RECONSTRUCTING THE FLOW IN THE WALL REGION FROM WALL SENSORS

In this paper we examine how the flow in the wall region can be predic ted from realistic (partial) measurements. The underlying motivation o f this study is the improvement of control schemes for near-wall flows . We propose a method based on the proper orthogonal decomposition whi ch provides estimated amplitudes for the coherent structures (i.e., th e large scales) of the flow from wall measurements. The method is test ed for the direct numerical simulation of a minimal flow unit. The lar ge scales obtained by reconstruction from wall data are compared to th ose of the velocity field in the wall layer. The dominant structures - the streamwise streaks - are well recovered, the cross-stream motions less so since they are associated with higher-order structures unacco unted for in our truncation. We defined ''rescaled'' eigenfunctions to try to improve the representation of the cross-stream components of t he how. Aliasing effects due to realistic (large) sensor spacings were examined. We find that the spanwise spacing is the limiting factor fo r the estimation, so that a realistic grid will affect the reconstruct ion by at least 20% compared to full wall information. (C) 1998 Americ an Institute of Physics.