A method for predicting the rudder shaft heat flux of a high-speed aircraft based on the boundary layer thickness

Abstract

The present invention belongs to the field of aerodynamic heat technology, and discloses a method for predicting the heat flux of the rudder shaft of a high-speed aircraft based on the boundary layer thickness. This method obtains the heat flux data of the measuring points or grid points on the surface of the air rudder shaft of the high-speed aircraft according to wind tunnel tests or numerical calculations, uses the CFD numerical calculation method to obtain the boundary layer thickness data of the aircraft, sorts the heat flux data of the rudder shaft according to the numerical size of the boundary layer thickness corresponding to the working conditions, adopts the polynomial fitting method to establish the fitting relationship between the boundary layer thickness data and the heat flux data of the rudder shaft for each measuring point or grid point, and finally uses this fitting relationship for predicting the heat flux of the rudder shaft. Based on the existing small amount of heat flux data of the rudder shaft, the polynomial fitting method is used to establish the fitting relationship from the boundary layer thickness to the heat flux of the rudder shaft for rapid prediction of the heat flux of the rudder shaft. The method is simple and reliable. Due to the high correlation between the heat flux of the rudder shaft gap and the boundary layer thickness, the idea of this method can be widely applied to the prediction of the heat flux of the rudder shaft gap under various conditions.

Description

Technical Field

[0001] The present invention belongs to the field of aerodynamic heat technology, and particularly relates to a method for predicting the heat flux of the rudder shaft of a high-speed aircraft based on the boundary layer thickness. Background Art

[0002] Due to the very serious aerodynamic heating effect of current high-speed aircraft, it is necessary to design a suitable thermal insulation layer for high-speed aircraft. The thermal protection problem has always been a key technology in the development of high-speed aircraft. As the design basis for the design of thermal protection structures and material selection, the aerodynamic heat problem on the surface of high-speed aircraft has always been the focus and key technology in hypersonic technology research. Accurately predicting the aerodynamic heat environment and its uncertainty is of great significance for the safe flight of high-speed aircraft and meeting the payload / range index.

[0003] However, at present, the conservative thermal protection design leads to overweight of the thermal protection structure, affecting the payload and range of high-speed aircraft, making the aircraft unable to meet the required combat and technical indicators; the aggressive thermal protection design makes the weight of the thermal protection structure lighter, which is beneficial for the aircraft to meet the payload and range indicators, but will cause high-speed aircraft to face great safety risks. High-speed aircraft use air rudders for control and stability, but there is a certain height gap between the air rudder and the surface of the fuselage cabin. The rudder shaft of the air rudder is directly exposed to the gap flow, and flow separation (flow unsteadiness) will occur at the root of the rudder shaft. The flow situation in the rudder shaft area is very complex. Due to the stagnation of the air rudder gap airflow on the windward surface of the rudder shaft, combined with the compression effect of the air rudder, the heat flux on the windward surface of the rudder shaft is very high. The peak heat flux of the rudder shaft measured in the shock tunnel thermal environment test reached several times the stagnation heat flux at most. Summary of the Invention

[0004] The object of the present invention is to provide a method for predicting the heat flux of the rudder shaft of a high-speed aircraft based on the boundary layer thickness, aiming to improve the inaccurate prediction result of the heat flux on the windward surface of the rudder shaft of the existing high-speed aircraft and the problem of large data requirements.

[0005] The technical solution adopted by the present invention is as follows: A method for predicting the heat flux of the rudder shaft of a high-speed aircraft based on the boundary layer thickness, the prediction method includes the following:

[0006] Under multiple working conditions, conduct wind tunnel tests or numerical calculations to obtain the heat flux data on the surface of the rudder shaft of the high-speed aircraft air rudder;

[0007] Obtain the boundary layer thickness of the undisturbed area in front of the air rudder under each working condition through the CFD numerical calculation method;

[0008] Sort the heat flux data on the rudder shaft surface according to the numerical size of the boundary layer thickness under the corresponding working conditions;

[0009] Taking the boundary layer thickness value as the independent variable and the heat flux data on the rudder shaft surface as the dependent variable, a polynomial fitting method is used to establish a fitting relationship for the heat flux data on the rudder shaft surface;

[0010] Predict the rudder shaft heat flux through the fitting relationship.

[0011] It should be noted that the CFD numerical calculation method is the numerical calculation method of computational fluid dynamics.

[0012] Furthermore, in order to make the calculated heat flux data more accurate, the heat flux data on the rudder shaft surface specifically includes the heat flux data of the measurement points or grid points on the rudder shaft surface.

[0013] Among them, the measurement point data: the heat flux density at a specified position on the rudder shaft surface; the grid point data: the heat flux density of each grid point after the rudder shaft surface is meshed.

[0014] Furthermore, in order to make the heat flux data on the rudder shaft surface calculated more accurate, measure the data under different working conditions, and the working conditions include Mach number M, Reynolds number Re, angle of attack, rudder deflection angle, gap height and flow state in front of the rudder. By changing the working conditions, obtain the heat flux data on the rudder shaft surface under multiple working conditions.

[0015] Furthermore, in order to avoid the interference of the rudder shaft structure or other components on the boundary layer characteristics and ensure the accuracy of the boundary layer thickness data, obtain the flow field data of the high-speed aircraft test model under each working condition through the CFD numerical calculation method, and then obtain the boundary layer parameter distribution data. According to the CFD data calculation results, obtain the boundary layer thickness of the interference-free area in front of the aircraft's control surface.

[0016] It should be noted that the boundary layer thickness is the distance from the region where the airflow has no shear layer (free stream) to the point where the wall velocity is zero, reflecting the boundary layer characteristics.

[0017] Furthermore, in order to facilitate the establishment of a clear input and output relationship for subsequent polynomial fitting, correspond the heat flux data of the measurement points or grid points with the boundary layer thickness values under the corresponding working conditions, and sort the boundary layer thickness values according to the heat flux data.

[0018] Furthermore, establishing the fitting relationship specifically includes establishing the corresponding fitting relationship for the heat flux data of the measurement points or grid points.

[0019] Furthermore, the prediction of the rudder shaft heat flux through the fitting relationship includes: under each working condition, calculate the boundary layer thickness value, and then input the boundary layer thickness value into the fitting relationship to calculate the heat flux data of the measurement points or grid points under the corresponding working conditions;

[0020] Judge the fitting effect according to the goodness-of-fit measure calculated by the fitting relationship;

[0021] Record the heat flux data and boundary layer thickness values of the measurement points or grid points with better fitting effects.

[0022] It should be noted that the accuracy of the fitting relationship is verified through experiments or numerical methods to ensure its accuracy.

[0023] Furthermore, the specific CFD numerical calculation method includes:

[0024] Analyze the airflow boundary layer in the undisturbed area by simulating the flow field in front of the air rudder.

[0025] Extract the boundary layer thickness data in the adjacent area in front of the rudder shaft under different working conditions.

[0026] Output the corresponding boundary layer thickness values under each working condition.

[0027] It should be noted that the undisturbed area refers to the area without the air rudder.

[0028] Furthermore, the fitting relationship uses a polynomial function as the fitting model and adopts the least squares method to fit independent functional relationships for the heat flux data of each measurement point or grid point respectively, obtaining the fitting relationship under the corresponding working conditions:

[0029] ;

[0030] where is the heat flux on the surface of the rudder shaft, is the boundary layer thickness, are the fitting coefficients.

[0031] Furthermore, the closer the goodness-of-fit measure is to 1, the better the fitting effect; on the contrary, the farther the goodness-of-fit measure is from 1, the worse the fitting effect.

[0032] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are:

[0033] 1. The method of the present invention requires a small amount of data samples, so when calculating and predicting the heat flux value of the rudder shaft, its cost is low, and it can significantly save costs.

[0034] 2. Based on the existing small amount of heat flux data of the rudder shaft, a fitting relationship from the boundary layer thickness to the heat flux of the rudder shaft is established by using the polynomial fitting method for rapid prediction of the heat flux of the rudder shaft. The method is simple and reliable, without considering the influence of the complex flow effect of the gap between the air rudder and the rudder shaft on the heat flux of the rudder shaft; while reducing costs, it significantly improves the prediction accuracy.

[0035] 3. Since the data of the rudder shaft gap heat flux and the boundary layer thickness are highly correlated, the method of the present invention can be widely applied to the prediction of the rudder shaft gap heat flux in various situations, with high applicability. Description of the Drawings

[0036] Figure 1 is a flowchart of the method of the present invention;

[0037] Figure 2 is a comparison diagram of the heat flux of the rudder shaft measurement point of the present invention changing with the boundary layer thickness;

[0038] Figure 3 is a diagram of the heat flux of the rudder shaft at measurement point 1 changing with the boundary layer thickness in the embodiment of the present invention. Detailed Embodiment

[0039] The present invention will be described in detail below with reference to the drawings.

[0040] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and 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.

[0041] As Figure 1 shown, a method for predicting the heat flux of a high-speed aircraft rudder shaft based on the boundary layer thickness, the prediction method includes the following:

[0042] Step S100: Under multiple working conditions, conduct a wind tunnel test or numerical calculation to obtain the heat flux data of the rudder shaft surface of the high-speed aircraft air rudder;

[0043] Wind tunnel test: Under controlled conditions, simulate the heat environment of the aircraft under different working conditions such as speed, angle, altitude, etc., and measure the heat flux density on the rudder shaft surface by setting sensors;

[0044] Numerical calculation: Adopt numerical simulation (such as the CFD method) to simulate the actual flight conditions in a virtual environment and generate the heat flux data of the rudder shaft surface;

[0045] The heat flux data of the rudder shaft surface specifically includes the heat flux data of the measurement points or grid points on the rudder shaft surface;

[0046] Measurement point data: The heat flux density at a specified position on the rudder shaft surface;

[0047] Grid point data: After dividing the grid on the rudder shaft surface, the heat flux density of each grid point;

[0048] Step S200: Obtain the boundary layer thickness of the undisturbed area in front of the air rudder under each working condition through the CFD numerical calculation method;

[0049] Step S300: Sort the heat flux data on the surface of the rudder shaft according to the numerical size of the boundary layer thickness under the corresponding working conditions;

[0050] Step S400: Using the boundary layer thickness value as the independent variable and the heat flux data on the surface of the rudder shaft as the dependent variable, adopt the polynomial fitting method to establish a fitting relationship for the heat flux data on the surface of the rudder shaft;

[0051] Step S500: Predict the rudder shaft heat flux through the fitting relationship.

[0052] In the said Step S100, the working conditions include data such as Mach number M, Reynolds number Re, angle of attack, rudder deflection angle, gap height, and flow state in front of the rudder. By changing the working conditions, the heat flux data on the surface of the rudder shaft under multiple working conditions are obtained.

[0053] In the said Step S200, the flow field data of the high-speed aircraft test model under each working condition are obtained through the CFD numerical calculation method, and then the boundary layer parameter distribution data are obtained. According to the CFD data calculation results, the boundary layer thickness of the interference-free area in front of the aircraft's air rudder is obtained.

[0054] The specific CFD numerical calculation method includes:

[0055] By simulating the flow field in front of the air rudder, analyze the airflow boundary layer of the interference-free area;

[0056] Extract the boundary layer thickness data of different working conditions in the adjacent area in front of the rudder shaft;

[0057] Output the corresponding boundary layer thickness values under each working condition.

[0058] In the said Step S300, the heat flux data of the measuring points or grid points are corresponded to the boundary layer thickness values under the corresponding working conditions, and the boundary layer thickness values are sorted according to the heat flux data.

[0059] In the said Step S400, establishing the fitting relationship specifically includes establishing the corresponding fitting relationship for the heat flux data of the measuring points or grid points.

[0060] The said fitting relationship uses a polynomial function as the fitting model and adopts the least squares method to respectively fit independent functional relationships for the heat flux data of each measuring point or grid point, and obtain the fitting relationship under the corresponding working conditions:

[0061] ;

[0062] Among them, is the heat flux on the surface of the rudder shaft, is the boundary layer thickness, is the fitting coefficient.

[0063] In step S500, the prediction of the rudder shaft heat flux through the fitting relationship includes: under various working conditions, calculating the boundary layer thickness value, and then inputting the boundary layer thickness value into the fitting relationship to calculate the heat flux data of the measurement points or grid points under the corresponding working conditions;

[0064] Judging the fitting effect according to the goodness-of-fit measure calculated by the fitting relationship;

[0065] The closer the goodness-of-fit measure is to 1, the better the fitting effect; on the contrary, the farther the goodness-of-fit measure is from 1, the worse the fitting effect.

[0066] Record the heat flux data and boundary layer thickness values of the measurement points or grid points with better fitting effects.

[0067] Based on the existing small amount of rudder shaft heat flux data, a fitting relationship from the boundary layer thickness to the rudder shaft heat flux is established by using the polynomial fitting method for rapid prediction of the rudder shaft heat flux. The method is simple and reliable, without considering the influence of the complex flow effect of the air rudder shaft gap on the rudder shaft heat flux; it reduces costs while significantly improving the prediction accuracy.

[0068] Embodiment

[0069] As Figures 2 - 3 shown, an embodiment of the present invention is a method for predicting the rudder shaft heat flux of a high-speed aircraft based on the boundary layer thickness for the rudder shaft heat flux data of a wind tunnel test. The method includes the following steps:

[0070] Step 1: Acquisition of rudder shaft heat flux data. Conduct a wind tunnel test to obtain the rudder shaft measurement point heat flux data under multiple working conditions and organize them. Among them, the shock wind tunnel test working condition table is shown in Table 1. The measurement means used in the wind tunnel test include columnar heat flux sensors and surface heat flux sensors. Install a surface heat flux sensor on the rudder shaft surface to measure the heat flux. The surface sensor uses glass as the base material, is ground into the shape of the rudder shaft leading edge, and a platinum thin film is deposited on the polished glass surface by the vacuum magnetron sputtering coating method to measure the surface heat flux with the platinum thin film. Arrange a column of columnar heat flux sensors on the center line in front of the air rudder to measure the heat flux to judge the flow state of the boundary layer in front of the rudder. The columnar sensors are mass-produced, also using glass as the base material, made into glass rods with a diameter of 2 mm and a length of 20 mm, with a platinum thin film deposited on the polished circular end face, and test leads are connected to make sensors.

[0071] Table 1 Shock wind tunnel test working condition table

[0072]

[0073] Step 2: Obtaining boundary layer thickness data. The flow field of the high-speed aircraft test model under various working conditions as shown in Table 1 is obtained by using the CFD numerical calculation method, and data such as the distribution of boundary layer parameters are obtained. According to the numerical calculation results, the boundary layer parameters of each working condition at the position of the windward centerline of the aircraft are shown in Table 2. The windward centerline is defined as follows.

[0074] Table 2 Boundary layer parameter table of each working condition at the position of the windward centerline of the aircraft

[0075]

[0076] Step 3: Sorting the heat flux data of the rudder shaft. As Figure 2 shown, for a specific measurement point, the heat flux data of the rudder shaft at the measurement point obtained under each working condition are sorted according to the magnitude of the boundary layer thickness value corresponding to the working condition. Figure 2 Figure 5 is a comparison chart of the heat flux of the rudder shaft measurement point varying with the boundary layer thickness under a 5-degree rudder deflection angle measurement point.

[0077] Step 4: Fitting relationship. Taking the boundary layer thickness value as the independent variable and the heat flux data of the rudder shaft as the dependent variable, a polynomial fitting method is used to establish a fitting relationship for the heat flux data of each measurement point. Taking measurement point 1 as an example, as Figure 3 shown, the polynomial fitting relationship obtained for measurement point 1 is shown in formula (1), and the goodness-of-fit measure is greater than 0.99, and the fitting effect is relatively good, indicating that there is indeed a strong correlation between the heat flux of the rudder shaft and the boundary layer thickness value.

[0078] (1)

[0079] (2)

[0080] where is the heat flux on the surface of the rudder shaft, is the boundary layer thickness, is the goodness-of-fit measure.

[0081] Step 5: Apply the fitting relation (1) to predict the rudder shaft heat flux at measuring point 1. When predicting, first calculate the boundary layer thickness value corresponding to the working condition, and substitute it into the fitting relation (1) to predict the rudder shaft heat flux at measuring point 1 (the fitting relation corresponding to the corresponding measuring point must be used. If it is necessary to predict the heat flux at measuring point 2, the fitting relation corresponding to measuring point 2 must be used). Table 3 shows the prediction deviations of the fitting relations of the rudder shaft heat flux at 5 measuring points under six working conditions between the calculated results of the rudder shaft heat flux and the boundary layer thickness. It can be seen that the overall prediction deviation is small. Except for the large prediction deviation (-40.1%) at measuring point 1 under working condition 1, the other prediction results are less than 15%. Compared with the repeatability accuracy of the aerodynamic heat test in the rudder shaft area, this prediction deviation is reasonable. Moreover, the heat flux value at measuring point 1 under working condition 1 is the smallest among all heat flux values. It is a common situation that a large prediction deviation appears for a data with a small value.

[0082] Table 3 Prediction Deviations of the Fitting Relations between the Calculated Results of the Rudder Shaft Heat Flux and the Boundary Layer Thickness

[0083]

[0084] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for predicting heat flow of a high-speed aircraft rudder shaft based on boundary layer thickness, characterized in that: The prediction method includes the following: Under multiple working conditions, wind tunnel tests or numerical calculations are performed to obtain thermal flow data on the surface of the rudder shaft of the high-speed aircraft air rudder; The thickness of the boundary layer in the non-interference zone in front of the air rudder under various working conditions is obtained by CFD numerical calculation method; The heat flow data on the rudder shaft surface are sorted according to the numerical values ​​of the boundary layer thickness under the corresponding working conditions; Taking the boundary layer thickness as the independent variable and the heat flow data of the rudder shaft surface as the dependent variable, a polynomial fitting method is used to establish a fitting relationship for the heat flow data of the rudder shaft surface. The heat flux of the rudder shaft is predicted by fitting the relationship.

2. The method for predicting heat flow of a high-speed aircraft rudder shaft based on boundary layer thickness according to claim 1, characterized in that: The heat flow data of the rudder shaft surface specifically include heat flow data of measuring points or grid points on the rudder shaft surface.

3. The method for predicting heat flow of a high-speed aircraft rudder shaft based on boundary layer thickness according to claim 2, characterized in that: The working conditions include Mach number M, Reynolds number Re, angle of attack, rudder deflection angle, gap height and flow state in front of the rudder. By changing the working conditions, thermal flow data of the rudder shaft surface under multiple working conditions are obtained.

4. The method for predicting heat flow of a high-speed aircraft rudder shaft based on boundary layer thickness according to claim 1, characterized in that: The flow field data of the high-speed aircraft test model under various working conditions are obtained through the CFD numerical calculation method, and then the boundary layer parameter distribution data are obtained. According to the CFD data calculation results, the boundary layer thickness of the non-interference area in front of the aircraft air rudder is obtained.

5. The method for predicting heat flow of a high-speed aircraft rudder shaft based on boundary layer thickness according to claim 2, characterized in that: The heat flow data of the measuring points or grid points are matched with the boundary layer thickness values ​​under the corresponding working conditions, and the boundary layer thickness values ​​are sorted according to the heat flow data.

6. The method for predicting heat flow of a high-speed aircraft rudder shaft based on boundary layer thickness according to claim 2, characterized in that: Establishing the fitting relationship specifically includes establishing a corresponding fitting relationship for the heat flow data of the measuring point or grid point.

7. The method for predicting heat flow of a high-speed aircraft rudder shaft based on boundary layer thickness according to claim 2, characterized in that: Predicting the heat flow of the rudder shaft by fitting the relationship includes: calculating the boundary layer thickness value under various working conditions, and then inputting the boundary layer thickness value into the fitting relationship to calculate the heat flow data of the measuring point or grid point under the corresponding working conditions; The fitting effect is judged based on the goodness-of-fit measure calculated from the fitting relationship; The heat flow data and boundary layer thickness values ​​of the measuring points or grid points with better fitting effects are recorded.

8. The method for predicting heat flow of a high-speed aircraft rudder shaft based on boundary layer thickness according to claim 4, characterized in that: The CFD numerical calculation method specifically includes: By simulating the flow field in front of the air rudder, the airflow boundary layer in the non-interference area is analyzed; Extract the boundary layer thickness data under different working conditions in the vicinity of the rudder shaft; Output the corresponding boundary layer thickness values ​​under various working conditions.

9. The method for predicting heat flow of a high-speed aircraft rudder shaft based on boundary layer thickness according to claim 7, characterized in that: The fitting relationship uses a polynomial function as a fitting model and adopts the least squares method to fit an independent functional relationship to the heat flow data of each measuring point or grid point to obtain the fitting relationship under the corresponding working conditions: ； in, is the heat flux on the rudder shaft surface, is the boundary layer thickness, is the fitting coefficient.

10. The method for predicting heat flow of a high-speed aircraft rudder shaft based on boundary layer thickness according to claim 7, characterized in that: The closer the goodness-of-fit measure is to 1, the better the fit effect is; conversely, the further the goodness-of-fit measure is from 1, the worse the fit effect is.

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