High Rotation Number Effects on Heat Transfer in a Rectangular (AR=2:1) Two-Pass Channel

Abstract

This paper experimentally investigated the rotational effects on heat transfer in a smooth two-pass rectangular channel (AR=2:1), which is applicable to the cooling passages in the midportion of the gas turbine blade. The test channel has radially outward flow in the first passage and radially inward flow in the second passage after a 180 deg sharp turn. In the first passage, the flow is developing and heat transfer is increased compared with the fully developed case. Rotation slightly reduces the heat transfer on the leading surface and increases heat transfer on the trailing surface in the first pass. Heat transfer is highly increased by rotation in the turn portion of the first pass on both leading and trailing surfaces. Rotation increased heat transfer enhancement in the tip region up to a maximum Nu ratio (Nu/Nus) of 1.83. In the second passage, under rotating conditions, the leading surface experienced heat transfer enhancements above the stationary case while the trailing surface decreased. The current study has more than four times the range of the rotation number previously achieved for the 2:1 aspect ratio channel. The increased range of the rotation number and buoyancy parameter reached in this study are 0–0.45 and 0–0.8, respectively. The higher rotation number and buoyancy parameter have been correlated very well to predict the rotational heat transfer in the two-pass, 2:1 aspect ratio flow channel.

Heat transfer investigation in rotating smooth square U-duct with different wall-temperature ratios and channel orientations

“…The suggested explanation referred to the weaken effect of buoyancy and Coriolis forces which affected the local heat transfer coefficient. Huh et al [17] (Ro 6 0.45) showed that regional averaged Nusselt number ratios are affected by variations of buoyancy number in the same approximate qualitative manner as the rotation number changes. They concluded that Nu ratios increase with buoyancy number on the pressure side and decrease with buoyancy number on the suction side in the radially outward flow.…”

Buoyancy effect on heat transfer in rotating smooth square U-duct at high rotation number

“…And thus, the rotation effect on heat transfer diminished and the heat transfer difference between leading and trailing surface was reduced. In 2009 and 2010, Huh et al [8,9] [10] studied effect of channel aspect ratio on heat transfer for a 2:1, two-pass channel. Compared with square channel, heat transfer in 2:1 channel decreased on the leading surface while increased on the trailing surface in the first radially outward passage, and the opposite occurred in the second radially inward passage.…”

“…And they also included that the effect of entrance weakens as rotation number increases. Huh et al (2009) [8] investigated a sudden expansion from a circular tube to the rectangular cross section of the channel. They pointed out heat transfer is dominated by the entrance until the large Buoyancy number.…”

“…And thus, flow in rotating channels becomes extraordinary complicated and three-dimensional. Luckily, many investigations on rotating U-ducts have been published by many previous works over the past two decades [4][5][6][7][8][9][10][11][12][13][14][15][16][17].…”

The effect of a hub turning vane on turbulent flow and heat transfer in a four-pass channel at high rotation numbers

“…Flow separation on the leading wall was observed and explained. Huh et al [6] studied the rotation effect on heat transfer in a two-pass smooth rectangular channel (AR = 2:1) with developing flow in radial outward direction in the first passage. The rotation number varied from 0.0 to 0.45.…”