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Description
Wind tunnel experiment has been conducted on a cylinder with uniformly-distributed perforated holes to evaluate the efficacy of perforation as a means of passive flow control in reducing unsteady aerodynamic force on the unperforated cylinder. Both unperforated and perforated cylinders were investigated at Reynolds number ranging from 50,000 to 200,000 based on a freestream velocity from 5m/s to 20m/s (at an increment of 5m/s) and a diameter of 0.152 m. The aerodynamic force was measured using a 6-axis load cell. Comparisons indicate that the perforated cylinder with an 8% porosity and a hole diameter of about 2% of that of the cylinder gives both substantially less unsteady drag and lift than those of the unperforated cylinder for the entire Reynolds number range tested, with the r.m.s. force reduction from 8% to 82% for the drag and 64% to 85% for the lift. Consistent with the above results, power spectral analysis of the force measurement signals indicates that there is an overall reduction in fluctuation amplitude across the spectrum for the perforated cylinder when compared with the unperforated cylinder. The hot-wire wake survey at 5 different measurement stations downstream of the cylinder model shows that, significant reductions for velocity r.m.s. fluctuations were achieved for the perforated cylinder in comparison with the unperforated one, with 9% reduction at the edge of the wake and 32% reduction at the center of the wake. Similarly, Aerodynamic force measurements have been conducted for a unperforated and a perforated hollow sphere with a 2.4% porosity formed by uniformly-distributed perforated holes at Reynolds number ranges from 65,000 to 260,000 based on a sphere diameter of 0.2032m and a freestream velocity from 5 m/s to 20 m/s at an increment of 5m/s. There is an overall reduction in fluctuation amplitude across the spectrum for the perforated sphere at the 10 m/s freestream speed. In addition, at that freestream speed, the peak frequency value of the spectrum plot is also shifted to a lower frequency by 0.1 Strouhal number for perforated sphere in comparison with the unperforated one.
