The Effect of Turbulator Lean on Heat Transfer and Friction in a Square Channel

Abstract

An experimental study has been performed to investigate the convective heat transfer coefficients and friction factors present in square cooling passages with non-normal, or leaned turbulators. The standard form of turbulated channels used in virtually all turbine vanes and blades is that of nearly square turbulators, or rib rougheners, cast in an orthogonal orientation to the channel surface. While turbulators may be oriented at an angle to the bulk flow direction, the projection of the turbulator is still normal to the cast surface. Non-orthogonal lean angle presents an additional variable which may be used to improve or optimize performance, a factor hitherto not investigated. The present study has performed a series of experiments measuring both detailed heat transfer coefficient distributions and friction factors within a square channel with flow Reynolds numbers up to 400,000. Turbulator lean angles of 45, 22.5, 0, −22.5, and −45-degrees to the surface normal have been tested with a turbulator configuration of 45-degree orientation to the bulk flow, pitch-to-height ratio of 10, and height-to-hydraulic diameter ratio of 0.1. Results show up to a 20% reduction in heat transfer capability, and as much as 30% increase in friction factor. The local distributions of heat transfer are also more variable with lean angle. The conclusion is made that normal turbulators provide the best overall performance.