Pergamotl Inr. J. Hear Mass Transfer. Vol. 38, No. 7, pp. 1,51-1159, ,995 Copyright 0 1995 Elsevier Science Ltd Pnnted in Great Britain. All rights reserved 0017-9310/95 S9.50+0.00 0017-9310(94)00246-0 Effec:t of model orientation and wall heating condition on local heat transfer in a rotating two-pass square channel with rib turbulators JAMES A. PARSONS, JE-CHIN HAN? and YUMING ZHANG Turbine Heat Transfer Laboratory, Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3123, U.S.A. (Received 13 December 1993 and injinalform 28 July 1994) Abstract--The influences of channel orientation and wall heating condition on the local surface heat transfer coefficient in a rotating, two-pass, square channel with 60” and 90” ribs on the leading and trailing walls were investigated for Reynolds numbers from 2500 to 25 000 and rotation numbers from 0 to 0.352. The two channel orientations were (1) square channel perpendicular to the axis of rotation and (2) square channel twisted at 45” to the axis of rotation. Two thermal boundary condition cases were studied : (A) all four walls at the same temperature and (B) all four walls at the same heat flux. Results show the Coriolis force effect is reduced for the 45” channel orientation. Thus, heat transfer coefficients decrease for the first pass trailing and second pass leading walls and increase for the first pass leading and second pass trailing walls, compared with their corresponding perpendicular channel orientation values. The increase of heat transfer coefficients for uneven wall heating condition Case (B) when compared to their corresponding heat transfer coefficients for Case A is greater for the 45” channel orientation than for the perpendicular channel orientation. INTRODUCTION As turbine inlet temperature increases in gas turbine engines so does the heat load to the turbine blades. To maintain acceptable blade life, methods such as film cooling, impingement cooling, and augmented convective cooling in internal serpentine and pin fin channels reduce the amount of heat reaching the blades and remove the heat from the blades. Some investigations for the heat transfer in internal coolant channels of turbine blades have concentrakd on non- rotating models that did not include the Coriolis and the centrifugal .buoyancy forces effect on coolant motion and heat transfer [l, 21. However, some researchers reported on the heat transfer charac- teristics due to rotation in straight channels with smooth or rib turbulated walls and radial outward flow [3-91. References [lO-131 studied the effect of rotation on the local heat transfer coefficient in a serpentine squax coolant channel (three-pass) with smooth and ribbed walls for a systematic variation of parameters similar to typical engine conditions. References [14, 1151 also showed results for rotation effects on the local heat transfer coefficient but in a four-pass smooth and ribbed square channel. Ref- erence [16] predicted the channel fluid velocities and heat transfer coefIicients in rotating smooth channels with radial outward flow, which agreed within lO- 30% with the smooth wall data shown in ref. [lo]. References [17-201 present the effect of wall heating condition on local heat transfer coefficients in a two- 7 Author to whom correspondence should be addressed. pass square channel with smooth and rib turbulated walls. The results of refs. [17, 181 agreed with those of refs. [ 10, 1 l] for the rotating smooth wall channel with uniform wall temperature conditions, i.e. all walls at the same temperature. However, refs. [17-201 found that for the uniform wall heat flux and simulated engine wall heating conditions, the rotating leading surface heat transfer coefficients of the first coolant pass (radial outward flow) and the rotating trailing surface heat transfer coefficients of the second coolant pass (radial inward flow) were 50-100% greater than those for the uniform wall temperature conditions. Many of the above used coolant channel walls per- pendicular to the axis (or direction) of rotation with radial outward (and inward) flow. However, Figs. 1 and 2 show that the orientation of the cooling channel in the leading and trailing edge regions of the turbine blade may be at an angle /I to the axis of rotation. Reference [21] recently investigated the effect of channel orientation for uniform wall temperature conditions. Since the wall heating condition sig- nificantly affects heat transfer for rib turbulated sur- faces [ 19,201 of a rotating channel, it is unknown how effects due to wall heating condition change when these channel walls are at an angle /I to the axis of rotation for both radial outward and inward flow. Therefore, this study will investigate the effects of channel orientation and wall heating condition on local surface heat transfer coefficients in a rotating two-pass square channel with 60” and 90” ribs on the leading and trailing walls. Two channel orientations are studied : p = 0” corresponding to the mid-portion of a turbine blade (data from refs. [19, 20]), and 1151