Numerical study of the flow through a contraction

Flow through contractions and other channel transitions can be seen at various locations of different kinds of drainage structures. At these transitions, a supercritical flow may occur, where the width varies, causes an additional force on the sidewalls due to a change in fluid flow, and a portion of the kinetic energy of the is converted into the potential energy of pressure. Shock waves are common in supercritical flow passing through a contraction and pose the risk of flow overtopping. To design a contraction, information regarding the effects of flow along the contraction geometry and details of the flow pattern is then needed.

In this work, we explore a sloped contraction flow numerically using VOF model within interFoam solver. In particular, its ability to define the supercritical flow near the wall deflection, the height and pattern of the generated shock wave and its reflection as well as the general waveforms along the contraction and the downstream sections, i.e., the definition of the three distinct waves already reported, in the literature for a straight-walled contraction: 1) downstream from the contraction point; 2) in the chute axis and wall, and 3) beyond the contraction end.

The CFD model was validated using experimental data measured at the hydraulic laboratory of the University of Coimbra, as it successfully reproduced the experimental data in the contraction. Experimental and Numerical data are also analyzed taking into account achievements already reached and published. Besides, a relation to water depth, Froude number and the force on the sidewall was developed.