Tomomi Uchiyama

A numerical method for gas-solid two-phase free turbulent flow using a vortex method

Abstract This paper presents a numerical method for gas–solid two-phase free turbulent flow. The computation of the gas flow by a vortex method and the Lagrangian calculation of the particle motion are simultaneously performed, in which the change in the vorticity for the gas-phase by the interaction between the two phases is taken into account. The change due to the force exerted by the particle on the gas-phase is evaluated by an area weighting method, while the change by the viscous effect is simulated through a core spreading method. The present numerical method is also applied to calculate a two-dimensional gas–solid two-phase mixing layer to confirm the applicability. The numerical results, such as the number density, velocity and turbulent intensity of the particle, are favorably compared with the experimental data.

Numerical simulation of gas-particle two-phase mixing layer by vortex method

Abstract Gas-particle two-phase mixing layer is simulated by a two-way vortex method to investigate the effects of the mass loading ratio and the particle diameter on the flow. The method, proposed by the authors in a prior paper, simultaneously calculates the behavior of the vortex elements, discretizing the gas flow field, and the particle motion by the Lagrangian approach. The loaded particle delays the pairing process of the vortex element. When the mass loading ratio m is increased, the pairing process becomes less apparent and the flow structures are elongated in the streamwise direction. With an increment in m, the gas velocity gradient in the cross-stream section becomes gentler and the center of the mixing layer shifts toward the low-speed side. The velocity fluctuation of the gas lessens at the center of the mixing layer and heightens at the edges of the layer due to the loaded particles. These changes are unremarkable when large particles are loaded.

Three-Dimensional Calculation of Air-Water Two-Phase Flow in Centrifugal Pump Impeller Based on a Bubbly Flow Model

To predict the behavior of gas-liquid two-phase flows in a centrifugal pump impeller, a three-dimensional numerical method is proposed on the basis of a bubbly flow model. Under the assumption of homogeneous bubbly flow entraining fine bubbles, the equation of motion of the mixture is represented by that of liquid-phase and the liquid velocity is expressed as a potential for a quasi-harmonic equation. This equation is solved with a finite element method to obtain the velocities, and the equation of motion of an air bubble is integrated numerically in the flow field to obtain the void fraction. These calculations are iterated to obtain a converged solution. The method has been applied to a radial-flow pump, and the results obtained have been confirmed by experiments within the range of bubbly flow regime.

Prediction of Air-Water Two-Phase Flow Performance of a Centrifugal Pump Based on One-Dimensional Two-Fluid Model

To predict the performance of centrifugal pumps under air-water two-phase flow conditions, a consistent one-dimensional two-fluid model with fluid viscosity and air-phase compressibility in a rotating impeller is proposed by considering energy changes in the transitional flow from the rotating impeller to the stationary volute casing. The two-fluid model is numerically solved for the case of a radial-flow pump after various constitutive equations are applied

ALE finite element method for gas-liquid two-phase flow including moving boundary based on an incompressible two-fluid model

Abstract This paper proposes an ALE (Arbitrary Lagrangian–Eulerian) finite element method for gas–liquid two-phase flow, based on an incompressible two-fluid model, to analyze the two-phase flow including moving boundaries. The basic equations are derived by describing the two-fluid model in the ALE form. The solution algorithm is parallel to a fractional step method, and the Galerkin method is employed for the formulation. A quadrilateral element with four nodes is used for the discretization of the computational domain. The present method is also applied to calculate the flow around a circular cylinder, which is forced to oscillate in a quiescent air–water two-phase mixture. The drag coefficients of the cylinder exhibit periodical change in accordance with the variation of the flow around the cylinder. The time variations of the flow field and drag coefficients are discussed in relation to the oscillation of the cylinder.

Numerical simulation of cavitating flow using the upstream finite element method

Abstract A finite element method is proposed to predict cavitating flows in arbitrarily shaped channels. An upwind scheme, based on the Petrov–Galerkin method using an exponential weighting function, is employed to eliminate the numerical instability due to the advection term. The solution algorithm is parallel to a fractional step method. The calculation domain is divided into quadrilateral elements. The pressure is defined at the centroid of the element and assumed to be constant within the element. The other variables, such as the velocity and void fraction, are defined on the nodes. Cavitating flows around a circular cylinder are simulated by the present finite element method. The cavitation occurrence relates closely to the vortex motion of the water in the sheared layer in accordance with experimental observations, and the cavitation regions almost coincide with the regions where cavitation bubbles are observed frequently in experiments. This indicates that the present method is indeed applicable to the prediction of cavitating flows.

Catheter Insertion Mechanism and Feedback Control using Magnetic Motion Capture Sensor

Autonomous catheter insertion systems are desirables in fields of cardiology and neurology to reduce the use of X-rays during catheter insertion surgeries. A key point to reach an autonomous catheter insertion system is to provide to a catheter insertion mechanism enough information about the catheter tip position and speed to change its motion according to a predefined point in space to choose a path, and according to the catheter tips speed to detect if the catheter is jammed. In this research we propose the use of magnetic motion capture sensor to provide this information feedback to a catheter insertion mechanism. The system was tested inside a silicon solid arterial model, a silicon membranous arterial and ureter silicon membranous models to simulate a catheter insertion surgery in the upper aorta and inside the kidney. The system changed its motion successfully during the insertions along the models depending on the sensor position compared to a software map of the organ model, also automatic reconfigurations of the motion of the system were done using the speed of the sensor as feedback source

Numerical simulation of gas-liquid two-phase flow around a rectangular cylinder by the incompressible two-fluid model

Air-water two-phase flows around a rectangular cylinder located in vertical upward flows are analyzed by an incompressible two-fluid model using the two-dimensional upstream finite element method proposed earlier, The Reynolds number, based on the cross-stream width of the cylinder and the free-stream velocity of the liquid phase, is 2.0 x 10 4 , and the volumetric fraction of the gas phase upstream of the cylinder α g0 ranges from 0 to 0.075. Three kinds of cylinders with the thickness-to-width ratios D/B of 0.5, 1, and 1.5 are employed. The calculated flows exhibit unsteady behavior with the von Karman vortices shedding from the cylinder into the wake at every α g0 value. The volumetric fraction of the gas phase is higher in the wake and achieves maximum value at the center of the vortices, where the pressure reaches its minimum value. The flow field and the vortex-shedding frequency are greatly affected not only by the α g0 value but also by the D/B ratio.

Direct numerical simulation of a turbulent channel flow by an improved vortex in cell method

Purpose – This study is concerned with the direct numerical simulation (DNS) of a turbulent channel flow by an improved vortex in cell (VIC) method. The paper aims to discuss these issues. Design/methodology/approach – First, two improvements for VIC method are proposed to heighten the numerical accuracy and efficiency. A discretization method employing a staggered grid is presented to ensure the consistency among the discretized equations as well as to prevent the numerical oscillation of the solution. A correction method for vorticity is also proposed to compute the vorticity field satisfying the solenoidal condition. Second, the DNS for a turbulent channel flow is conducted by the improved VIC method. The Reynolds number based on the friction velocity and the channel half width is 180. Findings – It is highlighted that the simulated turbulence statistics, such as the mean velocity, the Reynolds shear stress and the budget of the mean enstrophy, agree well with the existing DNS results. It is also shown...

Numerical Analysis of Air-Water Two-Phase Flow Across a Staggered Tube Bundle Using an Incompressible Two-Fluid Model

Abstract The air-water two-phase flow across a staggered tube bundle at a pitch-to-diameter ratio of 1.4 is analyzed by an incompressible two-fluid model using the upstream finite element method proposed in a prior study. The Reynolds number, based on the tube diameter and the volumetric velocity of the liquid phase at the tube gap, is 41 000, and the volumetric fraction of the gas phase upstream of the bundle αg0 ranges from 0 to 0.15. The calculated flows exhibit unsteady and complicated behavior irrespective of αg0. The change in the drag coefficient of a tube in the bundle due to αg0 agrees with the experimental result. The distribution of the volumetric fraction of the gas phase around the tube is also in good agreement with the measurement trend. These results indicate that the finite element method is usefully applicable to the two-phase-flow analysis in staggered tube bundles. It is also clarified that the unsteady flows are attributable to the occurrence and movement of vortices of both phases around the tubes.