Analysis Of Typical Flow Fields And Noise Characteristics Of Helicopter Rotor And Noise Control Investigation

Helicopters have unique advantages,such as vertical take-off and landing,hovering,and high maneuverability,which make them be widely used in military and civilian fields.However,the noise of helicopter greatly limites its application range,and low noise has become an important development direction of the new generation of helicopter technology.Carrying out related research has significant economic benefits and military values.Rotor blade-vortex interaction noise and high-speed impulsive noise are the main noise sources of helicopters and are closely related to the specific flow phenomena of rotor blades.The collision of the rotor blade tip vortex and the rear blade will produce strong blade-vortex interaction noise.When the helicopter is flying forward at high speed,the forward blade of the rotor is partially transonic.When the blade tip speed increases to a certain value,the blade surface shock wave"delocalizes" and generates high-speed impulsive noise.Numerical simulation research on the two typical flow/noise characteristics of rotor blade-vortex interaction and transonic flow is conducted,and corresponding flow control methods are developed,which not only has academic research value but also has important engineering significance.In this paper,the governing equation of flow field is the compressible NavierStokes equation.Spatial dispersion adopts Roe format.Time discretization adopts second order implicit method.The rotor rotation simulation uses slidding mesh technology.Turbulence simulation adopts DDES model based on Spalart-Allmaras.The rotor noise simulation uses the method of solving the FW-H equations.The cases of Caradonna-Tung,AH-1,and UH-1H rotors verify the correctness of the numerical method of rotor flow field/noise.In this paper,the numerical simulations of two typical flow/noise characteristics of rotor blade-vortex interaction and transonic flow are carried out.The directivities of blade-vortex interaction noise and high-speed impulsive noise are investigated,and subsequently the influences of flight status parameters on these two types of noise are investigated.The result shows that the balde-vortex interaction noise exhibits a pulse characteristic,and the direction of propagation is directional.Blade-vortex interaction noise dominates the obliquely downward direction of the rotor.When the blade tip Mach number is high,the blade tip shock wave "delocalizes" and shock wave disturbance propagates to the far field,which generates high-speed impulsive noise.High-speed impulsive noise is mainly concentrated in the direction of the rotor blade plane,and the bigger the angle from the paddle plane,the weaker the high-speed impulsive noise.As the blade tip Mach number increases,the high-speed impulsive noise also increases rapidly.The method of slotted tip is used to investigate the control of rotor blade-vortex interaction flow/noise and transonic flow/noise.The effects of slotted tip on blade tip vortex structure,blade-vortex interaction noise and aerodynamic performance are investigated,and the effects on the transonic flow and high-speed impulsive noise are studied.The result shows that the method of slotted tip can effectively weaken the strength of the blade tip vortex and accordingly accelerated the dissipation of the blade tip vortex,thereby reducing blade-vortex interaction noise.And it can also weaken the blade shock wave and reduce the high-speed impulsive noise.A numerical simulation is carried out in advance for the effects of active flaps on rotor flow/noise.The effects of the fixed flap on blade tip vortex structure,aerodynamic performance and noise characteristics are investigated.On this basis,the effects of the flap parameters such as angle,position and length are studied,which provides a reference for subsequent active flaps investigation.The result shows that the flap side edges can produce new vortex tubes.When the flap angle is small,the vortex generated by the flap side edge is weak.When the flap angle is large,the vortex strength of the flap side edge sharply increases.Therefore,the angle of the flaps should not be too large.When the flap is at the tip of the blade,the sound pressure level is lower than that of the inner flaps.The sound pressure level of the flap length of 0.1R is lower than that of the flap length of 0.2R.