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This paper investigates the flow structure nearby a rectangular cooling hole on a flat plate by numerical simulations and topological analysis. The velocity ratio ranges from 0.5 to 1.5. Steady Reynolds-averaged NavierStokes simulations and unsteady detached eddy simulations are performed based on the Spalart-Allmaras turbulence model. The time-averaged velocity profiles in the central plane are verified by grid convergence study and comparison with the experimental data. The discussions mainly focus on the effect of the velocity ratio on the vortex structure and the stability of the jet-in-crossflow (JICF) system. The simulation results show that a bifurcation of the vortex system exists with respect to the velocity ratio. The averaged flow goes from a symmetric structure to an asymmetric structure on this bifurcation. The detached eddy simulation results show that both the symmetric vortex system and the asymmetric vortex system with different velocity ratios are stable.

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