Tail thrust paddle design method considering fuselage wake interference

Abstract

The invention belongs to the field of aerodynamics, and relates to a tail thrust paddle design method considering fuselage wake interference. The method comprises the following steps: deducing the relationship between the inflow velocity of tail thrust and the radial position of a blade element according to a boundary layer protection function; and on the basis of 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 section airfoil of the tail thrust are calculated and derived by adopting a tension paddle design method.

Description

Technical Field

[0001] The invention belongs to the field of aerodynamics and relates to a tail thrust propeller design method taking fuselage wake interference into consideration. Background Art

[0002] Propellers provide forward power for aircraft, and their efficiency is higher than that of jet propulsion in the subsonic range. Commonly used propellers are often placed in front of the fuselage or wing to pull the helicopter forward. At this time, the inflow condition of the propeller is approximately uniform inflow, and existing propeller aerodynamic design methods are based on this assumption.

[0003] The research on the design and performance calculation of thrust propellers at home and abroad is relatively mature. Gold-Stein proposed the vortex theory of propellers, laying the theoretical foundation for propeller design. Black et al. proposed the design concept of crowned propellers and conducted performance tests on them. Angelo et al. proposed a design method for the maximum efficiency propeller with the optimal chord length and torsion angle under given working conditions. Hu Ying et al. conducted aerodynamic design of the propeller according to the design requirements of a high-altitude airship propeller, and numerically optimized the chord length and installation angle of the propeller by the penalty function method. Cheng Yufeng et al. analyzed the aerodynamic performance of high-altitude propellers and obtained the variation law of the aerodynamic performance of high-altitude propellers with the number of blades, blade diameter length, rotation speed and forward speed. Summary of the invention

[0004] Purpose of the invention: To establish a tail thrust propeller design method that takes into account the fuselage wake interference, so as to quickly obtain the aerodynamic layout of the tail thrust propeller.

[0005] Technical solution: A tail thrust propeller design method considering fuselage wake interference is provided, including: 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 optimal twist angle of each cross-section of the tail thrust airfoil are calculated and derived using the pull propeller design method.

[0006] Furthermore, the expression for the relationship between the inflow velocity of the tail thrust and the radial position of the blade element is: ; Where V is the inflow velocity, δ h is the nominal boundary layer thickness averaged in the annular direction, V 0 The average annular velocity at the outer edge of the boundary layer, r is the radial position of the blade element, R 0 is the hub radius.

[0007] Furthermore, 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 each cross-section airfoil of the tail thrust, including: For the i-th section of the blade along the blade radial direction, calculate the Lagrange constant; Calculate the angle of the actual incoming flow relative to the rotating plane, the induced angle of attack, and the dimensionless actual velocity, and thus calculate the Reynolds number and Mach number at each station; By using the Reynolds number and the cross-sectional Mach number of each station, the lift-drag characteristics of the i-th cross-sectional airfoil with different chord length b values ​​are calculated, and the angle of attack corresponding to the maximum lift-drag ratio (Cl / Cd ) of the i-th cross-sectional airfoil with different b values ​​is obtained. , lift coefficient Cl max , Drag coefficient Cd max ; Using what you get , Cl max 、Cd max Calculate the dimensionless chord length B; calculate the difference , when the minimum difference is taken, the corresponding b is the optimal dimensionless chord length of the i-th section, then the actual chord length of the section is , the minimum difference corresponds to is the effective angle of attack of the ith section, and the torsion angle of the ith section is .

[0008] Furthermore, the calculation formula of the Lagrange constant K is: , In the formula , , Vt is the blade tip speed.

[0009] Furthermore, the angle The calculation formula is: ; For the forward ratio, is the dimensionless coordinate of the ith section, and ri is the radial position of the blade element of the ith section.

[0010] Furthermore, the induced angle of attack The calculation formula is: ; Dimensionless actual speed The calculation formula is: ; Interface Reynolds number at each station and the cross-sectional Mach number at each station The calculation formula is: ; Furthermore, the calculation formula of the dimensionless chord length B is: .

[0011] Beneficial effects: The present invention adopts the tail thrust propeller design method to iteratively obtain a thrust propeller scheme that meets the design requirements. Calculation and verification show that the designed thrust propeller meets the thrust requirements under a given power, and the propulsion efficiency reaches 86%. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of blade element movement.

[0013] Figure 2 is the inflow velocity distribution diagram. DETAILED DESCRIPTION

[0014] Given the flight altitude, flight speed V, number of blades n, and required thrust T, if the thrust propeller is to work at the highest efficiency, its energy loss must be minimized while ensuring that the thrust meets the requirements. After selecting a suitable propeller-specific airfoil, the propeller can work at the highest efficiency by twisting the blades so that all airfoils in the radial direction of the blades are in the state of maximum lift-to-drag ratio.

[0015] Aircraft equipped with tail thrust propellers may have high flight speeds and high propeller speeds, so the propeller diameter must be determined by comprehensively considering design criteria and blade tip Mach number limitations. Figure 1 The velocity vector triangle of the blade element motion.

[0016] The high-speed propeller blade design process is as follows: 1) Determine the propeller inflow velocity distribution. The hub radius is R 0 , 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: (1) in δ h is the nominal boundary layer thickness averaged in the annular direction, which can be obtained by computational fluid dynamics simulation of the fuselage during the design stage, V is the propeller inflow velocity distribution, and V 0 The annular average velocity at the outer edge of the boundary layer, r is the radial position of the blade element.

[0017] 2) Divide the blade into m sections (a total of m+1 sections) and determine the airfoil distribution of each section along the radial direction of the blade.

[0018] 3) Calculate the Lagrange constant K, the integral equation is as follows: , In the formula , , Vt is the blade tip speed.

[0019] 4) After calculating the Lagrange constant, calculate the chord length and torsion angle of the blade. First, calculate the angle between the actual incoming flow and the rotating plane. : , where For the forward ratio; is the dimensionless coordinate of the ith section, and ri is the radial position of the blade element of the ith section.

[0020] 5) Induced angle of attack Calculate as follows:

[0021] 6) Define dimensionless actual velocity Calculate as follows: ; The dimensionless chord length b ranges from 0.005 to 0.21. The local Reynolds number and local Mach number are calculated as follows: , where Re is the free stream Reynolds number, , ρ is the atmospheric density, μ is the atmospheric dynamic viscosity; Ma is the free stream Mach number, Ma=V / a, a is the speed of sound.

[0022] 7) By using this Reynolds number and the cross-sectional Mach number of each station, the lift-drag characteristics of each cross-sectional airfoil when the chord length takes different b values ​​are calculated, and the angle of attack corresponding to the maximum lift-drag ratio (Cl / Cd ) of each cross-sectional airfoil at different b values ​​is obtained. , lift coefficient Cl max , Drag coefficient Cd max . Using the above , Cl max 、Cd max Compute the dimensionless chord length: , calculate the difference |Bb|, and when the minimum difference is taken, the corresponding b is the optimal dimensionless chord length of the i-th section. Then the actual chord length of the section is , the minimum difference corresponds to is the effective angle of attack of the ith section, and the torsion angle of the ith section is .

[0023] Repeat steps 4)-7) to calculate the optimal chord length and optimal twist angle of each cross-section airfoil of the high-speed propeller.

[0024] The main steps of the present invention are: Step 1, obtaining the inflow velocity distribution of the tail thrust propeller by computational fluid dynamics simulation of the fuselage; Step 2: Determine the overall parameters, and calculate the optimal chord length and installation angle for each section based on the overall parameters and airfoil configuration.

[0025] Step 3: Advanced blade tip shapes can overcome or delay the generation of shock waves, while reducing blade noise levels, thereby improving tail thrust performance. According to the design characteristics of high-speed tail thrusters, blades usually adopt swept or saber-shaped blade tips, and the appropriate plane layout is determined based on the chord length distribution obtained from the above design.

[0026] Step 4: Construct the designed thrust propeller geometry and calculate and evaluate its aerodynamic performance. Obtain the increase in fuselage resistance caused by the propeller interference to determine whether it meets the overall index requirements. If it does, the thrust propeller design is reasonable; if not, return to step 2 to step 3, reselect the overall parameters, determine the torsion and chord length distribution, until the thrust propeller meets the design requirements.

Claims

1. A tail thrust propeller design method considering fuselage wake interference, characterized in that: include: 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 optimal twist angle of each cross-section of the tail thrust airfoil are calculated and derived using the pull propeller design method.

2. The method according to claim 1, characterized in that The expression for the relationship between the inflow velocity of the tail thrust and the radial position of the blade element is: ； Where V is the inflow velocity, δ h is the circumferentially averaged nominal boundary layer thickness, V0 is the circumferentially averaged velocity at the outer edge of the boundary layer, r is the radial position of the blade element, and R0 is the hub radius.

3. The method according to claim 2, characterized in that 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 optimal twist angle of each section of the tail thrust airfoil are calculated and derived using the pull propeller design method, including: For the i-th section of the blade along the blade radial direction, calculate the Lagrange constant; Calculate the angle of the actual incoming flow relative to the rotating plane, the induced angle of attack, and the dimensionless actual velocity, and thus calculate the Reynolds number and Mach number at each station; By using the Reynolds number and the cross-sectional Mach number of each station, the lift-drag characteristics of the i-th cross-sectional airfoil with different chord length b values ​​are calculated, and the angle of attack corresponding to the maximum lift-drag ratio (Cl / Cd ) of the i-th cross-sectional airfoil with different b values ​​is obtained. , lift coefficient Cl max , Drag coefficient Cd max ; Using what you get , Cl max 、Cd max Calculate the dimensionless chord length B; calculate the difference , when the minimum difference is taken, the corresponding b is the optimal dimensionless chord length of the i-th section, then the actual chord length of the section is , the minimum difference corresponds to is the effective angle of attack of the ith section, and the torsion angle of the ith section is .

4. The method according to claim 3, characterized in that: The calculation formula of Lagrange constant K is: ， In the formula , , Vt is the blade tip speed.

5. The method according to claim 4, characterized in that Angle The calculation formula is: ； For the forward ratio, is the dimensionless coordinate of the ith section, and ri is the radial position of the blade element of the ith section.

6. The method according to claim 5, characterized in that Induced angle of attack The calculation formula is: ； Dimensionless actual speed The calculation formula is: ； Interface Reynolds number at each station and the cross-sectional Mach number at each station The calculation formula is: 。 7. The method according to claim 6, characterized in that The dimensionless chord length B is calculated as: 。 8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 7 is implemented.

Images