1515 円管内オリフィス下流における熱伝達構造の非定常挙動

Abstract

A technique using high-speed infrared thermography was used to measure the spatio-temporal heat transfer to a turbulent water pipe flow around an orifice plate (bore ratio: d/D = 0.49, Re_D ≈ 13000). The spatio-temporal distribution of the heat transfer coefficient was evaluated based on the temperature fluctuation of a heated thin-foil measured using infrared thermography. In this work, we tried to evaluate the convection velocity of the heat transfer structure on the heated surface, which is considered to be associated with the convection of the vortical structure in the near-wall region. As a result, it was confirmed that the maximum position of the heat transfer in the time-averaged distribution was not coincide with the time-averaged flow reattachment position, as reported in the literature. In order to investigate the mechanism of this difference, ensemble-averaged heat transfer coefficients were calculated on the condition that instantaneous reattachment appeared at specific streamwise positions. The ensemble-averaged heat transfer distribution shows a noticeable peak at the flow reattachment position, comparing with the time-averaged distribution. Also, the peak value of the ensemble-averaged heat transfer distribution tended to decrease toward downstream. This trend indicates that reattachment at upstream contributes to the heat transfer enhancement more significant than that at downstream. This is the reason why the maximum position of the time-averaged heat transfer exists upstream of the time-averaged flow reattachment position.