A method for designing tail thrust propeller considering interference of fuselage wake

Abstract

The application belongs to the field of aerodynamics and relates to a tail thrust propeller design method considering the interference of fuselage wake. The method comprises the following steps: according to a boundary layer protection function, a relationship between the inflow velocity of the tail thrust and the radial position of the blade element is derived; and based on the relationship between the inflow velocity of the tail thrust and the radial position of the blade element, the optimal chord length and the optimal torsion angle of each cross-section airfoil of the tail thrust are calculated and derived by using a pull propeller design method.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of aerodynamics, and relates to a tail thrust propeller design method considering the interference of fuselage wake. BACKGROUND

[0002] The propeller provides forward power for the aircraft, and its efficiency is higher than that of the jet propulsion method in the subsonic speed range. The commonly used propeller is usually placed in the front part of the fuselage or wing, and pulls the helicopter forward, at this time, the inflow condition of the propeller is approximately uniform inflow, and the existing propeller aerodynamic design method is based on this assumption.

[0003] The design and performance calculation of the pull propeller are relatively mature at home and abroad. Gold-Stein proposed the vortex theory of the propeller, which laid the theoretical foundation for the design of the propeller. Black et al. proposed the design idea of the shrouded propeller, and carried out performance test. Angelo et al. proposed a maximum efficiency propeller design method for designing the optimal chord length and twist angle under given working conditions. Hu Ying et al. carried out aerodynamic design of the propeller according to the design requirements of a high-altitude airship propeller, and carried out numerical optimization of the chord length and installation angle of the propeller by the penalty function method. Cheng Yufeng et al. analyzed the aerodynamic performance of the high-altitude propeller, and obtained the variation law of the aerodynamic performance of the high-altitude propeller with the number of blades, propeller diameter, rotation speed and forward speed. SUMMARY

[0004] The present application provides a tail thrust propeller design method considering the interference of fuselage wake, which can quickly obtain the aerodynamic layout of the tail thrust propeller.

[0005] TECHNICAL SCHEME

[0006] The present application provides a tail thrust propeller design method considering the interference of fuselage wake, which can quickly obtain the aerodynamic layout of the tail thrust propeller.

[0007] According to the boundary layer protection function, the relationship between the inflow velocity of the tail thrust and the radial position of the blade element is derived;

[0008] Based on the relationship between the inflow velocity of the tail thrust and the radial position of the blade element, the pull propeller design method is used to calculate and derive the optimal chord length and optimal twist angle of the tail thrust cross-sectional airfoil.

[0009] Further, the expression of the relationship between the inflow velocity of the tail thrust and the radial position of the blade element is:

[0010] ;

[0011] Wherein, V is the inflow velocity, δ h is the nominal boundary layer thickness averaged in the circumferential direction, V0 is the circumferential average velocity at the outer edge of the boundary layer, r is the radial position of the blade element, and R0 is the hub radius.

[0012] Further, based on the relationship between the inflow velocity of the tail thrust and the radial position of the element, the optimal chord length and optimal torsion angle of the tail thrust section airfoil are calculated by using the pull force propeller design method, including:

[0013] For the i-th section of the blade along the radial direction of the blade, the Lagrange constant is calculated;

[0014] The actual inflow angle relative to the rotation plane, the induced angle of attack, and the dimensionless actual velocity are calculated, so as to calculate the Reynolds number of each station and the Mach number of each station;

[0015] By the Reynolds number of each station and the section Mach number of each station, the lift-drag characteristics of the i-th section airfoil are calculated when the chord length takes different b values, and the maximum lift-drag ratio (Cl / Cd) corresponding to the angle of attack of the i-th section at different b values is obtained , lift coefficient Cl max , and drag coefficient Cd max ;

[0016] The dimensionless chord length B is calculated by using the obtained , Cl max , and Cd max ; the difference value is calculated, and the b corresponding to the minimum difference value is the optimal dimensionless chord length of the i-th section, so that the actual chord length of the section is , the corresponding to the minimum difference value is the effective angle of attack of the i-th section, and the torsion angle of the i-th section is .

[0017] Advantages:

[0018] The tail thrust propeller design method can iteratively obtain a thrust propeller scheme that meets the design requirements. Through calculation and verification, the designed thrust propeller meets the thrust requirement under a given power, and the propelling efficiency reaches 86%. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a schematic diagram of element motion.

[0020] Figure 2 is an inflow velocity distribution diagram. DETAILED DESCRIPTION

[0021] Given the flight height, flight speed V, number of blades n, and required thrust T, in order to make the working efficiency of the thrust propeller highest under the premise of ensuring that the thrust meets the requirements, it is necessary to ensure that the energy loss is minimized. After selecting a suitable propeller special airfoil, the working efficiency of the propeller is highest by twisting the blades so that all the airfoils in the radial direction of the blades are in the maximum lift-drag ratio state.

[0022] The aircraft with tail propeller can fly at high speed, and the propeller rotates at high speed. The diameter of the propeller is determined by considering the design criteria and the tip Mach number limit. Figure 1 Velocity vector triangle of blade element motion.

[0023] The high-speed propeller blade design process is as follows:

[0024] 1) Determine the propeller inflow velocity distribution. The hub radius is R0, and the air flows from the head to the tail, and the boundary layer gradually thickens. According to the boundary layer protection function proposed by Menter in the DDES method, the inflow velocity can be written as:

[0025] (1)

[0026] Where δ h is the circumferentially averaged nominal boundary layer thickness, which can be obtained by computational fluid dynamics simulation of the fuselage at the design stage, V is the propeller inflow velocity distribution, V0 is the circumferentially averaged velocity at the outer edge of the boundary layer, and r is the radial position of the element.

[0027] 2) Divide the blade into m sections (m+1 sections in total), and determine the airfoil distribution along the radial sections of the blade.

[0028] 3) Calculate the Lagrange constant K.

[0029] 4) After calculating the Lagrange constant, calculate the chord length and twist angle of the blade. First, calculate the angle between the actual flow and the rotation plane .

[0030] 5) Calculate the induced angle of attack .

[0031] 6) Define the dimensionless actual velocity ; the dimensionless chord length b ranges from 0.005 to 0.21. Calculate the local Reynolds number and the local Mach number.

[0032] 7) Calculate the lift-drag characteristics of each section airfoil when the chord length takes different b values through the Reynolds number and the section Mach number at each station, and obtain the corresponding angle of attack , lift coefficient Cl max , and drag coefficient Cd max of the maximum lift-drag ratio (Cl / Cd) of each section at different b values. Use the above obtained , Cl max , and Cd max to calculate the dimensionless chord length B, calculate the difference , and take the minimum difference as the optimal dimensionless chord length of the i-th section. Then the actual chord length of the section is The minimum difference corresponds to The effective angle of attack of the i-th section is .

[0033] Repeat steps 4) - 7), and calculate the optimal chord length and optimal twist angle of each section of the high-speed propeller airfoil.

[0034] The main steps of the application are:

[0035] Step 1: Obtain the inflow velocity distribution of the tail thrust propeller by computational fluid dynamics simulation of the fuselage.

[0036] Step 2: Determine the overall parameters, and calculate the optimal chord length and installation angle under each section according to the overall parameters and airfoil configuration.

[0037] Step 3: The advanced propeller tip shape can overcome or delay the generation of shock waves, while reducing the propeller noise level, thereby improving the tail thrust performance. According to the design characteristics of high-speed tail thrust, the propeller usually adopts a swept-back or sabre-shaped propeller tip. The appropriate planform is determined according to the chord length distribution obtained by the above design.

[0038] Step 4: Build the geometric shape of the designed thrust propeller and calculate and evaluate its aerodynamic performance. Obtain the increase of fuselage drag caused by the interference of the propeller, and determine whether it meets the overall index requirements. If it meets the requirements, the thrust propeller design is reasonable; if it does not meet the requirements, return to steps 2-3, and reselect the overall parameters, determine the twist and chord length distribution, until the thrust propeller meets the design requirements.

Claims

1. A method for designing a tail thrust propeller considering the interference of the fuselage wake, characterized in that, Comprise: According to the boundary layer protection function, the relationship between the inflow velocity of the tail thrust and the radial position of the blade element is derived; Based on the relationship between the inflow velocity of the tail thrust and the radial position of the blade element, the optimal chord length and the optimal torsion angle of the tail thrust cross-section airfoil are calculated and derived by using the tension propeller design method; Specifically: For the i-th cross section of the blade along the radial direction of the blade, the Lagrange constant is calculated; The actual flow relative to the rotation plane, the induced angle of attack, and the dimensionless actual velocity are calculated, so as to calculate the Reynolds number of each station and the Mach number of each station; The lift-drag characteristics of the i-th cross section airfoil with different b values are calculated by the Reynolds number of each station and the cross section Mach number of each station, and the maximum lift-drag ratio Cl / Cd of the i-th cross section at different b values is obtained, and the corresponding attack angle α, lift coefficient Cl max , and drag coefficient Cd max ; Using the obtained a, Cl max , Cd max Calculate the dimensionless chord length B; Calculate the difference |B-b|, and take the minimum difference value corresponding to b as the optimal dimensionless chord length of the i-th section, then the actual chord length of the section is l i =bR, the minimum difference value corresponding to a is the effective angle of attack of the i-th section, then the twist angle of the i-th section is θ=δ+α; Alpha is the angle of attack, and delta is the angle.

2. The method of claim 1, wherein, The expression of the relationship between the inflow velocity of the tail thrust and the radial position of the blade element: where V is the inflow velocity, δ h is the tangentially averaged nominal boundary layer thickness, V0 the tangentially averaged velocity at the outer edge of the boundary layer, r the radial position of the blade element, and Ro the hub radius.

3. A computer-readable storage medium having stored thereon a computer program, characterized in that The computer program is executed by the processor to realize the method in any one of claims 1-2.

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