S.J. Lee

Flow structure around two finite circular cylinders located in an atmospheric boundary layer: side-by-side arrangement

The flow structure around the free-end region of two adjacent finite circular cylinders embedded in an atmospheric boundary layer (ABL) was investigated experimentally. The experiments were carried out in a closed-return-type subsonic wind tunnel, in which two finite cylinders with an aspect ratio of 6 were mounted vertically on a flat plate in a side-by-side arrangement. The Reynolds number based on the cylinder diameter was about Re=2×104. Systems with gap ratios (i.e., center-to-center distance/cylinder diameter) in the range 1.0–2.0 were investigated. A hot-wire anemometer was employed to measure the wake velocity, and the mean pressure distribution on the cylinder surface was also measured. The flow past two finite cylinders was found to have a complicated three-dimensional wake structure in the region near the free ends. As the gap ratio increases, regular vortex-shedding becomes dominant, but the length of the vortex formation region decreases. The pressure distribution and flow structure around two cylinders were found to differ substantially from the behavior of a two-dimensional circular cylinder due to mutual interference. The three-dimensional flow structure seems to originate from the strong entrainment of irrotational fluids caused by the downwash counter-rotating vortices separated from the finite cylinder (FC) free ends.

Effect of suction nozzle modification on the performance and aero-acoustic noise of a vacuum cleaner

The suction nozzle of a vacuum cleaner was modified to enhance the power performance and to reduce the airflow-induced acoustic noise. The suction power efficiencies of the vacuum cleaner were measured for various nozzles: (1) original nozzle, (2) original nozzle with modified trench height, (3) original nozzle with modified connecting chamber, and (4) a combination of (2) and (3). In addition, the suction pressure and sound pressure level around the suction nozzle were measured to validate the reduction of acoustic noise. The power efficiency and mean suction pressure increased when the trench height of the suction nozzle was increased. This was attributed to the suppression of the flow separation in the suction channel. Modification of the connecting chamber in the original nozzle, which had an abrupt contraction from a rectangular chamber into a circular pipe, into a smooth converging contraction substantially improved the suction flow into the connecting pipe. When both modifications were applied simultaneously, the resulting suction nozzle was more effective from the viewpoints of aerodynamic power increase and sound pressure level reduction.

Hemodynamic investigation on blood flow in a rugged microchannel

The biological flow characteristics inside a rugged surface type microchannel are investigated experimentally using a micro-particle image velocimetry (micro-PIV) method. The main objectives of this study are to understand the blood flow structure inside a micro-domain blood vessel and to identify the feasibility of nano-scale fluorescent particles for velocity field measurement in a micron-sized channel. The flow field is analyzed with a spatial resolution of 1K×1K pixels at low Reynolds number flow. To obtain the spatial distributions of mean velocity, 100 instantaneous velocity fields are captured and ensemble-averaged. As a result, for the case of blood flow, there are substantial cell deformation and variations to pass through the rugged surface of a microchannel and the clear velocity vector field was acquired by using the present micro-PIV technique.