High-speed aircraft folding rudder aerodynamic configuration design method based on aerodynamic thermal constraint

Abstract

The invention discloses a high-speed aircraft folding rudder aerodynamic configuration design method based on aerodynamic thermal constraint, which comprises the following steps of: determining a rudder leading edge radius and a rudder leading edge sweepback angle by taking a current state nominal trajectory as a basis and taking a rudder leading edge thermal response temperature as a judgment standard; secondly, the cone angle of one conical surface of the folded rudder is determined through iterative calculation, so that the chordwise size of the high-temperature-resistant refractory metal material and the thickness of a skin and a heat-proof coating at the cone position are designed; and thirdly, through the design of the interference position of the arched shock wave of the heat-proof cup, the gap between the fixed rudder and the movable rudder avoids the interference area of the arched shock wave, so that the chordwise distance between the folding gap and the rudder shaft is determined. By means of the aerodynamic configuration design method, the radius of the front edge of the rudder can be as low as 3 mm, the taper angle is as low as 4 degrees, it can be guaranteed that ablation deformation does not occur when the maximum heat flow of the front edge of the rudder does not exceed 10 MW / m < 2 >, the resistance characteristic of a high-speed aircraft can be effectively reduced, the characteristic of near-zero ablation is achieved, and the good aerodynamic configuration is maintained.

Description

Technical Field

[0001] The present invention belongs to the technical field of aircraft, and particularly relates to a design method for the aerodynamic configuration of a folding rudder of a high-speed aircraft based on aerodynamic heat constraints. Background Art

[0002] At present, the development trend of various aircraft is to have a longer range, a smaller volume, and a lighter mass. In order to facilitate transportation and storage, the aircraft and its launch device must be miniaturized. Therefore, the aircraft needs to adopt foldable rudder wings.

[0003] As a key component of flight control, the folding rudder bears extremely harsh aerodynamic heat and aerodynamic load conditions during high-speed flight. Traditional folding rudders of high-speed aircraft all adopt ablation-type thermal protection solutions. Restricted by the production processability of composite materials, this type of folding rudder usually has a relatively large leading-edge radius, which is a compromise of the drag reduction goal for thermal protection and cannot adapt to the development trend of high-speed aircraft. In addition, serious ablation will occur at the leading edge of the ablation-type folding rudder, objectively resulting in a further increase in the drag of the folding rudder. Therefore, researching a low-drag non-ablation folding rudder suitable for high-speed aircraft is a key problem to be solved urgently. For the design process of non-ablation folding rudders, it usually ensures to meet the structural space requirements first, and then meets the basic aerodynamic performance indicators. In the design process, usually the aerodynamics proposes an initial shape, and then its aerodynamic heat environment is evaluated. If the aerodynamic heat response temperature does not meet the requirements for the use of structural materials, the aerodynamic shape of the folding rudder needs to be improved. After several iterations of such a design cycle, the final shape of the folding rudder is obtained.

[0004] This design method that mainly focuses on aerodynamic force and supplements with aerodynamic heat is not optimal in terms of design results and design cycle. The main disadvantages are as follows: First, the designed tail rudder shape mainly focuses on meeting the requirements of aerodynamic performance indicators. The result of aerodynamic design is often only able to meet the basic aerodynamic performance indicator requirements, and the structural heat response temperature is not relatively optimal; Second, the design cycle is relatively long. Usually, structural designers only design the tail rudder shape by meeting the aerodynamic performance indicators and cannot meet the allowable requirements of the material temperature for use. This will lead to an extended design iteration cycle for aerodynamic force and aerodynamic heat. Therefore, how to streamline the design process, shorten the design cycle, and at the same time take into account the aerodynamic heat and aerodynamic force performance of the folding rudder has become a technical problem urgently to be solved in the aerodynamic design of supersonic non-ablation lateral folding tail rudders. Summary of the Invention

[0005] To overcome the deficiencies of the prior art, the present invention provides a method for designing the aerodynamic configuration of a folding rudder for a high-speed aircraft based on pneumatic heat constraint. Based on the nominal trajectory of the current state and using the thermal response temperature of the rudder leading edge as the determination criterion, the radius of the rudder leading edge and the sweep angle of the rudder leading edge are determined. Secondly, the cone angle of one conical surface of the folding rudder is determined through iterative calculation, thereby designing the chordwise dimension of the refractory metal material with high temperature resistance, as well as the thickness of the skin and the thermal protection coating at the first cone. Thirdly, through the design of the interference position of the shock wave of the thermal protection cup, the gap between the fixed rudder and the movable rudder is avoided from the interference area of the shock wave, thereby determining the chordwise distance between the folding gap and the rudder shaft. Through this aerodynamic configuration design method, the radius of the rudder leading edge can be as low as 3 mm, and the first cone angle can be as low as 4°. It can ensure that there is no ablation deformation when the maximum heat flux at the rudder leading edge does not exceed 10 MW / m 2 ², effectively reducing the drag characteristics of the high-speed aircraft. Compared with the traditional high-speed air rudder with a thermal protection sleeve + skin skeleton, it has the characteristics of nearly zero ablation and maintains a good aerodynamic shape.

[0006] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0007] Step 1: Design of the initial rudder surface shape;

[0008] According to the overall indicators, the tail rudder indicators are decomposed and designed. The decomposed indicators are: the lift-drag characteristics of the entire missile, the minimum static stability characteristics, the maximum lift-drag ratio, the control efficiency, and the maximum overload. According to the folding size limit, the maximum span of the rudder surface is determined. Secondly, according to the minimum static stability characteristics, the projected area of the rudder surface is determined, and based on the initial leading-edge sweep angle of the rudder surface, the root chord length and the tip chord length of the rudder surface are determined.

[0009] Step 2: Design of the radius and sweep angle of the rudder leading edge;

[0010] The leading edge of the rudder uses a refractory metal material with high temperature resistance, leaving a design margin. Based on the thermal response temperature at the stagnation point, the fillet radius of the rudder leading edge and the leading-edge sweep angle are inversely designed.

[0011] Step 3: Design of the first cone angle of the rudder surface;

[0012] By iteratively calculating the highest temperature on the first cone of the rudder surface, the bevel angle at the first cone of the rudder surface is inversely calculated, thereby designing the chordwise length of the insert strip, as well as the thickness of the skin and the thermal protection coating at the first cone.

[0013] Step 4: Design of the gap at the junction of the fixed rudder and the movable rudder;

[0014] Through the simulation analysis of the thermal protection cup of the rudder shaft, the interference area of the shock wave generated by the thermal protection cup is calculated, so that the gap between the fixed rudder and the movable rudder avoids the shock wave, thereby determining the distance between the fixed rudder gap and the thermal protection cup of the rudder shaft, and obtaining the chordwise length of the fixed rudder.

[0015] Preferably, step 2 is specifically as follows:

[0016] According to the wide speed range and wide airspace flight envelope of the high-speed aircraft, an engineering calculation formula for the stagnation heat flux density of the control surface is introduced as follows:

[0017]

[0018] Where: q represents the heat flux density on the leading edge stagnation line; R represents the leading edge stagnation radius of the control surface; ρ ∞ represents the free-stream atmospheric density, v ∞ represents the free-stream velocity, h w represents the wall enthalpy value, h s represents the stagnation enthalpy value, n represents the power coefficient, ∧ e represents the effective sweep angle of the leading edge of the control surface;

[0019] Taking the allowable temperature of the material as the limit temperature, the maximum heat flux at the leading edge of the control surface is calculated inversely, and then the fillet radius and leading edge sweep angle of the control surface leading edge are optimized and iteratively selected.

[0020] Preferably, step 3 is specifically as follows:

[0021] The strip method is used to calculate the heat flux on the wing surface. The wing surface is divided into many strips parallel to the free-stream direction, and it is assumed that there is no influence between the spanwise sections, so as to transform the three-dimensional problem into a two-dimensional problem for calculation;

[0022] The laminar and turbulent Eckert flat plate reference enthalpy method is adopted. The laminar heat flux calculation formula is:

[0023]

[0024] In the formula, q w,l represents the laminar heat flux density, P r represents the Prandtl number, ρ e represents the density at the outer edge of the boundary layer, u e represents the velocity at the outer edge of the boundary layer, Re s represents the stagnation Reynolds number, ρ * represents the density at the reference temperature, μ * represents the viscosity coefficient at the reference temperature, μ e represents the viscosity coefficient at the outer edge of the boundary layer;

[0025] The turbulent heat flux calculation formula is:

[0026]

[0027] In the formula, q w,t represents the turbulent heat flux density, C c represents the compression factor;

[0028] Calculate the interference region of the oblique shock wave on the rudder surface according to the flat plate with a blunt leading edge. The expressions for the oblique shock wave on the rudder surface and a cone deflection angle are as follows

[0029]

[0030] In the formula, M1 is the Mach number before the shock wave, β is the oblique shock wave angle, θ is the flow deflection angle, and γ is the specific heat ratio.

[0031] Preferably, the specific step 4 is as follows:

[0032] By calculating the interference region of the bow shock wave generated by the heat protection cup, the gap between the fixed rudder and the moving rudder is avoided from the bow shock wave. The expression for the distance between the bow shock wave and the heat protection cup is as follows:

[0033]

[0034] Where: D represents the diameter of the heat protection cup, which needs to be determined according to the thermal protection material system of the heat protection structure; Ma represents the free-stream Mach number. According to different Mach numbers, the maximum position of the bow shock wave from the rudder axis is calculated to avoid the interference of the shock wave on the gap between the moving rudder and the static rudder.

[0035] Preferably, when the effective sweep angle of the leading edge satisfies 30 ≤ ∧ e ≤ 60, n = 1.5.

[0036] Preferably, the high-temperature refractory metal material is molybdenum alloy or niobium-tungsten alloy.

[0037] The beneficial effects of the present invention are as follows:

[0038] The present invention proposes a pneumatic configuration design method for a folding rudder of a high-speed aircraft based on aerodynamic heat constraints, and designs a non-ablation rudder with excellent aerodynamic performance and light structural weight. This method has broad application prospects.

[0039] (1) The material of the rudder leading edge is selected as a high-temperature refractory metal material. Through the comprehensive optimization design of the leading edge radius and sweep angle of the rudder surface, the leading edge radius of the rudder can be as low as 3 mm, and the leading edge sweep angle is not greater than 55°. It can ensure that no ablation deformation occurs when the maximum heat flux at the rudder leading edge does not exceed 10 MW / m 2 ;

[0040] (2) The overall thickness of the folding rudder is small, and the one-cone bevel angle of the rudder surface is not greater than 4°, and no ablation deformation occurs, and the aerodynamic drag is small;

[0041] (3) The gap between the fixed rudder and the moving rudder of the folding rudder effectively avoids the interference area of the bow shock wave generated by the heat protection cup on the rudder surface, and reduces the interference of the shock wave on the gap between the fixed rudder and the moving rudder. Description of the Drawings

[0042] Figure 1This is the flowchart of the method of the present invention.

[0043] Figure 2 This is a schematic diagram of the external shape of the folding rudder in the deployed state.

[0044] Reference numerals: 1. Radius of rounding at the leading edge of the rudder surface; 2. Sweep angle at the leading edge of the rudder surface; 3. Stripe at the leading edge of the rudder surface; 4. First conical surface of the rudder surface (including the thickness of the skin and coating); 5. Gap between the fixed rudder and the movable rudder. Specific embodiments

[0045] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0046] As Figure 1 and Figure 2 shown, a method for designing the aerodynamic configuration of a folding rudder for a high-speed aircraft based on aerodynamic heat constraints is as follows:

[0047] Step 1: Design of the initial rudder surface shape;

[0048] According to the overall indicators, decompose and design the tail rudder indicators. The decomposed indicators are: lift-drag characteristics of the aircraft, minimum static stability characteristics, maximum lift-drag ratio, control efficiency, and maximum overload. The key is to determine the maximum span of the rudder surface according to the folding size limit, and secondly, determine the projected area of the rudder surface according to the minimum static stability characteristics, and determine the root chord length and tip chord length of the rudder surface based on the initial leading edge sweep angle of the rudder surface.

[0049] Step 2: Design of the radius and sweep angle at the leading edge of the rudder surface;

[0050] The leading edge of the rudder is made of a high-temperature refractory metal material, with a design margin reserved. Based on the thermal response temperature at the stagnation point, the radius of rounding at the leading edge of the rudder surface and the leading edge sweep angle are inversely designed.

[0051] Step 3: Design of the first conical angle of the rudder surface;

[0052] By iteratively calculating the highest temperature on the first conical surface of the rudder surface, the bevel angle at the first conical surface of the rudder surface is inversely calculated, so as to design the chordwise length of the stripe, and the thickness of the skin and heat protection coating at the first conical surface.

[0053] Step 4: Design of the gap at the junction of the fixed rudder and the movable rudder;

[0054] By simulating the radius size of the heat protection cup of the rudder shaft, calculate the interference area of the bow shock wave generated by the heat protection cup, so that the gap between the fixed rudder and the movable rudder avoids the bow shock wave, thereby determining the distance between the gap of the fixed rudder and the heat protection cup of the rudder shaft, and obtaining the chordwise length of the fixed rudder.

[0055] Embodiment:

[0056] Taking the layout form of a typical wingless high-speed aircraft as an example, the present invention will be further described in detail:

[0057] Step 1, initial control surface design;

[0058] Decompose and design the tail rudder indicators according to the overall indicators. The decomposed indicators are: the lift-drag characteristics of the whole missile, the minimum static stability characteristics, the maximum lift-drag ratio, the control efficiency, and the maximum overload. The key is to determine the maximum span of the control surface according to the folding size limit. Secondly, determine the projected area of the control surface according to the minimum static stability characteristics, and determine the root chord length and tip chord length of the control surface based on the initial leading-edge sweep angle of the control surface.

[0059] Step 2, design of the leading-edge radius and sweep angle of the control surface;

[0060] According to the wide-speed and wide-airspace flight envelope of high-speed aircraft, in order to quickly iterate the aerodynamic heat of the control surface, an engineering calculation formula for the stagnation heat flux density function of the missile body is introduced as follows:

[0061]

[0062] To ensure that the leading edge of the rudder still has sufficient strength and shaping ability under ultra-high temperature heat loads, refractory metals with high temperature resistance are used for the leading edge of the rudder. Molybdenum alloy, niobium-tungsten alloy, etc. can be selected. Taking the allowable temperature of the material as the limit temperature, the maximum heat flux at the leading edge of the control surface is calculated inversely, and then the fillet radius and leading-edge sweep angle of the leading edge of the control surface are optimized and iteratively selected.

[0063] Step 3, design of the first cone angle of the control surface;

[0064] In order to verify the chordwise length of the leading-edge strip of the control surface, it is necessary to iteratively calculate the aerodynamic heat on the first cone surface of the control surface to meet the heat flux density constraint conditions and design and determine the first cone angle of the control surface.

[0065] The heat flux calculation on the wing surface can be carried out by the strip method. The wing surface is divided into many strips parallel to the oncoming flow direction, and it is assumed that there is no influence between the cross-sections in the spanwise direction, and the three-dimensional problem is transformed into a two-dimensional problem for calculation. Overall, the windward surface of the wing is quite flat, and it is obviously appropriate to use the blunt leading-edge flat plate heat flux formula along the strip. The Eckert flat plate reference enthalpy method for laminar flow and turbulent flow is selected here. The laminar heat flux calculation formula is:

[0066]

[0067] The turbulent heat flux calculation formula is:

[0068]

[0069] Calculate the oblique shock interference area of the control surface according to the blunt leading-edge flat plate. It is mainly calculated according to the flow deflection angle of the first cone surface. The expressions of the oblique shock wave of the control surface and the deflection angle of the first cone are as follows:

[0070]

[0071] Step 4, the interference area of the rudder shaft heat protection cup;

[0072] The principle of the gap design between the fixed rudder and the moving rudder of the folding rudder is as follows: by calculating the interference area of the bow shock wave generated by the heat protection cup, the gap between the fixed rudder and the moving rudder is avoided from the bow shock wave. The distance expression between the bow shock wave and the heat protection cup is as follows:

[0073]

[0074] Where: D represents the diameter of the heat protection cup, which needs to be determined according to the heat protection material system of the heat protection structure; Ma represents the free stream Mach number. According to different Mach numbers, the maximum position of the bow shock wave from the rudder shaft is calculated, so as to avoid the interference of the shock wave on the gap between the moving rudder and the static rudder.

Claims

1. A pneumatic thermal constraint-based aerodynamic configuration design method for folding rudders of high-speed aircraft, characterized in that It includes the following steps: Step 1: Initial rudder surface profile design; Decompose and design the tail rudder indicators according to the overall indicators. The decomposed indicators are: the lift-drag characteristics of the whole missile, the minimum static stability characteristics, the maximum lift-drag ratio, the control efficiency, and the maximum overload; Determine the maximum span of the rudder surface according to the folding size limit. Secondly, determine the projected area of the rudder surface according to the minimum static stability characteristics. Based on the initial leading-edge sweep angle of the rudder surface, determine the root chord length and tip chord length of the rudder surface; Step 2: Design of the rudder leading-edge radius and sweep angle; The rudder leading edge uses a high-temperature refractory metal material, leaving a design margin. According to the thermal response temperature at the stagnation point, inversely design the fillet radius and leading-edge sweep angle of the rudder surface; Step 3: Design of the first cone angle of the rudder surface; By iteratively calculating the highest temperature on the first cone of the rudder surface, inversely calculate the bevel angle at the first cone of the rudder surface, so as to design the chordwise length of the inlay strip, and the thickness of the skin and thermal protection coating at the first cone; Step 4: Design of the gap between the fixed rudder and the moving rudder; Through the simulation analysis of the thermal protection cup of the rudder shaft, calculate the interference area of the bow shock wave generated by the thermal protection cup, so that the gap between the fixed rudder and the moving rudder avoids the bow shock wave, thereby determining the distance between the fixed rudder gap and the thermal protection cup of the rudder shaft, and obtaining the chordwise length of the fixed rudder.

2. The aerodynamic configuration design method of a folding rudder for a high-speed aircraft based on aerodynamic heat constraint according to claim 1, wherein, The specific content of step 2 is as follows: According to the wide-speed-range and wide-airspace flight envelope of the high-speed aircraft, introduce the engineering calculation formula for the stagnation heat flux density of the rudder surface as follows: Among them: q represents the heat flux density on the leading edge stagnation line; R represents the leading edge stagnation radius of the rudder surface; ρ ∞ represents the free-stream atmospheric density, v ∞ represents the free-stream velocity, h w represents the wall enthalpy value, h s represents the stagnation enthalpy value, n represents the power coefficient, ∧ e represents the effective sweep angle of the leading edge of the rudder surface; Taking the allowable temperature of the material as the limit temperature, inversely calculate the maximum heat flux at the leading edge of the rudder surface, so as to optimize and iteratively select the fillet radius and leading-edge sweep angle of the rudder leading edge.

3. The aerodynamic configuration design method of a folding rudder for a high-speed aircraft based on aerodynamic heat constraint according to claim 2, wherein, The specific content of step 3 is as follows: The strip method is used to calculate the surface heat flux of the wing surface. The wing surface is divided into many strips parallel to the oncoming flow direction, and it is assumed that there is no influence between the cross-sections in the spanwise direction, so as to transform the three-dimensional problem into a two-dimensional problem for calculation; The laminar and turbulent Eckert flat-plate reference enthalpy method is adopted. The calculation formula for laminar heat flux is: where q w,l represents the laminar heat flux density, P r represents the Prandtl number, ρ e represents the density at the outer edge of the boundary layer, u e represents the velocity at the outer edge of the boundary layer, Re s represents the stagnation Reynolds number, ρ * represents the density at the reference temperature, μ * represents the viscosity coefficient at the reference temperature, μ e represents the viscosity coefficient at the outer edge of the boundary layer; The calculation formula for turbulent heat flux is: where q w,t represents the turbulent heat flux density, and C c represents the compressibility factor; Calculate the oblique shock interference area of the rudder surface according to the blunt leading-edge flat plate. The expressions for the oblique shock wave of the rudder surface and the deflection angle of the first cone are as follows In the formula, M1 is the Mach number before the shock wave, β is the oblique shock wave angle, θ is the flow deflection angle, and γ is the specific heat ratio.

4. A pneumatic configuration design method for folding rudders of high-speed aircraft based on pneumatic heat constraint according to claim 3, characterized in that The specific content of step 4 is as follows: By calculating the interference area of the bow shock wave generated by the thermal protection cup, make the gap between the fixed rudder and the moving rudder avoid the bow shock wave. The expression for the distance between the bow shock wave and the thermal protection cup is as follows: Among them: D represents the diameter of the thermal protection cup, which needs to be determined according to the thermal protection material system of the thermal protection structure; Ma represents the free-stream Mach number, and the maximum position of the bow shock wave from the rudder shaft is calculated according to different Mach numbers, so as to avoid the interference of the shock wave on the gap between the moving rudder and the static rudder.

5. A method for designing the aerodynamic configuration of a folding rudder for a high-speed aircraft based on aerodynamic heat constraint according to claim 4, characterized in that The effective sweep angle of the leading edge satisfies 30 ≤ ∧ e ≤ 60, and n = 1.

5.

6. The aerodynamic configuration design method of a folding rudder for a high-speed aircraft based on aerodynamic heat constraint according to claim 5, wherein The high-temperature refractory metal material is molybdenum alloy or niobium-tungsten alloy.

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