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This work presents a coupled numerical methodology, based on a hybrid Navier-Stokes (NS) and Direct Simulation Monte Carlo (DSMC) method, for high-speed compressible gas flows—involving a combination of continuum and rarefied flow regions. Implementation details of coupling cycle are presented along with the validation and performance studies for three cases (Mach number M a 1 = 3.38 , 6.5 and 9) of normal shock waves in argon and three cases (Inlet pressure pin = 1.0 atm, 0.5 atm and 0.1 atm) of flow through a micro-scale convergent-divergent (CD) nozzle. In comparison with our DSMC method-based solutions in the complete domain, the hybrid NS-DSMC method solutions achieve almost similar accuracy in a substantially reduced computational time—44% to 50% for the normal shock problem and 67% to 85% for the micro-scale CD nozzle problem. For the first time in literature, the hybrid NS-DSMC method is presented as a Cartesian-grid method, which is becoming popular nowadays. [ABSTRACT FROM AUTHOR]

Background: Seed preservation in the context of changing climatic conditions and retaining quality is a big challenge, especially for marginal farmers who does not have appropriate seed storage facilities. Moisture and temperature variations (both seasonal and diurnal) during storage result in moulds, bacteria, insects, mites and rodents attacks. Tropical regions with higher ambient temperatures and relative humidity variations need to address the storage issue. Methods: This research work discusses the process of design, fabrication and testing of a low-cost seed storage unit (SSU) for community-based seed banks. The SSU of 200 L storage capacity was cooled using a thermoelectric cooler (TEC) to provide the temperature range of 15°C to 18°C and relative humidity <70% inside the SSU. The SSU was field-tested at fourteen different agro-climatic locations for seeds of paddy (Oryza sativa), gram (Cicer arietinum), onion (Allium cepa), groundnut (Arachis hypogaea) and maize (Zea mays) during the period 18 months between 2017 to 2019. These seeds were tested for germination count (GC) and moisture content (MC). Result: Results obtained indicated that the SSU developed can retain essential seed quality parameters i.e. more than 80% germination count (GC), except for groundnut seeds over a period of 18 months as against loss of seed viability in 8 months’ time in traditional storage at ambient temperature. Based on the field performance testing, we recommend the use of such devices for farmers’ and farmers’ producer companies for a decentralised seed storage capacity of 100 to 200 kg. [ABSTRACT FROM AUTHOR]

A new ab initio based chemical model for a Direct Simulation Monte Carlo (DSMC) study suitable for simulating rarefied flows with a high degree of non-equilibrium is presented. To this end, Collision Induced Dissociation (CID) cross sections for N2 +N2 → N2 + 2N are calculated and published using a global complete active space self-consistent field-complete active space second order perturbation theory N4 potential energy surface and quasi-classical trajectory algorithm for high energy collisions (up to 30 eV). CID cross sections are calculated for only a selected set of ro-vibrational combinations of the two nitrogen molecules, and a fitting scheme based on spectroscopic weights is presented to interpolate the CID cross section for all possible ro-vibrational combinations. The new chemical model is validated by calculating equilibrium reaction rate coefficients that can be compared well with existing shock tube and computational results. High-enthalpy hypersonic nitrogen flows around a cylinder in the transition flow regime are simulated using DSMC to compare the predictions of the current ab initio based chemical model with the prevailing phenomenological model (the total collision energy model). The differences in the predictions are discussed. [ABSTRACT FROM AUTHOR]

Collision-induced dissociation cross section database for high energy O2–O2 collisions (up to 30 eV) is generated and published using the quasiclassical trajectory method on the singlet, triplet, and quintet spin ground state O4 potential energy surfaces. At equilibrium conditions, these cross sections predict reaction rate coefficients that match those obtained experimentally. The main advantage of the cross section database based on ab initio computations is in the study of complex flows with high degree of non-equilibrium. Direct simulation Monte Carlo simulations using the reactive cross section databases are carried out for high enthalpy hypersonic oxygen flow over a cylinder at rarefied ambient conditions. A comparative study with the phenomenological total collision energy chemical model is also undertaken to point out the difference and advantage of the reported ab initio reaction model. [ABSTRACT FROM AUTHOR]

High-resolution extensions to six Riemann solvers and three flux vector splitting schemes are developed within the framework of a reconstruction-evolution approach. Third-order spatial accuracy is achieved using two different piecewise parabolic reconstructions and a weighted essentially nonoscillatory scheme. A three-stage TVD Runge-Kutta time stepping is employed for temporal integration. The modular development of solvers provides an ease in selecting a reconstruction scheme and/or a Riemann solver/flux vector splitting scheme. The performances of these high-resolution solvers are compared for several one- and two-dimensional test cases. Based on a comprehensive assessment of the solutions obtained with all solvers, it is found that the use of the weighted essentially nonoscillatory reconstruction with the van Leer flux vector splitting scheme provides solutions for a variety of problems with acceptable accuracy. [ABSTRACT FROM AUTHOR]

Two-dimensional direct simulation Monte Carlo (DSMC) was used to investigate the effect of wall accommodation on different modes of operation of a nozzle under high Knudsen number conditions. Substantial performance enhancement was seen at higher values of converging–diverging angles, because a reduction in the surface area-to-volume ratio decreased the wall effects. Though the normal energy accommodation had a negligible influence on the nozzle performance, it was seen to be a critical factor for accurate prediction of gas temperature along the wall. At higher Knudsen numbers, the flow tended to become one-dimensional even for the case of complete accommodation. [ABSTRACT FROM PUBLISHER]

Collision-induced dissociation cross section database for high energy O 2 -O 2 collisions (up to 30 eV) is generated and published using the quasiclassical trajectory method on the singlet, triplet, and quintet spin ground state O 4 potential energy surfaces. At equilibrium conditions, these cross sections predict reaction rate coefficients that match those obtained experimentally. The main advantage of the cross section database based on ab initio computations is in the study of complex flows with high degree of non-equilibrium. Direct simulation Monte Carlo simulations using the reactive cross section databases are carried out for high enthalpy hypersonic oxygen flow over a cylinder at rarefied ambient conditions. A comparative study with the phenomenological total collision energy chemical model is also undertaken to point out the difference and advantage of the reported ab initio reaction model.