Thomas Rees

The remobilisation and mixing of locked magma mushes underlies all volcanic processes. Recently published discrete element model (DEM) simulations suggest that this mixing occurs as a localised fluidisation event, where mixing occurs over a small region of the magma mush. This thesis investigates how well these small scale simulations scale-up to full scale magma chambers. This is done by simulating these phenomena with the two-fluid granular temperature model, a multiphase flow model which… Show more

The remobilisation and mixing of locked magma mushes underlies all volcanic processes. Recently published discrete element model (DEM) simulations suggest that this mixing occurs as a localised fluidisation event, where mixing occurs over a small region of the magma mush. This thesis investigates how well these small scale simulations scale-up to full scale magma chambers. This is done by simulating these phenomena with the two-fluid granular temperature model, a multiphase flow model which models the crystals as a second continuum that fully interpenetrates the fluid phase. Validation of the code shows that the granular temperature model can reasonably model localised fluidisation phenomena. A dimensional analysis of the governing equations shows that there are five dimensionless numbers which govern the hydrodynamic scaling behaviour of the system, and that the dimensionless numbers associated with the small scale DEM simulations are not representative of a realistic magma chamber. This is confirmed by granular temperature model simulations of large scale magma chambers, which show significantly different behaviour from the small scale simulation results. Most strikingly, the large scale simulations show no evidence of the localised behaviour observed in the small scale simulation. Instead, the large scale simulations show mixing occurring across the entire
magma chamber domain. Furthermore, the simulations show that mixing can occur at
low melt fractions. Show less

With recent developments in scramjet technology such as the X-51A Waverider as well as the emergence of the private space industry, hypersonic flight is becoming more and more prevalent. One of the most important considerations in the design of hypersonic vehicles is the boundary-layer laminar-turbulent transition as this affects important design factors such as wall heating, scramjet operability, lift, and drag. A review of previous research on the topic of roughness-induced boundary-layer… Show more

With recent developments in scramjet technology such as the X-51A Waverider as well as the emergence of the private space industry, hypersonic flight is becoming more and more prevalent. One of the most important considerations in the design of hypersonic vehicles is the boundary-layer laminar-turbulent transition as this affects important design factors such as wall heating, scramjet operability, lift, and drag. A review of previous research on the topic of roughness-induced boundary-layer transition shows that although much data has been collected on the subject, and some progress has been made in understanding the flow physics behind the phenomenon, there are still many factors which have not been studied nor understood. An evaluation of roughnesses associated with hypersonic vehicles, including new materials being developed for use on these vehicles, highlights the importance of these gaps in the literature. The most notable of these is the effect of distributed roughness. It is recommended that future research programmes explore this subject in a structured and methodical manner by defining both canonical distributed roughness patterns and flows. In these studies, new experimental techniques and advanced numerical methods should be leveraged to provide insight into the flow physics of distributed roughness-induced transition. This will not only develop understanding of the flow phenomena but will also develop the methods themselves. Show less

The Von Karman Institute is developing new methods to better characterise the enthalpy of the flow generated in the Plasmatron high-enthalpy wind tunnel. A probe permitting the direct enthalpy measurement of the plasma flow had been designed and developed at the VKI. The primary objective of this project was firstly to validate the results obtained with the enthalpy probe, and to develop a better understanding of the errors attached to the results. Finally, suggestions and recommendations for… Show more

The Von Karman Institute is developing new methods to better characterise the enthalpy of the flow generated in the Plasmatron high-enthalpy wind tunnel. A probe permitting the direct enthalpy measurement of the plasma flow had been designed and developed at the VKI. The primary objective of this project was firstly to validate the results obtained with the enthalpy probe, and to develop a better understanding of the errors attached to the results. Finally, suggestions and recommendations for improvements to the probe and its process were made. Show less

The suitability for supersonic flight regimes of the current fixed block system for launch-tower integration on PERSEUS rockets is unknown. In order to reduce wave drag, new retractable blocks were developed at the cost of a greater weight. The aim of this study was to deduce whether the trade-off of higher weight for drag reduction was justified. 3D CFD calculations around rockets fitted with different block systems were made at various Mach numbers ranging from Mach 0.9 to 1.5. It was found… Show more

The suitability for supersonic flight regimes of the current fixed block system for launch-tower integration on PERSEUS rockets is unknown. In order to reduce wave drag, new retractable blocks were developed at the cost of a greater weight. The aim of this study was to deduce whether the trade-off of higher weight for drag reduction was justified. 3D CFD calculations around rockets fitted with different block systems were made at various Mach numbers ranging from Mach 0.9 to 1.5. It was found that the new retractable system resulted in a drag reduction that far outweighed the added weight, at all Mach numbers tested. Show less