A spectral multidomain penalty method model for the simulation of high Reynolds number localized incompressible stratified turbulence

A spectral multidomain penalty method model has been developed for the simulation of high Reynolds number localized stratified turbulence. This is the first time that a penalty method, with a particular focus on subdomain interface treatment, has been used with a multidomain scheme to simulate incompressible flows. The temporal discretization ensures maximum temporal accuracy by combining third order stiffly stable and backward differentiation schemes with a high-order boundary condition for the pressure. In the non-periodic vertical direction, a spectral multidomain discretization is used and its stability for under-resolved simulations at high Reynolds numbers is ensured through use of penalty techniques, spectral filtering and strong adaptive interfacial averaging. The penalty method is implemented in different formulations for both the explicit non-linear term advancement and the implicit treatment of the viscous terms. The multidomain model is validated by comparing results of simulations of the mid-to-late time stratified turbulent wake with non-zero net momentum to the corresponding laboratory data for a towed sphere. The model replicates correctly the characteristic vorticity and internal wave structure of the stratified wake and exhibits robust agreement with experiments in terms of the temporal power laws in the evolution of mean profile characteristic velocity and lengthscales. (C) 2004 Elsevier Inc. All rights reserved

Experimental study of the initial growth of a localized turbulent patch in a stably stratified fluid

We present a laboratory experiment of the initial growth of a turbulent patch in a stably stratified fluid. The patch is created due to a localized source of turbulence, generated by a horizontally oriented and vertically oscillating grid much smaller than the tank size and far from solid boundaries. Synchronized and overlapping particle image velocimetry(PIV) and planar laser induced fluorescence (PLIF) measurements capture the evolution of the patch through its initial growth until it reached a maximum size. The simultaneous measurements of density and velocity fields allow for a direct quantification of the distribution of kinetic energy, buoyancy and degree of mixing within the patch. We can also relate the propagation speed of the turbulent/non-turbulent interface and its thickness to the properties of the turbulent fluid inside the evolving patch. The velocity measurements in this setup indicate significant transient effects inside the patch during its growth. A local analysis of the turbulent/non-turbulent interface provides direct measurements of the entrainment velocity we as compared to the local vertical velocity and turbulent intensity at the proximity of the interface. The detailed information about the growth of localized sources of turbulence in stratified environment might be of use in stealth design of autonomous underwater vehicles