2次元丘模型上流から点源放出されたエチレン乱流拡散過程のスペクトル解析

抄録

We have investigated experimentally the turbulent diffusion processes of ethylene emitted from a point source in the upstream region of a two-dimensional hill model. By using the fast-response flame ionization detector (FFID), the mean and fluctuating concentration distributions are measured quantitatively. From a spectrum analysis of the concentration fluctuations, both in a flat-plate boundary layer flow and a flow over a two-dimensional hill model, the power spectra of concentration fluctuation show the contribution from two distinct frequencies, i.e., a low frequency (about 10 Hz) near the wall and a high frequency (about 100 Hz) at the outer edge of concentration boundary layer. It is found that only high-frequency but small-amplitude fluctuations remain in the separated region behind the hill, though the mean concentration keeps a high value due to the accumulation of mass convected from the upstream region.