Computational fluid dynamics using Graphics Processing Units: Challenges and opportunities

A new paradigm for computing fluid flows is the use of Graphics Processing Units (GPU), which have recently become very powerful and convenient to use. In the past three years, we have implemented five different fluid flow algorithms on GPUs and have obtained significant speed-ups over a single CPU. Typically, it is possible to achieve a factor of 50-100 over a single CPU. In this review paper, we describe our experiences on the various algorithms developed and the speeds achieved

Doctor of Philosophy

dissertationAccording to a UN report, more than 50% of the total world's population resides in urban areas and this fraction is increasing. Urbanization has a wide range of potential environmental impacts, including those related to the dispersion of potentially dangerous substances emitted from activities such as combustion, industrial processing or from deliberate harmful releases. This research is primarily focused on the investigation of various factors which contribute to the dispersion of certain classes of materials in a complex urban environment and improving both of the fundamental components of a fast response dispersion modeling system - wind modeling and dispersion modeling. Specifically, new empirical parameterizations have been suggested for an existing fast response wind model for street canyon flow fields. These new parameterizations are shown to produce more favorable results when compared with the experimental data. It is also demonstrated that the use of Graphics Processing Unit (GPU) technology can enhance the efficiency of an urban Lagrangian dispersion model and can achieve near real-time particle advection. The GPU also enables real-time visualizations which can be used for creating virtual urban environments to aid emergency responders. The dispersion model based on the GPU architecture relies on the so-called "simplified Langevin equations (SLEs)" for particle advection. The full or generalized form of the Langevin equations (GLEs) is known for its stiffness which tends to generate unstable modes in particle trajectory, where a particle may travel significant distances in a small time step

Development of the marker and cell method for use with unstructured meshes.

The marker and cell method is an efficient co-volume technique suitable for the solution of incompressible flows using a Cartesian mesh. For flows around complex geometries the use of an unstructured mesh is desirable. For geometric flexibility an unstructured mesh implementation is desirable. A co-volume technique requires a dual orthogonal mesh, in the triangular case the Delaunay-Voronoi dual provides the means for determining this dual orthogonal mesh in an unstructured mesh framework. Certain mesh criteria must be placed on the Delaunay-Voronoi to ensure it meets the dual orthogonal requirements. The two dimensional extension of the marker and cell method to an unstructured framework is presented. The requirements of the mesh are defined and methods in their production are discussed. Initially an explicit time stepping scheme is implemented which allows efficient simulation of incompressible fluid flow problems. Limitations of the explicit time stepping scheme that were discovered, mean that high Reynolds number flows that require the use of stretched meshes cannot produce solutions in a reasonable time period. A semi-implicit time stepping routine removes this limitation allowing these types of flows to be successfully modelled. To validate the solvers accuracy and demonstrate its performance, a number of test cases are presented. These include the lid driven cavity, flow over a backward facing step, inviscid flow around a circular cylinder, unsteady flow around a circular cylinder, flow around an SD7003 aerofoil, flow around a NACA0012 aerofoil and flow around a multi element aerofoil. The investigation although revealing a high dependence on the quality of the mesh still demonstrates that accurate results can be obtained efficiently. The efficiency is demonstrated by comparison to the in-house 2D incompressible finite volume solver for flow around a circular cylinder. For this case the unstructured MAC method produced a solution four times faster than the finite volume code