Influence of Base Nozzle Contour Design on Flow Instabilities in Dual Bell Nozzle at Low Altitude Operation

Flow instabilities under low-altitude operation mode in dual-bell nozzles are examined. Influences of base nozzle contour are investigated with two types of base nozzle contours: a truncated perfect (TP) nozzle and a compressed truncated perfect (CTP) nozzle. Experimental and numerical results show that the Mach disk oscillation in the axial direction occurs in the dual-bell nozzle with the CTP base nozzle. Such Mach disk oscillation causes higher level wall pressure oscillations than those in the dual bell nozzle with the TP base nozzle. Influences of geometric area ratio of the dual bell nozzle are also examined. As a result, the geometric area ratio does not affect the characteristics of the flow oscillation modes except for the amplitude of the wall pressure fluctuations.