3D CFD modelling of water flow in the sand trap of Khimti Hydropower Plant, Nepal

A three-dimensional numerical model was used to compute the water velocities in a sand trap. The numerical model solved the Navier-Stokes equations on a three-dimensional non-orthogonal finite volume grid. The SIMPLE method was used to compute the pressure, and the k-epsilon model was used to calculate the turbulence. The computed velocity profiles were compared with the measurements in the physical laboratory model. Good agreement was found using the first order Power-Law Scheme together with Strickler-Mannings roughness coefficient of 75. Higher or lower roughness coefficients caused more deviation between computed and measured velocities. The first-order scheme gave significantly better results than the second-order upstream scheme, which predicted a non-uniform profile with a jet along the bed and the side walls. This may be due to over/undershoots of the second-order scheme.