Controlling Flow Separation over a Curved Ramp Using Vortex Generator Microjets

TL;DR

This study numerically investigates how microjet vortex generators can actively control flow separation over a curved ramp, demonstrating that multiple jets significantly reduce separation bubble size and separation zone length.

Contribution

It introduces a numerical analysis of microjet vortex generators for flow separation control, comparing single and multiple jets and their effects on flow parameters.

Findings

Three-jet array reduces separation bubble size by 2.75 times compared to a single jet.

Using jets decreases the separation zone length by up to 78%.

Positioning of jets significantly influences flow control effectiveness.

Abstract

Introducing a fluid microjet into the boundary layer to increase fluid momentum and hence delay separation is a method for actively controlling a flow separation region. The present work numerically analyzed the control of a separation bubble behind a ramp. For this purpose, we first verified the numerical results for a flow (without a jet) over the ramp against reliable experimental studies from the literature. Next, the effects of introducing a microjet to the flow were also verified. A jet was then placed at three different distances above the ramp to study its impact on various parameters, including velocities, Reynolds stresses, pressure, vorticity, streamlines, and the separation bubble size. As the jet was moved further back, the jet-induced upwash region grew considerably. Finally, the effects of using three identical jets were studied and compared against those of a single jet. The results indicated that using a three-jet array shrank the separation bubble. Using an array with d/D = 15 can limit laterally the separation bubble about 2.75 times smaller than a single jet in the z-direction. Also, the employment of the jet managed to decrease the length of the separation zone in the x-direction up to 78%, in the case of Lx/L1 = 0.0143 and d/D = 10.