CN114580320A - Non-contact type hot film testing equipment, and method and application for judging local instability of gas compressor - Google Patents
Non-contact type hot film testing equipment, and method and application for judging local instability of gas compressor Download PDFInfo
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Abstract
The invention discloses non-contact hot film testing equipment, a method for judging local instability of a gas compressor and application. The method comprises the steps of firstly obtaining the velocity distribution of a flow field around a compressor rotor based on non-contact hot film testing equipment, and further obtaining the axial momentum of fluid in the compressor rotor through the velocity distribution and a reasonable calculation method. According to the physical definition of the axial momentum, the axial momentum in the compressor rotor can be associated with the stable flow condition, so that the local area and the instability form of the compressor are finally defined. The invention carries out a great deal of experimental research on applying stability expansion measures aiming at different axial flow compressors, and the result shows that the stability expansion mechanisms of various stability expansion measures have uniformity, namely the low-energy fluid at the end region of the compressor is effectively excited and expanded by a momentum exchange mode. Therefore, based on the method, the accurate judgment of the instability region of the compressor is beneficial to adding control measures in the design to expand the stable working range of the compressor and improve the stability margin.
Description
Technical Field
The invention belongs to the technical field of instability judgment, is particularly suitable for determining a region where local instability disturbance of a high-load compressor occurs, can accurately judge the stall type of the compressor and enlarge the stable working range of the compressor, and relates to non-contact hot film testing equipment, a method for judging local instability of the compressor and application.
Background
Flow instability is an important problem for limiting the stable working margin of the current compressor, and rotating stall and surge are two common ways for causing the flow instability of the compressor. When surging occurs, the flow of the compressor generates pulsation oscillation, so that severe mechanical vibration is caused, and even the engine is seriously damaged. Rotating stall is a non-axisymmetric phenomenon caused by one or more stall groups, and the flow fluctuation of a compressor is not large, but the compressor loses the processing capacity, so that the performance of an engine is seriously influenced. Because the flow instability of the air compressor is unavoidable, the instability precursors causing surge and rotating stall are always the focus of research of domestic and foreign scholars and are one of the important directions of the current air compressor research. Through extensive studies by a large number of scholars, there are two classic precursors of destabilization that have been demonstrated: modal waves and spike waves. The modal wave is a large-scale disturbance caused by circumferential nonuniformity of the compressor, and the wavelength scale is similar to the circumference of the compressor. The sharp wave is a three-dimensional and local small-scale stall disturbance, and the wavelength scale of the sharp wave is similar to the length of a compressor blade channel.
After several ways of inducing instability of the compressor are defined, factors of inducing instability of the compressor of a specific model need to be defined, and therefore the stable working margin of the compressor is improved in an effective stability expansion mode. For the surge problem, the one-dimensional oscillation of the fluid in the axial direction of the compressor is mainly used, so that the current surge detection method at home and abroad basically takes the pressure of the outlet flow field of the compressor as an object and carries out the surge algorithm research according to the time domain or frequency domain characteristics of a pressure signal. The surge detection algorithm based on the pressure signal time domain characteristics mainly comprises the following steps: rate of change methods, autocorrelation function methods, differential pressure methods, statistical signature methods, analysis of variance methods, short-term energy methods, and the like. Aiming at the one-dimensional axial oscillation problem of surge, the judgment can be carried out only by detecting the pressure at the outlet of the air compressor. However, the rotating stall problem is complicated and its inducers relate to the fluid flow structure at different locations in the compressor flow field. For the modal wave problem, more researchers have conducted related research works. The fan theory developed by Moore and Greitzer et al first predicts the presence of modal waves. Tryfonidis and the like monitor the modal wave disturbance of the compressor by adopting a space Fourier decomposition method and utilizing the relative difference of reverse energy and forward energy of a rotor based on a traveling wave energy method. Brown et al propose a spatial correlation method, which uses two axially adjacent sensors to perform correlation analysis, and quantitatively analyzes modal waves by fixing a corresponding function between windows.
With the continuous improvement of the design level of an engine, the instability of a compressor with higher load is mostly the integral instability of the compressor caused by the instability of a local three-dimensional flow structure in a flow field. The change situation of typical characteristic signals of the compressor during pneumatic instability is explained by methods such as time-frequency analysis, data fusion statistics, pattern recognition and the like by the domestic famous expert Lissangzheng and the like. The tension and the like utilize wavelet principle to research the instability process of a compression system, and find that wavelet analysis has the capability of monitoring small disturbance of a near stall region. The method obtains some theoretical and simulation research results for aerodynamic instability and prediction, but the theoretical and simulation still have some errors compared with the actual. For a concrete compressor engineering experiment, a solution is still needed at present based on which means to obtain important characteristic parameters and further based on how to accurately judge the instability mode of the compressor based on the existing parameters. Therefore, it is necessary to obtain the main characteristic parameters of the flow field of the compressor rotor by proper measuring equipment, and further to determine the flow instability form of the compressor by a proper discrimination method.
In addition, the applicant patent application: application No.: CN2017105463075, publication no: CN107271714A, disclosing a hot wire test device applicable to a rotating condition, the technical scheme includes a dynamic-static conversion device, a rotating end rotating with the fluid to be tested in the test process, and a data receiving end placed statically; the dynamic and static conversion device is connected with the rotating end and the data receiving end; the rotating end transmits an electric signal generated in the rotating process of the fluid to be tested to the dynamic and static conversion device, the dynamic and static conversion device transmits the electric signal to the data receiving end, and the data receiving end stores the electric signal. The prior art only describes the specific structure of the hot wire test device, however, the test device does not describe how to obtain the velocity distribution of the flow field near the high-speed compressor rotor, and further calculate the maximum axial momentum to represent the stable flow condition of the compressor.
Disclosure of Invention
The invention aims to define a local area of the high-load compressor with instability disturbance by adopting an experimental means. Specifically, the speed distribution of a flow field near a high-speed compressor rotor is obtained based on non-contact hot film testing equipment, and then the maximum axial momentum is calculated to represent the stable flowing condition of the compressor.
The invention discloses a method for judging local instability of a gas compressor based on non-contact hot film testing equipment, which is characterized by comprising the following steps: the method comprises the following steps:
step 1: obtaining the velocity distribution of a flow field near a rotor component of the high-speed compressor;
step 2: calculating the axial momentum of the fluid near the rotor of the compressor through the velocity distribution;
and step 3: the correlation between the axial momentum of fluid in the compressor and the flow stability is determined;
and 4, step 4: and (4) determining a local instability region of the compressor and judging the instability form of the compressor.
The invention also discloses a method for judging the flow instability of the high-load compressor, which is applied to the compressor instability detection system.
When the method for judging the local instability of the gas compressor is executed, non-contact hot film based testing equipment is adopted, and the equipment obtains the speed distribution of a flow field near a high-speed gas compressor rotor through wireless data acquisition, transmission and dynamic data storage analysis, so that the maximum axial momentum is calculated to represent the stable flow condition of the gas compressor. For the non-contact thermal film testing apparatus, it is characterized in that: comprises a rotary transmitter, a static receiver and a signal receiving and processing box. The rotary emitter is fixed on a rotating shaft of the compressor and is mainly used for emitting a speed signal collected from a boundary layer to the static receiver; the static receiver is coaxially opposite to the rotary transmitter, and provides electric energy for the rotary transmitter in an electric field induction mode and receives signals transmitted by the rotary transmitter, so that the flow field speed information near the rotor blade is stored; the signal receiving and processing box is connected with the static receiver through a serial bus interface so as to carry out dynamic data analysis on the information stored by the static receiver.
Advantageous effects
The invention is based on non-contact hot film test equipment, can obtain the real distribution of the fluid speed near the compressor rotor, and greatly increases the integrity of the experimental database through the combination of the equipment and the aeroengine; the method for judging the local instability of the air compressor by using the non-contact hot film testing system and the application thereof enable the instability form of the air compressor to be accurately judged, play an instructive role in the application of subsequent stability expansion measures, improve the stability expansion benefit to the maximum extent and increase the stable working margin of parts of the air compressor.
Drawings
In order to more clearly illustrate the accuracy of judging the flow instability of the compressor based on the axial momentum obtained by the non-contact hot film testing equipment in the experiment, a plurality of embodiments are selected for quantitative analysis. The drawings needed for the analysis of the embodiments will be briefly described below, it being apparent that the drawings described below are some embodiments of this patent, and that other drawings may be derived from those drawings by one of ordinary skill in the art without inventive effort.
FIG. 1 is a variation trend of stability margin variation/circumferential distortion strength with axial momentum variation in the present patent embodiment;
FIG. 2 is a schematic diagram of a control body and four control surfaces Z +, Z-, Bottom and casting in the embodiment of the present invention;
FIG. 3 is a flow chart of forward design of the instability extending measure based on the instability discrimination method;
FIG. 4 is a relationship between the amount of change in axial momentum and the stability margin in the embodiment of the present patent;
FIG. 5 is a schematic view of a control body taken at a specific axial position in the embodiment of the present patent.
Detailed Description
In order to make the results, technical solutions and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the calculation method in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
Non-contact thermal film test apparatus characterized by: comprises a rotary transmitter, a static receiver and a signal receiving and processing box.
The rotary emitter needs to be fixed on a rotating shaft of the air compressor, rotates along with the air compressor and is mainly used for emitting a speed signal collected from a boundary layer to the static receiver;
The static receiver and the rotary transmitter are coaxially opposite, and a 2mm interval is kept between the static receiver and the rotary transmitter; the static receiver provides electric energy for the rotating transmitter in an electric field induction mode and receives signals transmitted by the rotating transmitter, so that the flow field speed information near the rotor blade is stored;
the signal receiving and processing box is connected with the static receiver through a serial bus interface so as to carry out dynamic data analysis on the information stored by the static receiver.
The rotary emitter comprises a thermal film probe, a CTA module and an A/D conversion module; the thermal film probe is connected with the input end of the CTA module, and the output end of the CTA module is connected with the input end of the A/D conversion module; the output end of the A/D conversion module is connected with the non-contact test instrument; wherein, when measuring the speed of the turbulent boundary layer of the fluid to be tested, the thermal film probe is arranged on the surface of the rotor component to be tested, and the CTA module is used for measuring an electric signal on the thermal film probe and transmitting the electric signal to the A/D conversion module; the A/D conversion module converts the electric signal into a digital signal and transmits the digital signal to the non-contact test instrument.
The CTA module includes a wheatstone bridge. The CTA module is 70mm by 40mm by 20mm in size; the A/D conversion module has the size of 50mm multiplied by 60mm multiplied by 15 mm. Compared with other bridges, the Wheatstone bridge avoids the error caused by the change of the power supply along with time, so that the measuring result is more accurate, and the bridge is cheaper and easier to select in order to achieve the same measuring effect. Furthermore, the dimensions of the apparatus, which can only be used for measuring the velocity of a fluid at rest, are approximately 50cm x 15 cm. The thermal membrane testing equipment suitable for the rotating condition provided in this embodiment controls the size of each module, for example, the size (length, width, height) of a CTA module is 70mm × 40mm × 20mm, and the size (length, width, height) of an a/D conversion module is 50mm × 60mm × 15mm, so that the size of the rotating end is smaller, an excessive burden on equipment bearing a fluid to be tested is avoided in the process that the rotating end rotates along with the fluid to be tested, and the speed of a turbulent boundary layer of the fluid to be tested is measured under the condition that the rotation of the fluid to be tested is not affected.
The static receiver is also used for converting the digital signal into the speed of the boundary layer near the rotor component to be tested according to the corresponding relation between the digital signal and the speed of the turbulent boundary layer, wherein the digital signal is stored in advance. In addition, the static receiving end provides electric energy for the rotating transmitter in an electric field induction mode, and due to the fact that the transmission distance of the device is required to be 1-3mm in magnitude, the sensor and the power are only required to be dozens of watts, electromagnetic induction type non-contact electric energy transmission is selected.
The device also comprises a display module; the display module is used for displaying the speed of the turbulent boundary layer of the fluid to be tested.
The working process of the non-contact type thermal film testing equipment comprises the following steps: firstly, a hot film probe is arranged near a compressor rotor, an CTA module transmits an electric signal acquired by the hot film probe to an A/D conversion module, the electric signal is converted into a digital signal by the A/D conversion module, and a rotary transmitter comprising the three main components further transmits the digital signal representing the velocity distribution of a flow field near the rotor to a static receiving end. And the static receiving end supplies electric energy to the rotating transmitter in an electric field induction mode and stores digital signals representing the velocity distribution of a flow field near the rotor. And finally, the static receiving end transmits the digital signals to a signal receiving and processing box through a universal serial bus interface. The signal receiving and processing box is simultaneously connected with the display so as to carry out dynamic data analysis on the flow field speed parameters.
Example 2
The method for judging the local instability of the air compressor based on the non-contact hot film test equipment is characterized by comprising the following steps: the method comprises the following steps:
step 1: through non-contact hot film testing equipment, the velocity distribution of a flow field near a high-speed compressor rotor component is obtained, and the specific content is as follows:
Before the speed measurement is carried out through the hot film probe, calibration and temperature compensation experiments need to be carried out on the hot film probe; the calibration experiment needs to be carried out on a hot film probe in the same height and different temperature environments, the fluid medium of a wind tunnel is clean wind during wind speed measurement, then in the temperature range of 0-70 ℃, 2-3 ℃ is taken as an interval, 30 different central temperatures are selected for calibration in total, 2m/s is taken as a calibration interval for each temperature calibration in the wind speed range of 1-100 m/s at the same height position, 50 different central wind speeds are selected in total, 20 groups of instantaneous wind speed values and output voltage values are collected at each central wind speed, and finally data are displayed and stored on a computer interface; after the calibration experiment is finished, the experimental data is sorted, the average output voltage value of the wind speed sensor is used as a horizontal coordinate, the average wind speed of the American TSI9565-P multi-parameter wind speed tester is used as a vertical coordinate, Excel software is adopted to perform curve fitting on the data to obtain a fitting curve equation of the wind speed sensor, the invention predicts that the calibration experiment obtains 30 groups of fitting curve equations in total, explores the law of influence of different temperatures on wind speed measurement, performs temperature compensation on the wind speed sensor, and improves the speed measurement accuracy; finally, the wind speed is measured at any temperature within the temperature range, and comparison is carried out on the standard wind speed to verify the effectiveness of compensation.
The hot film wind speed measuring equipment is a basic part of non-contact hot film testing equipment, wherein speed measurement is based on the heat transfer principle of a heating element in a fluid medium, when fluid passes through a sensor, heat is transferred from the sensor to the medium, and the transferred heat is increased along with the increase of flow. Based on the relationship between heat dissipation and fluid velocity, the following equation is given:
H＝(A+B*(U^0.5))*(Ts-T0) Wherein H is the heat dissipation, A, B are constants, U is the fluid velocity, TSIs the temperature of the hot-film probe, T0Is ambient temperature.
The heat generated by the energized current passing through the thermal film sensor probe is:
Q＝I2R
wherein, R is the tachometer resistance of the thermal film sensor probe, I is the current passing through the thermal film sensor probe, and Q represents the heat generated by the thermal film sensor probe.
The heat generated by the probe of the thermal film sensor during the power-on process is equal to the heat transferred by the fluid medium, that is, based on the principle of thermal balance, so that if H is Q, then:
I2R＝(A+B*(U^0.5))*(TS-T0)
the above equation shows that the relationship of hot film test wind speed is that it can be concluded: at the temperature T of the environment in which the fluid medium is located0Under certain conditions, the fluid velocity U is the current I passing through the hot film probe and the temperature T of the hot film probesWhen one of the two variables is fixed, a single-value functional relation between the fluid speed U and the other variable can be obtained; when the temperature T of the probe is fixed sThe fluid speed U can be obtained by utilizing the current I passing through the hot film probe, and the working mode is the constant-temperature hot film test sensor adopted in the equipment.
The relationship correlates the temperature sensed by the hot film probe with the velocity of the fluid, and spatial distribution of the velocity of the flow field near the rotor blade of the compressor can be obtained by further installing hot film test sensors at different positions on the surface of the blade.
And 2, step: calculating the axial momentum of the fluid near the compressor rotor through the velocity distribution, wherein the specific contents are as follows:
after the velocity distribution of the flow field near the compressor rotor is obtained through the step 1, a proper control body needs to be established for calculating the axial momentum. The established control body needs to be capable of reasonably quantifying the main flow structure of the main flow and the leakage flow and effectively providing the change rule of the axial momentum along with the flow direction. Each discrete control body unit of the control body is formed by surrounding four control surfaces, namely an upper surface vertical to the radial direction of the blade, a lower surface in the blade channel and planes vertical to the axial direction at two sides. To obtain information that the axial momentum obtained by the non-contact thermal film testing equipment varies continuously along the axial direction, a series of discrete control bodies are divided along the axial direction within the flow range of primary interest, extending from the casing wall surface down to a range of radial blade heights, circumferentially spanning a pitch distance, encompassing all circumferential flow between two periodic surfaces. Each discrete control volume is intersected by two planes perpendicular to the axis of rotation. The control bodies are discrete, the first control body being located upstream of the leading edge of the rotor and the last control body being located downstream of the trailing edge of the rotor.
For the established suitable control body, the special meaning of each control surface is transported. For a specific research object, the axial momentum transport on the casing surface of the control body is observed, and the exchange condition of the flow in the circumferential groove and the gap can be known; the axial momentum transport on the lower surface of the control body is observed, so that the interaction condition of the end area of the blade and the fluid in the blade channel can be known; meanwhile, the two equal axial surfaces of the control body describe the axial momentum carried by the fluid in the control body when the fluid passes through the equal axial surfaces, and the flow performance of the main flow and the leakage flow in most control bodies can be sensed.
To obtain information that the axial momentum obtained by the non-contact thermal film testing apparatus varies continuously along the axial direction, a series of discrete control bodies are divided along the axial direction within the flow range of primary interest. Extending down the casing wall to a radial blade height, circumferentially spanning a pitch distance, encompassing all circumferential flow between the two periodic surfaces. Each discrete control volume is intersected by two planes perpendicular to the axis of rotation. The control bodies are discrete, the first control body being located upstream of the leading edge of the rotor and the last control body being located downstream of the trailing edge of the rotor. The control body is flexible in the radial selection range and needs to be set specifically for the flow problem to be analyzed, and the surface forces on the four control surfaces on each control body unit include the pressure and the shearing force of the fluid. In addition, the force of the fluid acting on the vanes should be considered as a source term, and according to the impulse theorem, the axial resultant external force acting on the control body is the change of the axial momentum. For the compressor rotor which rotates at high speed concerned by the patent, the axial resultant external force acting on the control body is the change of the axial momentum, and further the axial momentum equation on each discrete control body unit can be deduced based on the speed change as follows:
Wherein: [ integral ] represents the sign of integral, PZ-Pressure, P, on the left surface of the control bodyZ+Pressure, P, on the right surface of the control bodyCSPressure, P, of the casing surfaceBTRepresenting the pressure of the lower surface in the vane passage, τCSRepresenting shear stress on the surface of the casing, τBTRepresenting shear stress on the lower surface within the blade channel,
represents the density of the fluid, WzWhich is representative of the axial velocity of the fluid,
representing the fluid velocity (including direction),
unit vector, dA, representing the normal direction of the surface of the control bodyZ-Representing the area of the infinitesimal on the left surface of the control volume,dAZ+representing the area of infinitesimal elements on the right surface of the control body, dACSRepresenting the area of infinitesimal elements on the surface of the casing, dABTRepresenting the area of the infinitesimal on the inner and lower surface of the blade channel. Z + and Z-represent the left and right sides of the control body, respectively, CS (casting surface) represents the casing surface, BT (bottom surface) represents the lower surface in the blade channel, T represents the shear stress on the surface of the control body, FBLADE-ZRepresenting the additional force caused by the rotation of the control body, dA represents the area of a infinitesimal on the surface of the control body, and Z represents the axial direction.
According to the momentum equation obtained by impulse theorem, the axial momentum on the control surface can be expressed as:
wherein ^ represents integral sign, rho represents fluid density, W zRepresenting the axial velocity of the fluid (the axes of rotation of the compressors are each defined as the Z direction),
representing the fluid velocity (including direction),
represents the unit vector of the normal direction of the surface of the control body, and dA represents the area of the infinitesimal on the surface of the control body.
The following describes a specific calculation flow of the axial momentum in this patent by taking a specific study as an example. The operation platform is realized based on ANSYS CFX-Post commercial software, a rotor area is divided into a plurality of control bodies, more than 97% of spread positions are taken as examples, and a hollow circular arc plate in the figure 1 represents a schematic diagram of the control bodies at a certain axial position. The actual operation flow is as follows: iso-surface 1 and Iso-surface 2 were taken at axial positions 21 and Z2, and Iso clips were taken as Z + and Z-on Iso-surface 1 and Iso-surface 2, respectively, with Span Normalized > 0.97. Taking the Turbo Surface at 0.97Span and the Iso Clip between the Turbo Surface axial position 21 and z2 as Bottom. Finally, take Iso Clip as CS (casting surface) between axial positions z1 and z2 on the Shroud face. Thus, a control body can be obtained together with Z +, Z-,BT (bottom surface) and CS. Fig. 2 represents the stress situation of the control established above, and 4 surfaces are respectively subjected to positive pressure P and shearing force τ. The magnitude of the axial momentum on the control surface is determined by both the direction of the mass flow through the surface and the direction of the axial velocity. For control bodies CS, BT, Z according to a definition of the axial momentum on the control surface +And calculating and accumulating the axial momentum of the Z four control surfaces to obtain the axial momentum value of a single control body, wherein the respective signs of the four items are required to be noticed. The axial momentum distribution condition of the fluid near the compressor rotor can be obtained through the actual operation process.
And 3, step 3: and (3) determining the relation between the axial momentum of fluid in the compressor and the flow stability:
the size of the axial momentum around the rotor is obtained through a proper control body established around the rotor of the gas compressor and an axial momentum calculation formula. Based on this formula, it can be seen that the magnitude of the axial momentum on the control surface is determined by both the direction of the mass flow through the surface and the direction of the axial velocity. When WzWhen the value is positive, the projection of the velocity component representing the fluid on the Z axis is positive, that is, the fluid has a tendency to move from the upstream of the rotor to the downstream of the rotor. WzNegative values indicate that the fluid has a flow tendency opposite to the axial direction. For the flow condition inside the compressor rotor, the fact that the flow direction of the fluid is consistent with the axial direction means that the flow is stable, and the fact that the flow is opposite means that the flow is separated and forms a vortex. Furthermore, a larger amplitude indicates a more pronounced flow separation, and the more flow blockage caused by the vortex structure, and the stronger flow instability in this region.
According to a well-defined calculation method of the axial momentum, based on the three-dimensional space velocity distribution obtained by non-contact hot film testing equipment, the amplitudes of the axial momentum of different areas near the compressor rotor are obtained through calculation. The equation further shows that the magnitude of the axial momentum through the control surface is determined by both the direction of the mass flow through the surface and the direction of the axial velocity. When WzWhen the value is positive, the projection of the velocity component representing the fluid on the Z axis is positive, i.e. the fluid has self-vibrationThe tendency of the rotor to move upstream to downstream. W is a group ofzNegative values indicate that the fluid has a flow tendency opposite to the axial direction. For the flow condition inside the compressor rotor, the fact that the flow direction of the fluid is consistent with the axial direction means that the flow is stable, and the fact that the flow is opposite means that the flow is separated and forms a vortex. Furthermore, a larger amplitude indicates a more pronounced flow separation, and the more severe the flow blockage caused by the vortex structure, and the stronger the flow instability in this region. Therefore, the amplitude values of the axial momentum of different areas near the compressor rotor are obtained through calculation, and the area where the maximum axial momentum occurs is further compared, analyzed and specified, and the area where the local instability occurs at present is the area.
Taking a blade top jet experiment as an example, the condition of an interface between a leakage flow and a main flow can be obtained by measuring wall surface dynamic pressure signals at the same flow point under three conditions of uniform air inlet, distorted air inlet and distorted air inlet applied jet respectively. Compared with the uniform incoming flow condition, the research shows that the circumferential total pressure distortion and the blade tip total pressure distortion cause the load of the blade tip in a distortion area to be increased, and the boundary surface of blade tip leakage flow and main flow moves towards the front edge of the blade. And when the jet is applied, the fluctuation intensity of the leakage flow of the rotor is obviously weakened, and meanwhile, the interface of the leakage flow and the main flow pushes towards the tail edge of the blade. By calculating the axial momentum of the gas, the larger the jet momentum ratio, the stronger the suppression effect on the unsteady fluctuation of the leakage flow, and the larger the backward movement of the interface between the leakage flow and the main flow. Compared with the working condition without air injection, the air injection is carried out on the rotor, so that the fluctuation strength of the leakage flow of the rotor can be obviously weakened, and meanwhile, the boundary surface of the leakage flow and the main flow is pushed towards the tail edge of the blade. The result shows that the unstable flow state of the local area of the compressor is really represented by adopting the axial momentum change as the characteristic quantity.
And 4, step 4: defining a local instability region of the gas compressor, and judging the instability form of the gas compressor:
The definition of the axial momentum shows the relationship between the positive and negative of the result and the flowing direction of the fluid, and the relationship between the axial momentum of the compressor and the flowing stability is further defined according to the influence of the flowing direction of the fluid along the axial direction on the flowing stability. The position of the maximum axial momentum is found out by calculating the axial momentum of different positions near the rotor of the compressor. The maximum axial momentum generating position can be defined as the region with the strongest flow instability through definition, and then the local instability generating region in the compressor rotor is determined. Further, for the compressor instability process, there are several generally recognized instability forms, such as abrupt sharp wave, modal wave, blade root instability, etc., which cause local instability positions of these different instability forms to be different. The abrupt sharp wave is caused by local instability of a rotor blade tip region, the blade root instability is unstable flow of a blade root region, and the modal wave is an unstable problem caused by the fact that a whole rotor blade height region is close to an instability boundary at the same time. Therefore, the local instability position judged based on the maximum axial momentum is matched with a common instability form, and the specific instability form of the compressor to be researched can be judged.
Similarly, according to the result of the blade top jet experiment, the total pressure distortion also influences the stability margin of the compressor by changing the local load distribution of the blade tip, and under the condition of distorted air inlet, the quantitative relation between the axial momentum change and the stability margin is still applicable, and the axial momentum change and the stability margin can be associated through distortion strength. Taking a circumferential distortion example, fig. 3 shows a variation trend of the stability margin variation/circumferential distortion strength with the axial momentum variation, where a square broken line represents the stability margin variation and a triangle broken line represents the axial momentum variation. The calculation based on the maximum axial momentum determines the tip region of the leading edge of the rotor to be a local instability region, which corresponds to the tip waveform instability process. Further, as the circumferential distortion intensity increases, the stall margin decreases and the amount of change in axial momentum decreases. In the experiment, the load of the local instability region of the blade tip is reduced, so that the axial momentum of the blade tip is improved, and the stability margin of the compressor is increased, and therefore the local instability region is the spatial position of the most leading compressor integral instability.
The above embodiments illustrate the specific real-time operation flow of the present patent, and the determination of the instability form is finally to add a suitable and effective flow control means. In order to further embody the practical application condition of the patent of the invention, the invention also carries out experimental exploration on a research object based on the most widely applied stability expanding measure of the treatment casing at present.
Although the principle and the mode of excitation generated by different treatment casings are different, the flow blockage of the blade tip area is reduced, and the flow capacity of the blade tip is improved, so that the effect of widening the stability margin of the gas compressor is realized. Through research summary, the stability expansion mechanism of the processing casing is realized by reducing the blade tip load essentially, and after the processing casing is added, the load of the blade tip area of the rotor is obviously reduced, so that the load is far away from the critical load when the solid-wall casing is unstable, and the stability margin of the gas compressor is widened. In the experimental process, a stability augmentation design parameter-axial momentum increment correlation data set, a stability augmentation geometric optimization platform and a characteristic value stability prediction model are established based on non-contact hot film testing equipment, and the method for forward design of the stability augmentation measures is preliminarily formed. The forward design method of the stability augmentation measure in fig. 4 is a main flow established for the core based on the orientation in the patent specification. The method comprises the following steps of firstly obtaining the axial momentum of a blade tip region through numerical values/experimental results based on the given geometry and characteristics of the compressor, and meanwhile roughly determining the increment requirement of the axial momentum of the blade tip according to the margin requirement of a research target. According to the target requirement, based on non-contact thermal film testing equipment, in a design parameter-blade tip axial momentum increment correlation data set, determining the type of the stability augmentation measure, determining the approximate range of main design parameters of the stability augmentation measure, and completing preliminary design work. Then, the stability augmentation measure parameterized optimization platform developed in the patent is used for optimizing various parameters, modeling curves and the like in the range, and the detailed design of the stability augmentation measure is completed. The stability expansion scheme is applied to carry out CFD flow field calculation, a characteristic value stability prediction model is adopted based on the calculation result, the stability boundary of the stability expansion measure condition is applied to the gas compressor and is estimated, and whether the target requirement is met is judged. If the target is reached, determining the current stability augmentation measure scheme as a final scheme; and if the standard is not met, returning to the detailed design stage of the stability expansion measure, and further optimizing the design result.
Through the established stability augmentation measure design method, a large number of experimental results carried out by the invention are summarized, and it is found that for the instability of the sharp waveform, when the axial momentum of the front edge of the rotor is increased and the position of the maximum value is pushed backwards, the stability margin of the corresponding gas compressor is improved, and the quantitative correlation between the axial momentum of the front edge of the rotor and the position of the maximum value is shown in fig. 5. Therefore, the axial momentum change of the front edge of the rotor can be used as a measuring method for reducing the load capacity of the blade tip by using stability expanding measures, and the correlation between the flow state and the stability margin of the compressor is quantized.
In summary, the invention provides a method suitable for judging flow instability of a gas compressor. Firstly, the speed distribution of a flow field near a high-speed compressor rotor is obtained through non-contact hot film testing equipment, the problem of monitoring main characteristic parameters of fluid near the rotor is solved, and the detailed description of the three-dimensional flow field in the rotor component based on experimental means is helpful for improving the understanding of the complex flow in the compressor. In addition, the definition of the related axial momentum and the calculation and analysis of the related parameters realize the judgment of the local instability occurrence region and define the instability form of the compressor. The benefit of the stability expanding means is greatly improved, and the stable working margin of the aero-engine is increased to the maximum extent.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present patent, not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. A method for judging local instability of an air compressor based on non-contact hot film testing equipment is characterized by comprising the following steps: the method comprises the following steps:
step 1: obtaining the velocity distribution of a flow field near a rotor component of the high-speed compressor;
step 2: calculating the axial momentum of the fluid near the rotor of the compressor through the velocity distribution;
and step 3: determining the correlation between the axial momentum of fluid in the compressor and the flow stability;
and 4, step 4: and determining a local instability region of the compressor and judging the instability form of the compressor.
2. The method for judging the local instability of the compressor based on the non-contact hot film testing equipment as claimed in claim 1, is characterized in that: the step 1 further comprises the following steps:
The speed of the boundary layer near the surface of the rotating part to be tested is measured through the hot film, electric signals related to the speed of the turbulent boundary layer of the rotating part to be tested are collected in real time, and finally data are transmitted to a computer through a universal serial bus interface of a front panel of the signal receiving and processing box, so that the speed distribution of a flow field near the gas compressor rotor is obtained.
3. The method for judging the local instability of the compressor based on the non-contact type hot film testing equipment as claimed in claim 1 is characterized in that: the step 2 further comprises the following steps:
in order to quantitatively analyze the axial momentum balance inside the compressor, the velocity distribution of a flow field near a compressor rotor needs to be obtained through an experimental measurement means, and the following formula is provided based on the relationship between heat dissipation and fluid velocity:
H＝(A+B*(U^0.5))*(Ts-T0)
wherein H is the heat dissipation, A, B are constants, U is the fluid velocity, TSIs the temperature of the hot-film probe, T0Is ambient temperature;
the heat generated by the energized current passing through the thermal film sensor probe is:
Q＝I2R
wherein, R is a tachometer resistance of the thermal film sensor probe, I is a current passing through the thermal film sensor probe, and Q represents heat generated by the thermal film sensor probe; the heat generated by the probe of the thermal film sensor during the power-on process is equal to the heat transferred by the fluid medium, that is, based on the principle of thermal balance, so that if H is Q, then:
I2R＝(A+B*(U^0.5))*(TS-T0)
Based on the relational expression of the speed and the temperature of the fluid near the compressor rotor, the local temperature can be converted into the speed distribution of the flow field near the compressor rotor after the local temperature is obtained through the hot film probe.
4. The method for judging the local instability of the compressor based on the non-contact thermal film testing equipment according to claim 1, wherein the step 3 further comprises the following steps:
based on a proper control body established around the rotor of the gas compressor, the axial momentum of the fluid can be calculated by combining the flow field velocity distribution measured through experiments; for the compressor rotor rotating at high speed, the axial resultant external force acting on the control body is the change of the axial momentum, and an axial momentum equation on each discrete control body unit is derived based on the speed change as follows:
wherein: [ integral ] represents the sign of integral, PZ-Pressure, P, on the left surface of the control bodyZ+Pressure, P, on the right surface of the control bodyCSRepresenting the pressure of the casing surface, PBTRepresenting the pressure of the lower surface in the vane passage, τCSRepresenting shear stress on the casing surface, τBTRepresenting shear stress on the lower surface within the blade channel,
represents the density of the fluid, WzWhich is representative of the axial velocity of the fluid, 
Representing the velocity (including direction) of the fluid,
unit vector, dA, representing the normal direction of the surface of the control bodyZ-Representing the area of the infinitesimal on the left surface of the control body, dAZ+Representing the area of the infinitesimal on the right surface of the control body, dACSRepresenting the area of infinitesimal elements on the surface of the cartridge, dABTRepresenting the area of the infinitesimal on the inner lower surface of the blade channel; z + and Z-represent the left and right sides of the control body, respectively, CS (casting surface) represents the casing surface, BT (bottom surface) represents the lower surface in the blade channel, T represents the shear stress on the surface of the control body, FBLADE-ZRepresenting the additional force caused by the rotation of the control body, dA representing the area of the infinitesimal on the surface of the control body, and Z representing the axial direction;
according to the momentum equation obtained by impulse theorem, the axial momentum on the control surface can be expressed as:
wherein ^ represents integral sign, rho represents fluid density, WzRepresenting the axial velocity of the fluid, wherein the axes of rotation of the compressors are each defined as the Z direction,
which is representative of the velocity of the fluid,
representing the unit vector of the normal direction of the surface of the control body, and dA representing the area of the infinitesimal on the surface of the control body; based on the formula, the velocity distribution of the flow field around the compressor rotor can be converted into the axial momentum.
5. The method for judging the local instability of the compressor based on the non-contact hot film testing equipment as claimed in claim 1, is characterized in that: the step 4 further comprises the following steps:
Calculated by means of suitable control bodies built around the compressor rotor and axial momentumObtaining the condition of the axial momentum around the rotor by a formula; based on this equation, it is known that the magnitude of the axial momentum on the control surface is determined by both the direction of the mass flow through the surface and the direction of the axial velocity, when WzWhen positive, the component representing the velocity of the fluid is positive in the Z-axis projection, i.e. the fluid has a tendency to move from upstream of the rotor to downstream of the rotor, WzWhen the value is negative, the flow has a flow trend opposite to the axial direction, for the flow condition inside the compressor rotor, the flow direction of the fluid is consistent with the axial direction, the flow is stable, the opposite direction means that the flow is separated and the vortex is formed, in addition, the larger the amplitude value is, the more obvious the flow separation is, the more serious the flow blockage caused by the vortex structure is, and the stronger the flow instability in the region is.
6. The method for judging the local instability of the compressor based on the non-contact type hot film testing equipment according to any one of claims 1 to 5 is applied to a system for detecting the local instability of the compressor.
7. A non-contact hot film testing device is applied to the method for judging the local instability of the gas compressor based on the non-contact hot film testing device, which is characterized in that the device obtains the speed distribution of a flow field near a high-speed gas compressor rotor through wireless data acquisition, transmission and dynamic data storage analysis, and then calculates the maximum axial momentum to represent the stable flowing condition of the gas compressor, and the method is characterized in that: comprises a rotary transmitter, a static receiver and a signal receiving and processing box;
The rotary emitter is fixed on a rotating shaft of the air compressor and is used for emitting a speed signal collected from a boundary layer to the static receiver;
the static receiver is coaxially opposite to the rotary transmitter, and provides electric energy for the rotary transmitter in an electric field induction mode and receives signals transmitted by the rotary transmitter, so that the flow field speed information near the rotor blade is stored;
and the signal receiving and processing box is connected with the static receiver through a serial bus interface and is used for carrying out dynamic data analysis on the information stored by the static receiver.
8. A non-contact thermal film based test apparatus according to claim 7, wherein: the rotary emitter comprises a thermal film probe, a CTA module and an A/D conversion module; the thermal film probe is connected with the input end of the CTA module, and the output end of the CTA module is connected with the input end of the A/D conversion module; the A/D conversion module is used for transmitting signals to the static receiver.
9. A non-contact thermal film based test apparatus according to claim 8, wherein: when the speed of a turbulent boundary layer of a fluid to be tested is measured, the thermal film probe is placed on the surface of the rotor component to be tested, and the CTA module is used for measuring an electric signal on the thermal film probe and transmitting the electric signal to the A/D conversion module; the A/D conversion module converts the electrical signal to a digital signal and transmits the digital signal to the stationary receiver.
10. A non-contact thermal film based test apparatus according to claim 8, wherein: the CTA module comprises a Wheatstone bridge; the CTA module is 70mm by 40mm by 20mm in size; the A/D conversion module has the size of 50mm multiplied by 60mm multiplied by 15 mm.
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