Initiation, evolution and global consequencies of coherent structures in turbulent shear flows

Experimental and numerical methods of studying of turbulent shear flow in order to both understand and manipulate turbulence are explored. Computer simulation of turbulent flows encompasses techniques of short exposure visualization, analysis of multi-probe signals, pattern recognition, and a complex two-point cross power spectral density analysis. It is noted that periodic stimulation of the flow has permitted strengthening and stabilization of coherent flow structures. An experiment involving acoustic excitation of a channel flow over sandpaper is described. Equal excitations were observed with all applied frequencies, as was widening of the flow. The effects of the boundary conditions on flow development are detailed as an aid to elimination of experimental error. Excitation of a turbulent flow is noted to delay three-dimensional decay and reduce the fluctuation strength in the region.