A RBF partition of unity collocation method based on finite difference for initial-boundary value problems

Meshfree radial basis function (RBF) methods are popular tools used to numerically solve partial differential equations (PDEs). They take advantage of being flexible with respect to geometry, easy to implement in higher dimensions, and can also provide high order convergence. Since one of the main disadvantages of global RBF-based methods is generally the computational cost associated with the solution of large linear systems, in this paper we focus on a localizing RBF partition of unity method (RBF-PUM) based on a finite difference (FD) scheme. Specifically, we propose a new RBF-PUM-FD collocation method, which can successfully be applied to solve time-dependent PDEs. This approach allows to significantly decrease ill-conditioning of traditional RBF-based methods. Moreover, the RBF-PUM-FD scheme results in a sparse matrix system, reducing the computational effort but maintaining at the same time a high level of accuracy. Numerical experiments show performances of our collocation scheme on two benchmark problems, involving unsteady convection-diffusion and pseudo-parabolic equations

Solution of 3-dimensional time-dependent viscous flows. Part 2: Development of the computer code

There is considerable interest in developing a numerical scheme for solving the time dependent viscous compressible three dimensional flow equations to aid in the design of helicopter rotors. The development of a computer code to solve a three dimensional unsteady approximate form of the Navier-Stokes equations employing a linearized block emplicit technique in conjunction with a QR operator scheme is described. Results of calculations of several Cartesian test cases are presented. The computer code can be applied to more complex flow fields such as these encountered on rotating airfoils

Hydrogen Research for Spaceport and Space-Based Applications: Hydrogen Production, Storage, and Transport

The activities presented are a broad based approach to advancing key hydrogen related technologies in areas such as fuel cells, hydrogen production, and distributed sensors for hydrogen-leak detection, laser instrumentation for hydrogen-leak detection, and cryogenic transport and storage. Presented are the results from research projects, education and outreach activities, system and trade studies. The work will aid in advancing the state-of-the-art for several critical technologies related to the implementation of a hydrogen infrastructure. Activities conducted are relevant to a number of propulsion and power systems for terrestrial, aeronautics and aerospace applications. Hydrogen storage and in-space hydrogen transport research focused on developing and verifying design concepts for efficient, safe, lightweight liquid hydrogen cryogenic storage systems. Research into hydrogen production had a specific goal of further advancing proton conducting membrane technology in the laboratory at a larger scale. System and process trade studies evaluated the proton conducting membrane technology, specifically, scale-up issues

Modelling of explosion deflagrating flames using Large Eddy Simulation

Encouraged by the recent demand for eco-friendly combustion systems, advancements in the predictive capability of turbulent premixed combustion are considered to be essential. The explosion and deflagrating flame are modelled with the numerical method by applying the Large Eddy Simulation (LES) technique. It has evolved itself as a powerful tool for the prediction of turbulent premixed flames. In the LES, Sub-Grid Scale (SGS) modelling plays a pivotal role in accounting for various SGS effects. The chemical reaction rate in LES turbulent premixed flames is a SGS phenomenon and must be accounted for accurately. The Dynamical Flame Surface Density (DFSD) model which is based on the classical laminar flamelet theory is a prominent and well accepted choice in predicting turbulent premixed flames in RANS modelling. The work presented in this thesis is mainly focused upon the implementation of a dynamic flame surface density (DFSD) model for the calculation of transient, turbulent premixed propagating flames using the LES technique. The concept of the dynamism is achieved by the application of a test filter in combination with Germano identity, which provides unresolved SGS flame surface density information. The DFSD model is coupled with the fractal theory in order to evaluate the instantaneous fractal dimension of the propagating turbulent flame front. LES simulations are carried out to simulate stoichiometric propane/air flame propagating past solid obstacles in order to validate the model developed in this work with the experiments conducted by the combustion group at The University of Sydney. Various numerical tests were carried out to establish the confidence of LES. A detailed analysis has been carried out to determine the regimes of combustion at different stages of flame propagation inside the chamber. LES predictions using the DFSD model are evaluated and validated against experimental measurements for various flow configurations. The LES predictions were identified to be in strong agreement with experimental measurements. The impact of the number and position of the baffles with respect to ignition origin has also been studied. LES results were found to be in very good agreement with experimental measurements in all these cases

Development of a dynamic LES model for premixed turbulent flames

In numerical modelling, Large Eddy Simulations (LES) has evolved itself as a powerful tool for the prediction of turbulent premixed flames. In LES, sub-grid scale (SGS) modelling plays a pivotal role in accounting for various SGS effects. Chemical reaction rate in LES turbulent premixed flames is a SGS phenomenon and must be accounted accurately. Flame surface density (FSD) models based on laminar flamelet concepts are simple and efficient in accounting the chemical reaction rate, which is the main motive of this research (...continues

Combustion of PTFE: The effects of gravity on ultrafine particle generation

The objective of this project is to obtain an understanding of the effect of gravity on the toxicity of ultrafine particle and gas phase materials produced when fluorocarbon polymers are thermally degraded or burned. The motivation for the project is to provide a basic technical foundation on which policies for spacecraft health and safety with regard to fire and polymers can be formulated