Investigation on the characteristics of turbulence transport for momentum and heat in a drag-reducing surfactant solution flow

F. C. Li, Y. Kawaguchi, Koichi Hishida

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Abstract

Simultaneous measurements of the velocity (u and v in the streamwise and wall-normal directions, respectively) and temperature fluctuations (θ) in the thermal boundary layer were carried out for a heated drag-reducing surfactant solution flow in a two-dimensional channel by means of a two-component laser Doppler velocimetry and a fine-wire thermocouple probe. The drag-reducing fluid tested was a dilute aqueous solution of a cationic surfactant, cetyltrimethylammonium chloride (CTAC), with 30 ppm concentration. Measurements were performed for CTAC solution flows at an inlet temperature of 31 °C and at three Reynolds numbers of 3.5 × 104, 2.5 × 104, and 1.5 × 104, respectively, and for water flow at the Reynolds number of 2.5× 104. Drag reduction (DR) and heat transfer reduction (HTR) for the three CTAC solution flows were DR(HTR) = 33.0(20.2), 70.0(77.3), and 65.1(77.0) percentage, respectively. At a high HTR level, a large temperature gradient appeared when y+ <50 in the measured range (the superscript "+" denotes normalization with inner variables). Temperature fluctuation intensity, θ'-, and the streamwise turbulent heat flux, u+θ+, were enhanced in the layer with large temperature gradient for the drag-reducing flow, whereas the wall-normal turbulent heat flux, -v+θ+, was depressed throughout the measured range. The depression of -v+θ+ was due to a cause similar to that of the depression of the Reynolds shear stress -u+v+, i.e., in addition to the decrease of v'+, decorrelation between the two variables occurred. The decrease of -v+θ+ resulted in HTR, which was similar to that of the decrease of -u+v+ resulted in DR for the drag-reducing flow by additives. The turbulence production terms, -u+v+(∂U+/∂y+) and solution flows were both decreased. The turbulent Prandtl number deviated from that of the water flow near the heated wall with a value close to the molecular Prandtl number of the solvent.

Original languageEnglish
Pages (from-to)3281-3295
Number of pages15
JournalPhysics of Fluids
Volume16
Issue number9
DOIs
Publication statusPublished - 2004 Sep

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ASJC Scopus subject areas

  • Mechanics of Materials
  • Computational Mechanics
  • Physics and Astronomy(all)
  • Fluid Flow and Transfer Processes
  • Condensed Matter Physics

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