INFLUENCE OF SHORTENED NOZZLE SHAPE WITH A BELL-SHAPED TIP ON THE GAS FLOW CHARACTERISTICS

Abstract

Interest in nozzles with great shortened profiles arose in connection with the development of high-density aircraft. A shortened nozzle profile significantly reduces or eliminates the free volumes required to accommodate a full-size nozzle contoured along the flowline. This paper examines flow in a similar nozzle with various possible combinations of a shortened Laval nozzle section with a bell-shaped tip with an exit angle of 0°. The aim is to investigate the gas flow characteristics in a shortened rocket engine nozzle with a bell-shaped tip under varying nozzle geometry and pressures upstream of the nozzle and the ambient air. The study found that the relative length of the shortened conical section of the nozzle, located upstream of the nozzle, has a significant effect on the flow characteristics in the nozzle. The overall nozzle length (with the same geometric expansion ratio) and the nozzle inlet angle have less influence on the flow pattern in the nozzle. At low nozzle inlet pressures and high external pressure, a well-developed separation zone is observed between the jet boundary and the nozzle wall, extending upstream from the tip exit to the exit of the shortened nozzle. The characteristics of this zone depend on the flow expansion ratio in the shortened nozzle. The nozzle thrust coefficient decreases with increasing relative pressure at the nozzle inlet due to the reduced influence of external pressure on the flow in the tip. At higher flow misalignments, the thrust coefficient is higher for a nozzle with a longer conical section.