  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.
