Experiments on turbulent flows in rough pipes: spectral scaling laws and the spectral link

Zuniga Zamalloa, Carlo

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Description

Title

Experiments on turbulent flows in rough pipes: spectral scaling laws and the spectral link

Author(s)

Zuniga Zamalloa, Carlo

Issue Date

2012-09-18T21:13:12Z

Director of Research (if dissertation) or Advisor (if thesis)

Gioia, Gustavo

Doctoral Committee Chair(s)

Gioia, Gustavo

Committee Member(s)

• Chrakraborty, Pinaki
• Christensen, Kenneth T.
• Freund, Jonathan B.

Department of Study

Mechanical Sci & Engineering

Discipline

Theoretical & Applied Mechans

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• turbulence
• rough pipe
• energy spectra
• hotwire
• friction factor

Abstract

Motivated by a recently proposed theory that entails the existence of a “spectral link” between the turbulent energy spectra and the attendant turbulent mean velocity profile in a pipe flow, we establish new scaling laws for the turbulent energy spectra of pipe flows. These new scaling laws— an inner scaling law and an outer scaling law—differ from the scaling laws that were predicated on Townsend’s attached–eddy hypothesis in that they are proper analogues (or spectral counterparts) of the classical scaling properties of the turbulent mean velocity profile. To test the new scaling laws, we have recourse to (1) published computational data from direct numerical simulations and (2) new experimental data from unprecedented measurements, carried out in our laboratory, of the streamwise component of the turbulent energy spectrum on numerous locations along the radii of three rough-walled pipes, for flows spanning a decade in Reynolds number. We show that the new scaling laws are consistent with the turbulent energy spectra of both smooth– and rough– walled flows. In addition, we use the new experimental data to probe the spatial distribution of the streamwise turbulent kinetic energy u2 , the longitudinal integral length scale L11 , and the Kolmogorov length scale η in turbulent rough–walled pipe flows. We document in our rough– pipe flows a striking phenomenon recently discovered in smooth–pipe flows: the occurrence of an outer peak in u+2 (y + ), whose magnitude is an increasing function of the Reynolds number, but the Reynolds number where the outer peak emerges is an order of magnitude smaller than the corresponding Reynolds number in smooth pipes. Last, we carry out a comparative study of the three canonical wall–bounded turbulent flows: pipe flow, channel flow, and boundary layer flow. We are able to trace the similarities and disparities among the turbulent mean velocity profiles of the three canonical flows to corresponding similarities and disparities among the attendant turbulent energy spectra—new evidence of the existence of a spectral link between the turbulent mean-velocity profile and the turbulent energy spectra.

Graduation Semester

2012-08

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Copyright and License Information

Copyright 2012 Carlo Zuniga Zamalloa

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