Controlling flow separation over a curved ramp using vortex generator microjets

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 steady-state 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 (distance between microjets over microjet diameter) 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 L-x/L-1 = 0.0143 (longitudinal distance of microjet from above the ramp over ramp length) and d/D = 10. Published under an exclusive license by AIP Publishing.

Automated summary

This study numerically analyzed the control of a separation bubble behind a ramp by introducing a fluid microjet. The results showed that the microjet could effectively reduce the size of the separation bubble, and using a three-jet array had a better performance compared to a single jet.