Method for predicting static stability and static divergence dynamic pressure of wind tunnel model strut system

Abstract

The present invention discloses a method for estimating the static stability and static divergence dynamic pressure of a wind tunnel model strut system, which relates to the field of wind tunnel tests, and comprises: S1, taking the wind tunnel model strut system as an object, establishing a static model considering the model and strut structure parameters; S2, based on the static model obtained in S1 and the set parameter values, estimating the static divergence critical dynamic pressure of the wind tunnel model strut system q ; S3, the actual operating dynamic pressure during the wind tunnel test q 0 Critical dynamic pressure with static divergence q The present invention provides a method for estimating the static stability and static divergence dynamic pressure of a wind tunnel model strut system, and provides a method for calculating the divergence critical dynamic pressure of the model strut system. The method can analyze the static stability of the model strut system during the test in the design stage before the test is carried out, and quickly estimate the dynamic pressure of the model strut system when static divergence occurs.

Description

Technical Field

[0001] The present invention relates to the field of wind tunnel testing, and more specifically, to a method for estimating the static stability and static divergence dynamic pressure of a wind tunnel model strut system. Background Art

[0002] In conventional force measurement wind tunnel tests, the tail strut support model is usually used for research and verification. The strut support has the advantages of being simple and convenient with little support interference. During the test, the model / strut system will deform under the action of aerodynamic forces, resulting in changes in the static stability of the model / strut system. When the aerodynamic loads and structural parameters acting on the model / strut system meet specific conditions, the system will show instability, which is manifested in the inability of the elastic restoring force of the structural deformation to maintain balance with the aerodynamic force acting on the model, and the static elastic deformation of the strut increases infinitely, eventually leading to structural damage.

[0003] During the wind tunnel test, damage to the model / strut system can lead to serious losses. On the one hand, the damaged model will fly into the rear section of the wind tunnel with the airflow, smashing related components and causing the wind tunnel to shut down for repairs. This is especially fatal for large continuous wind tunnels, directly threatening the safety of the compressor rotor components and causing huge economic losses. On the other hand, test interruptions will result in the inability to obtain relevant test data, directly affecting the R&D cycle and cost of related products of the test implementation department, causing important time nodes to be delayed and losing product competitiveness.

[0004] In the current field of wind tunnel test technology, there is no clear method for estimating the static stability and static divergence dynamic pressure of wind tunnel models / strut systems. Usually, only the strength of the system under the maximum aerodynamic force is verified, and the stability of the model / strut system under the coupling of aerodynamic force and structure is not considered, which poses certain risks.

[0005] The European ETW test manual gives the static stability margin value for the wind tunnel model / strut system, but does not explain the specific implementation method. The field of aeroelastic analysis has proposed a method to use software to calculate the static stability of the system, but it requires professional software for analysis and cannot achieve rapid estimation during the test plan formulation stage. Summary of the invention

[0006] An object of the present invention is to solve at least the above problems and / or disadvantages and to provide at least the advantages which will be described hereinafter.

[0007] In order to achieve these objects and other advantages of the present invention, a method for estimating the static stability and static divergence dynamic pressure of a wind tunnel model strut system is provided, comprising:

[0008] S1. Taking the wind tunnel model strut system as the object, a static model considering the model and strut structure parameters is established;

[0009] S2, based on the static model obtained in S1 and the set parameter values, the static divergence critical dynamic pressure of the wind tunnel model strut system is estimated by the following formula: q :

[0010]

[0011] In the above formula, R Indicates the length of the support rod, θ It is the additional elastic attack angle generated when the model deforms elastically along with the support rod due to the wind blowing. C m is the pitching moment coefficient, C L is the lift coefficient, is the reference length of the wind tunnel model, S is the reference area of ​​the wind tunnel model, E is the elastic modulus of the support rod, I is the section moment of the support rod, e is the distance from the aerodynamic center to the rigid center;

[0012] S3. The actual operating dynamic pressure during the wind tunnel test q 0 and static divergence critical dynamic pressure q A comparison is made to determine the static stability of the wind tunnel model support system during the entire test process.

[0013] Preferably, in S1, the process of acquiring the static model includes:

[0014] S10. Under static equilibrium conditions, in wind tunnel tests, if the model gravity is considered when the model is initially leveled, the force and moment equilibrium equations of the system are expressed by the following equations:

[0015]

[0016] in, k 11 , k 12 , k 21 , k 22 They represent the displacement stiffness of the support rod at the rigid center, the displacement stiffness caused by the pitch angle, the pitch angle stiffness caused by the displacement, and the pitch angle stiffness, respectively. ;

[0017] S11. Under the quasi-steady aerodynamic theory, the aerodynamic force in the static model is represented by the following formula:

[0018]

[0019] In the above formula, Lis the lift acting on the aircraft model, M z is the pitching moment acting on the aircraft model.

[0020] Preferably, in S2, the static divergence critical dynamic pressure q The estimated formula is obtained as follows:

[0021] S20, assuming the initial angle of attack is θ 0, then the additional angle of attack caused by the wind has the following relationship:

[0022]

[0023] In the above formula, h is the longitudinal translation displacement of the model;

[0024] S21. Based on the additional angle of attack in S20, the elastic additional angle of attack caused by blowing is characterized by the following formula:

[0025]

[0026] S22. When the elastic additional angle of attack in S21 satisfies the denominator equal to 0, the model strut system exhibits static divergence. Then the critical dynamic pressure of static divergence of the angle of attack divergence is q for:

[0027] .

[0028] Preferably, in S3, the static stability of the wind tunnel model support rod system during the entire test process is determined as follows:

[0029] when q The value of 0 is always less than q , then the wind tunnel model support system is determined to be statically stable during the entire test process. However, as long as there is a moment in the entire test process t , so that q 0> q or q <0, then the wind tunnel model support rod system at time t is judged to be dynamically unstable.

[0030] Preferably, when the wind tunnel model strut system is determined to be statically unstable, the strut diameter is increased. D , reduce the length of the support rod R To increase any of q .

[0031] The present invention includes at least the following beneficial effects: the present invention establishes a simplified static model of the model strut system, takes into account the strut structure parameters, model structure parameters, angle of attack, and simulation results of the model aerodynamic coefficients, and provides a method for calculating the divergent critical dynamic pressure of the model strut system. This method can analyze the static stability of the model strut system during the test in the design stage before the test is carried out, and quickly estimate the dynamic pressure of the model strut system when static divergence occurs.

[0032] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a simplified static model schematic diagram of the wind tunnel model support rod system in the present invention;

[0034] Figure 2 In the embodiment of the present invention, when the length of the support rod is R Schematic diagram of the estimated results of static divergence dynamic pressure at 1.2m;

[0035] Figure 3 In the embodiment of the present invention, when the length of the support rod is R Schematic diagram of numerical simulation results of static elastic deformation of the wind tunnel model support rod system at 1.2m;

[0036] Figure 4 In the embodiment of the present invention, when the length of the support rod is R Schematic diagram of the estimated results of static divergence dynamic pressure at 0.8m;

[0037] Figure 5 In the embodiment of the present invention, when the length of the support rod is R Schematic diagram of the numerical simulation results of the static elastic deformation of the wind tunnel model / strut system at 0.8m. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0039] In order to reduce the risk of static divergence of the wind tunnel model / strut system during conventional force measurement wind tunnel tests, the present invention proposes a method for estimating the static stability and static divergence dynamic pressure of the wind tunnel model strut system, which is applicable to conventional force measurement wind tunnel tests carried out using a strut support method at the tail of the model, and mainly includes the following steps:

[0040] Step 1: Establish a simplified static model of the wind tunnel model / strut system.

[0041] Taking the aircraft model in the wind tunnel as the object, a static model considering the strut is established, such as Figure 1 As shown. Among them, point O represents the fixed position of the support rod, point A represents the rigid center of the model fixed on the support rod, and point B represents the aerodynamic center; L is the lift acting on the aircraft model; M z is the pitching moment acting on the aircraft model; R Indicates the length of the support rod; D Indicates the diameter of the support rod; e It indicates the distance from the aerodynamic center to the rigid center, and is positive before the rigid center; c It indicates the distance from the center of gravity to the center of rigidity, and is positive before the center of rigidity; h is the longitudinal translation displacement of the model, which is positive upward; θ It is the elastic additional angle of attack generated when the wind causes the model to deform elastically along with the support rod.

[0042] Step 2: Determine the values ​​of the main parameters in the model.

[0043] The main parameters that need to be determined include: elastic modulus of the support rod E , the length of the support rod R , the cross-sectional moment of the support rod I , the distance between the aerodynamic center B of the wind tunnel model and the rigid center A where the model is fixed on the support rod e , wind tunnel model reference area S , wind tunnel model reference length , lift coefficient C L Angle of attack for wind tunnel models α The derivative of , pitch moment coefficient C m Angle of attack for wind tunnel models α The derivative of wait.

[0044] Elastic modulus of the support rod E Directly derived from the material properties of the support rod;

[0045] Length of the support rod R Take it as the axial distance from the fixed end of the support rod to the supporting end of the model;

[0046] Section moment of the support rod I By calculation formula If the support rod is a hollow structure, then .in, D is the cross-sectional outer diameter of the support rod, d is the inner diameter of the support rod. When the support rod is almost entirely of equal diameter except for the two ends of the connection, D Take the equal diameter section diameter as the diameter. When the variable diameter section of the support rod accounts for a large proportion, D Take it as the equivalent diameter calculated according to the actual stiffness of the support rod;

[0047] Wind tunnel model reference area S and wind tunnel model reference length is the known quantity of the experimental scheme;

[0048] Lift coefficient C L The wind tunnel model provider provides the lift coefficient through simulation prediction results before the test. C L Angle of attack α Taking the derivative we get ;

[0049] Similarly, the pitch moment coefficient C m The wind tunnel model provider also provides the pitch moment coefficient through simulation prediction results before the test. C m Angle of attack α Taking the derivative we get .

[0050] Step 3: Calculate the critical dynamic pressure of the static divergence of the wind tunnel model / strut system q .

[0051] Critical dynamic pressure of static divergence of strut system in wind tunnel model q The derivation process of the calculation equation is as follows:

[0052] Under static equilibrium conditions, in the wind tunnel test, if the model gravity is considered when the model is initially leveled, the gravity term on the right side offsets the initial elastic restoring force of the support rod, and the force and moment equilibrium equation of the system can be expressed as:

[0053]

[0054] in, k 11 , k 12 , k 21 , k 22 They represent the displacement stiffness of the support rod at the rigid center, the displacement stiffness caused by the pitch angle, the pitch angle stiffness caused by the displacement, and the pitch angle stiffness. According to the material properties of the straight section support rod, we know that:

[0055]

[0056] in, E is the elastic modulus of the support rod; I is the section moment of the support rod.

[0057] Under the quasi-steady aerodynamic theory, the aerodynamic force can be expressed as:

[0058]

[0059] in, q is the critical dynamic pressure of static divergence; S is the reference area of ​​the wind tunnel model; is the reference length of the wind tunnel model; C L is the lift coefficient; C M is the pitching moment coefficient.

[0060] Assume that the initial angle of attack is θ 0, the additional angle of attack caused by the wind has the following relationship:

[0061]

[0062] Rearranging the above formula yields:

[0063]

[0064] Solve for the additional elastic angle of attack caused by wind blowing:

[0065]

[0066] Obviously, when the denominator of the above formula is equal to 0, the model strut system will have static divergence, that is, the critical condition of angle of attack divergence is:

[0067]

[0068] In conventional force measurement tests, the C L and C m The curve estimates the variation of divergent dynamic pressure with angle of attack.

[0069] Substituting the main parameters determined in step 2 into the calculation equation in step 3, the static divergence critical dynamic pressure of the wind tunnel model strut system can be obtained: q .

[0070] Step 4: Analyze the static stability of the wind tunnel model / strut system.

[0071] The actual operating dynamic pressure during the wind tunnel test q 0 and static divergence critical dynamic pressure q For comparison, if the dynamic pressure q The value of 0 is always less than the critical dynamic pressure of static divergence q , it means that the wind tunnel model / strut system is statically stable during the entire test process, that is, the test will not have static divergence problems; if the running dynamic pressure q 0 value appears at a certain moment greater than the critical dynamic pressure of static divergenceq If the wind tunnel model / strut system is statically unstable at this moment, the test has the risk of static divergence. In this case, the diameter of the strut must be increased. D Or reduce the length of the support rod R , and repeat steps 2 to 4 until the dynamic pressure is q The value of 0 is always less than the critical dynamic pressure of static divergence q .

[0072] Example:

[0073] Step 1: Create Figure 1 The simplified static model of the wind tunnel model / strut system shown, where point O represents the fixed position of the strut, point A represents the rigid center of the model fixed on the strut, point B represents the aerodynamic center, and point C represents the center of gravity; L is the lift acting on the aircraft model; M z is the pitching moment acting on the aircraft model; R Indicates the length of the support rod; D Indicates the diameter of the support rod; e It indicates the distance from the aerodynamic center to the rigid center, and is positive before the rigid center; c It indicates the distance from the center of gravity to the center of rigidity, and is positive before the center of rigidity; h is the longitudinal translation displacement of the model, which is positive upward; θ is the pitch angle of the model generated by elastic deformation of the support rod.

[0074] Step 2: Determine the values ​​of the main parameters in the model.

[0075] In this example, the elastic modulus of the strut is E Take 2.01×10 11 Pa;

[0076] Length of the support rod R Take 1.2m;

[0077] Rod diameter D Take 0.05m, considering the hollow structure of the support rod, the inner diameter of the support rod d Take 0.02m, then the section moment I of the support rod is given by The result is 2.9894×10 -7 m 4 ;

[0078] The distance between the aerodynamic center B of the wind tunnel model and the rigid center A where the model is fixed on the support rod e Take it as 0.12m;

[0079] The experimental model reference area in this example S 0.279 m 2 , wind tunnel model reference length 0.189 m;

[0080] Lift coefficient C L and the pitching moment coefficient C m The value of α The changes are shown in Table 1:

[0081] Table 1

[0082]

[0083] The lift coefficient C L Angle of attack α Taking the derivative we get , the pitching moment coefficient C m Angle of attack α Taking the derivative we get The results are shown in Table 2:

[0084] Table 2

[0085] Step 3: Calculate the critical dynamic pressure of the static divergence of the wind tunnel model / strut system q .

[0086] Critical dynamic pressure of static divergence of strut system in wind tunnel model q The calculation equation is:

[0087]

[0088] Substitute the main parameters determined in step 2 into the above q In the calculation equation of , the static divergence critical dynamic pressure obtained in this example is q With angle of attack α The changes are shown in Table 3.

[0089] Table 3

[0090]

[0091] Step 4: Analyze the static stability of the wind tunnel model / strut system.

[0092] The actual operating dynamic pressure during the wind tunnel test q 0 and static divergence critical dynamic pressure q For comparison, the actual operating dynamic pressure of this example q 0 is 33160 Pa; after the critical dynamic pressure of static divergence q Contrast, such as Figure 2 The comparison results show that when the angle of attack is 3.5°, the critical dynamic pressure of static divergenceq The value is greater than the operating dynamic pressure q 0 is small, indicating that the wind tunnel model / strut system has a static divergence risk. At this time, the static elastic angular deformation analysis results of the wind tunnel model / strut system are as follows: Figure 3 As shown, the elastic angular deformation tends to infinity when the angle of attack is 3.5°, that is, the wind tunnel model / strut system undergoes static divergence.

[0093] At this time, the diameter of the support rod must be increased D Or reduce the length of the support rod R , this example reselects R is 0.8m, and repeat steps 2 to 4 to obtain a new static divergence critical dynamic pressure q With angle of attack α The changes are shown in Table 4:

[0094] Table 4

[0095]

[0096] The new static divergence critical dynamic pressure q With running dynamic pressure q 0 for comparison, such as Figure 4 As shown, the results show that changing the length of the strut R Critical dynamic pressure q Always greater than the operating dynamic pressure q 0, that is, there will be no static divergence risk during the test. This is the end of this implementation example.

[0097] Figure 5 is the length of the support rod R =0.8m, the static elastic angular deformation analysis results of the wind tunnel model / strut system show that the static elastic angular deformation during the entire test process belongs to the normal test situation, proving that the risk of static divergence has been eliminated.

[0098] It can be seen from the examples that the present invention establishes a simplified static model of the model strut system, takes into account the strut structure parameters, model structure parameters, angle of attack and simulation results of the model aerodynamic coefficients, and provides a method for calculating the critical dynamic pressure of the divergence of the model strut system. This method can analyze the static stability of the model strut system during the test in the design stage before the test is carried out, and quickly estimate the dynamic pressure of the model strut system when static divergence occurs, which helps to reduce the risks caused by static divergence in conventional force measurement wind tunnel tests and prevent economic losses caused by insufficient test risk assessment. It has important engineering application value for the design of conventional force measurement wind tunnel tests.

[0099] The above solution is only an illustration of a preferred embodiment, but is not limited thereto. When implementing the present invention, appropriate replacement and / or modification can be performed according to user needs.

[0100] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and the embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily realized. Therefore, without departing from the general concept defined by the claims and equivalent scope, the present invention is not limited to the specific details and the illustrations shown and described here.

Claims

1. A method for estimating the static stability and static divergence dynamic pressure of a wind tunnel model strut system, characterized in that: include: S1. Taking the wind tunnel model strut system as the object, a static model considering the model and strut structure parameters is established; S2, based on the static model obtained in S1 and the set parameter values, the static divergence critical dynamic pressure of the wind tunnel model strut system is estimated by the following formula: q : In the above formula, R Indicates the length of the support rod, θ It is the additional elastic attack angle generated when the model deforms elastically along with the support rod due to the wind blowing. C m is the pitching moment coefficient, C L is the lift coefficient, is the reference length of the wind tunnel model, S is the reference area of ​​the wind tunnel model, E is the elastic modulus of the support rod, I is the section moment of the support rod, e is the distance from the aerodynamic center to the rigid center; S3. The operating dynamic pressure during the actual wind tunnel test q 0 and static divergence critical dynamic pressure q Comparison is made to determine the static stability of the wind tunnel model support system during the entire test process; In S1, the process of obtaining the static model includes: S10. Under static equilibrium conditions, in wind tunnel tests, if the model gravity is considered when the model is initially leveled, the force and moment equilibrium equations of the system are expressed by the following equations: in, h is the longitudinal translation displacement of the model, k 11 , k 12 , k 21 , k 22 They represent the displacement stiffness of the support rod at the rigid center, the displacement stiffness caused by the pitch angle, the pitch angle stiffness caused by the displacement, and the pitch angle stiffness, respectively. ; S11. Under the quasi-steady aerodynamic theory, the aerodynamic force in the static model is represented by the following formula: In the above formula, L is the lift acting on the aircraft model, M z is the pitching moment acting on the aircraft model.

2. The method for estimating the static stability and static divergence dynamic pressure of a wind tunnel model strut system according to claim 1, characterized in that: In S2, the static divergence critical dynamic pressure q The estimated formula is obtained as follows: S20, assuming the initial angle of attack is θ 0, then the additional angle of attack caused by the wind has the following relationship: In the above formula, h is the longitudinal translation displacement of the model; S21. Based on the additional angle of attack in S20, the elastic additional angle of attack caused by blowing is characterized by the following formula: S22. When the elastic additional angle of attack in S21 satisfies the denominator equal to 0, the model strut system exhibits static divergence. Then the critical dynamic pressure of static divergence of the angle of attack divergence is q for: 。 3. The method for estimating the static stability and static divergence dynamic pressure of a wind tunnel model strut system according to claim 1, characterized in that: In S3, the static stability of the wind tunnel model strut system during the entire test process is determined as follows: when q The value of 0 is always less than q , then the wind tunnel model support system is determined to be statically stable during the entire test process. However, as long as there is a moment in the entire test process t , so that q 0> q or q <0, then the wind tunnel model support rod system at time t is judged to be dynamically unstable.

4. The method for estimating the static stability and static divergence dynamic pressure of a wind tunnel model strut system according to claim 1, characterized in that: When the wind tunnel model strut system is judged to be statically unstable, the strut diameter is increased. D , reduce the length of the support rod R To increase any of q .

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