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Post Roughness Dominant Regime in the Turbulent Flow Through Rough Pipes

DOI: 10.1615/THMT-18.1200
pages 1061-1063

C.M.M. Santos
Mechanical Engineering Program, Federal University of Rio de Janeiro, Brazil

H. R. Anbarlooei
Mechanical Engineering Program (PEM/COPPE), Universidade Federal do Rio de Janeiro, C.P. 68503, 21941-972, Rio de Janeiro, Brazil

D. O. A. Cruz
Mechanical Engineering Department, Federal University of Rio de Janeiro, Av. Moniz de Aragao 420, 21945-972 Rio de Janeiro, Brazil

F. Ramos
Department of Applied Mathematics, Institute of Mathematics, Federal University of Rio de Janeiro, Brazil

Abstract

The influence of the surface roughness on the turbulence structures has been studied extensively experimentally and numerically. It is well known that in addition to the size of the rough elements, their spatial distribution also affects the turbulence. Pioneering study of Nikuradse showed that the turbulence in not affected in Laminar, transitional and early turbulent regimes by presence of the roughness and this effect just becomes dominant only at high Reynolds numbers.
In the present work, the effect of the roughness geometry (height and spatial distribution) on the friction factor is experimentally investigated. Our main goal was to acquire data of carefully defined rough surfaces for further analytical and theoretical studies. However, unexpectedly, our results show that at high enough Reynolds number the classically fully rough regimes (constant friction factor) ends and normal smooth behaviour resumes. To our knowledge such a phenomenon has not been mentioned in the literature before.

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