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Sample records for forced rotating flows

  1. Modeling Rotating Turbulent Flows with the Body Force Potential Model.

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Amitabh; Perot, Blair

    2000-11-01

    Like a Reynolds Stress Transport equation model, the turbulent potential model has an explicit Coriolis acceleration term that appears in the model that accounts for rotation effects. In this work the additional secondary effects that system rotation has on the dissipation rate, return-to-isotropy, and fast pressure strain terms are also included in the model. The resulting model is tested in the context of rotating isotropic turbulence, rotating homogeneous shear flow, rotating channel flow, and swirling pipe flow. Many of the model changes are applicable to Reynolds stress transport equation models. All model modifications are frame indifferent.

  2. Laminar forced convection from a rotating horizontal cylinder in cross flow

    NASA Astrophysics Data System (ADS)

    Chandran, Prabul; Venugopal, G.; Jaleel, H. Abdul; Rajkumar, M. R.

    2017-04-01

    The influence of non-dimensional rotational velocity, flow Reynolds number and Prandtl number of the fluid on laminar forced convection from a rotating horizontal cylinder subject to constant heat flux boundary condition is numerically investigated. The numerical simulations have been conducted using commercial Computational Fluid Dynamics package CFX available in ANSYS Workbench 14. Results are presented for the non-dimensional rotational velocity α ranging from 0 to 4, flow Reynolds number from 25 to 40 and Prandtl number of the fluid from 0.7 to 5.4. The rotational effects results in reduction in heat transfer compared to heat transfer from stationary heated cylinder due to thickening of boundary layer as consequence of the rotation of the cylinder. Heat transfer rate increases with increase in Prandtl number of the fluid.

  3. Turbulent flow in rib-roughened channel under the effect of Coriolis and rotational buoyancy forces

    NASA Astrophysics Data System (ADS)

    Coletti, Filippo; Jacono, David Lo; Cresci, Irene; Arts, Tony

    2014-04-01

    The turbulent flow inside a rotating channel provided with transverse ribs along one wall is studied by means of two-dimensional time-resolved particle image velocimetry. The measurement set-up is mounted on the same rotating disk with the test section, allowing to obtain the same accuracy and resolution as in a non-rotating rig. The Reynolds number is 15 000, and the rotation number is 0.38. As the ribbed wall is heated, both the Coriolis force and the centrifugal force play a role in the fluid dynamics. The mean velocity fields highlight the major impact of the rotational buoyancy (characterized by a buoyancy number of 0.31) on the flow along the leading side of the duct. In particular, since the flow is directed radially outward, the near-wall layers experience significant centripetal buoyancy. The recirculation area behind the obstacles is enlarged to the point of spanning the whole inter-rib space. Also the turbulent fluctuations are significantly altered, and overall augmented, with respect to the non-buoyant case, resulting in higher turbulence levels far from the rib. On the other hand the centrifugal force has little or no impact on the flow along the trailing wall. Vortex identification, proper orthogonal decomposition, and two-point correlations are used to highlight rotational effects, and in particular to determine the dominant scales of the turbulent unsteady flow, the time-dependent behavior of the shear layer and of the recirculation bubble behind the wall-mounted obstacles, the lifetime and advection velocity of the coherent structures.

  4. Numerical and experimental study of flows in a rotating annulus with local convective forcing.

    NASA Astrophysics Data System (ADS)

    Scolan, Hélène; Su, Sylvie; Wright, Susie; Young, Roland M. B.; Read, Peter

    2016-04-01

    We present a numerical and experimental study of flows in a rotating annulus convectively forced by local thermal forcing via a heated annular ring at the bottom near the external wall and a cooled circular disk near the centre at the top surface of the annulus. This new configuration is a variant of the classical thermally-driven annulus analogue of the atmosphere circulation, where thermal forcing was previously applied uniformly on the sidewalls. Two vertically and horizontally displaced heat sources/sinks are arranged so that, in the absence of background rotation, statically unstable Rayleigh-Bénard convection would be induced above the source and beneath the sink, thereby relaxing strong constraints placed on background temperature gradients in previous experimental configurations to better mimic in fine local vigorous convection events in tropics and polar regions whilst also facilitating baroclinic motion in midlatitude regions in the Earth's atmosphere. By using the Met Office/ Oxford Rotating Annulus Laboratory (MORALS) code, we have investigated a series of equilibrated, 2D axisymmetric flows for a large range of dimensionless parameters and characterized them in terms of velocity and temperature fields. Several distinct and different flow regimes were identified, depending upon the rotation rate and strength of differential heating. These regimes will be presented with reference to variations of horizontal Ekman layer thickness versus the thermal boundary layer thickness and corresponding scalings for various quantities such as the azimuthal velocity or the heat transport. Experimental investigation of the same setup is carried out with a 1m diameter cylindrical container on a rotating platform: local heating is produced with an electrically heated annular ring at the bottom of the tank and cooling is imposed through a circular disk near the centre of the tank at the upper surface, cooled with circulating water. Different unstable circulation regimes

  5. Nonlinear and detuning effects of the nutation angle in precessionally forced rotating cylinder flow

    NASA Astrophysics Data System (ADS)

    Lopez, Juan M.; Marques, Francisco

    2016-06-01

    The flow in a rapidly rotating cylinder forced to precess through a nutation angle α is investigated numerically, keeping all parameters constant except α , and tuned to a triadic resonance at α =1∘ . When increasing α , the flow undergoes a sequence of well-characterized bifurcations associated with triadic resonance, involving heteroclinic and homoclinic cycles, for α up to about 4∘. For larger α , we identify two chaotic regimes. In the first regime, with α between about 4∘ and 27∘, the bulk flow retains remnants of the helical structures associated with the triadic resonance, but there are strong nonlinear interactions between the various azimuthal Fourier components of the flow. For the larger α regime, large detuning effects lead to the triadic resonance dynamics being completely swamped by boundary layer eruptions. The azimuthal mean flow at large angles results in a large mean deviation from solid-body rotation and the flow is characterized by strong shear at the boundary layers with temporally chaotic eruptions.

  6. The effect of power-law body forces on a thermally driven flow between concentric rotating spheres

    NASA Technical Reports Server (NTRS)

    Macaraeg, M. G.

    1986-01-01

    A numerical study is conducted to determine the effect of power-law body forces on a thermally-driven axisymmetric flow field confined between concentric co-rotating spheres. This study is motivated by Spacelab geophysical fluid-flow experiments, which use an electrostatic force on a dielectric fluid to simulate gravity; this force exhibits a (1/r)sup 5 distribution. Meridional velocity is found to increase when the electrostatic body force is imposed, relative to when the body force is uniform. Correlation among flow fields with uniform, inverse-square, and inverse-quintic force fields is obtained using a modified Grashof number.

  7. The effect of power law body forces on a thermally-driven flow between concentric rotating spheres

    NASA Technical Reports Server (NTRS)

    Macaraeg, M. G.

    1985-01-01

    A numerical study is conducted to determine the effect of power-law body forces on a thermally-driven axisymmetric flow field confined between concentric co-rotating spheres. This study is motivated by Spacelab geophysical fluid-flow experiments, which use an electrostatic force on a dielectric fluid to simulate gravity; this force exhibits a (1/r)sup 5 distribution. Meridional velocity is found to increase when the electrostatic body force is imposed, relative to when the body force is uniform. Correlation among flow fields with uniform, inverse-square, and inverse-quintic force fields is obtained using a modified Grashof number.

  8. Detailed flow and force measurements in a rotated triangular tube bundle subjected to two-phase cross-flow

    NASA Astrophysics Data System (ADS)

    Pettigrew, M. J.; Zhang, C.; Mureithi, N. W.; Pamfil, D.

    2005-05-01

    Two-phase cross-flow exists in many shell-and-tube heat exchangers. A detailed knowledge of the characteristics of two-phase cross-flow in tube bundles is required to understand and formulate flow-induced vibration parameters such as damping, fluidelastic instability, and random excitation due to turbulence. An experimental program was undertaken with a rotated-triangular array of cylinders subjected to air/water flow to simulate two-phase mixtures. The array is made of relatively large diameter cylinders (38 mm) to allow for detailed two-phase flow measurements between cylinders. Fiber-optic probes were developed to measure local void fraction. Local flow velocities and bubble diameters or characteristic lengths of the two-phase mixture are obtained by using double probes. Both the dynamic lift and drag forces were measured with a strain gauge instrumented cylinder.

  9. Numerical study of low-Reynolds number flow over rotating rigid helix: an investigation of the unsteady hydrodynamic force

    NASA Astrophysics Data System (ADS)

    Liou, William W.; Yang, Yang

    2015-08-01

    A helical flagellum filament can be modeled as a rigid helix. Numerical simulations of the unsteady flow around a rigid, finite length rotating helix are performed to examine the characteristics of the hydrodynamic force exerted on the helix by the fluid medium. Newtonian and non-Newtonian fluid models are used. The Reynolds numbers of the flows simulated range between {10}-6 and {10}2. Where appropriate, the calculated mean thrusts, obtained by using three different numerical solvers, are compared with that based on theoretical prediction. The simulated mean thrusts agree well with the theoretical predictions. Analyses show that hydrodynamic force variations, although of small amplitudes, are dominated by distinct discrete modes that are higher harmonics of the rotation frequency of the helix for the low-Reynolds number flows simulated. Simple correlations are developed for the dominant frequencies, where present, observed in the simulations of the helix with different sizes, rotation frequency, and fluid viscosity.

  10. History force on an asymmetrically rotating body in Poiseuille flow inducing particle migration across a slit pore

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Sukalyan

    2008-09-01

    Experimental evidence shows that suspended particles preferentially migrate away from confining boundaries due to the effect of a shear flow. In this paper, we consider an asymmetric particle in Poiseuille flow and determine an inertial lift force which can contribute to the particle migration. Under the influence of Poiseuille flow in a slit pore, an arbitrary particle undergoes periodic rotation which is described by Jeffery's orbit [G. Jeffery, Proc. R. Soc. London, Ser. A 102, 161 (1922)]. In the absence of rotational symmetry, a rotating particle produces an unsteady scattered field. The fluid inertia due to the unsteadiness causes an inertial force on the rotating body if the Reynolds number Re and the temporal variation in viscous force on the particle are nonzero. The resulting effect of this force on the particle migration can be significant especially for microfluidic systems, where gravitational contribution is negligible. In this paper, we consider two systems where the Reynolds number is assumed to be small but finite. In the first problem, we analyze the inertial force on a body asymmetrically rotating around its fixed center. In the second case, we focus on a freely suspended heavy particle which is considerably denser than the solvent so that the product of Re and the particle-solvent density ratio is greater than unity. For both systems, the Reynolds number and the temporal variation in viscous force are significant enough to produce a considerable inertial force on the particle. Our results indicate that the mean of this inertial component perpendicular to the boundaries is nonzero and acts in the direction away from the wall. The magnitude of this force is relatively larger near the wall and gradually decays as the particle-wall distance increases. Hence, we conclude that the discussed effect influences the preferential particle migration in conjunction with other factors.

  11. The drift force on an object in an inviscid weakly-varying rotational flow

    SciTech Connect

    Wallis, G.B.

    1995-12-31

    The force on any stationary object in an inviscid incompressible extensive steady flow is derived in terms of the added mass tensor and gradient of velocity of the undisturbed fluid. Taylor`s theorem is extended to flows with weak vorticity. There are possible applications to constitutive equations for two-phase flow.

  12. Effect of the History Force on Particle Trajectories within an Oscillatory Rotating Flow

    NASA Astrophysics Data System (ADS)

    Xu, Shujing; Nadim, Ali

    2012-11-01

    At a previous APS-DFD meeting it was reported, based on theoretical considerations, that particles denser than their suspending fluid can be made to migrate toward the rotation axis if the container undergoes oscillatory rigid-body rotation in an appropriate range of frequencies [Nadim et al., Bull. Am. Phys. Soc., 53, 191 (2008)]. This is contrary to ordinary centrifugation. However, the effect of the Basset history force was not accounted for in that analysis. It is shown here that while the history force significantly affects the dynamics of the particles, the oscillatory ``counter-centrifugation'' effect that was previously discovered continues to persist even when the history force is included in the analysis. Interestingly, inclusion of the history force can extend the parameter regime for which oscillatory counter-centrifugation might be observed.

  13. Examination of forced unsteady separated flow fields on a rotating wind turbine blade

    SciTech Connect

    Huyer, S

    1993-04-01

    The wind turbine industry faces many problems regarding the construction of efficient and predictable wind turbine machines. Steady state, two-dimensional wind tunnel data are generally used to predict aerodynamic loads on wind turbine blades. Preliminary experimental evidence indicates that some of the underlying fluid dynamic phenomena could be attributed to dynamic stall, or more specifically to generation of forced unsteady separated flow fields. A collaborative research effort between the University of Colorado and the National Renewable Energy Laboratory was conducted to systematically categorize the local and global effects of three- dimensional forced unsteady flow fields.

  14. Rotating cooloing flows

    NASA Technical Reports Server (NTRS)

    Kley, Wilhelm; Mathews, William G.

    1995-01-01

    We describe the evolution of the hot interstellar medium in a large, slowly rotating elliptical galaxy. Although the rotation assumed is a small fraction of the circular velocity, in accordance with recent observations, it is sufficient to have a profound influence on the X-ray emission and cooling geometry of the interstellar gas. The hot gas cools into a disk that extends out to approximately 10 kpc. The cool, dusty disks observed in the majority of elliptical galaxies may arise naturally from internal cooling rather than from mergers with gas-rich companions. As a result of angular momentum conservation in the cooling flow, the soft X-ray isophotes are quite noticeably flatter than those of the stellar image. The gas temperature is higer along the rotation axis. The rotational velocity of the gas several kiloparcsecs above the central disk far exceeds the local stellar rotation and approaches the local circular velocity as it flows toward the galactic core. The detailed appearance of the X-ray image and velocity field of the X-ray gas provide information about the global rotational properties of giant ellipticals at radii too distant for optical observations. The overall pattern of rotation in these galaxies retains information about the origin of ellipticals, particularly of their merging history. In ellipticals having radio jets, if the jets are aligned with the rotation axis of the inner cooling flow, rotation within the jet could be sustained by the rotating environment. Since most large ellipticals have modest rotation, the X-ray observations at low spatial resolution, when interpreted with spherical theoretical models, give the impression that hot gas undergoes localized cooling to very low temperatures many kiloparcsecs from the galactic core. We suggest that such apparent cooling can result in a natural way as gas cools onto a rotating disk.

  15. The break-up of Ekman theory in a flow subjected to background rotation and driven by a non-conservative body force

    NASA Astrophysics Data System (ADS)

    Duran-Matute, M.; Di Nitto, G.; Trieling, R. R.; Kamp, L. P. J.; van Heijst, G. J. F.

    2012-11-01

    We present an experimental/numerical study of a dipolar flow structure in a shallow layer of electrolyte driven by electromagnetic forcing and subjected to background rotation. The aim of this study is to determine the influence of a non-conservative body force on the range of applicability of the classical Ekman boundary layer theory in rapidly rotating systems. To address this question, we study the response of the flow to the three control parameters: the magnitude of the forcing, the rotation rate of the system, and the shallowness of the layer. This response is quantified taking into account the magnitude of the flow velocity (represented by the Reynolds number), the symmetry between both vortex cores, and the vertical profile of the horizontal velocity. As in the case without background rotation, the response of the flow exhibits two scaling regimes (a linear and a nonlinear regime) in which the flow exhibits different vertical profiles of velocity. The transition between the two regimes occurs when the convective acceleration becomes of the same order as the viscous damping. This suggests that the applicability of the Ekman theory depends on the existence of a balance between the forcing and the damping due to the Ekman layers and does not depend solely on the value of the Rossby number as for decaying flows. On the other hand, the cyclone/anticyclone asymmetry is governed exclusively by the Rossby number.

  16. Rotational scanning atomic force microscopy.

    PubMed

    Ulčinas, A; Vaitekonis, Š

    2017-03-10

    A non-raster scanning technique for atomic force microscopy (AFM) imaging which combines rotational and translational motion is presented. The use of rotational motion for the fast scan axis allows us to significantly increase the scanning speed while imaging a large area (diameter > 30 μm). An image reconstruction algorithm and the factors influencing the resolution of the technique are discussed. The experimental results show the potential of the rotational scanning technique for high-throughput large area AFM investigation.

  17. Rotational scanning atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Ulčinas, A.; Vaitekonis, Š.

    2017-03-01

    A non-raster scanning technique for atomic force microscopy (AFM) imaging which combines rotational and translational motion is presented. The use of rotational motion for the fast scan axis allows us to significantly increase the scanning speed while imaging a large area (diameter > 30 μm). An image reconstruction algorithm and the factors influencing the resolution of the technique are discussed. The experimental results show the potential of the rotational scanning technique for high-throughput large area AFM investigation.

  18. On rotational conical flow

    NASA Technical Reports Server (NTRS)

    Ferrari, Carlo

    1952-01-01

    Some general properties of isoenergetic rotational conical fields are determined. For such fields, provided the physical parameters of the fluid flow are known on a conical reference surface, it being understood that they satisfy certain imposed conditions, it is shown how to construct the hodographs in the various meridional semiplanes, as the envelope of either the tangents to the hodographs or of the osculatory circles.

  19. Current flow and pair creation at low altitude in rotation-powered pulsars' force-free magnetospheres: space charge limited flow

    NASA Astrophysics Data System (ADS)

    Timokhin, A. N.; Arons, J.

    2013-02-01

    We report the results of an investigation of particle acceleration and electron-positron plasma generation at low altitude in the polar magnetic flux tubes of rotation-powered pulsars, when the stellar surface is free to emit whatever charges and currents are demanded by the force-free magnetosphere. We apply a new 1D hybrid plasma simulation code to the dynamical problem, using Particle-in-Cell methods for the dynamics of the charged particles, including a determination of the collective electrostatic fluctuations in the plasma, combined with a Monte Carlo treatment of the high-energy gamma-rays that mediate the formation of the electron-positron pairs. We assume the electric current flowing through the pair creation zone is fixed by the much higher inductance magnetosphere, and adopt the results of force-free magnetosphere models to provide the currents which must be carried by the accelerator. The models are spatially one dimensional, and designed to explore the physics, although of practical relevance to young, high-voltage pulsars. We observe novel behaviour (a) When the current density j is less than the Goldreich-Julian value (0 < j/jGJ < 1), space charge limited acceleration of the current carrying beam is mild, with the full Goldreich-Julian charge density comprising the charge densities of the beam and a cloud of electrically trapped particles with the same sign of charge as the beam. The voltage drops are of the order of mc2/e, and pair creation is absent. (b) When the current density exceeds the Goldreich-Julian value (j/jGJ > 1), the system develops high voltage drops (TV or greater), causing emission of curvature gamma-rays and intense bursts of pair creation. The bursts exhibit limit cycle behaviour, with characteristic time-scales somewhat longer than the relativistic fly-by time over distances comparable to the polar cap diameter (microseconds). (c) In return current regions, where j/jGJ < 0, the system develops similar bursts of pair creation

  20. Dissipative particle dynamics simulation of flow generated by two rotating concentric cylinders: II. Lateral dissipative and random forces

    NASA Astrophysics Data System (ADS)

    Filipovic, N.; Haber, S.; Kojic, M.; Tsuda, A.

    2008-02-01

    Traditional DPD methods address dissipative and random forces exerted along the line connecting neighbouring particles. Espanol (1998 Phys. Rev. E 57 2930-48) suggested adding dissipative and random force components in a direction perpendicular to this line. This paper focuses on the advantages and disadvantages of such an addition as compared with the traditional DPD method. Our benchmark system comprises fluid initially at rest occupying the space between two concentric cylinders rotating with various angular velocities. The effect of the lateral force components on the time evolution of the simulated velocity profile was also compared with that of the known analytical solution. The results show that (i) the solution accuracy at steady state has improved and the error has been reduced by at least 30% (in one case by 75%), (ii) the DPD time to reach steady state has been halved, (iii) the CPU time has increased by only 30%, and (iv) no significant differences exist in density and temperature distributions.

  1. Current Flow and Pair Creation at Low Altitude in Rotation-Powered Pulsars' Force-Free Magnetospheres: Space Charge Limited Flow

    NASA Technical Reports Server (NTRS)

    Timokhin, A. N.; Arons, J.

    2013-01-01

    We report the results of an investigation of particle acceleration and electron-positron plasma generation at low altitude in the polar magnetic flux tubes of rotation-powered pulsars, when the stellar surface is free to emit whatever charges and currents are demanded by the force-free magnetosphere. We apply a new 1D hybrid plasma simulation code to the dynamical problem, using Particle-in-Cell methods for the dynamics of the charged particles, including a determination of the collective electrostatic fluctuations in the plasma, combined with a Monte Carlo treatment of the high-energy gamma-rays that mediate the formation of the electron-positron pairs.We assume the electric current flowing through the pair creation zone is fixed by the much higher inductance magnetosphere, and adopt the results of force-free magnetosphere models to provide the currents which must be carried by the accelerator. The models are spatially one dimensional, and designed to explore the physics, although of practical relevance to young, high-voltage pulsars. We observe novel behaviour (a) When the current density j is less than the Goldreich-Julian value (0 < j/j(sub GJ) < 1), space charge limited acceleration of the current carrying beam is mild, with the full Goldreich-Julian charge density comprising the charge densities of the beam and a cloud of electrically trapped particles with the same sign of charge as the beam. The voltage drops are of the order of mc(sup 2)/e, and pair creation is absent. (b) When the current density exceeds the Goldreich-Julian value (j/j(sub GJ) > 1), the system develops high voltage drops (TV or greater), causing emission of curvature gamma-rays and intense bursts of pair creation. The bursts exhibit limit cycle behaviour, with characteristic time-scales somewhat longer than the relativistic fly-by time over distances comparable to the polar cap diameter (microseconds). (c) In return current regions, where j/j(sub GJ) < 0, the system develops similar

  2. Numerical simulation of negative Magnus force on a rotating sphere

    NASA Astrophysics Data System (ADS)

    Muto, Masaya; Tsubokura, Makoto; Oshima, Nobuyuki

    2010-11-01

    Flow characteristics and fluid force on a sphere rotating along with axis perpendicular to mean air flow were investigated using Large Eddy Simulation at two different Reynolds numbers of 10,000 and 200,000. As a result of simulation, opposite flow characteristics around the sphere and displacement of the separation point were visualized depending on the Reynolds number even though the sphere rotates at the same rotation speed according to the Reynolds number. When Reynolds number is 10,000, flow characteristics agree with the flow field explained in the Magnus effect. However sphere rotates at the same rotation speed while increasing Reynolds number to 200,000, separation point moves in opposite direction and wake appears in the different direction. The reason of the negative Magnus force was discussed in terms of the boundary layer transition on the surface.

  3. Instability and transition in rotating disk flow

    NASA Technical Reports Server (NTRS)

    Malik, M. R.

    1981-01-01

    The stability of three dimensional rotating disk flow and the effects of Coriolis forces and streamline curvature were investigated. It was shown that this analysis gives better growth rates than Orr-Sommerfeld equation. Results support the numerical prediction that the number of stationary vortices varies directly with the Reynolds number.

  4. On rotational forces in the solar wind

    NASA Technical Reports Server (NTRS)

    Hollweg, J. V.; Isenberg, P. A.

    1981-01-01

    Solar rotational forces affecting the flow of minor ions in the solar wind are considered as corotating with the sun. Cold, noninteracting charged particles in the magnetic and gravitational fields of the sun rotate with the angular velocity of the sun, and calculations of lowest bulk order velocities show that differences in particle velocities decrease with increasing distance from the sun. A centrifugal potential in the corotating frame implies that ion motion is independent of protons, with velocities determined by the potential, which monotonically decreases without limit. The potential dominates the initial kinetic energy of the particles, and the equality of velocities within the potential is not due to interactions between particles as claimed by Mackenzie et al. (1979).

  5. Axisymmetric supersonic flow in rotating impellers

    NASA Technical Reports Server (NTRS)

    Goldstein, Arthur W

    1952-01-01

    General equations are developed for isentropic, frictionless, axisymmetric flow in rotating impellers with blade thickness taken into account and with blade forces eliminated in favor of the blade-surface function. It is shown that the total energy of the gas relative to the rotating coordinate system is dependent on the stream function only, and that if the flow upstream of the impeller is vortex-free, a velocity potential exists which is a function of only the radial and axial distances in the impeller. The characteristic equations for supersonic flow are developed and used to investigate flows in several configurations in order to ascertain the effect of variations of the boundary conditions on the internal flow and the work input. Conditions varied are prerotation of the gas, blade turning rate, gas velocity at the blade tips, blade thickness, and sweep of the leading edge.

  6. Lorentz Force: A Possible Driving Force for Sunspot Rotation

    NASA Astrophysics Data System (ADS)

    Su, Jiangtao; Liu, Yu; Liu, Jihong; Mao, Xinjie; Zhang, Hongqi; Li, Hui; Wang, Xiaofan; Xie, Wenbin

    2008-10-01

    Zhao and Kosovichev ( Astrophys. J. 591, 446, 2003) found two opposite sub-photospheric vortical flows in the depth range of 0 - 12 Mm around a fast rotating sunspot. So far there is no theoretical model explaining such flow motions. In this paper, we try to explain this phenomenon from the point of view of magnetic flux tubes interacting with large-scale vortical motions of plasma. In the deeper zone under the photosphere, the magnetic force may be less than the nonmagnetic force of plasma. The vortical flow located there twists the flux tube and magnetic free energy is built up in the tube. In the shallower zone under the photosphere, the magnetic force may be greater than the nonmagnetic force. Thus, part of the stored magnetic free energy is released to drive the plasma to rotate in two opposite directions, e.g., in the depth ranges of 0 - 3(5) and 9 - 12 Mm. In addition, we also define a vector of nonpotential magnetic stress τ, which can be related to flare occurrence. It is calculated for the active region NOAA 10930 on 11 December 2006. We find that: i) the integral of its line-of-sight (LOS) stress successively increases around the magnetic neutral line (MNL) prior to and during the flare and decreases to a minimum after the flare; ii) the integral of its transverse stress exceeds the integral of its LOS component by one order of magnitude over the whole field of view; iii) the transverse stress first points toward the MNL, then along it, and finally it points away from it. We need other data to verify whether or not the magnetic energy is transported in the horizontal direction to the neutral line, and then partly changes into the energy in LOS direction before and during the flare.

  7. Rotationally symmetric viscous gas flows

    NASA Astrophysics Data System (ADS)

    Weigant, W.; Plotnikov, P. I.

    2017-03-01

    The Dirichlet boundary value problem for the Navier-Stokes equations of a barotropic viscous compressible fluid is considered. The flow region and the data of the problem are assumed to be invariant under rotations about a fixed axis. The existence of rotationally symmetric weak solutions for all adiabatic exponents from the interval (γ*,∞) with a critical exponent γ* < 4/3 is proved.

  8. Turbulent Flow Between Rotating Cylinders

    NASA Technical Reports Server (NTRS)

    Shih-I, Pai

    1943-01-01

    The turbulent air flow between rotating cylinders was investigated. The distributions of mean speed and of turbulence were measured in the gap between a rotating inner and a stationary outer cylinder. The measurements led to the conclusion that the turbulent flow in the gap cannot be considered two dimensional, but that a particular type of secondary motion takes place. It is shown that the experimentally found velocity distribution can be fully understood under the assumption that this secondary motion consists of three-dimensional ring-shape vortices. The vortices occur only in pairs, and their number and size depend on the speed of the rotating cylinder; the number was found to decrease with increasing speed. The secondary motion has an essential part in the transmission of the moment of momentum. In regions where the secondary motion is negligible, the momentum transfer follows the laws known for homologous turbulence. Ring-shape vortices are known to occur in the laminar flow between rotating cylinders, but it was hitherto unknown that they exist even at speeds that are several hundred times the critical limit.

  9. An improved turbulence model for rotating shear flows*

    NASA Astrophysics Data System (ADS)

    Nagano, Yasutaka; Hattori, Hirofumi

    2002-01-01

    In the present study, we construct a turbulence model based on a low-Reynolds-number non-linear k e model for turbulent flows in a rotating channel. Two-equation models, in particular the non-linear k e model, are very effective for solving various flow problems encountered in technological applications. In channel flows with rotation, however, the explicit effects of rotation only appear in the Reynolds stress components. The exact equations for k and e do not have any explicit terms concerned with the rotation effects. Moreover, the Coriolis force vanishes in the momentum equation for a fully developed channel flow with spanwise rotation. Consequently, in order to predict rotating channel flows, after proper revision the Reynolds stress equation model or the non-linear eddy viscosity model should be used. In this study, we improve the non-linear k e model so as to predict rotating channel flows. In the modelling, the wall-limiting behaviour of turbulence is also considered. First, we evaluated the non-linear k e model using the direct numerical simulation (DNS) database for a fully developed rotating turbulent channel flow. Next, we assessed the non-linear k e model at various rotation numbers. Finally, on the basis of these assessments, we reconstruct the non-linear k e model to calculate rotating shear flows, and the proposed model is tested on various rotation number channel flows. The agreement with DNS and experiment data is quite satisfactory.

  10. Stochastically forced zonal flows

    NASA Astrophysics Data System (ADS)

    Srinivasan, Kaushik

    This thesis investigates the dynamics of multiple zonal jets, that spontaneously emerge on the barotropic beta-plane, driven by a homogenous and rapidly decorrelating forcing and damped by bottom drag. Decomposing the barotropic vorticity equation into the zonal-mean and eddy equations, and neglecting the eddy-eddy interactions, defines the quasi-linear (QL) system. Numerical solution of the QL system shows zonal jets with length scales comparable to jets obtained by solving the nonlinear (NL) system. Starting with the QL system, one can construct a deterministic equation for the evolution of the two-point single-time correlation function of the vorticity, from which one can obtain the Reynolds stress that drives the zonal mean flow. This deterministic system has an exact nonlinear solution, which is a homogenous eddy field with no jets. When the forcing is also isotropic in space, we characterize the linear stability of this jetless solution by calculating the critical stability curve in the parameter space and successfully comparing this analytic result with numerical solutions of the QL system. But the critical drag required for the onset of NL zonostrophic instability is up to a factor of six smaller than that for QL zonostrophic instability. The constraint of isotropic forcing is then relaxed and spatially anisotropic forcing is used to drive the jets. Meridionally drifting jets are observed whenever the forcing breaks an additional symmetry that we refer to as mirror, or reflexional symmetry. The magnitude of drift speed in our results shows a strong variation with both mu and beta: while the drift speed decreases almost linearly with decreasing mu, it actually increases as beta decreases. Similar drifting jets are also observed in QL, with the same direction (i.e. northward or southward) and similar magnitude as NL jet-drift. Starting from the laminar solution, and assuming a mean-flow that varies slowly with reference to the scale of the eddies, we obtain

  11. Laboratory study of forced rotating shallow water turbulence

    NASA Astrophysics Data System (ADS)

    Espa, Stefania; Di Nitto, Gabriella; Cenedese, Antonio

    2011-12-01

    During the last three decades several authors have studied the appearance of multiple zonal jets in planetary atmospheres and in the Earths oceans. The appearance of zonal jets has been recovered in numerical simulations (Yoden & Yamada, 1993), laboratory experiments (Afanasyev & Wells, 2005; Espa et al., 2008, 2010) and in field measurements of the atmosphere of giant planets (Galperin et al., 2001). Recent studies have revealed the presence of zonation also in the Earths oceans, in fact zonal jets have been found in the outputs of Oceanic General Circulation Models-GCMs (Nakano & Hasumi, 2005) and from the analysis of satellite altimetry observations (Maximenko et al., 2005). In previous works (Espa et al., 2008, 2010) we have investigated the impact of the variation of the rotation rate and of the fluid depth on jets organization in decaying and forced regimes. In this work we show results from experiments performed in a bigger domain in which the fluid is forced continuously. The experimental set-up consists of a rotating tank (1m in diameter) where the initial distribution of vorticity has been generated via the Lorentz force in an electromagnetic cell. The latitudinal variation of the Coriolis parameter has been simulated by the parabolic profile assumed by the free surface of the rotating fluid. Flow measurements have been performed using an image analysis technique. Experiments have been performed changing the tank rotation rate and the fluid thickness. We have investigated the flow in terms of zonal and radial flow pattern, flow variability and jet scales.

  12. Magnetorheological rotational flow with viscous dissipation

    NASA Astrophysics Data System (ADS)

    Ashrafi, Nariman

    2017-05-01

    Effects of a magnetic field and fluid nonlinearity are investigated for the rotational flow of the Carreau-type fluid while viscous dissipation is taken into account. The governing motion and energy balance equations are coupled, adding complexity to the already highly correlated set of differential equations. The numerical solution is obtained for the narrow-gap limit and steady-state base flow. Magnetic field effect on local entropy generation due to steady two-dimensional laminar forced convection flow was investigated. This study was focused on the entropy generation characteristics and its dependency on various dimensionless parameters. The effects of the Hartmann number, the Brinkman number, and the Deborah number on the stability of the flow were investigated. The introduction of the magnetic field induces a resistive force acting in the opposite direction of the flow, thus causing its deceleration. Moreover, the study shows that the presence of magnetic field tends to slow down the fluid motion. It, however, increases the fluid temperature. Moreover, the total entropy generation number decreases as the Hartmann number and fluid elasticity increase and increases with increasing Brinkman number.

  13. Forces and Torques on Rotating Spirochete Flagella

    NASA Astrophysics Data System (ADS)

    Yang, Jing; Huber, Greg; Wolgemuth, Charles W.

    2011-12-01

    Spirochetes are a unique group of motile bacteria that are distinguished by their helical or flat-wave shapes and the location of their flagella, which reside within the tiny space between the bacterial cell wall and the outer membrane (the periplasm). In Borrelia burgdorferi, rotation of the flagella produces cellular undulations that drive swimming. How these shape changes arise due to the forces and torques that act between the flagella and the cell body is unknown. It is possible that resistive forces come from friction or from fluid drag, depending on whether or not the flagella are in contact with the cell wall. Here, we consider both of these cases. By analyzing the motion of an elastic flagellum rotating in the periplasmic space, we show that the flagella are most likely separated from the bacterial cell wall by a lubricating layer of fluid. This analysis then provides drag coefficients for rotation and sliding of a flagellum within the periplasm.

  14. Forces and torques on rotating spirochete flagella.

    PubMed

    Yang, Jing; Huber, Greg; Wolgemuth, Charles W

    2011-12-23

    Spirochetes are a unique group of motile bacteria that are distinguished by their helical or flat-wave shapes and the location of their flagella, which reside within the tiny space between the bacterial cell wall and the outer membrane (the periplasm). In Borrelia burgdorferi, rotation of the flagella produces cellular undulations that drive swimming. How these shape changes arise due to the forces and torques that act between the flagella and the cell body is unknown. It is possible that resistive forces come from friction or from fluid drag, depending on whether or not the flagella are in contact with the cell wall. Here, we consider both of these cases. By analyzing the motion of an elastic flagellum rotating in the periplasmic space, we show that the flagella are most likely separated from the bacterial cell wall by a lubricating layer of fluid. This analysis then provides drag coefficients for rotation and sliding of a flagellum within the periplasm.

  15. Rotatable non-circular forebody flow controller

    NASA Technical Reports Server (NTRS)

    Moskovitz, Cary A. (Inventor)

    1991-01-01

    The invention is a rotatable, non-circular forebody flow controller. The apparatus comprises a small geometric device located at a nose of a forebody of an aircraft and a non-circular cross-sectional area that extends toward the apex of the aircraft. The device is symmetrical about a reference plane and preferably attaches to an axle which in turn attaches to a rotating motor. The motor rotates the device about an axis of rotation. Preferably, a control unit connected to an aircraft flight control computer signals to the rotating motor the proper rotational positioning of the geometric device.

  16. Laminar Flow past a Rotating Sphere

    NASA Astrophysics Data System (ADS)

    Kim, Dongjoo; Choi, Haecheon

    2000-11-01

    In this study, laminar flow past a rotating sphere is numerically investigated to understand the effect of the streamwise rotation on the flow characteristics behind a sphere. The present numerical method is based on a newly developed immersed boundary method in a cylindrical coordinate. Numerical simulations are performed at Re =100, 250 and 300 in the range of 0 <= ω^* <= 1.0, where ω^* is the maximum circumferential speed at the sphere surface normalized by the free-stream velocity. At ω^*=0 (without rotation), the flow past a sphere experiences steady axisymmetry, steady plane-symmetry, and unsteady plane-symmetry, respectively, at Re =100, 250 and 300. When the rotational speed increases, the drag increases for all the Reynolds numbers investigated, whereas the lift shows a non-monotonic behavior depending on the Reynolds number. At Re =100, the flow past a sphere shows steady axisymmetry for all the rotational speeds considered and thus the lift is zero. On the other hand, at Re =250 and 300, the flow becomes unsteady with rotation. With increasing rotational speed, the lift first decreases and then increases, showing a local minimum of lift at a specific rotational speed. The three-dimensional vortical structures behind a sphere are significantly modified by the streamwise rotation. For example, the vortical structures at Re =300 are completely changed and phase locked with rotation at ω^*=0.6.

  17. Effect of rotation rate on the forces of a rotating cylinder: Simulation and control

    NASA Technical Reports Server (NTRS)

    Burns, John A.; Ou, Yuh-Roung

    1993-01-01

    In this paper we present numerical solutions to several optimal control problems for an unsteady viscous flow. The main thrust of this work is devoted to simulation and control of an unsteady flow generated by a circular cylinder undergoing rotary motion. By treating the rotation rate as a control variable, we can formulate two optimal control problems and use a central difference/pseudospectral transform method to numerically compute the optimal control rates. Several types of rotations are considered as potential controls, and we show that a proper synchronization of forcing frequency with the natural vortex shedding frequency can greatly influence the flow. The results here indicate that using moving boundary controls for such systems may provide a feasible mechanism for flow control.

  18. Flow Split Venturi, Axially-Rotated Valve

    DOEpatents

    Walrath, David E.; Lindberg, William R.; Burgess, Robert K.; LaBelle, James

    2000-02-22

    The present invention provides an axially-rotated valve which permits increased flow rates and lower pressure drop (characterized by a lower loss coefficient) by using an axial eccentric split venturi with two portions where at least one portion is rotatable with respect to the other portion. The axially-rotated valve typically may be designed to avoid flow separation and/or cavitation at full flow under a variety of conditions. Similarly, the valve is designed, in some embodiments, to produce streamlined flow within the valve. An axially aligned outlet may also increase the flow efficiency. A typical cross section of the eccentric split venturi may be non-axisymmetric such as a semicircular cross section which may assist in both throttling capabilities and in maximum flow capacity using the design of the present invention. Such a design can include applications for freeze resistant axially-rotated valves and may be fully-opened and fully-closed in one-half of a complete rotation. An internal wide radius elbow typically connected to a rotatable portion of the eccentric venturi may assist in directing flow with lower friction losses. A valve actuator may actuate in an axial manner yet be uniquely located outside of the axial flow path to further reduce friction losses. A seal may be used between the two portions that may include a peripheral and diametrical seal in the same plane. A seal separator may increase the useful life of the seal between the fixed and rotatable portions.

  19. Flow between rotating disks. Part 1: Basic flow

    NASA Astrophysics Data System (ADS)

    Schneider, S. J.; Labbe, F.; Kaufman, H. N.; Szeri, A. Z.

    Multiplicity of basic flows, when the fluid is bounded by two infinite disks, reported by several investigators is examined with emphasis on whether, and under what conditions infinite disk flows approximate to laboratory flows between two finite disks. Laser Doppler velocity measurements were obtained in water between finite rotating disks, with and without through flow. Angular velocity ratios were studied for: (1) one disk rotating and the other stationary; (2) co-rotating disks of equal angular velocity; and (3) counter rotating disks of equal but opposite angular velocity. It is concluded that limiting flows are unique and are independent of flow history. With one disk rotating and the other stationary, the mid-radius limiting flow is recognized as the Batchelor profile of infinite disk theory. Other profiles, predicted by this theory to coexist with the Batchelor profile were neither observed experimentally nor were they calculated numerically by the finite disk solution obtained with a Galerkin, b-spline formulation.

  20. Geometry of tracer trajectories in rotating turbulent flows

    NASA Astrophysics Data System (ADS)

    Alards, Kim M. J.; Rajaei, Hadi; Del Castello, Lorenzo; Kunnen, Rudie P. J.; Toschi, Federico; Clercx, Herman J. H.

    2017-04-01

    The geometry of passive tracer trajectories is studied in two different types of rotating turbulent flows; rotating Rayleigh-Bénard convection (RBC; experiments and direct numerical simulations) and rotating electromagnetically forced turbulence (EFT; experiments). This geometry is fully described by the curvature and torsion of trajectories, and from these geometrical quantities we can subtract information on the typical flow structures at different rotation rates. Previous studies, focusing on nonrotating homogeneous isotropic turbulence (HIT), show that the probability density functions (PDFs) of curvature and torsion reveal pronounced power laws. However, the set-ups studied here involve inhomogeneous turbulence, and in RBC the flow near the horizontal plates is definitely anisotropic. We investigate how the typical shapes of the curvature and torsion PDFs, including the pronounced scaling laws, are influenced by this level of anisotropy and inhomogeneity and how this effect changes with rotation. A first effect of rotation is observed as a shift of the curvature and torsion PDFs towards higher values in the case of RBC and towards lower values in the case of EFT. This shift is related to the length scale of typical vortical structures that decreases with rotation in RBC, but increases with rotation in EFT, explaining the opposite shifts of the curvature (and torsion) PDFs. A second remarkable observation is that in RBC the HIT scaling laws are always recovered, as long as the boundary layer (BL) is excluded. This suggests that these scaling laws are very robust and hold as long as we measure in the turbulent bulk. In the BL of the RBC cell, however, the scaling deviates from the HIT prediction for lower rotation rates. This scaling behavior is found to be consistent with the coupling between the boundary layer dynamics and the bulk flow, which changes under rotation. In particular, it is found that the active coupling of the Ekman-type boundary layer with the

  1. Cavitation flow through a rotating pipe

    NASA Astrophysics Data System (ADS)

    Szumowski, A.; Laake, A.; Meier, G. E. A.

    1986-07-01

    A one-dimensional cavitation flow (without Coriolis accelaration) in a rotating pipe was investigated with a view to cooling of gas turbine blades and compressors. This flow becomes unsteady and oscillates. Thereby, and unsteady cavitation domain is produced, separating the two partial water columns. At increasing rotation speed the oscillation frequency decreases and the extension of the cavitation domain increases. Above a critical rotation speed the water column is pressed out of the pipe, and the cavitation domain disappears. The flow computation was performed using the Runge-Kutta method for an incompressible model, and the characteristics method for a compressible model. The results of the calculations are supported by experimental results.

  2. Microphotonic Forces from Superfluid Flow

    NASA Astrophysics Data System (ADS)

    McAuslan, D. L.; Harris, G. I.; Baker, C.; Sachkou, Y.; He, X.; Sheridan, E.; Bowen, W. P.

    2016-04-01

    In cavity optomechanics, radiation pressure and photothermal forces are widely utilized to cool and control micromechanical motion, with applications ranging from precision sensing and quantum information to fundamental science. Here, we realize an alternative approach to optical forcing based on superfluid flow and evaporation in response to optical heating. We demonstrate optical forcing of the motion of a cryogenic microtoroidal resonator at a level of 1.46 nN, roughly 1 order of magnitude larger than the radiation pressure force. We use this force to feedback cool the motion of a microtoroid mechanical mode to 137 mK. The photoconvective forces we demonstrate here provide a new tool for high bandwidth control of mechanical motion in cryogenic conditions, while the ability to apply forces remotely, combined with the persistence of flow in superfluids, offers the prospect for new applications.

  3. Algebraic disturbances and their consequences in rotating channel flow transition

    NASA Astrophysics Data System (ADS)

    Jose, Sharath; Kuzhimparampil, Vishnu; Pier, Benoît.; Govindarajan, Rama

    2017-08-01

    It is now established that subcritical mechanisms play a crucial role in the transition to turbulence of nonrotating plane shear flows. The role of these mechanisms in rotating channel flow is examined here in the linear and nonlinear stages. Distinct patterns of behavior are found: the transient growth leading to nonlinearity at low rotation rates R o , a highly chaotic intermediate R o regime, a localized weak chaos at higher R o , and complete stabilization of transient disturbances at very high R o . At very low R o , the transient growth amplitudes are close to those for nonrotating flow, but Coriolis forces assert themselves by producing distinct asymmetry about the channel centreline. Nonlinear processes are then triggered, in a streak-breakdown mode of transition. The high R o regimes do not show these signatures; here the leading eigenmode emerges as dominant in the early stages. Elongated structures plastered close to one wall are seen at higher rotation rates. Rotation is shown to reduce nonnormality in the linear operator, in an indirect manifestation of Taylor-Proudman effects. Although the critical Reynolds for exponential growth of instabilities is known to vary a lot with rotation rate, we show that the energy critical Reynolds number is insensitive to rotation rate. It is hoped that these findings will motivate experimental verification and examination of other rotating flows in this light.

  4. Theoretical study of fluid forces on a centrifugal impeller rotating and whirling in a volute

    NASA Astrophysics Data System (ADS)

    Tsujimoto, Y.; Acosta, A. J.; Brennen, C. E.

    1988-07-01

    Fluid forces on a rotating and whirling centrifugal impeller in a volute are analyzed with the assumption of a two-dimensional rotational, inviscid flow. For simplicity, the flow is assumed to be perfectly guided by the impeller vanes. The theory predicts the tangential and the radial force on the whirling impeller as functions of impeller geometry, volute spacing, and whirl ratio. A good qualitative agreement with experiment is found.

  5. Flow Transitions in a Rotating Magnetic Field

    NASA Technical Reports Server (NTRS)

    Volz, M. P.; Mazuruk, K.

    1996-01-01

    Critical Rayleigh numbers have been measured in a liquid metal cylinder of finite height in the presence of a rotating magnetic field. Several different stability regimes were observed, which were determined by the values of the Rayleigh and Hartmann numbers. For weak rotating magnetic fields and small Rayleigh numbers, the experimental observations can be explained by the existence of a single non-axisymmetric meridional roll rotating around the cylinder, driven by the azimuthal component of the magnetic field. The measured dependence of rotational velocity on magnetic field strength is consistent with the existence of laminar flow in this regime.

  6. Numerical Study of Rotating Turbulence with External Forcing

    NASA Technical Reports Server (NTRS)

    Yeung, P. K.; Zhou, Ye

    1998-01-01

    Direct numerical simulation at 256(exp 3) resolution have been carried out to study the response of isotropic turbulence to the concurrent effects of solid-body rotation and numerical forcing at the large scales. Because energy transfer to the smaller scales is weakened by rotation, energy input from forcing gradually builds up at the large scales, causing the overall kinetic energy to increase. At intermediate wavenumbers the energy spectrum undergoes a transition from a limited k(exp -5/3) inertial range to k(exp -2) scaling recently predicted in the literature. Although the Reynolds stress tensor remains approximately isotropic and three-components, evidence for anisotropy and quasi- two-dimensionality in length scales and spectra in different velocity components and directions is strong. The small scales are found to deviate from local isotropy, primarily as a result of anisotropic transfer to the high wavenumbers. To understand the spectral dynamics of this flow we study the detailed behavior of nonlinear triadic interactions in wavenumber space. Spectral transfer in the velocity component parallel to the axis of rotation is qualitatively similar to that in non-rotating turbulence; however the perpendicular component is characterized by a greatly suppressed energy cascade at high wavenumber and a local reverse transfer at the largest scales. The broader implications of this work are briefly addressed.

  7. Laminar flow past a rotating circular cylinder

    NASA Astrophysics Data System (ADS)

    Kang, Sangmo; Choi, Haecheon; Lee, Sangsan

    1999-11-01

    The present study numerically investigates two-dimensional laminar flow past a circular cylinder rotating with a constant angular velocity, for the purpose of controlling vortex shedding and understanding the underlying flow mechanism. Numerical simulations are performed for flows with Re=60, 100, and 160 in the range of 0⩽α⩽2.5, where α is the circumferential speed at the cylinder surface normalized by the free-stream velocity. Results show that the rotation of a cylinder can suppress vortex shedding effectively. Vortex shedding exists at low rotational speeds and completely disappears at α>αL, where αL is the critical rotational speed which shows a logarithmic dependence on Re. The Strouhal number remains nearly constant regardless of α while vortex shedding exists. With increasing α, the mean lift increases linearly and the mean drag decreases, which differ significantly from those predicted by the potential flow theory. On the other hand, the amplitude of lift fluctuation stays nearly constant with increasing α (<αL), while that of drag fluctuation increases. Further studies from the instantaneous flow fields demonstrate again that the rotation of a cylinder makes a substantial effect on the flow pattern.

  8. Librations induced zonal flow and differential rotation of free inner core in rotating spherical cavity

    NASA Astrophysics Data System (ADS)

    Kozlov, V. G.; Subbotin, S. V.

    2017-09-01

    The paper is devoted to the experimental study of the dynamics of a free solid core and a liquid in a spherical cavity rotating about a horizontal axis. The cavity rotation rate consists of two components: constant and oscillating ones (librations). Under the action of centrifugal force the core with the density less than the density of liquid is located near the rotation axis. The gravity field causes a small stationary displacement of the core from the cavity center. In turn, this displacement induces mean retrograde differential rotation of the core and the fluid. It is found that the librations generate the mean effects (zonal flow and the retrograde differential rotation of the core), which manifest themselves in sum with the ones caused by gravity. The intensity of zonal flow and the core differential rotation is proportional to the square of the libration amplitude. The additivity of mean effects connected with librations and gravity is observed in a wide range of the libration frequency excluding the areas of very low-frequency librations and resonant (close to the rotation frequency and natural frequencies of the core translational oscillations) ones. At low-frequency librations, the core rotation rate changes periodically with the libration frequency and is accompanied by the periodic variation of the core position in the cavity. At some part of the libration period, the relaxation oscillations of the core with natural frequency are excited. Librations with the frequency equal to the cavity rotation exert the strongest resonant effect on the core, generating the core translational oscillations with large amplitude and substantial change of the structure of mean zonal flows. In this case and when the libration frequency coincides with the natural frequency of the core oscillations, the dependence of the differential rotational rate on the libration amplitude is different from the quadratic. This specific response of the system on the librations is caused

  9. The influence of non-equilibrium pressure on rotating flows

    NASA Astrophysics Data System (ADS)

    Zardadkhan, Irfan Rashid

    This study was undertaken to investigate the influence of pressure relaxation on steady, incompressible flows with strong streamline curvature. In the early part of this dissertation research, the significance of non-equilibrium pressure forces in controlling the structure of a steady, two dimensional axial vortex was demonstrated. In order to extend the study of pressure relaxation influences on more complex rotating flows, this dissertation has examined other rotating flow features that can be associated with hurricanes, tornadoes and dust devils. To model these flows, modified boundary layer equations were developed for a fluid column rotating near a solid plane including the influence of non-equilibrium pressure forces. The far-field boundary conditions were inferred using the asymptotic behavior of the governing equations, and the boundary conditions for the axial and radial components of velocity were shown to be dependent on the pressure relaxation coefficient, η p, and the characteristic angular velocity of the rotating fluid column, ω. This research has shown for the first time that the inclusion of non-equilibrium pressure results in a free-standing stagnation plane at the top of a funnel shaped rotating fluid column, which is consistent with observational data for hurricanes, tornadoes and dust devils. It has also been shown that in the absence of non-equilibrium pressure, the stagnation plane for rotating flows cannot be observed. The velocity and pressure distributions resulting from incorporating non-equilibrium pressure effects were then compared with available observational data for tornadoes and dust devils. The general profiles of the velocity and pressure distributions were found to be in good agreement with physical measurements, which was not possible without introducing empirical turbulence effects, in the absence of non-equilibrium pressure effects.

  10. The effect of radial pressure force on rotating double tearing mode in compressible plasmas

    NASA Astrophysics Data System (ADS)

    Wang, Xian-Qu; Xiong, Guo-Zhen; Li, Xiao-Qing

    2016-05-01

    The role of radial pressure force in the interlocking dynamics of double tearing modes (DTMs) is investigated by force balance analysis based on the compressible magnetohydrodynamics (MHD) model. It is found that the stability of symmetric DTMs is dominated by the radial pressure force rather than the field line bending force. Owing to the compressibility of rotating plasmas, unbalanced radial forces can just result in the rotating islands drift toward each other in the radial direction but do not trigger the explosive growth of the mode in the interlocking process, which is different from that of antisymmetric DTM without flow.

  11. Coherent Structures and Extreme Events in Rotating Multiphase Turbulent Flows

    NASA Astrophysics Data System (ADS)

    Biferale, L.; Bonaccorso, F.; Mazzitelli, I. M.; van Hinsberg, M. A. T.; Lanotte, A. S.; Musacchio, S.; Perlekar, P.; Toschi, F.

    2016-10-01

    By using direct numerical simulations (DNS) at unprecedented resolution, we study turbulence under rotation in the presence of simultaneous direct and inverse cascades. The accumulation of energy at large scale leads to the formation of vertical coherent regions with high vorticity oriented along the rotation axis. By seeding the flow with millions of inertial particles, we quantify—for the first time—the effects of those coherent vertical structures on the preferential concentration of light and heavy particles. Furthermore, we quantitatively show that extreme fluctuations, leading to deviations from a normal-distributed statistics, result from the entangled interaction of the vertical structures with the turbulent background. Finally, we present the first-ever measurement of the relative importance between Stokes drag, Coriolis force, and centripetal force along the trajectories of inertial particles. We discover that vortical coherent structures lead to unexpected diffusion properties for heavy and light particles in the directions parallel and perpendicular to the rotation axis.

  12. Stabililty and laminarisation of turbulent rotating channel flow

    NASA Astrophysics Data System (ADS)

    Wallin, S.; Grundestam, O.; Johansson, A. V.

    The influence of moderate rotation rate on turbulent channel flow is that the turbulence is suppressed on the stable side and augmented on the unstable side because of the Coriolis force. With increasing rotation rate the turbulent region becomes restricted to a decreasing zone near the unstable wall. For the rotation number, Ro > 3 (normalized by bulk velocity and channel height) inviscid linear theory yields a stable laminar flow [1] and a recent DNS study [2] indicates that the turbulent flow laminarizes for Ro below 3. The critical Ro has been identified by a standard text-book linear stability analysis of rotating laminar channel flow including the viscous effects. The Reynolds number, Re = 10800 based on the bulk velocity and channel half height, is the same as in the recent DNS [2]. The most unstable mode consists of tilted slightly oblique streamwise vortices with a critical rotation number of Ro c = 2.805 and streamwise and spanwise wave numbers of α = 2.7 and β = 19 respectivelly. Steady streamwise roll-cells are slightly more stable.

  13. Spontaneous Core Rotation in Ferrofluid Pipe Flow

    NASA Astrophysics Data System (ADS)

    Krekhov, Alexei; Shliomis, Mark

    2017-03-01

    Ferrofluid flow along a tube of radius R in a constant axial magnetic field is revisited. Our analytical solution and numerical simulations predict a transition from an initially axial flow to a steady swirling one. The swirl dynamo arises above some critical pressure drop and magnetic field strength. The new flow pattern consists of two phases of different symmetry: The flow in the core resembles Poiseuille flow in a rotating tube of the radius r*flow remains purely axial. These phases are separated by a thin domain wall. The swirl appearance is accompanied with a sharp increase in the flow rate that might serve for the detection of the swirling instability.

  14. Flow of a magnetic fluid between eccentric rotating disks

    NASA Astrophysics Data System (ADS)

    Kaloni, P. N.; Venkatasubramanian, S.

    We discuss the flow of a magnetic fluid between two parallel disks rotating about non-coincident axes, normal to the disks, but with same angular velocity. This device is known as an orthogonal rheometer and has been used to measure the rheological properties of polymer melts and viscoelastic fluids. For a certain range of effective relaxation times, we obtain an exact solution of this three-dimensional problem in a magnetic fluid and determine the forces exerted by the fluid on one of the rotating disks.

  15. Rotating electrical machines: Poynting flow

    NASA Astrophysics Data System (ADS)

    Donaghy-Spargo, C.

    2017-09-01

    This paper presents a complementary approach to the traditional Lorentz and Faraday approaches that are typically adopted in the classroom when teaching the fundamentals of electrical machines—motors and generators. The approach adopted is based upon the Poynting vector, which illustrates the ‘flow’ of electromagnetic energy. It is shown through simple vector analysis that the energy-flux density flow approach can provide insight into the operation of electrical machines and it is also shown that the results are in agreement with conventional Maxwell stress-based theory. The advantage of this approach is its complementary completion of the physical picture regarding the electromechanical energy conversion process—it is also a means of maintaining student interest in this subject and as an unconventional application of the Poynting vector during normal study of electromagnetism.

  16. Single point modeling of rotating turbulent flows

    NASA Technical Reports Server (NTRS)

    Hadid, A. H.; Mansour, N. N.; Zeman, O.

    1994-01-01

    A model for the effects of rotation on turbulence is proposed and tested. These effects which influence mainly the rate of turbulence decay are modeled in a modified turbulent energy dissipation rate equation that has explicit dependence on the mean rotation rate. An appropriate definition of the rotation rate derived from critical point theory and based on the invariants of the deformation tensor is proposed. The modeled dissipation rate equation is numerically well behaved and can be used in conjunction with any level of turbulence closure. The model is applied to the two-equation kappa-epsilon turbulence model and is used to compute separated flows in a backward-facing step and an axisymmetric swirling coaxial jets into a sudden expansion. In general, the rotation modified dissipation rate model shows some improvements over the standard kappa-epsilon model.

  17. Flow in a partially filled rotating cylinder

    NASA Astrophysics Data System (ADS)

    Shadday, M. A., Jr.

    Axial flow in a rapidly rotating cylinder, partially filled with a viscous, incompressible fluid is measured with a laser-Doppler velocimeter. The cylinder has a vertical axis of rotation, and the axial circulation is induced by rotating a coaxially mounted disk at the top endcap slightly faster than the cylinder. The experimental results are compared with the predictions of a finite-difference model of the flow, and the correlation is qualitatively good. The axial circulation in the fluid layer is confined primarily to E(1/3) shear layers along the lateral boundaries, where E is the Ekman number. The radial transport in the Ekman layers is essentially unaffected by the presence of the free surface. It will be shown that this leads to axial transport in an E(1/3) boundary layer along the free surface.

  18. Flow in a partially filled rotating cylinder

    NASA Astrophysics Data System (ADS)

    Shadday, M. A., Jr.

    1982-05-01

    Axial flow in a rapidly rotating cylinder, partially filled with a viscous, incompressible fluid is measured with a laser Doppler velocimeter. The cylinder has a vertical axis of rotation, and the axial circulation is induced by rotating a coaxially mounted disk at the top endcap slightly faster than the cylinder. The experimental results are compared with the prediction of a finite difference model of the flow, and the correlation is qualitatively good. The axial circulation in the fluid layer is confined primarily to E/sup 1/3/ shear layers along the lateral boundaries, where E is the Ekman number. The radial transport in the Ekman layers is essentially unaffected by the presence of the free surface. It will be shown that this leads to axial transport in an E/sup 1/3/ boundary layer along the free surface.

  19. Turbulent Compressible Convection with Rotation. 2; Mean Flows and Differential Rotation

    NASA Technical Reports Server (NTRS)

    Brummell, Nicholas H.; Hurlburt, Neal E.; Toomre, Juri

    1998-01-01

    The effects of rotation on turbulent, compressible convection within stellar envelopes are studied through three-dimensional numerical simulations conducted within a local f-plane model. This work seeks to understand the types of differential rotation that can be established in convective envelopes of stars like the Sun, for which recent helioseismic observations suggest an angular velocity profile with depth and latitude at variance with many theoretical predictions. This paper analyzes the mechanisms that are responsible for the mean (horizontally averaged) zonal and meridional flows that are produced by convection influenced by Coriolis forces. The compressible convection is considered for a range of Rayleigh, Taylor, and Prandtl (and thus Rossby) numbers encompassing both laminar and turbulent flow conditions under weak and strong rotational constraints. When the nonlinearities are moderate, the effects of rotation on the resulting laminar cellular convection leads to distinctive tilts of the cell boundaries away from the vertical. These yield correlations between vertical and horizontal motions that generate Reynolds stresses that can drive mean flows, interpretable as differential rotation and meridional circulations. Under more vigorous forcing, the resulting turbulent convection involves complicated and contorted fluid particle trajectories, with few clear correlations between vertical and horizontal motions, punctuated by an evolving and intricate downflow network that can extend over much of the depth of the layer. Within such networks are some coherent structures of vortical downflow that tend to align with the rotation axis. These yield a novel turbulent alignment mechanism, distinct from the laminar tilting of cellular boundaries, that can provide the principal correlated motions and thus Reynolds stresses and subsequently mean flows. The emergence of such coherent structures that can persist amidst more random motions is a characteristic of turbulence

  20. Rimming flows and pattern formation inside rapidly rotating cylinder

    NASA Astrophysics Data System (ADS)

    Polezhaev, Denis; Dyakova, Veronika; Kozlov, Victor

    2014-11-01

    The dynamics of fluid and granular medium in a rotating horizontal cylinder is experimentally studied. In a rapidly rotating cylinder liquid and granular medium coat the cylindrical wall under centrifugal force. In the cavity frame gravity field performs rotation and produces oscillatory fluid flow which is responsible for the series of novel effects of pattern formation, namely, axial segregation of heavy particles and pattern formation in the form of sand regular hills extended along the axis of rotation. At least two types of axial segregation are found: a) patterns of spatial period of the same order of magnitude as fluid layer thickness which induced by steady flows generated by inertial waves; b) fine patterns which manifests Gortler - Taylor vortices developing as a consequence of centrifugal instability of viscous boundary layer near the cylindrical wall. Under gravity, intensive fluid shear flow induces partial fluidization of annular layer of granular medium. The oscillatory motion is followed by onset of regular ripples extended along the axis of rotation. The work is supported by Russian Scientific Foundation (project 14-11-00476).

  1. Experimental study on flow past a rotationally oscillating cylinder

    NASA Astrophysics Data System (ADS)

    Gao, Yang-yang; Yin, Chang-shan; Yang, Kang; Zhao, Xi-zeng; Tan, Soon Keat

    2017-08-01

    A series of experiments was carried out to study the flow behaviour behind a rotationally oscillating cylinder at a low Reynolds number (Re=300) placed in a recirculation water channel. A stepper motor was used to rotate the cylinder clockwise- and- counterclockwise about its longitudinal axis at selected frequencies. The particle image velocimetry (PIV) technique was used to capture the flow field behind a rotationally oscillating cylinder. Instantaneous and timeaveraged flow fields such as the vorticity contours, streamline topologies and velocity distributions were analyzed. The effects of four rotation angle and frequency ratios F r ( F r= f n/ f v, the ratio of the forcing frequency f n to the natural vortex shedding frequency f v) on the wake in the lee of a rotationally oscillating cylinder were also examined. The significant wake modification was observed when the cylinder undergoes clockwise-and-counterclockwise motion with amplitude of π, especially in the range of 0.6≤ F r≤1.0.

  2. The decay of turbulence in rotating flows

    NASA Astrophysics Data System (ADS)

    Teitelbaum, Tomas; Mininni, Pablo D.

    2011-06-01

    We present a parametric space study of the decay of turbulence in rotating flows combining direct numerical simulations, large eddy simulations, and phenomenological theory. Several cases are considered: (1) the effect of varying the characteristic scale of the initial conditions when compared with the size of the box, to mimic "bounded" and "unbounded" flows; (2) the effect of helicity (correlation between the velocity and vorticity); (3) the effect of Rossby and Reynolds numbers; and (4) the effect of anisotropy in the initial conditions. Initial conditions include the Taylor-Green vortex, the Arn'old-Beltrami-Childress flow, and random flows with large-scale energy spectrum proportional to k4. The decay laws obtained in the simulations for the energy, helicity, and enstrophy in each case can be explained with phenomenological arguments that consider separate decays for two-dimensional and three-dimensional modes and that take into account the role of helicity and rotation in slowing down the energy decay. The time evolution of the energy spectrum and development of anisotropies in the simulations are also discussed. Finally, the effect of rotation and helicity in the skewness and kurtosis of the flow is considered.

  3. Calculations of rotational flows using stream function

    NASA Technical Reports Server (NTRS)

    Hafez, M.; Yam, C.; Tang, K.; Dwyer, H.

    1989-01-01

    The stream function equation is solved for steady two-dimensional (and axisymmetric) rotational flows. Both finite differences and finite volumes discretization techniques are studied, using generalized body fitted coordinates and unstructured staggered grids, respectively. For inviscid transonic flows, a new artificial viscosity scheme which does not produce any artificial vorticity is introduced, for the stability of the mixed flow calculations and for capturing shocks. The solution of Euler equations, in primitive variables, are also considered. The effects of the artificial viscosity and numerical boundary conditions on the total enthalpy and the vorticity distributions are demonstrated.

  4. Flow in Rotating Serpentine Coolant Passages With Skewed Trip Strips

    NASA Technical Reports Server (NTRS)

    Tse, David G.N.; Steuber, Gary

    1996-01-01

    Laser velocimetry was utilized to map the velocity field in serpentine turbine blade cooling passages with skewed trip strips. The measurements were obtained at Reynolds and Rotation numbers of 25,000 and 0.24 to assess the influence of trips, passage curvature and Coriolis force on the flow field. The interaction of the secondary flows induced by skewed trips with the passage rotation produces a swirling vortex and a corner recirculation zone. With trips skewed at +45 deg, the secondary flows remain unaltered as the cross-flow proceeds from the passage to the turn. However, the flow characteristics at these locations differ when trips are skewed at -45 deg. Changes in the flow structure are expected to augment heat transfer, in agreement with the heat transfer measurements of Johnson, et al. The present results show that trips are skewed at -45 deg in the outward flow passage and trips are skewed at +45 deg in the inward flow passage maximize heat transfer. Details of the present measurements were related to the heat transfer measurements of Johnson, et al. to relate fluid flow and heat transfer measurements.

  5. Fluid flow through packings of rotating obstacles

    NASA Astrophysics Data System (ADS)

    Oliveira, Rafael S.; Andrade, José S.; Andrade, Roberto F. S.

    2015-03-01

    We investigate through numerical simulation the nonstationary flow of a Newtonian fluid through a two-dimensional channel filled with an array of circular obstacles of distinct sizes. The disks may rotate around their respective centers, modeling a nonstationary, inhomogeneous porous medium. Obstacle sizes and positions are defined by the geometry of an Apollonian packing (AP). To allow for fluid flow, the radii of the disks are uniformly reduced by a factor 0.6 ≤s ≤0.8 for assemblies corresponding to the four first AP generations. The investigation is targeted to elucidate the main features of the rotating regime as compared to the fixed disk condition. It comprises the evaluation of the region of validity of Darcy's law as well as the study of the nonlinear hydraulic resistance as a function of the channel Reynolds number, the reduction factor s , and the AP generation. Depending on a combination of these factors, the resistance of rotating disks may be larger or smaller than that of the corresponding static case. We also analyze the flow redistribution in the interdisk channels as a result of the rotation pattern and characterize the angular velocity of the disks. Here, the striking feature is the emergence of a stable oscillatory behavior of the angular velocity for almost all disks that are inserted into the assemblies after the second generation.

  6. Thermomechanical Fractional Model of TEMHD Rotational Flow.

    PubMed

    Hamza, F; Abd El-Latief, A; Khatan, W

    2017-01-01

    In this work, the fractional mathematical model of an unsteady rotational flow of Xanthan gum (XG) between two cylinders in the presence of a transverse magnetic field has been studied. This model consists of two fractional parameters α and β representing thermomechanical effects. The Laplace transform is used to obtain the numerical solutions. The fractional parameter influence has been discussed graphically for the functions field distribution (temperature, velocity, stress and electric current distributions). The relationship between the rotation of both cylinders and the fractional parameters has been discussed on the functions field distribution for small and large values of time.

  7. Thermomechanical Fractional Model of TEMHD Rotational Flow

    PubMed Central

    Hamza, F.; Abd El-Latief, A.; Khatan, W.

    2017-01-01

    In this work, the fractional mathematical model of an unsteady rotational flow of Xanthan gum (XG) between two cylinders in the presence of a transverse magnetic field has been studied. This model consists of two fractional parameters α and β representing thermomechanical effects. The Laplace transform is used to obtain the numerical solutions. The fractional parameter influence has been discussed graphically for the functions field distribution (temperature, velocity, stress and electric current distributions). The relationship between the rotation of both cylinders and the fractional parameters has been discussed on the functions field distribution for small and large values of time. PMID:28045941

  8. Turbulent rotating plane Couette flow: Reynolds and rotation number dependency of flow structure and momentum transport

    NASA Astrophysics Data System (ADS)

    Kawata, Takuya; Alfredsson, P. Henrik

    2016-07-01

    Plane Couette flow under spanwise, anticyclonic system rotation [rotating plane Couette flow (RPCF)] is studied experimentally using stereoscopic particle image velocimetry for different Reynolds and rotation numbers in the fully turbulent regime. Similar to the laminar regime, the turbulent flow in RPCF is characterized by roll cells, however both instantaneous snapshots of the velocity field and space correlations show that the roll cell structure varies with the rotation number. All three velocity components are measured and both the mean flow and all four nonzero Reynolds stresses are obtained across the central parts of the channel. This also allows us to determine the wall shear stress from the viscous stress and the Reynolds stress in the center of the channel, and for low rotation rates the wall shear stress increases with increasing rotation rate as expected. The results show that zero absolute vorticity is established in the central parts of the channel of turbulent RPCF for high enough rotation rates, but also that the mean velocity profile for certain parameter ranges shows an S shape giving rise to a negative velocity gradient in the center of the channel. We find that from an analysis of the Reynolds stress transport equation using the present data there is a transport of the Reynolds shear stress towards the center of the channel, which may then result in a negative mean velocity gradient there.

  9. Rotating flow transition related to surface switching

    NASA Astrophysics Data System (ADS)

    Tasaka, Yuji; Iima, Makoto; Ito, Kentaro

    2008-11-01

    We have investigated quantitatively the recently reported phenomena called "surface switching" that occurs in the flow driven by a rotating disk in an open cylindrical vessel [1]. The deformed free surface abruptly changes from an axisymmetric to a non-axisymmetric shape accompanying with a vertical oscillation at irregular intervals. We have studied the flow transition quantitatively using ultrasonic velocity profiling (UVP). The turbulent intensity shows a transition at the same Reynolds number as that for the surface switching. We find that the fluid-air interface becomes unstable at a smaller Reynolds number than the critical Reynolds number for the surface switching. Effects of the material of the rotating disk on the surface switching is discussed.

  10. The flow past a freely rotating sphere

    NASA Astrophysics Data System (ADS)

    Fabre, David; Tchoufag, Joël; Citro, Vincenzo; Giannetti, Flavio; Luchini, Paolo

    2016-08-01

    We consider the flow past a sphere held at a fixed position in a uniform incoming flow but free to rotate around a transverse axis. A steady pitchfork bifurcation is reported to take place at a threshold Re^OS=206 leading to a state with zero torque but nonzero lift. Numerical simulations allow to characterize this state up to Re≈ 270 and confirm that it substantially differs from the steady-state solution which exists in the wake of a fixed, non-rotating sphere beyond the threshold Re^SS=212 . A weakly nonlinear analysis is carried out and is shown to successfully reproduce the results and to give substantial improvement over a previous analysis (Fabre et al. in J Fluid Mech 707:24-36, 2012). The connection between the present problem and that of a sphere in free fall following an oblique, steady (OS) path is also discussed.

  11. Self-Rotation in Bouyancy Driven Flows

    NASA Astrophysics Data System (ADS)

    Pérez-Saborid, Miguel; Herrada, Miguel A.; Barrero, Antonio

    2000-11-01

    The appearance of self-rotation in buoyancy driven flows has been studied experimentally in a box with square section containing water. The experimental set up is very similar to that used by Torrance (JFM, 95, 477-495, 1979). The swirling and non-swirling regimes are visualized by injecting dye and by laser illumination and the critical Grashoff number is determined from Phase Doppler laser velocimetry. A numerical computation of the full Navier-Stokes equations in the Boussinesq approximation has been performed using a spectral method. The results have been compared with experiments for several values of the flow parameters.

  12. Rotational flow in gravity current heads.

    PubMed

    McElwaine, J N

    2005-07-15

    The structure of gravity currents and plumes, in an unbounded ambient, on a slope of arbitrary angle is analysed. Inviscid, rotational flow solutions in a wedge are used to study the flow near the front of a current, and used to show that the Froude number is radical2 and the angle of the front to the slope is 60 degrees. This extends the result of von Kármán (1940) to arbitrary slope angles and large internal current velocities. The predictions of the theory are briefly compared with experiments and used to explain the large negative (relative to ambient) pressures involved in avalanches.

  13. Flow mechanotransduction regulates traction forces, intercellular forces, and adherens junctions

    PubMed Central

    Ting, Lucas H.; Jahn, Jessica R.; Jung, Joon I.; Shuman, Benjamin R.; Feghhi, Shirin; Han, Sangyoon J.; Rodriguez, Marita L.

    2012-01-01

    Endothelial cells respond to fluid shear stress through mechanotransduction responses that affect their cytoskeleton and cell-cell contacts. Here, endothelial cells were grown as monolayers on arrays of microposts and exposed to laminar or disturbed flow to examine the relationship among traction forces, intercellular forces, and cell-cell junctions. Cells under laminar flow had traction forces that were higher than those under static conditions, whereas cells under disturbed flow had lower traction forces. The response in adhesion junction assembly matched closely with changes in traction forces since adherens junctions were larger in size for laminar flow and smaller for disturbed flow. Treating the cells with calyculin-A to increase myosin phosphorylation and traction forces caused an increase in adherens junction size, whereas Y-27362 cause a decrease in their size. Since tugging forces across cell-cell junctions can promote junctional assembly, we developed a novel approach to measure intercellular forces and found that these forces were higher for laminar flow than for static or disturbed flow. The size of adherens junctions and tight junctions matched closely with intercellular forces for these flow conditions. These results indicate that laminar flow can increase cytoskeletal tension while disturbed flow decreases cytoskeletal tension. Consequently, we found that changes in cytoskeletal tension in response to shear flow conditions can affect intercellular tension, which in turn regulates the assembly of cell-cell junctions. PMID:22447948

  14. Experimental calibration procedures for rotating Lorentz-force flowmeters

    NASA Astrophysics Data System (ADS)

    Hvasta, M. G.; Slighton, N. T.; Kolemen, E.; Fisher, A. E.

    2017-08-01

    Rotating Lorentz-force flowmeters are a novel and useful technology with a range of applications in a variety of different industries. However, calibrating these flowmeters can be challenging, time-consuming, and expensive. In this paper, simple calibration procedures for rotating Lorentz-force flowmeters are presented. These procedures eliminate the need for expensive equipment, numerical modeling, redundant flowmeters, and system down-time. The calibration processes are explained in a step-by-step manner and compared to experimental results.

  15. Experimental calibration procedures for rotating Lorentz-force flowmeters

    DOE PAGES

    Hvasta, M. G.; Slighton, N. T.; Kolemen, E.; ...

    2017-07-14

    Rotating Lorentz-force flowmeters are a novel and useful technology with a range of applications in a variety of different industries. However, calibrating these flowmeters can be challenging, time-consuming, and expensive. In this paper, simple calibration procedures for rotating Lorentz-force flowmeters are presented. These procedures eliminate the need for expensive equipment, numerical modeling, redundant flowmeters, and system down-time. Finally, the calibration processes are explained in a step-by-step manner and compared to experimental results.

  16. Incompressible fluid flows in rapidly rotating cavities

    NASA Astrophysics Data System (ADS)

    Fournier, Alexandre

    The subject of incompressible fluid flows in rapidly rotating cavities, relevant to the dynamics of the Earth's outer core, is addressed here by means of numerical modeling. We recall in the introduction what makes this topic fascinating and challenging, and emphasize the need for new, more flexible numerical approaches in line with the evolution of today's parallel computers. Relying upon recent advances in numerical analysis, we first introduce in chapter 2 a spectral element model of the axisymmetric Navier-Stokes equation, in a rotating reference frame. Comparisons with analytical or published numerical solutions are made for various test problems, which highlight the spectral convergence properties and adaptivity of the approach. In chapter 3, we couple this axisymmetric kernel with a Fourier expansion in longitude in order to describe the dynamics of three-dimensional convection flows. Again, several reference problems are studied. In the specific case of a rotating fluid undergoing thermal convection, this so-called Fourier-spectral element method (FSEM) proves to be as accurate as standard pseudo-spectral techniques. Having this numerical tool anchored on solid grounds, we study in chapter 4 fluid flows driven by thermal convection and precession at the same time. A new topic in the vast field of fluid mechanics, convecto-precessing flows are of particular importance for the Earth's core, and the equations governing their evolution are derived in detail. We solve these using the FSEM; results seem to indicate that to first order, thermal convection and precession ignore each other. We discuss the relevance of these calculations for the Earth's core and outline directions for future related research.

  17. Probe-rotating atomic force microscopy for determining material properties

    SciTech Connect

    Lee, Sang Heon

    2014-03-15

    In this paper, we propose a probe-rotating atomic force microscope that enables scan in an arbitrary direction in the contact imaging mode, which is difficult to achieve using a conventional atomic force microscope owing to the orientation-dependent probe and the inability to rotate the probe head. To enable rotation of the probe about its vertical axis, we employed a compact and light probe head, the sensor of which is made of an optical disk drive pickup unit. Our proposed mechanical configuration, operating principle, and control system enables axial and lateral scan in various directions.

  18. Enstrophy-based proper orthogonal decomposition of flow past rotating cylinder at super-critical rotating rate

    NASA Astrophysics Data System (ADS)

    Sengupta, Tapan K.; Gullapalli, Atchyut

    2016-11-01

    Spinning cylinder rotating about its axis experiences a transverse force/lift, an account of this basic aerodynamic phenomenon is known as the Robins-Magnus effect in text books. Prandtl studied this flow by an inviscid irrotational model and postulated an upper limit of the lift experienced by the cylinder for a critical rotation rate. This non-dimensional rate is the ratio of oncoming free stream speed and the surface speed due to rotation. Prandtl predicted a maximum lift coefficient as CLmax = 4π for the critical rotation rate of two. In recent times, evidences show the violation of this upper limit, as in the experiments of Tokumaru and Dimotakis ["The lift of a cylinder executing rotary motions in a uniform flow," J. Fluid Mech. 255, 1-10 (1993)] and in the computed solution in Sengupta et al. ["Temporal flow instability for Magnus-robins effect at high rotation rates," J. Fluids Struct. 17, 941-953 (2003)]. In the latter reference, this was explained as the temporal instability affecting the flow at higher Reynolds number and rotation rates (>2). Here, we analyze the flow past a rotating cylinder at a super-critical rotation rate (=2.5) by the enstrophy-based proper orthogonal decomposition (POD) of direct simulation results. POD identifies the most energetic modes and helps flow field reconstruction by reduced number of modes. One of the motivations for the present study is to explain the shedding of puffs of vortices at low Reynolds number (Re = 60), for the high rotation rate, due to an instability originating in the vicinity of the cylinder, using the computed Navier-Stokes equation (NSE) from t = 0 to t = 300 following an impulsive start. This instability is also explained through the disturbance mechanical energy equation, which has been established earlier in Sengupta et al. ["Temporal flow instability for Magnus-robins effect at high rotation rates," J. Fluids Struct. 17, 941-953 (2003)].

  19. Topological Structures in Rotating Stratified Flows

    NASA Astrophysics Data System (ADS)

    Redondo, J. M.; Carrillo, A.; Perez, E.

    2003-04-01

    Detailled 2D Particle traking and PIV visualizations performed on a series of large scale laboratory experiments at the Coriolis Platform of the SINTEF in Trondheim have revealed several resonances which scale on the Strouhal, the Rossby and the Richardson numbers. More than 100 experiments spanned a wide range of Rossby Deformation Radii and the topological structures (Parabolic /Eliptic /Hyperbolic) of the quasi-balanced stratified-rotating flows were studied when stirring (akin to coastal mixing) occured at a side of the tank. The strong asymetry favored by the total vorticity produces a wealth of mixing patterns.

  20. The flow external to a rotating torus

    NASA Astrophysics Data System (ADS)

    Calabretto, Sophie A. W.; Denier, James P.; Mattner, Trent W.

    2016-08-01

    Imparting a sudden rotation to a torus (or other symmetric smooth object) in an otherwise quiescent, viscous fluid serves to generate boundary layers at the object's surface. These boundary layers are known to exhibit a finite-time singularity at the equator which manifests in a thickening of the boundary layer and subsequent development of an equatorial jet. Here we consider the post-collision flow dynamics, demonstrating that the equatorial jet serves to shed a finite amplitude toroidal vortex pair. The radial jet is also shown to develop an absolute instability at suitably high Reynolds numbers.

  1. On the Behavior of Velocity Fluctuations in Rapidly Rotating Flows

    NASA Technical Reports Server (NTRS)

    Girimaji, S. S.; Ristorcelli, J. R.

    1997-01-01

    The behavior of velocity fluctuations subjected to rapid rotation is examined. The rapid rotation considered is any arbitrary combination of two basic forms of rotation, reference frame rotation and mean flow rotation. It is recognized that the two types of rotating flows differ in the manner in which the fluctuating fields are advected. The first category is comprised of flows in rotating systems of which synoptic scale geophysical flows are a good example. In this class of flows the fluctuating velocity field advects and rotates with the mean flow. In the rapid rotation limit, the Taylor-Proudman theorem describes the behavior of this class of fluctuations. Velocity fluctuations that are advected without rotation by the mean flow constitute the second category which includes vortical flows of aerodynamic interest. The Taylor-Proudman theorem is not pertinent to I his class flows and a new result appropriate to this second category of fluctuations is derived. The present development demonstrates that the fluctuating velocity fields are rendered two-dimensional and horizontally non-divergent in the limit of any large combination of reference frame rotation and mean-flow rotation. The concommitant 'geostrophic' balance of the momentum equation is, however, dependent upon the form of rapid rotation. It is also demonstrated that the evolution equations of a two-dimensional fluctuating velocity fields are frame-indifferent with any imposed mean-flow rotation. The analyses and results of this paper highlight many fundamental aspects of rotating flows and have important consequences for their turbulence closures in inertial and non-inertial frames.

  2. Numerical study of the effects of rotating forced downdraft in reproducing tornado-like vortices

    NASA Astrophysics Data System (ADS)

    Zhu, Jinwei; Cao, Shuyang; Tamura, Tetsuro; Tokyo Institute of Technology Collaboration; Tongji Univ Collaboration

    2016-11-01

    Appropriate physical modeling of a tornado-like vortex is a prerequisite to studying near-surface tornado structure and tornado-induced wind loads on structures. Ward-type tornado simulator modeled tornado-like flow by mounting guide vanes around the test area to provide angular momentum to converging flow. Iowa State University, USA modified the Ward-type simulator by locating guide vanes at a high position to allow vertical circulation of flow that creates a rotating forced downdraft in the process of generating a tornado. However, the characteristics of the generated vortices have not been sufficiently investigated till now. In this study, large-eddy simulations were conducted to compare the dynamic vortex structure generated with/without the effect of rotating forced downdraft. The results were also compared with other CFD and experimental results. Particular attention was devoted to the behavior of vortex wander of generated tornado-like vortices. The present study shows that the vortex center wanders more significantly when the rotating forced downdraft is introduced into the flow. The rotating forced downdraft is advantageous for modeling the rear flank downdraft phenomenon of a real tornado.

  3. Energetics of geostrophic adjustment in rotating flow

    NASA Astrophysics Data System (ADS)

    Juan, Fang; Rongsheng, Wu

    2002-09-01

    Energetics of geostrophic adjustment in rotating flow is examined in detail with a linear shallow water model. The initial unbalanced flow considered first falls tinder two classes. The first is similar to that adopted by Gill and is here referred to as a mass imbalance model, for the flow is initially motionless but with a sea surface displacement. The other is the same as that considered by Rossby and is referred to as a momentum imbalance model since there is only a velocity perturbation in the initial field. The significant feature of the energetics of geostrophic adjustment for the above two extreme models is that although the energy conversion ratio has a large case-to-case variability for different initial conditions, its value is bounded below by 0 and above by 1 / 2. Based on the discussion of the above extreme models, the energetics of adjustment for an arbitrary initial condition is investigated. It is found that the characteristics of the energetics of geostrophic adjustment mentioned above are also applicable to adjustment of the general unbalanced flow under the condition that the energy conversion ratio is redefined as the conversion ratio between the change of kinetic energy and potential energy of the deviational fields.

  4. Particle rotation in a Couette flow

    NASA Astrophysics Data System (ADS)

    Ye, J.; Roco, M. C.

    1992-02-01

    The rotational velocity of neutrally buoyant particles was measured in a planar Couette flow. The flow cross section is rectangular with a 4-to-1 (200 mm/50 mm) aspect ratio. The mixtures consist of uniform polystyrene spheres and a glycerol-water solution of specific density 1.052. Four sphere sizes have been tested: 3, 4.76, 6.35, and 7.94 mm. Particle motion in turbulent flow was recorded with a high-speed SP-2000 motion analysis system. The characteristics of particle motion, including particle spin, were measured as a function of the distance from the wall, at three shear rates corresponding to Re=4.6, 6.8, and 9.2×104. It was found that the particle angular velocity normalized by shear rate is a function of the normalized distance to the moving and stationary walls. The flow conditions are defined with measurements on mean velocities, particle velocity fluctuations, kinetic energy, inertial stresses, and diffusion coefficients.

  5. Density Stratification of Rotating Flow in Coaxial Cylinder

    NASA Astrophysics Data System (ADS)

    Lee, Sungsu; Son, Hyun Ah; Kim, Albert S.

    2012-11-01

    Flows containing particulates often pose problems in many engineering practices among which the separation of clean water from polluted solution is essential in environmental engineering. In this study, the stratification of density in a coaxial cylinder are investigated using computational fluid dynamics with Boussinesq approximation. Particulate flow is injected into the domain between the vertical coaxial cylinders and allowed to leave the domain through the exit located upper part of the inner cylinder. During the rotation initiated by the tangential momentum, the hydrodynamic forces stratifies the particulate flow and interact with gravitational force as well as friction, which make the flow instable and complex. This study includes parametric investigation by varying the density of the particulates in the flow and the size of the inner cylinder. The results will present the effectiveness of the stratification which corresponds to the vortex separation in many engineering practice. This work was financially supported by projects of the ``Development of Energy utilization technology with Deep Ocean Water,'' KIOST of Korea.

  6. Rotating and thermocapillary-buoyancy-driven flow in a cylindrical enclosure with a partly free surface

    NASA Astrophysics Data System (ADS)

    Wu, Chun-Mei; Li, You-Rong; Liao, Rui-Jin

    2014-10-01

    In order to understand the characteristics of the complex flow driven by the combined thermocapillary-buoyancy effect and differential rotation of a cylindrical pool and a disk on the free surface, a series of unsteady three-dimensional numerical simulations were performed. Results indicate that the flow is axisymmetric and steady at a small temperature difference and low rotation rates. The basic meridional flow structures are composed of toroidal circulations. With an increase of the rotation rate and/or temperature difference, the basic flow transits to a three-dimensional oscillatory flow. Without rotation, the unstable thermocapillary-buoyancy flow is characterized by pulsating spoke patterns with the periodic growth and decay of temperature and velocity oscillations. When the disk and/or cylinder rotate, the oscillatory flow behaves as temperature and velocity fluctuation waves traveling in the azimuthal direction. The wave propagation velocity and direction, fluctuation amplitude, and wave number depend on the interaction of the thermocapillary, buoyancy, centrifugal and Coriolis forces. The critical conditions for the flow transition are determined. It is found that the critical thermocapillary Reynolds number initially increases before decreasing with the increase of the disk rotation rate, but the rotation of cylinder always retards the flow instability. In addition, the mechanisms of the flow instabilities are discussed and briefly summarized.

  7. Forced vibration analysis of rotating cyclic structures in NASTRAN

    NASA Technical Reports Server (NTRS)

    Elchuri, V.; Gallo, A. M.; Skalski, S. C.

    1981-01-01

    A new capability was added to the general purpose finite element program NASTRAN Level 17.7 to conduct forced vibration analysis of tuned cyclic structures rotating about their axis of symmetry. The effects of Coriolis and centripetal accelerations together with those due to linear acceleration of the axis of rotation were included. The theoretical, user's, programmer's and demonstration manuals for this new capability are presented.

  8. Two-dimensionalization of the flow driven by a slowly rotating impeller in a rapidly rotating fluid

    NASA Astrophysics Data System (ADS)

    Machicoane, Nathanaël; Moisy, Frédéric; Cortet, Pierre-Philippe

    2016-11-01

    We characterize the two-dimensionalization process in the turbulent flow produced by an impeller rotating at a rate ω in a fluid rotating at a rate Ω around the same axis for Rossby number Ro=ω /Ω down to 10-2. The flow can be described as the superposition of a large-scale vertically invariant global rotation and small-scale shear layers detached from the impeller blades. As Ro decreases, the large-scale flow is subjected to azimuthal modulations. In this regime, the shear layers can be described in terms of wakes of inertial waves traveling with the blades, originating from the velocity difference between the nonaxisymmetric large-scale flow and the blade rotation. The wakes are well defined and stable at low Rossby number, but they become disordered at Ro of order of 1. This experiment provides insight into the route towards pure two-dimensionalization induced by a background rotation for flows driven by a nonaxisymmetric rotating forcing.

  9. Energetics of geostrophic adjustment in rotating flow

    NASA Astrophysics Data System (ADS)

    Fang, J.; Wu, R. S.

    2002-09-01

    Energetics of geostrophic adjustment in rotating how is examined in detail with a linear shallow water model. The Initial Unbalanced flow considered first falls under two classes. The first is similar to that adopted by Gill and is here referred to as it mass imbalance model, for the flow is initially motionless but with a sea surface displacement. The other is the same as that considered by Rossby and is referred to as I momentum imbalance model since there is only a velocity perturbation in the initial field. The significant feature of the energetics of geostrophic adjustment for the above two extreme models is that althongh the energy conversion ratio has a large case-to-case variability for different initial conditions, Its value is bounded below by 0 and above by 1 / 2. Based on the discussion of the above extreme models, the energetics of adjustment for an arbitrary initial condition is investigated. It is found that the characteristics of the energetics of geostrophic adjustment mentioned above are also applicable to adjustment of the general unbalanced flow under the condition that the energy conversion ratio is redefined as the conversion ratio between the change of kinetic energy and potential energy of the deviational fields.

  10. Absolute rotation detection by Coriolis force measurement using optomechanics

    NASA Astrophysics Data System (ADS)

    Davuluri, Sankar; Li, Yong

    2016-10-01

    In this article, we present an application of the optomechanical cavities for absolute rotation detection. Two optomechanical cavities, one in each arm, are placed in a Michelson interferometer. The interferometer is placed on a rotating table and is moved with a uniform velocity of \\dot{\\bar{y}} with respect to the rotating table. The Coriolis force acting on the interferometer changes the length of the optomechanical cavity in one arm, while the length of the optomechanical cavity in the other arm is not changed. The phase shift corresponding to the change in the optomechanical cavity length is measured at the interferometer output to estimate the angular velocity of the absolute rotation. An analytic expression for the minimum detectable rotation rate corresponding to the standard quantum limit of measurable Coriolis force in the interferometer is derived. Squeezing technique is discussed to improve the rotation detection sensitivity by a factor of \\sqrt{{γ }m/{ω }m} at 0 K temperature, where {γ }m and {ω }m are the damping rate and angular frequency of the mechanical oscillator. The temperature dependence of the rotation detection sensitivity is studied.

  11. A lifting surface theory in rotational flow

    NASA Technical Reports Server (NTRS)

    Shiau, M. J.; Lan, C. E.

    1983-01-01

    The partial differential equation for small disturbance steady rotational flow in three dimensions is solved through an integral equation approach. The solution is obtained by using the method of weighted residuals. Specific applications are directed to wings in nonuniform subsonic parallel streams with velocity varying in vertical and spanwise directions and to airfoils in nonuniform freestream. Comparison with limited known results indicates that the present method is reasonably accurate. Numerical results for the lifting pressure of airfoil, lift, induced drag, and pitching moments of airfoil, lift, induced drag, and pitching moments of elliptic, rectangular, and delta wings in a jet, wake, or monotonic sheared stream are presented. It is shown that, in addition to the effect of local dynamic pressures, a positive velocity gradient tends to enhance the lift.

  12. Particle image velocimetry measurements of massively separated turbulent flows with rotation

    NASA Astrophysics Data System (ADS)

    Visscher, Jan; Andersson, Helge I.

    2011-07-01

    Measurements of instantaneous velocity fields in the separated flow downstream of a backward-facing step in a rotating channel are presented for the first time. Particle image velocimetry (PIV) measurements were made for 13 different rotation numbers Ro at a bulk flow Reynolds number of about 5600. The expansion ratio 2:1 was the same as in the flow visualization study by Rothe and Johnston [ASME J. Fluids Eng. 101, 117 (1979)] which covered about the same range of Ro. The measured mean flow pattern exhibited substantial variations with the rate of system rotation. In particular, the length of the primary separation bubble decreased monotonically with increasing anti-cyclonic rotation and increased with increasing rate of cyclonic rotation, in keeping with the earlier observations. At the highest anti-cyclonic rotation rate, the flow field also separated from the planar wall where the shear layer flow was subjected to cyclonic rotation. The PIV data for the in-plane components of the Reynolds stress tensor were severely affected by the imposed system rotation. Almost all the striking affects of the Coriolis force observed herein could be explained by means of the exact production terms in the transport equation for the second-moments of the velocity fluctuations. These changes were in turn consistent with the observed alterations of the mean flow field.

  13. Effects of rotating flows on combustion and jet noise.

    NASA Technical Reports Server (NTRS)

    Schwartz, I. R.

    1972-01-01

    Experimental investigations of combustion in rotating (swirling) flow have shown that the mixing and combustion processes were accelerated, flame length and noise levels significantly decreased, and flame stability increased relative to that obtained without rotation. Unsteady burning accompanied by a pulsating flame, violent fluctuating jet, and intense noise present in straight flow burning were not present in rotating flow burning. Correlations between theory and experiment show good agreement. Such effects due to rotating flows could lead to suppressing jet noise, improving combustion, reducing pollution, and decreasing aircraft engine size. Quantitative analysis of the aero-acoustic relationship and noise source characteristics are needed.-

  14. Numerical simulation of two-dimensional steady granular flows in rotating drum: On surface flow rheology

    NASA Astrophysics Data System (ADS)

    Renouf, M.; Bonamy, D.; Dubois, F.; Alart, P.

    2005-10-01

    The rheology of two-dimensional steady surface flow of cohesionless cylinders in a rotating drum is investigated through nonsmooth contact dynamics simulations. Profiles of volume fraction, translational and angular velocity, rms velocity, strain rate, and stress tensor are measured at the midpoint along the length of the surface-flowing layer, where the flow is generally considered as steady and homogeneous. Analysis of these data and their interrelations suggest the local inertial number—defined as the ratio between local inertial forces and local confinement forces—to be the relevant dimensionless parameter to describe the transition from the quasistatic part of the packing to the flowing part at the surface of the heap. Variations of the components of the stress tensor as well as the ones of rms velocity as a function of the inertial number are analyzed within both the quasistatic and the flowing phases. Their implications are discussed.

  15. Dynamo action in dissipative, forced, rotating MHD turbulence

    NASA Astrophysics Data System (ADS)

    Shebalin, John V.

    2016-06-01

    Magnetohydrodynamic (MHD) turbulence is an inherent feature of large-scale, energetic astrophysical and geophysical magnetofluids. In general, these are rotating and are energized through buoyancy and shear, while viscosity and resistivity provide a means of dissipation of kinetic and magnetic energy. Studies of unforced, rotating, ideal (i.e., non-dissipative) MHD turbulence have produced interesting results, but it is important to determine how these results are affected by dissipation and forcing. Here, we extend our previous work and examine dissipative, forced, and rotating MHD turbulence. Incompressibility is assumed, and finite Fourier series represent turbulent velocity and magnetic field on a 643 grid. Forcing occurs at an intermediate wave number by a method that keeps total energy relatively constant and allows for injection of kinetic and magnetic helicity. We find that 3-D energy spectra are asymmetric when forcing is present. We also find that dynamo action occurs when forcing has either kinetic or magnetic helicity, with magnetic helicity injection being more important. In forced, dissipative MHD turbulence, the dynamo manifests itself as a large-scale coherent structure that is similar to that seen in the ideal case. These results imply that MHD turbulence, per se, may play a fundamental role in the creation and maintenance of large-scale (i.e., dipolar) stellar and planetary magnetic fields.

  16. Dynamo action in dissipative, forced, rotating MHD turbulence

    SciTech Connect

    Shebalin, John V.

    2016-06-15

    Magnetohydrodynamic (MHD) turbulence is an inherent feature of large-scale, energetic astrophysical and geophysical magnetofluids. In general, these are rotating and are energized through buoyancy and shear, while viscosity and resistivity provide a means of dissipation of kinetic and magnetic energy. Studies of unforced, rotating, ideal (i.e., non-dissipative) MHD turbulence have produced interesting results, but it is important to determine how these results are affected by dissipation and forcing. Here, we extend our previous work and examine dissipative, forced, and rotating MHD turbulence. Incompressibility is assumed, and finite Fourier series represent turbulent velocity and magnetic field on a 64{sup 3} grid. Forcing occurs at an intermediate wave number by a method that keeps total energy relatively constant and allows for injection of kinetic and magnetic helicity. We find that 3-D energy spectra are asymmetric when forcing is present. We also find that dynamo action occurs when forcing has either kinetic or magnetic helicity, with magnetic helicity injection being more important. In forced, dissipative MHD turbulence, the dynamo manifests itself as a large-scale coherent structure that is similar to that seen in the ideal case. These results imply that MHD turbulence, per se, may play a fundamental role in the creation and maintenance of large-scale (i.e., dipolar) stellar and planetary magnetic fields.

  17. Fluid forces on rotating centrifugal impeller with whirling motion

    NASA Technical Reports Server (NTRS)

    Shoji, H.; Ohashi, H.

    1980-01-01

    Fluid forces on a centrifugal impeller, whose rotating axis whirls with a constant speed, were calculated by using unsteady potential theory. Calculations were performed for various values of whirl speed, number of impeller blades and angle of blades. Specific examples as well as significant results are given.

  18. Instability of a thin film flowing on a rotating horizontal or inclined plane.

    PubMed

    Dávalos-Orozco, L A; Busse, F H

    2002-02-01

    In this paper the instability of a thin fluid film flowing under the effects of gravity, Coriolis, and centrifugal forces is investigated. It is supposed that the film flows far from the axis of rotation on a plane which may be horizontal or inclined with respect to the horizontal. In the former case, the flow is only driven by the centrifugal force while in the latter case, the flow is driven by the components of centrifugal force and gravity along the plane. This case may also be considered as the flow down a rotating cone but far from the apex. The stabilizing influence of rotation on the film flow increases with the rotation rate. Up to a certain critical rate of rotation, the film flowing down the rotating inclined plane (or cone) is more stable than the flow on the horizontal rotating plane while above this rate of rotation the situation is reversed. The instability above the critical rate is associated with a finite wave number in contrast to the vanishing wave number of the instability below the critical rate. The possibility of Ekman layer instabilities is also investigated. An equation describing the nonlinear evolution of surface waves is also obtained. Moreover, this equation is simplified for the case in which the amplitudes are very small. An equation including dissipation as well as dispersion is derived whose solutions may possess solitary waves, as in the case of similar equations considered in the literature. These solutions are likely to correspond to the solitary spiral waves observed in experiments.

  19. Differentially rotating relativistic magnetic jets. Asymptotic trans-field force-balance including differential rotation.

    NASA Astrophysics Data System (ADS)

    Fendt, C.

    1997-07-01

    Highly collimated jets are observed in various astronomical objects, as active galactic nuclei, galactic high energy sources, and also young stellar objects. There is observational indication that these jets originate in accretion disks, and that magnetic fields play an important role for the jet collimation and plasma acceleration. The rapid disk rotation close to the central object leads to relativistic rotational velocities of the magnetic field lines. The structure of these axisymmetric magnetic flux surfaces follows from the trans-field force-balance described by the Grad-Schlueter-Shafranov equation. In this paper, we investigate the asymptotic field structure of differentially rotating magnetic jets, widening the study by Appl & Camenzind (1993A&A...270...71A, 1993A&A...274..699A). In general, our results show that, with the same current distribution, differentially rotating jets are collimated to smaller jet radii as compared with jets with rigidly rotating field. Differentially rotating jets need a stronger net poloidal current in order to collimate to the same asymptotic radius. Current-free solutions are not possible for differentially rotating disk-jet magnetospheres with cylindrical asymptotics. We present a simple analytical relation between the poloidal current distribution and magnetic field rotation law. A general relation is derived for the current strength for jets with maximum differential rotation and minimum differential rotation. Analytical solutions are also given in the case of a field rotation leading to a degeneration of the light cylinder. By linking the asymptotic solution to a Keplerian accretion disk, 'total expansion rates' for the jets, and also the flux distribution at the foot points of the flux surfaces are derived. Large poloidal currents imply a strong opening of flux surfaces, a stronger gradient of field rotation leads to smaller expansion rates. There is indication that AGN jet expansion rates are less than in the case of

  20. Simulating the effect of centrifugal forces in rapidly rotating magnetospheres

    NASA Astrophysics Data System (ADS)

    Vogt, M. F.; Kivelson, M. G.; Khurana, K. K.; Walker, R. J.

    2011-12-01

    Centrifugal forces play an important role in the dynamics of rapidly rotating magnetospheres such as Jupiter and Saturn. For example, at Jupiter, centrifugal stresses are thought to be the dominant factor in driving the release of mass and energy from the system. It has also been proposed that the effects of rotation and field line stretching can explain local time asymmetries in the thickness of Jupiter's plasma sheet. Observations show that Jupiter's plasma sheet is thinnest in the post-midnight to dawn local time sectors, thickens as it rotates through the morning sector through noon, and becomes thickest near dusk. Kivelson and Southwood [2005] attributed the dusk side plasma sheet heating and thickening to centrifugal forces due to Jupiter's rapid rotation, suggesting that as a result of rotation, low energy particles gain parallel velocity as they move radially outward, and the resulting anisotropy makes the plasma sheet become unstable. We have developed a large-scale kinetic (LSK) simulation [Ashour-Abdalla et al., 1992] to test the key physical processes in this idea that rotation and field line stretching can produce an increase in net energy and particle anisotropy. In this simulation the Jovian magnetic field is represented by a simplified, axisymmetric version of the Khurana [1997] field, which we vary in time to reproduce the stretching that occurs as field lines rotate from noon to dusk. Here we will present the most recent results from this simulation project. Because we are testing only the key physical processes, our findings should help us understand the effects of rapid rotation and centrifugal stresses at both Jupiter and Saturn.

  1. Centrifugal force induced by relativistically rotating spheroids and cylinders

    NASA Astrophysics Data System (ADS)

    Katz, Joseph; Lynden Bell, Donald; Bičák, Jiří

    2011-03-01

    Starting from the gravitational potential of a Newtonian spheroidal shell we discuss electrically charged rotating prolate spheroidal shells in the Maxwell theory. In particular we consider two confocal charged shells which rotate oppositely in such a way that there is no magnetic field outside the outer shell. In the Einstein theory we solve the Ernst equations in the region where the long prolate spheroids are almost cylindrical; in equatorial regions the exact Lewis 'rotating cylindrical' solution is so derived by a limiting procedure from a spatially bound system. In the second part we analyze two cylindrical shells rotating in opposite directions in such a way that the static Levi-Civita metric is produced outside and no angular momentum flux escapes to infinity. The rotation of the local inertial frames in flat space inside the inner cylinder is thus exhibited without any approximation or interpretational difficulties within this model. A test particle within the inner cylinder kept at rest with respect to axes that do not rotate as seen from infinity experiences a centrifugal force. Although in suitably chosen axes the spacetime there is exactly Minkowskian out to the inner cylinder, nevertheless, those inertial frame axes rotate with respect to infinity, so relative to the inertial frame inside the inner cylinder a test particle is traversing a circular orbit.

  2. The effects of flow multiplicity on GaN deposition in a rotating disk CVD reactor

    NASA Astrophysics Data System (ADS)

    Gkinis, P. A.; Aviziotis, I. G.; Koronaki, E. D.; Gakis, G. P.; Boudouvis, A. G.

    2017-01-01

    The effect of gas flow multiplicity, i.e. the possibility of two very different flow regimes prevailing at random in a rotating disk metalorganic chemical vapor deposition (MOCVD) reactor, on the deposited GaN film is investigated. A transport model coupled with a system of chemical reactions in the gas phase and on the wafer where the film is formed, is implemented in the parameter regions where multiple flows are possible. In the region of multiplicity where either plug flow, imposed by forced convection, or buoyancy-dominated flow is possible, the results in the latter case indicate high deposition rate and decreased uniformity. In the former case, increasing the pressure and the rotation rate has a favorable effect on the deposition rate without sacrificing uniformity. In the parameter window of multiplicity where either rotation or combined rotation/buoyancy may prevail, the effects of buoyancy lead to higher deposition rate at the center of the wafer and reduced uniformity. The Arrhenius plots in the regions of multiplicity for exactly the same operating conditions reveal that the system operates in a diffusion-limited regime in the plug flow and in the rotation-dominated flow, in the first and second region of multiplicity respectively. In contrast, in the buoyancy-dominated flow and the combined rotation/buoyancy flow (first and second region of multiplicity respectively) the process shifts into the kinetics-limited regime.

  3. Zonal flow regimes in rotating anelastic spherical shells (Invited)

    NASA Astrophysics Data System (ADS)

    Gastine, T.; Wicht, J.; Aurnou, J. M.; Heimpel, M. H.

    2013-12-01

    The surface zonal winds observed in the giant planets form a complex jet pattern with alternating prograde and retrograde direction. While the main equatorial band is prograde on the gas giants, both ice giants have a pronounced retrograde equatorial jet. The depth of these jets is however poorly known and highly debated. Theoretical scenarios range from "shallow models", that assume that these zonal flows are restricted to the outer stably stratified layer; to "deep models" that hypothesise that the surface winds are the signature of deep-seated convection. Most of the numerical models supporting the latter idea employed the Boussinesq approximation where compressibility effects are ignored. While this approximation is suitable for modelling the liquid iron core of terrestrial planets, this becomes questionable in the gas giants interiors, where density increases by several orders of magnitude. To tackle this problem, several numerical models using the "anelastic approximation" have been recently developed to study the compressibility effects while filtering out the fast acoustic waves. Here, we consider such anelastic models of rapidly-rotating spherical shells to explore the properties of the zonal winds in different regimes where either rotation or buoyancy dominates the force balance. We conduct several parameter studies to quantify the dependence of zonal flows on the background density stratification and the driving of convection. We find that the direction of the equatorial wind is controlled by the ratio of buoyancy and Coriolis force. The prograde equatorial band maintained by Reynolds stresses is found in the rotation-dominated regime. At low Ekman numbers, several alternating jets form at high latitude in a similar way to some previous Boussinesq calculations. In cases where buoyancy dominates Coriolis force, the angular momentum per unit mass is homogenised and the equatorial band is retrograde, reminiscent to those observed in the ice giants

  4. Conversion of rotational output to linear force-a transmission

    SciTech Connect

    Montalbano, P.J.

    1991-08-27

    This patent describes a transmission device for converting rotational torque into linear force. It comprises a combination large internally toothed annular gear and large flywheel rotatable within a housing by bearing means, in operative interconnection with a small externally toothed circular gear mounted within it annulus and provided with a source of variable rotary motion for driving the annular gear, a second large internally toothed annular gear, located above the first the annular gear, rotatable within a housing by bearing means and provided with a clutch connection to first annular gear, is in operative connection with three small externally toothed circular gears driven by the second annular gear, a member pivotably supported along the axis of the annular gear and rockable on the axis, the member having an upper and a lower arm, the upper arm in interconnection with two of the respective gears and the lower arm in interconnection with one of the respective gears, the gears driven by the second annular gear, in upper arm the gears causing the rocker element to move two off- centered weights, the first weight rotatable with one of the gears, the second weight rotatable in the opposite direction and mounted within the rocker element driven by an additional small externally toothed circular gear in mesh with one of the small gears, the weights generating centrifugal forces.

  5. Direct numerical simulation of moderate-Reynolds-number flow past arrays of rotating spheres

    NASA Astrophysics Data System (ADS)

    Zhou, Qiang; Fan, Liang-Shih

    2015-07-01

    Direct numerical simulations with an immersed boundary-lattice Boltzmann method are used to investigate the effects of particle rotation on flows past random arrays of mono-disperse spheres at moderate particle Reynolds numbers. This study is an extension of a previous study of the authors [Q. Zhou and L.-S. Fan, "Direct numerical simulation of low-Reynolds-number flow past arrays of rotating spheres," J. Fluid Mech. 765, 396-423 (2015)] that explored the effects of particle rotation at low particle Reynolds numbers. The results of this study indicate that as the particle Reynolds number increases, the normalized Magnus lift force decreases rapidly when the particle Reynolds number is in the range lower than 50. For the particle Reynolds number greater than 50, the normalized Magnus lift force approaches a constant value that is invariant with solid volume fractions. The proportional dependence of the Magnus lift force on the rotational Reynolds number (based on the angular velocity and the diameter of the spheres) observed at low particle Reynolds numbers does not change in the present study, making the Magnus lift force another possible factor that can significantly affect the overall dynamics of fluid-particle flows other than the drag force. Moreover, it is found that both the normalized drag force and the normalized torque increase with the increase of the particle Reynolds number and the solid volume fraction. Finally, correlations for the drag force, the Magnus lift force, and the torque in random arrays of rotating spheres at arbitrary solids volume fractions, rotational Reynolds numbers, and particle Reynolds numbers are formulated.

  6. Jet Impingement and Forced Convection Cooling Experimental Study in Rotating Turbine Blades

    NASA Astrophysics Data System (ADS)

    Li, Hsin-Lung; Chiang, Hsiao-Wei D.; Hsu, Chih-Neng

    2011-06-01

    Both jet impingement and forced convection are attractive cooling mechanisms widely used in cooling gas turbine blades. Convective heat transfer from impinging jets is known to yield high local and area averaged heat transfer coefficients. Impingement jets are of particular interest in the cooling of gas turbine components where advancement relies on the ability to dissipate extremely large heat loads. Current research is concerned with the measurement and comparison of both jet impingement and forced convection heat transfer in the Reynolds number range of 10,000 to 30,000. This study is aimed at experimentally testing two different setups with forced convection and jet impingement in rotating turbine blades up to 700 RPM. This research also observes Coriolis force and impingement cooling inside the passage during rotating conditions within a cooling passage. Local heat transfer coefficients are obtained for each test section using thermocouple technique with slip rings. The cross section of the passage is 10 mm × 10 mm without ribs and the surface heating condition has enforced uniform heat flux. The forced convection cooling effects were studied using serpentine passages with three corner turns under different rotating speeds and different inlet Reynolds numbers. The impingement cooling study uses a straight passage with a single jet hole under different Reynolds numbers of the impingement flow and the cross flow. In summary, the main purpose is to study the rotation effects on both the jet impingement and the serpentine convection cooling types. Our study shows that rotation effects increase serpentine cooling and reduce jet impingement cooling.

  7. NASTRAN forced vibration analysis of rotating cyclic structures

    NASA Technical Reports Server (NTRS)

    Elchuri, V.; Smith, G. C. C.; Gallo, A. M.

    1983-01-01

    Theoretical aspects of a new capability developed and implemented in NASTRAN level 17.7 to analyze forced vibration of a cyclic structure rotating about its axis of symmetry are presented. Fans, propellers, and bladed shrouded discs of turbomachines are some examples of such structures. The capability includes the effects of Coriolis and centripetal accelerations on the rotating structure which can be loaded with: (1) directly applied loads moving with the structure and (2) inertial loas due to the translational acceleration of the axis of rotation (''base' acceleration). Steady-state sinusoidal or general periodic loads are specified to represent: (1) the physical loads on various segments of the complete structure, or (2) the circumferential harmonic components of the loads in (1). The cyclic symmetry feature of the rotating structure is used in deriving and solving the equations of forced motion. Consequently, only one of the cyclic sectors is modelled and analyzed using finite elements, yielding substantial savings in the analysis cost. Results, however, are obtained for the entire structure. A tuned twelve bladed disc example is used to demonstrate the various features of the capability.

  8. MASS TRANSFER TO ROTATING DISKS AND ROTATING RINGS IN LAMINAR, TRANSITION, AND FULLY DEVELOPED TURBULENT FLOW

    SciTech Connect

    Law Jr., C.G.; Pierini, P.; Newman, J.

    1980-07-01

    Experimental data and theoretical calculations are presented for the mass-transfer rate to rotating disks and rotating rings when laminar, transition, and fully developed turbulent flow exist upon different portions of the surface. Good agreement of data and the model is obtained for rotating disks and relatively thick rotating rings. Results of the calculations for thin rings generally exceed the experimental data measured in transition and turbulent flow. A y{sup +{sup 3}} form for the eddy diffusivity is used to fit the data. No improvement is noticed with a form involving both y{sup +{sup 3}} and y{sup +{sup 3}}.

  9. Second moment closure modeling for rotating stably stratified turbulent shear flow

    NASA Astrophysics Data System (ADS)

    Ji, Minsuk

    The general linear second moment closure (SMC) turbulence model is considered for flows subjected to buoyancy and rotation. Model response to external forces are analyzed with the aid of structural equilibrium analysis. A closed form equilibrium solution for the anisotropy tensor bij, dispersion tensor Kij, dimensionless scalar variance q2 /k(S/Stheta )2, and the ratio of mean to turbulent time scale epsilon/ Sk is obtained. The variable of particular interest to bifurcation analysis, epsilon/Sk is shown as a function of the parameters characterizing the body forces: O/S (the ratio of the rotation rate to the mean shear rate) for rotation and Rig (the gradient Richardson number) for buoyancy; it determines the bifurcation surface in the epsilon/Sk-O/S-Rig space. It is shown, with the use of the closed form solution, that the conventional general linear models do not have a real and stable equilibrium solution when rotational and buoyant forces of certain magnitudes are simultaneously imposed on the flow. When this occurs, time integration of the turbulence model results in a diverging solution. A new model is proposed that removes this unphysical behavior. It ensures the existence of stable, real solutions for all combinations of rotation and buoyancy. Further improvements to the model are made through bifurcation analysis. Model constants are adjusted such that the model's bifurcation characteristics are in agreement with the physically observed onset of turbulence stabilization due to stable stratification. Experimental data and numerical simulation results for stably stratified homogeneous shear flow suggest the critical gradient Richardson number of Ricrg = 0.25, and the new model is able to predict it correctly. In connection with the bifurcation analysis of SMC models, rapid distortion theory (RDT) of turbulence is applied to rotating, stably stratified shear flow to provide the stability characteristics of such flows. It is shown that the RDT predictions are

  10. Vortex flows impart chirality-specific lift forces

    NASA Astrophysics Data System (ADS)

    Hermans, Thomas M.; Bishop, Kyle J. M.; Stewart, Peter S.; Davis, Stephen H.; Grzybowski, Bartosz A.

    2015-01-01

    Recent reports that macroscopic vortex flows can discriminate between chiral molecules or their assemblies sparked considerable scientific interest both for their implications to separations technologies and for their relevance to the origins of biological homochirality. However, these earlier results are inconclusive due to questions arising from instrumental artifacts and/or insufficient experimental control. After a decade of controversy, the question remains unresolved—how do vortex flows interact with different stereoisomers? Here, we implement a model experimental system to show that chiral objects in a Taylor-Couette cell experience a chirality-specific lift force. This force is directed parallel to the shear plane in contrast to previous studies in which helices, bacteria and chiral cubes experience chirality-specific forces perpendicular to the shear plane. We present a quantitative hydrodynamic model that explains how chirality-specific motions arise in non-linear shear flows through the interplay between the shear-induced rotation of the particle and its orbital translation. The scaling laws derived here suggest that rotating flows can be used to achieve chiral separation at the micro- and nanoscales.

  11. Steady flows in rotating spherical cavity excited by multi-frequency oscillations of free inner core

    NASA Astrophysics Data System (ADS)

    Kozlov, Victor G.; Kozlov, Nikolai V.; Subbotin, Stanislav V.

    2017-01-01

    Fluid motion in a rotating spherical cavity in the conditions of resonant oscillations of free inner core is experimentally investigated. The centrifugal force retains a solid core with density less than the fluid density near the center of the cavity. In the absence of external force field the system "solid core - liquid" performs solid body rotation. The oscillations of the core are excited by an external oscillating force field and this results in differential rotation of the core with respect to the cavity. The direction of rotation is determined by the ratio of the oscillation frequency to the cavity angular velocity. The core oscillations with the radian frequency, which exceeds the cavity angular velocity, are investigated. It is found that a steady flow in the form of a system of nested fluid columns of circular cross section, which rotate at different angular velocities, is generated in the cavity as a result of oscillations of the core and the fluid. It is shown that at simultaneous influence of several oscillating fields the resulting steady flow is determined by a linear superposition of the flows, which are excited by the oscillations of the inner core with different frequencies. At a certain ratio of the vibration frequency to the rotation one the transformation of the circular shape of the column into the elliptical one is observed.

  12. Flow induction by pressure forces

    NASA Technical Reports Server (NTRS)

    Garris, C. A.; Toh, K. H.; Amin, S.

    1992-01-01

    A dual experimental/computational approach to the fluid mechanics of complex interactions that take place in a rotary-jet ejector is presented. The long-range goal is to perform both detailed flow mapping and finite element computational analysis. The described work represents an initial finding on the experimental mapping program. Test results on the hubless rotary-jet are discussed.

  13. The seismicity latitudinal structure, tidal forces, and the Earth rotation.

    NASA Astrophysics Data System (ADS)

    Levin, Dr; Domanski, Dr; Sasorova, Dr

    2012-04-01

    The concept about seismicity distribution dependence on the Earth's latitudinal disposition was formed in the last decade. It was stated that seismic activity of the planet is almost absent in the poles and in polar caps of the Earth, clearly expressed maximums in latitudes near 30-45° for both Hemispheres, and the stable minimum near equator reveal. These bimodal distributions are characteristic for a number of seismic events and for released energy as well. Analysis of lunar seismicity demonstrated similar form for the latitudinal distribution of moonquakes. The bimodal form of latitudinal distributions is typical not only for seismicity but also for distribution of hot spots at the Earth and for sunspots initiation regions. The noticeable effects upon earthquake occurrence besides tectonic forces is excited by the tidal forces and by the changes of the Earth figure induced by planet rotation velocity variation. We carried out the assessment of kinetic energy variation caused by deformation of its rotating solid shell. It was demonstrated that the polar radius and average radius of the Earth (under the condition of the equality of the sphere volume and of the geoid volume) are connected by linear relationship where Earth ellipticity plays a dominant role. An equation of ellipsoid of rotation in polar coordinates and equation of free surface of elastic compressible rotating sphere are described by general expression which contains zonal spherical function of latitude of the second-order. This expression has a following unique feature: at the latitude 35°15'52″ the length of radius-vector of geoid coincides with average radius of the Earth, doesn't depend on ellipticity and accordingly on angular velocity of the Earth rotation. At this latitude which received the name "critical latitude", the displacement of radius-vector of geoid is not occurring. Outside of this latitude a variation of angular velocity of the Earth rotation leads to a variation of

  14. Thermocapillary bubble flow and coalescence in a rotating cylinder: A 3D study

    NASA Astrophysics Data System (ADS)

    Alhendal, Yousuf; Turan, A.; Al-mazidi, M.

    2015-12-01

    The process of thermocapillary bubbles rising in a rotating 3D cylinder in zero gravity was analysed and presented numerically with the aid of computational fluid dynamics (CFD) by means of the volume of fluid (VOF) method. Calculations were carried out to investigate in detail the effect of the rotational speed of the hosted liquid on the trajectory of both single and group bubbles driven by the Marangoni force in zero-gravity conditions. For rotational speeds from 0.25 to 2 rad/s, bubble displacement with angular motion was found to be directed between the hotter surface and the rotational axis. This is contrary to the conventional bubble flow from areas of high pressure to low pressure, radial direction, or from cold to hot regions, axial direction. The results demonstrate that for the ratio of rotational speeds to the thermocapillary bubble velocity larger than unity, the surface tension gradient is the dominant force and the bubble motion towards the hotter. On the other hand, for ratio less than 1, the bubble motion is dominated and is significantly affected by centrifugal force. As rotation speed increases, the amount of deflection increases and the Marangoni effect vanishes. The current study is novel in the sense that single- and multi-bubble motion incorporating thermocapillary forces in a rotating liquid in a zero-gravity environment has never been numerically investigated.

  15. Comments on Frequency Swept Rotating Input Perturbation Techniques and Identification of the Fluid Force Models in Rotor/bearing/seal Systems and Fluid Handling Machines

    NASA Technical Reports Server (NTRS)

    Muszynska, Agnes; Bently, Donald E.

    1991-01-01

    Perturbation techniques used for identification of rotating system dynamic characteristics are described. A comparison between two periodic frequency-swept perturbation methods applied in identification of fluid forces of rotating machines is presented. The description of the fluid force model identified by inputting circular periodic frequency-swept force is given. This model is based on the existence and strength of the circumferential flow, most often generated by the shaft rotation. The application of the fluid force model in rotor dynamic analysis is presented. It is shown that the rotor stability is an entire rotating system property. Some areas for further research are discussed.

  16. Flow and heat transfer model for a rotating cryogenic motor

    SciTech Connect

    Dykhuizen, R.C.; Baca, R.G.; Bickel, T.C.

    1993-08-01

    Development of a high-temperature, superconducting, synchronous motor for large applications (>1000 HP) could offer significant electrical power savings for industrial users. Presently 60% of all electric power generated in the United States is converted by electric motors. A large part of two power is utilized by motors 1000 HP or larger. The use of high-temperature superconducting materials with critical temperatures above that of liquid nitrogen (77 K) in the field winding would reduce the losses in these motors significantly, and therefore, would have a definite impact on the electrical power usage in the US. These motors will be 1/3 to 1/2 the size of conventional motors of similar power and, thus, offer potential savings in materials and floor space. The cooling of the superconducting materials in the field windings of the rotor presents a unique application of cryogenic engineering. The rotational velocity results in significant radial pressure gradients that affect the flow distribution of the cryogen. The internal pressure fields can result in significant nonuniformities in the two-phase flow of the coolant. Due to the variable speed design, the flow distribution has the potential to change during operation. A multiphase-flow computer model of the cryogenic cooling is developed to calculate the boiling heat transfer and phase distribution of the nitrogen coolant in the motor. The model accounts for unequal phase velocities and nonuniform cooling requirements of the rotor. The unequal radial pressure gradients in the inlet and outlet headers result in a larger driving force for flow in the outer cooling channels. The effect of this must be accounted for in the design of the motor. Continuing improvements of the model will allow the investigation of the transient thermal issues associated with localized quenching of the superconducting components of the motor.

  17. Flow and heat transfer model for a rotating cryogenic motor

    NASA Astrophysics Data System (ADS)

    Dykhuizen, R. C.; Baca, R. G.; Bickel, T. C.

    1993-08-01

    Development of a high-temperature, superconducting, synchronous motor for large applications (greater than 1000 HP) could offer significant electrical power savings for industrial users. Presently 60% of all electric power generated in the United States is converted by electric motors. A large part of this power is utilized by motors 1000 HP or larger. The use of high-temperature superconducting materials with critical temperatures above that of liquid nitrogen (77 K) in the field winding would reduce the losses in these motors significantly, and therefore, would have a definite impact on the electrical power usage in the U.S. These motors will be 1/3 to 1/2 the size of conventional motors of similar power and, thus, offer potential savings in materials and floor space. The cooling of the superconducting materials in the field windings of the rotor presents a unique application of cryogenic engineering. The rotational velocity results in significant radial pressure gradients that affect the flow distribution of the cryogen. The internal pressure fields can result in significant nonuniformities in the two-phase flow of the coolant. Due to the variable speed design, the flow distribution has the potential to change during operation. A multiphase-flow computer model of the cryogenic cooling is developed to calculate the boiling heat transfer and phase distribution of the nitrogen coolant in the motor. The model accounts for unequal phase velocities and nonuniform cooling requirements of the rotor. The unequal radial pressure gradients in the inlet and outlet headers result in a larger driving force for flow in the outer cooling channels. The effect of this must be accounted for in the design of the motor. Continuing improvements of the model will allow the investigation of the transient thermal issues associated with localized quenching of the superconducting components of the motor.

  18. Numerical Simulations of Rapidly Rotating Boundary-Coupled Flows

    NASA Astrophysics Data System (ADS)

    Calkins, Michael Andrew

    Many of the large-scale fluid systems present on and within the Earth, other planetary bodies in the Solar System, and throughout our universe are characterized by large length scales, weak viscous forces, and a rapid background rotation. The combination of these attributes with various forcing mechanisms results in unique fluid dynamical phenomena that dictate the evolutionary path of our universe. However, even for relatively small fluid velocities (e.g. 10-4 m s-1), these systems are often characterized by large Reynolds numbers and the presence of localized boundary layers due to sharp hydrodynamic, thermal, chemical, or magnetic gradients that render laboratory or numerical modeling difficult. Furthermore, geophysical and planetary fluid flows often interact in a complex manner with bounding solid surfaces that result in further difficulties. Physical and mathematical simplifications are thus paramount for advancing our understanding of these fluid systems. In this document we explain our approach at attempting to understand two problems in the field of geophysical fluid dynamics using simplified, two-dimensional numerical simulations. Studies have shown that angular momentum is exchanged between the Earth's liquid outer core and solid mantle, resulting in measurable changes in the rotation rate of the Earth. The physical mechanism responsible for this exchange is not currently understood. One possibility is the interaction of flow in the core with topography present along the core-mantle boundary. Towards this end, we employ a quasi-two-dimensional thermal convection model in a spherical shell to carry out the first detailed study on the effects of core-mantle boundary topography. We find that the presence of topography can generate a spatially heterogeneous flow field and azimuthally dependent heat flux along the inner and outer boundaries. The total heat transfer and azimuthal velocities are typically enhanced in the presence of the topography. These

  19. Rotation of melting ice disks due to melt fluid flow

    NASA Astrophysics Data System (ADS)

    Dorbolo, S.; Adami, N.; Dubois, C.; Caps, H.; Vandewalle, N.; Darbois-Texier, B.

    2016-03-01

    We report experiments concerning the melting of ice disks (85 mm in diameter and 14 mm in height) at the surface of a thermalized water bath. During the melting, the ice disks undergo translational and rotational motions. In particular, the disks rotate. The rotation speed has been found to increase with the bath temperature. We investigated the flow under the bottom face of the ice disks by a particle image velocimetry technique. We find that the flow goes downwards and also rotates horizontally, so that a vertical vortex is generated under the ice disk. The proposed mechanism is the following. In the vicinity of the bottom face of the disk, the water eventually reaches the temperature of 4°C for which the water density is maximum. The 4°C water sinks and generates a downwards plume. The observed vertical vorticity results from the flow in the plume. Finally, by viscous entrainment, the horizontal rotation of the flow induces the solid rotation of the ice block. This mechanism seems generic: any vertical flow that generates a vortex will induce the rotation of a floating object.

  20. Rotation of melting ice disks due to melt fluid flow.

    PubMed

    Dorbolo, S; Adami, N; Dubois, C; Caps, H; Vandewalle, N; Darbois-Texier, B

    2016-03-01

    We report experiments concerning the melting of ice disks (85 mm in diameter and 14 mm in height) at the surface of a thermalized water bath. During the melting, the ice disks undergo translational and rotational motions. In particular, the disks rotate. The rotation speed has been found to increase with the bath temperature. We investigated the flow under the bottom face of the ice disks by a particle image velocimetry technique. We find that the flow goes downwards and also rotates horizontally, so that a vertical vortex is generated under the ice disk. The proposed mechanism is the following. In the vicinity of the bottom face of the disk, the water eventually reaches the temperature of 4 °C for which the water density is maximum. The 4 °C water sinks and generates a downwards plume. The observed vertical vorticity results from the flow in the plume. Finally, by viscous entrainment, the horizontal rotation of the flow induces the solid rotation of the ice block. This mechanism seems generic: any vertical flow that generates a vortex will induce the rotation of a floating object.

  1. Advances in wave turbulence: rapidly rotating flows

    NASA Astrophysics Data System (ADS)

    Cambon, C.; Rubinstein, R.; Godeferd, F. S.

    2004-07-01

    At asymptotically high rotation rates, rotating turbulence can be described as a field of interacting dispersive waves by the general theory of weak wave turbulence. However, rotating turbulence has some complicating features, including the anisotropy of the wave dispersion relation and the vanishing of the wave frequency on a non-vanishing set of 'slow' modes. These features prevent straightforward application of existing theories and lead to some interesting properties, including the transfer of energy towards the slow modes. This transfer competes with, and might even replace, the transfer to small scales envisioned in standard turbulence theories. In this paper, anisotropic spectra for rotating turbulence are proposed based on weak turbulence theory; some evidence for their existence is given based on numerical calculations of the wave turbulence equations. Previous arguments based on the properties of resonant wave interactions suggest that the slow modes decouple from the others. Here, an extended wave turbulence theory with non-resonant interactions is proposed in which all modes are coupled; these interactions are possible only because of the anisotropy of the dispersion relation. Finally, the vanishing of the wave frequency on the slow modes implies that these modes cannot be described by weak turbulence theory. A more comprehensive approach to rotating turbulence is proposed to overcome this limitation.

  2. Preparation of Geophysical Fluid Flow Experiments With The Rotating Spherical Gap Flow Model In Space

    NASA Astrophysics Data System (ADS)

    Egbers, C.

    The'GeoFlow' is an ESA experiment planned for the Fluid Science Laboratory on ISS under the scientific coordination (PI) of the Department of Aerodynamics and Fluid Mechanics (LAS) at the Brandenburg Technical University (BTU) of Cottbus, Germany. The objective of the experiment is to study thermal convection in the gap between two concentric rotating (full) spheres. A central symmetric force field simi- lar to the gravity field acting on planets can be produced by applying a high voltage between inner and outer sphere using the dielectrophoretic effect (rotating capacitor). To counter the unidirectional gravity under terrestrial conditions, this experiment re- quires a microgravity environment. The parameters of the experiment are chosen in analogy to the thermal convective motions in the outer core of the Earth. In analogy to geophysical motions in the Earth`s liquid core the experiment can rotate as solid body as well as differential (inner to outer). Thermal convection is produced by heat- ing the inner sphere and cooling the outer ones. Furtheron, the variation of radius ratio between inner and outer sphere is foreseen as a parameter variation. The flows to be investigated will strongly depend on the gap width and on the Prandtl number.

  3. Electromotive force due to magnetohydrodynamic fluctuations in sheared rotating turbulence

    DOE PAGES

    Squire, J.; Bhattacharjee, A.

    2015-11-02

    Here, this article presents a calculation of the mean electromotive force arising from general small-scale magnetohydrodynamical turbulence, within the framework of the second-order correlation approximation. With the goal of improving understanding of the accretion disk dynamo, effects arising through small-scale magnetic fluctuations, velocity gradients, density and turbulence stratification, and rotation, are included. The primary result, which supplements numerical findings, is that an off-diagonal turbulent resistivity due to magnetic fluctuations can produce large-scale dynamo action-the magnetic analog of the "shear-current" effect. In addition, consideration of alpha effects in the stratified regions of disks gives the puzzling result that there is nomore » strong prediction for a sign of alpha, since the effects due to kinetic and magnetic fluctuations, as well as those due to shear and rotation, are each of opposing signs and tend to cancel each other.« less

  4. Electromotive force due to magnetohydrodynamic fluctuations in sheared rotating turbulence.

    PubMed

    Squire, J; Bhattacharjee, A

    2015-11-01

    This article presents a calculation of the mean electromotive force arising from general small-scale magnetohydrodynamical turbulence, within the framework of the second-order correlation approximation. With the goal of improving understanding of the accretion disk dynamo, effects arising through small-scale magnetic fluctuations, velocity gradients, density and turbulence stratification, and rotation, are included. The primary result, which supplements numerical findings, is that an off-diagonal turbulent resistivity due to magnetic fluctuations can produce large-scale dynamo action-the magnetic analog of the "shear-current" effect. In addition, consideration of α effects in the stratified regions of disks gives the puzzling result that there is no strong prediction for a sign of α, since the effects due to kinetic and magnetic fluctuations, as well as those due to shear and rotation, are each of opposing signs and tend to cancel each other.

  5. Electromotive force due to magnetohydrodynamic fluctuations in sheared rotating turbulence

    SciTech Connect

    Squire, J.; Bhattacharjee, A.

    2015-11-02

    Here, this article presents a calculation of the mean electromotive force arising from general small-scale magnetohydrodynamical turbulence, within the framework of the second-order correlation approximation. With the goal of improving understanding of the accretion disk dynamo, effects arising through small-scale magnetic fluctuations, velocity gradients, density and turbulence stratification, and rotation, are included. The primary result, which supplements numerical findings, is that an off-diagonal turbulent resistivity due to magnetic fluctuations can produce large-scale dynamo action-the magnetic analog of the "shear-current" effect. In addition, consideration of alpha effects in the stratified regions of disks gives the puzzling result that there is no strong prediction for a sign of alpha, since the effects due to kinetic and magnetic fluctuations, as well as those due to shear and rotation, are each of opposing signs and tend to cancel each other.

  6. Dynamics of rotating gaseous ellipsoid in external force fields

    NASA Astrophysics Data System (ADS)

    Tatematsu, Yoshinori; Fujimoto, Mitsuaki

    1990-04-01

    General and computationally-tractable equations are presented for the large-amplitude motion of a uniform gaseous ellipsoid rotating in an external force field. When this force is expressed as a linear function of the rectangular coordinates in the space under consideration, the equation of motion is reduced to a set of ordinary differential equations for the angular velocity, semimajor-axes of the ellipsoid, circulation, and temperature of the gaseous medium; they are integrated as an initial-value problem. Ad hoc (though fairly realistic) equations are used for cooling and viscosity to reproduce the gravitational contractions of the rotating gaseous ellipsoid. As one application, a series of equilibrium states of a uniform interstellar gas cloud in the tidal force of the Galaxy was determined, and their gravitational contraction was followed to a compact elongated structure. Two types of contractions are also found; the one is smooth contraction and the other is a violent one in which the prolate ellipsoid tumbles end-over-end with large-scale gas circulation within it.

  7. A Microfluidic Approach for Inducing Cell Rotation by Means of Hydrodynamic Forces

    PubMed Central

    Torino, Stefania; Iodice, Mario; Rendina, Ivo; Coppola, Giuseppe; Schonbrun, Ethan

    2016-01-01

    Microfluidic technology allows to realize devices in which cells can be imaged in their three-dimensional shape. However, there are still some limitations in the method, due to the fact that cells follow a straight path while they are flowing in a channel. This can result in a loss in information, since only one side of the cell will be visible. Our work has started from the consideration that if a cell rotates, it is possible to overcome this problem. Several approaches have been proposed for cell manipulation in microfluidics. In our approach, cells are controlled by only taking advantages of hydrodynamic forces. Two different devices have been designed, realized, and tested. The first device induces cell rotation in a plane that is parallel (in-plane) to the observation plane, while the second one induce rotation in a plane perpendicular (out-of-plane) to the observation plane. PMID:27548187

  8. The emergence of zonal jets in forced rotating shallow water turbulence: A laboratory study

    NASA Astrophysics Data System (ADS)

    Espa, S.; Di Nitto, G.; Cenedese, A.

    2010-11-01

    The emergence of a sequence of alternating intense and elongated eastward-westward bands i.e. zonal jets in the atmosphere of the giant planets and in Earth's oceans have been widely investigated. Nevertheless jets formation and role as material barriers remain still unclear. Jets are generated in a quasi-2D turbulent flow due to the latitudinal variation of the Coriolis parameter (the so-called β-effect) which modifies the inverse cascade process channeling energy towards zonal modes. In previous experiments we have investigated the impact of the variation of the rotation rate, of the domain geometry and of the initial spectra on jets organization in a decaying regime. In this work we investigate the formation of jets in a continuously forced flow, we characterize the observed regime and also we attempt to verify the existence of an universal regime corresponding to the so-called zonostrophic turbulence. The experimental set-up consists of a rotating tank where turbulence is generated by electromagnetically forcing a shallow layer of an electrolyte solution, and the variation of the Coriolis parameter has been simulated by the parabolic profile assumed by the free surface of the fluid under rotation. Flow measurements have been performed using image analysis.

  9. Effects of uniform rotational flow on predator-prey system

    NASA Astrophysics Data System (ADS)

    Lee, Sang-Hee

    2012-12-01

    Rotational flow is often observed in lotic ecosystems, such as streams and rivers. For example, when an obstacle interrupts water flowing in a stream, energy dissipation and momentum transfer can result in the formation of rotational flow, or a vortex. In this study, I examined how rotational flow affects a predator-prey system by constructing a spatially explicit lattice model consisting of predators, prey, and plants. A predation relationship existed between the species. The species densities in the model were given as S (for predator), P (for prey), and G (for plant). A predator (prey) had a probability of giving birth to an offspring when it ate prey (plant). When a predator or prey was first introduced, or born, its health state was assigned an initial value of 20 that subsequently decreased by one with every time step. The predator (prey) was removed from the system when the health state decreased to less than zero. The degree of flow rotation was characterized by the variable, R. A higher R indicates a higher tendency that predators and prey move along circular paths. Plants were not affected by the flow because they were assumed to be attached to the streambed. Results showed that R positively affected both predator and prey survival, while its effect on plants was negligible. Flow rotation facilitated disturbances in individuals’ movements, which consequently strengthens the predator and prey relationship and prevents death from starvation. An increase in S accelerated the extinction of predators and prey.

  10. Self-Rotation in Electrocapillary Flows, Swirl Pumping and Accumulation

    NASA Astrophysics Data System (ADS)

    Herrada, M. A.; Gordillo, J. M.; Barrero, A.

    1999-11-01

    A striking example of spontaneous appearance of rotation in fluid flows inside electrified menisci is presented. Self-rotation appears as bifurcation from a primary swirl-free meridional recirculating flow when the Reynolds number reaches a critical value. The unsteady motion of a viscous liquid inside an axisymmetrical conical domain driven by a tangential stress acting on the cone surface (which in Taylor cones is due to the electric field) has been solved numerically to gain insight about the nature and characteristics of this kind of self-rotation. The numerical resuls agree well to the experimental obsevations. There is considerable evidence that identical self-rotation mechanism applies in other natural flows and engeneering applications.

  11. Rotational superradiant scattering in a vortex flow

    NASA Astrophysics Data System (ADS)

    Torres, Theo; Patrick, Sam; Coutant, Antonin; Richartz, Maurício; Tedford, Edmund W.; Weinfurtner, Silke

    2017-09-01

    When an incident wave scatters off of an obstacle, it is partially reflected and partially transmitted. In theory, if the obstacle is rotating, waves can be amplified in the process, extracting energy from the scatterer. Here we describe in detail the first laboratory detection of this phenomenon, known as superradiance. We observed that waves propagating on the surface of water can be amplified after being scattered by a draining vortex. The maximum amplification measured was 14% +/- 8%, obtained for 3.70 Hz waves, in a 6.25-cm-deep fluid, consistent with the superradiant scattering caused by rapid rotation. We expect our experimental findings to be relevant to black-hole physics, since shallow water waves scattering on a draining fluid constitute an analogue of a black hole, as well as to hydrodynamics, due to the close relation to over-reflection instabilities.

  12. Efficient forced vibration reanalysis method for rotating electric machines

    NASA Astrophysics Data System (ADS)

    Saito, Akira; Suzuki, Hiromitsu; Kuroishi, Masakatsu; Nakai, Hideo

    2015-01-01

    Rotating electric machines are subject to forced vibration by magnetic force excitation with wide-band frequency spectrum that are dependent on the operating conditions. Therefore, when designing the electric machines, it is inevitable to compute the vibration response of the machines at various operating conditions efficiently and accurately. This paper presents an efficient frequency-domain vibration analysis method for the electric machines. The method enables the efficient re-analysis of the vibration response of electric machines at various operating conditions without the necessity to re-compute the harmonic response by finite element analyses. Theoretical background of the proposed method is provided, which is based on the modal reduction of the magnetic force excitation by a set of amplitude-modulated standing-waves. The method is applied to the forced response vibration of the interior permanent magnet motor at a fixed operating condition. The results computed by the proposed method agree very well with those computed by the conventional harmonic response analysis by the FEA. The proposed method is then applied to the spin-up test condition to demonstrate its applicability to various operating conditions. It is observed that the proposed method can successfully be applied to the spin-up test conditions, and the measured dominant frequency peaks in the frequency response can be well captured by the proposed approach.

  13. Heat transfer in rotating serpentine passages with trips normal to the flow

    NASA Technical Reports Server (NTRS)

    Wagner, J. H.; Johnson, B. V.; Graziani, R. A.; Yeh, F. C.

    1991-01-01

    Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large scale, multipass, heat transfer model with both radially inward and outward flow. Trip strips on the leading and trailing surfaces of the radial coolant passages were used to produce the rough walls. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages: coolant-to-wall temperature ratio, Rossby number, Reynolds number, and radius-to-passage hydraulic diameter ratio. The first three of these four parameters were varied over ranges which are typical of advanced gas turbine engine operating conditions. Results were correlated and compared to previous results from stationary and rotating similar models with trip strips. The heat transfer coefficients on surfaces, where the heat increased with rotation and buoyancy, varied by as much as a factor of four. Maximum values of the heat transfer coefficients with high rotation were only slightly above the highest levels obtained with the smooth wall model. The heat transfer coefficients on surfaces, where the heat transfer decreased with rotation, varied by as much as a factor of three due to rotation and buoyancy. It was concluded that both Coriolis and buoyancy effects must be considered in turbine blade cooling designs with trip strips and that the effects of rotation were markedly different depending upon the flow direction.

  14. Biomechanics of Forearm Rotation: Force and Efficiency of Pronator Teres

    PubMed Central

    Ibáñez-Gimeno, Pere; Galtés, Ignasi; Jordana, Xavier; Malgosa, Assumpció; Manyosa, Joan

    2014-01-01

    Biomechanical models are useful to assess the effect of muscular forces on bone structure. Using skeletal remains, we analyze pronator teres rotational efficiency and its force components throughout the entire flexion-extension and pronation-supination ranges by means of a new biomechanical model and 3D imaging techniques, and we explore the relationship between these parameters and skeletal structure. The results show that maximal efficiency is the highest in full elbow flexion and is close to forearm neutral position for each elbow angle. The vertical component of pronator teres force is the highest among all components and is greater in pronation and elbow extension. The radial component becomes negative in pronation and reaches lower values as the elbow flexes. Both components could enhance radial curvature, especially in pronation. The model also enables to calculate efficiency and force components simulating changes in osteometric parameters. An increase of radial curvature improves efficiency and displaces the position where the radial component becomes negative towards the end of pronation. A more proximal location of pronator teres radial enthesis and a larger humeral medial epicondyle increase efficiency and displace the position where this component becomes negative towards forearm neutral position, which enhances radial curvature. Efficiency is also affected by medial epicondylar orientation and carrying angle. Moreover, reaching an object and bringing it close to the face in a close-to-neutral position improve efficiency and entail an equilibrium between the forces affecting the elbow joint stability. When the upper-limb skeleton is used in positions of low efficiency, implying unbalanced force components, it undergoes plastic changes, which improve these parameters. These findings are useful for studies on ergonomics and orthopaedics, and the model could also be applied to fossil primates in order to infer their locomotor form. Moreover, activity

  15. Biomechanics of forearm rotation: force and efficiency of pronator teres.

    PubMed

    Ibáñez-Gimeno, Pere; Galtés, Ignasi; Jordana, Xavier; Malgosa, Assumpció; Manyosa, Joan

    2014-01-01

    Biomechanical models are useful to assess the effect of muscular forces on bone structure. Using skeletal remains, we analyze pronator teres rotational efficiency and its force components throughout the entire flexion-extension and pronation-supination ranges by means of a new biomechanical model and 3D imaging techniques, and we explore the relationship between these parameters and skeletal structure. The results show that maximal efficiency is the highest in full elbow flexion and is close to forearm neutral position for each elbow angle. The vertical component of pronator teres force is the highest among all components and is greater in pronation and elbow extension. The radial component becomes negative in pronation and reaches lower values as the elbow flexes. Both components could enhance radial curvature, especially in pronation. The model also enables to calculate efficiency and force components simulating changes in osteometric parameters. An increase of radial curvature improves efficiency and displaces the position where the radial component becomes negative towards the end of pronation. A more proximal location of pronator teres radial enthesis and a larger humeral medial epicondyle increase efficiency and displace the position where this component becomes negative towards forearm neutral position, which enhances radial curvature. Efficiency is also affected by medial epicondylar orientation and carrying angle. Moreover, reaching an object and bringing it close to the face in a close-to-neutral position improve efficiency and entail an equilibrium between the forces affecting the elbow joint stability. When the upper-limb skeleton is used in positions of low efficiency, implying unbalanced force components, it undergoes plastic changes, which improve these parameters. These findings are useful for studies on ergonomics and orthopaedics, and the model could also be applied to fossil primates in order to infer their locomotor form. Moreover, activity

  16. Growth and decay of disturbances in stratified shear flow in a rotating frame

    NASA Technical Reports Server (NTRS)

    Korycansky, D. G.

    1992-01-01

    The stability of stratified plane Couette flow in a rotating frame is investigated for a case in which the gravitational force is parallel to the rotation vector. Partial differential equations describing the behavior of disturbances in the linear regime are derived. Unstratified flow is stable as long as the angular momentum gradient is positive. If the gradient is negative, nonaxisymmetric disturbances grow as a power law in time, if the gradient is sufficiently steep. In flow which is unstable to convection, all perturbations asymptotically grow at the rate given by the Brunt-Vaisala frequency. If heat diffusion is included, all nonaxisymmetric perturbations now eventually decay as t exp -2, even if the flow is unstable to convection. If heat diffusion and viscosity are weak, nonaxisymmetric disturbances in convectively unstable flow will undergo a large transient growth before their eventual decay.

  17. 'Coriolis resonance' within a rotating duct. [flow induced vibrations in centrifugal compressors

    NASA Technical Reports Server (NTRS)

    Kurosaka, M.; Caruthers, J. E.

    1982-01-01

    An investigation of the unsteady disturbances of a fixed frequency within a radial duct rotating at a set speed is presented. The flow is assumed to be compressible, inviscid, and of a fluid which is a perfect gas. Equations are developed for the steady and the unsteady parts of the flow in cylindrical coordinates. The unsteady disturbances are expressed by Fourier decomposition in angular position, distance into the duct, and in time. It is found that a resonance is possible when the frequency of flow disturbances is twice the shaft-rotation frequency, considering only the radial and tangential disturbances and not the radial and circumferential disturbances. The particular point at which the resonance occurs indicates the occurrence is due to the Coriolis force, which is only present in the radial and tangential directions. It is noted that the Coriolis force can only be present in open-ended ducts, such as those found in centrifugal compressors.

  18. 'Coriolis resonance' within a rotating duct. [flow induced vibrations in centrifugal compressors

    NASA Technical Reports Server (NTRS)

    Kurosaka, M.; Caruthers, J. E.

    1982-01-01

    An investigation of the unsteady disturbances of a fixed frequency within a radial duct rotating at a set speed is presented. The flow is assumed to be compressible, inviscid, and of a fluid which is a perfect gas. Equations are developed for the steady and the unsteady parts of the flow in cylindrical coordinates. The unsteady disturbances are expressed by Fourier decomposition in angular position, distance into the duct, and in time. It is found that a resonance is possible when the frequency of flow disturbances is twice the shaft-rotation frequency, considering only the radial and tangential disturbances and not the radial and circumferential disturbances. The particular point at which the resonance occurs indicates the occurrence is due to the Coriolis force, which is only present in the radial and tangential directions. It is noted that the Coriolis force can only be present in open-ended ducts, such as those found in centrifugal compressors.

  19. Subsychronous vibration of multistage centrifugal compressors forced by rotating stall

    NASA Technical Reports Server (NTRS)

    Fulton, J. W.

    1987-01-01

    A multistage centrifugal compressor, in natural gas re-injection service on an offshore petroleum production platform, experienced subsynchronous vibrations which caused excessive bearing wear. Field performance testing correlated the subsynchronous amplitude with the discharge flow coefficient, demonstrating the excitation to be aerodynamic. Adding two impellers allowed an increase in the diffuser flow angle (with respect to tangential) to meet the diffuser stability criteria based on factory and field tests correlated using the theory of Senoo (for rotating stall in a vaneless diffuser). This modification eliminated all significant subsynchronous vibrations in field service, thus confirming the correctness of the solution. Other possible sources of aerodynamically induced vibrations were considered, but the judgment that those are unlikely has been confirmed by subsequent experience with other similar compressors.

  20. A rotating annulus driven by localized convective forcing: a new atmosphere-like experiment

    NASA Astrophysics Data System (ADS)

    Scolan, Hélène; Read, Peter L.

    2017-06-01

    We present an experimental study of flows in a cylindrical rotating annulus convectively forced by local heating in an annular ring at the bottom near the external wall and via a cooled circular disk near the axis at the top surface of the annulus. This new configuration is distinct from the classical thermally driven annulus analogue of the atmosphere circulation, in which thermal forcing is applied uniformly on the sidewalls, but with a similar aim to investigate the baroclinic instability of a rotating, stratified flow subjected to zonally symmetric forcing. Two vertically and horizontally displaced heat sources/sinks are arranged, so that in the absence of background rotation, statically unstable Rayleigh-Bénard convection would be induced above the source and beneath the sink, thereby relaxing strong constraints placed on background temperature gradients in previous experimental configurations based on the conventional rotating annulus. This better emulates local vigorous convection in the tropics and polar regions of the atmosphere while also allowing stably-stratified baroclinic motion in the central zone of the annulus, as in mid-latitude regions in the Earth's atmosphere. Regimes of flow are identified, depending mainly upon control parameters that in turn depend on rotation rate and the strength of differential heating. Several regimes exhibit baroclinically unstable flows which are qualitatively similar to those previously observed in the classical thermally driven annulus. However, in contrast to the classical configuration, they typically exhibit more spatio-temporal complexity. Thus, several regimes of flow demonstrate the equilibrated co-existence of, and interaction between, free convection and baroclinic wave modes. These new features were not previously observed in the classical annulus and validate the new setup as a tool for exploring fundamental atmosphere-like dynamics in a more realistic framework. Thermal structure in the fluid is

  1. Forced generation of solitary waves in a rotating fluid and their stability

    NASA Astrophysics Data System (ADS)

    Choi, Wooyoung

    The primary objective of this graduate research is to study forced generation of solitary waves in a rotating fluid and their stability properties. For axisymmetric flow of a non-uniformly rotating fluid within a long cylindrical tube, an analysis is presented to predict the periodic generation of upstream-advancing vortex solitons by axisymmetric disturbance steadily moving with a transcritical velocity as a forcing agent. The phenomenon is simulated using the forced Korteweg-de Vries (fKdV) equation to model the amplitude function of the Stokes stream function for describing this family of rotating flows of an inviscid and incompressible fluid. The numerical results for the weakly nonlinear and weakly dispersive wave motion show that a sequence of well-defined axisymmetrical recirculating eddies is periodically produced and emitted to radiate upstream of the disturbance, soon becoming permanent in the form as a procession of vortex solitons, which we call vortons. Two primary flows, the Rankine vortex and the Burgers vortex, are adopted to exhibit in detail the process of producing the upstream vortons by the critical motion of a slender body moving along the central axis, with the Burgers vortex being found the more effective of the two in the generation of vortons. To investigate the evolution of free or forced waves within a tube of non-uniform radius, a new forced KdV equation is derived which models the variable geometry with variable coefficients. A set of section-mean conservation laws is derived specially for this class of rotational tube flows of an inviscid and incompressible fluid, in both differential and integral forms. A new aspect of stability theory is analyzed for possible instabilities of the axisymmetric solitary waves subject to non-axisymmetric disturbances. The present linear analysis based on the model equation involving the bending mode shows that the axisymmetric solitary wave is neutrally stable with respect to small bending mode

  2. Laboratory experiments with a buoyancy forced circulation in a rotating basin

    NASA Astrophysics Data System (ADS)

    Vreugdenhil, Catherine; Griffiths, Ross; Gayen, Bishakhdatta

    2016-11-01

    We consider the relative influence of buoyancy forcing and Coriolis effects on convection forced by a differential in heating at a horizontal surface in a rectangular basin. Laboratory experiments with water are reported for a rotating f-plane basin and a range of Ekman number E = 2 ×10-7 - 1 ×10-5 . Heating is applied over half of the base as a uniform flux and cooling applied over the other half as a uniform temperature, resulting in a flux Rayleigh number RaF = O (1014) large enough to ensure turbulent convection, where RaF defined in terms of domain length L. Compared to the non-rotating circulation where Nusselt number (a measure of the convective to conductive heat transfer) scales as Nu RaF1 / 6 , the strongly rotating regime is determined by a geostrophic balance of the larger scales of horizontal flow in the inviscid thermal boundary with Nu Ro 1 / 6 , where Ro =B 1 / 2 / (f 3 / 2 L) is the natural Rossby number (B is buoyancy flux per unit area and f is Coriolis parameter). We also find evidence for a further transition into a regime where the circulation is dominated by deep 'chimney' convection in a field of small vortical plumes and Nu is more weakly dependent on rotation.

  3. Asymptotically reduced equations for rapidly rotating and stably stratified flow

    NASA Astrophysics Data System (ADS)

    Nieves, David; Julien, Keith

    2015-11-01

    Observations by van Haren & Millot (2005) of the deep Western Mediterranean Sea and by Timmermans et al. (2006) of the deep Canadian Basin find vertical fluid motions to be as significant as horizontal motions for ocean dynamics. Since the classical quasi-geostrophic equations do not allow for such vertical motions reduced equations for geostrophically balanced flow with O(1) vertical motions are presented alongside their numerical solutions and results. The reduced equations describe flow constrained by rapid rotation and stable stratification and, in fact, are the stably stratified counterpart to the reduced equations used by Julien et al. in successful studies of rapidly rotating Rayleigh-Bénard convection. Specifically, the equations are valid in the small Rossby number (Ro 1) and O(1) Froude number limit. The focus here is a comparison to similar studies of rotating and stratified flow by Smith & Waleffe (2002), Wingate et al. (2011), and Marino et al. (2013) among others.

  4. Rotation rate of rods in turbulent fluid flow.

    PubMed

    Parsa, Shima; Calzavarini, Enrico; Toschi, Federico; Voth, Greg A

    2012-09-28

    The rotational dynamics of anisotropic particles advected in a turbulent fluid flow are important in many industrial and natural settings. Particle rotations are controlled by small scale properties of turbulence that are nearly universal, and so provide a rich system where experiments can be directly compared with theory and simulations. Here we report the first three-dimensional experimental measurements of the orientation dynamics of rodlike particles as they are advected in a turbulent fluid flow. We also present numerical simulations that show good agreement with the experiments and allow extension to a wide range of particle shapes. Anisotropic tracer particles preferentially sample the flow since their orientations become correlated with the velocity gradient tensor. The rotation rate is heavily influenced by this preferential alignment, and the alignment depends strongly on particle shape.

  5. Rotating water table for the determination of non-steady forces in a turbine stage through modified hydraulic analogy

    NASA Astrophysics Data System (ADS)

    Rao, J. S.; Raghavacharyulu, E.; Seshadri, V.; Rao, V. V. R.

    1983-10-01

    Determination of non-steady forces in a real turbine stage is difficult due to the local flow conditions, for example high pressures, high temperatures and in-accessibility to the region etc. Experimentation in a real turbine is also prohibitive due to the costs involved. An alternate method of arriving at these non-steady forces through the use of modified hydraulic analogy is discussed. A rotating water table facility, developed and fabricated based on the principles of modified hydraulic analogy is described. A flat plate stage is simulated on the rotating water table, and the results obtained are presented.

  6. Flow patterns in a rotating horizontal cylinder partially filled with liquid

    NASA Astrophysics Data System (ADS)

    Kozlov, Victor; Polezhaev, Denis

    2015-07-01

    The dynamics of an annular layer of low-viscosity liquid inside a rapidly rotating horizontal cylinder is experimentally studied. Under gravity, the liquid performs forced azimuthal oscillations in the cavity frame. We examined the stability of the two-dimensional azimuthal flow and discovered two novel types of axisymmetric liquid flows. First, a large-scale axially symmetric flow is excited near the end walls. The inertial modes generated in the corner regions are proven to be responsible for such a flow. Second, a small-scale flow in the form of the Taylor-Gortler vortices appears due to the centrifugal instability of the oscillatory liquid flow. The spatial period of the vortices is in qualitative agreement with the data obtained in the experimental and numerical studies of cellular flow in librating containers.

  7. Effect of advanced and delayed rotation on the dominant flow pattern and its temporal evolution

    NASA Astrophysics Data System (ADS)

    Uksul, Esra; Krishna, Swathi; Mulleners, Karen

    2015-11-01

    During a flapping cycle of an insect, complex time dependent flows are produced as the wing reciprocates, producing a maximum lift at the stroke reversals. By flipping the wing rapidly at the end of each stroke, the insect modulates the flow around the wing and hence the aerodynamic forces necessary to hover. The duration and starting point of the flip play an important role in determining the amount of lift produced. To understand and tailor the effect of wing kinematics on the aerodynamic performance we focussed on the vortex dynamics of the flow field. Phase-averaged data from particle image velocimetry was used to evaluate the flow features inherent to changes in rotation during a stroke of a flat plate, which is modelled based on hoverfly characteristics. The period of rotation is one-third of the total time period. A +10% phase shift is used for delayed rotation, a -10% phase shift for advanced rotation. Vortex detection methods like the λ2 and Γ2 criteria are used to determine the effect of a delay or early rotation on the trajectories, size, shape and location of the prominent vortical structures. Proper orthogonal decomposition is used to study the influence of the phase-shifts on the dominant mode structure and the related time-scales.

  8. Forced Flow Flame-Spreading Test (FFFT)

    NASA Technical Reports Server (NTRS)

    1997-01-01

    The Forced Flow Flame-Spreading Test was designed to study flame spreading over solid fuels when air is flowing at a low speed in the same direction as the flame spread. Previous research has shown that in low-speed concurrent airflows, some materials are more flammable in microgravity than earth. This image shows a 10-cm flame in microgravity that burns almost entirely blue on both sides of a thin sheet of paper. The glowing thermocouple in the lower half of the flame provides temperature measurements.

  9. Instability of flow around a rotating, semi-infinite cylinder

    NASA Astrophysics Data System (ADS)

    Derebail Muralidhar, Srikanth; Pier, Benoît; Scott, Julian F.

    2016-09-01

    Stability of flow around a rotating, semi-infinite cylinder placed in an axial stream is investigated. Assuming large Reynolds number, the basic flow is computed numerically as described by Derebail Muralidhar et al. [Proc. R. Soc. London, Ser. A 472, 20150850 (2016), 10.1098/rspa.2015.0850], while numerical solution of the local stability equations allows calculation of the modal growth rates and hence determination of flow stability or instability. The problem has three nondimensional parameters: the Reynolds number Re , the rotation rate S , and the axial location Z . Small amounts of rotation are found to strongly affect flow stability. This is the result of a nearly neutral mode of the nonrotating cylinder which controls stability at small S . Even small rotation can produce a sufficient perturbation that the mode goes from decaying to growing, with obvious consequences for stability. Without rotation, the flow is stable below a Reynolds number of about 1060 and also beyond a threshold Z . With rotation, no matter how small, instability is no longer constrained by a minimum Re nor a maximum Z . In particular, the critical Reynolds number goes to zero as Z →∞ , so the flow is always unstable at large enough axial distances from the nose. As Z is increased, the flow goes from stability at small Z to instability at large Z . If the critical Reynolds number is a monotonic decreasing function of Z , as it is for S between about 0.0045 and 5, there is a single boundary in Z , which separates the stable from the unstable part of the flow. On the other hand, when the critical Reynolds number is nonmonotonic, there can, depending on the choice of Re , be several such boundaries and flow stability switches more than once as Z is increased. Detailed results showing the critical Reynolds number as a function of Z for different rotation rates are given. We also obtain an asymptotic expansion of the critical Reynolds number at large Z and use perturbation theory to

  10. Hydrodynamic turbulence in quasi-Keplerian rotating flows

    NASA Astrophysics Data System (ADS)

    Shi, Liang; Hof, Björn; Rampp, Markus; Avila, Marc

    2017-04-01

    We report a direct-numerical-simulation study of the Taylor-Couette flow in the quasi-Keplerian regime at shear Reynolds numbers up to O (105) . Quasi-Keplerian rotating flow has been investigated for decades as a simplified model system to study the origin of turbulence in accretion disks that is not fully understood. The flow in this study is axially periodic and thus the experimental end-wall effects on the stability of the flow are avoided. Using optimal linear perturbations as initial conditions, our simulations find no sustained turbulence: the strong initial perturbations distort the velocity profile and trigger turbulence that eventually decays.

  11. Numerical simulation of fluid flow and heat transfer in a thin liquid film over a rotating disk

    NASA Technical Reports Server (NTRS)

    Rahman, M. M.; Faghri, A.

    1992-01-01

    The results of a numerical simulation of the flow field and associated heat transfer coefficient are presented for the free surface flow of a thin liquid film adjacent to a horizontal rotating disk. The computation has been performed for different flow rates and rotational velocities using a three-dimensional boundary-fitted coordinate system. Since the geometry of the free surface is unknown and dependent on flow rate, rate of rotation, and other parameters, an interative procedure had to be used to ascertain its location. The computed film height agreed well with existing experimental measurements. The flow was dominated by inertia near the entrance and close to the free surface, and dominated by centrifugal force at larger radii and adjacent to the disk. The rotation enhanced the heat transfer coefficient by a significant amount.

  12. Fluid flow up a spinning egg and the Coriolis force

    NASA Astrophysics Data System (ADS)

    Martinez, J. C.; Polatdemir, E.; Bansal, Ankita; Yifeng, Wang; Shengtao, Wang

    2006-07-01

    We study the dynamics of a spinning sphere whose south pole is in touch with the surface of a still body of liquid. When the sphere is turning fast enough, the fluid rises up the sphere, reaches the equator and is flung out as a fountain of droplets. Although the fountain forms for water a weakly viscous fluid, and for propylene glycol a much more viscous fluid, the dynamical situation is different for each. For flows at mid-latitudes on the sphere, we formulate the dynamical equations for the two liquids in terms of Newton's law in a rotating frame, noting that the Coriolis force plays an essential role in both liquids, and obtain qualitative agreement with observations. We also discuss the possible roles played by other forces.

  13. Heat transfer in rotating serpentine passages with trips skewed to the flow

    NASA Technical Reports Server (NTRS)

    Johnson, B. V.; Wagner, J. H.; Steuber, G. D.; Yeh, F. C.

    1992-01-01

    Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large scale, multi-pass, heat transfer model with both radially inward and outward flow. Trip strips, skewed at 45 deg to the flow direction, were machined on the leading and trailing surfaces of the radial coolant passages. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages: coolant-to-wall temperature, rotation number, Reynolds number, and radius-to-passage hydraulic diameter ratio. The first three of these four parameters were varied over ranges which are typical of advanced gas turbine engine operating conditions. Results were correlated and compared to previous results from similar stationary and rotating models with smooth walls and with trip strips normal to the flow direction. The heat transfer coefficients on surfaces, where the heat transfer decreased with rotation and buoyancy, decreased to as low as 40 percent of the value without rotation. However, the maximum values of the heat transfer coefficients with high rotation were only slightly above the highest levels previously obtained with the smooth wall models. It was concluded that (1) both Coriolis and buoyancy effects must be considered in turbine blade cooling designs with trip strips, (2) the effects of rotation are markedly different depending upon the flow direction, and (3) the heat transfer with skewed trip strips is less sensitive to buoyancy than the heat transfer in models with either smooth or normal trips. Therefore, skewed trip strips rather than normal trip strips are recommended and geometry-specific tests are required for accurate design information.

  14. Alignment of dust particles by ion drag forces in subsonic flows

    SciTech Connect

    Piel, Alexander

    2011-07-15

    The role of ion drag forces for the alignment of dust particles is studied for subsonic flows. While alignment by wake-field attraction is a well known mechanism for supersonic flows, it is argued here that ion-scattering forces become more important in subsonic ion flows. A model of non-overlapping collisions is introduced and numerical results are discussed. For typical conditions of dusty plasma experiments, alignment by drag forces is found strong enough to overcome the destabilizing force from Coulomb repulsion between dust particles. It turns out that the major contribution to the horizontal restoring force originates from the transverse momentum transfer, which is usually neglected in ion drag force calculations because of an assumed rotational symmetry of the flow.

  15. Moving objects in a rotating environment: rapid prediction of Coriolis and centrifugal force perturbations.

    PubMed

    Nowak, Dennis A; Hermsdörfer, Joachim; Schneider, Erich; Glasauer, Stefan

    2004-07-01

    Grip force adaptation to Coriolis and centrifugal force perturbations was tested in healthy subjects. Eight subjects were seated in a rotating chamber in a rotating axis position. They each grasped an instrumented object resting on the thumb, which was stabilized by the other fingers from above. Subjects performed horizontal point-to-point movements with the grasped object away and towards the trunk. These movements were directed in a nonparallel fashion towards the axis of rotation prior (40 pre-rotational movements), during (80 per-rotational movements) and following (40 post-rotational movements) clockwise body rotation. During pre- and post-rotational movements two load force peaks of similar magnitude occurred during the acceleratory and deceleratory phases of the movements. Accordingly, a Coriolis force, which was orthogonal and proportional to the linear velocity of the moving arm, as well as a centrifugal force proportional to the system's squared angular velocity and movement amplitude developed during per-rotational movements. The load perturbations altered the load force profile in a characteristic way. The first 10 per-rotational movement sequence revealed that there was a less precise coupling between grip and load force magnitudes and a reduced temporo-spatial co-ordination between grip and load force profiles. With increasing number of per-rotational movements, there was significant improvement in the temporo-spatial co-ordination and in the coupling in force magnitude between grip and load force profiles, indicating an ongoing adaptation process. The coupling between grip and load forces proved to be similarly precise for the last 10 per-rotational movements and for pre-rotational movements, suggesting complete adaptation. Significant effects were observed for the first post rotational movements following adaptation to the per-rotational load characteristics both for the temporal co-ordination between grip and load forces and for the coupling in

  16. The stability of unbounded two- and three-dimensional flows subject to body forces - Some exact solutions

    NASA Astrophysics Data System (ADS)

    Craik, A. D. D.

    1989-01-01

    An account is given of those flows influenced by body forces that admit exact solutions similar to those identified by Craik and Criminale (1986) when body forces are absent. Bayly's (1986) inviscid Floquet stability analysis of elliptical flows is extended to incorporate a Coriolis force. With the exception of a narrow band of rotation speeds, it is found that elliptical-vortex flows are inviscidly unstable to three-dimensional plane-wave disturbances.

  17. Experimental Study of the Flow in a Rotating CVD Reactor

    NASA Astrophysics Data System (ADS)

    Wong, Sun; Meng, Jiandong; Jaluria, Yogesh

    2013-11-01

    An experimental model is developed to study the rotating, vertical, impinging chemical vapor deposition reactor. Deposition occurs only when the system has enough thermal energy. Therefore, understanding the fluid flow and thermal characteristics of the system would provide a good basis to model the thin film deposition process. The growth rate and the uniformity of the film are the two most important factors in the CVD process and these depend strongly on the flow and the thermal transport within the system. Operating parameters, such as inflow velocity, susceptor temperature and rotational speed, are used to create different design simulations. Fluid velocities and temperature distributions are recorded to obtain the effects of different operating parameters. Velocities are recorded by using a rotameter and a hot wire anemometer. The temperatures are recorded by using thermocouples and an infrared thermometer. The effects of buoyancy and rotation are examined. The expermental study is also coupled with a numerical study for validation of the numerical model and to expand the domain. Comparisons between the two models are presented, indicating fair agreement. The numerical model also includes simulation of Gallium Nitride (GaN) thin film deposition. This simulation thus includes mass transport and gas kinetics, along with the flow and heat transfer within the system. A three dimensional simulation is needed due to the rotation of the susceptor. The results obtained as well as the underlying fluid flow phenomena are discussed.

  18. Linear and nonlinear stability of a thermally stratified magnetically driven rotating flow in a cylinder.

    PubMed

    Grants, Ilmars; Gerbeth, Gunter

    2010-07-01

    The stability of a thermally stratified liquid metal flow is considered numerically. The flow is driven by a rotating magnetic field in a cylinder heated from above and cooled from below. The stable thermal stratification turns out to destabilize the flow. This is explained by the fact that a stable stratification suppresses the secondary meridional flow, thus indirectly enhancing the primary rotation. The instability in the form of Taylor-Görtler rolls is consequently promoted. These rolls can only be excited by finite disturbances in the isothermal flow. A sufficiently strong thermal stratification transforms this nonlinear bypass instability into a linear one reducing, thus, the critical value of the magnetic driving force. A weaker temperature gradient delays the linear instability but makes the bypass transition more likely. We quantify the non-normal and nonlinear components of this transition by direct numerical simulation of the flow response to noise. It is observed that the flow sensitivity to finite disturbances increases considerably under the action of a stable thermal stratification. The capabilities of the random forcing approach to identify disconnected coherent states in a general case are discussed.

  19. Unidirectional solidification of Sn- Pb alloys under forced melt flow

    NASA Astrophysics Data System (ADS)

    Kovács, J.; Rogozsán, B.; Rónaföldi, A.; Roósz, A.

    2012-01-01

    Cylindrical Sn-Pb alloy samples of different compositions (10, 20 and 30 wt.-% Pb) were prepared from high purity (4N) components. After metals have been melted, a rotating magnetic field (RMF) with an induction of 150 mT and a frequency of 50 Hz was switched on in order to homogenize the liquid. The electromagnetic field was generated by a 3-phase, 2-pole inductor. Just before the start of the solidification process, the magnetic field was switched off to achieve a microstructure free of melt flow influence. The sample translation velocity was constant (0.05 mm/s), and the temperature gradient changed from 7 to 3 K/mm during the solidification process. The first half part of each sample solidified without influence of rotating magnetic field while solidification of the second half part proceeded under the action of the RMF. The columnar microstructure formed in the absence of RMF induced fluid flow was replaced after switching on the RMF by a characteristic "Christmas tree"- like macro-segregated structure with equiaxed dendrites. The secondary dendrite arm spacing and the volume fraction of primary tin phase (dendrite) were measured by an automatic image analyzer on the longitudinal polished sections along the whole length of the samples. The effect of the forced melt flow and alloy composition on its micro- and macrostructure development was investigated.

  20. Toward a Turbulence Constitutive Relation for Rotating Flows

    NASA Technical Reports Server (NTRS)

    Ristorcelli, J. R.

    1996-01-01

    In rapidly rotating turbulent flows the largest scales of the motion are in approximate geostrophic balance. Single-point turbulence closures, in general, cannot attain a geostrophic balance. This article addresses and resolves the possibility of constitutive relation procedures for single-point second order closures for a specific class of rotating or stratified flows. Physical situations in which the geostrophic balance is attained are described. Closely related issues of frame-indifference, horizontal nondivergence, Taylor-Proudman theorem and two-dimensionality are, in the context of both the instantaneous and averaged equations, discussed. It is shown, in the absence of vortex stretching along the axis of rotation, that turbulence is frame-indifferent. A derivation and discussion of a geostrophic constraint which the prognostic equations for second-order statistics must satisfy for turbulence approaching a frame-indifferent limit is given. These flow situations, which include rotating and nonrotating stratified flows, are slowly evolving flows in which the constitutive relation procedures are useful. A nonlinear non-constant coefficient representation for the rapid-pressure strain covariance appearing in the Reynolds stress and heat flux equations consistent with the geostrophic balance is described. The rapid-pressure strain model coefficients are not constants determined by numerical optimization but are functions of the state of the turbulence as parameterized by the Reynolds stresses and the turbulent heat fluxes. The functions are valid for all states of the turbulence attaining their limiting values only when a limit state is achieved. These issues are relevant to strongly vortical flows as well as flows such as the planetary boundary layers, in which there is a transition from a three-dimensional shear driven turbulence to a geostrophic or horizontal turbulence.

  1. Turbulent Compressible Convection with Rotation. Part 1; Flow Structure and Evolution

    NASA Technical Reports Server (NTRS)

    Brummell, Nicholas H.; Hurlburt, Neal E.; Toomre, Juri

    1996-01-01

    The effects of Coriolis forces on compressible convection are studied using three-dimensional numerical simulations carried out within a local modified f-plane model. The physics is simplified by considering a perfect gas occupying a rectilinear domain placed tangentially to a rotating sphere at various latitudes, through which a destabilizing heat flux is driven. The resulting convection is considered for a range of Rayleigh, Taylor, and Prandtl (and thus Rossby) numbers, evaluating conditions where the influence of rotation is both weak and strong. Given the computational demands of these high-resolution simulations, the parameter space is explored sparsely to ascertain the differences between laminar and turbulent rotating convection. The first paper in this series examines the effects of rotation on the flow structure within the convection, its evolution, and some consequences for mixing. Subsequent papers consider the large-scale mean shear flows that are generated by the convection, and the effects of rotation on the convective energetics and transport properties. It is found here that the structure of rotating turbulent convection is similar to earlier nonrotating studies, with a laminar, cellular surface network disguising a fully turbulent interior punctuated by vertically coherent structures. However, the temporal signature of the surface flows is modified by inertial motions to yield new cellular evolution patterns and an overall increase in the mobility of the network. The turbulent convection contains vortex tubes of many scales, including large-scale coherent structures spanning the full vertical extent of the domain involving multiple density scale heights. Remarkably, such structures align with the rotation vector via the influence of Coriolis forces on turbulent motions, in contrast with the zonal tilting of streamlines found in laminar flows. Such novel turbulent mechanisms alter the correlations which drive mean shearing flows and affect the

  2. The processes of nonequilibrium exchange in rotating plasma flows

    NASA Astrophysics Data System (ADS)

    Karimov, A. R.; Shatokhin, V. L.; Yu, M. Y.; Stenflo, L.

    2016-09-01

    The mechanisms of energy/momentum exchange in rotating and compressing plasma flows have been discussed. It has been shown that such flows are capable of transforming the energy of different degrees of freedom into the energy of one degree owing to the interaction of the coupled nonlinear radial, axial and azimuthal electron-ion oscillations. These processes may lead to the additional acceleration of the flow in azimuthal or axial direction so they might be instrumental for the creation of space thrusters employing pulse transformations for propulsion.

  3. Structure parameters in rotating Couette-Poiseuille channel flow

    NASA Technical Reports Server (NTRS)

    Knightly, George H.; Sather, D.

    1986-01-01

    It is well-known that a number of steady state problems in fluid mechanics involving systems of nonlinear partial differential equations can be reduced to the problem of solving a single operator equation of the form: v + lambda Av + lambda B(v) = 0, v is the summation of H, lambda is the summation of one-dimensional Euclid space, where H is an appropriate (real or complex) Hilbert space. Here lambda is a typical load parameter, e.g., the Reynolds number, A is a linear operator, and B is a quadratic operator generated by a bilinear form. In this setting many bifurcation and stability results for problems were obtained. A rotating Couette-Poiseuille channel flow was studied, and it showed that, in general, the superposition of a Poiseuille flow on a rotating Couette channel flow is destabilizing.

  4. Centrifugal Force Based Magnetic Micro-Pump Driven by Rotating Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Kim, S. H.; Hashi, S.; Ishiyama, K.

    2011-01-01

    This paper presents a centrifugal force based magnetic micro-pump for the pumping of blood. Most blood pumps are driven by an electrical motor with wired control. To develop a wireless and battery-free blood pump, the proposed pump is controlled by external rotating magnetic fields with a synchronized impeller. Synchronization occurs because the rotor is divided into multi-stage impeller parts and NdFeB permanent magnet. Finally, liquid is discharged by the centrifugal force of multi-stage impeller. The proposed pump length is 30 mm long and19 mm in diameter which much smaller than currently pumps; however, its pumping ability satisfies the requirement for a blood pump. The maximum pressure is 120 mmHg and the maximum flow rate is 5000ml/min at 100 Hz. The advantage of the proposed pump is that the general mechanical problems of a normal blood pump are eliminated by the proposed driving mechanism.

  5. Flow behavior inside a novel rotating fluidized bed for solar gasification of biomass

    NASA Astrophysics Data System (ADS)

    Lu, Zhao; Jafarian, Mehdi; Chinnici, Alfonso; Arjomandi, Maziar; Nathan, Graham J.

    2017-06-01

    The present paper reports a numerical investigation of the iso-thermal flow field and particle deposition onto the reactor window of a novel concept of Rotating Fluidized Bed Solar Reactor (RFBSR) and their sensitivity to reactor inner diameter. The RFBSR differs from conventional fluidized bed solar reactors in that it relies on the centrifugal force generated through rotation to counteract the drag force produced by the fluidizing gas on the particles. A three dimensional Computational Fluid Dynamics (CFD) model of the RFBSR was developed and combined with a Lagrangian particle tracking model to investigate the flow velocity components at various locations and particle concentration onto the window surface. The CFD model was partially verified by comparing its predictions with the published experimental measurements in a rotating porous cylindrical vessel with a radially injected flow. It was found that the Baseline Reynold Stress Model (RSM BSL) produces more agreeable predictions with the experimental measurements than Re-Normalization Group (RNG) k-ɛ and k-ω Shear Stress Transport (SST) models. Also, it was found that for the reactor configurations investigated here, reducing the reactor diameter has the effects of increasing the core axial flow velocity and particle deposition onto the window. The results presented assist in developing an understanding of the operation of the RFBSR.

  6. Internal Flow of Contra-Rotating Small Hydroturbine at Off- Design Flow Rates

    NASA Astrophysics Data System (ADS)

    SHIGEMITSU, Toru; TAKESHIMA, Yasutoshi; OGAWA, Yuya; FUKUTOMI, Junichiro

    2016-11-01

    Small hydropower generation is one of important alternative energy, and enormous potential lie in the small hydropower. However, efficiency of small hydroturbines is lower than that of large one. Then, there are demands for small hydroturbines to keep high performance in wide flow rate range. Therefore, we adopted contra-rotating rotors, which can be expected to achieve high performance. In this research, performance of the contra-rotating small hydroturbine with 60mm casing diameter was investigated by an experiment and numerical analysis. Efficiency of the contra-rotating small hydroturbine was high in pico-hydroturbine and high efficiency could be kept in wide flow rate range, however the performance of a rear rotor decreased significantly in partial flow rates. Then, internal flow condition, which was difficult to measure experimentally, was investigated by the numerical flow analysis. Then, a relation between the performance and internal flow condition was considered by the numerical analysis result.

  7. Control of Oscillatory Forces on a Circular Cylinder by Rotation

    DTIC Science & Technology

    1991-08-01

    coefficients. Of special interest is the formulation of an optimal control problem for the case of constant speed of rotation. We find an optimal rotation rate that achieves the maximum value of time -averaged lift/drag ratio.

  8. Viscous free-surface flows on rotating elliptical cylinders

    NASA Astrophysics Data System (ADS)

    Li, Weihua; Carvalho, Marcio S.; Kumar, Satish

    2017-09-01

    The flow of liquid films on rotating discrete objects having complicated cross sections is encountered in coating processes for a broad variety of products. To advance fundamental understanding of this problem, we study viscous free-surface flows on rotating elliptical cylinders by solving the governing equations in a rotating reference frame using the Galerkin finite-element method. Results of our simulations agree well with Hunt's maximum-load condition [Hunt, Numer. Methods Partial Differ. Eqs. 24, 1094 (2008), 10.1002/num.20307], which was obtained in the absence of surface tension and inertia. The simulations are also used to track the transient behavior of the free surface. For O (1 ) cylinder aspect ratios, cylinder rotation results in a droplike liquid bulge hanging on the upward-moving side of the cylinder. This bulge shrinks in size due to surface tension provided that the liquid load is smaller than a critical value, leaving a relatively smooth coating on the cylinder. A decrease in cylinder aspect ratio leads to larger gradients in film thickness, but enhances the rate of bulge shrinkage and thus shortens the time required to obtain a smooth coating. Moreover, with a suitably chosen time-dependent rotation rate, more liquid can be supported by the cylinder relative to the constant-rotation-rate case. For cylinders with even smaller aspect ratios, film rupture and liquid shedding may occur over the cylinder tips, so simultaneous drying and rotation along with the introduction of Marangoni stresses will likely be especially important for obtaining a smooth coating.

  9. Energetic dynamics of a rotating horizontal convection model of an ocean basin with wind forcing

    NASA Astrophysics Data System (ADS)

    Zemskova, Varvara; White, Brian; Scotti, Alberto

    2016-11-01

    We analyze the energetic dynamics in a rotating horizontal convection model, where flow is driven by a differential buoyancy forcing along a horizontal surface. This model is used to quantify the influence of surface heating and cooling and surface wind stress on the Meridional Overturning Circulation. We study a model of the Southern Ocean in a rectangular basin with surface cooling on one end (the South pole) and surface warming on the other end (mid-latitudes). Free-slip boundary conditions are imposed in the closed box, while zonally periodic boundary conditions are enforced in the reentrant channel. Wind stress and differential buoyancy forcing are applied at the top boundary. The problem is solved numerically using a 3D DNS model based on a finite-volume AMR solver for the Boussinesq Navier-Stokes equations with rotation. The overall dynamics, including large-scale overturning, baroclinic eddying, turbulent mixing, and resulting energy cascades are investigated using the local Available Potential Energy framework introduced in. We study the relative contributions of surface buoyancy and wind forcing along with the effects of bottom topography to the energetic balance of this dynamic model. This research is part of the Blue Waters sustained-petascale computing project, supported by the NSF (awards OCI-0725070, ACI-1238993 and ACI-14-44747) and the state of Illinois.

  10. Dynamics and Statistical Mechanics of Rotating and non-Rotating Vortical Flows

    SciTech Connect

    Lim, Chjan

    2013-12-18

    Three projects were analyzed with the overall aim of developing a computational/analytical model for estimating values of the energy, angular momentum, enstrophy and total variation of fluid height at phase transitions between disordered and self-organized flow states in planetary atmospheres. It is believed that these transitions in equilibrium statistical mechanics models play a role in the construction of large-scale, stable structures including super-rotation in the Venusian atmosphere and the formation of the Great Red Spot on Jupiter. Exact solutions of the spherical energy-enstrophy models for rotating planetary atmospheres by Kac's method of steepest descent predicted phase transitions to super-rotating solid-body flows at high energy to enstrophy ratio for all planetary spins and to sub-rotating modes if the planetary spin is large enough. These canonical statistical ensembles are well-defined for the long-range energy interactions that arise from 2D fluid flows on compact oriented manifolds such as the surface of the sphere and torus. This is because in Fourier space available through Hodge theory, the energy terms are exactly diagonalizable and hence has zero range, leading to well-defined heat baths.

  11. Zonal shear and super-rotation in a magnetized spherical Couette-flow experiment.

    PubMed

    Brito, D; Alboussière, T; Cardin, P; Gagnière, N; Jault, D; La Rizza, P; Masson, J-P; Nataf, H-C; Schmitt, D

    2011-06-01

    We present measurements performed in a spherical shell filled with liquid sodium, where a 74-mm-radius inner sphere is rotated while a 210-mm-radius outer sphere is at rest. The inner sphere holds a dipolar magnetic field and acts as a magnetic propeller when rotated. In this experimental setup called "Derviche Tourneur Sodium" (DTS), direct measurements of the velocity are performed by ultrasonic Doppler velocimetry. Differences in electric potential and the induced magnetic field are also measured to characterize the magnetohydrodynamic flow. Rotation frequencies of the inner sphere are varied between -30 Hz and +30 Hz, the magnetic Reynolds number based on measured sodium velocities and on the shell radius reaching to about 33. We have investigated the mean axisymmetric part of the flow, which consists of differential rotation. Strong super-rotation of the fluid with respect to the rotating inner sphere is directly measured. It is found that the organization of the mean flow does not change much throughout the entire range of parameters covered by our experiment. The direct measurements of zonal velocity give a nice illustration of Ferraro's law of isorotation in the vicinity of the inner sphere, where magnetic forces dominate inertial ones. The transition from a Ferraro regime in the interior to a geostrophic regime, where inertial forces predominate, in the outer regions has been well documented. It takes place where the local Elsasser number is about 1. A quantitative agreement with nonlinear numerical simulations is obtained when keeping the same Elsasser number. The experiments also reveal a region that violates Ferraro's law just above the inner sphere.

  12. Compressibility effects on the flow past a rotating cylinder

    NASA Astrophysics Data System (ADS)

    Teymourtash, A. R.; Salimipour, S. E.

    2017-01-01

    In this paper, laminar flow past a rotating circular cylinder placed in a compressible uniform stream is investigated via a two-dimensional numerical simulation and the compressibility effects due to the combination of the free-stream and cylinder rotation on the flow pattern such as forming, shedding, and removing of vortices and also the lift and drag coefficients are studied. The numerical simulation of the flow is based on the discretization of convective fluxes of the unsteady Navier-Stokes equations by second-order Roe's scheme and an explicit finite volume method. Because of the importance of the time dependent parameters in the solution, the second-order time accurate is applied by a dual time stepping approach. In order to validate the operation of a computer program, some results are compared with previous experimental and numerical data. The results of this study show that the effects due to flow compressibility such as normal shock wave caused the interesting variations on the flow around the cylinder even at a free-stream with a low Mach number. At incompressible flow around the rotating cylinder, increasing the speed ratio, α (ratio of the surface speed to free-stream velocity), causes the ongoing increase in the lift coefficient, but in compressible flow for each free-stream Mach number, increasing the speed ratio results in obtaining a limited lift coefficient (a maximum mean lift coefficient). In addition, results from the compressible flow indicate that by increasing the free-stream Mach number, the maximum mean lift coefficient is decreased, while the mean drag coefficient is increased. It is also found that by increasing the Reynolds number at low Mach numbers, the maximum mean lift coefficient and critical speed ratio are decreased and the mean drag coefficient and Strouhal number are increased. However at the higher Mach numbers, these parameters become independent of the Reynolds number.

  13. Heat transfer in rotating serpentine passages with trips skewed to the flow

    NASA Technical Reports Server (NTRS)

    Johnson, B. V.; Wagner, J. H.; Steuber, G. D.; Yeh, F. C.

    1992-01-01

    Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large scale, multi-pass heat transfer model with both radially inward and outward flow. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages: coolant-to-wall temperature, rotation number, Reynolds number, and radius-to-passage hydraulic diameter ratio. Results were correlated and compared to previous results from similar stationary and rotating models with smooth walls and with trip strips normal to the flow direction. It was concluded that (1) both Coriolis and buoyancy must be considered in turbine blade cooling designs with trip strips, (2) the effects of rotation are markedly different depending upon the flow direction, and (3) the heat transfer with skewed trip strips is less sensitive to buoyancy than the heat transfer models with either smooth or normal trips. Therefore, skewed trip strips rather than normal trip strips are recommended and geometry-specific tests are required for accurate design.

  14. Rotating permanent magnet excitation for blood flow measurement.

    PubMed

    Nair, Sarath S; Vinodkumar, V; Sreedevi, V; Nagesh, D S

    2015-11-01

    A compact, portable and improved blood flow measurement system for an extracorporeal circuit having a rotating permanent magnetic excitation scheme is described in this paper. The system consists of a set of permanent magnets rotating near blood or any conductive fluid to create high-intensity alternating magnetic field in it and inducing a sinusoidal varying voltage across the column of fluid. The induced voltage signal is acquired, conditioned and processed to determine its flow rate. Performance analysis shows that a sensitivity of more than 250 mV/lpm can be obtained, which is more than five times higher than conventional flow measurement systems. Choice of rotating permanent magnet instead of an electromagnetic core generates alternate magnetic field of smooth sinusoidal nature which in turn reduces switching and interference noises. These results in reduction in complex electronic circuitry required for processing the signal to a great extent and enable the flow measuring device to be much less costlier, portable and light weight. The signal remains steady even with changes in environmental conditions and has an accuracy of greater than 95%. This paper also describes the construction details of the prototype, the factors affecting sensitivity and detailed performance analysis at various operating conditions.

  15. The energy transfer mechanism of a perturbed solid-body rotation flow in a rotating pipe

    NASA Astrophysics Data System (ADS)

    Feng, Chunjuan; Liu, Feng; Rusak, Zvi; Wang, Shixiao

    2017-04-01

    Three-dimensional direct numerical simulations of a solid-body rotation superposed on a uniform axial flow entering a rotating constant-area pipe of finite length are presented. Steady in time profiles of the radial, axial, and circumferential velocities are imposed at the pipe inlet. Convective boundary conditions are imposed at the pipe outlet. The Wang and Rusak (Phys. Fluids 8:1007-1016, 1996. doi: 10.1063/1.86882) axisymmetric instability mechanism is retrieved at certain operational conditions in terms of incoming flow swirl levels and the Reynolds number. However, at other operational conditions there exists a dominant, three-dimensional spiral type of instability mode that is consistent with the linear stability theory of Wang et al. (J. Fluid Mech. 797: 284-321, 2016). The growth of this mode leads to a spiral type of flow roll-up that subsequently nonlinearly saturates on a large amplitude rotating spiral wave. The energy transfer mechanism between the bulk of the flow and the perturbations is studied by the Reynolds-Orr equation. The production or loss of the perturbation kinetic energy is combined of three components: the viscous loss, the convective loss at the pipe outlet, and the gain of energy at the outlet through the work done by the pressure perturbation. The energy transfer in the nonlinear stage is shown to be a natural extension of the linear stage with a nonlinear saturated process.

  16. The energy transfer mechanism of a perturbed solid-body rotation flow in a rotating pipe

    NASA Astrophysics Data System (ADS)

    Feng, Chunjuan; Liu, Feng; Rusak, Zvi; Wang, Shixiao

    2017-03-01

    Three-dimensional direct numerical simulations of a solid-body rotation superposed on a uniform axial flow entering a rotating constant-area pipe of finite length are presented. Steady in time profiles of the radial, axial, and circumferential velocities are imposed at the pipe inlet. Convective boundary conditions are imposed at the pipe outlet. The Wang and Rusak (Phys. Fluids 8:1007-1016, 1996. doi: 10.1063/1.86882) axisymmetric instability mechanism is retrieved at certain operational conditions in terms of incoming flow swirl levels and the Reynolds number. However, at other operational conditions there exists a dominant, three-dimensional spiral type of instability mode that is consistent with the linear stability theory of Wang et al. (J. Fluid Mech. 797: 284-321, 2016). The growth of this mode leads to a spiral type of flow roll-up that subsequently nonlinearly saturates on a large amplitude rotating spiral wave. The energy transfer mechanism between the bulk of the flow and the perturbations is studied by the Reynolds-Orr equation. The production or loss of the perturbation kinetic energy is combined of three components: the viscous loss, the convective loss at the pipe outlet, and the gain of energy at the outlet through the work done by the pressure perturbation. The energy transfer in the nonlinear stage is shown to be a natural extension of the linear stage with a nonlinear saturated process.

  17. A theoretical study of fluid forces on a centrifugal impeller rotating and whirling in a vaned diffuser

    NASA Technical Reports Server (NTRS)

    Tsujimoto, Yoshinobu; Acosta, Allan J.; Yoshida, Yoshiki

    1989-01-01

    The fluid forces on a centrifugal impeller rotating and whirling in a vaned diffuser are analyzed on the assumption that the number of impeller and diffuser vanes is so large that the flows are perfectly guided by the vanes. The flow is taken to be two dimensional, inviscid, and incompressible, but the effects of impeller and diffuser losses are taken into account. It is shown that the interaction with the vaned diffuser may cause destabilizing fluid forces. From these discussions, it is found that the whirling forces are closely related to the steady head-capacity characteristics of the impeller. This physical understanding of the whirling forces can be applied also to the cases with volute casings. At partial capacities, it is shown that the impeller forces change greatly when the flow rate and whirl velocity are near to the impeller or vaned diffuser attributed rotating stall onset capacity, and the stall propagation velocity, respectively. In such cases the impeller forces may become destabilizing for impeller whirl.

  18. Drag Force Anemometer Used in Supersonic Flow

    NASA Technical Reports Server (NTRS)

    Fralick, Gustave C.

    1998-01-01

    To measure the drag on a flat cantilever beam exposed transversely to a flow field, the drag force anemometer (beam probe) uses strain gauges attached on opposite sides of the base of the beam. This is in contrast to the hot wire anemometer, which depends for its operation on the variation of the convective heat transfer coefficient with velocity. The beam probe retains the high-frequency response (up to 100 kHz) of the hot wire anemometer, but it is more rugged, uses simpler electronics, is relatively easy to calibrate, is inherently temperature compensated, and can be used in supersonic flow. The output of the probe is proportional to the velocity head of the flow, 1/2 rho u(exp 2) (where rho is the fluid density and u is the fluid velocity). By adding a static pressure tap and a thermocouple to measure total temperature, one can determine the Mach number, static temperature, density, and velocity of the flow.

  19. Slip flow by a variable thickness rotating disk subject to magnetohydrodynamics

    NASA Astrophysics Data System (ADS)

    Imtiaz, Maria; Hayat, Tasawar; Alsaedi, Ahmed; Asghar, Saleem

    Objective of the present study is to determine the characteristics of magnetohydrodynamic flow by a rotating disk having variable thickness. At the fluid-solid interface we consider slip velocity. The governing nonlinear partial differential equations of the problem are converted into a system of nonlinear ordinary differential equations. Obtained series solutions of velocity are convergent. Impact of embedded parameters on fluid flow and skin friction coefficient is graphically presented. It is observed that axial and radial velocities have an opposite impact on the thickness coefficient of disk. Also surface drag force has a direct relationship with Hartman number.

  20. Experimental study of convective heat transfer of compressed air flow in radially rotating ducts

    SciTech Connect

    Hwang, G.J,; Tzeng, S.C.; Mao, C.P.

    1999-07-01

    The convective heat transfer of pressurized air flow in radially rotating serpentine channel is investigated experimentally in the present study. The main governing parameters are the Prandtl number, the Reynolds number for forced convection, the rotation number for the Coriolis force induced cross stream secondary flow and the Grashof number for natural convection. To simulate the operation conditions of a real gas turbine, the present study kept the parameters in the test rig approximately the same as those in a real engine. The air in the present serpentine channel was pressurized to increase the air density for making up the low rotational speed in the experiment. Before entering the rotating ducts, the air was also cooled to gain a high density ratio of approximately 1/3 in the ducts. This high density ratio will give a similar order of magnitude of Grashof number in a real operation condition. The local heat transfer rate on the four channel walls are present and compared with that in existing literature.

  1. Measuring Photospheric Rotational and Meridional Flows Using Magnetic Feature Tracking

    NASA Astrophysics Data System (ADS)

    Lamb, Derek

    2016-05-01

    Long-lived rotational and meridional flows are important ingredients of the solar cycle. Using magnetic field images to measure these flows on the solar surface has typically been performed by cross-correlating thin longitudinal strips or square patches across sufficiently long time gaps. Here, I use one month of SDO/HMI line-of-sight magnetic field observations, combined with the SWAMIS magnetic feature tracking algorithm to measure the motion of individual features in these magnetograms. By controlling for perturbations due to short-lived flows and due to false motions from feature interactions, I effectively isolate the long-lived flows traced by the magnetic features. This allows me to produce high-fidelity differential rotation measurements with well-characterized variances and covariances of the fit parameters. I also produce medium-fidelity measurements of the much weaker meridional flow that is broadly consistent with previous results, showing a peak flow of 16.7 m/s at 45 degrees latitude. This work shows that measuring the motions of individual features in photospheric magnetograms can produce high precision results in relatively short time spans, which suggests that high resolution non-longitudinally averaged photospheric velocity residual measurements could be produced to compare with coronal results, and to provide other diagnostics of the solar dynamo. This work has been partially supported by NASA Grants NNX11AP03G and NNX14AJ67G.

  2. Granular flow along the interior surface of rotating cones

    SciTech Connect

    Pitts, J.H.; Walton, O.R.

    1984-04-26

    Relationships are developed between the effective cone half-angle, ..cap alpha../sub eff/, and the actual cone half-angle, ..cap alpha.., for subcritical flow of granular material along the inside surface of a rotating cone. Rotational speed must be high enough to keep the granular material against the wall. If ..cap alpha../sub eff/ is between the wall friction angle, phi/sub w/ and the angle of repose, phi/sub r/, the flowrate may be controlled at the exit and depends on the exit aperture area and the rotational speed. Laboratory experiments show that exit control is possible over the entire range of effective cone half-angles from phi/sub w/ < ..cap alpha../sub eff/ < phi/sub r/ and even beyond these limits. The most uniform thickness of granular material is obtained when the cone half-angle is close to phi/sub r/.

  3. Flow development through HP & LP turbines, Part I: Inward rotating cavity flow with superimposed throughflow

    NASA Astrophysics Data System (ADS)

    Gao, Jinhai; Du, Qiang; Liu, Jun; Liu, Guang; Wang, Pei; Liu, Hongrui; Du, Meimei

    2017-08-01

    With the aid of numerical method, both flow field and its accompanied loss mechanism within the rotating cavity are investigated in detail in the 1st part of the two parts paper. For ease of comparison, rotating cavity is further classified as the rotor-stator cavity case and the rotor-rotor cavity case. Results indicate that flow within both kinds of the cavity act as the inviscid flow except that the flow near walls, neighboring the lower G region and in the vicinity of the rotating orifices. In the regions except such inviscid-flow-dominate domains, the theoretical core rotation factor can be safely used to predict the swirl ratio within the cavity. When detailed flow pattern is considered, Ekman-type flow exists near periphery of the surface's boundary layer where viscous effect is non-negligible. However, due to the complex profile of the simulated cavity case, vortices structure is varied within the cavity. By comparison, swirl ratio can be used to predict the magnitude of loss. Due to the relatively evident rotating effects of the rotor-rotor cavity, swirl ratio even increases to 1.4 in the current model, which means that flow is moving faster than the surrounding disc. Further investigation finds that this kind of highly rotating flow is accompanied with serious undesirable pressure loss. Parenthetically, unlike its counterpart, swirl ratio above 1.0 doesn't happen when fluid passes through the rotor-stator cavity. So it is suggested that rotor-rotor flow cavity with the superimposed inward throughflow should be avoided in the engine design or certain measurements should be provided when such structure design is unavoidable. Simulation done in the current paper is meaningful since these dimensional parameters are typical in the design of state-of-art. Relatively lower range of Re φ and C w is not considered in the current two parts paper.

  4. Liquid-metal flow in a finite-length cylinder with a high-frequency rotating magnetic field

    NASA Astrophysics Data System (ADS)

    Witkowski, L. Martin; Marty, P.; Walker, J. S.

    2001-06-01

    A liquid-metal flow driven by a rotating magnetic field in a finite-length cylinder is studied numerically as a function of the field frequency. In the high-frequency case, the magnetic field is expelled from the liquid-metal except in a skin-depth layer along the side and top walls of the cylinder. In the corner region, where the skin-depth layers intersect, the body force exhibits a large positive and negative azimuthal component as well as inward radial and axial components which are rotational. The flows for various frequencies are compared to the low-frequency flow.

  5. Flow of an electrorheological fluid between eccentric rotating cylinders

    NASA Astrophysics Data System (ADS)

    Průša, Vít; Rajagopal, K. R.

    2012-01-01

    Electrorheological fluids have numerous potential applications in vibration dampers, brakes, valves, clutches, exercise equipment, etc. The flows in such applications are complex three-dimensional flows. Most models that have been developed to describe the flows of electrorheological fluids are one-dimensional models. Here, we discuss the behavior of two fully three-dimensional models for electrorheological fluids. The models are such that they reduce, in the case of simple shear flows with the intensity of the electric field perpendicular to the streamlines, to the same constitutive relation, but they would not be identical in more complicated three-dimensional settings. In order to show the difference between the two models, we study the flow of these fluids between eccentrically placed rotating cylinders kept at different potentials, in the setting that corresponds to technologically relevant problem of flow of electrorheological fluid in journal bearing. Even though the two models have quite a different constitutive structure, due to the assumed forms for the velocity and pressure fields, the models lead to the same velocity field but to different pressure fields. This finding illustrates the need for considering the flows of fluids described by three-dimensional constitutive models in complex geometries, and not restricting ourselves to flows of fluids described by one-dimensional models or simple shear flows of fluids characterized by three-dimensional models.

  6. Theory of rotating electrohydrodynamic flows in a liquid film.

    PubMed

    Shiryaeva, E V; Vladimirov, V A; Zhukov, M Yu

    2009-10-01

    The mathematical model of rotating electrohydrodynamic flows in a thin suspended liquid film is proposed and studied. The flows are driven by the given difference of potentials in one direction and constant external electric field E(out) in another direction in the plane of a film. To derive the model, we employ the spatial averaging over the normal coordinate to a film that leads to the average Reynolds stress that is proportional to |E(out)|3. This stress generates tangential velocity in the vicinity of the edges of a film that, in turn, causes the rotational motion of a liquid. The proposed model is used to explain the experimental observations of the liquid film motor.

  7. Retinal flow is sufficient for steering during observer rotation

    NASA Technical Reports Server (NTRS)

    Li, Li; Warren, William H Jr

    2002-01-01

    How do people control locomotion while their eyes are simultaneously rotating? A previous study found that during simulated rotation, they can perceive a straight path of self-motion from the retinal flow pattern, despite conflicting extraretinal information, on the basis of dense motion parallax and reference objects. Here we report that the same information is sufficient for active control ofjoystick steering. Participants steered toward a target in displays that simulated a pursuit eye movement. Steering was highly inaccurate with a textured ground plane (motion parallax alone), but quite accurate when an array of posts was added (motion parallax plus reference objects). This result is consistent with the theory that instantaneous heading is determined from motion parallax, and the path of self-motion is determined by updating heading relative to environmental objects. Retinal flow is thus sufficient for both perceiving self-motion and controlling self-motion with a joystick; extraretinal and positional information can also contribute, but are not necessary.

  8. Precession of a rapidly rotating cylinder flow: traverse through resonance

    NASA Astrophysics Data System (ADS)

    Lopez, Juan; Marques, Francisco

    2014-11-01

    The flow in a rapidly rotating cylinder that is titled and also rotating around another axis can undergo sudden transitions to turbulence. Experimental observations of this have been associated with triadic resonances. The experimental and theoretical results are well-established in the literature, but there remains a lack of understanding of the physical mechanisms at play in the sudden transition from laminar to turbulent flow with very small variations in the governing parameters. Here, we present direct numerical simulations of a traverse in parameter space through an isolated resonance, and describe in detail the bifurcations involved in the sudden transition. U.S. National Science Foundation Grant CBET-1336410 and Spanish Ministry of Education and Science Grant (with FEDER funds) FIS2013-40880.

  9. Steady particulate flows in a horizontal rotating cylinder

    SciTech Connect

    Yamane, K.; Nakagawa, M.; Altobelli, S.A.; Tanaka, T.; Tsuji, Y.

    1998-06-01

    Results of discrete element method (DEM) simulation and magnetic resonance imaging (MRI) experiments are compared for monodisperse granular materials flowing in a half-filled horizontal rotating cylinder. Because opacity is not a problem for MRI, a long cylinder with an aspect ratio {approximately}7 was used and the flow in a thin transverse slice near the center was studied. The particles were mustard seeds and the ratio of cylinder diameter to particle diameter was approximately 50. The parameters compared were dynamic angle of repose, velocity field in a plane perpendicular to the cylinder axis, and velocity fluctuations at rotation rates up to 30 rpm. The agreement between DEM and MRI was good when the friction coefficient and nonsphericity were adjusted in the simulation for the best fit. {copyright} {ital 1998 American Institute of Physics.}

  10. Retinal flow is sufficient for steering during observer rotation

    NASA Technical Reports Server (NTRS)

    Li, Li; Warren, William H Jr

    2002-01-01

    How do people control locomotion while their eyes are simultaneously rotating? A previous study found that during simulated rotation, they can perceive a straight path of self-motion from the retinal flow pattern, despite conflicting extraretinal information, on the basis of dense motion parallax and reference objects. Here we report that the same information is sufficient for active control ofjoystick steering. Participants steered toward a target in displays that simulated a pursuit eye movement. Steering was highly inaccurate with a textured ground plane (motion parallax alone), but quite accurate when an array of posts was added (motion parallax plus reference objects). This result is consistent with the theory that instantaneous heading is determined from motion parallax, and the path of self-motion is determined by updating heading relative to environmental objects. Retinal flow is thus sufficient for both perceiving self-motion and controlling self-motion with a joystick; extraretinal and positional information can also contribute, but are not necessary.

  11. Finite-amplitude solutions in rotating Hagen-Poiseuille flow

    NASA Astrophysics Data System (ADS)

    Pier, Benoît; Kumar, Abhishek; Govindarajan, Rama

    2015-11-01

    While the pipe Poiseuille base flow is linearly stable at all Reynolds numbers, a small amount of rotation of the pipe around its axis induces linear instability beyond a low critical Reynolds number Rc ~= 83 [Pedley, J. Fluid Mech. 1969]. More recently [Fernandez-Feria and del Pino, Phys. Fluids 2002], this configuration has been shown to become absolutely unstable at Reynolds numbers of the same order of magnitude. Using direct numerical simulations, we investigate here finite-amplitude solutions resulting from saturation of exponentially growing small-amplitude initial perturbations. The base flow depends on two dynamical parameters (axial Reynolds number and rotation rate) and the initial perturbation is characterized by its axial wavenumber and its azimuthal mode number. The range of nonlinear waves prevailing in this configuration, the associated nonlinear dispersion relation and the spatial structure of these solutions are systematically obtained by exploring the parameter space. Funding from CEFIPRA is gratefully acknowledged.

  12. An experimental and numerical investigation of thin film flow in an axially rotating horizontal cylinder

    NASA Astrophysics Data System (ADS)

    Lay, Keary; Schultz, William; Perlin, Marc

    2003-11-01

    Two dimensional film flow in an axially rotating horizontal cylinder is studied both experimentally and numerically. The physical setup is a 610 cm long glass tube with inside radius of 1.634 cm. This tube is filled partially with four different fluids: treated water and 1, 20, and 500 cSt silicone oils (dimethylpolysiloxane). The free surface profile is captured via video imaging and laser sheet illumination of the dye laden fluid. Transition to rimming flow (snap through") during rotational acceleration as well as from rimming flow during deceleration is recorded. A long working distance microscope observes the depth of the thin film region as it reenters the "puddle" during non-rimming flow. A lubrication analysis numerical study includes centrifugal force in addition to pressure gradients in the direction of the polar angle [1]. Surface profiles generated from the experiments are compared with this simulation as well as other numerical and analytical studies. 1. Liu, Z. 2001 "Film flow within an axially rotating horizontal cylinder and contact lines on an oscillating plate," Ph.D. dissertation, University of Michigan.

  13. On the low-Reynolds-number flow about two rotating circular cylinders

    NASA Astrophysics Data System (ADS)

    Ueda, Y.; Sellier, A.; Kida, T.; Nakanishi, M.

    2003-11-01

    The viscous and steady flow about two distinct parallel infinite rotating circular cylinders is theoretically investigated. Because any inner steady Stokes flow is not quiescent far from the cylinders, a strictly steady analysis requires matching an inner steady Stokes approximation with an outer solution of the steady Navier Stokes equations. However, except for the case of identical cylinders of equal angular velocities, it is impossible to determine this outer solution. In the same spirit as Nakanishi et al. (1997) and Ueda et al. (2001), the present work therefore first addresses the unsteady viscous flow induced by cylinders impulsively set into both steady rotation and translation {bm W}. Using integral representations of the stream function and the vorticity, the resulting long-time flow is approximated in the limit of large viscosity. Letting time tend to infinity for {bm W} non-zero extends Lee & Leal (1986) and agrees with Watson (1996), whereas the required steady flow is obtained by making {bm W} vanish before letting time go to infinity. At the obtained leading-order approximation, the ‘lift’ and ‘drag’ forces on each cylinder (parallel and normal to the line of centres) are respectively zero and independent of the Reynolds number. The drag experienced by each body is plotted versus the gap between the cylinders for several values of the rotation, both for identical and non-identical cylinders.

  14. The impact of rotator cuff tendinopathy on proprioception, measuring force sensation.

    PubMed

    Maenhout, Annelies G; Palmans, Tanneke; De Muynck, Martine; De Wilde, Lieven F; Cools, Ann M

    2012-08-01

    The impact of rotator cuff tendinopathy and related impingement on proprioception is not well understood. Numerous quantitative and qualitative changes in shoulder muscles have been shown in patients with rotator cuff tendinopathy. These findings suggest that control of force might be affected. This investigation wants to evaluate force sensation, a submodality of proprioception, in patients with rotator cuff tendinopathy. Thirty-six patients with rotator cuff tendinopathy and 30 matched healthy subjects performed force reproduction tests to isometric external and internal rotation to investigate how accurately they could reproduce a fixed target (50% MVC). Relative error, constant error, and force steadiness were calculated to evaluate respectively magnitude of error made during the test, direction of this error (overshoot or undershoot), and fluctuations of produced forces. Patients significantly overshoot the target (mean, 6.04% of target) while healthy subjects underestimate the target (mean, -5.76% of target). Relative error and force steadiness are similar in patients with rotator cuff tendinopathy and healthy subjects. Force reproduction tests, as executed in this study, were found to be highly reliable (ICC 0.849 and 0.909). Errors were significantly larger during external rotation tests, compared to internal rotation. Patients overestimate the target during force reproduction tests. This should be taken into account in the rehabilitation of patients with rotator cuff tendinopathy; however, precision of force sensation and steadiness of force exertion remains unaltered. This might indicate that control of muscle force is preserved. Copyright © 2012 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Mosby, Inc. All rights reserved.

  15. Experiments on Thermal Convection in Rotating Spherical Shells With Radial Gravity: The Geophysical Fluid Flow Cell

    NASA Technical Reports Server (NTRS)

    Hart, John E.

    1996-01-01

    Experiments designed to study the fluid dynamics of buoyancy driven circulations in rotating spherical shells were conducted on the United States Microgravity Laboratory 2 spacelab mission. These experiments address several aspects of prototypical global convection relevant to large scale motions on the Sun, Earth, and on the giant planets. The key feature is the consistent modeling of radially directed gravity in spherical geometry by using dielectric polarization forces. Imagery of the planforms of thermally driven flows for rapidly-rotating regimes shows an initial separation and eventual merger of equatorial and polar convection as the heating (i.e. the Rayleigh number) is increased. At low rotation rates, multiple-states of motion for the same external parameters were observed.

  16. Wave-front propagation of rinsing flows on rotating semiconductor wafers

    NASA Astrophysics Data System (ADS)

    Frostad, John M.; Ylitalo, Andy; Walls, Daniel J.; Mui, David S. L.; Fuller, Gerald G.

    2016-11-01

    The semiconductor manufacturing industry is migrating to a cleaning technology that involves dispersing cleaning solutions onto a rotating wafer, similar to spin-coating. Advantages include a more continuous overall fabrication process, lower particle level, no cross contamination from the back side of a wafer, and less usage of harsh chemicals for a lower environmental impact. Rapid rotation of the wafer during rinsing can be more effective, but centrifugal forces can pull spiral-like ribbons of liquid radially outward from the advancing wave-front where particles can build up, causing higher instances of device failure at these locations. A better understanding of the rinsing flow is essential for reducing yield losses while taking advantage of the benefits of rotation. In the present work, high-speed video and image processing are used to study the dynamics of the advancing wave-front from an impinging jet on a rotating substrate. The flow-rate and rotation-speed are varied for substrates coated with a thin layer of a second liquid that has a different surface tension than the jet liquid. The difference in surface tension of the two fluids gives rise to Marangoni stresses at the interface that have a significant impact on the rinsing process, despite the extremely short time-scales involved.

  17. Unsteady laminar flow with convective heat transfer through a rotating curved square duct with small curvature

    SciTech Connect

    Mondal, Rabindra Nath Shaha, Poly Rani; Roy, Titob; Yanase, Shinichiro

    2016-07-12

    Unsteady laminar flow with convective heat transfer through a curved square duct rotating at a constant angular velocity about the center of curvature is investigated numerically by using a spectral method, and covering a wide range of the Taylor number −300≤Tr≤1000 for the Dean number Dn = 1000. A temperature difference is applied across the vertical sidewalls for the Grashof number Gr = 100, where the outer wall is heated and the inner wall cooled, the top and bottom walls being adiabatic. Flow characteristics are investigated with the effects of rotational parameter, Tr, and the pressure-driven parameter, Dn, for the constant curvature 0.001. Time evolution calculations as well as their phase spaces show that the unsteady flow undergoes through various flow instabilities in the scenario ‘multi-periodic → chaotic → steady-state → periodic → multi-periodic → chaotic’, if Tr is increased in the positive direction. For negative rotation, however, time evolution calculations show that the flow undergoes in the scenario ‘multi-periodic → periodic → steady-state’, if Tr is increased in the negative direction. Typical contours of secondary flow patterns and temperature profiles are obtained at several values of Tr, and it is found that the unsteady flow consists of two- to six-vortex solutions if the duct rotation is involved. External heating is shown to generate a significant temperature gradient at the outer wall of the duct. This study also shows that there is a strong interaction between the heating-induced buoyancy force and the centrifugal-Coriolis instability in the curved channel that stimulates fluid mixing and consequently enhances heat transfer in the fluid.

  18. Flow interaction and noise from a counter rotating propeller

    NASA Technical Reports Server (NTRS)

    Chung, Jin-Deog; Walls, James L.; Nagel, Robert T.

    1991-01-01

    The aerodynamic interaction between the forward and rear rotors in a counter rotating propeller (CRP) system, has been examined using a conditional sampling technique applied to three-dimensional thermal anemometer data. The technique effectively freezes the rotors in any desired relative position and provides the inter-rotor flow field. Axial, radial and circumferential mean flow between rotors is shown relative to the 'fixed' forward rotor for various 'fixed' aft rotor positions. Acoustic far field noise data have also been collected for the same operating conditions. The acoustic results are presented with emphasis on the blade passing frequencies and interaction tone of the CRP.

  19. Flow interaction and noise from a counter rotating propeller

    NASA Technical Reports Server (NTRS)

    Chung, Jin-Deog; Walls, James L.; Nagel, Robert T.

    1991-01-01

    The aerodynamic interaction between the forward and rear rotors in a counter rotating propeller (CRP) system, has been examined using a conditional sampling technique applied to three-dimensional thermal anemometer data. The technique effectively freezes the rotors in any desired relative position and provides the inter-rotor flow field. Axial, radial and circumferential mean flow between rotors is shown relative to the 'fixed' forward rotor for various 'fixed' aft rotor positions. Acoustic far field noise data have also been collected for the same operating conditions. The acoustic results are presented with emphasis on the blade passing frequencies and interaction tone of the CRP.

  20. Modeling turbulence in flows with a strong rotational component

    SciTech Connect

    Burgess, D.E.; O`Rourke, P.J.

    1993-11-01

    We consider the effectiveness of various turbulence models in flows with a strong rotational component. To evaluate the models, we implement them into a one-dimensional test code and make comparisons with experimental data for swirling flow in a cylinder. The K - {epsilon} type turbulence models do poorly in predicting the experimental results. However, we find that the incorporation of a Reynolds stress evolution equation gives good agreement with the experimentally measured mean flow. Modeling the pressure-strain correlation tensor correctly is the key for obtaining good results. A combination of Launder`s basic model together with Yakhot`s dissipation rate equation {sup 3} works best in predicting both the mean flow and the turbulence intensity.

  1. Granular flow in a rotating drum: Experiments and theory

    NASA Astrophysics Data System (ADS)

    Hung, C. Y.; Stark, C. P.; Capart, H.; Li, L.; Smith, B.; Grinspun, E.

    2015-12-01

    Erosion at the base of a debris flow fundamentally controls how large the flow will become and how far it will travel. Experimental observations of this important phenomenon are rather limited, and this lack has led theoretical treatments to making ad hoc assumptions about the basal process. In light of this, we carried out a combination of laboratory experiments and theoretical analysis of granular flow in a rotating drum, a canonical example of steady grain motion in which entrainment rates can be precisely controlled. Our main result is that basal sediment is entrained as the velocity profile adjusts to imbalance in the flow of kinetic energy.Our experimental apparatus consisted of a 40cm-diameter drum, 4cm-deep, half-filled with 2.3mm grains. Rotation rates varied from 1-70 rpm. We varied the effective scale by varying effective gravity from 1g to 70g on a geotechnical centrifuge. The field of grain motion was recorded using high-speed video and mapped using particle tracking velocimetry. In tandem we developed a depth-averaged theory using balance equations for mass, momentum and kinetic energy. We assumed a linearized GDR Midi granular rheology [da Cruz, 2005] and a Coulomb friction law along the sidewalls [Jop et al., 2005]. A scaling analysis of our equations yields a dimensionless "entrainment number" En, which neatly parametrizes the flow geometry in the drum for a wide range of variables, e.g., rotation rate and effective gravity. At low En, the flow profile is planar and kinetic energy is balanced locally in the flow layer. At high En, the flow profile is sigmoidal (yin-yang shaped) and the kinetic energy is dominated by longitudinal, streamwise transfer. We observe different scaling behavior under each of these flow regimes, e.g., between En and kinetic energy, surface slope and flow depth. Our theory correctly predicts their scaling exponents and the value of En at which the regime transition takes place. We are also able to make corrections for

  2. Network flow model of force transmission in unbonded and bonded granular media

    NASA Astrophysics Data System (ADS)

    Tordesillas, Antoinette; Tobin, Steven T.; Cil, Mehmet; Alshibli, Khalid; Behringer, Robert P.

    2015-06-01

    An established aspect of force transmission in quasistatic deformation of granular media is the existence of a dual network of strongly versus weakly loaded particles. Despite significant interest, the regulation of strong and weak forces through the contact network remains poorly understood. We examine this aspect of force transmission using data on microstructural fabric from: (I) three-dimensional discrete element models of grain agglomerates of bonded subspheres constructed from in situ synchrotron microtomography images of silica sand grains under unconfined compression and (II) two-dimensional assemblies of unbonded photoelastic circular disks submitted to biaxial compression under constant volume. We model force transmission as a network flow and solve the maximum flow-minimum cost (MFMC) problem, the solution to which yields a percolating subnetwork of contacts that transmits the "maximum flow" (i.e., the highest units of force) at "least cost" (i.e., the dissipated energy from such transmission). We find the MFMC describes a two-tier hierarchical architecture. At the local level, it encapsulates intraconnections between particles in individual force chains and in their conjoined 3-cycles, with the most common configuration having at least one force chain contact experiencing frustrated rotation. At the global level, the MFMC encapsulates interconnections between force chains. The MFMC can be used to predict most of the force chain particles without need for any information on contact forces, thereby suggesting the network flow framework may have potential broad utility in the modeling of force transmission in unbonded and bonded granular media.

  3. Network flow model of force transmission in unbonded and bonded granular media.

    PubMed

    Tordesillas, Antoinette; Tobin, Steven T; Cil, Mehmet; Alshibli, Khalid; Behringer, Robert P

    2015-06-01

    An established aspect of force transmission in quasistatic deformation of granular media is the existence of a dual network of strongly versus weakly loaded particles. Despite significant interest, the regulation of strong and weak forces through the contact network remains poorly understood. We examine this aspect of force transmission using data on microstructural fabric from: (I) three-dimensional discrete element models of grain agglomerates of bonded subspheres constructed from in situ synchrotron microtomography images of silica sand grains under unconfined compression and (II) two-dimensional assemblies of unbonded photoelastic circular disks submitted to biaxial compression under constant volume. We model force transmission as a network flow and solve the maximum flow-minimum cost (MFMC) problem, the solution to which yields a percolating subnetwork of contacts that transmits the "maximum flow" (i.e., the highest units of force) at "least cost" (i.e., the dissipated energy from such transmission). We find the MFMC describes a two-tier hierarchical architecture. At the local level, it encapsulates intraconnections between particles in individual force chains and in their conjoined 3-cycles, with the most common configuration having at least one force chain contact experiencing frustrated rotation. At the global level, the MFMC encapsulates interconnections between force chains. The MFMC can be used to predict most of the force chain particles without need for any information on contact forces, thereby suggesting the network flow framework may have potential broad utility in the modeling of force transmission in unbonded and bonded granular media.

  4. Numerical study of a rotational MHD flow containing polydisperse nonconducting inclusions in a cylindrical pipe

    SciTech Connect

    Blinov, V.I.; Kazachkov, I.V.; Kolesnichenko, A.F.

    1988-01-01

    Average characteristics are determined for the first stage of MHD flow in a conducting liquid containing nonconducting inclusions in a channel having nonmetallic walls exposed to crossed electric and magnetic fields. For the second stage, a structural approach is used to evaluate particle paths, clumping, and effects on clumping. Using these criteria, the angular velocity of the stationary rotational motion can be approximated. Particle motion in this rotating flow was considered. Particle paths were determined with an M-4030 computer by solving a second-order differential system. The Runge-Kutta method was used. Raising the field frequency and selecting the optimum ratio for the bulk electromagnetic forces was found to increase the particle concentration and the coagulation rate at the center.

  5. Large-scale anisotropy in stably stratified rotating flows

    DOE PAGES

    Marino, R.; Mininni, P. D.; Rosenberg, D. L.; ...

    2014-08-28

    We present results from direct numerical simulations of the Boussinesq equations in the presence of rotation and/or stratification, both in the vertical direction. The runs are forced isotropically and randomly at small scales and have spatial resolutions of up tomore » $1024^3$ grid points and Reynolds numbers of $$\\approx 1000$$. We first show that solutions with negative energy flux and inverse cascades develop in rotating turbulence, whether or not stratification is present. However, the purely stratified case is characterized instead by an early-time, highly anisotropic transfer to large scales with almost zero net isotropic energy flux. This is consistent with previous studies that observed the development of vertically sheared horizontal winds, although only at substantially later times. However, and unlike previous works, when sufficient scale separation is allowed between the forcing scale and the domain size, the total energy displays a perpendicular (horizontal) spectrum with power law behavior compatible with $$\\sim k_\\perp^{-5/3}$$, including in the absence of rotation. In this latter purely stratified case, such a spectrum is the result of a direct cascade of the energy contained in the large-scale horizontal wind, as is evidenced by a strong positive flux of energy in the parallel direction at all scales including the largest resolved scales.« less

  6. Large-scale anisotropy in stably stratified rotating flows

    SciTech Connect

    Marino, R.; Mininni, P. D.; Rosenberg, D. L.; Pouquet, A.

    2014-08-28

    We present results from direct numerical simulations of the Boussinesq equations in the presence of rotation and/or stratification, both in the vertical direction. The runs are forced isotropically and randomly at small scales and have spatial resolutions of up to $1024^3$ grid points and Reynolds numbers of $\\approx 1000$. We first show that solutions with negative energy flux and inverse cascades develop in rotating turbulence, whether or not stratification is present. However, the purely stratified case is characterized instead by an early-time, highly anisotropic transfer to large scales with almost zero net isotropic energy flux. This is consistent with previous studies that observed the development of vertically sheared horizontal winds, although only at substantially later times. However, and unlike previous works, when sufficient scale separation is allowed between the forcing scale and the domain size, the total energy displays a perpendicular (horizontal) spectrum with power law behavior compatible with $\\sim k_\\perp^{-5/3}$, including in the absence of rotation. In this latter purely stratified case, such a spectrum is the result of a direct cascade of the energy contained in the large-scale horizontal wind, as is evidenced by a strong positive flux of energy in the parallel direction at all scales including the largest resolved scales.

  7. Energetic dynamics of a rotating horizontal convection model with wind forcing

    NASA Astrophysics Data System (ADS)

    Zemskova, Varvara; White, Brian; Scotti, Alberto

    2015-11-01

    We present a new test case for rotating horizontal convection, where the flow is driven by differential buoyancy forcing along a horizontal surface. This simple model is used to understand and quantify the influence of surface heating and cooling and wind stress on the Meridional Overturning Circulation. The domain is a rectangular basin with surface cooling at both ends (the poles) and surface warming in the middle (equatorial) region. To model the effect of the Antarctic Circumpolar Current, reentrant channel is placed near the Southern pole. Free-slip boundary conditions are imposed in the closed box, while zonally periodic boundary conditions are enforced in the channel. The problem is solved numerically using a 3D DNS model based on a finite-volume AMR solver for the Boussinesq Navier-Stokes equations with rotation. The relative contributions of surface buoyancy and wind forcing and the energetic balance are analyzed at a Rayleigh number of 108 and a relatively high aspect ratio of [5, 10, 1] in zonal, meridional and vertical directions, respectively. The overall dynamics, including large-scale overturning, baroclinic eddying, and turbulent mixing are investigated using the local Available Potential Energy framework introduced in [Scotti and White, J. Fluid Mech., 2014]. This research is part of the Blue Waters sustained-petascale computing project, supported by the NSF (awards OCI-0725070, ACI-1238993 and ACI-14-44747) and the state of Illinois.

  8. External forcing modulates Pine Island Glacier flow

    NASA Astrophysics Data System (ADS)

    Christianson, K. A.; Bushuk, M.; Holland, D.; Dutrieux, P.; Joughin, I.; Parizek, B. R.; Alley, R. B.; Anandakrishnan, S.; Heywood, K. J.; Jenkins, A.; Nicholls, K. W.; Webber, B.; Muto, A.; Stanton, T. P.

    2015-12-01

    Nearly 50 years ago, Mercer first suggested the Eemian sea-level high stand was a result of a collapse of the marine portions of the West Antarctic ice sheet. Recently, special attention has been paid to West Antarctica's Amundsen Sea Embayment due to its steeply sloping retrograde beds that are well below sea level, and observations of rapid grounding-line retreat, high ice-shelf basal-melt rates, and basin-wide glacier thinning and acceleration. Despite this focus, accurate assessments of the past and future behavior of this embayment remain elusive due to a lack of understanding of calving processes and ice-ocean interactions. Here we present a continuous two-year (2012-2014) time series of oceanographic, borehole, glaciological, and seismological observations of Pine Island Glacier ice shelf, its sub-ice ocean cavity, and the adjacent Amundsen Sea. With these data, we captured the ice shelf's response to a large fluctuation in the temperature of the water (~1 °C) entering the sub-ice-ocean cavity. Initially, the ice shelf slowed by 5%, but, by the end of 2014, it had nearly recovered its earlier speed. The generally smooth changes in ice flow were punctuated by rapid (2-3 week), high-amplitude (~2.5% of the background speed) speedups and slowdowns. Satellite and seismological observations indicate that rapid speedups are caused by reduction of lateral drag along the ice stream's shear margins as a large iceberg calves and that rapid slowdowns may be due to periodic regrounding on bed highs at low tide. Coupled ice-stream/ice-shelf/ocean-plume flowband modeling informed by these new data indicates that the more-gradual changes in speed are related to ocean temperature, ice-front position, and past ice-flow history. Our observations highlight an ice shelf's rapid response to external forcings and that past ice-flow behavior affects subsequent ice response to external forcing. Thus, long-term, multifaceted investigations are necessary to determine whether a

  9. The relation between the instantaneous center of rotation and facet joint forces - A finite element analysis.

    PubMed

    Schmidt, Hendrik; Heuer, Frank; Claes, Lutz; Wilke, Hans-Joachim

    2008-03-01

    The instantaneous center of rotation in a functional spinal unit is an indicator for mechanical disorders and is relevant for the development of motion preserving techniques. In addition to the intervertebral disc, the facet joints also play a major role for load transmission through the spine, providing stability to it. The relationship between the rotation center and facet joint forces is not fully understood, since previous studies have separated both; spinal motion and facet forces. A finite element model of a L4-5 lumbar spinal segment was exposed to an axial compression preload of 500 N. Pure unconstrained moments of 7.5 Nm were additionally applied in the three anatomical main planes. The instantaneous center of rotation and the facet joint forces were investigated. For small moments, the center of rotation was found to be almost in the center of the disc, no matter what motion direction. With an increasing flexion moment, the center of rotation moved anteriorly. The facet joints remained unloaded in flexion. With proceeding extension movement, the center of rotation moved posteriorly. The facet forces increased up to 50 N. In lateral bending, with increasing moment the center of rotation migrated posteriorly in the ipsilateral side of the disc. The forces in the facet joints rose to 36 N. In axial rotation, the center of rotation migrated towards the compressed facet joint with increasing moment. Axial rotation yielded the maximum facet forces with 105 N. The determination of the rotation center is highly sensible against measurement resolution obtained during in vivo and in vitro studies. This finite element method can be used to complement the knowledge of the rotation center location from former experimental findings.

  10. Prediction of fluid forces acting on a hand model in unsteady flow conditions.

    PubMed

    Kudo, Shigetada; Yanai, Toshimasa; Wilson, Barry; Takagi, Hideki; Vennell, Ross

    2008-01-01

    The aim of this study was to develop a method to predict fluid forces acting on the human hand in unsteady flow swimming conditions. A mechanical system consisting of a pulley and chain mechanism and load cell was constructed to rotate a hand model in fluid flows. To measure the angular displacement of the hand model a potentiometer was attached to the axis of the rotation. The hand model was then fixed at various angles about the longitudinal axis of the hand model and rotated at different flow velocities in a swimming flume for 258 different trials to approximate a swimmer's stroke in unsteady flow conditions. Pressures were taken from 12 transducers embedded in the hand model at a sampling frequency of 200Hz. The resultant fluid force acting on the hand model was then determined on the basis of the kinetic and kinematic data taken from the mechanical system at the frequency of 200Hz. A stepwise regression analysis was applied to acquire higher order polynomial equations that predict the fluid force acting on the accelerating hand model from the 12 pressure values. The root mean square (RMS) difference between the resultant fluid force measured and that predicted from the single best-fit polynomial equation across all trials was 5N. The method developed in the present study accurately predicted the fluid forces acting on the hand model.

  11. Mean flow interactions of a counter-rotating propeller

    NASA Astrophysics Data System (ADS)

    Chung, Jin-Deog

    The aerodynamic interaction between the forward and rear rotors in a counter rotating (CRP) system, has been examined using a double conditional sampling methodology applied to 3-D thermal anemometer data. The technique effectively freeze the rotors in any desired relative position and provides the inter-rotor flow field. Axial, radial and circumferential steady mean flow between rotors is shown relative to the 'fixed' forward rotor for various 'fixed' rear rotor positions. The effects of the upstream disturbance from the rear rotor on the wakes of the forward rotor blades have been documented. This disturbance occurs in all three flow components and varies with distance from the rear rotor and with radial location. Modulations of the forward wakes depend upon the relative rear rotor locations. As the rear rotor continues to rotate past the forward blade, the location of the peak velocity from the forward blades moves circumferentially and springs back as the cycle repeats for the next rear blade. This is a 'wiggling' motion. Double conditional sampling is also used to evaluate the determining CRP flow field by superposing the flow that would occur as a result of the forward and rear rotors operating separately. Simulation of conditions on both rotors that occur in the CRP configuration is attempted by duplicating alternately RPM's, inflow conditions, angles of attack and power and thrust coefficients. The superposition for the various single rotor operating conditions does not yield an acceptable accuracy of wave forms and magnitude simultaneously. The velocity vectors of the cross-stream component show that superposition does not produce the identical flow direction and magnitude of the actual flow.

  12. Mean Flow Interactions of a Counter-Rotating Propeller

    NASA Astrophysics Data System (ADS)

    Chung, Jin-Deog

    The aerodynamic interaction between the forward and rear rotors in a counter rotating (CRP) system, has been examined using a double conditional sampling methodology applied to 3-D thermal anemometer data. The technique effectively freeze the rotors in any desired relative position and provides the inter-rotor flow field. Axial, radial and circumferential steady mean flow between rotors is shown relative to the "fixed" forward rotor for various "fixed" rear rotor positions. The effects of the upstream disturbance from the rear rotor on the wakes of the forward rotor blades have been documented. This disturbance occurs in all three flow components and varies with distance from the rear rotor and with radial location. Modulations of the forward wakes depend upon the relative rear rotor locations. As the rear rotor continues to rotate past the forward blade, the location of the peak velocity from the forward blades moves circumferentially and springs back as the cycle repeats for the next rear blade. This is a "wiggling" motion. Double conditional sampling is also used to evaluate the determining the CRP flow field by superposing the flow that would occur as a result of the forward and rear rotors operating separately. Simulation of conditions on the both rotors that occur in the CRP configuration is attempted by duplicating alternately RPM's, inflow conditions, angles of attack and power and thrust coefficients. The superposition for the various single rotor operating conditions does not yield an acceptable accuracy of wave forms and magnitude simultaneously. The velocity vectors of the cross-stream component show that superposition does not produce the identical flow direction and magnitude of the actual flow.

  13. Mode competition and destabilization of microfluidic channel flows by the Coriolis force

    NASA Astrophysics Data System (ADS)

    Sengupta, Saunak; Saha, Sandeep; Chakraborty, Suman

    2016-11-01

    Understanding flow stability in inertial microfluidics is very important due to its increased application in medical and chemical engineering. On a steady rotating platform centrifugal actuation drives fluid flow but Coriolis force can destabilize the flow and enhance mixing in a short span. We investigate the role of Coriolis force in micro-mixing and the structure of the roll-cells formed in rotating channel flow using linear stability theory. We conduct a parametric study at different rotation numbers, Reynolds number, axial and spanwise wavenumbers. Our results reveal existence of multiple competing unstable modes (Types I to IV) due to Coriolis force: Types I and II have been reported in literature and are responsible for the formation of evenly-spaced roll-cells. We find new instabilities (Types III and IV) which contribute to the formation of twisted roll cells. The existence of the instabilities is clearly demarcated on a regime map to assist future experiments to identify them. The kinetic energy budget has been analyzed to gain insight into the mechanism of energy transfer by Coriolis force from the mean flow to the perturbations. We make a qualitative comparison of roll-cells predicted by linear stability with previously reported experiments.

  14. Turbulent statistics and flow structures in spanwise-rotating turbulent plane Couette flows

    NASA Astrophysics Data System (ADS)

    Gai, Jie; Xia, Zhenhua; Cai, Qingdong; Chen, Shiyi

    2016-09-01

    A series of direct numerical simulations of spanwise-rotating turbulent plane Couette flows at a Reynolds number of 1300 with rotation numbers Ro between 0 and 0.9 is carried out to investigate the effects of anticyclonic rotation on turbulent statistics and flow structures. Several typical turbulent statistics are presented, including the mean shear rate at the centerline, the wall-friction Reynolds number, and volume-averaged kinetic energies with respect to the secondary flow field, turbulent field, and total fluctuation field. Our results show that the rotation changes these quantities in different manners. Volume-averaged balance equations for kinetic energy are analyzed and it turns out that the interaction term acts as a kinetic energy bridge that transfers energy from the secondary flow to the turbulent fluctuations. Several typical flow regimes are identified based on the correlation functions across the whole channel and flow visualizations. The two-dimensional roll cells are observed at weak rotation Ro=0.01 , where alternant clustering of vortices appears. Three-dimensional roll cells emerge around Ro≈0.02 , where the clustering of vortices shows the meandering and bifurcating behavior. For moderate rotation 0.07 ≲Ro≲0.36 , well-organized structures are observed, where the herringbonelike vortices are clustered between streaks from the top view of three-dimensional flow visualization and form annuluses. More importantly, the vortices are rather confined to one side of the walls when Ro≤0.02 and are inclined from the bottom to upper walls when Ro≥0.07 .

  15. Macroscopic Characteristics of Unsteady Granular Flows in Rotating Tumblers

    NASA Astrophysics Data System (ADS)

    Paprocki, Daniel; Pohlman, Nicholas

    2010-11-01

    Flow of silicate beads in rotating tumblers of triangular cross-sections are explored with respect to transient response of macroscopic properties. High-speed digital images are synchronized to tumbler orientation through an in-line rotary encoder. Image processing toolboxes are utilized to generate quantitative data for analysis. Time-dependent properties of free surface length, flowing layer curvature, and dynamic angle of repose are reported. The correlation of these properties with the orientation exhibits a phase difference that is a function of tumbler dimensions and fill fraction. Concurrent measurements of input energy to the system may lead to control algorithms to generate steady flow in inherently unsteady systems that would improve efficiency of granular transport methods.

  16. Axisymmetric compressible flow in a rotating cylinder with axial convection

    NASA Astrophysics Data System (ADS)

    Ungarish, M.; Israeli, M.

    1985-05-01

    The steady compressible flow of an ideal gas in a rotating annulus with thermally conducting walls is considered for small Rossby number epsilon and Ekman number E and moderate rotational Mach numbers M. Attention is focused on nonlinear effects which show up when sigma and epsilon M-squared are not small (sigma = epsilon/H square root of E, H is the dimensionless height of the container). These effects are not properly predicted by the classical linear perturbation analysis, and are treated here by quasi-linear extensions. The extra work required by these extensions is only the numerical solution of one ordinary differential equation for the pressure. Numerical solutions of the full Navier-Stokes equations in the nonlinear range are presented, and the validity of the present approach is confirmed.

  17. Modeling and eddy simulation of rotating and curved turbulent flows

    NASA Astrophysics Data System (ADS)

    Arolla, Sunil Kumar

    In the first part of this work, two different approaches to incorporate the effects of rotation and curvature in scalar eddy viscosity models have been explored. One is the "Modified coefficients approach"---to parameterize the model coefficients such that the growth rate of turbulent kinetic energy is suppressed or enhanced. The other is the "Bifurcation approach"---to parameterize eddy-viscosity coefficient such that the equilibrium solution bifurcates from healthy to decaying solution branches. Simple, yet, predictive models in each of these two approaches are proposed and validated on some benchmark test cases characterized by profound effects of system rotation and/or streamline curvature. The results obtained with both the models are encouraging. Application of the models to some practically relevant flow configurations is also discussed. In the second part, a computational framework is developed with recycling and rescaling method of inflow generation to perform eddy simulation of turbomachinery flows. A systematic validation is carried out on a spatially developing boundary layer on flat plate, flow through a channel and an annulus. Then, large eddy simulation of turbine transition duct is performed to demonstrate the effectiveness of this methodology.

  18. Rotating Polygon Instability of a Swirling Free Surface Flow

    NASA Astrophysics Data System (ADS)

    Tophøj, L.; Mougel, J.; Bohr, T.; Fabre, D.

    2013-05-01

    We explain the rotating polygon instability on a swirling fluid surface [G. H. Vatistas, J. Fluid Mech. 217, 241 (1990)JFLSA70022-1120 and Jansson et al., Phys. Rev. Lett. 96, 174502 (2006)PRLTAO0031-9007] in terms of resonant interactions between gravity waves on the outer part of the surface and centrifugal waves on the inner part. Our model is based on potential flow theory, linearized around a potential vortex flow with a free surface for which we show that unstable resonant states appear. Limiting our attention to the lowest order mode of each type of wave and their interaction, we obtain an analytically soluble model, which, together with estimates of the circulation based on angular momentum balance, reproduces the main features of the experimental phase diagram. The generality of our arguments implies that the instability should not be limited to flows with a rotating bottom (implying singular behavior near the corners), and indeed we show that we can obtain the polygons transiently by violently stirring liquid nitrogen in a hot container.

  19. Analysis and Applications of Radiometric Forces in Rarefied Gas Flows

    DTIC Science & Technology

    2010-06-16

    Forces in Rarefied Gas Flows 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Sergey F. Gimelshein & Natalia E. Gimelshein (ERC, Inc...Forces in Rarefied Gas Flows Sergey F. Gimelshein∗, Natalia E. Gimelshein∗, Andrew D. Ketsdever† and Nathaniel P. Selden∗∗ ∗ERC, Inc, Edwards AFB, CA 93524...geometries. Keywords: Radiometric force, shear, ES-BGK equation PACS: 51.10.+y INTRODUCTION Rarefied gas flow surrounding a thin vane with a temperature

  20. The Rotational Spectrum and Anharmonic Force Field of Chlorine Dioxide, OClO

    NASA Technical Reports Server (NTRS)

    Muller, Holger S. P.; Sorensen, G.; Birk, Manfred; Friedl, Randy R.

    1997-01-01

    The ground state rotational and quartic centrifugal distortion constants, their vibrational changes, and the sextic centrifugal distortion constants were used in a calculation of the quartic force field together with data from infrared studies.

  1. The Rotational Spectrum and Anharmonic Force Field of Chlorine Dioxide, OClO

    NASA Technical Reports Server (NTRS)

    Muller, Holger S. P.; Sorensen, G.; Birk, Manfred; Friedl, Randy R.

    1997-01-01

    The ground state rotational and quartic centrifugal distortion constants, their vibrational changes, and the sextic centrifugal distortion constants were used in a calculation of the quartic force field together with data from infrared studies.

  2. The effect of the Coriolis force on the stability of rotating magnetic stars

    NASA Technical Reports Server (NTRS)

    Sakurai, K.

    1972-01-01

    The effect of the Coriolis force on the stability of rotating magnetic stars in hydrostatic equilibrium is investigated by using the method of the energy principle. It is shown that this effect is to inhibit the onset of instability.

  3. The effect of the Coriolis force on the stability of rotating magnetic stars.

    NASA Technical Reports Server (NTRS)

    Sakurai, K.

    1972-01-01

    The effect of the Coriolis force on the stability of rotating magnetic stars in hydrostatic equilibrium is investigated by using the method of the energy principle. It is shown that this effect is to inhibit the onset of instability.

  4. Confinement of Plasma along Shaped Open Magnetic Fields from the Centrifugal Force of Supersonic Plasma Rotation

    SciTech Connect

    Teodorescu, C.; Young, W. C.; Swan, G. W. S.; Ellis, R. F.; Hassam, A. B.; Romero-Talamas, C. A.

    2010-08-20

    Interferometric density measurements in plasmas rotating in shaped, open magnetic fields demonstrate strong confinement of plasma parallel to the magnetic field, with density drops of more than a factor of 10. Taken together with spectroscopic measurements of supersonic ExB rotation of sonic Mach 2, these measurements are in agreement with ideal MHD theory which predicts large parallel pressure drops balanced by centrifugal forces in supersonically rotating plasmas.

  5. Direct optical monitoring of flow generated by bacterial flagellar rotation

    SciTech Connect

    Kirchner, Silke R.; Nedev, Spas; Carretero-Palacios, Sol; Lohmüller, Theobald E-mail: feldmann@lmu.de; Feldmann, Jochen E-mail: feldmann@lmu.de; Mader, Andreas; Opitz, Madeleine

    2014-03-03

    We report on a highly sensitive approach to measure and quantify the time dependent changes of the flow generated by the flagella bundle rotation of single bacterial cells. This is achieved by observing the interactions between a silica particle and a bacterium, which are both trapped next to each other in a dual beam optical tweezer. In this configuration, the particle serves as a sensitive detector where the fast-Fourier analysis of the particle trajectory renders, it possible to access information about changes of bacterial activity.

  6. Translational versus rotational energy flow in water solvation dynamics

    NASA Astrophysics Data System (ADS)

    Rey, Rossend; Hynes, James T.

    2017-09-01

    Early molecular dynamics simulations discovered an important asymmetry in the speed of water solvation dynamics for charge extinction and charge creation for an immersed solute, a feature representing a first demonstration of the breakdown of linear response theory. The molecular level mechanism of this asymmetry is examined here via a novel energy flux theoretical approach coupled to geometric probes. The results identify the effect as arising from the translational motions of the solute-hydrating water molecules rather than their rotational/librational motions, even though the latter are more rapid and dominate the energy flow.

  7. Detailed Validation Assessment of Turbine Stage Disc Cavity Rotating Flows

    NASA Astrophysics Data System (ADS)

    Kanjiyani, Shezan

    The subject of this thesis is concerned with the amount of cooling air assigned to seal high pressure turbine rim cavities which is critical for performance as well as component life. Insufficient air leads to excessive hot annulus gas ingestion and its penetration deep into the cavity compromising disc life. Excessive purge air, adversely affects performance. Experiments on a rotating turbine stage rig which included a rotor-stator forward disc cavity were performed at Arizona State University. The turbine rig has 22 vanes and 28 blades, while the rim cavity is composed of a single-tooth rim lab seal and a rim platform overlap seal. Time-averaged static pressures were measured in the gas path and the cavity, while mainstream gas ingestion into the cavity was determined by measuring the concentration distribution of tracer gas (carbon dioxide). Additionally, particle image velocimetry (PIV) was used to measure fluid velocity inside the rim cavity between the lab seal and the overlap. The data from the experiments were compared to an 360-degree unsteady RANS (URANS) CFD simulations. Although not able to match the time-averaged test data satisfactorily, the CFD simulations brought to light the unsteadiness present in the flow during the experiment which the slower response data did not fully capture. To interrogate the validity of URANS simulations in capturing complex rotating flow physics, the scope of this work also included to validating the CFD tool by comparing its predictions against experimental LDV data in a closed rotor-stator cavity. The enclosed cavity has a stationary shroud, a rotating hub, and mass flow does not enter or exit the system. A full 360 degree numerical simulation was performed comparing Fluent LES, with URANS turbulence models. Results from these investigations point to URANS state of art under-predicting closed cavity tangential velocity by 32% to 43%, and open rim cavity effectiveness by 50% compared to test data. The goal of this thesis

  8. Numerical modeling of multidimensional flow in seals and bearings used in rotating machinery

    NASA Technical Reports Server (NTRS)

    Hendricks, R. C.; Tam, L. T.; Przekwas, A.; Muszynska, A.; Braun, M. J.; Mullen, R. L.

    1988-01-01

    The rotordynamic behavior of turbomachinery is critically dependent on fluid dynamic rotor forces developed by various types of seals and bearings. The occurrence of self-excited vibrations often depends on the rotor speed and load. Misalignment and rotor wobbling motion associated with differential clearance were often attributed to stability problems. In general, the rotative character of the flowfield is a complex three dimensional system with secondary flow patterns that significantly alter the average fluid circumferential velocity. A multidimensional, nonorthogonal, body-fitted-grid fluid flow model is presented that describes the fluid dynamic forces and the secondary flow pattern development in seals and bearings. Several numerical experiments were carried out to demonstrate the characteristics of this complex flowfield. Analyses were performed by solving a conservation form of the three dimensional Navier-Stokes equations transformed to those for a rotating observer and using the general-purpose computer code PHOENICS with the assumptions that the rotor orbit is circular and that static eccentricity is zero. These assumptions have enabled a precise steady-state analysis to be used. Fluid injection from ports near the seal or bearing center increased fluid-film direct dynamic stiffness and, in some cases, significantly increased quadrature dynamic stiffness. Injection angle and velocity could be used for active rotordynamic control; for example, injection, when compared with no injection, increased direct dynamic stiffness, which is an important factor for hydrostatic bearings.

  9. Angular momentum transport in turbulent flow between independently rotating cylinders.

    PubMed

    Paoletti, M S; Lathrop, D P

    2011-01-14

    We present measurements of the angular momentum flux (torque) in Taylor-Couette flow of water between independently rotating cylinders for all regions of the (Ω1, Ω2) parameter space at high Reynolds numbers, where Ω1 (Ω2) is the inner (outer) cylinder angular velocity. We find that the Rossby number Ro = (Ω1 - Ω2)/Ω2 fully determines the state and torque G as compared to G(Ro = ∞) ≡ G∞. The ratio G/G∞ is a linear function of Ro(-1) in four sections of the parameter space. For flows with radially increasing angular momentum, our measured torques greatly exceed those of previous experiments [Ji et al., Nature (London), 444, 343 (2006)], but agree with the analysis of Richard and Zahn [Astron. Astrophys. 347, 734 (1999)].

  10. Angular Momentum Transport in Turbulent Flow between Independently Rotating Cylinders

    NASA Astrophysics Data System (ADS)

    Paoletti, M. S.; Lathrop, D. P.

    2011-01-01

    We present measurements of the angular momentum flux (torque) in Taylor-Couette flow of water between independently rotating cylinders for all regions of the (Ω1, Ω2) parameter space at high Reynolds numbers, where Ω1 (Ω2) is the inner (outer) cylinder angular velocity. We find that the Rossby number Ro=(Ω1-Ω2)/Ω2 fully determines the state and torque G as compared to G(Ro=∞)≡G∞. The ratio G/G∞ is a linear function of Ro-1 in four sections of the parameter space. For flows with radially increasing angular momentum, our measured torques greatly exceed those of previous experiments [Ji et al., Nature (London)NATUAS0028-0836, 444, 343 (2006)10.1038/nature05323], but agree with the analysis of Richard and Zahn [Astron. Astrophys. 347, 734 (1999)AAEJAF0004-6361].

  11. Angular Momentum Transport in Turbulent Flow between Independently Rotating Cylinders

    SciTech Connect

    Paoletti, M. S.; Lathrop, D. P.

    2011-01-14

    We present measurements of the angular momentum flux (torque) in Taylor-Couette flow of water between independently rotating cylinders for all regions of the ({Omega}{sub 1}, {Omega}{sub 2}) parameter space at high Reynolds numbers, where {Omega}{sub 1} ({Omega}{sub 2}) is the inner (outer) cylinder angular velocity. We find that the Rossby number Ro=({Omega}{sub 1}-{Omega}{sub 2})/{Omega}{sub 2} fully determines the state and torque G as compared to G(Ro={infinity}){identical_to}G{sub {infinity}.} The ratio G/G{sub {infinity}} is a linear function of Ro{sup -1} in four sections of the parameter space. For flows with radially increasing angular momentum, our measured torques greatly exceed those of previous experiments [Ji et al., Nature (London), 444, 343 (2006)], but agree with the analysis of Richard and Zahn [Astron. Astrophys. 347, 734 (1999)].

  12. SOLAR ROTATION EFFECTS ON THE HELIOSHEATH FLOW NEAR SOLAR MINIMA

    SciTech Connect

    Borovikov, Sergey N.; Pogorelov, Nikolai V.; Ebert, Robert W.

    2012-05-01

    The interaction between fast and slow solar wind (SW) due to the Sun's rotation creates corotating interaction regions (CIRs), which further interact with each other creating complex plasma structures at large heliospheric distances. We investigate the global influence of CIRs on the SW flow in the inner heliosheath between the heliospheric termination shock (TS) and the heliopause. The stream interaction model takes into account the major global effects due to slow-fast stream interaction near solar minima. The fast and slow wind parameters are derived from the Ulysses observations. We investigate the penetration of corotating structures through the TS and their further propagation through the heliosheath. It is shown that the heliosheath flow structure may experience substantial modifications, including local decreases in the radial velocity component observed by Voyager 1.

  13. Thermocapillary Flow and Coalescences of Heterogeneous Bubble Size Diameter in a Rotating Cylinder: 3D Study

    NASA Astrophysics Data System (ADS)

    Alhendal, Yousuf; Turan, Ali

    2016-12-01

    Two dimensional axisymmetric and three-dimensional VOF simulations of gas/liquid transient flow were performed using a multiphase flow algorithm based on the finite-volume method. The results for motion of a multiple bubbles of a heterogeneous sizes aligned horizontally and perpendicular to a hot surface incorporating thermocapillary forces in a rotating liquid in a zero-gravity environment have been presented for the first time. No bubbles broke in any of the cases observed. The results also show that collision and agglomeration of bubbles of unequal sizes diameter are different from those of similar size diameters presented from earlier research work of Alhendal et al. Acta Astronaut. 117, 484-496 (2015). Different flow patterns such as thermocapillary bubble migration, collision, and stream function were observed and presented for the 2-D and 3-D models.

  14. Vortex Stability In Two -layer Rotating Shallow-water Flows

    NASA Astrophysics Data System (ADS)

    Carton, Xavier; Baey, Jean-Michel

    The stability of circular vortices subject to an initial normal-mode perturbation is studied in a two-layer shallow-water fluid with rigid lid, flat bottom and constant background rotation. Considerable similarity with quasi-geostrophic dynamics is found for linear (barotropic or baroclinic) instability, except in the frontal and nonlinear barotropic limits. This discrepancy is explained by asymptotic models. In many cases, the elliptical mode of deformation is the most unstable one. The ability of these perturbed circular vortices to stabilize nonlinearly as long-lived multipoles is then investigated. For elliptical perturbations, steady tripoles form from moderately unstable vortices as in the quasi-geostrophic limit. These tripoles, which exhibit various 3D structures, are robust when perturbed by non coherent disturbances. More unstable circular vortices break as two dipoles, propagating in opposite directions. Triangular perturbations can also lead to stationary quadrupoles or to dipolar breaking. The similarity with quasi-geostrophic dynamics, which ext ends to these nonlinear regimes, is related to the weakness of the divergent circulation, as shown by the analysis of the Lighthill equation. J.M. Baey &X. Carton, 2001: "Piecewise-constant vortices in a two-layer shallow - water flow". Advances in mathematical modelling of atmosphere and ocean dynamics, Kluwer Acad. Publ., 61, p.87-92. J.M. Baey &X. Carton, 2002: "Vortex multipoles in two-layer rotating shallow -water flows". To appear in J. Fluid Mech.

  15. Flow behaviour of snow in a rotating drum

    NASA Astrophysics Data System (ADS)

    Heil, Kilian; Reiweger, Ingrid; Fischer, Jan-Thomas; Kaitna, Roland

    2017-04-01

    Snow, rapidly moving in an avalanche, transforms along the avalanche path, and consequently changes the flow behaviour over time. Recent studies showed that this expected change is particularly pronounced at temperatures above -2°C. Since investigations in the field are connected to considerable challenges, we aim to investigate the flow behaviour and the dynamic transformation of snow continuously at (relatively) controlled boundary conditions at a scale as large as possible. We therefore create a continuous movement of snow in a vertically rotating drum with a diameter 2.5 m and a rectangular cross section of 0.45 m. Experiments in our outdoor facility were carried out at temperatures below freezing and at tangential velocities between 0.1 and 1 m/s. To avoid basal slip semi-circular roughness elements with a height of 1 cm were installed. We present results of measurements of snow temperature, the liquid water content of snow, as well as flow geometry, basal normal stress distribution, and bulk shear stress over time. Furthermore we link the thermal energy increase to the equivalent vertical travel distance of the flow. The outcomes of this study shall increase our understanding of the material snow and consequently contribute to an improved model building for avalanche simulations.

  16. Flow transition in surface switching of rotating fluid

    NASA Astrophysics Data System (ADS)

    Tasaka, Yuji; Ito, Kentaro; Iima, Makoto

    2007-11-01

    This study aims to investigate the flow transition appearing in a process of ``surface switching.'' In a flow driven by a rotating disk in a cylindrical open vessel, the free surface changes irregularly its shape from axisymmetric to nonaxisymmetric and v.v. while repeating its up-and-down motion of the center part of the free surface (so-called ``surface switching'' [Suzuki et al., Phys. Fluids, 18 (2006), 101701(1-4)]). The instantaneous velocity profile of the flow along the radial direction was measured by ultrasonic velocity profiling, UVP, to investigate the flow transition quantitatively. It is revealed that the turbulent intensity shows a transition at the same Reynolds number as that for the surface switching. Also, the detailed analysis of the turbulent intensity and the power spectrum of velocity profile shows that the fluid-air interface becomes unstable at a smaller Reynolds number than the critical Reynolds number for the surface switching. By decreasing Reynolds number after the onset of the switching, a hysteresis phenomenon in the switching is observed; two different states stably exist at the same Reynolds number.

  17. Effects of surface thermal forcing on stratified flow past an isolated obstacle

    NASA Astrophysics Data System (ADS)

    Reisner, Jon

    1992-02-01

    The present study investigates basic aspects of the flow of a density-stratified fluid past three-dimensional obstacles for Froude number is approximately O(1) and isolated surface thermal forcing representative of diurnally varying mesoscale flows past mountainous islands such as Hawaii. In order to minimize parameter space, we have excluded the effects of friction, rotation, nonuniform ambient flow, and the complexities of realistic surface boundary layer and terrain. Through simple scaling arguments, we deduce that the parameter eta* controls thermally forced flows for a given Froude number, and we provide crude estimates of a flow response for a range of eta*. The principal question addressed is for what values of eta* will a transition occur from the low-Froude-number flow regime, characterized by the stagnation and splitting of the lower upwind flow, to the regime in which flow passes over rather than around the obstacle. We show that the linear theory captures such a tendency consistently with simple scaling arguments. To provide quantitative measures of flow variability with the Froude number and eta*, we employ an efficient isentropic numerical code and summarize the results of numerous simulations in the form of a regime diagram. The principal result is a simple criterion for the transition of a heated flow from the blocked to unblocked flow regime. We illustrate the relevance of the idealized study to natural flows with an example of applications to a flow past the Hawaiian Archipelago.

  18. Reynolds-Stress and Triple-Product Models Applied to Flows with Rotation and Curvature

    NASA Technical Reports Server (NTRS)

    Olsen, Michael E.

    2016-01-01

    Predictions for Reynolds-stress and triple product turbulence models are compared for flows with significant rotational effects. Driver spinning cylinder flowfield and Zaets rotating pipe case are to be investigated at a minimum.

  19. Air-structure coupling features analysis of mining contra-rotating axial flow fan cascade

    NASA Astrophysics Data System (ADS)

    Chen, Q. G.; Sun, W.; Li, F.; Zhang, Y. J.

    2013-12-01

    The interaction between contra-rotating axial flow fan blade and working gas has been studied by means of establishing air-structure coupling control equation and combining Computational Fluid Dynamics (CFD) and Computational solid mechanics (CSM). Based on the single flow channel model, the Finite Volume Method was used to make the field discrete. Additionally, the SIMPLE algorithm, the Standard k-ε model and the Arbitrary Lagrangian-Eulerian dynamic grids technology were utilized to get the airflow motion by solving the discrete governing equations. At the same time, the Finite Element Method was used to make the field discrete to solve dynamic response characteristics of blade. Based on weak coupling method, data exchange from the fluid solver and the solid solver was processed on the coupling interface. Then interpolation was used to obtain the coupling characteristics. The results showed that the blade's maximum amplitude was on the tip of the last-stage blade and aerodynamic force signal could reflect the blade working conditions to some extent. By analyzing the flow regime in contra-rotating axial flow fan, it could be found that the vortex core region was mainly in the blade surface, the hub and the blade clearance. In those regions, the turbulence intensity was very high. The last-stage blade's operating life is shorter than that of the pre-stage blade due to the fatigue fracture occurs much more easily on the last-stage blade which bears more stress.

  20. On the nonlinear interfacial instability of rotating core-annular flow

    NASA Technical Reports Server (NTRS)

    Coward, Aidrian V.; Hall, Philip

    1993-01-01

    The interfacial stability of rotating core-annular flows is investigated. The linear and nonlinear effects are considered for the case when the annular region is very thin. Both asymptotic and numerical methods are used to solve the flow in the core and film regions which are coupled by a difference in viscosity and density. The long-term behavior of the fluid-fluid interface is determined by deriving its nonlinear evolution in the form of a modified Kuramoto-Sivashinsky equation. We obtain a generalization of this equation to three dimensions. The flows considered are applicable to a wide array of physical problems where liquid films are used to lubricate higher or lower viscosity core fluids, for which a concentric arrangement is desired. Linearized solutions show that the effects of density and viscosity stratification are crucial to the stability of the interface. Rotation generally destabilizes non-axisymmetric disturbances to the interface, whereas the centripetal forces tend to stabilize flows in which the film contains the heavier fluid. Nonlinear affects allow finite amplitude helically travelling waves to exist when the fluids have different viscosities.

  1. Statistical equilibria of the coupled barotropic flow and shallow water flow on a rotating sphere

    NASA Astrophysics Data System (ADS)

    Ding, Xueru

    The motivation of this research is to build equilibrium statistical models that can apply to explain two enigmatic phenomena in the atmospheres of the solar system's planets: (1) the super-rotation of the atmospheres of slowly-rotating terrestrial planets---namely Venus and Titan, and (2) the persistent anticyclonic large vortex storms on the gas giants, such as the Great Red Spot (GRS) on Jupiter. My thesis is composed of two main parts: the first part focuses on the statistical equilibrium of the coupled barotropic vorticity flow (non-divergent) on a rotating sphere; the other one has to do with the divergent shallow water flow rotating sphere system. The statistical equilibria of these two systems are simulated in a wide range of parameter space by Monte Carlo methods based on recent energy-relative enstrophy theory and extended energy-relative enstrophy theory. These kind of models remove the low temperatures defect in the old classical doubly canonical energy-enstrophy theory which cannot support any phase transitions. The other big difference of our research from previous work is that we work on the coupled fluid-sphere system, which consists of a rotating high density rigid sphere, enveloped by a thin shell of fluid. The sphere is considered to have infinite mass and angular momentum; therefore, it can serve as a reservoir of angular momentum. Unlike the fluid sphere system itself, the coupled fluid sphere system allows for the exchange of angular momentum between the atmosphere and the solid planet. This exchange is the key point in any model that is expected to capture coherent structures such as the super-rotation and GRS-like vortices problems in planetary atmospheres. We discovered that slowly-rotating planets can have super-rotation at high energy state. All known slowly-rotating cases in the solar system---Venus and Titan---have super-rotation. Moreover, we showed that the anticyclonicity in the GRS-like structures is closely associated with the

  2. Three-dimensional analytic probabilities of coupled vibrational-rotational-translational energy transfer for DSMC modeling of nonequilibrium flows

    SciTech Connect

    Adamovich, Igor V.

    2014-04-15

    A three-dimensional, nonperturbative, semiclassical analytic model of vibrational energy transfer in collisions between a rotating diatomic molecule and an atom, and between two rotating diatomic molecules (Forced Harmonic Oscillator–Free Rotation model) has been extended to incorporate rotational relaxation and coupling between vibrational, translational, and rotational energy transfer. The model is based on analysis of semiclassical trajectories of rotating molecules interacting by a repulsive exponential atom-to-atom potential. The model predictions are compared with the results of three-dimensional close-coupled semiclassical trajectory calculations using the same potential energy surface. The comparison demonstrates good agreement between analytic and numerical probabilities of rotational and vibrational energy transfer processes, over a wide range of total collision energies, rotational energies, and impact parameter. The model predicts probabilities of single-quantum and multi-quantum vibrational-rotational transitions and is applicable up to very high collision energies and quantum numbers. Closed-form analytic expressions for these transition probabilities lend themselves to straightforward incorporation into DSMC nonequilibrium flow codes.

  3. Computation of turbulent rotating channel flow with an algebraic Reynolds stress model

    NASA Technical Reports Server (NTRS)

    Warfield, M. J.; Lakshminarayana, B.

    1986-01-01

    An Algebraic Reynolds Stress Model has been implemented to modify the Kolmogorov-Prandtl eddy viscosity relation to produce an anisotropic turbulence model. The eddy viscosity relation becomes a function of the local turbulent production to dissipation ratio and local turbulence/rotation parameters. The model is used to predict fully-developed rotating channel flow over a diverse range of rotation numbers. In addition, predictions are obtained for a developing channel flow with high rotation. The predictions are compared with the experimental data available. Good predictions are achieved for mean velocity and wall shear stress over most of the rotation speeds tested. There is some prediction breakdown at high rotation (rotation number greater than .10) where the effects of the rotation on turbulence become quite complex. At high rotation and low Reynolds number, the laminarization on the trailing side represents a complex effect of rotation which is difficult to predict with the described models.

  4. A continuous-flow biodiesel production process using a rotating packed bed.

    PubMed

    Chen, Yi-Hung; Huang, Yu-Hang; Lin, Rong-Hsien; Shang, Neng-Chou

    2010-01-01

    The continuous-flow transesterification of soybean oil with methanol using a rotating packed bed (RPB) for the production of fatty acid methyl esters (biodiesel) is presented herein. The RPB, which provides high centrifugal force and has an adjustable rotational speed, is employed as a novel transesterification reactor. In this study, biodiesel is synthesized via the methanolysis of soybean oil using potassium hydroxide as the catalyst. The following variables were investigated for their effects on transesterification efficiency: the methanol-oil molar ratio, the estimated hydraulic retention time, the rotational speed of the packed-bed rotator, the reaction temperature, and the catalyst dosage. The yield of the fatty acid methyl esters (Y(FAME)) in the RPB system depends significantly on the experimental conditions, which influence the residence time distribution, the transesterification reaction rate, and the micromixing intensity. Due to its excellent micromixing characteristics, the RPB system shows satisfactory transesterification efficiency. The values of Y(FAME), productivity of FAMEs (P(FAME)), and P(FAME) per unit reactor volume (P(FAME)/V(R)) in the RPB are used to evaluate the performance for biodiesel production and allow for further comparison with other continuous transesterification reactors. Consequently, a RPB is considered a practical transesterification reactor with high transesterification efficiency.

  5. Force and vortical flow development on pitching wings at high rates

    NASA Astrophysics Data System (ADS)

    Bernal, Luis; Yu, Huai-Te; Ol, Michael; Granlund, Kenneth

    2014-11-01

    Recent experimental results of pitching flat plate wings are presented. High pitch-rate perching maneuvers are frequently used by birds for feeding and landing. Insects use very fast rotation rates at the end of each flapping stroke, which results in high thrust and precise flight. These wing motions are also of interest for engineered micro air vehicles to achieve semi-autonomous landing by unskilled operators. The wing motion considered is a constant rotation rate pitch motion from 0 to 45 degrees of an aspect-ratio-4 flat-plate wing. The goal is to gain a better understanding of force generation mechanisms and their relationship to two- and three-dimensional vortical flow structures. Leading edge, trailing edge, and tip vortices form with large separated flow regions over the wing, however comparison with linear potential flow theory gives good agreement. The evolution of the leading edge vortex is delayed for pivot axes locations downstream of the leading edge. Large forces at the end of the motion slowly return to the steady state value over more than 30 convective times. The flow in the near wake shows a brief period of vortex shedding and strong three dimensional effects. Two different three-dimensional flow features are observed: A rapid development of three-dimensionality in the core of the leading and trailing edge vortices and a swirl motion in the near wake. However the impact of these three-dimensional flow features on force development is small.

  6. Stochastic Rotation Dynamics simulations of wetting multi-phase flows

    NASA Astrophysics Data System (ADS)

    Hiller, Thomas; Sanchez de La Lama, Marta; Brinkmann, Martin

    2016-06-01

    Multi-color Stochastic Rotation Dynamics (SRDmc) has been introduced by Inoue et al. [1,2] as a particle based simulation method to study the flow of emulsion droplets in non-wetting microchannels. In this work, we extend the multi-color method to also account for different wetting conditions. This is achieved by assigning the color information not only to fluid particles but also to virtual wall particles that are required to enforce proper no-slip boundary conditions. To extend the scope of the original SRDmc algorithm to e.g. immiscible two-phase flow with viscosity contrast we implement an angular momentum conserving scheme (SRD+mc). We perform extensive benchmark simulations to show that a mono-phase SRDmc fluid exhibits bulk properties identical to a standard SRD fluid and that SRDmc fluids are applicable to a wide range of immiscible two-phase flows. To quantify the adhesion of a SRD+mc fluid in contact to the walls we measure the apparent contact angle from sessile droplets in mechanical equilibrium. For a further verification of our wettability implementation we compare the dewetting of a liquid film from a wetting stripe to experimental and numerical studies of interfacial morphologies on chemically structured surfaces.

  7. Rotator cuff tear reduces muscle fiber specific force production and induces macrophage accumulation and autophagy

    PubMed Central

    Gumucio, Jonathan P; Davis, Max E; Bradley, Joshua R; Stafford, Patrick L; Schiffman, Corey J; Lynch, Evan B; Claflin, Dennis R; Bedi, Asheesh; Mendias, Christopher L

    2012-01-01

    Summary Full-thickness tears to the rotator cuff can cause severe pain and disability. Untreated tears progress in size and are associated with muscle atrophy and an infiltration of fat to the area, a condition known as “fatty degeneration.” To improve the treatment of rotator cuff tears, a greater understanding of the changes in the contractile properties of muscle fibers and the molecular regulation of fatty degeneration is essential. Using a rat model of rotator cuff injury, we measured the force generating capacity of individual muscle fibers and determined changes in muscle fiber type distribution that develop after a full thickness rotator cuff tear. We also measured the expression of mRNA and miRNA transcripts involved in muscle atrophy, lipid accumulation, and matrix synthesis. We hypothesized that a decrease in specific force of rotator cuff muscle fibers, an accumulation of type IIb fibers, an upregulation in fibrogenic, adipogenic, and inflammatory gene expression occur in torn rotator cuff muscles. Thirty days following rotator cuff tear, we observed a reduction in muscle fiber force production, an induction of fibrogenic, adipogenic and autophagocytic mRNA and miRNA molecules, and a dramatic accumulation of macrophages in areas of fat accumulation. PMID:22696414

  8. Rotator cuff tear reduces muscle fiber specific force production and induces macrophage accumulation and autophagy.

    PubMed

    Gumucio, Jonathan P; Davis, Max E; Bradley, Joshua R; Stafford, Patrick L; Schiffman, Corey J; Lynch, Evan B; Claflin, Dennis R; Bedi, Asheesh; Mendias, Christopher L

    2012-12-01

    Full-thickness tears to the rotator cuff can cause severe pain and disability. Untreated tears progress in size and are associated with muscle atrophy and an infiltration of fat to the area, a condition known as "fatty degeneration." To improve the treatment of rotator cuff tears, a greater understanding of the changes in the contractile properties of muscle fibers and the molecular regulation of fatty degeneration is essential. Using a rat model of rotator cuff injury, we measured the force generating capacity of individual muscle fibers and determined changes in muscle fiber type distribution that develop after a full thickness rotator cuff tear. We also measured the expression of mRNA and miRNA transcripts involved in muscle atrophy, lipid accumulation, and matrix synthesis. We hypothesized that a decrease in specific force of rotator cuff muscle fibers, an accumulation of type IIb fibers, and an upregulation in fibrogenic, adipogenic, and inflammatory gene expression occur in torn rotator cuff muscles. Thirty days following rotator cuff tear, we observed a reduction in muscle fiber force production, an induction of fibrogenic, adipogenic, and autophagocytic mRNA and miRNA molecules, and a dramatic accumulation of macrophages in areas of fat accumulation. Copyright © 2012 Orthopaedic Research Society.

  9. Flow of Fluid and Particle Assemblages in Rotating Systems

    NASA Technical Reports Server (NTRS)

    Kizito, John; Hiltner, David; Niederhaus, Charles; Kleis, Stanley; Hudson, Ed; Gonda, Steve

    2004-01-01

    NASA-designed bioreactors have been highly successful in growing three-dimensional tissue structures in a low shear environment both on earth and in space. The goal of the present study is to characterize the fluid flow environment within the HFB-S bioreactor and determine the spatial distribution of particles that mimic cellular tissue structures. The results will be used to obtain optimal operating conditions of rotation rates and media perfusehnfuse rates which are required for cell culture growth protocols. Two types of experiments have been performed so far. First, we have performed laser florescent dye visualization of the perfusion loop to determine the mixing times within the chamber. The second type of experiments involved particles which represent cellular tissue to determine the spatial distribution with the chamber. From these experiments we established that mixing times were largely dependant on the speed ratio and sign of the difference between the spinner and the dome. The shortest mixing times occurred when the spinner rotates faster than the dome and longest mixing times occurs with no relative motion between the dome and spinner. Also, we have determined the spatial and temporal distribution of particle assemblages within the chamber.

  10. Radiative flow due to stretchable rotating disk with variable thickness

    NASA Astrophysics Data System (ADS)

    Hayat, Tasawar; Qayyum, Sumaira; Imtiaz, Maria; Alsaedi, Ahmed

    Present article concerns with MHD flow of viscous fluid by a rotating disk with variable thickness. Heat transfer is examined in the presence of thermal radiation. Boundary layer approximation is applied to the partial differential equations. Governing equations are then transformed into ordinary differential equations by utilizing Von Karman transformations. Impact of physical parameters on velocity, temperature, skin friction coefficient and Nusselt number is presented and examined. It is observed that with an increase in disk thickness and stretching parameter the radial and axial velocities are enhanced. Prandtl number and radiation parameter have opposite behavior for temperature field. Skin friction decays for larger disk thickness index. Magnitude of Nusselt number enhances for larger Prandtl number.

  11. ROTATING ACCRETION FLOWS: FROM INFINITY TO THE BLACK HOLE

    SciTech Connect

    Li, Jason; Ostriker, Jeremiah; Sunyaev, Rashid

    2013-04-20

    Accretion onto a supermassive black hole of a rotating inflow is a particularly difficult problem to study because of the wide range of length scales involved. There have been broadly utilized analytic and numerical treatments of the global properties of accretion flows, but detailed numerical simulations are required to address certain critical aspects. We use the ZEUS code to run hydrodynamical simulations of rotating, axisymmetric accretion flows with Bremsstrahlung cooling, considering solutions for which the centrifugal balance radius significantly exceeds the Schwarzschild radius, with and without viscous angular momentum transport. Infalling gas is followed from well beyond the Bondi radius down to the vicinity of the black hole. We produce a continuum of solutions with respect to the single parameter M-dot{sub B}/ M-dot{sub Edd}, and there is a sharp transition between two general classes of solutions at an Eddington ratio of M-dot{sub B}/M-dot{sub Edd}{approx}few Multiplication-Sign 10{sup -2}. Our high inflow solutions are very similar to the standard Shakura and Sunyaev results. But our low inflow results are to zeroth order the stationary Papaloizou and Pringle solution, which has no accretion. To next order in the small, assumed viscosity they show circulation, with disk and conical wind outflows almost balancing inflow. These solutions are characterized by hot, vertically extended disks, and net accretion proceeds at an extremely low rate, only of order {alpha} times the inflow rate. Our simulations have converged with respect to spatial resolution and temporal duration, and they do not depend strongly on our choice of boundary conditions.

  12. The flow and hydrodynamic stability of a liquid film on a rotating disc

    NASA Astrophysics Data System (ADS)

    Kim, Tae-Sung; Kim, Moon-Uhn

    2009-06-01

    The flow of a liquid film on a rotating disc is investigated in the case where a liquid is supplied at a constant flow rate. We propose thin film equations by the integral method with a simple approach to satisfy the boundary conditions on a disc and a free surface, and the results are compared with those of the Navier-Stokes equations. The radial film velocity is assumed to be a quartic profile in our analysis, whereas it was assumed to be a quadratic one, neglecting the inertia force so that the boundary conditions were not completely satisfied, in the analysis of Sisoev et al (2003 J. Fluid Mech. 229 531-54). The basic flow and its stability are analyzed using the thin film equations even in the region where the inertia force is not negligible. A local stability analysis of the flow is conducted using the linearized disturbance equations and correctly predicts Needham's simple instability criterion. The present thin film equations give a good approximation of the Navier-Stokes equations.

  13. Effective slip for flow in a rotating channel bounded by stick-slip walls

    NASA Astrophysics Data System (ADS)

    Ng, Chiu-On

    2016-12-01

    This paper aims to look into how system rotation may modify the role played by boundary slip in controlling flow through a rotating channel bounded by stick-slip walls. A semianalytical model is developed for pressure-driven flow in a slit channel that rotates about an axis perpendicular to its walls, which are superhydrophobic surfaces patterned with periodic alternating no-shear and no-slip stripes. The cases where the flow is driven by a pressure gradient parallel or normal to the stripes are considered. The effects of the no-shear area fraction on the velocities and effective slip lengths for the primary and secondary flows are investigated as functions of the rotation rate and the channel height. It is mathematically proved that the secondary flow rate is exactly the same in the two cases, irrespective of whether the primary flow is parallel or normal to the wall stripes. For any rotation speed, there is an optimal value of the no-shear area fraction at which the primary flow rate is maximum. This is a consequence of two competing effects: the no-shear part of the wall may serve to reduce the wall resistance, thereby enhancing the flow especially at low rotation, but it also weakens the formation of the near-wall Ekman layer, which is responsible for pumping the flow especially at high rotation. Wall slip in a rotating environment is to affect flow in the Ekman layer, but not flow in the geostrophic core.

  14. Effective slip for flow in a rotating channel bounded by stick-slip walls.

    PubMed

    Ng, Chiu-On

    2016-12-01

    This paper aims to look into how system rotation may modify the role played by boundary slip in controlling flow through a rotating channel bounded by stick-slip walls. A semianalytical model is developed for pressure-driven flow in a slit channel that rotates about an axis perpendicular to its walls, which are superhydrophobic surfaces patterned with periodic alternating no-shear and no-slip stripes. The cases where the flow is driven by a pressure gradient parallel or normal to the stripes are considered. The effects of the no-shear area fraction on the velocities and effective slip lengths for the primary and secondary flows are investigated as functions of the rotation rate and the channel height. It is mathematically proved that the secondary flow rate is exactly the same in the two cases, irrespective of whether the primary flow is parallel or normal to the wall stripes. For any rotation speed, there is an optimal value of the no-shear area fraction at which the primary flow rate is maximum. This is a consequence of two competing effects: the no-shear part of the wall may serve to reduce the wall resistance, thereby enhancing the flow especially at low rotation, but it also weakens the formation of the near-wall Ekman layer, which is responsible for pumping the flow especially at high rotation. Wall slip in a rotating environment is to affect flow in the Ekman layer, but not flow in the geostrophic core.

  15. The centrifugal instability of the boundary layer on a slender rotating cone in a forced free-stream

    NASA Astrophysics Data System (ADS)

    Hussain, Zahir; Garrett, Stephen; Stephen, Sharon

    2010-11-01

    The laminar-turbulent transition of flow within the boundary layer over a slender rotating nose cone (for example a spinning missile) can lead to increases in drag, with negative implications for control and targeting. However, continuing developments on spinning projectiles, which have furthered understanding of the onset of laminar-turbulent transition over rotating cones, may lead to design modifications and significant cost savings. Experiments in the literature have shown that increasing the incident free-stream has a stabilizing effect on these spiral vortices. Furthermore, Kobayashi (1981) has calculated the stability diagram for a slender cone of half-angle 15^o using the Orr-Sommerfeld approximation. In this study, we provide a new mathematical description of the onset of counter-rotating spiral vortices observed for a 15^o rotating cone placed in forced free-streams of varying strength. In particular, we resolve appropriate scalings in order to include variations in the basic-flow profiles, accounting for the influence of streamline curvature. A combined large Reynolds number and large vortex wavenumber analysis is used to obtain the asymptotic branch of neutral stability. Our results capture the effects of the governing centrifugal Görtler instability mechanism, and lead to favorable comparisons with existing numerical neutral stability curve results.

  16. Force and torque on spherical particles in micro-channel flows using computational fluid dynamics

    PubMed Central

    Suo, Jin; Edwards, Erin E.; Anilkumar, Ananyaveena; Sulchek, Todd; Giddens, Don P.

    2016-01-01

    To delineate the influence of hemodynamic force on cell adhesion processes, model in vitro fluidic assays that mimic physiological conditions are commonly employed. Herein, we offer a framework for solution of the three-dimensional Navier–Stokes equations using computational fluid dynamics (CFD) to estimate the forces resulting from fluid flow near a plane acting on a sphere that is either stationary or in free flow, and we compare these results to a widely used theoretical model that assumes Stokes flow with a constant shear rate. We find that while the full three-dimensional solutions using a parabolic velocity profile in CFD simulations yield similar translational velocities to those predicted by the theoretical method, the CFD approach results in approximately 50% larger rotational velocities over the wall shear stress range of 0.1–5.0 dynes cm−2. This leads to an approximately 25% difference in force and torque calculations between the two methods. When compared with experimental measurements of translational and rotational velocities of microspheres or cells perfused in microfluidic channels, the CFD simulations yield significantly less error. We propose that CFD modelling can provide better estimations of hemodynamic force levels acting on perfused microspheres and cells in flow fields through microfluidic devices used for cell adhesion dynamics analysis. PMID:27493783

  17. Force and torque on spherical particles in micro-channel flows using computational fluid dynamics.

    PubMed

    Suo, Jin; Edwards, Erin E; Anilkumar, Ananyaveena; Sulchek, Todd; Giddens, Don P; Thomas, Susan N

    2016-07-01

    To delineate the influence of hemodynamic force on cell adhesion processes, model in vitro fluidic assays that mimic physiological conditions are commonly employed. Herein, we offer a framework for solution of the three-dimensional Navier-Stokes equations using computational fluid dynamics (CFD) to estimate the forces resulting from fluid flow near a plane acting on a sphere that is either stationary or in free flow, and we compare these results to a widely used theoretical model that assumes Stokes flow with a constant shear rate. We find that while the full three-dimensional solutions using a parabolic velocity profile in CFD simulations yield similar translational velocities to those predicted by the theoretical method, the CFD approach results in approximately 50% larger rotational velocities over the wall shear stress range of 0.1-5.0 dynes cm(-2). This leads to an approximately 25% difference in force and torque calculations between the two methods. When compared with experimental measurements of translational and rotational velocities of microspheres or cells perfused in microfluidic channels, the CFD simulations yield significantly less error. We propose that CFD modelling can provide better estimations of hemodynamic force levels acting on perfused microspheres and cells in flow fields through microfluidic devices used for cell adhesion dynamics analysis.

  18. Advanced heat transfer devices based on mass forces in coiled flows

    NASA Astrophysics Data System (ADS)

    Fedorovich, Evgeny D.; Tarasevich, Sergei S.; Repnikova, Elena A.

    2002-01-01

    Advanced heat transfer devices in the form of different channels where artificial mass forces influence on hydrodynamics stability in low gravity area and argumentation of heat transfer is considered. Experiments are fulfilled with large variety of geometrical forms of channels (inserts in straight tubes, fluted tubes, annular channels with rotation of flow, spiral coils, twisted tubes etc.) and different heat transfer media and their vapor (liquid metals, water, cryogenic liquids). .

  19. Laminar Flow About a Rotating Body of Revolution in an Axial Airstream

    NASA Technical Reports Server (NTRS)

    Schlichting, H.

    1956-01-01

    We have set ourselves the problem of calculating the laminar flow on a body of revolution in an axial flow which simultaneously rotates about its axis. The problem mentioned above, the flow about a rotating disk in a flow, which we solved some time ago, represents the first step in the calculation of the flow on the rotating body of revolution in a flow insofar as, in the case of a round nose, a small region about the front stagnation point of the body of revolution may be replaced by its tangential plane. In our problem regarding the rotating body of revolution in a flow, for laminar flow, one of the limiting cases is known: that of the body which is in an axial approach flow but does not rotate. The other limiting case, namely the flow in the neighborhood of a body which rotates but is not subjected to a flow is known only for the rotating circular cylinder, aside from the rotating disk. In the case of the cylinder one deals with a distribution of the circumferential velocity according to the law v = omega R(exp 2)/r where R signifies the cylinder radius, r the distance from the center, and omega the angular velocity of the rotation. The velocity distribution as it is produced here by the friction effect is therefore the same as in the neighborhood of a potential vortex. When we treat, in what follows, the general case of the rotating body of revolution in a flow according to the calculation methods of Prandtl's boundary-layer theory, we must keep in mind that this solution cannot contain the limiting case of the body of revolution which only rotates but is not subjected to a flow. However, this is no essential limitation since this case is not of particular importance for practical purposes.

  20. Flow Simulations of The Dynamics of a Perturbed Solid-Body Rotation Flow

    NASA Astrophysics Data System (ADS)

    Wang, Shixiao; Feng, Chunjuan; Liu, Feng; Rusak, Zvi

    2016-11-01

    DNS is conducted to study the 3-D flow dynamics of a base solid-body rotation flow with a uniform axial velocity in a finite-length pipe. The simulation results describe the neutral stability line in response to either axisymmetric or 3-dimensional perturbations in a diagram of Reynolds number (Re , based on inlet axial velocity and pipe radius) versus the incoming flow swirl ratio (ω). This line is in good agreement with the neutral stability line recently predicted by the linear stability theory of Wang et al. (2016). The Wang & Rusak (1996) axisymmetric instability mechanism and evolution to an axisymmetric breakdown state is recovered in the simulations at certain operational conditions in terms of Re and ω. However, at other operational conditions there exists a dominant, 3-dimensional spiral type of instability mode that agrees with the linear stability theory of Wang et al. (2016). The growth of this mode leads to a spiral type of flow roll-up that subsequently nonlinearly saturates on a rotating spiral type of vortex breakdown. The computed time history of the velocity components at a certain point in the flow is used to describe 3-dimensional phase portraits of the flow global dynamics and its long-term behavior.

  1. Identification of dominant flow structures in rapidly rotating convection of liquid metals using Dynamic Mode Decomposition

    NASA Astrophysics Data System (ADS)

    Horn, S.; Schmid, P. J.; Aurnou, J. M.

    2016-12-01

    The Earth's metal core acts as a dynamo whose efficiency in generating and maintaining the magnetic field is essentially determined by the rotation rate and the convective motions occurring in its outer liquid part. For the description of the primary physics in the outer core the idealized system of rotating Rayleigh-Bénard convection is often invoked, with the majority of studies considering only working fluids with Prandtl numbers of Pr ≳ 1. However, liquid metals are characterized by distinctly smaller Prandtl numbers which in turn result in an inherently different type of convection. Here, we will present results from direct numerical simulations of rapidly rotating convection in a fluid with Pr ≈ 0.025 in cylindrical containers and Ekman numbers as low as 5 × 10-6. In this system, the Coriolis force is the source of two types of inertial modes, the so-called wall modes, that also exist at moderate Prandtl numbers, and cylinder-filling oscillatory modes, that are a unique feature of small Prandtl number convection. The obtained flow fields were analyzed using the Dynamic Mode Decomposition (DMD). This technique allows to extract and identify the structures that govern the dynamics of the system as well as their corresponding frequencies. We have investigated both the regime where the flow is purely oscillatory and the regime where wall modes and oscillatory modes co-exist. In the purely oscillatory regime, high and low frequency oscillatory modes characterize the flow. When both types of modes are present, the DMD reveals that the wall-attached modes dominate the flow dynamics. They precess with a relatively low frequency in retrograde direction. Nonetheless, also in this case, high frequency oscillations have a significant contribution.

  2. Lateral Casimir Force on a Rotating Particle near a Planar Surface.

    PubMed

    Manjavacas, Alejandro; Rodríguez-Fortuño, Francisco J; García de Abajo, F Javier; Zayats, Anatoly V

    2017-03-31

    We study the lateral Casimir force experienced by a particle that rotates near a planar surface. The origin of this force lies in the symmetry breaking induced by the particle rotation in the vacuum and thermal fluctuations of its dipole moment, and therefore, in contrast to lateral Casimir forces previously described in the literature for corrugated surfaces, it exists despite the translational invariance of the planar surface. Working within the framework of fluctuational electrodynamics, we derive analytical expressions for the lateral force and analyze its dependence on the geometrical and material properties of the system. In particular, we show that the direction of the force can be controlled by adjusting the particle-surface distance, which may be exploited as a new mechanism to manipulate nanoscale objects.

  3. Thermo-capillary driven flow under the influence of rotation and magnetic fields

    NASA Astrophysics Data System (ADS)

    Bhattacharjee, Pratik

    Microgravity conditions pose unique challenges for fluid handling and heat transfer applications. By controlling (curtailing or augmenting) the buoyant and thermocapillary convection, the latter being the dominant convective flow in a microgravity environment, significant advantages can be achieved in space based processing. The control of this surface tension gradient driven flow is sought using (1) rotation and (2) magnetic field, and the effects of these are computationally studied in two separate parts. In the first part, the main parameters are the solutal Marangoni number Mc, representing the surface tension gradient force and the Taylor number Ta representing the rotational effect. For given values of Mc, certain values of Ta were detected where the Sherwood number Sh, representing the convective solute flux, and the convective flow effects are noticeably reduced. These results can provide conditions under which convective flow transport approaches the diffusion limited transport, which is desirable, for example in the production of higher quality protein crystals. In the second part, a two-fluid layer system, with the lower fluid being a non-conducting ferrofluid, is considered under the influence of a horizontal temperature gradient. To capture the deformable interface, a numerical method to solve the Navier-Stokes equations, Heat equations and Maxwell's equations was developed using a hybrid Level Set/Volume-of-Fluid technique. The convective velocities and heat fluxes were studied under various regimes of the thermal Marangoni number Ma, the external field represented by the magnetic Bond number Bom, and various gravity levels, Fr. Regimes where the convection were either curtailed or augmented were identified. It was found that the surface force due to the step change in the magnetic permeability at the interface could be suitably utilized to control the instability at the interface.

  4. Studies in Forced and Time Varying Turbulent Flows

    NASA Technical Reports Server (NTRS)

    Grosch, Chester E.

    2005-01-01

    The reasearch focused on two areas; (a) the dynamics of forced turbulent flows and (b) time filtered Large Eddy Simulations (TLES). The dynamics of turbulent flows arising from external forcing of the turbulence are poorly understood. In particular, here are many unanswered questions relating the basic dynamical balances and the existence or nonexistence of statistical equilibrium of forced turbulent flows. This research used rapid distortion theory and direct numerical simulations to explore these questions. The properties of the temporally filtered Navier-Stokes equations were also studied.

  5. Some questions on the Coriolis force, the structure of rotational states and the IBM

    SciTech Connect

    Khoo, T.L.

    1980-01-01

    Participants in the Round Table Discussion at the International Conference on Band Structure and Nuclear Dynamics were to make editorial comments on what transpired during the conference. This paper contains comments of one panel member on questions which he feels were not addressed during the meeting. His comments concern the Coriolis force in rotating nuclei and its relation to the nucleon-nucleon interaction, the microscopic origin of rotational states, and the interacting boson model. (RWR)

  6. Reaching during virtual rotation: context specific compensations for expected coriolis forces

    NASA Technical Reports Server (NTRS)

    Cohn, J. V.; DiZio, P.; Lackner, J. R.

    2000-01-01

    Subjects who are in an enclosed chamber rotating at constant velocity feel physically stationary but make errors when pointing to targets. Reaching paths and endpoints are deviated in the direction of the transient inertial Coriolis forces generated by their arm movements. By contrast, reaching movements made during natural, voluntary torso rotation seem to be accurate, and subjects are unaware of the Coriolis forces generated by their movements. This pattern suggests that the motor plan for reaching movements uses a representation of body motion to prepare compensations for impending self-generated accelerative loads on the arm. If so, stationary subjects who are experiencing illusory self-rotation should make reaching errors when pointing to a target. These errors should be in the direction opposite the Coriolis accelerations their arm movements would generate if they were actually rotating. To determine whether such compensations exist, we had subjects in four experiments make visually open-loop reaches to targets while they were experiencing compelling illusory self-rotation and displacement induced by rotation of a complex, natural visual scene. The paths and endpoints of their initial reaching movements were significantly displaced leftward during counterclockwise illusory rotary displacement and rightward during clockwise illusory self-displacement. Subjects reached in a curvilinear path to the wrong place. These reaching errors were opposite in direction to the Coriolis forces that would have been generated by their arm movements during actual torso rotation. The magnitude of path curvature and endpoint errors increased as the speed of illusory self-rotation increased. In successive reaches, movement paths became straighter and endpoints more accurate despite the absence of visual error feedback or tactile feedback about target location. When subjects were again presented a stationary scene, their initial reaches were indistinguishable from pre

  7. Reaching during virtual rotation: context specific compensations for expected coriolis forces.

    PubMed

    Cohn, J V; DiZio, P; Lackner, J R

    2000-06-01

    Subjects who are in an enclosed chamber rotating at constant velocity feel physically stationary but make errors when pointing to targets. Reaching paths and endpoints are deviated in the direction of the transient inertial Coriolis forces generated by their arm movements. By contrast, reaching movements made during natural, voluntary torso rotation seem to be accurate, and subjects are unaware of the Coriolis forces generated by their movements. This pattern suggests that the motor plan for reaching movements uses a representation of body motion to prepare compensations for impending self-generated accelerative loads on the arm. If so, stationary subjects who are experiencing illusory self-rotation should make reaching errors when pointing to a target. These errors should be in the direction opposite the Coriolis accelerations their arm movements would generate if they were actually rotating. To determine whether such compensations exist, we had subjects in four experiments make visually open-loop reaches to targets while they were experiencing compelling illusory self-rotation and displacement induced by rotation of a complex, natural visual scene. The paths and endpoints of their initial reaching movements were significantly displaced leftward during counterclockwise illusory rotary displacement and rightward during clockwise illusory self-displacement. Subjects reached in a curvilinear path to the wrong place. These reaching errors were opposite in direction to the Coriolis forces that would have been generated by their arm movements during actual torso rotation. The magnitude of path curvature and endpoint errors increased as the speed of illusory self-rotation increased. In successive reaches, movement paths became straighter and endpoints more accurate despite the absence of visual error feedback or tactile feedback about target location. When subjects were again presented a stationary scene, their initial reaches were indistinguishable from pre

  8. Reaching during virtual rotation: context specific compensations for expected coriolis forces

    NASA Technical Reports Server (NTRS)

    Cohn, J. V.; DiZio, P.; Lackner, J. R.

    2000-01-01

    Subjects who are in an enclosed chamber rotating at constant velocity feel physically stationary but make errors when pointing to targets. Reaching paths and endpoints are deviated in the direction of the transient inertial Coriolis forces generated by their arm movements. By contrast, reaching movements made during natural, voluntary torso rotation seem to be accurate, and subjects are unaware of the Coriolis forces generated by their movements. This pattern suggests that the motor plan for reaching movements uses a representation of body motion to prepare compensations for impending self-generated accelerative loads on the arm. If so, stationary subjects who are experiencing illusory self-rotation should make reaching errors when pointing to a target. These errors should be in the direction opposite the Coriolis accelerations their arm movements would generate if they were actually rotating. To determine whether such compensations exist, we had subjects in four experiments make visually open-loop reaches to targets while they were experiencing compelling illusory self-rotation and displacement induced by rotation of a complex, natural visual scene. The paths and endpoints of their initial reaching movements were significantly displaced leftward during counterclockwise illusory rotary displacement and rightward during clockwise illusory self-displacement. Subjects reached in a curvilinear path to the wrong place. These reaching errors were opposite in direction to the Coriolis forces that would have been generated by their arm movements during actual torso rotation. The magnitude of path curvature and endpoint errors increased as the speed of illusory self-rotation increased. In successive reaches, movement paths became straighter and endpoints more accurate despite the absence of visual error feedback or tactile feedback about target location. When subjects were again presented a stationary scene, their initial reaches were indistinguishable from pre

  9. On the nature of magnetic turbulence in rotating, shearing flows

    NASA Astrophysics Data System (ADS)

    Walker, Justin; Lesur, Geoffroy; Boldyrev, Stanislav

    2016-03-01

    The local properties of turbulence driven by the magnetorotational instability (MRI) in rotating, shearing flows are studied in the framework of a shearing-box model. Based on numerical simulations, we propose that the MRI-driven turbulence comprises two components: the large-scale shear-aligned strong magnetic field and the small-scale fluctuations resembling magnetohydrodynamic (MHD) turbulence. The energy spectrum of the large-scale component is close to k-2, whereas the spectrum of the small-scale component agrees with the spectrum of strong MHD turbulence k-3/2. While the spectrum of the fluctuations is universal, the outer-scale characteristics of the turbulence are not; they depend on the parameters of the system, such as the net magnetic flux. However, there is remarkable universality among the allowed turbulent states - their intensity v0 and their outer scale λ0 satisfy the balance condition v0/λ0 ˜ dΩ/dln r, where dΩ/dln r is the local orbital shearing rate of the flow. Finally, we find no sustained dynamo action in the Pm = 1 zero net-flux case for Reynolds numbers as high as 45 000, casting doubts on the existence of an MRI dynamo in the Pm ≤ 1 regime.

  10. Chaotic rotation of a spheroidal particle in simple shear flow

    NASA Astrophysics Data System (ADS)

    Rosén, Tomas

    2017-06-01

    The angular motion of a neutrally buoyant prolate spheroidal particle in simple shear flow has previously been found to follow two-dimensional dynamics similar to a Duffing-van der Pol oscillator as a consequence of inertia of the surrounding fluid. This behavior was however only present if the aspect ratio is large enough. When decreasing the particle aspect ratio, the particle could be found to perform period-doubled or chaotic orbits as effects of particle inertia also influence the dynamics. In this work, it is demonstrated that the onset of complex dynamics is through a Shilnikov bifurcation as the log-rolling state (particle is rotating around its symmetry axis, which is parallel to the vorticity direction) is transformed from a regular saddle node into a saddle focus when particle inertia is increased. Furthermore, it is shown that the same also applies for the two dimensional Duffing-van der Pol oscillator when including inertial terms. These results open up the possibility of developing a reduced model to mimic the influence of both fluid and particle inertia on the angular dynamics of spheroidal particles in simple shear flow, which can be used in fluid simulations with Lagrangian particles.

  11. Perturbations of Axisymmetric Rotational Flows in Rocket Chambers

    NASA Astrophysics Data System (ADS)

    Short, M.; Buckmaster, J.; Balachandar, S.

    1998-11-01

    In a solid-propellant rocket chamber the effects of gases from the propellant surface blows off the boundary layer and the rotational flow field is, nominally, an inviscid one. This type of flow was first discussed by G.I. Taylor[1], and the axially symmetric solution appropriate for rockets was derived by F. Culick [2]. We will describe what happens when axisymmetric solution is perturbed, because cross-section is not circular, or because efflux at the wall is not uniform. O(ɛ ) perturbations generate O(ɛ ) axial vorticity which is convected towards the axis and grows like 1/r^2 as r arrow 0 where r is the radial distance from the axis. Consequently, even for small perturbations, there is an inviscid nonlinear domain of radius (ɛ )^1/2 in which the axial vorticity is O(1). The solution in this inviscid domain is, in turn, regularized at the axis by viscous terms in a domain of radius (Re)-1/2. Implicit here is the assumption ɛ << 1, ɛ >> 1/Re. If on the other hand, ɛ << 1/Re << 1 there is no nonlinear domain, simply a viscous patch of radius (Re)-1/2 in which vorticity is O(ɛ Re), surrounded by an inviscid annulus in which vorticity is O(ɛ ). These asymptotic results are verified with fully nonlinear simulations. [1] G.I. Taylor Proc. Roy. Soc. A (1956) 234, 456. [2] F.E.C. Culick AIAA J. (1966) 4, 1462.

  12. Dynamic flow reattachment on a rotating blade undergoing dynamic stall

    NASA Astrophysics Data System (ADS)

    Raghav, Vrishank; Komerath, Narayanan

    2016-11-01

    A 2-bladed rigid rotor undergoing retreating blade dynamic stall in a low-speed wind tunnel was used to study the 3-dimensional flow reattachment at the end of the dynamic stall cycle. Phase-locked stereoscopic Particle Image Velocimetry was used to capture the velocity field during reattachment. Continuing from prior studies on the inception and progression of 3-D rotating dynamic stall for this test case, phase-resolved, ensemble-averaged results are presented for different values of rotor advance ratio at varying spanwise stations along the blade. The results show the nominal reattachment getting delayed in rotor azimuth with higher advance ratio. At low advance ratio reattachment starts at the leading-edge and progresses towards the trailing-edge with vortex shedding transporting excess vorticity away from the leading-edge. At higher advance ratio, vortex shedding is not observed, instead the vortical structure shrinks in size while the flow close to the trailing-edge appears to reattach. At the higher advance ratio conditions, spanwise vorticity transport appears to be the mechanism to transport excess vorticity away from the leading-edge. The possible causes for a switch in mechanism of vorticity transport are also presented.

  13. The effect of grip force, stroke rotation and frequency on discomfort for a torqueing tasks.

    PubMed

    Bano, Farheen; Mallick, Zulqernian; Khan, Abid Ali

    2015-08-08

    Occupational tasks involve awkward upper limb postures, especially movement of forearm with repetitive combined gripping and torqueing exertions, which may lead to development of WMSDs. From the literature survey it was observed that there was a lack of studies focussed on the combined effect of torque and grip exertions on forearm discomfort. The present study was to investigate the effects of grip force, stroke rotation and frequency of exertions on discomfort and Electromyography (EMG) activities of the forearm muscles in a repetitive torqueing task. Twenty-seven male participants volunteered in this study. The participants performed repetitive exertions for a 5 minutes duration for each combination of the different levels of stroke rotation, grip force and frequency of exertions. Three levels of stroke rotation, three levels of grip force and three levels of frequency of exertion were chosen as independent variables. Therefore a 3 × 3 customized factorial design was used for the experiment for each level of grip force. Hence, the study was divided into three groups on the basis of grip force (50N, 70N and 90N). The ANOVA showed that stroke rotation and frequency of exertion were significant on discomfort. Further Students Newmann test (SNK) revealed that discomfort was increased with increasing stroke rotation and frequency of exertion. The multivariate analysis of variances (MANOVA) performed on EMG data instead of ANOVA because EMG activities of five muscles simultaneously were recorded. The Results found that extensor muscles were more fatigued in torqueing with gripping task. It was found that stroke rotation for the torqueing tasks must be kept below 45°. It was concluded that it is important to control stroke rotation to improve performance of repetitive torqueing activity.

  14. THE FORCE-FREE MAGNETOSPHERE OF A ROTATING BLACK HOLE

    SciTech Connect

    Contopoulos, Ioannis; Kazanas, Demosthenes

    2013-03-10

    We revisit the Blandford-Znajek process and solve the fundamental equation that governs the structure of the steady-state force-free magnetosphere around a Kerr black hole. The solution depends on the distributions of the magnetic field angular velocity {omega} and the poloidal electric current I. These are not arbitrary. They are determined self-consistently by requiring that magnetic field lines cross smoothly the two singular surfaces of the problem: the inner ''light surface'' located inside the ergosphere and the outer ''light surface'' which is the generalization of the pulsar light cylinder. We find the solution for the simplest possible magnetic field configuration, the split monopole, through a numerical iterative relaxation method analogous to the one that yields the structure of the steady-state axisymmetric force-free pulsar magnetosphere. We obtain the rate of electromagnetic extraction of energy and confirm the results of Blandford and Znajek and of previous time-dependent simulations. Furthermore, we discuss the physical applicability of magnetic field configurations that do not cross both ''light surfaces''.

  15. The Force-Free Magnetosphere of a Rotating Black Hole

    NASA Technical Reports Server (NTRS)

    Contopoulos, Ioannis; Kazanas, Demosthenes; Papadopoulos, Demetrios B.

    2013-01-01

    We revisit the Blandford-Znajek process and solve the fundamental equation that governs the structure of the steady-state force-free magnetosphere around a Kerr black hole. The solution depends on the distributions of the magnetic field angular velocity and the poloidal electric current. These are not arbitrary. They are determined self-consistently by requiring that magnetic field lines cross smoothly the two singular surfaces of the problem: the inner "light surface" located inside the ergosphere and the outer "light surface" which is the generalization of the pulsar light cylinder.We find the solution for the simplest possible magnetic field configuration, the split monopole, through a numerical iterative relaxation method analogous to the one that yields the structure of the steady-state axisymmetric force-free pulsar magnetosphere. We obtain the rate of electromagnetic extraction of energy and confirm the results of Blandford and Znajek and of previous time-dependent simulations. Furthermore, we discuss the physical applicability of magnetic field configurations that do not cross both "light surfaces."

  16. Field measurement of basal forces generated by erosive debris flows

    USGS Publications Warehouse

    McCoy, S.W.; Tucker, G.E.; Kean, J.W.; Coe, J.A.

    2013-01-01

    It has been proposed that debris flows cut bedrock valleys in steeplands worldwide, but field measurements needed to constrain mechanistic models of this process remain sparse due to the difficulty of instrumenting natural flows. Here we present and analyze measurements made using an automated sensor network, erosion bolts, and a 15.24 cm by 15.24 cm force plate installed in the bedrock channel floor of a steep catchment. These measurements allow us to quantify the distribution of basal forces from natural debris‒flow events that incised bedrock. Over the 4 year monitoring period, 11 debris‒flow events scoured the bedrock channel floor. No clear water flows were observed. Measurements of erosion bolts at the beginning and end of the study indicated that the bedrock channel floor was lowered by 36 to 64 mm. The basal force during these erosive debris‒flow events had a large‒magnitude (up to 21 kN, which was approximately 50 times larger than the concurrent time‒averaged mean force), high‒frequency (greater than 1 Hz) fluctuating component. We interpret these fluctuations as flow particles impacting the bed. The resulting variability in force magnitude increased linearly with the time‒averaged mean basal force. Probability density functions of basal normal forces were consistent with a generalized Pareto distribution, rather than the exponential distribution that is commonly found in experimental and simulated monodispersed granular flows and which has a lower probability of large forces. When the bed sediment thickness covering the force plate was greater than ~ 20 times the median bed sediment grain size, no significant fluctuations about the time‒averaged mean force were measured, indicating that a thin layer of sediment (~ 5 cm in the monitored cases) can effectively shield the subjacent bed from erosive impacts. Coarse‒grained granular surges and water‒rich, intersurge flow had very similar basal force distributions despite

  17. Flow regime map and deposition rate uniformity in vertical rotating-disk OMVPE reactors

    NASA Astrophysics Data System (ADS)

    Biber, Catharina R.; Wang, Christine A.; Motakef, Shahryar

    1992-10-01

    A quantitative map of flow regimes has been developed for rotating-disk organometallic vapor epitaxy reactors. Scaling laws and flow visualization experiments over a wide range of reactor geometries and processing conditions were used to generate analytical relationships for boundaries separating the plug-flow regime from the bouyancy- and rotation-induced-flow regimes. For the growth of epitaxial layers with a high degree of uniformity and interface abruptness, the plug-flow regime is preferred. The locus of maximum deposition rate uniformity within the plug-flow regime was found by numerical simulation studies. Operation at high rotation rates close to the boundary between the plug-flow and rotation-induced-flow regimes provides for nearly uniform deposition rates.

  18. On the Inertial Force Experienced by a Solid Body Undergoing Rotation about Two Axes

    SciTech Connect

    Christov, I. C.; Christov, C. I.

    2009-10-29

    The theory of rigid body motion is used to derive the governing equations, in terms of the Eulerian angles, of a top rotating about two axes. Then, a formula for the 'lifting' component of the net inertial force (as function of the angle of inclination, the top's two angular velocities and its moments of inertia) is derived for a particular motion termed constrained nutation. In a distinguished limit, the critical value of the angle of inclination, i.e., the value for which the vertical component of the net inertial force acting on the top overcomes the weight of the rotating system, is calculated.

  19. Forced rotation of nanograting in glass by pulse-front tilted femtosecond laser direct writing.

    PubMed

    Dai, Ye; Ye, Junyi; Gong, Min; Ye, Xiuyi; Yan, Xiaona; Ma, Guohong; Qiu, Jianrong

    2014-11-17

    Femtosecond pulse laser with tilted intensity front demonstrates the capability of rotating the writing of nanograting in glass in 3D space. Other than the light polarization, this phenomenon is also associated with the quill-writing effect, which depends on the correlation between the sample movement and the pulse front tilt. This is because a pondermotive force, perpendicular to the tilted intensity plane, can push the excited electron plasma forward towards the pulse front. This behavior further tilts the electrical field plane and eventually result in a forced rotation of nanograting in 3D space.

  20. Tool design in friction stir processing: dynamic forces and material flow

    SciTech Connect

    D. E. Clark; K. S. Miller; C. R. Tolle

    2006-08-01

    Friction stir processing involves severe plastic flow within the material; the nature of this flow determines the final morphology of the weld, the resulting microstructures, and the presence or absence of defects such as internal cavities or "wormholes." The forces causing this plastic flow are a function of process parameters, including spindle speed, travel speed, and tool design and angle. Some of these forces are directly applied or a result of the mechanical constraints and compliance of the apparatus, while others are resolved forces resulting from an interaction of these applied forces and tool forces governed by processing parameters, and can be diminished or even reversed in sign with appropriate choices of process parameters. The present investigation is concerned mostly with the friction stir processing of 6061-T6 aluminum plates in a low-cost apparatus built from a commercial milling machine. A rotating dynamometer allows in-process measurement of actual spindle speed, torque, and forces in the x-, y-, and z-directions, as well as force control on these axes. Two main types of tool, both unthreaded, were used. The first had a pin about 4 mm in diameter and 4 mm in length, with a shoulder about 10 mm in diameter, and produced wormhole defects; the second, with a tapered pin about 5 mm long, a base diameter of about 6 mm, a tip diameter of about 4 mm, and a shoulder diameter (flat or dished) of about 19 mm, produced sound welds over a wide range of parameters.

  1. Shoulder muscle forces during driving: Sudden steering can load the rotator cuff beyond its repair limit.

    PubMed

    Pandis, Petros; Prinold, Joe A I; Bull, Anthony M J

    2015-10-01

    Driving is one of the most common everyday tasks and the rotator cuff muscles are the primary shoulder stabilisers. Muscle forces during driving are not currently known, yet knowledge of these would influence important clinical advice such as return to activities after surgery. The aim of this study is to quantify shoulder and rotator cuff muscle forces during driving in different postures. A musculoskeletal modelling approach is taken, using a modified driving simulator in combination with an upper limb musculoskeletal model (UK National Shoulder Model). Motion data and external force vectors were model inputs and upper limb muscle and joint forces were the outputs. Comparisons of the predicted glenohumeral joint forces were compared to in vivo literature values, with good agreement demonstrated (61 SD 8% body weight mean peak compared to 60 SD 1% body weight mean peak). High muscle activation was predicted in the rotator cuff muscles; particularly supraspinatus (mean 55% of the maximum and up to 164 SD 27 N). This level of loading is up to 72% of mean failure strength for supraspinatus repairs, and could therefore be dangerous for some cases. Statistically significant and large differences are shown to exist in the joint and muscle forces for different driving positions as well as steering with one or both hands (up to 46% body weight glenohumeral joint force). These conclusions should be a key consideration in rehabilitating the shoulder after surgery, preventing specific upper limb injuries and predicting return to driving recommendations. Copyright © 2015. Published by Elsevier Ltd.

  2. Multidimensional traction force microscopy reveals out-of-plane rotational moments about focal adhesions.

    PubMed

    Legant, Wesley R; Choi, Colin K; Miller, Jordan S; Shao, Lin; Gao, Liang; Betzig, Eric; Chen, Christopher S

    2013-01-15

    Recent methods have revealed that cells on planar substrates exert both shear (in-plane) and normal (out-of-plane) tractions against the extracellular matrix (ECM). However, the location and origin of the normal tractions with respect to the adhesive and cytoskeletal elements of cells have not been elucidated. We developed a high-spatiotemporal-resolution, multidimensional (2.5D) traction force microscopy to measure and model the full 3D nature of cellular forces on planar 2D surfaces. We show that shear tractions are centered under elongated focal adhesions whereas upward and downward normal tractions are detected on distal (toward the cell edge) and proximal (toward the cell body) ends of adhesions, respectively. Together, these forces produce significant rotational moments about focal adhesions in both protruding and retracting peripheral regions. Temporal 2.5D traction force microscopy analysis of migrating and spreading cells shows that these rotational moments are highly dynamic, propagating outward with the leading edge of the cell. Finally, we developed a finite element model to examine how rotational moments could be generated about focal adhesions in a thin lamella. Our model suggests that rotational moments can be generated largely via shear lag transfer to the underlying ECM from actomyosin contractility applied at the intracellular surface of a rigid adhesion of finite thickness. Together, these data demonstrate and probe the origin of a previously unappreciated multidimensional stress profile associated with adhesions and highlight the importance of new approaches to characterize cellular forces.

  3. Green's formula and variational principles for cosmic-ray transport with application to rotating and shearing flows

    NASA Technical Reports Server (NTRS)

    Webb, G. M.; Jokipii, J. R.; Morfill, G. E.

    1994-01-01

    Green's theorem and Green's formula for the diffusive cosmic-ray transport equation in relativistic flows are derived. Green's formula gives the solution of the transport equation in terms of the Green's function of the adjoint transport equation, and in terms of distributed sources throughout the region R of interest, plus terms involving the particle intensity and streaming on the boundary. The adjoint transport equation describes the time-reversed particle transport. An Euler-Lagrange variational principle is then obtained for both the mean scattering frame distribution function f, and its adjoint f(dagger). Variations of the variational functional with respect to f(dagger) yield the transport equation, whereas variations of f yield the adjoint transport equation. The variational principle, when combined with Noether's theorem, yields the conservation law associated with Green's theorem. An investigation of the transport equation for steady, azimuthal, rotating flows suggests the introduction of a new independent variable H to replace the comoving frame momentum variable p'. For the case of rigid rotating flows, H is conserved and is shown to be analogous to the Hamiltonian for a bead on a rigidly rotating wire. The variable H corresponds to a balance between the centrifugal force and the particle inertia in the rotating frame. The physical interpretation of H includes a discussion of nonrelativistic and special relativistic rotating flows as well as the cases of aziuthal, differentially rotating flows about Schwarzs-child and Kerr black holes. Green's formula is then applied to the problem of the acceleration of ultra-high-energy cosmic rays by galactic rotation. The model for galactic rotation assumes an angular velocity law Omega = Omega(sub 0)(omega(sub 0)/omega), where omega denotes radial distance from the axis of rotation. Green's functions for the galactic rotation problem are used to investigate the spectrum of accelerated particles arising from

  4. Green's formula and variational principles for cosmic-ray transport with application to rotating and shearing flows

    NASA Technical Reports Server (NTRS)

    Webb, G. M.; Jokipii, J. R.; Morfill, G. E.

    1994-01-01

    Green's theorem and Green's formula for the diffusive cosmic-ray transport equation in relativistic flows are derived. Green's formula gives the solution of the transport equation in terms of the Green's function of the adjoint transport equation, and in terms of distributed sources throughout the region R of interest, plus terms involving the particle intensity and streaming on the boundary. The adjoint transport equation describes the time-reversed particle transport. An Euler-Lagrange variational principle is then obtained for both the mean scattering frame distribution function f, and its adjoint f(dagger). Variations of the variational functional with respect to f(dagger) yield the transport equation, whereas variations of f yield the adjoint transport equation. The variational principle, when combined with Noether's theorem, yields the conservation law associated with Green's theorem. An investigation of the transport equation for steady, azimuthal, rotating flows suggests the introduction of a new independent variable H to replace the comoving frame momentum variable p'. For the case of rigid rotating flows, H is conserved and is shown to be analogous to the Hamiltonian for a bead on a rigidly rotating wire. The variable H corresponds to a balance between the centrifugal force and the particle inertia in the rotating frame. The physical interpretation of H includes a discussion of nonrelativistic and special relativistic rotating flows as well as the cases of aziuthal, differentially rotating flows about Schwarzs-child and Kerr black holes. Green's formula is then applied to the problem of the acceleration of ultra-high-energy cosmic rays by galactic rotation. The model for galactic rotation assumes an angular velocity law Omega = Omega(sub 0)(omega(sub 0)/omega), where omega denotes radial distance from the axis of rotation. Green's functions for the galactic rotation problem are used to investigate the spectrum of accelerated particles arising from

  5. Mixed convection flow and heat transfer in entrance region of rectangular ducts rotating about a parallel axis

    SciTech Connect

    Soong, C.Y.; Yan, W.M.

    1995-12-31

    The objective of the present work is to investigate the laminar mixed convection flow and heat transfer in the entrance region of heated rectangular ducts rotating about a parallel axis. Heating conditions of isothermal and iso-flux are both considered. Boussinesq approximation is invoked to take into account buoyancy effect induced by centrifugal force. Navier-Stokes/Boussinesq system can be cast into a dimensionless form, in which five governing parameters, the Prandtl number Pr, rotational Reynolds number J, rotational Grashof number Gr{sub {Omega}}, aspect ratio {gamma} and the eccentricity E, are involved. Mechanisms of secondary vortex development in the ducts are explored by a theoretical analysis on vorticity transport equation. The values of Pr and E are fixed as 0.7 and 10, respectively. For various combinations of the other thee parameters, a vorticity-velocity method implemented with a marching technique is employed to solve the resultant three-dimensional system for simultaneously developing flow and temperature fields. The emphasis is placed on the rotational effects, including both coriolis force and centrifugal buoyancy; on the non-isothermal flow and the related heat transfer. The results reveal that the friction factors and heat transfer rates can be enhanced by Coriolis and rotation-induced buoyancy effects; and the variations of the local values are closely related to the evolution of the secondary vortices in ducts. The differences in flow behaviors and thermal characteristics for UWT and UHF are also investigated by the present theoretical analysis on secondary flow mechanism as well as the computational results.

  6. A rotating two-phase gas/liquid flow for pressure reduction in underwater plasma arc welding

    SciTech Connect

    Steinkamp, H.; Creutz, M.; Mewes, D.; Bartzsch, J.

    1994-12-31

    Plasma arc welding processes are used in off-shore industry for the construction and maintenance in the wet surrounding of underwater structures and pipelines. In greater water depth the density of the plasma gas increase because of the greater hydrostatic pressure. This causes an increase of the conductive heat losses to the wet surrounding. To keep up the energy flux to the workpiece a pressure reduction is favorable against the surrounding. To keep up the energy flux to the workpiece a pressure reduction is favorable against the surrounding. The plasma arc has to burn in a locally dry area. This requirement can be fulfilled by a rotating disc placed above the workpiece. In the gap between the lower end of the cylinder and the workpiece a rotating two-phase flow is maintained. The flow around the rotating disc is experimentally investigated. The rotating disc is placed above the surface of the workpiece which is simulated by a flat plate. Water is forced out of the cylinder due to centrifugal forces set up by the rotating disc and flat plate. The velocity distribution in the flow is measured by Laser-Doppler-Anemometry. The phase distribution in the two-phase flow in the gap is measured by local electrical probes. The static pressure in the gaseous atmosphere is reduced in comparison to the hydrostatic pressure of the surrounding water. The pressure reduction is given by the void fraction, the phase distribution and the volume flow rates of both phases in the gap as well as by the speed of revolution and the design of the disc and the work surface. Apart from the investigations on the fluid dynamics, the method to reduce the pressure was technically proved. Experiments were carried out under water with a plasma MIG welder.

  7. Computed Tomography Analysis of Postsurgery Femoral Component Rotation Based on a Force Sensing Device Method versus Hypothetical Rotational Alignment Based on Anatomical Landmark Methods: A Pilot Study.

    PubMed

    Kreuzer, Stefan W; Pourmoghaddam, Amir; Leffers, Kevin J; Johnson, Clint W; Dettmer, Marius

    2016-01-01

    Rotation of the femoral component is an important aspect of knee arthroplasty, due to its effects on postsurgery knee kinematics and associated functional outcomes. It is still debated which method for establishing rotational alignment is preferable in orthopedic surgery. We compared force sensing based femoral component rotation with traditional anatomic landmark methods to investigate which method is more accurate in terms of alignment to the true transepicondylar axis. Thirty-one patients underwent computer-navigated total knee arthroplasty for osteoarthritis with femoral rotation established via a force sensor. During surgery, three alternative hypothetical femoral rotational alignments were assessed, based on transepicondylar axis, anterior-posterior axis, or the utilization of a posterior condyles referencing jig. Postoperative computed tomography scans were obtained to investigate rotation characteristics. Significant differences in rotation characteristics were found between rotation according to DKB and other methods (P < 0.05). Soft tissue balancing resulted in smaller deviation from anatomical epicondylar axis than any other method. 77% of operated knees were within a range of ±3° of rotation. Only between 48% and 52% of knees would have been rotated appropriately using the other methods. The current results indicate that force sensors may be valuable for establishing correct femoral rotation.

  8. Computed Tomography Analysis of Postsurgery Femoral Component Rotation Based on a Force Sensing Device Method versus Hypothetical Rotational Alignment Based on Anatomical Landmark Methods: A Pilot Study

    PubMed Central

    Kreuzer, Stefan W.; Pourmoghaddam, Amir; Leffers, Kevin J.; Johnson, Clint W.; Dettmer, Marius

    2016-01-01

    Rotation of the femoral component is an important aspect of knee arthroplasty, due to its effects on postsurgery knee kinematics and associated functional outcomes. It is still debated which method for establishing rotational alignment is preferable in orthopedic surgery. We compared force sensing based femoral component rotation with traditional anatomic landmark methods to investigate which method is more accurate in terms of alignment to the true transepicondylar axis. Thirty-one patients underwent computer-navigated total knee arthroplasty for osteoarthritis with femoral rotation established via a force sensor. During surgery, three alternative hypothetical femoral rotational alignments were assessed, based on transepicondylar axis, anterior-posterior axis, or the utilization of a posterior condyles referencing jig. Postoperative computed tomography scans were obtained to investigate rotation characteristics. Significant differences in rotation characteristics were found between rotation according to DKB and other methods (P < 0.05). Soft tissue balancing resulted in smaller deviation from anatomical epicondylar axis than any other method. 77% of operated knees were within a range of ±3° of rotation. Only between 48% and 52% of knees would have been rotated appropriately using the other methods. The current results indicate that force sensors may be valuable for establishing correct femoral rotation. PMID:26881086

  9. Effects of Taylor-Görtler vortices on turbulent flows in a spanwise-rotating channel

    NASA Astrophysics Data System (ADS)

    Dai, Yijun; Huang, Weixi; Xu, Chunxiao

    2016-11-01

    Fully developed turbulent channel flow with spanwise rotation has been studied by direct numerical simulation at Rem = 2800, 7000 and 20000 with rotation number 0 <= Rom <= 0.5. The width of the computational box is adjusted for each case to contain two pairs of Taylor-Görtler (TG) vortices. Under a low rotation rate, the turbulent vortical structures are strongly affected by the TG vortices. A conditional average method is employed to investigate the effects. In the upwash region where the fluid is pumped away from the pressure wall by the TG vortices, turbulence is enhanced, while the reverse is the case in the downwash region. Through budget analysis of the transport equation of vorticity fluctuation, it is revealed that the stretching along the wall-normal direction caused by the TG vortices plays an important role in initiating the difference of turbulence intensity between the two regions, which is further augmented by the Coriolis force in the streamwise direction. The effects of TG vortices is weakened at higher Reynolds number. Meanwhile, the shear stress on the suction wall is observed to fluctuate in a quasi-periodic manner at Rem = 7000 and Rom = 0.3, which is induced by the TG vortices. The work is supported by National Natural Science Foundation of China (Project No. 11490551, 11472154, 11322221, 11132005).

  10. Effects of toroidal rotation on electron heat transport via changes in inertial force and impurity density

    NASA Astrophysics Data System (ADS)

    Narita, E.; Honda, M.; Yoshida, M.; Hayashi, N.; Urano, H.; Ide, S.

    2017-04-01

    Two types of JT-60U discharges are studied with an emphasis on toroidal rotation: in one discharge, which is characterized by the existence of an internal transport barrier (ITB), electron heat transport in the core region is affected by the toroidal rotation direction, while in the other discharge, which is a conventional H-mode plasma without an ITB, the clear correlation between the toroidal rotation direction and electron heat transport is not observed. In both discharges, the impurity density is also found to vary together with the rotation velocity profile. With a flux-tube gyrokinetic code, we have found that the effects of the changes in the rotation velocity profile and the impurity density on electron heat transport are different between these discharges. Including the effects explains the tendency observed in the experiments. First, regarding the rotation velocity profile, which influences heat transport through the inertial force, the dependence of heat transport on the rotation direction changes, according to the gradient of the rotation velocity. Next, an increase in the impurity density stabilizes the ion temperature gradient mode, but can destabilize the trapped electron mode. Therefore, it is found that the difference in the impact of the impurity density on electron heat transport in these discharges can be attributed to the difference in the dominant instability.

  11. Turbulent Flows Driven by the Mechanical Forcing of an Ellipsoidal Container

    NASA Astrophysics Data System (ADS)

    Favier, Benjamin; Le Bars, Michael; Grannan, Alexander; Ribeiro, Adolfo; Aurnou, Jonathan; Irphe Team; Spinlab Team

    2015-11-01

    We present a combination of laboratory experiments and numerical simulations modelling geophysically relevant mechanical forcings. Libration and tides correspond to the periodic perturbation of a body's rotation rate and shape, and are both due to gravitational interactions with orbiting companions. Such mechanical forcings can convey a fraction of the rotational energy available and generate intense turbulence in the fluid interior of satellites and planets. We investigate the fluid motions inside a librating or tidally deformed triaxial ellipsoidal container filled with an incompressible fluid. In both cases, the turbulent flow is driven by the elliptic instability which is a triadic resonance between two inertial modes and the base flow. We characterize the transition to turbulence as triadic resonances develop while also investigating both intermittent and sustained regimes. It is shown that the flow is largely independent of the properties of the mechanical forcing, hinting at a possible universal behaviour of the saturated elliptical instability. The existence of such intense flows may play an important role in understanding the thermal and magnetic evolution of celestial bodies. This work was funded by the French Agence Nationale pour la Recherche and the National Science Foundation Geophysics Program.

  12. Unsteady MHD free convection flow of rotating Jeffrey fluid embedded in a porous medium with ramped wall temperature

    NASA Astrophysics Data System (ADS)

    Zin, N. A. Mohd; Khan, I.; Shafie, S.

    2017-09-01

    The effect of radiative heat transfer on unsteady magnetohydrodynamic (MHD) free convection flow of rotating Jeffrey fluid past an infinite vertical plate saturated in a porous medium with ramped wall temperature is investigated. The incompressible fluid is taken electrically conducting under influence of transverse magnetic field which perpendicular to the flow. An appropriate dimensionless variables are employed to the governing equations and solved analytically by Laplace transform technique. The results of several controlling parameters for both ramped wall temperature and an isothermal plate are presented graphically with comprehensive discussions. It has been observed that, an increase in rotation parameter, reduced the primary velocity, but an opposite behaviour is noticed for the secondary velocity. Moreover, large values of Hartmann number tends to retard the fluid flow due to the Lorentz force.

  13. Flutter and oscillating air-force calculations for an airfoil in two-dimensional supersonic flow

    NASA Technical Reports Server (NTRS)

    Garrick, I E; Rubinow, S I

    1946-01-01

    A connected account is given of the Possio theory of non-stationary flow for small disturbances in a two-dimensional supersonic flow and of its application to the determination of the aerodynamic forces on an oscillating airfoil. Further application is made to the problem of wing flutter in the degrees of freedom - torsion, bending, and aileron rotations. Numerical tables for flutter calculations are provided for various values of the Mach number greater than unity. Results for bending-torsion wing flutter are shown in figures and are discussed. The static instabilities of divergence and aileron reversal are examined as is a one-degree-of-freedom case of torsional oscillatory instability.

  14. Reduced muscle fiber force production and disrupted myofibril architecture in patients with chronic rotator cuff tears.

    PubMed

    Mendias, Christopher L; Roche, Stuart M; Harning, Julie A; Davis, Max E; Lynch, Evan B; Sibilsky Enselman, Elizabeth R; Jacobson, Jon A; Claflin, Dennis R; Calve, Sarah; Bedi, Asheesh

    2015-01-01

    A persistent atrophy of muscle fibers and an accumulation of fat, collectively referred to as fatty degeneration, commonly occur in patients with chronic rotator cuff tears. The etiology of fatty degeneration and function of the residual rotator cuff musculature have not been well characterized in humans. We hypothesized that muscles from patients with chronic rotator cuff tears have reduced muscle fiber force production, disordered myofibrils, and an accumulation of fat vacuoles. The contractility of muscle fibers from biopsy specimens of supraspinatus muscles of 13 patients with chronic full-thickness posterosuperior rotator cuff tears was measured and compared with data from healthy vastus lateralis muscle fibers. Correlations between muscle fiber contractility, American Shoulder and Elbow Surgeons (ASES) scores, and tear size were analyzed. Histology and electron microscopy were also performed. Torn supraspinatus muscles had a 30% reduction in maximum isometric force production and a 29% reduction in normalized force compared with controls. Normalized supraspinatus fiber force positively correlated with ASES score and negatively correlated with tear size. Disordered sarcomeres were noted, along with an accumulation of lipid-laden macrophages in the extracellular matrix surrounding supraspinatus muscle fibers. Patients with chronic supraspinatus tears have significant reductions in muscle fiber force production. Force production also correlates with ASES scores and tear size. The structural and functional muscle dysfunction of the residual muscle fibers is independent of the additional area taken up by fibrotic tissue. This work may help establish future therapies to restore muscle function after the repair of chronically torn rotator cuff muscles. Copyright © 2015 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.

  15. Effect of Rotational Axis Position of Wheelchair Back Support on Shear Force when Reclining

    PubMed Central

    Kobara, Kenichi; Osaka, Hiroshi; Takahashi, Hisashi; Ito, Tomotaka; Fujita, Daisuke; Watanabe, Susumu

    2014-01-01

    [Purpose] The purpose of this study was to investigate the influence of the rotational axis position of a reclining wheelchair’s back support on fluctuations in the shear force applied to the buttocks while the back support is reclined. [Subjects] The subjects were 12 healthy adult men. [Methods] The shear force applied to the buttocks was measured using a force plate. This study used two different experimental conditions. The rotational axis of the back support was positioned at the joint between the seat and the back support for the rear-axis condition, and was moved 13 cm forward for the front-axis condition. [Results] With the back support fully reclined, the shear forces were 11.2 ± 0.8%BW and 14.1 ± 2.5%BW under the rear-axis and front-axis conditions, respectively. When returned to an upright position, the shear forces were 17.1 ± 3.1%BW and 13.8 ± 1.7%BW under the rear-axis and front-axis conditions, respectively. Significant differences appeared between the two experimental conditions (p < 0.01). [Conclusion] These results suggest that the shear force value could be changed by altering the position of the back support’s rotational axis during reclining. PMID:24926135

  16. Forced flow evaporator for unusual gravity conditions

    NASA Technical Reports Server (NTRS)

    Niggemann, Richard E. (Inventor); Ellis, Wilbert E. (Inventor)

    1987-01-01

    Low efficiency heat transfer in evaporators subject to unusual gravitational conditions is avoided through the use of a spiral evaporator conduit 12 receiving at an inlet 14 a vaporizable coolant at least partly in the liquid phase. Flow of the coolant through the conduit 12 demists the coolant by centrifuging the liquid phase against a pressurre wall 44 of the conduit 12. Vapor flow 40 induces counterrotating vortices 46, 48 which circulate the liquid phase coolant around the interior of the conduit 12 to wet all surfaces thereof.

  17. Laboratory experiment for the study of friction forces using rotating apparatus

    NASA Astrophysics Data System (ADS)

    Kladivová, Mária; Kovaľaková, Mária; Gibová, Zuzana; Fričová, Oľga; Hutníková, Mária; Kecer, Ján

    2016-11-01

    The standard experimental set-up enabling observation of rotational motion of a bar around its centre of mass, which is set into motion due to the external torque generated by the small weight, was extended with an optical gate and position sensor and connected to a computer with software, which made it possible to display measured values of bar half-rotations during accelerated and decelerated motion as well as to process the data immediately. The detailed analysis of experimental data obtained for decelerated rotational motion due to frictional torque only (without small weight) showed that, besides the constant term due to dry friction at an axle, the expression for friction forces in the system has to include terms depending on the first and/or second power of angular speed, which is evidence that viscous forces influence the motion of a bar. The frictional torque due to viscous forces can be evaluated as the difference between the effective frictional torque acting on the system and the frictional torque due to dry friction at an axle. The data obtained in the experiment in which the bar performed damped oscillatory motion provided the values of effective frictional torque and the moment of inertia of rotating bodies. The frictional torque due to dry friction can be obtained as a minimum torque (calculated using minimum mass of weight) needed to start rotational motion. The last two proposed experiments can be included in undergraduate laboratory practicals.

  18. The residual zonal flow in tokamak plasmas toroidally rotating at arbitrary velocity

    SciTech Connect

    Zhou, Deng

    2014-08-15

    Zonal flows, initially driven by ion-temperature-gradient turbulence, may evolve due to the neoclassic polarization in a collisionless tokamak plasma. In our previous work [D. Zhou, Nucl. Fusion 54, 042002 (2014)], the residual zonal flow in a tokamak plasma rotating toroidally at sonic speed is found to have the same form as that of a static plasma. In the present work, the form of the residual zonal flow is presented for tokamak plasmas rotating toroidally at arbitrary velocity. The gyro-kinetic equation is analytically solved for low speed rotation to give the expression of residual zonal flows, and the expression is then generalized for cases with arbitrary rotating velocity through interpolation. The zonal flow level decreases as the rotating velocity increases. The numerical evaluation is in good agreement with the former simulation result for high aspect ratio tokamaks.

  19. Rotational and vibrational nonequilibrium effects in rarefied, hypersonic flow

    NASA Technical Reports Server (NTRS)

    Boyd, Iain D.

    1989-01-01

    Results are reported for an investigation into the methods by which energy transfer is calculated in the Direct Simulation Monte Carlo method. Description is made of a recently developed energy exchange model that deals with the translational and rotational modes. A new model for simulating the transfer of energy between the translational and vibrational modes is also explained. This model allows the vibrational relaxation time to follow the temperature dependence predicted by the Landau-Teller theory at moderate temperatures. For temperatures in excess of about 8000K the vibrational model is extended to include an empirical result for the relaxation time. The effect of introducing these temperature dependent collision numbers into the DSMC technique is assessed by making calculations representative of the stagnation streamline of a hypersonic space vehicle. Both thermal and chemical nonequilibrium effects are included while the flow conditions have been chosen such that ionization and radiation may be neglected. The introduction of these new models is found to significantly affect the degree of thermal nonequilibrium observed in the flowfield. Larger, and more widely ranging, differences in the results obtained with the different energy exchange probabilities are found when a significant amount of internal energy is included in the calculation of chemical nonequilibrium.

  20. Stability analysis of the rimming flow inside a uniformly heated rotating horizontal cylinder

    NASA Astrophysics Data System (ADS)

    Kumawat, Tara Chand; Tiwari, Naveen

    2017-03-01

    The stability analysis is presented for a thin viscous liquid film flowing inside a uniformly heated horizontal cylinder that is rotating about its axis. The free surface evolution equation for the liquid-gas interface is obtained by simplifying the Navier-Stokes and energy equations within the lubrication approximation. Various dimensionless numbers are obtained that quantify the effect of gravity, viscous drag, inertia, surface tension, and thermocapillary stress. The film thickness evolution equation is solved numerically to obtain two-dimensional, steady state solutions neglecting axial variations. A liquid pool forms at the bottom of the cylinder when gravity dominates other forces. This liquid pool is shifted in the direction of rotation when inertia or viscous drag is increased. Small axial perturbations are then imposed to the steady solutions to study their stability behavior. It is found that the inertia and capillary pressure destabilize whereas the gravity and thermocapillary stress stabilize the rimming flow. The influence of Marangoni number is reported by computing the stable and unstable parametric regions. Thicker films are shown to be more susceptible to become unstable.

  1. The Forced Flow Flame-Spreading Test (FFFT)

    NASA Technical Reports Server (NTRS)

    1997-01-01

    The Forced Flow Flame-Spreading Test was designed to study flame spreading over solid fuels when air is flowing at a low speed concurrent airflows, some materials are more flammable in microgravity than earth. 1.5 cm flame in microgravity that melts a polyethylene cylinder into a liquid ball.

  2. Gravitomagnetic Field of the Universe and Coriolis Force on the Rotating Earth

    ERIC Educational Resources Information Center

    Veto, B.

    2011-01-01

    The Machian effect of distant masses of the universe in the frame of reference of the rotating Earth is demonstrated using the gravitomagnetic approach of general relativity. This effect appears in the form of a gravitomagnetic Lorentz force acting on moving bodies on the Earth. The gravitomagnetic field of the universe--deduced from a simple…

  3. Gravitomagnetic Field of the Universe and Coriolis Force on the Rotating Earth

    ERIC Educational Resources Information Center

    Veto, B.

    2011-01-01

    The Machian effect of distant masses of the universe in the frame of reference of the rotating Earth is demonstrated using the gravitomagnetic approach of general relativity. This effect appears in the form of a gravitomagnetic Lorentz force acting on moving bodies on the Earth. The gravitomagnetic field of the universe--deduced from a simple…

  4. Particle orbits in a force-balanced, wave-driven, rotating torus

    NASA Astrophysics Data System (ADS)

    Ochs, I. E.; Fisch, N. J.

    2017-09-01

    A wave-driven rotating torus is a recently proposed fusion concept where the rotational transform is provided by the E × B drift resulting from a minor radial electric field. This field can be produced, for instance, by the RF-wave-mediated extraction of fusion-born alpha particles. In this paper, we discuss how macroscopic force balance, i.e., balance of the thermal hoop force, can be achieved in such a device. We show that this requires the inclusion of a small plasma current and vertical magnetic field and identify the desirable reactor regime through free energy considerations. We then analyze particle orbits in this desirable regime, identifying velocity-space anisotropies in trapped (banana) orbits, resulting from the cancellation of rotational transforms due to the radial electric and poloidal magnetic fields. The potential neoclassical effects of these orbits on the perpendicular conductivity, current drive, and transport are discussed.

  5. Analysis and modeling of flow in rotating spiral microchannels: towards math-aided design of microfluidic systems using centrifugal pumping.

    PubMed

    Wang, Lin; Kropinski, Mary-Catherine; Li, Paul C H

    2011-06-21

    This paper describes the experimental measurement and mathematical modeling of centrifugally-pumped flow in spiral microchannels. Here, the liquid is delivered by the rotation of a circular microchip as depicted before (X. Y. Peng, P. C. H. Li, H. Z. Yu, M. Parameswaran and W. L. Chou, Sens. Actuators, B, 2007, 128, 64-69). The spiral microchannel in it was specially designed to produce a constant centrifugal force component. From experimental measurements, it was found that the flow velocity inside the spiral microchannels was associated with the rotation speed only, but not with the length of the liquid column. The mathematical modeling of liquid flow was constructed based on solving the Navier-Stokes equations of incompressible flow formulated in a new orthogonal curvilinear coordinate system aligned with the channel geometry. The governing equations were simplified under various assumptions, rendering a mathematically-tractable physical model. In addition, a commercial computational fluid dynamics (CFD) program was used to simulate the flow in the spiral microchannel. The predicted liquid flow velocities from the mathematical model and the CFD program showed reasonable agreement with the experimental data. Under proper assumptions, the mathematical model gave a flexible and rather accurate analytical solution using much less computing power. The proposed study demonstrated the effectiveness of the spiral microchannel design in microfluidic applications using centrifugal force. With modifications, this study could be adapted to the simulation and modeling of other centrifugal-pumping microflow systems.

  6. On the flow processes in sharply inclined and stalled airfoils in parallel movement and rotation

    NASA Technical Reports Server (NTRS)

    Kohler, M.

    1984-01-01

    The purpose of this study is to obtain a deeper insight into the complicated flow processes on airfoils in the region of the buoyancy maxima. To this end calculated and experimental investigations are carried out on a straight stationary, a twisted stationary and a straight rotating rectangular wing. According to the available results the method gives results which can be applied sufficiently for flow applied firmly on all sides for all rotation values. The reliability of the method may be questioned for a flow undergoing transition from the attached to the separated state or for totally separated flow and higher rotation values.

  7. Tokamak Plasma Flows Induced by Local RF Forces

    NASA Astrophysics Data System (ADS)

    Chen, Jiale; Gao, Zhe

    2015-10-01

    The tokamak plasma flows induced by the local radio frequency (RF) forces in the core region are analyzed. The effective components of local RF forces are composed of the momentum absorption term and the resonant parallel momentum transport term (i.e. the parallel component of the resonant ponderomotive forces). Different momentum balance relations are employed to calculate the plasma flows depending on different assumptions of momentum transport. With the RF fields solved from RF simulation codes, the toroidal and poloidal flows by these forces under the lower hybrid current drive and the mode conversion ion cyclotron resonance heating on EAST-like plasmas are evaluated. supported by National Natural Science Foundation of China (Nos. 11405218, 11325524, 11375235 and 11261140327), in part by the National Magnetic Confinement Fusion Science Program of China (Nos. 2013GB111002, 2013GB112001 and 2013GB112010), and the Program of Fusion Reactor Physics and Digital Tokamak with the CAS “One-Three-Five” Strategic Planning

  8. The magnitude of basset forces in unsteady multiphase flow computations

    SciTech Connect

    Li, L.; Michaelides, E.E. . Dept. of Mechanical Engineering)

    1992-09-01

    This paper reports on the equation of motion of a small spherical particle moving in a fluid which is solved numerically with the radius of the sphere and the ratio of fluid to particle densities being parameters. The Basset force term is computed and compared to the total force on the particle for the case of turbulent flow in a duct. It is found that the Basset force may be neglected in the equation of motion of the particle only when the fluid to particle density ratio is very high and the particle diameter is greater than 1[mu]m. A dimensional analysis is also performed for the case when the particle size and the characteristic flow dimension are of the same order of magnitude. In the latter case, it is deduced that the Basset force is significant whenever the flow Reynolds number is greater than one.

  9. Elbow joint stability in relation to forced external rotation: An experimental study of the osseous constraint.

    PubMed

    Deutch, Søren R; Jensen, Steen L; Olsen, Bo S; Sneppen, Otto

    2003-01-01

    The objective of this study was to evaluate the osseous constraint related to forced forearm external rotation as the initial stage in a posterior elbow dislocation. Six joint specimens without soft tissues were examined in a joint analysis system developed for simulation of dislocation. The osseous stability, expressed as the maximal torque needed for pathologic external forearm rotation, increased from varus to valgus stress (P =.0001) and from 10 degrees to 90 degrees of elbow flexion (P =.012) and also tended to increase from forearm supination to pronation. The work of pathologic external forearm rotation until the point of maximal torque decreased from a maximum in full extension to a minimum at 30 degrees of elbow flexion (P =.03). The elbow in a slightly flexed position, varus stress, and forearm external rotation trauma might be the important biomechanical factors in the posterior elbow dislocation, and they might serve as guidelines during clinical investigation for posterolateral instability.

  10. Identification of dominant flow structures in rapidly rotating convection of liquid metals using Dynamic Mode Decomposition

    NASA Astrophysics Data System (ADS)

    Horn, Susanne; Aurnou, Jonathan M.; Schmid, Peter J.

    2016-11-01

    We will present results from direct numerical simulations of rapidly rotating convection in a fluid with Pr 0 . 025 in cylindrical containers and Ekman numbers as low as 5 ×10-6 . In this system, the Coriolis force is the source of two types of inertial modes, the so-called wall modes, that also exist at moderate Prandtl numbers, and cylinder-filling oscillatory modes, that are a unique feature of small Prandtl number convection. The obtained flow fields were analyzed using the Dynamic Mode Decomposition (DMD). This technique allows to extract and identify the structures that govern the dynamics of the system as well as their corresponding frequencies. We have investigated both the regime where the flow is purely oscillatory and the regime where wall modes and oscillatory modes co-exist. In the purely oscillatory regime, high and low frequency oscillatory modes characterize the flow. When both types of modes are present, the DMD reveals that the wall-attached modes dominate the flow dynamics. They precess with a relatively low frequency in retrograde direction. Nonetheless, also in this case, high frequency oscillations have a significant contribution.

  11. Homogeneous-heterogeneous reactions in nonlinear radiative flow of Jeffrey fluid between two stretchable rotating disks

    NASA Astrophysics Data System (ADS)

    Hayat, Tasawar; Qayyum, Sumaira; Imtiaz, Maria; Alsaedi, Ahmed

    This article addresses MHD Jeffrey fluid flow between two stretchable rotating disks. Momentum equation with magnetic field is presented. Energy equation is constructed in presence of heat source/sink and nonlinear radiation. Thermal stratification and homogeneous-heterogeneous reactions are accounted. The related systems have been solved for convergent solutions. Velocity, temperature, concentration, skin friction coefficient and Nusselt number are analyzed. The velocities (radial, axial, tangential) are increasing functions of Deborah number. Decline in axial velocity is noticed at lower disk for larger ratio of relaxation to retardation times constant. Thermal field is enhanced for temperature ratio parameter. Concentration has opposite behavior for larger homogeneous parameter and Schmidt number. Surface drag force decays for larger ratio of relaxation to retardation times at both disks. Heat transfer rate enhances for temperature ratio parameter.

  12. Effect of fluid and particle inertia on the rotation of an oblate spheroidal particle suspended in linear shear flow.

    PubMed

    Rosén, T; Do-Quang, M; Aidun, C K; Lundell, F

    2015-05-01

    This work describes the inertial effects on the rotational behavior of an oblate spheroidal particle confined between two parallel opposite moving walls, which generate a linear shear flow. Numerical results are obtained using the lattice Boltzmann method with an external boundary force. The rotation of the particle depends on the particle Reynolds number, Re(p)=Gd(2)ν(-1) (G is the shear rate, d is the particle diameter, ν is the kinematic viscosity), and the Stokes number, St=αRe(p) (α is the solid-to-fluid density ratio), which are dimensionless quantities connected to fluid and particle inertia, respectively. The results show that two inertial effects give rise to different stable rotational states. For a neutrally buoyant particle (St=Re(p)) at low Re(p), particle inertia was found to dominate, eventually leading to a rotation about the particle's symmetry axis. The symmetry axis is in this case parallel to the vorticity direction; a rotational state called log-rolling. At high Re(p), fluid inertia will dominate and the particle will remain in a steady state, where the particle symmetry axis is perpendicular to the vorticity direction and has a constant angle ϕ(c) to the flow direction. The sequence of transitions between these dynamical states were found to be dependent on density ratio α, particle aspect ratio r(p), and domain size. More specifically, the present study reveals that an inclined rolling state (particle rotates around its symmetry axis, which is not aligned in the vorticity direction) appears through a pitchfork bifurcation due to the influence of periodic boundary conditions when simulated in a small domain. Furthermore, it is also found that a tumbling motion, where the particle symmetry axis rotates in the flow-gradient plane, can be a stable motion for particles with high r(p) and low α.

  13. The effect of diamagnetic flows on turbulent driven ion toroidal rotation

    SciTech Connect

    Lee, J. P.; Barnes, M.; Parra, F. I.; Belli, E. A.; Candy, J.

    2014-05-15

    Turbulent momentum redistribution determines the radial profile of rotation in a tokamak. The momentum transport driven by diamagnetic flow effects is an important piece of the radial momentum transport for sub-sonic rotation, which is often observed in experiments. In a non-rotating state, the diamagnetic flow and the E × B flow must cancel. The diamagnetic flow and the E × B flow have different effects on the turbulent momentum flux, and this difference in behavior induces intrinsic rotation. The momentum flux is evaluated using gyrokinetic equations that are corrected to higher order in the ratio of the poloidal Larmor radius to the minor radius, which requires evaluation of the diamagnetic corrections to Maxwellian equilibria. To study the momentum transport due to diamagnetic flow effects, three experimental observations of ion rotation are examined. First, a strong pressure gradient at the plasma edge is shown to result in a significant inward momentum transport due to the diamagnetic effect, which may explain the observed peaking of rotation in a high confinement mode. Second, the direction of momentum transport is shown to change as collisionality increases, which is qualitatively consistent with the observed reversal of intrinsic rotation by varying plasma density and current. Last, the dependence of the intrinsic momentum flux on the magnetic shear is found, and it may explain the observed rotation changes in the presence of lower hybrid current drive.

  14. Direct numerical simulation of turbulent flow in a rotating square duct

    SciTech Connect

    Dai, Yi-Jun; Huang, Wei-Xi Xu, Chun-Xiao; Cui, Gui-Xiang

    2015-06-15

    A fully developed turbulent flow in a rotating straight square duct is simulated by direct numerical simulations at Re{sub τ} = 300 and 0 ≤ Ro{sub τ} ≤ 40. The rotating axis is parallel to two opposite walls of the duct and normal to the main flow. Variations of the turbulence statistics with the rotation rate are presented, and a comparison with the rotating turbulent channel flow is discussed. Rich secondary flow patterns in the cross section are observed by varying the rotation rate. The appearance of a pair of additional vortices above the pressure wall is carefully examined, and the underlying mechanism is explained according to the budget analysis of the mean momentum equations.

  15. Application of DTM for kerosene-alumina nanofluid flow and heat transfer between two rotating plates

    NASA Astrophysics Data System (ADS)

    Mahmoodi, M.; Kandelousi, Sh.

    2015-07-01

    In this paper, the differential transformation method (DTM) is applied to solve the governing equations of nanofluid flow and heat transfer between two parallel plates in a rotating system. The working fluid is a kerosene-alumina nanofluid. The influences of viscosity parameter, rotation parameter, nanoparticle volume fraction and Eckert number on the flow and heat transfer characteristics have been investigated. Results indicate that skin friction is a decreasing function of the viscosity and rotation parameters. Also it can be found that the Nusselt number has a direct relationship with the rotation parameter and the nanoparticle volume fraction while it has a reverse relationship with the viscosity parameter and the Eckert number.

  16. First experimental evaluation of cardiac apex rotation with an epicardial coriolis force sensor.

    PubMed

    Marcelli, Emanuela; Plicchi, Gianni; Cercenelli, Laura; Bortolami, Filippo

    2005-01-01

    Cardiac apex rotation, quantified by sophisticated techniques (radiopaque markers and tagged magnetic resonance), has been shown to provide a sensitive index of left ventricle (LV) dynamics. The authors describe the first experimental assessment of cardiac apex rotation using a gyroscopic sensor based on Coriolis force, epicardially glued on the apex. Dynamics of apex rotation were evaluated in a sheep at baseline, after a positive inotropic drug infusion, and after impairment of cardiac function induced by coronary ligation. To evaluate the efficacy of the sensor to monitor cardiac function, results were compared to contractility variations expressed by the maximum value of the first derivative of LV pressure (LVdP/dtMAX). After inotropic drug infusion, a parallel increasing trend resulted for LVdP/dtMAX, for the maximum value of angular velocity measured by the sensor, and for apex rotation angle derived from velocity signal (+146%, +155%, and +11% from baseline, respectively), whereas a decreasing trend of all three parameters resulted after coronary ligation (-35%, -31%, and -65%). The twist pattern also was altered from baseline. These initial results suggest that the use of an implantable rotation sensor based on Coriolis force can be an efficient and effective tool to assess LV torsional deformation both in normal and failing hearts.

  17. Turbulence and turbulent drag reduction in swirling flow: Inertial versus viscous forcing.

    PubMed

    Burnishev, Yuri; Steinberg, Victor

    2015-08-01

    We report unexpected results of a drastic difference in the transition to fully developed turbulent and turbulent drag reduction (TDR) regimes and in their properties in a von Karman swirling flow with counter-rotating disks of water-based polymer solutions for viscous (by smooth disks) as well as inertial (by bladed disks) forcing and by tracking just torque Γ(t) and pressure p(t) . For the viscous forcing, just a single TDR regime is found with the transition values of the Reynolds number (Re) Re turb c =Re TDR c ≃(4.8±0.2)×10(5) independent of ϕ , whereas for the inertial forcing two turbulent regimes are revealed. The first transition is to fully developed turbulence, and the second one is to the TDR regime with both Re turb c and Re TDR c depending on polymer concentration ϕ . Both regimes differ by the values of C f and C p , by the scaling exponents of the fundamental turbulent characteristics, by the nonmonotonic dependencies of skewness and flatness of the pressure PDFs on Re, and by the different frequency power spectra of p with the different dependencies of the main vortex peak frequency in the p power spectra on ϕ and Re. Thus our experimental results show the transition to the TDR regime in a von Karman swirling flow for the viscous and inertial forcings in a sharp contrast to the recent experiments [Phys. Fluids 10, 426 (1998); Phys. Rev. E 47, R28(R) (1993); and J. Phys.: Condens. Matter 17, S1195 (2005)] where the transition to TDR is observed in the same swirling flow with counter-rotating disks only for the viscous forcing. The latter result has led its authors to the wrong conclusion that TDR is a solely boundary effect contrary to the inertial forcing associated with the bulk effect, and this conception is currently rather widely accepted in literature.

  18. Erosion and basal forces in granular flow experiments

    NASA Astrophysics Data System (ADS)

    Sanvitale, Nicoletta; Bowman, Elisabeth

    2016-04-01

    Extreme mass wasting avalanche events such as rock, snow and ice avalanches, debris flows, and pyroclastic flows are among the most hazardous geological phenomena. These events driven by gravity, can travel for long distance and high speed, increasing their volumes as they can entertain material along their path. The erosion of material and its entrainment can greatly affect the overall dynamics of transportation, either enhancing or impeding the avalanche mobility depending on flow dynamics and characteristics of the substrate. However, the mechanisms and processes acting at the base as they travel over deformable or erodible substrates are still poor understood. Experiments, simulations and field measurements indicate that large fluctuations can occur in basal forces and stresses, which may be the result of non-uniform load transfer within the mass, and rolling, bouncing and sliding of the particles along the bed. In dense granular materials, force distributions can propagate through filamentary chain structures that carry a large fraction of the forces within the system. Photoelastic experiments on two-dimensional, monodisperse, gravity-driven flows have shown that force chains can transmit high localized forces to the boundary of dense granular flows. Here we describe the preliminary setup and results of 2D experiments on polydisperse granular flows of photoelastic disks down a small flume designed to acquire the forces exerted at the boundaries of the flow and to analyze their effects on an erodible bed. The intended outcome of this research is to provide better information on the complex mechanism of erosion and its effects on avalanche behaviour.

  19. The effect of the nonlinear velocity and history dependencies of the aerodynamic force on the dynamic response of a rotating wind turbine blade

    NASA Astrophysics Data System (ADS)

    van der Male, Pim; van Dalen, Karel N.; Metrikine, Andrei V.

    2016-11-01

    Existing models for the analysis of offshore wind turbines account for the aerodynamic action on the turbine rotor in detail, requiring a high computational price. When considering the foundation of an offshore wind turbine, however, a reduced rotor model may be sufficient. To define such a model, the significance of the nonlinear velocity and history dependency of the aerodynamic force on a rotating blade should be known. Aerodynamic interaction renders the dynamics of a rotating blade in an ambient wind field nonlinear in terms of the dependency on the wind velocity relative to the structural motion. Moreover, the development in time of the aerodynamic force does not follow the flow velocity instantaneously, implying a history dependency. In addition, both the non-uniform blade geometry and the aerodynamic interaction couple the blade motions in and out of the rotational plane. Therefore, this study presents the Euler-Bernoulli formulation of a twisted rotating blade connected to a rigid hub, excited by either instantaneous or history-dependent aerodynamic forces. On this basis, the importance of the history dependency is determined. Moreover, to assess the nonlinear contributions, both models are linearized. The structural response is computed for a stand-still and a rotating blade, based on the NREL 5-MW turbine. To this end, the model is reduced on the basis of its first three free-vibration mode shapes. Blade tip response predictions, computed from turbulent excitation, correctly account for both modal and directional couplings, and the added damping resulting from the dependency of the aerodynamic force on the structural motion. Considering the deflection of the blade tip, the history-dependent and the instantaneous force models perform equally well, providing a basis for the potential use of the instantaneous model for the rotor reduction. The linearized instantaneous model provides similar results for the rotating blade, indicating its potential

  20. Investigations of Reduced Equations for Rotating, Stratified and Non-hydrostatic Flows

    NASA Astrophysics Data System (ADS)

    Nieves, David J.

    boundary conditions. These results imply that any horizontal thermal variation along the boundaries that varies on the scale of the convection has no leading order influence on the interior convection, thus providing insight into geophysical and astrophysical flows where stress-free mechanical boundary conditions are often assumed. The final study presented here contrasts the previous investigations. It presents an investigation of rapidly rotating and stably stratified turbulence where the stratification strength is varied from weak (large Froude number) to strong (small Froude number). The investigation is set in the context of the asymptotically reduced model which efficiently retains anisotropic inertia-gravity waves with order-one frequencies and highlights a regime of wave-eddy interactions. Numerical simulations of the reduced model are performed where energy is injected by a stochastic forcing of vertical velocity. The simulations reveal two regimes: one characterized by the presence of well-formed, persistent and thin turbulent layers of locally-weakened stratification: the other characterized by the absence of layers at large Froude numbers. Both regimes are characterized by a large-scale barotropic dipole in a sea of small-scale turbulence. When the Reynolds number is not too large a direct cascade of barotropic kinetic energy is observed and leads to an equilibration of total energy. We examine net energy exchanges that occur through vortex stretching and vertical buoyancy flux and diagnose the horizontal scales active in these exchanges. We find that baroclinic motions inject energy directly to the largest scales of the barotropic mode governed by the two-dimensional vorticity equation, and implies that the large-scale barotropic dipole is not the end result of an inverse cascade within the two-dimensional barotropic mode. An additional yet brief look into the linear vortical and wave modes is considered.

  1. Blade design loads on the flow exciting force in centrifugal pump

    NASA Astrophysics Data System (ADS)

    Xu, Y.; Yang, A. L.; Langand, D. P.; Dai, R.

    2012-11-01

    The three-dimensional viscous flow field of two centrifugal pumps, which have the same volute, design head, design flow rate and rotational speed but the blade design load, are analyzed based on large eddy simulation. The comparisons are implemented including the hydraulic efficiencies, flow field characteristics, pressure pulsations and unsteady forces applied on the impellers to investigate the effect of the design blade load on hydraulic performance and flow exciting force. The numerical results show that the efficiency of the pump, the impeller blade of which has larger design load, is improved by 1.1%~2.9% compared to the centrifugal pump with lower blade design load. The pressure fluctuation of the pump with high design load is more remarkable. Its maximum amplitude of coefficient of static pressure is higher by 43% than the latter. At the same time the amplitude of unsteady radial force is increased by 11.6% in the time domain. The results also imply that the blade design load is an important factor on the excitation force in centrifugal pumps.

  2. Acute effects of force and vibration on finger blood flow

    PubMed Central

    Bovenzi, M; Welsh, A J L; Vedova, A Della; Griffin, M J

    2006-01-01

    Objectives To investigate the effects of contact force at the finger on acute changes in finger circulation during exposure to vibration. Methods Each of 10 subjects attended 11 sessions in which they experienced five successive experimental 5‐minute periods: (i) no force and no vibration; (ii) force and no vibration; (iii) force and vibration; (iv) force and no vibration; (v) no force and no vibration. During periods (ii) to (iv), the intermediate phalanx of the right middle finger applied one of two forces (2 N or 5 N) on a platform that vibrated during period (iii) at one of two frequencies: 31.5 Hz (at 4 or 16 ms−2 r.m.s.) or 125 Hz (at 16 or 64 ms−2 r.m.s.). Finger blood flow was measured in the exposed right middle finger, the unexposed right little finger, and the unexposed left middle fingers throughout the 25 minutes of each session. Results The application of force alone caused a reduction in finger blood flow in the exposed finger, but not other fingers. There were additional reductions in finger blood flow caused by vibration, with greater reductions at the higher vibration magnitudes at both frequencies but no difference between the two frequencies when using unweighted acceleration. The vibration caused a similar vasoconstriction in vibrated and non‐vibrated fingers. Conclusions Modest levels of force applied by a finger can have a large effect on the finger blood flow, possibly due to the constriction of local blood vessels. The acute vascular effects of vibration cause additional reductions in finger blood flow that are not limited to the finger experiencing force and vibration. In all fingers (exposed and not exposed to vibration), the greater the magnitude of vibration, the greater the reduction in finger blood flow. In all fingers (exposed and not exposed to vibration), when the vibration was frequency weighted according to current standards, 125 Hz vibration caused greater reductions in finger blood flow than 31.5

  3. Optical investigation of the heat transfer from a rotating cylinder in a cross flow

    NASA Astrophysics Data System (ADS)

    Gschwendtner, M. A.

    . The heat transfer from a rotating cylinder in an air-cross flow was investigated by purely optical measuring techniques. Flow velocities were measured by a two-dimensional LDV both in the vicinity of the cylinder and in the boundary layer. A new optical device based on light-deflection in a temperature field was developed to examine local temperature gradients in the boundary layer of the rotating cylinder. Finally, a Michelson-interferometer was installed to produce real-time pictures of isothermal lines around the heated cylinder. The impact of rotation on flow patterns, boundary layer behaviour and heat transfer could be clearly identified. It appears that the velocity-ratio Ω acts like an independent parameter, in that flow patterns correspond to this dimensionless number. Furthermore, it seems that rotation dominates over cross flow, both fluid-dynamically and thermally above Ω = 2.

  4. Laminar flow between a stationary and a rotating disk with radial throughflow

    SciTech Connect

    Nesreddine, H.; Nguyen, C.T.; Vo-Ngoc, D.

    1995-05-01

    The problem of axisymmetric laminar flow of a viscous incompressible fluid that occurs between a stationary and a rotating disk subjected to a uniform radial throughflow has been numerically investigated for a large range of flow parameters. Results show that the basic flow structure is rather complex and depends strongly on both the rotational and the flow structure is rather complex and depends strongly on both the rotational and the throughflow Reynolds numbers. In general, the basic unicellular structure has been observed. With the increase of the throughflow Reynolds number, a multicellular flow structure may be found. The phenomenon of multiple solutions has been clearly observed for cases with sufficiently high rational Re and/or high throughflow Re. Among these solutions, stable as well as unstable solutions have been determined by applying Rayleigh`s stability criterion. The influence of the starting conditions on the stability of the flow has also been investigated for various ranges of flow parameters.

  5. Joint representation of translational and rotational components of optic flow in parietal cortex

    PubMed Central

    Sunkara, Adhira; DeAngelis, Gregory C.; Angelaki, Dora E.

    2016-01-01

    Terrestrial navigation naturally involves translations within the horizontal plane and eye rotations about a vertical (yaw) axis to track and fixate targets of interest. Neurons in the macaque ventral intraparietal (VIP) area are known to represent heading (the direction of self-translation) from optic flow in a manner that is tolerant to rotational visual cues generated during pursuit eye movements. Previous studies have also reported that eye rotations modulate the response gain of heading tuning curves in VIP neurons. We tested the hypothesis that VIP neurons simultaneously represent both heading and horizontal (yaw) eye rotation velocity by measuring heading tuning curves for a range of rotational velocities of either real or simulated eye movements. Three findings support the hypothesis of a joint representation. First, we show that rotation velocity selectivity based on gain modulations of visual heading tuning is similar to that measured during pure rotations. Second, gain modulations of heading tuning are similar for self-generated eye rotations and visually simulated rotations, indicating that the representation of rotation velocity in VIP is multimodal, driven by both visual and extraretinal signals. Third, we show that roughly one-half of VIP neurons jointly represent heading and rotation velocity in a multiplicatively separable manner. These results provide the first evidence, to our knowledge, for a joint representation of translation direction and rotation velocity in parietal cortex and show that rotation velocity can be represented based on visual cues, even in the absence of efference copy signals. PMID:27095846

  6. A photosynthetic rotating annular bioreactor (Taylor-Couette type flow) for phototrophic biofilm cultures.

    PubMed

    Paule, A; Lauga, B; Ten-Hage, L; Morchain, J; Duran, R; Paul, E; Rols, J L

    2011-11-15

    In their natural environment, the structure and functioning of microbial communities from river phototrophic biofilms are driven by biotic and abiotic factors. An understanding of the mechanisms that mediate the community structure, its dynamics and the biological succession processes during phototrophic biofilm development can be gained using laboratory-scale systems operating with controlled parameters. For this purpose, we present the design and description of a new prototype of a rotating annular bioreactor (RAB) (Taylor-Couette type flow, liquid working volume of 5.04 L) specifically adapted for the cultivation and investigation of phototrophic biofilms. The innovation lies in the presence of a modular source of light inside of the system, with the biofilm colonization and development taking place on the stationary outer cylinder (onto 32 removable polyethylene plates). The biofilm cultures were investigated under controlled turbulent flowing conditions and nutrients were provided using a synthetic medium (tap water supplemented with nitrate, phosphate and silica) to favour the biofilm growth. The hydrodynamic features of the water flow were characterized using a tracer method, showing behaviour corresponding to a completely mixed reactor. Shear stress forces on the surface of plates were also quantified by computer simulations and correlated with the rotational speed of the inner cylinder. Two phototrophic biofilm development experiments were performed for periods of 6.7 and 7 weeks with different inoculation procedures and illumination intensities. For both experiments, biofilm biomasses exhibited linear growth kinetics and produced 4.2 and 2.4 mg cm(-)² of ash-free dry matter. Algal and bacterial community structures were assessed by microscopy and T-RFLP, respectively, and the two experiments were different but revealed similar temporal dynamics. Our study confirmed the performance and multipurpose nature of such an innovative photosynthetic bioreactor

  7. Multigrid Computations of 3-D Incompressible Internal and External Viscous Rotating Flows

    NASA Technical Reports Server (NTRS)

    Sheng, Chunhua; Taylor, Lafayette K.; Chen, Jen-Ping; Jiang, Min-Yee; Whitfield, David L.

    1996-01-01

    This report presents multigrid methods for solving the 3-D incompressible viscous rotating flows in a NASA low-speed centrifugal compressor and a marine propeller 4119. Numerical formulations are given in both the rotating reference frame and the absolute frame. Comparisons are made for the accuracy, efficiency, and robustness between the steady-state scheme and the time-accurate scheme for simulating viscous rotating flows for complex internal and external flow applications. Prospects for further increase in efficiency and accuracy of unsteady time-accurate computations are discussed.

  8. Effect of gravitational force upon traffic flow with gradients

    NASA Astrophysics Data System (ADS)

    Komada, Kazuhito; Masukura, Shuichi; Nagatani, Takashi

    2009-07-01

    We study the effect of gravitational force upon traffic flow on a highway with sag, uphill, and downhill. We extend the optimal velocity model to take into account the gravitational force which acts on vehicles as an external force. We study the traffic states and jamming transitions induced by the slope of highway. We derive the fundamental diagrams (flow-density diagrams) for the traffic flow on the sag, the uphill, and downhill by using the extended optimal velocity model. We clarify where and when traffic jams occur on a highway with gradients. We show the relationship between densities before and after the jam. We derive the dependence of the fundamental diagram on the slope of gradients.

  9. Influence of the saffman force, lift force, and electric force on sand grain transport in a wind-sand flow

    NASA Astrophysics Data System (ADS)

    Gorchakov, G. I.; Karpov, A. V.; Kopeikin, V. M.; Sokolov, A. V.; Buntov, D. V.

    2016-03-01

    Quasi-horizontal trajectories of salting sand grains were found using high-speed video-recording in the desertified territory of the Astrakhan region. The sizes and displacement velocities of the saltating sand grains were determined. A piecewise logarithmic approximation of the wind profile in a quasi-stationary wind-sand flow is suggested, which is consistent with the data of observations and modeling. It was established that, in the regime of stationary saltation, the wind profile in the lower saltation layer of the wind-sand flow depends only slightly on the wind profile variations in the upper saltation layer. The vertical profiles of the horizontal wind component gradient in a quasi-stationary wind-sand flow were calculated and plotted. It was shown using high-speed video recording of the trajectory of a sand grain with an approximate diameter of 95 μm that the weightlessness condition in the desertified territory of the Astrakhan region in a stationary wind-sand flow is satisfied at a height of approximately 0.15 mm. The electric parameters of a wind-sand flow, which can provide for compensation of the force of gravity by the electric force, were estimated. In particular, if the specific charge of a sand grain is 100 μC/kg, the force of gravity applied to the sand grain can be compensated by the electric force if the vertical component of the electric field in a wind-sand flow reaches approximately 100 kV/m. It was shown that the quasi-horizontal transport of sand grains in the lower millimeter saltation layer observed in the desertified territory can be explained by the joint action of the aerodynamic drag, the force of gravity, the Saffman force, the lift force, and the electric force.

  10. Forcing of oceanic mean flows by dissipating internal tides

    NASA Astrophysics Data System (ADS)

    Grisouard, Nicolas; Buhler, Oliver

    2012-11-01

    We present a theoretical study of the effective mean force exerted on an oceanic mean flow due to the presence of small-amplitude internal waves that are forced by a barotropic tide flowing over a topography and are also subject to dissipation. Although the details of our computation are quite different, we recover the main action-at-a-distance result familiar from atmospheric wave-mean interaction theory, namely that the effective mean force that is felt by the mean flow is located in regions of wave dissipation, and not necessarily near the topographic wave source. Specifically, using a perturbation series in small wave amplitude, we compute the three-dimensional leading-order wave field using a Green's function approach, derive an explicit expression for the leading-order effective mean force at the next order within the framework of generalized Lagrangian-mean theory, discuss in detail the range of situations in which a strong, secularly growing mean-flow response can be expected, and finally compute the effective mean force numerically in a number of illustrative examples with simple topographies. Financial support under the United States National Science Foundation grants NSF/OCE 1024180 and NSF/DMS 1009213 is gratefully acknowledged.

  11. Full-scale solutions to particle-laden flows: Multidirect forcing and immersed boundary method.

    PubMed

    Luo, Kun; Wang, Zeli; Fan, Jianren; Cen, Kefa

    2007-12-01

    Towards getting the full-scale solutions to particle-laden flows, a multidirect forcing technique and immersed boundary method are proposed in the present work. The immersed solid boundary is represented by Lagrangian points and the no-slip condition is efficiently satisfied by exerting multidirect forcing. The hydrodynamic interactions between the stationary or moving solid boundary and the Newtonian fluid are able to be accurately described. This method is simple but efficient which is validated by simulating the flows around a stationary circular disc at different Reynolds numbers and the free sedimentation of a particle. The predicted results agree well with previous experimental and numerical data. When applying this method to study particle sedimentation near a vertical wall, the rotation shifting phenomenon is observed besides the anomalous rolling and the lateral migration.

  12. Ultrasonic Imaging of Hemodynamic Force in Carotid Blood Flow

    NASA Astrophysics Data System (ADS)

    Nitta, N.; Homma, K.

    Hemodynamic forces including blood pressure and shear stress affect vulnerable plaque rupture in arteriosclerosis and biochemical activation of endothelium such as NO production. In this study, a method for estimating and imaging shear stress and pressure gradient distributions in blood vessel as the hemodynamic force based on viscosity estimation is presented. Feasibility of this method was investigated by applying to human carotid blood flow. Estimated results of shear stress and pressure gradient distributions coincide with the ideal distributions obtained by numerical simulation and flow-phantom experiment.

  13. Erosion by sliding wear in granular flows: Experiments with realistic contact forces

    NASA Astrophysics Data System (ADS)

    Stark, C. P.; Hung, C. Y.; Smith, B.; Li, L.; Grinspun, E.; Capart, H.

    2015-12-01

    Debris flow erosion is a powerful and sometimes dominant process in steep channels. Despite its importance, this phenomenon is relatively little studied in the lab. The large drum experiments of Hsu are a notable exception, in which almost-field-scale impact forces were generated at the head of a synthetic debris flow whose properties (grain size, proportion of fines, etc) were varied widely.A key challenge in these and similar experiments is to explore how erosion rate varies as a function of the scale of the flow (thereby varying inertial stresses, impact forces, etc). The geometrical limitations of most lab experiments, and their short run time, severely limit the scope of such explorations.We achieve this scale exploration in a set of drum erosion experiments by varying effective gravity across several orders of magnitude (1g, 10g, 100g) in a geotechnical centrifuge. By half-filling our 40cm-diameter drum with dry 2.3mm grains, placing a synthetic rock plate at the back and a glass plate at the front 3cm apart, and rotating the drum at 1-50rpm, we simulate wear in a channelized dry granular flow. In contrast to Hsu's experiments, we focus on sliding wear erosion at the flow boundary rather than impact/frictional wear at the flow head. By varying effective gravity from 1g-100g we can tune the pressure exerted by the grains at the boundary without having to change the scale of our apparatus. Using a recently developed depth-averaged, kinetic-energy closure theory for granular flow, we can simultaneously tune the drum rotation rate such that the flow dynamics remain invariant. We can thereby explore how changing the scale of a granular flow, and thus the contact forces of grains on the boundary, controls the rate of rock erosion. Using a small apparatus we can simulate the erosion generated by debris flows several meters deep involving grains up to 10cm in diameter.Our results suggest that sliding wear is the main erosion process, and are consistent with Archard

  14. Three-dimensional rotational plasma flows near solid surfaces in an axial magnetic field

    SciTech Connect

    Gorshunov, N. M. Potanin, E. P.

    2016-11-15

    A rotational flow of a conducting viscous medium near an extended dielectric disk in a uniform axial magnetic field is analyzed in the magnetohydrodynamic (MHD) approach. An analytical solution to the system of nonlinear differential MHD equations of motion in the boundary layer for the general case of different rotation velocities of the disk and medium is obtained using a modified Slezkin–Targ method. A particular case of a medium rotating near a stationary disk imitating the end surface of a laboratory device is considered. The characteristics of a hydrodynamic flow near the disk surface are calculated within the model of a finite-thickness boundary layer. The influence of the magnetic field on the intensity of the secondary flow is studied. Calculations are performed for a weakly ionized dense plasma flow without allowance for the Hall effect and plasma compressibility. An MHD flow in a rotating cylinder bounded from above by a retarding cap is considered. The results obtained can be used to estimate the influence of the end surfaces on the main azimuthal flow, as well as the intensities of circulating flows in various devices with rotating plasmas, in particular, in plasma centrifuges and laboratory devices designed to study instabilities of rotating plasmas.

  15. Study of Particle Rotation Effect in Gas-Solid Flows using Direct Numerical Simulation with a Lattice Boltzmann Method

    SciTech Connect

    Kwon, Kyung; Fan, Liang-Shih; Zhou, Qiang; Yang, Hui

    2014-09-30

    A new and efficient direct numerical method with second-order convergence accuracy was developed for fully resolved simulations of incompressible viscous flows laden with rigid particles. The method combines the state-of-the-art immersed boundary method (IBM), the multi-direct forcing method, and the lattice Boltzmann method (LBM). First, the multi-direct forcing method is adopted in the improved IBM to better approximate the no-slip/no-penetration (ns/np) condition on the surface of particles. Second, a slight retraction of the Lagrangian grid from the surface towards the interior of particles with a fraction of the Eulerian grid spacing helps increase the convergence accuracy of the method. An over-relaxation technique in the procedure of multi-direct forcing method and the classical fourth order Runge-Kutta scheme in the coupled fluid-particle interaction were applied. The use of the classical fourth order Runge-Kutta scheme helps the overall IB-LBM achieve the second order accuracy and provides more accurate predictions of the translational and rotational motion of particles. The preexistent code with the first-order convergence rate is updated so that the updated new code can resolve the translational and rotational motion of particles with the second-order convergence rate. The updated code has been validated with several benchmark applications. The efficiency of IBM and thus the efficiency of IB-LBM were improved by reducing the number of the Lagragian markers on particles by using a new formula for the number of Lagrangian markers on particle surfaces. The immersed boundary-lattice Boltzmann method (IBLBM) has been shown to predict correctly the angular velocity of a particle. Prior to examining drag force exerted on a cluster of particles, the updated IB-LBM code along with the new formula for the number of Lagrangian markers has been further validated by solving several theoretical problems. Moreover, the unsteadiness of the drag force is examined when a

  16. Numerical prediction of impact force in cavitating flows

    NASA Astrophysics Data System (ADS)

    Zhu, B.; Wang, H.

    2010-08-01

    An analytical method including a macroscopic cavitation model based on the homogeneous flow theory and a microscopic cavitation model based on the bubble dynamic was proposed for the prediction of the impact force caused by cavitation bubbles collapse in cavitating flows. A Large Eddy Simulation (LES) solver incorporated the macroscopic cavitation model was applied to simulate the unsteady cavitating flows. Based on the simulated flow field, the evolution of the cavitation bubbles was determined by a microscopic cavitation model from the resolution of a Rayleigh-Plesset equation including of the effects of the surface tension, the viscosity and compressibility of fluid, thermal conduction and radiation, the phase transition of water vapor at interface and chemical reactions. The cavitation flow around a hydrofoil was simulated to validate the macroscopic cavitation model. A good quantitative agreement was obtained between the prediction and the experiment. The proposed analytical method was applied to predict the impact force at cavitation bubbles collapse on a KT section in cavitating flows. It was found that the shock pressure caused by cavitation bubble collapse is very high. The impact force was predicted accurately comparing with the experimental data.

  17. Improper trunk rotation sequence is associated with increased maximal shoulder external rotation angle and shoulder joint force in high school baseball pitchers.

    PubMed

    Oyama, Sakiko; Yu, Bing; Blackburn, J Troy; Padua, Darin A; Li, Li; Myers, Joseph B

    2014-09-01

    In a properly coordinated throwing motion, peak pelvic rotation velocity is reached before peak upper torso rotation velocity, so that angular momentum can be transferred effectively from the proximal (pelvis) to distal (upper torso) segment. However, the effects of trunk rotation sequence on pitching biomechanics and performance have not been investigated. The aim of this study was to investigate the effects of trunk rotation sequence on ball speed and on upper extremity biomechanics that are linked to injuries in high school baseball pitchers. The hypothesis was that pitchers with improper trunk rotation sequence would demonstrate lower ball velocity and greater stress to the joint. Descriptive laboratory study. Three-dimensional pitching kinematics data were captured from 72 high school pitchers. Subjects were considered to have proper or improper trunk rotation sequences when the peak pelvic rotation velocity was reached either before or after the peak upper torso rotation velocity beyond the margin of error (±3.7% of the time from stride-foot contact to ball release). Maximal shoulder external rotation angle, elbow extension angle at ball release, peak shoulder proximal force, shoulder internal rotation moment, and elbow varus moment were compared between groups using independent t tests (α < 0.05). Pitchers with improper trunk rotation sequences (n = 33) demonstrated greater maximal shoulder external rotation angle (mean difference, 7.2° ± 2.9°, P = .016) and greater shoulder proximal force (mean difference, 9.2% ± 3.9% body weight, P = .021) compared with those with proper trunk rotation sequences (n = 22). No other variables differed significantly different between groups. High school baseball pitchers who demonstrated improper trunk rotation sequences demonstrated greater maximal shoulder external rotation angle and shoulder proximal force compared with pitchers with proper trunk rotation sequences. Improper sequencing of the trunk and torso alter

  18. Effect of heat transfer on rotating electroosmotic flow through a micro-vessel: haemodynamical applications

    NASA Astrophysics Data System (ADS)

    Sinha, A.; Mondal, A.; Shit, G. C.; Kundu, P. K.

    2016-08-01

    This paper theoretically analyzes the heat transfer characteristics associated with electroosmotic flow of blood through a micro-vessel having permeable walls. The analysis is based on the Debye-Hückel approximation for charge distributions and the Navier-Stokes equations are assumed to represent the flow field in a rotating system. The velocity slip condition at the vessel walls is taken into account. The essential features of the rotating electroosmotic flow of blood and associated heat transfer characteristics through a micro-vessel are clearly highlighted by the variation in the non-dimensional flow velocity, volumetric flow rate and non-dimensional temperature profiles. Moreover, the effect of Joule heating parameter and Prandtl number on the thermal transport characteristics are discussed thoroughly. The study reveals that the flow of blood is appreciably influenced by the elctroosmotic parameter as well as rotating Reynolds number.

  19. Manipulation After Object Rotation Reveals Independent Sensorimotor Memory Representations of Digit Positions and Forces

    PubMed Central

    Zhang, Wei; Gordon, Andrew M.; Fu, Qiushi

    2010-01-01

    Planning of object manipulations is dependent on the ability to generate, store, and retrieve sensorimotor memories of previous actions associated with grasped objects. However, the sensorimotor memory representations linking object properties to the planning of grasp are not well understood. Here we use an object rotation task to gain insight into the mechanisms underlying the nature of these sensorimotor memories. We asked subjects to grasp a grip device with an asymmetrical center of mass (CM) anywhere on its vertical surfaces and lift it while minimizing object roll. After subjects learned to minimize object roll by generating a compensatory moment, they were asked to rotate the object 180° about a vertical axis and lift it again. The rotation resulted in changing the direction of external moment opposite to that experienced during the prerotation block. Anticipatory grasp control was quantified by measuring the compensatory moment generated at object lift onset by thumb and index finger forces through their respective application points. On the first postrotation trial, subjects failed to generate a compensatory moment to counter the external moment caused by the new CM location, thus resulting in a large object roll. Nevertheless, after several object rotations subjects reduced object roll on the initial postrotation trials by anticipating the new CM location through the modulation of digit placement but not tangential forces. The differential improvement in modulating these two variables supports the notion of independent memory representations of kinematics and kinetics and is discussed in relation to neural mechanisms underlying visuomotor transformations. PMID:20357064

  20. Manipulation after object rotation reveals independent sensorimotor memory representations of digit positions and forces.

    PubMed

    Zhang, Wei; Gordon, Andrew M; Fu, Qiushi; Santello, Marco

    2010-06-01

    Planning of object manipulations is dependent on the ability to generate, store, and retrieve sensorimotor memories of previous actions associated with grasped objects. However, the sensorimotor memory representations linking object properties to the planning of grasp are not well understood. Here we use an object rotation task to gain insight into the mechanisms underlying the nature of these sensorimotor memories. We asked subjects to grasp a grip device with an asymmetrical center of mass (CM) anywhere on its vertical surfaces and lift it while minimizing object roll. After subjects learned to minimize object roll by generating a compensatory moment, they were asked to rotate the object 180 degrees about a vertical axis and lift it again. The rotation resulted in changing the direction of external moment opposite to that experienced during the prerotation block. Anticipatory grasp control was quantified by measuring the compensatory moment generated at object lift onset by thumb and index finger forces through their respective application points. On the first postrotation trial, subjects failed to generate a compensatory moment to counter the external moment caused by the new CM location, thus resulting in a large object roll. Nevertheless, after several object rotations subjects reduced object roll on the initial postrotation trials by anticipating the new CM location through the modulation of digit placement but not tangential forces. The differential improvement in modulating these two variables supports the notion of independent memory representations of kinematics and kinetics and is discussed in relation to neural mechanisms underlying visuomotor transformations.

  1. Series Solution for Rotating Flow of an Upper Convected Maxwell Fluid over a Stretching Sheet

    NASA Astrophysics Data System (ADS)

    Sajid, M.; Z., Iqbal; Hayat, T.; Obaidat, S.

    2011-10-01

    The equations for two-dimensional flow of an upper convected Maxwell (UCM) fluid in a rotating frame are modeled. The resulting equations are first simplified by a boundary layer approach and then solved by a homotopy analysis method (HAM). Convergence of series solution is discussed through residual error curves. The results of the influence of viscoelastic and rotation parameters are plotted and discussed.

  2. Performance and internal flow of sirocco fan using contra-rotating rotors

    NASA Astrophysics Data System (ADS)

    Fukutomi, J.; Shigemitsu, T.; Yasunobu, T.

    2008-03-01

    A sirocco fan using contra-rotating rotors in which an inner rotor is settled inside the sirocco fan rotor and each rotor rotates in an opposite direction was proposed for the purpose of getting the higher pressure and making the structure of a sirocco fan more compact. If the high discharge pressure is obtained with the adoption of the contra-rotating rotors, it could be used for various purposes. Pressure coefficient of a sirocco fan with contra-rotating rotors is 2.5 times as high as the conventional sirocco fan and the maximum efficiency point of contra-rotating rotors shifts to larger flow rate than a conventional sirocco fan. On the other hand, it was clarified from the flow measurement results that circumferential velocity component at the outlet of the outer rotor of contra-rotating rotors becomes larger than a conventional one. In the present paper, the performance of a conventional sirocco fan and a sirocco fan with contra-rotating rotors are shown and the internal flow field at the outlet of outer rotor of both cases is clarified. Then, the effect of different kind of contra-rotating rotors on the performance and internal flow field is investigated and the rotor design with higher performance would be discussed.

  3. The Characteristics Method Applied to Stationary Two-Dimensional and Rotationally Symmetrical Gas Flows

    NASA Technical Reports Server (NTRS)

    Pfeiffer, F.; Meyer-Koenig, W.

    1949-01-01

    By means of characteristics theory, formulas for the numerical treatment of stationary compressible supersonic flows for the two-dimensional and rotationally symmetrical cases have been obtained from their differential equations.

  4. Flow mechanism and experimental investigation of a rotating stall in transonic compressors

    NASA Technical Reports Server (NTRS)

    Yajun, L.; Shunlin, Z.

    1983-01-01

    The flow characteristics of the rotating stall in compressors is studied, and a flow model is developed along with a theoretical calculation method based on vortex theory. A detailed theoretical calculation is completed for a two dimensional flow field in a transonic rotor in a rotating stall, and the result is in good agreement with experimental findings. The oscillograms of time-varying stall characteristic parameters recorded for the onset, growth, and cessation processes of rotating stall are analyzed, and some new flow phenomena deserving of further investigation are discovered. These include serious separation of individual blades, often preceding the onset of rotating stall in compressors with very small blade-camber angles, and periodical variation of the circumferential width of the stall cell with time, accompanied by periodical oscillation of the width of the stall cell in the radial direction of the blade. The circumferential and radial oscillation frequencies are the same.

  5. Linear stability of a circular Couette flow under a radial thermoelectric body force.

    PubMed

    Yoshikawa, H N; Meyer, A; Crumeyrolle, O; Mutabazi, I

    2015-03-01

    The stability of the circular Couette flow of a dielectric fluid is analyzed by a linear perturbation theory. The fluid is confined between two concentric cylindrical electrodes of infinite length with only the inner one rotating. A temperature difference and an alternating electric tension are applied to the electrodes to produce a radial dielectrophoretic body force that can induce convection in the fluid. We examine the effects of superposition of this thermoelectric force with the centrifugal force including its thermal variation. The Earth's gravity is neglected to focus on the situations of a vanishing Grashof number such as microgravity conditions. Depending on the electric field strength and of the temperature difference, critical modes are either axisymmetric or nonaxisymmetric, occurring in either stationary or oscillatory states. An energetic analysis is performed to determine the dominant destabilizing mechanism. When the inner cylinder is hotter than the outer one, the circular Couette flow is destabilized by the centrifugal force for weak and moderate electric fields. The critical mode is steady axisymmetric, except for weak fields within a certain range of the Prandtl number and of the radius ratio of the cylinders, where the mode is oscillatory and axisymmetric. The frequency of this oscillatory mode is correlated with a Brunt-Väisälä frequency due to the stratification of both the density and the electric permittivity of the fluid. Under strong electric fields, the destabilization by the dielectrophoretic force is dominant, leading to oscillatory nonaxisymmetric critical modes with a frequency scaled by the frequency of the inner-cylinder rotation. When the outer cylinder is hotter than the inner one, the instability is again driven by the centrifugal force. The critical mode is axisymmetric and either steady under weak electric fields or oscillatory under strong electric fields. The frequency of the oscillatory mode is also correlated with the

  6. Mathematical modeling of the flow field and particle motion in a rotating bioreactor at unit gravity and microgravity

    NASA Technical Reports Server (NTRS)

    Boyd, Ernest J.

    1990-01-01

    The biotechnology group at NASA Johnson Space Center is developing systems for culturing mammalian cells that stimulate some aspect of microgravity and provide a low shear environment for microgravity-based studies on suspension and anchorage dependent cells. The design of these vessels for culturing cells is based on the need to suspend cells and aggregates of cells and microcarrier beads continually in the culturing medium. The design must also provide sufficient circulation for adequate mass transfer of nutrients to the cells and minimize the total force on the cells. Forces, resulting from sources such as hydrodynamic fluid shear and collisions of cells and walls of the vessels, may damage delicate cells and degrade the formation of three dimensional structures. This study examines one particular design in both unit gravity and microgravity based on two concentric cylinders rotating in the same direction at different speeds to create a Couette flow between them. A numerical simulation for the flow field and the trajectories of particles in the vessel. The flow field for the circulation of the culturing medium is modeled by the Navier-Stokes equations. The forces on a particle are assumed to be drag from the fluid's circulation, buoyancy from the gravitational force and centrifugal force from the rotation of the vessel. The problem requires first solving the system of partial differential equations for the fluid flow by a finite difference method and then solving the system of ordinary differential equations for the trajectories by Gear's stiff method. Results of the study indicate that the trajectories in unit gravity and microgravity are very similar except for small spatial deviations on the fast time scale in unit gravity. The total force per unit cross sectional area on a particle in microgravity, however, is significantly smaller than the corresponding value in unit gravity, which is also smaller than anticipated. Hence, this study indicates that this

  7. Reynolds-Stress and Triple-Product Models Applied to a Flow with Rotation and Curvature

    NASA Technical Reports Server (NTRS)

    Olsen, Michael E.

    2016-01-01

    Turbulence models, with increasing complexity, up to triple product terms, are applied to the flow in a rotating pipe. The rotating pipe is a challenging case for turbulence models as it contains significant rotational and curvature effects. The flow field starts with the classic fully developed pipe flow, with a stationary pipe wall. This well defined condition is then subjected to a section of pipe with a rotating wall. The rotating wall introduces a second velocity scale, and creates Reynolds shear stresses in the radial-circumferential and circumferential-axial planes. Furthermore, the wall rotation introduces a flow stabilization, and actually reduces the turbulent kinetic energy as the flow moves along the rotating wall section. It is shown in the present work that the Reynolds stress models are capable of predicting significant reduction in the turbulent kinetic energy, but triple product improves the predictions of the centerline turbulent kinetic energy, which is governed by convection, dissipation and transport terms, as the production terms vanish on the pipe axis.

  8. Effects of Taylor-Görtler vortices on turbulent flows in a spanwise-rotating channel

    NASA Astrophysics Data System (ADS)

    Dai, Yi-Jun; Huang, Wei-Xi; Xu, Chun-Xiao

    2016-11-01

    Fully developed turbulent channel flow with system rotation in the spanwise direction has been studied by direct numerical simulation at Rem = 2800 and 7000 with 0 ≤ Rom ≤ 0.5. The width of the computational domain is adjusted for each case to contain two pairs of Taylor-Görtler (TG) vortices. Under a relatively low rotation rate, the turbulent vortical structures are strongly influenced by the TG vortices. A conditional average method is employed to investigate the effects of these TG vortices on turbulence. In the upwash region where the fluid is pumped away from the pressure wall by the TG vortices, turbulence is found to be enhanced, while the opposite scenario occurs in the downwash region where the fluid is shifted toward the pressure wall. The statistics along the centerlines of the two regions of a TG vortex are presented in detail. Through the budget analysis of the transport equation of vorticity fluctuations, we found that the wall-normal stretching term caused by the TG vortices plays an important role in initiating the differences of turbulence intensities between the two regions, which are further augmented by the Coriolis force term in the streamwise direction. Meanwhile, the shear stress on the suction wall is observed to fluctuate in a quasi-periodic manner at Rem = 7000 and Rom = 0.3, which is also revealed to be induced by the TG vortices. Such quasi-periodicity is not found at Rem = 2800 and Rom = 0.3, where turbulence on the suction side is strongly suppressed by rotation.

  9. Bingham liquid flow between two cylinders induced by inner ring rotation

    NASA Astrophysics Data System (ADS)

    Jaroslav, Štigler; Simona, Fialová

    2017-09-01

    This paper deals with the fluid flow between two cylinders induced by inner ring rotation. The gap width between the cylinders, in case that they are both concentric, is 1mm, the gap and inner ring radius ratio 0.013 and the radius ratio 0.987. Attention is focused on rotation speed and eccentricity influence on the flow. Calculations were done for both Newtonian liquid and Bingham plastic liquid with the yield stress threshold 50 Pa.

  10. Comments on the Rotational State and Non-Gravitational Forces of Comet 46/WIRTANEN. Revised

    NASA Technical Reports Server (NTRS)

    Samarasinha, Nalin H.; Mueller, Beatrice E. A.; Belton, Michael J. S.

    1995-01-01

    We apply our experience of modeling the rotational state and non-gravitational forces of comet 1 P/Halley and other comets to comet 46P/Wirtanen. While the paucity of physical data on 46P/Wirtanen makes this process somewhat speculative, this comet's place as target for the important Rosetta mission gives significance to such a study. Our arguments are based on the summary of observational data provided by Jorda and Rickman (1995) and a comparative study of the behavior of other periodic comets. We find 46P/Wirtanen to have a level of surface activity relative to its mass that is dynamically more akin to that found in comet 1 P/Halley than in a typical periodic comet. We show through an illustrative numerical example that this apparent fact should likely lead to an excited spin state for this comet and that significant changes in the spin period could occur in a single pass through perihelion. We argue that the available observations are not sufficient to substantiate the claim of Jorda and Rickman (1995) that the nucleus is undergoing retrograde rotation and it is possible that the rotation is either prograde as well as retrograde. The substantial requirements that must be placed on any future observing program necessary to determine the precise rotational state are outlined. We advocate an extended (approx. two month) southern hemisphere observing campaign to determine the nuclear rotational state in 1996 if possible before activity turns on.

  11. Studies of heat transport to forced-flow He II

    SciTech Connect

    Dresner, L.; Kashani, A.; Van Sciver, S.W.

    1985-01-01

    Analytical and experimental studies of heat transport to forced-flow He II are reported. The work is pertinent to the transfer of He II in space. An analytical model has been developed that establishes a condition for two-phase flow to occur in the transfer line. This condition sets an allowable limit to the heat leak into the transfer line. Experimental measurements of pressure drop and flow meter performances indicate that turbulent He II can be analyzed in terms of classical pressure drop correlations.

  12. Single phase channel flow forced convection heat transfer

    SciTech Connect

    Hartnett, J.P.

    1999-04-01

    A review of the current knowledge of single phase forced convection channel flow of liquids (Pr > 5) is presented. Two basic channel geometries are considered, the circular tube and the rectangular duct. Both laminar flow and turbulent flow are covered. The review begins with a brief overview of the heat transfer behavior of Newtonian fluids followed by a more detailed presentation of the behavior of purely viscous and viscoelastic Non-Newtonian fluids. Recent developments dealing with aqueous solutions of high molecular weight polymers and aqueous solutions of surfactants are discussed. The review concludes by citing a number of challenging research opportunities.

  13. Analysis of heat transfer for unsteady MHD free convection flow of rotating Jeffrey nanofluid saturated in a porous medium

    NASA Astrophysics Data System (ADS)

    Mohd Zin, Nor Athirah; Khan, Ilyas; Shafie, Sharidan; Alshomrani, Ali Saleh

    In this article, the influence of thermal radiation on unsteady magnetohydrodynamics (MHD) free convection flow of rotating Jeffrey nanofluid passing through a porous medium is studied. The silver nanoparticles (AgNPs) are dispersed in the Kerosene Oil (KO) which is chosen as conventional base fluid. Appropriate dimensionless variables are used and the system of equations is transformed into dimensionless form. The resulting problem is solved using the Laplace transform technique. The impact of pertinent parameters including volume fraction φ , material parameters of Jeffrey fluid λ1 , λ , rotation parameter r , Hartmann number Ha , permeability parameter K , Grashof number Gr , Prandtl number Pr , radiation parameter Rd and dimensionless time t on velocity and temperature profiles are presented graphically with comprehensive discussions. It is observed that, the rotation parameter, due to the Coriolis force, tends to decrease the primary velocity but reverse effect is observed in the secondary velocity. It is also observed that, the Lorentz force retards the fluid flow for both primary and secondary velocities. The expressions for skin friction and Nusselt number are also evaluated for different values of emerging parameters. A comparative study with the existing published work is provided in order to verify the present results. An excellent agreement is found.

  14. Forces on the solid constituent in a multiphase flow

    SciTech Connect

    Passman, S.L.

    1986-10-01

    I use a representation theorem of continuum mechanics, along with a systematic approximation, to establish an exact correspondence between the momentum interaction on the solid constituent in a multiphase flow, and the Stokes drag, the Faxen force, the Saffman lift, and the Ho and Leal lift on a particle in a viscous fluid.

  15. Nonlinear energy transfers and phase diagrams for geostrophically balanced rotating-stratified flows.

    PubMed

    Herbert, Corentin

    2014-03-01

    Equilibrium statistical mechanics tools have been developed to obtain indications about the natural tendencies of nonlinear energy transfers in two-dimensional and quasi-two-dimensional flows like rotating and stratified flows in geostrophic balance. In this article we consider a simple model of such flows with a nontrivial vertical structure, namely, two-layer quasigeostrophic flows, which remain amenable to analytical study. We obtain the statistical equilibria of the system in the case of a linear vorticity-stream function relation, build the corresponding phase diagram, and discuss the most probable outcome of nonlinear energy transfers, both on the horizontal and on the vertical, in the presence of stratification and rotation.

  16. Flow measurement in base cooling air passages of a rotating turbine blade

    NASA Technical Reports Server (NTRS)

    Liebert, C. H.; Pollack, F. G.

    1974-01-01

    The operational performance is decribed of a shaft-mounted system for measuring the air mass flow rate in the base cooling passages of a rotating turbine blade. Shaft speeds of 0 to 9000 rpm, air mass flow rates of 0.0035 to 0.039 kg/sec (0.0077 to 0.085 lbm/sec), and blade air temperatures of 300 to 385 K (80 to 233 F) were measured. Comparisons of individual rotating blade flows and corresponding stationary supply orifice flows agreed to within 10 percent.

  17. Spatiotemporal intermittency in the torsional Couette flow between a rotating and a stationary disk

    NASA Astrophysics Data System (ADS)

    Cros, A.; Le Gal, P.

    2002-11-01

    This work is devoted to the experimental study of the transition to turbulence of a flow confined in a narrow gap between a rotating and a stationary disk. When the fluid layer thickness is of the same order of magnitude as the boundary layer depths, the azimuthal velocity axial gradient is nearly constant and this rotating disk flow tends to be a torsional Couette flow. As in the plane Couette flow or the Taylor-Couette flow, transition to turbulence occurs via the appearance of turbulent domains inside a laminar background. In the rotating disk case, the nucleation of turbulent spirals, previously called "solitary waves" in the rotating disk flow literature, is connected to the birth of structural defects in a periodic underlying roll pattern. As the rotation rate is increased, the lifetime of these turbulent structures increases until a threshold is reached where they then form permanent turbulent spirals arranged nearly periodically all around a circumference. However, since the number of these turbulent spirals decreases with the rotational frequency, the transition to a fully turbulent regime is not achieved. Thus the turbulent fraction of the pattern saturates to a value lower than 0.5. After a geometrical description of the structures, we present a statistical analysis of sizes and lifetimes of the turbulent and laminar domains in order to compare this transition to already observed spatiotemporal intermittent behavior.

  18. Measurement of Flow Pattern Within a Rotating Stall Cell in an Axial Compressor

    NASA Technical Reports Server (NTRS)

    Lepicovsky, Jan; Braunscheidel, Edward P.

    2006-01-01

    Effective active control of rotating stall in axial compressors requires detailed understanding of flow instabilities associated with this compressor regime. Newly designed miniature high frequency response total and static pressure probes as well as commercial thermoanemometric probes are suitable tools for this task. However, during the rotating stall cycle the probes are subjected to flow direction changes that are far larger than the range of probe incidence acceptance, and therefore probe data without a proper correction would misrepresent unsteady variations of flow parameters. A methodology, based on ensemble averaging, is proposed to circumvent this problem. In this approach the ensemble averaged signals acquired for various probe setting angles are segmented, and only the sections for probe setting angles close to the actual flow angle are used for signal recombination. The methodology was verified by excellent agreement between velocity distributions obtained from pressure probe data, and data measured with thermoanemometric probes. Vector plots of unsteady flow behavior during the rotating stall regime indicate reversed flow within the rotating stall cell that spreads over to adjacent rotor blade channels. Results of this study confirmed that the NASA Low Speed Axial Compressor (LSAC) while in a rotating stall regime at rotor design speed exhibits one stall cell that rotates at a speed equal to 50.6 percent of the rotor shaft speed.

  19. Traction Forces of Endothelial Cells under Slow Shear Flow

    PubMed Central

    Perrault, Cecile M.; Brugues, Agusti; Bazellieres, Elsa; Ricco, Pierre; Lacroix, Damien; Trepat, Xavier

    2015-01-01

    Endothelial cells are constantly exposed to fluid shear stresses that regulate vascular morphogenesis, homeostasis, and disease. The mechanical responses of endothelial cells to relatively high shear flow such as that characteristic of arterial circulation has been extensively studied. Much less is known about the responses of endothelial cells to slow shear flow such as that characteristic of venous circulation, early angiogenesis, atherosclerosis, intracranial aneurysm, or interstitial flow. Here we used a novel, to our knowledge, microfluidic technique to measure traction forces exerted by confluent vascular endothelial cell monolayers under slow shear flow. We found that cells respond to flow with rapid and pronounced increases in traction forces and cell-cell stresses. These responses are reversible in time and do not involve reorientation of the cell body. Traction maps reveal that local cell responses to slow shear flow are highly heterogeneous in magnitude and sign. Our findings unveil a low-flow regime in which endothelial cell mechanics is acutely responsive to shear stress. PMID:26488643

  20. Scaling in three-dimensional and quasi-two-dimensional rotating turbulent flows

    NASA Astrophysics Data System (ADS)

    Baroud, Charles N.; Plapp, Brendan B.; Swinney, Harry L.; She, Zhen-Su

    2003-08-01

    We have made velocity time series measurements (using hot film probes) and velocity field measurements (using particle image velocimetry) on turbulent flow in a rotating annulus. For low annulus rotation rates the Rossby number was of order unity and the flow was three-dimensional (3D), but at high rotation rates the Rossby number was only about 0.1, comparable to the value for oceans and the atmosphere on large length scales. The low Rossby number (quasi-geostrophic) flow was nearly two-dimensional (2D), as expected from the Taylor-Proudman theorem. For the 3D flow we found that the probability distribution function (PDF) for velocity differences along the direction of the flow, δv(d)=v(x0+d)-v(x0), was Gaussian for large separations d and non-Gaussian (with exponential tails) for small d, as has been found for nonrotating turbulent flows. However, for low Rossby number flow, the PDF was self-similar (independent of d) and non-Gaussian. The exponents characterizing the structure functions, Sp=<(δv)p>˜dζp were obtained by the extended self-similarity method. For 3D flow the exponents departed from p/3 with increasing p, as has been found for turbulence in nonrotating flows, while for the quasi-2D turbulent flow, the exponents increased linearly with p, as expected for a self-similar flow. We applied the β-test of the hierarchical structure model [She and Lévêque, Phys. Rev. Lett. 72, 336 (1994)] and found that β remained constant at β≃0.75 as the rotation was increased from the 3D to the 2D regime; this indicates that both the quasi-2D and 3D flows are highly intermittent. The PIV images provided another indication of the intermittency—both the quasi-2D and 3D flows had coherent vortices which could be distinguished from the background flow. We also applied the γ-test of the hierarchical structure model and found that γ increased from 0.18 for the 3D flow to 0.34 for the quasi-2D flow; the latter value is in accord with expectation for self

  1. Flow control mechanism of capillary driven flow in microchannel using non-mechanical forces

    NASA Astrophysics Data System (ADS)

    Nunna, Bharath Babu; Zhuang, Shiqiang; Lee, Eon Soo

    2016-11-01

    The capillary driven flow in microchannel is a self-driven flow by the natural phenomenon called surface tension of the fluid. The gradients in surface tension force which influence the flow field in microchannel is generated by the modulation of contact angle through a defined hydrophilization of the PDMS (Polydimethylsiloxane) microchannel surface. PDMS which is hydrophobic in nature is treated with various surface treatments in order to convert it to hydrophilic. The contact angle made by the fluid with the PDMS microchannel surface is altered when the surface is converted from hydrophobic to hydrophilic. The flow rate of fluid in the microchannel is directly proportional to the hydrophilicity of that microchannel since the capillary force which is the driving force of the flow is dependent on the contact angle. Flow control mechanism of capillary driven flow in microchannel using non-mechanical forces is developed by treating the microchannel surfaces with various surface treatments. The precise control of the surface characteristics like hydrophilicity and roughness of the miocrochannel helps to control the capillary flow in microchannel. The flow rate variation with respect to the various surface treated channels are studied. Principal Investigator.

  2. Radiation Force induced Liquid Flow within a Homogeneous Medium

    NASA Astrophysics Data System (ADS)

    Choi, Honggu; Joo, Boram; Jisung, Jeong; Oh, Kyunghwan; Yonsei Univ Collaboration

    2015-05-01

    The visualization of optical force required refractive index inhomogeneous boundary, or absorption to generate radiation pressure. However, the dilute liquid medium with low attenuation coefficient is affected by light carrying momentum, and generated flow. The optical force density within a dielectric medium oscillates, and their time averaged value was regarded as a vanishing parameter, however the existence of light carrying momentum within a dielectric media generates material momentum density and it results localized liquid flow. We used 980 nm fiber laser source guided along HI1060 single mode fiber which guides localized single mode Poynting vector, in order to generate effectively measureable radiation pressure during light propagation within deionized water. The micro beads with 2 micrometer diameter were deployed to visualize the flow and their location was out of beam to reject the effect of radiation pressure at the refractive index inhomogeneity between water and polymer beads.

  3. Single Molecule Study of Force-Induced Rotation of Carbon-Carbon Double Bonds in Polymers.

    PubMed

    Huang, Wenmao; Zhu, Zhenshu; Wen, Jing; Wang, Xin; Qin, Meng; Cao, Yi; Ma, Haibo; Wang, Wei

    2017-01-24

    Carbon-carbon double bonds (C═C) are ubiquitous in natural and synthetic polymers. In bulk studies, due to limited ways to control applied force, they are thought to be mechanically inert and not to contribute to the extensibility of polymers. Here, we report a single molecule force spectroscopy study on a polymer containing C═C bonds using atomic force microscope. Surprisingly, we found that it is possible to directly observe the cis-to-trans isomerization of C═C bonds at the time scale of ∼1 ms at room temperature by applying a tensile force ∼1.7 nN. The reaction proceeds through a diradical intermediate state, as confirmed by both a free radical quenching experiment and quantum chemical modeling. The force-free activation length to convert the cis C═C bonds to the transition state is ∼0.5 Å, indicating that the reaction rate is accelerated by ∼10(9) times at the transition force. On the basis of the density functional theory optimized structure, we propose that because the pulling direction is not parallel to C═C double bonds in the polymer, stretching the polymer not only provides tension to lower the transition barrier but also provides torsion to facilitate the rotation of cis C═C bonds. This explains the apparently low transition force for such thermally "forbidden" reactions and offers an additional explanation of the "lever-arm effect" of polymer backbones on the activation force for many mechanophores. This work demonstrates the importance of precisely controlling the force direction at the nanoscale to the force-activated reactions and may have many implications on the design of stress-responsive materials.

  4. Rotating flow of a nanofluid due to an exponentially stretching surface with suction

    NASA Astrophysics Data System (ADS)

    Salleh, Siti Nur Alwani; Bachok, Norfifah; Arifin, Norihan Md

    2017-08-01

    An analysis of the rotating nanofluid flow past an exponentially stretched surface with the presence of suction is studied in this work. Three different types of nanoparticles, namely, copper, titania and alumina are considered. The system of ordinary differential equations is computed numerically using a shooting method in Maple software after being transformed from the partial differential equations. This transformation has considered the similarity transformations in exponential form. The physical effect of the rotation, suction and nanoparticle volume fraction parameters on the rotating flow and heat transfer phenomena is investigated and has been described in detail through graphs. The dual solutions are found to appear when the governing parameters reach a certain range.

  5. Rotation induced flow suppression around two tandem circular cylinders at low Reynolds number

    NASA Astrophysics Data System (ADS)

    Chatterjee, Dipankar; Gupta, Krishan; Kumar, Virendra; Varghese, Sachin Abraham

    2017-08-01

    The rotation to a bluff object is known to have a stabilizing effect on the fluid dynamic transport around the body. An unsteady periodic flow can be degenerated into a steady flow pattern depending on the rate of rotation imparted to the body. On the other hand, multiple bodies placed in tandem arrangement with respect to an incoming flow can cause destabilization to the flow as a result of the complicated wake interaction between the bodies. Accordingly, the spacing between the bodies and the rate of rotation have significant impact on the overall fluid dynamic transport around them. The present work aims to understand how these two competing factors are actually influencing the fluidic transport across a pair of identical rotating circular cylinders kept in tandem arrangement in an unconfined medium. The cylinders are subjected to a uniform free stream flow and the gaps between the cylinders are varied as 0.2, 0.7, 1.5 and 3.0. Both the cylinders are made to rotate in the clockwise sense. The Reynolds number based on the free stream flow is taken as 100. A two-dimensional finite volume based transient computation is performed for a range of dimensionless rotational speeds of the cylinders (0 ≤ Ω ≤ 2.75). The results show that the shedding phenomena can be observed up to a critical rate of rotation (Ωcr) depending on the gap spacing. Beyond Ωcr, the flow becomes stabilized and finally completely steady as Ω increases further. Increasing the gap initially causes a slight decrease in the critical rotational speed, however, it increases at a rapid rate for larger gap spacing.

  6. The numerical calculation of rotating fluid flows at low Rossby numbers

    NASA Astrophysics Data System (ADS)

    Page, M. A.

    Numerical methods which can be used to calculate flows in a rapidly rotating fluid are presented. The flows considered are those within a closed cylindrical container rotating about an axis aligned with the sidewalls, with a slow motion superposed upon the rigid rotation of the fluid. The Rossby number in this case is small; the Eckman number is also considered to be small, so that viscous diffusion is confined to the thin layers of the fluid. The flows calculated are those in the geostrophic region of the fluid, where the motion is depth-independent and the governing equations are two-dimensional. Between the geostatic flow and the walls of the container, however, there are ageostrophic layers of two types. By analyzing these layers theoretically, appropriate boundary conditions on the geostrophic flow can be calculated.

  7. Flow past a rotating cylinder at high Reynolds number using PANS method

    NASA Astrophysics Data System (ADS)

    Kumar, Rajesh

    2016-11-01

    In the present study, high-Reynolds number flow past a rotating cylinder has been simulated using Partially-Averaged Navier-Stokes (PANS) method. The simulations are performed at Re = 140000. The spin ratio of the cylinder, which is defined by the ratio of the circumferential speed of the cylinder to the free-stream speed, varies from a = 0 to a = 4. The resolved and the modeled physical scales have been compared with the corresponding LES data for better understanding of the efficacy of the PANS method. The comparison of PANS results with the LES results showed good agreement. It has been recognized that the PANS simulation is able to produce fairly acceptable results using even a coarse-mesh. It is recognized that the time-averaged flow statistics obtained using PANS and URANS simulations are approximately same. However the vortex structure is much better captured by the PANS method. With the increase in the spin ratio, decrease in the time-averaged drag and increase in the time-averaged lift force acting on the cylinder have been observed. The vortices in far wake region are displaced and deformed but those in the vicinity of the cylinder are stretched at the bottom and accumulated over the top of the cylinder.

  8. Computation and volume rendering of large-scale EOF coherent modes in rotating turbulent flow data

    NASA Astrophysics Data System (ADS)

    Ostrouchov, G.; Pugmire, D.; Rosenberg, D. L.; Chen, W.; Pouquet, A.

    2013-12-01

    The computation of empirical orthogonal functions (EOF) is used to extract major coherent modes of variability in spatio-temporal data. We explore the computation of EOF in three spatial dimensions over time and present the result with volume rendering software. To accomplish this, we use an HPC extension of the R language, pbdR (see r-pbd.org), that we embed in the VisIt visualization system. VisIt provides parallel data reader capability as well as the volume rendering ability to present the computed EOFs. The data we consider derives from direct numerical simulation on a grid of 20483 points of rapidly rotating turbulent flows that are forced at intermediate scales. Injection of energy at these scales at small Rossby number (~0.04) leads to a direct cascade of energy to small scales, and an inverse cascade to large scales. We will use pdbR to examine the spatio-temporal interactions and ergodicity of waves and turbulent eddies in these flows.

  9. Unconfined laminar nanofluid flow and heat transfer around a rotating circular cylinder in the steady regime

    NASA Astrophysics Data System (ADS)

    Bouakkaz, Rafik; Salhi, Fouzi; Khelili, Yacine; Quazzazi, Mohamed; Talbi, Kamel

    2017-06-01

    In this work, steady flow-field and heat transfer through a copper- water nanofluid around a rotating circular cylinder with a constant nondimensional rotation rate α varying from 0 to 5 was investigated for Reynolds numbers of 5-40. Furthermore, the range of nanoparticle volume fractions considered is 0-5%. The effect of volume fraction of nanoparticles on the fluid flow and heat transfer characteristics are carried out by using a finite-volume method based commercial computational fluid dynamics solver. The variation of the local and the average Nusselt numbers with Reynolds number, volume fractions, and rotation rate are presented for the range of conditions. The average Nusselt number is found to decrease with increasing value of the rotation rate for the fixed value of the Reynolds number and volume fraction of nanoparticles. In addition, rotation can be used as a drag reduction technique.

  10. Study on shearing force and impact force of a volcanic mud flow on Mt. Sakurajima

    Treesearch

    Yoshinobu Taniguchi

    1991-01-01

    Two kinds of shearing stress meters (type A and type B) were set on the channel bottom in the Arimura River and the Mochiki River on Mt. Sakurajima. Volcanic mud flows take place there about 100 times a year. The results of the surveys demonstrated that the actual shearing force of a volcanic mud flow on Mt. Sakurajima was from 0.46 to 2.50 kgf/cm2...

  11. Reliability of forced internal rotation and active internal rotation to assess lateral instability of the biceps pulley

    PubMed Central

    ARRIGONI, PAOLO; ROSE, GIACOMO DELLE; D’AMBROSI, RICCARDO; ROTUNDO, GIORGIO; CAMPAGNA, VINCENZO; PIRANI, PIERGIORGIO; PANASCÌ, MANLIO; PETRICCIOLI, DARIO; BERTONE, CELESTE; GRASSO, ANDREA; LATTE, CARMINE; COSTA, ALBERTO; VIOLA, GINO; DE GIORGI, SILVANA; PANELLA, ANTONELLO; PADUA, ROBERTO; BECCARINI, ALESSANDRO; SALCHER, BARBARA; OLIVIERI, MATTEO; MUGNAINI, MARCO; PANNONE, ANTONELLO; CEOLDO, CHIARA; LONGO, UMILE GIUSEPPE; DENARO, VINCENZO; CERCIELLO, SIMONE; PANNI, ALFREDO SCHIAVONE; AVANZI, PAOLO; ZORZI, CLAUDIO; RAGONE, VINCENZA; CASTAGNA, ALESSANDRO; RANDELLI, PIETRO

    2015-01-01

    Purpose the aim of this study was to investigate the relationship between positive painful forced internal rotation (FIR) and lateral pulley instability in the presence of a pre-diagnosed posterosuperior cuff tear. The same investigation was conducted for painful active internal rotation (AIR). Methods a multicenter prospective study was conducted in a series of patients scheduled to undergo arthroscopic posterosuperior cuff repair. Pain was assessed using a visual analog scale (VAS) and the Disabilities of the Arm, Shoulder and Hand questionnaire (DASH) was administered. The VAS score at rest, DASH score, and presence/absence of pain on FIR and AIR were recorded and their relationships with lesions of the lateral pulley, cuff tear patterns and shape of lesions were analyzed. Results the study population consisted of 115 patients (mean age: 55.1 years) recruited from 12 centers. The dominant arm was affected in 72 cases (62.6%). The average anteroposterior extension of the lesion was 1.61 cm. The mean preoperative VAS and DASH scores were 6.1 and 41.8, respectively. FIR and AIR were positive in 94 (81.7%) and 85 (73.9%) cases, respectively. The lateral pulley was compromised in 50 cases (43.4%). Cuff tears were partial articular in 35 patients (30.4%), complete in 61 (53%), and partial bursal in 19 (16.5%). No statistical correlation between positive FIR or AIR and lateral pulley lesions was detected. Positive FIR and AIR were statistically associated with complete lesions. Negative FIR was associated with the presence of partial articular tears. Conclusions painful FIR in the presence of a postero-superior cuff tear does not indicate lateral pulley instability. When a cuff tear is suspected, positive FIR and AIR are suggestive of full-thickness tear patterns while a negative FIR suggests a partial articular lesion. Level of evidence: level I, validating cohort study with good reference standards. PMID:26151035

  12. Simulation of Effects of the Saffman Force and the Magnus Force on Sand Saltation in Turbulent Flow

    SciTech Connect

    Zheng, Zhongquan C.; Zou, Xueyong; Yang, Xiaofan; Cheng, Hong

    2011-12-11

    The effects of both the Saffman force and Magnus force on sand saltation are investigated. Turbulent flows in a channel and over a barchans dune are considered with sand particles injected into the flow. The results show that both of the forces increase the height and skipping distance of sand saltation, with the Magnus force giving more significant effect on the height. These forces can also increase the sand settling at the lee side of the barchans dune.

  13. NURBS-based isogeometric analysis for the computation of flows about rotating components

    NASA Astrophysics Data System (ADS)

    Bazilevs, Y.; Hughes, T. J. R.

    2008-12-01

    The ability of non-uniform rational B-splines (NURBS) to exactly represent circular geometries makes NURBS-based isogeometric analysis attractive for applications involving flows around and/or induced by rotating components (e.g., submarine and surface ship propellers). The advantage over standard finite element discretizations is that rotating components may be introduced into a stationary flow domain without geometric incompatibility. Although geometric compatibility is exactly achieved, the discretization of the flow velocity and pressure remains incompatible at the interface between the stationary and rotating subdomains. This incompatibility is handled by using a weak enforcement of the continuity of solution fields at the interface of the stationary and rotating subdomains.

  14. MHD Flow of the Micropolar Fluid between Eccentrically Rotating Disks

    PubMed Central

    Srivastava, Neetu

    2014-01-01

    This analytical investigation examines the magnetohydrodynamic flow problem of an incompressible micropolar fluid between the two eccentrically placed disks. Employing suitable transformations, the flow governing partial differential equations is reduced to ordinary differential equations. An exact solution representing the different flow characteristic of micropolar fluid has been derived by solving the ordinary differential equations. Analysis of the flow characteristics of the micropolar fluid has been done graphically by varying the Reynolds number and the Hartmann number. This analysis has been carried out for the weak and strong interactions. PMID:27355040

  15. Inception mechanism and suppression of rotating stall in an axial-flow fan

    NASA Astrophysics Data System (ADS)

    Nishioka, T.

    2013-12-01

    Inception patterns of rotating stall at two stagger-angle settings for the highly loaded rotor blades were experimentally investigated in a low-speed axial-flow fan. Rotor-tip flow fields were also numerically investigated to clarify the mechanism behind the rotating stall inception. The stall inception patterns depended on the rotor stagger-angle settings. The stall inception from a rotating instability was confirmed at the design stagger-angle settings. The stall inception from a short length-scale stall cell (spike) was also confirmed at the small stagger-angle setting. The spillage of tip-leakage flow and the tip-leakage vortex breakdown influence the rotating stall inception. An air-separator has been developed based on the clarified inception mechanism of rotating stall. The rotating stall was suppressed by the developed air-separator, and the operating range of fan was extended towards low flow rate. The effect of developed air-separator was also confirmed by application to a primary air fan used in a coal fired power plant. It is concluded from these results that the developed air-separator can provide a wide operating range for an axial-flow fan.

  16. Correlating Lagrangian structures with forcing in two-dimensional flow

    NASA Astrophysics Data System (ADS)

    Ouellette, Nicholas T.; Hogg, Charlie A. R.; Liao, Yang

    2016-01-01

    Lagrangian coherent structures (LCSs) are the dominant transport barriers in unsteady, aperiodic flows, and their role in organizing mixing and transport has been well documented. However, nearly all that is known about LCSs has been gleaned from passive observations: they are computed in a post-processing step after a flow has been observed and used to understand why the mixing and transport proceeded as it did. In many applications, the ability instead to control the presence or location of LCSs via imposed forcing would be valuable. With this goal in mind, we study the relationship between LCSs and external forcing in an experimental quasi-two-dimensional weakly turbulent flow. We find that the likelihood of finding a repelling LCS at a given location is positively correlated with the mean strain rate injected at that point and negatively correlated with the mean speed, and that it is not correlated with the vorticity. We also find that mean time between successive LCSs appearing at a fixed location is related to the structure of the forcing field. Finally, we demonstrate a surprising difference in our results between LCSs computed forward and backward in time, with forward-time (repelling) LCSs showing much more correlation with the forcing than backwards-time (attracting) LCSs.

  17. Forces on stationary particles in near-bed turbulent flows

    USGS Publications Warehouse

    Schmeeckle, M.W.; Nelson, J.M.; Shreve, R.L.

    2007-01-01

    In natural flows, bed sediment particles are entrained and moved by the fluctuating forces, such as lift and drag, exerted by the overlying flow on the particles. To develop a better understanding of these forces and the relation of the forces to the local flow, the downstream and vertical components of force on near-bed fixed particles and of fluid velocity above or in front of them were measured synchronously at turbulence-resolving frequencies (200 or 500 Hz) in a laboratory flume. Measurements were made for a spherical test particle fixed at various heights above a smooth bed, above a smooth bed downstream of a downstream-facing step, and in a gravel bed of similarly sized particles as well as for a cubical test particle and 7 natural particles above a smooth bed. Horizontal force was well correlated with downstream velocity and not correlated with vertical velocity or vertical momentum flux. The standard drag formula worked well to predict the horizontal force, but the required value of the drag coefficient was significantly higher than generally used to model bed load motion. For the spheres, cubes, and natural particles, average drag coefficients were found to be 0.76, 1.36, and 0.91, respectively. For comparison, the drag coefficient for a sphere settling in still water at similar particle Reynolds numbers is only about 0.4. The variability of the horizontal force relative to its mean was strongly increased by the presence of the step and the gravel bed. Peak deviations were about 30% of the mean force for the sphere over the smooth bed, about twice the mean with the step, and 4 times it for the sphere protruding roughly half its diameter above the gravel bed. Vertical force correlated poorly with downstream velocity, vertical velocity, and vertical momentum flux whether measured over or ahead of the test particle. Typical formulas for shear-induced lift based on Bernoulli's principle poorly predict the vertical forces on near-bed particles. The

  18. Time-dependent Force-free Pulsar Magnetospheres: Axisymmetric and Oblique Rotators

    SciTech Connect

    Spitkovsky, Anatoly; /KIPAC, Menlo Park

    2006-04-10

    Magnetospheres of many astrophysical objects can be accurately described by the low-inertia (or ''force-free'') limit of MHD. We present a new numerical method for solution of equations of force-free relativistic MHD based on the finite-difference time-domain (FDTD) approach with a prescription for handling spontaneous formation of current sheets. We use this method to study the time-dependent evolution of pulsar magnetospheres in both aligned and oblique magnetic geometries. For the aligned rotator we confirm the general properties of the time-independent solution of Contopoulos et al. (1999). For the oblique rotator we present the 3D structure of the magnetosphere and compute, for the first time, the spindown power of pulsars as a function of inclination of the magnetic axis. We find the pulsar spindown luminosity to be L {approx} ({mu}{sup 2}{Omega}{sub *}{sup 4}/c{sup 3})(1 + sin{sup 2}{alpha}) for a star with the dipole moment {mu}, rotation frequency {Omega}{sub *}, and magnetic inclination angle {alpha}. We also discuss the effects of current sheet resistivity and reconnection on the structure and evolution of the magnetosphere.

  19. FORCE2: A multidimensional flow program for gas solids flow theory guide

    SciTech Connect

    Burge, S.W.

    1991-05-01

    This report describes the theory and structure of the FORCE2 flow program. The manual describes the governing model equations, solution procedure and their implementation in the computer program. FORCE2 is an extension of an existing B&V multidimensional, two-phase flow program. FORCE2 was developed for application to fluid beds by flow implementing a gas-solids modeling technology derived, in part, during a joint government -- industry research program, ``Erosion of FBC Heat Transfer Tubes,`` coordinated by Argonne National Laboratory. The development of FORCE2 was sponsored by ASEA-Babcock, an industry participant in this program. This manual is the principal documentation for the program theory and organization. Program usage and post-processing of code predictions with the FORCE2 post-processor are described in a companion report, FORCE2 -- A Multidimensional Flow Program for Fluid Beds, User`s Guide. This manual is segmented into sections to facilitate its usage. In section 2.0, the mass and momentum conservation principles, the basis for the code, are presented. In section 3.0, the constitutive relations used in modeling gas-solids hydrodynamics are given. The finite-difference model equations are derived in section 4.0 and the solution procedures described in sections 5.0 and 6.0. Finally, the implementation of the model equations and solution procedure in FORCE2 is described in section 7.0.

  20. Numerical study for MHD peristaltic flow in a rotating frame.

    PubMed

    Hayat, T; Zahir, Hina; Tanveer, Anum; Alsaedi, A

    2016-12-01

    The aim of present investigation is to model and analyze the magnetohydrodynamic (MHD) peristaltic transport of Prandtl fluid in a channel with flexible walls. The whole system consisting of fluid and channel are in a rotating frame of reference with uniform angular velocity. Viscous dissipation in thermal equation is not ignored. The channel boundaries satisfy the convective conditions in terms of temperature. The arising complicated problems are reduced in solvable form using large wavelength and small Reynolds number assumptions. Numerical solution for axial and secondary velocities, temperature and heat transfer coefficient are presented. Main emphasis is given to the outcome of rotation and material parameters of Prandtl fluid on the physical quantities of interest.

  1. A method for measuring cooling air flow in base coolant passages of rotating turbine blades

    NASA Technical Reports Server (NTRS)

    Liebert, C. H.; Pollack, F. G.

    1975-01-01

    Method accurately determines actual coolant mass flow rate in cooling passages of rotating turbine blades. Total and static pressures are measured in blade base coolant passages. Mass flow rates are calculated from these measurements of pressure, measured temperature and known area.

  2. Flow in a differentially rotated cylindrical drop at moderate Reynolds number

    NASA Astrophysics Data System (ADS)

    Harriott, G. M.; Brown, R. A.

    1984-07-01

    Galerkin finite-element approximations are combined with computer-implemented perturbation methods for tracking families of solutions to calculate the steady axisymmetric flows in a differentially rotated cylindrical drop as a function of Reynolds number Re, drop aspect ratio and the rotation ratio between the two end disks. The flows for Reynolds numbers below 100 are primarily viscous and reasonably described by an asymptotic analysis. When the disks are exactly counter-rotated, multiple steady flows are calculated that bifurcate to higher values of Re from the expected solution with two identical secondary cells stacked symmetrically about the axial midplane. The new flows have two cells of different size and are stable beyond the critical value Re sub c. The slope of the locus of Re sub c for drops with aspect ratio up to 3 disagrees with the result for two disks of infinite radius computed assuming the similarity form of the velocity field. Changing the rotation ratio for exact counter-rotation ruptures the junction of the multiple flow fields into two separated flow families.

  3. Pair mobility functions for rigid spheres in concentrated colloidal dispersions: Force, torque, translation, and rotation.

    PubMed

    Zia, Roseanna N; Swan, James W; Su, Yu

    2015-12-14

    and rotation, for arbitrary colloid volume fraction ϕ. The pair mobilities (describing entrainment of one particle by the disturbance flow created by another) decay slowly with separation distance: as 1/r, for volume fractions 0.05 ≤ ϕ ≤ 0.5. For the relative mobility, we find an initially rapid growth as a pair separates, followed by a slow, 1/r growth. Up to ϕ ≤ 0.4, the relative mobility does not reached the far-field value even beyond separations of many particle sizes. In the case of ϕ = 0.5, the far-field asymptote is reached but only at a separation of eight radii and after a slow 1/r growth. At these higher concentrations, the coefficients also reveal liquid-like structural effects on pair mobility at close separations. These results confirm that long-range many-body hydrodynamic interactions are an essential part of the dynamics of concentrated systems and that care must be taken when applying renormalization schemes.

  4. Pair mobility functions for rigid spheres in concentrated colloidal dispersions: Force, torque, translation, and rotation

    NASA Astrophysics Data System (ADS)

    Zia, Roseanna N.; Swan, James W.; Su, Yu

    2015-12-01

    and rotation, for arbitrary colloid volume fraction ϕ. The pair mobilities (describing entrainment of one particle by the disturbance flow created by another) decay slowly with separation distance: as 1/r, for volume fractions 0.05 ≤ ϕ ≤ 0.5. For the relative mobility, we find an initially rapid growth as a pair separates, followed by a slow, 1/r growth. Up to ϕ ≤ 0.4, the relative mobility does not reached the far-field value even beyond separations of many particle sizes. In the case of ϕ = 0.5, the far-field asymptote is reached but only at a separation of eight radii and after a slow 1/r growth. At these higher concentrations, the coefficients also reveal liquid-like structural effects on pair mobility at close separations. These results confirm that long-range many-body hydrodynamic interactions are an essential part of the dynamics of concentrated systems and that care must be taken when applying renormalization schemes.

  5. Pair mobility functions for rigid spheres in concentrated colloidal dispersions: Force, torque, translation, and rotation

    SciTech Connect

    Zia, Roseanna N. Su, Yu; Swan, James W.

    2015-12-14

    translation and rotation, for arbitrary colloid volume fraction ϕ. The pair mobilities (describing entrainment of one particle by the disturbance flow created by another) decay slowly with separation distance: as 1/r, for volume fractions 0.05 ≤ ϕ ≤ 0.5. For the relative mobility, we find an initially rapid growth as a pair separates, followed by a slow, 1/r growth. Up to ϕ ≤ 0.4, the relative mobility does not reached the far-field value even beyond separations of many particle sizes. In the case of ϕ = 0.5, the far-field asymptote is reached but only at a separation of eight radii and after a slow 1/r growth. At these higher concentrations, the coefficients also reveal liquid-like structural effects on pair mobility at close separations. These results confirm that long-range many-body hydrodynamic interactions are an essential part of the dynamics of concentrated systems and that care must be taken when applying renormalization schemes.

  6. The three-dimensional flow past a rapidly rotating circular cylinder

    NASA Technical Reports Server (NTRS)

    Denier, James P.; Duck, Peter W.

    1993-01-01

    The high Reynolds number (Re) flow past a rapidly rotating circular cylinder is investigated. The rotation rate of the cylinder is allowed to vary (slightly) along the axis of the cylinder, thereby provoking three-dimensional flow disturbances, which are shown to involve relatively massive (O(Re)) velocity perturbations to the flow away from the cylinder surface. Additionally, three integral conditions, analogous to the single condition determined in two dimensions by Batchelor, are derived, based on the condition of periodicity in the azimuthal direction.

  7. Evolution of forced shear flows in polytropic atmospheres: a comparison of forcing methods and energetics

    NASA Astrophysics Data System (ADS)

    Witzke, V.; Silvers, L. J.; Favier, B.

    2016-11-01

    Shear flows are ubiquitous in astrophysical objects including planetary and stellar interiors, where their dynamics can have significant impact on thermochemical processes. Investigating the complex dynamics of shear flows requires numerical calculations that provide a long-time evolution of the system. To achieve a sufficiently long lifetime in a local numerical model, the system has to be forced externally. However, at present, there exist several different forcing methods to sustain large-scale shear flows in local models. In this paper, we examine and compare various methods used in the literature in order to resolve their respective applicability and limitations. These techniques are compared during the exponential growth phase of a shear flow instability, such as the Kelvin-Helmholtz (KH) instability, and some are examined during the subsequent non-linear evolution. A linear stability analysis provides reference for the growth rate of the most unstable modes in the system and a detailed analysis of the energetics provides a comprehensive understanding of the energy exchange during the system's evolution. Finally, we discuss the pros and cons of each forcing method and their relation with natural mechanisms generating shear flows.

  8. The Rotational Spectrum and Anharmonic Force Field of Chlorine Dioxide, OClO

    NASA Astrophysics Data System (ADS)

    Müller, Holger S. P.; Sørensen, G. Ole; Birk, Manfred; Friedl, Randall R.

    1997-11-01

    The rotational spectra of O35ClO and O37ClO in their (000), (100), (010), (001), and (020) states have been reinvestigated in selected regions between 130 and 526 GHz. About 800 newly measured lines spanning the quantum numbers 2 ≤N≤ 65 and 0 ≤Ka≤ 17 have been analyzed together with data from two previous microwave and millimeter wave studies. In particular, the spectroscopic constants in the ground vibrational states have been improved enabeling precise predictions of line positions into the submillimeter region. The newly derived ground state rotational and quartic centrifugal distortion constants, their vibrational changes, and the sextic centrifugal distortion constants were used together with data from infrared studies in a calculation of the quartic force field.

  9. Motion and decay of vortex rings submerged in a rotational flow

    NASA Technical Reports Server (NTRS)

    Ishii, K.; Liu, C. H.

    1987-01-01

    The interaction between vortex rings of finite strength and an axisymmetric rotational background flow is studied by a singular perturbation method, because it is difficult to use a finite-difference method to analyze the viscous decay in the small core of a vortex ring. The analysis is carried out by combining a composite solution of a vortex ring and an unsteady Euler solution for the background rotational flow. Using the method of averaging, a numerical scheme is developed to obtain an Euler solution in which the grid and time-step sizes depend solely on the length and velocity scales of the background flow. Numerical results are presented to illustrate the interaction between the trajectories and decay rates of the vortex rings and the background rotational flow.

  10. The effect of particle rotation in multi-particle flow simulations

    NASA Astrophysics Data System (ADS)

    Sierakowski, Adam; Prosperetti, Andrea

    2013-11-01

    In multi-particle flow simulations, particle rotation is difficult to calculate and is often imprecisely accounted for or ignored altogether. We examine the effect of these procedures on the overall flow characteristics through large systems of particles when the particle center is fixed and either allowed or not to rotate. We use a newly developed GPU-centric implementation of the Physalis method for the solution of the Navier-Stokes equations in the presence of finite-size spheres. We investigate periodic systems of more than 100 randomly-distributed particles at Reynolds numbers up to 100. By considering flow characteristics such as mean velocity and pressure drop, we shed light on the importance of including particle rotation effects in large particle-flow simulations. Study supported by NSF grant CBET 1258398.

  11. Experimental Investigations of Exciting Forces Caused by Flow in Labyrinth Seals

    NASA Technical Reports Server (NTRS)

    Thieleke, G.; Stetter, H.

    1991-01-01

    The interaction of the flow through the labyrinth seals with the shaft of the rotor can have an effect on the stability of turbomachines. Thus, the excited forces, so-called cross forces or nonconservative forces, arise, which act perpendicular to the rotor eccentricity. This effect is caused by an unsymmetrical pressure distribution within the labyrinth cavities. Experimental studies were carried out for different types of labyrinth geometries: two staggered labyrinths with teeth on the stator and grooved rotor as well as a full and a convergent stepped labyrinth. These labyrinths can be found on the tip shrouding of bladings in steam or gas turbines. The following parameters were varied in the test facility: geometry of the labyrinth seals (number of cavities, inlet region), shaft rotation, pressure difference on the seal, entry swirl and eccentricity of the rotor. The results are presented for stiffness coefficients of the labyrinth seals, leakage flow and circumferential flow in each cavity which was measured with special probes. Generally, the inlet swirl has the greatest influence on the coefficients of the seals. The experimental results were compared with theoretical results and were in good agreement.

  12. Enhanced external counterpulsation and traction therapy ameliorates rotational vertebral artery flow insufficiency resulting from cervical spondylosis.

    PubMed

    Xin, Wang; Fangjian, Guo; Hua, Wang; Jiangtao, Xie; Shouyi, Wang; Yingchun, Zhao; Xiong, Li

    2010-07-01

    Clinical trial of patients with rotational vertebrobasilar insufficiency (VBI) resulting from cervical spondylosis. To investigate the effectiveness of enhanced external counterpulsation (EECP) and traction therapy for these patients. EECP would reduce arterial stiffness and vascular resistance, and increase regional blood flow of vertebral arteries, thus may ameliorate symptoms in these patients. One hundred sixty-three patients who were clinically suspected rotational VBI caused by cervical spondylosis were enrolled in this study. They were randomly allocated into 3 groups: EECP + traction, EECP, and traction group. All patients and 50 healthy volunteers received transcranial color Doppler examination of the vertebral artery and basilar artery in both a neutral cervical spine position and a rotational position. Within 3 days after treatment, 47 (84%) patients in EECP + traction group, 32 (61%) patients in EECP group, and 8 (15%) patients in traction group achieved successful outcomes, while at 3 months' follow-up, 45 (80%) patients in EECP + traction group, 34 (64%) in EECP group, and 3 (6%) in traction group achieved successful outcomes. With head rotation, the percentage of reduction of blood flow velocities of the vertebrobasilar artery (VBA) in patients was much greater than that of the healthy volunteers (P < 0.01). After treatment, rotational blood flow velocity reduction percentage of VBA in each treatment group was much lower than that of each group before treatment. EECP + traction group experienced the greatest decrease of rotational blood flow velocity reduction percentage of VBA, while EECP group experienced second greatest. EECP and traction therapy can relieve the symptoms of rotational VBI, improve the rotational reduction of vertebrobasilar blood flow, and reduce the increased arterial impedance.

  13. Incompressible Navier-Stokes computations of rotating flows

    NASA Technical Reports Server (NTRS)

    Kiris, Cetin; Chang, Leon; Kwak, Dochan; Rogers, Stuart

    1993-01-01

    Flow through pump components, such as an inducer and an impeller, is efficiently simulated by solving the incompressible Navier-Stokes equations. The solution method is based on the pseudocompressibility approach and uses an implicit-upwind differencing scheme together with the Gauss-Seidel line relaxation method. Current computations use one-equation Baldwin-Barth turbulence model which is derived from a simplified form of the standard k-epsilon model equations. The resulting computer code is applied to the flow analysis inside a generic rocket engine pump inducer, a fuel pump impeller, and SSME high-pressure fuel turbopump impeller. Numerical results of inducer flow are compared with experimental measurements. Flow analyses at 80-, 100-, and 120-percent of design conditions are presented.

  14. The flow of a thin liquid film on a stationary and rotating disk. II - Theoretical prediction

    NASA Technical Reports Server (NTRS)

    Rahman, M. M.; Faghri, A.; Hankey, W. L.

    1990-01-01

    The existing theoretical models are improved and a systematic procedure to compute the free surface flow of a thin liquid film is suggested. The solutions for axisymmetric radial flow on a stationary horizontal disk and for the disk rotating around its axis are presented. The theoretical predictions are compared with the experimental data presented in Part I of this report. The analysis shows results for both supercritical and subcritical flows and the flow structure in the vicinity of a hydraulic jump which isolates these two flow types. The detailed flow structure in a hydraulic jump was computed and shown to contain regions of separation including a 'surface roller'. The effects of surface tension are found to be important near the outer edge of the disk where the fluid experiences a free fall. At other locations, the surface tension is negligible. For a rotating disk, the frictional resistance in the angular direction is found to be as important as that in the radial direction.

  15. Dynamic Torque and Vertical Force Analysis during Nickel-titanium Rotary Root Canal Preparation with Different Modes of Reciprocal Rotation.

    PubMed

    Tokita, Daisuke; Ebihara, Arata; Nishijo, Miki; Miyara, Kana; Okiji, Takashi

    2017-10-01

    The purpose of the present study was to compare 2 modes of reciprocal movement (torque-sensitive and time-dependent reciprocal rotation) with continuous rotation in terms of torque and apical force generation during nickel-titanium rotary root canal instrumentation. A custom-made automated root canal instrumentation and torque/force analyzing device was used to prepare simulated canals in resin blocks and monitor the torque and apical force generated in the blocks during preparation. Experimental groups (n = 7, each) consisted of (1) torque-sensitive reciprocal rotation with torque-sensitive vertical movement (group TqR), (2) time-dependent reciprocal rotation with time-dependent vertical movement (group TmR), and (3) continuous rotation with time-dependent vertical movement (group CR). The canals were instrumented with TF Adaptive SM1 and SM2 rotary files (SybronEndo, Orange, CA), and the torque and apical force were measured during instrumentation with SM2. The mean and maximum torque and apical force values were statistically analyzed using 1-way analysis of variance and the Tukey test (α = 0.05). The recordings showed intermittent increases of upward apical force and clockwise torque, indicating the generation and release of screw-in forces. The maximum upward apical force values in group TmR were significantly smaller than those in group CR (P < .05). The maximum torque values in clockwise and counterclockwise directions in groups TqR and TmR were significantly smaller than those in group CR (P < .05). Under the present experimental conditions using TF Adaptive instruments, both torque-sensitive and time-dependent reciprocal rotation generated significantly lower maximum torque and may have advantages in reducing stress generation caused by screw-in forces when compared with continuous rotation. Copyright © 2017 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

  16. Flow and heat transfer in 180-degree turn square ducts: Effects of turning configuration and system rotation

    NASA Astrophysics Data System (ADS)

    Wang, Ten-See; Chyu, Ming-King

    1993-07-01

    Forced flow through channels connected by sharp bends is frequently encountered in various rocket and gas turbine engines. For example, the transfer ducts, the coolant channels surround the combustion chamber, the internal cooling passage in a blade or vane, the flow path in the fuel element of a nuclear rocket engine, the flow around a pressure relieve valve piston, and the recirculated base flow of multiple engine clustered nozzles. Transport phenomena involved in such a flow passage are complex and considered to be very different from those of conventional turning flow with relatively mild radii of curvature. While previous research pertaining to this subject has been focused primarily on the experimental heat transfer, very little analytical work is directed to understanding the flowfield and energy transport in the passage. Therefore, the primary goal of this paper is to benchmark the predicted wall heat fluxes using a state-of-the-art computational fluid dynamics (CFD) formulation against those of measurement for a rectangular turn duct. Other secondary goals include studying the effects of turning configurations, e.g., the semi-circular turn, and the rounded-corner turn, and the effect of system rotation. The computed heat fluxes for the rectangular turn duct compared favorably with those of the experimental data. The results show that the flow pattern, pressure drop, and heat transfer characteristics are different among the three turning configurations, and are substantially different with system rotation. Also demonstrated in this work is that the present computational approach is quite effective and efficient and will be suitable for flow and thermal modeling in rocket and turbine engine applications.

  17. Towards the development of a novel experimental shoulder simulator with rotating scapula and individually controlled muscle forces simulating the rotator cuff.

    PubMed

    Baumgartner, Daniel; Tomas, Daniel; Gossweiler, Lukas; Siegl, Walter; Osterhoff, Georg; Heinlein, Bernd

    2014-03-01

    A preclinical analysis of novel implants used in shoulder surgery requires biomechanical testing conditions close to physiology. Existing shoulder experiments may only partially apply multiple cycles to simulate postoperative, repetitive loading tasks. The aim of the present study was therefore the development of an experimental shoulder simulator with rotating scapula able to perform multiple humeral movement cycles by simulating individual muscles attached to the rotator cuff. A free-hanging, metallic humerus pivoted in a polyethylene glenoid is activated by tension forces of linear electroactuators to simulate muscles of the deltoideus (DELT), supraspinatus (SSP), infraspinatus/teres minor and subscapularis. The abductors DELT and SSP apply forces with a ratio of 3:1 up to an abduction angle of 85°. The rotating scapular part driven by a rotative electro actuator provides one-third to the overall arm abduction. Resulting joint forces and moments are measured by a 6-axis load cell. A linear increase in the DELT and SSP motors is shown up to a maximum of 150 and 50 N for the DELT and SSP, respectively. The force vector in the glenoid resulted in 253 N at the maximum abduction. The present investigation shows the contribution of individual muscle forces attached to the moving humerus to perform active abduction in order to reproducibly test shoulder implants.

  18. Investigation of Rotating Stall Phenomena in Axial Flow Compressors. Volume I. Basic Studies of Rotating Stall

    DTIC Science & Technology

    1976-06-01

    1500 rpm. An external hydraulic pump systen powered by’ hor• e-cwcr elect’.tc motor is used to provide power for the hydraulic motor. The modified...nodel has been developed to predict the sound pressure level and total power radiated at harmonics of the blade passage frequency for a rotor-stator...electrically powered two- speed axial flow fan is used as the source of suction. Continuous control of the mass flow is achieved through the use of variable

  19. Numerical Simulation of Non-Rotating and Rotating Coolant Channel Flow Fields. Part 1

    NASA Technical Reports Server (NTRS)

    Rigby, David L.

    2000-01-01

    Future generations of ultra high bypass-ratio jet engines will require far higher pressure ratios and operating temperatures than those of current engines. For the foreseeable future, engine materials will not be able to withstand the high temperatures without some form of cooling. In particular the turbine blades, which are under high thermal as well as mechanical loads, must be cooled. Cooling of turbine blades is achieved by bleeding air from the compressor stage of the engine through complicated internal passages in the turbine blades (internal cooling, including jet-impingement cooling) and by bleeding small amounts of air into the boundary layer of the external flow through small discrete holes on the surface of the blade (film cooling and transpiration cooling). The cooling must be done using a minimum amount of air or any increases in efficiency gained through higher operating temperature will be lost due to added load on the compressor stage. Turbine cooling schemes have traditionally been based on extensive empirical data bases, quasi-one-dimensional computational fluid dynamics (CFD) analysis, and trial and error. With improved capabilities of CFD, these traditional methods can be augmented by full three-dimensional simulations of the coolant flow to predict in detail the heat transfer and metal temperatures. Several aspects of turbine coolant flows make such application of CFD difficult, thus a highly effective CFD methodology must be used. First, high resolution of the flow field is required to attain the needed accuracy for heat transfer predictions, making highly efficient flow solvers essential for such computations. Second, the geometries of the flow passages are complicated but must be modeled accurately in order to capture all important details of the flow. This makes grid generation and grid quality important issues. Finally, since coolant flows are turbulent and separated the effects of turbulence must be modeled with a low Reynolds number

  20. Bistable flows forced by precession in planetary cores

    NASA Astrophysics Data System (ADS)

    Cebron, D.

    2015-12-01

    The presence of the Moon leads the Earth to precess, which forces a flow in its outer core via the spheroidal Core-Mantle Boundary (CMB). Reciprocally, this is also true for the liquid core core of the Moon, but the CMB is rather a triaxial ellipsoid in this case. In this work, we investigate if the precession can force two different stable flows for the same control parameters, allowing then the core to switch from one state to the other in presence of noise (convection, turbulence, etc.). To do so, we systematically study the parameter ranges where the well-known equations obtained by Busse (1968 J. Fluid Mech. 33 739-51) lead to multiple solutions. Then, using the models recently proposed by Noir and Cébron (2013 J. Fluid Mech. 737 412-39), which are more generic in the inviscid limit than the equations of Busse, we analytically describe these multiple solutions, their conditions of existence, and their stability. We also report for the first time the theoretical possibility that time-dependent multiple flows can coexist in precessing triaxial ellipsoids (such as the liquid core of the Moon). Finally, using the formula we have derived from pre-existent models of the literature, we conclude that the Earth and the Moon do not undergo such a bistable flow forced by precession. However, according to the models of the literature, such a bistable precession forced state exists for geophysically relevant ranges of parameters, and is thus always possible a priori in precessing liquid cores of terrestrial bodies.

  1. A semi-direct solver for compressible three-dimensional rotational flow

    NASA Technical Reports Server (NTRS)

    Chang, S.-C.; Adamczyk, J. J.

    1983-01-01

    An iterative procedure is presented for solving steady inviscid 3-D subsonic rotational flow problems. The procedure combines concepts from classical secondary flow theory with an extension to 3-D of a novel semi-direct Cauchy-Riemann solver. It is developed for generalized coordinates and can be exercised using standard finite difference procedures. The stability criterion of the iterative procedure is discussed along with its ability to capture the evolution of inviscid secondary flow in a turning channel.

  2. A semi-direct solver for compressible 3-dimensional rotational flow

    NASA Technical Reports Server (NTRS)

    Chang, S. C.; Adamczyk, J. J.

    1983-01-01

    An iterative procedure is presented for solving steady inviscid 3-D subsonic rotational flow problems. The procedure combines concepts from classical secondary flow theory with an extension to 3-D of a novel semi-direct Cauchy-Riemann solver. It is developed for generalized coordinates and can be exercised using standard finite difference procedures. The stability criterion of the iterative procedure is discussed along with its ability to capture the evolution of inviscid secondary flow in a turning channel.

  3. A new framework for simulating forced homogeneous buoyant turbulent flows

    NASA Astrophysics Data System (ADS)

    Carroll, Phares L.; Blanquart, Guillaume

    2015-06-01

    This work proposes a new simulation methodology to study variable density turbulent buoyant flows. The mathematical framework, referred to as homogeneous buoyant turbulence, relies on a triply periodic domain and incorporates numerical forcing methods commonly used in simulation studies of homogeneous, isotropic flows. In order to separate the effects due to buoyancy from those due to large-scale gradients, the linear scalar forcing technique is used to maintain the scalar variance at a constant value. Two sources of kinetic energy production are considered in the momentum equation, namely shear via an isotropic forcing term and buoyancy via the gravity term. The simulation framework is designed such that the four dimensionless parameters of importance in buoyant mixing, namely the Reynolds, Richardson, Atwood, and Schmidt numbers, can be independently varied and controlled. The framework is used to interrogate fully non-buoyant, fully buoyant, and partially buoyant turbulent flows. The results show that the statistics of the scalar fields (mixture fraction and density) are not influenced by the energy production mechanism (shear vs. buoyancy). On the other hand, the velocity field exhibits anisotropy, namely a larger variance in the direction of gravity which is associated with a statistical dependence of the velocity component on the local fluid density.

  4. Radial forces analysis and rotational speed test of radial permanent magnetic bearing for horizontal axis wind turbine applications

    NASA Astrophysics Data System (ADS)

    Kriswanto, Jamari

    2016-04-01

    Permanent magnet bearings (PMB) are contact free bearings which utilize the forces generated by the magnets. PMB in this work is a type of radial PMB, which functions as the radial bearings of the Horizontal Axis Wind Turbine (HAWT) rotor shaft. Radial PMB should have a greater radial force than the radial force HAWT rotor shaft (bearing load). This paper presents a modeling and experiments to calculate the radial force of the radial PMB. This paper also presents rotational speed test of the radial PMB compared to conventional bearings for HAWT applications. Modeling using COMSOL Multiphysics 4.3b with the magnetic fields physics models. Experiments were conducted by measuring the displacement of the rotor to the stator for a given load variation. Results of the two methods showed that the large displacement then the radial force would be greater. Radial forces of radial PMB is greater than radial forces of HAWT rotor shaft. The rotational speed test results of HAWT that used radial PMB produced higher rotary than conventional bearings with an average increase of 87.4%. Increasing rotational speed occured because radial PMB had no friction. HAWT that used radial PMB rotated at very low wind speeds are 1.4 m/s with a torque of 0.043 Nm, while the HAWT which uses conventional bearing started rotating at a wind speed of 4.4 m/s and required higher torque of 0.104 N.

  5. Numerical and Experimental study of secondary flows in a rotating two-phase flow: the tea leaf paradox

    NASA Astrophysics Data System (ADS)

    Calderer, Antoni; Neal, Douglas; Prevost, Richard; Mayrhofer, Arno; Lawrenz, Alan; Foss, John; Sotiropoulos, Fotis

    2015-11-01

    Secondary flows in a rotating flow in a cylinder, resulting in the so called ``tea leaf paradox'', are fundamental for understanding atmospheric pressure systems, developing techniques for separating red blood cells from the plasma, and even separating coagulated trub in the beer brewing process. We seek to gain deeper insights in this phenomenon by integrating numerical simulations and experiments. We employ the Curvilinear Immersed boundary method (CURVIB) of Calderer et al. (J. Comp. Physics 2014), which is a two-phase flow solver based on the level set method, to simulate rotating free-surface flow in a cylinder partially filled with water as in the tea leave paradox flow. We first demonstrate the validity of the numerical model by simulating a cylinder with a rotating base filled with a single fluid, obtaining results in excellent agreement with available experimental data. Then, we present results for the cylinder case with free surface, investigate the complex formation of secondary flow patterns, and show comparisons with new experimental data for this flow obtained by Lavision. Computational resources were provided by the Minnesota Supercomputing Institute.

  6. Flow Straightener for a Rotating-Drum Liquid Separator

    NASA Technical Reports Server (NTRS)

    O'Coin, James R.; Converse, David G.; Rethke, Donald W.

    2004-01-01

    A flow straightener has been incorporated into a rotary liquid separator that originally comprised an inlet tube, a shroud plate, an impeller, an inner drum, an outer drum, a housing, a pitot tube, and a hollow shaft motor. As a consequence of the original geometry of the impeller, shroud, inner drum, and hollow shaft, swirl was created in the airflow inside the hollow shaft during operation. The swirl speed was large enough to cause a significant pressure drop. The flow straightener consists of vanes on the back side of the shroud plate. These vanes compartmentalize the inside of the inner drum in such a way as to break up the flow path and thereby stop the air from swirling; as a result, the air enters the hollow shaft with a predominantly axial velocity instead of a swirl. Tests of the rotary liquid separator at an airflow rate of 10 cu ft/min (0.0047 cu m/s) revealed that the dynamic pressure drop was 8 in. of water (approx.=2 kPa) in the absence of the flow straightener and was reduced to 1 in. of water (approx.=0.25 kPa) in the presence of the flow straightener.

  7. Channel flow modeling of impingement cooling of a rotating turbine blade

    NASA Technical Reports Server (NTRS)

    Koo, J. J.

    1984-01-01

    Local heat transfer distributions in impingement cooling have been measured by Kreatsoulas and Prieser for a range of conditions which model those in actual turbine blades, including the effects of rotation. These data were reported as local Nusselt numbers, but referred to coolant supply conditions. By means of a channel flow modeling of the flow in the supply and impingement passages, the same data are here presented in terms of local Nusselt number distributions such as are used in design. The results in this form are compared to the nonrotating impingement results of Chupp and to the rotating but nonimpingement results of Morris. Rotation reduces the mean Nusselt numbers from these found by Chupp by about 30 percent, and introduces important radial variations which are sensitive to rotation and to leading edge stagger angle.

  8. Rotations

    Treesearch

    John R. Jones; Wayne D. Shepperd

    1985-01-01

    The rotation, in forestry, is the planned number of years between formation of a crop or stand and its final harvest at a specified stage of maturity (Ford-Robertson 1971). The rotation used for many species is the age of culmination of mean usable volume growth [net mean annual increment (MAI)]. At that age, usable volume divided by age reaches its highest level. That...

  9. Rotational transformations and transverse energy flow in paraxial light beams: linear azimuthons.

    PubMed

    Bekshaev, Aleksandr; Soskin, Marat

    2006-07-15

    Paraxial beams whose transverse structure rotates upon free propagation (spiral beams) can be treated as analogs of azimuthons recently found in nonlinear media [Phys. Rev. Lett.95, 203904 (2005)]. These linear azimuthons have essentially a nonlocalized character and can possess an almost arbitrary rotation rate independent of the angular momentum of the beam. Such beams can be assimilated into fluent mechanical bodies with intrinsic mass flows determined by transverse energy redistribution over the beam cross section.

  10. Effect of baffle on slosh reaction forces in rotating liquid helium subjected to a lateral impulse in microgravity

    NASA Technical Reports Server (NTRS)

    Hung, R. J.; Long, Y. T.

    1995-01-01

    Sloshing dynamics within a partially filled rotating Dewar of superfluid He II are investigated in response to a lateral impulse. The study investigates several factors, including how the rotating bubble of superfluid He II reacts to the impulse in microgravity, how the amplitudes of slosh reaction forces act on the Dewar with various rotating speeds, how the frequencies of the sloshing modes excited differ in terms of differences in rotating speeds, and how the sloshing dynamics differ with and without a baffle. The numerical computation of sloshing dynamics is based on the noninertial frame spacecraft-bound coordinates. Results of the simulations are illustrated.

  11. Mixed convection flow of couple stress fluid between rotating discs with chemical reaction and double diffusion effects

    NASA Astrophysics Data System (ADS)

    Kaladhar, K.; Srinivasacharya, D.

    2016-12-01

    The chemical reaction, Soret and Dufour effects on steady flow of a couple stress fluid between two rotating disks are studied. The lower disc is rotating with angular velocity Ω1 where as the upper disc is rotating with Ω2. The density variation in centrifugal and Coriolis force terms are taken into consideration by invoking a linear density-temperature relation and Boussinesq approximation to account the buoyancy effects. The non-linear governing partial differential equations are transformed into system of ordinary differential equations by using the similarity transformations. Homotopy Analysis Method (HAM) has been used to solve the resulting equations. Graphical illustrations of the dimensionless velocity, concentration and temperature profiles are presented at different values of the emerging parameter of the present study. It has been found that as an increase in couple stresses leads to the decrease in velocity, temperature and increase in concentration of the fluid. Flow velocities, temperature and concentration profiles are decreases with an increase in reaction parameter.

  12. Forced motion and acoustic radiation of an elastic cylinder in axial flow

    NASA Astrophysics Data System (ADS)

    Manela, A.; Miloh, T.

    2012-07-01

    We study the forced motion and far-field acoustic radiation of an elastic cylinder subject to uniform axial flow and actuated at its upstream end by small-amplitude periodic displacement and rotation. The linearized problem is analysed under subcritical conditions of low nondimensional stream-flow velocity, uflow. It is found that the forced motion at subcritical conditions is affected by the properties of the in vacuo system. A resonance is excited when the cylinder is actuated at one of its in vacuo eigenfrequencies, ωres, manifested by relatively large deflections. Fluid flow acts to regularize this behavior by transferring energy from the upstream driver to the fluid. The dynamical description is used as a source term in the formulation of the vibroacoustic problem. Assuming the cylinder is well-streamlined and neglecting the effect of vortex shedding, the far field sound is attributed directly to cylinder vibration. Acoustic radiation of a dipole type is found in the limit where the cylinder is acoustically compact. Following the dynamical description, it is shown that fluid flow reduces the sound level compared to that in the absence of mean flow, when actuation is applied close to ω=ωres. In addition, we demonstrate that far-field sound can be controlled by varying the actuation parameters. Analytical description of the dynamical and acoustic fields is obtained in the limit u≪1, and found in close agreement with the exact numerical solution up to u˜O(1). Discrepancies between the approximate and exact solutions are observed close to the resonance frequencies, and rationalized in terms of the strong fluid-structure coupling occurring when ω→ωres. At ω=ωres, a qualitative description of the effect of fluid stream flow on the system behavior is supplied.

  13. Numerical flow simulation of a reusable sounding rocket during nose-up rotation

    NASA Astrophysics Data System (ADS)

    Kuzuu, Kazuto; Kitamura, Keiichi; Fujimoto, Keiichiro; Shima, Eiji

    2010-11-01

    Flow around a reusable sounding rocket during nose-up rotation is simulated using unstructured compressible CFD code. While a reusable sounding rocket is expected to reduce the cost of the flight management, it is demanded that this rocket has good performance for wide range of flight conditions from vertical take-off to vertical landing. A rotating body, which corresponds to a vehicle's motion just before vertical landing, is one of flight environments that largely affect its aerodynamic design. Unlike landing of the space shuttle, this vehicle must rotate from gliding position to vertical landing position in nose-up direction. During this rotation, the vehicle generates massive separations in the wake. As a result, induced flow becomes unsteady and could have influence on aerodynamic characteristics of the vehicle. In this study, we focus on the analysis of such dynamic characteristics of the rotating vehicle. An employed numerical code is based on a cell-centered finite volume compressible flow solver applied to a moving grid system. The moving grid is introduced for the analysis of rotating motion. Furthermore, in order to estimate an unsteady turbulence, we employed DDES method as a turbulence model. In this simulation, flight velocity is subsonic. Through this simulation, we discuss the effect on aerodynamic characteristics of a vehicle's shape and motion.

  14. Accelerated micropolar fluid-flow past an uniformly rotating circular cylinder

    NASA Astrophysics Data System (ADS)

    Siddiqui, Abuzar Abid

    2016-10-01

    In this paper, we formulated the non-steady flow due to the uniformly accelerated and rotating circular cylinder from rest in a stationary, viscous, incompressible and micropolar fluid. This flow problem is examined numerically by adopting a special scheme comprising the Adams-Bashforth Temporal Fourier Series method and the Runge-Kutta Temporal Special Finite-Difference method. This numerical scheme transforms the governing equation into a system of finite-difference equations. This system was further solved numerically by point successive-over-relaxation method. These results were also further extrapolated by the Richardson extrapolation method. This scheme is valid for all values of the flow and fluid-parameters and for all time. Moreover the boundary conditions of the vorticity and the spin at points far from the cylinder are being imposed and encountered too. The results are compared with existing results (for non-rotating circular cylinder in Newtonian fluids). The comparison is good. The enhancement of lift and reduction in drag is observed if the micropolarity effects are intensified. Same is happened if the rotation of a cylinder increases. Furthermore, the vortex-pair in the wake is delayed to successively higher times as rotation parameter increases. In addition, the rotation helps not only in dissolving vortices adjacent to the cylinder and adverse pressure region but also in dissolving the boundary layer separation. Furthermore, the rotation reduces the micropolar spin boundary layer.

  15. Numerical investigations of passive scalar transport in Taylor-Couette flows: Counter-rotation effect

    NASA Astrophysics Data System (ADS)

    Ouazib, Nabila; Salhi, Yacine; Si-Ahmed, El-Khider; Legrand, Jack; Degrez, G.

    2017-07-01

    Numerical methods for solving convection-diffusion-reaction (CDR) scalar transport equation in three-dimensional flow are used in the present investigation. The flow is confined between two concentric cylinders both the inner cylinder and the outer one are allowed to rotate. Direct numerical simulations (DNS) have been achieved to study the effects of the gravitational and the centrifugal potentials on the stability of incompressible Taylor-Couette flow. The Navier-Stokes equations and the uncoupled convection-diffusion-reaction equation are solved using a spectral development in one direction combined together with a finite element discretization in the two remaining directions. The complexity of the patterns is highlighted. Since, it increases as the rotation rates of the cylinders increase. In addition, the effect of the counter-rotation of the cylinders on the mass transfer is pointed out.

  16. Volatile organic compounds absorption in a cross-flow rotating packed bed.

    PubMed

    Chen, Yu-Shao; Hsu, Yi-Chun; Lin, Chia-Chang; Tai, Clifford Yi-Der; Liu, Hwai-Shen

    2008-04-01

    A cross-flow rotating packed bed (RPB) process was evaluated for its absorption of some volatile organic compounds (VOCs) into water, including isopropyl alcohol, acetone, and ethyl acetate. The experimental results showed that the mass transfer coefficient (KGa) increased with increasing rotational speed, liquid rate, and gas rate, and thus an empirical correlation of KGa was proposed for the cross-flow RPB for the first time. It was found thatthis correlation could reasonably estimate our experimental KGa data as well as those reported in literatures. Although the mass transfer coefficient was lower than that in a countercurrent-flow RPB, a cross-flow RPB is believed to be capable of handling a higher gas rate because of its flow pattern.

  17. Linear stability of a nonorthogonal axisymmetric stagnation flow on a rotating cylinder

    NASA Astrophysics Data System (ADS)

    Amaouche, Mustapha; Bouda, Faïçal Nait; Sadat, Hamou

    2006-12-01

    The present analysis deals with the onset of instability in an axisymmetric stagnation flow obliquely impinging on a uniformly rotating circular cylinder. The basic flow is described by an exact solution of the Navier-Stokes equations, discovered by Weidmann and Putkaradze [Eur. J. Mech. B/Fluids 22, 123 (2003)]. An eigenvalue problem for the linear stability is formulated, regardless of the free stream obliqueness, and then solved numerically by means of a collocation method using Laguerre's polynomials. It is established that the basic stagnation flow is stable for sufficiently high Reynolds numbers. This is in conformity with the unconditional linear stability of two-dimensional Hiemenz stagnation flow. Instability occurs for Reynolds numbers smaller than some threshold value that increases with the rotation rate of the cylinder. At criticality, the flow undergoes a Hopf bifurcation, leading then to an oscillatory secondary motion.

  18. Turbulence and turbulent drag reduction in swirling flow: Inertial versus viscous forcing

    NASA Astrophysics Data System (ADS)

    Burnishev, Yuri; Steinberg, Victor

    2015-08-01

    We report unexpected results of a drastic difference in the transition to fully developed turbulent and turbulent drag reduction (TDR) regimes and in their properties in a von Karman swirling flow with counter-rotating disks of water-based polymer solutions for viscous (by smooth disks) as well as inertial (by bladed disks) forcing and by tracking just torque Γ (t ) and pressure p (t ) . For the viscous forcing, just a single TDR regime is found with the transition values of the Reynolds number (Re) Recturb=RecTDR≃(4.8 ±0.2 ) ×105 independent of ϕ , whereas for the inertial forcing two turbulent regimes are revealed. The first transition is to fully developed turbulence, and the second one is to the TDR regime with both Recturb and RecTDR depending on polymer concentration ϕ . Both regimes differ by the values of Cf and Cp, by the scaling exponents of the fundamental turbulent characteristics, by the nonmonotonic dependencies of skewness and flatness of the pressure PDFs on Re, and by the different frequency power spectra of p with the different dependencies of the main vortex peak frequency in the p power spectra on ϕ and Re. Thus our experimental results show the transition to the TDR regime in a von Karman swirling flow for the viscous and inertial forcings in a sharp contrast to the recent experiments [Phys. Fluids 10, 426 (1998), 10.1063/1.869532; Phys. Rev. E 47, R28(R) (1993), 10.1103/PhysRevE.47.R28; and J. Phys.: Condens. Matter 17, S1195 (2005), 10.1088/0953-8984/17/14/008] where the transition to TDR is observed in the same swirling flow with counter-rotating disks only for the viscous forcing. The latter result has led its authors to the wrong conclusion that TDR is a solely boundary effect contrary to the inertial forcing associated with the bulk effect, and this conception is currently rather widely accepted in literature.

  19. The Effect of Magnetic Field on Mean Flow Generation by Rotating Two-dimensional Convection

    NASA Astrophysics Data System (ADS)

    Currie, Laura K.

    2016-11-01

    Motivated by the significant interaction of convection, rotation, and magnetic field in many astrophysical objects, we investigate the interplay between large-scale flows driven by rotating convection and an imposed magnetic field. We utilize a simple model in two dimensions comprised of a plane layer that is rotating about an axis inclined to gravity. It is known that this setup can result in strong mean flows; we numerically examine the effect of an imposed horizontal magnetic field on such flows. We show that increasing the field strength in general suppresses the time-dependent mean flows, but in some cases it organizes them, leading to stronger time-averaged flows. Furthermore, we discuss the effect of the field on the correlations responsible for driving the flows and the competition between Reynolds and Maxwell stresses. A change in behavior is observed when the (fluid and magnetic) Prandtl numbers are decreased. In the smaller Prandtl number regime, it is shown that significant mean flows can persist even when the quenching of the overall flow velocity by the field is relatively strong.

  20. Numerical investigation of the unsteady tip leakage flow and rotating stall inception in a transonic compressor

    NASA Astrophysics Data System (ADS)

    Zhang, Yanfeng; Lu, Xingen; Chu, Wuli; Zhu, Junqiang

    2010-08-01

    It is well known that tip leakage flow has a strong effect on the compressor performance and stability. This paper reports on a numerical investigation of detailed flow structures in an isolated transonic compressor rotor-NASA Rotor 37 at near stall and stalled conditions aimed at improving understanding of changes in 3D tip leakage flow structures with rotating stall inception. Steady and unsteady 3D Navier-Stokes analyses were conducted to investigate flow structures in the same rotor. For steady analysis, the predicted results agree well with the experimental data for the estimation of compressor rotor global performance. For unsteady flow analysis, the unsteady flow nature caused by the breakdown of the tip leakage vortex in blade tip region in the transonic compressor rotor at near stall condition has been captured with a single blade passage. On the other hand, the time-accurate unsteady computations of multi-blade passage at near stall condition indicate that the unsteady breakdown of the tip leakage vortex triggered the short length-scale — spike type rotating stall inception at blade tip region. It was the forward spillage of the tip leakage flow at blade leading edge resulting in the spike stall inception. As the mass flow ratio is decreased, the rotating stall cell was further developed in the blade passage.

  1. Effects of a compression garment on shoulder external rotation force outputs during isotonic contractions.

    PubMed

    Tsuruike, Masaaki; Ellenbecker, Todd S

    2013-02-01

    The use of compression garments (CGs) has been advocated for performance enhancement and recovery in athletes. The effect of a CG on humeral rotation motor control has not been previously tested. The purpose of this study was to examine the isotonic contraction of external rotation (ER) of the glenohumeral joint at different force outputs to determine the effect of wearing a long sleeve CG on muscular performance. Twelve male college tennis players and 12 male college soccer players were tested for ER of the dominant shoulder during both concentric and eccentric isotonic contractions. The subjects performed 5 consecutive repetitions of both concentric and eccentric ER at 20-30% and 40-50% of maximum voluntary isometric contraction (MVIC) intensities. All subjects were tested with and without CG as well as with and without ongoing visual feedback information (OVFI). The order of CG wearing and the presence of OVFI were randomly assigned across all subjects. The results indicated a significant 3-way interaction between CG wearing and OVFI across 2 loads. Specifically, significantly different mean value of the completion time was found between OVFI and no-OVFI without CG wearing at 40-50% of MVIC, whereas no difference in the completion time was found with and without OVFI with CG wearing. Taken together, with CG wearing, athletes may have ER at 40-50% of MVIC more readily maintained by peripheral feedback without visuomotor control imposed on force outputs as compared without CG wearing.

  2. Mean and turbulent flow development through an array of rotating elements

    NASA Astrophysics Data System (ADS)

    Craig, Anna; Dabiri, John; Koseff, Jeffrey

    2014-11-01

    The adjustment of an incoming boundary layer profile as it impacts and interacts with an array of elements has received significant attention in the context of terrestrial and aquatic canopies and more recently in the context of horizontal axis wind farms. The distance required for the mean flow profile to stabilize, the energy transport through the array, and the structure of the turbulence within the array are directly dependent upon such factors as the element height, density, rigidity/flexibility, frontal area distribution, element homogeneity, and underlying topography. In the present study, the mean and turbulent development of the flow through an array of rotating elements was examined experimentally. Element rotation has been shown to drastically alter wake dynamics of single and paired elements, but the possible extension of such rotation-driven dynamics had not previously been examined on larger groups of elements. Practically, such an array of rotating elements may provide insight into the flow dynamics of an array of vertical axis wind turbines. 2D particle image velocimetry was used along the length of the array in order to examine the effects of an increasing ratio of cylinder rotation speed to streamwise freestream velocity on flow development and structure. Work supported by a NSF Graduate Research Fellowship & Stanford Graduate Fellowship to A.E.C, by funding to J.O.D. from ONR N000141211047 and the Gordon and Betty Moore Foundation through Grant GBMF2645, and by funding from the EFML.

  3. Preconditioned iterative methods for unsteady non-Newtonian flow between eccentrically rotating cylinders

    SciTech Connect

    Gwynllyw, D.Rh.; Phillips, T.N.

    1994-12-31

    The journal bearing is an essential part of all internal combustion engines as a means of transferring the energy from the piston rods to the rotating crankshaft. It consists essentially of an inner cylinder (the journal), which is part of the crankshaft, and an outer cylinder (the bearing), which is at the end of the piston rod. In general, the two cylinders are eccentric and there is a lubricating film of oil separating the two surfaces. The addition of polymers to mineral (Newtonian) oils to minimize the variation of viscosity with temperature has the added effect of introducing strain-dependent viscosity and elasticity. The physical problem has many complicating features which need to be modelled. It is a fully three-dimensional problem which means that significant computational effort is required to solve the problem numerically. The system is subject to dynamic loading in which the journal is allowed to move under the forces the fluid imparts on it and also any other loads such as that imparted by the engine force. The centre of the journal traces out a nontrivial locus in space. In addition, there is significant deformation of the bearing and journal and extensive cavitation of the oil lubricant. In the present study the authors restrict themselves to the two-dimensional statically loaded problem. In previous work a single domain spectral method was used which employed a bipolar coordinate transformation to map the region between the journal and the bearing onto a rectangle. The flow variables were then approximated on this rectangle using Fourier-Chebyshev expansions. However, to allow for future possible deformation of the journal and bearing surfaces due to increased load in the dynamically loaded case they have decided to use a more versatile spectral element formulation.

  4. Identification of complex flows in Taylor-Couette counter-rotating cavities

    NASA Technical Reports Server (NTRS)

    Czarny, O.; Serre, E.; Bontoux, P.; Lueptow, R. M.

    2001-01-01

    The transition in confined rotating flows is a topical problem with many industrial and fundamental applications. The purpose of this study is to investigate the Taylor-Couette flow in a finite-length cavity with counter-rotating walls, for two aspect ratios L=5 or L=6. Two complex regimes of wavy vortex and spirals are emphasized for the first time via direct numerical simulation, by using a three-dimensional spectral method. The spatio-temporal behavior of the solutions is analyzed and compared to the few data actually available. c2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.

  5. Identification of complex flows in Taylor-Couette counter-rotating cavities

    NASA Technical Reports Server (NTRS)

    Czarny, O.; Serre, E.; Bontoux, P.; Lueptow, R. M.

    2001-01-01

    The transition in confined rotating flows is a topical problem with many industrial and fundamental applications. The purpose of this study is to investigate the Taylor-Couette flow in a finite-length cavity with counter-rotating walls, for two aspect ratios L=5 or L=6. Two complex regimes of wavy vortex and spirals are emphasized for the first time via direct numerical simulation, by using a three-dimensional spectral method. The spatio-temporal behavior of the solutions is analyzed and compared to the few data actually available. c2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.

  6. Flow in isothermal layers of ferrofluid by action of uniform rotating magnetic field

    SciTech Connect

    Kashevskii, B.E.

    1986-01-01

    The author attempts to determine how intense the flow of a ferrofluid in a rotating magnetic field can become owing to the temperature dependence of the properties when a nonuniform temperature field has been produced within the volume of such a fluid. It was found that in a channel with a strong temperature dependence of viscosity, a uniform rotating magnetic field is capable of effectively influencing the flow of a ferrofluid within nonisothermal layers, which may be of interest in solving problems of heat transfer.

  7. Identification of complex flows in Taylor-Couette counter-rotating cavities.

    PubMed

    Czarny, O; Serre, E; Bontoux, P; Lueptow, R M

    2001-10-01

    The transition in confined rotating flows is a topical problem with many industrial and fundamental applications. The purpose of this study is to investigate the Taylor-Couette flow in a finite-length cavity with counter-rotating walls, for two aspect ratios L=5 or L=6. Two complex regimes of wavy vortex and spirals are emphasized for the first time via direct numerical simulation, by using a three-dimensional spectral method. The spatio-temporal behavior of the solutions is analyzed and compared to the few data actually available.

  8. Mathematical Analysis of Hall Effect on Transient Hartman Flow about a Rotating Horizontal Permeable Surface in a Porous Medium under Inclined Magnetic Field.

    PubMed

    Suresh, M; Manglik, A

    2014-01-01

    This paper proposes the exact solution for unsteady flow of a viscous incompressible electrically conducting fluid past a impulsively started infinite horizontal surface which is rotating with an angular velocity embedded in a saturated porous medium under the influence of strong magnetic field with hall effect. Our study focuses on the change of direction of the external magnetic field on the flow system which leads to change in the flow behavior and skin frictional forces at the boundary. Systems of flow equations are solved using Laplace transform technique. The impacts of control parameters Hartman number, rotation of the system, hall effect, inclination of the magnetic field, and Darcy number on primary and secondary velocities are shown graphically, skin friction at horizontal boundary in tabular form. For validating our results, in the absence of permeability of the porous medium and inclination of the magnetic field the results are in good agreement with the published results.

  9. Mathematical Analysis of Hall Effect on Transient Hartman Flow about a Rotating Horizontal Permeable Surface in a Porous Medium under Inclined Magnetic Field

    PubMed Central

    Suresh, M.; Manglik, A.

    2014-01-01

    This paper proposes the exact solution for unsteady flow of a viscous incompressible electrically conducting fluid past a impulsively started infinite horizontal surface which is rotating with an angular velocity embedded in a saturated porous medium under the influence of strong magnetic field with hall effect. Our study focuses on the change of direction of the external magnetic field on the flow system which leads to change in the flow behavior and skin frictional forces at the boundary. Systems of flow equations are solved using Laplace transform technique. The impacts of control parameters Hartman number, rotation of the system, hall effect, inclination of the magnetic field, and Darcy number on primary and secondary velocities are shown graphically, skin friction at horizontal boundary in tabular form. For validating our results, in the absence of permeability of the porous medium and inclination of the magnetic field the results are in good agreement with the published results. PMID:27433540

  10. The swimming speed of a confined rotating helix in creeping flow

    NASA Astrophysics Data System (ADS)

    Angeles, Veronica; Zenit, Roberto

    2016-11-01

    Recent theoretical and numerical studies have shown that the swimming speed of a rotating helix confined in a tube or between walls is higher that the unconfined case, for the same helix properties (helix geometry and rotation speed). We conduct experiments using a magnetic self-propelled force-free robot placed in between two walls or inside a cylinder. We vary the degree of confinement and measure the translation speed for different helix geometries and rotation speeds. We do find an increase of the swimming speeds, which is in good agreement with the predictions of a wall-corrected resistive-force theory. However, since the torque also increases as a result of confinement, the experiments are restricted by the available magnetic torque. Therefore, the increase in swimming speed is only observed for low confinement levels.

  11. Lagrangian statistics and flow topology in forced 2-D turbulence

    SciTech Connect

    Kadoch, B.; Del-Castillo-Negrete, Diego B; Bos, W.J.T.; Schneider, Kai

    2011-01-01

    A study of the relationship between Lagrangian statistics and flow topology in fluid turbulence is presented. The topology is characterized using the Weiss criterion, which provides a conceptually simple tool to partition the flow into topologically different regions: elliptic (vortex dominated), hyperbolic (deformation dominated), and intermediate (turbulent background). The flow corresponds to forced two-dimensional Navier-Stokes turbulence in doubly periodic and circular bounded domains, the latter with no-slip boundary conditions. In the double periodic domain, the probability density function (pdf) of the Weiss field exhibits a negative skewness consistent with the fact that in periodic domains the flow is dominated by coherent vortex structures. On the other hand, in the circular domain, the elliptic and hyperbolic regions seem to be statistically similar. We follow a Lagrangian approach and obtain the statistics by tracking large ensembles of passively advected tracers. The pdfs of residence time in the topologically different regions are computed introducing the Lagrangian Weiss field, i.e., the Weiss field computed along the particles' trajectories. In elliptic and hyperbolic regions, the pdfs of the residence time have self-similar algebraic decaying tails. In contrast, in the intermediate regions the pdf has exponential decaying tails. The conditional pdfs (with respect to the flow topology) of the Lagrangian velocity exhibit Gaussian-like behavior in the periodic and in the bounded domains. In contrast to the freely decaying turbulence case, the conditional pdfs of the Lagrangian acceleration in forced turbulence show a comparable level of intermittency in both the periodic and the bounded domains. The conditional pdfs of the Lagrangian curvature are characterized, in all cases, by self-similar power-law behavior with a decay exponent of order - 2.

  12. Experiments on the Flow of a Thin Liquid Film Over a Horizontal Stationary and Rotating Disk Surface

    NASA Technical Reports Server (NTRS)

    Ozar, B.; Cetegen, B. M.; Faghri, A.

    2003-01-01

    Experiments on characterization of thin liquid films flowing over stationary and rotating disk surfaces are described. The thin liquid film was created by introducing deionized water from a flow collar at the center of an aluminum disk with a known initial film thickness and uniform radial velocity. Radial film thickness distribution was measured using a non-intrusive laser light interface reflection technique that enabled the measurement of the instantaneous film thickness over a finite segment of the disk. Experiments were performed for a range of flow rates between 3.01pm and 15.01pm, corresponding to Reynolds numbers based on the liquid inlet gap height and velocity between 238 and 1,188. The angular speed of the disk was varied from 0 rpm to 300 rpm. When the disk was stationary, a circular hydraulic jump was present in the liquid film. The liquid-film thickness in the subcritical region (down-stream of the hydraulic jump) was an order of magnitude greater than that in the supercritical region (upstream of the hydraulic jump) which was of the order of 0.3 mm. As the Reynolds number increased, the hydraulic jump migrated toward the edge of the disk. In the case of rotation, the liquid-film thickness exhibited a maximum on the disk surface. The liquid-film inertia and friction influenced the inner region where the film thickness progressively increased. The outer region where the film thickness decreased was primarily affected by the centrifugal forces. A flow visualization study of the thin film was also performed to determine the characteristics of the waves on the free surface. At high rotational speeds, spiral waves were observed on the liquid film. It was also determined that the angle of the waves which form on the liquid surface was a function of the ratio of local radial to tangential velocity.

  13. Correlation analysis of spatio-temporal images for estimating two-dimensional flow velocity field in a rotating flow condition

    NASA Astrophysics Data System (ADS)

    Yu, Kwonkyu; Kim, Seojun; Kim, Dongsu

    2015-10-01

    Flow velocity estimation in actual rivers using image processing technique has been highlighted for hydrometric communities in the last decades, and this technique is called Large Scale Particle Image Velocimetry (LSPIV). Although LSPIV has been successfully tested in many flow conditions, it has addressed several limitations estimating mean flow field because of difficult flow conditions such as rotating, lack of light and seeds, and noisy flow conditions. Recently, an alternative technique named STIV to use spatio-temporal images based on successively recorded images has been introduced to overcome the limitations of LSPIV. The STIV was successfully applied to obtain one-dimensional flow component in the river for estimating streamflow discharge, where the main flow direction is known. Using the 5th order of central difference scheme, the STIV directly calculated the mean angle of slopes which appeared as strips in the spatio-temporal images and has been proved to be more reliable and efficient for the discharge estimation as compared with the conventional LSPIV. However, yet it has not been sufficiently qualified to derive two-dimensional flow field in the complex flow, such as rotating or locally unsteady flow conditions. We deemed that it was because the strips in the given spatio-temporal images from not properly oriented for main flow direction are not narrow enough or clearly visible, thus the direct estimating strip slope could give erroneous results. Thereby, the STIV has been mainly applied for obtaining one-dimensional flow component. In this regard, we proposed an alternative algorithm to estimate the mean slope angle for enhancing the capability of the STIV, which used correlation coefficient between odd and even image splits from the given spatio-temporal image. This method was named CASTI (Correlation Analysis of Spatio-Temporal Image). This paper described the step-by-step procedure of the CASTI and validated its capability for estimating two

  14. Active unsteady aerodynamic suppression of rotating stall in an incompressible flow centrifugal compressor with vaned diffuser

    NASA Technical Reports Server (NTRS)

    Lawless, Patrick B.; Fleeter, Sanford

    1991-01-01

    A mathematical model is developed to analyze the suppression of rotating stall in an incompressible flow centrifugal compressor with a vaned diffuser, thereby addressing the important need for centrifugal compressor rotating stall and surge control. In this model, the precursor to to instability is a weak rotating potential velocity perturbation in the inlet flow field that eventually develops into a finite disturbance. To suppress the growth of this potential disturbance, a rotating control vortical velocity disturbance is introduced into the impeller inlet flow. The effectiveness of this control is analyzed by matching the perturbation pressure in the compressor inlet and exit flow fields with a model for the unsteady behavior of the compressor. To demonstrate instability control, this model is then used to predict the control effectiveness for centrifugal compressor geometries based on a low speed research centrifugal compressor. These results indicate that reductions of 10 to 15 percent in the mean inlet flow coefficient at instability are possible with control waveforms of half the magnitude of the total disturbance at the inlet.

  15. Modeling the Material Flow and Heat Transfer in Reverse Dual-Rotation Friction Stir Welding

    NASA Astrophysics Data System (ADS)

    Shi, L.; Wu, C. S.; Liu, H. J.

    2014-08-01

    Reverse dual-rotation friction stir welding (RDR-FSW) is a novel modification of conventional friction stir welding (FSW) process. During the RDR-FSW process, the tool pin and the assisted shoulder are separated and rotate with opposite direction independently, so that there are two material flows with reverse direction. The material flow and heat transfer in RDR-FSW have significant effects on the microstructure and properties of the weld joint. A 3D model is developed to quantitatively analyze the effects of the separated tool pin and the assisted shoulder which rotate in reverse direction on the material flow and heat transfer during RDR-FSW process. Numerical simulation is conducted to predict the temperature profile, material flow field, streamlines, strain rate, and viscosity distributions near the tool. The calculated results show that as the rotation speed of the tool pin increases, the temperature near the tool gets higher, the zone with higher temperature expands, and approximately symmetric temperature distribution is obtained near the tool. Along the workpiece thickness direction, the calculated material flow velocity and its layer thickness near the tool get lowered because the effect of the shoulder is weakened as the distance away from the top surface increases. The model is validated by comparing the predicted values of peak temperature at some typical locations with the experimentally measured ones.

  16. Numerical simulation of fluid flow and heat transfer in a thin liquid film over a stationary and rotating disk and comparison with experimental data

    NASA Technical Reports Server (NTRS)

    Faghri, Amir; Swanson, Theodore D.

    1990-01-01

    In the first section, improvements in the theoretical model and computational procedure for the prediction of film height and heat-transfer coefficient of the free surface flow of a radially-spreading thin liquid film adjacent to a flat horizontal surface of finite extent are presented. Flows in the presence and absence of gravity are considered. Theoretical results are compared to available experimental data with good agreement. In the presence of gravity, a hydraulic jump is present, isolating the flow into two regimes: supercritical upstream from the jump and subcritical downstream of it. In this situation, the effects of surface tension are important near the outer edge of the disk where the fluid experiences a free fall. A region of flow separation is present just downstream of the jump. In the absence of gravity, no hydraulic jump or separated flow region is present. The variation of the heat-transfer coefficient for flows in the presence and absence of gravity are also presented. In the second section, the results of a numerical simulation of the flow field and associated heat transfer coefficients are presented for the free surface flow of a thin liquid film adjacent to a horizontal rotating disk. The computation was performed for different flow rates and rotational velocities using a 3-D boundary-fitted coordinate system. Since the geometry of the free surface is unknown and dependent on flow rate, rate of rotation, and other parameters, an iterative procedure had to be used to ascertain its location. The computed film height agreed well with existing experimental measurements. The flow is found to be dominated by inertia near the entrance and close to the free surface and dominated by centrifugal force at larger radii and adjacent to the disk. The rotation enhances the heat transfer coefficient by a significant amount.

  17. Actuator disk theory for incompressible highly rotating flows.

    NASA Technical Reports Server (NTRS)

    Oates, G. C.

    1971-01-01

    A solution has been obtained for a stator-rotor pair operating in an annulus with constant hub and tip radii. The stator and rotor are represented as actuator discs, and perfect fluid flow is assumed. The solutions are exact within these limitations, no linearization being required. The forms of blade loadings considered allow the introduction of large vorticity by either the rotor or stator. As a result, the rotor may be a ?nonconstant-work' row. The solutions obtained are of summational form, but many of the summations are obtained in closed form, the resultant formulas allowing rapid calculation of desired examples. An example numerical result is included.

  18. Euler-like modelling of dense granular flows: application to a rotating drum

    NASA Astrophysics Data System (ADS)

    Bonamy, D.; Chavanis, P.-H.; Cortet, P.-P.; Daviaud, F.; Dubrulle, B.; Renouf, M.

    2009-04-01

    General conservation equations are derived for 2D dense granular flows from the Euler equation within the Boussinesq approximation. In steady flows, the 2D fields of granular temperature, vorticity and stream function are shown to be encoded in two scalar functions only. We checked such prediction on steady surface flows in a rotating drum simulated through the Non-Smooth Contact Dynamics method even though granular flows are dissipative and therefore not necessarily compatible with Euler equation. Finally, we briefly discuss some possible ways to predict theoretically these two functions using statistical mechanics.

  19. Particle image velocimetry analysis of the flow around circular cylinder induced by arc discharge rotating in magnetic field

    NASA Astrophysics Data System (ADS)

    Munhoz, D. S.; Bityurin, V. A.; Klimov, A. I.; Moralev, I. A.

    2016-11-01

    An experimental study of the flow around a circular cylinder model with magnetohydrodynamic (MHD) actuator was carried out in subsonic wind tunnels (M < 0.2). Combined (high frequency and pulsed-periodic) electrical discharge was used in this MHD actuator. This intense pulsed-periodic discharge had the following characteristics: voltage amplitude up to 15 kV, current amplitude up to 16 A and frequency up to 1 kHz. Permanent magnets with an induction of B = 0.1 T on the model surface were placed inside the cylindrical model. Annular electrodes were situated on the surface of the cylindrical model. The Lorentz force causes the rotation of the electric arc on the model surface. In turn, the movement of the arc discharge induces the rotation of the gas near the surface of the model. In this experiment were carried out the measurement of the flow velocity profile near the surface of the model on the following operational modes: with plasma and without plasma. A parametric study of the aerodynamic performance of the model was fulfilled with respect to the discharge parameters and the flow velocity. To measure the velocity profile was used particle image velocimetry method.

  20. Restoration of anterior-posterior rotator cuff force balance improves shoulder function in a rat model of chronic massive tears.

    PubMed

    Hsu, Jason E; Reuther, Katherine E; Sarver, Joseph J; Lee, Chang Soo; Thomas, Stephen J; Glaser, David L; Soslowsky, Louis J

    2011-07-01

    The rotator cuff musculature imparts dynamic stability to the glenohumeral joint. In particular, the balance between the subscapularis anteriorly and the infraspinatus posteriorly, often referred to as the rotator cuff "force couple," is critical for concavity compression and concentric rotation of the humeral head. Restoration of this anterior-posterior force balance after chronic, massive rotator cuff tears may allow for deltoid compensation, but no in vivo studies have quantitatively demonstrated an improvement in shoulder function. Our goal was to determine if restoring this balance of forces improves shoulder function after two-tendon rotator cuff tears in a rat model. Forty-eight rats underwent detachment of the supraspinatus and infraspinatus. After four weeks, rats were randomly assigned to three groups: no repair, infraspinatus repair, and two-tendon repair. Quantitative ambulatory measures including medial/lateral forces, braking, propulsion, and step width were significantly different between the infraspinatus and no repair group and similar between the infraspinatus and two-tendon repair groups at almost all time points. These results suggest that repairing the infraspinatus back to its insertion site without repair of the supraspinatus can improve shoulder function to a level similar to repairing both the infraspinatus and supraspinatus tendons. Clinically, a partial repair of the posterior cuff after a two-tendon tear may be sufficient to restore adequate function. An in vivo model system for two-tendon repair of massive rotator cuff tears is presented. Copyright © 2011 Orthopaedic Research Society.

  1. Restoration of Anterior-Posterior Rotator Cuff Force Balance Improves Shoulder Function in a Rat Model of Chronic Massive Tears

    PubMed Central

    Hsu, Jason E.; Reuther, Katherine E.; Sarver, Joseph J.; Lee, Chang Soo; Thomas, Stephen J.; Glaser, David L.; Soslowsky, Louis J.

    2011-01-01

    The rotator cuff musculature imparts dynamic stability to the glenohumeral joint. In particular, the balance between the subscapularis anteriorly and the infraspinatus posteriorly, often referred to as the rotator cuff “force couple,” is critical for concavity compression and concentric rotation of the humeral head. Restoration of this anterior-posterior force balance after chronic, massive rotator cuff tears may allow for deltoid compensation, but no in vivo studies have quantitatively demonstrated an improvement in shoulder function. Our goal was to determine if restoring this balance of forces improves shoulder function after two-tendon rotator cuff tears in a rat model. Forty-eight rats underwent detachment of the supraspinatus and infraspinatus. After four weeks, rats were randomly assigned to three groups: no repair, infraspinatus repair, and two-tendon repair. Quantitative ambulatory measures including medial/lateral forces, braking, propulsion, and step width were significantly different between the infraspinatus and no repair group and similar between the infraspinatus and two-tendon repair groups at almost all time points. These results suggest that repairing the infraspinatus back to its insertion site without repair of the supraspinatus can improve shoulder function to a level similar to repairing both the infraspinatus and supraspinatus tendons. Clinically, a partial repair of the posterior cuff after a two tendon tear may be sufficient to restore adequate function. An in vivo model system for two-tendon repair of massive rotator cuff tears is presented. PMID:21308755

  2. The role of the complete Coriolis force in weakly stratified oceanic flows

    NASA Astrophysics Data System (ADS)

    Tort, M.; Winters, K. B.; Ribstein, B.; Zeitlin, V.

    2016-02-01

    Ocean dynamics is usually described using the primitive equations based on the so-called traditional approximation (TA), where the Coriolis force associated with the horizontal component of the planetary rotation is neglected (also called non-traditional (NT) part proportional to cosΦ, see Fig 1.). However, recent studies have shown that the NT part of the Coriolis force plays a non-negligible dynamical role in some particular oceanic flows (see Gerkema et al., 2008 for an extensive review of NT effects for geophysical and astrophysical flows). Here we explore the relevance of including the NT component of the Coriolis force in ocean models, by presenting particular results regarding two different mid-latitude flow configurations after relaxing the TA: Propagation of wind-induced near-inertial waves (NIWs). Under the TA, NIWs propagate toward the equator, the inertially poleward propagation being internally reflected at a depth-independent critical latitude. The combined effects of the NT Coriolis force and weak stratification in the deep ocean leads to the existence of waveguides for sub-inertial waves, which get trapped and propagate further poleward (Winters et al., 2011). Here we consider storm-induced NIWs and their evolution in a non-linear Boussinesq model on the β-plane in the NT approximation. Preliminary results are presented concerning the behavior of the waves in a weakly stratified mixed-layer, where NT effects are expected to be significant. Inertial instability. A detailed linear stability analysis of the Bickley jet at large Rossby numbers in the NT approximation on the f-plane is performed for long waves in a continuously stratified Boussinesq model. For a sufficiently weak stratification, both symmetric and asymmetric inertial instabilities have substantially higher growth rates than in the TA while no discernible differences between the two approximations are observed for strong enough stratifications (Tort et al., 2015).

  3. On the selection of prognostic equations for the rotating motion in simulating Czochralski flow

    SciTech Connect

    Kim, C.J.; Ro, S.T.

    1995-12-01

    When the fluid flow in the Czochralski crystal growth system involves swirling motion due to rotation effects, numerical simulation of the Czochralski flow can be performed using either the azimuthal velocity component or the angular momentum per unit mass, viz., the swirl, as the dependent variable to resolve the rotating motion. In the presence of a strong inward flow toward the axis, the Coriolis coupling in the azimuthal velocity equation can be a source of computational instability. This difficulty has been overcome by transforming the prognostic equation for the azimuthal velocity into the so-called swirl equation. In this article the authors show that although these two prognostic equations are mathematically identical to each other, numerical simulations based on them could yield appreciably different results under certain circumstances. This important as yet unresolved aspect of the Czochralski flow simulation is highlighted and the underlying cause of the discrepancy is addressed in the present study.

  4. Banded surface flow maintained by convection in a model of the rapidly rotating giant planets.

    PubMed

    Sun, Z P; Schubert, G; Glatzmaier, G A

    1993-04-30

    In three-dimensional numerical simulations of a rapidly rotating Boussinesq fluid shell, thermally driven convection in the form of columns parallel to the rotation axis generates an alternately directed mean zonal flow with a cylindrical structure. The mean structure at the outer spherical surface consists of a broad eastward flow at the equator and alternating bands of westward and eastward flows at higher latitudes in both hemispheres. The banded structure persists even though the underlying convective motions are time-dependent. These results, although still far from the actual motions seen on Jupiter and Saturn, provide support for theoretical suggestions that thermal convection can account for the remarkable banded flow structures on these planets.

  5. Banded surface flow maintained by convection in a model of the rapidly rotating giant planets

    NASA Astrophysics Data System (ADS)

    Sun, Z.-P.; Schubert, G.; Glatzmaier, G. A.

    1993-04-01

    In three-dimensional numerical simulations of a rapidly rotating Boussinesq fluid shell, thermally driven convection in the form of columns parallel to the rotation axis generates an alternately directed mean zonal flow with a cylindrical structure. The mean structure at the outer spherical surface consists of a broad eastward flow at the equator and alternating bands of westward and eastward flows at higher latitudes in both hemispheres. The banded structure persists even though the underlying convective motions are time-dependent. These results, although still far from the actual motions seen on Jupiter and Saturn, provide support for theoretical suggestions that thermal convection can account for the remarkable banded flow structures on these planets.

  6. Zero absolute vorticity: insight from experiments in rotating laminar plane Couette flow.

    PubMed

    Suryadi, Alexandre; Segalini, Antonio; Alfredsson, P Henrik

    2014-03-01

    For pressure-driven turbulent channel flows undergoing spanwise system rotation, it has been observed that the absolute vorticity, i.e., the sum of the averaged spanwise flow vorticity and system rotation, tends to zero in the central region of the channel. This observation has so far eluded a convincing theoretical explanation, despite experimental and numerical evidence reported in the literature. Here we show experimentally that three-dimensional laminar structures in plane Couette flow, which appear under anticyclonic system rotation, give the same effect, namely, that the absolute vorticity tends to zero if the rotation rate is high enough. It is shown that this is equivalent to a local Richardson number of approximately zero, which would indicate a stable condition. We also offer an explanation based on Kelvin's circulation theorem to demonstrate that the absolute vorticity should remain constant and approximately equal to zero in the central region of the channel when going from the nonrotating fully turbulent state to any state with sufficiently high rotation.

  7. Attractive and Repulsive Forces on Particles in Oscillatory Flow

    NASA Astrophysics Data System (ADS)

    Agarwal, Siddhansh; Rallabandi, Bhargav; Raju, David; Thameem, Raqeeb; Hilgenfeldt, Sascha

    2016-11-01

    A large class of oscillating flows gives rise to rectified streaming motion of the fluid. It has recently been shown that particle transport in such flows, excited by bubbles oscillating at ultrasound frequencies, leads to differential displacement and efficient sorting of microparticles by size. We derive a general expression for the instantaneous radial force experienced by a small spherical particle in the vicinity of an oscillating interface, and generalize the radial projection of the Maxey-Riley equation to include this effect. Varying relevant system parameters, we show that the net effect on the particle can be either an attraction to or a repulsion from the bubble surface, depending in particular on the particle size and the particle/fluid density contrast. We demonstrate that these predictions are in agreement with a variety of experiments.

  8. Performance comparison of optical flow and block matching methods in shearing and rotating models

    NASA Astrophysics Data System (ADS)

    Liu, Zhi; Luo, Jianwen

    2017-03-01

    Accurate estimation of myocardial motion based on ultrasound imaging is of great value for evaluation of cardiac function. Typically, myocardium undergoes complex motion and deformation including shear deformation and rotation. Thus a compression model is insufficient for investigating the performance of different algorithms. In this study, simulated shearing and rotating models are used to study the performance of optical flow (OF) and block matching (BM) methods based on ultrasound radio-frequency (RF) data. A deforming model was simulated with applied axial shear strains of 2- 6%, respectively. In addition, a rotating model was simulated with rotation angles of 0.5°-4°, respectively. Axial strains of 0%, 1% and 2% were also applied to these two models to study the influence of applied strain on the estimation of axial shear strain and rotation. To quantify the estimation performance, the root mean square error (RMSE) was used as the evaluation criterion. The results show that OF has lower RMSEs of the estimated displacement, strain and rotation angle than BM, especially at large axial shear strains and rotation angles. For the shearing model, the RMSEs of axial strains, lateral strains, and axial shear strains are reduced by up to 95.5%, 70.3% and 90.0%, respectively. For the rotating model, the RMSEs of axial strains, lateral strains, and rotation angles are reduced by up to 96.9%, 93.4% and 89.7%, respectively. OF is proved to outperform BM and thus is recommended to be used for shear strain and rotation estimation. The validations of phantom and in-vivo experiments are still required.

  9. Numerical simulation of flows in a circular pipe transversely subjected to a localized impulsive body force with applications to blunt traumatic aortic rupture

    NASA Astrophysics Data System (ADS)

    Di Labbio, G.; Keshavarz-Motamed, Z.; Kadem, L.

    2017-06-01

    Much debate surrounds the mechanisms responsible for the occurrence of blunt traumatic aortic rupture in car accidents, particularly on the role of the inertial body force experienced by the blood due to the abrupt deceleration. The isolated influence of such body forces acting on even simple fluid flows is a fundamental problem in fluid dynamics that has not been thoroughly investigated. This study numerically investigates the fundamental physical problem, where the pulsatile flow in a straight circular pipe is subjected to a transverse body force on a localized volume of fluid. The body force is applied as a brief rectangular impulse in three distinct cases, namely during the accelerating, peak, and decelerating phases of the pulsatile flow. A dimensionless number, termed the degree of influence of the body force (Ψ), is devised to quantify the relative strength of the body force over the flow inertia. The impact induces counter-rotating cross-stream vortices at the boundaries of the forced section accompanied by complex secondary flow structures. This secondary flow is found to develop slowest for an impact occurring during an accelerating flow and fastest during a decelerating flow. The peak skewness of the velocity field, however, occurred at successively later times for the three respective cases. After the impact, these secondary flows act to restore the unforced state and such dominant spatial structures are revealed by proper orthogonal decomposition of the velocity field. This work presents a new class of problems that requires further theoretical and experimental investigation.

  10. MHD Convective rotating flow past an oscillating porous plate with chemical reaction and Hall effects

    NASA Astrophysics Data System (ADS)

    Veera Krishna, M.; Gangadhar Reddy, M.

    2016-09-01

    In this paper, we have considered Hall effects on the unsteady MHD free convective rotating flow of visco-elastic fluid with heat and mass transfer near oscillating porous plate. The equations of the flow are solved by perturbation method for small elastic parameter. The analytical expressions for the velocity, temperature, concentration have been derived and also its behaviour is computationally discussed with the help of graphs. The skin friction, Nusselt number, and Sherwood number are also obtained analytically and their behaviour discussed.

  11. Forced instability of core-annular flow in capillary constrictions

    NASA Astrophysics Data System (ADS)

    Beresnev, Igor; Gaul, William; Vigil, R. Dennis

    2011-07-01

    Instability of fluid cylinders and jets, a highly nonlinear hydrodynamic phenomenon, has fascinated researchers for nearly 150 years. A subset of the phenomenon is the core-annular flow, in which a non-wetting core fluid and a surrounding wall-wetting annulus flow through a solid channel. The model, for example, represents the flow of oil in petroleum reservoirs. The flow may be forced to break up when passing through a channel's constriction. Although it has long been observed that the breakup occurs near the neck of the constriction, the exact conditions for the occurrence of the forced breakup and its dynamic theory have not been understood. Here, we test a simple geometric conjecture that the fluid will always break in the constrictions of all channels with sufficiently long wavelengths, regardless of the fluid properties. We also test a theory of the phenomenon. Four constricted glass tubes were fabricated above and below the critical wavelength required for the fluid disintegration. In a direct laboratory experiment, the breakup occurred according to the conjecture: the fluids were continuous in the shorter tubes but disintegrated in the longer tubes. The evolution of the interface to its pinch-off was recorded using high-speed digital photography. The experimentally observed core-annulus interface profiles agreed well with the theory, although the total durations of the process agreed less satisfactorily. Nonetheless, as the theory predicts, the ratio between the experimental and theoretical times of the breakup process tends to one with decreasing capillary number. The breakup condition and the dynamic theory of fluid disintegration in constricted channels can serve as quantitative models of this important natural and technical phenomenon.

  12. Instability in Rotating Machinery

    NASA Technical Reports Server (NTRS)

    1985-01-01

    The proceedings contain 45 papers on a wide range of subjects including flow generated instabilities in fluid flow machines, cracked shaft detection, case histories of instability phenomena in compressors, turbines, and pumps, vibration control in turbomachinery (including antiswirl techniques), and the simulation and estimation of destabilizing forces in rotating machines. The symposium was held to serve as an update on the understanding and control of rotating machinery instability problems.

  13. On the correlation between force production and the flow field around a flapping flat-plate wing

    NASA Astrophysics Data System (ADS)

    Öz, Sören; Krishna, Swathi; Mulleners, Karen

    2015-11-01

    One of the several sophisticated flight skills that insects exhibit is hovering, which is accomplished largely by modulating the wing kinematics and thereby the flow field around the wings. Along with the prolonged attachment of the leading edge vortex, the wing reversal mechanisms form the basis by which insects regulate the magnitude and direction of forces produced. The duration and starting point of these directional flips are studied in the current experimental investigation. Particle image velocimetry is conducted to evaluate the flow features inherent to changes in wing reversal during the stroke of a flat plate, which is modelled based on hoverfly characteristics. The duration of rotation is one-third of the total time period. A +10% phase shift is used for delayed rotation, a -10% phase shift for advanced rotation. Phase-averaged data is analysed to understand the influence of a delayed or advanced rotation on the formation and evolution of large and small scale structures, their interactions with the wing, and disintegration. Additionally, force data is used to quantify the effects of phase-shift in terms of lift and drag variation and is correlated with the vortex dynamics.

  14. On the receptivity and nonparallel stability of traveling disturbances in rotating-disk flow

    NASA Technical Reports Server (NTRS)

    Balakumar, P.; Malik, M. R.; Hall, P.

    1991-01-01

    The generation and evolution of small amplitude long wavelength traveling disturbances in rotating-disk flow are discussed. The steady rotational speed of the disk is perturbed so as to introduce high-frequency oscillations in the flow field. Secondly, surface imperfections on the disk such as roughness elements are introduced. The interaction of these two disturbances will generate the instability waves whose evolution is governed by parabolic partial differential equations which are solved numerically. It is found that, for the class of disturbances considered here (wavelength on the order of Reynolds number), eigensolutions exist which decay or grow algebraically in the radial direction. However, these solutions grow only for frequencies larger than 4.58 times the steady rotational speed of the disk. The computed receptivity coefficient shows that there is an optimum size of roughness for which these modes are preferentially excited.

  15. Using flow information to support 3D vessel reconstruction from rotational angiography.

    PubMed

    Waechter, Irina; Bredno, Joerg; Weese, Juergen; Barratt, Dean C; Hawkes, David J

    2008-07-01

    For the assessment of cerebrovascular diseases, it is beneficial to obtain three-dimensional (3D) morphologic and hemodynamic information about the vessel system. Rotational angiography is routinely used to image the 3D vascular geometry and we have shown previously that rotational subtraction angiography has the potential to also give quantitative information about blood flow. Flow information can be determined when the angiographic sequence shows inflow and possibly outflow of contrast agent. However, a standard volume reconstruction assumes that the vessel tree is uniformly filled with contrast agent during the whole acquisition. If this is not the case, the reconstruction exhibits artifacts. Here, we show how flow information can be used to support the reconstruction of the 3D vessel centerline and radii in this case. Our method uses the fast marching algorithm to determine the order in which voxels are analyzed. For every voxel, the rotational time intensity curve (R-TIC) is determined from the image intensities at the projection points of the current voxel. Next, the bolus arrival time of the contrast agent at the voxel is estimated from the R-TIC. Then, a measure of the intensity and duration of the enhancement is determined, from which a speed value is calculated that steers the propagation of the fast marching algorithm. The results of the fast marching algorithm are used to determine the 3D centerline by backtracking. The 3D radius is reconstructed from 2D radius estimates on the projection images. The proposed method was tested on computer simulated rotational angiography sequences with systematically varied x-ray acquisition, blood flow, and contrast agent injection parameters and on datasets from an experimental setup using an anthropomorphic cerebrovascular phantom. For the computer simulation, the mean absolute error of the 3D centerline and 3D radius estimation was 0.42 and 0.25 mm, respectively. For the experimental datasets, the mean absolute

  16. Using flow information to support 3D vessel reconstruction from rotational angiography.

    PubMed

    Waechter, Irina; Bredno, Joerg; Weese, Juergen; Barratt, Dean C; Hawkes, David J

    2008-07-01

    For the assessment of cerebrovascular diseases, it is beneficial to obtain three-dimensional (3D) morphologic and hemodynamic information about the vessel system. Rotational angiography is routinely used to image the 3D vascular geometry and we have shown previously that rotational subtraction angiography has the potential to also give quantitative information about blood flow. Flow information can be determined when the angiographic sequence shows inflow and possibly outflow of contrast agent. However, a standard volume reconstruction assumes that the vessel tree is uniformly filled with contrast agent during the whole acquisition. If this is not the case, the reconstruction exhibits artifacts. Here, we show how flow information can be used to support the reconstruction of the 3D vessel centerline and radii in this case. Our method uses the fast marching algorithm to determine the order in which voxels are analyzed. For every voxel, the rotational time intensity curve (R-TIC) is determined from the image intensities at the projection points of the current voxel. Next, the bolus arrival time of the contrast agent at the voxel is estimated from the R-TIC. Then, a measure of the intensity and duration of the enhancement is determined, from which a speed value is calculated that steers the propagation of the fast marching algorithm. The results of the fast marching algorithm are used to determine the 3D centerline by backtracking. The 3D radius is reconstructed from 2D radius estimates on the projection images. The proposed method was tested on computer simulated rotational angiography sequences with systematically varied x-ray acquisition, blood flow, and contrast agent injection parameters and on datasets from an experimental setup using an anthropomorphic cerebrovascular phantom. For the computer simulation, the mean absolute error of the 3D centerline and 3D radius estimation was 0.42 and 0.25mm, respectively. For the experimental datasets, the mean absolute error

  17. Computational Study of Fluid Flow in a Rotational Chemical Vapor Deposition (CVD) Reactor

    NASA Astrophysics Data System (ADS)

    Wong, Sun; Jaluria, Yogesh

    2015-11-01

    In a typical Chemical Vapor Deposition (CVD) reactor, the flow of the reacting gases is one of the most important considerations that must be precisely controlled in order to obtain desired film quality. In general, the fluids enter the reactor chamber, travel over to the heated substrate area, where chemical reactions lead to deposition, and then exit the chamber. However, the flow inside the reactor chamber is not that simple. It would often develop recirculation at various locations inside the reactor due to reactor geometry, flow conditions, buoyancy effects from temperature differences and rotational effects cause by the rotating substrate. This recirculation causes hot spots and affects the overall performance of the reactor. A recirculation fluid packet experiences a longer residence time inside the reactor and, thus, it heats up to higher temperatures causing unwanted chemical reactions and decomposition. It decreases the grow rate and uniformity on the substrate. A mathematical and computational model has been developed to help identify these unwanted hot spots occurring inside the CVD reactor. The model can help identify the user parameters needed to reduce the recirculation effects and better control the flow. Flow rates, pressures, rotational speeds and temperatures can all affect the severity of the recirculation within the reactor. The model can also help assist future designs as the geometry plays a big role in controlling fluid flow. The model and the results obtained are discussed in detail.

  18. Lateral Migration and Rotational Motion of Elliptic Particles in Planar Poiseuille Flow

    NASA Technical Reports Server (NTRS)

    Qi, Dewei; Luo, Li-Shi; Aravamuthan, Raja; Strieder, William; Bushnell, Dennis M. (Technical Monitor)

    2002-01-01

    Simulations of elliptic particulate suspensions in the planar Poiseuille flow are performed by using the lattice Boltzmann equation. Effects of the multi-particle on the lateral migration and rotational motion of both neutrally and non-neutrally buoyant elliptic particles are investigated. Low and intermediate total particle volume fraction f(sub a) = 13%, 15%, and 40% are considered in this work.

  19. Coriolis effects on rotating Hele-Shaw flows: a conformal-mapping approach.

    PubMed

    Miranda, José A; Gadêlha, Hermes; Dorsey, Alan T

    2010-12-01

    The zero surface tension fluid-fluid interface dynamics in a radial Hele-Shaw cell driven by both injection and rotation is studied by a conformal-mapping approach. The situation in which one of the fluids is inviscid and has negligible density is analyzed. When Coriolis force effects are ignored, exact solutions of the zero surface tension rotating Hele-Shaw problem with injection reveal suppression of cusp singularities for sufficiently high rotation rates. We study how the Coriolis force affects the time-dependent solutions of the problem, and the development of finite time singularities. By employing Richardson's harmonic moments approach we obtain conformal maps which describe the time evolution of the fluid boundary. Our results demonstrate that the inertial Coriolis contribution plays an important role in determining the time for cusp formation. Moreover, it introduces a phase drift that makes the evolving patterns rotate. The Coriolis force acts against centrifugal effects, promoting (inhibiting) cusp breakdown if the more viscous and dense fluid lies outside (inside) the interface. Despite the presence of Coriolis effects, the occurrence of finger bending events has not been detected in the exact solutions.

  20. Forced Magnetic Reconnection and Field Penetration of an Externally Applied Rotating Helical Magnetic Field in the TEXTOR Tokamak

    SciTech Connect

    Kikuchi, Y.; Finken, K. H.; Jakubowski, M.; Koslowski, H. R.; Kraemer-Flecken, A.; Lehnen, M.; Liang, Y.; Reiser, D.; Wolf, R. C.; Zimmermann, O.; Bock, M. F. M. de; Jaspers, R.; Matsunaga, G.

    2006-08-25

    The magnetic field penetration process into a magnetized plasma is of basic interest both for plasma physics and astrophysics. In this context special measurements on the field penetration and field amplification are performed by a Hall probe on the dynamic ergodic divertor (DED) on the TEXTOR tokamak and the data are interpreted by a two-fluid plasma model. It is observed that the growth of the forced magnetic reconnection by the rotating DED field is accompanied by a change of the plasma fluid rotation. The differential rotation frequency between the DED field and the plasma plays an important role in the process of the excitation of tearing modes. The momentum input from the rotating DED field to the plasma is interpreted by both a ponderomotive force at the rational surface and a radial electric field modified by an edge ergodization.

  1. Experimental Observations and Discrete Element Simulations of Bed Force Anomalies due to Force Chains in Dense Granular flows

    NASA Astrophysics Data System (ADS)

    Estep, J.; Dufek, J.

    2012-12-01

    Surficial flows on volcanic edifices are often comprised of high concentrations of granular materials either derived from juvenile eruptive material or material sourced from an unstable edifice. Although much attention has been given to granular flow mobility, the physics that govern their internal behavior are still poorly understood. Our work builds on previous research showing that force chains transmit extreme localized forces to the substrates of free surface granular flows, and combines experimental and computational approaches to further investigate the forces at the bed of a simplified granular flow. A photoelastic experimental approach is used to resolve discrete forces in the granular flows, while discrete element model (DEM) simulations reproduce the experimental flows. Input parameters for the DEM are derived from measurable physical material properties, and DEM simulations using properties of natural materials corroborate experimental results. The DEM results show particular sensitivity to values prescribed for contact stiffness, which is in contrast with previous reports indicating that stiffness values have insignificant influence on flow behavior. The forces at the bed generated by force chain structures can transiently greatly exceed (by several 100%) the bed forces predicted from continuum approaches, and natural materials are more prone to excessive bed forces than photoelastic materials due to their larger contact stiffnesses. By varying the ratios of a bidisperse grain size population, continuing experiments investigate how further complexity in the granular flow regime influences force transmission via force chains. This work suggests that force chain activity may play an important role in the bed physics of dense volcanic flows by influencing substrate entrainment.

  2. Void fraction and phase distribution of a rotating two-phase gas-liquid flow around a plasma arc under water

    SciTech Connect

    Steinkamp, H.; Mewes, D.

    1994-12-31

    Plasma arc welding processes are used in off-shore industry for construction and maintenance in the wet surrounding of underwater structures and pipelines. In greater water depth the density of the plasma gas increase because of the greater hydrostatic pressure. This causes the increase of conductive heat losses to the wet surrounding. To keep up the energy flux to the workpiece to be welded, the plasma arc has to burn in a local dry area with an inside pressure of 1 bar. This requirement can be fulfilled by a rotating cylinder with a liquid film flowing down the inner wall. The flow around the rotating cylinder to create a local dry area around the plasma arc under water is experimentally investigated. The rotating cylinder is placed above the work surface which is simulated by a flat plate. According to the centrifugal forces of the rotating flow inside the gap between the lower end of the cylinder and the flat plate the water is forced out of the cylinder. The velocity distribution in the flow is measured by Laser-Doppler anemometry. The phase distribution in the two-phase flow in the gap is measured by local electrical probes. The static pressure inside the gaseous atmosphere is reduced in comparison to the hydrostatic pressure of the surrounding water. The pressure reduction is given by the void fraction, the phase distribution and the volume flow rates of both phases in the gap as well as by the speed of revolution and the design of the cylinder and the work surface. The influence of these parameters on the heat transfer from the workpiece to the two-phase flow regime is also investigated.

  3. Flow in complex domains simulated by Dissipative Particle Dynamics driven by geometry-specific body-forces

    NASA Astrophysics Data System (ADS)

    Yazdani, Alireza; Deng, Mingge; Caswell, Bruce; Karniadakis, George Em

    2016-01-01

    We demonstrate how the quality of simulations by Dissipative Particle Dynamics (DPD) of flows in complex geometries is greatly enhanced when driven by body forces suitably tailored to the geometry. In practice, the body force fields are most conveniently chosen to be the pressure gradient of the corresponding Navier-Stokes (N-S) flow. In the first of three examples, the driving-force required to yield a stagnation-point flow is derived from the pressure field of the potential flow for a lattice of counter-rotating line vortices. Such a lattice contains periodic squares bounded by streamlines with four vortices within them. Hence, the DPD simulation can be performed with periodic boundary conditions to demonstrate the value of a non-uniform driving-force without the need to model real boundaries. The second example is an irregular geometry consisting of a 2D rectangular cavity on one side of an otherwise uniform channel. The Navier-Stokes pressure field for the same geometry is obtained numerically, and its interpolated gradient is then employed as the driving-force for the DPD simulation. Finally, we present a third example, where the proposed method is applied to a complex 3D geometry of an asymmetric constriction. It is shown that in each case the DPD simulations closely reproduce the Navier-Stokes solutions. Convergence rates are found to be much superior to alternative methods; in addition, the range of convergence with respect to Reynolds number and Mach number is greatly extended.

  4. Force Outputs during Squats Performed Using a Rotational Inertia Device under Stable versus Unstable Conditions with Different Loads.

    PubMed

    Vázquez-Guerrero, Jairo; Moras, Gerard; Baeza, Jennifer; Rodríguez-Jiménez, Sergio

    2016-01-01

    The purpose of the study was to compare the force outputs achieved during a squat exercise using a rotational inertia device in stable versus unstable conditions with different loads and in concentric and eccentric phases. Thirteen male athletes (mean ± SD: age 23.7 ± 3.0 years, height 1.80 ± 0.08 m, body mass 77.4 ± 7.9 kg) were assessed while squatting, performing one set of three repetitions with four different loads under stable and unstable conditions at maximum concentric effort. Overall, there were no significant differences between the stable and unstable conditions at each of the loads for any of the dependent variables. Mean force showed significant differences between some of the loads in stable and unstable conditions (P < 0.010) and peak force output differed between all loads for each condition (P < 0.045). Mean force outputs were greater in the concentric than in the eccentric phase under both conditions and with all loads (P < 0.001). There were no significant differences in peak force between concentric and eccentric phases at any load in either stable or unstable conditions. In conclusion, squatting with a rotational inertia device allowed the generation of similar force outputs under stable and unstable conditions at each of the four loads. The study also provides empirical evidence of the different force outputs achieved by adjusting load conditions on the rotational inertia device when performing squats, especially in the case of peak force. Concentric force outputs were significantly higher than eccentric outputs, except for peak force under both conditions. These findings support the use of the rotational inertia device to train the squatting exercise under unstable conditions for strength and conditioning trainers. The device could also be included in injury prevention programs for muscle lesions and ankle and knee joint injuries.

  5. Force Outputs during Squats Performed Using a Rotational Inertia Device under Stable versus Unstable Conditions with Different Loads

    PubMed Central

    Vázquez-Guerrero, Jairo; Moras, Gerard

    2016-01-01

    The purpose of the study was to compare the force outputs achieved during a squat exercise using a rotational inertia device in stable versus unstable conditions with different loads and in concentric and eccentric phases. Thirteen male athletes (mean ± SD: age 23.7 ± 3.0 years, height 1.80 ± 0.08 m, body mass 77.4 ± 7.9 kg) were assessed while squatting, performing one set of three repetitions with four different loads under stable and unstable conditions at maximum concentric effort. Overall, there were no significant differences between the stable and unstable conditions at each of the loads for any of the dependent variables. Mean force showed significant differences between some of the loads in stable and unstable conditions (P < 0.010) and peak force output differed between all loads for each condition (P < 0.045). Mean force outputs were greater in the concentric than in the eccentric phase under both conditions and with all loads (P < 0.001). There were no significant differences in peak force between concentric and eccentric phases at any load in either stable or unstable conditions. In conclusion, squatting with a rotational inertia device allowed the generation of similar force outputs under stable and unstable conditions at each of the four loads. The study also provides empirical evidence of the different force outputs achieved by adjusting load conditions on the rotational inertia device when performing squats, especially in the case of peak force. Concentric force outputs were significantly higher than eccentric outputs, except for peak force under both conditions. These findings support the use of the rotational inertia device to train the squatting exercise under unstable conditions for strength and conditioning trainers. The device could also be included in injury prevention programs for muscle lesions and ankle and knee joint injuries. PMID:27111766

  6. Modulation of rotation-induced lift force for cell filtration in a low aspect ratio microchannel

    PubMed Central

    Zhou, Jian; Giridhar, Premkumar Vummidi; Kasper, Susan; Papautsky, Ian

    2014-01-01

    Cell filtration is a critical step in sample preparation in many bioapplications. Herein, we report on a simple, filter-free, microfluidic platform based on hydrodynamic inertial migration. Our approach builds on the concept of two-stage inertial migration which permits precise prediction of microparticle position within the microchannel. Our design manipulates equilibrium positions of larger microparticles by modulating rotation-induced lift force in a low aspect ratio microchannel. Here, we demonstrate filtration of microparticles with extreme efficiency (>99%). Using multiple prostate cell lines (LNCaP and human prostate epithelial tumor cells), we show filtration from spiked blood, with 3-fold concentration and >83% viability. Results of a proliferation assay show normal cell division and suggest no negative effects on intrinsic properties. Considering the planar low-aspect-ratio structure and predictable focusing, we envision promising applications and easy integration with existing lab-on-a-chip systems. PMID:25379097

  7. The rotational spectrum, geometry, and intermolecular force constant of the heterodimer of hydrogen cyanide and fluoroform

    NASA Astrophysics Data System (ADS)

    Goodwin, Elizabeth J.; Legon, A. C.

    1986-02-01

    The ground-state rotational spectra of six isotopic species of an intermolecular complex formed by hydrogen cyanide and fluoroform have been measured using the pulsed-nozzle, Fourier-transform microwave technique. The rotational constant B0, the centrifugal distortion constants DJ,DJK,HJ, HJK, and HKJ, and, where appropriate, the nuclear quadrupole coupling constants χ(14N) and χ(D) have been determined for each of the species HC14NṡṡṡHCF3, DC14NṡṡṡHCF3, HC14ṡṡṡDCF3, HC15NṡṡṡHCF3, HC15NṡṡṡDCF3, and DC15NṡṡṡHCF3. For HC14NṡṡṡHCF3 the values are as follows: B0=1151.2991(4) MHz, DJ=1.91(1) kHz, DJK=282.75(6) kHz, HJ=-0.1(1) Hz, HJK=44.3(5) Hz, HKJ=53(5) Hz, and χ(14N)=3.948(8) MHz. The form of the spectra and magnitudes of the rotational constants allow the conclusion that the geometry of the complex is of C3V symmetry with the nuclei in the order HCNṡṡṡHCF3 and lead to r(NṡṡṡC)=3.489(2) Å for HCF3 species but 3.483(1) Å for DCF3 species. The intermolecular stretching force constant determined from DJ is kσ=3.52 N m-1.

  8. Motion of micrometer sized spherical particles exposed to a transient radial flow: attraction, repulsion, and rotation.

    PubMed

    Gonzalez-Avila, S Roberto; Huang, Xiaohu; Quinto-Su, Pedro A; Wu, Tom; Ohl, Claus-Dieter

    2011-08-12

    It is now accepted that the physical forces in ultrasonic cleaning are due to strongly pulsating bubbles driven by the sound field. Here we have a detailed look at bubble induced cleaning flow by analyzing the transport of an individual particle near an expanding and collapsing bubble. The induced particulate transport is compared with a force balance model. We find two important properties of the flow which explain why bubbles are effectively cleaning: During bubble expansion a strong shear layer loosens the particle from the surface through particle spinning and secondly an unsteady boundary layer generates an attractive force, thus collecting the contamination in the bubble's close proximity.

  9. Cell exclusion in couette flow: evaluation through flow visualization and mechanical forces.

    PubMed

    Leslie, Laura J; Marshall, Lindsay J; Devitt, Andrew; Hilton, Andrew; Tansley, Geoff D

    2013-03-01

    Cell exclusion is the phenomenon whereby the hematocrit and viscosity of blood decrease in areas of high stress. While this is well known in naturally occurring Poiseuille flow in the human body, it has never previously been shown in Couette flow, which occurs in implantable devices including blood pumps. The high-shear stresses that occur in the gap between the boundaries in Couette flow are known to cause hemolysis in erythrocytes. We propose to mitigate this damage by initiating cell exclusion through the use of a spiral-groove bearing (SGB) that will provide escape routes by which the cells may separate themselves from the plasma and the high stresses in the gap. The force between two bearings (one being the SGB) in Couette flow was measured. Stained erythrocytes, along with silver spheres of similar diameter to erythrocytes, were visualized across a transparent SGB at various gap heights. A reduction in the force across the bearing for human blood, compared with fluids of comparable viscosity, was found. This indicates a reduction in the viscosity of the fluid across the bearing due to a lowered hematocrit because of cell exclusion. The corresponding images clearly show both cells and spheres being excluded from the gap by entering the grooves. This is the first time the phenomenon of cell exclusion has been shown in Couette flow. It not only furthers our understanding of how blood responds to different flows but could also lead to improvements in the future design of medical devices.

  10. Forced Solutions of Streamwise Constant Plane Couette Flow

    NASA Astrophysics Data System (ADS)

    Gayme, Dennice; McKeon, Beverley; Bamieh, Bassam; Doyle, John; Papachristodoulou, Antonis

    2010-11-01

    A two-dimensional, three-velocity component (2D/3C) model simulated under small-amplitude Gaussian forcing has been shown to capture salient features of turbulent plane Couette flow (Gayme et. al 2010). Periodic spanwise/wall-normal plane stream functions are used as input to develop forced 2D/3C streamwise velocities. The resulting steady-state solutions are qualitatively similar to a fully turbulent spatial field of DNS. Our analysis indicates that the momentum transfer which produces a `turbulent-like' mean profile requires a nonlinear streamwise velocity equation. A system theoretic approach is used to study amplification mechanisms which arise through this 2D/3C nonlinear coupling. The forcing required to produce each input is used to define an induced norm. The associated input-output response determines the energy optimal spanwise wavelength over a range of Reynolds numbers. We identify an important tradeoff between the linear amplification mechanism and the nonlinearity required to develop an appropriately shaped turbulent velocity profile. Acknowledgements: The research is supported by Boeing and AFOSR. B.J.M. gratefully acknowledges NSF-CAREER award no. 0747672 (program managers W. W. Schultz & H. H. Winter).

  11. A numerical investigation of flow around octopus-like arms: near-wake vortex patterns and force development.

    PubMed

    Kazakidi, A; Vavourakis, V; Tsakiris, D P; Ekaterinaris, J A

    2015-01-01

    The fluid dynamics of cephalopods has so far received little attention in the literature, due to their complexity in structure and locomotion. The flow around octopuses, in particular, can be complicated due to their agile and dexterous arms, which frequently display some of the most diverse mechanisms of motion. The study of this flow amounts to a specific instance of the hydrodynamics problem for rough tapered cylinder geometries. The outstanding manipulative and locomotor skills of octopuses could inspire the development of advanced robotic arms, able to operate in fluid environments. Our primary aim was to study the hydrodynamic characteristics of such bio-inspired robotic models and to derive the hydrodynamic force coefficients as a concise description of the vortical flow effects. Utilizing computational fluid dynamic methods, the coefficients were computed on realistic morphologies of octopus-like arm models undergoing prescribed solid-body movements; such motions occur in nature for short durations in time, e.g. during reaching movements and exploratory behaviors. Numerical simulations were performed on translating, impulsively rotating, and maneuvering arms, around which the flow field structures were investigated. The results reveal in detail the generation of complex vortical flow structures around the moving arms. Hydrodynamic forces acting on a translating arm depend on the angle of incidence; forces generated during impulsive rotations of the arms are independent of their exact morphology and the angle of rotation; periodic motions based on a slow recovery and a fast power stroke are able to produce considerable propulsive thrust while harmonic motions are not. Parts of these results have been employed in bio-inspired models of underwater robotic mechanisms. This investigation may further assist elucidating the hydrodynamics underlying aspects of octopus locomotion and exploratory behaviors.

  12. Optimization of the levels of grip force, stroke rotation, frequency and grip span for a torqueing task.

    PubMed

    Bano, Farheen; Mallick, Zulqernian; Ali Khan, Abid

    2015-01-01

    This study was to investigate the effects of grip force, frequency, stroke rotation and grip-span on discomfort and obtain best posture for hand tool users. Fifteen male participants volunteered in this study. Participants performed combined gripping with torqueing exertions for 5 min for two levels of frequency (10 and 20 exertions/min) at two levels of grip force (50 and 70 N), two levels of stroke rotation (30(○) and 60(○)) and three levels of grip-span (4.7, 6 and 7.3 cm). Therefore, a 2×2×2×3 full factorial design was used. The analysis of variance (ANOVA) showed that frequency, stroke rotation and grip-span were significant on discomfort score. Minimum discomfort and comfortable posture was found to be 90 N grip force with 10 exertions/min for 60° stroke rotation at 6-cm grip-span. The grip force, frequency and stroke rotation were found significant on EMG activity of forearm muscles using multivariate analysis of variance (MANOVA). The extensor muscles were found more activated than flexor muscles during the given task.

  13. On the flow between a rotating and a coaxial fixed disc - Numerical validation of the radial similarity hypothesis

    NASA Astrophysics Data System (ADS)

    Oliveira, L. A.; Pecheux, J.; Restivo, A. O.

    1991-06-01

    The rotating flow between coaxial disks in a radially confined geometry is studied by numerical integration of the full Navier-Stokes equations. The results indicate that both Batchelor's and Stewartson's flow structures can be observed near the axis of rotation, depending on what conditions are set at the peripheral boundary.

  14. Helmholtz decomposition coupling rotational to irrotational flow of a viscous fluid

    PubMed Central

    Joseph, Daniel D.

    2006-01-01

    In this work, I present the form of the Navier–Stokes equations implied by the Helmholtz decomposition in which the relation of the irrotational and rotational velocity fields is made explicit. The idea of self-equilibration of irrotational viscous stresses is introduced. The decomposition is constructed by first selecting the irrotational flow compatible with the flow boundaries and other prescribed conditions. The rotational component of velocity is then the difference between the solution of the Navier–Stokes equations and the selected irrotational flow. To satisfy the boundary conditions, the irrotational field is required, and it depends on the viscosity. Five unknown fields are determined by the decomposed form of the Navier–Stokes equations for an incompressible fluid: the rotational component of velocity, the pressure, and the harmonic potential. These five fields may be readily identified in analytic solutions available in the literature. It is clear from these exact solutions that potential flow of a viscous fluid is required to satisfy prescribed conditions, like the no-slip condition at the boundary of a solid or continuity conditions across a two-fluid boundary. It can be said that equations governing the Helmholtz decomposition describe the modification of irrotational flow due to vorticity, but the analysis shows the two fields are coupled and cannot be completely determined independently. PMID:16983077

  15. Wave propagation reversal for wavy vortices in wide-gap counter-rotating cylindrical Couette flow

    NASA Astrophysics Data System (ADS)

    Altmeyer, S.; Lueptow, Richard M.

    2017-05-01

    We present a numerical study of wavy supercritical cylindrical Couette flow between counter-rotating cylinders in which the wavy pattern propagates either prograde with the inner cylinder or retrograde opposite the rotation of the inner cylinder. The wave propagation reversals from prograde to retrograde and vice versa occur at distinct values of the inner cylinder Reynolds number when the associated frequency of the wavy instability vanishes. The reversal occurs for both twofold and threefold symmetric wavy vortices. Moreover, the wave propagation reversal only occurs for sufficiently strong counter-rotation. The flow pattern reversal appears to be intrinsic in the system as either periodic boundary conditions or fixed end wall boundary conditions for different system sizes always result in the wave propagation reversal. We present a detailed bifurcation sequence and parameter space diagram with respect to retrograde behavior of wavy flows. The retrograde propagation of the instability occurs when the inner Reynolds number is about two times the outer Reynolds number. The mechanism for the retrograde propagation is associated with the inviscidly unstable region near the inner cylinder and the direction of the global average azimuthal velocity. Flow dynamics, spatio-temporal behavior, global mean angular velocity, and torque of the flow with the wavy pattern are explored.

  16. The investigation of flow instabilities on a rotating disk with curvature in the radial direction

    NASA Technical Reports Server (NTRS)

    Intemann, P. A.; Clarkson, M. H.

    1982-01-01

    The major objective is to explore any visible differences of the flow field with wall curvature of the test body, including possible interaction between Taylor-Gortler instabilities present along concave walls and the inflexional instabilities investigated here. An experimental study was conducted with emphasis placed on making visual observations and recording photographically the flow instabilities present under three different rotating bodies: a flat disk, a concave paraboloid, and a convex paraboloid. The data collected for the three test bodies lead to the conclusion that the wall curvature of the concave and convex paraboloids did not alter the observed flow field significantly from that observed on the flat disk.

  17. On the inverse Magnus effect for flow past a rotating cylinder

    NASA Astrophysics Data System (ADS)

    John, Benzi; Gu, Xiao-Jun; Barber, Robert W.; Emerson, David R.

    2016-11-01

    Flow past a rotating cylinder has been investigated using the direct simulation Monte Carlo method. The study focuses on the occurrence of the inverse Magnus effect under subsonic flow conditions. In particular, the variations in the coefficients of lift and drag have been investigated as a function of the Knudsen and Reynolds numbers. Additionally, a temperature sensitivity study has been carried out to assess the influence of the wall temperature on the computed aerodynamic coefficients. It has been found that both the Reynolds number and the cylinder wall temperature significantly affect the drag as well as the onset of lift inversion in the transition flow regime.

  18. Phase transitions and marginal ensemble equivalence for freely evolving flows on a rotating sphere.

    PubMed

    Herbert, C; Dubrulle, B; Chavanis, P H; Paillard, D

    2012-05-01

    The large-scale circulation of planetary atmospheres such as that of the Earth is traditionally thought of in a dynamical framework. Here we apply the statistical mechanics theory of turbulent flows to a simplified model of the global atmosphere, the quasigeostrophic model, leading to nontrivial equilibria. Depending on a few global parameters, the structure of the flow may be either a solid-body rotation (zonal flow) or a dipole. A second-order phase transition occurs between these two phases, with associated spontaneous symmetry breaking in the dipole phase. This model allows us to go beyond the general theory of marginal ensemble equivalence through the notion of Goldstone modes.

  19. Linearized numerical solution method for rotating coaxial disk flows at moderate Reynolds numbers

    NASA Astrophysics Data System (ADS)

    Wu, J.; Delgado, A.; Rath, H. J.

    A linearized solution method for rotating coaxial disk flows at moderate Reynolds numbers is discussed below. The analytical or numerical linearized similarity solutions agree with the nonlinear ones for infinite disk flows of the Stewartson-type as well as of the Batchelor-type with a small difference between angular velocities of both the disks. Over the inner portion of shrouded flows the computed results of the linearized partial differential equations have, overall, a good agreement with the solutions of the nonlinear von Karman similarity one and also with the complete Navier-Stokes solution.

  20. 3D numerical study of a feed jet in a rotating flow-field

    NASA Astrophysics Data System (ADS)

    Jiang, D. J.; Zeng, S.

    2016-09-01

    A contribution of a feed drive in the total counter-current flow in a gas centrifuge for isotope separation is an important problem in optimization of its separation performance. A 3D model is used to simulate flow structures of a feed jet in a rotating flow-field. By using a CFD code, the details of a feed jet are obtained under the axial feed jet boundary condition. It is demonstrated that because of the vacuum regime in the region near the axis of rotation, the results of numerical simulation of a CFD code bring errors. The 3D DSMC simulation is a feasible method to overcome this problem in the future.

  1. Velocity measurements of streamwise roll cells in rotating plane Couette flow

    NASA Astrophysics Data System (ADS)

    Suryadi, Alexandre; Tillmark, Nils; Alfredsson, P. Henrik

    2013-11-01

    For the first time, quantitative velocity measurements in rotating plane Couette flow are demonstrated. Particle image velocimetry is used at a low Reynolds number with anti-cyclonic, i.e. destabilising rotation, where the instability is expected to give rise to steady streamwise-oriented roll cells. The streamwise and spanwise velocities of the roll cells were measured on the centreplane of the flow and at two planes on either side. The streamwise velocity is spanwise periodic with an amplitude variation approximately ±42 % of half the velocity difference between the moving walls. The wall-normal velocity was estimated by assuming steady, laminar and streamwise-independent flow. Despite the large amplitude of the disturbance, both the spanwise wave length and amplitude ratio between the streamwise and wall-normal components were close to what is obtained from linear theory. A splitting event of a roll cell was also captured by the velocity measurements and its development followed in time.

  2. NUMERICAL SIMULATIONS OF Z-PINCH EXPERIMENTS TO CREATE SUPERSONIC DIFFERENTIALLY ROTATING PLASMA FLOWS

    SciTech Connect

    Bocchi, M.; Ummels, B.; Chittenden, J. P.; Lebedev, S. V.; Frank, A.; Blackman, E. G.

    2013-04-10

    The physics of accretion disks is of fundamental importance for understanding of a wide variety of astrophysical sources that includes protostars, X-ray binaries, and active galactic nuclei. The interplay between hydrodynamic flows and magnetic fields and the potential for turbulence-producing instabilities is a topic of active research that would benefit from the support of dedicated experimental studies. Such efforts are in their infancy, but in an effort to push the enterprise forward we propose an experimental configuration which employs a modified cylindrical wire array Z-pinch to produce a rotating plasma flow relevant to accretion disks. We present three-dimensional resistive magnetohydrodynamic simulations which show how this approach can be implemented. In the simulations, a rotating plasma cylinder or ring is formed, with typical rotation velocity {approx}30 km s{sup -1}, Mach number {approx}4, and Reynolds number in excess of 10{sup 7}. The plasma is also differentially rotating. Implementation of different external magnetic field configurations is discussed. It is found that a modest uniform vertical field of 1 T can affect the dynamics of the system and could be used to study magnetic field entrainment and amplification through differential rotation. A dipolar field potentially relevant to the study of accretion columns is also considered.

  3. Unsteady Casson nanofluid flow over a rotating cone in a rotating frame filled with ferrous nanoparticles: A numerical study

    NASA Astrophysics Data System (ADS)

    Raju, C. S. K.; Sandeep, N.

    2017-01-01

    In this study, we investigated the momentum and heat transfer characteristics of Casson nanofluid flow over a rotating cone in a rotating frame filled with water based CoFe2O4 nano particles. Heat flux conditions and wall tem