A numerical study of penetrative turbulence in convective boundary layers

Hossain, Mohammad Alamgir (2015) A numerical study of penetrative turbulence in convective boundary layers. Masters thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (11MB)

Abstract

A weighted residual collocation method is investigated to study penetrative turbulence in the atmospheric boundary layer (ABL). In designing such a numerical model for the ABL, one needs to minimize or avoid artificial energy dissipation at the resolved scale, and parameterize the effect of unresolved turbulent mixing to account for the subgrid scale energy dissipation. In this research, the standard mesoscale filtering of conservation laws (mass, momentum, and energy) has been adopted based on the assumption that the characteristic scale of circulation is much less than the density scale hight of the atmosphere. Such mesoscale equations have been filtered with a Deslauriers-Dubuc (DD) interpolating wavelet system along with a Smagorinsky type eddy viscosity model. The time integration is performed by projecting the solution onto a Krylov subspace, and by solving the system with the GMRES (generalized minimal residual) algorithm. The numerical model is verified with the analytical solution of two-dimensional advection-diffusion phenomena, and with two benchmark simulations such as dry thermal rising in the neutrally stratified environment and stationary solutions of urban heat island circulation. The generation of internal waves by a turbulent buoyant element impinging upon the interface between the boundary layer and free atmosphere is characterized. Finally, penetrative turbulence due to differentially heated earth’s surface is investigated for a wide range of surface heat flux variations, 25 ≤ H0 ≤ 930 W m⁻². Results indicate that the downscale energy cascade is associated with the onset of temporal oscillations in mesoscale circulation, although a fraction of kinetic energy is transferred by internal waves.

Actions (login required)

View Item