Heat Transfer in Rotating Serpentine Passages With Trips Normal to the Flow

TLDR

The study investigates how buoyancy and Coriolis forces affect heat transfer in turbine blade coolant passages. A large‑scale, multi‑pass heat‑transfer model with radially inward/outward flow and trip strips on the coolant passages was used, varying coolant‑to‑wall temperature ratio, Rossby number, and Reynolds number over typical turbine ranges, and results were correlated with previous stationary and rotating models. Four parameters—coolant‑to‑wall temperature ratio, Rossby number, Reynolds number, and radius‑to‑passage hydraulic diameter ratio—control heat transfer, with coefficients varying up to four‑fold when increased by rotation and buoyancy and up to three‑fold when decreased, leading to the conclusion that Coriolis and buoyancy effects must be considered in turbine blade cooling designs with trip strips and that rotation effects differ markedly with flow direction.

Abstract

Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large scale, multi–pass, heat transfer model with both radially inward and outward flow. Trip strips on the leading and trailing surfaces of the radial coolant passages were used to produce the rough walls. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages: coolant–to–wall temperature ratio, Rossby number, Reynolds number and radius–to–passage hydraulic diameter ratio. The first three of these four parameters were varied over ranges which are typical of advanced gas turbine engine operating conditions. Results were correlated and compared to previous results from stationary and rotating similar models with trip strips. The heat transfer coefficients on surfaces, where the heat transfer increased with rotation and buoyancy, varied by as much as a factor of four. Maximum values of the heat transfer coefficients with high rotation were only slightly above the highest levels obtained with the smooth wall model. The heat transfer coefficients on surfaces, where the heat transfer decreased with rotation, varied by as much as a factor of three due to rotation and buoyancy. It was concluded that both Coriolis and buoyancy effects must be considered in turbine blade cooling designs with trip strips and that the effects of rotation were markedly different depending upon the flow direction.