Bluff-body flow simulation using a viscous vortex-element method

Doug Shiels, Caltech

The significant forces experienced by bluff bodies are of much practical concern and are induced by complex flowfields. The separation and wake development which dictate these flows render them resistant to prediction despite a large body of research in the area. Computations will be discussed concerning two particular situations in which recent experiments revealed surprising behavior. The first concerns a circular cylinder undergoing rotational oscillation. A significant drag reduction triggered by the rotation at Reynolds numbers well below the turbulent transition has been observed experimentally. Computations from Re=150-15000 verify the experimental observation of significant drag reduction for certain forcing parameters. These simulations also illuminate the mechanism which renders this control effective - a forced boundary layer instability triggering premature shedding. The second situation concerns flow over a model of an elastically mounted cylinder. A two-dimensional cylinder modeled as a damped oscillator can serve as an approximation to three-dimensional situations such as a cable under tension. Recent experiments revealed behavior of the system which ran contrary to traditional expectations. Simulations offered insight into the behavior of such a two-dimensional system and revealed an unexpected adaptivity in wake evolution. New scaling is also suggested which better classifies the behaviors of this model system under certain conditions. The computational vortex methods used for these simulations are also discussed. Vortex methods offer the potential of efficient, grid-free simulation and progress in dealing with the difficulty of viscous diffusion in an accurate and efficient manner will be discussed.

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Last Modified: March 28, 1998