SUMMARYA two-dimensional numerical simulation solving unsteady incompressible Navier -Stokes equations is used to study the natural varicose instability of a plane jet in the Reynolds number range of 100 -900. A transient train of vortices is observed at the beginning of the computation. It disappears yielding a steady flow. This flow is then used at the basis for forced excitation in order to study the space time development of instability. A Reynolds number dependant behaviour is observed which implies that viscosity directly affects the vortex dynamics.

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A computational study is conducted to explore the effect of vertical wall suction or blowing on two-dimensional confined wall jet hydrodynamic characteristics. Using an implicit finite volume technique in Cartesian coordinate system, several parameters have been investigated for a wide range of Lewis numbers by fixing the Prandtl number at 7 that corresponds to water. The main purpose is to analyze the control size and location effectiveness on the flow pattern as well as heat and mass transfer rates. Detailed numerical simulations demonstrated that as the local blowing is moved downstream, discrete vortex formation begins at a critical location then shedding phenomenon occurs behind the slot at advanced positions. Since the flow dynamic structure is mainly altered, averages skin friction and thermo-solutal coefficients distributions are largely influenced. Approximately for ≤ 4 (upstream of the natural vortex emission position), Nusselt and Sherwood numbers slightly increase with the control location. However, they gradually decrease as the blowing slot approaches the domain exit. Optimum values were obtained when locating the slot just downstream of the uncontrolled Kelvin-Helmholtz instability onset. Furthermore, computations illustrated that an appropriate suction slot length selection could be a simple and efficient tool to delay or even suppress natural structure emission and development. This choice is essentially related to the recirculation cell size.

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A two‐dimensional simulation of a plane jet exhausting from a channel has been performed using the vortex in cell algorithm in the Reynolds number range of 100–900. The vorticity is generated on the wall of the entrance channel whose length has been fixed in order to obtain a fully developed velocity profile at the entry of the jet. The transient behaviour of the velocity field starting from rest has been observed until reaching a quasi steady regime. The mean value of the velocity field is compared with the results of a finite volume computation on the same mesh. The velocity fluctuations obtained using this method are analysed. Their effect on the mean flow is estimated to be smaller than the viscous effect. Copyright © 2006 John Wiley & Sons, Ltd.