A cone transition prediction method based on three-dimensional flow field boundary layer characteristic parameter database

Abstract

The application provides a cone body transition prediction method based on a three-dimensional flow field boundary layer characteristic parameter database. The method realizes rapid judgment of transition flow in a complex region of an aircraft by establishing a transition database, and meets the actual needs of aircraft engineering design. The application realizes rapid judgment of transition in a complex flow region of an aircraft, meets the engineering design needs, can obtain a three-dimensional transition array surface of the aircraft, and helps to deeply understand the transition development process of the surface of the aircraft.

Description

Technical Field

[0001] This application relates to the field of high-speed aircraft cone transition prediction technology, specifically to a cone transition prediction method based on a three-dimensional flow field boundary layer characteristic parameter database. Background Technology

[0002] After a high-speed boundary layer transitions from laminar to turbulent flow, the local frictional drag and heat flux on the aircraft surface increase dramatically, significantly impacting the aircraft's aerodynamic / thermal characteristics and consequently affecting its flight efficiency and safety. Predicting the boundary layer transition on the aircraft surface is no longer merely a matter of "design margin," but a critical issue concerning the aircraft's "flight success or failure."

[0003] For high-altitude aircraft, factors influencing boundary layer transition on the aircraft surface include incoming turbulence, surface roughness, wall temperature, and crossflow effects. Among these, incoming turbulence, surface roughness, and wall temperature are flow-direction instabilities that affect transition flows over large areas of the aircraft's cone-shaped structure. For complex flow regions, such as near the control rudder, the crossflow effect is crucial. Therefore, determining transition in complex aircraft regions requires consideration of both flow-direction and crossflow instabilities. Lau, Zhou, and others, based on criteria for judging flow-direction and crossflow instabilities and building upon existing research, proposed an intermittent factor model. Since this model requires calculations of the external flow field and extraction of boundary layer characteristic parameters, determining surface transition necessitates CFD numerical simulations of the flow field at multiple state points along the trajectory profile. This time-consuming process cannot meet the rapid iteration requirements of engineering design, and currently, this method has not been applied to the practical engineering design of high Mach number aircraft.

[0004] This invention, based on all ballistic profile data of an aircraft, employs CFD numerical simulation technology to establish a flow field database covering all ballistic profiles. By extracting characteristic parameters of the boundary layer on the aircraft wall in the flow field, an intermittent factor characterizing the transition features of the aircraft surface is calculated. Based on previous flight tests, this database is revised to form a transition database for judging the flow regime on the aircraft surface. This database enables rapid determination of transitional flows in complex regions under different aircraft states, improving aircraft design efficiency and meeting the engineering design requirements of high Mach number aircraft.

[0005] To address the problem that intermittent factor models cannot be applied to the rapid determination of transitions in complex regions of an aircraft, this invention provides a determination method based on a transition database. The technical features of this method are: pre-establishing a transition database covering the designed trajectory, and using data interpolation techniques to achieve rapid determination of transitions in complex regions under different aircraft states. Summary of the Invention

[0006] To address the aforementioned technical issues, this application proposes a conical transition prediction method based on a three-dimensional flow field boundary layer characteristic parameter database. By establishing a transition database, this application enables rapid judgment of transition flows in complex regions of an aircraft, meeting the practical needs of aircraft engineering design.

[0007] The technical solution adopted in this application is as follows:

[0008] A method for predicting cone transition based on a three-dimensional flow field boundary layer characteristic parameter database, the method comprising the following steps:

[0009] Step 1: Establish an aircraft flow field database that covers multiple flight profiles through CFD numerical simulation;

[0010] Step 2: Based on the aircraft flow field database, extract the boundary layer feature parameters of complex regions on the aircraft surface;

[0011] Step 3: Calculate the transition criterion intermittent factor γ for complex regions on the aircraft surface using the boundary layer characteristic parameters; based on the aircraft flight test results, correct the transition criterion γ value, and finally form a transition criterion database covering all ballistic profiles;

[0012] Step 4: Based on the transition criterion database covering all ballistic profiles, and according to engineering design requirements, determine the transition flow in complex areas of the aircraft.

[0013] Furthermore, the aircraft flow field database includes flow field databases under different flight altitudes, angles of attack, and Mach numbers.

[0014] Furthermore, in step 2, the boundary layer characteristic parameters of the complex region on the aircraft surface include boundary layer thickness, boundary layer outer edge density, outer edge velocity, and outer edge Mach number.

[0015] Furthermore, in step 2, the extraction of boundary layer feature parameters of complex regions on the aircraft surface includes: calculating the boundary layer momentum thickness, momentum thickness Reynolds number, and crossflow Reynolds number based on the boundary layer feature parameters of complex regions on the aircraft surface.

[0016] Furthermore, the formula for calculating the boundary layer momentum thickness is as follows:

[0017]

[0018] Where ρ represents density, with units of kg / m³. 3 u represents velocity, with units of m / s; ρ e This represents the outer edge density of the boundary layer, in kg / m³. 3 ;u eδ represents the outer edge velocity of the boundary layer in m / s; y represents the distance from the wall to the normal direction in m; and δ represents the near-wall boundary layer thickness in m.

[0019] Furthermore, the formula for calculating the Reynolds number of the boundary layer momentum thickness is as follows:

[0020]

[0021] Where, μ e This represents the viscosity coefficient at the outer edge of the boundary layer, expressed in Pa·s.

[0022] Furthermore, the formula for calculating the crossflow Reynolds number of the boundary layer is as follows:

[0023]

[0024] Among them, W max This represents the maximum crossflow velocity within the boundary layer.

[0025] Furthermore, in step 3, the calculation formula for the transition criterion intermittent factor γ of complex regions on the aircraft surface is as follows:

[0026]

[0027] Where C1 and C2 represent constants, both taking a value of 1; the subscript crit indicates the critical value, the magnitude of which is corrected based on actual flight tests; M e This represents the Mach number at the outer edge of the boundary layer.

[0028] Furthermore, in step 4, based on multiple flight trajectory profiles, a CFD flow field database containing different combinations of altitudes, Mach numbers, and angles of attack is established. This database can cover various typical states of the aircraft trajectory. CFD numerical calculations are performed on the various typical states to obtain a flow field database that can cover all typical states of the aircraft trajectory.

[0029] Furthermore, based on the flow field database obtained by CFD calculation, the characteristic parameters of the boundary layer on the surface of the aircraft in the flow field are extracted. According to the flight trajectory parameters of the engineering design, similar states are selected from the established transition database to perform linear interpolation calculation on γ, and the γ distribution under the design trajectory parameters is obtained.

[0030] The following technical effects can be achieved through the embodiments of this application:

[0031] (1) The present invention enables rapid determination of transitions in complex flow regions of aircraft, meeting engineering design requirements.

[0032] (2) The present invention can obtain the three-dimensional transition surface of the aircraft, which helps to understand the transition development process of the aircraft surface. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic flowchart of the cone-shaped transition prediction method of the present invention;

[0035] Figure 2 A schematic diagram of the boundary layer characteristic parameters of the windward surface of the conical body of an aircraft.

[0036] Figure 3 Gamma cloud map for determining the transition criteria of the conical frontal surface of an aircraft under different conditions;

[0037] Figure 4 Gamma cloud diagram for aircraft transition criteria at a 15° angle of attack;

[0038] Figure 5 γ-cloud diagram for aircraft transition criteria at an angle of attack of 20°;

[0039] Figure 6 Gamma cloud diagram for aircraft transition criteria at an angle of attack of 17°. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0041] Figure 1 This is a schematic flowchart of the cone-shaped transition prediction method of the present invention;

[0042] The method includes the following steps:

[0043] Step 1: Establish an aircraft flow field database that covers multiple flight profiles through CFD numerical simulation;

[0044] The aircraft flow field database includes flow field databases under different flight altitudes, angles of attack, and Mach numbers.

[0045] Step 2: Based on the aircraft flow field database, extract the boundary layer feature parameters of complex regions on the aircraft surface;

[0046] The boundary layer characteristic parameters of the complex region on the surface of the aircraft include boundary layer thickness, boundary layer outer edge density, outer edge velocity and outer edge Mach number, and based on these parameters, boundary layer momentum thickness, momentum thickness Reynolds number and crossflow Reynolds number are calculated;

[0047] The formula for calculating the boundary layer momentum thickness is as follows:

[0048]

[0049] Where ρ represents density, with units of kg / m³. 3 u represents velocity, with units of m / s; ρ e This represents the outer edge density of the boundary layer, in kg / m³. 3 ;u e y represents the outer edge velocity of the boundary layer, in m / s; y represents the distance from the wall to the normal direction, in m; δ represents the near-wall boundary layer thickness, in m.

[0050] The formula for calculating the Reynolds number of the boundary layer momentum thickness is as follows:

[0051]

[0052] Where, μ e This represents the viscosity coefficient at the outer edge of the boundary layer, expressed in Pa·s.

[0053] The formula for calculating the crossflow Reynolds number of the boundary layer is as follows:

[0054]

[0055] Among them, W max This represents the maximum crossflow velocity within the boundary layer.

[0056] Step 3: Calculate the transition criterion intermittent factor γ for complex regions on the aircraft surface using the boundary layer characteristic parameters; based on the aircraft flight test results, correct the transition criterion γ value, and finally form a transition criterion database covering all ballistic profiles;

[0057] The formula for calculating the intermittent factor γ, the transition criterion for complex regions on the aircraft surface, is as follows:

[0058]

[0059] Where C1 and C2 represent constants, both taking a value of 1; the subscript crit indicates the critical value, the magnitude of which is corrected based on actual flight tests; M e Indicates the Mach number at the outer edge of the boundary layer;

[0060] Step 4: Based on the transition criterion database covering all ballistic profiles, and according to engineering design requirements, determine the transition flow in complex areas of the aircraft.

[0061] In this step, a CFD flow field database is established based on multiple flight trajectory profiles, containing various combinations of altitudes, Mach numbers, and angles of attack. This database covers various typical states of the aircraft's trajectory. For example, if an aircraft flies at an altitude between 5 km and 60 km, the altitude is taken in increments of 5 km (5 km, 10 km, ... 60 km), resulting in 12 states; the Mach number range is between 1 and 6, with Mach number taken in increments of 1 (1, 2, ... 6), resulting in 6 states; and the angle of attack range is between -10° and 10°, with angle of attack taken in increments of 5° (-10°, -5°, ..., 10°), resulting in 5 states. This database contains a total of 12 × 6 × 5 = 360 states. CFD numerical calculations are performed on each state to obtain a flow field database covering all typical states of the aircraft's trajectory.

[0062] Figure 2 This is a schematic diagram of the boundary layer characteristic parameters of the windward surface of the conical body of an aircraft. Figure 3 Gamma cloud map of the cone transition criteria for different states of the windward side of the aircraft cone. Figure 2 A boundary layer characteristic parameter cloud map of a typical state conical flow region of an aircraft, extracted based on CFD numerical simulation results, is presented. The map shows the characteristic parameters of boundary layer thickness and boundary layer momentum thickness. The transition criterion γ cloud map of the aircraft surface is calculated using these boundary layer characteristic parameters, as shown below. Figure 3 The figure shows the cone transition criterion γ contour maps under two conditions: transition criterion γ at small angles of attack and transition criterion γ at large angles of attack. These contour maps provide a clear understanding of the transition front in the cone region. Establishing a transition database covering multiple flight profiles enables rapid and comprehensive assessment of transition flows in the cone region of the aircraft.

[0063] Based on the flow field database obtained from CFD calculations, characteristic parameters of the aircraft surface boundary layer in the flow field are extracted according to the theoretical methods in steps 2 and 3, and the boundary layer transition criterion γ cloud map is calculated. In the actual design of aircraft engineering, based on the flight trajectory parameters of the engineering design, similar states are selected from the established transition database to perform linear interpolation calculations on γ, quickly obtaining the γ distribution under the design trajectory parameters. For example, Figure 4 , 5 These are γ-ray cloud maps of the transition criteria on the windward side of an aircraft's conical fuselage at a certain altitude and speed, with angles of attack of 15° and 20°, respectively. If the actual trajectory, assuming the same altitude and speed, results in an angle of attack of 17°, linear interpolation can be performed using the γ-ray transition criteria from the 15° and 20° databases to quickly obtain the γ-ray cloud map of the aircraft's transition criteria at a 17° angle of attack, as shown below. Figure 6As shown, this method eliminates the need for CFD numerical simulation at a 17° angle of attack, enabling rapid identification of the three-dimensional transition region on the windward side of the cone at this angle, significantly improving design efficiency.

Claims

1. A method for predicting conical transitions based on a three-dimensional flow field boundary layer characteristic parameter database, characterized in that, The method includes the following steps: Step 1: Establish an aircraft flow field database that covers multiple flight profiles through CFD numerical simulation; Step 2: Based on the aircraft flow field database, extract the boundary layer feature parameters of complex regions on the aircraft surface; Step 3: Calculate the transition criterion intermittent factor for complex regions on the aircraft surface using the boundary layer feature parameters. ; Based on the flight test results of the aircraft, the transition criteria were revised. The values ​​ultimately form a transition criterion database covering all ballistic profiles; Step 4: Based on the transition criterion database covering all ballistic profiles, and according to engineering design requirements, to achieve the judgment of transition flows in complex areas of the aircraft; In step 2, the boundary layer characteristic parameters of the complex region on the aircraft surface include boundary layer thickness, boundary layer outer edge density, outer edge velocity, and outer edge Mach number; In step 2, the extraction of boundary layer feature parameters for complex regions on the aircraft surface includes: Based on the boundary layer characteristic parameters of the complex region on the surface of the aircraft, the boundary layer momentum thickness, momentum thickness Reynolds number, and crossflow Reynolds number are calculated. The formula for calculating the boundary layer momentum thickness is as follows: in, Density is expressed in kg / m³. 3 ; Expresses speed, measured in m / s; This represents the outer edge density of the boundary layer, in kg / m³. 3 ; This represents the velocity at the outer edge of the boundary layer, in m / s. This indicates the normal distance from the wall, in meters (m). This indicates the near-wall boundary layer thickness, in meters (m). The formula for calculating the Reynolds number of the boundary layer momentum thickness is as follows: in, This represents the viscosity coefficient at the outer edge of the boundary layer, expressed in Pa·s. The formula for calculating the crossflow Reynolds number of the boundary layer is as follows: in, This represents the maximum crossflow velocity within the boundary layer. In step 3, the transition criterion for complex regions on the aircraft surface is the intermittent factor. The calculation formula is as follows: in, , The constants are all 1; the subscript crit indicates the critical value, which is adjusted based on actual flight tests. This represents the Mach number at the outer edge of the boundary layer.

2. The method according to claim 1, characterized in that, The aircraft flow field database includes flow field databases under different flight altitudes, angles of attack, and Mach numbers.

3. The method according to claim 1, characterized in that, In step 4, based on multiple flight trajectory profiles, a CFD flow field database containing different combinations of altitudes, Mach numbers, and angles of attack is established. This database can cover various typical states of the aircraft trajectory. CFD numerical calculations are performed on the various typical states to obtain a flow field database that can cover all typical states of the aircraft trajectory.

4. The method according to claim 1, characterized in that, Based on the flow field database obtained from CFD calculations, characteristic parameters of the boundary layer on the aircraft surface are extracted from the flow field. Then, according to the flight trajectory parameters in the engineering design, similar state pairs are selected from the established transition database. Perform linear interpolation calculations to obtain the designed ballistic parameters. distributed.

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