This work addresses the issue of transverse combustion instabilities in annular gas turbine combustor geometries. While modern low-emissions combustion strategies have made great strides in reducing the production of toxic emissions in aircraft engines and power generation gas turbines, combustion instability remains one of the foremost technical challenges in the development of next generation combustor technology. To that end, this work investigates the response of a swirling flow and swirl-stabilized flame to a transverse acoustic field is using a variety of high-speed laser techniques, especially high-speed particle image velocimetry (PIV) for detailed velocity measurements of this highly unsteady flow phenomenon. A description of the velocity-coupled transverse instability mechanism is explained with companion measurements describing each of the velocity disturbance pathways. Dependence on acoustic frequency, amplitude, and field symmetry is discussed. Significant emphasis is placed on the response of a swirling flow field to a transverse acoustic field. Details of the dynamics of the vortex breakdown bubble and the shear layers are explained using a wide variety of measurements for both non-reacting and reacting flow cases. This thesis concludes with an overview of the impact of this work and suggestions for future research in this area.

Thesis (Ph. D.)--Mississippi State University. Department of Mechanical Engineering. / Title from title screen. Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains xii, 121 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 117-119).

No description available.

A 2-D CFD / FEM model to simulate thermal stresses in a turbine blade has been set up using the software FLUENT and FIDAP. The model was validated against the data of Bohn et. al. (1995) and was used to simulate 5 test cases. The numerical model was set up for a single Mark II nozzle guide vane (NGV) and utilised the appropriate boundary conditions for the surrounding flow field. A commercially available software code, FLUENT, was used to resolve the flow field, and heat transfer to the blade. The resulting surface temperature profile was then plotted and used as the boundary conditions in FIDAP (a commercial FEM code) to resolve the temperature and stress profile in the blade. An additional solver within FLUENT essentially superimposes an additional flow field as a result of the NGV vibration in the flow field. The pressure, temperature and heat transfer coefficient distribution, from FLUENT, were compared to those from Bohn et. al. (1995). The model predicted the distributions trends correctly, with an average over-prediction for temperature, of 10 % on the suction side and 6 % on the pressure side. This was restricted to the region from leading edge to 40 % chord on both sides of the blade. The blade temperature and equivalent stress contour trends were also correctly predicted by FIDAP. The blade temperature was over-predicted by and average of 1.7 %, while the equivalent stress magnitude was under-predicted by a worst case of 43 %, but the locations of maximum stress were correctly predicted. The reason for the differences between the stresses predicted by FLUENT / FIDAP and the data given in Bohn et. al. (1995), is believed to be the results of the temperature dependence of the material properties for the blade (ASTM 310 stainless steel), used in the two studies, not being identical. The reasoning behind this argument is because the distribution trends and contour variation, predicted by the model, compared favourably with the data of Bohn et. aI., and only the equivalent stress magnitude differed significantly. This completed the validation of the FLUENT / FIDAP model. The model was used to simulate test cases where temperature (i.e. turbine inlet temperature or TIT), at the model inlet (Le. the pressure inlet boundary in FLUENT), was set up to be time varying. Four simplified cases, viz single shock, multiple shocks, simplified cycle and multiple cycles, and a complex cycle (a mission profile) were simulated. The mission profile represented typical gas turbine operational data. The simulation results showed that stress was proportional to TIT. Changes in TIT were seen at a later time in the stress curve, due to conduction through the blade. Steep TIT changes, such as the shock loads, affected stress later than gentler TIT changes - the simplified and multiple cycles. These trends were consistently seen in the complex cycle. The maximum equivalent stress was plotted against TIT to try and develop a loose law that gives maximum equivalent stress as a function of TIT. A 4th order polynomial was fitted through the maxima and minima of the maximum equivalent stress plot, which gave the maximum and minimum stress as a function of TIT. This function was used calculate the maximum and minimum and mean equivalent stress using the TIT data for the mission profile. Thus, the FLUENT I FIDAP model was successfully validated, used to simulated the test cases and a law relating the equivalent stress as a function of TIT was developed. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2002.

No description available.

No description available.

The simple gas turbine engine Operates on the basic Joule-Brayton cycle and it is notorious for its poor thermal efficiency. Several modifications have been made to the simple cycle in order to increase its thermal efficiency but, within the thermal and mechanical stress constrains, the efficiency still ranges between 28 and 35%. However, higher values of energy utilisation efficiency have been claimed in recent years by using low grade heat from the engine exhaust either for district heating or for raising low pressure steam for chemical processes. Both applications are not very attractive in hot countries. The concept of using the low grade thermal energy from the gas turbine exhaust to raise steam in order to drive a steam turbine and generate additional electricity, i. e. the combined power and power or CPP plant would be more attractive in hot countries than the CHP plant. It was hypothesized that the operational parameters, hence the performance of the CPP plant, would depend on the allowable gas turbine entry temperature. Hence, the exhaust gas temperature could not be decided arbitrarily. This thesis deals with the performance of the gas turbine engine operating as a part of the combined power and power plant. In a CPP plant, the gas turbine does not only produce power but also the thermal energy that is required to operate the steam turbine plant at achievable thermal efficiency. The combined gas turbine-steam turbine cycles are thermodynamically analysed. A parametric study for different configurations of the combined gas-steam cycles has been carried out to show the influence of the main parameters on the CPP cycle performance. The parametric study was carried out using realistic values in view of the known constraints and taking into account any feasible future developments. The results of the parametric study show that the maximum CPP cycle efficiency would be at a point for which the gas turbine cycle would have neither its maximum efficiency nor its maximum specific work output. It has been shown that supplementary heating or gas turbine reheating would decrease the CPP cycle efficiency; hence, it could only be justified at low gas turbine inlet temperatures. Also it has been shown that although gas turbine intercooling would enhance the performance of the gas turbine cycle, it would have only a slight effect on the CPP cycle performance. A graphical method for studying operational compatibility, i.e. matching, between gas turbine components has been developed for a steady state or equilibrium operation. The author would like to submit that the graphical method offers a novel and easy to understand approach to the complex problem of component matching. It has been shown that matching conditions between the compressor and the turbine could be satisfied by superimposing the turbine performance characteristics on the compressor performance characteristics providing the axes of both were normalised. This technique can serve as a valuable tool to determine the operating range and the engine running line. Furthermore, it would decide whether the gas turbine engine was operating in a region of adequate compressor and turbine efficiencies. A computer program capable of simulating the steady state off-design conditions of the gas turbine engine as part of the CPP plant has been developed. The program was written in Visual Basic. Also, another program was developed to simulate the steady state off-design operation of the steam turbine power plant. A combination of both programs was used to simulate the combined power plant. Finally, it could be claimed that the computer simulation of the CPP plant makes significant contribution to the design of thermal power plants as it would help in investigating the effects of the performance characteristics of the components on the performance of complete engines at the design and off-design conditions. This investigation of the CPP plant performance can be carried out at the design and engineering stages and thus help to reduce the cost of manufacturing and testing the expensive prototype engines.

The increasing price of fuel and energy, combined with environmental laws and regulations, have led many different energy producers to integrate renewable, clean energy sources with non-renewable ones, forming the idea of energy hubs. Energy hubs are systems of technologies where different energy forms are conditioned and transformed. These energy hubs offer many advantages compared to traditional single-energy sources, including increased reliability and security of meeting energy demand, maximizing use of energy and materials resulting in increasing the overall system efficiency. In this thesis, we consider an energy hub consisting of natural gas (NG) turbines for the main source of energy— electricity and heat— combined with two renewable energy sources—wind turbines and PV solar cells. The hub designed capacity is meant to simulate and replace the coal-fired Nanticoke Generating Station with NG-fired power plant. The generating station is integrated with renewable energy sources, including wind and solar. The hub will also include water electrolysers for hydrogen production. The hydrogen serves as an energy storage vector that can be used in transportation applications, or the hydrogen can be mixed into the NG feed stream to the gas turbines to improve their emission profile. Alkaline electrolysers’ technology is fully mature to be applied in large industrial applications. Hydrogen, as an energy carrier, is becoming more and more important in industrial and transportation sectors, so a significant part of the thesis will focus on hydrogen production and cost. In order to achieve the goal of replacing the Nanticoke Coal-fired Power Plant by introducing the energy hub concept, the study investigates the modeling of the combined system of the different technologies used in terms of the total energy produced, cost per kWh, and emissions. This modeling is done using GAMS® in order to make use of the optimization routines in the software. The system is modeled so that a minimum cost of energy is achieved taking into account technical and thermodynamic constrains. Excess energy produced during off-peak demand by wind turbines and PV solar cells is used to feed the electrolyser to produce H2 and O2. Through this method, a significant reduction in energy cost and greenhouse gas (GHG) emissions are achieved, in addition to an increased overall efficiency.

This thesis describes an experimental investigation of lean blowoff for H2/CO/CH4 mixtures in a swirling combustor. This investigation consisted of three thrusts. The first thrust focused on correlations of the lean blowoff limits of H2/CO/CH4 mixtures under different test conditions. It was found that a classical Damköhler number approach with a diffusion correction could correlate blowoff sensitivities to fuel composition over a range of conditions. The second part of this thesis describes the qualitative flame dynamics near blowoff by systematically characterizing the blowoff phenomenology as a function of hydrogen level in the fuel. These near blowoff dynamics are very complex, and are influenced by both fluid mechanics and chemical kinetics; in particular, the role of thermal expansion across the flame and extinction strain rate were suggested to be critical in describing these influences. The third part of this thesis quantitatively analyzed strain characteristics in the vicinity of the attachment point of stable and near blowoff flames. Surprisingly, it was found that in this shear layer stabilized flame, flow deceleration is the key contributor to flame strain, with flow shear playing a relatively negligible role. Near the premixer exit, due to strong flow deceleration, the flame is negatively strained i.e., compressed. Moving downstream, the strain rate increases towards zero and then becomes positive, where flames are stretched. As the flame moves toward blowoff, holes begin to form in the flame sheet, with a progressively higher probability of occurrence as one moves downstream. It is suggested that new holes form with a more uniform probability, but that this behavior reflects the convection of flame holes downstream by the flow. It has been shown in prior studies, and affirmed in this work, that flames approach blowoff by first passing through a transient phase manifested by local extinction events and the appearance of holes on the flame. A key conclusion of this work is that the onset of this boundary occurs at a nearly constant extinction strain rate. As such, it is suggested that Damköhler number scalings do not describe blowoff itself, but rather the occurrence of this first stage of blowoff. Given the correspondence between this first stage and the actual blowoff event, this explains the success of classical Damköhler number scalings in describing blowoff, such as shown in the first thrust of this thesis. The physics process associated with the actual blowoff event is still unclear and remains a key task for future work.