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

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

Zuniga Zamalloa, Carlo

关键词: turbulence;    rough pipe;    energy spectra;    hotwire;    friction factor;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/34359/Zuniga-Zamalloa_Carlo.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Motivated by a recently proposed theory that entails the existence of a “spectral link” betweenthe turbulent energy spectra and the attendant turbulent mean velocity profile in a pipe flow, weestablish 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 onTownsend’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 scalinglaws, 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, ofthe streamwise component of the turbulent energy spectrum on numerous locations along the radiiof three rough-walled pipes, for flows spanning a decade in Reynolds number. We show that thenew 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 distributionof the streamwise turbulent kinetic energy u2 , the longitudinal integral length scale L11 , and theKolmogorov 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 anouter peak in u+2 (y + ), whose magnitude is an increasing function of the Reynolds number, butthe Reynolds number where the outer peak emerges is an order of magnitude smaller than thecorresponding Reynolds number in smooth pipes. Last, we carry out a comparative study of thethree canonical wall–bounded turbulent flows: pipe flow, channel flow, and boundary layer flow. Weare able to trace the similarities and disparities among the turbulent mean velocity profiles of thethree canonical flows to corresponding similarities and disparities among the attendant turbulentenergy spectra—new evidence of the existence of a spectral link between the turbulent mean-velocityprofile and the turbulent energy spectra.