The numerical modelling of impinging jet flows is not straightforward as it should not only solve the shear layer development in the free jet region, but also the near-wall behaviour (streamline curvature) and the resulting wall jets after impingement. This study presents a validation study of steady Reynolds-averaged Navier-Stokes turbulence models for predicting isothermal plane turbulent impinging jets at two different slot Reynolds numbers, i.e. Re = 8,000 (case I) and Re = 13,000 (case II), based on 2D particle image velocimetry measurements. In addition, an in-depth analysis of the results provided by the five different turbulence models: standard k-ε (SKE), realizable k-ε (RKE), RNG k-ε, SST k-ω, and a Reynolds stress model (RSM), is performed.The results show that: (1) for both Reynolds numbers the best agreement with measured velocities and turbulent kinetic energy in the region near the jet nozzle is achieved with SST; (2) the best predictions of potential core length are provided by RNG (case I) and RKE (case II); (3) centreline distributions of velocities and turbulent kinetic energy are most accurately predicted by RNG and RKE for case I, while for case II the best agreement with experimental data is obtained by SKE and RNG; (4) the best overall performance for both cases in predicting velocities is provided by RKE, and by RKE and RNG when considering turbulent kinetic energy; (5) all models more accurately predict the jet spreading rate in the intermediate region than in the potential core region; (6) for both Reynolds numbers SKE provides the most accurate estimation of jet decay rate.
Instabilities and long-term evolution of two-dimensional circular flows around a rigid circular cylinder (island) are studied analytically and numerically. For that we consider a base flow consisting of two concentric neighbouring rings of uniform but different vorticity, with the inner ring touching the cylinder. We first study the inviscid linear stability of such flows to perturbations of the free edges of the rings. For a given ratio of the vorticity in the rings, the governing parameters of the problem are the radii of the inner and outer rings scaled on the cylinder radius. In this two-dimensional parameter space, we determine analytically the regions of linear stability/instability of each azimuthal mode m = 1, 2, . . . . In the physically most meaningful case of zero net circulation, for each mode m > 1, two regions are identified: a regular instability region where mode m is unstable along with some other modes, and a unique instability region where only mode m is unstable. After the conditions of linear instability are established, inviscid contour-dynamics and high-Reynolds-number finite-element simulations are conducted. In the regular instability regions, simulations of both kinds typically result in the formation of vortical dipoles or multipoles. In the unique instability regions, where the inner vorticity ring is much thinner than the outer ring, the inviscid contour-dynamics simulations do not reveal dipole emission. In the viscous simulation, because viscosity has time to widen the inner ring, the instability develops in the same manner as in the regular instability regions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.