An experimental method for evaluating pressure field and fluid forces on a bluff body structure is studied using instantaneous velocity data measured by particle image velocimetry (PIV). This method solves a pressure Poisson equation numerically with the experimental velocity data by PIV. The measurement of the velocity field around a circular cylinder is carried out using two CCD cameras placed side by side, which allows simultaneous measurement of velocity near and far field around the circular cylinder. The pressure and fluid forces on the stationary cylinder evaluated by this method agree closely with those in the literature, suggesting the validity of this technique. The present technique is also applied to a circular cylinder with rotational oscillation at Reynolds number 2000. It is found that the drag force on a circular cylinder is magnified at low-frequency oscillation and reduced at high-frequency oscillation. The drag coefficient at high-frequency oscillation is reduced by 30% with respect to the stationary cylinder, while the fluctuating lift is slightly increased due to the generation of synchronized vortex shedding at high-frequency oscillation.
Abs ract : The interaction of two parallel plane jets of different velocities is studied by flow visualization and PIV measurement to examine the influence of velocity ratio on the development of jets in the initial region. It is found that the parallel plane jets develop toward the high velocity side and the jet width is reduced with a decrease in the jet velocity ratio. Corresponding to the variation of mean velocity field to the velocity ratio, the magnitudes of turbulence intensities, Reynolds stress and static pressure are weakened in the merging region of the jets and their peak locations of the properties are shifted to the high velocity side. These results indicate that the interaction of two parallel jets is weakened with a decrease in the velocity ratio of the jets. t
This work attempts to optimize stents that are implanted at the neck of coronary or cerebral aneurysms to effect a flow diversion. A two-dimensional version of the stent, which is a series of struts and gaps placed at the neck, is considered as the first step. Optimization is carried out based on the principles of exploration of design space using reductions in velocity and vorticity in the aneurysm dome as the objective functions. Latin hypercube sampling first develops 30–60 samples of a strut-gap arrangement. Flow past an aneurysm with each of these samples is computed using the commercial software FLUENT and the objective functions evaluated. This is followed by a Kriging procedure that identifies the nondominated solutions to the system, which are the optimized candidates. Three different cases of stents with rectangular or circular struts are considered. It is found that placing struts in the proximal region of the neck gives the best flow diversion.
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