The design of efficient rotor blades is affected by the accuracy of aerodynamic prediction methods for load distributions and power computations. Research showed that the accuracy of BEMT-based industrial codes decreases at high inflow-speed under uniform aligned steady conditions. The identified reasons are inaccuracies in the semi-empirical corrections for 3D effects such as stall delay and tip-losses. This study scrutinizes such corrections by comparison with URANS CFD simulations. Results confirm that the accuracy of the rotor thrust and power coefficients reduces up to 30% for a tip speed ratio of 4. The identified causes in the inboard blade are: (1) a more than twice as large drag coefficient given by the Eggers stall delay correction, (2) a 20% loading overestimation due to the unaccounted root-vortex downwash. Furthermore, the linear interpolation between the cylinder and the DU40 airfoil polars near the root as well as the modeling of 2D separation affect the accuracy at least as much as the stall delay correction at a tip speed ratio of 4. Next, the inadequacy of the Prandtl tip-loss factor at a tip speed ratio of 10 provides 5 to 15% higher loads in the outboard blade. It is recommended to extend stall delay corrections or tune the Prandtl root-loss correction to the location of the maximum chord to capture the root-vortex downwash effect, as the phenomenon is observed on the CFD-extracted lift polar and blade flow streamlines. Finally, 2D RANS simulations of the inboard blade profiles should be compared with the 3D ones from the rotating blade to isolate the effect of stall delay on the pressure and skin friction coefficient distributions to further address the modeling of the drag coefficient.@en

This paper establishes the effect of blade deflections on wind turbine noise directivity. Fast turn-around methods are used in a framework of integrated aeroelastic and aeroacoustic simulations: the blade element momentum theory is coupled with a RANS-informed Amiet's model for the aeroacoustic modelling of trailing-and leading-edge noise. This approach is applied to the NREL 5 MW wind turbine and the results of rigid and flexible blades are compared. The overall sound pressure level computed with flexible blades increases up to 13 dBA for listeners close to the rotor plane. This effect is attributed to the flapwise angular deflection of the wind turbine blade. Furthermore, the symmetry of the results with respect to the rotor plane is lost when the flapwise deflection is considered, indicating that the modelling of this rotation is of fundamental importance for the acoustic simulation.

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Active flow control is demanding for new actuation technologies as none of the actual available actuators has reached all the criterions for expecting an implementation in the coming years. Here, a new type of pulsed jet is designed and preliminary measurements of its performances in quiescent flow are conducted. Pulsed operation has been chosen because of the expected high efficiency of pulsed actuation in comparison to continuous blowing. The traditional pulsed jets being limited in term of frequency because of the use of a mechanical valve to achieve the desired pneumatic opening and closing of a jet provided by an external pressure source, the fast response of electrical discharge is exploited in the present investigation. The objective is to modulate the output of a small jet exhausting from a pressurized chamber. A spark discharge is used to affect the thermodynamic state of the gas in order to electrically achieve periodic cancellation of the chocked flow conditions at the throat upstream the jet exit. In the present study, such actuator with additional neck extension and jet diameter enlargement is investigated. The configuration results in a high-speed subsonic jet whose velocity amplitude is modified by an arc discharge with deposited energy from 18 to 780 mJ. Some characteristics of the jet are provided using optical methods such as high-speed Schlieren and PIV. In particular, it is shown that the jet flow velocity can be increased from 50 m.s-1 to 190 m.s-1.@en

The current energy transition imposes a rapid implementation of energy storage systems with high energy density and eminent regeneration and cycling efficiency. Metal hydrides are potential candidates for generalized energy storage, when coupled with fuel cell units and/or batteries. An overview of ongoing research is reported and discussed in this review work on the light of application as hydrogen and heat storage matrices, as well as thin films for hydrogen optical sensors. These include a selection of single-metal hydrides, Ti–V(Fe) based intermetallics, multi-principal element alloys (high-entropy alloys), and a series of novel synthetically accessible metal borohydrides. Metal hydride materials can be as well of important usefulness for MH-based electrodes with high capacity (e.g. MgH₂ ~ 2000 mA h g⁻¹) and solid-state electrolytes displaying high ionic conductivity suitable, respectively, for Li-ion and Li/Mg battery technologies. To boost further research and development directions some characterization techniques dedicated to the study of M-H interactions, their equilibrium reactions, and additional quantification of hydrogen concentration in thin film and bulk hydrides are briefly discussed.

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