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Experiments in Fluids

, 60:28 | Cite as

Experimental characterization of turbulent mixing performance using simultaneous stereoscopic particle image velocimetry and planar laser-induced fluorescence

  • Emmanuel Hitimana
  • Rodney O. Fox
  • James C. Hill
  • Michael G. OlsenEmail author
Research Article

Abstract

Simultaneous measurements of velocity and concentration using stereoscopic particle image velocimetry (stereo-PIV) and planar laser-induced fluorescence (PLIF) were used to investigate the mixing performance of a scaled-up multi-inlet vortex reactor (MIVR). Data were collected in three measurement planes located at different heights from the reactor bottom (¼, ½, and ¾ of the reactor height) for Reynolds numbers of 3250 and 8125 based on the reactor inlet velocity and hydraulic diameter. The collected data were analyzed to determine turbulent flow statistics such as turbulent viscosity, turbulent diffusivity, and turbulent Schmidt number. When analyzed across 16 different azimuth angles and radial positions (r) normalized by the reactor radius (Ro), the turbulent viscosity was found to be nearly axisymmetric. In the free-vortex region (r/Ro > 0.2), the turbulent viscosity results were nearly constant. Near the center of the reactor in the forced-vortex region (r/Ro < 0.1), the turbulent viscosity significantly increased, with peak values occurring near the center. The turbulent viscosity and Reynolds shear stress were highest near the reactor exit at the ¾ plane. The dominance of high turbulent fluxes and low concentration gradients near the reactor center led to high turbulent diffusivity. Away from the center, the turbulent diffusivity was reduced because of large concentration gradients and low turbulence intensity in the spiral arm region. The turbulent Schmidt numbers were also found to correlate with concentration gradients. The turbulent Schmidt number values were found to vary from 0.1 to 1.2. The highest spatial variation in \(S{c_t}\) was observed in the spiral arms region, where the concentration gradients are also the highest. This spatial variation in Schmidt number contrasts with the common assumption of constant \(S{c_t}\) in Reynolds-averaged CFD models.

Graphical abstract

A typical stereo-PIV/PLIF simultaneous instantaneous measurement for Re = 8125. The color and vectors represent the instantaneous mixture fraction and in-plane velocity field, respectively. (a) ¼ Plane. (b) ½ Plane. (c) ¾ Plane.

Notes

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  • Emmanuel Hitimana
    • 1
  • Rodney O. Fox
    • 2
  • James C. Hill
    • 2
  • Michael G. Olsen
    • 1
    Email author
  1. 1.Department of Mechanical EngineeringIowa State University of Science and TechnologyAmesUSA
  2. 2.Department of Chemical and Biological EngineeringIowa State University of Science and TechnologyAmesUSA

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