A Semiempirical Noise Modeling Method for Helicopter Maneuvering Flight Operations

Abstract

A new model for Blade-Vortex Interaction noise generation during maneuvering flight is developed in this paper. Acoustic and performance data from both flight and wind tunnels are used to derive a non-dimensional and analytical performance/acoustic model that describes BVI noise in steady flight. The model is extended to transient maneuvering flight (pure pitch and roll transients) by using quasisteady assumptions throughout the prescribed maneuvers. Ground noise measurements, taken during maneuvering flight of a Bell 206B helicopter, show that many of the noise radiation details are captured.

Fundamental investigation using active plasma control to reduce blade–vortex interaction noise

“…The path of the tip wake-vortex is computed using the equations mentioned by Greenwood et al 43,44 and are plotted in Figure 22. The vortices that are shed from two blades are shown in different colors in Figure 22 for a vehicle moving forward in the x direction.…”

“…The third major effort involved is predicting BVI noise from the wind tunnel experiments and CFD simulations. For this purpose, we modify the BVI noise model of Greenwood et al 43,44 with a modified vortex strength model, dependent on the plasma actuators and given flight conditions. BVI noise is most sensitive to the vortex strength, Γ, its radius, and its path through the rotor.…”

“…We now describe the BVI noise prediction model and its implementation. Our model is based on a slightly modified form of the Fundamental Rotorcraft Acoustic Modeling from Experiments (FRAME) technique developed by Greenwood et al 43,44 The BVI noise is calculated by coupling a wake-vortex model with the Ffowcs Williams and Hawkings 48 (FWH) solver. The wake-vortex model predicts the alteration of pressures on the blades during descent, which corresponds to maximum BVI noise cases.…”

“…The position of the wake-vortex and its strength is based on the combined freestream flow and prescribed inflow distribution over the rotor. The path of the tip vortex location is ascertained using the same equations mentioned by Greenwood et al 43,44 Various empirical coefficients are involved in predicting the path of the tip vortex. These coefficients are calibrated using the experimental measurements.…”

“…The non-dimensional swirl velocity is calculated using the Vatistas et al 57 model asThe velocity perturbations on the rotor cause unsteady aerodynamic loading effects on the rotor blade. The unsteady aerodynamic loading effects are accounted for by using a two-dimensional incompressible indicial aerodynamics method by Greenwood et al 43,44 A simplified approach using Bernoulli’s equation is implemented in the current work.…”