CN112729748A - Measuring method for aerodynamic characteristic experiment of wing profile of direct-current air-breathing wind tunnel - Google Patents
Measuring method for aerodynamic characteristic experiment of wing profile of direct-current air-breathing wind tunnel Download PDFInfo
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Abstract
The invention discloses a measuring method for a direct-current air suction type wind tunnel wing aerodynamic characteristic experiment, which comprises the following steps of 1) installing a support frame, and fixing a support flat plate on the support frame; 2) installing a six-component balance and a servo motor; 3) placing the wing section in the wind tunnel test section, and installing an attack angle turntable; 4) equipment safety inspection; 5) starting the wind tunnel, and adjusting the frequency of the control cabinet to obtain a set wind speed; 6) collecting static pressure data of the airfoil sections under different wind speeds and attack angles; 7) setting the sampling frequency and the sampling time of the pressure sensor; 8) acquiring instantaneous dynamic pressure data of the airfoil section; 9) completing the collection of pressure data of the wing profile under different working conditions; 10) setting the sampling frequency and the sampling time of the hot-wire anemometer; 11) acquiring instantaneous pulse speed data of the tail trace of the airfoil section; 12) processing data; the invention can accurately acquire the instantaneous pressure condition of the surface of the airfoil profile under the conditions of static and dynamic pitching motions of the airfoil profile section at various wind speeds, and can accurately acquire the instantaneous wake flow field change.
Description
Technical Field
The invention relates to a wind tunnel test and a wing aerodynamic characteristic test method, in particular to a measurement method for a direct-current air suction type wind tunnel wing aerodynamic characteristic test.
Background
The energy is the power of social development, and the stable, reliable and clean energy is the guarantee of human civilization and social progress. The increasing exhaustion of fossil energy and its negative effects make the development and utilization of renewable energy urgent, wherein wind energy is one of the main forms of renewable energy as a sustainable, vast-reserve green energy.
The wind generating set is the most effective wind energy conversion device, and the airfoil shape is used as a component part of a wind turbine blade, and the aerodynamic characteristics of the airfoil shape influence the output power of the whole wind generating set. The research on the aerodynamic characteristics of the airfoil is divided into a static characteristic and a dynamic characteristic, and the dynamic stall phenomenon frequently occurs when the blades of the fan are in dynamic change in actual operation, so that the research on the dynamic stall characteristics of the airfoil is significant. The airfoil dynamic stall refers to a strong unsteady and nonlinear stall delay flow phenomenon caused by large-range airflow separation above an airfoil when an attack angle changes periodically or sharply and dynamically with time on a lift component such as an airfoil or a blade. The phenomenon generally exists on a wind turbine blade in yaw motion, the aerodynamic efficiency of the wind turbine blade is suddenly reduced due to dynamic stall, the high-speed operation range of the wind turbine blade is sharply reduced, even a resonance instability phenomenon can be generated, and the whole wind turbine system is threatened, so that the wind turbine blade has important engineering significance for the research of dynamic stall control. Because the experiment cost is higher, the platform is difficult to build or complex to operate, the numerical simulation is mainly used for researching the aerodynamic characteristics of the wing profile at present, and the dynamic characteristics of the wing profile under different working conditions are rarely researched in the wind tunnel experiment.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides a measuring method for a direct-current air suction type wind tunnel wing aerodynamic characteristic experiment, which can accurately acquire the instantaneous pressure condition of the wing surface under the conditions of static and dynamic pitching motions of a wing section at various wind speeds and can accurately acquire the instantaneous wake flow field change.
The purpose of the invention is realized as follows: a measuring method for aerodynamic characteristic experiments of direct current air suction type wind tunnel wing profiles comprises the following steps:
step 1) mounting a support frame on the bottom of the wind tunnel by using an aluminum alloy square tube, fixing a support flat plate on the support frame, and reserving a threaded hole fixedly connected with a six-component balance when the support flat plate is designed;
step 2) connecting the six-component balance with a reserved threaded hole on a support flat plate, connecting a servo motor with the six-component balance through two I-shaped frames, connecting the bottoms of the I-shaped frames with the threaded hole on the six-component balance, and connecting the top of each I-shaped frame with the servo motor through the reserved hole by using a bolt;
step 3) placing a wing section at the wind tunnel test section, wherein a rotating shaft of the wing section is connected with a servo motor through a coupler, an attack angle rotating disc is further installed on the rotating shaft of the wing section, a plurality of pressure measuring holes are arranged on the side surface of the attack angle rotating disc, the capillary steel pipes and plastic hoses extend and are connected to a pressure scanning valve, a hollow shaft rotating angle potentiometer is installed on the rotating shaft of the wing section, a plurality of rows of pressure measuring holes are arranged near the middle section of the wing section, the capillary steel pipes and the plastic hoses are connected to the pressure scanning valve, and the upper end of the rotating shaft of the wing section is fixed on; mounting and arranging a three-dimensional movable support and a hot wire anemoscope, and arranging a hot wire probe right behind the tail edge of the wing profile;
step 4), equipment safety check comprises the following steps: whether the bolt of the bottom support frame is screwed up and fixed or not; whether the fixing bolt of the support flat plate and the support frame is loosened or not is judged; whether the six-component balance and the support flat plate screw are screwed up or not; whether the connecting bolts of the I-shaped frame, the six-component balance and the servo motor are loosened or not; whether the shaft coupling is fixed with the servo motor shaft and the wing section rotating shaft or not; checking whether the servo motor is correctly connected with a servo motor controller circuit and normally operates; checking whether the pressure measuring holes are correctly connected to the pressure scanning valve or not, and ensuring that each pipeline is kept smooth and free of blockage; ensuring the interior of the wind tunnel to be clean;
step 5) adjusting parameters of a servo motor controller, controlling a servo motor to determine an attack angle of an airfoil section, starting a wind tunnel, and adjusting the frequency of a control cabinet to obtain a set wind speed;
step 6) setting the sampling frequency and the sampling time of the pressure sensor, repeating the step (5), and sequentially acquiring static pressure data of the airfoil section at different wind speeds and attack angles;
step 7) adjusting a servo motor controller to set the average attack angle, amplitude and frequency of the pitching motion of the wing profile; starting the wind tunnel to enable the incoming flow wind speed to reach the set wind speed; opening an air compressor, leading the air flow to a boundary attack angle when the disc performs pitching motion by a plastic hose, and setting the sampling frequency and the sampling time of the pressure sensor;
step 8) acquiring instantaneous dynamic pressure data of the airfoil section under the current wind speed, average attack angle, amplitude and frequency;
step 9) changing the wind speed, the average attack angle, the amplitude and the frequency in sequence, repeating the step (8), and completing the collection of pressure data of the airfoil profile under all working conditions of different wind speeds, average attack angles, amplitudes and frequencies;
step 10) adjusting a servo motor controller to set the average attack angle, amplitude and frequency of the pitching motion of the wing profile; starting the wind tunnel to enable the incoming flow wind speed to reach the set wind speed; setting the sampling frequency and the sampling time of the hot-wire anemometer;
step 11) changing the wind speed, the average attack angle, the amplitude and the frequency in sequence, repeating the step (10), and collecting instantaneous pulsating speed data of the tail track of the airfoil section under the current wind speed, the average attack angle, the amplitude and the frequency;
and step 12) data processing, namely calculating the pressure coefficient, the lift resistance coefficient and the instantaneous wake change of the airfoil under each working condition, and analyzing the aerodynamic characteristics of the airfoil under different working conditions.
Compared with the prior art, the invention adopts the technical scheme, and has the beneficial effects that: the manufacturing materials are simple and easy to obtain, the platform is flexibly and conveniently built, the manufacturing materials mainly comprise an aluminum alloy support with a supporting function and a resin material 3D printed supporting flat plate, the aluminum alloy support can be assembled and disassembled only through right-angle bolts, and the convenience and flexibility are realized; the balance is also connected to the support flat plate through bolts, and the static and dynamic aerodynamic characteristics of the wing section can be measured only by ensuring the balance to be horizontally placed; the power device can achieve the pitching motion power effect provided by the existing large-scale crank sliding block mechanism only by a small servo motor, the fixed installation mode of the power device is also that the resin material 3D printing I-shaped frame is connected through the bolt, the method is cheap and convenient, the instantaneous pressure conditions on the surface of the airfoil section under the static and dynamic pitching motion conditions of the airfoil section under various wind speeds can be accurately collected, and the instantaneous wake flow field change can be accurately obtained.
As a further improvement of the invention, in consideration of the time sequence correspondence problem of the multipath pressure signals of the pressure scanning valve and the real-time attack angle controlled by the servo motor, the step 12) processes data, calculates a cubic spline interpolation coefficient through an equation (1), and determines the pitching motion period of the airfoil profile and the change relation of the attack angle through an equation (2):
yi＝ai+bi(x-xi)+ci(x-xi)2+di(x-xi)3 (2)
in the formula: i is an integer from 0 to n-1, n is a spline data node, hiTo calculate the step size, miIs a second order differential value, ai、bi、ci、diIs the coefficient of a spline curve, xiInstantaneous pressure number of corresponding attack angle sequence moment collected for pressure scanning valveAccordingly, x is the desired instantaneous desired angle of attack sequence; y isiInstantaneous pressure data corresponding to a desired angle of attack.
As a further improvement of the invention, in order to reduce the measurement error, step 12) the data processing adopts a zero-phase low-pass filter of formula (3) to filter the electrical signal of the hollow shaft rotation angle potentiometer collected by the hot-wire anemometer:
in the formula: transfer function
Wherein Hg(w) is the gain of the filter,
is the phase of the filter. win (window)2N-1(n) is a convolution window function sequence and d is a time domain transfer function.
As a further improvement of the present invention, in order to improve the accuracy of the wind tunnel test result, the disturbance amount of the tunnel wall of the wind tunnel test should be reduced as much as possible, and the residual tunnel wall disturbance effect should be corrected, in step 12) data processing, the flow around the airfoil profile will be changed by the tunnel wall of the wind tunnel during the test, and the airfoil profile data measured in the two-dimensional wind tunnel can be corrected into the free flow by using the following formula (4):
in the formula: c. ClIs the coefficient of airfoil lift, cdIs the airfoil drag coefficient, cmFor the airfoil moment coefficient, Ma is a mach number, and τ and σ are parameters of the airfoil with respect to the wind tunnel dimensions, specifically τ ═ 0.25(c/k), σ ═ pi-2/48(c/k)2C is airfoil chord length, k is a ratio of wind tunnel test sections, Λ is a dimensionless parameter of the airfoil shape, a superscript 'represents an upstream incoming flow of the airfoil, and the airfoil parameter superscript' represents an uncorrected parameter obtained by wind tunnel test.
Drawings
FIG. 1 is a front view of the device of the present invention.
Figure 2 is a side view of the device of the present invention.
FIG. 3 is a schematic view of the structure of the support plate of the device of the present invention.
Fig. 4 is a schematic structural diagram of an i-shaped frame of the device.
FIG. 5 is a schematic structural view of a three-section airfoil of the inventive device.
FIG. 6 is a schematic view of the angle of attack turntable of the present invention.
FIG. 7 is a schematic structural diagram of the empty-axis rotation angle potentiometer according to the present invention.
FIG. 8 shows the surface pressure coefficients of the reference airfoil at different moments during 0-25 ° pitching under the conditions of 9.4% turbulence and 0.01454 attenuation frequency k;
FIG. 9 dynamic and static lift coefficients for the present invention at wind speeds of 15 m/s.
FIG. 10 current field distribution profile at airfoil section aft velocity measured by hot wire according to the present invention.
FIG. 11 is a hot-line measurement of the instant flow field profile of velocity after an airfoil section according to the present invention.
The device comprises a support frame 1, a support flat plate 2, bolt holes 2-1, 2-2 and 2-3, a balance 3 with six components, an I-shaped frame 4, through holes 4-1 and 4-2, a servo motor 5, a coupler 6, a potentiometer 7, a first pin 7-1, a second pin 7-2, a third pin 7-3, a potentiometer fixing support 7-4, an angle of attack turntable 8, small holes 8-1, an airfoil section 9, an upper airfoil section 9-1, an airfoil section 9-2, a lower airfoil section 9-3, pressure measuring holes 9-4 and a cuboid test box 10.
Detailed Description
A measuring method for a direct-current air suction type wind tunnel wing aerodynamic characteristic experiment specifically comprises the following steps:
step 1) installing a support frame 1 at the bottom of the wind tunnel by using an aluminum alloy square tube, fixing a support flat plate 2 on the support frame 1, and reserving a threaded hole fixedly connected with a six-component balance 3 when the support flat plate 2 is designed;
step 2) connecting a six-component balance 3 with a threaded hole reserved on a support flat plate 2, connecting a servo motor with the six-component balance 3 through two I-shaped frames 4, connecting the bottoms of the I-shaped frames 4 with the threaded hole on the six-component balance 3, and connecting the top of each I-shaped frame 4 with the servo motor 5 through a reserved hole by using a bolt;
step 3) placing an airfoil section 9 in a rectangular test box 10, namely a wind tunnel test section, connecting a rotating shaft of the airfoil section with a servo motor 5 through a coupler 6, further installing an attack angle turntable 8 on the rotating shaft, arranging a plurality of pressure measuring holes 8-1 on the side surface of the attack angle turntable 8, extending and connecting capillary steel pipes and plastic hoses to a pressure scanning valve, installing a hollow shaft rotating angle potentiometer 7 on the rotating shaft, arranging a plurality of rows of pressure measuring holes 9-4 near the section of the middle airfoil section 9-2, connecting the capillary steel pipes and the plastic hoses to the pressure scanning valve, and fixing the upper end of the rotating shaft of the airfoil section on the upper surface of the wind tunnel test section through a bearing; mounting and arranging a three-dimensional movable support and a hot wire anemoscope, and arranging a hot wire probe right behind the tail edge of the wing profile;
in order to solve the corresponding relation between the pitching motion position and the pressure signal time sequence, an attack angle rotary table 8 is designed to determine the pitching motion period of the wing profile and the change relation with an attack angle, the diameter of the attack angle rotary table 8 is 150mm, the thickness of the attack angle rotary table is 10mm, small holes 8-1 with the diameter of 1mm are arranged on the central circumference of the side wall of the rotary table, the small holes are communicated with the lower surface of the rotary table and are connected to a pressure scanning valve through capillary steel pipes and plastic hoses, the small holes 8-1 are arranged one at intervals of 3 degrees and are arranged in a half circumference from-90 degrees to 90 degrees; the attack angle rotary table 8 is fixed with the rotating shaft of the wing section by a key groove and rotates coaxially with the wing section 9; an upper through opening and a lower through opening are reserved on the other half circumference of the turntable, so that the pressure measuring hose can be conveniently wired; simultaneously, an air outlet of the air compressor is led to a small hole corresponding to the initial attack angle of the rotary table by using a plastic hose, and the plastic hose is fixed by using a magnet support frame fixed on the outer wall of the wind tunnel; therefore, the same acquisition device is adopted for the angle of attack signal and the surface pressure acquisition signal of the airfoil profile, the acquired angle of attack signal and the acquired surface pressure signal can be completely consistent, and the specific method comprises the following steps: in a periodic stroke of 0-20 degrees,there are 14 data nodes in total, namely: (x)0,y0),(x1,y1),(x2,y2),(x3,y3)……(x13,y13) Then the step size is calculated as: h isi＝xi+1-xi(ii) a Substituting the data nodes and the specified end point conditions into the solved matrix equation; solving the matrix equation to obtain a quadratic differential value mi(ii) a Calculating spline curve coefficients:
yi＝ai+bi(x-xi)+ci(x-xi)2+di(x-xi)3 (2)
in the formula: i is an integer of 0 to 13, hiTo calculate the step size, miIs a second order differential value, ai、bi、ci、diIs the coefficient of a spline curve, xiInstantaneous pressure data of a corresponding attack angle sequence moment collected by a pressure scanning valve, wherein x is an expected instantaneous expected attack angle sequence; y isiInstantaneous pressure data corresponding to a desired angle of attack;
in order to solve the problem that a hot wire device measures the real-time attack angle of dynamic wake airfoil motion and acquires a wind speed signal, a hollow shaft rotating angle potentiometer 7 is adopted to determine the corresponding relation of the attack angle, the potentiometer is fixed with a rotating shaft of a servo motor through a spring gasket and a potentiometer fixing support 7-4, the resistance value of the potentiometer is 5K, the effective angle is 90 degrees, and three pins output by the potentiometer, namely a hollow shaft rotation angle first pin 7-1 and a hollow shaft rotation angle potentiometer third pin 7-3 are electrically connected with the positive electrode and the negative electrode of the 5V switching power supply, a hollow shaft rotation angle potentiometer second pin 7-2 and a hollow shaft rotation angle potentiometer third pin 7-3 are electrically connected with the positive electrode and the negative electrode of the hot wire speed collector, the real-time change of the wing-shaped attack angle is converted into a real-time voltage signal by the hollow shaft rotation angle potentiometer for collection, and the corresponding relation between the real-time speed and the real-time attack angle can be determined. The specific design method of the zero-phase digital low-pass filter is as follows: the filter order 16 is selected and the transfer function of the filter is designed according to requirements. The design method of the transfer function is realized by a frequency domain sampling method, and the time domain transfer function of the filter is obtained through inverse Fourier transform. And (4) obtaining a 15-order matrix by expanding and shifting the high-order time domain transfer function. And multiplying the convolution window and the time domain matrix to obtain a time domain transfer function of the full-phase digital filter, which is shown as the following formula:
in the formula: transfer function
Wherein Hg(w) is the gain of the filter,
is the phase of the filter. win (window)2N-1(n) is a convolution window function sequence and d is a time domain transfer function.
Step 4), equipment safety check comprises the following steps: whether the bolt of the bottom support frame 1 is screwed up and fixed or not; the fixing bolts of the support flat plate 2 and the support frame 1 are loosened or not; whether the six-component balance 3 and the support flat plate 2 are screwed up or not; whether the connecting bolts of the I-shaped frame 4, the six-component balance 3 and the servo motor 5 are loosened or not; whether the coupler 6 is fixed with the servo motor shaft and the wing section rotating shaft or not is judged; checking whether the servo motor 5 is correctly connected with a servo motor controller circuit and normally operates; checking whether the pressure measuring holes are correctly connected to the pressure scanning valve or not, and ensuring that each pipeline is kept smooth and free of blockage; ensuring the interior of the wind tunnel to be clean;
step 5) adjusting parameters of a servo motor controller CM36l-10, controlling a servo motor to determine an attack angle of an airfoil section, starting a wind tunnel, and adjusting the frequency of a control cabinet to obtain a set wind speed;
step 6) setting the sampling frequency 333Hz and the sampling time 15s of the pressure sensor, repeating the step (5), and sequentially collecting static pressure data of the airfoil section under 7.5m/s, 10m/s, 21m/s wind speed and 0-30 degrees attack angle (interval 2 degrees);
step 7) adjusting a servo motor controller to set the average attack angle of the pitching motion of the wing profile to be 12.5 degrees, the amplitude to be 12.5 degrees and the frequency to be 0.495; starting the wind tunnel to enable the incoming flow wind speed to reach the set wind speed of 15 m/s; opening an air compressor, leading the air flow to a boundary attack angle during the pitching motion of the disc by a plastic hose, and setting the sampling frequency 333Hz and the sampling time 15s of the pressure sensor;
step 8) acquiring instantaneous dynamic pressure data of the airfoil section at the current wind speed of 15m/s, the average attack angle of 12.5 degrees, the amplitude of 12.5 degrees and the frequency of 0.495;
step 9) changing the wind speeds to 7.5m/s, 10m/s and 21m/s in sequence, the average attack angle to 3 degrees, 10 degrees, 12 degrees, 18 degrees, 21 degrees, the amplitude to 3 degrees, 6 degrees and 10 degrees and the frequency to 0.358 and 0.446, repeating the step (8), and finishing the acquisition of pressure data of all working conditions of the airfoil profile under different wind speeds, average attack angles, amplitudes and frequencies;
step 10) adjusting a servo motor controller to set the average attack angle of 12 degrees, the amplitude of 3.2 degrees and the frequency of 0.625 of the pitching motion of the wing profile; starting the wind tunnel to enable the incoming flow wind speed to reach the set wind speed of 15 m/s; setting the sampling frequency of the hot wire anemometer to be 5KHz and the sampling time to be 20 s;
step 11) changing the wind speed to 7.5m/s, 10m/s and 21m/s in sequence, the average attack angle to 10 degrees and 13 degrees, the amplitude to 4 degrees and 10 degrees and the frequency to 0.358 and 0.446, repeating the step 10, and collecting the instantaneous pulsation speed data of the tail track of the airfoil section under the current wind speed, the average attack angle, the amplitude and the frequency;
and step 12) data processing, namely calculating the pressure coefficient, the lift resistance coefficient and the instantaneous wake change of the airfoil under each working condition, and analyzing the aerodynamic characteristics of the airfoil under different working conditions.
After the surface pressure of the section of the airfoil under each working condition is measured, the lift resistance coefficient of the airfoil can be obtained by a surface pressure method, the pressure measured from the pressure measuring hole on the surface of the airfoil is generally expressed by a dimensionless form of the pressure measuring hole, and the pressure coefficient is defined as:
in the formula, CpiTo representPressure coefficient of airfoil surface i point; piA measured pressure representing an i-point of the airfoil surface; p∞Representing the incoming hydrostatic pressure; u. of∞Representing the far incoming wind speed; ρ is the air density;
the lift force and the drag force of the airfoil are decomposed into two orthogonal components, namely a normal force N and a tangential force T along the chord line direction and the direction vertical to the chord line direction, and a dimensionless normal force coefficient C is introducednAnd coefficient of tangential force Ct: the pressure measured from the pressure taps on the airfoil surface is usually expressed in its dimensionless form, with the pressure coefficient defined as:
in the formula, Cpu、CplRepresenting the pressure coefficients of the upper surface and the lower surface of the airfoil; cpq、CphRepresenting the pressure coefficients of the front and the rear of the maximum thickness of the airfoil;
representing a dimensionless quantity of the x coordinate with respect to the chord length c;
representing a dimensionless quantity of the y coordinate with respect to the chord length c;
and the dimensionless quantity of the maximum ordinate of the upper surface and the lower surface of the airfoil relative to the chord length c is represented.
The uncorrected lift coefficient of the airfoil can be obtained according to the normal force coefficient and the tangential force coefficient, and the expression is as follows:
c'1＝Cncosα-Ct sinα
the uncorrected moment coefficient of the wing profile can be obtained according to the integral of the pressure difference of the upper surface and the lower surface of the wing profile:
in consideration of the interference effect of the tunnel wall, the tunnel wall is corrected, and the airfoil profile data measured in the two-dimensional wind tunnel can be corrected into the free flow through the following formula:
in the formula: c. ClIs the coefficient of airfoil lift, cdIs the airfoil drag coefficient, cmIs airfoil moment coefficient, M'aTau and sigma are parameters of the wing profile relative to the wind tunnel size, specifically tau-0.25 (c/k) and sigma-pi for upstream incoming flow mach number2/48(c/k)2C is the airfoil chord length, k is the ratio of the wind tunnel test section,Λand the upper mark 'represents the upstream incoming flow of the airfoil, and the upper mark' represents the uncorrected parameters obtained by wind tunnel test.
FIG. 8 shows the surface pressure coefficient over a period with an average angle of attack of 12.5 degrees, an amplitude of 12.5 degrees, and a frequency of oscillation of 0.495, where it can be seen that at the first 30% of the period, the airfoil is in the linear section, no stall occurs, and the surface pressure coefficient gradually increases, reaching a peak at 30% of the period; in the period of 30% -50%, the wing profile is in the upward bending stage, but the surface pressure coefficient is rapidly reduced and gradually stabilized, and the wing profile is subjected to flow separation; and then the wing profile enters a dive stage, the flow self-reconstruction is difficult to realize around the wing profile, so the wing profile is still in a flow separation stage, and the wing profile gradually recovers to a linear section when the wing profile is not stalled as the attack angle is continuously reduced.
FIG. 9 is a graph showing the dynamic and static lift coefficient curves at a wind speed of 15m/s measured by the surface pressure method. As shown in fig. 9, in a small attack angle range, the airfoil is in a stage of stable increase of the lift coefficient, no stall phenomenon occurs, and as the attack angle gradually increases, the airfoil also enters a stall stage, and the lift coefficient is suddenly reduced; the data measured by the balance and the data measured by the surface pressure are basically consistent in the figure. And a lift coefficient hysteresis curve surrounds the static lift curve when the rotor oscillates within a small range of the attack angle. Almost all the lift force hysteresis curve is positioned above the static lift force coefficient curve within the range of 0-6 degrees, the curve direction is anticlockwise, and the upward bending stage curve is basically overlapped with the static lift force coefficient curve; in the range of 9-15 degrees, a cross point appears on a lift coefficient curve of an upward pitch stage and a downward pitch stage of the airfoil profile, the range of the attack angle contains both an unslotted section and a stalled section, and flow separation begins to occur; in the range of 15-21 and 18-24, the hysteresis loop curve is oriented clockwise, all of which are in the stall phase.
FIG. 10 is a plot of the current-sharing field at static velocity as measured by hot wire at 15 meters per second, where it can be seen that the velocity value is the smallest behind the leading and trailing edges of the airfoil, the velocity loss is the largest, and in the cross-wind direction, as the value of x/c (the lateral distance from the chord) changes to positive and negative, the wake velocity gradually increases until x/c is-0.06 and 0.13, the wake velocity substantially returns to the free incoming velocity; in the downstream direction, the smaller y/c (axial distance to chord length), the greater the velocity deficit, and the greater y/c, the narrower the velocity deficit band.
Fig. 11 shows a dynamic wake velocity hysteresis loop measured at a trailing edge y/c of 0.3 and x/c of-0.1 at an average angle of attack of 12 °, an amplitude of 3.2 °, and an oscillation frequency of 0.625, as shown in fig. 11, where the wake velocity at the point at the maximum angle of attack is the smallest, and since the angle of attack is in the stall phase, dynamic separation vortices are generated, flow reconstruction is difficult, and thus a wider hysteresis loop is present, and at the minimum angle of attack, since it is in the non-stall phase, no vortices are generated, and the velocity is far from the trailing edge, and thus the velocity approaches the free incoming velocity.
The device for measuring the wing aerodynamic characteristics of the direct-current air-breathing wind tunnel comprises a support frame 1, a support plate 2 is fixed on the support frame 1, a six-component balance 3 is arranged on the support plate 2, the upper end of the six-component balance 3 is connected with a servo motor 5 through an I-shaped frame 4, the servo motor 5 is connected with a wing section rotating shaft through a coupler 6, an attack angle turntable 8 is arranged on the wing section rotating shaft, the upper end of the wing section rotating shaft is fixed in a cuboid test box 10 through a bearing, a wing section 9 is arranged in the cuboid test box 10, the wing section 9 is connected with the upper end of the wing section rotating shaft, and pressure measuring holes 9-4 are arranged on different height sections of the wing section 9.
The bottom support frame 1 is constructed by an aluminum alloy square tube, the cross section of the square tube is 30 mm-30 mm square, and the square tube is fixed by a right-angle bolt; the size of the support frame 1 is determined by the bottom space of the direct-current air suction type wind tunnel, and the length, width and height of the support frame 1 are designed to be 390mm, 340mm and 550 mm; the design size of the support plate 2 is designed to match the size of the support frame 1, and the length, width and height are 390mm, 340mm, 5 mm.
As shown in fig. 3, four square corners of the support plate 2 with the size of 30mm by 30mm are removed, in order to fix the support plate 2 on the support frame 1, 4 threaded holes 2-1 with the diameter of 12mm are designed in the centers of the four sides of the plate and at a position 15mm away from the sides, and then the support plate is fixed on the support frame 1 by bolts; selecting a Gamma series balance of ATI, wherein eight threaded holes with the diameter of 3mm are formed in the bottom of a six-component balance 3 and are equidistantly distributed on a ring with the diameter of 68mm, eight threaded holes 2-2 with the diameter of 3.1mm are designed on a supporting flat plate 1, the threaded holes 2-2 are equidistantly distributed on the ring with the diameter of 68mm, and the balance is fixed on the supporting flat plate 2 through screws; connecting the six-component balance 3 with a threaded hole reserved on the support flat plate 2; four threaded holes 2-3 with the diameter of 6mm are formed in the supporting flat plate 2, the threaded holes 2-3 are equidistantly distributed on a circular ring with the diameter of 50mm, and when the six-component balance 3 is not arranged, the supporting flat plate 2 can be directly fixed with the I-shaped frame 4 through the threaded holes 2-3 through screws.
As shown in fig. 4, the servo motor 5 is fixed on the six-component balance 3 through the i-shaped frame 4, the i-shaped frame 4 is designed to be composed of two identical Contraband-shaped structures, the height of the i-shaped frame 4 is greater than that of the servo motor 5 by considering the size of the motor, the design height is 190mm, four through holes 4-1 are reserved on the bottom surface of the i-shaped frame and fixed with threaded holes of the six-component balance 3 through bolts, four through holes 4-2 are arranged on the top surface of the i-shaped frame and fixed with four through holes on the upper surface of the.
As shown in fig. 5, the airfoil section 9 is composed of an upper section, a middle section and a lower section, the middle section airfoil section 9-2 is penetrated by a rigid rotating shaft, and the rigid rotating shaft is connected with the servo motor shaft of the lower 80AEA07320-SC3 through a rigid coupling shaft; the airfoil sections 9 are all manufactured by adopting a 3D printing technology after modeling is completed; in order to lead out the surface pressure measuring holes by using a capillary steel pipe and a plastic hose, the middle airfoil section 9-2 adopts a hollow design, and the pressure measuring holes 9-4 are arranged on the middle section position of the surface of the middle airfoil section 9-2 and used for measuring the pressure distribution of the airfoil surface; the lower wing section 9-3 adopts a hollow design, so that a hose with the middle section connected with a pressure measuring hole can be conveniently led to the bottom end of the wing section from the hollow channel; 3 rows of 63 pressure measuring holes 9-4 in total are arranged on the section of the middle wing section 9-2 from the front edge point to the 95 percent chord length of the wing; the model is a DTU-221 airfoil, the chord length of the model is 150mm, the span length of the model is 370mm, and the pitch oscillation transmission shaft is located at the chord length of 1/4. 21 pressure measuring holes 9-4 with the diameter of 1mm are respectively arranged at the sections of 190mm, 200mm and 210mm of the wing profile in a staggered mode, and then the pressure measuring holes 9-4 extend to the bottom of the wing profile section to be connected with pressure measuring hoses of the scanning valves.
As shown in fig. 6, the diameter of the attack angle rotary table 8 is 150mm, the thickness is 10mm, a small hole 8-1 with the diameter of 1mm is arranged on the central circumference of the side wall of the attack angle rotary table 8, the inside of the small hole 8-1 is communicated with the lower surface of the rotary table and is connected to a pressure scanning valve through a capillary steel pipe and a plastic hose, and a small hole 8-1 is arranged at intervals of 3 degrees on the semi-circumference of the attack angle rotary table 8 from-90 degrees to 90 degrees; the attack angle rotary table 8 and the rotating shaft of the wing section are fixed through key grooves and rotate coaxially with the wing section 9, and an upper through opening and a lower through opening are reserved on the other half circumference of the attack angle rotary table 8, so that the pressure measuring hose can be conveniently wired; the small hole corresponding to the initial attack angle of the attack angle rotary table 8 is connected with the air outlet of the air compressor through a plastic hose, and the plastic hose is fixed by a magnet support frame fixed on the outer wall of the wind tunnel; therefore, the same acquisition device is adopted for the angle of attack signal and the surface pressure acquisition signal of the airfoil profile, and the acquired angle of attack signal and the acquired surface pressure signal can be completely consistent.
As shown in fig. 7, a hollow shaft rotation angle potentiometer 7 is used for determining the corresponding relationship of the attack angle, the potentiometer is fixed with a rotating shaft of a servo motor through a spring washer and a potentiometer fixing support 7-4, the resistance value of the potentiometer is 5K, the effective angle is 90 degrees, three pins output by the potentiometer, a first pin 7-1 of the hollow shaft rotation angle potentiometer and a third pin 7-3 of the hollow shaft rotation angle potentiometer are electrically connected with the positive electrode and the negative electrode of a 5V switch power supply, a second pin 7-2 of the hollow shaft rotation angle potentiometer and a third pin 7-3 of the hollow shaft rotation angle potentiometer are electrically connected with the positive electrode and the negative electrode of a hot wire speed collector, the real-time change of the airfoil type attack angle is converted into a real-time voltage signal by the hollow shaft rotation angle potentiometer.
The present invention is not limited to the above-mentioned embodiments, and based on the technical solutions disclosed in the present invention, those skilled in the art can make some substitutions and modifications to some technical features without creative efforts according to the disclosed technical contents, and these substitutions and modifications are all within the protection scope of the present invention.
Claims (4)
1. A measuring method for aerodynamic characteristic experiments of wing profiles of direct-current air-breathing wind tunnels is characterized by comprising the following steps:
step 1) mounting a support frame on the bottom of the wind tunnel by using an aluminum alloy square tube, fixing a support flat plate on the support frame, and reserving a threaded hole fixedly connected with a six-component balance when the support flat plate is designed;
step 2) connecting the six-component balance with a reserved threaded hole on a support flat plate, connecting a servo motor with the six-component balance through two I-shaped frames, connecting the bottoms of the I-shaped frames with the threaded hole on the six-component balance, and connecting the top of each I-shaped frame with the servo motor through the reserved hole by using a bolt;
step 3) placing a wing section at the wind tunnel test section, wherein a rotating shaft of the wing section is connected with a servo motor through a coupler, an attack angle rotating disc is further installed on the rotating shaft of the wing section, a plurality of pressure measuring holes are arranged on the side surface of the attack angle rotating disc, the capillary steel pipes and plastic hoses extend and are connected to a pressure scanning valve, a hollow shaft rotating angle potentiometer is installed on the rotating shaft of the wing section, a plurality of rows of pressure measuring holes are arranged near the middle section of the wing section, the capillary steel pipes and the plastic hoses are connected to the pressure scanning valve, and the upper end of the rotating shaft of the wing section is fixed on; mounting and arranging a three-dimensional movable support and a hot wire anemoscope, and arranging a hot wire probe right behind the tail edge of the wing profile;
step 4), equipment safety check comprises the following steps: whether the bolt of the bottom support frame is screwed up and fixed or not; whether the fixing bolt of the support flat plate and the support frame is loosened or not is judged; whether the six-component balance and the support flat plate screw are screwed up or not; whether the connecting bolts of the I-shaped frame, the six-component balance and the servo motor are loosened or not; whether the shaft coupling is fixed with the servo motor shaft and the wing section rotating shaft or not; checking whether the servo motor is correctly connected with a servo motor controller circuit and normally operates; checking whether the pressure measuring holes are correctly connected to the pressure scanning valve or not, and ensuring that each pipeline is kept smooth and free of blockage; ensuring the interior of the wind tunnel to be clean;
step 5) adjusting parameters of a servo motor controller, controlling a servo motor to determine an attack angle of an airfoil section, starting a wind tunnel, and adjusting the frequency of a control cabinet to obtain a set wind speed;
step 6) setting the sampling frequency and the sampling time of the pressure sensor, repeating the step (5), and sequentially acquiring static pressure data of the airfoil section at different wind speeds and attack angles;
step 7) adjusting a servo motor controller to set the average attack angle, amplitude and frequency of the pitching motion of the wing profile; starting the wind tunnel to enable the incoming flow wind speed to reach the set wind speed; opening an air compressor, leading the air flow to a boundary attack angle when the disc performs pitching motion by a plastic hose, and setting the sampling frequency and the sampling time of the pressure sensor;
step 8) acquiring instantaneous dynamic pressure data of the airfoil section under the current wind speed, average attack angle, amplitude and frequency;
step 9) changing the wind speed, the average attack angle, the amplitude and the frequency in sequence, repeating the step (8), and completing the collection of pressure data of the airfoil profile under all working conditions of different wind speeds, average attack angles, amplitudes and frequencies;
step 10) adjusting a servo motor controller to set the average attack angle, amplitude and frequency of the pitching motion of the wing profile; starting the wind tunnel to enable the incoming flow wind speed to reach the set wind speed; setting the sampling frequency and the sampling time of the hot-wire anemometer;
step 11) changing the wind speed, the average attack angle, the amplitude and the frequency in sequence, repeating the step (10), and collecting instantaneous pulsating speed data of the tail track of the airfoil section under the current wind speed, the average attack angle, the amplitude and the frequency;
and step 12) data processing, namely calculating the pressure coefficient, the lift resistance coefficient and the instantaneous wake change of the airfoil under each working condition, and analyzing the aerodynamic characteristics of the airfoil under different working conditions.
2. The measurement method for the aerodynamic characteristic experiment of the wing profile of the direct-current air-suction wind tunnel according to claim 1, wherein the step 12) is used for processing data, calculating a cubic spline interpolation coefficient through an equation (1), and determining the pitching motion period of the wing profile and the relation between the pitching motion period and the change of the attack angle through an equation (2):
yi＝ai+bi(x-xi)+ci(x-xi)2+di(x-xi)3 (2)
in the formula: i is an integer from 0 to n-1, n is a spline data node, hiTo calculate the step size, miIs a second order differential value, ai、bi、ci、diIs the coefficient of a spline curve, xiInstantaneous pressure data of a corresponding attack angle sequence moment collected by a pressure scanning valve, wherein x is an expected instantaneous expected attack angle sequence; y isiInstantaneous pressure data corresponding to a desired angle of attack.
3. The measurement method for the aerodynamic characteristic experiment of the wing profile of the direct-current air-breathing wind tunnel according to claim 1, wherein the step 12) data processing adopts a zero-phase low-pass filter of formula (3) to filter the electrical signal of the hollow shaft rotation angle potentiometer collected by the hot-wire anemometer:
in the formula: transfer function
Wherein Hg(w) is the gain of the filter,
is the phase of the filter. win (window)2N-1(n) is a convolution window function sequence and d is a time domain transfer function.
4. The method for measuring the aerodynamic characteristics of the wing profile of the direct-current air-breathing wind tunnel according to claim 1, wherein the flow around the wing profile is changed by considering the wall of the wind tunnel during the data processing in step 12), and the wing profile data measured in the two-dimensional wind tunnel can be corrected into the free flow by using the formula (4) as follows:
in the formula: c. ClIs the coefficient of airfoil lift, cdIs the airfoil drag coefficient, cmFor the airfoil moment coefficient, Ma is a mach number, and τ and σ are parameters of the airfoil with respect to the wind tunnel dimensions, specifically τ ═ 0.25(c/k), σ ═ pi-2/48(c/k)2C is airfoil chord length, k is a ratio of wind tunnel test sections, Λ is a dimensionless parameter of the airfoil shape, a superscript 'represents an upstream incoming flow of the airfoil, and the airfoil parameter superscript' represents an uncorrected parameter obtained by wind tunnel test.
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| CN113654707A (en) * | 2021-08-12 | 2021-11-16 | 北京航空航天大学 | Atmospheric parameter sensing system based on pressure and flow rate and demand parameter calculation method |
| CN114021277A (en) * | 2021-11-02 | 2022-02-08 | 华北电力大学 | Method and system for evaluating dynamic aerodynamic characteristics of wind turbine |
| CN114993606A (en) * | 2022-05-31 | 2022-09-02 | 中国科学院力学研究所 | Wind tunnel test result processing method for unsteady pressure and aerodynamic data |
| CN116222952A (en) * | 2023-05-10 | 2023-06-06 | 中国航空工业集团公司哈尔滨空气动力研究所 | Air suction device for reducing thickness of boundary layer of wind tunnel floor |
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2020
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113654707A (en) * | 2021-08-12 | 2021-11-16 | 北京航空航天大学 | Atmospheric parameter sensing system based on pressure and flow rate and demand parameter calculation method |
| CN113654707B (en) * | 2021-08-12 | 2022-08-16 | 北京航空航天大学 | Atmospheric parameter sensing system based on pressure and flow rate and demand parameter calculation method |
| CN114021277A (en) * | 2021-11-02 | 2022-02-08 | 华北电力大学 | Method and system for evaluating dynamic aerodynamic characteristics of wind turbine |
| CN114993606A (en) * | 2022-05-31 | 2022-09-02 | 中国科学院力学研究所 | Wind tunnel test result processing method for unsteady pressure and aerodynamic data |
| CN116222952A (en) * | 2023-05-10 | 2023-06-06 | 中国航空工业集团公司哈尔滨空气动力研究所 | Air suction device for reducing thickness of boundary layer of wind tunnel floor |
| CN116222952B (en) * | 2023-05-10 | 2023-07-04 | 中国航空工业集团公司哈尔滨空气动力研究所 | Air suction device for reducing thickness of boundary layer of wind tunnel floor |
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