A Semipotential Flow Theory for the Dynamics of Cylinder Arrays in Cross Flow

1985 ◽  
Vol 107 (4) ◽  
pp. 500-506 ◽  
Author(s):  
M. P. Paidoussis ◽  
S. J. Price ◽  
D. Mavriplis
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Fluid Dynamic ◽  
Dynamic Stiffness ◽  
Cross Flow ◽  
Flow Region ◽  
High Mass ◽  
Duct Flow ◽  
Cylinder Arrays ◽  
Fluidelastic Instability

This paper presents a semianalytical model, involving the superposition of the empirically determined cross flow about a cylinder in an array and the analytically determined vibration-induced flow field in still fluid, for the purpose of analyzing the stability of cylinder arrays in cross flow and predicting the threshold of fluidelastic instability. The flow field is divided into two regions: a viscous bubble of separated flow, and an inviscid, sinuous duct-flow region elsewhere. The only empirical input required by the model in its simplest form is the pressure distribution about a cylinder in the array. The results obtained are in reasonably good accord with experimental data, only for low values of the mass-damping parameter (e.g., for liquid flows), where fluidelastic instability is predominantly caused by negative fluid-dynamic damping terms. For high mass-damping parameters (e.g., for gaseous flows), where fluidelastic instability is evidently controlled by fluid-dynamic stiffness terms, the model greatly overestimates the threshold of fluidelastic instability. However, once measured fluid-dynamic stiffness terms are included in the model, agreement with experimental data is much improved, yielding the threshold flow velocities for fluidelastic instability to within a factor of 2 or better.

An Investigation on the Use of Connors’ Equation to Predict Fluidelastic Instability in Cylinder Arrays

2001 ◽  
Vol 123 (4) ◽  
pp. 448-453 ◽  
Author(s):  
Stuart J. Price
Keyword(s):  
Experimental Data ◽  
Cross Flow ◽  
Theoretical Models ◽  
Implicit Assumption ◽  
Cylinder Arrays ◽  
Fluidelastic Instability

The use of Connors’ equation, or variations thereof, to predict the velocity at which fluidelastic instability occurs in cylinder arrays subject to cross-flow has become ubiquitous. The implicit assumption being that this equation accurately models the physics of fluidelastic instability, and all that is required is to find the “correct” value of Connors’ constant. The evidence for and against this assumption is examined in this paper. Other theoretical models of fluidelastic instability are reviewed and compared with Connors’ analysis. In addition, evidence from experimental data is considered. It is concluded that there are many deficiencies associated with Connors’ equation, and that if better “design guides” are to be obtained, more emphasis must be put on examining the physics of fluidelastic instability.

Modeling of Fluidelastic Instability Forces in Fully Flexible Tube Arrays

2007 ◽  
Author(s):  
Faisal Mahmood ◽  
Marwan Hassan
Keyword(s):  
Flow Field ◽  
Time Domain ◽  
Tube Bundle ◽  
Cross Flow ◽  
High Mass ◽  
System Response ◽  
Domain Modeling ◽  
Flexible Tube ◽  
Proposed Model ◽  
Fluidelastic Instability

Fluidelastic instability remains the most devastating phenomenon in tube bundles subjected to cross-flow. Models have been developed to estimate the threshold of instability. Moreover, several time-domain models of fluidelastic instability have been developed to determine tube/support interaction parameters of tubes with loose supports. The present work deals with time domain modeling of fluid-elastic instability forces in a fully flexible tube array subjected to cross-flow. The model is based on the flow redistribution theory proposed initially by Lever and Weaver [1]. The proposed model utilizes fewer input parameters and can model various tube bundle geometries with any pitch-to-diameter ratio. Finite element method is used for solving the system response. The flow field inside the tube array is discretized into flow subdomains, each of which is surrounded by 4 tubes. The perturbation in the flow field, within each subdomain, is obtained by superimposing the effects of neighboring tube motions. The model has been applied to assess the response of a single flexible tube as well as multiple flexible tubes. It is shown that the single flexible model overestimates the stability threshold compared to the multiple flexible tube counterpart, especially at high mass-damping parameters. The results show a good agreement between the predicted and the experimental results. The proposed model does not assume any predetermined tube response or any tube motion pattern.

Supersonic and hypersonic flow with attached shock waves over delta wings

1971 ◽  
Vol 325 (1561) ◽  
pp. 251-268 ◽  
Keyword(s):  
Shock Waves ◽  
Flow Field ◽  
Hypersonic Flow ◽  
Delta Wing ◽  
Cross Flow ◽  
Flow Region ◽  
Lower Surface ◽  
Uniform Flow ◽  
Nonuniform Flow ◽  
Sonic Line

A unified theory is developed for supersonic and hypersonic flow with attached shock waves over the lower surface of a delta wing at an angle of attack. The flow field on the lower surface of a delta wing consists of uniform flow regions near the leading edges, where the cross flow is supersonic and a nonuniform flow region near the central part, where the cross flow is subsonic. In the nonuniform flow region, the theory is based on the assumption that the flow differs slightly from the corresponding two-dimensional flow over a flat plate. Thus a linearized perturbation on a nonlinear flow field is first calculated and then strained and corrected so that the flow is matched continuously to the uniform flow which is obtained exactly. When compared with available exact numerical solutions the theory gives, in all cases, almost identical results, except near the crossflow sonic line where existing numerical methods fail to produce a discontinuous slope in the pressure curve, whereas the present theory predicts such a discontinuity and shows that the slope has a square root singularity at the crossflow sonic line similar to that in the supersonic linear theory.

Numerical Simulation and Experimental Verification of a Vertical Jet in Swirling Cross-Flow

2012 ◽  
Vol 235 ◽  
pp. 90-95
Author(s):  
Shun Li Kou ◽  
Guo Neng Li
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Flow Velocity ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Tunable Laser ◽  
Simulation Method ◽  
Numerical Results ◽  
Cross Flow Velocity ◽  
Vertical Jet

In order to investigate the bending and mixing characteristics in a vertical jet issuing into a swirling cross-flow, large eddy simulation method was employed to simulate the flow field of a jet in swirling cross-flow. Several jet to cross-flow velocity ratios (r=15, 30, 60) were investigated. The numerical results were compared to the experimental data measured from a phase tunable laser and CCD system. The Reynolds number Re based on the characteristic length of the cross-flow tunnel and the jet velocity lies between 22,537 and 90,146. Numerical results showed that the penetration depth of the vertical jet maintains nearly unchanged when the jet to cross-flow velocity ratio is large enough (r>30), which agreed well with the experimental data and was different from the flow field of jet in straight cross-flow. On the other hand, the case of r=60 obtained largest spread width, and the spread width maintains relatively large in a large penetration zone, which is consist with the experimental finding.

Study on In-Flow Fluidelastic Instability of Triangular Tube Arrays Subjected to Air Cross Flow

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Tomomichi Nakamura ◽  
Yoshiaki Fujita ◽  
Takuya Sumitani
Keyword(s):  
Transverse Direction ◽  
Flow Instability ◽  
Flow Direction ◽  
Present Report ◽  
Air Flow ◽  
Cross Flow ◽  
Thin Plates ◽  
Cylinder Arrays ◽  
Cylinder Array ◽  
Fluidelastic Instability

The in-flow instability of cylinder arrays corresponds to the in-plane instability of U-bend tubes in steam generators. This rarely occurring phenomenon has recently been observed in a nuclear power plant in the U.S. For this reason, the importance of studying this instability has recently increased. The fluidelastic instability of a cylinder array caused by cross-flow was found to easily occur in air-flow and hardly in water-flow in our previous report. The present report introduces the results of this phenomenon in several patterns of triangular cylinder arrays in air-flow. The pitch spacing between cylinders is one of the parameters, which varies from P/D = 1.2 to 1.5, for a five-by-five cylinder array. The instability is examined both in the in-flow direction and in the transverse direction. The test cylinders are supported with thin plates to move in one direction. The number and the location of the flexibly supported cylinders are the other parameters. Differences between the instability in the in-flow and in the transverse direction are found. Among these differences the most important is the fact that the fluidelastic instability has not been observed for a single flexible cylinder in the in-flow direction, although it is observed in the transverse direction. However, the present preliminary results suggest that the in-flow instability may be estimated with the Connors' type formula as likely as in the transverse direction case.

On Cross-Flow Fan Theoretical Performance and Efficiency Curves: An Energy Loss Analysis on Experimental Data

2004 ◽  
Vol 126 (5) ◽  
pp. 743-751 ◽  
Author(s):  
Andrea Toffolo
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Cross Flow ◽  
Experimental Measurements ◽  
Loss Analysis ◽  
Numerical Reconstruction ◽  
Global And Local ◽  
Cross Flow Fan ◽  
Systematic Database ◽  
Theoretical Performance

Contrary to conventional turbomachinery, cross-flow fan flow field is non-axisymmetrical and its complex configuration strongly affects performance and efficiency characteristic curves. The formulation of a theory on cross-flow fan operation is made even tougher since the strength and the eccentricity of the vortex that forms within the impeller are deeply influenced by the geometry of the impeller and of the casing as well. In this paper, a numerical reconstruction of the flow field, validated against an extensive systematic database of global and local experimental measurements, is analyzed. The aim is to achieve a general interpretation of performance and efficiency curves, and to lead them back to one theoretical archetype, whatever the fan configuration being considered.

The Effects of Tube Array Geometry on Fluidelastic Instability in Heat Exchanger Tube Arrays in Cross Flow

2017 ◽  
Author(s):  
Marwan Hassan ◽  
David S. Weaver
Keyword(s):  
Experimental Data ◽  
Research Effort ◽  
Cross Flow ◽  
Triangular Arrays ◽  
Small Pitch ◽  
Fluidelastic Instability ◽  
Significant Research ◽  
Current Design ◽  
Pitch Ratio ◽  
Array Geometry

The shut-down of the San Onofre Nuclear Generating Station (SONGS) has been attributed to damaging streamwise Fluidelastic Instability (FEI) of the steam generator tubes, a phenomenon which has traditionally been assumed not to occur. This has generated a significant research effort to better understand this phenomenon and to develop appropriate design criteria for its prevention. Most current design codes are based on Connors criterion for FEI which neglects both streamwise FEI and the effects of tube array pattern and pitch ratio. It is becoming clear that array geometry and pitch ratio are important determining factors in FEI, especially in the streamwise direction. This paper presents an extension of the theory of Lever and Weaver to consider arrays of flexible fluid-coupled tubes which are free to become unstable in both the transverse and streamwise directions. This simplified modelling approach has the advantages of being very tractable for numerical parametric studies and having no need for experimental data input. Previous research by the authors has shown that the predictions of this model agree very well with the available experiments for parallel triangular arrays for both transverse and streamwise FEI. In this paper, the results of such studies are presented for the both transverse and streamwise FEI for square inline and normal triangular arrays and compared with the authors’ previous results for parallel triangular arrays. It is shown that FEI is strongly influenced by array geometry, especially for small pitch ratio arrays operating at low values of the mass damping parameter. The results show good agreement with the available experimental data.

scholarly journals Numerical and Experimental Study of the Flow Field Structure Evolution in the Circular Recess of Oil Cavity

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
Feng Shen ◽  
Conglian Chen ◽  
Zhaomiao Liu
Keyword(s):  
Flow Field ◽  
Stokes Equations ◽  
Fluid Dynamic ◽  
Great Influence ◽  
Flow Region ◽  
Field Structure ◽  
Numerical Control ◽  
Navier Stokes ◽  
Structure Evolution ◽  
Finite Volume Approach

The laminar radial flow in the oil cavity of heavy-duty computer numerical control (CNC) machines is very complicated and has not been fully explored. Navier-Stokes equations have been applied through the whole flow region using finite volume approach to explore this complicated flow phenomenon, including the influences of the clearance height (h), inlet nozzle Reynolds number (Re), and geometrical aspect ratio (e) on flow behaviors. A fluid dynamic experiment has been conducted to study the flow structure by using particle image velocimetry (PIV). Numerical simulation results have been compared with the experimental results, finding a good agreement with the studied cases. The results suggest that there are complex vortices in the oil cavity. Flow field structure of the oil cavity largely depends onh, Re, ande. Re andehave a great influence on the size and amount of vortices, andhhas slight effects on the size of the vortices. The lengths of primary, secondary, and tertiary isolated vortices have a linear relationship withh. The lengths of the primary and secondary isolated vortices increase linearly with ascendingeaseis small. But when Re andeare large enough, the size of the three vortices decreases.

The mechanisms underlying flow-induced instabilities of cylinder arrays in crossflow

1988 ◽  
Vol 187 ◽  
pp. 45-59 ◽  
Author(s):  
M. P. Paiudoussis ◽  
S. J. Price
Keyword(s):  
Degrees Of Freedom ◽  
Dynamic Theory ◽  
Fluid Dynamic ◽  
Dynamic Stiffness ◽  
Flexible Cylinder ◽  
System Parameters ◽  
Fluid Forces ◽  
Physical Mechanisms ◽  
Cylinder Arrays ◽  
Dynamic Damping

This paper aims to shed some light on the physical mechanisms involved in flowinduced instabilities of arrays of cylinders in crossflow. In the framework of quasi-steady fluid-dynamic theory, two distinct mechanisms are discussed. The first is similar but not identical to that associated with classical galloping; i.e. it is a negative fluid-dynamic damping mechanism and may obtain even if a single cylinder in the array is free to oscillate with only one degree of freedom. Unlike classical galloping, it is intimately related to the time delay experienced in the wake structure, and hence the fluid forces, adjusting to displacements of the cylinder. The second mechanism is similar to wake flutter; i.e. it is controlled by non-conservative fluid-dynamic stiffness effects and generally requires relative motion between adjacent cylinders in the array, although there is no reason why it should not occur for a single flexible cylinder with two degrees of freedom. The two mechanisms generally coexist, but each is predominant over different ranges of system parameters.

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