A Combined Spatial and Temporal Decomposition of the Coherent Structures in the Three-Dimensional Wall Jet

Abstract

The organized vortical motions in a turbulent three-dimensional wall jet formed using a long rectangular channel with aspect-ratio Ar = 4 were examined using 15 instantaneous measurements of the ∞uctuating wall pressure across the jet in conjunction with point measurements of the turbulent velocity fleld. The Linear Stochastic Estimation (LSE) technique was used to predict the streamwise and lateral turbulent velocity components in the near and intermediate fleld of the wall jet using the instantaneous wall pressure measurements. The wall pressure flelds were spatially flltered in the lateral direction using the Proper Orthogonal Decomposition (POD) technique and the velocity flelds associated with the contribution of the flrst two POD modes were then examined. In this ∞ow, the spectral LSE technique yields signiflcantly more information about the passage of the structures in the ∞ow than commonly used \one-time LSE techniques. By high and low pass flltering the spatially decomposed ∞uctuating pressure fleld and using the spectral LSE technique, structures with difierent time-scales could be examined. It was determined that there are two difierent types of structures in the intermediate fleld of this jet, a large asymmetric horseshoe type structure and a near wall structure near the center of the jet.