Device and method for dynamic measurement of surface friction of wind tunnel test model

Abstract

The invention relates to a device and a measuring method for the dynamic measurement of the surface friction of a wind tunnel test model, belonging to the technical field of wind tunnel tests. In order to solve the problem of unstable measurement results using a pitot tube probe, the present invention includes a pitot tube probe, a support, a spur rack, a gear, a stepping motor, a baffle, and a motor connection seat; a through hole is provided in the middle of the support for placing the pitot tube probe, the bottom of the through hole of the support is connected to a pressure measuring tube, the lower surface of the top of the support is fixedly connected to a spur rack, the spur rack is connected to a gear, and the gear is connected to a stepping motor through a motor connection seat; the side of the motor connection seat is fixedly connected to a baffle, and screw holes are provided on the baffle. The present invention can quickly scan and measure the boundary layer velocity profile at a low cost, and then obtain the wall friction resistance coefficient. The present invention can be used in most wind tunnel test scenarios, and can achieve near-wall measurement for both flat plates and curved surfaces of the body surface, and is not easily damaged under high temperature, high pressure and high speed conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of wind tunnel tests, and in particular relates to a device and a method for dynamically measuring the surface friction of a wind tunnel test model. Background Art

[0002] According to the characteristics of turbulent boundary layer flow, the measurement of wall friction stress is divided into direct measurement method and indirect measurement method. Indirect measurement method refers to the measurement of indirectly sensitive intermediate physical quantities, such as boundary layer velocity profile, pressure gradient along the stream direction, heat exchange in the near-wall area, etc. The wall friction drag coefficient can be obtained by fitting the logarithmic law and the stream direction velocity distribution. At present, the measurement instruments used for turbulent velocity measurement mainly include laser Doppler velocimeter (LDV), hot wire anemometer (HWA), particle image velocimeter (PIV) based on tracer particle velocity measurement, etc.

[0003] If the turbulent velocity is simply measured, the hot wire probe can conveniently measure the instantaneous pulsation value and statistical average value of the turbulent velocity, which is particularly suitable for the measurement of low-speed fluid turbulence. However, the hot wire probe measurement system is of different types and has its own differences. The error source is difficult to uniformly determine and eliminate. In addition, the stability of the measurement system is affected by the quality of electronic components and control circuits. In particular, when measuring related models in a wind tunnel environment, the hot wire is very easy to break, and it is necessary to combine the corresponding stability control method to ensure high measurement performance. In contrast, PIV can achieve non-contact measurement, and the speed measurement range is larger than the other two technologies, but it is difficult to measure near the wall, the time resolution is low, the device is complex, and the price is expensive. The advantage of using a pitot tube probe is that the device is simple and easy to implement, and the cost is relatively low. In addition, the initial measurement position can be close to the wall. The design parameters such as the inner and outer diameters of the pitot tube can conveniently calibrate the distance from the wall, thereby determining the reference distance. In contrast, hot wire probes are difficult to do, but the measurement results are not stable enough. Summary of the invention

[0004] The problem to be solved by the present invention is the instability of the measurement result using a pitot tube probe, and a device and a method for dynamic measurement of the surface friction of a wind tunnel test model are proposed.

[0005] To achieve the above object, the present invention is implemented through the following technical solutions:

[0006] A device for dynamic measurement of surface friction of a wind tunnel test model, comprising a pitot tube probe, a support, a spur rack, a gear, a stepping motor, a baffle, and a motor connection seat;

[0007] A through hole is provided in the middle of the support for placing a pitot tube probe, a pressure measuring tube is connected to the bottom of the through hole of the support, a spur rack is fixedly connected to the lower surface of the top of the support, the spur rack is connected to a gear, and the gear is connected to a stepper motor through a motor connecting seat;

[0008] The side surface of the motor connection seat is fixedly connected to a baffle, and the baffle is provided with screw holes.

[0009] Furthermore, the device for dynamic measurement of surface friction of a wind tunnel test model is installed at a measuring point on the surface of the wind tunnel test model through a screw hole on the baffle.

[0010] Furthermore, the outer diameter of the through hole of the support is less than 0.3 mm.

[0011] Furthermore, the stepper motor is controlled by a stepper motor driver, the stepper motor driver is respectively connected to a stepper motor controller and a stepper motor driver power supply, the stepper motor controller is connected to a stepper motor controller power supply, and the stepper motor drives the gear to rotate at a fixed frequency to realize the up and down movement of the Pitot tube probe.

[0012] Furthermore, the number of the screw holes is 4.

[0013] A measuring method of a device for dynamically measuring the surface friction of a wind tunnel test model is implemented based on the device for dynamically measuring the surface friction of a wind tunnel test model, and comprises the following steps:

[0014] S1. Before the wind tunnel test, the device for dynamic measurement of the surface friction of the wind tunnel test model is installed at the measurement point on the surface of the wind tunnel test model. The initial position of the pitot tube probe is close to the wall to measure the total pressure data. The static pressure point is set on the surface of the wind tunnel test model to collect the static pressure data.

[0015] S2. When the wind tunnel is in a windless state, estimate the boundary layer thickness by knowing the wind speed and characteristic length of the wind tunnel, set the rising speed, rising height and acquisition frequency of the pitot tube probe, start the stepper motor and data acquisition equipment, and ensure that the pitot tube probe works normally, the data acquisition equipment works normally and there is no leakage or blockage in the pressure measuring tube;

[0016] S3. Start the wind tunnel operation, wait for the flow field in the wind tunnel to stabilize, then start the stepper motor and data acquisition equipment synchronously, the pitot tube probe starts to rise from the initial position, and the data acquisition equipment dynamically collects data. The pitot tube probe automatically stops when it rises to the set height. After 10 seconds, the data acquisition equipment and wind tunnel are turned off, completing the data acquisition of one working condition;

[0017] S4. After completing one working condition, adjust the pitot tube probe to descend to the initial position and collect data for the next working condition;

[0018] S5. Process the collected data to obtain the boundary layer velocity profile and calculate the friction drag coefficient of the wind tunnel test model surface.

[0019] Furthermore, the specific implementation method of step S5 for processing the collected data includes the following steps:

[0020] S5.1. Calculate the average dynamic pressure based on the collected total pressure data and static pressure data;

[0021] S5.2. According to the actual test conditions, the flow velocity is calculated by the average dynamic pressure obtained in step S5.1. Under the condition that the compressibility effect is negligible under low and high speed conditions, the calculation expression is:

[0022] ;

[0023] in, is the average dynamic pressure, is the incoming flow velocity, is the fluid density;

[0024] S5.3. Correct the incoming flow velocity obtained in step S5.2 by using the pitot tube related correction method. The correction method is as follows:

[0025] Firstly based on < 100, viscosity correction is performed, and the expression is:

[0026] ;

[0027] ;

[0028] in, is the tube Reynolds number, is the outer diameter of the tube, is the kinematic viscosity of the fluid;

[0029] Then perform shear correction and compensate for the streamline offset at the probe position. After compensation, the speed value corresponding to the new position is the accurate value. The expression is:

[0030] ;

[0031] 0.15tanh(4 );

[0032] ;

[0033] in, is the dimensionless offset, is a dimensionless parameter, is the normal height;

[0034] Then for , applying the near-wall correction, the expression is:

[0035] ;

[0036] in, is the speed increase, is the dimensionless outer diameter, , is the wall friction velocity, is the kinematic viscosity of the fluid;

[0037] Then the turbulence correction is performed, and the expression is:

[0038] ;

[0039] in, To measure speed, is the flow direction component, is the corrected incoming flow velocity;

[0040] S5.4. Calculate the wall shear stress by the kinematic viscosity of the fluid and the velocity gradient obtained from the measured velocity curve. Calculate the wall friction velocity by the wall shear stress and the fluid density. Then, make the corrected incoming flow velocity curve dimensionless and calculate using the following formula:

[0041] ;

[0042] ;

[0043] ;

[0044] ;

[0045] in, is the wall friction velocity, is the kinematic viscosity of the fluid, is the wall shear stress, ρ is the fluid density, y is the normal height, is the inner scale characteristic length, is the dimensionless height, is the dimensionless velocity;

[0046] From this we get - The curve is finally logarithmized to obtain the boundary layer velocity profile;

[0047] S5.5. The friction coefficient of the wind tunnel test model surface is calculated by fitting the logarithmic law of the boundary layer velocity profile and the following formula:

[0048] ;

[0049] in, is the von Karman constant, B is the intercept;

[0050] The velocity distribution formula of the applicable range is used to reduce uncertainty, and the expression of the friction law of the flat plate turbulent boundary layer is:

[0051] ;

[0052] in, is the Reynolds number based on momentum thickness, is the friction coefficient of the wind tunnel test model surface, is a characteristic constant.

[0053] Furthermore, in step S5.5 .

[0054] Beneficial effects of the present invention:

[0055] The device for dynamic measurement of surface friction of a wind tunnel test model described in the present invention can quickly scan and measure the boundary layer velocity profile at a low cost, and then obtain the wall friction resistance coefficient. The present invention can be used in most wind tunnel test scenarios, and can achieve near-wall measurement for both flat plates and curved surfaces of the body surface, and is not easily damaged under high temperature, high pressure and high speed conditions, providing a new option for the measurement of existing turbulent boundary layer velocity profiles. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a structural schematic diagram of a device for dynamic measurement of surface friction of a wind tunnel test model according to the present invention;

[0057] Figure 2 It is a schematic diagram of the structure of the pitot tube probe of the present invention;

[0058] Figure 3 It is a flow chart of a measuring method of a device for dynamic measurement of surface friction of a wind tunnel test model according to the present invention;

[0059] in, Figure 1 1 is the Pitot tube probe, 2 is the support, 3 is the pressure measuring tube, 4 is the spur rack, 5 is the gear, 6 is the stepper motor, 7 is the baffle, 8 is the motor connection seat, and 9 is the screw hole. DETAILED DESCRIPTION

[0060] In order to make the purpose, technical solution and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the specific embodiments described are only part of the embodiments of the present invention, rather than all of the specific embodiments. The components of the specific embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations, and the present invention can also have other embodiments.

[0061] Therefore, the following detailed description of the specific embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents the selected specific embodiments of the present invention. Based on the specific embodiments of the present invention, all other specific embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0062] In order to further understand the content, features and effects of the present invention, the following specific implementation methods are given as examples, and the attached Figure 1 -Attached Figure 3 The detailed instructions are as follows:

[0063] Embodiment 1:

[0064] A device for dynamic measurement of surface friction of a wind tunnel test model, comprising a pitot tube probe 1, a support 2, a spur rack 4, a gear 5, a stepping motor 6, a baffle 7, and a motor connection seat 8;

[0065] A through hole is provided in the middle of the support 2 for placing a pitot tube probe 1, a pressure measuring tube 3 is connected to the bottom of the through hole of the support 2, a spur rack 4 is fixedly connected to the lower surface of the top of the support 2, the spur rack 4 is connected to a gear 5, and the gear 5 is connected to a stepper motor 6 via a motor connecting seat 8;

[0066] The side of the motor connection seat 8 is fixedly connected to the baffle plate 7 , and the baffle plate 7 is provided with screw holes 9 .

[0067] Furthermore, the device for dynamic measurement of surface friction of the wind tunnel test model is installed at the measurement point on the surface of the wind tunnel test model through the screw hole 9 on the baffle 7.

[0068] Furthermore, the outer diameter of the through hole of the support 2 is less than 0.3 mm.

[0069] Furthermore, the stepper motor 6 is controlled by a stepper motor driver, the stepper motor driver is respectively connected to a stepper motor controller and a stepper motor driver power supply, the stepper motor controller is connected to a stepper motor controller power supply, and the stepper motor 6 drives the gear 5 to rotate at a fixed frequency to realize the up and down movement of the Pitot tube probe 1.

[0070] Furthermore, the number of the screw holes 9 is four.

[0071] Furthermore, the front end of the Pitot tube probe is provided with a total pressure hole, and the bottom hole is connected to a pressure measuring tube for measuring the total pressure of the boundary layer; the support is connected to the gear and the stepper motor through a spur rack to drive the Pitot tube probe to move up and down; the stepper motor controller and the stepper motor driver are used to drive the gear to rotate at a fixed frequency; the dynamic pressure sensor and the data acquisition equipment are connected to the Pitot tube probe through the pressure measuring tube for total pressure and static pressure data collection.

[0072] Embodiment 2:

[0073] A measuring method of a device for dynamically measuring the surface friction of a wind tunnel test model is implemented based on the device for dynamically measuring the surface friction of a wind tunnel test model described in Example 1, and includes the following steps:

[0074] S1. Before the wind tunnel test, the device for dynamic measurement of the surface friction of the wind tunnel test model is installed at the measurement point on the surface of the wind tunnel test model. The initial position of the pitot tube probe is close to the wall to measure the total pressure data. The static pressure point is set on the surface of the wind tunnel test model to collect the static pressure data.

[0075] S2. When the wind tunnel is in a windless state, estimate the boundary layer thickness by knowing the wind speed and characteristic length of the wind tunnel, set the rising speed, rising height and acquisition frequency of the pitot tube probe, start the stepper motor and data acquisition equipment, and ensure that the pitot tube probe works normally, the data acquisition equipment works normally and there is no leakage or blockage in the pressure measuring tube;

[0076] S3. Start the wind tunnel operation, wait for the flow field in the wind tunnel to stabilize, then start the stepper motor and data acquisition equipment synchronously, the pitot tube probe starts to rise from the initial position, and the data acquisition equipment dynamically collects data. The pitot tube probe automatically stops when it rises to the set height. After 10 seconds, the data acquisition equipment and wind tunnel are turned off, completing the data acquisition of one working condition;

[0077] S4. After completing one working condition, adjust the pitot tube probe to descend to the initial position and collect data for the next working condition;

[0078] S5. Process the collected data to obtain the boundary layer velocity profile and calculate the surface friction drag coefficient of the wind tunnel test model.

[0079] Furthermore, the specific implementation method of step S5 for processing the collected data includes the following steps:

[0080] S5.1. Calculate the average dynamic pressure based on the collected total pressure data and static pressure data;

[0081] S5.2. According to the actual test conditions, the flow velocity is calculated by the average dynamic pressure obtained in step S5.1. Under the condition that the compressibility effect is negligible under low and high speed conditions, the calculation expression is:

[0082] ;

[0083] in, is the average dynamic pressure, is the incoming flow velocity, is the fluid density;

[0084] S5.3. Correct the incoming flow velocity obtained in step S5.2 by using the pitot tube related correction method. The correction method is as follows:

[0085] Firstly based on < 100, viscosity correction is performed, and the expression is:

[0086] ;

[0087] ;

[0088] in, is the tube Reynolds number, is the outer diameter of the tube, is the kinematic viscosity of the fluid;

[0089] Then perform shear correction and compensate for the streamline offset at the probe position. After compensation, the speed value corresponding to the new position is the accurate value. The expression is:

[0090] ;

[0091] 0.15tanh(4 );

[0092] ;

[0093] in, is the dimensionless offset, is a dimensionless parameter, is the normal height;

[0094] Then for , applying the near-wall correction, the expression is:

[0095] ;

[0096] in, is the speed increase, is the dimensionless outer diameter, , is the wall friction velocity, is the kinematic viscosity of the fluid;

[0097] Then the turbulence correction is performed, and the expression is:

[0098] ;

[0099] in, To measure speed, is the flow direction component, is the corrected incoming flow velocity;

[0100] S5.4. Calculate the wall shear stress by the kinematic viscosity of the fluid and the velocity gradient obtained from the measured velocity curve. Calculate the wall friction velocity by the wall shear stress and the fluid density. Then, make the corrected incoming flow velocity curve dimensionless and calculate using the following formula:

[0101] ;

[0102] ;

[0103] ;

[0104] ;

[0105] in, is the wall friction velocity, is the kinematic viscosity of the fluid, is the wall shear stress, ρ is the fluid density, y is the normal height, is the inner scale characteristic length, is the dimensionless height, is the dimensionless velocity;

[0106] From this we get - The curve is finally logarithmized to obtain the boundary layer velocity profile;

[0107] S5.5. The friction coefficient of the wind tunnel test model surface is calculated by fitting the logarithmic law of the boundary layer velocity profile and the following formula:

[0108] ;

[0109] in, is the von Karman constant, B is the intercept;

[0110] The velocity distribution formula of the applicable range is used to reduce uncertainty, and the expression of the friction law of the flat plate turbulent boundary layer is:

[0111] ;

[0112] in, is the Reynolds number based on momentum thickness, is the friction coefficient of the wind tunnel test model surface, is a characteristic constant.

[0113] Furthermore, in step S5.5 .

[0114] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0115] Although the present application has been described above with reference to specific embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, as long as there is no structural conflict, the various features in the specific embodiments disclosed in the present application may be used in combination with each other in any manner, and the fact that these combinations are not exhaustively described in this specification is only for the sake of omitting space and saving resources. Therefore, the present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A measuring method of a device for dynamically measuring the surface friction of a wind tunnel test model, which is realized by using a device for dynamically measuring the surface friction of a wind tunnel test model, comprising a pitot tube probe (1), a support (2), a spur rack (4), a gear (5), a stepping motor (6), a baffle (7), and a motor connecting seat (8); A through hole is provided in the middle of the support (2) for placing a pitot tube probe (1); the bottom of the through hole of the support (2) is connected to a pressure measuring tube (3); the lower surface of the top of the support (2) is fixedly connected to a spur rack (4); the spur rack (4) is connected to a gear (5); and the gear (5) is connected to a stepping motor (6) via a motor connecting seat (8); The side of the motor connection seat (8) is fixedly connected to a baffle (7), and the baffle (7) is provided with a screw hole (9); The device for dynamic measurement of surface friction of a wind tunnel test model is installed at a measurement point on the surface of the wind tunnel test model through a screw hole (9) on the baffle (7); It is characterized in that The steps include: S1. Before the wind tunnel test, the device for dynamic measurement of the surface friction of the wind tunnel test model is installed at the measurement point on the surface of the wind tunnel test model. The initial position of the pitot tube probe is close to the wall to measure the total pressure data. Static pressure points are set on the surface of the wind tunnel test model to collect static pressure data. S2. When the wind tunnel is in a windless state, estimate the boundary layer thickness by knowing the wind speed and characteristic length of the wind tunnel, set the rising speed, rising height and acquisition frequency of the pitot tube probe, start the stepper motor and data acquisition equipment, and ensure that the pitot tube probe works normally, the data acquisition equipment works normally and there is no leakage or blockage in the pressure measuring tube; S3. Start the wind tunnel operation, wait for the flow field in the wind tunnel to stabilize, then start the stepper motor and data acquisition equipment synchronously, the pitot tube probe starts to rise from the initial position, and the data acquisition equipment dynamically collects data. The pitot tube probe automatically stops when it rises to the set height. After 10 seconds, the data acquisition equipment and wind tunnel are turned off, completing the data acquisition of one working condition; S4. After completing one working condition, adjust the pitot tube probe to descend to the initial position and collect data for the next working condition; S5. Processing the collected data to obtain the boundary layer velocity profile and calculating the friction coefficient of the surface of the wind tunnel test model; The specific implementation method of step S5 for processing the collected data includes the following steps: S5.

1. Calculate the average dynamic pressure based on the total pressure data and static pressure data collected; S5.

2. According to the actual test conditions, the flow velocity is calculated by the average dynamic pressure obtained in step S5.

1. Under the condition that the compressibility effect is negligible under low and high speed conditions, the calculation expression is: Among them, ΔP is the average dynamic pressure, U is the incoming flow velocity, and ρ is the fluid density; S5.

3. Correct the incoming flow velocity obtained in step S5.2 by using the pitot tube related correction method. The correction method is as follows: First, based on Re d <100, make viscosity correction, the expression is: Re d =ρUd p / v Among them, Re d is the tube Reynolds number, d p is the outer diameter of the tube, v is the kinematic viscosity of the fluid; Then, shear correction is performed to compensate for the streamline offset at the probe position. After compensation, the velocity value corresponding to the new position is the accurate value. The expression of the offset Δy is: Δy=∈d p Among them, ∈ is the dimensionless offset, α is the dimensionless parameter, and y is the normal height; Then for y<2d p , applying the near-wall correction, the expression is: Where ΔU is the speed increase, d + is the dimensionless outer diameter, U τ is the wall friction velocity, v is the kinematic viscosity of the fluid; Then the turbulence correction is performed, and the expression is: Among them, U m is the measured velocity, u is the flow direction component, U * is the corrected incoming flow velocity; S5.

4. Calculate the wall shear stress by the kinematic viscosity of the fluid and the velocity gradient obtained from the measured velocity curve. Calculate the wall friction velocity by the wall shear stress and the fluid density. Then, make the corrected incoming flow velocity curve dimensionless and calculate using the following formula: Among them, U τ is the wall friction velocity, v is the kinematic viscosity of the fluid, τ w is the wall shear stress, ρ is the fluid density, y is the normal height, δ v is the inner scale characteristic length, y + is the dimensionless height, u + is the dimensionless velocity; So we get y + -u + The curve is finally logarithmized to obtain the boundary layer velocity profile; S5.

5. The friction coefficient of the wind tunnel test model surface is calculated by fitting the logarithmic law of the boundary layer velocity profile and the following formula: Among them, κ is the von Karman constant, B is the intercept; The velocity distribution formula of the applicable range is used to reduce uncertainty, and the expression of the friction law of the flat plate turbulent boundary layer is: Among them, Re θ is the Reynolds number based on momentum thickness, C f is the friction coefficient of the wind tunnel test model surface, and L is the characteristic constant.

2. The measuring method of the device for dynamic measurement of surface friction of a wind tunnel test model according to claim 1, characterized in that: In step S5.5, κ=0.384, B=3.160, L=6.

907.

3. The measuring method of the device for dynamic measurement of surface friction of a wind tunnel test model according to claim 2, characterized in that: The outer diameter of the through hole of the support (2) is less than 0.3 mm.

4. The measuring method of the device for dynamic measurement of surface friction of a wind tunnel test model according to claim 3 is characterized in that: The number of the screw holes (9) is 4.

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