High-speed aircraft rudder shaft heat flow prediction method based on boundary layer thickness

Abstract

The invention belongs to the technical field of aerodynamic heat, and discloses a high-speed aircraft rudder shaft heat flow prediction method based on boundary layer thickness, and the method comprises the steps: obtaining high-speed aircraft aerial rudder shaft surface measurement point or grid point heat flow data according to a wind tunnel test or numerical calculation, and obtaining aircraft boundary layer thickness data through employing a CFD numerical calculation method; and sequencing the rudder shaft heat flow data according to the boundary layer thickness values of the corresponding working conditions, establishing a fitting relational expression between the boundary layer thickness data and the rudder shaft heat flow data for each measuring point or grid point by adopting a polynomial fitting method, and finally applying the fitting relational expression to rudder shaft heat flow prediction. Based on a small amount of existing rudder shaft heat flow data, a fitting relational expression from the boundary layer thickness to the rudder shaft heat flow is established through a polynomial fitting method, and the method is used for rapid prediction of the rudder shaft heat flow and is simple and reliable. The method can be widely applied to rudder shaft gap heat flow prediction under various conditions.

Description

Technical Field

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

[0002] Since the aerodynamic heating effect of current high-speed aircraft is very serious, a suitable heat-insulating layer must be designed for high-speed aircraft. Thermal protection has always been a key technology in the development of high-speed aircraft. As the design basis for thermal protection structure design and material selection, the aerodynamic thermal problem on the surface of high-speed aircraft has always been the focus and key technology of hypersonic technology research. Accurately predicting the aerodynamic thermal environment and its uncertainty is of great significance for the safe flight of high-speed aircraft and meeting the payload / range indicators.

[0003] However, at present, conservative heat protection design leads to overweight of heat protection structure, which affects the payload and range of high-speed aircraft, and makes the aircraft fail to meet the required combat technical indicators; radical heat protection design makes the heat protection structure lighter, which is conducive to the aircraft meeting the payload and range indicators, but it will cause high-speed aircraft to face great safety risks. High-speed aircraft use air rudders for control and stability, but a certain height gap is formed between the air rudder and the surface of the bomb body, and the rudder shaft of the air rudder is directly exposed to the gap flow. Flow separation will occur at the root of the rudder shaft (flow is unsteady), and the flow situation in the rudder shaft area is very complicated. Due to the stagnation of the air rudder gap airflow on the windward surface of the rudder shaft, coupled 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 thermal environment test of the shock wave wind tunnel reached several times the stagnation heat flux. Summary of the invention

[0004] The purpose of the present invention is to provide a method for predicting the heat flow of a high-speed aircraft rudder shaft based on boundary layer thickness in order to improve the problem that the existing prediction results of the heat flow of the windward surface of the rudder shaft of a high-speed aircraft are inaccurate and require a large amount of data.

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

[0006] It should be noted that the CFD numerical calculation method is the computational fluid dynamics numerical calculation method.

[0007] Furthermore, in order to make the calculated heat flow data more accurate, the heat flow data on the rudder shaft surface specifically includes heat flow data of measuring points or grid points on the rudder shaft surface.

[0008] Among them, the measurement point data: the heat flux density at the specified position on the rudder shaft surface; the grid point data: the heat flux density at each grid point after the rudder shaft surface is divided into grids.

[0009] Furthermore, in order to make the calculated heat flow data of the rudder shaft surface more accurate, data of different working conditions are measured, 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, the heat flow data of the rudder shaft surface under multiple working conditions are obtained.

[0010] Furthermore, in order to avoid interference of the rudder shaft structure or other components on the boundary layer characteristics and ensure the accuracy of the boundary layer thickness data, 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 is obtained. The boundary layer thickness of the interference-free area in front of the aircraft air rudder is obtained according to the CFD data calculation results.

[0011] It should be noted that the boundary layer thickness is the distance over which the airflow gradually decelerates from the shear layer-free region of the flow (free stream) to the wall where the velocity is zero, reflecting the boundary layer characteristics.

[0012] Furthermore, in order to facilitate the subsequent polynomial fitting to establish a clear input and output relationship, 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.

[0013] Furthermore, establishing the fitting relationship specifically includes establishing a corresponding fitting relationship for the heat flow data of the measuring point or the grid point.

[0014] Furthermore, the prediction of 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.

[0015] It should be noted that the accuracy of the fitting relationship is verified through experiments or numerical verification to ensure the accuracy of the fitting relationship.

[0016] Furthermore, 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.

[0017] It should be noted that the non-interference area refers to the non-air rudder area.

[0018] Furthermore, 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 condition: ; in, is the heat flux on the rudder shaft surface, is the boundary layer thickness, is the fitting coefficient.

[0019] Furthermore, the closer the goodness of fit measure is to 1, the better the fitting effect is; conversely, the further the goodness of fit measure is from 1, the worse the fitting effect is.

[0020] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 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, the cost is low, which can significantly save costs.

[0021] 2. Based on the small amount of existing rudder shaft heat flow data, a polynomial fitting method is used to establish a fitting relationship from boundary layer thickness to rudder shaft heat flow, which is used for rapid prediction of rudder shaft heat flow. The method is simple and reliable, and does not need to consider the influence of the complex flow effect of the air rudder shaft gap on the rudder shaft heat flow; it reduces costs while significantly improving the accuracy of the prediction.

[0022] 3. Since the data of rudder shaft gap heat flux and boundary layer thickness are highly correlated, the method of the present invention can be widely used in the prediction of rudder shaft gap heat flux in various situations and has high applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flow chart of the method of the present invention; Figure 2 This is a comparison diagram of the heat flow at the rudder shaft measuring point of the present invention versus the thickness of the boundary layer; Figure 3 This is a graph showing the variation of heat flux of the rudder shaft at measuring point 1 with the thickness of the boundary layer in an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The present invention will be described in detail below in conjunction with the accompanying drawings.

[0025] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0026] like Figure 1 As shown, a method for predicting thermal flow of a high-speed aircraft rudder shaft based on boundary layer thickness is provided, and the prediction method includes the following steps: Step S100: performing wind tunnel tests or numerical calculations under multiple working conditions to obtain heat flow data on the surface of the rudder shaft of the high-speed aircraft air rudder; Wind tunnel test: Under controlled conditions, simulate the thermal environment of the aircraft at different speeds, angles, altitudes, etc., and measure the heat flux density on the rudder shaft surface by setting sensors; Numerical calculation: numerical simulation (such as CFD method) is used to simulate actual flight conditions in a virtual environment to generate heat flow data on the rudder shaft surface; The heat flow data on the rudder shaft surface specifically include heat flow data of measuring points or grid points on the rudder shaft surface; Measuring point data: heat flux density at a specified position on the rudder shaft surface; Grid point data: heat flux density at each grid point after the rudder shaft surface is divided into grids; Step S200: obtaining the thickness of the boundary layer in the non-interference zone in front of the air rudder under various working conditions by using a CFD numerical calculation method; Step S300: sorting the heat flow data on the rudder shaft surface according to the values ​​of the boundary layer thickness under the corresponding working conditions; Step S400: using the boundary layer thickness value as an independent variable and the heat flow data of the rudder shaft surface as a dependent variable, a polynomial fitting method is used to establish a fitting relationship for the heat flow data of the rudder shaft surface; Step S500: predicting the heat flow of the rudder shaft by fitting a relational expression. In step S100, the operating 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 operating conditions, thermal flow data of the rudder shaft surface under multiple operating conditions are obtained.

[0027] In step S200, the flow field data of the high-speed aircraft test model under various working conditions are obtained by the CFD numerical calculation method, and then the boundary layer parameter distribution data is obtained, and the boundary layer thickness of the interference-free zone in front of the aircraft air rudder is obtained according to the CFD data calculation results.

[0028] 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.

[0029] The step S300 is to correspond the heat flow data of the measuring points or grid points to the boundary layer thickness values ​​under the corresponding working conditions, and to sort the boundary layer thickness values ​​according to the heat flow data.

[0030] The step S400 of establishing a fitting relationship specifically includes establishing a corresponding fitting relationship for the heat flow data of the measuring point or the grid point.

[0031] 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 condition: ; in, is the heat flux on the rudder shaft surface, is the boundary layer thickness, is the fitting coefficient.

[0032] The step S500, predicting the heat flow of the rudder shaft by fitting the relationship, comprises: 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 closer the goodness of fit measure is to 1, the better the fitting effect is; conversely, the further the goodness of fit measure is from 1, the worse the fitting effect is.

[0033] The heat flow data and boundary layer thickness values ​​of the measuring points or grid points with better fitting effects are recorded.

[0034] Based on the existing small amount of rudder shaft heat flow data, a polynomial fitting method is used to establish a fitting relationship from boundary layer thickness to rudder shaft heat flow, which is used for rapid prediction of rudder shaft heat flow. The method is simple and reliable, and does not need to consider the influence of the complex flow effect of the air rudder shaft gap on the rudder shaft heat flow. It reduces the cost and significantly improves the accuracy of the prediction.

[0035] Example like Figure 2-Figure 3 As shown, one embodiment of the present invention is a method for predicting heat flow of a rudder shaft of a high-speed aircraft based on boundary layer thickness for heat flow data of a rudder shaft in a wind tunnel test, the method comprising the following steps: Step 1: Acquisition of heat flow data of the rudder shaft. Carry out wind tunnel tests to obtain and organize the heat flow data of the rudder shaft measuring points under multiple working conditions. The shock wave wind tunnel test working condition table is shown in Table 1. The measurement methods used in the wind tunnel test include columnar heat flow sensors and profile heat flow sensors. Profile heat flow sensors are installed on the surface of the rudder shaft to measure the heat flow. The profile sensor uses glass as the base material and is ground into the shape of the leading edge of the rudder shaft. The vacuum magnetron sputtering coating method is used to coat platinum film on the polished glass surface, and the surface heat flow is measured with platinum film. A row of columnar heat flow sensors is arranged on the center line of the air rudder front model to measure the heat flow and determine the flow state of the boundary layer in front of the rudder. The columnar sensors are mass-produced. They are also made of glass as the base material and made into glass rods with a diameter of 2 mm and a length of 20 mm. Platinum film is coated on the polished circular end surface and connected to the test lead to make a sensor.

[0036] Table 1 Shock wave wind tunnel test conditions

[0037] Step 2: Boundary layer thickness data acquisition: CFD numerical calculation method is used to obtain the flow field of the high-speed aircraft test model under various working conditions as shown in Table 1, and the boundary layer parameter distribution data are obtained. Based on the numerical calculation results, the windward centerline of the aircraft is obtained. The boundary layer parameters of each working condition at the position are shown in Table 2. The windward center line.

[0038] Table 2 Aircraft windward centerline Boundary layer parameter table for each working condition at the location

[0039] Step 3: Sort the heat flow data of the rudder shaft, such as Figure 2 As shown in the figure, for a specific measuring point, the heat flux data of the rudder axis of the measuring point obtained under each working condition are sorted according to the value of the boundary layer thickness of the corresponding working condition. Figure 2 This is a comparison chart of the heat flux at the rudder axis measuring point and the boundary layer thickness when the rudder deflection angle is 5 degrees.

[0040] Step 4: Fitting relationship, with boundary layer thickness as independent variable and rudder axis heat flow data as dependent variable, using polynomial fitting method, to establish fitting relationship for heat flow data of each measuring point. Taking measuring point 1 as an example, Figure 3 As shown, the polynomial fitting relationship obtained for measurement point 1 is shown in formula (1), and the goodness of fit metric is It is greater than 0.99, and the fitting effect is relatively good, which shows that the heat flux of the rudder shaft does have a large correlation with the boundary layer thickness value.

[0041] (1) (2) in, is the heat flux on the rudder shaft surface, is the boundary layer thickness, is a goodness-of-fit measure.

[0042] Step 5: Use the fitting relationship (1) to predict the heat flux of the rudder shaft at measuring point 1. When predicting, first calculate the boundary layer thickness value of the corresponding working condition, and substitute it into the fitting relationship (1) to predict the heat flux of the rudder shaft at measuring point 1 (the fitting relationship corresponding to the corresponding measuring point must be used. If the heat flux of measuring point 2 needs to be predicted, the fitting relationship corresponding to measuring point 2 must be used). Table 3 shows the prediction deviation of the fitting relationship of the rudder shaft heat flux and boundary layer thickness calculation results of the five measuring points of the rudder shaft under six working conditions. It can be seen that the prediction deviation is small overall. Except for the large prediction deviation of measuring point 1 under working condition 1 (-40.1%), the other prediction results are all less than 15%. Compared with the repeatability accuracy of the aerodynamic thermal test measurement of the rudder shaft area, this prediction deviation is reasonable. In addition, the heat flux value of measuring point 1 under working condition 1 is the smallest value among all heat flux values. It is common for data with small values ​​to have large prediction deviations.

[0043] Table 3 Prediction deviation of fitting relationship between rudder shaft heat flux and boundary layer thickness calculation results

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should 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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