Experimental study of thermally stratified co-axial jets with trip ring excitation

Abstract

Experimental investigation of the mean flow characteristics in the velocity field as well as the thermal field of thermally stratified free and trip ring excited coaxial jets have been carried out for different flow conditions. Isothermal as well as thermally stratified or non-isothermal co-axial jet flows are developed by issuing two jets with different unidirectional velocities from a concentric compound nozzle. The hot central jet comes out from a central nozzle while the annular ambient jet is emitted through the annular space between the outer and the central nozzle. Four outer to inner jet velocity ratios have been considered in the experiment. The temperature of the central jet is varied to establish different temperature gradient between the central jet and the annular jet by varying the supply voltage to the heater placed upstream of the central nozzle. Three different values of temperature ratios have been considered. The excitation is made by two trip rings, one placed inside the central nozzle called inner trip ring and the other placed outside the central nozzle called outer trip ring. Measurements of mean velocity and mean temperature are made in the mixing zone of these two jets with the help of a pitot static tube with embedded thermocouple in it. For the nozzle configurations used in the present study, mlxmg as well as momentum exchange in co-axial jets occur more readily at lower velocity ratio than those of the higher one. Thermal diffusion from the hot central jet is also found to occur more rapidly at lower velocity ratio. In case of inner or outer trip ring excited co-axial jets, a negative pressure zone is created due to the presence of the wake. This wake facilitates better mixing between two jets. Amongst the inner and outer trip ring excited and unexcited configurations of this experiment inner trip ring is found the most efficient one in mixing different jets both dynamically and thermally.