CFD/CSD INVESTIGATION OF BVI NOISE REDUCTION USING HARMONIC ACTIVE TWIST CONTROL

摘要

Numerical predictions of the acoustic characteristics of an Active Twist Rotor (ATR) using a loosely coupled Computational Fluid Dynamics (CFD)/Computational Structural Dynamics (CSD) method are presented. The method utilizes the CFD code OVERFLOW2 to compute the rotor blade aerodynamics and the comprehensive code CAMRAD Ⅱ to predict the elastic blade motion for the ATR. The resulting aerodynamics and blade motion results from this method are then used in the acoustics code PSU-WOPWOP to predict acoustic pressures on a horizontal flat plane of observers located 1.1 rotor diameters beneath the rotor. The distribution of acoustic pressure on the observer plane is used to compute the blade-vortex interaction sound pressure level (BVISPL) representing baseline and actuated conditions. This CFD/CSD method was validated in previous work, and is not used to examine the influence of active twist upon BVI noise reduction. This paper examines a single flight condition of a helicopter in descending flight. The results identify three primary sets of active-twist control inputs which result in the largest decrease in the maximum BVISPL on the observer plane relative to the baseline maximum. Further analysis indicates that the reductions in BVI noise on the observer plane are due to a number of factors - modified rotor disk airloads, changes in the orientation of the vortex relative to the rotor blades, the rate at which the wake is convected away from the rotor, and the induced velocity - all of which have been modified as a result of using active-twist control.