TWO PHASE FLOW MODELING IN SHAFT-SPILLWAYS USING VOLUME OF FLUID (VOF) METHOD

In this paper, the optimum inlet shape of morning-glory spillway is discussed. The
effect of some parameters including maximum discharge coefficient and minimum possibility
of cavitation (cavitation index) are investigated. For this purpose, using computational fluid
dynamics (CFD) in the form of finite volume method, 3D Navier-Stokes equations of flow at
different inlet shapes are solved. Free water surface is modeled by water-air two phase flow
and equations are solved by volume of fluid (VOF) method. Flow turbulence is modeled by
“K-Є model”. Based on experimental results, models are verified and discharge, velocity,
pressure and cavitation index for different inlet shapes are computed and compared with each
other. The morning-glory spillway inlet is modeled using different types of equations
including WAGNER equation (Y=aX^3.88), CREAGER equation (Y=aX^1.87) and circular
form for their funnel profile shapes. In each model changing the head (h) versus discharge (Q)
diagram is drawn and results are compared.