Flow method and device

In a device for delivering a gaseous medium to utilization equipment having variable pressure conditions at its intake comprising, in combination, means defining a gaseous medium intake zone connecting with means defining a variable area throat zone for constricting the flow of the gaseous medium to increase the velocity thereof to sonic, means for adjustably varying the area of the throat zone in correlation with operating demands imposed upon the utilization equipment, wall means downstream from the throat zone arranged to provide a gradually diverging zone for efficiently recovering a substantial portion of the kinetic energy of the high velocity gaseous medium as static pressure whereby the velocity of the gaseous medium through the throat zone is sonic over a wide range of pressure conditions at the intake of the utilization equipment, the improvement comprising perforations in the wall means downstream and spaced from the throat zone and upstream and spaced from the exit of the gradually diverging zone, and passageway means behind the wall means interconnecting the perforations with the exit from the gradually diverging zone for recirculating a portion of the gaseous medium from the exit of the diverging zone to the perforations to thereby disturb the flow and shift the location of shock upstream from where it would otherwise occur to the location of the perforations when the pressure drop across the device is high.