Investigation on flows in a supersonic isolator with an adjustable cowl convergence angle

• A special isolator configuration provides unsymmetrical incoming flow condition.
• The cowl convergence angle can be adjusted for studying its effects on isolator starting.
• A blockage degree adjustor is installed to simulate the impacts of reverse pressure from the exit.
• Turbulent boundary layer, separation, Mach disk, slip lines and shock waves are revealed by NPLS (Nano-tracer Planar Laser Scattering) to present the impacts of different isolator configurations on flow structures.

This paper presents an investigation of supersonic isolator flow behavior considering the impacts from variable cowl convergence angles and blockage ratios at the exit. An isolator was designed with a cowl convergence angle varying from 0° to 16°, which can provide unsymmetrical incoming flow condition. A blockage adjustor was installed at the exit of the isolator to simulate the choked flow. Flow visualization using Nano-tracer Planar Laser Scattering (NPLS) technique and pressure measurement were employed to represent the characteristics of isolator flows from totally unblocked state to the choked state at different cowl convergence angles. Results show that flow structures such as supersonic boundary layer, separation flow, shock waves, Mach disk and slip lines could be revealed distinctly by NPLS. The starting performance of isolator with different cowl angles which greatly affected the entrance condition was evaluated. Flow structures and pressure profiles show that a favorable contraction ratio provided a moderate starting. While an excessive contraction or deficient contraction corresponding to the cowl convergence angle of 0° and 16° suffer a harder starting which resulted from the pressure rise and severe separation on the ramp wall at the inlet entrance. Both pressure profiles and flow visualization results come to a good agreement with each other. Pressure profiles indicated that isolator with a 8° cowl convergence angle had the largest pressure endurance. And flow decelerated to sonic at the exit when the blockage ratio increased to nearly chock the whole isolator.