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Efficacy of Delta-Tab in Controlling the Mixing Characteristics of Mach 1.8 Jet
Author(s): Balkrishan Mahabir, Pradhyumn Bhale, Mrinal Kaushik
Keywords: Centerline pressure decay, Jet mixing; Core length, Mach contours, Numerical Schlieren, RANS
Supersonic jets are ubiquitous in the aerospace industry due to their several applications, particularly, in thrust generation and combustion augmentation in a high-speed aircraft. Indeed, in order to optimize their performance, effects on noise attenuation, effective mixing, core length reduction, efficient combustion, and the mixing characteristics of the jets should be thoroughly understood and controlled. Among the investigated passive control methods, a tab is found to be quite efficient in modifying the mixing characteristics of the jets. There is a good amount of literature available on this subject, but most of them are experimental investigations and detailed computational studies on supersonic jet controls using tabs is hardly being carried out. Therefore, in this study the mixing promoting effectiveness of two tabs, mounted at diametrically opposite locations at the exit of a Mach 1.8 convergent-divergent circular nozzle, have been computationally investigated, for NPRs from 4 to 8 which covers overexpanded, correctly-expanded and underexpanded states of the jet. In order to minimize the thrust loss, the geometric blockage offered by each delta tab is kept within 2.5%. The steady flow computations were carried out in a three-dimensional numerical domain using SST κ-ω Reynolds-Averaged Navier-Stokes turbulence model. ANSYS FLUENT flow solver was used to solve the flow domain with a finite volume approach to discretize the governing equations. The rapidity of the jet mixing was quantified by comparing centreline pressure decay plots of both uncontrolled and controlled jets. A maximum core reduction of 70.81% was observed in underexpanded state corresponding to NPR (nozzle pressure ratio) 6. In addition to reducing the core length these tabs were found to be better in weakening the waves and shortening the shock cells length as illustrated through Schlieren images captured numerically. The findings of the study are found to be in agreement with the experimental results published in the literature.