Experimental Study of Flow past a Warped Transition

Abstract

Irrigation networks use a warped transition to connect a narrow rectangular channel section with a relatively wide trapezoidal earth-channel section. The flow through the transition often separates from its sidewalls. This can cause significant head losses and increase the risk of eroding the downstream channel, which is undesirable. This paper experimentally investigates the use of a single vane and three vanes located in the warped transition to reduce flow separation. Laser Doppler anemometry measurements of flow velocity were obtained and used for the determination of three-dimensional flow parameters, including the longitudinal flow profile, energy loss in the transition, and maximum velocity in the transition exit flow. The details of flow separation, turbulence intensity, and secondary flow characteristics were studied. The experimental results indicated that the three-vane system was the most efficient transition case, producing such desirable characteristics as flow uniformity, the reduction of secondary flow intensity, and the reduction of maximum velocity in a short reach of the downstream channel. The improvements of the flow characteristics in vane systems are attributed to the effective reduction of flow separation and hence the energy loss. The findings from this experimental study have a direct application to the design of efficient irrigation channels.