Dye Visualization and P.I.V. in the Cross-Stream Plane of a Turbulent Channel Flow

Abstract

Illuminating in a quasi-cross-stream plane of an open channel flow of water at low Re and injecting fluorescene dye from a bed slit, mushroom patterns reliably inferred to result from counter-rotating streamwise vortices are found to be typically oriented at some 30° from the cross-stream vertical. PIV in the cross-stream plane shows that the averaged field, and two-point correlation, of the quantity \({Q_x} = \left( {\omega _x^2 - S_x^2} \right)/2,\left( {{S_x} = \frac{{\partial v}}{{\partial z}} + \frac{{\partial w}}{{\partial y}}} \right)\) exhibit preferred directions in the cross-stream plane at about 45 degrees to the vertical. Spatio-temporal measurements of streamwise vorticity provide direct experimental evidence, possibly the first, for the staggered arrangement of streamwise vortices previously educed from DNS data.