Master of Science in Mechanical Engineering (MSME), Wright State University, 2018, Mechanical Engineering

High-lift low-pressure turbine blades produce significant losses at the junction with the endwall. The losses are caused by several complex three-dimensional vortical flow structures, which interact with the blade suction surface boundary layer. This study investigates the unsteady characteristics of these endwall flow structures on a highly loaded research profile and the adjacent endwall using surface-mounted hot-film sensors. Experiments were conducted in a low-speed linear cascade wind tunnel. The front-loaded blade profile was subjected to three different inlet conditions, consisting of two turbulence levels, and three incoming boundary layer thicknesses. Multiple surface-mounted hot-film sensors were installed throughout the passage. This thesis progressed in three stages of research. The first verified that the hot-film sensors could be used to detect flow structures in the cascade. The second used the results from installed hot-films to examine the unsteady characteristics of vortices formed near the leading edge and the propagation of the passage vortex across the passage where it interacts with a corner separation along the suction surface. Simultaneous measurements from the hot-film sensors were analyzed for frequency spectra and time lag in order to provide new insight into the endwall flow dynamics. Finally, signatures from the hot-films were linked to specific flow phenomena through concurrent flow visualization. At each stage of the investigation, results were compared to the results of a numerical simulation.

Committee: Mitch Wolff Ph.D. (Advisor); Rolf Sondergaard Ph.D., P.E. (Committee Member); Christopher Marks Ph.D. (Committee Member) Subjects: Aerospace Engineering; Engineering; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2009, Mechanical Engineering

As the demand for greater efficiency and reduced specific fuel consumption from gas turbine engines continues to increase, design tools must be improved to better handle complicated flow features such as vane inlet temperature distortions, film cooling, and disk purge flow. In order to understand the physics behind these features, a new generation of turbine experiments is needed to investigate these features of interest for a realistic environment.This dissertation presents for the first time measurements and analysis of the flow features of a high-pressure one and one-half stage turbine operating at design corrected conditions with vane and purge cooling as well as vane inlet temperature profile variation. It utilizes variation of cooling flow rates from independent circuits through the same geometry to identify the regions of cooling influence on the downstream blade row. The vane outer cooling circuit, which supplies the film cooling on the outer endwall of the vane and the trailing edge injection from the vane, has the largest influence on temperature and heat-flux levels for the uncooled blade. Purge cooling has a more localized effect, but it does reduce the Stanton Number deduced for the blade platform and on the pressure and suction surfaces of the blade airfoil. Flow from the vane inner cooling circuit is distributed through film cooling holes across the vane airfoil surface and inner endwall, and its injection is entirely designed with vane cooling in mind. As such, it only has a small influence on the temperature and heat-flux observed for the downstream blade row. In effect, the combined influence of these three cooling circuits can be observed for every instrumented surface of the blade. The influence of cooling on the pressure surface of the uncooled blade is much smaller than on the suction surface, but a local area of influence can be observed near the platform. This is also the first experimental program to investigate the influence of vane inlet (open full item for complete abstract)

Committee: Dr. Michael Dunn PhD (Advisor); Dr. Sandip Mazumder PhD (Committee Member); Dr. William Rich PhD (Committee Member); Dr. Mohammad Samimy PhD (Committee Member) Subjects: Fluid Dynamics; Mechanical Engineering

Doctor of Philosophy, Case Western Reserve University, 2010, Chemical Engineering

Patterning processes combined metal masking and selective diamond growth to fabricate conductive diamond patterns on various substrates, allowing either the growth or nucleation surfaces to be applied as electrodes. These processes enable novel applications of diamond electrodes integrating diamond films into existing sensor systems and novel, temperature intolerant, polymer-based systems. A patterning process was initially developed for thermally oxidized silicon. Two nucleation (BEN and sonication seeding) and two growth (HFCVD and MPCVD) methods were evaluated. Feature dimensions and spacing down to 8 μm were obtained, having a minimal thickness of 1 μm. The films were high-quality polycrystalline diamond, as analyzed by Raman spectroscopy. As electrochemical sensors, the films detected dopamine (10 μM in PBS) with redox properties typical of microcrystalline diamond. Attempts using BEN to selectively deposit diamond on insulating surfaces (alumina, high-temperature borosilicate glass) required metal coating of the back and sides of substrates. With alumina, adhesion problems prevented growth of complete films (or patterns). With glass, interactions between the tungsten and substrate prevented etching of the mask, compromising the pattern. Patterns on silicon dioxide were transferred to a polynorbornene polymer support with metal (Au, or Cr/Au/Cr) contacts to create the first diamond-on-polymer sensors - making the smooth, diamond nucleation surface the active electrode surface. The patterning process was scaled from ¼” chips to 3” wafers, to fabricate multi-electrode arrays (10 singly addressable pads). Sonication seeding was used to seed wafer-scale substrates due to limitations in implementing BEN with larger scale substrates. As-fabricated, diamond-on-polymer electrodes from the wafer-scale process showed a highly capacitive dielectric response. XPS depth profiling revealed a SiOxCy layer on the electrode (diamond nucleation) surface, an issue introduced by t (open full item for complete abstract)

Committee: Heidi B. Martin PhD (Committee Chair); R. Mohan Sankaran PhD (Committee Member); C. C. Liu PhD (Committee Member); Christian A. Zorman PhD (Committee Member) Subjects: Chemical Engineering