摘要

This paper presents the result of an experimental study of impingement cooling from a row of five jets striking a concave surface, in a semi-cylindrical cooling passage that rotates about an axis parallel to that of the jets. This configuration is used to cool internally the leading edge of rotating gas-turbine blades. The jets are symmetrically placed along the centre-line of the flat surface of the passage, spaced 4 diameters apart, with the third jet positioned at the mid point along its length. Tests have been carried out at a mean flow Reynolds number, based on jet diameter, of 15,000 and for rotation numbers ranging from 0 to 0.18 for both clockwise and anticlockwise rotation. The working fluid is water, with a Prandtl number of 6.09 at the operating temperature.
Local Nusselt number measurements using the liquid crystal technique show that, as expected, under stationary conditions a high Nusselt number region develops around each impingement point, with secondary Nu peaks half-way between impingement points. Ran important discovery is that rotation reduces overall heat transfer levels, leads to the eventual disappearance of the secondary peaks and also to the disappearance of some of the primary peaks in Nusselt number associated with impingement.
Flow visualization tests suggest that these changes in thermal behavior are caused because rotation increases the spreading rate of the jets. Theoretical considerations suggest that the increase in spreading rate occurs because the Coriolis force raises the turbulent shear stress at the jet exits. Future work that includes CFD predictions and LDA measurements will help develop a clearer theoretical understanding.