The thermal performance of two different V-shaped rib configurations is measured in a rotating, two-pass rectangular cooling channel. Modeling modern, high pressure turbine blades, the cross-sectional area of the cooling channel varies from the first passage to the second passage. The coolant air travels radially outward in the rectangular first passage with an aspect ratio (AR) of 4:1. Near the tip region, the coolant turns 180°, and travels radially inward into a 2:1 rectangular second passage.  The serpentine passage is positioned in such way that both the first and second passes are oriented 90° to the direction of rotation.  The leading and trailing surfaces of both the first and second pass of the channel are roughened with V-shaped rib turbulators.  The thermal performance of two V-shaped configurations is measured in this two-pass channel. The first V-shaped configuration is similar to a traditional V-shaped turbulator with a narrow gap at the apex of the V to reduce the pressure drop. The configuration is modified by off-setting one leg of the V to create a discrete, V-shaped configuration. For both turbulator geometries, the ribs are profiled to match the shape of cast turbulators without sharp corners. The ribs are aligned with one another on the leading and trailing surfaces, and they are oriented 45° relative to the streamwise coolant direction. In both passes, the rib spacing is P/e = 10 and the rib height – to – channel height is e/H = 0.16. The heat transfer enhancement and frictional losses are measured for both rib configurations with varying Reynolds and rotation numbers. The Reynolds number varies from 10,000 to 45,000 in the AR = 4:1 first pass; this corresponds to 16,000 to 73,500 in the AR = 2:1 second pass. Considering the effect of rotation, the rotational speed of the channel varies from 0 – 400 rpm with maximum rotation numbers of 0.39 and 0.16 in the first and second passes, respectively. The discrete V-shaped ribs produce a lower pressure loss than the tradition V-shaped ribs. The copper plate method is applied to obtain the averaged heat transfer coefficient in each flow regions. The heat transfer enhancement on both the leading and trailing surfaces of the first pass of the 45° V-shaped channel is slightly reduced with rotation. In the second pass, the heat transfer increases on the leading surface while it decreases on the trailing surface. The 45° discrete V-shaped ribs provide increased heat transfer and thermal performance compared to the more traditional V-shaped geometry. Both V-shaped configurations yield improved thermal performance compared to standard, 45° angled rib turbulators.


Heat Transfer in a Rotating, Two-Pass, Variable Aspect Ratio Cooling Channel With Profiled V-Shaped Ribs

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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