A series of numerical parametric studies on active control of separation flow over a hump model are presented. The model is a generic model for both internal and external flow

designated by NASA for CFD validation of active separation control.The focus is on the influence of steady suction and injection when a variety of operating parameters are varied.An in-house-use CFD code is first validated against experimental data and other CFD results

followed by a series of numerical simulations.Results show that the behaviors of steady suction are significantly different from that of steady injection.At the given geometry

the suction alone cannot completely eliminate the separation bubble in the flow-field of the hump model regardless of how much suction flow rate is used

but the injection can.The detailed flow structure and mechanisms are also presented and discussed.