Publication Date

2020

Document Type

Thesis

Committee Members

Mitch Wolff, Ph.D. (Advisor); Rolf Sondergaard, Ph.D., P.E. (Committee Member); Christopher Marks, Ph.D. (Committee Member)

Degree Name

Master of Science in Mechanical Engineering (MSME)

Abstract

Flow through the turbine section of gas turbine engines is inherently unsteady due to a variety of factors, such as the relative motion of rotors and stators. In low pressure turbines, periodic wake passing has been shown to impact boundary layer separation, blade surface pressure distribution, and loss generation. The effect of periodic disturbances on the endwall flow is less understood. Endwall flow in a low-pressure turbine occurs in the boundary layer region of the flow through the blade passage where the blade attaches to the hub in the turbine. The response of an endwall vortical structure, the passage vortex, to various upstream disturbances is considered in this investigation. The passage vortex is a three-dimensional unsteady flow feature which generates aerodynamic losses as it interacts with the flow along the blade suction surface. High-speed velocimetry and numerical simulations have shown that the vortex intermittently loses coherence and varies in strength and position over time. The intermittent loss of coherence of the passage vortex is believed to be related to the leading-edge junction flow dynamics. An array of pneumatic devices was installed upstream of a linear cascade of low-pressure turbine blades to produce periodic disturbances that impact the blade leading edge region. A small disturbance and a large disturbance were created and characterized by their maximum velocity deficit and nondimensionalized solenoid valve on time using a plane of particle image velocimetry. A plane of high-speed stereoscopic particle image velocimetry data was collected inside the blade passage to examine how the disturbances impacted the vortex. Surface-mounted hot-film data was collected near the leading edge and in passage region to help relate flow behavior in both locations. The size and frequency of the disturbances had a nonlinear impact on the vortex size and strength. Fourier analysis revealed that the actuation frequency caused a harmonic response, and a change in the temporal behavior of the passage vortex. Each actuation frequency caused a different response from the vortex, but the vortex dynamics did not lock-on to the disturbance frequency.

Page Count

134

Year Degree Awarded

2020


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