Large eddy simulation of vortex flow in intake channel of hydropower facility

Three-dimensional unsteady flow in the intake channel of a small-scale hydroelectric power facility has been simulated numerically using a large eddy simulation technique. The basic numerical method is the highly simplified MAC iteration method modified for the free-surface flow. The standard Smagorinsky model with near-wall damping and correction for irrotational strain was used to evaluate the sub-grid scale stresses. Using the numerical grid that marginally resolves the near-wall flow of laboratory-scale Reynolds number, the complex and unsteady nature of the vortical flow can be reproduced well. The free-surface depression associated with the formation of a free-surface vortex and its time development, which have so far been difficult to be reproduced numerically, are particularly well captured. The present study shows that this method is relevant for predicting the intake flows with possible air entrainment.