Flow separation in diffusers leads to loss in energy recovery and is o
ften a source of unsteadiness due to stall movements. This paper inves
tigates the use of wall jets as a remedy to these problems. New jet ge
ometries are compared to the conventional annular blowing. Steady wall
jets are found to be capable of raising the mean pressure recovery in
both conical and rectangular air diffusers, but high injected mass fl
ow rates are required before the flow in rectangular diffusers becomes
steady. Active feedback control is applied to reduce this flow unstea
diness. To implement the control, the air supplied through the wall je
ts is modulated in response to the unsteady pressures within the diffu
ser. Results are presented for two feedback mechanisms. Both are found
to be effective with the level of attenuation well predicted by theor
y. A combination of steady and unsteady blowing is found to be capable
of giving both a good mean pressure recovery and reduced pressure osc
illations.