.
Fig. 3 is a schematic structural diagram of a calibration system for a CFD model in a cylinder of a vehicle engine according to an embodiment of the present invention. The system for calibrating the CFD model in the cylinder of the vehicle engine according to this embodiment may refer to the related description of the above embodiment. Specifically, the calibration system comprises a vehicle optical engine 30, a PIV test system 2 and a calibration device 4; the PIV testing system 2 is configured to obtain, through testing, a planar flow field image of each of a plurality of different in-cylinder feature planes of the vehicle optical engine 30 at least one preset crank angle, and send the planar flow field image to the calibration device 4, so that the calibration device 4 obtains a corresponding planar flow field according to the planar flow field image; the calibration device 4 comprises: a processor 40, a memory 41 and a computer program stored in said memory 41 and operable on said processor 40, such as a calibration system program for a CFD model in a cylinder of a vehicle engine. The processor 40, when executing the computer program, performs the steps in the various vehicle engine in-cylinder CFD model calibration system method embodiments described above. Alternatively, the processor 40 implements the functions of the modules/units in the above device embodiments when executing the computer program.
Illustratively, the computer program may be partitioned into one or more modules/units that are stored in the memory 41 and executed by the processor 40 to implement the present invention. The one or more modules/units may be a series of computer program instruction segments capable of performing specific functions, which are used to describe the execution process of the computer program in the calibration apparatus/device.
The calibration device/equipment can be computing equipment such as a desktop computer, a notebook computer, a palm computer and a cloud server. The calibration apparatus/device may include, but is not limited to, a processor 40, a memory 41. It will be understood by those skilled in the art that the schematic diagram is merely an example of a calibration apparatus/device, and does not constitute a limitation of the calibration apparatus/device, and may include more or less components than those shown, or combine some components, or different components, for example, the calibration apparatus/device may further include an input-output device, a network access device, a bus, etc.
The Processor 40 may be a Central Processing Unit (CPU), other general purpose Processor 40, a Digital Signal Processor 40 (DSP), an Application Specific Integrated Circuit (ASIC), an off-the-shelf Programmable Gate Array (FPGA) or other Programmable logic device, discrete Gate or transistor logic, discrete hardware components, etc. The general purpose processor 40 may be a microprocessor 40 or the processor 40 may be any conventional processor 40 or the like, the processor 40 being the control center of the calibration apparatus/device, various interfaces and lines connecting the various parts of the entire calibration apparatus/device.
The memory 41 may be used for storing the computer programs and/or modules, and the processor 40 implements various functions of the calibration apparatus/device by running or executing the computer programs and/or modules stored in the memory 41 and calling up the data stored in the memory 41. The memory 41 may mainly include a program storage area and a data storage area, wherein the program storage area may store an operating system, an application program required by at least one function (such as a sound playing function, an image playing function, etc.), and the like; the storage data area may store data (such as audio data, a phonebook, etc.) created according to the use of the cellular phone, and the like. Further, the memory 41 may include a high speed random access memory 41, and may also include a non-volatile memory 41, such as a hard disk, a memory, a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) Card, a Flash memory Card (Flash Card), at least one piece of disk memory 41, a Flash memory device, or other volatile solid state memory 41.
Wherein the calibration means/device integrated module/unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, all or part of the flow of the method according to the embodiments of the present invention may also be implemented by a computer program, which may be stored in a computer-readable storage medium, and when the computer program is executed by the processor 40, the steps of the method embodiments may be implemented. Wherein the computer program comprises computer program code, which may be in the form of source code, object code, an executable file or some intermediate form, etc. The computer-readable medium may include: any entity or device capable of carrying said computer program code, recording medium, usb disk, removable hard disk, magnetic disk, optical disk, computer Memory 41, read-Only Memory 41 (ROM), random Access Memory 41 (RAM), electrical carrier wave signal, telecommunication signal, software distribution medium, etc. It should be noted that the computer readable medium may contain content that is subject to appropriate increase or decrease as required by legislation and patent practice in jurisdictions, for example, in some jurisdictions, computer readable media does not include electrical carrier signals and telecommunications signals as is required by legislation and patent practice.
It should be noted that the above-described embodiments of the apparatus are merely illustrative, where the units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. In addition, in the drawings of the embodiment of the apparatus provided by the present invention, the connection relationship between the modules indicates that there is a communication connection between them, and may be specifically implemented as one or more communication buses or signal lines. One of ordinary skill in the art can understand and implement it without inventive effort.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.
Claims (10)
1. A method of calibrating an in-cylinder CFD model of a vehicle engine, comprising:
determining the tumble center of a planar flow field of a plurality of different in-cylinder characteristic planes of the vehicle optical engine under at least one preset crank angle; the plane flow field is obtained by pre-measuring under a preset first experiment working condition;
correspondingly calculating the tumble ratio of each planar flow field under each preset crank angle according to the tumble center of each planar flow field under at least one preset crank angle;
averaging the tumble ratios of all the planar flow fields under each preset crank angle to obtain an average tumble ratio under each preset crank angle;
adjusting model parameters of the in-cylinder CFD model according to the average tumble ratio under each preset crank angle and a model tumble ratio pre-calculated by the in-cylinder CFD model of the vehicle engine under at least one preset crank angle after being set as the first experimental working condition so that the adjusted in-cylinder CFD model meets a preset condition:
and the absolute value of the difference value between the model tumble ratio recalculated under the preset second experiment working condition and the average tumble ratio calculated under the same experiment working condition and the same crank angle is smaller than a preset threshold value.
2. The method for calibrating the in-cylinder CFD model of the vehicle engine according to claim 1, wherein the determining the tumble center of the planar flow field of each of the plurality of different in-cylinder feature planes of the vehicle optical engine at least one preset crank angle is performed by:
determining in-cylinder airflow simulation centroid coordinates of an in-cylinder CFD model of a vehicle engine at least one preset crank angle after being set to the first experimental operating condition;
and correspondingly determining the tumble centers of the plane flow fields of a plurality of different in-cylinder characteristic planes of the vehicle optical engine under at least one preset crank angle according to the in-cylinder airflow simulation mass center coordinates under at least one preset crank angle.
3. The method of calibrating an in-cylinder CFD model of a vehicle engine of claim 1, wherein the model parameters include at least one of: turbulence dissipation, initial turbulence energy, and cylinder wall temperature.
4. A method of calibrating an in-cylinder CFD model of a vehicle engine as set forth in any one of claims 1 to 3, wherein the vehicle optical engine includes a cylinder that is a transparent cylinder block; then, a plurality of the in-cylinder feature planes includes at least: an in-cylinder plane passing through a center of a cylinder of the cylinder and an in-cylinder plane passing through a center of an intake valve of the cylinder.
5. The method for calibrating the CFD model in the cylinder of the vehicle engine according to claim 4, wherein the top of the cylinder has two intake valves, a first intake valve and a second intake valve, and the plurality of in-cylinder characteristic planes comprise: the cylinder inner plane of the center of the first air inlet valve, the cylinder inner plane of the cylinder between the side wall of the cylinder close to the first air inlet valve and the first air inlet valve, the cylinder inner plane of the center of the first air inlet valve and the cylinder, the cylinder inner plane of the center of the second air inlet valve, the cylinder inner plane of the cylinder between the side wall of the cylinder close to the second air inlet valve and the second air inlet valve, and the cylinder inner plane of the center of the second air inlet valve and the cylinder;
and the cylinder inner plane passing through the center of the cylinder is positioned between the cylinder inner plane of the center of the first air inlet valve and the cylinder inner plane of the center of the second air inlet valve.
6. A calibration apparatus for a CFD model in a cylinder of a vehicle engine, comprising:
the system comprises a tumble center determining module, a tumble center determining module and a control module, wherein the tumble center determining module is used for determining the tumble centers of plane flow fields of a plurality of different in-cylinder characteristic planes of the vehicle optical engine under at least one preset crank angle; the plane flow field is obtained by pre-measuring under a preset first experiment working condition;
the tumble ratio calculation module is used for correspondingly calculating the tumble ratio of each planar flow field under each preset crank angle according to the tumble center of each planar flow field under at least one preset crank angle;
the average tumble ratio calculation module is used for averaging the tumble ratios of all the planar flow fields under each preset crank angle to obtain the average tumble ratio under each preset crank angle;
a model adjustment module to: adjusting model parameters of the in-cylinder CFD model according to the average tumble ratio under each preset crank angle and a model tumble ratio pre-calculated by the in-cylinder CFD model of the vehicle engine under at least one preset crank angle after being set as the first experimental working condition so that the adjusted in-cylinder CFD model meets a preset condition:
and the absolute value of the difference value between the model tumble ratio recalculated under the preset second experiment working condition and the average tumble ratio calculated under the same experiment working condition and the same crank angle is smaller than a preset threshold value.
7. The apparatus for calibrating a CFD model in a cylinder of a vehicle engine according to claim 6, wherein the tumble center determining module includes:
the first determining unit is used for determining in-cylinder airflow simulation mass center coordinates of an in-cylinder CFD model of a vehicle engine under at least one preset crank angle after the in-cylinder CFD model is set to be under the first experimental working condition;
and the second determining unit is used for correspondingly determining the tumble centers of the plane flow fields of a plurality of different in-cylinder characteristic planes of the vehicle optical engine under at least one preset crank angle according to the in-cylinder airflow simulation mass center coordinate under at least one preset crank angle.
8. A calibration system of a CFD model in a vehicle engine cylinder is characterized by comprising an optical engine system with a vehicle optical engine, a PIV test system and a calibration device;
the PIV testing system is used for testing and obtaining a plane flow field image of each of a plurality of different in-cylinder characteristic planes of the vehicle optical engine under at least one preset crank angle, and sending the plane flow field image to the calibration equipment so that the calibration equipment can obtain a corresponding plane flow field according to the plane flow field image;
the calibration apparatus comprises a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, the processor when executing the computer program implementing the method of calibrating a vehicle engine in-cylinder CFD model according to any one of claims 1 to 5.
9. The system for calibrating an in-cylinder CFD model of a vehicle engine of claim 8, wherein said PIV testing system comprises:
the laser emitter is used for emitting a sheet-shaped laser beam into a cylinder of the vehicle optical engine so as to form a laser beam plane in the cylinder of the vehicle optical engine;
the particle generator is used for generating trace particles and inputting the trace particles into a cylinder of the vehicle optical engine;
the CMOS camera is used for imaging the area in the cylinder where the laser beam plane is located, imaging the area into a plane flow field image and sending the plane flow field image to the calibration equipment; and a process for the preparation of a coating,
and the synchronizer is used for synchronizing the work of the laser transmitter, the particle generator and the CMOS camera.
10. A computer-readable storage medium, comprising a stored computer program, wherein the computer program, when executed, controls an apparatus in which the computer-readable storage medium is located to perform a method of calibrating an in-cylinder CFD model of a vehicle engine as recited in any one of claims 1 through 5.
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| CN104777164A (en) * | 2015-03-30 | 2015-07-15 | 天津大学 | Large-size measuring experimental apparatus and method for air flow in cabin based on PIV |
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