Toru Ishikawa

Hybrid Particle/Grid Method for Predicting Motion of Micro- and Macrofree Surfaces

We developed a method of hybrid particle/cubic interpolated propagation (CIP) to predict the motion of micro- and macrofree surfaces within gas-liquid flows. Microfree surfaces (smaller than the grid sizes) were simulated with the particle method, and macrofree surfaces (larger than the grid sizes) were simulated with the grid method (CIP is a kind of grid method). With the hybrid, velocities given by the advection part of the particle method were combined with those given by the advection part of CIP. Furthermore, the particles used with the particle method were assigned near the macrofree surfaces by using the volume fraction of liquid that was calculated with CIP. The method we developed was used to predict the collapse of a liquid column. Namely, it was simultaneously able to predict both large deformation in the liquid column and its fragmentation, and the predicted configurations for the liquid column agreed well with the experimentally measured ones. It was also used to predict the behavior of liquid films at the outlet of a fuel injector used for automobile engines. The particle method in the simulation was mainly used for liquid films in the air region and the grid method was used for the other regions to shorten the computational time. The predicted profile of the liquid film was very sharp in the air region where the liquid film became thinner than the grid sizes; there was no loss of liquid film with numerical diffusion.

Simulation of Liquid Jet Breakup of a Swirl-Type Fuel Injector for Automobile Engines

To simulate multi-scale free surfaces, we developed a hybrid particle/grid method by which the free surfaces within sub-grid regions are simulated by the particle method, and other regions are simulated with the grid method. The particle method uses two types of particles to model gas and liquid fluids in order to simulate the interaction between them. We tested the new method on fragmentation of a water column, and the predicted configurations of the water column are consistent with measurements of Koshizuka and Oka. We also simulated the fuel spray near the outlet of an automobile-engine fuel injector and found that this method qualitatively simulated the breakup of the liquid film.Copyright

Fuel Spray Pattern Control Using L-Step Nozzle for Swirl-Type Injector

We propose a spray pattern control method for swirl-type injectors in direct injection (Dl) gasoline engines. An L-cut orifice nozzle (L-Step nozzle) that produces a horseshoe spray pattern is used to create a rich and lean concentration region. To further control the distribution of fuel, the relationship between the nozzle geometry and the spray pattern is investigated. The mechanism for a horseshoe spray formation is hypothesized and verified through experiment. The spray shape and fuel distribution is found to be controllable by configuring the L-cut step-walls. Furthermore, it is discovered that independent control of rich and lean region distribution is possible by arranging the step-wall position and height.

Simulation of Liquid Jet Breakup Using a Combination of Particle and Grid Methods

Fine atomization of the liquid jet from a fuel injector in an automobile engine lowers engine emissions and improves fuel efficiency. The breakup length of liquid films and the lengths of ligaments near the injector outlet after the breakup of liquid films are important parameters for predicting the atomization. These parameters have been predicted mainly using the Eulerian-grid method. (We refer to this as the ‘grid method’.) However, the grid method causes a loss of the liquid film with numerical diffusion, and it requires a large amount of computation time in practical engineering aspect because fine meshes smaller than the ligaments must be used. On the other hand, the particle method, an alternative (particle-based) method for representing the continuum Navier-Stokes equation which can simulate a ligament using a group of particles, does not cause numerical diffusion. However, a large number of particles are needed to simulate the entire computational domain within the injectors. In this study, we have focused on the flow field only near the injector outlet, and have tried to simulate the breakup of liquid films by using groups of particles in the particle method. In the simulation, the particle method was applied only to the liquid film and the grid method was used in other regions to shorten the computation time. Furthermore, we tried to integrate Brackbill’s surface-tension model, which is widely used in the grid method, into the particle method. To evaluate this approach, we compared the breakup lengths obtained for a cylindrical liquid jet in a uniform air stream with measurements done by Arai and Hashimoto; the breakup lengths agreed well with their measurements. We then simulated the breakup of a liquid film near the outlet of a fuel injector used for automobile engine, and found that our hybrid method could simulate the breakup of the liquid film into ligaments.Copyright

Particle/CIP Hybrid Method for Predicting Motions of Micro and Macro Free Surfaces

To predict motions of micro and macro free surfaces simultaneously within gas-liquid flows, we have developed a particle/CIP (Cubic Interpolated Propagation) hybrid method. The micro free surfaces (smaller than grid sizes) were simulated by the particle method, and the macro free surfaces (larger than grid sizes) were simulated by the CIP method. And then the particles used in the particle method were assigned near the macro free surfaces by using volume fraction of liquid that was calculated by the CIP method. The developed method was used to predict the collapse of a liquid column. Namely, it predicted both the large deformation of the liquid column and the fragmentation of it simultaneously, and the predicted configurations of the liquid column agreed well with the experimentally measured ones. It was also used to predict breakup of liquid films in a fuel injector used for engines of automobiles, and the predicted profile of the liquid film was sharp in an air region where the thickness of the liquid film became thinner than the grid sizes.© 2004 ASME