AN INVESTIGATION OF USING TIP LEAKAGE INTERRUPTER AND BLADE SLIT TO MITIGATE AERODYNAMIC LOSSES IN AXIAL TURBINE STAGE
Open Access
- Author:
- Andichamy, Veerandra Chakkarava
- Graduate Program:
- Aerospace Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 09, 2019
- Committee Members:
- Cengiz Camci, Dissertation Advisor/Co-Advisor
Cengiz Camci, Committee Chair/Co-Chair
Savas Yavuzkurt, Outside Member
Jose Palacios, Committee Member
Michael P Kinzel, Committee Member
Yong W Kim, Special Member
Amy Ruth Pritchett, Program Head/Chair - Keywords:
- Axial Turbines
Tip Leakage Flow
Blade Slit
TLI
Turbomachinery - Abstract:
- The flow field near the blade tip in a turbine stage is highly three dimensional with multiple vortical systems. They are a major source of energy loss in the turbine passage. The current study uses two new concepts called Blade Slit and Tip Leakage Interrupters (TLI) to mitigate some of the adverse effects of these vortical structures and improve the efficiency of an axial turbine stage. A Blade Slit is a small cut (slit) is made on the blade to facilitate high momentum fluid on the pressure side of the blade to pass through the blade and reach the suction side. This flow, on reaching the suction side, acts as a jet and interacts with the local vortical structures. The slit, when strategically placed, facilitates the jet to impinge the core of the low momentum vortex systems. This interaction effectively reduces the strength of these vortices and thereby reduces the aerodynamic loss in the turbine passage. TLIs are a system of vortex generators attached to the suction side of the turbine blade tip. They operate by inducing controlled vortical structures originating from strategically shaped/oriented multiple and sub-miniature vortex generators. They also act as a flow obstruction for the existing vortex system in the passage. When properly placed on the blade surface, these TLIs interact with the tip leakage vortex and passage vortex present in the turbine passage. This interaction reduces the damaging aerodynamic effects of these vortices. Both of these designs are developed as proof of concepts and their aerodynamic loss mitigation characteristics are studied in this thesis. In this investigation, the design parameters associated with these concepts such as their local orientation and location on the blade surface are varied. The influence of these design parameters over the loss reduction properties of the Blade Slit and TLI is studied. Both of these designs are experimentally and computationally analyzed in this study. The experiments in this study are carried out in a single-stage, low-speed axial turbine facility, while the computational work is performed using one to one computational model of the experimental configuration. The results from the Blade Slit design show that not all the fluid exiting the slit imparts high momentum to the vortical structures. Some of these fluids interact with the main flow on the suction side and creates additional aerodynamic losses in the turbine passage. In the case of TLI, the orientation of TLI with respect to the local blade surface determines the nature of interaction between the TLI and the vortical structures in the passage and hence its ability to reduce the aerodynamic losses. The study draws conclusions about the significance of individual design parameters associated with Blade Slit and TLI. It also shows that significant loss reduction might be possible with simple modifications to the blade geometry. All the modifications on the blade should be limited to the highly vortical region near the blade tip. Any modification which changes the flow properties of the main flow results in an additional aerodynamic loss in the turbine passage. In addition to analyzing Blade Slit and TLI design, the aerodynamic influence of blade tip modifications and the blade tip clearances in a turbine passage have also been studied.