A device for reducing sidewall interference in transient wind tunnel airfoil tests

Abstract

The present invention proposes a device for reducing side wall interference in a temporary wind tunnel airfoil test, which belongs to the field of aerodynamic test technology in aerospace wind tunnel tests. The purpose is to reduce the interference effect of the side wall during a temporary wind tunnel airfoil test. The present invention includes an airfoil to be tested, an isolation device, a wind tunnel wall and a conformable cover plate; a square support structure is provided at both ends of the airfoil to be tested, and is fixed to the wind tunnel wall through the support structure, and two conformable cover plates are fixed to the upper and lower sides of the support structure by a second fixing screw, and a mounting groove is provided between the conformable cover plate and the airfoil to be tested; the isolation device is disc-shaped as a whole, and a rectangular through hole of the same size as the support structure is provided in the middle of the disc, and the isolation device is installed in the mounting groove and fixedly connected to the side of the airfoil to be tested by a first fixing screw. The present invention effectively reduces the interference effect of the side wall during a temporary wind tunnel airfoil test, improves the efficiency of the temporary wind tunnel airfoil test, and reduces the test cost.

Description

Technical Field

[0001] The invention relates to the technical field of aerodynamic testing in aerospace wind tunnel tests, and in particular to a device for reducing sidewall interference in a transient wind tunnel airfoil test. Background Art

[0002] Airfoil design is a very important part of aircraft design because it determines the lift and drag of the aircraft during flight. Through airfoil wind tunnel testing, the aerodynamic performance of the airfoil can be verified and improved, so that the aircraft has better controllability, stability and fuel efficiency. Therefore, airfoil wind tunnel testing is an indispensable part of aircraft development, and is even more indispensable in the fields of transportation, wind energy utilization, etc. Although numerical simulation has been widely used in recent years, for complex flow conditions, experiments are still needed to verify and correct the calculation results. Airfoil wind tunnel testing is an important means to verify theoretical models, optimize designs, study aerodynamic characteristics, and evaluate aircraft safety. Through wind tunnel testing, accurate and reliable test data can be obtained, providing strong support for aviation engineers and designers, and promoting the development and improvement of aircraft technology.

[0003] Generally speaking, wind tunnel tests on airfoils focus on their two-dimensional nature, usually using pressure measurement. By measuring the pressure distribution on the airfoil surface and integrating it, data such as the airfoil's lift and drag are obtained. Aerodynamic characteristics such as the airfoil's shock wave position and critical Ma number are also obtained. The airfoil model is usually supported on the two side walls of the wind tunnel in the wind tunnel test section, with pressure measurement points arranged in the mid-section of the airfoil to study the airfoil's aerodynamic characteristics. In airfoil wind tunnel tests, the influence of the tunnel walls on the test data can be divided into interference from the upper and lower walls and interference from the sidewall boundary layer. Generally speaking, the airfoil spanning the wind tunnel is relatively thin, and the upper and lower tunnel walls are far away from the airfoil. At the same time, the upper and lower tunnel walls have openings and slots that eliminate interference from the tunnel walls and the boundary layer. Therefore, in airfoil tests, the interference from the upper and lower tunnel walls is often small and can be ignored. The side walls of the wind tunnel are directly connected to the airfoil, and the side walls of the wind tunnel are usually solid walls in order to install the airfoil. Therefore, the thickness of the side wall boundary layer of the wind tunnel in the airfoil area is much thicker than the boundary layer of the airfoil. When conducting airfoil tests, there is a large adverse pressure gradient on the airfoil surface, which causes the airflow to separate at the intersection of the airfoil and the side wall boundary layer, and then propagate along the span direction, thereby affecting the flow of the middle measurement section. At supersonic speeds, the shock waves on the airfoil will cause the airflow separation of the side wall boundary layer, thereby affecting the middle measurement section along the span direction. Since it is difficult to correct the side wall interference, and in some cases, the test data cannot be corrected.

[0004] In summary, it is urgent to design a device that can reduce the interference effect of the side wall during the temporary wind tunnel airfoil test, improve the efficiency of the temporary wind tunnel airfoil test, and reduce the test cost. Summary of the Invention

[0005] A brief overview of the present invention is provided below to provide a basic understanding of certain aspects of the present invention. It should be understood that this overview is not an exhaustive overview of the present invention. It is not intended to identify key or important aspects of the present invention, nor is it intended to limit the scope of the present invention. Its purpose is simply to present certain concepts in a simplified form as a prelude to the more detailed description discussed later.

[0006] In view of this, in order to reduce the interference effect of the side wall during a temporary wind tunnel airfoil test, the present invention provides a device for reducing the side wall interference during a temporary wind tunnel airfoil test.

[0007] Solution: A device for reducing sidewall interference in a transient wind tunnel airfoil test, comprising an airfoil to be tested, an isolation device, a wind tunnel wall, and a conformable cover plate;

[0008] The two ends of the airfoil to be measured are provided with square support structures and fixed to the wind tunnel wall through the support structures. Two conformable cover plates are fixed to the upper and lower sides of the support structures by second fixing screws. A mounting groove is provided between the conformable cover plates and the airfoil to be measured.

[0009] The isolation device is disc-shaped as a whole, with a rectangular through hole of the same size as the supporting structure provided in the middle of the disc. The isolation device is installed in the mounting groove and fixedly connected to the side surface of the airfoil to be measured by a first fixing screw.

[0010] Furthermore, the isolation device has a thickness of 12 mm.

[0011] Furthermore, the front edge of the isolation device is semi-wedge-shaped, and the wedge chamfer is 15°.

[0012] Furthermore, the distance between the isolation device and the wind tunnel wall is greater than the thickness of the isolation device.

[0013] Furthermore, the center of the isolation device coincides with the center point of rotation of the airfoil to be measured.

[0014] Furthermore, the conformable cover plate has the same shape as the airfoil to be measured.

[0015] The present invention has the following beneficial effects compared to the prior art:

[0016] 1. The device of the present invention is installed at both ends of the airfoil. It separates the test model from the wind tunnel sidewall boundary layer, forming three channels. This reduces the induced velocity and induced angle of attack of the central section caused by the trailing vortex caused by the change in the circulation within the wind tunnel sidewall boundary layer.

[0017] 2. The device of the present invention effectively reduces the interference effect of the sidewall during transient wind tunnel airfoil testing, reducing test interruptions and invalid data caused by sidewall boundary layer problems, shortening the airfoil wind tunnel test cycle and reducing testing costs.

[0018] 3. The device of the present invention can adapt to the wind tunnel test requirements of different types of airfoils and different speed conditions, broadening the application boundaries of airfoil wind tunnel testing and enabling experimental research to cover more extreme conditions and special designs. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0020] Figure 1 The figure is a schematic diagram of the structure of a device for reducing sidewall interference in a transient wind tunnel airfoil test;

[0021] Figure 2 is the position relationship diagram between the conformal cover and the airfoil to be measured;

[0022] Figure 3 This is a schematic diagram of the structure for installing the isolation device;

[0023] Figure 4 It is the cross-sectional view of the installation groove;

[0024] Figure 5 This is a schematic diagram of the installation of the flexible cover;

[0025] Figure 6 This is a comparison chart of the impact of the side wall with and without the isolation device installed on the airfoil span-wise pressure distribution; the abscissa is the distance from the airfoil center to the hole wall, and the ordinate is the pressure distribution coefficient of the airfoil along the span.

[0026] In the figure: 1-airfoil to be measured, 2-isolation device, 3-wind tunnel wall, 4-first fixing screw, 5-support structure, 6-conformal cover, 7-second fixing screw, 8-mounting slot. DETAILED DESCRIPTION

[0027] To make the technical solutions and advantages of the embodiments of the present invention more clearly understood, exemplary embodiments of the present invention are further described in detail below with reference to the accompanying drawings. It should be noted that the embodiments described are only a portion of the embodiments of the present invention, and are not an exhaustive list of all embodiments. It should be noted that the embodiments of the present invention and the features thereof may be combined with each other unless they conflict.

[0028] Example 1, reference Figure 1-5 The present embodiment is described as follows: a device for reducing sidewall interference in a temporary wind tunnel airfoil test comprises an airfoil to be tested 1, an isolation device 2, a wind tunnel wall 3, and a conformable cover plate 6;

[0029] The two ends of the airfoil to be measured 1 are provided with square support structures 5, and are fixed to the wind tunnel wall 3 through the support structures 5. Two conformable cover plates 6 are fixed to the upper and lower sides of the support structures 5 by second fixing screws 7. A mounting groove 8 is provided between the conformable cover plates 6 and the airfoil to be measured 1;

[0030] The isolation device 2 is disc-shaped as a whole, with a rectangular through hole of the same size as the supporting structure 5 provided in the middle of the disc. The isolation device 2 is installed in the mounting groove 8 and is fixedly connected to the side of the airfoil 1 to be measured by a first fixing screw 4.

[0031] Furthermore, the isolation device 2 has a thickness of 12 mm.

[0032] Furthermore, the front edge of the isolation device 2 is semi-wedge-shaped, and the wedge chamfer is 15°.

[0033] Furthermore, the distance between the isolation device 2 and the wind tunnel wall 3 is greater than the thickness of the isolation device 2 .

[0034] Furthermore, the center of the isolation device 2 coincides with the center point of rotation of the airfoil 1 to be measured.

[0035] Furthermore, the conformable cover plate 6 has the same outer shape as the airfoil 1 to be measured.

[0036] Example 2, reference Figure 1-5 This embodiment is described by conducting an experimental verification using a device for reducing sidewall interference in a transient wind tunnel airfoil test;

[0037] The circular radius of the isolation device 2 is calculated, and four radii are selected: R / c=0.7, R / c=0.85, R / c=1, and R / c=1.15 for numerical simulation, where R is the radius of the circular device and c is the chord length of the airfoil;

[0038] The free flow of the airfoil 1 to be tested with the device of the present invention and the 2D airfoil 1 to be tested were compared and calculated. The computational grids used in all models were structured grids, and the grid generation platform was Icemcfd. The unstructured grid format *.cgns was exported and input into the UNSMB platform for calculation. The turbulence model used in all calculations was the SST model.

[0039] Under subsonic conditions, before the chord length reaches 30%, the upper surface of the airfoil 1 to be tested is installed with the isolation device 2 with a radius of R / c=1 The value is closest to the 2D free stream airfoil value, and after the chord length reaches 30%, the effect of the size of the isolation device 2 on the pressure distribution on the upper surface of the airfoil 1 to be tested weakens;

[0040] Under transonic conditions, the isolation devices of different diameters have an impact on the upper surface of the airfoil. Influence, before the chord length is 30%, the upper surface of the airfoil 1 to be tested with the isolation device 2 having a radius of R / c≥1 is installed The value is closest to the 2D free stream airfoil value, after 30% of the chord length, on the upper surface of the airfoil 1 to be tested with the isolation device 2 with a radius of R / c=1 The value is closest to the 2D free stream airfoil value, and the isolation device 2 is the lower surface of the airfoil 1 to be measured. The impact is small.

[0041] After the isolation device 2 is added to the airfoil 1 to be measured, in addition to the influence of the front end of the isolation device 2 on the surface pressure distribution of the airfoil 1 to be measured, the isolation device 2 itself will also generate a boundary layer, which will affect the surface of the airfoil 1 to be measured along the span direction. Through calculation, it can be obtained that the isolation device 2 has a great influence on the surface of the airfoil 1 to be measured along the span direction. The distribution of influence is that the larger the device R / c, the greater the impact range on the surface of the airfoil 1 to be measured. When R / c ≤ 1, the impact range on the surface of the airfoil 1 to be measured can be controlled within 10%C. Without adding the isolation device 2, the theoretical sidewall impact area is 1 times the chord length of the airfoil 1 to be measured. The impact of adding the isolation device 2 on the boundary layer is much smaller than when not adding the isolation device 2. Currently, the pressure measurement points of the airfoil 1 to be measured are distributed in the middle of the airfoil 1 to be measured. The isolation device 2 with R / c = 1 will not affect the flow on the airfoil surface.

[0042] The above test proves that when the circular radius of the isolation device 2 is R / c=1, the pressure distribution on the airfoil surface of the airfoil 1 to be tested is less affected;

[0043] in ; is the airfoil pressure coefficient, is the airfoil surface pressure, is the static pressure of the incoming flow, Wind tunnel dynamic pressure.

[0044] Furthermore, the direction of the arrow is the incoming flow direction.

[0045] Through the present invention, the interference effect of the side wall during the temporary wind tunnel airfoil test is effectively reduced, the test interruption and data invalidation caused by the side wall boundary layer problem are reduced, the airfoil wind tunnel test cycle is shortened, and the test cost is reduced; the device of the present invention is installed at both ends of the airfoil, and the test model is separated from the wind tunnel side wall boundary layer by the device of the present invention to form three channels, thereby reducing the induced velocity and induced angle of attack of the tail vortex on the central section caused by the change of the circulation in the wind tunnel side wall boundary layer.

[0046] The present invention can adapt to the wind tunnel test requirements of different types of airfoils and different speed conditions, broaden the application boundaries of airfoil wind tunnel tests, and enable experimental research to cover more extreme conditions and special designs.

[0047] Although the present invention has been described with respect to a limited number of embodiments, it will be apparent to those skilled in the art, having benefit of the foregoing description, that other embodiments are contemplated within the scope of the invention thus described. Furthermore, it should be noted that the language used in this specification has been selected primarily for readability and didactic purposes, rather than for the purpose of explaining or limiting the subject matter of the present invention. Consequently, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the present invention is intended to be illustrative rather than restrictive of the scope of the invention, which is defined by the appended claims.

Claims

1. A device for reducing sidewall interference in a transient wind tunnel airfoil test, characterized in that: It includes an airfoil to be tested (1), an isolation device (2), a wind tunnel wall (3) and a conforming cover plate (6); The two ends of the airfoil to be measured (1) are provided with square support structures (5), and are fixed to the wind tunnel wall (3) through the support structures (5); two conforming cover plates (6) are fixed to the upper and lower sides of the support structure (5) through second fixing screws (7); and a mounting groove (8) is provided between the conforming cover plates (6) and the airfoil to be measured (1); The isolation device (2) is disc-shaped as a whole, and a rectangular through hole of the same size as the supporting structure (5) is provided in the middle of the disc. The isolation device (2) is installed in the installation groove (8) and is fixedly connected to the side of the airfoil (1) to be measured by a first fixing screw (4).

2. The device for reducing sidewall interference in a transient wind tunnel airfoil test according to claim 1, characterized in that: The isolation device (2) has a thickness of 12 mm.

3. The device for reducing sidewall interference in a transient wind tunnel airfoil test according to claim 2, characterized in that: The front edge of the isolation device (2) is semi-wedge-shaped, and the wedge chamfer angle is 15°.

4. The device for reducing sidewall interference in a transient wind tunnel airfoil test according to claim 1, characterized in that: The distance between the isolation device (2) and the wind tunnel wall (3) is greater than the thickness of the isolation device (2).

5. The device for reducing sidewall interference in a transient wind tunnel airfoil test according to claim 1, characterized in that: The center of the circle of the isolation device (2) coincides with the center point of rotation of the airfoil (1) to be measured.

6. The device for reducing sidewall interference in a transient wind tunnel airfoil test according to claim 1, characterized in that: The conformable cover plate (6) has the same shape as the airfoil (1) to be measured.

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