Abstract
The aim of the study is to investigate and mitigate the secondary losses in a variable turbine area nozzle vane by modifying its pivot shape. The variable area nozzle vane (VANT) is used to actively control the mass flow rate and improve the off-design performance of the turbine stages. However, the clearance required for the pivot mechanism introduces tip leakage losses, which can render the benefits of the variable area nozzle vane useless.
The study uses the 2nd stage of low-pressure turbine vane from the Energy Efficient Engine proposed by Pratt and Whitney. The vane passage is modified to implement the VANT concept, and the effect of different pivot profiles and modifications on the bottom surface near the suction side is investigated at various setting angles. The numerical simulations are performed using Ansys ICEM CFD® and ANSYS CFX®, and the results are analyzed using parameters such as non-dimensional vorticity, static entropy, and total pressure loss coefficient.
The study shows that the improvement upon introduction of shape modifications to the pivot, a) elliptical passage in pivot b) tapered pivot, reduces the total pressure loss coefficient by 4% as compared to the vane passage with unmodified circular pivot. The interaction between the leakage flow and the main passage flow is also observed using three dimensional streamlines. Overall, the study provides insights into the sources of secondary losses in variable turbine area nozzle vanes and demonstrates that modifying the geometrical shape can help mitigate these losses and improve the efficiency of the turbine.
