Turbulent channel flow perturbed by triangular ripples

Author(s)

Cunez, Fernando David ^[1] ; Gomes de Oliveira, Gabriel Victor ^[1] ; Franklin, Erick de Moraes ^[1]

Affiliation

^[1] Univ Campinas UNICAMP, Sch Mech Engn, Campinas, SP - Brazil

• Document type: Journal article
• Source: Journal of the Brazilian Society of Mechanical Sciences and Engineering; v. 40, n. 3 MAR 2018.
• Web of Science Citations: 2

Abstract

This paper presents an experimental investigation of the perturbation of a turbulent closed-conduit flow by two-dimensional triangular ripples. Two ripple configurations were employed: one single asymmetric triangular ripple, and two consecutive asymmetric triangular ripples, all of them with the same geometry. Different water flows were imposed over either one or two ripples fixed to the bottom wall of a closed conduit, and the flow field was measured by particle image velocimetry (PIV). Reynolds numbers based on the channel height were moderate, varying between 27500 and 34700. The regime was hydraulically smooth, and the blockage ratio was significant. Experimental data for this specific case remain scarce, and the physics involved has yet to be fully elucidated. Using the instantaneous flow fields, the mean velocities and fluctuations were computed, and the shear stresses over the ripples were determined. The velocities and stresses obtained in this way for the single ripple and for the pair of ripples are compared, and the surface shear stress is discussed in terms of bed stability. Our results show that for the single and upstream ripples, the shear stress increases at the leading edge and decreases toward the crest, while for the downstream ripple it decreases monotonically between the reattachment point and the crest. The stress distribution over the downstream ripple, which is different from both the upstream and single ripples, is shown to sustain existing ripples over loose beds. (AU)

• FAPESP's process: 12/19562-6 - The transport of grains as bed-load and the instabilities of a granular bed
• Grantee: Erick de Moraes Franklin
• Support type: Research Grants - Young Investigators Grants
• FAPESP's process: 16/18189-0 - Liquid-fluidized beds in narrow pipes: dynamics and instabilities
• Grantee: Fernando David Cúñez Benalcázar
• Support type: Scholarships in Brazil - Doctorate
• FAPESP's process: 16/13474-9 - Instabilities on dense granular flows
• Grantee: Erick de Moraes Franklin
• Support type: Regular Research Grants
• FAPESP's process: 15/15001-8 - Turbulent boundary layer perturbed by a hill
• Grantee: Gabriel Victor Gomes de Oliveira
• Support type: Scholarships in Brazil - Master