CFD contributions to high-speed shock-related problems

Computational Fluid Dynamics (CFD) has contributed extensively to high speed shock-wave research. With study examples by the author’s group in the past, effectiveness of CFD both for design of transportation vehicles and for understanding of fluid physics is discussed. Trends of CFD for further use are then discussed based on recent applications and three key features: computer progress, spectral-like high-resolution schemes and LES and LES/RANS hybrid methods are focused. Recent CFD research reveals that high-speed flows, even the ones considered to be steady state have inherently unsteady nature that requires LES-like computations for successful simulations. Such simulations require remarkably higher grid resolution, but emerging numerical techniques having spectral-like high resolution would help reducing the number of grid points required for such simulations and make them feasible. The paper is summarized by addressing issues of future CFD.     

An accurate quantitative analysis of polymorphic content by chemometric X-ray powder diffraction.

Data from X-ray powder diffraction (XRD) were subjected to a partial least-squares regression analysis (PLS) to build a calibration model for predicting the polymorphic content of carbamazepine (CBZ). The effectiveness of the PLS method in the construction of calibration models was analyzed by a scientific approach based on a regulation vector. CBZ forms I and III were characterized by differential scanning calorimetry (DSC) and XRD. Powder mixtures of forms I and III at various ratios (0-100% w/w; form III) were subjected to XRD. Five diffraction peaks were used for the peak-area method to compare with PLS. The results obtained by PLS had a better predictive accuracy compared to those of the peak-area method. The XRD-PLS method was established as a non-destructive, non-contact way to avoid the particle orientation effect based on statistical theory.     

Nano structure of low crystallinity carbon materials analyzed by using high energy X-ray diffraction

In this study, we tried to characterize a kind of low crystallinity carbon materials. The structure of polyparaphenylene(PPP)-based carbon was analyzed by means of high energy X-ray diffraction using the apparatus of SPring-8. The experimental results revealed the existence of basic structural units (BSU) in the highly disordered materials like PPP-based carbon. It is thought that the PPP-based carbons consist of small turbostratic particles, which have a few piled up poly-aromatic layers. The structure of the PPP-based carbon which seemed to be amorphous was estimated to have hexagonal carbon layers with the size of up to 1 nm. The pores in the PPP-based carbon seem to be clearances formed among the BSUs and amorphous carbon. The pore size of PPP-based carbon was estimated from the result of N₂ absorption measurement. The experimental results suggested that the lithium ion charge mechanism in the PPP-based carbon differs from that in graphite.      

Synthesis of substituted furans by platinum-catalyzed cyclization of propargylic oxiranes in aqueous media

The reaction of propargylic oxiranes with platinum catalyst in aqueous media is described. Furans having a variety of substituents were conveniently synthesized with high efficiency.     

Dominant parameters for maximum velocity induced by body-force models for plasma actuators

This study investigates the relationship between body-force fields and maximum velocity induced in quiescent air for development of a simple body-force model of a plasma actuator. Numerical simulations are conducted with the body force near a wall. The spatial distribution and temporal variation of the body force are a Gaussian distribution and steady actuation, respectively. The dimensional analysis is performed to derive a reference velocity and Reynolds number based on the body-force distribution. It is found that the derived Reynolds number correlates well with the nondimensional maximum velocity induced in quiescent conditions when the center of the Gaussian distribution is fixed at the wall. Additionally, two flow regimes are identified in terms of the Reynolds number. Considering the variation of the center of gravity of force fields, another Reynolds number is defined by introducing a new reference length. The nondimensional maximum velocity is found to be scaled with the latter Reynolds number, i.e., the maximum induced velocity in quiescent conditions is determined from three key parameters of the force field: the total induced momentum per unit time, the height of the center of gravity, and the standard deviation from it. This scaling turns out to be applicable to existing body-force models of the plasma actuator, despite the force distributions different from the Gaussian distribution. Comparisons of velocity profiles with experimental data validate the results and show that the flow induced by a plasma actuator can be simulated with simple force distributions by adjustment of the key body-force parameters.     

Numerical simulation of the disintegration of forced liquid jets using volume-of-fluid method

The present numerical study investigates the effect of finite sinusoidal velocity modulations imposed on an otherwise unperturbed cylindrical liquid jet issuing into stagnant gas using Volume-of-Fluid (VOF) methodology. Variation of the simulation parameters, comprising of the mean liquid jet velocity, modulation amplitude and frequency grouped together using a set of non-dimensional parameters, leads to the formation of a wide gamut of reproducible liquid structures such as surface waves, upstream/downstream directed bells and chains of droplets similar to those observed in experiments. The computations efficiently capture the diverse flow structures generated by the evolving modulated liquid jet inclusive of several nonlinear dynamics such as growth of surface waves, ligament interaction with shear vortices and its subsequent thinning process. The simulations identify the deterministic behaviour of modulated liquid jets to predict liquid disintegration modes under given set of non-dimensional parameters.     

A synthesis of multisubstituted vinylsilanes via ynolates: stereoselective formation of beta-silyl-beta-lactones followed by decarboxylation

(Z)-Selective synthesis of multisubstituted vinylsilanes was achieved by stereoselective protonation or alkylation of beta-silyl-beta-lactone enolates, prepared by cycloadditions of acylsilanes with ynolates, followed by decarboxylation.     

The first general method for Z-selective olefination of acylsilanes via ynolate anions providing multisubstituted alkenes

We have developed the first general method for a stereoselective olefination of acylsilanes via ynolate anions to produce (Z)-beta-silyl-alpha,beta-unsaturated ester, which leads to tri- and tetrasubstituted alkenes.