Simultaneous measurements of velocity and temperature fluctuations in thermal boundary layer in a drag-reducing surfactant solution flow期刊界 All Journals 搜尽天下杂志传播学术成果专业期刊搜索期刊信息化学术搜索

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Simultaneous measurements of velocity and temperature fluctuations in thermal boundary layer in a drag-reducing surfactant solution flow

Authors:	F-C Li D-Z Wang Y Kawaguchi K Hishida

Institution:	(1) Center for Smart Control of Turbulence, Turbomachinery Research Group, Institute for Energy Utilization, National Institute of Advanced Industrial Science and Technology, 305-8564 Tsukuba, Japan;(2) School of Mechanical Engineering, Shanghai Jiao Tong University, 1954 Huashan Road, 200030 Shanghai, Peoples Republic of China;(3) Department of System Design Engineering, Keio University, 223-8522 Yokohama, Japan

Abstract:	The mechanism of turbulent heat transfer in the thermal boundary layer developing in the channel flow of a drag-reducing surfactant solution was studied experimentally. A two-component laser Doppler velocimetry and a fine-wire thermocouple probe were used to measure the velocity and temperature fluctuations simultaneously. Two layers of thermal field were found: a high heat resistance layer with a high temperature gradient, and a layer with a small or even zero temperature gradient. The peak value of $\overline{{u^{ + } \theta ^{ + } }}$ was larger for the flow with the drag-reducing additives than for the Newtonian flow, and the peak location was away from the wall. The profile of $- \overline{{v^{ + } \theta ^{ + } }}$ was depressed in a similar manner to the depression of the profile of $- \overline{{u^{ + } v^{ + } }}$ in the flow of the surfactant solution, i.e., decorrelation between v and compared with decorrelation between u and v. The depression of the Reynolds shear stress resulted in drag reduction; similarly, it was conjectured that the heat transfer reduction is due to the decrease in the turbulent heat flux in the wall-normal direction for a flow with drag-reducing surfactant additives.List of symbols $\overline{{{\left( \cdot \right)}}}$ ensemble averaged value - (·)⁺ normalized by the inner wall variables - (·) root-mean-square value - C concentration of cetyltrimethyl ammonium chloride (CTAC) solution - c _p heat capacity - D hydraulic diameter - f friction factor - H channel height - h heat transfer coefficient - j _H Colburn factor - l length - Nu Nusselt number, h - Pr Prandtl number, c _p/ - q _w wall heated flux - Re Reynolds number, U _b/ - T temperature - T _b bulk temperature - T _i inlet temperature - T _w wall temperature - T friction temperature, q _w /c _p u - U local time-mean streamwise velocity - U ₁ velocity signals from BSA1 - U ₂ velocity signals from BSA2 - U _b bulk velocity - u streamwise velocity fluctuation - u1 velocity in abscissa direction in transformed coordinates - u friction velocity, $\equiv {\sqrt {{\tau _{{\text{w}}} } \mathord{\left/ {\vphantom {{\tau _{{\text{w}}} } \rho }} \right. \kern-\nulldelimiterspace} \rho } }$ - v wall-normal velocity fluctuation - v1 velocity in ordinate direction in transformed coordinates - var(·) variance - x streamwise direction - y wall-normal direction - z spanwise direction - _j junction diameter of fine-wire TC - _w wire diameter of fine-wire TC - angle of principal axis of joint probability function p(u,v) - _f heat conduction of fluid - _w heat conduction of wire of fine-wire TC - kinematic viscosity - local time-mean temperature difference, T _w–T - temperature fluctuation - standard deviation - density - _w wall shear stress

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