A study on backward facing step flow in low Reynolds number manipulated by synthetic jets - Effect of different jet velocities -

Abstract

This study presents the detailed structure of separated flow downstream of a backward facing step affected by a non-uniform periodic disturbance along spanwise direction induced by a synthetic jet array. The laminar channel geometry over a backward-facing step with an expansion ratio of 1.67 and with a step height of 4.0 mm was used in this study. The Reynolds number based on the step height ranged from 300 to 900. The frequency of the synthetic jet actuation was selected within the acceptance frequency range of separating shear layer. Periodic transverse vortices were generated changing their sizes and shapes corresponding to the strength of the disturbance by the synthetic jet array. The effect of different injection velocities in the jet array from those of adjacent jets on the transverse vortex structure and resulting reattachment process is discussed based on the wall shear stress measured by the Micro Flow Sensor (MFS) and flow visualization. Near wall behavior of the transverse vortex above the MFS was related to the sensor output. The results show that non-uniform injection velocity manipulated in the jet array induces remarkable difference in the distorted vortex structure and reattachment distribution in spanwise direction, which strongly depend on the Reynolds number and injection velocities of the synthetic jet array.

Keywords

• backward facing step
• low reynolds number
• synthetic jet
• transverse vortex
• reattachment process
• micro flow sensor