Numerical Analysis of Fluidelastic Instability in a Normal Triangular Tube Array

2009 ◽  
Author(s):  
Stephen Gillen ◽  
Craig Meskell
Keyword(s):  
Tube Bundle ◽  
Pressure Coefficient ◽  
Navier Stokes ◽  
Force Coefficients ◽  
Fluidelastic Instability ◽  
Pitch Ratio ◽  
Flow Through ◽  
Critical Velocities ◽  
Experimental Values ◽  
Reynolds Number Dependence

Investigation of steady flow through a normal triangular tube bundle is carried out numerically using a 2D Reynolds Averaged Navier-Stokes solver. Pitch to diameter ratios of 1.25 and 1.32 are simulated with a single tube displaced and the resulting force coefficients measured. Comparison of pressure coefficient with experimental data indicates simulations provide a reliable indication of Reynolds number dependence. These fluid force coefficients are then used as input into the quasi-unsteady model in order to predict the critical velocity of damping controlled fluidelastic instability for a single degree of freedom tube within an array. The predicted critical velocities are in the range of empirical data from the literature. The predicted critical velocities for the pitch ratio of 1.25 are within 30% of the experimental values previously reported.

Three-Dimensional Effects on Slamming Loads

2021 ◽  
Author(s):  
Shan Wang ◽  
C. Guedes Soares
Keyword(s):  
3D Model ◽  
Numerical Solutions ◽  
Pressure Coefficient ◽  
Three Dimensional ◽  
The Body ◽  
Navier Stokes ◽  
Courant Number ◽  
Dimensional Effects ◽  
Coefficient Distribution ◽  
Experimental Values

Abstract Three-dimensional effects on slamming loads predictions of a ship section are investigated numerically using the unsteady incompressible Reynolds-Average Navier-Stokes (RANS) equations and volume of fluid (VOF) method, which are implemented in interDyMFoam solver in open-source library OpenFoam. A convergence and uncertainty study is performed considering different resolutions and constant Courant number (CFL) following the ITTC guidelines. The numerical solutions are validated through comparisons of slamming loads and motions between the CFD simulations and the available experimental values. The total slamming force and slamming pressures on a 2D ship section and the 3D model are compared and discussed. Three-dimensional effects on the sectional force and the pressures are quantified both in transverse and longitudinal directions of the body considering various entry velocities. The non-dimensional pressure coefficient distribution on the 3D model is presented.

Numerical Estimation of Fluidelastic Instability in Staggered Tube Arrays

2009 ◽  
Author(s):  
H. Omar ◽  
M. Hassan ◽  
A. Gerber
Keyword(s):  
Moving Boundary ◽  
Tube Bundle ◽  
Navier Stokes ◽  
Numerical Estimation ◽  
Arbitrary Lagrangian Eulerian ◽  
Fluid Forces ◽  
Damping Parameter ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Reynolds Average

This study investigates the unsteady flow and the resulting fluidelastic forces in a tube bundle. Numerical simulations are presented for normal triangle tube arrays with pitch-to-diameter (P/d) ratios of 1.35, 1.75, and 2.5 utilizing a 2-dimensional model. In this model a single tube was forced to oscillate within an otherwise rigid array. Fluid forces acting on the oscillating tube and the surrounding tubes were estimated. The predicted forces were utilized to calculate fluid force coefficients for all tubes. The numerical model solves the Reynolds-Average Navier-Stokes (RANS) equations for unsteady turbulent flow, and is cast in an Arbitrary Lagrangian-Eulerian (ALE) form to handle mesh the motion associated with a moving boundary. The fluidelastic instability (FEI) was predicted for both single and fully flexible tube arrays over a mass damping parameter (MDP) range of 0.1 to 200. The effect of the P/d ratio and the Reynolds number on the FEI threshold was investigated in this work.

Numerical Characterization of the Area Perturbation and Timelag for a Vibrating Tube Subjected to Cross-Flow

2014 ◽  
Author(s):  
Salim El Bouzidi ◽  
Marwan Hassan ◽  
Lais L. Fernandes ◽  
Atef Mohany
Keyword(s):  
Tube Bundle ◽  
Cross Flow ◽  
Theoretical Models ◽  
Design Guidelines ◽  
Navier Stokes ◽  
Arbitrary Lagrangian Eulerian ◽  
Dynamic Simulations ◽  
Numerical Characterization ◽  
Fluidelastic Instability ◽  
The Impact

Fluidelastic instability can have disastrous effects on the integrity of steam generators. Over the last five decades there has been a great deal of research done in an attempt to understand this phenomenon. These efforts have resulted in several theoretical models and design guidelines. The semi-analytical model of fluidelastic instability initially developed by Lever and Weaver is based on a single tube in a channel flow. The mechanism responsible for instability was found to be one of flow redistribution. While previous studies have been able to characterize the pressure and velocity within a tube bundle, the behaviour of the area of the channel has not yet been fully investigated. The current study aims to characterize the area of the channel surrounding the tube. Reynolds Averaged Navier Stokes (RANS) equations are cast in an Arbitrary Lagrangian Eulerian (ALE) form and are used to compute the flow conditions in a rigid tube bundle due to a single flexible tube vibrating in the transverse direction. The properties of the velocity field are used to determine the channel boundaries. Properties of the channel area such as area perturbation, mean area, and area phase are investigated for various reduced flow velocities. Dynamic simulations are conducted to determine the impact on the stability threshold for transverse fluid force cases using a mass damping parameter range of 10–200.

SRANS and URANS CFD Simulations of Turbulent VHTR Lower Plenum Flow

2007 ◽  
Author(s):  
A. Ridluan ◽  
A. Tokuhiro
Keyword(s):  
Nuclear Reactor ◽  
Tube Bundle ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Cfd Simulations ◽  
Eddy Simulation ◽  
Flow Phenomena ◽  
Flow Through ◽  
Reynolds Averaged Navier Stokes

Time-dependent and time-independent CFD simulations of the flow through a staggered tube bundle were performed. This flow configuration partially simulates the anticipated flow in the lower plenum of a Very High Temperature Reactor (VHTR) design. To design a nuclear reactor with confidence, one needs strict benchmarking as part of a validation and verification exercise for any and all commercial CFD codes. Thus CFD simulations (FLUENT) of isothermal (at present), periodic flow through a tube bundle using both Steady Reynolds Averaged Navier-Stokes (SRANS) and Unsteady Reynolds Averaged Navier-Stokes (URANS) equations were investigated. Selected turbulence models for a single tube diameter and inlet velocity based Re-number, Re ∼ 1.8 × 104, were investigated. The first-order turbulence models were: a standard k-ε turbulence model, a Renormalized Group (RNG) k-ε model, and lastly, a Shear Stress Transport (SST) k-ε model; the second-order model was a Reynolds Stress Model (RSM). Comparison of CFD simulations against experimental results of Simonin and Barcouda was undertaken at five stations (x, y) locations. Under the SRANS, we found the ability of the models to predict the turbulence stresses (u′u′, v′v′, u′v′) generally marginal to poor. However, upon adapting a concept from Large Eddy Simulation (LES), our URANS simulation with RSM revealed a spatiotemporal, oscillating flow structures in the wake. In contrast, it appears that the URANS with (even a) RNG k-ε model is unable to simulate this flow phenomena. In fact, the data suggests that the RNG k-ε model is too spatiotemporally dissipative. Some aspects of the SRANS versus URANS and using the aforementioned turbulence models will be presented.

Computation of Velocity Profiles and Pressure Coefficients for a Laminar Flow of Air Over Staggered Array of Tubes

2005 ◽  
Author(s):  
Ramin Rahmani ◽  
Ahad Ramezanpour ◽  
Iraj Mirzaee ◽  
Hassan Shirvani
Keyword(s):  
Laminar Flow ◽  
Stokes Equations ◽  
Tube Bundle ◽  
Pressure Coefficient ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Tube Arrays ◽  
Volume Method

In this study a two dimensional, steady state and incompressible laminar flow for staggered tube arrays in crossflow is investigated numerically. A finite-volume method is used to discretize and solve the governing Navier-Stokes equations for the geometries expressed by a boundary-fitted coordinate system. Solutions for Reynolds numbers of 100, 300, and 500 are obtained for a tube bundle with 10 longitudinal rows. Local velocity profiles on top of each tube and corresponding pressure coefficient are presented at nominal pitch-to-diameter ratios of 1.33, 1.60, and 2.00 for ES, ET, and RS arrangements. Differences in location of separation points are compared for three different arrangements. The predicted results on flow field for pressure coefficient showed a good agreement with available experimental measurements.

LES and PANS of Turbulent Flow Through a Staggered Tube Bundle

2017 ◽  
Author(s):  
G. Minelli ◽  
S. Krajnović ◽  
B. Basara
Keyword(s):  
Experimental Data ◽  
Large Eddy Simulation ◽  
Tube Bundle ◽  
Dominant Frequency ◽  
Navier Stokes ◽  
Numerical Techniques ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Through ◽  
Good Agreement

Two unsteady numerical techniques, Partially-Averaged Navier Stokes (PANS) and Large Eddy Simulation (LES), are used to predict the flow in a tube bundle. The results were compared with the existing experimental data. Both methods predicted the flow in a relatively good agreement with the experimental data although the PANS simulation used only fifty percent of the computational nodes compared to the LES. The results of the simulations are used to study the unsteadiness in the flow and identify a dominant frequency of the flow.

scholarly journals Transient Pressure-Driven Electroosmotic Flow through Elliptic Cross-Sectional Microchannels with Various Eccentricities

Computation ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 27
Author(s):  
Nattakarn Numpanviwat ◽  
Pearanat Chuchard
Keyword(s):  
Laplace Transform ◽  
Electroosmotic Flow ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Mathieu Functions ◽  
Navier Stokes Equations ◽  
Flow Rates ◽  
Elliptic Cross ◽  
Flow Through ◽  
Relative Errors

The semi-analytical solution for transient electroosmotic flow through elliptic cylindrical microchannels is derived from the Navier-Stokes equations using the Laplace transform. The electroosmotic force expressed by the linearized Poisson-Boltzmann equation is considered the external force in the Navier-Stokes equations. The velocity field solution is obtained in the form of the Mathieu and modified Mathieu functions and it is capable of describing the flow behavior in the system when the boundary condition is either constant or varied. The fluid velocity is calculated numerically using the inverse Laplace transform in order to describe the transient behavior. Moreover, the flow rates and the relative errors on the flow rates are presented to investigate the effect of eccentricity of the elliptic cross-section. The investigation shows that, when the area of the channel cross-sections is fixed, the relative errors are less than 1% if the eccentricity is not greater than 0.5. As a result, an elliptic channel with the eccentricity not greater than 0.5 can be assumed to be circular when the solution is written in the form of trigonometric functions in order to avoid the difficulty in computing the Mathieu and modified Mathieu functions.

On LES Methods Applied to Seal Geometries

2012 ◽  
Author(s):  
James Tyacke ◽  
Richard Jefferson-Loveday ◽  
Paul Tucker
Keyword(s):  
Maximum Error ◽  
Labyrinth Seal ◽  
Navier Stokes ◽  
Final Solution ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Wide Range ◽  
Large Eddy ◽  
Rans Models ◽  
Flow Through

Nine Large Eddy Simulation (LES) methods are used to simulate flow through two labyrinth seal geometries and are compared with a wide range of Reynolds-Averaged Navier-Stokes (RANS) solutions. These involve one-equation, two-equation and Reynolds Stress RANS models. Also applied are linear and nonlinear pure LES models, hybrid RANS-Numerical-LES (RANS-NLES) and Numerical-LES (NLES). RANS is found to have a maximum error and a scatter of 20%. A similar level of scatter is also found among the same turbulence model implemented in different codes. In a design context, this makes RANS unusable as a final solution. Results show that LES and RANS-NLES is capable of accurately predicting flow behaviour of two seals with a scatter of less than 5%. The complex flow physics gives rise to both laminar and turbulent zones making most LES models inappropriate. Nonetheless, this is found to have minimal tangible results impact. In accord with experimental observations, the ability of LES to find multiple solutions due to solution non-uniqueness is also observed.

scholarly journals On Damping and Fluidelastic Instability in a Tube Bundle Subjected to Two-Phase Cross-Flow

2007 ◽  
Author(s):  
Joaquin E. Moran ◽  
David S. Weaver
Keyword(s):  
Flow Regime ◽  
Void Fraction ◽  
Tube Bundle ◽  
Damping Ratio ◽  
Pressure Fluctuations ◽  
Cross Flow ◽  
Phase Changes ◽  
Working Fluid ◽  
Two Phase ◽  
Fluidelastic Instability

An experimental study was conducted to investigate damping and fluidelastic instability in tube arrays subjected to two-phase cross-flow. The purpose of this research was to improve our understanding of these phenomena and how they are affected by void fraction and flow regime. The working fluid used was Freon 11, which better models steam-water than air-water mixtures in terms of vapour-liquid mass ratio as well as permitting phase changes due to pressure fluctuations. The damping measurements were obtained by “plucking” the monitored tube from outside the test section using electromagnets. An exponential function was fitted to the tube decay trace, producing consistent damping measurements and minimizing the effect of frequency shifting due to fluid added mass fluctuations. The void fraction was measured using a gamma densitometer, introducing an improvement over the Homogeneous Equilibrium Model (HEM) in terms of density and velocity predictions. It was found that the Capillary number, when combined with the two-phase damping ratio (interfacial damping), shows a well defined behaviour depending on the flow regime. This observation can be used to develop a better methodology to normalize damping results. The fluidelastic results agree with previously presented data when analyzed using the HEM and the half-power bandwidth method. The interfacial velocity is suggested for fluidelastic studies due to its capability for collapsing the fluidelastic data. The interfacial damping was introduced as a tool to include the effects of flow regime into the stability maps.

Estimation of the Time Delay Associated With Damping Controlled Fluidelastic Instability in a Normal Triangular Tube Array

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
John Mahon ◽  
Craig Meskell
Keyword(s):  
Time Delay ◽  
Cross Flow ◽  
Fluid Forces ◽  
Fluidelastic Instability ◽  
Order Of Magnitude ◽  
Sample Frequency ◽  
Pitch Ratio ◽  
Parameterized Model ◽  
Semi Empirical ◽  
Insight Into

Fluidelastic instability (FEI) produces large amplitude self-excited vibrations close to the natural frequency of the structure. For fluidelastic instability caused by the damping controlled mechanism, there is a time delay between tube motion and the resulting fluid forces but magnitude and physical cause of this is unclear. This study measures the time delay between tube motion and the resulting fluid forces in a normal triangular tube array with a pitch ratio of 1.32 subject to air cross-flow. The instrumented cylinder was forced to oscillate in the lift direction at three excitation frequencies for a range of flow velocities. Unsteady surface pressures were monitored with a sample frequency of 2 kHz at the mid plane of the instrumented cylinder. The instantaneous fluid forces were obtained by integrating the surface pressure data. A time delay between the tube motion and resulting fluid forces was obtained. The nondimensionalized time delay was of the same order of magnitude assumed in the semi-empirical quasi-steady model (i.e., τ2 = 0.29 d/U). Although, further work is required to provide a parameterized model of the time delay which can be embedded in a model of damping controlled fluidelastic forces, the data already provides some insight into the physical mechanism responsible.

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