Demonstration of a coupled floating offshore wind turbine analysis with high-fidelity methods

This paper presents results of numerical computations for floating off-shore wind turbines using, as an example, a machine of 10-MW rated power. The aerodynamic loads on the rotor are computed using the Helicopter Multi-Block flow solver developed at the University of Liverpool. The method solves the Navier–Stokes equations in integral form using the arbitrary Lagrangian–Eulerian formulation for time-dependent domains with moving boundaries. Hydrodynamic loads on the support platform are computed using the Smoothed Particle Hydrodynamics method, which is mesh-free and represents the water and floating structures by a set of discrete elements, referred to as particles. The motion of the floating offshore wind turbine is computed using a Multi-Body Dynamic Model of rigid bodies and frictionless joints. Mooring cables are modelled as a set of springs and dampers. All solvers were validated separately before coupling, and the results are presented in this paper. The importance of coupling is assessed and the loosely coupled algorithm used is described in detail alongside the obtained results

Assessment and calibration of the γ equation transition model for a wide range of Reynolds numbers at low Mach

The numerical simulation of flows over large-scale wind turbine blades without considering the transition from laminar to fully turbulent flow may result in incorrect estimates of the blade loads and performance. Thanks to its relative simplicity and promising results, the Local-Correlation based Transition Modelling concept represents a valid way to include transitional effects into practical CFD simulations. However, the model involves coefficients to be tuned to match the required application. In this paper, the γ-equation transition model is assessed and calibrated, for a wide range of Reynolds numbers at low Mach, as needed for wind turbine applications. Different airfoils are used to evaluate the original model and calibrate it, whereas a large-scale wind turbine blade is employed to show that the calibrated model can lead to reliable solution for complex three-dimensional flows. The calibrated model shows promising results for both two-dimensional and three-dimensional flows, even if cross-flow instabilities are neglected

Integrated simulation of off-shore wind turbine

This thesis presents coupled model for the floating off-shore wind turbines, using a 10-MW machine as an example. The idea put forward is to employ high fidelity Navier-Stokes solvers for air and water. For this reason, the Helicopter Multi-Block solver was used for air, and the Smoothed Particles Hydrodynamic method was used for water. A multi-body solver was implemented to solve for the wind turbine dynamics. All solvers were validated before coupling, and results are presented in this thesis. The employed, loosely coupled, algorithm is described in detail, and the importance of coupling is assessed. Additional aerodynamic cases were studied to form the foundation for further model development. The study started from the aerodynamic analysis of a 10-MW wind turbine. Straight and pre-bent configurations of the blade were investigated under the assumption of uniform inflow. Next, the effects of the atmospheric boundary inflow and atmospheric turbulence were studied. For this, the power law wind speed profile was employed, and atmospheric turbulence was introduced using Mann’s model. The aero-elasticity of the 10-MW rotor was studied next. The structural model was constructed using NASTRAN, and the natural frequencies and modes were compared to published results, showing good agreement. This model was then used for steady and unsteady aero-elastic computations. The effects of employing deformable trailing and leading edge flaps on a 10-MW wind turbine were also investigated. The results showed that the trailing edge flap can be used to control flap-wise bending of the blade, whilst the leading edge flap can be used to counter additional pitching moment created by the trailing edge flap. A floating 10-MW rotor was considered next, as well as forced yaw and pitch oscillations of the machine. The results showed large variations in thrust and power as the wind turbine pitched about a point located 119m below the rotor. The vortex ring state was also encountered when the wind turbine was forced to a pitching motion with amplitude of 5° and period of 8.8s. A coupled method for the analysis of the dynamics of floating off-shore wind turbines was finally described, along with the test cases and numerical parameters. The results of decoupled and coupled computations are presented and analysed. The results showed that the employed floating turbine under studied conditions did not enter a vortex ring state. A turbulent wake state was encountered, but only at the initial pitching phase. The gyroscopic effects were also small for studied system, and did not cause significant rotations due to large inertia of the employed floater

Flow of red blood cells through microchannel with a confluence

Micro-visualization techniques have been used to investigate the in vitro blood flow through straight glass capillaries. Although the glass microchannels present certain similarities to in vivo microcirculation, it is also clear that these kind of in vitro experiments differ from microvessels in several respects, such as: elasticity of microvessels, effect of the endothelial surface layer and microvascular networks composed with short irregular vessel segments which are linked by numerous bifurcations and convergences. Thus it was not surprising that several studies on blood flow in glass microtubes and in microvessels have yielded conflicting results with respect to blood viscosity and flow resistance. The main purpose of this work is to improve our understanding about the effect of a confluence on the rheological properties of in vitro blood. The flow behaviour of both pure water (PW) and dextran 40 (Dx40) containing about 14% (14Hct) of human red blood cells (RBCs) will be investigated by means of a confocal micro-PTV system. The experimental measurements obtained will be compared numerically by using the commercial finite element software package POLYFLOW® and different constitutive models to describe the rheology of the blood, namely: constant viscosity, power-law model and Carreau model

10-MW wind turbine performance under pitching and yawing motion

The possibility of a wind turbine entering vortex ring state (VRS) during pitching oscillations is explored in this paper. The work first validated the employed computational fluid dynamics (CFD) method, and continued with computations at fixed yaw of the NREL phase VI wind turbine. The aerodynamic performance of the rotor was computed using the helicopter multiblock (HMB) flow solver. This code solves the Navier–Stokes equations in integral form using the arbitrary Lagrangian–Eulerian formulation for time-dependent domains with moving boundaries. With confidence on the established method, yawing and pitching oscillations were performed suggesting partial vortex ring state during pitching motion. The results also show the strong effect of the frequency and amplitude of oscillations on the wind turbine performance

Coupled NS/SPH Analysis of Off-Shore Wind Turbine

This paper presents results of numerical computations for floating off-shore wind turbines (FOWTs) using, as an example, a machine of 10-MW rated power. The aerodynamic loads on the rotor are computed by the Helicopter Multi-Block (HMB2) flow solver developed at University of Liverpool. HMB2 solves the Navier-Stokes equations in integral form using the arbitrary Lagrangian-Eulerian formulation for time-dependent domains with moving boundaries. Hydrodynamic loads on the support platform are computed using the Smoothed Particle Hydrodynamics (SPH) method, which is mesh-free and represents the water and floating structures by a set of discrete elements, referred to as particles. The motion of the FOWT is predicted using a multi-body dynamic model (MBDM) of rigid bodies and frictionless joints. Mooring cables are modelled as a set of springs and dampers. All solvers were validated separately before coupling, and the results are presented in this work. The importance of coupling is assessed and information about coupling algorithms is presented. The loosely coupled algorithm used in present work is described in details alongside the obtained results

Flow of red blood cells through microchannel with a confluence

Over the years micro-visualization techniques have been used to investigate in vitro blood flow through straight microchannels with dimensions close to in vivo capillaries. However, a few detailed studies have been performed in complex in vitro microvascular networks composed by diverging and converging bifurcations. The main purpose of present work is to show the application of a confocal micro-PTV system to track both flourescent particles and red blood cells (RBCs) through a rectangular polydimethysiloxane (PDMS) microchannel with a confluence. The measurements of the flow behaviour of trace particles suspended in pure water and RBCs in concentrated suspensions were performed in the surroundings of a confluence. After performing simulations with the commercial finite element software package POLYFLOW®, some experimental results were compared with the numerical ones. Experimental results for pure water were in a good agreement with numerical results. Overall, the RBCs velocities were higher than those for fluorescent particles which suggest that RBC deformability and cell-free layer formation around the apex of the confluence may play an important role on the observed deviationsThe authors acknowledge the financial support provided by: PTDC/SAU-BEB/108728/2008 and PTDC/EME-MFE/099109/2008 from the FCT (Science and Technology Foundation) and COMPETE, Portugal

Flow of red blood cells in capillary networks

In the present work we have studied the flow of red blood cells through a column packed with soda lime glass spheres with diameter of 337.5 micron (pore diameter 150 micron). The ratio between the average velocity of the RBCs and the average velocity of the carrying fluid (physiological saline) was close to 0.9. The RBCs migrated faster through the column than the carrying fluid mainly due to a hydrodynamic chromatographic effect