Numerical Study of Seabed Boundary Layer Flow Around Monopile and Gravity-Based Wind Turbine Foundations

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Muk Chen Ong ◽  
Eirik Trygsland ◽  
Dag Myrhaug
Keyword(s):  
Boundary Layer ◽  
Wind Turbine ◽  
Boundary Layer Flow ◽  
Horseshoe Vortex ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Shear Stresses ◽  
Horseshoe Vortices ◽  
Layer Flow ◽  
Bottom Slab

Computational fluid dynamics (CFD) has been used to study the seabed boundary layer flow around monopile and gravity-based offshore wind turbine foundations. The gravity-based foundation has a hexagonal bottom slab (bottom part). The objective of the present study is to investigate the formation of horseshoe vortex and flow structures around two different bottom-fixed offshore wind turbine foundations in order to provide an assessment of potential scour for engineering design. Three-dimensional CFD simulations have been performed using Spalart–Allmaras delayed detached eddy simulation (SADDES) at a Reynolds number 4 × 106 based on the freestream velocity and the diameter of the monopile foundation, D. A seabed boundary layer flow with a boundary layer thickness D is assumed for all the simulations. Vortical structures, time-averaged results of velocity distributions and bed shear stresses are computed. The numerical results are discussed by studying the difference in flows around the monopile and the gravity-based foundations. A distinct horseshoe vortex is found in front of the monopile foundation. Two small horseshoe vortices are found in front of the hexagonal gravity-based foundation, i.e., one is on the top of the bottom slab and one is near the seabed in front of the bottom slab. The horseshoe vortex size for the hexagonal gravity-based foundation is found to be smaller than that for the monopile foundation. The effects of different foundation geometries on destroying the formation of horseshoe vortices (which is the main cause of scour problems) are discussed.

Numerical Study of Seabed Boundary Layer Flow Around Monopile and Gravity-Based Wind Turbine Foundations

2016 ◽  
Author(s):  
Muk Chen Ong ◽  
Eirik Trygsland ◽  
Dag Myrhaug
Keyword(s):  
Boundary Layer ◽  
Wind Turbine ◽  
Boundary Layer Flow ◽  
Horseshoe Vortex ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Shear Stresses ◽  
Horseshoe Vortices ◽  
Layer Flow ◽  
Bottom Slab

Computational fluid dynamics (CFD) has been used to study the seabed boundary layer flow around monopile and gravity-based offshore wind turbine foundations. The gravity-based foundation has a hexagonal bottom slab (bottom part). The objective of the present study is to study the flow structures around the bottom-fixed offshore wind turbine foundations in order to provide essential hydrodynamic coefficients for engineering design and an assessment of potential scour erosion. Three-dimensional CFD simulations have been performed using Spalart-Allmaras Delayed Detached Eddy Simulation (SADDES) at a Reynolds number 4×106 based on the free stream velocity and the diameter of the monopile foundation, D. A seabed boundary layer flow with a boundary layer thickness D is assumed for all the simulations. Vortical structures, time-averaged results of velocity distributions and bed shear stresses are computed. The numerical results are discussed by studying the difference in flows around the monopile and the gravity-based foundations. A distinct horseshoe vortex is found in front (upstream side) of the monopile foundation. Two small horseshoe vortices are found in front of the hexagonal gravity-based foundation, i.e. one is on the top of the bottom slab and one is near the seabed in front of the bottom slab. The horseshoe vortex size for the hexagonal gravity-based foundation (computed as the distance from the separation point to the foundation surface along the centerline on the seabed), is found to be smaller than that for the monopile foundation. The effects of different foundation geometries on destroying the formation of horseshoe vortices (which is the main cause of scour problems) are discussed.

The hydrodynamic stability of boundary-layer flow over a class of anisotropic compliant walls

1990 ◽  
Vol 220 ◽  
pp. 125-160 ◽  
Author(s):  
K. S. Yeo
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Reynolds Shear Stress ◽  
Flow Stability ◽  
Fibre Axis ◽  
Shear Stresses ◽  
Anisotropic Surface ◽  
Material Stiffness ◽  
Compliant Walls ◽  
Layer Flow

This paper examines the linear stability of zero-pressure-gradient boundary-layer flow over a class of anisotropically responding compliant walls. The anisotropic wall behaviour is derived from a material anisotropy which is characterized by relatively high tensile and compressive strength along a certain direction, termed the fibre axis. When the material stiffness along the fibre axis is sufficiently high, the resulting correlation between the horizontal and the vertical components of wall displacement induces at the flow–wall interface a Reynolds shear stress of a sign that is predetermined by the angle with which the fibre axis makes with the direction of the flow. The notion that anisotropic surface response could be employed to produce turbulent Reynolds shear stresses of predetermined sign at a surface was first explored by Grosskreutz (1971) in an experimental study on turbulent drag reduction. The present paper examines the implications of this interesting idea in the context of two-dimensional flow stability over anisotropic compliant walls. The study covers single- and two-layer compliant walls using the methodology described in Yeo (1988). The effects of wall anisotropy, as determined by the orientation of the fibre axis and the material stiffness along the fibre axis, on flow stability are examined for a variety of walls. The potential of some anisotropic compliant walls for delaying laminar–turbulent transition is investigated, and the contribution of the anisotropy to transition delay is appraised.

An Exact Solution of Oscillatory Couette Flow in a Rotating System

1991 ◽  
Vol 58 (4) ◽  
pp. 1104-1107 ◽  
Author(s):  
B. S. Mazumder
Keyword(s):  
Boundary Layer ◽  
Exact Solution ◽  
Unsteady Flow ◽  
Couette Flow ◽  
Coriolis Force ◽  
Boundary Layer Flow ◽  
Shear Stresses ◽  
Flat Plates ◽  
Rotating System ◽  
Layer Flow

An exact solution of oscillatory Ekman boundary layer flow bounded by two horizontal flat plates, one of which is oscillating in its own plane and other at rest, is obtained. The effect of coriolis force on the resultant velocities and shear stresses for steady and unsteady flow has been studied.

scholarly journals Scour Controlling Effect of Hybrid Mono-Pile as a Substructure of Offshore Wind Turbine: A Numerical Study

2020 ◽  
Vol 8 (9) ◽  
pp. 637 ◽  
Author(s):  
Yong-Jun Cho
Keyword(s):  
Wind Turbine ◽  
Numerical Study ◽  
Standing Waves ◽  
Wind Farms ◽  
Horseshoe Vortex ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Control Effect ◽  
Incoming Wave ◽  
Offshore Wind Farms

In Europe, which has been operating offshore wind farms well ahead of South Korea, most offshore wind turbines installed in shallow waters are suffering from severe scouring problems due to the horseshoe vortex. These operating experiences can serve as a valuable lesson for Korea. After a thorough review, we conclude that the horseshoe vortex’s intensity is proportional to the height of the standing waves near an offshore wind turbine. Based on this rationale, we propose a hybrid mono-pile, which is a mono-pile with an additional light turbine mounted at its toe that can dissipate the incoming wave energy with the rotation that occurs when the turbine is exposed to incoming waves or currents. The weakened standing waves in this manner would lead to less sediment transport. We proceeded to carry out the numerical simulation to verify the scouring control effect of the hybrid mono-pile. Numerical results show that the hybrid mono-pile could reduce scouring remarkably.

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