Absolute and Convective Instabilities of a Collapsible Tube

2002 ◽  
Author(s):  
Hamadiche Mahmoud
Keyword(s):  
Reynolds Number ◽  
Unstable Mode ◽  
Standing Waves ◽  
Cusp Point ◽  
Collapsible Tube ◽  
Convective Instabilities ◽  
Cusp Points ◽  
The Absolute ◽  
High Reynolds ◽  
Good Agreement

In this paper we extend a numerical method, developed previously by the author, to compute the eigen modes of collapsible viscoelastic duct convening a fowing fuid. A new technique is developed in order to eliminate the need for recurrence formula used in the old method. This gives a more powerful and tractable method to find the eigen modes of the system. The new method has allowed the identification of a new unstable modes in a collapsible tube. It is found that there is a set of standing non axisymmetric waves representing an absolute instabilities and a set of unstable upstream and downstream propagated waves representing a convective instabilities. Two standing waves have equal frequency in their cusp points. The frequency of the other standing waves, in their cusp points, are a multiple of the frequency of the first wave and that in good agreement with experimental finding available in the literature. It is found that the first absolute unstable mode becomes convective at high Reynolds number while the other standing wave remain absolutely unstable modes for Re higher than 100. The frequency ratio of the absolute unstable modes in their cusp point are preserved for all Reynolds number and that with an good agreement with the experience. The absolute unstable mode which becomes convective at high Reynolds number keeps a monochromatic wave with a frequency equal to the frequency of the second absolute unstable mode, in its cusp point, and that for all Reynolds number higher than the limit of absolute instability of the first mode in surprising agreement with the experimental results. It is founded that the viscosity of the solid stabilizes the standing wavesat different degree. The boundary separating the absolute instabilities zone from the convective instabilities zone are found.

Spectral energy transfer in high Reynolds number turbulence

1977 ◽  
Vol 79 (2) ◽  
pp. 337-359 ◽  
Author(s):  
K. N. Helland ◽  
C. W. Van Atta ◽  
G. R. Stegen
Keyword(s):  
Reynolds Number ◽  
Energy Transfer ◽  
Energy Spectrum ◽  
High Reynolds Number ◽  
Reynolds Numbers ◽  
Second Order ◽  
Spectral Energy ◽  
Local Isotropy ◽  
High Reynolds ◽  
Good Agreement

The spectral energy transfer of turbulent velocity fields has been examined over a wide range of Reynolds numbers by experimental and empirical methods. Measurements in a high Reynolds number grid flow were used to calculate the energy transfer by the direct Fourier-transform method of Yeh & Van Atta. Measurements in a free jet were used to calculate energy transfer for a still higher Reynolds number. An empirical energy spectrum was used in conjunction with a local self-preservation approximation to estimate the energy transfer at Reynolds numbers beyond presently achievable experimental conditions.Second-order spectra of the grid measurements are in excellent agreement with local isotropy down to low wavenumbers. For the first time, one-dimensional third-order spectra were used to test for local isotropy, and modest agreement with the theoretical conditions was observed over the range of wavenumbers which appear isotropic according to second-order criteria. Three-dimensional forms of the measured spectra were calculated, and the directly measured energy transfer was compared with the indirectly measured transfer using a local self-preservation model for energy decay. The good agreement between the direct and indirect measurements of energy transfer provides additional support for both the assumption of local isotropy and the assumption of self-preservation in high Reynolds number grid turbulence.An empirical spectrum was constructed from analytical spectral forms of von Kármán and Pao and used to extrapolate energy transfer measurements at lower Reynolds number to Rλ = 105 with the assumption of local self preservation. The transfer spectrum at this Reynolds number has no wavenumber region of zero net spectral transfer despite three decades of $k^{-\frac{5}{3}}$. behaviour in the empirical energy spectrum. A criterion for the inertial subrange suggested by Lumley applied to the empirical transfer spectrum is in good agreement with the $k^{-\frac{5}{3}}$ range of the empirical energy spectrum.

An experimental investigation of high Reynolds number steady streaming generated by oscillating cylinders

1974 ◽  
Vol 64 (3) ◽  
pp. 589-598 ◽  
Author(s):  
Arnold F. Bertelsen
Keyword(s):  
Boundary Layer ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Incompressible Fluid ◽  
High Reynolds Number ◽  
Viscous Incompressible Fluid ◽  
Steady Streaming ◽  
Harmonic Motion ◽  
High Reynolds ◽  
Good Agreement

The steady streaming generated in the boundary layer on a cylinder performing simple harmonic motion in a viscous incompressible fluid which is otherwise at rest is investigated in the case where the Reynolds numberRsassociated with this streaming is large. Comparison is made between experimental results obtained here and the theories of Riley (1965) and Stuart (1966). This comparison shows good agreement between the theories and the experiment close to the cylinder, but away from the cylinder significant discrepancies are observed. Possible reasons for these discrepancies are discussed.

Flow Regulation Characteristics of Thin-Walled Compliant Tubes: Part I—Theoretical Analysis

1990 ◽  
Vol 112 (3) ◽  
pp. 319-329
Author(s):  
Ifiyenia Kececioglu
Keyword(s):  
Reynolds Number ◽  
Wave Speed ◽  
Active Element ◽  
Flow Regulation ◽  
Collapsible Tube ◽  
Speed Flow ◽  
Thin Walled ◽  
Flow Regulator ◽  
High Reynolds ◽  
Set Up

The objective of this investigation is the study of the flow limitation behavior of thin-walled compliant tubes for the design of a flow regulator employing a collapsible tube as its active element. In this paper, the theoretical basis is set up for the high-Reynolds-number wave-speed flow regulation and the low-Reynolds-number frictional flow regulation behaviors of thin-walled compliant tubes. In Part II of this paper [1], experimental results and design criteria are provided in support of the analytically derived characteristic flow regulation curve for the wave-speed flow regulator.

scholarly journals A Numerical and Experimental Study of the Aerodynamics and Stability of a Horizontal Parachute

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Mazyar Dawoodian ◽  
Abdolrahman Dadvand ◽  
Amir Hassanzadeh
Keyword(s):  
Experimental Study ◽  
Reynolds Number ◽  
Numerical Simulations ◽  
Drag Coefficient ◽  
Reynolds Numbers ◽  
Flow Conditions ◽  
High Reynolds Numbers ◽  
High Reynolds ◽  
The Stability ◽  
Good Agreement

The flow past a parachute with and without a vent hole at the top is studied both experimentally and numerically. The effects of Reynolds number and vent ratio on the flow behaviour as well as on the drag coefficient are examined. The experiments were carried out under free-flow conditions. In the numerical simulations, the flow was considered as unsteady and turbulent and was modelled using the standard - turbulence model. The experimental results reveal good agreement with the numerical ones. In both the experiments and numerical simulations, the Reynolds number was varied from 85539 to 357250 and the vent ratio was increased from zero to 20%. The results show that the drag coefficient decreases by increasing the Reynolds number for all the cases tested. In addition, it was found that at low and high Reynolds numbers, the parachutes, respectively, with 4% vent ratio and without vent are deemed more efficient. One important result of the present work is related to the effect of vent ratio on the stability of the parachute.

scholarly journals Mixing efficiency in run-down gravity currents

2016 ◽  
Vol 809 ◽  
pp. 691-704 ◽  
Author(s):  
G. O. Hughes ◽  
P. F. Linden
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
Gravity Currents ◽  
Mixing Efficiency ◽  
The Novel ◽  
High Reynolds Numbers ◽  
High Reynolds ◽  
Good Agreement

This paper presents measurements of mixing efficiency of the two counter-flowing gravity currents created by symmetric lock exchange in a channel. The novel feature of this work is that the buoyancy Reynolds number of the currents is higher than in previous experiments, so that the mixing is not significantly affected by viscosity. We find that the mixing efficiency asymptotes to 0.08 at high Reynolds numbers. We present a model of the mixing based on the evolution of idealized mean profiles of velocity and density at the interface between the two currents, the results of which are in good agreement with the measurements of mixing efficiency.

scholarly journals Asymptotic analysis of the attractors in two-dimensional Kolmogorov flow

2017 ◽  
Vol 29 (3) ◽  
pp. 393-416 ◽  
Author(s):  
W. R. SMITH ◽  
J. G. WISSINK
Keyword(s):  
Reynolds Number ◽  
High Reynolds Number ◽  
Necessary Conditions ◽  
Travelling Waves ◽  
Standing Waves ◽  
Two Dimensional ◽  
Kolmogorov Flow ◽  
New Findings ◽  
High Reynolds ◽  
Periodic Standing Waves

The high Reynolds-number structure of the laminar, chaotic and turbulent attractors is investigated in a two-dimensional Kolmogorov flow. The laminar attractors include the families of multi-phased travelling waves and quasi-periodic standing waves both of which form the backbone of the transition to a turbulent flow. At leading order, each laminar attractor under study is obtained by solving the Euler equations on a manifold subject to the appropriate periodicity and symmetry conditions. The manifold is determined by a finite number of vorticity equations, these being required to suppress the secular terms at the next order. Our results show that, for the multi-phased travelling waves, the first phase velocity can be determined by an integral conservation law for kinetic energy and the subsequent phase velocities can be evaluated by a non-linear eigenvalue problem. The results also reveal that whereas viscosity determines the smallest scales and controls the amplitude of the flow, the inertial terms govern the shape and form of the flow. The comparison of our analytical predictions for evaluating the stable single-phased travelling wave with the direct numerical simulation of the Navier–Stokes equations has been undertaken, the agreement being excellent. For sufficiently high Reynolds number, after the bifurcation to chaotic flow, all of the multi-phased travelling waves and quasi-periodic standing waves become unstable non-wandering sets. Based on the above new findings for these unstable non-wandering sets and other travelling and standing waves of this kind in phase space, necessary conditions for the invariant manifolds of the chaotic and turbulent attractors are obtained, these necessary conditions being conjectured to be also sufficient.

scholarly journals RANS Simulations of Flow Past an DU-91-W2-250 Airfoil at High Reynolds Number

2018 ◽  
Vol 44 ◽  
pp. 00150
Author(s):  
Krzysztof Rogowski ◽  
Martin O.L. Hansen
Keyword(s):  
Reynolds Number ◽  
Navier Stokes ◽  
Transient Model ◽  
Drag Coefficients ◽  
Pressure Distributions ◽  
Sst Turbulence Model ◽  
Rans Simulations ◽  
High Reynolds ◽  
Lift And Drag ◽  
Good Agreement

This paper presents numerical results of the DU-91-W2-250 airfoil. Reynolds-averaged Navier–Stokes (RANS) simulations of the 2D profile are performed employing the Transient SST turbulence model. The airfoil was investigated for the Reynolds number of 6 106. Lift and drag coefficients are compared with the experimental data from LM Low Speed Wind Tunnel (LSWT). The results of lift and drag coefficients obtained using the SST Transient model are in a good agreement in comparison with the experiment in the angle of attack range from -10° to 10°. The static pressure distributions calculated by the SST Transition model are also in good agreement with the experiment.

Tire Vibrations

1977 ◽  
Vol 5 (4) ◽  
pp. 202-225 ◽  
Author(s):  
G. R. Potts ◽  
C. A. Bell ◽  
L. T. Charek ◽  
T. K. Roy
Keyword(s):  
Natural Frequencies ◽  
Standing Waves ◽  
Resonant Mode ◽  
Mode Shapes ◽  
Resonant Vibrations ◽  
Resonant Frequencies ◽  
Radial Tire ◽  
Analysis Techniques ◽  
Thin Ring ◽  
Good Agreement

Abstract Natural frequencies and vibrating motions are determined in terms of the material and geometric properties of a radial tire modeled as a thin ring on an elastic foundation. Experimental checks of resonant frequencies show good agreement. Forced vibration solutions obtained are shown to consist of a superposition of resonant vibrations, each rotating around the tire at a rate depending on the mode number and the tire rotational speed. Theoretical rolling speeds that are upper bounds at which standing waves occur are determined and checked experimentally. Digital Fourier transform, transfer function, and modal analysis techniques used to determine the resonant mode shapes of a radial tire reveal that antiresonances are the primary transmitters of vibration to the tire axle.

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