Effect of Rib Density on Flow and Heat Transfer in an Internal Cooling Passage

<jats:p>Effect of rib density on mechanism of flow and heat transfer enhancement in an internally-cooled channel with rib turbulators have been investigated numerically. Based on the experimental setup in the previous study [32], flowfield and heat transfer coefficient distributions were predicted with LES approach. The rib pitch-to-height ratios were 3 and 11, and Reynolds number based on the channel hydraulic diameter and bulk velocity was set at 30,000. Comparison of time-averaged flow and heat transfer characteristics between numerical and experimental results showed that prediction accuracy of the present numerical setup was reasonable.</jats:p> <jats:p>The previous study [33] suggested that, for higher rib density, low-frequency velocity fluctuation characterizes heat transfer. To investigate its flow and heat transfer mechanism, instantaneous velocity and temperature fields were compared. For smaller rib density, small vortices constantly occurred from each rib and were dissipated into the mainstream before reaching the next rib. On the other hand, for higher rib density, relatively large vortex occurs above the ribs in addition to smaller vortices inside the cavity between the ribs. The large vortex occurs intermittently behind the second rib of the channel, and increases its size by interacting with smaller vortex downstream. For each rib pitch, similar trend was observed in the measured result obtained using Particle Image Velocimetry. This unsteady vortex structure would contribute to enhancing the heat transfer of a cooling channel with densely-arranged rib turbulators.</jats:p>