A Caltech Library Service

Large Structure in the Far Wakes of Two-Dimensional Bluff Bodies


Cimbala, John Michael (1984) Large Structure in the Far Wakes of Two-Dimensional Bluff Bodies. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/KZ05-YC02.


Smoke-wire flow visualization and hot-wire anemometry have been used to study near and far wakes of two-dimensional bluff bodies. For the case of a circular cylinder at 70 < Re < 2000, a very rapid (exponential) decay of velocity fluctuations at the Karman vortex street frequency is observed. Beyond this region of decay, larger-scale (lower wave-number) structure can be seen. In the far wake (beyond one hundred diameters) a broad band of frequencies is selectively amplified and then damped, the center of the band shifting to lower frequencies as downstream distance is increased.

The far-wake structure does not depend directly on the scale or frequency of the original Karman vortices; the growth of this structure is due to hydro-dynamic instability of the developing mean wake profile; it is not caused by amalgamation of the Karman vortices. Under certain conditions amalgamation can take place, but is purely incidental, and is not the driving mechanism responsible for the growth of larger-scale structure. Similar large structure is observed downstream of porous flat plates (Re ≈ 6000), which do not initially shed Karman-type vortices into the wake.

Hot-wire measurements show that two-dimensional locally-parallel inviscid linear stability theory is adequate to explain the growth of downstream structure. Namely, measured prominent frequencies in the cylinder wake are in close agreement with those predicted by the theory, when streamwise growth of wake width is taken into account.

Finally, three-dimensionality in the far wake of a circular cylinder is briefly discussed.

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:
  • Coles, Donald Earl (chair)
  • Kubota, Toshi
  • Saffman, Philip G.
  • Raichlen, Fredric
  • Roshko, Anatol
Defense Date:27 April 1984
Funding AgencyGrant Number
Office of Naval Research (ONR)N00014-76-C-0260
Achievement Rewards for College Scientists FoundationUNSPECIFIED
Los Angeles Area Chamber of CommerceUNSPECIFIED
Record Number:CaltechETD:etd-09132005-131650
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3515
Deposited By: Imported from ETD-db
Deposited On:14 Sep 2005
Last Modified:21 Dec 2019 03:54

Thesis Files

PDF (Cimbala_jm_1984.pdf) - Final Version
See Usage Policy.


Repository Staff Only: item control page