Dr Chamil Abeykoon

Lecturer

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Possible Postgraduate Research Areas

- Mathematical modelling of heat transfer and fluid flow inside gas turbines

- Computational modelling and simulation of polymer melt flow in extrusion

- A soft sensor for die melt temperature profile prediction of polymer extrusion

- Polymer extrusion control with artificial intelligence techniques

- Modelling and optimization of polymer extrusion

Possible Topics for Postgraduate Research

Some collaborative projects listed below (with the School of Mechanical, Aerospace and Civil Engineering) are available in the areas relating to Gas Turbine Technology (heat transfer and fluid flow) and Renewable Energy Technologies, for self-funded students only. If interested, please contact me.

- Active Noise Control around Wind Turbines

- Computational design and development of rotating heat pipes for gas turbine cooling

- Hybrid Gas Turbine Fuel Cell Systems

- Integrated PV - Fuel Cell Generation Methodologies - Design , Development and Optimization for Distributed Power Applications

- Thermoacoustic Technologies for Electricity Generation in Small Scale Incineration and CHP Units

- Automated design of gas turbines for the chemical industry

 

Other projects available at the moment

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Project 1: Computational Studies on Tip Clearance Influence Regarding Flow and Heat Transfer Characteristics of Modern Aero Turbines

This study addresses the study of the flow and heat transfer at the tip clearance region in aero turbines. Fluid dynamics at this region tends to be extremely complex. The flow is inherently unsteady and three dimensional due to interactions of the tip leakage flow/vortex with other flow structures, interactions between adjacent rows of blades and viscous effects including shock-boundary layer interaction. Large Eddy Simulation(LES) /RANS might be used in order to resolve the significant flow structures in time and space, to figure out turbulent flow parameters and apprehend the details of the unsteady flow. These are necessary steps towards investigating new methods for enhancing isentropic turbine/engine efficiency. A major source of losses in axial turbomachinery stems from the secondary flow imposed on top of the primary one, as the flow passes each blade row. According to well-known empirical correlations, such as Howell’s model, the secondary flow typically accounts for most losses when the flow conditions are close to the design point . Among the various forms of secondary flow encountered in turbomachinery, either compressor or turbine, the tip leakage flow accounts for a major chunk of the total losses, nearly 20% to 40% depending on the machine, while the corresponding loss in efficiency can be anywhere between 2% to 4% . The phenomenon appears more intense and performance-wise more important in turbines rather than in compressors, since the driving force of the tip leakage flow – the pressure difference between the blade’s suction and pressure side – is by far greater.

The area under consideration is extremely confined, the clearance gap between an unshrouded rotor blade tip and the outer-casing wall is ~ O(1%) of the blade span, corresponding typically to a physical length ~ O(1mm) or less. The direct loss associated with the flow passing through the clearance gap without change in angular momentum represents a fairly small fraction of the total tip leakage losses. The leakage, however, of the tip clearance region affects dramatically the mean flow, downstream and inwards to a considerable portion of the blade span. The leakage flow escaping from the pressure side separates (with possible reattachment) on top of the blade tip, and subsequently rolls up at the suction side forming the leakage vortex, which interacts with the other flow structures, such as the passive vortex at the central region of the row passage, the trailing edge vortices at the blade’s wake and the boundary layer at the annulus. Strong three-dimensionality is therefore introduced into the mean flow leading to losses associated with the kinetic energy of the velocity perturbations of the various flow structures, which diffuse downstream and eventually dissipate by viscous forces. The latter indirect loss mechanism (the mixing losses) produces the major fraction of the total tip leakage losses. More complexity is introduced when compressibility effects are present, for instance at high-subsonic or transonic tip speeds present at high pressure turbines. In such cases, shock-boundary layer interactions occur at the tip clearance region regarding both confining walls at the annulus and the tip. High tip speed also gives rise to the scrapping of the annulus boundary layer by the moving rotor blade, which subsequently results into the formation of the scrapping vortex at the pressure side. At low pressure turbines, on the other hand, periodical transition from laminar to turbulent flow affects the separation pattern on the blade tip surface. Additionally, the heat transfer at the tip is heavily affected by the tip leakage flow/vortex, with a subsequent impact on the cooling requirements of the region.

The above described perturbations in the velocity and the temperature fields are perceived by the succeeding stator blade row as an inlet distortion, making an impact to both the flow development and heat transfer and leading to a subsequent distortion to the nozzle row outflow, which affects the inlet of the next rotor blade row and so forth.

While it is neither possible nor intended to fully describe the flow field within the present proposal, the complexity of the aerophysics taking place in the vicinity of the tip clearance has already become apparent. The main flow features that build up the complexity can be summarised as follows:

1) The flow is inherently unsteady,

2) The geometries involved are complicated,

3) There is relative motion between the rotor and stator blade rows and between the rotor blade rows and the outer casing,

4) The flow periodically transitions between laminar and turbulent,

5) Shock-boundary layer interactions occur at high tip speeds.

Project 2: Design and Development of an Expander for Optimum Power for Organic Rankine Cycles

It is well known that gas and steam cycles play a dominant role in large-scale stationary power generation. Open-cycle gas turbines (often combined with steam cycles) are widely used, especially where low-cost natural gas is available, while steam cycles are the preferred solution when the energy source characteristics, typically coal or nuclear, require a closed-cycle power plant. However, there is a large variety of energy sources for which neither gas nor steam cycles offer a technically and/or economically viable solution to generate electric power. When the temperature and/or the thermal power available from the energy source is limited, it becomes attractive to adopt a different class of prime movers, universally known with the acronym ORC (Organic Rankine Cycle). This project will concentrate on the design and development of turbomachinery appropriate for the above relatively modest temperature heat sources utilizing organic working fluids constrained by the unusual thermodynamic and thermophysical attributes of the prevailing circumstances. The activity will employ appropriate analytical/computational tools primarily mean streamline analysis and three dimensional state of the art CFD algorithms validated where appropriate with data form the literature for optimum energy recovery.

Project 3: Hybrid Gas Turbine Fuel Cell Systems

The main objective of the proposed research is to generate much-needed information on the hybrid systems, so that one can start to develop an understanding of the working principles of fuel cells and gas turbines. Subsequently, efforts can  developed to find out how an economical integrated design is created to increase efficiency. In order achieve this purpose; each component of the hybrid systems will be examined by using thermodynamic entropy based modelling activities. For example as the followings may be investigated:

For fuel cells

v Understanding of pressurized operation

v Design for pressurized operation

v Changing materials and fuels

For gas turbines

v Increased pressure ratio

v Increased compressor and turbine aerodynamic efficiencies

v Recuperative cycle configurations

v Reduced combustor emissions

Project 4: Design and Development Binary Cycles and Engineering Hardware for Optimum Power for Organic Rankine Cycles

It is well known that gas and steam cycles play a dominant role in large-scale stationary power generation. Open-cycle gas turbines (often combined with steam cycles) are widely used, especially where low-cost natural gas is available, while steam cycles are the preferred solution when the energy source characteristics, typically coal or nuclear, require a closed-cycle power plant. However, there is a large variety of energy sources for which neither gas nor steam cycles offer a technically and/or economically viable solution to generate electric power. When the temperature and/or the thermal power available from the energy source is limited, it becomes attractive to adopt a different class of prime movers, universally known with the acronym ORC (Organic Rankine Cycle). This project will concentrate on the design and development of turbomachinery appropriate for the above relatively modest temperature heat sources utilizing organic working fluids constrained by the unusual thermodynamic and thermophysical attributes of the prevailing circumstances. The activity will employ appropriate analytical/computational tools primarily mean streamline analysis and three dimensional state of the art CFD algorithms validated where appropriate with data form the literature for optimum energy recovery.

Project 5: Numerical Modelling of Melt Flows in Polymer Extrusion

In polymer extrusion, the behaviour of the flow of materials along the screw shows highly variable nature as it is gradually changing from solid to molten state. There are a number of aspects that have not yet been well understood on processing of polymeric materials such as the contact between metal-polymer and polymer-polymer at the solid/molten state; the way of forming and progression of melt pools; conveying of solid materials in the equipment (friction, shear, formation and breakup of solid beds); clear correlation/s between materials properties or melt thermal quality and process energy consumption, etc. Hence, this project aims to understand the flow behaviour of an extruder via combining numerical/computational modelling techniques with conventional empirical modelling. A computational algorithm to simulate the flow driven temperature evolution during the extrusion is required to formulate. Navier–Stokes formulations will then be applied in a fixed grid to solve energy, momentum and continuity equations addressing the algorithm. The temperature/pressure dependent properties of the melt will be incorporated the computations as polynomials of respective parameters (under incompressible flow regime). Extruder screw rotation and barrel heater parameters will be taken as inputs to define boundary conditions to the model. Contact behaviours between metal-polymer (at the solid and molten states) and polymer-polymer (at the solid state) will be incorporated to through empirical approach, based on experimental observations. Software codes will be developed to simulate varying process and material conditions. Then, the experimentally measured parameters (melt pressure and melt temperature)  can be compared with the computational and empirical model predictions for verification and validation purposes.

Project 6: Modelling of polymer resin flow through fibres in composite manufacturing

The fluid (resin) flow behaviour through and across the reinforcement is really important in polymeric materials based composites manufacturing to achieve the desired properties. In the processes such as resin transfer moulding (RTM), two flows occur simultaneously as resin is injected into a cavity: macro-flow, in which the resin flows through the gaps between the bundles of fibres which make up the preform, and micro-flow, in which the resin penetrates the pores within the fibre bundles to wet the individual fibres. Both of these flows must be completed before significant reaction occurs and the viscosity of the resin begins to rise rapidly. If macro-flow is incomplete, a "short shot" will result while an incomplete micro-flow is not visually obvious, but as the mechanical properties of a composite are highly dependent on the interfacial adhesion between the matrix and reinforcement, it is important to maximize the degree of fibre wetting.

The resin flow behavior though/across fibre matrix during composites manufacturing can be numerically modelled. Such a model will help to elucidate the fundamental understanding which could underpin advanced composite processing capabilities to achieve the desired properties. It is expected to employee the concept of the flow of a slurry (which represent the resin) through a porous medium (fiber matrix). As the initial step, numerical formulation can be verified against the generic porous medium models. If required, 4D imaging can be used as an advanced tool to validate such models.

Project 7: A soft sensor for die melt temperature profile prediction of polymer extrusion

Polymeric materials play a major role in production industry and hence advanced process monitoring is invaluable for improving the product quality and process efficiency. Extrusion is a fundamental method of processing polymeric materials. An extruder is a machine which processes materials by conveying it along a screw and forcing it through a die at a certain pressure. The main function of an extruder is to deliver a homogeneous, well mixed polymer melt at a specified uniform temperature and pressure. Currently, there are no industrially well-established techniques for online measurement/prediction of the die melt temperature profile and viscosity of the melt output. Hence, this project aims to first explore the existing melt temperature and viscosity monitoring techniques used in polymer processing and then propose novel, industrially-compatible techniques for online monitoring of melt viscosity and melt temperature profile across the die. Initially, the efficacy of the novel techniques will be explored via simulation and then will be tested on a medium scale industrial extruder with commonly used polymeric materials. The aim is that the newly proposed techniques should facilitate advanced process monitoring and hence to the development of advanced control strategies to optimize the process energy efficiency and product quality.

Project 8: Investigation of the processing behaviour of recycled polymers in compression moulding (MPhil)

This project is a collaborative project with industry and aims to use a few recycled materials (mainly Axplas MEP plastic chips) to explore their processing behaviour in compression moulding. A set of sample mixtures of Axplas MEP plastics chips (ABS/PS/PPTF mixtures) in 5 - 8 mm size range will be used in experimental studies. It is expected to explore possible relationship(s) between key parameters such as thicknesses, compression ratio, heating time, temperature in terms of the type of the block/plank created in compression moulding. Then, it expected to investigate the desired target operating zone to make a viable product and to measure the strength of the different blocks made under some controlled conditions. Also, it is expected to come up with some recommendations on how the products could be scaled up/down to make desired commercial products (e.g., such as  planter boxes/cylinders  for horticultural  use) and also what factors would impact upon a production process as a using typical compression moulding techniques.

Project 9: Investigation of the structure formation of 3D printed crystalline polymers (MPhil)

Semi-crystalline polymers are important class of polymeric materials used in various industrial applications. The crystal structures can mostly dominate the mechanical and functional properties of such semi-crystalline polymers. Particularly, when combined with modern 3D printing processes, controlling of crystalline features can be controlled by varying process parameters to construct advanced materials with tailor made properties.

Transmission light microscopes with multi-imaging-mode approaches are very useful tools to study crystalline features in polymeric materials; however it requires a detailed image analysis. This project is aimed to develop an experimental capacity to establish a detailed process parameter – structure – property relationship for 3D printed crystalline polymers.  

Project 10: Numerical Modelling of Radial Die Melt Temperature Profile in Polymer Extrusion (MPhil)

Project 11: Enhancement of the properties of concrete with recycled polymers (MPhil)

Project 12: Use of phase change materials in heat transfer applications (MPhil)

 

 (For self-funded MPhil/PhD candidates) Ask for more details