Experimental investigations into the nature of airflows near bluff bodies with aspiration, with implications to aerosol sampling.
Sreenath A; Ramachandran G; Vincent JH
Atmos Environ 1997 Aug; 31(15):2349-2359
The nature of air flow around widely used aerosol samplers was examined. Tests with cylindrical and spherical samplers were performed in a small, open loop wind tunnel. Smoke was generated for flow visualization using the smoke wire method. Flow visualization was enhanced by slit illumination using an overhead transparency projector. The visualized flow around the cylindrical and spherical samplers was photographed, allowing the locations of the stagnation points to be determined. A capacitive micromanometer was employed for determining the frequency of vortex shedding for the cylindrical body. When the angular position of the sink with respect to the free stream equaled zero and the aspiration flow rate for the cylinder equaled 0.01, the locations of the stagnation points were not significantly altered. When the aspiration flow rate for the cylinder equaled 0.25, the forward facing stagnation point split symmetrically into two stagnation points at an angular position of +/-12 degrees with respect to the free stream. The angular width of the stagnation region increased with increasing angular position of the sink. For a cylinder without aspiration, the vortex shedding frequency decreased with increasing Reynolds number (Re). For a cylinder with aspiration, the vortex shedding frequency depended on both the Re and the aspiration flow rate. For a spherical body, one side of the stagnation region decreased in width as the angular position of the sink increased. The other side of the stagnation region increased in width as the angular position of the sink increased. Overall, agreement between the observed findings and the predicted results was good. The authors conclude that the potential flow theory describing the flow field near the sampler is adequate for slot orientations up to about 140 degrees. The above findings help to elucidate the nature of air flow around aerosol samplers.
NIOSH-Publication; NIOSH-Grant; Grants-other; Air-flow; Aerosol-sampling; Air-samplers; Fluid-mechanics; Air-sampling-equipment; Analytical-models
Environmental Health University of Minnesota 420 Delaware Street SE Minneapolis, MN 55455
Other Occupational Concerns; Grants-other
University of Minnesota Twin Cities, Minneapolis, Minnesota