Experimental investigation on the transition of separation/attachment in steady laminar juncture flows

Hu, Bo; Zhang, Hua; Younis, Muhammad Yamin; Li, Yan; Raza, Malik Shaheryar

doi:10.1007/s00348-015-1943-5

Cited by 10 publications

(7 citation statements)

References 23 publications

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“…The spanwise distance between the vortices is 3h. This vortex pair is assumed to be the trailing part of a horseshoe vortex originating from the separated region upstream of the cylinder (Baker, 1979;Hu et al, 2015). The ` vortex wraps around the roughness element and bends downstream, resulting into two streamwise counterrotating vortices.…”

Section: Near Wake Flow Topologymentioning

confidence: 99%

Geometry effect of isolated roughness on boundary layer transition investigated by tomographic PIV

Schrijer

Scarano

2016

International Journal of Heat and Fluid Flow

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Boundary layer transition over isolated roughness elements is investigated in the incompressible flow regime using tomographic PIV. Four different geometries (cylinder, square, hemisphere and micro-ramp) are considered maintaining constant height and span of the element. The main target is to compare the different flow topologies and study the effect of the element shape on accelerating boundary layer transition. The measurement domain encompasses the full transition process until the turbulent regime is established. The flow behavior is described by means of vortex topology and by statistical analysis of the velocity fluctuations. The instantaneous flow topology elucidates the mechanism of transition along its stages. A main distinction is observed between the bluff front elements that induce a horseshoe vortex due to upstream flow separation, leading to more rapid transition and the slender micro-ramp, requiring significant longer distance for transition onset. The mechanism of sideward propagation of the turbulent non-turbulent interface features a continuous convection and generation of hairpin-like vortices and remains the common denominator among all elements considered.

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Section: Near Wake Flow Topologymentioning

confidence: 99%

Geometry effect of isolated roughness on boundary layer transition investigated by tomographic PIV

Schrijer

Scarano

2016

International Journal of Heat and Fluid Flow

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“…15 In the junction flow two types of topologies namely, separation or attachment have been found and discussed in detail by Visbal, 8 Coon and Tobak, 4 Hung et al., 9 Younis et al., 10 Hu et al. 16 and Younis et al. 17 In a separation topology, the first singularity occurring over the surface of the end-wall is a half saddle point, whereas it is a half depleting node in the case of an attachment topology.…”

Section: Review Of Previous Work On Junction Flowsmentioning

confidence: 99%

Topological investigation of junction flow between cylinder and flat plate

Abhilash¹,

Kim

Lal³

2021

Proceedings of the Institution of Mechanical Engineers, Part C:

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The paper presents a numerical investigation on the junction flow occurring at the intersection between a wall and a protruding circular cylinder. Simulations of flow for Reynolds number ( Re) in the range [125 - 20000] have been carried out using OpenFOAM, an open source CFD tool. Plots of stream tracers have been used to qualitatively characterize the flow topology as either attachment or separation based on the type of singular points, classified as nodes and saddle points. Quantitative variations of momentum flux have been applied to identify a key mechanism for the transition of topology using the relative momentum strength of the incoming and reverse flow. Effect of a thinner boundary layer has been assessed by (i) imposing a reduced wall shear stress, and (ii) increasing the Reynolds number. Features of a typical unsteady flow, in the transition regime, at Re = 20000 have been predicted using Large Eddy Simulation (LES) with a one-equation eddy viscosity sub-grid scale model. Description of the time evolution of the topology at Re = 20000 has been able to validate the one-equation model in OpenFoam as well as to further validate the key mechanism identified for topology transition.

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“…Much work has been done for the HSV at a cylinder in steady currents. Many researchers investigated the HSV at a flatbed for the laminar case [14][15][16]. However, most of the practical HSVs occur with turbulent approach boundary layers [17].…”

Section: Local Scour Around a Monopile 21 General Description And Scmentioning

confidence: 99%

Local Scour around a Monopile Foundation for Offshore Wind Turbines and Scour Effects on Structural Responses

Qi¹,

Gao²

2020

Geotechnical Engineering - Advances in Soil Mechanics and Foundation Engineering

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Monopile is the most commonly used foundation type for offshore wind turbines. The local scour at a monopile foundation generated by the incoming shear flow has significant influence on both quasi-static lateral responses and dynamic responses of the monopile. This chapter focuses particularly on characterizing the local scour in both spatial and temporal scales and revealing the scour mechanisms associated with the flow field around a monopile. The predicting methods for the equilibrium scour depth and the time scale of scour are detailed under various representative flow conditions in the marine environment. The scale effect while extrapolating the results of model tests to prototype conditions is highlighted. The local scour imposes significant influence not only on the deformation and stiffness of the monopile foundation, but also on the natural frequency and fatigue life of the structure system. Monopiles with diameters up to 10 m have become a feasible option as the industry is currently advancing into deeper waters. More meticulous considerations for monopile design associated with the scour depth prediction and evaluation of scour effects are still in need to efficiently minimize the cost while remaining safety simultaneously.

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Experimental investigation on the transition of separation/attachment in steady laminar juncture flows

Cited by 10 publications

References 23 publications

Geometry effect of isolated roughness on boundary layer transition investigated by tomographic PIV

Geometry effect of isolated roughness on boundary layer transition investigated by tomographic PIV

Topological investigation of junction flow between cylinder and flat plate

Local Scour around a Monopile Foundation for Offshore Wind Turbines and Scour Effects on Structural Responses

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