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Aerodynamic sound derived from bluff bodies can be considerably reduced by flow control. In this paper, the authors propose a new method in which porous material covers a body surface as one of the flow control methods. From wind tunnel tests on flows around a bare cylinder and a cylinder with porous material, it has been clarified that the application of porous materials is effective in reducing aerodynamic sound. Correlation between aerodynamic sound and aerodynamic force fluctuation, and a surface pressure distribution of cylinders are measured to investigate a mechanism of aerodynamic sound reduction. As a result, the correlation between aerodynamic sound and aerodynamic force fluctuation exists in the flow around the bare cylinder and disappears in the flow around the cylinder with porous material. Moreover, the aerodynamic force fluctuation of the cylinder with porous material is less than that of the bare cylinder. The surface pressure distribution of the cylinder with porous material is quite different from that of the bare cylinder. These facts indicate that aerodynamic sound is reduced by suppressing the motion of vortices because aerodynamic sound is induced by the unstable motion of vortices. In addition, an instantaneous flow field in the wake of the cylinder is measured by application of the PIV technique. Vortices that are shed alternately from the bare cylinder disappear by application of porous material, and the region of zero velocity spreads widely behind the cylinder with porous material. Shear layers between the stationary region and the uniform flow become thin and stable. These results suggest that porous material mainly affects the flow field adjacent to bluff bodies and reduces aerodynamic sound by depriving momentum of the wake and suppressing the unsteady motion of vortices.

We have proposed a novel model of a self-interstitial defect in crystalline Si. It contains four Si interstitials and has the structural features as follows: All silicon atoms are four coordinated, in contrast to previously proposed models; the defect is characterized by five-, six-, and seven-membered atomic rings. The total energy, the relaxed atomic configuration, and the electronic structure of the defect have been determined using the transferable semiempirical tight binding method. [S0031-9007(97)03265-1]

SUMMARY Acoustic pulses were detected fiom a patient treated by a pulsed proton radiation beam. The dose rate of the proton beam was 0.3 cGy/pulse. The signals from 100 to 700 pulses were accumulated to improve the signal to noise ratio. After accumulation, the random noise level was negligibly small compared to the signal. These results suggest the feasibility of non-invasive monitoring of proton dose distributions in patients by sensing acoustic pulses generated during irradiation by a pulsed proton radiation beam. Radiat Oncol Invest 1995;3:42-45. 0 1995 Wdey-Liss, lnc.

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