The propagation of a passive admixture from a local instantaneous source in a turbulent mixing zone in a stable stratified fluid (two-dimensional problem) is simulated numerically. The location of the source does not coincide with the center of the turbulent zone. The calculation results indicate that the average admixture concentration distribution depends significantly on the initial data. The location of the maximum concentration in homogeneous and linearly stratified fluid is fairly slowly displaced toward the center of the zone. Calculations in a pycnocline show that situations are possible when the propagation of a passive admixture is largely determined by a convective flow generated by the turbulent mixing zone.
532.517.4 1. Introduction. Turbulent wakes behind bodies of revolution in a stratified fluid have been considered in many publications . In [1], Schooley and Steward have analyzed experimentally the dynamics of a turbulent wake behind a self-propelled body in a linearly stratified medium. In addition, they have demonstrated collapse and generation by the wake of internal waves. The phenomenon of momentumless wake collapse in a linearly stratified medium has been studied experimentally by Merrit in [2]. In laboratory tests, Lin and Pax) [3] (see also [4]) have investigated in detail the turbulence characteristics in the wakes behind bodies moving in a linearly stratified medium. In [5], Gilreath and Brandt have analyzed experimentally the pattern of internal waves generated during the motion of bodies in stratified fluids. In addition, they have given theoretical estimates of internal waves, including the waves induced by the collapse of the turbulent wake in pycnocline.A series of studies [6-13] deals with the flow occurring during motion of a towed sphere in a linearly stratified fluid. Various flow regimes have been studied, depending on the Reynolds and Froude numbers both in the near and far wakes. In [10], Bonneton et al. have studied theoretically internal waves produced by the turbulent wake of a sphere moving in a linearly stratified fluid. In addition, they have considered the wake's wave component that is associated with coherent structures. In [12, 14], Chashechkin and Voisin have comprehensively analyzed experimental data on turbulent-wake degeneration behind towed and self-propelled bodies in linearly stratified fluids and also have estimated theoretically the parameters of internal waves.The initial stage of development of the wake in a linearly stratified fluid has been considered theoretically by Onufriev [15] using the algebraic model of Reynolds stresses and fluxes. In [16], Lewellen et al. have modeled numerically the turbulent wake and collapse-produced internal waves at small distances from a self-propelled body in a linearly stratified medium, which is based on the model of a Iocai-equilibrium approach.To analyze numerically the wakes behind self-propelled and towed bodies in a linearly stratified medium, Hassid [4] used a modified model of the locally equilibrium approach with involvement of the equations of turbulent-energy transfer and its dissipation rate. He obtained satisfactory agreement with the experimental data obtained by Lin and Pao which are concerned with the measurement of the characteristic sizes of the wake, velocity defect, and turbulence energy on the wake axis as a function of the distance from a body (for one of the values of the Froude number). However, as correctly noted in [22], for a self-propelled body, the action of stratification turned out to be stronger than in experiments.As an illustration of application of the implicit variant of the splitting method in terms of physical processes for stratified-flow calculations, Danilenko et al. [17] have considered th...
We numerically analyse the momentumless turbulent wake evolution in a linearly stratified medium, using two mathematical models. The computational results are compared with experimental data. We consider the model, which satisfactorily describes the process of anisotropy turbulence decay in the wake, taking into account the buoyancy effect in the algebraic model of third-order correlations in the velocity field.
We numerically analyse the evolution of a far momentumless turbulent wake in a linearly strati ed medium, using three mathematical models. We compare the computational results with experimental data. The model that includes a differential equation for the transport of the triple correlations of vertical velocity component uctuations adequately describes the process of anisotropy decay of turbulence in a wake. ¤ Institute of Computational Technologies of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk 630090, Russia y S. S. Kutateladze Institute of Thermophysics of the Siberian Branch of the Russian Academy of Sciences,
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