Kazuto Kuzuu

Numerical simulation of premixed flame propagation in a closed tube

Premixed flame propagation of methane-air mixture in a closed tube is estimated through a direct numerical simulation of the three-dimensional unsteady Navier-Stokes equations coupled with chemical reaction. In order to deal with a combusting flow, an extended version of the MAC method, which can be applied to a compressible flow with strong density variation, is employed as a numerical method. The chemical reaction is assumed to be an irreversible single step reaction between methane and oxygen. The chemical species are CH4, O2, N2, CO2, and H2O. In this simulation, we reproduce a formation of a tulip flame in a closed tube during the flame propagation. Furthermore we estimate not only a two-dimensional shape but also a three-dimensional structure of the flame and flame-induced vortices, which cannot be observed in the experiments. The agreement between the calculated results and the experimental data is satisfactory, and we compare the phenomenon near the side wall with the one in the corner of the tube.

Real time visualization of flow fields using open GL system

We, introduce a newly developed flow visualization system. This system was designed so that we could observe progress in a flow calculation. In particular, a visualization process of this system automatically reads renewal data from a flow calculation process in a specific mode. This faculty could not have been realized on a conventional PC system whose OS was based on a 16 bit process. The present visualization system built on a 32 bit OS, Windows NT, removes this problem by means of a preemptive multi-task facil i ty equipped with the OS. Furthermore, an improvement of MPU performance and Open GL realize a true real time visualization in this system. In this paper, we discuss prospects of a real time flow simulation from some examples of an actual use and its operation time.

Numerical simulation of flame-flow interaction in enclosures

The flame-flow interaction that occurred in a combustion vessel was investigated through a DNS (Direct Numerical Simulation) method. Calculations were carried out based on the three-dimensional full Navier-Stokes equations coupled with a single step chemical reaction model. The working gas is a methene-air mixture, and chemical species are limited to CH^, O^, NZ, COz and H2O. In order to reproduce the interaction in this simulation, we put an orifice plate into the vessel. This plate played a role as a vortex generator, and we could manage to observe the phenomena by means of this system. In this study, we tried to estimate differences of the flow fields by strength of generated vortices. For this purpose, we set four sizes of orifices, and then compared each result. In particular, we focused on the estimation of changes of vorticity distributions during a combustion process. The major characteristic was vorticities rapidly decreased after the passage of the flame. As a result, we found that this effect reduces disturbances in the vessel.

Effect of vessel shapes and boundary conditions on premixed flame propagation

The behavior of premixed flame propagation in a closed vessel is investigated through a direct numerical simulation of the three-dimensional unsteady Navier-Stokes equations coupled with chemical reaction rate equations. We made calculations regarding various types of boundary conditions and vessel configurations. Prom our results, it is confirmed that the transformation process of a premixed flame is strongly affected by wall boundary layers and flame-flow interactions. In particular, an expansion flow induced by combustion has a complicated three-dimensional structure in a vessel. We observed some interactions between a flame and a flow field. In this study, we employed an extended version of the MAC method as a numerical scheme. This method can be applied to a compressible flow condition where strong density variations exist, but effects of the speed of sound are small enough. A chemical reaction is assumed to be an irreversible single step reaction between methane and oxygen, and chemical species are limited to CH^, O%, N%, and H2O.

NUMERICAL SIMULATION OF COMBUSTING FLOW AROUND A DROPLET

The combusting flow around a droplet was investigated through a direct numerical simulation method. The purpose of this simulation was to understand the relationship between droplet combustion and flow field. Calculation was based on the three-dimensional full Navier-Stokes equations coupled with a single step chemical reaction model. Although the situation corresponded to a compressible flow problem, free stream velocity was so small that zero Mach number approximation was employed in the solution. The droplet was liquid octane, and the composition of free stream gas was equal to that of air. The temperature of the droplet was assumed to be constant, and then we considered only a gas-phase combustion process. Calculations were carried out under some free stream conditions, velocity and temperature. From our results, we found that there were two characteristic tendencies about droplet combustion. One was the fact that although large free stream velocity enhanced the heat release of chemical reaction, temperature distribution around the droplet was not so severe. On the other hand, effects of free stream temperature on the combustion was sensitive in lower temperature conditions.

Direct numerical simulation of combusting flow around a droplet

The burning of a spherical fuel particle was investigated through a direct numerical simulation based on the three-dimensional full Navier-Stokes equations. In this study, we focused on effects of forced convection on a burning speed and a flame shape. Liquid fuel was octane, and a chemical reaction was assumed to be a single step irreversible process between gaseous octane and oxygen. Results showed the d-square law. a fundamental behavior of droplet combustion, and we observed typical differences of flame shapes by strength of forced convection as well. Furthermore, the evaporation constants of a droplet were in good agreement with theoretical values at small convection velocities. On the other hand, we managed to reproduce a situation that theoretical values based on spherically symmetrical assumptions are incorrect at large convection velocities.