2-D simulation of flow structures over dunes for flow characteristics estimation

Abstract

Rivers have undulated beds, which are called bedforms. Depending on the hydraulic conditions, the bedforms have different types that cause resistance in the flow. Despite various research and experiments on bedforms, the topic is still debatable and requires further research. The present study is mainly focused on simulating the flow motion numerically on dunes in open channels to evaluate the effect of dune geometry on flow structure. Twenty-nine simulations were conducted to study the effect of the geometry of five types of dunes with different angles and heights under different hydraulic conditions and bed roughnesses. RANS and DES turbulence models were used to simulate small and large-scale dunes, respectively. The results of the numerical model were compared with the experimental results of previous researchers to validate the work, indicating the appropriate accuracy of the numerical model. Then, an empirical equation was adopted to evaluate the effect of dune geometry on flow hydraulics by considering the equations of previous researchers. Finally, sensitivity analyses were carried out to determine the dependence of each parameter in this equation.