Effect of wall roughness on secondary flow choking in supersonic air ejector with adjustable motive nozzle

Abstract

Wall roughness is present to a certain extent in all engineering devices and systems. However, it is rarely considered during numerical simulations of supersonic ejectors. In this study, the effect of wall roughness on choking within a supersonic ejector with an adjustable motive nozzle was investigated in detail. Wall roughness was studied through numerical simulations. Characteristic curves showed that roughness had almost no influence on secondary flow choking when choking occured geometrically before the mixing chamber. By contrast, when choking occurred within the mixing chamber, its phenomenology was significantly altered by wall roughness. In addition, the results confirmed the ability of an ejector to switch from the on-design working regime to the off-design one when wall roughness is considered. The numerical results were also compared with available experimental data. Accounting for wall roughness in the numerical analysis significantly improved the agreement between the experimental and numerical data, especially in terms of wall static pressure distributions. This study sheds light on secondary flow choking within a supersonic ejector considering wall roughness.