Experimental Investigation of Mixing Characteristics of Non-axisymmetric Subsonic and Sonic Jets

Mixing enhancement in jet flows is an essential and critical factor in aerospace, mechanical, environmental science, and flow control applications. In particular for aerospace applications, improved mixing of jet fluid with ambient fluid helps in improving combustion efficiency, reducing infrared radiation, mitigating aeroacoustic noise and thrust vectoring. This mixing can be achieved by manipulating the flow behavior at the exit of the nozzle by introducing passive control techniques. The present experimental study examines one such passive control at Mach numbers 0.8 and 1.0 using non-circular (elliptic and square) geometries. A circular jet of equal exit area is also investigated for comparisons at the same test conditions. The centerline total pressure decay, decay rate, jet half-width, spread rate, shear layer thickness and pressure profiles are presented to demonstrate the effect of non-circularity in the jet mixing. The nozzle with an elliptical shape exhibited shorter potential core length, the highest decay and spread rates, and greater shear layer thickness for both the Mach numbers studied here. The elliptical jet achieved a maximum percentage reduction of 22% potential core length, indicating superior mixing and rapid decay capabilities than the square and round jets. Jet half-width profiles and pressure profiles along two directions revealed that the axis-switching phenomena observed in the elliptical and square jets due to differential spreading across their axes are the primary reason for the improved mixing abilities of the non-circular jets.