Turbulence measurement in nonuniform open-channel flow using acoustic Doppler velocimeter (ADV)

Measurements of the mean and turbulence characteristics in nonuniform open- channel flows were carried out using a 3D acoustic Doppler velocimeter. Bot h accelerating and decelerating flows were investigated. Analyses based on the Reynolds equation and the continuity equation of 2D open-channel flow s how that a flow will be in equilibrium if the pressure-gradient parameter b eta is a constant at different sections along the flow direction. The exper imental data show that all the flows investigated are in equilibrium. The e ffect of the flow nonuniformity on the mean velocity and turbulence profile s was also examined. The study shows that (1) the log law is still valid fo r both accelerating and decelerating flows in the inner region. The Goles l aw can be used for the entire region, but the wake-strength parameter Pi de pends on the beta -value; and (2) the turbulence intensities and the Reynol ds stress decrease in accelerating flow and increase in decelerating flow, when compared with those in uniform flow. Finally, using the Reynolds equat ion and the continuity equation of 2D open-channel flow, the theoretical ex pressions for the distribution of vertical velocity and the Reynolds stress have been developed. The measured vertical velocity and the Reynolds stres s profile compare well with the derived expressions.