Active control of base pressure using micro jets for area ratio of 7.56

Abstract

Use of active and passive control techniques are reported in the literature for regulation of the base pressure in order to reduce the base drag in aerodynamic vehicles. In this work, air flow from a nozzle expanded suddenly into a duct of larger area than the nozzle exit area is studied in detail using active control. Using four micro jets each of 1 mm diameter placed on the periphery of the nozzle exit, the base pressure is actively controlled. The flow Mach number operated is 1.7, 2.3, and 2.7 whereas the length to diameter (L/D) ratio of the enlarged duct is reduced from 10 to 2. The nozzle pressure ratio (NPR) chosen is 1 to 10 for each value of Mach number and L/D ratio with and without control. The area ratio is fixed at 7.56. A detailed comparative base pressure variation analysis is performed using a controlled and uncontrolled flow. The results show that the at higher L/D ratio the base pressure variation using control is negligible whereas, at lower L/D ratio and Mach 1.7, the base pressure variation is significant for both the cases of control and without control.