Empirical scaling analysis of supersonic jet control using steady fluidic injection

Following our previous work [Kumar et al., “Fluidic injectors for supersonic jet control,” Phys. Fluids 30(12), 126101 (2018)], we experimentally investigate the effect of fluidic injection on the mixing enhancement of a Mach 2.0 jet. The mass flow rate ratio Cm of the injectors to that of the main jet and the expansion ratio pe/pa (where pe and pa are the nozzle exit and atmospheric pressures, respectively) to understand the mixing capability at design and off-design conditions are examined in detail. Extensive Pitot pressure measurements are performed along the jet centerline, and the jet stream has been visualized using the shadowgraph technique in the orthogonal planes of the manipulated jet. The mixing capability of the manipulated jet quantified based on the reduction in supersonic core length ΔLc* exhibits a strong dependence on Cm and pe/pa. Empirical scaling analysis of the jet control reveals that the relationship ΔLc* = f1(Cm, pe, pa, D, d) may be reduced to ΔLc* = f2(ξ), where f1 and f2 are different functions and the scaling factor ξ = MRpe/pa(Dd)1.3, where MR is the momentum ratio of the injector to the main jet, D and d are the nozzle exit diameter and the injector exit diameter, respectively. The scaling parameter ΔLc* = f2(ξ) provides important insights into the jet control physics.