Blocking in the Rotating Axial Flow in a Corotating Flexible Shell

2008 ◽  
Vol 76 (1) ◽  
Author(s):  
F. Gosselin ◽  
M. P. Païdoussis
Keyword(s):  
Traveling Waves ◽  
Physical Phenomenon ◽  
Axial Flow ◽  
Critical Value ◽  
Inviscid Fluid ◽  
Shell Wall ◽  
Stagnation Region ◽  
Linear Dynamics ◽  
Shell Equations ◽  
Rotating Cylindrical Shell

By coupling the Donnell–Mushtari shell equations to an analytical inviscid fluid solution, the linear dynamics of a rotating cylindrical shell with a corotating axial fluid flow is studied. Previously discovered mathematical singularities in the flow solution are explained here by the physical phenomenon of blocking. From a reference frame moving with the traveling waves in the shell wall, the flow is identical to the flow in a rigid varicose tube. When the ratio of rotation rate to flow velocity approaches a critical value, the phenomenon of blocking creates a stagnation region between the humps of the wall. Since the linear model cannot account for this phenomenon, the solution blows up.

scholarly journals Multitype Branching Brownian Motion and Traveling Waves

2014 ◽  
Vol 46 (01) ◽  
pp. 217-240
Author(s):  
Yan-Xia Ren ◽  
Ting Yang
Keyword(s):  
Brownian Motion ◽  
Traveling Waves ◽  
Traveling Wave ◽  
Traveling Wave Solutions ◽  
Critical Value ◽  
System Of Equations ◽  
Moment Conditions ◽  
Asymptotic Behaviors ◽  
Branching Brownian Motion ◽  
Parabolic System Of Equations

In this article we study the parabolic system of equations which is closely related to a multitype branching Brownian motion. Particular attention is paid to the monotone traveling wave solutions of this system. Provided with some moment conditions, we show the existence, uniqueness, and asymptotic behaviors of such waves with speed greater than or equal to a critical value c̲ and nonexistence of such waves with speed smaller than c̲.

scholarly journals Numerical Simulation of the Effects of the Helical Angle on the Decaying Swirl Flow of the Hole Cleaning Device

Processes ◽  
2019 ◽  
Vol 7 (2) ◽  
pp. 109 ◽  
Author(s):  
Jingyu Qu ◽  
Tie Yan ◽  
Xiaofeng Sun ◽  
Zijian Li ◽  
Wei Li
Keyword(s):  
Flow Direction ◽  
Tangential Velocity ◽  
Axial Flow ◽  
Critical Value ◽  
Swirl Flow ◽  
Swirl Number ◽  
Hole Cleaning ◽  
Helical Angle ◽  
Swirl Intensity ◽  
Cleaning Device

The application of the hole cleaning device in downhole is a new technology that can improve the problem of cuttings accumulation in the annulus and improve the hole cleaning effect of the wellbore during drilling. In this paper, the Reynolds Averaged Navier–Stokes model, together with the Realizable k-ε turbulence model, are used to perform transient simulations. The effects of rotational speed, blade shape, and helical angle on the initial swirl intensity and its decay behavior along the flow direction are studied. The swirl number, the initial swirl intensity, the decay rate, the tangential velocity distribution, and the variation of pressure are analyzed. The results indicate that the swirl number of the swirl flow exponentially decays along the flow direction. The straight blade and V-shaped blade have different swirl flow induction mechanisms. Under specific drilling parameters, the critical helical angle is determined for both types of blades. When the selection of the helical angle is close to the critical value, the swirl flow will be close to the axial flow, which is of little help in hole cleaning. Moreover, the rotation direction of swirl flow will change when the helical angle exceeds the critical value.

scholarly journals Maximum and Minimum Energy in Vortex Motion

2017 ◽  
Vol 1 (2) ◽  
Author(s):  
Amna Mohammed Osman Elzebair
Keyword(s):  
Conference Proceedings ◽  
Rayleigh Number ◽  
Silicone Oil ◽  
Minimum Energy ◽  
Vortex Motion ◽  
Critical Value ◽  
Inviscid Fluid ◽  
Two Dimensional ◽  
Electronic Format ◽  
Benard Convection

  This paper is discussion the Maximum and minimum energy in vortex motion exploited the conservation of vorticity as well as energy in two-dimensional motion of an incompressible inviscid fluid, to find some quite general criteria for stability of steady basic flows, and also steady Bènard convection sets in at the critical value of the Rayleigh number. This paper also discussion some experiments with a silicone oil (of Prandtl number100). (Abstract text Times New Roman, size 12, italic. Spacing-SINGLE). These guidelines provide instructions to format your paper. Please write directly into the template or copy your finished text into it choosing ‘match destination formatting’. Please use the predefined formatting styles instead of applying your individual settings. The paper shall be written in compliance with these instructions. Please review this document to learn about the formatting of text, table captions and references. The conference proceedings will be published in an electronic format. The Abstract should be no more than 200 words and one paragraph only. Avoid quotation and citing references in your abstract.  

scholarly journals Constrained flow around a magnetic obstacle

2008 ◽  
Vol 610 ◽  
pp. 131-156 ◽  
Author(s):  
EVGENY V. VOTYAKOV ◽  
EGBERT ZIENICKE ◽  
YURI B. KOLESNIKOV
Keyword(s):  
Magnetic Field ◽  
Electrostatic Field ◽  
Numerical Study ◽  
Three Dimensional ◽  
Inertial Force ◽  
Critical Value ◽  
Local Magnetic Field ◽  
Dimensional System ◽  
Ekman Pumping ◽  
Stagnation Region

Many practical applications exploit an external local magnetic field – magnetic obstacle – as an essential part of their operation. It has been demonstrated that the flow of an electrically conducting fluid influenced by an external field can show several kinds of recirculation. The present paper reports a three-dimensional numerical study, some results of which are compared with an experiment on such a flow in a rectangular duct. First, we derive equations to compute analytically the external magnetic field and verify these equations by comparing with experimentally measured field intensity. Then, we study flow characteristics for different magnetic field configurations. The flow inside the magnetic gap is dependent mainly on the interaction parameter N, which represents the ratio of the Lorentz force to the inertial force. Depending on the constrainment factor κ = My/Ly, where My and Ly are the half-widths of the external magnet and duct, the flow can show different stationary recirculation patterns: two magnetic vortices at small κ, a six-vortex ensemble at moderate κ, and no vortices at large κ. Recirculation appears when N is higher than a critical value Nc,m. The driving force for the recirculation is the reverse electromotive force that arises to balance the reverse electrostatic field. The reversal of the electrostatic field is caused by the concurrence of internal and external vorticity respectively related to the internal and external slopes in the M-shaped velocity profile. The critical value of Nc,m grows quickly as κ increases. For the case of well-developed recirculation, the numerical reverse velocity agrees well with that obtained in experiments. Two different magnetic systems can induce the same electric field and stagnation region provided these systems have the same power of recirculation, given by the N/Nc,m ratio. The three-dimensional helical characteristics of the vortices are elaborated, and an analogy is shown to exist between helical motion inside the recirculation studied and secondary motion in Ekman pumping. Finally, it is shown that a two-dimensional model fails to properly produce stable two- and six-vortex structures as found in the three-dimensional system. Interestingly, these recirculation patterns appear only as time-dependent and unstable transitional states before a Kármán vortex street forms, when one suddenly applies a retarding local magnetic field to a constant flow.

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.

Experimental Analysis of an Additively Manufactured Cooled Ultra Compact Combustor Vane

2019 ◽  
Author(s):  
Tylor C. Rathsack ◽  
Brian T. Bohan ◽  
Marc D. Polanka ◽  
James L. Rutledge
Keyword(s):  
Film Cooling ◽  
Guide Vane ◽  
Axial Flow ◽  
Pressure Rise ◽  
Leading Edge ◽  
Stagnation Region ◽  
Radial Temperature ◽  
Combustion Gases ◽  
Film Cooling Holes ◽  
The Impact

Abstract The Ultra Compact Combustor (UCC) offers a means to reduce overall combustor size. Unlike traditional axial flow combustors, the UCC utilizes an outboard circumferential cavity as the primary combustion zone. This combustor design enables the implementation of a Hybrid Guide Vane (HGV), located radially inboard of the circumferential cavity, to be positioned with the leading edge axially upstream of the hot combustion gases. Previous Computational Fluid Dynamics (CFD) efforts determined the viability of a passive cooling scheme where cooler compressor air was drawn into an opening at the stagnation region of the HGV and used for both internal and film-cooling of the vane. The present study investigates the performance of five cooled HGV configurations each having a unique combination of film-cooling, internal passage area, and internal passage geometry. The effectiveness of film-cooling holes to both protect the hardware and alter the flow path of the hot gases exiting the combustor cavity were evaluated for a range of core flow conditions. Further, the impact of a trailing edge slot to maintain an appropriate coolant flow rate through the HGV was evaluated. Results confirmed the efficacy of HGV with passive air ingestion. A solid structure located inside the cooled vanes affected the internal coolant mass flow and pressure rise and thus the overall cooling effectiveness. Further, optimal blowing ratios were demonstrated to buffer hot streaks in the freestream path resulting in a more uniform radial temperature distribution.

Investigations on Instabilities of Electric Arcs

1974 ◽  
Vol 29 (4) ◽  
pp. 556-567 ◽  
Author(s):  
K. Ragaller
Keyword(s):  
Growth Rate ◽  
Frictional Force ◽  
Stability Criterion ◽  
Dimensionless Parameter ◽  
Axial Flow ◽  
Critical Value ◽  
Electric Arc ◽  
Electric Arcs ◽  
Flow Component ◽  
Magnetic Forces

A general formalism is derived, that allows the evaluation of magnetic instabilities of all types of electric arc. It is shown that a stability criterion exists which is determined by the interaction between the magnetic forces, the frictional force and the so-called isotherm movement. This criterion can be expressed in terms of a dimensionless parameter Mk: when Mk is smaller than a critical value Mkcr, then the arc is absolutely stable, when Mk = Mkcr a stationary, deflected condition arises, and when Mk>Mkcr the arc is unstable. Depending on the magnitude of the growth rate however, a convective stabilisation, caused by an axial flow component, can result. The results of the theory are applied to a variety of technically interesting arcs, such as axially blown arcs, arcs in gaps and transversely blown arcs.

Exit Flow Behavior of Axial Fan Flows With/Without Impingement

2009 ◽  
Vol 131 (6) ◽  
Author(s):  
D. Sui ◽  
S. S. Wang ◽  
J. R. Mao ◽  
T. Kim ◽  
T. J. Lu
Keyword(s):  
Flow Behavior ◽  
Axial Flow ◽  
Electronics Cooling ◽  
Wall Pressure ◽  
Axial Fan ◽  
Stagnation Region ◽  
Flow Recirculation ◽  
Plate Spacing ◽  
Flow Interaction ◽  
Plate Center

The exit flow patterns of an axial flow fan widely used in electronics cooling are experimentally characterized both in free exit and in the presence of a flat impingement plate. The axial fan is rotated with 12.0 V input from a dc power supply, leading to a nominal Reynolds number of Re=9.0×103 based on fan diameter. One shear layer each is found to form between the exit flow from the axial fan and the surrounding fluid at rest, and between the exit flow and the flow along the fan axis. In addition to creating a highest wall pressure region (the primary stagnation region), the presence of the flat plate induces a flow recirculation zone (the secondary stagnation region) at the plate center. When the fan exit-to-plate spacing normalized by fan diameter (H/D) equals to about 0.6, the wall pressure is minimized in the secondary stagnation region due to the maximized “recirculation” as a result of intensified flow interaction. Within the range considered (0.2≤H/D≤2.0) and with the case of H/D∼0.6 serving as a reference, the flow interaction tends to be suppressed by the proximity of the plate at H/D=0.2 and weakened due to the momentum dissipation at H/D∼2.0.

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