CFD-Tool for Thermal-Hydraulics Pressurised Thermal Shock Analysis: Qualification of the Code_Saturne

This paper explains the numerical program concerning the new thermalhydraulic Code_Saturne qualification for Safety Injection studies. Within the frame of the plant life time project, an analysis has shown that the most severe loading conditions are generated by a pressurised injection of cold water in the downcomer of a Reactor Pressure Vessel. For this kind of transients, a thermal hydraulics study has to be carried out in order to better adjust the accurate distribution of the fluid temperature in the downcomer. For that, the numerical tools have to be able to simulate the physical phenomena present during the Pressurised Thermal Shock. (PTS). For this qualification task, we have investigated one configuration related to an injection of cold water particularly in cold leg but also in a downcomer. One experiment test case has been studied and this paper gives a comparison between experiment and numerical results in terms of temperature field.

Solution Adaptive Grids Applied to Low Reynolds Number Flow

A numerical study has been undertaken to investigate the use of a solution adaptive grid for flow around a cylinder in the laminar flow regime. The main purpose of this work is twofold. The first aim is to investigate the suitability of a grid adaptation algorithm and the reduction in mesh size that can be obtained. Secondly, the uniform asymmetric flow structures are ideal to validate the mesh structures due to mesh refinement and consequently the selected refinement criteria. The refinement criteria in this work are derived from turbulent viscosity, which is not applied to the flow simulation, but instead used as a measure for grid refinement.

Fluid-Structure Interaction for Hydrodynamic Problems: Impact Between a Tanker Bow Flare and a Submarine

A methodology to predict the capacity of a nuclear submarine hull to act as a protective container and energy absorber under impact by an another underwater structure is needed. Principia Marine, company of Research in Shipbuilding (formerly IRCN, Institut de Recherche en Construction Navale), is responding to this need by developing an underwater impact crash prediction methodology based upon LS-DYNA3D software. Several physical phenomena with their own characteristic times follow one another at the time of the shock. So different but complementary tasks to develop this methodology were worked individually. This paper deals with contribution to this ongoing program that breaks up into two objectives. The first goal aims to highlight the effect of water on the structural deformation at the time of the collision between a nuclear submarine and a tanker ram bow, which is generally plane. The two-dimensional modelling of this collision uses an Eulerian formulation for the fluid and a Lagrangian formulation for the structure. The fluid-structure interaction is treated by an Euler/Lagrange penalty coupling. This method of coupling, which makes it possible to transmit the efforts in pressure of the Eulerian grid to the Lagrangian grid and conversely, is relatively a recent algorithmic development. It was successfully used in many scientific and industrial applications: the modelling of the attack of birds on the fuselage of a Jet for the Boeing Corporation, the underwater explosion shaking the oil platforms, and airbag simulation… The requirements of modelling for this algorithm are increasingly pointed. Thus, the second objective of this paper is to compare the results in pressures and velocities near the bulb for two cases, in the first one, the bulb is modelled by a slip boundary condition, in the second one, the bulb is a rigid Lagrangian structure, which involves the use of the Euler/Lagrange penalty coupling.

Optimisation of Loads in Piping Systems by Realistic Calculation Method Applying FSI and Dynamic Friction

To reduce costs and to extend the lifetime of piping systems their design loads due to valve action have to be optimised. To get the best effect the results of the fluiddynamic and structural calculations should be realistic as far as possible. Therefore the calculation programs were coupled to consider the fluid structure interaction and the effect of dynamic fluid friction was introduced to get realistic results of oscillations due to pressure surges. Detailed modelling of check valve behaviour allows to minimise the pressure surge loading by improving the valve function and adapting it to the system behaviour. The method was validated at measurements of load cases in power plant piping systems. Results with different load cases show the effectiveness of reducing the fluid forces on piping. Examples are given to prove the reduction of supports.

Fluid-Structure Interaction of Stirrers in Mixing Vessels: Part I — Development of the Mechanical Model

Mixing stirrers are subject to severe damages when the rotational speed approaches the Eigenfrequency. Damping due to fluid-structure interaction between the mixing stirrer and the fluid in the vessel has major influence on the Eigenfrequency. Therefore coupled analysis of the flow field within a mixing vessel and the structural dynamic response of the stirrer should be conducted in order to evaluate vibrational amplitudes to guarantee life time safety for the stirrer. In some previous works at our institute CFD analysis of mixing stirrers has been carried out for both one-phase and two-phase flow. In this paper a simplified numerical model based on Newmark’s integration scheme is developed for the stirrer dynamics that is suitable to be implemented in the CFD code as a user subroutine. Results in terms of Eigenfrequencies are compared to results of analytical formulae and FEM results and show excellent agreement. In the second part of the paper the fully fluid-structure coupled analysis is presented (Part II).

Design of Tunnels in Swelling Soils: Determination of Swelling Soil Properties

This paper includes a study of soil swelling for tunnels projects. It is performed using a flexible odometer which authorizes a lateral deformation of the soil sample during swelling and allows the measurement of the lateral swell pressure. The paper is composed of three parts. The first one concerns analysis of swelling phenomenon in tunnel projects. The second one presents the swelling odometer which was used in this work. The last one presents results obtained on clay and discusses the influence of the swelling condition on both axial and lateral soils expansion.

CFD Simulation of Soil Flow Over Augers

The modelling of soil as an engineering material is confined, in the most part, to the investigation of how it behaves under loading and unloading. A key assumption made in existing models is that the soil is similar in behaviour to a solid and is generally elastic-perfectly plastic and has a linear stress strain relationship. The rapid displacement of soil, such as flow, has been studied far less. The aim of this paper is to study such behaviour and present the initial results of the flow around a rotating auger assuming the soil acts as a fluid. These initial simulations rely on the governing equations of fluid flow assuming Newtonian viscosity. Although evidence points to soil not having constant coefficient of viscosity, this study and a further study by Tardos [1] shows that for loose soils with a low angle of internal friction, such as liquefied sand, the Newtonian viscosity is an acceptable assumption. The patterns of soil movement around the auger are shown over two different drilling tools. Visual and numerical results of soil movement are presented.

Fluid-Structure Interaction of Stirrers in Mixing Vessels: Part II — Fully Coupled Simulation

Mixing Stirrers are subjected to severe damages [Strohmeier (1996), Strohmeier and Ho¨lzl (1998)] when the rotational speed approaches the critical rotational speed nkrit (eigenfrequency). Because of resonant vibrations, the stirrer deflection approaches infinity (no damping case). The possibilities of an accurate design of mixing stirrers with analytical calculations [Fischer and Strohmeier (2000)] are often very unsatisfactional, due to the complex effects of the fluid medium on the structure (impeller), and consequently its critical speed and its vibrational amplitudes cannot be readily defined. To consider transient fluid effects and out-of-balance forces, it is necessary to implement a coupled analysis of flow field and structural dynamic response of the stirrer in the CFD code as a user subroutine. As a new aspect, a rotating grid (sliding mesh) was combined with a deformable grid to simulate the impeller movement. The results are compared to experimental and analytical data and show good agreement.

Modeling of Flow Around a Circular Cylinder in Sub-Critical Flow Regime With the Use of Dynamic Grid Adaptation

In the present study a Dynamic Grid Adaptation (DGA) algorithm is used for predicting flow around a circular cylinder in sub-critical flow regime at a Reynolds number of 1.4·105. The reason for adopting a DGA algorithm is to use the flow field as a driving criteria for mesh refinement rather then the geometry of the computational domain or the judgment of the CFD user as common in conventional mesh. It is demonstrated how DGA reduces the mesh size significantly and also makes time consuming mesh testing unnecessary. The concept being adopted is to concentrate mesh refinement in regions with high gradients and high turbulent viscosity, while in the region further downstream where the flow is fully developed a coarser mesh will develop and turbulence is modeled with the Large Eddy Simulation (LES) turbulence model. The aim of the study is to present an appropriate variable for mesh refinement, which accomplishes a high rate of mesh refinement in the region with high gradients. The new variable is a product of the local mesh cell size and the rate of strain and includes two additional variables to allow control over the refinement behaviour.

Initial CFD Simulations of High Aspect Ratio Jets

High aspect ratio jets are significant in many industrial settings and can be crucial to safety and performance. As more of these flows are being modelled it is therefore essential that the behaviour of these jets is understood and if necessary modelled correctly. Failure to do so could result in jeopardising human life and have considerable environmental implications. Upon an offshore superstructure there exists many high pressure pipelines carrying hydrocarbons often at high temperature. Much safety work before the commissioning of offshore superstructures is done numerically and it is therefore of vital importance to have confidence in the assumptions and models used. This paper concentrates on the numerical modelling of the release of gas at high pressures into the atmosphere and is based on existing experimental work. Initial numerical work with the k-ε two-equation turbulence model was undertaken to compare against this existing experimental data. In revisiting the use of the standard k-ε turbulence model with an elliptical solver replacing the parabolic used in the past for a complex flow and validating it against experimental data could have implications for the CFD modelling of complex flows.