Yasufumi Yamamoto

Large-eddy simulation of turbulent gas–particle flow in a vertical channel: effect of considering inter-particle collisions

The interaction between a turbulent gas flow and particle motion was investigated by numerical simulations of gas–particle turbulent downward flow in a vertical channel. In particular the effect of inter-particle collision on the two-phase flow field was investigated. The gas flow field was obtained by large-eddy simulation (LES). Particles were treated by a Lagrangian method, with inter-particle collisions calculated by a deterministic method. The spatial resolution for LES of gas–solid two-phase turbulent flow was examined and relations between grid resolution and Stokes number are presented. Profiles of particle mean velocity, particle wall-normal fluctuation velocity and number density are flattened as a result of inter-particle collisions and these results are in good agreement with experimental measurements. Calculated turbulence attenuation by particles agrees well with experimental measurements for small Stokes numbers, but not for large Stokes number particle. The shape and scale of particle concentrations calculated considering inter-particle collision are in good agreement with experimental observations.

Dye Visualization and P.I.V. in the Cross-Stream Plane of a Turbulent Channel Flow

Illuminating in a quasi-cross-stream plane of an open channel flow of water at low Re and injecting fluorescene dye from a bed slit, mushroom patterns reliably inferred to result from counter-rotating streamwise vortices are found to be typically oriented at some 30° from the cross-stream vertical. PIV in the cross-stream plane shows that the averaged field, and two-point correlation, of the quantity \({Q_x} = \left( {\omega _x^2 - S_x^2} \right)/2,\left( {{S_x} = \frac{{\partial v}}{{\partial z}} + \frac{{\partial w}}{{\partial y}}} \right)\) exhibit preferred directions in the cross-stream plane at about 45 degrees to the vertical. Spatio-temporal measurements of streamwise vorticity provide direct experimental evidence, possibly the first, for the staggered arrangement of streamwise vortices previously educed from DNS data.

Numerical analysis of contact line dynamics passing over a single wettable defect on a wall

In this study, the dynamics of a contact line passing a single defect, which was represented by a locally wettable part (whose static contact angle is less than the other part, namely, chemically heterogeneous and physically flat part), was analyzed using numerical simulations employing the front-tracking method and the generalized Navier boundary condition. We observed that the contact line was distorted with a logarithmic shape far from the defect; however, the distortion was dependent on the wall velocity. The apparent (averaged) dynamic contact angle of the wall with a defect was evaluated using a macroscopic energy balance. The apparent dynamic contact angles estimated from the energy balance agree well with the arithmetic averaged angles obtained from the present simulations. The macroscopic energy balance is useful to consider the effect of heterogeneity or roughness of the wall on the relation between the dynamic contact angle and contact line speed.

A New Super-Resolution PIV Accelerated by Characteristic Pixel Selection

AbsractA new high-speed super-resolution PIV was proposed using characteristic pixel selection to accelerate the successive abandonment (SA) with recursive window subdivision. The performance and applicability of the proposed PIV were evaluated. In the SA calculation with the characteristic pixel selection, 1000 candidates are narrowed down to only one at over 50 % of the measurement points, and the number of error vectors is reduced because the difference between the cumulative intensities of a correct candidate and of other ones becomes clear due to the characteristics of selected pixels. In all recursive processes, error checks are carefully performed using the summation of the distribution of the cumulative intensity difference distribution, which is suitable for the SA method. In a comparison of the time per velocity vector, the present super-resolution PIV was shown to be 10 times faster than the former ordinary resolution PIV. Another feature of the present super-resolution PIV is that the velocity vectors are obtained in the region very close to the image boundaries and masked regions by using the recursive algorithm.

Rule Based Questionnaire Results Interpretation in Requirement Analysis

Abstract Requirement analysis is one of the most important processes in the system planning. A questionnaire survey is frequently performed as an effective method for the requirement analysis. However, it needs skillful techniques to adequately analyze questionnaire results. Therefore, a support system for this task is demanded. In this paper, a support method for questionnaire results analysis is presented. Using a rule base which has been constructed based on expertise knowledge, characteristic data are extracted and comments for the data are generated from questionnaire results. The performance of the data extraction method is almost equal to experts

Numerical Simulation of a Contaminated Droplet by Front-Tracking Method Taking the Effect of Surfactant Transport on the Interface

In this study, a front-tracking (FT) method combined with a solver of interfacial transport of surfactant was proposed in order to resolve interfacial flows affected by contamination. In the FT method, because the interfaces are presented explicitly, advection-diffusion equation on the interface can be easily treated and can be solved highly accurately. In this study, a scheme which conserves the total amount of surfactant completely was constructed. Numerical simulations of a water drop sinking in silicone oil were performed taking the Marangoni effect into account. The effects of three parameters, a damping coefficient of interfacial tension, a diffusion coefficient and a total amount of surfactant, were evaluated. Calculated results were compared with PTV measurement results and were in very good agreement with them on the points of stagnant cap size, flow separation point, peak of shear stress and so on. So, we can expect that our simulations can estimate the conditions of surfactant on the interfaces, which is very difficult to be measured.Copyright

Improvement and consideration of color defocus method

By adding a color separation teclinique to the conventional defocus method, the capabil i ty and performance of the method can he expanded. The new method named color-defocus method can process much dense part ic le d is t r ibu t ion and its the depth of measurable area is expanded about twice. This papev deals w i t h fur ther improvements of the col o r dc focus method. They consists of two points, one is the method to reduce the l igh t absorption by color-filters, and the other is the ut i l izat ion of colored light, laser for example, i l luminat ion. The conventional color defocus method uses a three-pinholes aperture mask w i t h RGB filters, and whi te l i gh t i l luminat ion . In order to obtain clearer particle images, light-color fi l ters and color separation technique are introduced. Ami the color separation technique enables introduction of various color filters other than RGB f i l ters. This approach easily leads to realization of colored i l luminat ion that enables the PTV using fluorescent part icles and laser i l luminat ions.

Numerical Simulation of a Drop Sliding Down an Inclined Plane by Front-Tracking Method

In this paper, we present a front-tracking method containing an accurate representation of solid surface condition, and simulate a drop sliding down an inclined plate employing some slip models. Numerical results are compared with experimental observations by Le Grand et al. (Journal of Fluid Mechanics, 2005), and then which slip model is well-suited is examined. Drop shapes, in particular advancing and receding contact angles, and drop velocity reproduced by our simulations without explicit slip model are qualitatively good agreement with experimental observations for capillary number Ca<0.01.Copyright

Color eccentric aperture method to measure positions of particles scattered in 3-D space

In order to measure instantaneous three-dimensional velocity distributions in a small space, three-dimensional micro-PIV technique have to be developed. In this paper, the improved eccentric aperture method that could be conveniently applied to the three-dimensional PIV measurement in a small space is discussed. By introducing a color separation technique, the measurement distance can be expanded twice, and it can process dense tracer pictures. Some experimental examples are shown.

High Resolution Imaging of small objects using a micro-focus X-ray source

In order to make the X-ray micro-PIV technique as a common technology, the alternative X-ray source to Synchrotron Radiation (SR) facility is indispensable. The characteristics of micro-focus X-ray (MFX) source are examined for the micro-PIV. The MFX source seems better than the SR, in respect of the availability, the flexibility for PIV systems, and image enlargement. X-ray PIV is the only method that provides us with a method to realize three-dimensional micro-PIV measuring flows in complex channels. The spatial resolution, intensities, and imaging methods are discussed. Three dimensional shape of a spiral shape of fine metal wire is reconstructed from a two-dimensional micro-focus X-ray picture.