Method for calculating upwash interference factor K1 of wind tunnel test section

Abstract

The invention discloses a method for calculating an upwash interference factor K1 of a wind tunnel test section, belongs to the field of experimental aerodynamics, and aims at meeting the requirement for accurately calculating the upwash interference factor K1 of the wind tunnel test section. The method comprises the following steps: S1, sorting lift coefficient linear segment data; s2, calculating the lift line slope of the test original data; s3, calculating a lift line slope of the reference non-cave-wall interference data; s4, calculating a lift line slope difference caused by tunnel wall interference; s5, obtaining a K1 quantity value of the current test state; and S6, repeating the steps S1 to S5 to obtain K1 values in different test states. According to the method, the lift coefficient and attack angle data processing flow of the transonic wind tunnel test model is combined, the linear curve slope is calculated through the lift coefficient and the attack angle in the test original result and the reference result, and the magnitude of the upwash interference factor K1 is calculated based on the slope difference. The K1 magnitude is calculated through the fitting result of all the data points of the curve linear segment, the data processing difficulty can be reduced, and the result accuracy can be improved.

Description

Technical Field

[0001] This application relates to the field of experimental aerodynamics, and in particular to a method for calculating the upwash interference factor K1 of a wind tunnel test section. Background Technology

[0002] Tunnel wall interference can be divided into two parts: blockage interference and lift interference. Lift interference includes three parts: angle of attack correction, induced drag correction, and pitching moment correction. The corresponding correction amounts are calculated using three interference factors, K1, K2, and K3, in conjunction with the original test results. The angle of attack correction is directly proportional to the lift coefficient of the test model, and the proportionality coefficient is the upwash interference factor K1. K1 characterizes the distribution characteristics of the tunnel wall-induced normal disturbance velocity in the lift surface region of the model, and its value is closely related to the tunnel wall permeability, Mach number, and Reynolds number during the test. For solid-wall test sections in low-speed wind tunnels, the lift interference can be calculated using numerical simulation methods to obtain the upwash interference factor K1. However, for transonic wind tunnel test sections with openings or slots, since accurate boundary conditions cannot be constructed, a comparative trial-and-error method using corrected results is necessary. This involves correcting the original test results using a series of upwash interference factors K1 with different values, then comparing them with reference results, and using the closest value as the K1 value for the current test state. This method has two drawbacks: (1) Each data point includes dozens or even hundreds of data points, and the amount of calculation before and after data extraction and correction is large and the processing is complicated; (2) The fluctuation of experimental data points affects the accuracy of the results, and the subjective judgment of the operator when extracting data has a significant impact on the results.

[0003] Therefore, a new method is urgently needed to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to provide a method for accurately calculating the upwash interference factor K1 in wind tunnel test sections, addressing the need for accurate calculation. Unlike existing technologies, this application combines the lift coefficient and angle of attack data processing flow of a transonic wind tunnel test model. It calculates the slope of the linear segment curve using the lift coefficient and angle of attack from the original test results and reference results, and then calculates the value of the upwash interference factor K1 based on the slope difference. This application calculates the K1 value using the fitting results of all data points on the linear segment of the curve, which reduces data processing difficulty and improves the accuracy of the results.

[0005] To achieve the above objectives, this application adopts the following technical solution.

[0006] A method for calculating the upwash interference factor K1 of a wind tunnel test section includes the following steps:

[0007] S1. Organize the linear segment data of the lift coefficient to form two sets of data points: the original experimental data and the reference data, with N and M data points respectively. The relevant formulas are as follows:

[0008] (11);

[0009] In the formula, The angle of attack for the original test data, The lift coefficient is the original data from the experiment. Angle of attack for reference data, The lift coefficient is for reference data;

[0010] S2. Calculate the slope of the lift line in the original experimental data, using the following formula:

[0011] (12);

[0012] In the formula, The slope of the lift line in the original experimental data;

[0013] S3. Calculate the slope of the lift line from the reference data without cavity wall interference, using the following formula:

[0014] (13);

[0015] In the formula, The slope of the lift line is used as a reference.

[0016] S4. Calculate the difference in the slope of the lift line caused by the interference from the tunnel wall, using the following formula:

[0017] (14);

[0018] In the formula, This is the correction amount for the slope of the lift line caused by lift disturbance;

[0019] S5. Substitute the above data into the formula for the washing interference factor K1 to obtain the K1 value for the current experimental state. The formula is as follows:

[0020] (15);

[0021] S6. Repeat steps S1 to S5 to obtain the K1 value under different experimental conditions.

[0022] The linear segment of the lift coefficient refers to the lift coefficient of the aircraft within a small angle of attack range. With angle of attack A section of the curve that increases proportionally and steadily.

[0023] The slope of the lift line The change in lift coefficient caused by a unit change in angle of attack within the linear segment of the lift coefficient is expressed in units of 1 / °.

[0024] If the K1 value that has not been tested needs to be used, the K1 value under the corresponding state is calculated by interpolation.

[0025] As mentioned earlier, the upwash interference factor K1 of the solid wall in a low-speed wind tunnel can currently be calculated using numerical simulation to determine the induced velocity of the tunnel wall in the model's wing region, followed by calculating the model's angle of attack correction using a weighted average method based on specific location points. However, for transonic permeable wall test sections, accurate boundary conditions cannot be established, requiring inverse calculation based on the angle of attack difference through trial and error. Both methods result in errors in the upwash interference factor K1. Therefore, this invention proposes a method to calculate the K1 value by fitting the difference between all data points in a linear segment, thereby improving the accuracy of the calculation results.

[0026] First, according to the definition of tunnel wall interference, the upwash interference factor K1 is the model angle of attack correction amount caused by tunnel wall interference. With lift coefficient The proportionality coefficient is calculated using the following formula:

[0027] (1).

[0028] Plot the lift coefficient versus angle of attack curve with the lift coefficient as the ordinate and the angle of attack as the abscissa. For any two data points 1 and 2 on the linear segment of the lift coefficient versus angle of attack curve, the angles of attack of the original experimental data model are respectively... The lift coefficients are respectively The angle of attack correction caused by tunnel wall interference is calculated using the following formula:

[0029] (2);

[0030] (3);

[0031] In the formula, , These are the angle of attack corrections at test data points 1 and 2, respectively.

[0032] The formula for calculating the slope of the lift line in the original experimental data model is as follows:

[0033] (4);

[0034] In the formula, The slope of the lift line is the original data from the experiment.

[0035] The formula for calculating the slope of the lift line in the data model after correction for tunnel wall interference is as follows:

[0036] (5);

[0037] In the formula, The slope of the lift line is used as a reference.

[0038] The formula for calculating the correction amount of the lift line slope caused by tunnel wall interference is as follows:

[0039] (6);

[0040] In the formula, This is the correction amount for the slope of the lift line caused by lift disturbance.

[0041] The following calculation formula can be obtained by reorganizing:

[0042] (7);

[0043] Substituting the proportional relationship between the angle of attack correction and the lift coefficient into formula (7), we obtain the following calculation formula:

[0044] (8);

[0045] Rearranging formula (8), we obtain the following calculation formula:

[0046] (9);

[0047] Simplifying formula (9), we obtain the following calculation formula:

[0048] (10).

[0049] Using the original experimental data and the linear segment data of the lift coefficient in the reference interference-free data, the least squares method is used for fitting, and the K1 value of the current experimental state is calculated using the difference in slope. The specific steps are as follows.

[0050] S1. Organize the linear segment data of the lift coefficient to form two sets of data points: the original experimental data and the reference data, with N and M data points respectively. The relevant formulas are as follows:

[0051] (11);

[0052] In the formula, The angle of attack for the original test data, The lift coefficient is the original data from the experiment. Angle of attack for reference data, The lift coefficient is for reference data.

[0053] S2. Calculate the slope of the lift line in the original experimental data, using the following formula:

[0054] (12);

[0055] In the formula, The slope of the lift line is the original data from the experiment.

[0056] S3. Calculate the slope of the lift line from the reference data without cavity wall interference, using the following formula:

[0057] (13);

[0058] In the formula, The slope of the lift line is used as a reference.

[0059] S4. Calculate the difference in the slope of the lift line caused by the interference from the tunnel wall, using the following formula:

[0060] (14);

[0061] In the formula, This is the correction amount for the slope of the lift line caused by lift disturbance.

[0062] S5. Substitute the above data into the formula for the washing interference factor K1 to obtain the K1 value for the current experimental state. The formula is as follows:

[0063] (15);

[0064] S6. Repeat steps S1 to S5 to obtain the K1 value under different experimental conditions.

[0065] The linear segment of the lift coefficient refers to the lift coefficient of the aircraft within a small angle of attack range. With angle of attack A section of the curve that increases proportionally and steadily.

[0066] The slope of the lift line The lift coefficient slope refers to the change in lift coefficient caused by a unit change in angle of attack within the linear segment of the lift coefficient curve. The unit is 1 / °. The least squares method can be used to fit and calculate the data points within ±2° of the angle of attack.

[0067] If the K1 value that has not been tested needs to be used, the K1 value under the corresponding state is calculated by interpolation.

[0068] This invention uses the lift coefficient and angle of attack fitting curves of the original test data and reference data to calculate the slope. By calculating the slope difference in reverse, the value of the upwash interference factor K1 can be quickly determined. This invention can be used for wind tunnel test section lift interference factor K1 variation with test operation parameters and can be used for tunnel wall interference assessment and correction.

[0069] Furthermore, the method proposed in this invention is not limited to model layout and wind tunnel form, and can be quickly promoted and applied to other similar wind tunnels, with good engineering applicability. Attached Figure Description

[0070] The present invention will be described by way of example and with reference to the accompanying drawings, wherein:

[0071] Figure 1 This is a schematic diagram comparing the lift coefficient-angle of attack slope of the original test data and the reference data.

[0072] Figure 2 This is a comparison chart of the lift coefficient-angle of attack curves between the original and corrected data from the test at Mach 0.85 in Example 1.

[0073] Figure 3 The graph shows the variation of the washing interference factor K1 with the experimental Mach number in Example 1. Detailed Implementation

[0074] All features disclosed in this specification, or all steps in all disclosed methods or processes, may be combined in any way, except for mutually exclusive features and / or steps.

[0075] Any feature disclosed in this specification, unless specifically stated otherwise, can be replaced by other equivalent or similar features. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features. The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0076] Example 1

[0077] A large aircraft model force measurement test was conducted in a 2-meter wind tunnel within the Ma range of 0.15 to 0.90, obtaining the raw test data; test data of the same model in a 5-meter wind tunnel were used as reference data. Figure 1 A schematic diagram comparing the lift coefficient-angle of attack slope of the raw experimental data and the reference data is provided.

[0078] Taking the test data of Ma=0.15, 0.20, 0.40, 0.60, 0.80, 0.85, 0.89 as an example, the calculation process of K1 coefficient in a 2-meter wind tunnel is explained, and the variation law of K1 coefficient with Mach number is obtained.

[0079] In one instance (Ma=0.85), a comparison of the lift coefficient-angle of attack curves between the original test data and the reference data is shown in the appendix. Figure 2The data points within ±2° of the model's angle of attack are shown in the table below, with 12 data points in each range. Since the lift coefficient-angle of attack curves of the original experimental data and the reference data are fitted using the least squares method, the difference in the number of data points between the original experimental data and the reference data does not affect the calculations of this method.

[0080] Table 1. Raw and reference data of the experiment (Ma=0.85)

[0081]

[0082] Using the data in Table 1, calculate the lift coefficient-angle of attack slope of the raw and reference data:

[0083] ;

[0084] .

[0085] Among them, the lift coefficient-angle of attack curve slope , The unit is (1 / °).

[0086] Calculate the difference between the lift coefficient and the slope of the angle of attack curve caused by tunnel wall interference:

[0087] .

[0088] Substituting the above data into the formula for the washing interference factor K1, we obtain the value of K1 for the current experimental state:

[0089] .

[0090] Among them, the difference between the lift coefficient and the slope of the angle of attack curve The unit is (1 / °), and the unit of the upwash interference factor K1 is (°).

[0091] Using the same method, the K1 values ​​were calculated at different experimental Mach numbers. The original experimental data and reference data are shown in Tables 2 to 7, and the calculation results of the lift coefficient-angle of attack curve slope are shown in Table 8.

[0092] Table 2. Raw and reference data of the experiment (Ma=0.15)

[0093]

[0094] Table 3. Raw and reference data of the experiment (Ma=0.20)

[0095]

[0096] Table 4. Raw and reference data of the experiment (Ma=0.40)

[0097]

[0098] Table 5. Raw and reference data of the experiment (Ma=0.60)

[0099]

[0100] Table 6. Raw and reference data of the experiment (Ma=0.80)

[0101]

[0102] Table 7. Raw and reference data of the experiment (Ma=0.89)

[0103]

[0104] Table 8. Calculation results of lift coefficient-angle of attack curve slope at different Mach numbers

[0105]

[0106] The final K1 results are shown in Table 9, and the curves showing the variation with Mach number are attached. Figure 3 As the Mach number increases, the value of K1 increases.

[0107] Table 9. Calculation results of upwash interference factor K1 at different Mach numbers

[0108]

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

[0110] This invention is not limited to the specific embodiments described above. The invention extends to any new feature or combination disclosed in this specification, as well as any new method or process step or combination disclosed herein.

Claims

1. A method for calculating the upwash interference factor K1 of a wind tunnel test section, characterized in that, Includes the following steps: S1. Organize the linear segment data of the lift coefficient to form two sets of data points: the original experimental data and the reference data, with N and M data points respectively. The relevant formulas are as follows: （11）； In the formula, The angle of attack for the original test data, The lift coefficient is the original data from the experiment. Angle of attack for reference data, The lift coefficient is for reference data; S2. Calculate the slope of the lift line in the original experimental data, using the following formula: （12）； In the formula, The slope of the lift line in the original experimental data; S3. Calculate the slope of the lift line from the reference data without cavity wall interference, using the following formula: （13）； In the formula, The slope of the lift line is used as a reference. S4. Calculate the difference in the slope of the lift line caused by the interference from the tunnel wall, using the following formula: （14）； In the formula, This is the correction amount for the slope of the lift line caused by lift disturbance; S5. Substitute the above data into the formula for the washing interference factor K1 to obtain the K1 value for the current experimental state. The formula is as follows: （15）； S6. Repeat steps S1 to S5 to obtain the K1 value under different experimental conditions.

2. The method for calculating the upwash interference factor K1 of a wind tunnel test section according to claim 1, characterized in that, The linear segment of the lift coefficient refers to the lift coefficient of the aircraft within a small angle of attack range. With angle of attack A section of the curve that increases proportionally and steadily.

3. The method for calculating the upwash interference factor K1 of a wind tunnel test section according to claim 1, characterized in that, The slope of the lift line The change in lift coefficient caused by a unit change in angle of attack within the linear segment of the lift coefficient is expressed in units of 1 / °.

4. The method for calculating the upwash interference factor K1 of a wind tunnel test section according to claim 1, characterized in that, If the K1 value that has not been tested needs to be used, the K1 value under the corresponding state is calculated by interpolation.

5. The method for calculating the upwash interference factor K1 of a wind tunnel test section according to claim 1, characterized in that, Using the original experimental data and the linear segment data of the lift coefficient in the reference interference-free data, the least squares method is used for fitting, and the K1 value of the current experimental state is calculated using the difference in slope.

6. The method for calculating the upwash interference factor K1 of a wind tunnel test section according to claim 5, characterized in that, According to the definition of tunnel wall interference, the upwash interference factor K1 is the model angle of attack correction amount caused by tunnel wall interference. With lift coefficient The proportionality coefficient is calculated using the following formula: （1）； Plot the lift coefficient versus angle of attack curve with the lift coefficient as the ordinate and the angle of attack as the abscissa. For any two data points 1 and 2 on the linear segment of the lift coefficient versus angle of attack curve, the angles of attack of the original experimental data model are respectively... The lift coefficients are respectively The angle of attack correction caused by tunnel wall interference is calculated using the following formula: （2）； （3）； In the formula, , These are the angle of attack corrections at points 1 and 2 of the original test data; The formula for calculating the slope of the lift line in the original experimental data model is as follows: （4）； In the formula, The slope of the lift line in the original experimental data; The formula for calculating the slope of the lift line in the data model after correction for tunnel wall interference is as follows: （5）； In the formula, The slope of the lift line is used as a reference. The formula for calculating the correction amount of the lift line slope caused by tunnel wall interference is as follows: （6）； In the formula, This is the correction amount for the slope of the lift line caused by lift disturbance; The following calculation formula is obtained after sorting: （7）； Substituting the proportional relationship between the angle of attack correction and the lift coefficient into formula (7), we obtain the following calculation formula: （8）； Rearranging formula (8), we obtain the following calculation formula: （9）； Simplifying formula (9), we obtain the following calculation formula: （10）。

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