Modulation of fluid temperature fluctuations by particles in turbulence

Modulation of fluid temperature fluctuations by particles due to thermal interaction in homogeneous isotropic turbulence is studied. For simplicity, only thermal coupling between the fluid and particles is considered, and momentum coupling is neglected. Application of the statistical theory used in cloud turbulence research leads to the prediction that modulation of the intensity of fluid temperature fluctuations by particles is expressed as a function of the Damköhler number, which is defined as the ratio of the turbulence large-eddy turnover time to the fluid thermal relaxation time. Direct numerical simulations are conducted for two-way thermal coupling between the fluid temperature field and point particles in homogeneous isotropic turbulence. The simulation results are shown to agree well with the theoretical predictions.

Experimental demonstration of cylindrical vector spatiotemporal optical vortex

We experimentally generate cylindrically polarized wavepackets with transverse orbital angular momentum, demonstrating the coexistence of spatiotemporal optical vortex with spatial polarization singularity. The results in this paper extend the study of spatiotemporal wavepackets to a broader scope, paving the way for its applications in various areas such as light–matter interaction, optical tweezers, spatiotemporal spin–orbit angular momentum coupling, etc.

Solitons in spin-tensor–momentum-coupled Bose–Einstein condensates

Recently spin-tensor–momentum coupling (STMC) has been proposed to realize in the Bose–Einstein condensate (BEC). Here, we study the bright soliton in spin-1 three components BEC with STMC. The properties of the bright solitons are discussed by the analytical solutions and numerical solutions. In addition, we also study its dynamic evolution and discover the spontaneous motion, which is different from the spin-orbit-coupled solitons.

Homogenization of piezoelectric planar Willis materials

Homogenization theories provide models that simplify the constitutive relations of heterogeneous media while retaining their macroscopic features. These theories have shown how the governing fields can be macroscopically coupled, even if they are microscopically independent. A prominent example is the Willis theory which predicted the strain-momentum coupling in elastodynamic metamaterials. Recently, a theory that is based on the Green’s function method predicted analogous electro-momentum coupling in piezoelectric metamaterials. Here, we develop a simpler scheme for fibrous piezoelectric composites undergoing antiplane shear waves. We employ a source- driven approach that delivers a unique set of effective properties for arbitrary frequency-wavevector pairs. We numerically show how the resultant homogenized model recovers exactly the dispersion of free waves in the composite. We also compute the effective properties in the long-wavelength limit and off the dispersion curves, and show that the resultant model satisfy causality, reciprocity and energy conservation. By contrast, we show how equivalent models that neglect the electromomentum coupling violate these physical laws.

Simulation and analysis of an aero-engine combustor with a slinger fuel injection system

The use of Computational Fluid Dynamics (CFD) is now central to the design process of aero-engine combustors, enabling optimal, safe and stable operation, increased efficiencies, and the reduction of pollutant emission. To benefit maximally from the use of CFD it is essential to account for the relevant physical phenomena, in particular the fuel spray breakup and its evaporation. Different strategies for modelling the injection of fuel spray are applied - in the simplest approach the fuel is assumed to be gaseous upon injection, in the most advanced approach the fuel is modelled, using a Lagrangian-Eulerian approach, as a liquid spray which breaks up, evaporates and eventually burns inside the combustion chamber. The effects of the various modelling strategies on the flow, temperature, and compositional fields are investigated. The radial distribution of the simulated temperature field is compared to experimental data, demonstrating that acceptable accuracy is only achieved when the fuel is modelled as a liquid spray and a two-way momentum coupling between the spray and the gas-phase is accounted for.