CN110749075A - Stepped guide plate device for jet flow vortex elimination in limited space - Google Patents
Stepped guide plate device for jet flow vortex elimination in limited space Download PDFInfo
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- CN110749075A CN110749075A CN201910930450.3A CN201910930450A CN110749075A CN 110749075 A CN110749075 A CN 110749075A CN 201910930450 A CN201910930450 A CN 201910930450A CN 110749075 A CN110749075 A CN 110749075A
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
- F24F13/00—Details common to, or for air-conditioning, air-humidification, ventilation or use of air currents for screening
- F24F13/08—Air-flow control members, e.g. louvres, grilles, flaps or guide plates
- F24F13/081—Air-flow control members, e.g. louvres, grilles, flaps or guide plates for guiding air around a curve
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Abstract
The invention provides a stepped flow guide plate device for jet flow vortex elimination in a limited space, which comprises a first-step annular flow guide structure, a second-step annular flow guide structure and an Nth-step annular flow guide structure which are sequentially connected, wherein the diameter of the Nth-step annular flow guide structure is sequentially increased, and the diameter of the first-step annular flow guide structure is the smallest; the first-stage annular flow guide structure is provided with a first cavity for fluid to pass through at the central position of one side close to the fluid inlet, and the other side far away from the fluid inlet is provided with a second cavity for fluid to pass through. The stepped guide plate device for the jet flow vortex elimination in the confined space can effectively reduce the influence range of the vortex area in the confined space flow field.
Description
Technical Field
The invention relates to industrial ventilation, in particular to a stepped flow guide plate device for jet vortex elimination in a flow-limited space.
Background
In the actual industrial ventilation field, mainly relate to the ventilation control of industrial operation in welding workshop or special confined space, factors such as jet distribution, pollutant diffusion law, confined space shape, size all can influence the comprehensive ventilation effect in confined space during the ventilation, bring great degree of difficulty for the ventilation in confined space. When workers weld inside, a large amount of welding smoke dust is generated, and the smoke dust is retained inside due to a vortex area generated by space limitation and cannot be removed, so that the physical health of the workers is seriously influenced, and the occupational disease incidence rate is high. Therefore, the vortex-eliminating device is added in the limited space to eliminate the unfavorable vortex and improve the working environment of workers. The limitation of the side wall of the limited space of the jet flow causes the pressure gradient of the near wall to be increased, the existence of the pressure gradient causes the expansion rate of the jet flow, the shape of the velocity distribution and the growth rate of the boundary layer to be changed in the limited space, and particularly, the reverse pressure gradient causes the flow of the jet flow to be complicated. The confined jet is generally divided into a plurality of zones, a fundamental zone, a loop zone, and a pipe flow development zone.
Different from the development process of free jet flow, the jet flow enters a limited space at an air supply port, the jet flow expands under turbulence pulsation, meanwhile, the surrounding fluid is sucked by the coil, at the moment, the jet flow width is increased along the flow direction, the cross-sectional area of the jet flow is increased, the flow rate is increased along the way, and similar speed distribution is formed as a basic section. But the jet flow is quickly sucked to meet the wall surface to generate a vortex area, and the speed direction of the jet flow in the jet flow is reversely changed in a large vortex group vortex area generated at the position close to the pipe wall. This is because the inlet velocity of the surrounding fluid is zero, and no upstream flow is supplemented after being entrained by the jet, and at this time, the downstream fluid backflow close to the wall in the space is the circulation flow. According to the Bernoulli equation, when the jet meets the sudden expansion of the boundary, the flow speed at the position close to the wall surface is reduced, and the pressure is increased, so that the adverse pressure gradient is generated. The boundary layer separation is caused under the combined action of the reverse pressure gradient and the fluid viscosity at the position close to the wall, so that the wrapping vortex is expanded to form a vortex area, and the working condition range is larger. Then the restricted jet flow is developed to the wall surface, and a larger adverse pressure gradient appears in the near-wall area, so that the velocity distribution of the restricted space section begins to change continuously along the flow direction and gradually becomes a fully developed pipe flow. It can be seen that the vortex at the side wall of the limited space of the second stage circulation section can cause adverse effect on the ventilation of the limited space, and the problems of low ventilation efficiency and the like can occur.
Disclosure of Invention
Aiming at the defects and shortcomings in the prior art, the invention aims to provide a stepped guide plate device for vortex elimination of confined space jet flow, and solves the technical problems that the vortex area in the existing confined space flow field has a large influence range and cannot meet the engineering requirements.
In order to achieve the purpose, the invention has the following realization process:
a ladder-type guide plate device for jet flow vortex elimination in a confined space comprises a first-order annular guide structure, a second-order annular guide structure and an Nth-order annular guide structure which are sequentially connected, wherein N is more than 1 and less than or equal to 32, the first-order annular guide structure is close to one side of a fluid inlet, the diameters of the N-order annular guide structures are sequentially increased, and the diameter of the first-order annular guide structure is the smallest;
a first cavity for allowing fluid to pass through is arranged at the central position of one side of the first-stage annular flow guide structure close to the fluid inlet, and the diameter of the first cavity is smaller than that of the first-stage annular flow guide structure;
a second cavity for allowing fluid to pass through is arranged on the other side, away from the fluid inlet, of the first-stage annular flow guide structure, and the diameter of the second cavity is equal to that of the first-stage annular flow guide structure;
and an N +1 th cavity for allowing fluid to pass through is arranged on the other side of the nth-step annular flow guide structure away from the fluid inlet, and the diameter of the N +1 th cavity is equal to that of the nth-step annular flow guide structure.
Specifically, the height H of the N-step annular flow guide structure is: h is more than 0 and less than or equal to 0.2D, D is the hydraulic diameter of the limited space, the hydraulic diameter refers to the ratio of four times of the area of the flow cross section to the perimeter, and for a circular pipe, the real diameter of the circular pipe is the hydraulic diameter.
Furthermore, the height h of the first-stage annular flow guide structure is equal to the difference d between the radius of one side of the first-stage annular flow guide structure close to the fluid inlet and the radius of the cavity1；
The height h of the rest Nth-step annular flow guide structures is equal to the radius of the Nth-step annular flow guide structure and the Nth-1 st-step annular flow guide nodeRadius difference d of structure2；
And d is1＝d2。
Furthermore, the length y and N of the vortex region of the flow field need to satisfy a functional relationship: y is a + bN;
a and b are constants, and the values are both-1.
Specifically, the stepped deflector device is wholly vertical to the longitudinal axis direction of the limited space.
Compared with the prior art, the invention has the beneficial effects that:
the stepped guide plate device for jet flow vortex elimination in the confined space has the main contribution that the influence range of a vortex area in a flow field of the confined space can be effectively reduced, the minimum value of the length of the vortex area can reach 0.18m (the length of the original vortex area is 0.45m), the aim of effectively controlling the characteristics of the flow field of the jet flow confined space to meet the actual requirements of engineering can be achieved, and a good flow equalizing effect can be achieved.
Drawings
FIG. 1 is a three-dimensional schematic view of the apparatus of the present invention.
Fig. 2 is a flow chart of the flow field of the restricted space of the original jet.
Fig. 3 is a flow diagram of a flow field in a jet confined space in which the present invention is installed.
Fig. 4 is a comparison graph of a fitted curve of the length of the vortex region in the confined space varying with the number of stages of the baffle device and the original state in the embodiment.
Fig. 5 and 6 are an overall structure diagram and a cross-sectional view of the embodiment of the invention, respectively.
The various reference numbers in the figures represent:
1-a speed inlet, 2-a deflector device, 3-a limited cylindrical drum shell, 4-a speed outlet, 5-a first cavity, 6-a second cavity and 7-an Nth cavity.
Detailed Description
The jet flow limited space refers to a phenomenon that fluid passes through the limited space, is common in engineering, and mainly relates to ventilation control of industrial operation in a welding workshop or a special limited space in the field of actual industrial ventilation. When workers weld inside, a large amount of welding smoke dust is generated, and the smoke dust is retained inside due to a vortex area generated by space limitation and cannot be removed, so that the physical health of the workers is seriously influenced, and the occupational disease incidence rate is high. Therefore, the vortex-eliminating device is added in the limited space to eliminate the unfavorable vortex and improve the working environment of workers. In engineering, the length of the vortex region needs to be controlled according to actual conditions so as to reasonably utilize the length of the vortex region, and the influence of the overlong length of the vortex region of the deflector device is too large, which is unfavorable in engineering.
The invention researches the relationship between the length y of the vortex area of the guide plate device and the length N according to the following method:
the method comprises the following steps:
step one, determining the flow field state of the stepped flow deflector device at a certain position of a jet flow limited space, and changing the order N of the stepped flow deflector device according to the size of the limited space, wherein N satisfies the inequality 1 < N < 32. Applying a Reynolds stress model and combining a SIMPLE algorithm:
the basic control equation is as follows:
equation of continuity
Equation of momentum
R component
z component
Turbulent kinetic energy equation (k equation)
Diffusion equation (Epsilon equation)
In the above equation: sνIs a source item;ρfluid density, kg/m3(ii) a P is static pressure, Pa; mu is a turbulent viscosity coefficient Pa x s;
σεthe Plantt number of the diffusivity epsilon of turbulent energy is 1.3, η0＝4.38；β＝0.012；Cμ,C1ε,C2εTaking the empirical constants of 0.09, 1.44 and 1.92 respectively;
then simulating a velocity field in a jet flow limited space before the stepped flow guide plate device is added, so as to obtain the flow field distribution after the stepped flow guide plate device is added under different working conditions;
and step two, determining the length y of the vortex area of the flow field of the stepped flow deflector after the stepped flow deflector is added into the flow field along with the order x of the stepped flow deflector, obtaining the numerical change of the length of the vortex area along with the order x of the stepped flow deflector according to the step one, and obtaining a fitting curve (correlation coefficient 0.73) of the length y of the vortex area of the flow field along with the order N of the stepped flow deflector by utilizing a statistical principle, wherein the fitting curve is shown in figure 4. And fitting equation of the length y of the vortex area of the flow field along with the change of the order N of the stepped flow deflector device:
y＝a+bN
wherein x satisfies the inequality 1 < N < 32, ab is constant, and the value is between-1 and 1.
Specific examples of the present invention are given below.
Example 1:
as shown in fig. 1-6, the present embodiment provides a flow deflector device for vortex suppression of jet flow in a confined space, where the flow deflector device includes a first-order annular flow guiding structure, a second-order annular flow guiding structure, and an nth-order annular flow guiding structure, where N is greater than 1 and less than or equal to 32, the first-order annular flow guiding structure is close to one side of a fluid inlet, diameters of the N-order annular flow guiding structures are sequentially increased, and the diameter of the first-order annular flow guiding structure is the smallest;
a first cavity for allowing fluid to pass through is arranged at the central position of one side of the first-stage annular flow guide structure close to the fluid inlet, and the diameter of the first cavity is smaller than that of the first-stage annular flow guide structure;
a second cavity for allowing fluid to pass through is arranged on the other side, away from the fluid inlet, of the first-stage annular flow guide structure, and the diameter of the second cavity is equal to that of the first-stage annular flow guide structure;
and an N +1 th cavity for allowing fluid to pass through is arranged on the other side of the nth-step annular flow guide structure away from the fluid inlet, and the diameter of the N +1 th cavity is equal to that of the nth-step annular flow guide structure.
Specifically, the height H of the N-step annular flow guide structure is: h is more than 0 and less than or equal to 0.2D, and D is the hydraulic diameter of the limited space.
Furthermore, the height h of the first-stage annular flow guide structure is equal to the difference d between the radius of one side of the first-stage annular flow guide structure close to the fluid inlet and the radius of the cavity1；
The height h of the rest Nth-step annular flow guide structures is equal to the difference d between the radius of the Nth-step annular flow guide structure and the radius of the (N-1) th-step annular flow guide structure2；
And d is1＝d2。
Furthermore, the length y and N of the vortex region of the flow field need to satisfy a functional relationship: y is a + bN;
b and b are constants, and values are in the range of-1 to 1.
Specifically, the stepped deflector device is wholly vertical to the longitudinal axis direction of the limited space.
The original state is that the airflow enters the restricted space through the inlet, and a vortex area is formed quickly in the first half section of the restricted space due to the limitation of the side wall, so that the flow field characteristic becomes unstable, and the airflow is retained in the restricted space and is difficult to remove, as shown in fig. 2. Therefore, the guide plate device is placed at the front end of the limited space, and the air flow is rectified and guided through the guide plate device, so that the air flow is quickly discharged from the limited space, and the purpose of eliminating unfavorable vortex is achieved, as shown in fig. 3.
According to the technical scheme, by taking the internal vortex elimination of the cylindrical limited drum model as an example, a two-dimensional rotation axis symmetry model is adopted during simulation so as to accelerate the operation speed and save the storage space. First, the dimensions of each part of the restricted cylindrical drum model were determined, where the cylindrical drum length L was 1.35m, the diameter D was 300mm, the velocity inlet diameter D was 150mm, and the velocity outlet diameter was 300 mm. A coordinate system is established as shown in figure 2, and the small diameter of the small circle of the upper bottom surface of the stepped guide plate device is 100mm, the large diameter of the circle of the lower bottom surface of the stepped guide plate device is 1100mm, and the starting point and the end point of the step are fixed at the points (0.05 and 0.11), regardless of the thickness of the stepped guide plate device. The change of the number of the steps N of the stepped diversion plate device is shown in the table 1, the three-dimensional schematic diagram of the embodiment model is shown in fig. 5, and the sectional view is shown in fig. 6.
And then simulating a velocity field in a jet flow limited space before the stepped flow deflector device is arranged, wherein the boundary of a jet flow inlet adopts parallel flow air supply, and is a velocity-inlet. The circular jet velocity is 1m/s with a direction positive along the x-axis and the exit boundary is pressure-outlet. Because the operating position of personnel and the position and the temperature of a heat source are not considered, only the restricted circular jet flow field law is studied, and the rest surfaces are all heat insulation walls in a pressure-velocity coupling mode. The turbulence model adopts a Realizable k-epsilon two-equation model. Two-dimensional windward format dispersion is adopted, the pressure correction setting of the relaxation iteration factor is 0.3, the momentum correction is 0.7, and the columnar limited space wall surface adopts non-slip boundary conditions. The numerical simulation calculation is more efficient by adopting a two-dimensional model, the space in the solver selects axisymmetric swirl, and the two-dimensional model can generate a multi-dimensional revolving body by revolving the x coordinate axis by adopting an axis symmetric boundary. Carrying out initial expansion calculation by taking a jet flow velocity inlet as a starting point, and setting convergence residual errors of a continuity equation and a momentum equation to be 10-4。
The number of the change of the length of the vortex region extracted by post-processing of the simulation result along with the order N of the stepped deflector device is shown in the table 1:
TABLE 1 vortex length data sheet for each working condition
By using the statistical principle, a fitting curve (correlation coefficient 0.73)) of the length y of the vortex region of the flow field along with the change of the order N of the stepped deflector device is obtained and is shown in FIG. 4. And fitting equation of the length y of the vortex area of the flow field along with the change of the order N of the stepped flow deflector device:
y＝0.19+0.01N
wherein N satisfies the inequality 1 < N < 32. When N is 2, the length y of the vortex area of the flow field is 0.18 m.
Compared with the original state, the vortex area length is obviously shortened and the influence range is reduced after the stepped guide plate device is added in the limited boiler barrel, so that the effective control on the jet flow limited space flow field characteristic is achieved, and the purpose of meeting the actual engineering requirement is realized.
Claims (5)
1. A ladder-type guide plate device for jet flow vortex elimination in a confined space is characterized by comprising N-step annular guide structures which are connected in sequence, wherein N is more than 1 and less than or equal to 32, N is a natural number, the diameters of the N-step annular guide structures are increased in sequence, and the diameter of the first-step annular guide structure is the smallest;
the first-stage annular flow guide structure is close to one side of the fluid inlet, a first cavity for allowing fluid to pass through is arranged at the central position of one side of the first-stage annular flow guide structure close to the fluid inlet, and the diameter of the first cavity is smaller than that of the first-stage annular flow guide structure;
a second cavity for allowing fluid to pass through is arranged on the other side, away from the fluid inlet, of the first-stage annular flow guide structure, and the diameter of the second cavity is equal to that of the first-stage annular flow guide structure;
and an N +1 th cavity for allowing fluid to pass through is arranged on the other side of the nth-step annular flow guide structure away from the fluid inlet, and the diameter of the N +1 th cavity is equal to that of the nth-step annular flow guide structure.
2. The baffle device for vortex shedding of a confined space jet of claim 1, wherein the height H of the N-step annular flow guiding structure is taken as: h is more than 0 and less than or equal to 0.2D, and D is the hydraulic diameter of the limited space.
3. As in claimThe baffle device for vortex suppression of jet flow in a confined space of claim 1, wherein the height h of the first-stage annular flow guiding structure is equal to the difference d between the radius of the first-stage annular flow guiding structure on the side close to the fluid inlet and the radius of the cavity1；
The height h of the rest Nth-step annular flow guide structures is equal to the difference d between the radius of the Nth-step annular flow guide structure and the radius of the (N-1) th-step annular flow guide structure2；
And d is1＝d2。
4. The baffle device for confined space jet vortex suppression as claimed in claim 1 wherein the length y and N of the flow field vortex region are in a functional relationship:
y＝a+bN；
wherein a and b are constants and values of-1.
5. The baffle means for vortex shedding of a confined space jet as claimed in claim 1 wherein said stepped baffle means is generally perpendicular to the longitudinal axis of the confined space.
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