Generality of rotating partial cavitation in two-dimensional cascades

Numerical simulations of 2-dimensional (2D) unsteady cavitating flows were carried out under various conditions of the number of blades, incidence angles and cavitation numbers. When the incidence angle increased or the cavitation number decreased, the steady balanced cavitation transited to unsteady and non-uniform patterns. Typical patterns reported in the previous studies such as rotating, asymmetric and alternating for 3- and 4-blades were successfully reproduced. In this study, cascades of the larger number of blades were dealt with to consider the generality of unsteadiness by reducing the influence of periodicity. The cavitation is basically triggered in the backward next section. However, the period of time for growing causes complexity in the discrimination of propagation. In most cases of rotating partial cavitation, except for 4-blades, the cavity develops in the second passage of backward direction after the decay of largest cavity. In case of many blades, multiple cavities rotate simultaneously and the particular patterns observed in cascades of small even numbers of blades attenuate.http://deepblue.lib.umich.edu/bitstream/2027.42/84276/1/CAV2009-final90.pd

On the Fertilization of the Triploid Ginbuna

The ferilization process of the gynogenetic triploid ginbuna Carassius auratus langsdorfii were observed histologically. In the triploid female, it has been reported that the sperm nucleus remains in condensed condition throughout the ferilization to first cleavage. This sperm nucleus does not fuse with female pronucleus, producing the all female triploid offsprings gynogenetically. On the other hand, in the present experiment, in some triploid eggs, the penetrated sperm nucleus swells to form male pronucleus. Some of these eggs develop into tetraploid other than triploid fish. On the scale transplantation experiments between these offsprings, in which all of the sperm nuclei had swollen at the time of fertilization, the unidirectional rejection were observed in two combinations. One of these donors was tetraploid and other was triploid. It seems probable that the former unidirectional rejection might be caused by the introduction of paternal genome, and the later might be caused by the recombination of genes at meiosis or the mutation of the donor and/or the host. From these observation, it was ascertained that the offsprings of triploid ginbuna were not always belonging to the same clone but that some of them differenciated their genome during the gametogenesis or early developmental stage.Article信州大学理学部紀要 19(1): 53-61(1984)departmental bulletin pape

Low dimensional POD-Galerkin modeling of rolling mode in a fully developed turbulent channel flow

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.Low dimensional POD-Galerkin model is developed for a fully developed turbulent channel flow. This model is based on the extraction of the Proper Orthogonal Decomposition (POD) eigenfunctions from a DNS data set of a channel flow at Re¿ = 150. The POD eigenfunctions are optimal in energy sense and ordered with the first eigenfunction represents the most energetic structure. POD analysis shows that, POD mode 1, 2 and 3 capture 63 %, 18% and 8.5% of total kinetic energy, respectively. Stream-wise mode zero (stream-wise rolls) contains about 22% of total energy. A Galerkin projection is then used to drive dynamical systems. To investigate coherent structures near the wall in a low dimensional system, only energetic modes are considered. The coupling of stream-wise and wallnormal velocity components is sustained by the implicit coupling in the POD eigenfunctions. Statistics of the flow which is generated by the model compare fairly well with the corresponding POD reconstruction of DNS data from which POD basis are extracted.cs201

Fluid permeation through a membrane with infinitesimal permeability under Reynolds lubrication

This article has been published in a revised form in Journal of Mechanics [https://doi.org/10.1017/jmech.2020.38]. This version is published under a Creative Commons CC-BY-NC-ND. No commercial re-distribution or re-use allowed. Derivative works cannot be distributed. © 2020 The Society of Theoretical and Applied Mechanics

A direct numerical simulation method for complex modulus of particle dispersions

We report an extension of the smoothed profile method (SPM)[Y. Nakayama, K. Kim, and R. Yamamoto, Eur. Phys. J. E {\bf 26}, 361(2008)], a direct numerical simulation method for calculating the complex modulus of the dispersion of particles, in which we introduce a temporally oscillatory external force into the system. The validity of the method was examined by evaluating the storage $G'(\omega)$ and loss $G"(\omega)$ moduli of a system composed of identical spherical particles dispersed in an incompressible Newtonian host fluid at volume fractions of $\Phi=0$, 0.41, and 0.51. The moduli were evaluated at several frequencies of shear flow; the shear flow used here has a zigzag profile, as is consistent with the usual periodic boundary conditions

Simulating (electro)hydrodynamic effects in colloidal dispersions: smoothed profile method

Previously, we have proposed a direct simulation scheme for colloidal dispersions in a Newtonian solvent [Phys.Rev.E 71,036707 (2005)]. An improved formulation called the ``Smoothed Profile (SP) method'' is presented here in which simultaneous time-marching is used for the host fluid and colloids. The SP method is a direct numerical simulation of particulate flows and provides a coupling scheme between the continuum fluid dynamics and rigid-body dynamics through utilization of a smoothed profile for the colloidal particles. Moreover, the improved formulation includes an extension to incorporate multi-component fluids, allowing systems such as charged colloids in electrolyte solutions to be studied. The dynamics of the colloidal dispersions are solved with the same computational cost as required for solving non-particulate flows. Numerical results which assess the hydrodynamic interactions of colloidal dispersions are presented to validate the SP method. The SP method is not restricted to particular constitutive models of the host fluids and can hence be applied to colloidal dispersions in complex fluids

Understanding the asymmetry between advancing and receding microscopic contact angles

By means of molecular dynamics simulation, the advancing and receding microscopic contact angles were analyzed for a shear flow of two mono-atomic fluids confined between parallel non-polar solid walls. We defined the microscopic dynamic contact angle based on the coarse-grained microscopic density distribution of the fluids (the instantaneous interface method [Willard and Chandler, J. Phys. Chem. B, 2010, 114, 1954-1958]) near the moving contact line. We have found that the asymmetric change of fluid density near the wall with respect to the moving contact line results in a different dependence between the advancing and receding contact angles on the contact line velocity in a system where the two fluids across the interface have unequal wettability to the solid wall. This difference between the advancing and receding contact angles leads to different flow resistance caused by the advancing and receding contact lines, which should have impact on the industrial applications of the fine fluid transportation with contact lines.T. Omori, Y. Kobayashi, Y. Yamaguchi, T. Kajishima. Understanding the asymmetry between advancing and receding microscopic contact angles. Soft Matter, 2019, 15(19), 3923-2928. https://doi.org/10.1039/C9SM00521H

Investigation of turbulent modulation by cavitation for subgrid-scale modeling in LES

The two-way interaction between cavitation and turbulence was nvestigated by the direct numerical simulation of a spatially-developing mixing layer. Namely, the vortical structure and Reynolds stress components were compared between cavitating and non-cavitating conditions. Under cavitating condition, cavitation mainly occur in the regions of low pressure which are corresponding to vortices. Under cavitating condition, instability of mixing layer is caused more easily due to disturbance by cavitation to the flow field. Therefore, cavitation excites the instability of shear layer. vortices generating and pairing. As a result of stimulated pairing, the pitch of roll-cell vortices become longer than that in non-cavitating condition. One of the circumferential components of roll-cell vortices is suppressed by the decreasing of the number of roll-cell vortices. Circumferential component of streamwise vortices, on the other hand, tends to increase in comparison with noncavitating condition. This is explained by volume fluctuation by cavitation. The modulation of Reynolds stress is consistently described by these changes in vortical stractures.http://deepblue.lib.umich.edu/bitstream/2027.42/84275/1/CAV2009-final89.pd