No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

The successful design of a long-lived and efficient gas turbine engine requires a good knowledge of the thermal and aerodynamic performances of the components of the turbine. Of particular importance, is the heat transfer rate from the hot gases to the cooled turbine blades, since this limits the maximum turbine entry temperatures which can be obtained. Much gas turbine research is concentrated on experimental modelling and measurements to assist in the development of improved theoretical prediction techniques. The difficulties of instrumenting fully rotational rigs, which are necessary for a full understanding of the complex three dimensional flow in the turbine, have, however, to a large extent, limited most experimental research to stationary facilities. A technique is described which will allow heat transfer rate measurements to be made on fully rotating test facilities using mutlilayered model turbine blades comprising an electrical insulator on a metal base. An accurate and computationally efficient method for determining the surface heat flux to a multi-layered model turbine blade is developed theoretically, together with a method for calibrating the thermal properties of the multi-layered system. This method allows the existing successful heat flux measurement technique, which utilises electronic analogue circuitry in conjunction with thin film surface thermometers on a model made from a thermal insulator, to be extended for application to multi-layered models. The production of test models by the application of a vitreous enamel (as an electrical insulator), to a mild steel, is identified as the most suitable coating technique for experimental application. Radiant and wind tunnel testing of multi-layered cylindrical models are described, which confirm that the method is both practical and accurate.

Experiments were performed using an Isentropic Light Piston Tunnel, a transient facility which enables conditions representative of those in engines to be attained. The results were interpreted using a superposition model, which is shown to be a valuable and concise method of characterising the effects of injection.

In many practical combustion devices, including those used in gas turbine engines for aircraft and power generation, a high energy spark kernel is necessary to reliably ignite the turbulently flowing flammable gases. Complicating matters, the spark kernel is sometimes generated in a region where a non-flammable mixture is present, or where there is no fuel at all. This requires the spark kernel to travel to a flammable region before rapid combustion can begin in non-premixed or stratified flows. This transit time allows for chemical reactions to take place within the kernel as well as mixing with surrounding gases. Despite these demanding conditions, the majority of research in ignition has been for low energy sparks and premixed conditions, not resembling those found in many combustion devices. Similarly, there is little work addressing this issue of spark kernel evolution in the non-premixed flowing environment, and none available that control the time allowed for transit. The goal of this thesis is to understand the development of a spark kernel issued into a non-premixed flow and the sensitivities of the ignition process. To this effect, a stratified flow facility for ignition experiments has been fabricated utilizing a high speed schlieren and emission imaging system for visualizing the kernel motion and ignition success. Additionally, OH chemiluminescence and CH PLIF were used to track chemical species during the ignition process. This facility is also used to control the important variables regarding the flow and spark kernel interaction to quantify the influence on ignition probability. A reduced order model employing a perfectly stirred reactor (PSR) has also been developed based on experimental observations of the entrainment of fluid into the evolving kernel. The simulations provide additional insight to the chemical development in the kernel under different input conditions. This model was enhanced by introducing random perturbations to the input variables, mimicking a practical situation. A computationally efficient support vector machine was trained to replicate the numerical model outputs and predict ignition probabilities for nominal input conditions, providing comparison to experimental results. Experimental and numerical results show that initial mixing with non-flammable fluid quickly reduces the ability for the kernel to ignite the flammable flow, resulting in a strong influence of the inlet temperature and the kernel transit time on the probability of ignition. Once the kernel reaches the flammable mixture, entrainment of this flow occurs, which requires on the order of a vortex turn-over time before chemistry can begin. Initial chemical reactions include endothermic fuel decomposition, further reducing the kernel temperature prior to heat release, creating a competition between the cooling effect of additional mass entrainment and the delayed heat release reactions. CH PLIF results show that flame chemistry is initially confined to a thin region that corresponds to the interface layer where the flammable gases mix with the hot kernel fluid from the vortex entrainment of ambient gas. The dependence of the ignition probability to variations in flow conditions is captured reasonably well by the reduced order model, validating the PSR approach and the probability prediction tool. The development of this reduced order model is a major contribution of this work with the ability to predict the effects of the important physical ignition processes, which can be used when considering an ignition system's feasibility. This work will provide knowledge to guide the use and design practices in industry, as well as a simple model to test ignition feasibility based on mixing, entrainment, and chemical reactions. Furthermore, the flow facility is well characterized, and a database has been developed that can provide validation points for future computational simulations. Future modeling will be important to further understand fluid dynamic effects that are difficult to measure experimentally, and study a broader range of conditions.

No description available.