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Mixing in high Schmidt number turbulent jets


Miller, Paul Lewis (1991) Mixing in high Schmidt number turbulent jets. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/PN2P-RK49.


NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. This thesis is an experimental investigation of the passive scalar (species concentration) field in the far-field of round, axisymmetric, high Schmidt number (liquid phase), turbulent jets issuing into a quiescent reservoir, by means of a quantitative laser-induced fluorescence technique. Single-point concentration measurements are made on the jet centerline, at axial locations from 100 to 305 nozzle diameters downstream, and Reynolds numbers of 3,000 to 102,000, yielding data with a resolved temporal dynamic range up to [...], and capturing as many as 504 large-scale structure passages. Long-time statistics of the jet concentration are found to converge slowly. Between 100 and 300 large-scale structure passages are required to reduce the uncertainty in the mean to 1%, or so. The behavior of the jet varies with Reynolds number. The centerline concentration pdf's become taller and narrower with increasing Re, and the normalized concentration variances correspondingly decrease with Re. The concentration power spectra also evolve with Re. The behavior of the spectral slopes is examined. No constant -1 (Batchelor) spectral slope range is present. Rather, in the viscous region, the power spectra exhibit log-normal behavior, over a range of scales exceeding a factor of 40, in some cases. The frequency of the beginning of this log-normal range scales like [...] (Kolmogorov scaling). Mixing in the far-field is found to be susceptible to initial conditions. Disturbances in the jet plenum fluid and near the nozzle exit strongly influence the scalar variance, with larger disturbances causing larger variances, i.e., less homogeneous mixing. The plenum/nozzle geometry also influences the variance. These effects of initial conditions persist for hundreds of diameters from the nozzle exit, over hundreds of large scales. Mixing in these jets differs from gas-phase, order unity Sc, jet mixing. At low to moderate Re, the higher Sc jet is less well mixed. The difference is less pronounced at higher Re. Flame length estimates imply either an increase in entrainment and/or an increase in molecular mixing, with increasing Re. Experimental considerations such as buoyancy and resolution are shown not to influence these results.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Batchelor; concentration; experiment; fluorescence; jet; Kolmogorov; mixing; PDF; Reynolds number; Schmidt number; spectrum; turbulence
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Applied Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Dimotakis, Paul E.
Thesis Committee:
  • Unknown, Unknown
Defense Date:25 April 1991
Record Number:CaltechETD:etd-11142005-152828
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:4551
Deposited By: Imported from ETD-db
Deposited On:14 Nov 2005
Last Modified:21 Dec 2019 04:21

Thesis Files

PDF (Miller_pl_1991.pdf) - Final Version
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