Physical meaning of advection velocity estimated from phase delay of heat transfer coefficients

Abstract

Clarifying the relationship between heat transfer and flow in energy devices is crucial. However, directly measuring heat transfer and flow is challenging. To address this issue, we apply a method for estimating the flow velocity near the wall based on wall thermal data, and we verify the physical meaning of the estimated velocity. Focusing on the channel turbulence at Reynolds numbers of 2,700, 3,300 and 3,800, the heat transfer coefficient was calculated from the wall temperature data experimentally obtained via infrared thermography. The advection velocity of the fluid was estimated based on the phase difference of the time-series fluctuations of the heat transfer coefficients at the upstream and downstream locations. The estimated advection velocity was compared with that obtained via particle image velocimetry (PIV). The time-averaged advection velocity reflects the increase in the mean flow velocity for each Reynolds number. Furthermore, the time-averaged advection velocity corresponded to the PIV results at y⁺= 14.5 ± 1.9, which was within the buffer layer (5 < y⁺ < 30). In addition, we confirm that the proposed method can capture instantaneous velocity to some extent.