Keywords

aerodynamics, cfd, turbomachinery, diffuser, experimental fluid mechanics

Abstract

A commonly observed flow interaction in industrial gas turbine (IGT) exhaust diffuser configurations is investigated, where upstream structural wakes interact with downstream airfoil-like components, potentially leading to unsteady loading. To better understand the mechanisms contributing to this behavior, a scale-model is designed. Dynamic similarity is achieved by matching the Strouhal number (St) of the vortex shedding from the strut. A bell-mouth followed by a swirler is installed in front of the strut to mimic the flow angles at the inlet section of the turbine exhaust. Experiments are conducted for three swirl angles, namely, 30°, 45°, and 60°. Power spectra computed from the static-pressure signals on the airfoil reveal a sharp peak denoting intense pressure fluctuation at the highest swirl angle of $60°. Surface oil flow visualization captures a large separation bubble on the manway airfoil confirming massive separation. These findings are further corroborated by numerical simulations showing unsteady strut-manway interactions in the annular cylinder. Vorticity contours suggest that coherent vortex structures convect downstream and interact with the leading edge (L.E) of the airfoil. Finally, a representative upstream flow modification is explored to assess its influence on downstream unsteady loading.  Power spectra of pressure fluctuations obtained in this case shows no distinct peak confirming the validity of the solution.

Completion Date

2026

Semester

Fall

Committee Chair

Bhattacharya, Samik

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Mechanical and Aerospace Engineering

Document Type

Dissertation/Thesis

Identifier

DP0053152

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