Advertisement

Structural Features of the Near Region of an Asymmetric Turbulent Wake

  • M. Shokr
  • J. F. Keffer
  • J. G. Kawall

Abstract

Statistical properties of the turbulent/non-turbulent interfaces in the near region of an asymmetric wake generated by a pair of closely-spaced, unequal-diameter cylinders have been determined by means of digital image analysis of ciné flow visualization pictures of the flow. The results, comprising moments, burst rates, correlations and auto-spectra, indicate that the lower interface of the flow, which is associated with the large cylinder, has markedly steeper slopes, on the average, than the upper interface and its motion is considerably less random than that of the latter. Moreover, they establish that a “Kármán vortex street”, centred in the lower part of the wake and with a characteristic frequency corresponding to a Strouhal number significantly less than that pertaining to the symmetric cylinder.

Keywords

Strouhal Number Digital Image Analysis Interface Position Turbulent Wake Lower Interface 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Abbreviations

Nomenclature

D1

lower cylinder diameter, mm

D2

upper cylinder diameter, mm

D

equivalent diameter equal to (D 1 + D 2)/2 + L, mm

E

auto-spectrum, s

F

flatness factor

\(\hat f\)

burst rate, Hz

\({\hat f_{\text{o}}}\)

burst rate at the mean interface position, Hz

L

spacing between cylinder centres

N

number of ciné picture frames

n

frequency, Hz

ns

vortex shedding frequency, Hz

S

skewness factor

t

time, s

U1

free-stream velocity, ms −1

x

streamwise coordinate

Y

instantaneous lateral interface position, mm

\(\overline Y\)

mean value of Y, mm

y

lateral coordinate, or instantaneous lateral interface position relative to \(\overline Y\), mm

y

root-mean-square value of Y, mm

z

spanwise coordinate

α

reference variable

β

reference variable

Δt

time interval between ciné pictures frames, s

ϱ

auto- or cross-correlation function

τ

time lag, s

Ф

instantaneous interface slope, equivalent to ∂Y/∂x

\(\overline \Phi\)

mean value of Ф, deg

ϕ

instantaneous interface slope relative to \(\overline \Phi\)

ϕ

root-mean-square of Ф

Subscripts

U

upper

L

lower

y

position

ϕ

slope

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Béguier, C., Giralt, F., Fulachier, L., Keffer, J. F.: Negative production in turbulent shear flows, in Structure and Mechanisms of Turbulence II, ed. by H. Fiedler, Lecture Notes Phys. Vol. 76 ( Springer, Berlin, Heidelberg, New York 1978 ) pp. 22–35Google Scholar
  2. Budny, R. S., Kawall, J. G., Keffer, J. F.: Vortex street evolution in the wake of a circular cylinder, in Proc. 2nd Symp. on Turbulent Shear Flows ( Imperial College, London 1979 )Google Scholar
  3. Diaz, F., Gavaldä, J., Kawall, J. G., Giralt, F.: Interpretation of the complex turbulent flow generated by a rotating circular cylinder, in Structure of Complex Turbulent Shear Flow, IUTAM Symposium Marseille 1982, ed. by R. Dumas, L. Fulachier ( Springer, Berlin, Heidelberg, New York 1983 ) pp. 175–184Google Scholar
  4. Gavaldä, J., Diaz, F., Giralt, F., Kawall, J. G., Keffer, J. F. (1984): Analysis of the wake generated by the interaction of a rotating cylinder and a stationary cylinder. To be submitted to J. Fluid Mech.Google Scholar
  5. Keffer, J. F., Kawall, J. G., Giralt, F., Beguier, C.: Analysis of turbulent structures in complex shear flows, in Proc. 2nd Symp. on Turbulent Shear Flows ( Imperial College, London 1979 )Google Scholar
  6. Palmer, M. D., Keffer, J. F. (1972): An experimental investigation of an asymmetrical turbulent wake. J. Fluid Mech. 53, 593ADSCrossRefGoogle Scholar
  7. Shokr, M., Keffer, J. F.: Digital image analysis of a complex turbulent wake, in Structure of Complex Turbulent Shear Flow, IUTAM Symposium Marseille 1982, ed. by R. Dumas, L. Fulachier ( Springer, Berlin, Heidelberg, New York 1983 ) pp. 175–184Google Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 1985

Authors and Affiliations

  • M. Shokr
    • 1
  • J. F. Keffer
    • 1
  • J. G. Kawall
    • 1
  1. 1.Department of Mechanical EngineeringUniversity of TorontoTorontoCanada

Personalised recommendations