Modelling and Numerical Simulation for Flow Control

Abstract

This study deals with numerical prediction through Improved-Delayed-Detached-Eddy Simulation of the separating-reattaching flow over a backward-facing step and the manipulated flow with harmonic actuation for investigating the mechanism of reattaching acceleration. The predicted base flow agrees well with the experimental results in terms of both the time-averaged sense and the spectra content. Mode decomposition analyses, including Proper Orthogonal Decomposition and Dynamic Mode Decomposition are applied to the base flow data to extract the salient coherent structures, that is, shear layer mode and shedding mode. Then the base flow is excited with slot-shaped harmonic actuators with different excitation amplitudes and frequencies corresponding to those of the salient coherent structures. The flow data are analyzed with Triple Decomposition Technique to recognize the excited flow due to the actuation. We find that the reattachment is accelerated under the excitation of shear layer mode, while a significant promotion obtained under the excitation of vortex pairing. A better understanding of the separating-reattaching flow is presented and the mechanism of reattaching acceleration is finally proposed.