Turbulence characteristics in rough non-uniform open-channel flow

Laboratory experiments on the turbulence structure of rough, non-uniform open-channel flow are reported. Velocity, turbulence-intensity and Reynolds-stress profiles were measured. It was found that: (a) non-uniform flow can be parameterized by using an equilibrium pressure-gradient parameter defined as β = (D/τ0)(&partp*/&partx); β = -1 for uniform, β -1 for decelerating flow; (b) the universal law of the wall explains the inner-region data; in the outer region, the data follow the Coles' law of the wake, whose Π-values depend on the pressure-gradient parameter β; (c) the turbulence intensities u′/u* and v′/u*, as well as the Reynolds stress -ufvfu*2 decrease in accelerating and increase in decelerating flows (compared with the ones in uniform flow); (d) the eddy viscosity vt/δu* decreases in accelerating and increases in decelerating flow; (e) the energy spectra for non-uniform flow are essentially the same as for uniform flow and display the inertial sub-range characteristics.