Computational Investigation of Different Turbulent Models When Predicting Airflow in an Enclosure

In the present study, a numerical investigation is carried out for an isothermal case, a hot case and a cold case with FLUENT code. Three turbulence models are considered: the k-ε realisable model, the RNG k-ε model and the RSM linear model. The obtained results are compared to experiments and show generally a good agreement for the mean velocities and temperatures, but less satisfactory for the turbulent stress. The performance of the RSM model is remarkable. Even if none of the models is able to give the exact experimental pattern on the map of turbulence, the RSM model seems able to predict such configuration.

Applicability of the Wavy-Wall Model of Fluidelastic Instability to a Normal Triangular Tube Array

The Yetisir and Weaver formulation of the Lever and Weaver “wavy-wall” model for fluidelastic instability in tube arrays has been implemented for both normal triangular and in-line square arrays. The sensitivity of this model to the input parameters (i.e. attachment and separation points, decay function and phase lag function) has been examined. It was found that variations in the decay function were most significant and that the model behaved similarly for both array types. The predicted surface pressure perturbation due to tube displacement has then been compared with experimental data. For the in-line array the model behaviour compared well, while for the normal triangular array, the predictions were not representative of the experimental data. It is concluded that while the Yetisir and Weaver model can be applied successfully to in-line square arrays, it is not appropriate for densely packed normal triangular arrays.

Wind Effects on Sloshing of a Floating Roof in a Cylindrical Liquid Storage Tank

Sloshing of a floating roof in an open-topped cylindrical liquid storage tank under wind loads is investigated analytically. Wind tunnel test in a turbulent boundary layer is carried out to measure the wind pressure distributing over the roof surface. The measured data for the wind pressure is then utilized to predict the wind-induced dynamic response of the floating roof, which is idealized herein as an isotropic elastic plate of uniform stiffness and mass. The dynamic interaction between the liquid and the floating roof is taken into account exactly within the framework of linear potential theory. Numerical results are presented which illustrate the significant effect of wind loads on the sloshing response of the floating roof.

Interaction Between Wind Loading and Japanese Slates: Effect on Vibration and Scattering

A series of wind tunnel tests was conducted on the vibration and scattering behavior of full-sized model of roof tiles, which were used widely for roofings of Japanese wooden dwellings. This study has investigated the nature and source of the vibrating and scattering behavior of roof tiles with the aim of providing a better insight to the mechanism. The roof tiles were set up on the pitched roof in the downstream of the flow from the wind tunnel. The vibrations for the roof tiles were measured by the Laser Doppler Vibrometry and the accelerometer, and the practical natural frequencies of the roof tiles were analyzed by the impulse force hammer test method. The motions of the vibration and scattering were observed by the high-speed video camera. Based on the consideration on the results of the measurements, there is a basic mechanism which can lead to flow-induced vibrations of the roof tiles. This mechanism is similar to that of the so-called fluttering instability, which appears as the self-excited oscillation in the natural mode of the structure at the certain critical flow speed. The values of the frequencies for the oscillating relate to the values of natural frequencies of the vibration.

Toward a Global Model for FSI in Tube Bundles

It is well known that a fluid may strongly influence the dynamic behaviour of a structure. Many different physical phenomena may take place, depending on the conditions: fluid at rest, fluid flow, little or high displacements of the structure. Inertial effects can take place, with lower vibration frequencies, dissipative effects also, with damping, instabilities due to the fluid flow (Fluid Induced Vibration). In this last case the structure is excited by the fluid. The paper deals with the vibration of tube bundles in a fluid, under a seismic excitation or an impact. In this case the structure moves under an external excitation, and the movement is influenced by the fluid. The main point in such system is that the geometry is complex, and could lead to very huge sizes for a numerical analysis. Many works has been made in the last years to develop homogenization methods for the dynamic behaviour of tube bundles (/2/ and /3/). The size of the problem is reduced, and it is possible to make numerical simulations on wide tubes bundles with reasonable computer times. These homogenization methods are valid for “little displacements” of the structure (the tubes), in a fluid at rest. The fluid movement is governed by the Euler equations. In this case, only “inertial effects” will take place, with globally lower frequencies. It is well known that dissipative effects due to the fluid may take place, even if the displacements of the tube are no so high, or if the fluid is not still (/4/, /5/, /6/ and /8/). Such effects may be described in the homogenized models by using a Rayleigh damping, but the basic assumption of the model remains the “perfect fluid” hypothesis. It seem necessary, in order to get a best description of the physical phenomena, to build a more general model, based on the general Navier Stokes equation for the fluid. The homogenization of such system will be much more complex than for the Euler equations. The paper doesn’t pretend to give a general solution of the problem, but only points out the most important key points to build such homogenized model for the dynamic behaviour of tubes bundles in a fluid.

Transient Dynamic Responses of an Integrated Air-Liquid-Elastic Tank Interaction System Subject to Earthquake Excitations

Sloshing problems in partially filled tanks are of increasing concerns in many engineering fields such as marine, chemical, aerospace engineering and automobile industry. The interactive dynamic behaviour of liquid and tank due to their interaction under various loading conditions can have vital impact on the integrity and safe operation of the system. Studies of liquid sloshing and its dynamic effect on the containers are necessary in the early design stage. Currently, most investigations on sloshing problems mainly focus on the analysis of liquids in rigid tanks where the fluid-structure interactions were neglected. Studies on fluid-structure interactions are limited to two phases of liquid-tank interactions. Three phase interactions involving air, liquid and elastic tank are rarely considered. In this paper, the dynamic behaviour of an air-liquid-elastic tank interaction system is investigated. The tank filled with air and liquid is supported at four equally spaced positions around the outer shell. The dynamic pressure in the liquid / air and the displacement in the elastic solid are used as variables to formulate the numerical model incorporating a substructure-subdomain approach and numerical simulations are presented based on a developed computer program. The natural frequencies in association with the corresponding vibration modes and the transient dynamic responses of the complex coupled system subject to earthquake excitations are presented. The ground motion data recorded from El-Centro earthquake is used as an earthquake load to the system. Different interactive cases are examined. These include liquid sloshing in a rigid tank, air-liquid interactions in a rigid tank, liquid-elastic tank interactions and three phase air-liquid-tank interactions. The numerical results obtained reveal the complex coupled behaviour of the system as well as the air effect on dynamic displacement and sloshing pressure. This study provides information for the design of liquid / gas filled tanks in which sloshing behaviour is of interest.

A Numerical Simulation of Vortex Induced Vibration on a Elastically Supported Circular Rigid Cylinder at Moderate Reynolds Numbers

The present paper is the sequel of a previously published study which is concerned with the numerical simulation of vortex-induced-vibration (VIV) on an elastically supported rigid circular cylinder in a fluid cross-flow (A. Placzek, J.F. Sigrist, A. Hamdouni; Numerical Simulation of Vortex Shedding Past a Circular Cylinder at Low Reynolds Number with Finite Volume Technique. Part I: Forced Oscillations, Part II: Flow Induced Vibrations; Pressure Vessel and Piping, San Antonio, 22–26 July 2007). Such a problem has been thoroughly studied over the past years, both from the experimental and numerical points of view, because of its theoretical and practical interest in the understanding on flow-induced vibration problems. In this context, the present paper aims at exposing a numerical study based on a fully coupled fluid-structure simulation. The numerical technique is based on a finite volume discretisation of the fluid flow equations together with i) a re-meshing algorithm to account for the cylinder motion ii) a projection subroutine to compute the forces induced by the fluid on the cylinder and iii) a coupling procedure to describe the energy exchanges between the fluid flow and solid motion. The study is restricted to moderate Reynolds numbers (Re∼2.000–10.000) and is performed with an industrial CFD code. Numerical results are compared with existing literature on the subject, both in terms of cylinder amplitude motion and fluid vortex shedding modes. Ongoing numerical studies with different numerical techniques, such as ROM (Reduced Order Models)-based methods, will complete the approach and will be published in next PVP conference. These numerical simulations are proposed for code validation purposes prior to industrial applications in tube bundle configuration.

Multi-Scale Simulation of Fluid-Structure Interaction Induced Erosion on the Pipe Surface

Erosion results from interactions between the pipe surface and fluids traveling along the surface. Fluid-structure interactions have a profound influence on the erosion that takes place. The location, rate and extent of thinning or loss of a protective surface film depend strongly on the nature of the flow regime and interactions. Erosion-corrosion involves the modification, thinning and removal of protective films composed of corrosion product or scale deposits from a susceptible metal surface by fluid shear stress under high turbulence conditions. In the paper, multi-scale simulation of fluid-structure interactions between the flow and the protective films on the pipe surface is presented. The fluid shear stress and pressure of the flow in a pipe with a step is obtained by macro-fluid dynamic analysis. Viscous forces and the system’s pressure impose forces to the surface of the pipe. Using micro-simulation method, the fluid-structure interactions between the flow and the protective films is modeled. The deformation of the protective films is shown and changed with the different velocity and flow regime. Using the multi-scale simulation of fluid-structure interactions, the location, rate and extent of the erosion on the pipe surface can be predicted. The results are proved by the actual instances.

Effect of Vertical Pipe Length on the Thermal Stratification in Nuclear Power Plant Surgeline

During operating transients of the pressurizer, thermal stratification effect may occur especially in the horizontal parts of the surge line. US NRC requires consideration of thermal stratification in surge line as phenomenon that must be considered in the design basis of the surge line. Generally, the fatigue usage factor of the surge line is comparative high, due to its operating temperature and pressure transients and its thermal stratification loads. In this study we have performed some parametric fluid-structure interaction analyses with different length variables of the vertical part of the surge line to study the relationship between the magnitude of thermal stratification and the length of vertical part of the surge line. The conservativeness of the traditional finite element model for thermal stratification analysis based on the conservative assumption in the surge line was also discussed by comparison of the results of three-dimensional time transient fluid-structure interaction analysis of this study. Stresses calculated with three-dimensional time transient model were considerably reduced comparing with the traditional analysis.

Wave Propagation in Thin-Walled Aortic Analogues

Research wave propagation in liquid filled vessels is often motivated by the need to understand arterial blood flow. Theoretical and experimental investigation of the propagation of waves in flexible tubes has been studied by many researchers. The analytical one dimensional frequency domain wave theory has a great advantage of providing accurate results without the additional computational cost related to the modern time domain simulation models. For assessing the validity of analytical and numerical models well defined in-vitro experiments are of great importance. The objective of this paper is to present a frequency domain transmission line analytical model based on one-dimensional wave propagation theory and validate it against experimental data obtained for aortic analogues. The elastic and viscoelastic properties of the wall are included in the analytical model. The pressure, flow and wall distention results obtained from the analytical model are compared with experimental data in two straight tubes with aortic relevance. The analytical models and the experimental measurements were found to be in good agreement when the viscoelastic properties of the wall are taken into account.