Results are presented from a laboratory study on the free-surface signal generated over an array of submerged circular cylinders, representative of submerged aquatic vegetation. We aim to understand whether aquatic ecosystems generate a surface signature that is indicative of both what is beneath the water surface as well as how it is altering the flow. A shear layer forms over the canopy, generating coherent vortex structures which eventually manifest in the free-surface slope field. We connect the vortex properties measured at the surface with measurements of the bulk flow, and show that correlations between these quantities are adequate to create a parameterized model in which the interior velocity profile can be predicted solely from measurements taken at the free surface. Experimental surface observations yield a Strouhal number that is twice the most amplified mode predicted by linear stability theory, suggesting that vortices may evolve between generation at the canopy height and their manifestation at the water surface. Additionally, the surface signal continues evolving with distance downstream, with vortices becoming spread farther apart and the passage frequency gradually decreasing. By the trailing edge of the canopy, surface-impacting boils emerge for canopies with higher submergence ratios, suggesting a transition from coherent two-dimensional rollers to transversely varying structures.

Abstract

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This paper reports a mathematical model for predicting the fluid and heat flow characteristics of a Z-shaped corrugated perforated plate heat sink. Experiments were carried out to validate overall pressure drop as well as heat transfer predictions. A two-pronged approach was undertaken to design a corrugated perforated fin geometry: (a) macroscopic packaging, where the flow is distributed into conduits before being fed into perforated plates, and (b) microscopic design, where the pores are sized to maximize heat dissipation. A methodology typically used for predicting flow maldistribution is extended for packaging porous perforated plates in the macroscopic approach. An illustrative study is carried that estimates the optimum number of porous perforated plate fins that can be packaged within a given volume under fixed pressure drop constraint. In the microscopic approach, an order of magnitude analysis was carried out to decide the optimum diameter to maximize the heat transfer rate and expression for optimum diameter, and maximum achievable heat flux is proposed. Numerical simulations were carried out by considering full perforated plate porous fin geometry and single-channel geometry, and good agreement in their results was found. Finally, this study elaborates on the importance of achieving uniform flow distribution across the porous perforated plate fins.