Large-eddy simulation of air flow around a wall-mounted circular cylinder and a tripod tower

Abstract

This paper models the air flow around a wall-mounted tripod platform that mimics a meteorological tripod tower placed in shallow water for air–sea interaction measurements to study the flow distortion by the tower. We adopt large-eddy simulation technique, which is based on the characteristic Galerkin, fractional four-step finite element method. For model validation, we examine flow characteristics around a wall-mounted circular cylinder with two length-to-diameter ratios of 2.5 and 10. The results are in good agreement with existing experimental data and numerical simulations. The tip, von Kármán, and horseshoe vortices around the cylinder are properly resolved. Several differences are manifest between the short- and long-cylinder cases. In particular, the downdraft behind the top free end of the long cylinder is much stronger than that of the short cylinder. The vorticity intensity in the wake region of the long cylinder is also stronger than that of the short cylinder. Furthermore, the vortex shedding in the upper region of the long cylinder is not in phase with that of the lower region. We then examine the flow around the tripod tower with three approach wind directions. The results show that the measurements in the wake region of the tower are not generally dependable; hence, for this configuration, data should be measured away from the platform of the tower. A sequence of Kelvin–Helmholtz vortices and an elongated tip vortex in addition to those observed in the cylinder cases are formed due to the presence of the platform of the tower.

Keywords:

• Large-eddy simulation
• Finite element method
• Circular cylinder
• Air–sea interaction tower
• Flow distortion

Acknowledgement

The authors acknowledge financial support from the Office of Naval Research through award # N00014–05–1–0295.