A method for evaluating the impact of Reynolds number on propeller wind tunnel test aerodynamic noise data

Abstract

A method for evaluating the impact of Reynolds number on propeller wind tunnel test aerodynamic noise data belongs to the technical field of wind tunnel test. In order to evaluate the error range of aerodynamic noise data caused by Reynolds number deviation, the present invention determines the Reynolds number of the propeller under the actual working state and wind tunnel test state according to the propeller size and working conditions; judges whether the test Reynolds number is less than the critical Reynolds number required for simulation in the test, if so, an impact assessment is required; evaluates the impact of Reynolds number on the aerodynamic characteristics of the propeller, and expresses it with the error range of the aerodynamic force obtained by the test data statistics; calculates the aerodynamic noise impact caused by the difference in aerodynamic performance according to the propeller load noise theoretical estimation method; measures the propeller aerodynamic noise test, and obtains the propeller noise spectrum and total sound pressure level data OASPL after data processing; uses the noise impact amount △SPL to evaluate the uncertainty of the sound pressure level of discrete peaks such as the total sound pressure level and the blade passing frequency in the noise spectrum.

Description

Technical Field

[0001] The invention belongs to the technical field of wind tunnel tests, and in particular relates to a method for evaluating the influence of Reynolds number on aerodynamic noise data of a propeller wind tunnel test. Background Art

[0002] A wind tunnel is a device that uses a power device to drive a controllable airflow that simulates real atmospheric conditions for use in various aerodynamic tests. Propeller aerodynamic noise is the noise generated by the interaction between the propeller blades and the air during the rotation of the propeller, and is one of the important indicators of today's air propeller design. The propeller aerodynamic noise wind tunnel test is a test method that uses a propeller model to conduct test measurements to evaluate and study the propeller aerodynamic noise characteristics. During the test, the different working conditions of the propeller are simulated by changing the model's pitch angle, rotation speed, test wind speed and other conditions, and the propeller aerodynamic noise data under the corresponding state is measured by the noise test system.

[0003] Propeller wind tunnel tests usually use scaled models. In addition to geometric similarity, the main similarity parameters simulated include: advance ratio and Mach number. Due to the scale of the model, the model feature size is smaller than the actual propeller. Therefore, in conventional acoustic wind tunnels, while ensuring the similarity of the advance ratio and Mach number, the test Reynolds number must be smaller than the Reynolds number under actual working conditions. Studies have shown that when the test Reynolds number is greater than 0.5×10 6 When the propeller performance is not significantly affected, the test Reynolds number is less than 0.5×10 6 , there is a certain error between the aerodynamic performance test results and the actual working conditions. Since the propeller aerodynamic load is directly related to the noise level, this influence will inevitably lead to the difference between the propeller aerodynamic noise wind tunnel test data and the actual working conditions. Since the influence mechanism of low Reynolds number on propeller flow and noise is relatively complex, a reliable influence correction method has not yet been formed. Therefore, when the characteristic Reynolds number of the propeller wind tunnel test is small due to the actual test conditions, a method is needed to evaluate the error range of the aerodynamic noise data caused by the Reynolds number deviation, so as to serve as a reference for the uncertainty evaluation of the test data or the correction of the test data. Summary of the invention

[0004] The problem to be solved by the present invention is to evaluate the error range of aerodynamic noise data caused by Reynolds number deviation, and propose a method for evaluating the influence of Reynolds number on aerodynamic noise data of propeller wind tunnel test.

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

[0006] A method for evaluating the impact of Reynolds number on propeller wind tunnel test aerodynamic noise data comprises the following steps:

[0007] S1. Determine the Reynolds number Re of the propeller under the actual working condition according to the propeller size and working conditions. real , according to the wind tunnel test model size and test conditions, determine the propeller test Reynolds number ; Since the propeller wind tunnel test model is usually a scaled model of the real propeller, and in order to ensure that the Mach number and advance ratio are equal, the test Reynolds number is set Less than the Reynolds number Re under actual working conditions real , experimental Reynolds number The expression is:

[0008] (1)

[0009] in, is the experimental Reynolds number, To test the atmospheric density, is the cross-sectional velocity at 0.7 times the radius, is the characteristic chord length of the section at 0.7 times the radius, is the atmospheric viscosity coefficient;

[0010] S2. Determine whether the test Reynolds number is less than the critical Reynolds number 0.5×10 6 ,like ≥0.5×10 6 , it is considered that the test Reynolds number has little effect on the propeller aerodynamic noise; if <0.5×10 6 , then continue with the Reynolds number impact assessment;

[0011] S3. The error of aerodynamic force obtained by statistical test data , the effect of Reynolds number on propeller aerodynamic characteristics is evaluated, and the formula is as follows:

[0012] (2)

[0013] in, is the tensile coefficient test value, is the correction value of tension coefficient;

[0014] S4. When the blade tip Mach number is subsonic and the thickness noise and quadrupole noise are weak, it is considered that the propeller aerodynamic noise is mainly composed of load noise. According to the propeller load noise theoretical estimation method and formula (2), the load noise influence is obtained: The evaluation formula is as follows:

[0015] (3)

[0016] S5. Using the load noise influence obtained in step S4 as a reference for the error range, a range assessment is performed on the total sound pressure level data and the blade passing frequency discrete peak value.

[0017] Furthermore, the propeller aerodynamic noise test is measured and the propeller noise spectrum and total sound pressure level data OASPL are obtained through data processing.

[0018] Furthermore, the data processing method after the propeller aerodynamic noise test measurement is Fourier transform and sound pressure level calculation, and the specific method includes the following steps:

[0019] Step 1. Calculate the root mean square effective value of the time domain sound pressure data obtained from the test measurement to obtain the effective sound pressure p e ;

[0020] Step 2. Set the effective sound pressure p e Input sound pressure level Calculation formula: , the sound pressure level data obtained is the total sound pressure level;

[0021] Step 3. Perform Fourier transform on the time domain sound pressure data to obtain frequency domain sound pressure data. By calculating the sound pressure level, the sound pressure level at each frequency, i.e., the noise spectrum, is obtained.

[0022] Beneficial effects of the present invention:

[0023] The method for evaluating the influence of Reynolds number on aerodynamic noise data of a propeller wind tunnel test described in the present invention can evaluate the influence of aerodynamic noise test data caused by Reynolds number simulation differences, provide a reference for error range evaluation of wind tunnel test noise data, improve the reliability of mapping wind tunnel test data to actual propeller performance, and provide more reliable noise test data for aviation propeller design and evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The figure is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0025] 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.

[0026] 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.

[0027] 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 The detailed instructions are as follows:

[0028] Embodiment 1:

[0029] A method for evaluating the impact of Reynolds number on propeller wind tunnel test aerodynamic noise data comprises the following steps:

[0030] S1. Determine the Reynolds number Re of the propeller under the actual working condition according to the propeller size and working conditions. real , according to the wind tunnel test model size and test conditions, determine the propeller test Reynolds number ; Since the propeller wind tunnel test model is usually a scaled model of the real propeller, and in order to ensure that the Mach number and advance ratio are equal, the test Reynolds number is set Less than the Reynolds number Re under actual working conditions real , experimental Reynolds number The expression is:

[0031] (1)

[0032] in, is the experimental Reynolds number, To test the atmospheric density, is the cross-sectional velocity at 0.7 times the radius, is the characteristic chord length of the section at 0.7 times the radius, is the atmospheric viscosity coefficient;

[0033] S2. Determine whether the test Reynolds number is less than the critical Reynolds number 0.5×10 6 ,like ≥0.5×10 6 , it is considered that the test Reynolds number has little effect on the propeller aerodynamic noise; if <0.5×10 6 , then continue with the Reynolds number impact assessment;

[0034] S3. The error of aerodynamic force obtained by statistical test data , the effect of Reynolds number on propeller aerodynamic characteristics is evaluated, and the formula is as follows:

[0035] (2)

[0036] in, is the tensile coefficient test value, is the correction value of tension coefficient;

[0037] S4. When the blade tip Mach number is subsonic and the thickness noise and quadrupole noise are weak, it is considered that the propeller aerodynamic noise is mainly composed of load noise. According to the propeller load noise theoretical estimation method and formula (2), the load noise influence is obtained: The evaluation formula is as follows:

[0038] (3)

[0039] and:

[0040] ;

[0041] Since the mechanism of the influence of Reynolds number on propeller flow is extremely complex, the influence on aerodynamic force is based on the error range obtained from test data. It is the noise sound pressure level influence range estimated by the error range, so it is recommended to be used as a reference of error range;

[0042] S5. Using the load noise influence obtained in step S4 as a reference for the error range, a range assessment is performed on the total sound pressure level data and the blade passing frequency discrete peak value.

[0043] Furthermore, the propeller aerodynamic noise test is measured and the propeller noise spectrum and total sound pressure level data OASPL are obtained through data processing.

[0044] Furthermore, the data processing method after the propeller aerodynamic noise test measurement is Fourier transform and sound pressure level calculation, and the specific method includes the following steps:

[0045] Step 1. Calculate the root mean square effective value of the time domain sound pressure data obtained from the test measurement to obtain the effective sound pressure p e ;

[0046] Step 2. Set the effective sound pressure p e Input sound pressure level Calculation formula: , the sound pressure level data obtained is the total sound pressure level;

[0047] Step 3. Perform Fourier transform on the time domain sound pressure data to obtain frequency domain sound pressure data. By calculating the sound pressure level, the sound pressure level at each frequency, i.e., the noise spectrum, is obtained.

[0048] The method of this embodiment is described as follows:

[0049] S1. Determine the Reynolds number Re of the propeller under the actual working condition according to the propeller size and working conditions. real , according to the wind tunnel test model size and test conditions, determine the propeller test Reynolds number The actual propeller has a diameter of 4m, a characteristic chord length of 0.25m, a rotation speed of 1000 rpm, and an incoming wind speed of 70m / s; the test model has a diameter of 0.5m, a characteristic chord length of 0.03125m, a rotation speed of 4000 rpm, and an incoming wind speed of 70m / s. The Reynolds number is calculated according to formula (1):

[0050] ;

[0051] ;

[0052] S2. Determine whether the test Reynolds number is less than the test critical Reynolds number 0.5×10 6 , <0.5×10 6 , then it is considered necessary to conduct a Reynolds number impact assessment;

[0053] S3. The effect of Reynolds number on propeller aerodynamic characteristics is evaluated by equation (2). The error of aerodynamic force obtained by statistical analysis of test data is as follows:

[0054] ;

[0055] S4. When the blade tip Mach number is subsonic and the thickness noise and quadrupole noise are weak, it is considered that the propeller aerodynamic noise is mainly composed of load noise. According to the propeller load noise theoretical estimation method and formula (2), the load noise influence is obtained: :

[0056] ;

[0057] S5. Using the load noise influence obtained in step S4 as a reference for the error range, the total sound pressure level data and the blade passing frequency discrete peak are evaluated within the range;

[0058] Based on the test measurement, the total sound pressure level at a certain measuring point is OASPL=92 , the blade passes the discrete peak frequency 86 ;

[0059] The uncertainty assessment of the total sound pressure level is: After that, the total sound pressure level OASPL ranges from 90.6 to 92 The sound pressure level of the blade passing frequency discrete peak ranges from 84.6 to 86 .

[0060] The present embodiment provides an evaluation method for the influence of Reynolds number on propeller aerodynamic noise wind tunnel tests. The method is suitable for wind tunnel tests in which the simulation of propeller aerodynamic acoustic characteristics deviates due to small model size and low test Reynolds number. The method can provide a noise error range through evaluation, effectively improve the rationality of acoustic wind tunnel test data under low Reynolds number conditions, and improve the reliability of mapping noise data under wind tunnel test conditions to actual flight conditions.

[0061] 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.

[0062] 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 method for evaluating the impact of Reynolds number on propeller wind tunnel test aerodynamic noise data, characterized in that: The steps include: S1. Determine the Reynolds number Re of the propeller under the actual working condition according to the propeller size and working conditions. real , according to the wind tunnel test model size and test conditions, determine the propeller test Reynolds number Re exp ; Since the propeller wind tunnel test model is usually a scaled model of the real propeller, and in order to ensure that the Mach number and advance ratio are equal, the test Reynolds number Re is set exp Less than the Reynolds number Re under actual working conditions real , experimental Reynolds number Re exp The expression is: Among them, Re exp is the test Reynolds number, ρ is the test atmospheric density, v is the cross-sectional velocity at 0.7 times the radius, l is the characteristic chord length of the cross-sectional area at 0.7 times the radius, and μ is the atmospheric viscosity coefficient; S2. Determine whether the test Reynolds number is less than the critical Reynolds number 0.5×10 6 , such as Re exp ≥0.5×10 6 , it is considered that the test Reynolds number has little effect on the propeller aerodynamic noise; if Re exp <0.5×10 6 , then continue with the Reynolds number impact assessment; S3. The error ε of the aerodynamic force obtained by statistical test data is used to evaluate the effect of Reynolds number on the aerodynamic characteristics of the propeller. The formula is as follows: Among them, C T.exp is the tensile coefficient test value, C T.real is the correction value of tension coefficient; S4. When the blade tip Mach number is subsonic and the thickness noise and quadrupole noise are weak, it is considered that the propeller aerodynamic noise is mainly composed of load noise. According to the propeller load noise theoretical estimation method and formula (2), the evaluation formula of the load noise influence ΔSPL is obtained as follows: ΔSPL=20×log(ε) (3) S5. Using the load noise influence obtained in step S4 as a reference for the error range, the total sound pressure level data and the blade passing frequency discrete peak are evaluated within the range; Through propeller aerodynamic noise test measurement and data processing, the propeller noise spectrum and total sound pressure level data OASPL are obtained; The data processing method after the propeller aerodynamic noise test measurement is Fourier transform and sound pressure level calculation. The specific method includes the following steps: Step 1. Calculate the root mean square effective value of the time domain sound pressure data obtained from the test measurement to obtain the effective sound pressure p e ; Step 2. Set the effective sound pressure p e Substitute into the sound pressure level SPL calculation formula: The sound pressure level data obtained is the total sound pressure level; Step 3. Perform Fourier transform on the time domain sound pressure data to obtain frequency domain sound pressure data. By calculating the sound pressure level, the sound pressure level at each frequency, i.e., the noise spectrum, is obtained.

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