Unsteady aerodynamic interaction in a closely-coupled turbine consistent with contra-rotation

Date of Award

2014

Degree Name

M.S. in Aerospace Engineering

Department

Department of Mechanical and Aerospace Engineering

Advisor/Chair

Advisor: Aaron Altman

Second Advisor

Advisor: John P. Clark

Abstract

A significant design concern for turbomachinery parts is forced vibrational response due to unsteady pressure fields. Shortened component lives, increased maintenance costs, and catastrophic engine failure can result due to unmitigated vibrational stresses. Geometry changes, increased airfoil count and wall thickness, and the inclusion of damping systems are a few of the current strategies employed by designers in order to move modal frequencies out of the engine running range or reduce the vibrational stresses on the airfoil. However, these techniques have a negative impact on performance, system weight, and/or life cycle cost. The focus of the study presented here was to investigate the reaction between the blade and downstream vane of the stage-and-a-half High Impact Technologies (HIT) Research Turbine via CFD analysis and experimental data. Code Leo—a Reynolds-Averaged Navier-Stokes (RANS) flow solver with the two-equation Wilcox 1998 k-ω turbulence model—was used as the numerical analysis tool for comparison for all of the experiments conducted, which includes two- and three-dimensional geometries and both time-averaged and time-accurate simulations. The rigorous blade and downstream vane interaction study was accomplished by first testing the midspan and quarter-tip two-dimensional geometries of the blade in a linear transonic cascade. The effects of varying the incidence angle and pressure ratio on the pressure distribution were captured both numerically and experimentally. This was used during the stage-and-one-half post-test analysis to confirm that the target corrected speed and pressure ratio were achieved. Then, in a full annulus facility, the first vane itself was tested in order to characterize the flow field exiting the vane that would be provided to the blade row during the rotating experiments. Finally, the full stage-and-a-half Research Turbine was tested in the full annulus cascade with a data resolution not seen in any studies to date. A rigorous convergence study was conducted that assessed the grid, iterative, periodic, temporal, and geometric convergences to sufficiently model the flow physics of the Research Turbine. The surface pressure traces and the Discrete Fourier Transforms thereof were compared to the numerical analysis. To track the trajectory of the shocks, time lags to maximum correlations coefficient were analyzed also. Very good agreement was seen when comparing the numerical analysis to the experimental data. The unsteady interaction between the blade and downstream vane was accurately modeled in the numerical analysis.

Keywords

Turbines Vibration, Unsteady flow (Aerodynamics), Blades Fatigue, Aerospace Engineering, Mechanical Engineering, turbine, unsteady aerodynamics, vane-blade interaction, contra-rotation, reflected shocks, rotor-stator interaction

Rights Statement

Copyright © 2014, author

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