Session: 14-04 Systems

Paper Number: 83129

83129 - Experimental Investigation of a High-Speed Turbine With Rainbow Rotor and Rim Seal Purge Flow 

The paper presents a detailed analysis on the aerothermal flow field in a high-pressure turbine (HPT) stage with rim seal purge injection. The experimental study is carried out at engine-relevant flow conditions in the high-speed turbine rig of the von Karman Institute. The test section is representative of the first stage of a two-stage HPT turbine and the rotor is operated in “rainbow” configuration to allow the simultaneous testing of a selection of optimized blade tip and hub platform geometries. While the first part of the paper focuses on the description of the experimental and numerical setup, the second part focuses on the characterization of the turbine flow physics through a comparison between experimental and numerical datasets.

The aerothermal flow study is performed first on the baseline airfoil geometry, presenting an axisymmetric hub and a squealer tip profile. Time-resolved static pressure and heat transfer measurements at the rotor casing are combined with RANS flow predictions to characterize the over-tip flow field. The experimental adiabatic wall temperature and heat transfer coefficient are computed in order to quantify the aerodynamic and thermal contribution to the casing heat transfer. The same analysis is performed on the numerical dataset and a reduced order model is exploited to validate the over-tip work exchange mechanism driving the adiabatic wall temperature variation. The study shows that the thermal contribution to the casing heat transfer is dominant in the regions of higher flow turning (pressure side rim) while the heat transfer coefficient is enhanced in the regions where the leakage flow impinges on the external casing (blade leading edge).

 At the rotor outlet, time-resolved contours of experimental absolute yaw angle, total pressure and Mach number are presented and analyzed against the numerical flow predictions for both design and off-design purge flow conditions. The simulations are shown to correctly capture the outlet flow topology in the upper 50% of the rotor blade span, while the near-hub region presents significant discrepancies with respect to the experimental data, showing the limitations of the RANS method in modelling the purge flow mixing with the main turbine stream. The rainbow rotor impact on the stage outlet flow field is analyzed by quantifying the sector-to-sector variations in terms of flow angle, total pressure and Mach number as a function of the hub geometry for the design and off-design purge flow conditions. 

Presenting Author: Bogdan Cezar Cernat von Karman Institute

Presenting Author Biography: Research Engineer at the von Karman Institute.

Authors:

Bogdan Cezar Cernat von Karman Institute
Jorge Pinho von Karman Institute
Mizuki Okada von Karman Institute
Sergio Lavagnoli von Karman Institute