Optimizing turbulent heat transfer using orthogonal decomposition-based contouring

Abstract

Large-scale simulations of cylindrical pin fins with a spanwise distance to fin diameter ratio of 2 and height over fin diameter ratio of 1 are performed and optimized based on orthogonal decomposition. The flow Reynolds number based on hydraulic channel diameter and bulk velocity () is chosen based on experimental results available in the open literature. The three-pin-wide domain was simulated using unsteady large eddy simulations. The resulting flow field consisting of velocity and temperature data is analyzed using an orthogonal decomposition technique based on temporal correlations of all flow variables, including temperature. The first seven temperature basis functions shows a near-zero amplitude, indicating their irrelevance for turbulent heat transfer augmentation. A mode combination ranking methodology based on enthalpy confirmed the potential for optimization. An isosurface of the most important mode’s temperature basis function is then used to contour the domain endwalls with a first-order approximation. Although some engineering thresholds are imposed to achieve a smooth and bounded wall deformation, the method as developed is still expected to be generally applicable to different flows and geometries. The mean heat transfer augmentation and pressure drop increased equivalently. Wall temperature fluctuations decreased on average and locally. Even though lower order modes show a zero temperature amplitude after wall contouring, the energy contained in those decreased. The increase in heat transfer stems mainly from the effect of wall contouring on vortex shedding. This is achieved by manipulating high energy modes which contain vortex shedding motions.

Keywords:

• orthogonal decomposition
• optimization
• turbulence
• heat transfer
• pin fin
• LES