Direct Numerical Simulation of Single and Multiple Square Jets in Cross-Flow

Abstract

Direct numerical simulations (DNSs) have been carried out for single and multiple square jets issuing normally into a cross-flow, with the primary aim of studying the flow structures and interaction mechanisms associated with the jet in cross-flow (JICF) problems. The single JICF configuration follows a similar study previously done by Sau et al. (2004, Phys. Rev. E, 69, p. 066302) and the multiple JICF configurations are arranged side-by-side in the spanwise direction with a jet-to-jet adjacent edge distance (H) for the twin-jet case and an additional third jet downstream along the centerline with a jet-to-jet adjacent edge distance (L) for the triple-jet case. Simulations are performed for two twin-jet cases with H=1D,2D, respectively, and for one triple-jet case with H=1D, L=2D, where D is the jet exit width. Flow conditions similar to Sau et al. are considered, i.e., the jet to the cross-flow velocity ratio R=2.5 and the Reynolds number 225, based on the freestream velocity and the jet exit width. For the single jet in cross-flow, the vortical structures from our DNS are in good qualitative agreement with the findings of Sau et al. For the side-by-side twin-jet configuration, results have shown that the merging process of the two initially separated counter-rotating vortex pairs (CRVPs) from each jet hole exit is strongly dependent on the jet-to-jet adjacent edge distance H with earlier merging observed for the case H=1D. Downstream, the flow is dominated by a larger CRVP structure, accompanied by a smaller inner vortex pair. The inner vortex pair is found not to survive in the far-field as it rapidly dissipates before exiting the computational domain. These observations are in good agreement with the experimental findings in the literature. Simulations of the triple-jet in cross-flow case have shown some complicated jet-jet and jet-cross-flow interactions with three vortex pairs observed downstream, significantly different from that seen in the twin-jet cases. The evidence of these flow structures and interaction characteristics could provide a valuable reference database for future in-depth flow physics studies of laboratory experimental and numerical investigations.

Effect of Jet Inclination Angle and Hole Exit Shape on Vortical Flow Structures in Low-Reynolds Number Jet in Cross-Flow

“…Due to the merging process whilst the vortex roller moving downstream, the scale of K-H vortices increases with the distance, similar to that in a free jet flow. Overall present observations are in good agreement with previous experimental and numerical predictions [12]. The influence of the streamline injection angle variations on the flow structures in jet cross-flow interaction has been assessed.…”

“…Following a previous numerical study of Sau et al [11], a computational grid of 241 points in the streamwise (with 11 points in the jet domain), 81 points in the wall normal, and 61 points in the spanwise direction (with 11 points in the jet domain) is adopted. Both domain influence and grid refinement studies have been carried out [12]. For example, simulations were performed on domain sizes of 24D × 9D × 8D and 24D × 6D × 12D (using similar grid resolutions and distributions) and computational meshes of 192 × 65 × 49 and 361 × 121 × 91 (both applied to the baseline domain), respectively.…”

On the Reliability of Reynolds-Averaged Navier Stokes Prediction of Mean Flow Characteristics of a Rectangular Turbulent Jet in Crossflow

“…13, contours of passive-scalar at several jet downstream XY planes and for different jet-to-crossflow velocity ratios are used to illustrate the main vortex structure characterizing the JICF configuration such as the Counter-Rotating Vortex Pair (CRVP). These contours clearly show the classic kidney-shaped Counter-Rotating Vortex Pair (CRVP), as seen in other studies (Strzelecki et al, 2009;Yao and Maidi, 2011;Salinas-Vazquez et al, 2005). Note that the kidney shape is evident even near the jet exit at x/l j = 1.…”

Numerical Simulations of Imperfect Bifurcation of Jet in Crossflow

“…Thus, steady Reynolds-averaged Navier-Stokes Simulation (RANS) is still the primary simulation approach used in this study. Nevertheless, for a JICF problem which is highly complex with a lot of streamline curvature and anisotropy, high resolution methods, such as Large Eddy Simulation (LES) (Jouhaud et al, 2007) and Direct Numerical Simulation (DNS) (Yao and Maidi, 2011), have been found outperforming RANS. However, the expensive computational cost could be a barrier to use these two methods.…”