Numerical simulation of forced-convection heat transfer in a ribbed channel with high blockage

Turbulence promoters in form of ribs are commonly used in various equipment such as turbine cooling channels, heat exchangers, nuclear reactors and solar air heaters. This artificial roughness surfaces modify the fluid dynamics by various mechanisms, such as periodic interruption of the boundary layer growth or periodic streamline deflection and in addition they promote turbulence development as their characteristic size is close to the turbulent microscales (the lower the Reynolds number, the larger the size of dissipative structures). The present study is focused on the turbulent forced convection in a channel with continuous transverse rib on both walls. The rib to channel height ratio here investigated result in a high blockage ratio. A constant temperature is applied on the lower and upper wall whereas the ribs are adiabatic. The calculations are carried out using a RANS approach. The ribs have a square cross section and are transverse to the main direction of the flow. Different pitch-to-height ratios (p/e=10, 20 or 40) and rib dimensions (e=2 mm or 4 mm) are considered. Three Reynolds numbers, based on bulk velocity and duct height, has been chosen (1771, 2942 and 4119) in order to have a turbulent flow regime typically encountered in the internal cooling channels of the turbine blades.