Conceptual development of casing Patterns to reduce the aerodynamic losses in an axial turbine stage
Open Access
- Author:
- Ranka, Amrat Arvind
- Graduate Program:
- Aerospace Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- November 21, 2019
- Committee Members:
- Cengiz Camci, Thesis Advisor/Co-Advisor
Dr. Sven Schmitz, Committee Member
Amy Ruth Pritchett, Program Head/Chair - Keywords:
- Turbines
axial gas turbine
casing grooves
computational fluid dynamics
CFD
Tip-Leakage losses
Tip-mitigation studies
Turbomachinery
AFTRF
leakage Vortex
Horseshoe Vortex - Abstract:
- In turbomachinery, presence of the gap between the rotor blade tip and the casing surface has been a significant source of aerodynamic loss in the turbine flow field. This thesis seeks to understand and mitigate the aerodynamic losses by embedding different groove patterns on the casing surface near the turbine blade tip. A similar approach has been used in the past for the compressor stage to improve its stall and surge characteristics. However, extensive studies have not been performed for the turbine stage. Three different casing designs, “Spherical Patterns”, “Axial Grooves”, “Circumferential Grooves”, were analyzed, and their effectiveness was measured against the smooth casing surface (baseline design). Based on the understanding of the preliminary casing designs, an improved casing design was developed. This thesis describes a comprehensive computational flow visualization study and aerodynamic experiments conducted at the Axial Flow Turbine Research Facility (AFTRF). Steady-state computational simulations were performed by solving three-dimensional Reynolds-Averaged-Navier-Stokes (RANS) flow equations. To accurately predict the flow near the tip section, including flow leaking through the tip gap, the Shear Stress Transport (SST) k-w turbulence model with gamma-transition is employed. At first, the computational results were validated against the experimental results obtained for the preliminary casing designs. Furthermore, numerical studies were performed for different casing patterns to understand the flow physics and analyze the changes caused by such casing patterns in the turbine stage. With the aid of 3-D flow visualization plots, tip leakage losses and vortex structures of all designs were analyzed. Along with these plots, numerical calculations were employed to quantify the aerodynamic performance of different designs.