Direct Numerical Simulation of Transitional Noncircular Buoyant Reactive Jets

Abstract

The near field dynamics of transitional buoyant reactive jets established on noncircular geometries, including a rectangular nozzle with an aspect ratio of 2 : 1 and a square nozzle with the same cross-sectional area, are investigated by three-dimensional spatial direct numerical simulations. Without applying external perturbations at the inflow boundary, large vortical structures develop naturally in the flow field due to buoyancy effects. Simulation results and analysis describe the details and clarify mechanisms of vortex dynamics of the noncircular buoyant reactive jets. The interaction between density gradients and gravity initiates the flow vorticity. Among the major vorticity transport terms, the gravitational term mainly promotes flow vorticity in the cross-streamwise direction. For the baroclinic torque, it can either create or destroy flow vorticity depending on the local flow structure. The vortex stretching term has different effects on the streamwise and cross-streamwise vorticity. Streamwise vorticity is mainly created by vortex stretching, while this term can either create or destroy cross-streamwise vorticity. Under the coupling effects of buoyancy and noncircular nozzle geometry, three-dimensional vortex interactions lead to the transitional behavior of the reactive jets. Simulations also show that the rectangular jet is more vortical than the square jet. The rectangular jet has a stronger tendency of transition to turbulence at the downstream due to the aspect ratio effect. Mean flow property calculations show that the rectangular buoyant reactive jet has a higher entrainment rate than its square counterpart.

Three‐dimensional numerical simulation of an equilateral triangular turbulent free jet

“…Rectangular and square free jets received most of the attention (e.g. Berg et al, 2006;de With and Holdo, 2005;Imine et al, 2004;Wilson and Imber, 2003;Rembold et al, 2002;Abdel-Hameed and Bellan, 2002;Jiang and Luo, 2001;Reddy et al, 1998Reddy et al, , 1999Wilson and Demuren, 1998;Grinstein, 1998;Zaman et al, 1997;Grinstein and DeVore, HFF 19,7 896 1996;Miller et al, 1995;Grinstein and Kailasanath, 1995;Teshima, 1989;Quinn and Militzer, 1988). However, only a few numerical studies were devoted to triangular jets (Imine et al, 2004;Abdel-Hameed and Bellan, 2002;Miller et al, 1995).…”