Latticework (Vortex) Cooling Effectiveness: Part 1 — Stationary Channel Experiments

Abstract

The present investigation provides detailed information concerning the heat transfer coefficients and pressures in latticework (vortex) cooling channels. Two test methods are used to determine the local and overall heat transfer coefficients for a vortex channel with crossing angle of 45-degrees. Both liquid crystal and infrared thermography methods are used on acrylic and metallic models to discern the heat transfer coefficients without and with the effects of internal rib fin effectiveness. Tests with insulating ribs determine the heat transfer on the primary surfaces representing the pressure and suction side walls of an airfoil. Tests with integral metal ribs determine the additional impact of the fin effectiveness provided by the ribs. A simple radial vortex channel design is employed throughout with subchannel aspect ratios near unity, and Reynolds numbers from 20,000 to 100,000. Pressure loss variations through typical vortex channels are also measured. The objectives of this research are to show the detailed development of heat transfer in vortex channels leading to an understanding of the two main effects of turning and fin enhancements. Detailed primary surface heat transfer coefficients average about 1.5 over smooth duct behavior, but reach local values of about 3 immediately after each turn. Pressure distributions show high turning losses on the order of those associated with serpentine 180-degree turn circuits. Local heat transfer coefficient distributions are remarkably uniform throughout the channels excepting the turns themselves. Turn enhancements are retained for relatively long distances. Overall vortex channel heat transfer coefficient enhancement levels are shown to be 2.5 to 3. The effects of subchannel internal ribs, which act as fins, are shown to be very important in the overall thermal picture. Test results show that treatment of the ribs as simple fins is appropriate and that each rib surface has about the same heat transfer coefficient on average as that of the primary surface. This first detailed study shows that latticework channels have significant potential and should be further investigated.