Direct numerical simulation of jets in cross-flow

Abstract

Direct numerical simulation (DNS) of jets in cross-flow (JICF) has been carried out in this study, aiming for the investigation of vortex structure formation and evolution process associated with JICF. A recently developed DNS code is used, which solves three-dimensional (3D) compressible unsteady Navier–Stokes (NS) equations using high-order finite differences and multi-block structure grid treatment for complex geometry. Jet flow from a square duct, perpendicular to the mainstream flow, is introduced and the flow Reynolds number is 100 based on the jet duct diameter (D) and free-stream quantities. Two-dimensional (2D) calculations using various jet to free-stream velocity ratio (R = V jet/V free) reveals different vortex patterns and a further 3D study continues focusing on a velocity ratio of R = 2, for which complex vortex structure is produced. It is found from the 3D simulation that a counter-rotating vortex pair (CRVP) forms immediately after the jet exits, as observed from the experimental test and reproduced by other numerical simulations. The CRVP originates from the near wall viscous layer and its core position moves away from the wall as it evolves downstream. For the condition simulated, the CRVP is finally weakened (due to viscous diffusion) at about 1.6D downstream from the centre of the jet exit. No asymmetric CRVP has been observed, which was reported by other researchers for high-Reynolds number simulations

Numerical visualization of vortex flow behavior in square jets in cross-flow

“…All other variables follow the standard notations as seen in Yao et al (2006). The code was developed for compressible flow.…”

“…In this application, we adopt low Mach number (~ 0.2) to reduce the compressibility effects. The code has been parallelized using the MPI library and validated extensively for numerous configurations including laminar boundary layer and channel flows (Yao et al, 2000), turbulent boundary layer (Yao et al, 2000), turbulent channel flows (Sandham et al, 2002;Hu et al, 2003), transonic flow over a bump geometry with shock/boundary layer and most recently jet in cross-flow (Yao et al, 2006).…”

Turbulent Characteristics and Design of Transverse Jet Mixers with Multiple Orifices

“…Over the past few decades, many researchers have devoted efforts to studying the mechanisms and the macroscale features of the transverse jet mixing process. For the mixing mechanisms, particularly the generation and evolution of the vortex structures, specific attention is generally paid to the single transverse jet, − about which extensive studies have been reviewed by Mahesh and Karagozian. , A general consensus is that the interactions of the jet and crossflow creates the vortex systems such as the counter-rotating vortex pair (CVP), jet shear-layer vortices in the nearfield region, horseshoe vortices wrapping around the jet column, and wake vortices in the lee of the jet.…”