Experimental and numerical investigation of transverse secondary injection in dual-bell nozzles for enhanced operating mode switch control

The present paper extends previous research on dual-bell nozzle flow control using transverse secondary injection under altitude-varying conditions by investigating the dual-bell nozzle flow in a steady-state simulations campaign. The flow predicted numerically for a dual-bell nozzle without operating secondary injection presented every key flow feature, but the separation location was not well predicted, especially in the vicinity of the transition nozzle pressure ratio. The discrepancy diminished by increasing the turbulence model’s structure parameter, a parameter limiting the turbulent shear stress in the boundary layer. The calibrated turbulence model was used for further simulations, where a secondary injection was operated in the extension section of the dual-bell nozzle. The simulations reproduced the increase in transition nozzle pressure ratio with an increase in secondary mass flow rate ratio observed experimentally. The numerical Schlieren images were in good agreement with the experiment, except in the vicinity of the transition nozzle pressure ratio; and the numerical wall pressure distribution indicated that the secondary injection effect limitation observed experimentally was attributed to the absence of interaction between the separation front and the inflexion point.