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

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. skewed at 45 degrees to the flow direction, were machined on the leading and trailing surfaces of the radial coolant passages. A n analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages:coolant-to-wall temperature ratio, rotation 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 similar stationary and rotating models with smooth walls and with trip strips normal to the flow direction. The heat transfer coefficients on surfaces, where the heat transfer decreased with rotation and huoyancy. decreased to as low as 40 percenl of the value wthout rotation. However, the maximum values of the heat transfer coefficients with high rotation were only slightly above the highest levels previously obtained with the smooth wall model. It was concluded that (1) both Coriolis and buoyancy effects must be considered in turbine blade cooling designs with trip strips. (2) the effects of rotation are markedly different depending upon the flow direction and (3) the heat transfer with skewed trip strips i s less sensitivity to buoyancy than the heat transfer in motleis with either smooth walls or normal trips. Therefore, skewed trip strips rather than normal trip strips are recommended and peometry-specific tests will be required for accurate design information.

Heat Transfer Enhancement by Detached S-Ribs for Twin-Pass Parallelogram Channel

“…The regionally averaged Nusselt number data detected from the two-pass square channel fitted with the attached 45 0 ribs using the present thermography method compared favorably with those generated by the NASA HOST program [27] using the thermocouple method. The detailed Nusselt number distributions over the front and back endwalls of the present twin-pass parallelogram channel enhanced by the detached S-ribs at Reynolds numbers of 5000, 10,000, and 15,000 are depicted in Figure 2.…”

Heat transfer in rotating scale-roughened trapezoidal duct at high rotation numbers

“…The lager degree of Coriolis effects, which provide the heat transfer elevations along the trailing edges from the zero-rotation references to larger extents, initiates from the immediate flow entrance but gradually decays in the streamwise direction onto a ''stable" condition at which the Coriolis secondary flows are maturely grown. A review of all the rotating test results [10,[12][13][14][15][16][17][18][19][20][21][22][23][24] ensures this particular Coriolis effects for the present rotating geometry. Interesting flow interactions between the accelerated entry flow through the abrupt entrance and the modified turbulence structures as well as the developing secondary flows induced by Coriolis forces and scales are worth of further investigations.…”

“…The present approach for rig simulation is to increase the hydraulic diameter (d) and reduce the mean flow velocity (W m ) with the coolant mass flow rate unchanged by increasing the pressure of flow inside the rotating test channel. This attempt increases both Ro and Bu at any specified Re that successfully extends the present parametric ranges of rotating flows to a great extent from the past research experiences [7][8][9][10][11][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] as indicated in Table 1. However, the maximum Re and Ro listed in Table 1 are not simultaneously attainable.…”

“…This buoyancy number can physically reflect the relative strength of rotating buoyancy force and is derived from the momentum equation based on the Boussinesq approximation [22]. Methods of heat transfer augmentation for rotating channels involve surface ribs [10,[18][19][20][21][22][23][24]30], array of longitudinal humps [25], pin-fins [26], dimples [27] and impingement [28,29]. In our previous study [31], the characteristics of heat transfer and pressure drop in a static narrow rectangular channel roughened by deepened scales were examined.…”

“…A large amount of laboratory-scale heat transfer experiments using simplified models of the real blade cooling geometry that examine their heat transfer performances in the rotating channels with various enhancement techniques is well documented. The geometries of enhanced rotating channels relevant to their cooling performances such as the type of surface enhancements, channel orientation, wall heating condition, channel cross-sectional shapes and multi-pass connections have been examined at various test conditions [10,[18][19][20][21][22][23][24][25][26][27][28][29][30] but only a few of these studies emulate the real engine conditions by operating the high pressure tests [10,19,22,29,30]. These experimental studies [10,[18][19][20][21][22][23][24][25][26][27][28][29][30] have agreed that the Reynolds (Re) and rotation (Ro) numbers characterize the forced convection and the Coriolis forces in their own rights with the buoyancy impact to be indexed by density ratio (Dq/q).…”