Browsing by Subject "Turbines"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Experimental simulation and mitigation of contaminant deposition on film cooled gas turbine airfoils(2011-05) Albert, Jason Edward; Bogard, David G.; da Silva, Alexandre K.; Ezekoye, Ofodike A.; Webber, Michael E.; Wenglarz, Richard A.Deposition of contaminant particles on gas turbine surfaces reduces the aerodynamic and cooling efficiency of the turbine and degrades its materials. Gas turbine designers seek a better understanding of this complicated phenomenon and how to mitigate its effects on engine efficiency and durability. The present study developed an experimental method in wind tunnel facilities to simulate the important physical aspects of the interaction between deposition and turbine cooling, particularly film cooling. This technique consisted of spraying molten wax droplets into the mainstream flow that would deposit and solidify on large scale, cooled, turbine airfoil models in a manner consistent with inertial deposition on turbine surfaces. The wax particles were sized to properly simulate the travel of particles in the flow path, and their adhesion to the surface was modeled by ensuring they remained at least partially molten upon impact. Initial development of this wax spray technique was performed with a turbine blade leading edge model with three rows of showerhead film cooling. It was then applied to turbine vane models with showerhead holes and row on pressure side consisting of either standard cylindrical holes or similar holes situated in a spanwise, recessed trench. Vane models were either approximately adiabatic or had a thermal conductivity selected to simulate the conjugate heat transfer of turbine airfoils at engine conditions. These models were also used to measure the adiabatic film effectiveness and overall cooling effectiveness in order to better assess how the cooling design interacted with deposition. Deposit growth was found to be sensitive to the mainstream air and the model surface temperatures and the solidification temperature of the wax. Deposits typically grew to an equilibrium thickness caused by a balance between erosion and adhesion. The existence of film cooling substantially redistributed deposit growth, but changes in blowing ratio had a minor effect. A hypothesis was proposed and substantiated for the physical mechanisms governing wax deposit growth, and its applicability to engine situations was discussed.Item Numerical and Experimental Analysis of Multi-Stage Axial Turbine Performance at Design and Off-Design Conditions(2013-08-07) Abdelfattah, Sherif AlykadryComputational fluid dynamics or CFD isan importanttool thatis used at various stages in the design of highly complex turbomachinery such as compressorand turbine stages that are used in land and air based power generation units. The ability of CFD to predict the performance characteristics of a specific blade design is challenged by the need to use various turbulence models to simulate turbulent flows as well as transition models to simulate laminar to turbulent transition that can be observed in various turbomachinery designs. Moreover, CFD is based on numerically solving highly complex differential equations, which through the use of a grid to discretize the geometry introduces numerical errors. Allthese factors combine to challenge CFD?s role as a predictor of blade performance. It has been generallyfound that CFD in its current state of the art is best used to compare between various design points and not as a pure predictor of performances. In this study the capability of CFD, and turbulence modeling, in turbomachinery based geometry is assessed.Three different blade designs are tested, that include an advanced two-stage turbine blade design, a three stage 2D or cylindrical design and finally a three stage bowed stator and rotor design. Allcases were experimentally tested at the Texas A&Muniversity Turbomachinery Performance and Flow Research Laboratory (TPFL).In all cases CFD provided good insights into fundamental turbomachinery flow physics, showing the expected improvement from using 2D cylindrical blades to 3D bowed blade designs in abating the secondary flow effects which are dominant loss generators.However, comparing experimentally measured performance results to numerically predicted shows a clear deficiency, where the CFD overpredicts performance when compared to experimentallyobtained data, largely underestimating the various loss mechanisms. In a relative sense, CFD as a tool allows the user to calculate the impact a new feature or change can have on a baseline design. CFD will also provide insight into what are the dominant physics that explain why a change can provide an increase or decrease in performance. Additionally,as part of this study, one of the main factors that affect the performance of modern turbomachinery is transition from laminar to turbulent flow.Transition is an influential phenomena especially in high pressure turbines, and is sensitive to factors such asupstream incidentwake frequency and turbulence intensity.A model experimentally developed, is implemented into a CFD solver and compared to various test results showing greater capability in modeling the effects of reduced frequency on the transition point and transitional flow physics. This model is compared to industry standard models showing favorable prediction performance due to its abilityto account for upstream wake effects which most current model are unable to account for.Item Vertical axis wind turbine wake velocity measurements and comparison with analysis(Texas Tech University, 1981-05) Sun, HuanmingMean velocity measurements were performed in the wake behind a Darrieus Turbine. In this experiment the turbine was towed through a tank filled with water. Reynolds' number scaling was used to relate the operation in water to that in air. The results were compared with predictions from the momentum and vortex models developed by previous workers. In addition, some data from a full scale rotor obtained by other workers are presented and compared with analytical results.