Ken Naitoh

Large eddy simulation and direct simulation of compressible turbulence and combusting flows in engines based on the BI-SCALES method

Physical features of turbulence and vortex-flame interaction in engines are investigated by performing large eddy simulation and direct numerical simulation of compressible flows. A BI-SCALES (Boundary-Inner Smoothly Coupled, Alternating multi-Level Equations System) is proposed, which is a mathematical formulation of the system of governing equations suitable for computations of compressible flows. A numerical method based on the proposed formulation is developed. Using the method, the transition to turbulence in the compression process and the cyclic variations are examined. Then, the vortex-flame interaction is studied, mainly on the relation between the flame structure and the Kalvoritz- and turbulent Reynolds number effect. Finally, the large wrinkle simulation (LWS) of engine combusting flow is performed.

Cyto-fluid dynamic theory

A universal theory describing the deformation and atomization processes of liquid droplets and columns is proposed on the basis of the first principle of fluid dynamics. Based on the proposed theory, previously reported empirical models such as the TAB model and the OPT model can be derived along with their arbitrary constants. Moreover, this theory provides a formulation for breakup phenomena when two droplets collide. It is also shown on the basis of this theory that the atomization processes of liquid droplets are mathematically similar to biological cell proliferation. This is because actual living cells mainly consist of liquid and because both systems are dominated by three essential forces, that is, internal convection, surface tension, and the internal pressure gradient due to energy input. Finally, it will be shown that the present theory offers a qualitative explanation of the unlacing processes of biological molecules such as the base pairs of purines and pyrimidines surrounded with water molecules, that is, the chemical reaction processes related to the hydrogen bonds.

A Wide-range single engine: operated from startup to hypersonic

A single lightweight engine capable of operating over a wide range of Mach numbers from startup to the hypersonic regime is proposed for aircrafts and spaceships. A compression system of colliding super multijets is proposed instead of a traditional turbofan. Computational fluid dynamics with a chemical reaction model clarifies a large potential and stability of this system. This ultimate engine system can be extended with a special piston and scram jet systems to achieve an improved fuel consumption rate at various situations between the ground and the space, while maintaining a very low noise level with silent detonation. The present engine system will also solve the problem of the buzz at highersonic conditions.

Stochastic-Determinism Approach for Simulating the Transition Points in Internal Flows with Various Inlet Disturbances

Large eddy simulation (LES) and direct numerical simulation (DNS) have been done for the transition to turbulence in straight channels. [MOIN82], [KAWAMURA85] However, these previous computations employ the cyclic boundary conditions between the inlet and outlet of the analytical domain, which can not simulate the transition position in space.

Stability limit of supermulti-jets convergence engine operated from startup to extremely-hypersonic conditions: Revealed by shock-tube experimens

Shock tube experiments reveal whether or not the single lightweight compression system of the supermultijets colliding with pulsation for aircars and aircraftsworks stably, which was proposed based on our previous three-dimensional unsteady computations. This compression system essentially differs from those in the traditional four types of engines with piston, turbofan, ran-scram, and pulse-detonation, because of the supermulti-jets colliding. The single compression system is capable of operating over a wide range of Mach numbers from startup to the hypersonic regime. Shocktube experiments clarify the stability range of this system in detail. Influence of the number of supermulti-jets on the stability will also be examined. This system can also be extended with a special piston and scram jet systems to achieve an improved fuel consumption rate at various situations between the ground and the space, while maintaining a low noise level and also solving the problem of the buzz at highersonic conditions.

Cycle-resolved computation of compressible turbulence and premixed flame in an engine

Abstract Cycle-resolved computations of the turbulent premixed flame in an internal combustion engine are performed for a wide range of operating conditions, such as engine speed and air—fuel ratio. For this purpose, first a multilevel mathematical formulation, which is suitable for both the large-eddy simulation and direct numerical simulation of the compressible turbulence and combusting flows in engines is derived, and then a suitable numerical algorithm is developed. With this method, the transition to turbulence near the end of the compression process and the supergrid fluctuations of the physical quantities can be calculated with less CPU time. For determining the subgrid turbulence and flame wrinkling, respectively, the Yakhot—Orszag turbulence model based on the renormalization group theory and a flame-sheet model are incorporated in the numerical code. Calculations are performed for a real engine with dual intake port and valves. The simulated results agree well with the experimental data for both turbulence intensity and pressure history. Cyclic variations of the flow field and flame propagation are also calculated.

Simultaneous attainment of light-weight, high-efficiency, and low noise: By the supermultijet-twister engine working from startup to hypersonic scram mode

A single lightweight engine capable of operating over a wide range of Mach numbers from startup to the hypersonic regime, which was proposed for aircars, aircrafts, and spaceships (Naitoh et al, 2010, 2011, 2012), has an impressive potential of low noise and high thermal efficiency. Its new compression principle is based on super multijets colliding with pulsation. Shocktube experiments and computational fluid dynamics with a chemical reaction model at about M=1 clarified the efficiency and stability of this engine system. In this report, computations for this engine system extended with a special twister piston show reduction of thermal loss and noise, even for low subsonic Mach number M 2. We also confirmed combustion occurrence by performing primitive testes for two prototype engines.

Engine for cerebral development

A deterministic theoretical model that simulates the developmental process of the human brain is proposed. Observations of the development of the human brain with a high-speed camera show that the bones of the skull become increasingly larger over the neck, and that a lot of soup-like fluid for generating brain cells enters the skull from the body. This process is essentially similar to the intake process of an internal combustion engine, because the volume of the engine’s cylinder, which increases according to the descent of the piston, geometrically corresponds to the development of the skull, and also because the human neck resembles the intake port that serves as the throat of the engine. A higher-order numerical computation of the Navier-Stokes equation reveals the similarity between the convexoconcave forms inside the brain and the flow structure in the internal combustion engine. We will show that the present computation also simulates the emergence of the eyeballs. Finally, we will clarify the reason why cerebral development is strongly influenced by fluid dynamics.

Macroscopic kinetic equation for a genetic algorithm

A macroscopic kinetic equation of only four variables for a simple genetic algorithm (SGA) with an on-off type of replication operator and a crossover operator is developed and used to predict several types of evolutionary routes for a wide range of metabolic-ratecontrolling parameters, initial conditions, string lengths, population sizes, and environments. The four variables correspond to the probabilities of the best-adapted species and three mutant groups into which degenerate and redundant strings are classified according to the Hamming distance (HD). The time-dependent frequency distribution along the fitness value is given by an implicit formulation. The environment is also defined in the HD-fitness value space as the frequency distribution of all the possible types of strings without redundancy. It is found that the SGA possesses the capability for exploring quasimacroevolution.

Wide-Range Single Engine Operated from Subsonic to Hypersonic Conditions: Designed by Computational Fluid Dynamics

A new type of single engine capable of operating over a wide range of Mach numbers from subsonic to hypersonic regimes is proposed for airplanes. Traditional piston engines, turbojet engines, and scram engines work only under a narrower range of operating conditions. The new engine has no compressors or turbines such as those used in conventional turbojet engines. A notable feature is its system of super multijets that collide to compress gas for the transonic regime. A numerical model simulating compressible turbulence with chemical reactions based on the CIP and BI-SCALES methods is employed to design the engine. The maximum power of this engine will be sufficient for actual use. For the higher Mach numbers in supersonic and hypersonic conditions, this engine can take the mode of a ram or scramjet engine.