Master of Engineering Science
Mechanical and Materials Engineering
The present work investigates the effect of free-stream turbulence (FST) on turbulent boundary layers and forced convective heat transfer from flat plates. High resolution, 2-D and 3-D, steady Reynolds-Averaged Navier-Stokes (RANS) simulations using Computational Fluid Dynamics (CFD) techniques were performed to analyze the influence of different free-stream conditions, such as turbulence intensity (TI), integral length scale (Lu) and free-stream velocity (Uo) on local and total skin friction and convective heat transfer coefficients (CHTC), as well as on turbulent boundary layer parameters (boundary layer thickness and momentum thickness). The present study shows that the Shear Stress Transport (SST) k-ω model with the low Reynolds number (Re) approach is the most suitable model for representing incident turbulent flow over isothermal flat plates, since it provides the correct skin friction and Nusselt number for turbulent boundary layers, along with the appropriate streamwise TI decay through the numerical domain. Using the results, a set of non-dimensional correlations for local and total skin friction, momentum thickness, local and total CHTC were developed. These are simple and useful tools for the prediction of skin friction and forced convective heat transfer from flat plates under FST, which can be helpful for many engineering applications such as photovoltaic systems.
Summary for Lay Audience
Various engineering applications involve interactions between a fluid and a solid surface with heat exchange. When a fluid flows over a solid surface, a thin layer of fluid in contact with this surface develops, which is called a boundary layer. The motion between the fluid and the surface involves friction (or resistance) to the movement as well as heat exchange (known as convection). For instance, when wind blows over a photovoltaic solar panel, the former takes heat from the latter which influences the panel’s electrical efficiency. The strength of resistance to motion (friction) and heat loss is numerically represented by skin friction and convective heat transfer coefficients (CHTC), respectively. Additionally, the air flow generally is chaotic and irregular with fluctuating velocities. Such complex flow is defined as turbulent and can be characterized by the level of velocity fluctuations (turbulence intensity) and the average size of the turbulent eddies (length scale). The present study applies computational methods known as Computational Fluid Dynamics (CFD) to evaluate the influence of different air flow parameters (velocity, turbulence intensity and length scale) on the skin friction and CHTC of flat plates. Furthermore, this work provides new equations for the estimation of skin friction and CHTC for a given set of air flow parameters, which is useful for the design of many engineering devices, such as photovoltaic panel systems.
Alfaia de Magalhaes, Ivian Carolina, "The effect of free-stream turbulence on turbulent boundary layers and convective heat transfer from flat plates" (2020). Electronic Thesis and Dissertation Repository. 7393.