• The KSFM Journal of Fluid Machinery
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• v.13 no.1
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• pp.17-22
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• 2010

In this paper, numerical study on a mixed-flow pump for irrigation and drainage has been performed based on three-dimensional viscous flow analysis. Reynolds-averaged Navier-Stokes equations with shear stress transport turbulence model are discretized by finite volume approximations and solved by the commercial CFD code ANSYS CFX-11.0. A structured grid system is constructed in the computational domain, which has O-type grids near the blade surfaces and H/J-type grids in other regions. The numerical results were validated with experimental data for the heads and efficiencies at different flow coefficients. The efficiency at the design flow coefficient is evaluated with the variation of two geometric variables related to area of discharge and length of the vane in the diffuser. The results show that efficiency of the mixed-flow pump at the design flow coefficient is improved by the modifications of the geometry.

• 한국전산유체공학회:학술대회논문집
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• 2008.08a
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• pp.40.2-40.2
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• 2008

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.359-364
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• 2005

Centrifugal pump shows the strongest secondary flow. Wake is formed near pressure surface close to hub at impeller exit for centrifugal pump impeller. Pressure gradient drives secondary flow in the inducer region, while in the remaining region the following sources drive together: > Pressure gradient > Coriolis force Low-momentum fluid near suction surface hub moves toward pressure surface hub in mixed-flow pump impeller. Tip leakage vortex dominate secondary flow in axial-flow pump impeller. Tip leakage vortex dominate secondary flow in axial-flow in axial-flow pump impeller

• Coupled systems mechanics
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• v.7 no.6
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• pp.649-668
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• 2018

In this paper, we present a numerical model for fluid-structure interaction between structure built of porous media and acoustic fluid, which provides both pore pressure inside porous media and hydrodynamic pressures and hydrodynamic forces exerted on the upstream face of the structure in an unified manner and simplifies fluid-structure interaction problems. The first original feature of the proposed model concerns the structure built of saturated porous medium whose response is obtained with coupled discrete beam lattice model, which is based on Voronoi cell representation with cohesive links as linear elastic Timoshenko beam finite elements. The motion of the pore fluid is governed by Darcy's law, and the coupling between the solid phase and the pore fluid is introduced in the model through Biot's porous media theory. The pore pressure field is discretized with CST (Constant Strain Triangle) finite elements, which coincide with Delaunay triangles. By exploiting Hammer quadrature rule for numerical integration on CST elements, and duality property between Voronoi diagram and Delaunay triangulation, the numerical implementation of the coupling results with an additional pore pressure degree of freedom placed at each node of a Timoshenko beam finite element. The second original point of the model concerns the motion of the outside fluid which is modeled with mixed displacement/pressure based formulation. The chosen finite element representations of the structure response and the outside fluid motion ensures for the structure and fluid finite elements to be connected directly at the common nodes at the fluid-structure interface, because they share both the displacement and the pressure degrees of freedom. Numerical simulations presented in this paper show an excellent agreement between the numerically obtained results and the analytical solutions.

• Journal of Korea Water Resources Association
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• v.30 no.6
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• pp.661-669
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• 1997

This paper presents a theoretical analysis for a velocity profile of fluid-granule mixed flow and a sheet erosion of an embankment having noncohesive materials due to overflow. The velocity profile were obtained using the stress-strain relationships based on a grain-inertia regime and an erosion depth was obtained using dynamic Coulomb criterion. Experiments were performed to compare with theoretical values and fairly good agreements were found. Theoretical results on velocity profiles, which can be applied to any type of velocity profiles in a fluid-granule mixed flow, showed a considerable improvement for the existing theories on a debris flow. for a design purpose, formulas and figure diagrams for obtaining a velocity profile, an erosion depth, an overflow depth and a granular discharge were proposed for given values of a flood discharge, particle properties and embankment scale.

• Journal of Mechanical Science and Technology
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• v.17 no.3
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• pp.457-466
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• 2003

In this paper, the numerical finite element formulations were derived for the linearized Navier-Stokes' equations with assumptions of two-dimensional incompressible, homogeneous viscous fluid field, and small oscillation and the FAMD (Fluid Added Mass and Damping) code was developed for practical applications calculating the fluid added mass and damping. In formulations, a fluid domain is discretized with C$\^$0/-type quadratic quadrilateral elements containing eight nodes using a mixed interpolation method, i.e., the interpolation function for the velocity variable is approximated by a quadratic function based on all eight nodal points and the interpolation function for the pressure variable is approximated by a linear function based on the four nodal points at vertices. Using the developed code, the various characteristics of the fluid added mass and damping are investigated for the concentric cylindrical shell and the actual hexagon arrays of the liquid metal reactor cores.

• Computers and Concrete
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• v.22 no.2
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• pp.161-166
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• 2018

This paper deals with the instability analysis of concrete pipes conveying viscous fluid-nanoparticle mixture. The fluid is mixed by $AL_2O_3$ nanoparticles where the effective material properties of fluid are obtained by mixture rule. The applied force by the internal fluid is calculated by Navier-Stokes equation. The structure is simulated by classical cylindrical shell theory and using energy method and Hamilton's principle, the motion equations are derived. Based on Navier method, the critical fluid velocity of the structure is calculated and the effects of different parameters such as fluid velocity, volume percent of nanoparticle in fluid and geometrical parameters of the pipe are considered. The results present that with increasing the volume percent of nanoparticle in fluid, the critical fluid velocity increase.

• International Journal of Fluid Machinery and Systems
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• v.2 no.1
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• pp.31-39
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• 2009

The flow instability in a low specific speed mixed-flow pump, having a positive slope of head-flow characteristics was investigated. Based on the static pressure measurements, it was found that a rotating stall in the vaned diffuser occurs at about 65% flow rate of best efficiency point (BEP). A dynamic Particle Image Velocimetry (DPIV) measurement and the numerical simulations were conducted in order to investigate the flow fields. As a result, the diffuser rotating stall was simulated even by Computational Fluid Dynamics (CFD) and the calculated periodic flow patterns agree well with the measured ones by DPIV. It is clarified that a periodical large scaled backflow, generated at the leading edge of the suction surface of the diffuser vane, causes the instability. Furthermore, the growth of the strong vortex at the leading edge of the diffuser vane induces the strong backflow from the diffuser outlet to the inlet. The scale of one stall cell is covered over four-passages in total thirteen vane-passages.

• Journal of Magnetics
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• v.18 no.3
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• pp.321-325
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• 2013

The problem of mixed convection in a differentially heated lid-driven square cavity filled with Cu-water nanofluid under effect of a magnetic field is investigated numerically. The left and right walls of the cavity are kept at temperatures of $T_h$ and $T_c$ respectively while the horizontal walls are adiabatic. The top wall of the cavity moves in own plane from left to right. The effects of some pertinent parameters such as Richardson number (ranging from 0.1 to 10), the volume fraction of the nanoparticles (ranging 0 to 0.1) and the Hartmann number (ranging from 0 to 60) on the fluid flow and temperature fields and the rate of heat transfer in the cavity are investigated. It must be noted that in all calculations the Prandtl number of water as the pure fluid is kept at 6.8, while the Grashof number is considered fixed at 104. The obtained results show that the rate of heat transfer increases with an increase of the Reynolds number, while but it decreases with increase in the Hartmann number. Moreover it is found that based the Richardson and Hartmann numbers by increase in volume fraction of the nanoparticles the rate of heat transfer can be enhanced or deteriorated compared to the based fluid.

• Progress in Superconductivity and Cryogenics
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• v.12 no.1
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• pp.66-70
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• 2010

The operational temperature range of thermosiphon is generally limited from the critical point to the triple point of the working fluid to maintain two-phase state. Thermosiphon with mixed working fluid has a potential to widen the operational temperature range. In this study, the physical behavior of mixed working fluid during the transient operation of thermosiphon was analyzed with temperature-mole fraction diagram. The condenser and the evaporator temperature variations were explained by the dew line and the bubble line of the mixture. It is encouraging that the thermosiphon operation commences early with larger fraction of high boiling point component, but the temperature gap between the condenser and the evaporator due to the separation of two components has a negative effect on the officient cool down process.