Effect of Rotation on Heat Transfer in Narrow Rectangular Cooling Channels (AR = 8:1 and 4:1) With Pin-Fins

Abstract

The effect of rotation on smooth narrow rectangular channels and narrow rectangular channels with pin-fins is investigated in this study. Pin-fins are commonly used in the narrow sections within the trailing edge of the turbine blade; the pin-fins act as turbulators to enhance internal cooling while providing structural support in this narrow section of the blade. The rectangular channel is oriented at 150° with respect to the plane of rotation, and the focus of the study involves narrow channels with aspect ratios of 4:1 and 8:1. The enhancement due to both conducting (copper) pin-fins and non-conducting (plexi-glass) pins is investigated. Due to the varying aspect ratio of the channel, the height-to-diameter ratio (hp/Dp) of the pins varies from two, for an aspect ratio of 4:1, to unity, for an aspect ratio of 8:1. A staggered array of pins with uniform streamwise and spanwise spacing (xp/Dp = sp/Dp = 2.0) is studied. With this array, 42 pin-fins are used, giving a projected surface density of 3.5 pins/in2 (0.543 pins/cm2), for the leading or trailing surfaces. The range of flow parameters include Reynolds number (ReDh = 5000–20000), rotation number (Ro = 0.0–0.302), and inlet coolant-to-wall density ratio (Δρ/ρ = 0.12). Heat transfer in a stationary pin-fin channel can be enhanced up to 3.8 times that of a smooth channel. Rotation enhances the heat transferred from the pin-fin channels 1.5 times that of the stationary pin-fin channels. Overall, rotation enhances the heat transfer from all surfaces in both the smooth and pin-fin channels. Finally, as the rotation number increases, spanwise variation increases in all channels.

Optimization of Rotating Cooling Channel with Pin Fins Downstream of Turning Region

“…In an experiment conducted by Wright et al [13], the level of heat transfer in a rotating channel with staggered arrays of the pin-fin type was higher than that in the stationary case. They found that rotation enhanced heat transfer from all heated surfaces, especially on the trailing surface.…”

“…1a, are considered to investigate the enhancement of heat transfer. The experimental test channel of Wright et al [13] consisted of 12 rows of pin fins arranged in staggered arrays on heated walls. In this work, however, a domain with only the first six rows of pin fins in the test channel of Wright et al [13] is considered in the computational domain, as shown in Fig.…”

“…1a. The reason for considering only six rows is a compromise between limited computational resources and knowing that the flow entering the pin-fin rows becomes fully developed after the fourth row, as described by Wright et al [13]. Three-dimensional RANS analyses of the fluid flow and convective heat transfer have been performed using ANSYS-CFX 11.0 [22], which employs an unstructured grid system.…”

“…A uniform heat flux was specified on the trailing and leading surfaces, and adiabatic conditions were used at the surfaces of the pin fins and side wall. The rotation number (Ro D h =U of the internal cooling channel was fixed at 0.15, as in Wright et al [13]. The rotation speed remained constant at 550 rpm as described by Wright et al [13].…”

Flow and Heat Transfer Prediction in Rotating Rectangular Pin-Fin Channels (AR = 10:1)

“…They showed that pin fins significantly reduce the effect of rotation, but they do not eliminate the effect. Wright et al [14] studied a staggered array of pins under the rotating condition and found that 1) rotation enhances the heat transferred from the pin-fin channels 1.5 times that of the stationary pin-fin channels. 2) Overall, rotation enhances the heat transfer from all surfaces in both the smooth and pin-fin channels.…”