Enhancement of the Thermohydraulic Performance in a Double Passage Square Duct with the Use of Inclined Ribs of 45°: A Comparative Computational Study

Abstract

The modern gas turbines need to run at very high inlet temperature to promote their power output. Thus, improvements in cooling technologies play a significant role for enhancing the gas turbine blade life. In this paper, thermohydraulic performance (THP) of a two-pass square channel with inclined ribs at 45° was scrutinized employing the $k–\epsilon$ realizable model with enhanced wall treatment in ANSYS Fluent. The calculations were performed for the rib pitch to height ratio ($p/e$) of 5-10, rib height to hydraulic diameter ratio ($e/D_h$) of 0.1-0.2, and Reynolds number ($\mathrm{Re}$) of 20,000-40,000. Detailed analysis of the flow structure in a double passage square duct was carried out to understand the interaction of the rib and bend-induced secondary flows and its contribution to heat transfer enhancement for the rib configurations with distinct $p/e$ and $e/D_h$, which was not available in any other existing numerical or experimental investigations. The results revealed that the ribs with higher $e/D_h$ generated the stronger stream-wise secondary flows which led to the augmentation of the cooling performance with the disadvantage of pressure loss increment. The maximum THP of 26.55% was achieved with the ribbed configuration having $p/e=5$ and $e/D_h=0.1$ at $\mathrm{Re}=\mathrm{20,000}$. The new correlations were developed from the computational data to predict the normalized Nusselt number and friction factor ($\text{Nu}/\text{N}{\text{u}}_0$ and $f/f_0$, where 0 is the correlation), taking the $e/D_h$ and flow $\mathrm{Re}$ into consideration.