The effects of droplet inertia and turbulent mixing on the droplet number density distribution in a turbulent flow field are studied. A formulation of the turbulent convective diffusion equation for the droplet number density, based on the modified Fully Lagrangian Approach, is proposed. The Fully Lagrangian Approach for the dispersed phase is extended to account for the Hessian of transformation from Eulerian to Lagrangian variables. Droplets with moderate inertia are assumed to be transported and dispersed by large scale structures of a filtered field in the Large Eddy Simulation (LES) framework. Turbulent fluctuations, not visible in the filtered solution for the droplet velocity field, induce an additional diffusion mass flux and hence additional dispersion of the droplets. The Lagrangian formulation of the transport equation for the droplet number density and the modified Fully Lagrangian Approach (FLA) make it possible to resolve the flow regions with intersecting droplet trajectories in the filtered flow field. Thus, we can cope successfully with the problems of multivalued filtered droplet velocity regions and caustic formation. The spatial derivatives for the droplet number density are calculated by projecting the FLA solution on the Eulerian mesh, resulting in a hybrid Lagrangian-Eulerian approach to the problem. The main approximations for the method are supported by the calculation of droplet mixing in an unsteady one-dimensional flow field formed by large-scale oscillations with an imposed small-scale modulation. The results of the calculations for droplet mixing in decaying homogeneous and isotropic turbulence are validated by the results of Direct Numerical Simulations (DNS) for several values of the Stokes number.
The unique aroma and flavor of oolong tea develop during the withering stage of postharvest processing. We explored the roles of miRNA-related regulatory networks during tea withering and their effects on oolong tea quality. We conducted transcriptome and miRNA analyses to identify differentially expressed (DE) miRNAs and target genes among fresh leaves, indoor-withered leaves, and solar-withered leaves. We identified 32 DE-miRNAs and 41 target genes involved in phytohormone signal transduction and ABC transporters. Further analyses indicated that these two pathways regulated the accumulation of flavor-related metabolites during tea withering. Flavonoid accumulation was correlated with the miR167d_1-ARF-GH3, miR845-ABCC1-3/ABCC2, miR166d-5p_1-ABCC1-2, and miR319c_3-PIF-ARF modules. Terpenoid content was correlated with the miR171b-3p_2-DELLA-MYC2 and miR166d-5p_1-ABCG2-MYC2 modules. These modules inhibited flavonoid biosynthesis and enhanced terpenoid biosynthesis in solar-withered leaves. Low auxin and gibberellic acid contents and circRNA-related regulatory networks also regulated the accumulation of flavor compounds in solar-withered leaves. Our analyses reveal how solar withering produces high-quality oolong tea.
The fully Lagrangian approach (FLA) to the calculation of the number density of inertial particles in dilute gas-particle flows is implemented into the CFD code ANSYS Fluent. The new version of ANSYS Fluent is applied to modelling dilute gas-particle flow around a cylinder and liquid droplets in a gasoline fuel spray. In a steady-state case, the predictions of the FLA for the flow around a cylinder and those based on the equilibrium Eulerian method (EE) are almost identical for small Stokes number, Stk, and small Reynolds number, Re, (Re = 1, Stk = 0.05). For the larger values of these numbers (Re = 10, 100; Stk = 0.1, 0.2) the FLA predicts higher values of the gradients of particle number densities in front of the cylinder compared with the ones predicted by the EE. For transient flows (Re = 200), both methods predict high values of the number densities between the regions of high vorticity and very low values in the vortex cores. For Stk ≥ 0.1 the maximal values predicted by FLA are shown to be several orders of magnitude higher than those predicted by the EE. An application of FLA to a direct injection gasoline fuel spray has focused on the calculation of the number densities of droplets. Results show good qualitative agreement between the numerical simulation and experimental observations. It is shown that small droplets with diameters dp = 2 µm tend to accumulate in the regions of trajectory intersections more readily, when compared with larger droplets (dp = 10 µm, dp = 20 µm). This leads to the prediction of the regions of high number densities of small droplets.KEY WORDS: Gas-particle flow Particle number densities Eulerian approach Fully Lagrangian approach Gasoline fuel sprays.
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