Abstract
This paper presents a 3-D Volume of Fluid method (VOF) applied for the flow in pool-and-weir fishways. In the 3-D VOF, 3-D incompressible continuity equation and Navier-Stokes (N-S) equations are solved incorporated with a convective equation of VOF function. The donor-cell scheme is employed to discretize the convective terms of N-S equations and the donor-accepter scheme characterizing the VOF is applied for discretization of the equation of VOF function. As for other spatial differencing terms, the second order central difference approximation is used. Two types of fishways are investigated; one is a pool-and-weir fishway with no notch and no orifice and the other is an ice-harbor fishway. Results from the former case demonstrated the numerical model used was able to reproduce two typical flow regimes, which are plunging and streaming modes, depending on the parameters. The ice-harbor fishway is a model of the fishway installed at Akaishi Second Headwork in Akaishi River, Aomori, Japan. Field observation of hydraulic structure was also conducted to obtain the data for validation of the numerical results. The numerical model was able to reproduce well the rapid flow over a notch and through an orifice. Circulating flow behind the non-submerged part of the baffle was also reproduced well. For further quantitative evaluation, modeling efficiency (EF) was introduced. The EF value made clear the longitudinal velocity component was reproduced better than transversal and vertical velocity components.
