Unsteady behavior in forced ow over a backward-facing step

Camila Chovet (1) , Marc Lippert (1) , Laurent Keirsbulck (1) , Jean-Marc Foucaut (2)

1 LAMIH - Laboratoire d'Automatique, de Mécanique et d'Informatique industrielles et Humaines - UMR 8201
2 LMFL - Laboratoire de Mécanique des Fluides de Lille - Kampé de Fériet

The unsteady behavior of a turbulent ow over a backward-facing step was investigated under controlled actuation at a Re h = 31500. Initial measurements were made changing the periodic forcing frequency St a from 0.045 to 0.453. The best forcing frequency was observed at a dimensionless frequency of St a = 0.226 and is associated with the shedding frequency. This frequency can eectively reduce the reattachment length and thus the recirculation area. A further study of the dynamical aspects of the un-actuated and actuated ows is also presented. The velocity elds were measured using a particle image velocimetry (Piv) system. Pod techniques were used to analyze the ow. With this procedure, the pressure uctuation power spectra was separated in 5 dierent modes. The two rst modes contained a predominant peak at around 0.12 corresponding to the apping motion (low frequency of the large scale structures). The other modes (from 3 to 5) showed a transitional and increasing peak that is related to the shedding phenomena. Results suggest that an excitation on the shedding frequency leads to a decrease of the external separation length L r , an increase of the internal separation length X r and a further decrease of the recirculation area.

Domaines: Physique [physics]; Sciences de l'ingénieur [physics]; Milieux fluides et réactifs

Camila Chovet, Marc Lippert, Laurent Keirsbulck, Jean-Marc Foucaut. Unsteady behavior in forced ow over a backward-facing step. Flow, Turbulence and Combustion, 2019, pp.145-165. ⟨10.1007/s10494-018-9944-0⟩. ⟨hal-02877329⟩