Characterizing the influence of upstream obstacles on very low head water-turbine performance

Abstract

ABSTRACTThe effect of an upstream obstacle – a backward-facing step (BFS) – on a very low head (VLH) water-turbine model has been investigated. The motivation of this study was to quantify the interaction between the VLH turbine and BFS, an abstraction of typical obstacles present in existing channels. Power measurements were obtained for three configurations; the turbine in the absence of the BFS was first examined as a baseline test, followed by configurations with the BFS placed at distances of half a turbine diameter and one turbine diameter upstream. It was found that turbine efficiency is comparable between the case with no step upstream and when the step is placed at one diameter. However, the configuration at half a diameter exhibited an efficiency deficit of approximately 7%. Particle image velocimetry measurements were then used to quantity the flowfield associated with loss in efficiency from the no step to the half a diameter step configuration. It was determined that the losses could be attributed to a highly non-uniform inlet velocity profile, which results in unsteady loading across the turbine blades.