This study presents a numerical investigation of the aerodynamic and aeroacoustics behavior of side-by-side rotors in proximity to the ground. The configuration developed in the European H2020 project ENODISE is used as a reference. It features two counter-rotating APC 6x4 propellers, positioned at a height H/R = 2 above the ground, where R is the propeller radius, with a tip-to-tip distance S/R = 2, operating at a rotational speed of 167 Hz. Scale-resolved simulation is carried out using the Lattice-Boltzmann/Very-Large-Eddy-Simulation CFD solver SIMULIA PowerFLOW®. Analysis of the data describes the spatio-temporal of the flow field and describes in detail the bi-stable behavior of wake in the presence of the ground, which is then re-ingested by the rotor disks. This motion, occurring at a frequency two orders of magnitude lower than the rotor blade passing frequency, is similar to what was found experimentally. In addition, the present work shows the impact of this phenomenon on far-field noise by comparing sound pressure levels (SPL) pre- and post-re-ingestion in a semi-spherical manner. The findings reveal a significant increase in SPL across a broad frequency range as the occurrence of the re-ingestion.@en

Nanoparticles are usually fluidized as agglomerates, which are in dynamic states of agglomeration and fragmentation. It is critical to consider the size distribution of agglomerates in modeling of the fluidization of nanoparticle agglomerates. In this article, the fluidization behavior of nanoparticle agglomerates is investigated using a two-fluid model─population balance model. The model includes the agglomeration and breakage kernel functions based on the continuum theory of cohesive particles developed by Kellogg et al. (J. Fluid Mech. 2017;832:345-382). The ratio of the critical breakage velocity to the critical agglomeration velocity is defined to represent the cohesion of nanoparticles. The predictions of bed pressure drop, bed expansion ratio, and bed collapse curves agree well with those of experiments. By changing the critical agglomeration velocity and the ratio between the critical velocities, the transition from almost defluidization to uniform fluidization is predicted. Finally, the model’s ability to simulate the fluidization of fine particles with a few micrometers is also shown. This study provides a practical tool for simulating the fluidization of nanoparticle agglomerates.

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Correction Notice 1. The vertical axis ticks in the subfigures of Fig 10 should be reverted to align with the global coordinate system of the simulation domain. The updated figure is presented below. Not the one presented in the original manuscript. (Figure Presented).

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This article presents a comparison study of different aerodynamic models for an X-shaped vertical-axis wind turbine and offers insight into the 3D aerodynamics of this rotor at fixed pitch offsets. The study compares six different numerical models: a double-multiple streamtube (DMS) model, a 2D actuator cylinder (2DAC) model, an inviscid free vortex wake model (from CACTUS), a free vortex wake model with turbulent vorticity (from QBlade), a blade-resolved unsteady Reynolds-averaged Navier–Stokes (URANS) model, and a lattice Boltzmann method (from PowerFLOW). All models, except URANS and PowerFLOW use the same blade element characteristics other than the number of blade elements. This comparison covers the present rotor configuration for several tip-speed ratios and fixed blade pitch offsets without unsteady corrections, except for the URANS and PowerFLOW which cover a single case. The results show that DMS and 2DAC models are inaccurate – especially at highly loaded conditions, are unable to predict the downwind blade vortex interaction, and do not capture the vertical/axial induction this rotor exhibits. The vortex models are consistent with each other, and the differences when compared against the URANS and PowerFLOW mostly arise due to the unsteady and flow curvature effects. Furthermore, the influence of vertical induction is very prominent for this rotor, and this effect becomes more significant with fixed pitch offsets where the flow at the blade root is considerably altered.@en