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research-article

EXPERIMENTAL AND NUMERICAL INVESTIGATION OF OPTIMIZED BLADE TIP SHAPES - PART II: TIP FLOW ANALYSIS AND LOSS MECHANISMS

[+] Author and Article Information
Marek Paty

von Karman Institute for Fluid Dynamics, Rhode Saint Genèse, Brussels BE-1640, Belgium
marek.paty@seznam.cz

Bogdan C. Cernat

von Karman Institute for Fluid Dynamics, Rhode Saint Genèse, Brussels BE-1640, Belgium
cernat@vki.ac.be

Cis De Maesschalck

von Karman Institute for Fluid Dynamics, Rhode Saint Genèse, Brussels BE-1640, Belgium
cis.demaesschalck@gmail.com

Sergio Lavagnoli

von Karman Institute for Fluid Dynamics, Rhode Saint Genèse, Brussels BE-1640, Belgium
lavagnoli@vki.ac.be

1Corresponding author.

ASME doi:10.1115/1.4041466 History: Received August 22, 2018; Revised September 08, 2018

Abstract

The leakage flows induced in the clearance between stationary and rotating parts in turbine stages generate signi?cant aerodynamic losses and thermal stresses. Shaping the tip geometry offers a considerable potential to modulate the tip ?ows and weaken the heat transfer onto the blade and casing. This paper presents a comprehensive study on the tip geometry impact on the over-tip aerodynamic and thermal fields. An experimental and numerical campaign has been performed on a high-pressure turbine stage adopting three different blade tip pro?les. The performance of two optimized tips (one with a fully contoured shape and the other featuring a multi-cavity squealer-like profile) is compared against a baseline squealer geometry. Reynolds-averaged Navier-Stokes simulations were run on high-density unstructured meshes in Numeca FINE/Open, adopting the Spalart-Allmaras turbulence model and experimental boundary conditions. The simulations were validated against time-averaged and time-resolved experimental data collected in an instrumented turbine stage at scaled engine representative conditions. Denton's mixing loss model is applied to quantify the loss reduction mechanisms of the alternative tip designs. An advanced method based on the local triple decomposition of relative motion is used to track the location, size and intensity of the vortical ?ow structures. The comparison between different profiles highlights distinct aerodynamic features in the associated gap ?ow ?eld. The analysis allows to quantify the impact of speci?c tip designs on the turbine aerodynamics and heat transfer.

Copyright (c) 2018 by ASME
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