In a gas turbine engine, turbine blades are exposed to temperatures above their melting point. Film-cooling and internal cooling techniques can prolong blade life and allow for higher engine temperatures. This study examines a novel cooling technique called a microcircuit, which combines internal convection and pressure side injection on a turbine blade tip. Holes on the tip called dirt purge holes expel dirt from the blade, so other holes are not clogged. Wind tunnel tests are used to observe how effectively dirt purge and microcircuit designs cool the tip. Tip gap size and blowing ratio are varied for different tip cooling configurations. Results show that the dirt purge holes provide significant film cooling on the leading edge with a small tip gap. Coolant injected from these holes impacts the shroud and floods the tip gap reducing tip leakage flow. With the addition of a microcircuit, coolant is delivered to a larger area of the tip. In all cases, cooling levels are higher for a small tip gap than a large tip gap. Increased blowing ratio does not have a dramatic effect on microcircuit film-cooling at the midchord but does improve internal cooling from the microcircuit. While the combined dirt purge holes and microcircuit cool the leading edge and midchord areas, there remains a small portion of the trailing edge that is not cooled. Also, results suggest that blowing from the microcircuit diminishes the tip leakage vortex. Overall, the microcircuit appears to be a feasible method for prolonging blade life. / Master of Science

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

yes / This paper presents a two-way thermally-coupled FEM-CFD co-simulation method for ventilated brake disc rotor heat transfer analysis. Using a third party coupling interface for data mapping and exchange, the FEM and CFD models run simultaneously under a standard heavy duty braking test condition. By comparison with conventional one-way coupling methods and experimental results, the performance of the co-simulation system has been investigated in terms of prediction of the heat transfer coefficient (HTC) and disc temperatures as well as computing time used. The results illustrate that this co-simulation method has good capacity in providing cooling effect and temperature predictions. It also shows that the data exchange between the FEM and CFD codes at every time increment is highly accurate and efficient throughout 10 brake applications. It can be seen that the cosimulation method is more time efficient, convenient and robust compared to previous oneway coupling methods. To utilize the potential of this method, future works are proposed.

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

An approximate method of calculating the minimum total weight of the two-insulation--two-coolant thermal protection system is developed. The equations derived in the development of the approximate method enable insight into the parameters that control the system weight. Two cases are considered: the case where the outer coolant location is unrestricted within the insulating wall and the case where the outer coolant location is restricted within the insulating wall. The effects on system weight of material properties and the outer coolant location within the insulating wall are discussed. A comparison of weights predicted by the approximate method and numerical solutions is shown. / Master of Science

In this dissertation, Immersed Boundary Method (IBM) is evaluated in ribbed duct geometries to show the potential of simulating complex geometry with a simple structured grid. IBM is first investigated in well-accepted benchmark cases: channel flow and pipe flow with circular cross-section. IBM captures all the flow features with very good accuracy in these two cases. Then a two side ribbed duct geometry is test using IBM at Reynolds number of 20,000 under fully developed assumption. The IBM results agrees well with body conforming grid predictions. A one side ribbed duct geometry is also tested at a bulk Reynolds number of 1.5⨉10⁴. Three cases have been examined for this geometry: a stationary case; a case of positive rotation at a rotation number (Ro=ΩDₕ/U) of 0.3 (destabilizing); and a case of negative rotation at Ro= -0.3 (stabilizing). Time averaged mean, turbulent quantities are presented, together with heat transfer. The overall good agreement between IBM, BCG and experimental results suggests that IBM is a promising method to apply to complex blade geometries. Due to the disadvantage of IBM that it requires large amount of cells to resolve the boundary near the immersed surface, wall modeled LES (WMLES) is evaluated in the final part of this thesis. WMLES is used for simulating turbulent flow in a developing staggered ribbed U-bend duct. Three cases have been tested at a bulk Reynolds number of 10⁵: a stationary case; a positive rotation case at a rotation number Ro=0.2; and a negative rotation case at Ro=-0.2. Coriolis force effects are included in the calculation to evaluate the wall model under the influence of these effects which are known to affect shear layer turbulence production on the leading and trailing sides of the duct. Wall model LES prediction shows good agreement with experimental data. / 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.

No description available.

Turbine blade cooling techniques have been around for many years, and the addition of coolant into the turbine blade section will remain to be a viable cooling option for many years to come. Film cooling, which will be the main subject of this research, is a form of convection cooling where holes are placed through the surface of the metal components. With the addition of this film coolant into the main flow, an increased amount of total pressure loss will be found downstream. This is caused by the difference of flow momentum of the coolant and main flow when the two fluids are mixed. The test rig used for the upcoming research will be the NASA-designed E3 rig. E3, standing for Energy Efficient Engine, was established to develop technology for improving the energy efficiency of future commercial transport aircraft engines. These engines were designed to provide real-world, actual test configurations in order to produce more efficient turbine engines, mainly to be used for propulsion. Tests were not focused just on heat transfer as its use will be, but with all aspects of the engine's components, especially aero. The annular cascade with 3-dimensional blade profiles as well as high Reynolds numbers make this setup an accurate test bed in which actual turbine conditions can be compared to. The focus of this research is on the increased amount of total pressure loss seen downstream in an annular cascade with 3D blade profiles with the addition of inner endwall film cooling in a high-speed setting. Also, the rig setup of closed vs. open-loop and its effect on the inlet conditions as well as total pressure loss will be investigated.

Thermal management is one of many critical tasks in the design of power electronic systems. It has become increasingly important as a result of the introduction of high power density and integrated modules. It has also been realized that higher temperatures do affect reliability due to a variety of physical failure mechanisms that involve thermal stresses and material degradation. Therefore, it is important to consider temperature as design parameter in developing power electronic modules. The NSF Center for Power Electronics System (CPES) at Virginia Tech previously developed a first generation (Gen-I) active Integrated Power Electronics Module (IPEM). This module represents CPES's approach to design a standard power electronic module with low labor and material costs and improved reliability compared to industrial Intelligent Power Modules (IPM). A preliminary Generation II (Gen-II.A) active IPEM was built using embedded power technology, which removes the wire bonds from the Gen-I IPEM. In this module, the three primary heat-generating devices are placed on a direct bonded copper substrate in a multi-chip module format. The overall goal of this research effort was to optimize the thermal performance of this Gen-II.A IPEM. To achieve this goal, a detailed three-dimensional active IPEM was modeled using the thermal-fluid analysis program ESC in I-DEAS to study the thermal performance of the Gen-II.A IPEM. Several design variables including the ceramic material, the ceramic thickness, and the thickness of the heat spreader were modeled to optimize IPEM geometric design and to improve the thermal performance while reducing the footprint. Input variables such as power loss and interface material thicknesses were studied in a sensitivity and uncertainty analysis. Other design constraints such as electrical design and packaging technology were also considered in the thermal optimization of the design. A new active IPEM design named Gen-II.C was achieved with reduced-size and improved thermal and electrical performance. The success of the new design will enable the replacement of discrete components in a front-end DC/DC converter by this standard module with the best thermal and electrical performance. Future improvements can be achieved by replacing the current silicon chip with a higher thermal-conductivity material, such as silicon carbide, as the power density increases, and by, exploring other possible cooling techniques. / Master of Science