Experimental and numerical investigation of supercritical flow in contraction and expansion of open channels

Shock wave formation is very important in studies of supercritical flow. Based on increasing water height more than inlet flow depth, spreading over a wide range of downstream channel and making disturbances in water surface, formation and propagation of these waves are unfavorable in engineering. The present paper is an attempt to study the supercritical flow in contraction and expansion, and wave formation patterns. In this regard, the height and instantaneous velocity at different points of shock waves in contraction and free-surface wave profiles in expansion were measured for four different Froude numbers. In order to 3D simulation, turbulence models of k-e RNG and RSM based on Fluent software were used. For calculating free-surface wave profiles using the k-e RNG and RSM models, the mean relative errors were obtained as 30.3% and 98.2% in contraction: 13% and 2.58% in expansion, respectively. Also, the mean relative errors of the k-e RNG and RSM models for wave velocity computation of contraction were calculated as 5.26% and 2.87%, respectively. The results indicated that RSM turbulence model performs better than k-e RNG in simulating velocity profiles of shock waves.