Aeroelastic Stability of Wide Webs and Narrow Ribbons in Cross Flow

2008 ◽  
Vol 75 (4) ◽  
Author(s):  
Rahul A. Bidkar ◽  
Arvind Raman ◽  
Anil K. Bajaj
Keyword(s):  
Three Dimensional ◽  
Cross Flow ◽  
Coupled System ◽  
Inviscid Fluid ◽  
Aeroelastic Stability ◽  
Aeroelastic Flutter ◽  
Panel Methods ◽  
Divergence Instability ◽  
Applied Tension ◽  
The Web

Aeroelastic flutter can lead to large amplitude oscillations of tensioned wide webs and narrow ribbons commonly used in the paper-handling, textile, sheet-metal, and plastics industries. In this article, we examine the aeroelastic stability of a web or a ribbon, which is submerged in an incompressible and inviscid fluid flow across its free edges. The web or ribbon is modeled as a uniaxially tensioned Kirchhoff plate with vanishingly small bending stiffness. A Galerkin discretization for the structural dynamics together with panel methods for the unsteady three dimensional potential flow are used to cast the coupled system into the form of a gyroscopic, nonconservative dynamical system. It is found that wide webs mainly destabilize through a divergence instability due to the cross-flow-induced conservative centrifugal effects. However, for certain values of applied tension, the wake-induced nonconservative effects can destabilize the web via a weak flutter instability. Contrarily, narrow ribbons in cross flow are nearly equally likely to undergo flutter or divergence instability depending on the value of applied tension.

Aeroelastic Stability of Wide Webs and Narrow Ribbons

2007 ◽  
Author(s):  
Rahul A. Bidkar ◽  
Arvind Raman ◽  
Anil K. Bajaj
Keyword(s):  
Fluid Flow ◽  
Critical Role ◽  
Cross Flow ◽  
Aeroelastic Stability ◽  
Lattice Method ◽  
Flutter Instability ◽  
Divergence Instability ◽  
Applied Tension ◽  
Unsteady Fluid ◽  
The Web

Uni-axially tensioned wide webs and narrow ribbons commonly used in the paper-handling, textile, sheet-metal, and plastics industries are known to undergo large amplitude vibrations characterized as aeroelastic flutter. The aeroelastic stability of stationary wide webs and narrow ribbons coupled with fluid flow across the free edges of the web or ribbon is investigated in this article. The web or ribbon is modeled as a uni-axially tensioned Kirchhoff plate with vanishingly small bending stiffness. The 3D unsteady fluid flow surrounding the web or ribbon is evaluated numerically by using the vortex-lattice method. Wide webs are mainly found to exhibit the divergence instability. For some values of the applied tension, the clustered web modes exhibit frequency curve veering accompanied by a weak flutter instability before the occurrence of the divergence instability. The applied tension plays a critical role in deciding the type of instability in narrow ribbons. In cross flow, depending on the applied tension, narrow ribbons undergo flutter instability or divergence instability or the simultaneous onset of both instabilities.

Aeroelastic Flutter at the Free Edges of Uni-Axially Tensioned Webs and Thin Films

2005 ◽  
Author(s):  
Rahul A. Bidkar ◽  
Arvind Raman ◽  
Anil K. Bajaj
Keyword(s):  
Fluid Flow ◽  
Elastic Stability ◽  
Order System ◽  
Machine Direction ◽  
Aeroelastic Flutter ◽  
Panel Methods ◽  
Space Formulation ◽  
Fluid Coupling ◽  
The Cross ◽  
The Web

Aero elastic flutter may play an important role in the breakage of thin membrane-like structures (a.k.a. webs) found in paper-handling, textile, sheet-metal and magnetic tapes industry. In this article, we examine the aero elastic stability of a web modeled as a uni-axially tensioned (along the machine direction) low aspect ratio Kirchhoff plate, which is subject to a fluid flow in the cross machine direction. Panel methods based on the distribution of singularity solutions (sources and doublets) on the surface of the web are used to numerically solve the problem of 3D unsteady potential flow surrounding the web. The equation of motion of the plate coupled to a fluid flow is discretized by using Galerkin’s method. The discretization is performed in the configuration space formulation of the gyroscopic eigenvalue problem. The linear stability of this reduced order system is investigated. The onset of flutter instability as a function of base fluid flow in the cross machine direction is studied. The effects of fluid coupling on the frequencies and modes of oscillations of the web are also studied.

Elastic Waves in Generalized Thermo-Piezoelectric Transversely Isotropic Circular Bar Immersed in Fluid

2015 ◽  
Vol 8 (1) ◽  
pp. 82-103
Author(s):  
Palaniyandi Ponnusamy
Keyword(s):  
Classical Theory ◽  
Cross Sections ◽  
Equations Of Motion ◽  
Three Dimensional ◽  
Transversely Isotropic ◽  
Coupled System ◽  
Theory Of Elasticity ◽  
Inviscid Fluid ◽  
Displacement Potential ◽  
Modes Of Vibration

AbstractIn this paper, a mathematical model is developed to study the wave propagation in an infinite, homogeneous, transversely isotropic thermo-piezoelectric solid bar of circular cross-sections immersed in inviscid fluid. The present study is based on the use of the three-dimensional theory of elasticity. Three displacement potential functions are introduced to uncouple the equations of motion and the heat and electric conductions. The frequency equations are obtained for longitudinal and flexural modes of vibration and are studied based on Lord-Shulman, Green-Lindsay and Classical theory theories of thermo elasticity. The frequency equations of the coupled system consisting of cylinder and fluid are developed under the assumption of perfect-slip boundary conditions at the fluid-solid interfaces, which are obtained for longitudinal and flexural modes of vibration and are studied numerically for PZT-4 material bar immersed in fluid. The computed non-dimensional frequencies are compared with Lord-Shulman, Green-Lindsay and Classical theory theories of thermo elasticity for longitudinal and flexural modes of vibrations. The dispersion curves are drawn for longitudinal and flexural modes of vibrations. Moreover, the dispersion of specific loss and damping factors are also analyzed for longitudinal and flexural modes of vibrations.

Numerical Investigation of the Effects of Part-Span Shrouds on Aerodynamic and Aeroelastic Characteristics of a Transonic Fan Rotor

2017 ◽  
Author(s):  
Di Zhou ◽  
Zhiliang Lu ◽  
Tongqing Guo
Keyword(s):  
Convergence Rates ◽  
Three Dimensional ◽  
Coupled System ◽  
Numerical Results ◽  
Structural Factors ◽  
Aeroelastic Stability ◽  
Stall Margin ◽  
Positive Effects ◽  
The Time Domain ◽  
Transonic Fan

In this paper, the aerodynamic and aeroelastic effects of part-span shrouds are both investigated by means of numerical simulations. Based on a well-publicized NASA Rotor 67, a modified transonic fan rotor with the inclusion of a fictitious but typical part-span shroud, is selected to be studied. First, by CFD technique, three-dimensional steady-state calculations are performed for aerodynamic study. Numerical results show that the flow blockage and associated flow losses are caused and would become more severe as the operating condition approaches to the stall margin. It is also found that the presence of part-span shrouds could delay the occurrence of stall and extends the operating range. Further, the pressure distributions at different sections of the unshrouded and shrouded blades are compared and relevant analysis is presented. On the other hand, for aeroelastic study, by directly coupling CFD and CSD computations in the time domain, an effective fluid-structure coupled system is constructed. Considering the speciality of the shrouded blade, some special issues on both aerodynamic and structural modeling are discussed. Particularly, respectively corresponding to situations of in-phase and anti-phase vibrations, a single passage model and a double passage model are used. Comparative study shows that the presence of part-span shrouds greatly improves the convergence rates of all modes, numerically verifying their positive effects on aeroelastic stability. Also it is shown that the blade vibrating in opposite phase has a better aeroelastic stability. Besides, since the aeroelastic effect of part-span shrouds is a combined result of aerodynamic and structural factors, this paper also solely assesses the influence of aerodynamic factor by ignoring the forces on the contact plane. The numerical results show that its effect may be negative but negligibly small.

A comparison between the CS-TOF and the CTA/DSA for WEB device management

2021 ◽  
pp. 159101992110147
Author(s):  
Oktay Algin ◽  
Gokhan Yuce ◽  
Ural Koc ◽  
Gıyas Ayberk
Keyword(s):  
Mr Angiography ◽  
Three Dimensional ◽  
Morphological Parameters ◽  
Perfect Agreement ◽  
Device Management ◽  
Web Device ◽  
Sensing Time ◽  
The Web

Purpose There is no study on the role of three-dimensional compressed sensing time of flight MR angiography (3D-CS-TOF) in the management of the WEB device. We evaluated the efficacy of 3-tesla 3D-CS-TOF for the management and follow-up of the WEB device implantations. Materials and methods Seventy-three aneurysms of 69 patients treated with the WEB device were retrospectively examined. Morphological parameters and embolization results of the aneurysms were assessed and compared on 3D-CS-TOF, CTA, and DSA images. Results Occluded, neck remnant, and recurrent aneurysms were observed in 61 (83.6%), 7 (9.6%), and 5 (6.8%) aneurysms, respectively. Inter- and intra-reader agreement values related to aneurysm size measurements were perfect. Aneurysms size, age, and proximal vessel tortuosity were negatively correlated with the visibility of the aneurysms and parent vessels on 3D-CS-TOF images (p = 0.043; p = 0.032; p < 0.001, respectively). Subarachnoid hemorrhage and age are associated with 3D-CS-TOF artifacts (p = 0.031; p = 0.005, respectively). 3D-CS-TOF findings are in perfect agreement with DSA or CT angiography (CTA) results (p < 0.001). Conclusion According to our results, 3D-CS-TOF can be an easy, fast, and reliable alternative for the management or follow-up of WEB assisted embolization.

Large Eddy Simulation of Cross Flow in Pipe Junction

2018 ◽  
Author(s):  
Jiajun Chen ◽  
Yue Sun ◽  
Hang Zhang ◽  
Dakui Feng ◽  
Zhiguo Zhang
Keyword(s):  
Large Eddy Simulation ◽  
Stokes Equations ◽  
Numerical Study ◽  
Three Dimensional ◽  
Cross Flow ◽  
Exciting Force ◽  
Navier Stokes ◽  
Pipe Network ◽  
Eddy Simulation ◽  
Large Eddy

Mixing in pipe junctions can play an important role in exciting force and distribution of flow in pipe network. This paper investigated the cross pipe junction and proposed an improved plan, Y-shaped pipe junction. The numerical study of a three-dimensional pipe junction was performed for calculation and improved understanding of flow feature in pipe. The filtered Navier–Stokes equations were used to perform the large-eddy simulation of the unsteady incompressible flow in pipe. From the analysis of these results, it clearly appears that the vortex strength and velocity non-uniformity of centerline, can be reduced by Y-shaped junction. The Y-shaped junction not only has better flow characteristic, but also reduces head loss and exciting force. The results of the three-dimensional improvement analysis of junction can be used in the design of pipe network for industry.

Some Remarks on the Behaviour of Surface Source Distributions near the Edge of a Body

1973 ◽  
Vol 24 (1) ◽  
pp. 25-33
Author(s):  
J W Craggs ◽  
K W Mangler ◽  
M Zamir
Keyword(s):  
Flow Direction ◽  
Three Dimensional ◽  
Cross Flow ◽  
Symmetric Case ◽  
The Body ◽  
Dimensional Problem ◽  
Surface Source ◽  
Asymmetric Case ◽  
Main Flow Direction ◽  
Flow Plane

SummaryWhen the incompressible potential flow past a three-dimensional body is represented by source distributions on the body surface, these source distributions have singularities near an edge or corner, for example á trailing edge of a wing or the (unfaired) intersection of a body and a wing. The nature of these singularities is discussed. When assuming slow variations of the geometry in the main flow direction we can consider a two-dimensional problem in the cross-flow plane. Here the tangential velocities and source distributions are proportional to certain powers of the distance from the corner. For example at a convex right-angled corner these powers are − ⅓ in the asymmetric case (the bisector is a potential line) and ⅓ in the symmetric case (the bisector is a streamline) for both sources and tangential velocities. At a concave right-angled corner the corresponding values for the source distributions are ⅓ (asymmetric case) and − ⅓ (symmetric case) whereas they are 1 and 3 respectively for the tangential velocities.

scholarly journals Modeling the 3-d flow around a cylinder using the SAS hybrid model

2014 ◽  
Vol 16 (5) ◽  
pp. 901-918 ◽  
Keyword(s):  
Turbulence Modeling ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Cross Flow ◽  
Numerical Code ◽  
Navier Stokes ◽  
Computational Domain ◽  
Mean Flow ◽  
Unstable Flow ◽  
Vortex Size

<div> <p>Three-dimensional calculations were performed to simulate the flow around a cylindrical vegetation element using the Scale Adaptive Simulation (SAS) model; commonly, this is the first step of the modeling of the flow through multiple vegetation elements. SAS solves the Reynolds Averaged Navier-Stokes equations in stable flow regions, while in regions with unstable flow it goes unsteady producing a resolved turbulent spectrum after reducing eddy viscosity according to the locally resolved vortex size represented by the von Karman length scale. A finite volume numerical code was used for the spatial discretisation of the rectangular computational domain with stream-wise, cross-flow and vertical dimensions equal to 30D, 11D and 1D, respectively, which was resolved with unstructured grids. Calculations were compared with experiments and Large Eddy Simulations (LES). Predicted overall flow parameters and mean flow velocities exhibited a very satisfactory agreement with experiments and LES, while the agreement of predicted turbulent stresses was satisfactory. Calculations showed that SAS is an efficient and relatively fast turbulence modeling approach, especially in relevant practical problems, in which the very high accuracy that can be achieved by LES at the expense of large computational times is not required.</p> </div> <p>&nbsp;</p>

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