The gas turbine blade/vane internal cooling is achieved by circulating the compressed air through the cooling passages inside the turbine blade. Leading edge and trailing edge of the turbine blade are two critical regions which need to be properly cooled. Leading edge region receives extremely hot mainstream flow and high heat transfer enhancement is required. Trailing edge region usually has narrow shaped geometry and applicable cooling techniques are restricted. Heat transfer will be investigated in the leading edge and trailing edge cooling channels at high rotation numbers close to the engine condition. Heat transfer and pressure drop has been investigated in an equilateral triangular channel (Dh=1.83cm) to simulate the cooling channel near the leading edge of the gas turbine blade. Three different rib configurations (45°, inverted 45°, and 90°) were tested at four different Reynolds numbers (10000-40000), each with five different rotational speeds (0-400 rpm). By varying the Reynolds numbers (10000-40000) and the rotational speeds (0-400 rpm), the rotation number and buoyancy parameter reached in this study were 0-0.58 and 0-2.3, respectively. 45° angled ribs show the highest thermal performance at stationary condition. 90° ribs have the highest thermal performance at the highest rotation number of 0.58. Heat transfer coefficients are also experimentally measured in a wedge-shaped cooling channel (Dh =2.22cm, Ac=7.62cm2) to model an internal cooling passage near the trailing edge of a gas turbine blade where the coolant discharges through the slot to the mainstream flow. Tapered ribs are put on the leading and trailing surfaces with an angle of attack of 45°. The ribs are parallel with staggered arrangement on opposite walls. The inlet Reynolds number of the coolant varies from 10,000 to 40,000 and the rotational speeds varies from 0 to 500 rpm. The inlet rotation number is from 0 - 1.0. The local rotation number and buoyancy parameter are determined by the rotational speeds and the local Reynolds number at each region. Results show that heat transfer is high near the regions where strong slot ejection exists. Both the rotation number and buoyancy parameter have been correlated to predict the rotational heat transfer enhancement.

Gas turbine blade/vane cooling is obtained by circulating the high pressure air from compressor to the internal cooling passage of the blade/vane. Heat transfer and cooling effect in the rotating blade is highly affected by rotation. The typical rotation number for the aircraft engine is in the range of 0~0.25 and for the land based power generation turbine in the range of 0~05. Currently, the heat transfer data at high rotation numbers are limited. Besides, the investigation of heat transfer phenomena in the turn region, especially near hub portion is rare. This dissertation is to study the heat transfer in rectangular channels with turns in the tip or the hub portion respectively at high rotation numbers close to the engine condition. The dissertation experimentally investigates the heat transfer phenomena in a two-pass rectangular channel (AR=W/H=2:1) with a 180 degree sharp turn in the tip portion. The flow in the first passage is radial outward and after the turn in the second passage, the flow direction is radial inward. The hydraulic diameter (Dh) of the channel is 16.9 mm. Parallel square ribs with an attack angle (alpha) of 45 degrees are used on leading and trailing surfaces to enhance the heat transfer. The rib height-to-hydraulic diameter ratio (e/Dh) is 0.094. For the baseline smooth case and the case with rib pitch-to-height ratio (P/e) 10, channel orientation angles (beta) of 90 degrees and 135 degrees were tried to model the cooling passage in the mid and rear portion of the blade respectively. Two other P/e ratios of 5 and 7.5 were studied at beta=135 degrees to investigate their effect on heat transfer. The data are presented under high rotation numbers and buoyancy parameters by varying the Reynolds number (Re=10,000~40,000) and rotation speed (rpm=0~400). Corresponding rotation number and buoyancy parameter are ranged as 0~0.45 and 0~0.8 respectively. The dissertation also studies the heat transfer in a two-pass channel (AR=2:1) connected by a 180 degree U bend in the hub portion. The flow in the first passage is radial inward and after the U bend, the flow in the second passage is radial outward. The cross-section dimension of this channel is the same as the previous one. To increase heat transfer, staggered square ribs (e/Dh=0.094) are pasted on leading and trailing walls with an attack angle (alpha) of 45 degrees and pitch-to-height ratio (P/e) of 8. A turning vane in the shape of half circle (R=18.5 mm, t=1.6 mm) is used in the turn region to guide the flow for both smooth and ribbed cases. Channel orientation angles (beta) of 90 degrees and 135 degrees were taken for both smooth and ribbed cases. The heat transfer data were taken at high rotation numbers close to previous test section.

In the design of mechanical components, numerical simulations and experimental methods are commonly used for design creation (or modification) and design optimization. However, a major challenge of using simulation and experimental methods is that they are timeconsuming and often cost-prohibitive for the designer. In addition, the simultaneous interactions between aerodynamic, thermodynamic and mechanical integrity objectives for a particular component or set of components are difficult to accurately characterize, even with the existing simulation tools and experimental methods. The current research and practice of using numerical simulations and experimental methods do little to address the simultaneous “satisficing” of multiple and often conflicting design objectives that influence the performance and geometry of a component. This is particularly the case for gas turbine systems that involve a large number of complex components with complicated geometries. Numerous experimental and numerical studies have demonstrated success in generating effective designs for mechanical components; however, their focus has been primarily on optimizing a single design objective based on a limited set of design variables and associated values. In this research, a multiobjective design optimization framework to solve a set of userspecified design objective functions for mechanical components is proposed. The framework integrates a numerical simulation and a nature-inspired optimization procedure that iteratively perturbs a set of design variables eventually converging to a set of tradeoff design solutions. In this research, a gas turbine engine system is used as the test application for the proposed framework. More specifically, the optimization of the gas turbine blade internal cooling channel configuration is performed. This test application is quite relevant as gas turbine engines serve a iv critical role in the design of the next-generation power generation facilities around the world. Furthermore, turbine blades require better cooling techniques to increase their cooling effectiveness to cope with the increase in engine operating temperatures extending the useful life of the blades. The performance of the proposed framework is evaluated via a computational study, where a set of common, real-world design objectives and a set of design variables that directly influence the set of objectives are considered. Specifically, three objectives are considered in this study: (1) cooling channel heat transfer coefficient, which measures the rate of heat transfer and the goal is to maximize this value; (2) cooling channel air pressure drop, where the goal is to minimize this value; and (3) cooling channel geometry, specifically the cooling channel cavity area, where the goal is to maximize this value. These objectives, which are conflicting, directly influence the cooling effectiveness of a gas turbine blade and the material usage in its design. The computational results show the proposed optimization framework is able to generate, evaluate and identify thousands of competitive tradeoff designs in a fraction of the time that it would take designers using the traditional simulation tools and experimental methods commonly used for mechanical component design generation. This is a significant step beyond the current research and applications of design optimization to gas turbine blades, specifically, and to mechanical components, in general.

The purpose of this study is to build, test, validate, and implement two heat transfer models, and couple them to an existing fluid flow solver, which can then be used for simulating multi-disciplinary problems. The first model is for heat conduction computations, the other one is a quasi-one-dimensional cooling channel model for water-cooled jacket structural analysis. The first model employs the integral, conservative form of the thermal energy equation, which is discretized by means of a finite-volume numerical scheme. A special algorithm is developed at the interface between the solid and fluid regions, in order to keep the heat flux consistent. The properties of the solid region materials can be temperature dependent, and different materials can be used in different parts of the domains, thanks to a multi-block gridding strategy. The cooling channel flow model is developed by using uasi-one-dimensional conservation laws of mass, momentum, and energy, taking into account the effects of heat transfer and friction. It is possible to have phase changes in the channel, and a mixture model is applied, which allows two phases to be present, as long as they move at the same bulk velocity and vapor quality does not exceed relatively small values. The coupling process of both models (with the fluid solver and with each other) is handled within the Loci system, and is detailed in this study. A hot-air nozzle wall problem is simulated, and the computed results are validated with available experimental data. Finally, a more complex case involving the water-cooled nozzle of a Rocket Based Combined Cycle(RBCC) gaseous oxygen/gaseous hydrogen thruster is simulated, which involves all three models, fully coupled. The calculated temperatures in the nozzle wall and at the cooling channel outlet compare favorably with experimental data.

High combustion temperatures and long operation durations require the use of cooling techniques in liquid propellant rocket engines. For high-pressure and high-thrust rocket engines, regenerative cooling is the most preferred cooling method. In regenerative cooling, a coolant flows through passages formed either by constructing the chamber liner from tubes or by milling channels in a solid liner. Traditionally, approximately square cross sectional channels have been used. However, recent studies have shown that by increasing the coolant channel height-to-width aspect ratio and changing the cross sectional area in non-critical regions for heat flux, the rocket combustion chamber gas side wall temperature can be reduced significantly without an increase in the coolant pressure drop. In this study, the regenerative cooling of a liquid propellant rocket engine has been numerically simulated. The engine has been modeled to operate on a LOX/Kerosene mixture at a chamber pressure of 60 bar with 300 kN thrust and kerosene is considered as the coolant. A numerical investigation was performed to determine the effect of different aspect ratio cooling channels and different number of cooling channels on gas-side wall and coolant temperature and pressure drop in cooling channel.

In this diploma thesis active aerodynamic components are designed, specifically brake cooling duct and active automotive wing. Cooling duct prototype and also active regulation controlling electronics including the software were created. Road test was performed to measure the duct parameters. Construction design and the active regulation function of the automotive wing were created. The influence of the wing on aerodynamic characteristics of the car was determined.

Sustainable growth and development in a society requires energy supply that is efficient, affordable, readily available and, in the long term, sustainable without causing negative societal impacts, such as environmental pollution and its attendant consequences. In this respect, proton exchange membrane (PEM) fuel cells offer a promising alternative to existing conventional fossil fuel sources for transport and stationary applications due to its high efficiency, low-temperature operation, high power density, fast start-up and its portability for mobile applications. However, to fully harness the potential of PEM fuel cells, there is a need for improvement in the operational performance, durability and reliability during usage. There is also a need to reduce the cost of production to achieve commercialisation and thus compete with existing energy sources. The present study has therefore focused on developing novel approaches aimed at improving output performance for this class of fuel cell. In this study, an innovative combined numerical computation and optimisation techniques, which could serve as alternative to the laborious and time-consuming trial-and-error approach to fuel cell design, is presented. In this novel approach, the limitation to the optimal design of a fuel cell was overcome by the search algorithm (Dynamic-Q) which is robust at finding optimal design parameters. The methodology involves integrating the computational fluid dynamics equations with a gradient-based optimiser (Dynamic-Q) which uses the successive objective and constraint function approximations to obtain the optimum design parameters. Specifically, using this methodology, we optimised the PEM fuel cell internal structures, such as the gas channels, gas diffusion layer (GDL) - relative thickness and porosity - and reactant gas transport, with the aim of maximising the net power output. Thermal-cooling modelling technique was also conducted to maximise the system performance at elevated working temperatures. The study started with a steady-state three-dimensional computational model to study the performance of a single channel proton exchange membrane fuel cell under varying operating conditions and combined effect of these operating conditions was also investigated. From the results, temperature, gas diffusion layer porosity, cathode gas mass flow rate and species flow orientation significantly affect the performance of the fuel cell. The effect of the operating and design parameters on PEM fuel cell performance is also more dominant at low operating cell voltages than at higher operating fuel cell voltages. In addition, this study establishes the need to match the PEM fuel cell parameters such as porosity, species reactant mass flow rates and fuel gas channels geometry in the system design for maximum power output. This study also presents a novel design, using pin fins, to enhance the performance of the PEM fuel cell through optimised reactant gas transport at a reduced pumping power requirement for the reactant gases. The results obtained indicated that the flow Reynolds number had a significant effect on the flow field and the diffusion of the reactant gas through the GDL medium. In addition, an enhanced fuel cell performance was achieved using pin fins in a fuel cell gas channel, which ensured high performance and low fuel channel pressure drop of the fuel cell system. It should be noted that this study is the first attempt at enhancing the oxygen mass transfer through the PEM fuel cell GDL at reduced pressure drop, using pin fin. Finally, the impact of cooling channel geometric configuration (in combination with stoichiometry ratio, relative humidity and coolant Reynolds number) on effective thermal heat transfer and performance in the fuel cell system was investigated. This is with a view to determine effective thermal management designs for this class of fuel cell. Numerical results shows that operating parameters such as stoichiometry ratio, relative humidity and cooling channel aspect ratio have significant effect on fuel cell performance, primarily by determining the level of membrane dehydration of the PEM fuel cell. The result showed the possibility of operating a PEM fuel cell beyond the critical temperature ( 80„aC), using the combined optimised stoichiometry ratio, relative humidity and cooling channel geometry without the need for special temperature resistant materials for the PEM fuel cell which are very expensive. In summary, the results from this study demonstrate the potential of optimisation technique in improving PEM fuel cell design. Overall, this study will add to the knowledge base needed to produce generic design information for fuel cell systems, which can be applied to better designs of fuel cell stacks. / Thesis (PhD)--University of Pretoria, 2012. / Mechanical and Aeronautical Engineering / unrestricted

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