Comparison of Simple and Conditional Averaging Methodology Based on Results of the HART II Wind Tunnel Test

Abstract

Based on test results of the Higher Harmonic Control Aeroacoustic Rotor Test (HART II), performed in the German/Dutch wind tunnel (DNW) in 2001 the conditional averaging methodology is shown to be mandatory to proper average essentially periodic data that are biased by spatial scatter and time jitter effects which are always present in both flight and wind tunnel test. The differences between conditional and simple averaging are demonstrated for various data of different physical origin. There are investigations with respect to the body and blade motion, measured optically by using Stereo Pattern Recognition (SPR), blade surface pressures, continuously measured by absolute pressure transducers, acoustic data obtained by microphones, and tip vortex flow field data, instantaneously measured by means of Stereo Particle Image Velocimetry (3C-PIV or SPIV).