Large Eddy Simulation of Flow and Heat Transfer in a Channel Roughened by Square or Semicircle Ribs

Abstract

The internal cooling passage of a gas turbine blade can be modeled as a ribbed channel. So far, most studies have considered square ribs. However, the ribs can be rounded due to improper manufacturing or wear during the operation. Round ribs have also been tested expecting that they may enhance the thermal and aerodynamic performance. Hence, we have studied two different rib geometries in this study, i.e. square and semicircle ribs. Large eddy simulations (LES) of turbulent flow in a ribbed channel with a dynamic subgrid-scale model are performed. In our simulation, the no-slip and no-jump conditions on the rib surface are satisfied in Cartesian coordinates using an immersed boundary method. We have also conducted an experimental study to validate the simulation. The velocity and temperature fields are measured using hot wire and thermocouple, respectively. The surface heat transfer is measured using the thermochromic liquid crystal with a high spatial resolution. LES predicts the detailed flow and thermal features such as the turbulence intensity around the ribs and the local heat transfer distribution between the ribs, which have not been captured by simulations using turbulence models. By investigating the instantaneous flow and thermal fields, we propose the mechanisms responsible for the local heat transfer distributions between the ribs; i.e. the entrainment of the cold fluid by the vortical motions and the impingement of the entrained cold fluid on the ribs. We also discuss the local heat transfer variation of the ribs in connection with flow separation and turbulent kinetic energy. The total drag and heat transfer are calculated and compared between the square and semicircle ribs, showing that two ribs produce nearly the same heat transfer, but the semicircle one yields lower drag than the square one.

Flow Features in a Fully Developed Ribbed Duct Flow as a Result of MILES

“…Among these, one may cite: [1,2,26,27,34,39]. Nevertheless, in most of these investigations, the main interest was focused on reproduction and prediction of the Eulerian statistics (average) and of the resolved turbulent field, without a real topology analysis.…”

Heat transfer enhancement by helical screw tape coupled with rib turbulators

“…In common, ribs are adopted to form artificial roughness, which provide heat transfer enhancement by generating vortices [23]. Therefore, the coupling ribs with HST is likely to give combined effect of common swirl and vortex in the flow which should give rise to stronger turbulent intensity and thus better fluid mixing as compared to those given by HST or ribs alone.…”

Large eddy simulation of flow and heat transfer in a channel with a detached rib array

“…The ribs are reported to enhance heat transfer by generating vortices [2], but they also create a separation bubble behind the rib, where heat transfer does not actively take place. To remove this region, Marumo et al [3] tried to displace the rib by a small distance from the wall and showed an improved heat transfer rate depending on the clearance between the rib and the wall, whose optimum value was suggested as c/e = 0.5, where c is the clearance and e is the rib height as schematically shown in Fig.…”