Kazuya Shimizu

Updated Kinetic Mechanism for High-Pressure Hydrogen Combustion

A chemical kinetic model for high-pressure combustion ofH2=O2 mixtures has been developed by updating some of the rate constants important under high-pressure conditions without any diluent. The revised mechanism is validated against experimental shock-tube ignition delay times and laminar flame speeds. Predictions of the present modelarealsocomparedwiththosebyseveralotherkineticmodelsproposedrecently.Althoughpredictionsofthose models (including the present model) agree quite well with each other and with the experimental data of ignition delay times and flame speeds at pressures lower than 10 atm, substantial differences are observed between recent experimental data of high-pressure mass burning rates and model predictions, as well as among the model predictions themselves. Different pressure dependencies of mass burning rates above 10 atm in different kinetic models result from using different rate constants in these models for HO2 reactions, especially for H HO2 and OH HO2 reactions.TherateconstantsforthereactionH HO2 involvingdifferentproductchannelswerefound to be very important for the prediction of high-pressure combustion characteristics. An updated choice of rate constants for those reactions is presented on the basis of recent experimental and theoretical studies. The role of O 1 D, which can be produced by the H HO2 reaction, in the high-pressure combustion of H2 is discussed.

Development of Ultra Small Shock Tube for High Energy Molecular Beam Source

A molecular beam source exploiting a small shock tube is described for potential generation of high energy beam in a range of 1–5 eV without any undesirable impurities. The performance of a non‐diaphragm type shock tube with an inner diameter of 2 mm was evaluated by measuring the acceleration and attenuation process of shock waves. With this shock tube installed in a molecular beam source, we measured the time‐of‐flight distributions of shock‐heated beams, which demonstrated the ability of controlling the beam energy with the initial pressure ratio of the shock tube.

A Noble Kinetic Model of H2/O2 System Applicable to Liquid Rocket Engine Combustion

A chemical kinetic model for high pressure combustion of H2/O2 mixtures has been developed. Some of the rate constants important in high pressure conditions were updated. Particular attention has been paid to different channels of the H+HO2 reaction, and to the third body efficiency in the H+O2+M and H+OH+M reactions. An analysis of the performance of an updated model is presented by comparing with various experimental data. Although the present model could reproduce most of shock tube data of ignition delay with variety of bath gases, there is still some discrepancy in the pressure dependence of flame speed between model predictions and recent experimental data. These models were validated against a wide range of experimental conditions and, in general, were found to be in good agreement with various experimental data including shock tube ignition delay, flow reactors, and laminar flame speed measurements. Basic characteristics of hydrogen combustion are now well understood because of those excellent modeling works and related experimental studies. Most recent kinetic model of Konnov 3 is probably the most extensively validated. The modeling range covers ignition delay measurements by shock tubes from 950 to 2700 K and from the atmospheric pressure up to 87 atm, and flow tube experiments at around 900 K with pressures from 0.3 to 15.7 atm. The mechanism is also validated against laminar flame burning velocities up to 4 atm. However, as pointed by Konnov, there is still some discrepancy between the model prediction and the measured flame velocities of hydrogen-oxygen-inert gas mixtures at higher pressures. The pressure dependences of mass burning rates for hydrogen mixtures have recently been studied experimentally and numerically by Burke et al. 4 . Flame speeds and mass burning rates were measured for equivalence ratios from 0.85 to 2.5, pressures from 1 to 25 atm. They found that the mass burning rate is increasing with pressure at low pressures, while at grater pressures, the mass burning rate is found to decrease with pressure. At lower pressures, predictions using recently published chemical kinetic models agree well with experimental data. However, the predicted mass burning rates differ significantly from model to model. Burk et al. suggested that

Continuum and stochastic approach for cell adhesion process based on Eulerian fluid-capsule coupling with Lagrangian markers

Abstract This paper presents a novel development for a full Eulerian coupling method between a fluid and capsule with hyperelastic membrane to address a cell adhesion process. The capsule motion in the fluid field and their mechanical interactions are expressed in the Eulerian framework, while solving the capsule adhesion process by stochastic events of ligand-receptor bindings in a discrete level, with using Lagrangian markers distributed on the implicit surface of the capsule. In addition to this, numerical improvements of the full Eulerian method for calculating an interface normal vector and dealing with multiple capsules by introducing the temporarily constructed level set function. A numerical validity of the present development is investigated through a comparison with available numerical data in a validation problem, and a capability for the capsule adhesion is shown in a single capsule adhesion and platelet adhesion in a suspension with blood cells.

Multiscale Simulations for Fluid Structure Interaction Problems with Biomedical Applications

A numerical method for massively parallel computing to solve fluid-structure interaction problems was developed and the method was employed for solving the multiscale problems in biomedical applications. As one of the examples, a platelet adhesion process to the vessel wall, which occurs at the initial stage of a thrombosis, was analyzed using the multiscale method of coupling continuum scale finite difference method with the molecular scale Monte Carlo method. The platelets adhesion to the injured vessel wall is caused by the protein-protein binding (GP1b-α on the platelet—VWF on the wall.). This protein-protein binding force is evaluated by Monte Carlo simulation, solving the stochastic process of each biding. Adhered platelets also feel the fluid mechanical force from blood flow and this force is affected by the presence of red blood cells, which causes the drastic change to the adhesion process. As another example of multiscale simulations, ultrasound therapy method using microbubbles are also explained.

An evaluation of the thermal properties of H2 and O2 on the basis of ab initio calculations for their intermolecular interactions

We have calculated the potential energy surfaces for the singlet state of H2–H2 and for the quintet state of using the coupled-cluster theory with singles, doubles and perturbative triple excitations [CCSD(T)] and an aug-cc-pVQZ basis set. Resulting interaction potentials were expanded in spherical harmonics, separating the radial and the angular dependencies to obtain analytical expressions. Monte-Carlo simulations for the NVT ensemble were performed to evaluate pressures and heat capacities of dense H2 and O2 fluids. The results were compared with the available experimental data in NIST thermodynamic database.

High‐Energy Molecular Beam Source Using a Small Shock Tube: Evaluation of Convergent Type Design

Molecular beam source using a small shock tube has the potential to frequently generate high energy molecular beam in a range of 1–5 eV without any undesirable impurities. We measured shock Mach numbers in 2 and 4‐mm‐diameter straight tubes to know about the propagation of shock wave in a very small shock tube. In addition, we measured shock Mach numbers in convergent shock tubes of which diameters linearly decrease from 4 mm to 2 mm, which demonstrated the possibility of a convergent shock tube to generate higher energy molecular beam than straight one.

Study on Development of Unified Simulation Method for Atomization and Combustion in a Coaxial Injector Flow

The numerical method for combustion flow in the super critical pressure condition has been developed in non conservative form. The method can treat the steep gradient of density, incompressible and compressible flow together and equation of state for real fluid. Numerical results about droplet vaporization show the separation at the wake of the droplet for the high Reynolds number. In the coaxial combustion flow analysis, the thin flame and the recirculation region in the mixing layer are shown. The validity of numerical method and the possibility of applying it to the injector flow analysis in a liquid rocket engine are confirmed from these test problems.

Buckling of a vibration‐isolation stack for gravity wave detectors

A semi‐analytic form for the axial buckling force of a multistage vibration‐isolation stack for gravitational radiation detectors is deduced. This is another version of Euler’s formula for simple pillars and gives a reference value both in design of isolation stacks and in numerical analysis for more complicated situations.