Heat transfer in convergent swirl chambers for cyclone cooling in turbine blades

Swirl flows in cyclone cooling systems are an innovative technique for internal cooling of the turbine blade leading edge. The present results are the first to quantify and characterize the influences of swirl tube convergence on thermal and flow characteristics for a broad range of configurations and conditions. Included are experimentally-measured results, obtained using transient liquid crystal thermography, and numerically-predicted results, obtained using Delayed Detached Eddy Simulations (DDES). Of particular interest are the influences of convergence angle, with values of 0.42deg, 0.61deg, and 0.72deg for Reynolds numbers from 10,000 to 40,000, and a design swirl number of 5.3. Also included are results for a swirl tube arrangement with a non-linear hyperbolic diameter variation, and a reference tube with constant diameter for comparisons. Results are provided in the form of Nusselt number augmentations and friction factor augmentations, relative to an ordinary pipe flow without swirl. A local Nusselt number correlation is also derived. When compared to a constant diameter tube, Nusselt numbers and Nusselt number augmentations decrease significantly with swirl chamber convergence. However, even with the largest convergence angle of 0.72deg, relatively high heat transfer augmentations in the vicinity of 2.45 continue to be present, but at the expense of especially high friction factor augmentations of about 51.7.