Investigation of Effect of Ground Downstream of Overexpanded Dual-Bell Nozzle During Vertical Takeoff and Landing

The dual-bell nozzle is one of altitude compensation nozzles for single stage launch vehicles. It can be used for the main engine of reusable vertical take-off and landing launch vehicles. Flow instabilities in dual-bell nozzle are examined with a wall simulating the ground downstream of the nozzle exit. Effects of the nozzle pressure ratio (NPR) and the distance of the wall from the nozzle exit are studied experimentally and numerically. Results show that the flow oscillation with discrete frequencies occurs at a certain range of the NPR. The frequencies depend on the NPR and the distance. Numerical results show the detailed flow pattern inside the nozzle.