Browsing by Keyword "turbulence"
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Assessment of turbulence model performance: Large streamline curvature and integral length scales
(Elsevier, 20151210)For the flow over curved surfaces, an extra wallnormal pressure gradient is imposed to the flow through excessive surface pressure, such that the flow turns in alignment with the surface. In turn, turbulent fluctuations ... 
Assessment of turbulence model performance: Severe acceleration with large integral length scales
(Elsevier, 20151217)Turbulence is substantially laminarised, when the mean flow experiences streamwise acceleration above a certain critical acceleration parameter. Recently, to essentially reveal aero engine intake acceleration scenarios, ... 
Contributions in fractional diffusive limit and wave turbulence in kinetic theory
(20150630)This thesis is split in two different topics. Firstly, we study anomalous transport from kinetic models. Secondly, we consider the equations coming from weak wave turbulence theory and we study them via meanfield limits ... 
Development and validation of a combustion model for a fuel cell offgas burner
(20081014)A lowemissions power generator comprising a solid oxide fuel cell coupled to a gas turbine has been developed by RollsRoyce Fuel Cell Systems. As part of the cycle, a fraction of the unreacted fuel (the offgas) and ... 
An experimental study of turbulent vortex rings using particle image velocimetry
(20101012)In this dissertation, the early development of turbulent vortex rings at two Reynolds numbers is studied using twodimensional and Stereoscopic Particle Image Velocimetry. In the late 1980s’ a similarity theory of turbulent ... 
Fibre behaviour in the spunbonding process. Part I: Characterisation of air flow and fibre motion
(Sage, 20151110)The random fibre oscillatory behaviour induced by turbulence in the diffuser of an industrial spunbonding rig is measured experimentally. The turbulent air flow is firstly characterised by constant temperature hotwire ... 
Fibre behaviour in the spunbonding process. Part II: Modelling fibre dynamics in turbulent flows
(Sage, 20151110)The behaviour of a fibre subject to the turbulent air flow in the diffuser in the spunbonding process is studied using a threedimensional dynamics model in which the fibre is discretised as a chain of beads connected by ... 
The Frequency Response of Acoustic Doppler Current Profilers : Spatiotemporal response and implications for tidal turbine site assessment
(2014)The lifespan of a tidal turbine is strongly affected by the unsteady loading it experiences, so knowledge of the mean flow speed is not sufficient: unsteadiness must also be quantified. One of the most common turbulence ... 
Generalised nonlinear stability of stratified shear flows: adjointbased optimisation, Koopman modes, and reduced models
(Department of Applied Mathematics and Theoretical Physics, University of Cambridge, 20161004)In this thesis I investigate a number of problems in the nonlinear stability of density stratified plane Couette flow. I begin by describing the history of transient growth phenomena, and in particular the recent application ... 
Gravitoturbulence and the excitation of smallscale parametric instability in astrophysical discs
(Oxford University Press, 20171011)Young protoplanetary discs and the outer radii of active galactic nuclei may be subject to gravitational instability and, as a consequence, fall into a ‘gravitoturbulent’ state. While in this state, appreciable angular ... 
Gravitoturbulence in magnetized protostellar discs
(Oxford University Press, 20160511)Gravitational instability (GI) features in several aspects of protostellar disc evolution, most notably in angular momentum transport, fragmentation, and the outbursts exemplified by FU Ori and EX Lupi systems. The outer ... 
Insights into the location and dynamics of the coolest Xray emitting gas in clusters of galaxies
(Oxford University Press, 20160911)We extend our previous study of the cool gas responsible for the emission of O $\tiny \text{VII}$ Xray lines in the cores of clusters and groups of galaxies. This is the coolest Xray emitting phase and connects the 10 ... 
Investigating prominence turbulence with Hinode SOT Dopplergrams
(EDP Sciences, 20161010)Quiescent prominences host a diverse range of flows, including RayleighTaylor instability driven upflows and impulsive downflows, and so it is no surprise that turbulent motions also exist. As prominences are believed to ... 
Large eddy simulation of premixed combustion using flamelets
(20160202)Large Eddy Simulation (LES) has potential to address unsteady phenomena in turbulent premixed flames and to capture turbulence scales and their influence on combustion. Thus, this approach is gaining interest in industry ... 
The magnetorotational instability in debrisdisc gas
(Oxford University Press, 20160621)Debris discs are commonly swathed in gas, which can be observed in UV, in fine structure lines in FIR, and in resolved maps of CO emission. Carbon and oxygen are overabundant in such gas, but it is severely depleted in ... 
MRI turbulence and thermal instability in accretion discs
(Oxford University Press, 201706)A longstanding puzzle in the study of black hole accretion concerns the presence or not of thermal instability. Classical theory predicts that the encircling accretion disc is unstable, as do some selfconsistent ... 
Nonaxisymmetric instabilities in discs with imposed zonal flows
(Oxford University Press, 20160906)We conduct a linear stability calculation of an ideal Keplerian flow on which a sinusoidal zonal flow is imposed. The analysis uses the shearing sheet model and is carried out both in isothermal and adiabatic conditions, ... 
On the convective overstability in protoplanetary discs
(Oxford University Press, 20160121)This paper explores the driving of lowlevel hydrodynamical activity in protoplanetarydisc dead zones. A small adverse radial entropy gradient, ordinarily stabilized by rotation, excites oscillatory convection (‘convective ... 
Phaseaveraged flow statistics in compressors using a rotated hotwire technique
(Springer, 20170501)A technique based on a rotated hot wire has been developed to characterise the unsteady, threedimensional flow field between compressor blade rows. Data are acquired from a slanted hot wire rotated through a number of ... 
The stress–pressure relationship in simulations of MRIinduced turbulence
(Oxford University Press, 20160101)We determine how MRI (magnetorotational instability)turbulent stresses depend on gas pressure via a suite of unstratified shearing box simulations. Earlier numerical work reported only a very weak dependence at best, ...