This article presents the implementation of a Particle Image Velocimetry (PIV) into the high-speed short-duration rotating turbine facility of the von Karman Institute. The advantage of PIV as a whole field measurement is emphasized in such circumstances for which the use of optical technique can drastically reduce the number of tests and the need for multiple intrusive expensive probes, ultimately lowering the testing cost. Practical solutions were demonstrated that address various challenges for the effective application of PIV. An endoscope delivered the laser sheet to the region of interest and a planoconcave window provided optical access for the measurement in the annular test section. A high-speed laser system and a high-speed camera were synchronized at 1 kHz sampling rate. Complementary measurements and dedicated image processing were performed to ensure the synchronization of the PIV images with the rotor position that was monitored through an encoder. The region of interest was the blade-to-blade plane at the 58% span turbine exit on a rectangular field of view covering approximately one rotor pitch and 0.15 rotor axial chord from the rotor trailing edge. Phase-locked-average velocity fields are obtained from PIV and compared against steady-state Reynolds Averaged Navier Stokes (RANS) simulations along with four-hole probe measurement results. Together with an uncertainty analysis, the results demonstrate the promising robustness and accuracy of PIV. A practical guideline for PIV application in such kind of turbine test rigs is provided as a conclusion of the paper.

The paper addresses the study of the flow established in a HPT with rim seal purge. The test section, operated at engine-relevant flow conditions in the high-speed turbine rig of the von Karman Institute, is instrumented for high-bandwidth aerothermal measurements. The rainbow rotor allows the simultaneous testing of six different sectors, each hosting a specific tip and platform geometry. This paper focuses on the baseline sector, equipped with an axisymmetric hub platform and a squealer tip, tested at purge flow rates of 1.74% and 1% of the stage mass flow. At the rotor shroud, the maximum heat transfer is measured along the front pressure side rim, whereas the squealer cavity generates a region of low static pressure and heat flux. The experimental adiabatic wall temperature is derived to quantify the thermal contribution to the shroud heat flux, demonstrating a temperature increase of up to 20% with respect to the stage inlet. An Euler-based model is proposed to evaluate the temperature-driving work-exchange mechanism in the gap. The peak in casing heat transfer coefficient (750 W/m2) is found above the tip leading edge. Unsteady flow measurements at the stage outlet confirm the phase and intensity of the tip leakage and upper passage vortex predicted by RANS computations performed with experimentally-calibrated boundary conditions. In the lower 50% of the span, the numerical calculations show significant limits in predicting the interaction between rim seal purge and turbine main flow.

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The present paper addresses the experimental and numerical study of the unsteady flow established in a high-pressure turbine stage with rim seal purge. The HPT test section, operated at engine-relevant flow conditions in the high-speed turbine rig of the von Karman Institute, is heavily instrumented for high-resolution, high-bandwidth aerothermal measurements. A rainbow rotor setup allows the simultaneous testing of six different sectors, each hosting a specific tip and platform geometry optimized for enhanced aerodynamic performance. This paper focuses on the flow over the baseline sector, equipped with an axisymmetric hub platform and a squealer tip, with a purge flow rate matching 1.74% and 1% of the stage mass flow. The numerical study relies on Reynolds-averaged Navier Stokes computations with test-calibrated boundary conditions. Unsteady pressure and heat transfer measurements are performed at the rotor shroud. The maximum heat transfer is achieved along the front pressure side rim, whereas the squealer cavity generates a region of uniformly low static pressure and heat flux. The experimental adiabatic wall temperature is derived to quantify the thermal contribution to the global heat flux, demonstrating an increase in over-tip gas temperature up to 1.2 T01 above the pressure side rim. A Euler-based model is proposed to evaluate the temperature-driving work-exchange mechanism in the tip gap. The peak in casing heat transfer coefficient (750 W/m2) is found at the tip leading edge. Time-resolved measurements of outlet total pressure, Mach number, and flow angle confirm the predicted phase and intensity of the tip leakage and upper passage vortex in the near-casing region. At 20% hr, the total pressure minimum is highly under-predicted by the RANS, indicating an inaccurate modeling of the interaction between rim seal purge and main flow. The measured impact of the purge flow variation is more significant than predicted by the RANS computations, with a negative offset of about 0.5% P01 in the lower 50% hr at lower purge flow rate.

This article presents the implementation of a Particle Image Velocimetry (PIV) into the high-speed short-duration rotating turbine facility of the von Karman Institute. The advantage of PIV as a whole field measurement is emphasized in such circumstances for which the use of optical technique can drastically reduce the number of tests and the need for multiple intrusive expensive probes, ultimately lowering the testing cost. Practical solutions were demonstrated that address various challenges for the effective application of PIV. An endoscope delivered the laser sheet to the region of interest and a planoconcave window provided optical access for the measurement in the annular test section. Sub-micron scale oil droplets were seeded into main flow through custom-made probes located upstream the nozzle guide vane and into a pipe line supplying rim seal purge flow. A high-speed laser system and a high-speed camera were synchronized at 1 kHz sampling rate. Complementary measurements and dedicated image processing were performed to ensure the synchronization of the PIV images with the rotor position that was monitored through an encoder. The region of interest was the blade-to-blade plane at the 58% span turbine exit on a rectangular field of view covering approximately one rotor pitch and 0.15 rotor axial chord from the rotor trailing edge. Phase-locked-average velocity fields are obtained from PIV and compared against steady-state Reynolds Averaged Navier Stokes (RANS) simulations along with four-hole probe measurement results. Together with an uncertainty analysis, the results demonstrate the promising robustness and accuracy of PIV. A practical guideline for PIV application in such kind of turbine test rigs is provided as a conclusion of the paper.