Numerical simulation of laminar circular and noncircular jets in cross-flow

Direct numerical simulations have been performed to investigate the complex process of three-dimensional flow interactions around square, round and elliptic jets injected normally into the cross-flow mainstream. The velocity ratio of the jet to that of the cross-flow is 2.5 and the Reynolds number based on the free stream quantities and the jet exit diameter is 225. The main objective of this study is to assess the effect of the hole exit geometry on the dynamics of large-scale structures in jets cross-flow interactions. The computer code uses a finite-difference methodology, which solves the compressible three-dimensional unsteady Navier-Stokes and total energy equations in the Cartesian coordinate system. The obtained results reveal that, for all cases of hole geometry, the near field of the jet is dominated by the large-scale dynamic structures of complex flow nature. These flow structures undergo several interaction mechanisms and processes including reconnecting and pairing phenomena. The identified structures include the counter rotating vortex pair (CRVP), the Kelvin-Helmholtz roll-up of the jet shear layer vortices and the horseshoe vortex system. Our results also show that the jet lift-off as well as the cross-flow entrainment into the near wall regions mechanisms depend on the hole geometry. The maximum jet lift-off is found in the elliptic hole geometry case. These findings are in good agreement with existing experimental observations qualitatively.