Numerical Studies on Chemical Non-Equilibrium Flow of the Base-Bleed Unit Wake

Abstract

ABSTRACTNumerical studies of compressible base flows with base bleed injection as an effective way to control the base flow for the base drag reduction and heat energy addition of axisymmetric projectiles with a boattailed afterbody in supersonic freestream are carried out by considering the base burning process. The idea developed in the study is to obtain the lowest base drag by analyzing the complex fluid dynamic characteristics found in a supersonic base flow field, including combined effects of boattailing and secondary combustion of the wake under different conditions. Overall fluid dynamic and chemical non-equilibrium flow are then simulated by incorporating the H2-CO combustion model with 12 reaction steps involving eight reactive species (H, H2, H2O, OH, CO, CO2, O, and O2) into a Navier–Stokes computer code. Various base flow and component distribution characteristics are obtained by changing injection parameter I, which is defined as the bleed mass flow rate normalized by the product of the base area and the freestream mass flux, and the bleed temperature. The results obtained through the present study show that, with increasing injection parameter I, the average base pressure is found to increase quickly initially, attain a slow increase near an injection parameter of I = 0.007, and then remain constant with further increase in I. Moreover, based on changing the bleed temperature, the base pressure rises and the heat energy addition as well as mass addition mechanisms associated with base secondary combustion are found to be higher than that without base secondary combustion. The secondary combustion results in a significant increase in flame temperature and changes the product composition, which cannot be ignored, although the chemical kinetics and fluid dynamic will fulfill another important role. Thus, a better effect on base drag reduction as well as base pressure increase can be attained by adopting appropriate injection parameter and bleed temperature.