The Instability of a Flexible Sheet in Uniform Parallel Flow

2007 ◽  
Author(s):  
Michael T. Morris-Thomas ◽  
Sverre Steen
Keyword(s):  
Spectral Method ◽  
Ideal Fluid ◽  
Flow Instability ◽  
Fluid Dynamic ◽  
Fluid Velocity ◽  
Critical Value ◽  
Elastic Model ◽  
Elastic Instability ◽  
Mass Ratio ◽  
Unique Aspect

When a flexible sheet immersed in a fluid is under the influence of uniform flow, instability can arise when the fluid velocity reaches some critical value. The fluid-elastic instability known as flutter is the focus of this present work. We present a fluid-elastic model for a flexible sheet whereby the fluid dynamic lift is accounted for by the classical slender body approximation of Lighthill [1] for an ideal fluid. We describe aspects of the system in terms of a mass ratio α and a tension to flexural ratio γ. The model is solved by a spectral method to determine the fluid velocity and frequency at which instability occurs. In addition, we consider the fluid friction and damping on the response of the flexible sheet. Moreover, we compare predictions for the flutter velocity and frequency with published results. The unique aspect of this work is an investigation into the effect of additional tension, in the form of the ratio γ, on stability.

scholarly journals A Fluidelastic Model for the Nonlinear Dynamics of Two-Dimensional Inverted Flags

2019 ◽  
Author(s):  
Mohammad Tavallaeinejad ◽  
Michael P. Païdoussis ◽  
Mathias Legrand ◽  
Mojtaba Kheiri
Keyword(s):  
Large Amplitude ◽  
Fluid Dynamic ◽  
Time Integration ◽  
Dynamic Modelling ◽  
Axial Flow ◽  
Beam Theory ◽  
Leading Edge ◽  
Elastic Model ◽  
Inviscid Fluid ◽  
Mass Ratio

Abstract A nonlinear fluid-elastic model is proposed for the study of the dynamics of inverted flags. The quasi-steady version of Theodorsen’s unsteady aerodynamic theory is used for inviscid fluid-dynamic modelling of the deforming flag in axial flow. Polhamus’s leading edge suction analogy is employed to model flow separation effects from the free end at moderate angles of attack via a nonlinear vortex-lift force. The flag is modelled structurally via a geometrically-exact Euler-Bernoulli beam theory. Using the extended Hamilton’s principle, the nonlinear partial-integro-differential equation governing the dynamics of the inverted flag in terms of the angle of rotation of the flag is obtained. The equation of motion is discretised spatially via the Galerkin method and is integrated in time via Gear’s backward differentiation formula. The bifurcation diagrams are obtained using a time-integration method and pseudo-arclength continuation. It is shown that inverted flags undergo multiple bifurcations with respect to flow velocity, and they generally exhibit four dynamical states: (i) stretched-straight, (ii) buckled, (iii) deflected-flapping, and (iv) large-amplitude flapping. Also, flapping of inverted flags probably develops through fluid-elastic instabilities. Our findings suggest that the system dynamics is sensitive to the mass ratio. It is shown that the mass ratio parameter does not affect the stability of the stretched-straight state and the onset of divergence; however, it controls the possibility of a direct transition from static undeflected equilibrium to large-amplitude flapping motion and it affects the amplitude of large-amplitude flapping.

Work in Progress in France Related to Computation of Profiles for Turbomachine Blades by Hodograph Method

1972 ◽  
Author(s):  
R. G. Legendre
Keyword(s):  
Ideal Fluid ◽  
Industrial Development ◽  
Critical Value ◽  
Hodograph Method ◽  
Subsonic Flows ◽  
Transonic Flows ◽  
The Real ◽  
Work In Progress ◽  
Real Fluid ◽  
Turbomachine Blade

The hodograph method has been used extensively in France for the computation of turbomachine blade profiles. The work started in 1939 but the industrial development took place during the last decades. This paper presents recent research and the results obtained. The method used in “Association Technique pour la Turbine à Gaz” (ATTAG) and in industry concerns the assimilation of the real fluid to the Chapligin ideal fluid. It permits only calculation of profiles for subsonic flows but provides quite satisfactory predictions for velocities near the critical value. It is easy to use. More complicated developments are undertaken for defining profiles adapted to reversible transonic flows, i.e., without shock. Different methods providing similar results are being studied by several groups in ONERA.

Effect of chain scission on flow characteristics of wormlike micellar solutions past a confined microfluidic cylinder: a numerical analysis

Soft Matter ◽  
2020 ◽  
Vol 16 (22) ◽  
pp. 5261-5272 ◽  
Author(s):  
Mohd Bilal Khan ◽  
C. Sasmal
Keyword(s):  
Numerical Analysis ◽  
Elastic Wave ◽  
Micellar Solution ◽  
Flow Characteristics ◽  
Chain Scission ◽  
Critical Value ◽  
Weissenberg Number ◽  
Elastic Instability ◽  
Micellar Solutions ◽  
Wave Phenomena

Elastic instability and elastic wave phenomena can be seen for the flow of a wormlike micellar solution past a confined microfluidic cylinder once the Weissenberg number exceeds a critical value.

Stability Criteria of the Steady Flow of a Liquid Containing Bubbles Along a Nozzle

2001 ◽  
Vol 123 (4) ◽  
pp. 836-840 ◽  
Author(s):  
A. Crespo ◽  
J. Garcı´a ◽  
J. Jime´nez-Ferna´ndez
Keyword(s):  
Bubble Dynamics ◽  
Volume Fraction ◽  
Flow Instability ◽  
Functional Dependence ◽  
Bubble Diameter ◽  
Critical Value ◽  
Stability Criteria ◽  
Flow Through ◽  
Gas Volume Fraction ◽  
Gas Volume

The steady cavitating flow through a converging-diverging nozzle is considered. A continuum model is assumed with the Rayleigh-Plesset equation to account for the bubble dynamics. A similar problem has been studied previously by Wang and Brennen, and they found that if the upstream gas volume fraction of the bubbles exceeds a critical value there is flashing flow instability. In the present work, a perturbation analysis is made introducing a small parameter, ε, that is the ratio of the initial bubble diameter to the length scale of the nozzle. As a result of this analysis, the critical value of the upstream void fraction is calculated as a function of the several parameters appearing in the problem, and turns out to be very small and proportional to ε3. A correlation is proposed giving explicitly the functional dependence of this critical value.

scholarly journals High-beta turbulence in two-dimensional magnetohydrodynamics

1976 ◽  
Vol 16 (2) ◽  
pp. 181-191 ◽  
Author(s):  
David Fyfe ◽  
David Montgomery
Keyword(s):  
Magnetic Fields ◽  
Turbulent Flows ◽  
Fluid Dynamic ◽  
Fluid Velocity ◽  
Navier Stokes ◽  
Magnetic Islands ◽  
Dissipation Energy ◽  
Energy Cascades ◽  
Wide Range ◽  
Current Filaments

Incompressible turbulent flows are investigated in the framework of ideal magnetohydrodynamics. All the field quantities vary with only two spatial dimensions. Equilibrium canonical distributions are determined in a phase space whose co-ordinates are the real and imaginary parts of the Fourier coefficients for the field variables. In the geometry considered, the magnetic field and fluid velocity have variable x and y components, and all field quantities are independent of z. Three constants of the motion are found (one of them new) which survive the truncation in Fourier space and permit the construction of canonical distributions with three independent temperatures. Spectral densities are calculated. One of the more novel physical effects is the appearance of macroscopic structures involving long wavelength, self-generated, magnetic fields (‘magnetic islands’) for a wide range of initial parameters. Current filaments show a tendency toward consolidation in much the same way that vorticity filaments do in the guiding-centre plasma case. In the presence of finite dissipation, energy cascades to higher wavenumbers can be accompanied by vector potential cascades to lower wavenumbers, in much the same way as, in the fluid dynamic (Navier-Stokes) case, energy cascades to lower wavenumbers accompany enstrophy cascades to higher wavenumbers. It is suggested that the techniques may be relevant to theories of the magnetic dynamo problem and to the generation of megagauss magnetic fields when pellets are irradiated by lasers.

STABILITY OF AN EXCITON BOUND TO AN IONIZED ACCEPTOR IN QUANTUM DOTS

2003 ◽  
Vol 17 (11) ◽  
pp. 2273-2279 ◽  
Author(s):  
S. BASKOUTAS ◽  
A. F. TERZIS ◽  
C. POLITIS
Keyword(s):  
Quantum Dots ◽  
Binding Energy ◽  
Quantum Dot ◽  
Numerical Method ◽  
Schrodinger Equation ◽  
Critical Radius ◽  
Critical Value ◽  
Two Dimensional ◽  
Mass Ratio ◽  
Acceptor Impurity

Binding energy for an exciton (X) bound in a parabolic two-dimensional quantum dot by an acceptor impurity A- located on the z-axis at a distance d from the dot plane, are calculated using the Hartree formalism with a recently developed numerical method (PMM) for the solution of the Schrödinger equation. As our analysis indicates there is a critical dot radius Rc such that for R < Rc the complex (A-, X) is unstable and with an increase of the impurity distance this critical radius increases. Furthermore, there is a critical value σc of the mass ratio [Formula: see text] such that for σ > σc the complex is stable.

Measurement of Steady-Flow Instability and Turbulence Levels in Dacron Vascular Grafts

1992 ◽  
Vol 114 (4) ◽  
pp. 521-526 ◽  
Author(s):  
D. G. Shombert
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Steady Flow ◽  
Flow Instability ◽  
Dynamic Properties ◽  
Fluid Dynamic ◽  
Vascular Grafts ◽  
Turbulent Regime ◽  
Number Range ◽  
Measured Transition

Fluid dynamic properties of Dacron vascular grafts were studied under controlled steady-flow conditions over a Reynolds number range of 800 to 4500. Knitted and woven grafts having nominal diameters of 6 mm and 10 mm were studied. Thermal anemometry was used to measure centerline velocity at the downstream end of the graft; pressure drop across the graft was also measured. Transition from laminar flow to turbulent flow was observed, and turbulence intensity and turbulent stresses (Reynolds normal stresses) were measured in the turbulent regime. Knitted grafts were found to have greater pressure drop than the woven grafts, and one sample was found to have a critical Reynolds number (Rc) of less than one-half the value of Rc for a smooth-walled tube.

scholarly journals A note on the flow induced by a line sink beneath a free surface

1991 ◽  
Vol 32 (3) ◽  
pp. 251-260 ◽  
Author(s):  
G. C. Hocking ◽  
L. K. Forbes
Keyword(s):  
Free Surface ◽  
Froude Number ◽  
Stagnation Point ◽  
Ideal Fluid ◽  
Critical Value ◽  
Homogeneous Fluid ◽  
Substitution Method ◽  
A Value ◽  
Line Sink ◽  
Low Froude Number

AbstractThe problem of withdrawing water through a line sink from a region containing an homogeneous fluid beneath a free surface is considered. Assuming steady, irrotational flow of an ideal fluid, solutions with low Froude number containing a stagnation point on the free surface above the sink are sought using a series substitution method. The solutions are shown to exist for a value of the Froude number up to a critical value of about 1.4. No solutions of this type are found for Froude numbers greater than this value.

scholarly journals Optimasi Gasifikasi Serbuk Tandan Kosong Kelapa Sawit Menggunakan Powder Gasifier Type Cyclone

2019 ◽  
Vol 39 (3) ◽  
pp. 258
Author(s):  
Riksa Prayogi Widyaprawira ◽  
Radi Radi ◽  
Bambang Purwantana
Keyword(s):  
Cfd Simulation ◽  
Fluid Dynamic ◽  
Fluid Velocity ◽  
Mass Rate ◽  
Empty Fruit Bunches ◽  
Fuel Ratio ◽  
Gasification Process ◽  
Air Speed ◽  
Fresh Fruit Bunches ◽  
Cfd Method

Every year, palm-oil production is increasing. Each ton of fresh fruit bunches produced to 22%–23% of oil palm empty fruit bunches (OPEFB). Based on the laboratory test, OPEFB contains 69,72% volatile and 3353,97 kcal/kg of calor. Aim of the research is to determine size material OPEFB in gasification process, determine combination AFR (Air Fuel Ratio) in gasifier tipe cyclone so that produce optimal energy and to prediction gasification process with CFD method (Computational Fluid Dynamic). The powder gasifier cyclone type method is used to convert this into renewable energy. The research method consists of OPEFB powder material with 14, 30 and 50 mesh treatment, 4 air-fuel ratio, and material mass rate treatments, and variations of the length of middle-pipe treatment. The weight of each sample is 500 g, added with 100 g of charcoal and repeated 3 times. The result shows the mesh A3 has the highest temperature at 348.23 °C, 1008,68 kcal/kg of heat value, 30.07% of efficiency, 97.81 kg/kg of AFR value, but has the lowest engine working capacity (EWC) with 14.65 kg/hours. Based on sensor test, A3 treatment, the voltage of monoxide sensor output is 1.45 mV; 1.81 mV of hydrogen; and methane at 0.66 mV. In the combination of air speed and screw rotational treatment, AFR values were generated by treatment B4 with EWC value of 20 kg/hour and AFR of 97.1 kg/kg. The highest gasmonoxide sensor results in treatment B4 is 1.58 mV; hydrogen 1.98 mV. Based on the length of the enter pipe in the reactor, treatment C1 produces an optimal value of the EWC value at 16.6 kg/hour, the heat energy value is 997 kcal/kg, the efficiency value is 29.73% and the AFR value is 82,87 kg/kg. In treatment C1 the gas monoxide sensor voltage is 1.6 mV; and methane is 1.46 mV. The CFD simulation shows that the distribution of temperature, fluid velocity and pressure in the middle iteration have a significant increase. This can be influenced by the dimensions of powder gasifier cyclone type with CFD simulation.

scholarly journals Comparative analysis of the theoretical models of ideal propulsor, ideal fluid brake, ideal screw propeller and ideal axial wind turbine

2013 ◽  
Vol 20 (2) ◽  
pp. 3-12 ◽  
Author(s):  
Tadeusz Koronowicz ◽  
Jan A. Szantyr
Keyword(s):  
Wind Turbine ◽  
Ideal Fluid ◽  
Fluid Dynamic ◽  
Theoretical Models ◽  
Design Procedures ◽  
Flow Losses ◽  
Maximum Value ◽  
Screw Propeller ◽  
Effectiveness Coefficient

Abstract The article presents a detailed discussion of the theoretical models of four different fluid dynamic devices: an ideal propulsor, an ideal fluid brake, an ideal screw propeller and an ideal turbine. The four models are presented with all relevant mathematical formulae regarding the forces, the power and the efficiency. It is demonstrated that the application of the model of an ideal optimum fluid brake according to the Betz theorem for determination of the maximum effectiveness coefficient of an axial wind turbine is not correct. In the case of a turbine the inclusion of important rotational flow losses may increase the maximum value of the turbine effectiveness coefficient above the level defined by Betz. Therefore the model of an ideal turbine should be an inversion of the model of an ideal screw propeller. This conclusion is supported by numerical calculations. It may influence the design procedures of wind turbines and may lead to increase in their efficiency.

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