Gas turbine blades are subject to harsh operating conditions that require innovative cooling techniques to insure reliable operation of parts. Film-cooling and internal cooling techniques can prolong blade life and allow for higher engine temperatures. This study examines several unique methods of cooling the turbine blade tip. The first method employs holes placed directly in the tip which inject coolant onto the blade tip. The second and third methods used holes placed on the pressure side of a blade near the tip representative of two different manufacturing techniques. The fourth method is a novel cooling technique called a microcircuit, which combines internal convection and injection from the pressure side near a turbine blade tip. Wind tunnel tests are used to observe how effectively these designs cool the tip through adiabatic effectiveness measurements and convective heat transfer measurements. Tip gap size and blowing ratio are varied for the different tip cooling configurations. Results from these studies show that coolant injection from either the tip surface or from the pressure side near the tip are viable cooling methods. All of these studies showed better cooling could be achieved at small tip gaps than large tip gaps. The results in which the two different manufacturing techniques were compared indicated that the technique producing more of a diffused hole provided better cooling on the tip. When comparing the thermal performance of all the cooling schemes investigated, the added benefit of the internal convective cooling shows that the microcircuit outperforms the other designs. / Master of Science

Cooling of turbine parts in a gas turbine engine is necessary for operation as the temperature of combustion gases is higher than the melting temperature of the turbine materials. The gap between rotating turbine blades and the stationary shroud provides an unintended flow path for hot gases. Gases that flow through the tip region cause pressure losses in the turbine section and high heat loads to the blade tip. This thesis studies the heat transfer on an innovative tip geometry intended to help reduce aerodynamic losses. The blade tip has a depression (shelf) on the tip surface along much of the pressure side of the blade and film-cooling holes along the depression. This research experimentally measured the effect of the shelf, coolant flow and tip gap on heat transfer on the blade tip. Stationary experiments were performed in a low speed wind tunnel on a linear cascade with two different tip gaps and multiple coolant flow rates through the film-cooling holes. Tests showed that baseline Nusselt numbers on the tip surface were reduced with the shelf tip compared with a flat tip. Measurements indicated that film-cooling was more effective with a small tip gap than with a large tip gap. Experimental and computational results demonstrated a lack of coolant spreading that was detrimental to regions between the film-cooling holes. While the coolant was effective on the blade tip, the leading and trailing edge regions were found to have high heat transfer coefficients with little available cooling. / Master of Science

The methodology used in analyzing the feasibility of installing direct and indirect intercooling systems on naval gas turbines is presented. The indirect system is comprised of two types of heat exchangers; an air to ethylene glycol, plate fin heat exchanger, and an ethylene glycol to seawater shell and tube heat exchanger. The direct system utilizes an air to seawater shell and tube heat exchanger. The analysis requires, as input, air mass flow rates, compressor efficiencies and pressure ratios. The output, based on given environmental constraints and an assumed overall intercooler effectiveness, provides mass flow rates of seawater and ethylene glycol, heat exchanger effectiveness and size, intermediate fluid temperatures, and air and seawater outlet temperatures. The output provides preliminary data for specific heat exchanger design and pump and piping selections. / Master of Science

Random vibration of a bladed-disk assembly is studied. A stochastic model for the excitation is developed. A unique feature of this model is the statistical periodicity of the blade forces called cyclostationary. A random process is called wide sense eyeclostationary and its statistics are periodic in time. Factors like the turbulent nature of the flow around the blades, the variability in their geometry, and their nonuniform deterioration contribute to the uncertainty in the excitation. In periodic structures, like the bladed-disk assembly, small variation in the blade excitation may lead to high variability in the response. The model developed includes both random and deterministic excitation. A comparison of the responses due to the random and the deterministic part shows the significance of taking into account the variability in the blade forces. Therefore the assumption that the blade forces are all equal, used by all methods for vibration analysis of bladed disk assemblies, may lead to erroneous estimates of their response, reliability and expected life. It is shown that the response is a cyclostationary process. Therefore the cyclostationary property is preserved from the input to the output. Furthermore the frequency of the second moment of the response is equal to two times the frequency of the excitation. / Master of Science

This thesis documents an experimental investigation into the effect of trailing edge Injection on the aerodynamic performance of turbine blades conducted at Virginia Polytechnic Institute and State University (VPl&SU). A brief description of the arrangement, instrumentation and data acquisition system of the VPl&SU Transonic Cascade Wind Tunnel is given. Testing was conducted under a number of test conditions. Baseline data was obtained for the blades with no trailing edge injection. The blades were then tested for two different blowing rates to test the effect of blowing rate on the total pressure loss coefficient, L. Tests were conducted at a variety of save cascade exit Mach numbers ranging from 0.79 to 1.36. Measurements were taken at three locations downstream of the cascade blade trailing edges. The algorithm used to calculate the L from the measured data is discussed. Results of the testing indicate that trailing edge injection has a negligible effect on the total pressure loss coefficient. Correlations of cascade exit Mach number to L are given. The development of L downstream of the blade trailing edge is discussed. / Master of Science

M.S.

The utilization of lean premixed combustors has become attractive to designers of industrial gas turbines as a means of meeting strict emissions standards without compromising efficiency.  Mixing the fuel and air prior to combustion allows for lower temperature flame zones, creating the potential for drastically reduced nitrous oxide emissions.  While effective, these systems are commonly plagued by combustion driven instabilities.  These instabilities produce large pressure and heat release rate fluctuations due to a resonant interaction between the combustor acoustics and the flame.  A primary feedback mechanism responsible for driving these systems is the propagation of Fuel/Air Ratio (FAR) fluctuations into the flame zone.  These fluctuations are formed inside of the premixing chamber when fuel is injected into and mixed with an oscillating air flow. The research presented here aimed to develop new technology for premixer designs, along with an application strategy, to avoid resonant thermo-acoustic events driven by FAR fluctuations.  A passive fuel control technique was selected for investigation and implementation. The selected technique utilized fuel injections at multiple, strategically placed axial locations to target and inhibit FAR fluctuations at the dominant resonant mode of the combustor.  The goal of this research was to provide an understanding of the mixing response inside a realistic premixer geometry and investigate the effectiveness of the proposed suppression technique. The mixing response was investigated under non-reacting flow conditions using a unique modular premixer.  The premixer incorporated variable axial fuel injection locations, as well as interchangeable mixing chamber geometries.  Two different chamber designs were tested: a simple annular chamber and one incorporating an axial swirler.  The mixing response of the simple annular geometry was well characterized, and it was found that multiple injections could be effectively configured to suppress the onset of an unstable event at very lean conditions. Energy dense flame zones produced at higher equivalence ratios, however, were found to be uncontrollable using this technique. Additionally, the mixing response of the swirl geometry was difficult to predict. This was found to be the result of large spatial gradients formed in the dynamic velocity field as acoustic waves passed through the swirl vanes. / Ph. D.

In this paper, an analysis of the internal water-cooling of a gas turbine was carried out. The density differences due to heating of the water in the blade and drum, combined with the very large force field associated with the centrifugal force caused by the rotation of water, sets up strong convection currents, which resulted in a very efficient heat transfer. Using the Havier-Stoke's and the continuity equations, applying Prandtl’s analogy between heat transfer and fluid friction and von Karman's - Nikuradse’s universal velocity distribution equation, the coefficient of heat transfer was derived and the maximum gas effective temperature predicted. For the conditions used in this investigation the following enumerated results can be stated: 1) The computed coefficient of heat transfer between cooling passage wall and water is 3850 Btu/(hr)(sq ft) (°F). 2) The rate of coolant flow is 11.35 lb/sec. 3) The effective gas temperature is 2510°F, assuming no radial heat flow alone the metal parts. 4) The average blade temperature is 600°F. 5) The blade has one cooling passage 4" long and .25" in diameter, and one equivalent in half to it in the cooling effect. / Master of Science

The ability of twelve distortion indices to predict stalling behavior in aircraft gas turbine engines was investigated using J85-GE-13 turbojet engine data, TF30-P-3 turbofan engine data, and modified T64-GE-6B compressor test-rig data. The indices were tested for correlation capability with constant speed loss in stall pressure ratio, constant mass loss in stall pressure ratio, and engine speed where appropriate. Predictive indices/models were compared directly with experimental data. In addition, the concept of including the effects of compressor dynamic response by modifying the inlet total pressure profile rather than the index was investigated. This was done by evaluating the accuracy of parallel compressor theory and two simple AP/P indices first using measured inlet total pressure data and then using modified or "effective" inlet total pressure profiles. A procedure was developed for deriving the effective inlet total pressure distribution from the measured distribution. / Master of Science

Heat transfer experiments were done on a flat plate to study the effect of internal counter-flow backside cooling on adiabatic film cooling effectiveness and heat transfer coefficient. In addition, the effects of density ratio (DR), blowing ratio (BR), diagonal length over diameter (L/D) ratio, and Reynolds number were studied using this new configuration. The results are compared to a conventional plenum fed case. Data were collected up to X/D =23 where X=0 at the holes, an S/D = 1.65 and L/D=1,2. Testing was done at low L/D ratios since short holes are normally found in double wall cooling applications in turbine components. A DR of 2 was used in order to simulate engine-like conditions and this was compared to a DR of 0.92 since relevant research is done at similar low DR. The BR range of 0.5 to 1.5 was chosen to simulate turbine conditions as well. In addition, previous research shows that peak effectiveness is found within this range. Infrared (IR) thermography was used to capture temperature contours on the surface of interest and the images were calibrated using a thermocouple and data analyzed through MATLAB software. A heated secondary fluid was used as 'coolant' in the present study. A steady state heat transfer model was used to perform the data reduction procedure. Results show that backside cooling configuration has a higher adiabatic film cooling effectiveness when compared to plenum fed configurations at the same conditions. In addition, the trend for effectiveness with varying BR is reversed when compared with traditional plenum fed cases. Yarn flow visualization tests show that flow exiting the holes in the backside cooling configuration is significantly different when compared to flow exiting the plenum fed holes. We hypothesize that backside cooling configuration has flow exiting the holes in various directions, including laterally, and behaving similar to slot film cooling, explaining the differences in trends. Increasing DR at constant BR shows an increase in adiabatic effectiveness and HTC in both backside cooling and plenum fed configurations due to the decreased momentum of the coolant, making film attachment to the surface more probable. The effects of L/D ratio in this study were negligible since both ratios used were small. This shows that the coolant flow is still underdeveloped at both L/D ratios. The study also showed that increasing turbulence through increasing Reynolds number decreased adiabatic effectiveness. / MS / Gas turbine engines are used for multiple applications for power (power plants) or thrust (aircraft propulsion). Engine efficiency is correlated with higher working temperatures, which exceed the melting points of the materials being used. Therefore, more efficient cooling techniques are needed in order to protect the engine turbine components, such as blades and vanes. Relatively cooler air is bypassed from the compressor to the turbine section to cool the turbine components from the high temperatures. The air flows through the turbine components and out through machined holes referred to as film cooling holes. A protective layer, or film, protects the external region of the blade or vane. Previous research has found that the geometry of the airfoils used and the flow conditions play a major role in heat transfer. Most of the relevant research use a model that contains one-sided heat transfer. The present study focuses on combined backside and film cooling heat transfer, with different geometries and flow conditions, using a steady-state model for the data reduction procedure.