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Effects of a Periodic Disturbance on Structure and Mixing in Turbulent Shear Layers and Wakes


Roberts, Fredrick Allen (1985) Effects of a Periodic Disturbance on Structure and Mixing in Turbulent Shear Layers and Wakes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/syy5-a334.


Large scale structure and mixing processes are investigated in chemically reacting wakes and shear layers to which a periodic disturbance is applied. The experiments employ a diffusion-limited acid-base reaction to directly measure the extent of mixing. Optical diagnostics used include laser absorption and laser induced fluorescence. Absorption of laser light by reacted product provides a measure of cross-stream average product. Fluorescence was measured by a self-scanning linear photodiode array using high speed computer data acquisition to obtain the product distribution across the layer.

Previous results showing that forcing alters the structure and growth rate of shear layers are confirmed. Forcing artificially extends the lifetime of vortices whose size is consistent with the disturbance wavelength. Amalgamation of smaller vortices is enhanced over that in the natural layer until the frequency locked scale is achieved. At high Reynolds number product measurements show reduction of product with forcing. At moderate Reynolds numbers, on the other hand, there is an increase in product when forced. In one case a five fold increase in product was observed. The differences are related to the different effects of forcing on entrainment, composition ratio and secondary structure.

A dramatic, order of magnitude increase in mixing was discovered for certain forced wake flows. This effect is strongly associated with an interaction between the spanwise organized wake vortices and the test-section side walls.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Aeronautics
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Aeronautics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Roshko, Anatol
Thesis Committee:
  • Broadwell, James E. (chair)
  • Dimotakis, Paul E.
  • Shair, Fredrick H.
  • Zukoski, Edward E.
  • Roshko, Anatol
Defense Date:12 September 1984
Funding AgencyGrant Number
Office of Naval Research (ONR)N00014-76-C-0260
Record Number:CaltechETD:etd-03252008-144801
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:1123
Deposited By: Imported from ETD-db
Deposited On:04 Apr 2008
Last Modified:16 Apr 2021 23:04

Thesis Files

PDF (Roberts_fa_1985.pdf) - Final Version
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