The possibility of misalignments at interfaces would be increased due to individual parts' assembly and external factors during its operation. In actual engine representative conditions, the upstream misalignments have effects on turbines performance through the nozzle guide vane passages. The current experimental aerodynamic investigation over the nozzle guide vane passage was concentrated on the backward-facing step of upstream misalignments. The tests were performed using two types of vane endwall platforms in a 2D linear cascade: flat endwall and axisymmetric converging endwall. The test conditions were a Mach number of 0.85, Re_ex 1.5*10^6 based on exit condition and axial chord, and a high freestream turbulence intensity (16%), at the Virginia tech transonic cascade wind tunnel. The experimental results from the surface flow visualization and the five-hole probe measurements at the vane-passage exit were compared with the two cases with and without the backward-facing step for both types of endwall platforms.
As a main source of secondary flow, a horseshoe vortex at stagnation region of the leading edge of the vane directly influences other secondary flows. The intensity of the vortex is associated with boundary layer thickness of inlet flow. In this regard, the upstream backward-facing step as a misalignment induces the separation and attachment of the inlet flow sequentially, and these cause the boundary layer of the inlet flow to reform and become thinner locally. The upstream-step positively affects loss reduction in aerodynamics due to the thinner inlet boundary layer, which attenuates a horseshoe vortex ahead of the vane cascade despite the development of the additional vortices. And converging endwall results in an increase of the effect of the upstream misalignment in aerodynamics, since the inlet boundary layer becomes thinner near the vane's leading edge due to local flow acceleration caused by steep contraction of the converging endwall. These results show good correlation with many previous studies presented herein. / Master of Science / In response to climate change and limited resources, fossil fuel prices are expected to rise and energy policies are expected to change. Under these circumstances, there is a growing demand in the industry to provide an affordable option for improving the efficiency of technology. Energy efficiency is one of most cost effective ways to improve the competitiveness of all businesses and reduce energy costs for consumers.
Regarding the current study topic in particular, the gas turbine is an internal combustion engine that extracts energy, which is resultant from the liquid fuel flow, and is then converted into mechanical energy to drive a compressor or other devices. Gas turbines are used in many applications such as, to power aircraft, electrical generators, pumps, and gas compressors in industrial fields.
Because the gas turbine has a probability of unaligned connections of components due to assembly characteristics of its huge size, performance is affected. To consider issue, an experimental study was conducted related to the energy efficiency for an actual engine’s representative conditions; the current study focuses on the upstream backward facing step of the unaligned connections and highlights the practical effects of the unaligned connection and converging geometry.
These backward facing unaligned connections are shown to have positive effects for reducing aerodynamic losses by weakening a main source of the loss, even despite the development of the additional losses. And, the application of converging geometry to the gas turbine also results in loss reduction due to local flow acceleration. These results show good correlation with the many previous studies presented herein.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/77924 |
| Date | 06 June 2017 |
| Creators | Lee, Yeong Jin |
| Contributors | Mechanical Engineering, Ng, Wing Fai, Wicks, Alfred L., Ekkad, Srinath |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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