Date of Award

4-22-2014

Access Type

Thesis - Open Access

Degree Name

Master of Science in Aerospace Engineering

Department

Aerospace Engineering

Committee Chair

Dr. Magdy Attia

First Committee Member

Dr. Sathya Gangadharan

Second Committee Member

Dr. Mark Ricklick

Abstract

Momentum differences between the neighboring streamlines at the end wall/primary flow interaction region of an axial turbine stage induce three-dimensional vortical flow structures, such as the leading edge horseshoe vortex, resulting in significant aerodynamic performance deterioration. Reducing the effect of such flow instabilities requires turbine blade modification to discourage boundary layer roll-up, but traditional structural modification design systems can be prohibitively complex and time-intensive.

To address this problem, this study contributes a blade modification method involving airfoil shape optimization, designed to adjust the leading edge airfoil shape in horseshoe vortex-affected turbine applications. The key insight is that airfoil design (treated as a blunt body) does not consider incoming flow possessing various layers with different momentum, and two-dimensional total pressure and temperature radial distributions are unrealistic; the hub and tip sections operate at off-design-like conditions, i.e., the velocity triangles are unrepresentative of actual boundary conditions. This airfoil shape optimization approach utilizes actual incoming span-wise boundary conditions, obtained from 3D CFD, to establish new velocity triangles at the hub and tip regions, and to redesign the corresponding airfoil sections in light of the newly acquired triangles.

The presented results from a 1.5-stage axial turbine simulation demonstrate that adapting rotor blade hub and tip sections to the incoming radial flow distribution can significantly diminish the rotor passage and horseshoe vortices and can considerably improve overall rotor blade efficiency.

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