Heat Transfer and Pressure Drop Measurements on Rotating Matrix Cooling Geometries for Airfoil Trailing Edges

Abstract

In the present paper the combined effects of rotation and channel orientation on heat transfer and pressure drop along two scaled up matrix geometries suitable for trailing edge cooling of gas turbine airfoils are investigated. Experimental tests were carried out under static and rotating conditions. Rotating tests were performed for two different orientations of the matrix channel with respect to the rotating plane: 0deg and 30deg. This latter configuration is representative of the exit angle of a real gas turbine blade. Test models are designed in order to replicate an internal geometry suitable for blade trailing edge cooling, with a 90deg turning flow before entering the matrix array which has an axial development. Both the investigated geometries have a cross angle of 45deg between ribs and different values of sub-channels and rib thickness: one has four sub-channels and lower rib thickness (open area 84.5%), one has six sub-channels and higher rib thickness (open area 53.5%). Both geometries have a converging angle of 11.4deg. Matrix models have been axially divided in 5 aluminum elements per side in order to evaluate the heat transfer coefficient in 5 different locations in the main flow direction. Metal temperature was measured with embedded thermocouples and thin-foil heaters were used to provide a constant heat flux during each test. Heat transfer coefficients were measured applying a steady state technique based on a regional average method and varying the sub-channel Reynolds number Res from 2000 to 10000 and the sub-channel Rotation number Ros from 0 to 0.250 in order to have both Reynolds and Rotation number similitude with the real conditions. A post-processing procedure, which takes into account the temperature gradients within the model, was developed to correctly compute average heat transfer coefficients starting from discrete temperature measurements.

Film Cooling Effectiveness Downstream of Optimised Cross Corrugated Slot Geometry with Exit Shaping

“…Goreloff et al (1990) also measured cooling effectiveness around the external surface of a blade. Experiments with lattice cooling applied to the radial passage feeding the trailing edge of the blade were conducted by Gillespie and Ireland (1997) and (Carcasci et al, 2015). The advantages in high heat transfer, low pressure loss, high structural integrity and suitability for investment casting are summarised by Bunker (2008).…”

A numerical framework for heat transfer and pressure loss estimation of matrix cooling geometry in stationary and rotational states

“…Comparable or higher thermal performance and added structural rigidity can make the lattice structure a suitable alternative of pin fins in trailing edge applications. Carcasci et al [14] used experimental tests to present the combined effects of rotation and channel orientation on heat transfer and pressure drop along two scaled-up matrix geometries suitable for trailing edge cooling of gas turbine airfoils. Rotation enhancement on heat transfer is substantially insensitive to the variation of model inclination from 0 to 30 with respect to the rotating plane.…”