Manipulation of high Mach number shear layers using control jets

The field of jet mixing enhancement has interested researchers for a long time because of its practical significance in many engineering areas: combustion, noise reduction, IR signature reduction. In the military aircraft context, the largest sources of IR radiation are the engine afterburner, propulsion nozzle, and jet exhaust plume, where gas and metal temperatures are highest. Rapid mixing of the jet plume with the ambient air offers a number of interesting possibilities for IR reduction, including noise reduction as an added benefit. Many techniques to achieve enhanced jet mixing have been proposed; all have limitations and no technique has been clearly proven to be optimum. An active control technique which has shown promise is the use of control jets - a discrete number of small radially penetrating jets introduced around the primary jet periphery at nozzle exit. The control jets may be steady or pulsed. However, the literature to date largely covers studies on control jet effectiveness at low Reynolds numbers and mostly under low Mach number, essentially incompressible, conditions - far removed from the regime of practical application. The fact that control jets can be designed according to requirements, and in particular can be turned off when not required, argues that this technique is worthy of further investigation, but with a specific emphasis on high Re, high Mach number compressible jet flows. This is the focus of the current study, which constituted both experimental and computational investigations. [Continues.]