Author(s): M. Martinez; Y. Ni~No
Keywords: Open channel contractions; Supercritical flow; Cross waves; Numerical models; Computational Fluid Dynamics
Abstract: This article compares the usual methods in the design of contractions in supercritical open channel flows with the capabilities of Computational Fluid Dynamics (CFD). Contractions in supercritical flow channels generate cross waves in the flow, which can greatly increase the runoff height at the point they are generated and downstream, due to the propagation of these waves. The usual analytical methods to determine the runoff height in contractions in supercritical flow underestimate the height for Froude numbers greater than 6, according to previous experiments, because these methods do not consider the conservation of momentum in the vertical direction, but only in the horizontal directions. Numerical modeling in three dimensions is presented as a support to the design of contractions in supercritical flow channels, since there are no limitations to the usual methods. The modeling is done using the ANSYS-CFX software of several scenarios, which were tested in previous experiments, obtaining results consistent with the observations made. The values obtained for the numerical simulations compared with experimental data, present a maximum error of 5.3%, delivering a better approximation than the analytical methods analyzed. For Froude numbers greater than 6, the flow is strongly governed by vertical accelerations, which makes the approximations made by the analytical methods studied ineffective. Therefore, the numerical simulation delivers results closer to the experimental ones when considering momentum conservation in the three directions. Thus, it is convenient to use numerical modeling for the design effects of contractions in supercritical flow channels with Froude numbers greater than 6.