Reducing Low-Pressure Turbine Shroud Leakage Loss By Optimizing Leakage-Mainstream Interaction

In turbomachinery, mixing in the blade tip region between
tip leakage and mainstream flow leads to irreversible entropy
production, which is detrimental to efficiency. Despite extensive
efforts to reduce leakage flows, the mixing process remains a significant
source of performance loss, even at small mass flow rates.
Introducing Vane Bleed Holes (VBH) into existing machines offers
a promising solution to reduce these losses. Vane Bleed Holes
operate by extracting the leakage flow from the rear section of
the outer air seal cavity of the rotor blade and reintroducing it
into the main gas path in the shroud region of the subsequent
vane. This process significantly reduces mixing losses between
leakage and mainstream flows and improves inflow conditions at
the vane’s near-endwall region.
The aim of this paper is to present the numerical design and
optimization of a Vane Bleed Hole that will be experimentally
integrated and tested in a 1.5-stage low-pressure turbine. Within
the framework of this study, a VBH geometry is generated, parameterized,
and optimized using a genetic algorithm to maximize
isentropic efficiency. The study particularly focuses on the quantitative
assessment of the loss-generating mechanisms using an
entropy production-based decomposition of the losses, which is
crucial for the development of future VBH improvement strategies.