Feedback control for drag reduction on a bluff body with a blunt trailing edge

Abstract

The objective of the present numerical study is to increase the base pressure on a backward-facing step via a simple feedback control method; to be ultimately translated to a drag reduction on a blunt-based blu body representative of a road vehicle. Two cases are considered: a simpli ed 2D ow at low Reynolds number and a fully turbulent 3D ow at a Reynolds of Re = 1500, deemed su cient to be representative of automobile applications. Using Large Eddy Simulation (LES), system identi cation is performed to characterize the ow response to actuation. The control is e ected by a full-span slot jet, with zero-net-massux, located near separation and injecting at an angle of 45 . In the two cases, a broad range of frequencies is tested with harmonic inputs. The 2D and 3D ows are found to respond di erently to actuation, yielding open-loop responses with di erent dynamics. The open-loop characterization is used to synthesize a feedback controller. The control target is set to the instantaneous pressure uctuations on the base of the step, which in turn is expected to give a reduction in time-mean pressure. For both the 2D and 3D cases, a substantial pressure increase, and hence drag reduction, is obtained with a simple controller based on disturbance attenuation.