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| Author(s): |
Gabriel Victor Gomes de Oliveira
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Mecânica |
| Defense date: | 2017-07-11 |
| Examining board members: |
Erick de Moraes Franklin;
Rogério Gonçalves dos Santos;
Guilherme José de Castilho
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| Advisor: | Erick de Moraes Franklin |
| Abstract | |
Turbulent boundary layers in the presence of low hills (hills of small aspect ratio) are often found in nature and industry. Some examples are air flows over sand dunes and ripples in deserts and water or oil flows over sequential sand ripples in closed conduits, such as happens in petroleum pipelines. The presence of these ripples alters the way in which velocities and stresses are distributed along the flow. In this study, we performed experiments on the perturbation of a fully-developed turbulent boundary layer by two sequential 2-D low hills of triangular shape. The experiments were performed by imposing different water flows in a closed conduit of rectangular cross-section, made of acrylic, and with the pair of triangular ripples fixed on the bottom of the test section. The flow rates used were 8 and 10 $\mathrm{m^3/h}$, corresponding to moderates Reynolds numbers based on the channel height of 27,500 and 35,000, respectively. The instantaneous flow fields were then measured by PIV (Particle Image Velocimetry). From the instantaneous velocity fields, the mean velocities and fluctuations were computed, and from them we could determine the viscous stresses, turbulent stresses and turbulent production. The general behaviors of velocities and stresses of the perturbed flow were compared to the unperturbed flow and the shear stress at the surface of the ripples is discussed in terms of granular bed stability. Our results show that for the upstream ripples the shear stress increases at the leading edge and decreases towards the crest, while for the downstream ripple it decreases monotonically between the reattachment point and the crest. The stress distribution over the pair of ripples sustain the existence of these ripples over movable beds (AU) | |
| FAPESP's process: | 15/15001-8 - Turbulent boundary layer perturbed by a hill |
| Grantee: | Gabriel Victor Gomes de Oliveira |
| Support Opportunities: | Scholarships in Brazil - Master |