Control of sonic jets by fluidic injection

Abstract

The present experimental study aims at investigating the effect of fluidic injection by means of air tabs on the core of circular and square sonic jets issuing from orifice at different levels of underexpansion. The experiments were conducted by varying the injection pressure ratio (IPR) from 3 to 5 for a fixed nozzle pressure ratio (NPR) 3, 4 or 5. Shadowgraph visualization was used to quantify core length of jet with and without fluidic injection. The injection in both circular and square sonic jets resulted in reduction of core length at all the NPRs. For each NPR, the maximum and minimum core length reductions occurred at IPRs 5 and 3, respectively, showing that the mixing promotion in circular or noncircular sonic jets is influenced by momentum of the injected jet. Among the NPRs, the reduction in core length was maximum at NPR 3 and minimum at NPR 5 for both circular and square jets at all the IPRs. The injection caused a highest reduction in the core of square jet than the circular jet all NPRs except NPR 5. A highest reduction of about 50% was achieved at NPR 3 and IPR 5 for square jet.