An Eigenvalue Analysis of Damping in Optical Thin Plasmas

In this work, the behaviour of magneto-hydrodynamic waves in optically thin plasmas considering dissipative processes, thermal and magnetic diffusion, a given ionization, and the heating and cooling functions are investigated for several particular cases. A numerical eigenvalues analysis of the dimensionless secular equations according to various cases is performed for the entire set of MHD equations.

Spanwise-coherent hydrodynamic waves around flat plates and airfoils

We investigate spanwise-coherent structures in the turbulent flow around airfoils, motivated by their connection with trailing-edge noise. We analyse well-resolved large-eddy simulations (LES) of the flow around NACA 0012 and NACA 4412 airfoils, both at a Reynolds number of 400 000 based on the chord length. Spectral proper orthogonal decomposition performed on the data reveals that the most energetic coherent structures are hydrodynamic waves, extending over the turbulent boundary layers around the airfoils with significant amplitudes near the trailing edge. Resolvent analysis was used to model such structures, using the mean field as a base flow. We then focus on evaluating the dependence of such structures on the domain size, to ensure that they are not an artefact of periodic boundary conditions in small computational boxes. To this end, we performed incompressible LES of a zero-pressure-gradient turbulent boundary layer, for three different spanwise sizes, with the momentum-thickness Reynolds number matching those near the airfoils trailing edge. The same coherent hydrodynamic waves were observed for the three domains. Such waves are accurately modelled as the most amplified flow response from resolvent analysis. The signature of such wide structures is seen in non-premultiplied spanwise wavenumber spectra, which collapse for the three computational domains. These results suggest that the spanwise-elongated structures are not domain-size dependent for the studied simulations, indicating thus the presence of very wide structures in wall-bounded turbulent flows.

A quantum hydrodynamical model of skyrmions with electrical dipole moments and novel magneto-electric skyrmion Hall effect

To introduce novel ways of manipulating the skyrmion dynamics we need to develop new fundamental models. Many-particle quantum hydrodynamics allows us to study inter-skyrmion interactions in the approximation of point-particle skyrmions, which were discovered in multiferroic insulators, where the spiral magnetic structure is accompanied by a finite electric dipole moment. We propose a new model of many-particle quantum hydrodynamics for dipolar skyrmions with dipole–dipole interaction, in the presence of electric and magnetic field gradients. Based on the developed model we find a new way to control the positions of skyrmions, using the crossed gradients of magnetic and electric fields or a novel magneto-electric Hall effect. We have shown that the influence of non-uniform magnetic field provides circular motion of the dipolar skyrmion in the plane with the frequency determined by the derivative of the external magnetic field and the amplitude of the dipole moment. We study the wave processes in the system of skyrmions. We investigate hydrodynamic waves in a skyrmion gas in crossed non-uniform electric and magnetic fields, and predict the generation of a new type of hydrodynamic waves and instabilities. Also, we predict a new type of polarization waves in a rigid skyrmion gas with the dipole–dipole interaction.