Multi-point measurement techniques used in the study of separated flows

A rake of flying crosswire probes as well as several stationary hot-wire probes has been used to examine the spatial and temporal evolution of the backward facing step flow. The back-step flow is a fundamental separated turbulent flowfield, many complex separated flow geometries can be modeled using the backstep flowfield. A greater understanding of the flow physics of fundamental separated flows can lead to more efficient schemes for controlling the characteristics of this class of flow. Two hotwire experiments were conducted, the first experiment used flying rakes of hotwire probes to measure the time averaged spatial correlations. The second experiment used stationary hot-wire probes to capture temporal information at certain locations in the flow. Proper Orthogonal Decomposition (POD) was used as an unbiased technique for extracting structures from this coherent flow. This technique decomposes the flow into modes on an energy weighted basis. The kernel of this technique is the two point correlation tensor. POD is a very robust technique for extracting spatial information about the flow. Linear Stochastic Estimation (LSE) can be used to estimate the flowheld at certain locations within the integral scale given the two-point spatial correlation tensor, and temporal information at known positions within the flowheld. The two techniques’can be combined to yield an experimental low dimensional model of the flowheld. The coefficients of this model can be used in a physics based control scheme.