Experimental study of drag-reduction mechanism for a dilute surfactant solution flow

• Published in: International journal of heat and mass transfer 2008-02, Vol.51 (3), p.835-843
• Main Authors: Li, Feng-Chen, Kawaguchi, Yasuo, Yu, Bo, Wei, Jin-Jia, Hishida, Koichi
• Format: Article
• Language: English
• Subjects: Channel flow; Drag reduction; Exact sciences and technology; Flows in ducts, channels, nozzles, and conduits; Fluid dynamics; Fundamental areas of phenomenology (including applications); Instrumentation for fluid dynamics; Physics; PIV; Surfactant solution; Turbulence control; Turbulent events; Turbulent flows, convection, and heat transfer
• ISSN: 0017-9310; 1879-2189
• DOI: 10.1016/j.ijheatmasstransfer.2007.04.048

The quantitative characteristics of vortex structures and turbulent events in turbulent channel flows with and without drag reduction were investigated experimentally. Drag reducing aqueous solutions of CTAC (CTAC – cetyltrimethyl ammonium chloride) with concentration of 25 ppm and 75 ppm at 30 °C were tested. Particle image velocimetry (PIV) was used to measure the instantaneous velocity field in the streamwise–wall-normal plane of the flow. Through visualizing the instantaneous vector fields, contour maps of the swirling strength and instantaneous value of uv ( u and v are the streamwise and wall-normal velocity fluctuations, respectively), the characteristic angle of vortex packets was quantified. It was shown that the drag-reducing CTAC additive reduced both the strength and frequency of turbulent bursts near the wall, and the characteristics of vortex structures and bursts were not only dependent on drag-reduction level but also on concentration of additive. From the quantified parameters characterizing turbulent events in a wall-bounded turbulent flow, it was obtained that f T was linearly proportional to the product of frequency and strength of turbulent events.