Reliable and Accurate Prediction of Three-Dimensional Separation in Asymmetric Diffusers Using Large-Eddy Simulation

Abstract

Reynolds-Averaged Navier-Stokes (RANS) calculations and Large-Eddy Simulations (LES) of the flow in two asymmetric three-dimensional diffusers were performed. The numerical setup was chosen to be in compliance with previous experiments. The aim of the present study is to find the least expensive method to compute reliably and accurately the impact of geometric sensitivity on the flow. RANS calculations fail to predict both the extent and location of the three-dimensional separation bubble. In contrast, LES is able to determine the amount of reverse flow and the pressure coefficient within the accuracy of experimental data.

Three‐dimensional vortex simulation of unsteady flow in hydraulic turbines

“…Examine the positions of the blobs and sticks, delete blobs entering the boundary layer and execute the transition from stick to blob. (2) Solve Equation (14) to satisfy the no-flux boundary condition and obtain the potential function.…”

“…Reynolds averaged Navier-Stokes (RANS) equations can make quick analyses for many turbine operating points; turbulent viscosity models, usually k " models, are applied to describe the complex character of a fluid through hydraulic turbines [5][6][7]. RANS is effective in the steady simulations of the flow, but there are some theoretical imperfections because 3D vortex methods in solving vortical flows makes us seek out an alternative numerical method to solve the unsteady viscous flows in hydraulic turbines, which is completely different from RANS [5][6][7] and LES simulations [8,14].…”

“…B. ZHU ET AL.RANS equations are used to simulate the unsteady flows through the hydraulic turbines. LES can produce good results about unsteady flows in many applications [8,14], but its usages are confined because of its steep resource requirements [15]. Moreover, DNS requires huge computational resources making it unavailable for engineering purposes [16].…”

Three‐dimensional vortex simulation of unsteady flow in hydraulic turbines

“…RANS is effective in the steady simulations of the flow, but there are some theoretical imperfections because RANS equations are used to simulate the unsteady flows through the hydraulic turbines. LES can produce good results about unsteady flows in many applications , but its usages are confined because of its steep resource requirements . Moreover, DNS requires huge computational resources making it unavailable for engineering purposes .…”

“…On the other hand, since Chorin proposed the vortex blob model , modern vortex methods have developed and have been applied for the analysis of vortical flows and simulation of unsteady flows in the engineering fields with high resolution. The maturity of the BEM in solving potential flows and the 3D vortex methods in solving vortical flows makes us seek out an alternative numerical method to solve the unsteady viscous flows in hydraulic turbines, which is completely different from RANS and LES simulations .…”