A method for controlling the Mach number of the incoming flow in a transient transonic wind tunnel airfoil test

Abstract

The application discloses a kind of temporary shock cross-speed wind tunnel airfoil test's Mach number control method, belong to wind tunnel airfoil test technical field.The existing technology is solved in traditional Mach number control method using conventional chamber reference point, it is difficult to be applicable to the problem that temporary shock cross-speed wind tunnel carries out airfoil test;The application selects standard airfoil model, carries out simulation calculation, obtains the distribution of airfoil model Mach number in free flow, i.e.no wind tunnel wall state;Using the same standard airfoil model as step S2, simulation calculation is carried out to the three-dimensional full simulation state of wind tunnel, according to the opening-closing ratio, the axial Mach number distribution of wind tunnel different opening-closing ratio test section side wall center line is obtained, in wind tunnel, by analysis, the Mach number at 3 times airfoil chord length from the leading edge of airfoil in flow direction is controlled to carry out standard airfoil model wind tunnel test.The application improves the precision of simulated flow Mach number and test section opening-closing ratio, and can be applied to temporary shock cross-speed wind tunnel airfoil test.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of methods for controlling the Mach number of incoming flow, in particular to a kind of methods for controlling the Mach number of incoming flow in the test of airfoil in transient transonic wind tunnel, belong to the technical field of wind tunnel airfoil test. BACKGROUND

[0002] Airfoil test can measure and obtain the pressure distribution of airfoil chord surface, lift, drag, moment, shock position and critical Mach number, etc. Aerodynamic characteristics, since there are many problems in directly measuring airfoil aerodynamic force with a balance, the more common test method is to place the airfoil model horizontally in the test section supported on both sides of the wall, by measuring the pressure distribution along the chord of the airfoil surface of the center section, and then obtaining the aerodynamic force of the airfoil by integration.

[0003] Airfoil test is usually carried out in a special two-dimensional wind tunnel (or two-dimensional test section, two-dimensional wind tunnel is generally referred to as airfoil wind tunnel), the height to width ratio of two-dimensional test section is generally 2-4, when the test section cross-sectional area is constant, the increase of test section height can reduce the disturbance of upper and lower tunnel wall to the flow around the model, can increase the chord length of airfoil model, and improve the test Reynolds number, but at the same time, the increase of chord length increases the influence of test section side wall boundary layer; Engineering test application also often uses three-dimensional wind tunnel to carry out airfoil test research, unlike two-dimensional wind tunnel, the height to width ratio of three-dimensional wind tunnel test section is generally about 1, the larger width of the wind tunnel must ensure that the airfoil model has a larger relative thickness to ensure that its aerodynamic elastic deformation can be ignored, so as to ensure that the flow along the airfoil chord is two-dimensional flow, increasing the relative thickness of the airfoil model means increasing the chord length of the model, which makes the blockage of the airfoil model in the wind tunnel larger, large blockage model will bring larger tunnel wall disturbance on one hand, which needs to use a weak tunnel wall disturbance structure to reduce the tunnel wall disturbance effect; on the other hand, large blockage model will seriously affect the accurate control and precise simulation of the Mach number of the incoming flow in the test section, so that there is a large deviation between the actual Mach number of the incoming flow in the model area and the reference point Mach number of the settling chamber used to control the Mach number of the incoming flow, and the actual Mach number of the incoming flow in the model area is affected by the coupling of test section opening-closing ratio τ, wall plate angle θw and settling chamber main flow injection slot ΔH, it is more complex to correct the difference between the actual Mach number of the incoming flow in the model area and the reference point Mach number of the settling chamber used to control the Mach number of the incoming flow. Therefore, when carrying out airfoil test in a conventional transient transonic wind tunnel, the method of using the conventional reference point Mach number of the settling chamber to control the Mach number of the incoming flow in the test section of the wind tunnel cannot accurately simulate the nominal Mach number corresponding to the free stream, and it is difficult to accurately control and simulate the Mach number of the incoming flow when carrying out airfoil test in a transient transonic wind tunnel, which makes it difficult for a conventional three-dimensional transient wind tunnel to carry out airfoil test.

[0004] In summary, a method for controlling the Mach number of incoming flow in the test of airfoil in transient transonic wind tunnel is needed. SUMMARY

[0005] The following presents a simplified summary of the application in order to provide a basic understanding of some aspects of the application. This summary is not an extensive overview of the application. It is not intended to identify key or critical elements of the application or to delineate the scope of the application. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.

[0006] In view of this, in order to solve the problem that the conventional Mach number control method using a conventional room reference point is difficult to be applied to the wing test of the transient shock transonic wind tunnel, the application provides a method for controlling the Mach number of the incoming flow in the wing test of the transient shock transonic wind tunnel.

[0007] The technical scheme is as follows: a method for controlling the Mach number of the incoming flow in the wing test of the transient shock transonic wind tunnel, comprising the following steps:

[0008] S1. selecting a standard wing model, performing simulation calculation through a CFD method, and obtaining the distribution of the Mach number of the incoming flow of the wing model in the free flow;

[0009] S2. selecting the standard wing model in step S1, performing simulation calculation on the three-dimensional full simulation state of the wind tunnel through the CFD method, and obtaining the axial Mach number distribution of the test section side wall center line of the wind tunnel at different opening-closing ratios, which includes two limit positions, i.e., the real wall and the maximum opening-closing ratio;

[0010] S3. in the wind tunnel, setting the opening-closing ratio of the wind tunnel to the appropriate opening-closing ratio selected in step S2, and performing the wind tunnel test of the standard wing model by controlling the Mach number at the position 3 times the wing chord length away from the leading edge of the wing in the incoming flow direction, to obtain the Mach number distribution at different positions of the test section side wall center line of the wind tunnel at the same opening-closing ratio;

[0011] S4. using the static pressure point at the position 3 times the wing chord length away from the leading edge of the wing in the incoming flow direction to control the Mach number of the incoming flow.

[0012] Further, in the S2, the axial Mach number distribution of the test section side wall center line of the wind tunnel at different opening-closing ratios has the following characteristics:

[0013] S21. in the free flow, the Mach number at the position 3 times the wing chord length away from the leading edge of the wing in the incoming flow direction is less than 0.002 lower than the Mach number of the far-field incoming flow, according to the requirement of the Mach number at this position is consistent with the Mach number of the far-field incoming flow, i.e., in the free flow, the wing has no interference with the Mach number distribution at the position 3 times the wing chord length away from the leading edge of the wing in the incoming flow direction;

[0014] S22. The axial Mach number distribution along the centerline of the test section sidewall in the flow direction is consistent with the free stream Mach number under the appropriate opening-closing ratio, that is, the Mach number of the flow far ahead of the airfoil is accurately simulated as the free stream Mach number under the appropriate opening-closing ratio;

[0015] S23. The Mach number at a position 3 chord lengths ahead of the airfoil in the flow direction is apparently lower than the free stream Mach number under the appropriate opening-closing ratio. In combination with S21 and S22, the Mach number at the position 3 chord lengths ahead of the airfoil in the flow direction is controlled to be consistent with the free stream Mach number, that is, consistent with the target Mach number of the flow, according to the CFD calculation results.

[0016] Further, in S3, the axial Mach number distribution along the centerline of the test section sidewall at different positions under the same opening-closing ratio has the following characteristics:

[0017] S31. It includes a plurality of different Mach numbers and angles of attack;

[0018] S32. The Mach number at a position 3 chord lengths ahead of the airfoil in the flow direction tends to be stable in the change affected by the airfoil, that is, the Mach number at the position in the wind tunnel test is not affected by the airfoil model and the change of the angle of attack.

[0019] The present application has the following advantages: the present application provides a method for controlling the Mach number of the incoming flow in a transient transonic wind tunnel wing test, and provides a method and principle for selecting the reference point position of the Mach number control static pressure of the incoming flow in a conventional three-dimensional transient wind tunnel wing test, which can quickly determine and accurately simulate the Mach number of the incoming flow and the opening-closing ratio of the test section; the present application adjusts the static pressure control point of the Mach number of the incoming flow in the transient wind tunnel from the static pressure control in the settling chamber to the static pressure at a proper position of the test section side wall from the leading edge of the wing, and can obtain a proper opening-closing ratio of the test section when the wind tunnel develops a wing, and can accurately control and simulate the nominal Mach number of the incoming flow; the present application selects the static pressure control reference point of the Mach number of the incoming flow at a proper position of the inlet of the test section side wall of the wind tunnel, avoids the influence of the opening-closing ratio of the test section, the wall plate angle and the main flow injection seam of the settling chamber on the Mach number of the test model area, and realizes the accurate control and simulation of the Mach number of the incoming flow when the conventional transient wind tunnel develops a wing test; the present application selects the static pressure control reference point of the Mach number of the incoming flow at a proper position of the inlet of the test section side wall of the wind tunnel, and the selection principle is that the Mach number at this position is not affected by the wing model in the free flow, and the Mach number at this position is not affected by the wing model and the change of the angle of attack in the wind tunnel. The actual Mach number at the Mach number control reference point determined by the principle can accurately simulate the Mach number of the incoming flow in the wing test, and determines a proper opening-closing ratio when the wind tunnel develops a wing test; the present application selects a position 3 times the chord length of the wing from the leading edge of the wing as the Mach number control reference point of the incoming flow, which can well solve the problem that the Mach number of the model area deviates greatly from the free flow due to the large blockage caused by the wing model across the entire test section, and cannot accurately control and simulate the Mach number of the incoming flow, and enables any conventional transient wind tunnel to have the ability to develop a wing test. BRIEF DESCRIPTION OF DRAWINGS

[0020] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the application. In the drawings:

[0021] Figure 1 It is a flowchart of a method for controlling the Mach number of the incoming flow in a transient transonic wind tunnel wing test;

[0022] Figure 2 It is a schematic diagram of the Mach number distribution of the free flow wing and the test section side wall centerline axis at different opening-closing ratios simulated by CFD simulation calculation;

[0023] Figure 3 It is a schematic diagram of the Mach number distribution of the test section side wall centerline axis at different positions during the wing test;

[0024] Figure 4 It is a schematic diagram of the standard wing pressure distribution comparison between the present application and the conventional method. DETAILED DESCRIPTION

[0025] In order to make the technical solutions and advantages in the embodiments of the present application clearer, the exemplary embodiments of the present application are further described in detail below with reference to the drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0026] Reference Figures 1-4 The present embodiment is described in detail, a Mach number control method for a transient cross-sonic wind tunnel airfoil test, specifically comprising the following steps:

[0027] S1. Select a standard airfoil model, perform simulation calculation by CFD means, and obtain the distribution of the Mach number of the airfoil model in the free flow direction (i.e. without the wind tunnel wall state), such as Figure 2 the green curve in the middle;

[0028] S2. Select the standard airfoil model described in step S1, perform simulation calculation by CFD means on the three-dimensional full simulation state of the wind tunnel (the three-dimensional full simulation state means that the calculation object includes the standard airfoil model, the real model of the transient cross-sonic wind tunnel cross-sonic test section), and obtain the axial Mach number distribution of the test section side wall center line at different opening-closing ratios of the wind tunnel, which includes two limit positions, i.e. the real wall ( Figure 2 the black curve in the middle) and the maximum opening-closing ratio ( Figure 2 the red curve in the middle);

[0029] S3. In the wind tunnel, set the opening-closing ratio of the wind tunnel to the appropriate opening-closing ratio selected in step S2, and at the same time, control the Mach number at 3 times the airfoil chord length from the airfoil leading edge in the flow direction to perform the wind tunnel test of the standard airfoil model, and obtain the Mach number distribution at different positions of the test section side wall center line at the same opening-closing ratio of the wind tunnel, such as Figure 3 ;

[0030] S4. The static pressure point at 3 times the airfoil chord length from the airfoil leading edge in the flow direction is used to control the Mach number of the incoming flow.

[0031] Further, in the S2, the axial Mach number distribution of the test section side wall center line of the wind tunnel at different opening-closing ratios has the following characteristics:

[0032] S21. In the free flow (green line in Figure 2 ), the near-field Mach number at 3 times the airfoil chord length from the airfoil leading edge in the flow direction is less than 0.002 lower than the far-field incoming flow Mach number, according to the requirements of , the Mach number here can be considered consistent with the far-field incoming flow Mach number, that is, it can be considered that the airfoil has no interference with the Mach number distribution at 3 times the airfoil chord length from the airfoil leading edge in the flow direction when the airfoil is in the free flow.

[0033] S22. The wind tunnel, under an appropriate opening / closing ratio ( Figure 2 (The blue curve represents 2.8%). Within a certain range, the axial Mach number distribution along the centerline of the test section sidewall in the direction of incoming flow completely coincides with the Mach number in free flow. That is, at this opening / closing ratio, the incoming flow Mach number within a certain range at the far front of the airfoil accurately simulates the incoming flow Mach number in free flow (Note: This process requires iterative optimization; if the axial Mach number distribution along the centerline of the test section sidewall in the direction of incoming flow completely coincides with the Mach number in free flow, then this opening / closing ratio is appropriate).

[0034] S23. Under an appropriate opening / closing ratio, the Mach number at a distance of 3 times the airfoil chord length from the airfoil leading edge in the direction of incoming flow is obviously lower than the Mach number at the same location in free flow. Combining S21 and S22, based on the CFD calculation results, the Mach number at a distance of 3 times the airfoil chord length from the airfoil leading edge in the wind tunnel should be controlled to be consistent with that in free flow, that is, consistent with the target Mach number of the incoming flow.

[0035] Furthermore, in S3, the Mach number distribution at different positions along the axial direction of the centerline of the test section sidewall for the same opening / closing ratio in the wind tunnel has the following characteristics:

[0036] S31. It includes multiple different Mach numbers and angles of attack to ensure the accuracy of the results;

[0037] S32. The Mach number at a certain distance of 3 times the airfoil chord from the airfoil leading edge in the direction of the incoming flow tends to be stable due to the influence of the airfoil. That is, the Mach number at this point is not affected by the airfoil model and its angle of attack during wind tunnel testing, so as to ensure that the Mach number at this point is not disturbed by the airfoil model.

[0038] Specifically, combining steps S1-S3, in the wind tunnel, due to excessive blockage of the airfoil model, there is a significant deviation between the near-field Mach number at a distance of 3 times the airfoil chord from the leading edge and the incoming flow Mach number at the entrance of the test section. Figure 3 In the test, the near-field Mach number at 3 times the airfoil chord length from the airfoil leading edge was about 0.01 lower than the far-field incoming flow Mach number at 6.9 times the airfoil chord length. Therefore, the incoming flow Mach number can be controlled by the static pressure point at the point where there is no free flow interference, i.e., 3 times the airfoil chord length in the direction of the incoming flow. This can represent the true Mach number at that point during the high-smotherm airfoil test.

[0039] refer to Figure 2 Ma represents the Mach number. The angle of attack of the airfoil is expressed in degrees (°), and C represents the airfoil chord length in mm. It is assumed that in free flow, the airfoil does not interfere with the Mach number distribution at a distance of 3 times the airfoil chord length from the leading edge of the airfoil in the direction of the incoming flow.

[0040] refer to Figure 3X represents the distance from the entrance of the test section. The distribution of Mach number at different positions along the axial direction of the centerline of the test section sidewall has the following characteristics: it includes multiple different Mach numbers and angles of attack; the Mach number at a distance of 3 times the airfoil chord from the airfoil leading edge in the direction of the incoming flow tends to be stable due to the influence of the airfoil, that is, the Mach number at this location is not affected by the airfoil model and its angle of attack during the wind tunnel test.

[0041] refer to Figure 4 X / C represents the relative position of the airfoil pressure measurement point, and Cp represents the pressure coefficient. The accuracy of airfoil pressure distribution obtained by the traditional method is extremely poor. However, by using the present invention, the obtained airfoil pressure distribution is completely consistent with the standard data. The present invention determines the position of the static pressure reference point of the incoming Mach number and the opening and closing ratio of the test section when the wind tunnel conducts airfoil tests by using a standard airfoil model. That is, it establishes the ability of the transient transonic wind tunnel to conduct airfoil tests. After the ability of the transient transonic wind tunnel to conduct airfoil tests is established, the wind tunnel has the ability to conduct airfoil tests.

[0042] The specific functions of the process in this invention are as follows:

[0043] (1) First, the distribution of Mach number in the direction of the airfoil model in free flow is obtained through CFD simulation calculation. Figure 2 The green line in the diagram aims to obtain the Mach number at an appropriate location on the leading edge of the airfoil model that can be considered as the "undisturbed" Mach number. Figure 2 (Point 3C of the green line in the middle).

[0044] (2) Then, by CFD simulation, different opening and closing ratios of the wind tunnel in a three-dimensional full simulation state are calculated to obtain the axial Mach number distribution of the test section sidewall centerline at different opening and closing ratios. The purpose is to obtain an opening and closing ratio in which the distribution of the axial Mach number of the test section sidewall centerline coincides with that in free flow. Figure 2 The blue line in the diagram corresponds to an opening / closing ratio of 2.8%, which meets this condition.

[0045] (3) With the support of (1) and (2) above, the wind tunnel opening and closing ratio is then set to 2.8%, and the Mach number of the static pressure point at 3 times the airfoil chord length in the direction of the incoming flow on the sidewall of the wind tunnel test section is controlled. The test is carried out accordingly, and the results can be obtained. Figure 4 The red curve in the middle is very satisfactory;

[0046] Traditional transient control methods are difficult to use for airfoil testing (resulting in incorrect test results). This invention is applicable to any wind tunnel and can achieve satisfactory control results.

[0047] While the application has been described in accordance with the various embodiments shown and described, it is to be understood that the application is not limited to those precise embodiments, and that various modifications and changes can be made by those skilled in the art without departing from the scope of the present application. Furthermore, the language used in this specification has been principally selected for readability and instructional purposes and can not have been selected to delineate or circumscribe the patent rights to which it refers. Accordingly, the present application is intended to be illustrative, but not limiting, of the scope of the application, which is set forth with particularity in the claims that follow.

Claims

1. A method for controlling the Mach number of the incoming flow in a transient transonic wind tunnel airfoil test, characterized in that, The method comprises the following steps: S1. Select a standard airfoil model, simulate and calculate by CFD means to obtain the distribution of the Mach number of the airfoil model in the flow direction in free flow; S2. Select the standard airfoil model in step S1, simulate and calculate the three-dimensional full simulation state of the wind tunnel by CFD means to obtain the axial Mach number distribution of the test section side wall center line of the wind tunnel at different opening-closing ratios, which includes two limit positions, i.e. the real wall and the maximum opening-closing ratio; S3. In the wind tunnel, set the opening-closing ratio of the wind tunnel to the appropriate opening-closing ratio selected in step S2, and control the Mach number at 3 times the airfoil chord length from the leading edge of the airfoil in the flow direction to perform a standard airfoil model wind tunnel test to obtain the axial Mach number distribution of the test section side wall center line of the wind tunnel at the same opening-closing ratio at different positions; S4. The static pressure point at 3 times the airfoil chord length in the flow direction is used to control the Mach number of the flow.

2. The method of claim 1, wherein the method is a method of controlling the Mach number of the incoming flow in a transonic wind tunnel wing profile test with a temporary shock, characterized in that, In S2, the axial Mach number distribution of the test section side wall center line of the wind tunnel at different opening-closing ratios has the following characteristics: S21. In free stream, the Mach number at the near field in the flow direction at 3 chord lengths from the leading edge of the airfoil is less than 0.002 lower than the Mach number of the far field flow, according to the requirement that the Mach number here is consistent with the Mach number of the far field flow, i.e. in free stream, the airfoil has no interference with the Mach number distribution of the flow in the flow direction at 3 chord lengths from the leading edge of the airfoil; S22. Under the appropriate opening-closing ratio of the wind tunnel, the axial Mach number distribution of the test section side wall center line in the flow direction is completely consistent with the Mach number in free flow, i.e. under the appropriate opening-closing ratio, the Mach number far in front of the airfoil accurately simulates the Mach number in the flow in the free flow state; S23. Under the appropriate opening-closing ratio of the wind tunnel, the Mach number at 3 times the airfoil chord length from the leading edge of the airfoil in the flow direction is obviously lower than the Mach number at this position in free flow, combined with S21 and S22, according to the CFD calculation result, the Mach number at 3 times the airfoil chord length from the leading edge of the airfoil in the flow direction in the wind tunnel is controlled to be consistent with that in free flow, i.e. consistent with the target Mach number of the flow.

3. The method of claim 2, wherein the method is characterized by: In S3, the axial Mach number distribution of the test section side wall center line of the wind tunnel at the same opening-closing ratio has the following characteristics: S31. It includes a plurality of different Mach numbers and angles of attack; S32. The Mach number at 3 times the airfoil chord length from the leading edge of the airfoil in the flow direction tends to be stable under the influence of the airfoil, i.e. the Mach number at this position in the wind tunnel is not affected by the airfoil model and the change of the angle of attack.

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