title: Investigation of flow-flow, flow-surface, and multiphase interaction problems in rarefied gas dynamics
Creators: name: Agir, Muhammed Burak
Publisher: name: University of Glasgow
Year: 2023

description: Presently, with the development of technology, the need to study and understand high-speed rarefied gas flows has become an impending reality in terms of its potential assets to a wide spectrum of industries, ranging from interplanetary travel to coating technology. This study addresses the interactions of high-speed rariefied gas flows with one another, surfaces, and solid particles in order to ascertain high-speed rarefied gas behaviours in various applications. Three different interaction scenarios -two of which rely on numerical analysis and one which is based on the development of a novel solver- are investigated, where computations are conducted with a direct simulation Monte Carlo (DSMC) solver, dsmcFoam+, and a particle laden rarefied gas multiphase flow solver, rarefiedMultiphaseFoam, within the framework of an open-source tool, OpenFOAM. Rarefied shock-shock interactions have a crucial impact on aerodynamic performance and aero-heating characteristics in supersonic and hypersonic flight platforms. A shock-shock interaction problem can arise in high-speed vehicles, where an oblique shock on one part of the body impinges on a bow shock from a different part of the body and the nature of the interaction can change as the vehicle increases in altitude to a more rarefied environment. Part of this research examines the outcomes of a numerical study investigating the formation of Edney shock patterns from type-I to type-VI as a result of shock-shock interactions at different rarefaction levels. The free-stream flow is at a Mach number of 10. Both geometrical and rarefaction parameters in shock-shock interaction problems determine what type of Edney pattern is formed. As the flow becomes more rarefied, the regions of enhanced thermo mechanical loading spread further over the surface but their peak values decrease. It is known that these shock interactions can have unsteady behaviour in the continuum regime; current works show that although increasing rarefaction tends to move the flow towards steady behaviour, it still possible to have unsteady flow behaviour under more rarefied conditions. In another case, the interactions of high-speed rarefied flows with one another and a surface are analysed. The canting axis of thrusters on space platforms, which likely operate in a vacuum environment with a high degree of flow rarefaction, is significant in order to create the desired torque for manoeuvring, maintaining orbit, eliminating perturbation forces, docking, etc. Therefore, the interactions of expanding plumes with one another and with solid surfaces in multi-nozzle arrays are inevitable. In order to gain a better understanding of the effect of nozzle configurations and conditions on the plume-plume and plume-surface interactions, a simulation matrix is carried out for a sonic nozzle. As nozzle arrays are packed more tightly together, the plume-plume interactions become stronger, which has an influence on the stagnation line density and temperature profiles. For a given stagnation temperature, the spacing between nozzles in the array does not have a strong influence on the normalised surface pressure, but there is an increase in the maximum normalised shear stress as the distance between the nozzles increases. There is a significant difference in the results for double and quadruple nozzle arrays, with greater normalised stagnation pressures and shear stresses found as the number of nozzles in the array is increased. For a single nozzle, increasing the stagnation temperature does not have a significant effect on the normalised surface pressures, but does increase the maximum normalised shear stress and the measured heat flux on the surface. For arrays of double and quadruple nozzles, the number of nozzles has a much greater influence on the measured surface pressure, surface shear stress, and surface heat transfer than the stagnation temperature. In the last case, the effect of the impingement height on the plume and surface parameters is discussed while maintaining all the parameters of the 1000 K single plume case but with varying impingement heights. It is found that the smaller impingement height results in a denser plume, and a greater impact on the surface. However, higher impingement heights result in a wider distribution on the surface as the plume can expand more. With the awareness of a lack of a solver for rarefied gas flows-solid particle interactions, the final case in this thesis focuses on the development, benchmarking and testing of a multiphase open-source code, rarefiedMultiphaseFoam. Such a solver provides applicable benefits such as modelling of the transport of unburnt solid propellant in rocket a plume, and simulating of the impingement of two-phase plume on a surface in a vacuum environment, as well as providing numerical solutions in terms of surface coating technology, where multiphase gas and solid flows are employed, etc. This dsmcFoam+ based solver is capable of simulating one-way coupling interactions. This type of particle-laden rarefied gas flow has two components: the rarefied gas flow itself and the solid particles transported by the gas flow. The main restriction is that the solid phase surrounded by the gas phase is assumed to be in the free-molecular regime with respect to the solid particle diameters and that it is a one-way coupling, so that only the effect of gas particles on the solid particles is considered. rarefiedMultiphaseFoam can produce results for steady and transient one-way coupling problems in zero-dimensional (0D), one-dimesion (1D), two-dimensions (2D) (both planar and maxisymmetric), and three-dimensions (3D). Two benchmarking cases on momentum and energy transfer from gas molecules to solid particles, and free expansion of a two-phase jet flow are presented. The reliability of the solver is further demonstrated through a test case on surface coating using the Aerosol Deposition Method. The benchmarking cases yield results that are in good agreement with theoretical, experimental, and numerical data in the literature.