R. Prosser

• B.eng. Ph.D.
• Reader at The University of Manchester

The liquid piston gas compressor (LPGC) is a method of compressing gases with improved efficiency. Key to the success of this device is its operation in as close to an isothermal state as possible. This paper presents high-fidelity, three-dimensional, unsteady Reynolds-averaged Navier–Stokes (uRANS) simulations to better understand the heat transfe...

The flow of liquid crystals in the presence of electric fields is investigated as a possible means of flow control. The Beris-Edwards model is coupled to a free energy incorporating electric field effects. Simulations are conducted in straight channels and in junctions. Our findings reveal that local flow mediation can be achieved by the applicatio...

Despite the recognized role of liquid crystal microfluidics in generating programmable, self-organized and guided flow properties, to date, the flow behavior of LCs within curved channels remains unexplored. Using experiments and numerical simulations, we demonstrate that the curvature of microscale conduits allow programming of liquid crystal (LC)...

The aim of this paper is two-fold: (1) to provide a detailed investigation of the turbulent flow in an inline high-shear rotor stator mixer; (2) to provide a comparison of two different classes of turbulence models and solution methods currently available. The widely used multiple reference frame (MRF) method is contrasted against a more recently d...

Using experiments and numerical simulations, we demonstrate that the curvature of microscale conduits allow programming of liquid crystal (LC) flows. Focusing on a nematic LC flowing through U- and L-shaped channels of rectangular cross-section, our results reveal that curved flow paths can trigger gradients of flow-induced director field in the tr...

Thin films consisting of polymer solutions are typically produced through a combination of extrusion and shearing processes, where the anisotropic, non-Newtonian solution is deformed and subjected to thermal treatment. This paper investigates the shearing of polymeric thin films by studying the channel flow rheology of polymer solutions that experi...

The use of nematics in microfluidic devices offers methods of flow control that are inaccessible to isotropic fluids. While nematics have been used in channel flows found in lab on chip devices, their flow and microstructure formation still needs to be fully understood in geometries with a cylindrical cross-section. This paper investigates liquid c...

The formation of discrete water clusters in polymer electrolyte fuel cell gas diffusion layers (GDL) can lead to increased resistance for oxygen transport in the catalyst layer. This study investigates the effect of MPL crack propagation on the water cluster development in a X-ray computed tomography (CT) microstructure using the volume-of-fluid me...

Extrusion is an essential element in the production of nematic soft solids, ensuring that the final formulation is sufficiently refined and compacted. The interplay between complex microstructure and processing conditions affects the final product performance and may even lead to material degradation. This paper investigates the flow of nematic liq...

Proton exchange membrane fuel cells (PEMFC) electrochemically combine hydrogen and oxygen to produce electrical energy, heat and water. Therefore, PEMFC offer an alternative to vehicle electrification and reduction of greenhouse gas emissions. However, material limitations under high current density conditions limit the efficiency due to water floo...

3D printing and carbonisation is used to produce designed gas diffusion layer materials for polymer electrolyte membrane fuel cells (PEMFC). Using a desktop UV 3D printer, designed porous microstructures are printed with micro and macro-scale features. Successful improvement of the pyrolysis process maintains the structural accuracy during carbonis...

During the processing of nematic soft solids through process flow elements (pipe bends, elbows, etc.), the constitutive behaviour makes its presence felt via processing (with rheology driven effects increasing pressure drop) and the final product microstructure. This paper explores the flow and microstructure configurations of nematic liquid crysta...

Static mixers are an effective model system for investigating the effect of fluid rheology on pressure losses in laminar flow. Viscoelastic pressure drop enhancement in real process fluids was investigated using experimental methods and computer simulations of a SMX+TM mixer. The results were compared against classical friction factor correlations...

We study a fully developed creeping flow of nematic liquid crystals in a curved pipe with a circular cross-section. A special limit of zero Deborah number and an infinite Ericksen number limit is considered, so the flow and orientation of the director are described by the transversely isotropic fluid (TIF) model. Analytical solutions are obtained b...

Understanding the development of discrete water clusters in polymer electrolyte fuel cells is important in order to develop strategies to mitigate water flooding at high current density. Using x-ray computed tomography images of two different commercial gas diffusion layer materials (Toray & SGL), the dynamic water injection and cluster growth is s...

An anisotropic drop breakage model is applied to CFD–PBM simulations of turbulent emulsification in a high–pressure homogeniser. We compare the exponent of Sauter mean diameter – pressure drop correlations with published experimental results and with exponents obtained using existing drop breakage models. Its theoretical value assuming homogeneous...

The assumption of homogeneous isotropic turbulence when modeling drop breakage in industrially relevant geometries is questionable. We describe the development of an anisotropic breakage model, where the anisotropy is introduced via the inclusion of a perturbed turbulence spectrum. The selection of the perturbed spectrum is itself motivated by our...

This paper examines the fluid dynamics of a pilot–scale high–pressure homogeniser using large–eddy simulation. The mixer consists of a non–planar elliptic jet released into a confined cylindrical chamber. The simulated results are validated by comparing mean quantities with published experimental data. The evolution of the shear layers in the jet n...

This work investigates the simulation of dilute emulsions in a Model ACIP2 Sonolator using CFD and population balance methods. Two breakage frequency models are used, which differ in the expression of the drop breakage time. Drop breakage modeling based on homogeneous isotropic turbulence (HIT) shows poor agreement of the Sauter mean diameter when...

This paper examines the flow characteristics of a pilot-scale high shear mixer using Large Eddy Simulation (LES). The mixer consists of a non-planar el-liptic jet released into a confined cylindrical chamber. The simulated results are validated by comparing mean quantities with published PIV data. Fundamental turbulence quantities including turbule...

This work investigates the simulation of dilute, low-viscosity emulsions in a pilot-scale ACIP2 Sonolator using Computational Fluid Dynamics (CFD) and Population Balance Methods (PBM). Comparisons between the simulations and the experimental work of Ryan [1] show excellent agreement of the pressure drop (ΔP) and reasonable agreement of the Sauter m...

Rotor-Stator mixers such as the inline Silverson are widely used by the process industry. Existing literature on experimental and computational investigations of these devices focus on characterising the power draw and turbulent mixing of Newtonian fluids and non-Newtonian fluids such as emulsions. The current knowledge on the performance of these...

This paper examines the effects of scalar dissipation rate modelling on mean reaction rate predictions in turbulent premixed flames. The sensitivity of the mean reaction rate is explored by using different closures for scalar dissipation and the sensitivity of the scalar dissipation models themselves is also examined with respect to their defining...

This paper presents a combined RANS and LES methodology, which automates the dual-mesh hybrid LES/RANS approach and circumvents the need for wall-functions. Unlike RANS, wall-resolved LES is still unaffordable for studying high Reynolds number complex flows in industry and requires much user expertise when turbulence features are unknown a priori....

Computational fluid dynamics (CFD) is coupled to population balance modelling (PBM) for the simulation of turbulent drop dispersion and evolving rheology in concentrated oil–water emulsions flowing through a Silverson 150/250MS mixer. Unsteady Reynolds averaged Navier–Stokes (URANS) simulations on a sliding mesh were performed for the fluid dynamic...

The accurate resolution of flame structure is critically important to the Direct Numerical Simulation (DNS) of reacting flows. While grid resolution estimates are readily available for cold flows, premixed flames appear to have received relatively little attention. In this paper, a premixed flame characterised by single step chemistry at moderate t...

Tessellated continuum mechanics is an approach for the representation of thermo-mechanical behaviour of porous media on tessellated continua. It involves the application of iteration function schemes using affine contraction and expansion maps, respectively, for the creation of porous fractal materials and associated tessellated continua. Highly co...

In assessing whether nuclear plant components such as T-Junctions are likely to suffer thermal fatigue problems in service, CFD techniques need to provide accurate predictions for wall temperature fluctuations. Though it has been established that this is within the capabilities of wall-resolved LES, its high computational cost has prevented widespr...

This paper tests the hypothesis that the tessellation used in tessellated continuum mechanics can form a mesh in a continuous Galerkin finite element method. Although the tessellation is not unique, neither is it arbitrary, and its construction imposes constraints on any numerical analysis. A distinctive feature of the tessellation is that it can p...

Flows in pipe bends and T-Junctions are of great interest to the nuclear power industry, as turbulent temperature fluctuations in coolant flow can cause high cycle thermal fatigue in pipe walls. However, these flows often feature separation, streamline curvature and Reynolds stress anisotropy; as a result, they are challenging for RANS eddy viscosi...

Filtering of particle-based simulation data can lead to reduced computational costs and enable more efficient information transfer in multi-scale modelling. This paper compares the effectiveness of various signal processing methods to reduce numerical noise and capture the structures of nano-flow systems. In addition, a novel combination of these a...

Turbulent mixing of fluids in a T-Junction can generate oscillating thermal stresses in pipe walls, which may lead to high cycle thermal fatigue. This thermal stripping problem is an important safety issue in nuclear plant thermal-hydraulic systems, since it can lead to unexpected failure of the pipe material. Here, we carry out a large eddy simula...

Flame turbulence interaction (FTI) is an important term for modelling scalar dissipation in premixed turbulent combustion. In order to obtain an accurate representation of the flame turbulence interaction phenomenon, an evolution equation for FTI has recently been proposed. This equation gives a detailed insight into the flame turbulence interactio...

There existmany spatial discretization schemes that arewell able to provide accurate and stable approximations for isothermal turbulent flows. Comparatively little analysis has been made of the performance of these schemes in the presence of temperature gradients driven by combustion. In this paper, the effects of temperature gradients on numerical...

This paper tests the hypothesis that the analysis of heat transfer through a cellular structure represented by a fractal or a pre-fractal can be achieved through analysis on a tessellated continuum. A transport theory for fractals is introduced, which is coupled to a hole-fill mapping strategy, to facilitate the analysis of transport problems on a...

Flame turbulence interaction is one of the leading order terms in the scalar dissipation transport equation and is thus an important phenomenon in premixed turbulent combustion. Swaminathan and Grout and Chakraborty and Swaminathan have shown that the effect of strain rate on the transport of scalar dissipation is dominated by the interaction betwe...

Flame stabilization is an important issue in practical applications of combustion systems. The bluff-body configuration is a common technique that stabilizes the flame by producing a strong recirculation zone downstream of the bluff body. Gas turbines provide a typical application of the bluff-body configuration. In this paper, a computational stud...

Thermal fatigue is a major concern in the service-life management of nuclear plant thermal-hydraulics systems. Hybrid LES/RANS techniques have the potential to provide predictions which are computation-ally affordable for studies of this problem in industry, however they require further development and validation. The present work compares various...

There exist many spatial discretization schemes that are well able to provide accurate and stable approximations for isothermal turbulent flows. Comparatively little analysis has been made of the performance of these schemes in the presence of temperature gradients driven by combustion. In this paper, the effects of temperature gradients on numeric...

The Direct Numerical Simulation (DNS) of compressible low Mach number reacting flows imposes significant challenges on the schemes used for spatial discretization. The high order schemes used to date have typically required; (a) a stable internal scheme; (b) well behaved physical boundary condi-tions (for which there is some guidance) and; (c) High...

In this paper, a one dimensional premixed laminar methane flame is subjected to acoustic oscillations and studied. The purpose of this analysis is to investigate the effects of acoustic perturbations on the reaction rates of different species, with a view to their respective contribution to thermoacoustic instabilities. Acoustically transparent non...

Flame turbulence interaction is one of the leading order terms in the scalar dissipation ε c transport equation [1] and is thus an important phenomenon in premixed turbulent combustion. Swaminathan and Grout [2] and Chakraborty and Swaminathan [3, 4] have shown that the effect of strain rate on the transport of ε c is dominated by the interaction b...

A new delayed detached-eddy simulation (DDES) model is formulated that demonstrate both improved modeling of the near-wall physics and numerical robustnesss for industrial applications. For the majority of the flow, DDES formulations predict the correct level of turbulent shear stress and, therefore, a similar velocity profile to that of the refere...

Fractals can be used to represent intricate self-similar geometries, but their application to the representation of physical systems is beset with difficulties which stem from an inability to define traditionally derived-physical quantities such as stress, pressure, strain, heat etc. This paper describes a method for the determination of analytical...

A modified eddy viscosity model is proposed to codify the misalignment between stress and strain fields for variable density flows. The stress-strain misalignment is quantified by introducing a C as parameter. A transport equation for C as is derived from a full Reynolds stress model (RSM). The Cas transport equation is coupled to a standard EVM mo...

Recent work in the field of turbulence modelling has demonstrated the benefits of the wavelet-based multiresolution analysis technique as a tool for the formulation of the large-eddy simulation (LES) equations. In this formalism, the LES equations are obtained by projecting the Navier–Stokes equations onto a hierarchy of wavelet spaces. This paper...

A new formulation of Delayed Detached-Eddy Simulation (DDES) based on the − f elliptic relaxation model has been derived and calibrated. A suitable correction function Ψ and a model constant CDDES have been formulated and validated using decaying isotropic turbulence (DIT). The model has been applied to a 2D wall-mounted hump at high-Reynolds numbe...

In this paper, we develop a method of prescribing time dependent boundary conditions for reacting flows. The method builds on earlier results, and derives from a linearization of the flow field around a base state. The base state is specified in terms of the flow dilatation, and we establish a general expression for the dilatation in reacting flows...

Discretisation schemes based on the use of wavelet methods offer many potential advantages for the numerical simulation of combustion. In many cases of interest, flame structures are thin relative to the largest length scales of the problem and most length scales of the flow field, and so lend themselves to simulation using adaptive-mesh methods. W...

The flow around a trailing edge is computed with a new hybrid method designed to more clearly separate the effects of total and sub-grid turbulent stress-modelling on the time-averaged and instantaneous velocity fields, and in turn, mean momentum and kinetic energy balances. These two velocity fields independently define Reynolds averaged and sub-g...

In this paper, we provide sets of lifting coefficients for interpolating wavelets defined on a closed finite interval. Unlike previous constructions, these coefficients are resolution independent, and are suitable for applica-tions in computational physics.

A coupling methodology between an upstream Reynolds Averaged Navier–Stokes (RANS) simulation and a Large Eddy Simulation (LES) further downstream is presented. The focus of this work is on the RANS-to-LES interface inside an attached turbulent boundary layer, where an unsteady LES content has to be explicitly generated from a steady RANS solution....

The flow around a trailing edge is computed with a new hybrid method designed to split the influences of the averaged and instantaneous velocity fields. The model is first tested on channel flows at different Reynolds numbers and coarse meshes giving good predictions of mean velocities and stresses. On the trailing edge flow the predictions of the...

A novel wavelet-based method for the simulation of reacting flows on adaptive meshes is presented. The method is based on a subtraction algorithm, wherein the wavelet coefficients are calculated from the low resolution up (as op-posed to the standard top-down approach). The advantage of this new method is that it allows the calculation of wavelet c...

This paper presents the initial steps taken in order to determine the most effective method to predict flows in a transitional regime, which can then be applied to the rear wing of a Formula 1 vehicle. Recent literature [1][2] suggests that incorporation of laminar kinetic energy is a promising method of transition prediction for industrial require...

In the present study, the possibility of performing cheap and accurate LES computations using unstructured grids on complex geometries has been examined. The test case considered is a turbulent flow around a thin controlled diffusion airfoil at low speed, with angle of attack of 8° to the incoming free-stream flow. The flow velocity is set to satis...

The present paper summarizes the research conducted at the University of Manchester over the course of the Desider project on methods of generation of synthetic turbulence. A random procedure, referred to as the Synthetic Eddy Method (SEM), based on the classical view of turbulence as a superposition of coherent structures was developed and compare...

Abstract In this study, a 2D large eddy simulation of the flow around a thin, cambered, controlled-diffusion airfoil was carried out. An embedded local mesh refinement technique was used to achieve very fine near-wall resolution while maintaining a coarse mesh away from the airfoil. The flow was simulated at a geometric angle of attack of g• and a...

The use of wavelets - and more generally multi-resolution analysis (MRA) - for the solution of non-linear partial differential equations (PDEs) is an active area of research, with many schemes currently available. Recently, a scheme has been developed, which employs biorthogonal interpolating wavelets, and which has been applied to problems in comb...

A new wavelet-based method for the simulation of reacting flows on adaptive meshes is presented. The method is based on the removal of grid points whose wavelet coefficients are small with reference to some user-specified threshold. Unlike some other collocation methods, the scheme simulates flow behaviour in the physical (i.e. not transformed) dom...

The flow structure around wall mounted circular cylinders of finite heights is numerically investigated via large eddy simulation (LES). The cylinder aspect ratios (AR) are 6 and 10 and the Reynolds number (Re) based on cylinder diameter and free stream velocity is 20,000 for both cases. The cantilever cylinder mounted on a flat plate is chosen sin...

A Large Eddy Simulation of a bluff body flame has been carried out using an unstructured grid. The flame, burning a methane-hydrogen fuel with de- tailed combustion chemistry (based on a mechanism of 18 species) is simulated using STAR-CD. The mix- ture fraction is used as a conserved scalar, and a sub- sequently temperature, density and species ma...

Implicit methods for reacting flow systems are considered efficient when expressed in terms of a time step length. A drawback of these methods is the additional work required at each time step for solving the sparse matrix of algebraic equations, which degrades their efficiency. Explicit methods are easy to implement but require excessively small s...

In this paper we explore the specification of time dependent boundary conditions for the simulation of low Mach number reacting flows. A new approach is presented which is derived from the method of characteristics and an application of a Mach number based double expansion. Through the double expansion, it is possible to identify and seperate inert...

The generation of inflow data for spatially developing turbulent flows is one of the challenges that must be addressed prior to the application of LES to industrial flows and complex geometries. A new method of generation of synthetic turbulence, suitable for complex geometries and unstructured meshes, is presented herein. The method is based on th...

In the context of compressible flows, the standard non-reflecting boundary conditions of Hedstrom [J. Comput. Phys. 30 (1979) 222–237] produce spurious pressure oscillations when applied to turbulent flows. In this paper, we present an analysis of the characteristics used to define non-reflecting boundary conditions. The analysis is conducted in te...

In the process of simulating the trailing edge noise of an airfoil, perform- ing the unsteady simulations of these broadband noise sources cheaply and accurately remains a major challenge. In the present study, two different fine turbulent unsteady simulations are tested on a thin controlled diffusion airfoil at low speed and low angle of attack. The...

Discrete Diffusion Monte Carlo (DDMC) is a technique for increasing the efficiency of Monte Carlo particle-transport simulations in diffusive media. If standard Monte Carlo is used in such media, particle histories will consist of many small steps, resulting ...

The prospects presented by wavelets in the numerical analysis of chemically reacting turbulent flows are examined. In many flows of industrial relevance, combustion takes place in a stream of turbulent premixed gases. The mode of combustion is said to lie in the laminar flamelet regime. When a combustion process belonging to this regime occurs, it...

This paper focuses on the simulation of turbulent reacting flows via recent developments in wavelet-based analyses. The unique data compression properties of wavelet methods render them especially attractive for such simulations, in which the length and time-scales of interest originate from both physical and chemical processes and may span several...

The numerical simulation of combustion remains a challenging task. Flames are often thin and occupy a relatively small volume within the domain of interest. Nevertheless all of the combustion chemistry and much of the associated molecular transport takes place within the flame itself, giving rise to a structure that must be resolved if the simulate...

1. Motivation Direct Numerical Simulation (DNS) of turbulent flows is an activity severely limited by presently available computer power. It has long been known (e.g. Corrsin 1961) that in order to resolve accurately the governing Navier-Stokes equations, the number of computational cells required scales as a super-linear power of the Reynolds numb...

A number of different numerical methods are comparatively examined in the light of direct numerical simulations of premixed combustion. The schemes considered are; Fourier, Chebyshev and orthogonal wavelet pseudospectral collocation methods; compact finite difference schemes of 4th, 8th and 10th order; explicit centred difference schemes of 2nd...

OBSERVATIONS Flow over the rear-wing configuration below was simulated with RSM using a fine mesh [1]. It was then compared with experimental values. The resulting pressure coefficients at the centre and outermost cross-sections are shown in Figures 1 and 2. INTRODUCTION CFD is a powerful tool to validate automotive rear wing designs and configurat...

In this paper we explore the specification of time dependent boundary con- ditions suitable for the simulation of low Mach number reacting flows. The standard treatments used to date are based on the method of characteristics, and essentially set to zero the incoming characteristics; this practise has been shown to have deleterious effects on the f...