Improving the H-Darrieus rotor is often followed by the investigation of the influence of the turbine’s parameter design, notably, the aspect ratio, the solidity ( σ), the tip speed ratio, and the airfoil profile shape. In this work, we are interested in both the aerodynamic flows around a straight cambered blade profile and the rotor turbine wake separation of a Darrieus vertical axis wind turbine. The aim of this study is to better understand the evolution of the instantaneous torque and the generated-separated blade vortex during full rotation. Indeed, a three-dimensional computational fluid dynamics model of a vertical axis wind turbine with a straight cambered blade profile NACA4312 operating over a large range of tip speed ratio is considered. The flows are governed by Reynolds-averaged Navier–Stokes equations and the turbulence is modeled with shear stress transport formulations k- ω. This research revealed a high correlation between the evolution of the torque coefficient and the generated-separated blades vortex. In particular, a good correlation between the maximum tip vortices size and the torque coefficient peak is demonstrated.

This study demonstrates the ability to follow the change in morphology and hydration of an IVD using MR measurements, thereby providing valued information for a better understanding of IVD function.

Quantitative magnetic resonance imaging (MRI) provides useful information about intervertebral disc (IVD) biomechanical properties, especially those in relation to the fluid phase. These properties may improve IVD finite element (FE) models using data closer to physiological reality. The aim of this study is to investigate IVD degeneration-related properties using a coupling between MRI and FE modeling. To this end, proton density ([Formula: see text])-weighted MRI sequences of a porcine lumbar IVD were carried out to develop two biphasic swelling models with hyperelastic extracellular matrix behavior. The first model is isotropic, and the second one is anisotropic and takes into account the role of collagen fibers in the mechanical behavior of the IVD. MRI sequences permitted to determine the geometry and the real porosity mapping within the disc. The differentiation between disc components (nucleus pulposus, annulus fibrosus and cartilaginous end plates) was taken into account using spatial continuous distributions of the mechanical properties. The validation of the FE models was performed through two steps: the identification of the model's mechanical properties using relaxation compressive test and the comparison between the MRI after load porosity distributions and those numerically obtained using the set of identified properties. The results confirmed that the two developed FE models were able to predict the mechanical response of uniaxial time-dependent compressive test and the redistribution of porosity after load. A slight difference between the measured and the numerical local bulges of the disc was found. This study suggests that from the coupling between MRI imaging in different state of load and finite element modeling we can deduce relevant information that can be used in the assessment of the early intervertebral disc degeneration changes.

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The cyclic variations of the Angle of Attack (AoA) during the operation of H-Darrieus VAWT bring them to operate under fatigue-type loads which stakes the blade’s endurance and the lifetime of the wind turbines. At low wind speed, the AoA exceeds the stall angle and causes significant variations in aerodynamic loads on the blades. This behavior is considered one of the most recognized weaknesses of VAWT technology. To mitigate these cyclic variations, one of the approaches adopted is to prescribe either a fixed or dynamic control pitching angle to the rotor blades that prevent them from having too large AoAs. This research aims to investigate the effect of several dynamic pitch angle strategies on the aerodynamic behavior of the H-Darrieus rotor. Four pitch control strategies were pursued to explore the effect of the pitch angle on the H-Darrieus performance and the angle of attack. A novel modified pitch control strategy has been adopted to monitor the rate of change of blade direction that is relative to the incoming wind flow. Insight was devoted to investigating the impact of this parameter on the performance and self-starting capabilities of the H-Darrieus rotor, at optimum and low wind speed. 3D unsteady lifting line free vortex wake-based model was performed. The results revealed two ranges of values for the setting parameter for which the produced torque followed an increasing and decreasing trend and which is still higher than the non-pitched blades. Furthermore, at the optimal TSR, dynamic pitching control showed no significant effect on the VAWT performance, as less than 3% was achieved. At low TSR, the torque increased almost six times as compared to the fixed and zero-pitched blades.

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