Double-distribution-function discrete Boltzmann model for combustion

A 2-dimensional discrete Boltzmann model for combustion is presented. Mathematically, the model is composed of two coupled discrete Boltzmann equations for two species and a phenomenological equation for chemical reaction process. Physically, the model is equivalent to a reactive Navier-Stokes model supplemented by a coarse-grained model for the thermodynamic nonequilibrium behaviours. This model adopts 16 discrete velocities. It works for both subsonic and supersonic combustion phenomena with flexible specific heat ratio. To discuss the physical accuracy of the coarse-grained model for nonequilibrium behaviours, three other discrete velocity models are used for comparisons. Numerical results are compared with analytical solutions based on both the first-order and second-order truncations of the distribution function. It is confirmed that the physical accuracy increases with the increasing moment relations needed by nonequlibrium manifestations. Furthermore, compared with the single distribution function model, this model can simulate more details of combustion.Comment: Accepted for publication in Combustion and Flam

Multiple-Relaxation-Time Lattice Boltzmann Approach to Compressible Flows with Flexible Specific-Heat Ratio and Prandtl Number

A new multiple-relaxation-time lattice Boltzmann scheme for compressible flows with arbitrary specific heat ratio and Prandtl number is presented. In the new scheme, which is based on a two-dimensional 16-discrete-velocity model, the moment space and the corresponding transformation matrix are constructed according to the seven-moment relations associated with the local equilibrium distribution function. In the continuum limit, the model recovers the compressible Navier-Stokes equations with flexible specific-heat ratio and Prandtl number. Numerical experiments show that compressible flows with strong shocks can be simulated by the present model up to Mach numbers $Ma \sim 5$.Comment: Accepted for publication in EP

Theory and Application of No-Till Reseeding Technology in Degraded Grasslands in China

Grasslands occupy nearly 400 million hectares in China, accounting for about 40.7% of the total land area, provide multiple ecological and economic benefits. However, due to over-grazing and over-cultivation, more than 90% grasslands in China are threatened by degradation that has caused significant negative impact on biodiversity and ecosystem functioning, such as biodiversity losses, decreased productivity, increased soil erosion etc. Thus, restoration of degraded grassland is urgent for sustainable grassland management in China. No-till reseeding has been found to be an effective way for grassland vegetation regeneration with improved productivity and increased plant diversity via reseeding suitable species with minimum disturbance for the soil. Here, we present a conceptual framework integrating plant-soil feedback theory and subclimax management model. We show that field experiments with reseeding legumes into the degraded grasslands can restore forage production and plant diversity in degraded grassland. We also applied the no-till reseeding technology in degraded grasslands in China, such as Shanxi, Gansu, Qinghai and found that reseeding leguminous and gramineous forages are effective in improving productivity and nutritional quality of degraded grassland in China. Overall, no-till reseeding is an effective way in restoring degraded grassland and could play an important role for sustainable grassland management in China