Optical Methods for Data Processing in Heat and Fluid Flow

17

Application of Particle Image Velocimetry to Helicopter Vortex Interactions

R B Green and C J Doolan

Abstract

This Chapter presents flowfield measurements of a simulated helicopter tail rotor/main rotor vortex interaction using a particle image velocimetry (PIV) technique with a transverse vortex generator in a wind tunnel. The generated vortex passes a fixed blade, which has its axis nominally orthogonal to the vortex. The PIV technique uses two PIV systems that allow individual vortices to be tracked as they pass over the blade, and this helps to isolate the details of the blade-vortex interaction. Close to the blade surface a significant radial flow out of the vortex core was observed which led to distortion of the vortex. In addition a ridge of oppositely signed vorticity to the vortex was observed which is thought to be the result of the interaction of the vortex and blade boundary layer.

17.1 Introduction

Blade vortex interactions (BVI) are a source of unwanted noise and vibrations in rotorcraft (1). In this fluid dynamic event, the tip vortex generated from a main rotor blade can interact with either a following main rotor blade or travel downstream and collide with a tail rotor blade. In a tail rotor interaction, the vortex approaches the blade with their axes nominally orthogonal (Fig. 17.1) and the vortex is eventually cut by the blade. There has been much recent interest in the orthogonal interaction. This has included analytical (2, 3) numerical (4, 5) and experimental ...