M.Sc Thesis


M.Sc StudentShoshana Weiss Tewner
SubjectFormation and Evolution of Buoyancy Driven Vortices in
Stratified Shear Flow
DepartmentDepartment of Aerospace Engineering
Supervisor Full Professors Cohen Jacob
Full Thesis textFull thesis text - English Version


Abstract

Buoyancy-driven flows can be found both in nature and in industrial applications. In this work we concentrate on the evolution of a localized three dimensional temperature disturbance embedded in stationary or parallel shear flow with uniform or linearly stratified temperature. We have extended an Analytical-Based Numerical Method to include the energy equation and the temperature term in the vorticity equation. The method has been verified by comparing the results to those obtained using commercial DNS software.

The spatio-temporal development of a buoyant disturbance is explored through several governing parameters. The effect of initial disturbance geometry is shown to be negligible. The effect of the ratio between shear and buoyancy time scales is investigated. Stratification of a stationary base flow results in oscillation of various integral quantities, the frequency of which agrees with the Brunt Vaisala frequency. The effect of added shear to a stratified ambient is characterized by the Richardson number (Ri). We observe that for Ri>0.5 the disturbance grows transiently and eventually decays however for Ri<0.5 it continues to grow.