High Resolution Heat Transfer Measurement on Flat and Contoured Endwalls in a Linear Cascade

Abstract

In order to continue increasing the efficiency of gas turbines, a significant effort is being made to reduce losses induced by secondary flows in turbine stages. In addition to their impact on aerodynamic losses, these vortical structures are also the source of large heat transfer variations across the passage. A substantial reduction of the secondary flow losses can be achieved with a contoured endwall. However, a change in the vortical pattern can dramatically impact the thermal loads on the endwalls and lead to higher cooling requirements in those areas. This paper focuses on heat transfer measurements made in a passage with either flat or contoured endwalls. The experimental data are supplemented with numerical predictions of the heat transfer data. The measurements are carried out on an isothermal endwall equipped with symmetric airfoils. The paper presents measurements at M = 0.3, corresponding to a Reynolds number ReCax=4.6×105. An infrared camera is used to provide high-resolution surface temperature data on the endwall. The surface is equipped with an insulating layer (Kapton), allowing the calculation of heat flux through the endwall. The heat transfer quantities, namely the heat transfer coefficient and the adiabatic wall temperature, are then derived from a set of measurements at different isothermal plate temperatures. The numerical predictions clarify the link between the change in the heat transfer quantities and the changes in the flow field due to endwall contouring. Finally, numerically predicted heat transfer data are deduced from a set of adiabatic and diabatic simulations that are compared to the experimental data. The comparison focuses on the differences in the regions with endwall contouring, where a significant difference in the heat transfer coefficient between flat and contoured endwalls is measured but underpredicted numerically.

Purge flow effects on rotor hub endwall heat transfer with extended endwall contouring into the disk cavity

“…The small band of very high heat transfer at the beginning of the heated platform was consistent with results reported previously with a similar measurement setup (Lazzi Gazzini et al, 2017b;Laveau et al, 2013), and arose from the start of the thermal boundary layer. A wedge like region of increased heat transfer followed at the mid-passage position, extending to approximately 10% c ax from the leading edge measured at the mid-span (region A).…”

High-resolution heat transfer measurements on a rotating turbine endwall with infrared thermography

“…Popovic et al [1] and Lynch and Thole [2] have quantified the negative effect of increasing purge flow rates on stage efficiency and for the same configurations its influence on overall and local endwall heat transfer. Another stationary high-resolution heat transfer study is presented in Laveau et al [3]. Laveau's concept to simultaneously derive the heat transfer coefficient and the adiabatic wall temperature served as one reference for the study presented in Werschnik et al [4].…”

“…Laveau et al [15] successfully adopted the infrared based measurement concept, as developed for the linear cascade setup [3], to the endwall in the first vane passage of a full annular rotating turbine facility. Subsequently, the measurement concept was changed to an iso-energetic approach and established for the experimental determination of heat transfer quantities in the rotating frame of reference.…”