A method for accurately measuring the drag coefficient of a high-speed wind tunnel airfoil model

Abstract

The present invention belongs to the technical field of high-speed wind tunnel tests, and discloses a method for accurately measuring the drag coefficient of a high-speed wind tunnel airfoil model. The method for accurately measuring the drag coefficient of a high-speed wind tunnel airfoil model of the present invention comprises installing an airfoil model; installing a wake rake; conducting a high-speed wind tunnel airfoil model drag measurement test; calculating the static pressure of the wind tunnel incoming flow; calculating the static pressure of the airfoil model wake; calculating the plumb bob length corresponding to the airfoil model wake total pressure measurement point; and calculating the drag coefficient of the high-speed wind tunnel airfoil model. The method for accurately measuring the drag coefficient of a high-speed wind tunnel airfoil model of the present invention uses a wake rake to measure the wake total pressure and static pressure of the airfoil model, eliminates static pressure measurement points with large errors through a point selection rule based on the 3σ principle, and establishes a numerical integral equation for the drag coefficient of a high-speed wind tunnel airfoil model, thereby improving the accuracy of the drag coefficient measurement of a high-speed wind tunnel airfoil model, and has engineering application value.

Description

Technical Field

[0001] The invention belongs to the technical field of high-speed wind tunnel tests, and in particular relates to a method for accurately measuring the drag coefficient of a high-speed wind tunnel airfoil model. Background Art

[0002] As we all know, the wing is the main component of the aircraft to generate lift, and the two-dimensional airfoil is an important part of wing forming and a basic element of wing aerodynamic shape design. The aerodynamic characteristics of the two-dimensional airfoil directly affect the aerodynamic characteristics of the wing, the aircraft's cruising speed, take-off and landing performance, stall angle of attack and speed, handling quality and even the aerodynamic efficiency of all flight stages. Therefore, the two-dimensional airfoil is also called the heart of the aircraft and plays an important role in aerodynamic theory and aircraft design.

[0003] At present, "green aviation" has become one of the important development concepts in the field of civil aviation around the world, and its development goals are mainly to reduce carbon emissions and save energy. Wing drag is an important component of the drag encountered by an aircraft during cruising. Wing drag reduction design, especially two-dimensional airfoil drag reduction design, is an important aerodynamic design method to achieve the above development goals. In order to verify the effectiveness of two-dimensional airfoil drag reduction design, it is particularly important to accurately quantify and evaluate the airfoil drag coefficient.

[0004] Before the 1970s, the precise measurement of airfoil drag coefficient mainly relied on wind tunnel tests. With the development of computer technology and computational aerodynamics, although numerical simulation methods can be used to accurately design airfoils according to target pressure distribution and accurately measure airfoil drag, it is still inseparable from the typical state verification test of airfoil drag using wind tunnel tests. According to currently available literature, the principle of the drag coefficient measurement test of low-speed wind tunnel airfoil models is simple and the method is mature. However, for high-speed wind tunnels, due to the existence of compressibility, the principle of the drag coefficient measurement test of high-speed wind tunnel airfoil models is complicated, and the drag coefficient solution methods in different literatures are inconsistent, which limits the accuracy of the drag coefficient measurement of high-speed wind tunnel airfoil models and seriously restricts the safety and economy of aircraft.

[0005] Currently, there is an urgent need to develop a method for accurately measuring the drag coefficient of high-speed wind tunnel airfoil models. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for accurately measuring the drag coefficient of a high-speed wind tunnel airfoil model.

[0007] The method for accurately measuring the drag coefficient of a high-speed wind tunnel airfoil model of the present invention comprises the following steps:

[0008] S10. Install the airfoil model;

[0009] The airfoil model is connected to the window-turning mechanism and fixedly installed in the high-speed wind tunnel test section;

[0010] S20. Install the wake rake;

[0011] The wake rake is fixed on the middle bracket, and a pressure measuring section is set on the wake rake, including N Total pressure measuring points, L Static pressure measuring points, connect all pressure measuring points to the pressure scanning valve through hoses;

[0012] S30. Conduct high-speed wind tunnel airfoil model drag measurement test;

[0013] Open the high-speed wind tunnel and set the incoming Mach number After the flow field stabilizes, the pressure scanning valve is used to measure the total pressure measurement point of the wake of the airfoil model. , Static pressure measuring point , and simultaneously measure the total pressure in the stable section of the wind tunnel , Static pressure at room reference point ,in, i is the total pressure measurement point number on the wake rake, N is the total number of pressure measurement points on the wake rake, j is the number of the static pressure measurement point on the wake rake, L is the total number of static pressure measurement points on the wake rake; the total wake pressure measurement point The position coordinates in the plumb direction are ;

[0014] S40. Calculation of static pressure of wind tunnel inflow ;

[0015] According to the incoming flow Mach number , Total pressure in the stable section of the wind tunnel , Static pressure at reference point of the station Calculate the static pressure of wind tunnel inflow ;

[0016] S50. Calculate the wake static pressure of the airfoil model ;

[0017] According to the measurement result in step S30, the incoming flow Mach number is calculated. The static pressure of the wake of the airfoil model is ;

[0018] S60. Calculate the plumb bob length corresponding to the total pressure measurement point of the wake of the airfoil model ;

[0019] According to the total pressure measurement point in step S30 Position coordinates in the plumb direction , calculate the total pressure measurement point of the airfoil model wake The corresponding length in the plumb direction :

[0020] ;

[0021] S70. Calculation of drag coefficient of high-speed wind tunnel airfoil model ;

[0022] According to the equation of the drag coefficient of the two-dimensional airfoil considering compressibility, the drag coefficient of the high-speed wind tunnel airfoil model The numerical integration equation is as follows:

[0023] ,

[0024] In the formula, c is the chord length of the airfoil model, is the specific heat ratio of gases.

[0025] Furthermore, the step S40 includes the following steps:

[0026] S41. Calculate the static pressure of the wind tunnel inflow corresponding to the supersonic test section ;

[0027] When the high-speed wind tunnel body condition is the supersonic test section, the wind tunnel inflow static pressure The calculation method is:

[0028] ;

[0029] S42. Calculate the static pressure of the wind tunnel corresponding to the subsonic test section ;

[0030] When the high-speed wind tunnel body condition is the subsonic test section, according to the total pressure of the wind tunnel stable section , Static pressure at reference point of the station Calculate the reference Mach number in the chamber :

[0031] ,

[0032] The Mach number correction obtained from the flow field calibration , corrected to get the average Mach number of the incoming flow :

[0033] ,

[0034] According to the total pressure of the wind tunnel stable section and the average Mach number of the incoming flow Calculate the static pressure of wind tunnel inflow :

[0035] .

[0036] Furthermore, the step S50 includes the following steps:

[0037] S51. Calculate the average static pressure of the wake of the airfoil model ;

[0038] ;

[0039] S52. Calculate the static pressure measurement points of the wake of the airfoil model and mean static pressure The absolute difference :

[0040] ;

[0041] S53. Calculate the static pressure measurement points of the wake of the airfoil model Standard Deviation ;

[0042] ;

[0043] S54. Calculate the wake static pressure of the airfoil model ;

[0044] according to Principle, keep satisfied Static pressure measurement points corresponding to the conditions , recorded as the static pressure measurement point , q To satisfy The static pressure measurement point number corresponding to the condition, Q To satisfy The number of static pressure measurement points corresponding to the conditions, eliminating those that do not meet the conditions Static pressure measurement points corresponding to the conditions , static pressure of wake of airfoil model for:

[0045] .

[0046] The invention discloses a method for accurately measuring the drag coefficient of a high-speed wind tunnel airfoil model, which uses a wake rake to measure the total wake pressure and static pressure of the airfoil model. The point selection rule based on the principle eliminates the static pressure measurement points with large errors, and establishes the numerical integral equation of the drag coefficient of the high-speed wind tunnel airfoil model, which improves the accuracy of the measurement of the drag coefficient of the high-speed wind tunnel airfoil model and has engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 The present invention is a flow chart of the method for accurately measuring the internal resistance of a high-speed wind tunnel ventilation model. DETAILED DESCRIPTION

[0048] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0049] Example: Figure 1 As shown, the method for accurately measuring the drag coefficient of a high-speed wind tunnel airfoil model of this embodiment includes the following steps:

[0050] S10. Install the airfoil model;

[0051] The airfoil model is connected to the window-turning mechanism and fixedly installed in the high-speed wind tunnel test section;

[0052] S20. Install the wake rake;

[0053] The wake rake is fixed on the middle bracket, and a pressure measuring section is set on the wake rake, including N Total pressure measuring points, L Static pressure measuring points, connect all pressure measuring points to the pressure scanning valve through hoses;

[0054] S30. Conduct high-speed wind tunnel airfoil model drag measurement test;

[0055] Open the high-speed wind tunnel and set the incoming Mach number After the flow field stabilizes, the pressure scanning valve is used to measure the total pressure measurement point of the wake of the airfoil model. , Static pressure measuring point , and simultaneously measure the total pressure in the stable section of the wind tunnel , Static pressure at reference point of the station ,in, i is the total pressure measurement point number on the wake rake, N is the total number of pressure measurement points on the wake rake, j is the number of the static pressure measurement point on the wake rake, L is the total number of static pressure measurement points on the wake rake; the total wake pressure measurement point The position coordinates in the plumb direction are ;

[0056] S40. Calculation of static pressure of wind tunnel inflow ;

[0057] According to the incoming flow Mach number , Total pressure in the stable section of the wind tunnel , Static pressure at reference point of the station Calculate the static pressure of wind tunnel inflow ;

[0058] S50. Calculate the wake static pressure of the airfoil model ;

[0059] According to the measurement result in step S30, the incoming flow Mach number is calculated. The static pressure of the wake of the airfoil model is ;

[0060] S60. Calculate the plumb bob length corresponding to the total pressure measurement point of the wake of the airfoil model ;

[0061] According to the total pressure measurement point in step S30 Position coordinates in the plumb direction , calculate the total pressure measurement point of the airfoil model wake The corresponding length in the plumb direction :

[0062] ;

[0063] S70. Calculation of drag coefficient of high-speed wind tunnel airfoil model ;

[0064] According to the equation of the drag coefficient of the two-dimensional airfoil considering compressibility, the drag coefficient of the high-speed wind tunnel airfoil model The numerical integration equation is as follows:

[0065] ,

[0066] In the formula, c is the chord length of the airfoil model, is the specific heat ratio of gases.

[0067] Furthermore, the step S40 includes the following steps:

[0068] S41. Calculate the static pressure of the wind tunnel inflow corresponding to the supersonic test section ;

[0069] When the high-speed wind tunnel body condition is the supersonic test section, the wind tunnel inflow static pressure The calculation method is:

[0070] ;

[0071] S42. Calculate the static pressure of the wind tunnel corresponding to the subsonic test section ;

[0072] When the high-speed wind tunnel body condition is the subsonic test section, according to the total pressure of the wind tunnel stable section , Static pressure at reference point of the station Calculate the reference Mach number in the chamber :

[0073] ,

[0074] The Mach number correction obtained from the flow field calibration , corrected to get the average Mach number of the incoming flow :

[0075] ,

[0076] According to the total pressure of the wind tunnel stable section and the average Mach number of the incoming flow Calculate the static pressure of wind tunnel inflow :

[0077] .

[0078] Furthermore, the step S50 includes the following steps:

[0079] S51. Calculate the average static pressure of the wake of the airfoil model ;

[0080] ;

[0081] S52. Calculate the static pressure measurement points of the wake of the airfoil model and mean static pressure The absolute difference :

[0082] ;

[0083] S53. Calculate the static pressure measurement points of the wake of the airfoil model Standard Deviation ;

[0084] ;

[0085] S54. Calculate the wake static pressure of the airfoil model ;

[0086] according to Principle, keep satisfied Static pressure measurement points corresponding to the conditions , recorded as the static pressure measurement point , q To satisfy The static pressure measurement point number corresponding to the condition, Q To satisfy The number of static pressure measurement points corresponding to the conditions, eliminating those that do not meet the conditions Static pressure measurement points corresponding to the conditions , static pressure of wake of airfoil model for:

[0087] .

[0088] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and implementation modes. For those familiar with the art, without departing from the principles of the present invention, all features disclosed in the present invention, or steps in all methods or processes disclosed, except for mutually exclusive features and / or steps, can be combined in any way. The present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for accurately measuring the drag coefficient of a high-speed wind tunnel airfoil model, characterized in that: The following steps are involved: S10. Install the airfoil model; The airfoil model is connected to the window-turning mechanism and fixedly installed in the high-speed wind tunnel test section; S20. Install the wake rake; The wake rake is fixed on the middle bracket, and a pressure measuring section is set on the wake rake, including N Total pressure measuring points, L Static pressure measuring points, connect all pressure measuring points to the pressure scanning valve through hoses; S30. Conduct high-speed wind tunnel airfoil model drag measurement test; Open the high-speed wind tunnel and set the incoming Mach number After the flow field stabilizes, the pressure scanning valve is used to measure the total pressure measurement point of the wake of the airfoil model. , Static pressure measuring point , and simultaneously measure the total pressure in the stable section of the wind tunnel , Static pressure at room reference point ,in, i is the total pressure measurement point number on the wake rake, N is the total number of pressure measurement points on the wake rake, j is the number of the static pressure measurement point on the wake rake, L is the total number of static pressure measurement points on the wake rake; Wake total pressure measurement point The position coordinates in the plumb direction are ; S40. Calculation of static pressure of wind tunnel inflow ; According to the incoming flow Mach number , Total pressure in the stable section of the wind tunnel , Static pressure at room reference point Calculate the static pressure of the wind tunnel inflow ; S50. Calculate the static pressure of the wake of the airfoil model ; According to the measurement result in step S30, the incoming flow Mach number is calculated. The static pressure of the wake of the airfoil model is ; S60. Calculate the plumb bob length corresponding to the total pressure measurement point of the wake of the airfoil model ; According to the wake total pressure measurement point in step S30 Position coordinates in the plumb direction , calculate the total pressure measurement point of the airfoil model wake The corresponding length in the plumb direction : ； S70. Calculation of drag coefficient of high-speed wind tunnel airfoil model ; According to the equation of the drag coefficient of the two-dimensional airfoil considering compressibility, the drag coefficient of the high-speed wind tunnel airfoil model The numerical integration equation is as follows: ， In the formula, c is the chord length of the airfoil model, is the specific heat ratio of gases.

2. The method for accurately measuring the drag coefficient of a high-speed wind tunnel airfoil model according to claim 1 is characterized in that: The step S40 includes the following steps: S41. Calculate the static pressure of the wind tunnel inflow corresponding to the supersonic test section ; When the high-speed wind tunnel body condition is the supersonic test section, the wind tunnel inflow static pressure The calculation method is: ； S42. Calculate the static pressure of the wind tunnel corresponding to the subsonic test section ; When the high-speed wind tunnel body condition is the subsonic test section, according to the total pressure of the wind tunnel stable section , Static pressure at room reference point Calculate the reference Mach number in the chamber : ， The Mach number correction obtained from the flow field calibration , corrected to get the average Mach number of the incoming flow : ， According to the total pressure of the wind tunnel stable section and the average Mach number of the incoming flow Calculate the static pressure of the wind tunnel inflow : 。 3. The method for accurately measuring the drag coefficient of a high-speed wind tunnel airfoil model according to claim 1 is characterized in that: The step S50 comprises the following steps: S51. Calculate the average static pressure of the wake of the airfoil model ; ； S52. Calculate the static pressure measurement points of the wake of the airfoil model and mean static pressure The absolute difference : ； S53. Calculate the static pressure measurement points of the wake of the airfoil model Standard Deviation ; ； S54. Calculate the static pressure of the wake of the airfoil model ; according to Principle, keep satisfied Static pressure measurement points corresponding to the conditions , recorded as the static pressure measurement point , q To satisfy The static pressure measurement point number corresponding to the condition, Q To satisfy The number of static pressure measurement points corresponding to the conditions, eliminating those that do not meet the conditions Static pressure measurement points corresponding to the conditions , static pressure of wake of airfoil model for: 。

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