EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER IN A LEADING EDGE, TWO-PASS SERPENTINE PASSAGE AT HIGH ROTATION NUMBERS

The effect of rotation in a leading. edge, two-pass channel is experimentally investigated in this study. Cooling air, traveling radially outward, is supplied to a smooth, square channel. The coolant turns 180 degrees, and travels radially inward through a semi-circular, smooth channel. This semi-circular passage models a cooling channel located in the leading edge region of a modem turbine airfoil. For the radially outward flow in the square channel, the coolant Reynolds number is varied from 10000 - 40000. The rotational speed of the channel varies from 0 - 500 rpm, the rotation number in the first-pass channel varies from 0 to 1.2, and as a result, the buoyancy parameter can exceed 5.0 under the given flow conditions. Due to a slight reduction in the hydraulic diameter, the semi-circular, second-pass experiences Reynolds numbers ranging from 10300 - 41000, rotation numbers varying up to 1.0, and buoyancy numbers exceeding 4.0. With both passes of the serpentine passage instrumented, the effect of rotation on heat transfer with both radially outward and radially inward flow can be characterized under high rotation and buoyancy numbers. The channel is oriented 90 degrees to the direction of rotation, and the Nusselt numbers on both the leading and trailing surfaces deviate from those measured in a non-rotating channel. The degree of separation between the leading and trailing surfaces depends on the position within the passage; near the inlet of the channel, the effect of rotation is minimal as the heat transfer coefficients are more strongly influenced by the entrance geometry into the channel. Moving downstream of the entrance, the effect of rotation increases. With the current channel geometry, all regions in the second pass of the channel experience heat transfer enhancement with rotation, and the separation between the leading and trailing surfaces is reduced compared to the first pass.