Fluid Damping and Fluid Stiffness of a Tube Row in Crossflow

1994 ◽  
Vol 116 (4) ◽  
pp. 370-383 ◽  
Author(s):  
S. S. Chen ◽  
S. Zhu ◽  
J. A. Jendrzejczyk
Keyword(s):  
Flow Velocity ◽  
Water Channel ◽  
Excitation Frequency ◽  
Excitation Amplitude ◽  
Design Guideline ◽  
Fluid Forces ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Fluid Damping ◽  
Reliable Design

Motion-dependent fluid forces acting on a tube array were measured as a function of excitation frequency, excitation amplitude, and flow velocity. Fluid-damping and fluid-stiffness coefficients were obtained from measured motion-dependent fluid forces as a function of reduced flow velocity and excitation amplitude. The water channel and test setup provide a sound facility for obtaining key coefficients for fluidelastic instability of tube arrays in crossflow. Once the motion-dependent fluid-force coefficients have been measured, a reliable design guideline, based on the unsteady flow theory, can be developed for fluidelastic instability of tube arrays in crossflow.

Motion-Dependent Fluid Force Coefficients for Tube Arrays in Crossflow

2001 ◽  
Vol 123 (4) ◽  
pp. 429-436 ◽  
Author(s):  
S. S. Chen ◽  
G. S. Srikantiah
Keyword(s):  
Excitation Amplitude ◽  
Steam Generators ◽  
Fluid Force ◽  
Force Coefficients ◽  
Fluid Forces ◽  
Stiffness Coefficients ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Fluid Damping ◽  
Series Of Experiments

Fluidelastic instability of tube arrays in crossflow is interesting academically and important in steam generators and heat exchangers. The key elements necessary to accurately predict fluidelastic instability of tube arrays in crossflow are motion-dependent fluid force coefficients. This paper presents several series of experiments that measure motion-dependent fluid forces for various tube arrays. Fluid damping and stiffness coefficients based on the unsteady flow theory were obtained as a function of reduced flow velocity, excitation amplitude, and Reynolds number, and the characteristics of motion-dependent fluid force coefficients were applied to provide some additional insights into fluidelastic instability.

scholarly journals Vibration and Stability of Two Tubes in Cross-Flow

1997 ◽  
Vol 119 (2) ◽  
pp. 142-149 ◽  
Author(s):  
S. Zhu ◽  
S. S. Chen ◽  
Y. Cai
Keyword(s):  
Unsteady Flow ◽  
Flow Velocity ◽  
Water Channel ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Diameter Ratio ◽  
Coupled Vibration ◽  
Fluid Forces ◽  
Stiffness Coefficients ◽  
Fluid Damping

Two tubes in tandem and normal to flow were studied on the basis of the unsteady-flow theory. Motion-dependent fluid forces were measured in a water channel, and the pitch-to-diameter ratio was 1.35. From the measured fluid forces, fluid damping and stiffness were calculated as a function of reduced flow velocity and several Reynolds numbers. Once the fluid-damping and fluid-stiffness coefficients are known, coupled vibration and stability of the two tubes in cross-flow can be predicted.

An Analysis of In-Flow Fluidelastic Instability Based on a Physical Insight

2014 ◽  
Author(s):  
Tomomichi Nakamura
Keyword(s):  
Flow Velocity ◽  
Flow Instability ◽  
Pressure Sensors ◽  
Measured Data ◽  
Critical Flow ◽  
Nonlinear Phenomenon ◽  
Critical Flow Velocity ◽  
Fluid Force ◽  
Tube Arrays ◽  
Fluidelastic Instability

Fluidelastic vibration of tube arrays caused by cross-flow has recently been highlighted by a practical event. There have been many studies on fluidelastic instability, but almost all works have been devoted to the tube-vibration in the transverse direction to the flow. For this reason, there are few data on the fluidelastic forces for the in-flow movement of the tubes, although the measured data on the stability boundary has gradually increased. The most popular method to estimate the fluidelastic force is to measure the force acting on tubes due to the flow, combined with the movement of the tubes. However, this method does not give the physical explanation of the root-cause of fluidelastic instability. In the work reported here, the in-flow instability is assumed to be a nonlinear phenomenon with a retarded or delayed action between adjacent tubes. The fluid force acting on tubes are estimated, based on the measured data in another paper for the fixed cylinders with distributed pressure sensors on the surface of the cylinders. The fluid force acting on the downstream-cylinder is assumed in this paper to have a delayed time basically based on the distance between the separation point of the upstream-cylinder to the re-attachment point, where the fluid flows with a certain flow velocity. Two models are considered: a two-cylinder and three–cylinder models, based on the same dimensions as our experimental data to check the critical flow velocity. Both models show the same order of the critical flow velocity and a similar trend for the effect of the pitch-to-diameter ratio of the tube arrays, which indicates this analysis has a potential to explain the in-flow instability if an adequate fluid force is used.

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.

Flow Velocity Dependence of Damping in Tube Arrays Subjected to Liquid Cross-Flow

1981 ◽  
Vol 103 (2) ◽  
pp. 130-135 ◽  
Author(s):  
S. S. Chen ◽  
J. A. Jendrzejczyk
Keyword(s):  
Mathematical Modeling ◽  
Flow Velocity ◽  
Vortex Shedding ◽  
Cross Flow ◽  
Elastic Instability ◽  
Velocity Dependence ◽  
Tube Arrays ◽  
Fluid Damping ◽  
Lift And Drag

Experiments are conducted to determine the damping for a tube in tube arrays subjected to liquid cross-flow; damping factors in the lift and drag directions are measured for in-line and staggered arrays. It is found that: 1) fluid damping is not a constant, but a function of flow velocity; 2) damping factors in the lift and drag directions are different; 3) fluid damping depends on the tube location in an array; 4) flow velocity-dependent damping is coupled with vortex shedding process and fluid-elastic instability; and 5) flow velocity-dependent damping may be negative. This study demonstrates that flow velocity-dependent damping is important. These characteristics should be properly taken into account in the mathematical modeling of tube arrays subjected to cross-flow.

Coupling Between Acoustic Resonance and Fluidelastic Instability in Normal Triangular Tube Arrays

2006 ◽  
Author(s):  
John Mahon ◽  
Craig Meskell
Keyword(s):  
Flow Velocity ◽  
Sound Pressure ◽  
Physical Mechanism ◽  
Acoustic Resonance ◽  
Acoustic Power ◽  
Structural Damping ◽  
Duct Acoustics ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Independent Parameters

This paper reports on the interaction between fluidelastic instability (FEI) and acoustic resonance. In order to examine the interaction, the duct acoustics were excited with speakers placed adjacent to the tube array to artificially replicate flow-induced acoustic resonance. While the current study has clearly captured the phenomenon of interaction between the fluidelastic motion at ∼ 10 Hz and the acoustic field at ∼ 1kHz, it is not apparent what the physical mechanism at work might be. The paper details the effect on RMS level of tube vibration for three independent parameters: flow velocity, structural damping and acoustic power. The results presented show that there is a corresponding fall in the FEI vibration amplitude with increasing sound pressure level in the tube array. In addition, the effects of flow velocity and structural damping in conjunction with forced acoustics on the RMS of tube displacement are discussed.

Simulation of Fluidelastic Vibrations of Heat Exchanger Tubes With Loose Supports

2006 ◽  
Author(s):  
Marwan Hassan
Keyword(s):  
Fluid Flow ◽  
Heat Exchanger ◽  
Flow Velocity ◽  
Nonlinear Dynamic Analysis ◽  
Fretting Wear ◽  
Radial Clearance ◽  
Force Model ◽  
Forcing Function ◽  
Tube Arrays ◽  
Fluidelastic Instability

Fluidelastic instability is regarded as the most complex and destructive flow excitation mechanism in heat exchanger tube arrays subjected to cross fluid flow. Several attempts have been made for modelling fluidelastic instability in tube arrays in order to predict the stability threshold. However, fretting wear prediction requires a nonlinear computation of the tube dynamics in which proper modelling of the fluid forcing function is essential. In this paper, a time domain simulation of fluidelastic instability is presented for a single flexible tube in an otherwise rigid array subjected to cross fluid flow. The model is based on the unsteady flow theory proposed by Lever and Weaver [1] and Yetisir and Weaver [2]. The developed model has been implemented in INDAP (Incremental Nonlinear Dynamic Analysis Program), an in-house finite element code. Numerical investigations were performed for two linear tube-array geometries and compared with published experimental data. A reasonable agreement between the numerical simulation and the experimental results was obtained. The fluidelastic force model was also coupled with a tube/support interaction model. The developed numerical model was utilized to study a loosely-supported cantilever tube subjected to air flow. Tube-to-support clearance, random excitation level, and flow velocity were then varied. The results indicated that the loose support has a stabilizing effect on the tube response. Both rms impact force and normal work rate increased as a result of increasing the flow velocity or the support radial clearance. Contact ratio exhibited a sharp increase at a flow velocity higher than the instability threshold of the first unsupported mode. In addition, an interesting behaviour has been observed, namely the change of tube’s equilibrium position due to fluid forces. This causes a single-sided impact. At a higher turbulence level, double-sided impact conditions were dominant. The influence of these dynamic regimes on the tube/support parameters was also addressed.

Numerical Estimation of Fluidelastic Instability in Tube Arrays

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Marwan Hassan ◽  
Andrew Gerber ◽  
Hossin Omar
Keyword(s):  
Unsteady Flow ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Arbitrary Lagrangian Eulerian ◽  
Navier Stokes Equations ◽  
Fluid Forces ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Viable Approach ◽  
The Stability

This study investigates unsteady flow in tube bundles and fluid forces, which can lead to large tube vibration amplitudes, in particular, amplitudes associated with fluidelastic instability (FEI). The fluidelastic forces are approximated by the coupling of the unsteady flow model (UFM) with computational fluid dynamics (CFD). The CFD model employed solves the Reynolds averaged Navier–Stokes equations for unsteady turbulent flow and is cast in an arbitrary Lagrangian–Eulerian form to handle any motion associated with tubes. The CFD solution provides time domain forces that are used to calculate added damping and stiffness coefficients employed with the UFM. The investigation demonstrates that the UFM utilized in conjunction with CFD is a viable approach for calculating the stability map for a given tube array. The FEI was predicted for in-line square and normal triangle tube arrays over a mass damping parameter range of 0.1– 100. The effect of the P/d ratio and the Reynolds number on the FEI threshold was also investigated.

Effects of Acoustic Excitation on a Swirling Diffusion Flame

2010 ◽  
Vol 132 (12) ◽  
Author(s):  
Michael E. Loretero ◽  
Rong F. Huang
Keyword(s):  
Flow Field ◽  
Bluff Body ◽  
Excitation Frequency ◽  
Excitation Amplitude ◽  
Mie Scattering ◽  
Flame Length ◽  
Laser Doppler Velocimeter ◽  
Scattering Method ◽  
Acoustic Excitation ◽  
Characteristic Modes

A swirling double concentric jet is commonly used for nonpremixed gas burner application for safety reasons and to improve the combustion performance. Fuel is generally spurted at the central jet while the annular coflowing air is swirled. They are normally separated by a blockage disk where the bluff-body effects further enhance the recirculation of hot gas at the reaction zone. This paper aims to experimentally investigate the behavior of flame and flow in a double concentric jet combustor when the fuel supply is acoustically driven. Laser-light sheet assisted Mie scattering method has been used to visualize the flow, while the flame lengths were measured by a conventional photography technique. The fluctuating velocity at the jet exit was measured by a two-component laser Doppler velocimeter. Flammability and stability at first fuel tube resonant frequency are reported and discussed. The evolution of flame profile with excitation level is presented and discussed, together with the reduction in flame length. The flame in the unforced reacting axisymmetric wake is classified into three characteristic modes, which are weak swirling flame, lifted flame, and transitional reattached flame. These terms reflect their primary features of flame appearances, and when the acoustic excitation is applied, the flame behaviors change with the excitation frequency and amplitude. Four additional characteristic modes are identified; e.g., at low excitation amplitudes, wrinkling flame with a blue annular film is observed because the excitation induces vortices in the central fuel jet and hence gives rise to the wrinkling of flame. The central jet vortices become larger with the increase in excitation amplitude and thus lead to a wider and shorter flame. If the excitation amplitude is increased above a certain value, the central jet vortices change the rotation direction and pacing with the annular jet vortices. These changes in the flow field induce large turbulent intensity and mixing and therefore make the flame looks blue and short. Further increase in the excitation amplitude would lift the flame because the flow field would be dramatically modified.

Modeling and Experimental Validations of a Piezoelectric Energy Harvester Under Combined Galloping and Base Excitations

2014 ◽  
Author(s):  
Amin Bibo ◽  
Abdessattar Abdelkefi ◽  
Mohammed F. Daqaq
Keyword(s):  
Bluff Body ◽  
Energy Harvester ◽  
Constitutive Relations ◽  
Excitation Frequency ◽  
Primary Resonance ◽  
Beam Theory ◽  
Excitation Amplitude ◽  
The Body ◽  
Base Excitation ◽  
Piezoelectric Energy

This paper develops an experimentally validated model of a piezoelectric energy harvester under combined aeroelastic-galloping and base excitations. To that end, an energy harvester consisting of a thin piezoelectric cantilever beam subjected to vibratory base excitation is considered. To permit galloping excitation, a bluff body is rigidly attached at the free end such that a net aerodynamic lift is generated as the incoming airflow separates on both sides of the body giving rise to limit cycle oscillations when the flow velocity exceeds a critical value. A nonlinear electromechanical distributed-parameter model of the harvester under the combined excitation is derived using the energy approach and by adopting the nonlinear Euler-Bernoulli beam theory, linear constitutive relations for the piezoelectric transduction, and the quasi-steady assumption for the aerodynamic loading. The partial differential equations of the system are discretized and a reduced-order-model is obtained. The mathematical model is validated by conducting a series of experiments with different loading conditions represented by wind speed, base excitation amplitude, and excitation frequency around the primary resonance.

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