Numerical Analysis for Active Control of Drag over Flat Plate Using Sinusoidal Travelling Wave Method

The drag is present due to flow around bodies such as vehicles, aircraft, bullet trains or ships etc. It plays a significant role in vehicle performance, rate of fuel consumption and stability. This drag depends mainly on flow, fluid and surface properties. Different methods are used for drag reduction like controlling surface roughness and injecting long-chain polymers etc. In the current research, a method based on the generation of a spanwise mean velocity gradient in a flat plate boundary layer by applying a sinusoidal travelling wave in the spanwise direction before the transition to turbulence occurrence is used for the drag reduction purpose. A solver is developed using the open-source CFD software OpenFOAM libraries. It consists of routines for generating synthetic isotropic homogeneous turbulence at the inlet plane of the channel flow and solving the Navier Stokes equations using the Monotonically Integrated Large Eddy Simulation method (MILES). The implemented inlet boundary condition showed improvements in the predictions of turbulence structures within a streamwise distance of approximately 5 times the half channel height (δ) from the inlet plane, a shorter distance than the other similar previous boundary conditions can predict. These improvements resulted in a considerable reduction in overall channel length required for numerical simulations and hence reduction in the associated computation costs. In addition, a prediction method for getting the required friction Reynolds number for setting up any simulation case is been developed and verified. The MILES solver and the inlet boundary condition are used together to generate the bypass transition through the channel flow. A travelling sinusoidal wave in the spanwise direction is applied by the effect of blowing and suction from the bottom wall of the channel before the bypass transition occurrence. This travelling wave leads to a drop in the value of the skin friction coefficient which means a drop in the drag. This may be due to the increase of the mixing effect of the eddies and the induced streamwise travelling wave. The bypass transition onset also appears to be delayed when an inclined sinusoidal wave is applied in the streamwise direction. However, grid independence was not thoroughly tested in this study.