P.I.M.S. Summer School in Fluid Dynamics

Abstracts of Invited Talks

The Fluid Mechanics of Natural Ventilation
P. F. Linden, UCSD

Natural ventilation of buildings provides an attractive way to reduce energy usage and costs and has positive benefits in reduced CO2 emissions to the atmosphere. In recent years architects and designers have increasingly been using natural ventilation, either on its own or with mechanical and conditioned systems, particularly in commercial buildings. Modern designs, typically tall buildings with large glazed areas, require a detailed understanding of the air flow in order to operate efficiently and to the satisfaction of the occupants.

These lectures will describe recent research into the fluid mechanics of ventilated spaces. This research has been a combination of laboratory experiments and theoretical analysis based on plume theory. I will discuss the basic ventilation modes - mixing and displacement ventilation - and show how they are established and controlled. Mixing ventilation, as the name suggests, has little internal stratification while displacement ventilation is associated with strong stratification. The properties of the two modes are quite different, and have advantages and disadvantages depending on requirements. The transitions between the modes depends on the formation and breakdown of stratification and is determined by mixing and convective processes in stratified fluids. The effects of wind induced flow and mechanically driven ventilation will be discussed in this latter context, and it will be shown that buildings can exhibit behavior typical of nonlinear systems - multiple ventilation states and hysteresis.

The analysis will be demonstrated by discussion of some case studies of recent naturally ventilated buildings.

2pm, Tuesday August 8 and 2pm, Wednesday August 9 in room 243 Central Academic Building

Convection in a Rotating Environment
J. C. McWilliams, UCLA

Several lectures will be presented on the general topic of how rotation influences convection. This will be addressed in the context of three canonical problems:

Rayleigh-Benard Convection: the equilibrium state for uniform heat flux between two parallel plates.

Penetrative Convection: the encroachment of convection driven by an destabilizing boundary flux into an otherwise quiescent, stably stratified interior region.

Convective Modification of Geostrophic Eddies: boundary-driven convection is localized by pre-existing (pre-conditioning) geostrophic eddies in the stably stratified interior and, in turn, the eddies and stratification are modified by the non-uniform convective mixing

Noon, Tuesday August 8 and noon, Thursday August 10 in room 243 Central Academic Building

Introduction into Turbulence
F. T. W. Nieuwstadt, Delft University of Technology

Turbulence is a state of fluctuating, chaotic flow motion which occurs when a given flow parameter, such as the Reynolds number, has exceeded its critical value. Therefore a study of turbulence should begin with an investigation of flow stability. Given the conditions for which a flow becomes unstable we also consider shortly to the scenario by which fully developed turbulence is attained. The most convenient way to treat a turbulent flow is by statistical methods. With help of these methods we derive the equations for a turbulent flow, in particular the equations for the mean momentum, the turbulent kinetic energy and the vorticity fluctuations. Based on these equations we develop the standard picture of turbulence dynamics by which large-scale turbulent eddies take energy from the mean flow and transmit this energy through an inertial instability proces towards smaller turbulent eddies. This is known as the cascade process. The energy finally reaches the smallest scales where its is dissipated in heat by viscosity. These smallest scales are known as the Kolmogorov scales. Based on the classic picture of turbulence we also consider more recent results which gives insight of the flow processes that are involved in the dynamics of turbulence.

Noon, Monday August 7 and noon, Wednesday August 9 in room 243 Central Academic Building

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Bruce R. Sutherland, July 00.