Active control of high speed jets using air tabs

Abstract

An improved jet mixing would be of great interest in the field of aerospace engineering, in order to achieve better mixing properties in the combustion chamber and for reduction in acoustic emission. There are two distinct approaches available for the attainment of jet mixing enhancement, namely, active control and passive control. Even though the conventional solid tab, which is a passive control technique, enhances the jet mixing effectively, it also results in total pressure loss or thrust loss and increased drag. The total pressure loss and increased drag would directly affect the overall performance of an aircraft engine. Therefore, the present investigation is focused on active control of high speed jets by air tab technique, which is expected to give better jet mixing enhancement with minimum total pressure loss. Experiments and numerical simulations have been carried out in order to investigate the effect of air tab jets at different Mach numbers on the mixing and spreading characteristics of high speed jets. Air tabs are fluidic jet streams with significant momentum, injected into the primary jet at or downstream of the nozzle exit. A simple convergent nozzle was used for generating primary jet and two constant diameter tubes were used for creating fluidic jet streams, which are termed air tabs. In the present investigation, experiments were conducted with 45° and 90° air tabs inclined with respect to the primary jet centreline (X). The primary jet Mach numbers (MP) considered for the experiments as well as numerical simulations were 0.4, 0.6 and 0.8. A wide range of air tab jet Mach numbers (Mc) were considered for each Mach number of the primary jet (MP), at an interval of 0.1. The air tab jet Mach number (Mc) was varied from 0.3 to 1.0 (for primary jet Mach number 0.4), 0.5 to 1.2 (for primary jet Mach number 0.6) and 0.7 to 1.4 (for primary jet Mach number 0.8) at an interval of 0.1 newline