Bluff Body Flow and Noise Control Using Porous Media

This research is concerned with the application of porous materials for reducing noise from bluff bodies by stabilizing the vortex shedding and the wake region. To better understand the noise generation and reduction mechanism, steady and unsteady flow measurements have been carried out. Measurements have been performed for unsteady aerodynamics forces, wake velocity fields and frequency energy content of the turbulent structures within the wake. The study is performed using several types of porous materials, with different porosities and permeability constants and over a wide range of Reynolds number. Results show that the use of a porous cover leads to the reduction of drag in every case of square cylinder, but an increase in drag coefficient in the case of circular cylinder at high Reynold numbers. The effect of porous material on the fluctuating lift force has also been investigated and it has been shown that the lift fluctuations can be reduced significantly using porous covers at low frequencies. The PIV results have also shown that the porous cover can delay the vortex shedding and significantly increase the vortex formation length, leading to a very low turbulent near wake region. It has also been observed that the turbulent kinetic energy in the near wake region can be reduced significantly using the porous layer. These findings are particularly important in the case of noise from tandem cylinder configurations where the wake interaction is the primary source of noise.