Turbulent Flow of Viscoelastic Fluid Through Complicated Geometry

For the purpose of elucidating the mechanism of drag reduction by additives and finding a way to judge optimum drag-reducing additives through a simple rheological test, we performed DNS analysis of viscoelastic fluid turbulent flow in a two-dimensional channel. In this calculation, we employed the Giesekus constitutive equation to model the interaction between water-soluble polymer, or the elastic micellar network structure, and solvent. We calculated the fluid flow by varying the rheological parameters of the model. We examined the turbulent kinetic energy budget and studied the “viscoelastic contribution” term in the budget equation for turbulent intensity, which is not apparent in normal Newtonian fluid turbulence. Viscoelastic contribution has a characteristic effect on viscoelastic fluid turbulence. We concluded that the viscoelastic contribution plays a major role in turbulent frictional drag reduction. Dissipation and viscoelastic contribution serve as a key factor of turbulent kinetic energy loss in most areas of the channel. From the visualization of local and instantaneous eddy behavior, we discussed the relationship between viscoelastic contribution, elastic energy and turbulent production. We found that viscoelastic contribution serves as a direct local source of turbulent production, and that energy is stored in the elasticity.

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0606 Performance of Reynolds-stress model for turbulent flow of drag reducing viscoelastic fluid

The Proceedings of the Fluids engineering conference ◽

10.1299/jsmefed.2015._0606-1_ ◽

2015 ◽

Vol 2015 (0) ◽

pp. _0606-1_-_0606-4_

Author(s):

Shun INOUE ◽

Takahiro TSUKAHARA ◽

Yasuo KAWAGUCHI

Keyword(s):

Turbulent Flow ◽

Reynolds Stress ◽

Viscoelastic Fluid ◽

Reynolds Stress Model ◽

Stress Model

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Comparative Studies of Turbulence Models Application in Thermal Hydraulic Analysis of Nuclear Reactor Core

ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting: Volume 1, Symposia – Parts A, B, and C ◽

10.1115/fedsm-icnmm2010-30109 ◽

2010 ◽

Author(s):

Heyi Zeng ◽

Yun Guo

Keyword(s):

Fluid Dynamics ◽

Turbulent Flow ◽

Secondary Flow ◽

Nuclear Reactor ◽

Nuclear Reactors ◽

Reactor Core ◽

Turbulence Models ◽

Flow Phenomena ◽

Nuclear Reactor Core ◽

Complicated Geometry

Rod bundles are essential elements of pressurized water nuclear reactors. They consist of tightly packed arrays of rods, which contain the nuclear fuel and are surrounded by flowing liquid coolant. Flow phenomena in the subchannels bounded by adjacent rods are quite complex and exhibit patterns not present in pipe flows. Development of nuclear reactors and of fuel assemblies requires fluid dynamics analysis activities. The detailed prediction of velocity and temperature distributions inside a rod bundle is one of the main objectives of the current research in reactor thermal hydraulics. Computational fluid dynamics (CFD) simulation is of great interest for the design and safety analysis of nuclear reactors since it has recently achieved considerable advancements. In the present studies, numerical simulation were performed on developed turbulent flow through core subchannels with configurations of triangle and square lattice, and impact of different turbulence models built-in software package FLUENT upon simulation results of velocity distribution and hydraulic characteristics in channels with complicated geometry were compared and analyzed. Results show that simulation result greatly depends on turbulence models. Due to the complicated geometric construction, the complicated three-dimensional turbulent flow shows highly anisotropic characteristics. Turbulence models assuming isotropic turbulent viscosity failed to predict secondary flow phenomena during turbulent flow in fuel assembly channel. By solving Reynolds stresses transport equations, more elaborate Reynolds stress model (RSM) can catch secondary flow accurately. The present studies have provided valuable references and guidelines for further investigation on convective heat transfer simulation in complicated geometry and thermalhydrulic analysis of nuclear reactor core.

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