| Summary: | 博士 === 淡江大學 === 土木工程學系博士班 === 98 === Due to the structural efficiency and economic benefit, the hemispherical dome is a common structural geometry shape for large span sports stadiums or for storage purposes. The curved shape makes the accurate estimation of the wind pressure fluctuations on a hemispherical dome a difficult task due to the Reynolds number effects.
A series of wind tunnel tests were performed to investigate the effects of Reynolds number on the aerodynamic characteristics of hemispherical dome in smooth and turbulent boundary layer flows. Reynolds number of this study varies from 5.3 × 104 to 2.0 × 106. Instantaneous pressures were measured through high frequency electronic scanner system. Mean and RMS pressure coefficients on the center meridian and the overall pressure patterns of domes were calculated for comparative study. The results indicate that, In the smooth flow, the transition phenomenon of separated free shear layer occurs near Re=1.8×105 ~ 3.0×105；The separation/reattachment occurs in this Reynolds number region. The mean and R.M.S. pressure distributions become relatively stable after Re>3.0×105. The mean meridian drag coefficient decreases with Reynolds number for Re<3.0×105, and then increase monotonically up to Re=2.0×106; RMS meridian drag coefficient shows maximum and minimum values at Re≒1.5×105 and 3.0×105, respectively. The correlation coefficients of mean and RMS pressure contours indicate that, the pressure distributions become relatively stable at Re=2.0~3.0×105.
In turbulent flow, the transition phenomenon of separated free shear layer occurs at a lower Reynolds number, Re<1.1×105, and both mean and RMS pressure distributions approach Reynolds number independent when Re=1.2~1.5×105. The mean and RMS meridian drag coefficients, Cd and Cd’, become invariant when Re>2×105. The correlation coefficients of mean and RMS pressure contours indicate that, in turbulent boundary layer flow, the pressure distributions become Reynolds number independent at Re=1.0~2.0×105.
The Proper Orthogonal Decomposition (POD) was then applied to the pressure measurements of the uniformly distributed dome to study the wind load patterns of the hemisphere dome in both smooth and turbulent boundary layer flows. For a hemisphere dome submerges in a turbulent flow, the fluctuating energy concentrated the few POD mode. For the dome in smooth flow, however, the fluctuating energy is spread over large number of POD modes.
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