乱流境界層内の人工大規模構造がバースト現象に及ぼす影響

抄録

In the present study, dielectric barrier discharge plasma actuators (DBD-PA) arrays were used to blow the near wall low-velocity fluid into the log-region, so as to generate artificial large-scale motions (ALSMs) in a turbulent boundary layer (TBL). The DBD-PA was embedded in the wall to avoid disturbing the flow. To investigate the effect of the ALSMs on the burst phenomenon, a multi-point hot-wire probe consisting of a hot-wire rake and a single I-type hot-wire probe was used to measure the fluctuation velocity in the log-region and buffer layer in the TBL. As a result, it was confirmed from the mean velocity distribution in the log-region that there exists artificial low-velocity region flanked on either side by high-velocity region. These low- or high- velocity regions were regarded as the negative ALSMs (nALSMs) and positive ALSMs (pALSMs), respectively. The bursting phenomena were detected by the Variable-Interval Time-Averaging (VITA) method from the fluctuation velocity measured in the buffer layer. It was found that the bursting frequency under pALSMs is smaller than that of nALSMs. Furthermore, from the pre-multiplied power spectra calculated from the fluctuation velocity measured by the single I-type hot-wire probe, it was found that the near-wall turbulent fluctuation energy in a large range of frequency was suppresed under the ALSMs, especially under the pALSMs. This could be considered as that the nALSMs have lifted the near-wall flow having a high turbulent intensity out of the near-wall region and the pALSMs have introduced the flow having a lower turbulent fluctuation energy from the outer region into the near-wall region, therefore suppressed the bursting phenomenon.