PREDICTION OF TURBULENT-FLOW AND HEAT-TRANSFER IN A RIBBED RECTANGULAR DUCT WITH AND WITHOUT ROTATION

The present study deals with the numerical prediction of turbulent flo w and heat transfer in a 2:1 aspect ratio rectangular duct with ribs o n the two shorter sides. The ribs are of square cross section staggere d and aligned normal (90 deg) to the main flow direction. The ratio of rib height to duct hydraulic diameter equals 0.063, and the ratio of rib spacing to lib height equals 10. The duct may be stationary or rot ating. The axis of rotation is normal to the axis of the duct and para llel to the ribbed walls (i.e., the ribbed walls form the leading and the trailing faces). The problem is three dimensional and fully ellipt ic; hence, for computational economy, the present analysis deals only with a periodically fully developed situation where the calculation do main is limited to the region between two adjacent ribs. Turbulence is modeled with the k-epsilon model in conjunction with wall functions. However since the rib height if small use of wall functions necessitat es that the Reynolds number be kept high. (Attempts to use a two-layer model that permits integration to the wall did not yield satisfactory results and such modeling issues are discussed at length.) Computatio ns are made here far Reynolds number in the range 30,000-100,000 and f or Rotation number = 0 (stationary), 0.06, and 0.12. For the stationar y case, the predicted heat transfer agrees well with the experimental correlations. Due to the Coriolis-induced secondary flow, rotation is found to enhance heat transfer from the trailing and the side walls, w hile decreasing heat transfer from the leading face. Relative to the c orresponding stationary case, the effect of rotation is found to be le ss for a ribbed channel as compared to a smooth channel.