On Stationary Navier-Stokes Flows Around a Rotating Obstacle in Two-Dimensions

NASA Astrophysics Data System (ADS)

Higaki, Mitsuo; Maekawa, Yasunori; Nakahara, Yuu

2018-05-01

We study the two-dimensional stationary Navier-Stokes equations describing the flows around a rotating obstacle. The unique existence of solutions and their asymptotic behavior at spatial infinity are established when the rotation speed of the obstacle and the given exterior force are sufficiently small.

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.

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

Flow past a rotating cylinder

NASA Astrophysics Data System (ADS)

Mittal, Sanjay; Kumar, Bhaskar

2003-02-01

Flow past a spinning circular cylinder placed in a uniform stream is investigated via two-dimensional computations. A stabilized finite element method is utilized to solve the incompressible Navier Stokes equations in the primitive variables formulation. The Reynolds number based on the cylinder diameter and free-stream speed of the flow is 200. The non-dimensional rotation rate, [alpha] (ratio of the surface speed and freestream speed), is varied between 0 and 5. The time integration of the flow equations is carried out for very large dimensionless time. Vortex shedding is observed for [alpha] < 1.91. For higher rotation rates the flow achieves a steady state except for 4.34 < [alpha] < 4:70 where the flow is unstable again. In the second region of instability, only one-sided vortex shedding takes place. To ascertain the instability of flow as a function of [alpha] a stabilized finite element formulation is proposed to carry out a global, non-parallel stability analysis of the two-dimensional steady-state flow for small disturbances. The formulation and its implementation are validated by predicting the Hopf bifurcation for flow past a non-rotating cylinder. The results from the stability analysis for the rotating cylinder are in very good agreement with those from direct numerical simulations. For large rotation rates, very large lift coefficients can be obtained via the Magnus effect. However, the power requirement for rotating the cylinder increases rapidly with rotation rate.

Forcing function modeling for flow induced vibration

NASA Technical Reports Server (NTRS)

Fleeter, Sanford

1993-01-01

The fundamental forcing function unsteady aerodynamics for application to turbomachine blade row forced response are considered, accomplished through a series of experiments performed in a rotating annular cascade and a research axial flow turbine. In particular, the unsteady periodic flowfields downstream of rotating rows of perforated plates, airfoils and turbine blade rows are measured with a cross hot-wire and an unsteady total pressure probe. The unsteady velocity and static pressure fields were then analyzed harmonically and split into vortical and potential gusts, accomplished by developing a gust splitting analysis which includes both gust unsteady static pressure and velocity data. The perforated plate gusts closely were found to be linear theory vortical gusts, satisfying the vortical gust constraints. The airfoil and turbine blade row generated velocity perturbations did not satisfy the vortical gust constraints. However, the decomposition of the unsteady flow field separated the data into a propagating vortical component which satisfied these vortical gust constraints and a decaying potential component.

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.

Stress analysis of rotating propellers subject to forced excitations

NASA Astrophysics Data System (ADS)

Akgun, Ulas

Turbine blades experience vibrations due to the flow disturbances. These vibrations are the leading cause for fatigue failure in turbine blades. This thesis presents the finite element analysis methods to estimate the maximum vibrational stresses of rotating structures under forced excitation. The presentation included starts with the derived equations of motion for vibration of rotating beams using energy methods under the Euler Bernoulli beam assumptions. The nonlinear large displacement formulation captures the centrifugal stiffening and gyroscopic effects. The weak form of the equations and their finite element discretization are shown. The methods implemented were used for normal modes analyses and forced vibration analyses of rotating beam structures. The prediction of peak stresses under simultaneous multi-mode excitation show that the maximum vibrational stresses estimated using the linear superposition of the stresses can greatly overestimate the stresses if the phase information due to damping (physical and gyroscopic effects) are neglected. The last section of this thesis also presents the results of a practical study that involves finite element analysis and redesign of a composite propeller.

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

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.

On the flow generated by rotating flat plates of low aspect ratio

NASA Astrophysics Data System (ADS)

DeVoria, Adam C.

Low-aspect-ratio propulsors typically allow for high maneuverability at low-to-moderate speeds. This has made them the subject of much recent research aimed at employing such appendages on autonomous vehicles which are required to navigate tumultuous environments. This experimental investigation focuses on the fluid dynamic aspects associated with overly-simplified versions of such biologically-inspired propulsors. In doing so, fundamental contributions are made to the research area. The unsteady, three-dimensional flow of a low-aspect-ratio, trapezoidal flat plate undergoing rotation from rest at a 90° angle of attack and Reynolds numbers of O(103) is investigated experimentally. The objectives are to develop a straightforward protocol for vortex saturation, and to understand the effects of the root-to-tip flow for different velocity programs. The experiments are conducted in a glass-walled tank, and digital particle image velocimetry is used to obtain planar velocity measurements. A formation-parameter definition is investigated and is found to reasonably predict the state corresponding to the pinch-off of the initial tip vortex across the velocity programs tested. The flow in the region near the tip is relatively insensitive to Reynolds number over the range studied. The component normal to the plate is unaffected by total rotational amplitude while the tangential component has dependence on this angle. Also, an estimate of the first tip-vortex pinch-off time is obtained from the near-tip velocity data and agrees very well with values estimated using circulation. The angle of incidence of the bulk root-to-tip flow relative to the plate normal becomes more oblique with increasing rotational amplitude. Accordingly, the peak magnitude of the tangential velocity is also increased and as a result advects fluid momentum away from the plate at a higher rate. The more oblique impingement of the root-to-tip flow for increasing rotational amplitude is shown to have a

Viscoelastic flow in rotating curved pipes

NASA Astrophysics Data System (ADS)

Chen, Yitung; Chen, Huajun; Zhang, Jinsuo; Zhang, Benzhao

2006-08-01

Fully developed viscoelastic flows in rotating curved pipes with circular cross section are investigated theoretically and numerically employing the Oldroyd-B fluid model. Based on Dean's approximation, a perturbation solution up to the secondary order is obtained. The governing equations are also solved numerically by the finite volume method. The theoretical and numerical solutions agree with each other very well. The results indicate that the rotation, as well as the curvature and elasticity, plays an important role in affecting the friction factor, the secondary flow pattern and intensity. The co-rotation enhances effects of curvature and elasticity on the secondary flow. For the counter-rotation, there is a critical rotational number RΩ', which can make the effect of rotation counteract the effect of curvature and elasticity. Complicated flow behaviors are found at this value. For the relative creeping flow, RΩ' can be estimated according to the expression RΩ'=-4Weδ. Effects of curvature and elasticity at different rotational numbers on both relative creeping flow and inertial flow are also analyzed and discussed.

Simulation of two-dimensional turbulent flows in a rotating annulus

NASA Astrophysics Data System (ADS)

Storey, Brian D.

2004-05-01

Rotating water tank experiments have been used to study fundamental processes of atmospheric and geophysical turbulence in a controlled laboratory setting. When these tanks are undergoing strong rotation the forced turbulent flow becomes highly two dimensional along the axis of rotation. An efficient numerical method has been developed for simulating the forced quasi-geostrophic equations in an annular geometry to model current laboratory experiments. The algorithm employs a spectral method with Fourier series and Chebyshev polynomials as basis functions. The algorithm has been implemented on a parallel architecture to allow modelling of a wide range of spatial scales over long integration times. This paper describes the derivation of the model equations, numerical method, testing and performance of the algorithm. Results provide reasonable agreement with the experimental data, indicating that such computations can be used as a predictive tool to design future experiments.

Flows about a rotating circular cylinder by the discrete-vortex method

NASA Astrophysics Data System (ADS)

Kimura, Takeyoshi; Tsutahara, Michihisa

1987-01-01

A numerical study has been conducted for flows past a rotating circular cylinder at high Reynolds numbers, using the discrete-vortex method. It is noted that the reverse Magnus effect is caused by the retreat of the separation point on the acceleration side. At high rotating speed, the nascent vortices of opposite directions are mixed faster, the wake becomes narrower, and predominating frequencies in the lift force disappear.

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.

Precessing rotating flows with additional shear: stability analysis.

PubMed

Salhi, A; Cambon, C

2009-03-01

We consider unbounded precessing rotating flows in which vertical or horizontal shear is induced by the interaction between the solid-body rotation (with angular velocity Omega(0)) and the additional "precessing" Coriolis force (with angular velocity -epsilonOmega(0)), normal to it. A "weak" shear flow, with rate 2epsilon of the same order of the Poincaré "small" ratio epsilon , is needed for balancing the gyroscopic torque, so that the whole flow satisfies Euler's equations in the precessing frame (the so-called admissibility conditions). The base flow case with vertical shear (its cross-gradient direction is aligned with the main angular velocity) corresponds to Mahalov's [Phys. Fluids A 5, 891 (1993)] precessing infinite cylinder base flow (ignoring boundary conditions), while the base flow case with horizontal shear (its cross-gradient direction is normal to both main and precessing angular velocities) corresponds to the unbounded precessing rotating shear flow considered by Kerswell [Geophys. Astrophys. Fluid Dyn. 72, 107 (1993)]. We show that both these base flows satisfy the admissibility conditions and can support disturbances in terms of advected Fourier modes. Because the admissibility conditions cannot select one case with respect to the other, a more physical derivation is sought: Both flows are deduced from Poincaré's [Bull. Astron. 27, 321 (1910)] basic state of a precessing spheroidal container, in the limit of small epsilon . A Rapid distortion theory (RDT) type of stability analysis is then performed for the previously mentioned disturbances, for both base flows. The stability analysis of the Kerswell base flow, using Floquet's theory, is recovered, and its counterpart for the Mahalov base flow is presented. Typical growth rates are found to be the same for both flows at very small epsilon , but significant differences are obtained regarding growth rates and widths of instability bands, if larger epsilon values, up to 0.2, are considered. Finally

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.

Holographic flow visualization in rotating turbomachinery

NASA Astrophysics Data System (ADS)

Parker, R. J.; Reeves, M.

1990-11-01

Holographic flow visualization has found many applications in rotating turbomachinery. Applications in the design of aeroengine fans, automotive turbochargers, turbines, helicopter rotors, and advanced propfans are discussed. Work in ducted rotating flows and rotating free aerofoils is brought together and new developments in each field are revealed.

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.

Experimental and computational investigation on the flow behavior of granular particles through an inclined rotating chute

NASA Astrophysics Data System (ADS)

Shirsath, Sushil; Padding, Johan; Clercx, Herman; Kuipers, Hans

2013-11-01

In blast furnaces operated in the steel industry, particles like coke, sinter and pellets enter from a hopper and are distributed on the burden surface by a rotating chute. Such particulate flows suffer occasionally from particle segregation in chute, which hinders efficient throughflow. To obtain a more fundamental insight into these effects, monodisperse particles flowing through a rotating chute inclined at a fixed angle has been studied both with experiments and with a discrete particle model. We observe that the prevailing flow patterns depend strongly on the rotation rate of the chute. With increasing rotation rate the particles are moving increasingly to the side wall. The streamwise particle velocity is slightly reduced in the first half length of the chute due to the Coriolis force, but strongly increased in the second half due to the centrifugal forces. The particle bed height becomes a two-dimensional function of the position inside the chute, with a strong increase in bed height along the sidewall due to the Coriolis forces. It was found that the DPM model was agreed well with the experimental measurements. We will also discuss ongoing work, where we investigate the effects of binary particle mixtures with different particle size or density, different chute geometry.

Steady Flow Generated by a Core Oscillating in a Rotating Spherical Cavity

NASA Astrophysics Data System (ADS)

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

2018-01-01

Steady flow generated by oscillations of an inner solid core in a fluid-filled rotating spherical cavity is experimentally studied. The core with density less than the fluid density is located near the center of the cavity and is acted upon by a centrifugal force. The gravity field directed perpendicular to the rotation axis leads to a stationary displacement of the core from the rotation axis. As a result, in the frame of reference attached to the cavity, the core performs circular oscillation with frequency equal to the rotation frequency, and its center moves along a circular trajectory in the equatorial plane around the center of the cavity. For the differential rotation of the core to be absent, one of the poles of the core is connected to the nearest pole of the cavity with a torsionally elastic, flexible fishing line. It is found that the oscillation of the core generates axisymmetric azimuthal fluid flow in the cavity which has the form of nested liquid columns rotating with different angular velocities. Comparison with the case of a free oscillating core which performs mean differential rotation suggests the existence of two mechanisms of flow generation (due to the differential rotation of the core in the Ekman layer and due to the oscillation of the core in the oscillating boundary layers).

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wallis, G.B.

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.

Experimental analysis of flow structure in contra-rotating axial flow pump designed with different rotational speed concept

NASA Astrophysics Data System (ADS)

Cao, Linlin; Watanabe, Satoshi; Imanishi, Toshiki; Yoshimura, Hiroaki; Furukawa, Akinori

2013-08-01

As a high specific speed pump, the contra-rotating axial flow pump distinguishes itself in a rear rotor rotating in the opposite direction of the front rotor, which remarkably contributes to the energy conversion, the reduction of the pump size, better hydraulic and cavitation performances. However, with two rotors rotating reversely, the significant interaction between blade rows was observed in our prototype contra-rotating rotors, which highly affected the pump performance compared with the conventional axial flow pumps. Consequently, a new type of rear rotor was designed by the rotational speed optimization methodology with some additional considerations, aiming at better cavitation performance, the reduction of blade rows interaction and the secondary flow suppression. The new rear rotor showed a satisfactory performance at the design flow rate but an unfavorable positive slope of the head — flow rate curve in the partial flow rate range less than 40% of the design flow rate, which should be avoided for the reliability of pump-pipe systems. In the present research, to understand the internal flow field of new rear rotor and its relation to the performances at the partial flow rates, the velocity distributions at the inlets and outlets of the rotors are firstly investigated. Then, the boundary layer flows on rotor surfaces, which clearly reflect the secondary flow inside the rotors, are analyzed through the limiting streamline observations using the multi-color oil-film method. Finally, the unsteady numerical simulations are carried out to understand the complicated internal flow structures in the rotors.

Experimental analysis and flow visualization of a thin liquid film on a stationary and rotating disk

NASA Technical Reports Server (NTRS)

Thomas, S.; Faghri, A.; Hankey, W.

1991-01-01

The mean thickness of a thin liquid film of deionized water with a free surface on a stationary and rotating horizontal disk has been measured with a nonobtrusive capacitance technique. The measurements were taken when the rotational speed ranged from 0-300 rpm and the flow rate varied from 7.0-15.0 lpm. A flow visualization study of the thin film was also performed to determine the characteristics of the waves on the free surface. When the disk was stationary, a circular hydraulic jump was present on the disk. Upstream from the jump, the film thickness was determined by the inertial and frictional forces on the fluid, and the radial spreading of the film. The surface tension at the edge of the disk affected the film thickness downstream from the jump. For the rotating disk, the film thickness was dependent upon the inertial and frictional forces near the center of the disk and the centrifugal forces near the edge of the disk.

Large Eddy Simulation of turbulence induced secondary flows in stationary and rotating straight square ducts

NASA Astrophysics Data System (ADS)

Sudjai, W.; Juntasaro, V.; Juttijudata, V.

2018-01-01

The accuracy of predicting turbulence induced secondary flows is crucially important in many industrial applications such as turbine blade internal cooling passages in a gas turbine and fuel rod bundles in a nuclear reactor. A straight square duct is popularly used to reveal the characteristic of turbulence induced secondary flows which consists of two counter rotating vortices distributed in each corner of the duct. For a rotating duct, the flow can be divided into the pressure side and the suction side. The turbulence induced secondary flows are converted to the Coriolis force driven two large circulations with a pair of additional vortices on the pressure wall due to the rotational effect. In this paper, the Large Eddy Simulation (LES) of turbulence induced secondary flows in a straight square duct is performed using the ANSYS FLUENT CFD software. A dynamic kinetic energy subgrid-scale model is used to describe the three-dimensional incompressible turbulent flows in the stationary and the rotating straight square ducts. The Reynolds number based on the friction velocity and the hydraulic diameter is 300 with the various rotation numbers for the rotating cases. The flow is assumed fully developed by imposing the constant pressure gradient in the streamwise direction. For the rotating cases, the rotational axis is placed perpendicular to the streamwise direction. The simulation results on the secondary flows and the turbulent statistics are found to be in good agreement with the available Direct Numerical Simulation (DNS) data. Finally, the details of the Coriolis effects are discussed.

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.

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.

Dispersion and Mixing in Quasi-two-dimensional Rotating Flows

NASA Astrophysics Data System (ADS)

Wells, M. G.; Clercx, H. J. H.; van Heijst, G. J. F.

A new rotating-tank experiment has been set up to investigate several aspects of dispersion in forced quasi-two-dimensional turbulence. By superimposing a harmonically varying perturbation on the mean rotation rate the mean flow continually interacts with the no-slip boundaries and forms boundary layers with high-amplitude vorticity twice during the forcing period. By choosing the proper amplitude and frequency of the perturbation it is possible to continuously inject small-scale vorticity in the interior of the flow, either in the form of filamentary structures (detached boundary layers) or as small vortices (after the roll-up of detached boundary layers). We present measurements of the passive scalar spectrum which show good agreement with the k -1 spectrum predicted by Batchelor (J. Fluid Mech. 5:113, 1959). Using particle image velocimetry we are able to reconstruct the Lagrangian trajectories of particles. The relative dispersion rates of particle pairs show an initial exponential separation followed by the classical Richardson dispersion, R 2 ∝ t3.0± 0.1. The variance of the absolute particle displacement grows as σ ∝ t1.4, similar to the observations in the previous experiments by Solomon et al. (Phys. Rev. Lett. 71:3975, 1993) and Hansen et al. (Phys. Rev. E 58:7261, 1998). Finally, and indicating future directions of research, we present results of a simple chemical reaction in forced quasi-2D turbulence and show how the bulk reaction rate is controlled by the mixing and filamentation processes.

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.

One-dimensional analysis of the hydrodynamic and thermal characteristics of thin film flows including the hydraulic jump and rotation

NASA Technical Reports Server (NTRS)

Thomas, S.; Hankey, W.; Faghri, A.; Swanson, T.

1990-01-01

The flow of a thin liquid film with a free surface along a horizontal plane that emanates from a pressurized vessel is examined numerically. In one g, a hydraulic jump was predicted in both plane and radial flow, which could be forced away from the inlet by increasing the inlet Froude number or Reynolds number. In zero g, the hydraulic jump was not predicted. The effect of solid-body rotation for radial flow in one g was to 'wash out' the hydraulic jump and to decrease the film height on the disk. The liquid film heights under one g and zero g were equal under solid-body rotation because the effect of centrifugal force was much greater than that of the gravitational force. The heat transfer to a film on a rotating disk was predicted to be greater than that of a stationary disk because the liquid film is extremely thin and is moving with a very high velocity.

In-situ detection of convection and rotation striations by growth interface electromotive force spectrum

NASA Astrophysics Data System (ADS)

Zhu, Yunzhong; Tang, Feng; Yang, Xin; Yang, Mingming; Ma, Decai; Zhang, Xiaoyue; Liu, Yang; Lin, Shaopeng; Wang, Biao

2018-04-01

Nanoscale growth striations, induced by the crystal rotation and melt convection, are in-situ detected by the growth interface electromotive force (GEMF) spectrum during Czochralski (CZ) crystal growth. Specifically, the intensity and period of rotation and convection striations could be precisely revealed under different rotation rates. This is because the GEMF spectrum is affected by the combination effort of temperature difference in crystal rotation path and the melt flow in growth interface. Furthermore, the spectrum analysis (Fourier transform) reveals remarkable characteristics of periodic flow oscillation. More interestingly, in different rotation rates, the corresponding convection period and intensity show particular regularity that could barely be observed in semitransparent and high-temperature melt. Therefore, the GEMF spectrum reflects the subtle changes of a growing crystal that is far beyond the detecting precision of sensors in current CZ equipment. On the basis of this paper and our previous work, the real-time feedback of multiscale striations is established. GEMF spectrum could be a promising approach to reveal striation formation mechanism and optimize crystal quality.

A laboratory study of mean flow generation in rotating fluids by Reynolds stress gradients

NASA Astrophysics Data System (ADS)

McGuinness, D. S.; Boyer, D. L.; Fernando, H. J. S.

2001-06-01

Laboratory experiments were conducted that demonstrate that a mean azimuthal flow can be produced by introducing Reynolds stress gradients to a rotating fluid with zero initial mean flow. This mechanism may play a role in the generation of mean currents in coastal regions. The experiments entail the establishment of turbulence in a thin annular-shaped region centered within a cylindrical test cell through the use of a vertically oscillating grid. This region rests in a horizontal plane perpendicular to the vertical axis of the tank, and the entire system is placed on a turntable to simulate background rotation. Flow visualization techniques are used to depict qualitative features of the resulting flow field. Measurements of the mean and turbulent velocity fields are performed using a two-component laser-Doppler velocimeter. The results show how rectified currents (mean flows) can be generated via Reynolds stress gradients induced by periodic forcing of the grid. In the absence of background rotation, rectified flow is observed in the radial and vertical directions only. The presence of background rotation tends to organize these motions in that the flow tends to move parallel to the turbulent source, i.e., in the azimuthal direction, with the source (strong turbulence) located to the right, facing downstream. The influence of rotation on the Reynolds stresses and their gradients as well as on the ensuing mean flow is evaluated, and the observations are examined by considering individual contributions of the terms in the Reynolds-averaged momentum equations.

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.

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.

Analysis of high-speed rotating flow inside gas centrifuge casing

NASA Astrophysics Data System (ADS)

Pradhan, Sahadev, , Dr.

2017-10-01

The generalized analytical model for the radial boundary layer inside the gas centrifuge casing in which the inner cylinder is rotating at a constant angular velocity Ω_i while the outer one is stationary, is formulated for studying the secondary gas flow field due to wall thermal forcing, inflow/outflow of light gas along the boundaries, as well as due to the combination of the above two external forcing. The analytical model includes the sixth order differential equation for the radial boundary layer at the cylindrical curved surface in terms of master potential (χ) , which is derived from the equations of motion in an axisymmetric (r - z) plane. The linearization approximation is used, where the equations of motion are truncated at linear order in the velocity and pressure disturbances to the base flow, which is a solid-body rotation. Additional approximations in the analytical model include constant temperature in the base state (isothermal compressible Couette flow), high aspect ratio (length is large compared to the annular gap), high Reynolds number, but there is no limitation on the Mach number. The discrete eigenvalues and eigenfunctions of the linear operators (sixth-order in the radial direction for the generalized analytical equation) are obtained. The solutions for the secondary flow is determined in terms of these eigenvalues and eigenfunctions. These solutions are compared with direct simulation Monte Carlo (DSMC) simulations and found excellent agreement (with a difference of less than 15%) between the predictions of the analytical model and the DSMC simulations, provided the boundary conditions in the analytical model are accurately specified.

Analysis of high-speed rotating flow inside gas centrifuge casing

NASA Astrophysics Data System (ADS)

Pradhan, Sahadev, , Dr.

2017-09-01

The generalized analytical model for the radial boundary layer inside the gas centrifuge casing in which the inner cylinder is rotating at a constant angular velocity Ωi while the outer one is stationary, is formulated for studying the secondary gas flow field due to wall thermal forcing, inflow/outflow of light gas along the boundaries, as well as due to the combination of the above two external forcing. The analytical model includes the sixth order differential equation for the radial boundary layer at the cylindrical curved surface in terms of master potential (χ) , which is derived from the equations of motion in an axisymmetric (r - z) plane. The linearization approximation is used, where the equations of motion are truncated at linear order in the velocity and pressure disturbances to the base flow, which is a solid-body rotation. Additional approximations in the analytical model include constant temperature in the base state (isothermal compressible Couette flow), high aspect ratio (length is large compared to the annular gap), high Reynolds number, but there is no limitation on the Mach number. The discrete eigenvalues and eigenfunctions of the linear operators (sixth-order in the radial direction for the generalized analytical equation) are obtained. The solutions for the secondary flow is determined in terms of these eigenvalues and eigenfunctions. These solutions are compared with direct simulation Monte Carlo (DSMC) simulations and found excellent agreement (with a difference of less than 15%) between the predictions of the analytical model and the DSMC simulations, provided the boundary conditions in the analytical model are accurately specified.

Analysis of high-speed rotating flow inside gas centrifuge casing

NASA Astrophysics Data System (ADS)

Pradhan, Sahadev

2017-11-01

The generalized analytical model for the radial boundary layer inside the gas centrifuge casing in which the inner cylinder is rotating at a constant angular velocity Ωi while the outer one is stationary, is formulated for studying the secondary gas flow field due to wall thermal forcing, inflow/outflow of light gas along the boundaries, as well as due to the combination of the above two external forcing. The analytical model includes the sixth order differential equation for the radial boundary layer at the cylindrical curved surface in terms of master potential (χ) , which is derived from the equations of motion in an axisymmetric (r - z) plane. The linearization approximation is used, where the equations of motion are truncated at linear order in the velocity and pressure disturbances to the base flow, which is a solid-body rotation. Additional approximations in the analytical model include constant temperature in the base state (isothermal compressible Couette flow), high aspect ratio (length is large compared to the annular gap), high Reynolds number, but there is no limitation on the Mach number. The discrete eigenvalues and eigenfunctions of the linear operators (sixth-order in the radial direction for the generalized analytical equation) are obtained. The solutions for the secondary flow is determined in terms of these eigenvalues and eigenfunctions. These solutions are compared with direct simulation Monte Carlo (DSMC) simulations and found excellent agreement (with a difference of less than 15%) between the predictions of the analytical model and the DSMC simulations, provided the boundary conditions in the analytical model are accurately specified.

Influence of Beam Rotation on the Response of Cantilevered Flow Energy Harvesters Exploiting the Galloping Instability

NASA Astrophysics Data System (ADS)

Noel, James H.

Energy harvesters are scalable devices that generate microwatt to milliwatt power levels by scavenging energy from their ambient natural environment. Applications of such devices are numerous, ranging from wireless sensing to biomedical implants. A particular type of energy harvester is a device which converts the momentum of an incident fluid flow into electrical output by using flow-induced instabilities such as galloping, flutter, vortex shedding and wake galloping. Galloping flow energy harvesters (GFEHs), which represent the core of this thesis, consist of a prismatic tip body mounted on a long, thin cantilever beam fixed on a rigid base. When the bluff body is placed such that its leading edge faces a moving fluid, the flow separates at the edges of the leading face causing shear layers to develop behind the bluff face. The shear layer interacts with the surface area of the afterbody. An asymmetric condition in the shear layers causes a net lift which incites motion. This causes the beam to oscillate periodically at or near the natural frequency of the system. The periodic strain developed near the base of the oscillating beam is then transformed into electricity by attaching a piezoelectric layer to either side of the beam surface. This thesis focuses on characterizing the influence of the rotation of the beam tip on the response and output power of GFEHs. Previous modeling efforts of GFEHs usually adopt two simplifying assumptions. First, it is assumed that the tip rotation of the beam is arbitrarily small and hence can be neglected. Second, it is assumed that the quasi-steady assumption of the aerodynamic force can be adopted even in the presence of tip rotation. Although the validity of these two assumptions becomes debatable in the presence of finite tip rotations, which are common to occur in GFEHs, none the previous research studies have systematically addressed the influence of finite tip rotations on the validity of the quasi-steady assumption and

Low-to-moderate Reynolds number swirling flow in an annular channel with a rotating end wall.

PubMed

Davoust, Laurent; Achard, Jean-Luc; Drazek, Laurent

2015-02-01

This paper presents a new method for solving analytically the axisymmetric swirling flow generated in a finite annular channel from a rotating end wall, with no-slip boundary conditions along stationary side walls and a slip condition along the free surface opposite the rotating floor. In this case, the end-driven swirling flow can be described from the coupling between an azimuthal shear flow and a two-dimensional meridional flow driven by the centrifugal force along the rotating floor. A regular asymptotic expansion based on a small but finite Reynolds number is used to calculate centrifugation-induced first-order correction to the azimuthal Stokes flow obtained as the solution at leading order. For solving the first-order problem, the use of an integral boundary condition for the vorticity is found to be a convenient way to attribute boundary conditions in excess for the stream function to the vorticity. The annular geometry is characterized by both vertical and horizontal aspect ratios, whose respective influences on flow patterns are investigated. The vertical aspect ratio is found to involve nontrivial changes in flow patterns essentially due to the role of corner eddies located on the left and right sides of the rotating floor. The present analytical method can be ultimately extended to cylindrical geometries, irrespective of the surface opposite the rotating floor: a wall or a free surface. It can also serve as an analytical tool for monitoring confined rotating flows in applications related to surface viscosimetry or crystal growth from the melt.

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.

Experimental calibration procedures for rotating Lorentz-force flowmeters

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

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.

Flow Field Characteristics and Lift Changing Mechanism for Half-Rotating Wing in Hovering Flight

NASA Astrophysics Data System (ADS)

Li, Q.; Wang, X. Y.; Qiu, H.; Li, C. M.; Qiu, Z. Z.

2017-12-01

Half-rotating wing (HRW) is a new similar-flapping wing system based on half-rotating mechanism which could perform rotating-type flapping instead of oscillating-type flapping. The characteristics of flow field and lift changing mechanism for HRW in hovering flight are important theoretical basis to improve the flight capability of HRW aircraft. The driving mechanism and work process of HRW were firstly introduced in this paper. Aerodynamic simulation model of HRW in hovering flight was established and solved using XFlow software, by which lift changing rule of HRW was drawn from the simulation solution. On the other hand, the development and shedding of the distal vortex throughout one stroke would lead to the changes of the lift force. Based on analyzing distribution characteristics of vorticity, velocity and pressure around wing blade, the main features of the flow field for HRW were further given. The distal attached vortex led to the increase of the lift force, which would gradually shed into the wake with a decline of lift in the later downstroke. The wake ring directed by the distal end of the blade would generate the downward accelerating airflow which produced the upward anti-impulse to HRW. The research results mentioned above illustrated that the behavior characteristics of vortex formed in flow field were main cause of lift changing for HRW.

Dynamo action in dissipative, forced, rotating MHD turbulence

DOE Office of Scientific and Technical Information (OSTI.GOV)

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.more » 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.« less

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.-

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.

Unsteady flow over a decelerating rotating sphere

NASA Astrophysics Data System (ADS)

Turkyilmazoglu, M.

2018-03-01

Unsteady flow analysis induced by a decelerating rotating sphere is the main concern of this paper. A revolving sphere in a still fluid is supposed to slow down at an angular velocity rate that is inversely proportional to time. The governing partial differential equations of motion are scaled in accordance with the literature, reducing to the well-documented von Kármán equations in the special circumstance near the pole. Both numerical and perturbation approaches are pursued to identify the velocity fields, shear stresses, and suction velocity far above the sphere. It is detected that an induced flow surrounding the sphere acts accordingly to adapt to the motion of the sphere up to some critical unsteadiness parameters at certain latitudes. Afterward, the decay rate of rotation ceases such that the flow at the remaining azimuths starts revolving freely. At a critical unsteadiness parameter corresponding to s = -0.681, the decelerating sphere rotates freely and requires no more torque. At a value of s exactly matching the rotating disk flow at the pole identified in the literature, the entire flow field around the sphere starts revolving faster than the disk itself. Increasing values of -s almost diminish the radial outflow. This results in jet flows in both the latitudinal and meridional directions, concentrated near the wall region. The presented mean flow results will be useful for analyzing the instability features of the flow, whether of a convective or absolute nature.

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.

Effects of spanwise rotation on the structure of two-dimensional fully developed turbulent channel flow.

NASA Technical Reports Server (NTRS)

Johnston, J. P.; Halleen, R. M.; Lezius, D. K.

1972-01-01

Experiments on fully developed turbulent flow in a channel which is rotating at a steady rate about a spanwise axis are described. The Coriolis force components in the region of two-dimensional mean flow affect both local and global stability. Three stability-related phenomena were observed or inferred: (1) the reduction (increase) of the rate of wall-layer streak bursting in locally stabilized (destabilized) wall layers; (2) the total suppression of transition to turbulence in a stabilized layer; (3) the development of large-scale roll cells on the destabilized side of the channel by growth of a Taylor-Gortler vortex instability. Local effects of rotational stabilization, such as reduction of the turbulent stress in wall layers, can be related to the local Richardson number in a simple way. This paper not only investigates this effect, but also, by methods of flow visualization, exposes some of the underlying structure changes caused by rotation.-

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

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.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lim, Chjan

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-bodymore » 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.« less

Experimental studies of rotating exchange flow

NASA Astrophysics Data System (ADS)

Rabe, B.; Smeed, D. A.; Dalziel, S. B.; Lane-Serff, G. F.

2007-02-01

Ocean basins are connected by straits and passages, geometrically limiting important heat and salt exchanges which in turn influence the global thermohaline circulation and climate. Such exchange can be modeled in an idealized way by taking into consideration the density-driven two-layer flow along a strait under the influence of rotation. We use a laboratory model of a lock exchange between two reservoirs of different density through a flat-bottom channel with a horizontal narrows, set up on two different platforms: a 1 m diameter turntable, where density interface position was measured by dye attenuation, and the 14 m diameter turntable at Coriolis/LEGI (Grenoble, France), where correlation imaging velocimetry, a particle imaging technique, allowed us to obtain for the first time detailed measurements of the velocity fields in these flows. The influence of rotation is studied by varying a parameter, Bu, a type of Burger number given by the ratio of the Rossby radius to the channel width at the narrows. In addition, a two-layer version of the Miami Isopycnic Coordinate Model (MICOM) is used, to study the cases with low Burger number. Results from experiments by Dalziel [1988. Two-layer hydraulics: maximal exchange flows. Ph.D. Thesis, Department of Applied Mathematics and Theoretical Physics, University of Cambridge, see also ] are also included for comparison. Time-mean exchange fluxes for any Bu are in close agreement with the inviscid zero-potential vorticity theory of Dalziel [1990. Rotating two-layer sill flows. In: Pratt, L.J. (Ed.), The Physical Oceanography of Sea Straits. Kluwer Academic, Dordrecht, pp. 343-371] and Whitehead et al. [1974. Rotating hydraulics of strait and sill flows. Geophysical Fluid Dynamics 6, 101-125], who found that fluxes for Bu>1 mainly vary with channel width, similar to non-rotating flow, but for Bu<1 are only limited by the Rossby radius. We also show

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.

Vortex forcing model for turbulent flow over spanwise-heterogeneous topogrpahies: scaling arguments and similarity solution

NASA Astrophysics Data System (ADS)

Anderson, William; Yang, Jianzhi

2017-11-01

Spanwise surface heterogeneity beneath high-Reynolds number, fully-rough wall turbulence is known to induce mean secondary flows in the form of counter-rotating streamwise vortices. The secondary flows are a manifestation of Prandtl's secondary flow of the second kind - driven and sustained by spatial heterogeneity of components of the turbulent (Reynolds averaged) stress tensor. The spacing between adjacent surface heterogeneities serves as a control on the spatial extent of the counter-rotating cells, while their intensity is controlled by the spanwise gradient in imposed drag (where larger gradients associated with more dramatic transitions in roughness induce stronger cells). In this work, we have performed an order of magnitude analysis of the mean (Reynolds averaged) streamwise vorticity transport equation, revealing the scaling dependence of circulation upon spanwise spacing. The scaling arguments are supported by simulation data. Then, we demonstrate that mean streamwise velocity can be predicted a priori via a similarity solution to the mean streamwise vorticity transport equation. A vortex forcing term was used to represent the affects of spanwise topographic heterogeneity within the flow. Efficacy of the vortex forcing term was established with large-eddy simulation cases, wherein vortex forcing model parameters were altered to capture different values of spanwise spacing.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

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. Anmore » 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

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

Internal flows and force matrices in axial flow inducers

NASA Astrophysics Data System (ADS)

Bhattacharyya, Abhijit

1994-01-01

Axial flow inducers such as those used in high speed rocket engine turbopumps are subject to complex internal flows and fluid-induced lateral and rotordynamic forces. An investigation of these internal flows was conducted using boundary layer flow visualization on the blades, hub and housing of unshrouded and shrouded inducers. Results showed that the blade boundary layer flows have strong radial components at off-design conditions and remain attached to the blade surface at all flow coefficients tested. The origin of upstream swirling backflow was found to be at the discharge plane of the inducer. In addition, flow reversal was observed at the suction side blade tip near the leading edge in a shrouded inducer. Re-entry of the hub boundary layer flow, a downstream backflow, into the blade passage area was observed at flow coefficients below design. For unshrouded inducers the radially outward flow near the blade tip mixed with the leakage flow to form the upstream backflow. The lateral and rotordynamic forces acting on an inducer due to an imposed whirl motion was also investigated at various flow coefficients. It was found that the rotordynamic force data at various whirl frequency ratios does not allow a normal quadratic fit; consequently the conventional inertial, stiffness and damping coefficients cannot be obtained and a definite whirl ratio describing the instability region does not result. Application of an actuator disk theory proved to be inaccurate in estimating the rotordynamic tangential force in a non-whirling inducer. The effect of upstream and downstream flow distortions on the rotordynamic and lateral forces on an inducer were studied. It was found that at flow coefficients below design, large lateral forces occurred in the presence of a downstream asymmetry. Results of inlet distortion experiments show that a strong inlet shear causes a significant increase in the lateral force. Cavitation was found to have important consequences for fluid

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.

Effects of centrifugal acceleration on the flows and segregation in vertical Bridgman crystal growth with steady ampoule rotation

NASA Astrophysics Data System (ADS)

Lan, C. W.

2001-07-01

The effects of centrifugal acceleration on the flows and segregation in vertical Bridgman crystal growth with steady ampoule rotation are investigated through numerical simulation. The numerical model is based on the Boussinesq approximation in a rotating frame, and the fluid flow, heat and mass transfer, and the growth interface are solved simultaneously by a robust finite-volume/Newton method. The growth of gallium-doped germanium (GaGe) in the Grenoble furnace is adopted as an example. The calculated results at small Froude number (Fr<<1) are consistent with the previous prediction (Lan, J. Crystal growth 197 (1999) 983). However, at a high rotation speed or in reduced gravity, where the centrifugal acceleration becomes important (Fr˜1), the results are quite different due to the secondary flow induced. Since the direction of the induced flow is different from that of the buoyancy convection due to the concave interface, the flow damping is more effective than that due to the Coriolis force alone. More importantly, radial segregation can be reversed during the flow transition from one to the other.

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.

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.

Self-sustained flow oscillations and heat transfer in radial flow through co-rotating parallel disks

NASA Astrophysics Data System (ADS)

Mochizuki, S.; Inoue, T.

1990-03-01

An experimental study was conducted to determine the fluid flow and heat transfer characteristics in a passage formed by two parallel rotating disks. The local heat transfer coefficients along the disk radius were measured in detail and the flow patterns between the two rotating disks were visualized by using paraffin mist and a laser-light sheet. It was disclosed that: (1) the self-sustained laminar flow separation which is characteristic of the stationary disks still exists even when the disks are set in motion, giving significant influence to the heat transfer; (2) for small source flow Reynolds number, Re, and large rotational Reynolds number, Re(omega), rotating stall dominates the heat transfer; and (3) heat transfer for steady laminar flow occurs only when Re is less than 1200 and Re(omega) is less than 20.

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.

Spatial confinement of active microtubule networks induces large-scale rotational cytoplasmic flow

PubMed Central

Suzuki, Kazuya; Miyazaki, Makito; Takagi, Jun; Itabashi, Takeshi; Ishiwata, Shin’ichi

2017-01-01

Collective behaviors of motile units through hydrodynamic interactions induce directed fluid flow on a larger length scale than individual units. In cells, active cytoskeletal systems composed of polar filaments and molecular motors drive fluid flow, a process known as cytoplasmic streaming. The motor-driven elongation of microtubule bundles generates turbulent-like flow in purified systems; however, it remains unclear whether and how microtubule bundles induce large-scale directed flow like the cytoplasmic streaming observed in cells. Here, we adopted Xenopus egg extracts as a model system of the cytoplasm and found that microtubule bundle elongation induces directed flow for which the length scale and timescale depend on the existence of geometrical constraints. At the lower activity of dynein, kinesins bundle and slide microtubules, organizing extensile microtubule bundles. In bulk extracts, the extensile bundles connected with each other and formed a random network, and vortex flows with a length scale comparable to the bundle length continually emerged and persisted for 1 min at multiple places. When the extracts were encapsulated in droplets, the extensile bundles pushed the droplet boundary. This pushing force initiated symmetry breaking of the randomly oriented bundle network, leading to bundles aligning into a rotating vortex structure. This vortex induced rotational cytoplasmic flows on the length scale and timescale that were 10- to 100-fold longer than the vortex flows emerging in bulk extracts. Our results suggest that microtubule systems use not only hydrodynamic interactions but also mechanical interactions to induce large-scale temporally stable cytoplasmic flow. PMID:28265076

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.

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.

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.

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.

The Flow in a Model Rotating-Wall Bioreactor.

NASA Astrophysics Data System (ADS)

Smith, Marc K.; Neitzel, G. Paul

1997-11-01

Aggregates of mammalian cells can be grown on artificial polymer constructs in a reactor vessel in order to produce high-quality tissue for medical applications. The growth and differentiation of these cells is greatly affected by the fluid flow and mass transfer within the bioreactor. The surface shear stress on the constructs is an especially important quantity of interest. Here, we consider a bioreactor in the form of two concentric, independently-rotating cylinders with the axis of rotation in a horizontal plane. We shall examine the flow around a model tissue construct in the form of a disk fixed in the flow produced by the rotating walls of the bioreactor. Using CFD techniques, we shall determine the flow field and the surface shear stress distribution on the construct as a function of the wall velocities, the Reynolds number of the flow, and the construct size and position. The results will be compared to the PIV measurements of this system reported by Brown & Neitzel(1997 Meeting of the APS/DFD.).

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.

Direct numerical simulation of turbulent flow in a rotating square duct

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dai, Yi-Jun; Huang, Wei-Xi, E-mail: hwx@tsinghua.edu.cn; Xu, Chun-Xiao

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, andmore » the underlying mechanism is explained according to the budget analysis of the mean momentum equations.« less

Magnetized, mass-loaded, rotating accretion flows

NASA Astrophysics Data System (ADS)

Toniazzo, T.; Hartquist, T. W.; Durisen, R. H.

2001-03-01

We present a semi-analytical investigation of a simple one-dimensional, steady-state model for a mass-loaded, rotating, magnetized, hydrodynamical flow. Our approach is analogous to one used in early studies of magnetized winds. The model represents the infall towards a central point mass of the gas generated in a cluster of stars surrounding it, as is likely to occur in some active nuclei and starburst galaxies. We describe the properties of the different classes of infall solutions. We find that the flow becomes faster than the fast-mode speed, and hence decoupled from the centre, only for a limited range of parameter values, and when magnetic stresses are ineffective. Such flow is slowed as it approaches a centrifugal barrier, implying the existence of an accretion disc. When the flow does not become super-fast and the magnetic torque is insufficient, no steady solution extending inward to the centre exists. Finally, with a larger magnetic torque, solutions representing steady sub-Alfvénic flows are found, which can resemble spherical hydrodynamical infall. Such solutions, if applicable, would imply that rotation is not important and that any accretion disc formed would be of very limited size.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mondal, Rabindra Nath, E-mail: rnmondal71@yahoo.com; Shaha, Poly Rani; Roy, Titob

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 themore » 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.« less

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.

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.

Flow Modification Induced by Quincke Rotation in a Capillary

NASA Astrophysics Data System (ADS)

Cebers, A.; Lemaire, E.; Lobry, L.

When particles immersed in a semi-insulating liquid are submitted to a sufficiently high DC field, they can rotate spontaneously around any axis perpendicular to the field (Quincke rotation). Recently we have shown that due to Quincke effect the effective viscosity of a colloidal suspension could be reduced. When the suspension is submitted to a shear, the particles rotation is amplified by the electric torque and drives the suspending liquid. For a flow in a capillary, this effect manifests itself by an increase of the flow rate. We present the results of our experiments carried out with a rectangular cross section capillary. These results are compared with the direct determination of the apparent viscosity in a Couette flow rheometer.

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.

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.

Shear-induced autorotation of freely rotatable cylinder in a channel flow at moderate Reynolds number

NASA Astrophysics Data System (ADS)

Xia, Yi; Lin, Jianzhong; Ku, Xiaoke; Chan, Tatleung

2018-04-01

Flow past a center-pinned freely rotatable cylinder asymmetrically confined in a two-dimensional channel is simulated with the lattice Boltzmann method for a range of Reynolds number 0.1 ≤ Re ≤ 200, eccentricity ratio 0/8 ≤ ɛ ≤ 7/8, and blockage ratio 0.1 ≤ β ≤ 0.5. It is found that the inertia tends to facilitate the anomalous clockwise rotation of the cylinder. As the eccentricity ratio increases, the cylinder rotates faster in the counterclockwise direction and then slows down at a range of Re < 10. At a range of Re > 40, there exists an anomalous clockwise rotation for the cylinder at a low eccentricity ratio and the domain where the cylinder rotates anomalously becomes larger with the increase in the Reynolds number. In a channel with a higher blockage ratio, the rotation of the cylinder is more sensitive to the change of cylinder lateral position, and the separatrix at which the cylinder remains a state of rest moves upward generally. The cylinder is more likely to rotate counterclockwise and the rotating velocity is larger. At a lower blockage ratio, the anomalous clockwise rotation is more likely to occur, and the largest rotating velocity occurs when the blockage ratio is equal to 0.3. The mechanism of distinct rotational behavior of the cylinder is attributed to the transformation of distribution of shear stress which is resulted from the variation of pressure drop, the shift of maximum or minimum pressure zones along the upper and lower semi-cylinder surface, and the movement of stagnant point and separate point. Finally, the effects of the cylinder rotation on the flow structure and hydrodynamic force exerted on the cylinder surface are analyzed as well.

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.

Influence of rotation on the near-wake development behind an impulsively started circular cylinder

NASA Astrophysics Data System (ADS)

Coutanceau, M.; Menard, C.

1985-09-01

A rotating body, travelling through a fluid in such a way that the rotation axis is at right angles to the translational path, experiences a transverse force, called the Magnus force. The present study is concerned with a rotating cylinder which is in a state of translational motion. In the considered case, the existence of a lift force may be explained easily on the basis of the theory of inviscid fluids. An experimental investigation provides new information regarding the mechanism of the near-wake development of the classical unsteady flow and the influence of the rotational effects. Attention is given to the experimental technique, aspects of flow topology and notation, the time development of the wake flow pattern, the time evolution of certain flow properties, the flow structure in the neighborhood of the front stagnation point, and the influence of the Reynolds number on flow establishment.

Nonlinear travelling waves in rotating Hagen–Poiseuille flow

NASA Astrophysics Data System (ADS)

Pier, Benoît; Govindarajan, Rama

2018-03-01

The dynamics of viscous flow through a rotating pipe is considered. Small-amplitude stability characteristics are obtained by linearizing the Navier–Stokes equations around the base flow and solving the resulting eigenvalue problems. For linearly unstable configurations, the dynamics leads to fully developed finite-amplitude perturbations that are computed by direct numerical simulations of the complete Navier–Stokes equations. By systematically investigating all linearly unstable combinations of streamwise wave number k and azimuthal mode number m, for streamwise Reynolds numbers {{Re}}z ≤slant 500 and rotational Reynolds numbers {{Re}}{{Ω }} ≤slant 500, the complete range of nonlinear travelling waves is obtained and the associated flow fields are characterized.

Magnetic bucket for rotating unmagnetized plasma.

PubMed

Katz, Noam; Collins, Cami; Wallace, John; Clark, Mike; Weisberg, David; Jara-Almonte, Jon; Reese, Ingrid; Wahl, Carl; Forest, Cary

2012-06-01

A new experiment is described which generates flow in unmagnetized plasma. Confinement is provided by a cage of permanent magnets, arranged to form an axisymmetric, high-order, multipolar magnetic field. This field configuration-sometimes called a "magnetic bucket"-has a vanishingly small field in the core of the experiment. Toroidal rotation is driven by J × B forces applied in the magnetized edge. The cross-field current that is required for this forcing flows from anodes to thermionic cathodes, which are inserted between the magnet rings. The rotation at the edge reaches 3 km/s and is viscously coupled to the unmagnetized core plasma. We describe the conditions necessary for rotation, as well as a 0-dimensional power balance used to understand plasma confinement in the experiment.

Flow induced force of labyrinth seal

NASA Technical Reports Server (NTRS)

Iwatsubo, T.; Motooka, N.; Kawai, R.

1982-01-01

Flow induced instability force due to a labyrinth seal is analyzed. An approximate solution is given for the partial differential equation representing the flow in labyrinth seal and it is compared with the finite difference method in order to verify the accuracy of both methods. The effects of difference of inlet and outlet pressures of the seal, deflection of pressure and mass flow from the steady state, rotor diameter, seal clearance, seal interval and seal number on the flow induced force of the seal are investigated and it is known that some of these factors are very influential on the flow induced force.

An analysis of oscillatory hydromagnetic couette flow through a porous medium in a rotating system

NASA Astrophysics Data System (ADS)

Rajesh, K.; Govindarajan, A.; Vidhya, M.; Siva, E. P.

2018-04-01

Analysis of an exact solution of oscillatory Ekman boundary layer flow through a porous medium bounded by two horizontal flat plates is found. One of the plates is at rest and the other one is oscillating in its own plane. The whole of the system rotates about an axis normal to the plates. The effects of Coriolis force and the permeability of the porous medium on the flow field are studied. It is seen that even in the special case of resonance (w = 2Ω) the solution obtained by Mazumder is incorrect as contended by Ganapathy. It is found that the amplitude of the resultant velocity |A0| for the steady part increases with either an increase in the permeability parameter k0 (or) an increase in the rotation parameter R. But the above profiles have a reverse trend when there is an increase in the Hartmann number.

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.

Low Reynolds Number Wing Transients in Rotation and Translation

NASA Astrophysics Data System (ADS)

Jones, Anya; Schlueter, Kristy

2012-11-01

The unsteady aerodynamic forces and flow fields generated by a wing undergoing transient motions in both rotation and translation were investigated. An aspect ratio 2 flat plate wing at a 45 deg angle of attack was driven over 84 deg of rotation (3 chord-lengths of travel at 3/4 span) and 3 and 10 chord-lengths of translation in quiescent water at Reynolds numbers between 2,500 and 15,000. Flow visualization on the rotating wing revealed a leading edge vortex that lifted off of the wing surface, but remained in the vicinity of the wing for the duration of the wing stroke. A second spanwise vortex with strong axial flow was also observed. As the tip vortex grew, the leading edge vortex joined the tip vortex in a loop-like structure over the aft half of the wing. Near the leading edge, spanwise flow in the second vortex became entrained in the tip vortex near the corner of the wing. Unsteady force measurements revealed that lift coefficient increased through the constant-velocity portion of the wing stroke. Forces were compared for variations in wing acceleration and Reynolds number for both rotational and translational motions. The effect of tank blockage was investigated by repeating the experiments on multiple wings, varying the distance between the wing tip and tank wall. U.S. Air Force Research Laboratory, Summer Faculty Fellowship Program.

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.

Free and forced vibrations of an eccentrically rotating string on a viscoelastic foundation

NASA Astrophysics Data System (ADS)

Soedel, S. M.; Soedel, W.

1989-12-01

Equations of motion of an eccentrically rotating cord on a viscoelastic foundation, derived by way of Hamilton's principle, are solved for free and forced vibrations. The natural frequencies during rotation are bifurcations of the stationary string values. The natural modes are complex and can be interpreted as mode pairs spinning with and against the string rotation. The general forced solution is expanded in terms of these complex modes. Results are given for an example of steady state harmonic response because of its practical significance to aircraft or automobile tire design.

Hydraulic forces on a centrifugal impeller undergoing synchronous whirl

NASA Technical Reports Server (NTRS)

Allaire, P. E.; Sato, C. J.; Branagan, L. A.

1984-01-01

High speed centrifugal rotating machinery with large vibrations caused by aerodynamic forces on impellers was examined. A method to calculate forces in a two dimensional orbiting impeller in an unbounded fluid with nonuniform entering flow was developed. A finite element model of the full impeller is employed to solve the inviscid flow equations. Five forces acting on the impeller are: Coriolis forces, centripetal forces, changes in linear momentum, changes in pressure due to rotation and pressure changes due to linear momentum. Both principal and cross coupled stiffness coefficients are calculated for the impeller.

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.

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

DOE PAGES

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 thismore » 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.« less

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

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 thismore » 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.« less

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.

Pattern formation and three-dimensional instability in rotating flows

NASA Astrophysics Data System (ADS)

Christensen, Erik A.; Aubry, Nadine; Sorensen, Jens N.

1997-03-01

A fluid flow enclosed in a cylindrical container where fluid motion is created by the rotation of one end wall as a centrifugal fan is studied. Direct numerical simulations and spatio-temporal analysis have been performed in the early transition scenario, which includes a steady-unsteady transition and a breakdown of axisymmetric to three-dimensional flow behavior. In the early unsteady regime of the flow, the central vortex undergoes a vertical beating motion, accompanied by axisymmetric spikes formation on the edge of the breakdown bubble. As traveling waves, the spikes move along the central vortex core toward the rotating end-wall. As the Reynolds number is increased further, the flow undergoes a three-dimensional instability. The influence of the latter on the previous patterns is studied.

Control of finger forces during fast, slow and moderate rotational hand movements.

PubMed

Kazemi, Hamed; Kearney, Robert E; Milner, Theodore E

2014-01-01

The goal of this study was to investigate the effect of speed on patterns of grip forces during twisting movement involving forearm supination against a torsional load (combined elastic and inertial load). For slow and moderate speed rotations, the grip force increased linearly with load torque. However, for fast rotations in which the contribution of the inertia to load torque was significantly greater than slower movements, the grip force-load torque relationship could be segmented into two phases: a linear ascending phase corresponding to the acceleration part of the movement followed by a plateau during deceleration. That is, during the acceleration phase, the grip force accurately tracked the combined elastic and inertial load. However, the coupling between grip force and load torque was not consistent during the deceleration phase of the movement. In addition, as speed increased, both the position and the force profiles became smoother. No differences in the baseline grip force, safety margin to secure the grasp during hold phase or the overall change in grip force were observed across different speeds.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gorshunov, N. M., E-mail: gorshunov-nm@nrcki.ru; Potanin, E. P., E-mail: potanin45@yandex.ru

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 ofmore » 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.« less

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.

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.

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.

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.

Instabilities and spin-up behaviour of a rotating magnetic field driven flow in a rectangular cavity

NASA Astrophysics Data System (ADS)

Galindo, V.; Nauber, R.; Räbiger, D.; Franke, S.; Beyer, H.; Büttner, L.; Czarske, J.; Eckert, S.

2017-11-01

This study presents numerical simulations and experiments considering the flow of an electrically conducting fluid inside a cube driven by a rotating magnetic field (RMF). The investigations are focused on the spin-up, where a liquid metal (GaInSn) is suddenly exposed to an azimuthal body force generated by the RMF and the subsequent flow development. The numerical simulations rely on a semi-analytical expression for the induced electromagnetic force density in an electrically conducting medium inside a cuboid container with insulating walls. Velocity distributions in two perpendicular planes are measured using a novel dual-plane, two-component ultrasound array Doppler velocimeter with continuous data streaming, enabling long term measurements for investigating transient flows. This approach allows identifying the main emerging flow modes during the transition from stable to unstable flow regimes with exponentially growing velocity oscillations using the Proper Orthogonal Decomposition method. Characteristic frequencies in the oscillating flow regimes are determined in the super critical range above the critical magnetic Taylor number T ac≈1.26 ×1 05, where the transition from the steady double vortex structure of the secondary flow to an unstable regime with exponentially growing oscillations is detected. The mean flow structures and the temporal evolution of the flow predicted by the numerical simulations and observed in experiments are in very good agreement.

Visualization of a vortex flow in a rotating tank

NASA Astrophysics Data System (ADS)

Kawano, Yosuke

Flow structures of a vortex in a rotating tank were studied employing tracer method. The velocity measurements were made by photographing the motions of small polystyrene particles and analyzing strobo flash light pictures. The vortex flow is confined to a cylindrical region which is composed of a spiral upward flow in the center surrounded by an annular downward flow.

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.

Numerical simulation of fluid flow in a rotational bioreactor

NASA Astrophysics Data System (ADS)

Ganimedov, V. L.; Papaeva, E. O.; Maslov, N. A.; Larionov, P. M.

2017-10-01

Application of scaffold technology for the problem of bone tissue regeneration has great prospects in modern medicine. The influence of fluid shear stress on stem cells cultivation and its differentiation into osteoblasts is the subject of intensive research. Mathematical modeling of fluid flow in bioreactor allowed us to determine the structure of flow and estimate the level of mechanical stress on cells. The series of computations for different rotation frequencies (0.083, 0.124, 0.167, 0.2 and 0.233 Hz) was performed for the laminar flow regime approximation. It was shown that the Taylor vortices in the gap between the cylinders qualitatively change the distribution of static pressure and shear stress in the region of vortices connection. It was shown that an increase in the rotation frequency leads to an increase of the unevenness in distribution of the above mentioned functions. The obtained shear stress and static pressure dependence on the rotational frequency make it possible to choose the operating mode of the reactor depending on the provided requirements. It was shown that in the range of rotation frequencies chosen in this work (0.083 < f < 0.233 Hz), the shear stress does not exceed the known literature data (0.002 - 0.1 Pa).

Flow Structure and Force Variation with Aspect Ratio for a Two-Degree-of-Freedom Flapping Wing

NASA Astrophysics Data System (ADS)

Burge, Matthew; Favale, James; Ringuette, Matthew

2014-11-01

We investigate experimentally the effect of aspect ratio (AR) on the flow structure and forces of a two-degree-of-freedom flapping wing. Flapping wings are known to produce complex and unsteady vortex loop structures, and the objective is to characterize their variation with AR and how this influences the lift force. Previous results on rotating wings demonstrated that changes in AR significantly affect the three-dimensional flow structure and lift coefficient. This is primarily due to the relatively greater influence of the tip vortex for lower AR. At Reynolds number of order O(103) we test wings of AR = 2-4, values typically found in nature, with simplified planform shapes. The lift force is measured using a submersible transducer at the base of the wing in a glycerin-water mixture. The qualitative, three-dimensional vortex loop structure for different ARs is obtained using multi-color dye flow visualization. Guided by this, quantitative three-component flow information, namely vorticity, the Q-criterion, and circulation, is acquired from stereoscopic particle image velocimetry in key planes. Of interest is how these parameters and the vortex loop topology vary with AR, and their connection to features in the unsteady force signal. This work is supported by the National Science Foundation, Award Number 1336548, supervised by Dr. Dimitrios Papavassiliou.

Recirculation cells for granular flow in cylindrical rotating tumblers

NASA Astrophysics Data System (ADS)

D'Ortona, Umberto; Thomas, Nathalie; Lueptow, Richard M.

2018-05-01

To better understand the velocity field and flowing layer structure, we have performed a detailed discrete element method study of the flow of monodisperse particles in a partially filled three-dimensional cylindrical rotating tumblers. Similar to what occurs near the poles in spherical and conical tumblers, recirculation cells (secondary flows) develop near the flat endwalls of a cylindrical tumbler in which particles near the surface drift axially toward the endwall, while particles deeper in the flowing layer drift axially toward the midlength of the tumbler. Another recirculation cell with the opposite sense develops next to each endwall recirculation cell, extending to the midlength of the tumbler. For a long enough tumbler, each endwall cell is about one quarter of the tumbler diameter in length. Endwall cells are insensitive to tumbler length and relatively insensitive to rotation speed (so long as the flowing layer remains flat and continuously flowing) or fill level (from 25% to 50% full). However, for shorter tumblers (0.5 to 1.0 length/diameter aspect ratio) the endwall cell size does not change much, while center cells reduce their size and eventually disappear for the shortest tumblers. For longer tumblers (length/diameter aspect ratio larger than 2), a stagnation zone appears in between the central cells. These results provide insight into the mixing of monodisperse particles in rotating cylindrical tumblers as well as the frictional effects of the tumbler endwalls.

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.

Numerical analysis on the action of centrifuge force in magnetic fluid rotating shaft seals

NASA Astrophysics Data System (ADS)

Zou, Jibin; Li, Xuehui; Lu, Yongping; Hu, Jianhui

2002-11-01

The magnetic fluid seal is suitable for high-speed rotating shaft seal applications. Centrifuge force will have evident influence on magnetic fluid rotating shaft seals. The seal capacity of the rotating shaft seal can be improved or increased by some measures. Through hydrodynamic analysis the moving status of the magnetic fluid is worked out. By numerical method, the magnetic field and the isobars in the magnetic fluid of a seal device are computed. Then the influence of the centrifuge force on the magnetic fluid seal is calculated quantitatively.

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.

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

Transitions in rapidly rotating convection dynamos

NASA Astrophysics Data System (ADS)

Tilgner, A.

2013-12-01

It is commonly assumed that buoyancy in the fluid core powers the geodynamo. We study here the minimal model of a convection driven dynamo, which is a horizontal plane layer in a gravity field, filled with electrically conducting fluid, heated from below and cooled from above, and rotating about a vertical axis. Such a plane layer may be viewed as a local approximation to the geophysically more relevant spherical geometry. The numerical simulations have been run on graphics processing units with at least 960 cores. If the convection is driven stronger and stronger at fixed rotation rate, the flow behaves at some point as if it was not rotating. This transition shows in the scaling of the heat transport which can be used to distinguish slow from rapid rotation. One expects dynamos to behave differently in these two flow regimes. But even within the convection flows which are rapidly rotating according to this criterion, it will be shown that different types of dynamos exist. In one state, the magnetic field strength obeys a scaling indicative of a magnetostrophic balance, in which the Lorentz force is in equilibrium with the Coriolis force. The flow in this case is helical. A different state exists at higher magnetic Reynolds numbers, in which the magnetic energy obeys a different scaling law and the helicity of the flow is much reduced. As one increases the Rayleigh number, all other parameters kept constant, one may find both types of dynamos separated by an interval of Rayleigh numbers in which there are no dynamos at all. The effect of these transitions on energy dissipation and mean field generation have also been studied.

Flow visualization around a rotating body in a wind tunnel

NASA Astrophysics Data System (ADS)

Hiraki, K.; Zaitsu, D.; Yanaga, Y.; Kleine, H.

2017-02-01

The rotational behavior of capsule-shaped models is investigated in the transonic wind tunnel of JAXA. A special support is developed to allow the model to rotate around the pitch, yaw and roll axes. This 3-DOF free rotational mounting apparatus achieves the least frictional torque from the support and the instruments. Two types of capsule models are prepared, one is drag type (SPH model) and the other is lift type (HTV-R model). The developed mounting apparatus is used in the wind tunnel tests with these capsule models. In a flow of Mach 0.9, the SPH model exhibits oscillations in pitch and yaw, and it rolls half a turn during the test. Similarly, the HTV-R model exhibits pitch and yaw oscillations in a flow of Mach 0.5. Moreover, it rolls multiple times during the test. In order to investigate the flow field around the capsule, the combined technique of color schlieren and surface tufts is applied. This visualization clearly shows the flow reattachment on the back surface of a capsule, which is suspected to induce the rapid rolling motion.

Modeling the dissipation rate in rotating turbulent flows

NASA Technical Reports Server (NTRS)

Speziale, Charles G.; Raj, Rishi; Gatski, Thomas B.

1990-01-01

A variety of modifications to the modeled dissipation rate transport equation that have been proposed during the past two decades to account for rotational strains are examined. The models are subjected to two crucial test cases: the decay of isotropic turbulence in a rotating frame and homogeneous shear flow in a rotating frame. It is demonstrated that these modifications do not yield substantially improved predictions for these two test cases and in many instances give rise to unphysical behavior. An alternative proposal, based on the use of the tensor dissipation rate, is made for the development of improved models.

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.

Flow separation on flapping and rotating profiles with spanwise gradients.

PubMed

Wong, J G; laBastide, B P; Rival, D E

2017-02-15

The growth of leading-edge vortices (LEV) on analogous flapping and rotating profiles has been investigated experimentally. Three time-varying cases were considered: a two-dimensional reference case with a spanwise-uniform angle-of-attack variation α; a case with increasing α towards the profile tip (similar to flapping flyers); and a case with increasing α towards the profile root (similar to rotor blades experiencing an axial gust). It has been shown that the time-varying spanwise angle-of-attack gradient produces a vorticity gradient, which, in combination with spanwise flow, results in a redistribution of circulation along the profile. Specifically, when replicating the angle-of-attack gradient characteristic of a rotor experiencing an axial gust, the spanwise-vorticity gradient is aligned such that circulation increases within the measurement domain. This in turn increases the local LEV growth rate, which is suggestive of force augmentation on the blade. Reversing the relative alignment of the spanwise-vorticity gradient and spanwise flow, thereby replicating that arrangement found in a flapping flyer, was found to reduce local circulation. From this, we can conclude that spanwise flow can be arranged to vary LEV growth to prolong lift augmentation and reduce the unsteadiness of cyclic loads.

Weak rotating flow disturbances in a centrifugal compressor with a vaneless diffuser

NASA Technical Reports Server (NTRS)

Moore, F. K.

1988-01-01

A theory is presented to predict the occurrence of weak rotating waves in a centrifugal compression system with a vaneless diffuser. As in a previous study of axial systems, an undisturbed performance characteristic is assumed known. Following an inviscid analysis of the diffuser flow, conditions for a neutral rotating disturbance are found. The solution is shown to have two branches; one with fast rotation, the other with very slow rotation. The slow branch includes a dense set of resonant solutions. The resonance is a feature of the diffuser flow, and therefore such disturbances must be expected at the various resonant flow coefficients regardless of the compressor characteristic. Slow solutions seem limited to flow coefficients less than about 0.3, where third and fourth harmonics appear. Fast waves seem limited to a first harmonic. These fast and slow waves are described, and effects of diffuser-wall convergence, backward blade angles, and partial recovery of exit velocity head are assessed.

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.

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.

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.

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.

On effects of topography in rotating flows

NASA Astrophysics Data System (ADS)

Burmann, Fabian; Noir, Jerome; Jackson, Andrew

2017-11-01

Both, seismological studies and geodynamic arguments suggest that there is significant topography at the core mantle boundary (CMB). This leads to the question whether the topography of the CMB could influence the flow in the Earth's outer core. As a preliminary experiment, we investigate the effects of bottom topography in the so-called Spin-Up, where motion of a contained fluid is created by a sudden increase of rotation rate. Experiments are performed in a cylindrical container mounted on a rotating table and quantitative results are obtained with particle image velocimetry. Several horizontal length scales of topography (λ) are investigated, ranging from cases where λ is much smaller then the lateral extend of the experiment (R) to cases where λ is a fraction of R. We find that there is an optimal λ that creates maximum dissipation of kinetic energy. Depending on the length scale of the topography, kinetic energy is either dissipated in the boundary layer or in the bulk of the fluid. Two different phases of fluid motion are present: a starting flow in the from of solid rotation (phase I), which is later replaced by meso scale vortices on the length scale of bottom topography (phase II).

Direct and inverse energy cascades in a forced rotating turbulence experiment

NASA Astrophysics Data System (ADS)

Campagne, Antoine; Gallet, Basile; Moisy, Frédéric; Cortet, Pierre-Philippe

2014-12-01

We present experimental evidence for a double cascade of kinetic energy in a statistically stationary rotating turbulence experiment. Turbulence is generated by a set of vertical flaps, which continuously injects velocity fluctuations towards the center of a rotating water tank. The energy transfers are evaluated from two-point third-order three-component velocity structure functions, which we measure using stereoscopic particle image velocimetry in the rotating frame. Without global rotation, the energy is transferred from large to small scales, as in classical three-dimensional turbulence. For nonzero rotation rates, the horizontal kinetic energy presents a double cascade: a direct cascade at small horizontal scales and an inverse cascade at large horizontal scales. By contrast, the vertical kinetic energy is always transferred from large to small horizontal scales, a behavior reminiscent of the dynamics of a passive scalar in two-dimensional turbulence. At the largest rotation rate, the flow is nearly two-dimensional, and a pure inverse energy cascade is found for the horizontal energy. To describe the scale-by-scale energy budget, we consider a generalization of the Kármán-Howarth-Monin equation to inhomogeneous turbulent flows, in which the energy input is explicitly described as the advection of turbulent energy from the flaps through the surface of the control volume where the measurements are performed.

Small-scale anisotropy induced by spectral forcing and by rotation in non-helical and helical turbulence

NASA Astrophysics Data System (ADS)

Vallefuoco, Donato; Naso, Aurore; Godeferd, Fabien S.

2018-02-01

We study the effect of large-scale spectral forcing on the scale-dependent anisotropy of the velocity field in direct numerical simulations of homogeneous turbulence. ABC-type forcing and helical or non-helical Euler-type forcing are considered. We propose a scale-dependent characterisation of anisotropy based on a modal decomposition of the two-point velocity tensor spectrum. This produces direction-dependent spectra of energy, helicity and polarisation. We examine the conditions that allow anisotropy to develop in the small scales due to forcing and we show that the theoretically expected isotropy is not exactly obtained, even in the smallest scales, for ABC and helical Euler forcings. When adding rotation, the anisotropy level in ABC-forced simulations is similar to that of lower Rossby number Euler-forced runs. Moreover, even at low rotation rate, the natural anisotropy induced by the Coriolis force is visible at all scales, and two distinct wavenumber ranges appear from our fine-grained characterisation, not separated by the Zeman scale but by a scale where rotation and dissipation are balanced.

Rotating reactor studies

NASA Technical Reports Server (NTRS)

Roberts, Glyn O.

1991-01-01

Undesired gravitational effects such as convection or sedimentation in a fluid can sometimes be avoided or decreased by the use of a closed chamber uniformly rotated about a horizontal axis. In a previous study, the spiral orbits of a heavy or buoyant particle in a uniformly rotating fluid were determined. The particles move in circles, and spiral in or out under the combined effects of the centrifugal force and centrifugal buoyancy. A optimization problem for the rotation rate of a cylindrical reactor rotated about its axis and containing distributed particles was formulated and solved. Related studies in several areas are addressed. A computer program based on the analysis was upgraded by correcting some minor errors, adding a sophisticated screen-and-printer graphics capability and other output options, and by improving the automation. The design, performance, and analysis of a series of experiments with monodisperse polystyrene latex microspheres in water were supported to test the theory and its limitations. The theory was amply confirmed at high rotation rates. However, at low rotation rates (1 rpm or less) the assumption of uniform solid-body rotation of the fluid became invalid, and there were increasingly strong secondary motions driven by variations in the mean fluid density due to variations in the particle concentration. In these tests the increase in the mean fluid density due to the particles was of order 0.015 percent. To a first approximation, these flows are driven by the buoyancy in a thin crescent-shaped depleted layer on the descending side of the rotating reactor. This buoyancy distribution is balanced by viscosity near the walls, and by the Coriolis force in the interior. A full analysis is beyond the scope of this study. Secondary flows are likely to be stronger for buoyant particles, which spiral in towards the neutral point near the rotation axis under the influence of their centrifugal buoyancy. This is because the depleted layer is

Forces on particles in microstreaming flows

NASA Astrophysics Data System (ADS)

Hilgenfeldt, Sascha; Rallabandi, Bhargav; Thameem, Raqeeb

2015-11-01

In various microfluidic applications, vortical steady streaming from ultrasonically driven microbubbles is used in concert with a pressure-driven channel flow to manipulate objects. While a quantitative theory of this boundary-induced streaming is available, little work has been devoted to a fundamental understanding of the forces exerted on microparticles in boundary streaming flows, even though the differential action of such forces is central to applications like size-sensitive sorting. Contrary to other microfluidic sorting devices, the forces in bubble microstreaming act over millisecond times and micron length scales, without the need for accumulated deflections over long distances. Accordingly, we develop a theory of hydrodynamic forces on the fast time scale of bubble oscillation using the lubrication approximation, showing for the first time how particle displacements are rectified near moving boundaries over multiple oscillations in parallel with the generation of the steady streaming flow. The dependence of particle migration on particle size and the flow parameters is compared with experimental data. The theory is applicable to boundary streaming phenomena in general and demonstrates how particles can be sorted very quickly and without compromising device throughput. We acknowledge support by the National Science Foundation under grant number CBET-1236141.

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

Inverse Magnus force in free molecular flow

NASA Astrophysics Data System (ADS)

Herczynski, A.; Weidman, P.

2003-11-01

The sidewise force on a spinning sphere translating in a rarified gas is calculated assuming that the flow can be treated as a stream of free molecules. This approach was first introduced by Newton in his investigation of the drag force. While it is not fruitful at subsonic flows in normal conditions, it gives remarkably accurate results at hypersonic speeds. Here it is applied to the high Knudsen number flow over spinning spheres, cylinders, cubes and more generally any spinning parallelepiped. In all cases, the force is in the opposite direction to that of the classical Magnus effect in continuum flow. The simple calculation for a sphere reproduces the isothermal result obtained recently by Borg, et al. (Phys. Fluids, 15, 2003) using Maxwellian distribution functions. For any parallelepiped, including the cube, just like for the sphere and the cylinder, the force is shown to be steady. In each of these, the magnitude of the inverse Magnus force is proprtional to the product of the angular speed, translational speed, and the mas of the gas displaced by the object.

On the development of lift and drag in a rotating and translating cylinder

NASA Astrophysics Data System (ADS)

Martin-Alcantara, Antonio; Sanmiguel-Rojas, Enrique; Fernandez-Feria, Ramon

2014-11-01

The two-dimensional flow around a rotating cylinder is investigated numerically using a vorticity forces formulation with the aim of analyzing the flow structures, and their evolutions, that contribute to the lift and drag forces on the cylinder. The Reynolds number, based on the cylinder diameter and steady free-stream speed, considered is Re = 200 , while the non-dimensional rotation rate (ratio of the surface speed and free-stream speed) selected were α = 1 and 3. For α = 1 the wake behind the cylinder for the fully developed flow is oscillatory due to vortex shedding, and so are the lift and drag forces. For α = 3 the fully developed flow is steady with constant (high) lift and (low) drag. Each of these cases is considered in two different transient problems, one with angular acceleration of the cylinder and constant speed, and the other one with translating acceleration of the cylinder and constant rotation. Special attention is paid to explaining the mechanisms of vortex shedding suppression for high rotation (when α = 3) and its relation to the mechanisms by which the lift is enhanced and the drag is almost suppressed when the fully developed flow is reached. Supported by the Ministerio de Economia y Competitividad of Spain Grant No. DPI2013-40479-P.

Knudsen torque: A rotational mechanism driven by thermal force

NASA Astrophysics Data System (ADS)

Li, Qi; Liang, Tengfei; Ye, Wenjing

2014-09-01

Thermally induced mechanical loading has been shown to have significant effects on micro- and nano-objects immersed in a gas with a nonuniform temperature field. While the majority of existing studies and related applications focus on forces, we investigate the torque, and thus the rotational motion, produced by such a mechanism. Our study has found that a torque can be induced if the configuration of the system is asymmetric. In addition, both the magnitude and the direction of the torque depend highly on the system configuration, indicating the possibility of manipulating the rotational motion via geometrical design. Based on this feature, two types of rotational micromotor that are of practical importance, namely pendulum motor and unidirectional motor, are designed. The magnitude of the torque at Kn =0.5 can reach to around 2nN×μm for a rectangular microbeam with a length of 100μm.

Unsteady flow of fractional Oldroyd-B fluids through rotating annulus

NASA Astrophysics Data System (ADS)

Tahir, Madeeha; Naeem, Muhammad Nawaz; Javaid, Maria; Younas, Muhammad; Imran, Muhammad; Sadiq, Naeem; Safdar, Rabia

2018-04-01

In this paper exact solutions corresponding to the rotational flow of a fractional Oldroyd-B fluid, in an annulus, are determined by applying integral transforms. The fluid starts moving after t = 0+ when pipes start rotating about their axis. The final solutions are presented in the form of usual Bessel and hypergeometric functions, true for initial and boundary conditions. The limiting cases for the solutions for ordinary Oldroyd-B, fractional Maxwell and Maxwell and Newtonian fluids are obtained. Moreover, the solution is obtained for the fluid when one pipe is rotating and the other one is at rest. At the end of this paper some characteristics of fluid motion, the effect of the physical parameters on the flow and a correlation between different fluid models are discussed. Finally, graphical representations confirm the above affirmation.

Gyroscopic analogy of a rotating stratified flow confined in a tilted spheroid and its implication to stability of a heavy symmetrical top

NASA Astrophysics Data System (ADS)

Fukumoto, Yasuhide; Miyachi, Yuki

2017-11-01

We address the suppression of the gravitational instability of rotating stratified flows in a confined geometry in two ways, continuous and discontinuous stratification. A rotating flow of a stratified fluid confined in an ellipsoid, subject to gravity force, whose velocity and density fields are linear in coordinates, bears an analogy with a mechanical system of finite degrees of freedom, that is, a heavy rigid body. An insight is gained into the mechanism of system rotation for the ability of a lighter fluid of sustaining, on top of it, a heavier fluid when the angular velocity is greater than a critical value. The sleeping top corresponds to such a state. First we show that a rotating stratified flow confined in a tilted spheroid is equivalent to a heavy symmetrical top with the symmetric axis tilted from the top axis. This tilting effect of the symmetric axis on the linear stability of the sleeping top and its bifurcation is investigated in some detail. Second, we explore the incompressible two-layer RTI of a discontinuously stratified fluid confined in the lower-half of an upright spheroid rotating about the axis of symmetry oriented parallel to the vertical direction. The gyroscopic analogy accounts for decrease of the critical rotation rate with oblateness. This work was supported in part by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (Grant No. 16K05476).

Cohesive forces prevent the rotational breakup of rubble-pile asteroid (29075) 1950 DA.

PubMed

Rozitis, Ben; MacLennan, Eric; Emery, Joshua P

2014-08-14

Space missions and ground-based observations have shown that some asteroids are loose collections of rubble rather than solid bodies. The physical behaviour of such 'rubble-pile' asteroids has been traditionally described using only gravitational and frictional forces within a granular material. Cohesive forces in the form of small van der Waals forces between constituent grains have recently been predicted to be important for small rubble piles (ten kilometres across or less), and could potentially explain fast rotation rates in the small-asteroid population. The strongest evidence so far has come from an analysis of the rotational breakup of the main-belt comet P/2013 R3 (ref. 7), although that was indirect and poorly constrained by observations. Here we report that the kilometre-sized asteroid (29075) 1950 DA (ref. 8) is a rubble pile that is rotating faster than is allowed by gravity and friction. We find that cohesive forces are required to prevent surface mass shedding and structural failure, and that the strengths of the forces are comparable to, though somewhat less than, the forces found between the grains of lunar regolith.

Experimental study on rotating instability mode characteristics of axial compressor tip flow

NASA Astrophysics Data System (ADS)

Tian, Jie; Yao, Dan; Wu, Yadong; Ouyang, Hua

2018-04-01

This paper investigates the rotating instabilities that occurred on the single-stage axial compressor designed for aerodynamic performance validation, which was tested with two sets of circumferential measuring points in combination. Circumferential mode characteristics of compressors are usually too high to be captured experimentally, and aliasing of the circumferential mode order occurs when not enough sensors are used. A calibration and prediction method to capture the higher circumferential mode of unsteady flow in a compressor was proposed. Unsteady pressure fluctuations near the tip region in an axial compressor were studied, and high circumferential mode characteristics were captured on both the blade passing frequency (BPF) and the rotational instability frequency (RIF) under different flow rate conditions based on this novel method. The characteristic RI spectrum with a broadband hump was present in a large range of flow conditions. Both the frequency range and the dominant circumferential mode order decreased as the flow rate decreased. Based on the calibrated mode characteristics, a rotating aerodynamic source model is used to explain the side-by-side peak of RIF spectrum and rotating characteristics of RI. The calibration and prediction method of the high circumferential mode is beneficial for the research of unsteady flow in an axial compressor.

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.

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

Experimental investigation of the microscale rotor-stator cavity flow with rotating superhydrophobic surface

NASA Astrophysics Data System (ADS)

Wang, Chunze; Tang, Fei; Li, Qi; Wang, Xiaohao

2018-03-01

The flow characteristics of microscale rotor-stator cavity flow and the drag reduction mechanism of the superhydrophobic surface with high shearing stress were investigated. A microscale rotating flow testing system was established based on micro particle image velocimetry (micro-PIV), and the flow distribution under different Reynolds numbers (7.02 × 103 ≤ Re ≤ 3.51 × 104) and cavity aspect ratios (0.013 ≤ G ≤ 0.04) was measured. Experiments show that, for circumferential velocity, the flow field distributes linearly in rotating Couette flow in the case of low Reynolds number along the z-axis, while the boundary layer separates and forms Batchelor flow as the Reynolds number increases. The separation of the boundary layer is accelerated with the increase of cavity aspect ratio. The radial velocities distribute in an S-shape along the z-axis. As the Reynolds number and cavity aspect ratio increase, the maximum value of radial velocity increases, but the extremum position at rotating boundary remains at Z* = 0.85 with no obvious change, while the extremum position at the stationary boundary changes along the z-axis. The model for the generation of flow disturbance and the transmission process from the stationary to the rotating boundary was given by perturbation analysis. Under the action of superhydrophobic surface, velocity slip occurs near the rotating boundary and the shearing stress reduces, which leads to a maximum drag reduction over 51.4%. The contours of vortex swirling strength suggest that the superhydrophobic surface can suppress the vortex swirling strength and repel the vortex structures, resulting in the decrease of shearing Reynolds stress and then drag reduction.

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.

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

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.

Numerical simulation and experimental research of the flow force and forced vibration in the nozzle-flapper valve

NASA Astrophysics Data System (ADS)

Li, Lei; Yan, Hao; Zhang, Hengxuan; Li, Jing

2018-01-01

In the pilot stage of nozzle-flapper servo valve, the flow force on the flapper is the key reason that leads to forced vibration of the armature assembly, which may result in the fatigue of the flexure tube in torque motor. To master the principles and features of the flow force and the source of the forced vibration of the armature assembly, mathematical models of flow force and the forced vibration are deduced in this paper. For validating the model, a three-dimensional model is built and a finite element analysis of the flow force with different inlet pressure and deflections is presented and an innovative and experimental rig for measuring the steady and dynamic frequency of flow force is also designed. The characteristic of the main flow force, minor flow force and total flow force are analyzed contrastively, and the experimental results agree well with the CFD results and mathematical model analysis. To find the source of forced vibration of the armature assembly, a knocking method is proposed to measure the natural frequency of armature assembly. By comparing the spectrum of the pressure and vibration movement through experiments, a conclusion can be drawn that the inlet pressure fluctuation near the natural frequency of armature assembly and the asymmetric structure of pilot stage are the necessary and sufficient conditions to make the armature assembly yield forced vibration. In the end, some suggestions have been made to decrease the intensity of forced vibration of the pilot stage according to the findings.

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).

Dynamo Induced by Time-periodic Force

NASA Astrophysics Data System (ADS)

Wei, Xing

2018-03-01

To understand the dynamo driven by time-dependent flow, e.g., turbulence, we investigate numerically the dynamo induced by time-periodic force in rotating magnetohydrodynamic flow and focus on the effect of force frequency on the dynamo action. It is found that the dynamo action depends on the force frequency. When the force frequency is near resonance the force can drive dynamo, but when it is far away from resonance dynamo fails. In the frequency range near resonance to support dynamo, the force frequency at resonance induces a weak magnetic field and magnetic energy increases as the force frequency deviates from the resonant frequency. This is opposite to the intuition that a strong flow at resonance will induce a strong field. It is because magnetic field nonlinearly couples with fluid flow in the self-sustained dynamo and changes the resonance of driving force and inertial wave.

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.

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.

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.

Scaling laws in granular flow and pedestrian flow

NASA Astrophysics Data System (ADS)

Chen, Shumiao; Alonso-Marroquin, Fernando; Busch, Jonathan; Hidalgo, Raúl Cruz; Sathianandan, Charmila; Ramírez-Gómez, Álvaro; Mora, Peter

2013-06-01

We use particle-based simulations to examine the flow of particles through an exit. Simulations involve both gravity-driven particles (representing granular material) and velocity-driven particles (mimicking pedestrian dynamics). Contact forces between particles include elastic, viscous, and frictional forces; and simulations use bunker geometry. Power laws are observed in the relation between flow rate and exit width. Simulations of granular flow showed that the power law has little dependence on the coefficient of friction. Polydisperse granular systems produced higher flow rates than those produced by monodisperse ones. We extend the particle model to include the main features of pedestrian dynamics: thoracic shape, shoulder rotation, and desired velocity oriented towards the exit. Higher desired velocity resulted in higher flow rate. Granular simulations always give higher flow rate than pedestrian simulations, despite the values of aspect ratio of the particles. In terms of force distribution, pedestrians and granulates share similar properties with the non-democratic distribution of forces that poses high risks of injuries in a bottleneck situation.

Large-scale flows, sheet plumes and strong magnetic fields in a rapidly rotating spherical dynamo

NASA Astrophysics Data System (ADS)

Takahashi, F.

2011-12-01

Mechanisms of magnetic field intensification by flows of an electrically conducting fluid in a rapidly rotating spherical shell is investigated. Bearing dynamos of the Eartn and planets in mind, the Ekman number is set at 10-5. A strong dipolar solution with magnetic energy 55 times larger than the kinetic energy of thermal convection is obtained. In a regime of small viscosity and inertia with the strong magnetic field, convection structure consists of a few large-scale retrograde flows in the azimuthal direction and sporadic thin sheet-like plumes. The magnetic field is amplified through stretching of magnetic lines, which occurs typically through three types of flow: the retrograde azimuthal flow near the outer boundary, the downwelling flow of the sheet plume, and the prograde azimuthal flow near the rim of the tangent cylinder induced by the downwelling flow. It is found that either structure of current loops or current sheets is accompanied in each flow structure. Current loops emerge as a result of stretching the magnetic lines along the magnetic field, wheres the current sheets are formed to counterbalance the Coriolis force. Convection structure and processes of magnetic field generation found in the present model are distinct from those in models at larger/smaller Ekman number.

The sound field of a rotating dipole in a plug flow.

PubMed

Wang, Zhao-Huan; Belyaev, Ivan V; Zhang, Xiao-Zheng; Bi, Chuan-Xing; Faranosov, Georgy A; Dowell, Earl H

2018-04-01

An analytical far field solution for a rotating point dipole source in a plug flow is derived. The shear layer of the jet is modelled as an infinitely thin cylindrical vortex sheet and the far field integral is calculated by the stationary phase method. Four numerical tests are performed to validate the derived solution as well as to assess the effects of sound refraction from the shear layer. First, the calculated results using the derived formulations are compared with the known solution for a rotating dipole in a uniform flow to validate the present model in this fundamental test case. After that, the effects of sound refraction for different rotating dipole sources in the plug flow are assessed. Then the refraction effects on different frequency components of the signal at the observer position, as well as the effects of the motion of the source and of the type of source are considered. Finally, the effect of different sound speeds and densities outside and inside the plug flow is investigated. The solution obtained may be of particular interest for propeller and rotor noise measurements in open jet anechoic wind tunnels.

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.

Force-moment line element method for flexible slender bodies in Stokes flow.

PubMed

Jiang, H; Yang, B

2013-09-01

The hydrodynamics of flexible slender bodies in Stokes flow is studied by taking into account the fluid-structure interaction through both forces and coupled moments. The fluid subjected to line sources of forces and moments is described by using integral equations. Meanwhile, the flexible slender body is modeled using finite beam elements. The two sides are linked through interfacial continuity conditions. Upon discretization, it results in a higher-order line element method for efficient and accurate solution of slender-body hydrodynamics. Four examples are presented to demonstrate the validity and efficiency of the present method: (a) hydrodynamics of a flexible slender rod subjected to a torque at one end, (b) hydrodynamics of a flexible slender rod subjected to a bending moment at one end, (c) hydrodynamics of a flexible slender rod subjected to a cyclic force, and (d) hydrodynamics of a flexible slender rod with a magnetized head within a rotating magnetic field. Examples (a) and (b) may serve as benchmark solutions and examples (c) and (d) show how planar and spiral waves can be excited in a slender body.

Fluid flows and forces in development: functions, features and biophysical principles

PubMed Central

Freund, Jonathan B.; Goetz, Jacky G.; Hill, Kent L.; Vermot, Julien

2012-01-01

Throughout morphogenesis, cells experience intracellular tensile and contractile forces on microscopic scales. Cells also experience extracellular forces, such as static forces mediated by the extracellular matrix and forces resulting from microscopic fluid flow. Although the biological ramifications of static forces have received much attention, little is known about the roles of fluid flows and forces during embryogenesis. Here, we focus on the microfluidic forces generated by cilia-driven fluid flow and heart-driven hemodynamics, as well as on the signaling pathways involved in flow sensing. We discuss recent studies that describe the functions and the biomechanical features of these fluid flows. These insights suggest that biological flow determines many aspects of cell behavior and identity through a specific set of physical stimuli and signaling pathways. PMID:22395739

Intracycle angular velocity control of cross-flow turbines

NASA Astrophysics Data System (ADS)

Strom, Benjamin; Brunton, Steven L.; Polagye, Brian

2017-08-01

Cross-flow turbines, also known as vertical-axis turbines, are attractive for power generation from wind and water currents. Some cross-flow turbine designs optimize unsteady fluid forces and maximize power output by controlling blade kinematics within one rotation. One established method is to dynamically pitch the blades. Here we introduce a mechanically simpler alternative: optimize the turbine rotation rate as a function of angular blade position. We demonstrate experimentally that this approach results in a 59% increase in power output over standard control methods. Analysis of fluid forcing and blade kinematics suggest that power increase is achieved through modification of the local flow conditions and alignment of fluid force and rotation rate extrema. The result is a low-speed, structurally robust turbine that achieves high efficiency and could enable a new generation of environmentally benign turbines for renewable power generation.

Design parameters for rotating cylindrical filtration

NASA Technical Reports Server (NTRS)

Schwille, John A.; Mitra, Deepanjan; Lueptow, Richard M.

2002-01-01

Rotating cylindrical filtration displays significantly reduced plugging of filter pores and build-up of a cake layer, but the number and range of parameters that can be adjusted complicates the design of these devices. Twelve individual parameters were investigated experimentally by measuring the build-up of particles on the rotating cylindrical filter after a fixed time of operation. The build-up of particles on the filter depends on the rotational speed, the radial filtrate flow, the particle size and the gap width. Other parameters, such as suspension concentration and total flow rate are less important. Of the four mechanisms present in rotating filters to reduce pore plugging and cake build-up, axial shear, rotational shear, centrifugal sedimentation and vortical motion, the evidence suggests rotational shear is the dominant mechanism, although the other mechanisms still play minor roles. The ratio of the shear force acting parallel to the filter surface on a particle to the Stokes drag acting normal to the filter surface on the particle due to the difference between particle motion and filtrate flow can be used as a non-dimensional parameter that predicts the degree of particle build-up on the filter surface for a wide variety of filtration conditions. c2002 Elsevier Science B.V. All rights reserved.

Flow and Heat Transfer in 180-Degree Turn Square Ducts: Effects of Turning Configuration and System Rotation

NASA Technical Reports Server (NTRS)

Wang, Ten-See; Chyu, Ming-King

1993-01-01

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.

The flow of a thin liquid film on a stationary and rotating disk. I - Experimental analysis and flow visualization

NASA Technical Reports Server (NTRS)

Thomas, S.; Faghri, A.; Hankey, W.

1990-01-01

The mean thickness of a thin liquid film of deionized water with a free surface on a stationary and rotating horizontal disk has been measured with a nonobtrusive capacitance technique. The measurements were taken when the rotational speed was 0-300 RPM and the flow rate was 7.0-15.0 LPM. A flow visualization study of the thin film was also performed to determine the characteristics of the waves on the free surface. When the disk was stationary, a circular hydraulic jump was present on the disk. Surface waves were found in the supercritical and subcritical regions at all flow rates studied. When the rotational speed of the disk is low, a standing wave at the edge of the disk was present. As the rotational speed increased, the surface waves changed from the wavy-laminar region to a region in which the waves ran nearly radially across the disk on top of a thin substrate of fluid.

Nonmodal phenomena in differentially rotating dusty plasmas

NASA Astrophysics Data System (ADS)

Poedts, Stefaan; Rogava, Andria D.

2000-10-01

In this paper the foundation is layed for the nonmodal investigation of velocity shear induced phenomena in a differentially rotating flow of a dusty plasma. The simplest case of nonmagnetized flow is considered. It is shown that, together with the innate properties of the dusty plasma, the presence of differential rotation, Coriolis forces, and self-gravity casts a considerable richness on the nonmodal dynamics of linear perturbations in the flow. In particular: (i) dust-acoustic waves acquire the ability to extract energy from the mean flow and (ii) shear-induced, nonperiodic modes of collective plasma behavior-shear-dust-acoustic vortices-are generated. The presence of self-gravity and the nonzero Coriolis parameter (``epicyclic shaking'') makes these collective modes transiently unstable. .

Self-excited rotor whirl due to tip-seal leakage forces

NASA Technical Reports Server (NTRS)

Leie, B.; Thomas, H. J.

1980-01-01

The limitations in the performance of turbomachines which arise as a result of selfexcited vibration were investigated. Bearing forces, elastic hysteresis, and forces from fluid flow through clearances were considered as possible origins. A theoretical evaluation was made to determine the dependence of the forces form the leakage losses and from rotating flow in radial gaps.

Scaling of wet granular flows in a rotating drum

NASA Astrophysics Data System (ADS)

Jarray, Ahmed; Magnanimo, Vanessa; Ramaioli, Marco; Luding, Stefan

2017-06-01

In this work, we investigate the effect of capillary forces and particle size on wet granular flows and we propose a scaling methodology that ensures the conservation of the bed flow. We validate the scaling law experimentally by using different size glass beads with tunable capillary forces. The latter is obtained using mixtures of ethanol-water as interstitial liquid and by increasing the hydrophobicity of glass beads with an ad-hoc silanization procedure. The scaling methodology in the flow regimes considered (slipping, slumping and rolling) yields similar bed flow for different particle sizes including the angle of repose that normally increases when decreasing the particle size.

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

Using flow information to support 3D vessel reconstruction from rotational angiography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Waechter, Irina; Bredno, Joerg; Weese, Juergen

2008-07-15

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,more » 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

Flow control by combining radial pulsation and rotation of a cylinder in uniform flow

NASA Astrophysics Data System (ADS)

Oualli, H.; Hanchi, S.; Bouabdallah, A.; Gad-El-Hak, M.

2008-11-01

Flow visualizations and hot-wire measurements are carried out to study a circular cylinder undergoing simultaneous radial pulsation and rotation and placed in a uniform flow. The Reynolds number is in the range of 1,000--22,000, for which transition in the shear layers and near wake is expected. Our previous experimental and numerical investigations in this subcritical flow regime have established the existence of an important energy transfer mechanism from the mean flow to the fluctuations. Radial pulsations cause and enhance that energy transfer. Certain values of the amplitude and frequency of the pulsations lead to negative drag (i.e. thrust). The nonlinear interaction between the Magnus effect induced by the steady rotation of the cylinder and the near-wake modulated by the bluff body's pulsation leads to alteration of the omnipresent Kármán vortices and the possibility of optimizing the lift-to-drag ratio as well as the rates of heat and mass transfer. Other useful applications include the ability to enhance or suppress the turbulence intensity, and to avoid the potentially destructive lock-in phenomenon in the wake of bridges, electric cables and other structures.

Numerical investigation of laminar forced convection in Newtonian and non-Newtonian flows in eccentric annuli

NASA Astrophysics Data System (ADS)

Fang, Pingping

1998-12-01

An extended numerical investigation of fully developed, forced convective laminar flows with heat transfer in eccentric annuli has been carried out. Both Newtonian and non-Newtonian (power-law or Ostwald-de Waele) fluids are studied, representing typical applications in petrochemical, bio-chemical, personal care products, polymer/plastic extrusion and food industries. For the heat transfer problem, with an insulated outer surface, two types of thermal boundary conditions have been considered: Constant wall temperature (T), and uniform axial heat flux with constant peripheral temperature (H1) on the inner surface of the annulus. The governing differential equations for momentum and energy conservation are solved by finite-difference methods. Velocity and temperature distributions in the flow cross section, the wall shear-stress distribution, and isothermal f Re, Nu i,T and Nu i,H1 values for different eccentric annuli (0/leɛ/*/le0.6,/ 0.2/le r/sp/*/le0.8) are presented. In Newtonian flows, the eccentricity is found to have a very strong influence on the flow and temperature fields. In an annulus with relatively large inner cylinder eccentricity, the flow tends to stagnate in the narrow section and has higher peak velocities in the wide section of the annulus. There is considerable flow maldistribution in the azimuthal direction, which in turn produces greater nonuniformity in the temperature field and a consequent degradation in the average heat transfer. Also, the H1 wall condition sustains higher heat transfer coefficients relative to the T boundary condition on the inner surface. For viscous, power-law type non-Newtonian flows, both shear thinning (n<1) and shear thickening (n>1) fluids are considered. Here, the non-linear shear behavior of the fluid is found to further aggravate the flow and temperature maldistribution, and once again the eccentricity is seen to exhibit a very strong influence on the friction and heat transfer behavior. Finally, the

Monte Carlo calculations of diatomic molecule gas flows including rotational mode excitation

NASA Technical Reports Server (NTRS)

Yoshikawa, K. K.; Itikawa, Y.

1976-01-01

The direct simulation Monte Carlo method was used to solve the Boltzmann equation for flows of an internally excited nonequilibrium gas, namely, of rotationally excited homonuclear diatomic nitrogen. The semi-classical transition probability model of Itikawa was investigated for its ability to simulate flow fields far from equilibrium. The behavior of diatomic nitrogen was examined for several different nonequilibrium initial states that are subjected to uniform mean flow without boundary interactions. A sample of 1000 model molecules was observed as the gas relaxed to a steady state starting from three specified initial states. The initial states considered are: (1) complete equilibrium, (2) nonequilibrium, equipartition (all rotational energy states are assigned the mean energy level obtained at equilibrium with a Boltzmann distribution at the translational temperature), and (3) nonequipartition (the mean rotational energy is different from the equilibrium mean value with respect to the translational energy states). In all cases investigated the present model satisfactorily simulated the principal features of the relaxation effects in nonequilibrium flow of diatomic molecules.

Forced underwater laminar flows with active magnetohydrodynamic metamaterials

NASA Astrophysics Data System (ADS)

Culver, Dean; Urzhumov, Yaroslav

2017-12-01

Theory and practical implementations for wake-free propulsion systems are proposed and proven with computational fluid dynamic modeling. Introduced earlier, the concept of active hydrodynamic metamaterials is advanced by introducing magnetohydrodynamic metamaterials, structures with custom-designed volumetric distribution of Lorentz forces acting on a conducting fluid. Distributions of volume forces leading to wake-free, laminar flows are designed using multivariate optimization. Theoretical indications are presented that such flows can be sustained at arbitrarily high Reynolds numbers. Moreover, it is shown that in the limit Re ≫102 , a fixed volume force distribution may lead to a forced laminar flow across a wide range of Re numbers, without the need to reconfigure the force-generating metamaterial. Power requirements for such a device are studied as a function of the fluid conductivity. Implications to the design of distributed propulsion systems underwater and in space are discussed.

Direct and inverse energy cascades in a forced rotating turbulence experiment

NASA Astrophysics Data System (ADS)

Campagne, Antoine; Gallet, Basile; Moisy, Frédéric; Cortet, Pierre-Philippe

2014-11-01

Turbulence in a rotating frame provides a remarkable system where 2D and 3D properties may coexist, with a possible tuning between direct and inverse cascades. We present here experimental evidence for a double cascade of kinetic energy in a statistically stationary rotating turbulence experiment. Turbulence is generated by a set of vertical flaps which continuously injects velocity fluctuations towards the center of a rotating water tank. The energy transfers are evaluated from two-point third-order three-component velocity structure functions, which we measure using stereoscopic PIV in the rotating frame. Without global rotation, the energy is transferred from large to small scales, as in classical 3D turbulence. For nonzero rotation rates, the horizontal kinetic energy presents a double cascade: a direct cascade at small horizontal scales and an inverse cascade at large horizontal scales. By contrast, the vertical kinetic energy is always transferred from large to small horizontal scales, a behavior reminiscent of the dynamics of a passive scalar in 2D turbulence. At the largest rotation rate, the flow is nearly 2D and a pure inverse energy cascade is found for the horizontal energy.

Analogies between oscillation and rotation of bodies induced or influenced by vortex shedding

NASA Astrophysics Data System (ADS)

Lugt, H. J.

Vortex-induced or vortex-influenced rotation and oscillation of bodies in a parallel flow are discussed. A steady flow occurs if the body axis is parallel to the flow or if the axis of rotation is perpendicular to the flow. Flows around an oscillating body are quasi-steady only if the Strougal number is much smaller than unity. The connection between rotation and oscillation is demonstrated in terms of the autorotation of a Lanchester propeller, and conditions for stable autorotation are defined. The Riabouchinsky curve is shown to be typical of forces and torques on bodies with vortical wakes, including situations with fixed body axes perpendicular to the flow. A differential equation is formulated for rotational and oscillating bodies that shed vortices by extending the pendulum equation to include vortical effects expressed as a fifth-order polynomial.

Couple stress fluid flow in a rotating channel with peristalsis

NASA Astrophysics Data System (ADS)

Abd elmaboud, Y.; Abdelsalam, Sara I.; Mekheimer, Kh. S.

2018-04-01

This article describes a new model for obtaining closed-form semi-analytical solutions of peristaltic flow induced by sinusoidal wave trains propagating with constant speed on the walls of a two-dimensional rotating infinite channel. The channel rotates with a constant angular speed about the z - axis and is filled with couple stress fluid. The governing equations of the channel deformation and the flow rate inside the channel are derived using the lubrication theory approach. The resulting equations are solved, using the homotopy perturbation method (HPM), for exact solutions to the longitudinal velocity distribution, pressure gradient, flow rate due to secondary velocity, and pressure rise per wavelength. The effect of various values of physical parameters, such as, Taylor's number and couple stress parameter, together with some interesting features of peristaltic flow are discussed through graphs. The trapping phenomenon is investigated for different values of parameters under consideration. It is shown that Taylor's number and the couple stress parameter have an increasing effect on the longitudinal velocity distribution till half of the channel, on the flow rate due to secondary velocity, and on the number of closed streamlines circulating the bolus.

Comparison of reaction forces on the anterior cruciate and anterolateral ligaments during internal rotation and anterior drawer forces at different flexion angles of the knee joint.

PubMed

Uğur, Levent

2017-12-01

Having a complicated anatomy, the knee joint has been further detailed and a new formation defined, the anterolateral ligament (ALL), in recent studies. While the importance of this ligament, which previously was associated with Segond fractures, was explained via clinical, radiologic and biomechanical studies, and basically, is thought to be a fixator structures for the tibia against internal rotation stress. Although in recent studies efficient surgical treatment was applied to patients who underwent anterior cruciate ligament (ACL) operation, some patients having a positive pivot test highlights the clinical importance of the ALL. The aim of this study is to evaluate reaction forces of different flexion angles on the tibia during internal rotation and anterior drawer tests on both the ALL and ACL, and to examine theimportance of this ligament in knee biomechanics by a finite element analysis method. In this study, normal anatomy knee joint was modelled using Computed Tomography images from lower extremity length in DICOM format. 0°, 15°,30°,45°,60°,75° and 90° angles of flexion were applied, respectively, to these models and reaction force vectors formed on both ligaments were examined separately and as total vector and size by applying internal rotation and anterior drawer forces on each model. Non-linear analysis was conducted using ANSYS (version 17) with the same limit conditions applied to all models. After all models were examined, in general when comparing reaction forces, those on the ACL were found to be higher. However, when vectoral directions were examined, forces on ALL increased with increased flexion ratio and internal rotation momentum. Beyond 30° flexion, the tensile force on the ALL is increased and compressive overload on the ACL occurs. The ALL plays an important role in stability, especially against internal rotation forces, and an increased knee joint flexion ratio increases the stability contribution ratio. In particular, at 30�

Dynamical and fractal properties in periodically forced stretch-twist-fold (STF) flow

NASA Astrophysics Data System (ADS)

Aqeel, Muhammad; Ahmad, Salman; Azam, Anam; Ahmed, Faizan

2017-05-01

The periodically forced stretch-twist-fold (STF) flow is introduced in this article. The nonlinear behavior of the STF flow with periodic force along the y -axis is investigated analytically and numerically. The STF flow is a prototype of the dynamo theory that proposes a mechanism of magnetic field generation continuously. The stability analysis is done by Routh Huwritz criteria and Cardano method. Chasing chaos through numerical simulation is determined to demonstrate the chaotic behavior of the forced STF flow. With the help of fractal processes based on the forced STF flow, a multi-wing forced STF flow is obtained that gives a n -wing forced STF flow system.

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.

Numerical study of the radiometric phenomenon exhibited by a rotating Crookes radiometer

NASA Astrophysics Data System (ADS)

Anikin, Yu. A.

2011-11-01

The two-dimensional rarefied gas flow around a rotating Crookes radiometer and the arising radiometric forces are studied by numerically solving the Boltzmann kinetic equation. The computations are performed in a noninertial frame of reference rotating together with the radiometer. The collision integral is directly evaluated using a projection method, while second- and third-order accurate TVD schemes are used to solve the advection equation and the equation for inertia-induced transport in the velocity space, respectively. The radiometric forces are found as functions of the rotation frequency.

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.

Anomalous scaling of passive scalars in rotating flows.

PubMed

Rodriguez Imazio, P; Mininni, P D

2011-06-01

We present results of direct numerical simulations of passive scalar advection and diffusion in turbulent rotating flows. Scaling laws and the development of anisotropy are studied in spectral space, and in real space using an axisymmetric decomposition of velocity and passive scalar structure functions. The passive scalar is more anisotropic than the velocity field, and its power spectrum follows a spectral law consistent with ~ k[Please see text](-3/2). This scaling is explained with phenomenological arguments that consider the effect of rotation. Intermittency is characterized using scaling exponents and probability density functions of velocity and passive scalar increments. In the presence of rotation, intermittency in the velocity field decreases more noticeably than in the passive scalar. The scaling exponents show good agreement with Kraichnan's prediction for passive scalar intermittency in two dimensions, after correcting for the observed scaling of the second-order exponent.

Distorted turbulence submitted to frame rotation: RDT and LES results

NASA Technical Reports Server (NTRS)

Godeferd, Fabien S.

1995-01-01

The objective of this effort is to carry the analysis of Lee et al. (1990) to the case of shear with rotation. We apply the RDT approximation to turbulence submitted to frame rotation for the case of a uniformly sheared flow and compare its mean statistics to results of high resolution DNS of a rotating plane channel flow. In the latter, the mean velocity profile is modified by the Coriolis force, and accordingly, different regions in the channel can be identified. The properties of the plane pure strain turbulence submitted to frame rotation are, in addition, investigated in spectral space, which shows the usefulness of the spectral RDT approach. This latter case is investigated here. Among the general class of quadratic flows, this case does not follow the same stability properties as the others since the related mean vorticity is zero.

Drag and Lift Forces Between a Rotating Conductive Sphere and a Cylindrical Magnet

NASA Technical Reports Server (NTRS)

Nurge, Mark A.; Youngquist, Robert C.

2017-01-01

Modeling the interaction between a non-uniform magnetic field and a rotating conductive object allows study of the drag force which is used in applications such as eddy current braking and linear induction motors as well as the transition to a repulsive force that is the basis for magnetic levitation systems. Here, we study the interaction between a non-uniform field generated by a cylindrical magnet and a rotating conductive sphere. Each eddy current in the sphere generates a magnetic field which in turn generates another eddy current, eventually feeding back on itself. A two step mathematics process is developed to find a closed form solution in terms of only two eddy currents. However, the complete solution requires decomposition of the magnetic field into a summation of spherical harmonics, making it more suitable for a graduate level electromagnetism lecture or lab. Finally, the forces associated with these currents are calculated and then verified experimentally.

Drag and lift forces between a rotating conductive sphere and a cylindrical magnet

NASA Astrophysics Data System (ADS)

Nurge, Mark A.; Youngquist, Robert C.; Starr, Stanley O.

2018-06-01

Modeling the interaction between a non-uniform magnetic field and a rotating conductive object provides insight into the drag force, which is used in applications such as eddy current braking and linear induction motors, as well as the transition to a repulsive force, which is the basis for magnetic levitation systems. Here, we study the interaction between a non-uniform field generated by a cylindrical magnet and a rotating conductive sphere. Each eddy current in the sphere generates a magnetic field which in turn generates another eddy current, eventually feeding back on itself. A two-step mathematical process is developed to find a closed-form solution in terms of only three eddy currents. However, the complete solution requires decomposition of the magnetic field into a summation of spherical harmonics, making it more suitable for a graduate-level electromagnetism lecture or lab. Finally, the forces associated with these currents are calculated and then verified experimentally.

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.

Effect of centrifugal force on natural frequency of lateral vibration of rotating shafts

NASA Astrophysics Data System (ADS)

Behzad, M.; Bastami, A. R.

2004-07-01

This paper investigates the effect of shaft rotation on its natural frequency. Apart from gyroscopic effect, the axial force originated from centrifugal force and the Poisson effect results in change of shaft natural frequency. D'Alembert principle for shaft in cylindrical co-ordinate system, along with the stress-strain relation, gives the non-homogenous linear differential equation, which can be used to calculate axial stress in the shaft. Numerical results of this study show that axial stress produced by shaft rotation has a major effect on the natural frequency of long high-speed shafts, while shaft diameter has no influence on the results. In addition, change in lateral natural frequency due to gyroscopic effect is compared with the results of this study.

Multiscale Modeling of Primary Cilium Deformations Under Local Forces and Shear Flows

NASA Astrophysics Data System (ADS)

Peng, Zhangli; Feng, Zhe; Resnick, Andrew; Young, Yuan-Nan

2017-11-01

We study the detailed deformations of a primary cilium under local forces and shear flows by developing a multiscale model based on the state-of-the-art understanding of its molecular structure. Most eukaryotic cells are ciliated with primary cilia. Primary cilia play important roles in chemosensation, thermosensation, and mechanosensation, but the detailed mechanism for mechanosensation is not well understood. We apply the dissipative particle dynamics (DPD) to model an entire well with a primary cilium and consider its different components, including the basal body, microtubule doublets, actin cortex, and lipid bilayer. We calibrate the mechanical properties of individual components and their interactions from experimental measurements and molecular dynamics simulations. We validate the simulations by comparing the deformation profile of the cilium and the rotation of the basal body with optical trapping experiments. After validations, we investigate the deformation of the primary cilium under shear flows. Furthermore, we calculate the membrane tensions and cytoskeleton stresses, and use them to predict the activation of mechanosensitive channels.

Subgrid-scale models for large-eddy simulation of rotating turbulent flows

NASA Astrophysics Data System (ADS)

Silvis, Maurits; Trias, Xavier; Abkar, Mahdi; Bae, Hyunji Jane; Lozano-Duran, Adrian; Verstappen, Roel

2016-11-01

This paper discusses subgrid models for large-eddy simulation of anisotropic flows using anisotropic grids. In particular, we are looking into ways to model not only the subgrid dissipation, but also transport processes, since these are expected to play an important role in rotating turbulent flows. We therefore consider subgrid-scale models of the form τ = - 2νt S +μt (SΩ - ΩS) , where the eddy-viscosity νt is given by the minimum-dissipation model, μt represents a transport coefficient; S is the symmetric part of the velocity gradient and Ω the skew-symmetric part. To incorporate the effect of mesh anisotropy the filter length is taken in such a way that it minimizes the difference between the turbulent stress in physical and computational space, where the physical space is covered by an anisotropic mesh and the computational space is isotropic. The resulting model is successfully tested for rotating homogeneous isotropic turbulence and rotating plane-channel flows. The research was largely carried out during the CTR SP 2016. M.S, and R.V. acknowledge the financial support to attend this Summer Program.

Modeling dynamic stall on wind turbine blades under rotationally augmented flow fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guntur, S.; Schreck, S.; Sorensen, N. N.

It is well known that airfoils under unsteady flow conditions with a periodically varying angle of attack exhibit aerodynamic characteristics different from those under steady flow conditions, a phenomenon commonly known as dynamic stall. It is also well known that the steady aerodynamic characteristics of airfoils in the inboard region of a rotating blade differ from those under steady two-dimensional (2D) flow conditions, a phenomenon commonly known as rotational augmentation. This paper presents an investigation of these two phenomena together in the inboard parts of wind turbine blades. This analysis is carried out using data from three sources: (1) themore » National Renewable Energy Laboratory’s Unsteady Aerodynamics Experiment Phase VI experimental data, including constant as well as continuously pitching blade conditions during axial operation, (2) data from unsteady Delayed Detached Eddy Simulations (DDES) carried out using the Technical University of Denmark’s in-house flow solver Ellipsys3D, and (3) data from a simplified model based on the blade element momentum method with a dynamic stall subroutine that uses rotationally augmented steady-state polars obtained from steady Phase VI experimental sequences, instead of the traditional 2D nonrotating data. The aim of this work is twofold. First, the blade loads estimated by the DDES simulations are compared to three select cases of the N sequence experimental data, which serves as a validation of the DDES method. Results show reasonable agreement between the two data in two out of three cases studied. Second, the dynamic time series of the lift and the moment polars obtained from the experiments are compared to those from the dynamic stall subroutine that uses the rotationally augmented steady polars. This allowed the differences between the stall phenomenon on the inboard parts of harmonically pitching blades on a rotating wind turbine and the classic dynamic stall representation in 2D flow to be

Large amplitude forcing of a high speed 2-dimensional jet

NASA Technical Reports Server (NTRS)

Bernal, L.; Sarohia, V.

1984-01-01

The effect of large amplitude forcing on the growth of a high speed two dimensional jet was investigated experimentally. Two forcing techniques were utilized: mass flow oscillations and a mechanical system. The mass flow oscillation tests were conducted at Strouhal numbers from 0.00052 to 0.045, and peak to peak amplitudes up to 50 percent of the mean exit velocity. The exit Mach number was varied in the range 0.15 to 0.8. The corresponding Reynolds numbers were 8,400 and 45,000. The results indicate no significant change of the jet growth rate or centerline velocity decay compared to the undisturbed free jet. The mechanical forcing system consists of two counter rotating hexagonal cylinders located parallel to the span of the nozzle. Forcing frequencies up to 1,500 Hz were tested. Both symmetric and antisymmetric forcing can be implemented. The results for antisymmetric forcing showed a significant (75 percent) increase of the jet growth rate at an exit Mach number of 0.25 and a Strouhal number of 0.019. At higher rotational speeds, the jet deflected laterally. A deflection angle of 39 deg with respect to the centerline was measured at the maximum rotational speed.

Radial Flow Effects On A Retreating Rotor Blade

DTIC Science & Technology

2014-05-01

blades which are subject to the coupled effects of reactive centrifugal and Coriolis forces unique to the rotating environment. These forces are...coupled effects of centrifugal and Coriolis forces in the rotating environment add more complexity to the flow characteristics [96]. McCroskey’s [74...disk will definitely cause some non-linear effects on the radial velocity profile. These effects are not investigated in this study. The next of

Magnetic Fluctuation-Driven Intrinsic Flow in a Toroidal Plasma

NASA Astrophysics Data System (ADS)

Brower, D. L.; Ding, W. X.; Lin, L.; Almagri, A. F.; den Hartog, D. J.; Sarff, J. S.

2012-10-01

Magnetic fluctuations have been long observed in various magnetic confinement configurations. These perturbations may arise naturally from plasma instabilities such as tearing modes and energetic particle driven modes, but they can also be externally imposed by error fields or external magnetic coils. It is commonly observed that large MHD modes lead to plasma locking (no rotation) due to torque produced by eddy currents on the wall, and it is predicted that stochastic field induces flow damping where the radial electric field is reduced. Flow generation is of great importance to fusion plasma research, especially low-torque devices like ITER, as it can act to improve performance. Here we describe new measurements in the MST reversed field pinch (RFP) showing that the coherent interaction of magnetic and particle density fluctuations can produce a turbulent fluctuation-induced kinetic force, which acts to drive intrinsic plasma rotation. Key observations include; (1) the average kinetic force resulting from density fluctuations, ˜ 0.5 N/m^3, is comparable to the intrinsic flow acceleration, and (2) between sawtooth crashes, the spatial distribution of the kinetic force is directed to create a sheared parallel flow profile that is consistent with the measured flow profile in direction and amplitude, suggesting the kinetic force is responsible for intrinsic plasma rotation.

Heat and Mass Transfer in the Over-Shower Zone of a Cooling Tower with Flow Rotation

NASA Astrophysics Data System (ADS)

Kashani, M. M. Hemmasian; Dobrego, K. V.

2013-11-01

The influence of flow rotation in the over-shower zone of a natural draft wet cooling tower (NDCT) on heat and mass transfer in this zone is investigated numerically. The 3D geometry of an actual NDCT and three models of the induced rotation velocity fields are utilized for calculations. Two phases (liquid and gaseous) and three components are taken into consideration. The interphase heat exchange, heat transfer to the walls, condensation-evaporation intensity field, and other parameters are investigated as functions of the induced rotation intensity (the inclination of the velocity vector at the periphery). It is shown that the induced flow rotation intensifies the heat and mass transfer in the over-shower zone of an NDCT. Flow rotation leads to specific redistribution of evaporation-condensation areas in an NDCT and stimulates water condensation near its walls.

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).

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.

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

Experimental observation of steady inertial wave turbulence in deep rotating flows

NASA Astrophysics Data System (ADS)

Yarom, Ehud; Sharon, Eran

2015-11-01

We present experimental evidence of inertial wave turbulence in deep rotating fluid. Experiments were performed in a rotating cylindrical water tank, where previous work showed statistics similar to 2D turbulence (specifically an inverse energy cascade). Using Fourier analysis of high resolution data in both space (3D) and time we show that most of the energy of a steady state flow is contained around the inertial wave dispersion relation. The nonlinear interaction between the waves is manifested by the widening of the time spectrum around the dispersion relation. We show that as the Rossby number increases so does the spectrum width, with a strong dependence on wave number. Our results suggest that in some parameters range, rotating turbulence velocity field can be represented as a field of interacting waves (wave turbulence). Such formalism may provide a better understanding of the flow statistics. This work was supported by the Israel Science Foundation, Grant No. 81/12.

Variations in rotation rate and polar motion of a non-hydrostatic Titan

NASA Astrophysics Data System (ADS)

Coyette, Alexis; Baland, Rose-Marie; Van Hoolst, Tim

2018-06-01

Observation of the rotation of synchronously rotating satellites can help to probe their interior. Previous studies mostly assume that these large icy satellites are in hydrostatic equilibrium, although several measurements indicate that they deviate from such a state. Here we investigate the effect of non-hydrostatic equilibrium and of flow in the subsurface ocean on the rotation of Titan. We consider the variations in rotation rate and the polar motion due to (1) the gravitational force exerted by Saturn at orbital period and (2) exchanges of angular momentum between the seasonally varying atmosphere and the solid surface. The deviation of the mass distribution from hydrostaticity can significantly increase the diurnal libration and decrease the amplitude of the seasonal libration. The effect of the non-hydrostatic mass distribution is less important for polar motion, which is more sensitive to flow in the subsurface ocean. By including a large spectrum of atmospheric perturbations, the smaller than synchronous rotation rate measured by Cassini in the 2004-2009 period (Meriggiola et al., 2016) could be explained by the atmospheric forcing. If our interpretation is correct, we predict a larger than synchronous rotation rate in the 2009-2014 period.

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.

Low-speed wind-tunnel tests of single- and counter-rotation propellers

NASA Technical Reports Server (NTRS)

Dunham, D. M.; Gentry, G. L., Jr.; Coe, P. L., Jr.

1986-01-01

A low-speed (Mach 0 to 0.3) wind-tunnel investigation was conducted to determine the basic performance, force and moment characteristics, and flow-field velocities of single- and counter-rotation propellers. Compared with the eight-blade single-rotation propeller, a four- by four- (4 x 4) blade counter-rotation propeller with the same blade design produced substantially higher thrust coefficients for the same blade angles and advance ratios. The results further indicated that ingestion of the wake from a supporting pylon for a pusher configuration produced no significant change in the propeller thrust performance for either the single- or counter-rotation propellers. A two-component laser velocimeter (LV) system was used to make detailed measurements of the propeller flow fields. Results show increasing slipstream velocities with increasing blade angle and decreasing advance ratio. Flow-field measurements for the counter-rotation propeller show that the rear propeller turned the flow in the opposite direction from the front propeller and, therefore, could eliminate the swirl component of velocity, as would be expected.

Blood flow/pump rotation ratio as an artificial lung performance monitoring tool during extracorporeal respiratory support using centrifugal pumps

PubMed Central

Park, Marcelo; Mendes, Pedro Vitale; Hirota, Adriana Sayuri; dos Santos, Edzangela Vasconcelos; Costa, Eduardo Leite Vieira; Azevedo, Luciano Cesar Pontes

2015-01-01

Objective To analyze the correlations of the blood flow/pump rotation ratio and the transmembrane pressure, CO2 and O2 transfer during the extracorporeal respiratory support. Methods Five animals were instrumented and submitted to extracorporeal membrane oxygenation in a five-step protocol, including abdominal sepsis and lung injury. Results This study showed that blood flow/pump rotations ratio variations are dependent on extracorporeal membrane oxygenation blood flow in a positive logarithmic fashion. Blood flow/pump rotation ratio variations are negatively associated with transmembrane pressure (R2 = 0.5 for blood flow = 1500mL/minute and R2 = 0.4 for blood flow = 3500mL/minute, both with p < 0.001) and positively associated with CO2 transfer variations (R2 = 0.2 for sweep gas flow ≤ 6L/minute, p < 0.001, and R2 = 0.1 for sweep gas flow > 6L/minute, p = 0.006), and the blood flow/pump rotation ratio is not associated with O2 transfer variations (R2 = 0.01 for blood flow = 1500mL/minute, p = 0.19, and R2 = - 0.01 for blood flow = 3500 mL/minute, p = 0.46). Conclusion Blood flow/pump rotation ratio variation is negatively associated with transmembrane pressure and positively associated with CO2 transfer in this animal model. According to the clinical situation, a decrease in the blood flow/pump rotation ratio can indicate artificial lung dysfunction without the occurrence of hypoxemia. PMID:26340159

Blood flow/pump rotation ratio as an artificial lung performance monitoring tool during extracorporeal respiratory support using centrifugal pumps.

PubMed

Park, Marcelo; Mendes, Pedro Vitale; Hirota, Adriana Sayuri; dos Santos, Edzangela Vasconcelos; Costa, Eduardo Leite Vieira; Azevedo, Luciano Cesar Pontes

2015-01-01

To analyze the correlations of the blood flow/pump rotation ratio and the transmembrane pressure, CO2 and O2 transfer during the extracorporeal respiratory support. Five animals were instrumented and submitted to extracorporeal membrane oxygenation in a five-step protocol, including abdominal sepsis and lung injury. This study showed that blood flow/pump rotations ratio variations are dependent on extracorporeal membrane oxygenation blood flow in a positive logarithmic fashion. Blood flow/pump rotation ratio variations are negatively associated with transmembrane pressure (R2 = 0.5 for blood flow = 1500mL/minute and R2 = 0.4 for blood flow = 3500mL/minute, both with p < 0.001) and positively associated with CO2 transfer variations (R2 = 0.2 for sweep gas flow ≤ 6L/minute, p < 0.001, and R2 = 0.1 for sweep gas flow > 6L/minute, p = 0.006), and the blood flow/pump rotation ratio is not associated with O2 transfer variations (R2 = 0.01 for blood flow = 1500mL/minute, p = 0.19, and R2 = - 0.01 for blood flow = 3500 mL/minute, p = 0.46). Blood flow/pump rotation ratio variation is negatively associated with transmembrane pressure and positively associated with CO2 transfer in this animal model. According to the clinical situation, a decrease in the blood flow/pump rotation ratio can indicate artificial lung dysfunction without the occurrence of hypoxemia.

Lagrangian particle drift and surface deformation in a rotating wave on a free liquid surface

NASA Astrophysics Data System (ADS)

Fontana, Paul W.; Francois, Nicolas; Xia, Hua; Punzmann, Horst; Shats, Michael

2017-11-01

A nonlinear model of a rotating wave on the free surface of a liquid is presented. The flow is assumed to be inviscid and irrotational. The wave is constructed as a superposition of two perpendicular, monochromatic standing Stokes waves and is standing-wave-like, but with ``antinodes'' or cells consisting of rotating surface gradients of alternating polarity. Lagrangian fluid particle trajectories show a rotational drift about each cell in the direction of wave rotation, corresponding to a rotating Stokes drift. Each cell therefore has a circulating flow and localized angular momentum even though the Eulerian flow is irrotational. Meanwhile, the wave sets up a static displacement of the free surface, making a trough in each cell. This static surface gradient provides a centripetal force that may account for additional rotation seen in experiments.

Visualization and Measurement of Flow in a Model Rotating-Wall Bioreactor

NASA Astrophysics Data System (ADS)

Brown, Jason B.; Neitzel, G. Paul

1997-11-01

Fluid shear has been observed to have an effect on the in vitro growth of mammalian cells and is expected to play a role in the in vitro development of aggregates of cells into tissue. The interactions between culture media and cell constructs within a circular Couette flow bioreactor with independently rotating cylinders are investigated in model studies using flow visualization. Particle-Image Velocimetry (PIV) is used to quantify the velocity field in a plane perpendicular to the vessel axis which contains a cell construct model. This velocity field is then used to compute the instantaneous shear field. Experiments show the path of the model cell construct is dependent on the rotation rates of the cylinders.

Large eddy simulation of rotating turbulent flows and heat transfer by the lattice Boltzmann method

NASA Astrophysics Data System (ADS)

Liou, Tong-Miin; Wang, Chun-Sheng

2018-01-01

Due to its advantage in parallel efficiency and wall treatment over conventional Navier-Stokes equation-based methods, the lattice Boltzmann method (LBM) has emerged as an efficient tool in simulating turbulent heat and fluid flows. To properly simulate the rotating turbulent flow and heat transfer, which plays a pivotal role in tremendous engineering devices such as gas turbines, wind turbines, centrifugal compressors, and rotary machines, the lattice Boltzmann equations must be reformulated in a rotating coordinate. In this study, a single-rotating reference frame (SRF) formulation of the Boltzmann equations is newly proposed combined with a subgrid scale model for the large eddy simulation of rotating turbulent flows and heat transfer. The subgrid scale closure is modeled by a shear-improved Smagorinsky model. Since the strain rates are also locally determined by the non-equilibrium part of the distribution function, the calculation process is entirely local. The pressure-driven turbulent channel flow with spanwise rotation and heat transfer is used for validating the approach. The Reynolds number characterized by the friction velocity and channel half height is fixed at 194, whereas the rotation number in terms of the friction velocity and channel height ranges from 0 to 3.0. A working fluid of air is chosen, which corresponds to a Prandtl number of 0.71. Calculated results are demonstrated in terms of mean velocity, Reynolds stress, root mean square (RMS) velocity fluctuations, mean temperature, RMS temperature fluctuations, and turbulent heat flux. Good agreement is found between the present LBM predictions and previous direct numerical simulation data obtained by solving the conventional Navier-Stokes equations, which confirms the capability of the proposed SRF LBM and subgrid scale relaxation time formulation for the computation of rotating turbulent flows and heat transfer.

The Effect of Spanwise System Rotation on Turbulent Poiseuille Flow at Very-Low-Reynolds Number

NASA Astrophysics Data System (ADS)

Iida, Oaki; Fukudome, K.; Iwata, T.; Nagano, Y.

Direct numerical simulations (DNSs) with a spectral method are performed with large and small computational domains to study the effects of spanwise rotation on a turbulent Poiseuille flow at the very low-Reynolds numbers. In the case without system rotation, quasi-laminar and turbulent states appear side by side in the same computational domain, which is coined as laminar-turbulence pattern. However, in the case with system rotation, the pattern disappears and flow is dominated by quasi-laminar region including very long low-speed streaks coiled by chain-like vortical structures. Increasing the Reynolds number can not generate the laminar-turbulence pattern as long as system rotation is imposed.

Forced convection in vertical Bridgman configuration with the submerged heater

NASA Astrophysics Data System (ADS)

Meyer, S.; Ostrogorsky, A. G.

1997-02-01

Ga-doped Ge single crystals were grown in vertical Bridgman configuration, using the submerged heater method (SHM). When used without rotation, the submerged heater drastically reduces convection at the solid-liquid interface. When the submerged heater is set in to rotation or oscillatory rotation, it acts as a centrifugal viscous pump, inducing forced convection (radial-inward flow) along the interface. The flow produced by a rotation and oscillatory rotation of the submerged heater was visualized using a 1 : 1 scale model. The vigorous mixing produced by the oscillatory rotation creates a nearly perfectly stirred melt, and yields a uniform lateral distribution of the dopant. The crystals were free of unintentionally produced striae.

The effect of coracoacromial ligament excision and acromioplasty on the amount of rotator cuff force production necessary to restore intact glenohumeral biomechanics.

PubMed

Budoff, Jeffrey E; Lin, Cheng-Li; Hong, Chih-Kai; Chiang, Florence L; Su, Wei-Ren

2016-06-01

Coracoacromial ligament (CAL) excision and acromioplasty increase superior and anterosuperior glenohumeral translation. It is unknown how much of an increase in rotator cuff force production is required to re-establish intact glenohumeral biomechanics after these surgical procedures. We hypothesized that, after CAL excision and acromioplasty, an increase in rotator cuff force production would not be necessary to reproduce the anterosuperior and superior translations of the intact specimens. Nine cadaveric shoulders were subjected to loading in the superior and anterosuperior directions in the intact state after CAL excision, acromioplasty, and recording of the translations. The rotator cuff force was then increased to normalize glenohumeral biomechanics. After CAL excision at 150 and 200 N of loading, an increase in the rotator cuff force by 25% decreased anterosuperior translation to the point where there was no significant difference from the intact specimen's translation. After acromioplasty (and CAL excision) at 150 and 200 N, an increase in the rotator cuff force of 25% and 30%, respectively, decreased superior translation to the point where there was no significant difference from the intact specimen's translation. At 150 to 200 N of loading, CAL excision and acromioplasty increase the rotator cuff force required to maintain normal glenohumeral biomechanics by 25% to 30%. After a subacromial decompression, the rotator cuff has an increased force production requirement to maintain baseline glenohumeral mechanics. Under many circumstances, in vivo force requirements may be even greater after surgical attenuation of the coracoacromial arch. Basic Science Study; Biomechanics. Copyright © 2016 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.

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

PubMed Central

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

2015-01-01

Background 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. Methods 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. Findings 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). Interpretation These conclusions should be a key consideration in rehabilitating the shoulder after surgery, preventing specific upper limb injuries and predicting return to driving recommendations. PMID:26139549

Numerical analysis of the flow separation and adverse pressure gradient in laminar boundary layer over a flat plate due to a rotating cylinder in the vicinity

NASA Astrophysics Data System (ADS)

Afroz, Farhana; Sharif, Muhammad A. R.

2018-04-01

Generation of adverse pressure gradient (APG) in the boundary layer over a plane wall using a rotating cylinder close to the wall has been numerically investigated for a range of the freestream Reynolds number (50 ≤ Re ≤ 400), the cylinder rotation rate (0 ≤ α ≤ 2), and the cylinder to wall gap (0.125 ≤ G/D ≤ 2). Various combinations of these flow parameters have been considered and the transient flow is computed using the ANSYS Fluent CFD code. The magnitude of the APG has been quantified. The influence of the freestream Reynolds number on the dynamics of flow separation and cylinder wake has been examined. Reynolds number has strong effect on bubble size properties and APG magnitude. Drag and lift force coefficient on the cylinder are also computed which are found to be strong function of the Reynolds number. Higher Reynolds number results in complex laminar separation bubble on the wall. A parametric demarcation map showing the threshold combinations of the flow parameters for transition from steady to periodic unsteady flow is generated.

Flow shear stabilization of rotating plasmas due to the Coriolis effect.

PubMed

Haverkort, J W; de Blank, H J

2012-07-01

A radially decreasing toroidal rotation frequency can have a stabilizing effect on nonaxisymmetric magnetohydrodynamic (MHD) instabilities. We show that this is a consequence of the Coriolis effect that induces a restoring pressure gradient force when plasma is perturbed radially. In a rotating cylindrical plasma, this Coriolis-pressure effect is canceled by the centrifugal effect responsible for the magnetorotational instability. In a magnetically confined toroidal plasma, a large aspect ratio expansion shows that only half of the effect is canceled. This analytical result is confirmed by numerical computations. When the plasma rotates faster toroidally in the core than near the edge, the effect can contribute to the formation of transport barriers by stabilizing MHD instabilities.

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.

Confinement of plasma along shaped open magnetic fields from the centrifugal force of supersonic plasma rotation.

PubMed

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 E × B 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.

Heat transfer in rotating serpentine passages with selected model orientation for smooth or skewed trip walls

NASA Technical Reports Server (NTRS)

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

1993-01-01

Experiments were conducted to determine the effects of model orientation as well as buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. Turbine blades have internal coolant passage surfaces at the leading and trailing edges of the airfoil with surfaces at angles which are as large as +/- 50 to 60 degrees to the axis of rotation. Most of the previously-presented, multiple-passage, rotating heat transfer experiments have focused on radial passages aligned with the axis of rotation. Results from serpentine passages with orientations 0 and 45 degrees to the axis of rotation which simulate the coolant passages for the mid chord and trailing edge regions of the rotating airfoil are compared. The experiments were conducted with rotation in both directions to simulate serpentine coolant passages with the rearward flow of coolant or with the forward flow of coolant. The experiments were conducted for passages with smooth surfaces and with 45 degree trips adjacent to airfoil surfaces for the radial portion of the serpentine passages. At a typical flow condition, the heat transfer on the leading surfaces for flow outward in the first passage with smooth walls was twice as much for the model at 45 degrees compared to the model at 0 degrees. However, the differences for the other passages and with trips were less. In addition, the effects of buoyancy and Coriolis forces on heat transfer in the rotating passage were decreased with the model at 45 degrees, compared to the results at 0 degrees. The heat transfer in the turn regions and immediately downstream of the turns in the second passage with flow inward and in the third passage with flow outward was also a function of model orientation with differences as large as 40 to 50 percent occurring between the model orientations with forward flow and rearward flow of coolant.

Experimental Determination of Unsteady Forces on Contrarotating Propellers in Uniform Flow

DTIC Science & Technology

1976-03-01

Experimental Determination of Unsteady Forces on Contrarotating Propellers ini Uniform Flow ... EXPERIMENTAL DETERMINATION OF UNSTEADY FORCES E ON CONTP.AROTATING PROPELLERS IN UNIFORM FLOW0 0 cby -1 Marlin L. Miller 0 cc 0 z ~APPROVED FOR PUBLIC...tunnel. The experiments were conducted in uniform flow so that the unsteady forces would be due only to the interaction of the two

Excitation and propagation of nonlinear waves in a rotating fluid

NASA Astrophysics Data System (ADS)

Hanazaki, Hideshi

1993-09-01

A numerical study of the nonlinear waves excited in an axisymmetric rotating flow through a circular tube is described. The waves are excited by either an undulation of the tube wall or an obstacle on the axis of the tube. The results are compared with the weakly nonlinear theory (forced KdV equation). The computations are done when the upstream swirling velocity is that of Burgers' vortex type. The flow behaves like the solution of the forced KdV equation, and the upstream advancing of the waves appear even when the flow is critical or slightly supercritical to the fastest inertial wave mode.

Simulation of Effects of the Saffman Force and the Magnus Force on Sand Saltation in Turbulent Flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Zhongquan C.; Zou, Xueyong; Yang, Xiaofan

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.

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.

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.

Coherent flow structures and heat transfer in a duct with electromagnetic forcing

NASA Astrophysics Data System (ADS)

Himo, Rawad; Habchi, Charbel

2018-04-01

Coherent vortices are generated electromagnetically in a square duct flow. The vortices are induced by a Lorentz force applied in a small section near the entrance of the duct. The flow structure complexity increases with the electromagnetic forcing since the primary vortices propagating along the duct detach to generate secondary smaller streamwise vortices and hairpin-like structures. The Reynolds number based on the mean flow velocity and hydraulic diameter is 500, and five cases were studied by varying the electromagnetic forcing. Even though this Reynolds number is relatively low, a periodic sequence of hairpin-like structure flow was observed for the high forcing cases. This mechanism enhances the mixing process between the different flow regions resulting in an increase in the thermal performances which reaches 66% relative to the duct flow without forcing. In addition to the flow complexity, lower forcing cases remained steady, unlike high Lorentz forces that induced periodic instabilities with a Strouhal number around 0.59 for the transient eddies. The effect of the flow structure on the heat transfer is analyzed qualitatively and quantitatively using numerical simulations based on the finite volume method. Moreover, proper orthogonal decomposition (POD) analysis was performed on the flow structures to evaluate the most energetic modes contributing in the flow. It is found from the POD analysis that the primary streamwise vortices and hairpin legs are the flow structures that are the most contributing to the heat transfer process.

Experimental study of rotational oscillation of H-shaped bodies in the flow

NASA Astrophysics Data System (ADS)

Braun, Oleg; Ryabinin, Anatoly

2018-05-01

The rotational oscillations of H-shaped body in the air flow are studied in the wind tunnel. The body is elastically fixed in the test section and can rotate only around axis that is perpendicular to the velocity vector. Tenzometrical technique is used for measurement of amplitude of rotational oscillations. The dependencies of oscillation amplitude on aspect ratio of the H-shaped body and air velocity are obtained. It is found that the increase of the flange height leads to growth of the amplitude of the oscillations.

Effects of combined wrist flexion/extension and forearm rotation and two levels of relative force on discomfort.

PubMed

Khan, Abid Ali; O'Sullivan, Leonard; Gallwey, Timothy J

2009-10-01

This study investigated perceived discomfort in an isometric wrist flexion task. Independent variables were wrist flexion/extension (55%, 35% flexion, neutral, 35% and 55% extension ranges of motion (ROM)), forearm rotation (60%, 30% prone, neutral, 30% and 60% supine ROM) and two levels of flexion force (10% and 20% maximum voluntary contraction (MVC)). Discomfort was significantly affected by flexion force, forearm rotation and a two-way interaction of force with forearm rotation (each p < 0.05). High force for 60%ROM forearm pronation and supination resulted in increasingly higher discomfort for these combinations. Flexion forces were set relative to the MVC in each wrist posture and this appears to be important in explaining a lack of significant effect (p = 0.34) for flexion/extension on discomfort. Regression equations predicting discomfort were developed and used to generate iso-discomfort contours, which indicate regions where the risk of injury should be low and others where it is likely to be high. Regression equations predicting discomfort and iso-discomfort contours are presented, which indicate combinations of upper limb postures for which discomfort is predicted to be low, and others where it is likely to be high. These are helpful in the study of limits for risk factors associated with upper limb musculoskeletal injury in industry.

Baroclinic Vortices in Rotating Stratified Shearing Flows: Cyclones, Anticyclones, and Zombie Vortices

NASA Astrophysics Data System (ADS)

Hassanzadeh, Pedram

Large coherent vortices are abundant in geophysical and astrophysical flows. They play significant roles in the Earth's oceans and atmosphere, the atmosphere of gas giants, such as Jupiter, and the protoplanetary disks around forming stars. These vortices are essentially three-dimensional (3D) and baroclinic, and their dynamics are strongly influenced by the rotation and density stratification of their environments. This work focuses on improving our understanding of the physics of 3D baroclinic vortices in rotating and continuously stratified flows using 3D spectral simulations of the Boussinesq equations, as well as simplified mathematical models. The first chapter discusses the big picture and summarizes the results of this work. In Chapter 2, we derive a relationship for the aspect ratio (i.e., vertical half-thickness over horizontal length scale) of steady and slowly-evolving baroclinic vortices in rotating stratified fluids. We show that the aspect ratio is a function of the Brunt-Vaisala frequencies within the vortex and outside the vortex, the Coriolis parameter, and the Rossby number of the vortex. This equation is basically the gradient-wind equation integrated over the vortex, and is significantly different from the previously proposed scaling laws that find the aspect ratio to be only a function of the properties of the background flow, and independent of the dynamics of the vortex. Our relation is valid for cyclones and anticyclones in either the cyclostrophic or geostrophic regimes; it works with vortices in Boussinesq fluids or ideal gases, and non-uniform background density gradient. The relation for the aspect ratio has many consequences for quasi-equilibrium vortices in rotating stratified flows. For example, cyclones must have interiors more stratified than the background flow (i.e., super-stratified), and weak anticyclones must have interiors less stratified than the background (i.e., sub-stratified). In addition, this equation is useful to

Unsteady Force Calculations in Turbomachinery

DTIC Science & Technology

1991-07-01

Engineering for Gas Turbines and Power, Vol. 107, pp. 945-952, October 1985. Lefcort, M. P., "An Investigation into Unsteady Blade Forces in...generated unsteady flow around a rotating turbine blade row .. ..... 43 7 The rotating coordinate system with skew, 0, and rake, zr, defined at midchord...while Kerrebrock and Mikolajczak [19701 5 proved it experimentally. For a turbine blade passage, the wake fluid moves from the pressure 3 surface to the

Interaction forces between red cells agglutinated by antibody. II. Measurement of hydrodynamic force of breakup.

PubMed Central

Tha, S P; Shuster, J; Goldsmith, H L

1986-01-01

The expressions derived in the previous paper for the respective normal, F3, and shear forces, Fshear, acting along and perpendicular to the axis of a doublet of rigid spheres, were used to determine the hydrodynamic forces required to separate two red cell spheres of antigenic type B crosslinked by the corresponding antibody. Cells were sphered and swollen in isotonic buffered glycerol containing 8 X 10(-5) M sodium dodecyl sulfate, fixed in 0.085% glutaraldehyde, and suspended in aqueous glycerol (viscosity: 15-34 mPa s), containing 0.15 M NaCl and anti-B antibody from human hyperimmune antiserum at concentrations from 0.73 to 3.56 vol%. After incubating and mixing for 12 h, doublets were observed through a microscope flowing in a 178-micron tube by gravity feed between two reservoirs. Using a traveling microtube apparatus, the doublets were tracked in a constantly accelerating flow and the translational and rotational motions were recorded on videotape until breakup occurred. From a frame by frame replay of the tape, the radial position, velocity and orientation of the doublet were obtained and the normal and shear forces of separation at breakup computed. Both forces increased significantly with increasing antiserum concentration, the mean values of F3 increasing from 0.060 to 0.197 nN, and Fshear from 0.023 to 0.072 nN. There was no significant effect of glycerol viscosity on the forces of separation. It was not possible to determine whether the shear or normal force was responsible for doublet separation. Measurements of the mean dimensionless period of rotation, TG, of doublets in suspensions containing 0.73 and 2.40% antiserum undergoing steady flow were also made to test whether the spheres were rigidly linked or capable of some independent rotation. A fairly narrow distribution in TG about the value 15.64, predicted for rigidly-linked doublets, was obtained at both antiserum concentrations. Images FIGURE 1 PMID:3801572

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

Experiment measurement of Alford's force in axial-flow turbomachinery

NASA Technical Reports Server (NTRS)

Vance, J. M.; Laudadio, F. J.

1982-01-01

Results of experimental measurements made on a small high speed, axial flow test apparatus are presented to verify the existence of Alford's force (that circumferential variation of blade-tip clearances in axial-flow turbomachinery will produce cross-coupled (normal to the eccentricity) aerodynamic forces on the rotor) and to investigate the validity of his mathematical prediction model.

Method of analysis for compressible flow through mixed-flow centrifugal impellers of arbitrary design

NASA Technical Reports Server (NTRS)

Hamrick, Joseph T; Ginsburg, Ambrose; Osborn, Walter M

1952-01-01

A method is presented for analysis of the compressible flow between the hub and the shroud of mixed-flow impellers of arbitrary design. Axial symmetry was assumed, but the forces in the meridional (hub to shroud) plane, which are derived from tangential pressure gradients, were taken into account. The method was applied to an experimental mixed-flow impeller. The analysis of the flow in the meridional plane of the impeller showed that the rotational forces, the blade curvature, and the hub-shroud profile can introduce severe velocity gradients along the hub and the shroud surfaces. Choked flow at the impeller inlet as determined by the analysis was verified by experimental results.

Scaling laws for homogeneous turbulent shear flows in a rotating frame

NASA Technical Reports Server (NTRS)

Speziale, Charles G.; Mhuiris, Nessan Macgiolla

1988-01-01

The scaling properties of plane homogeneous turbulent shear flows in a rotating frame are examined mathematically by a direct analysis of the Navier-Stokes equations. It is proved that two such shear flows are dynamically similar if and only if their initial dimensionless energy spectrum E star (k star, 0), initial dimensionless shear rate SK sub 0/epsilon sub 0, initial Reynolds number K squared sub 0/nu epsilon sub 0, and the ration of the rotation rate to the shear rate omega/S are identical. Consequently, if universal equilibrium states exist, at high Reynolds numbers, they will only depend on the single parameter omega/S. The commonly assumed dependence of such equilibrium states on omega/S through the Richardson number Ri=-2(omega/S)(1-2 omega/S) is proven to be inconsistent with the full Navier-Stokes equations and to constitute no more than a weak approximation. To be more specific, Richardson number similarity is shown to only rigorously apply to certain low-order truncations of the Navier-Stokes equations (i.e., to certain second-order closure models) wherein closure is achieved at the second-moment level by assuming that the higher-order moments are a small perturbation of their isotropic states. The physical dependence of rotating turbulent shear flows on omega/S is discussed in detail along with the implications for turbulence modeling.

The effects of oscillating forces upon the flow of dental cements.

PubMed

Judge, R B; Wilson, P R

1999-11-01

The aim of this study was to evaluate the effect of oscillating forces upon the flow of five dental cements. A laboratory investigation was carried out using a crown and die. It showed that the application of oscillating forces improved the flow of the tested dental cements when combined with low static loads and wide crown-die separations. The oscillating forces enhanced the late, particle-dominated phase of cement flow. Further investigations characterised the nature of the oscillating forces applied in this experiment and revealed yield stress behaviour shown by one cement.

Extension and comparison of neoclassical models for poloidal rotation in tokamaks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stacey, W. M.

2008-01-15

Several neoclassical models for the calculation of poloidal rotation in tokamaks were rederived within a common framework, extended to include additional physics and numerically compared. The importance of new physics phenomena not usually included in poloidal rotation calculations (e.g., poloidal electric field, VxB force resulting from enhanced radial particle flow arising from the ionization of recycling neutrals) was examined. Extensions of the Hirshman-Sigmar, Kim-Diamond-Groebner, and Stacey-Sigmar poloidal rotation models are presented.

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…

Rotational flow in tapered slab rocket motors

NASA Astrophysics Data System (ADS)

Saad, Tony; Sams, Oliver C.; Majdalani, Joseph

2006-10-01

Internal flow modeling is a requisite for obtaining critical parameters in the design and fabrication of modern solid rocket motors. In this work, the analytical formulation of internal flows particular to motors with tapered sidewalls is pursued. The analysis employs the vorticity-streamfunction approach to treat this problem assuming steady, incompressible, inviscid, and nonreactive flow conditions. The resulting solution is rotational following the analyses presented by Culick for a cylindrical motor. In an extension to Culick's work, Clayton has recently managed to incorporate the effect of tapered walls. Here, an approach similar to that of Clayton is applied to a slab motor in which the chamber is modeled as a rectangular channel with tapered sidewalls. The solutions are shown to be reducible, at leading order, to Taylor's inviscid profile in a porous channel. The analysis also captures the generation of vorticity at the surface of the propellant and its transport along the streamlines. It is from the axial pressure gradient that the proper form of the vorticity is ascertained. Regular perturbations are then used to solve the vorticity equation that prescribes the mean flow motion. Subsequently, numerical simulations via a finite volume solver are carried out to gain further confidence in the analytical approximations. In illustrating the effects of the taper on flow conditions, comparisons of total pressure and velocity profiles in tapered and nontapered chambers are entertained. Finally, a comparison with the axisymmetric flow analog is presented.

Control of Meridional Flow by a Non-Uniform Rotational Magnetic Field

NASA Technical Reports Server (NTRS)

Mazuruk, Konstantin; Ramachandran, Narayanan

1999-01-01

The diffusive mass transfer of species during crystal growth in vertical ampoules is significantly affected by fluid flow in the liquid mother phase (melt). For electrically conductive melts, an elegant way of remotely inducing and controlling this flow is by utilizing a uniform rotational magnetic field (RMF) in the transverse direction. It induces an azimuthal flow which tends to homogenize the thermal and solutal fields. The rotating field also reduces the diffusion boundary layer, stabilizes temperature fluctuations, and promotes better overall crystal growth. For moderate strengths of the applied magnetic field (2-20 m Tesla) with frequencies of up to 400 Hz, the induced secondary meridional flow becomes significant. It typically consists of one roll at the bottom of the liquid column and a second roll (vortex) at the top. The flow along the centerline (ampoule axis) is directed from the growing solid (interface) towards the liquid (melt). In case of convex interfaces (e.g. in floating zone crystal growth) such flow behavior is beneficial since it suppresses diffusion at the center. However, for concave interfaces (e.g. vertical Bridgman crystal growth) such a flow tends to exacerbate the situation in making the interface shape more concave. It would be beneficial to have some control of this meridional flow- for example, a single recirculating cell with controllable direction and flow magnitude will make this technique even more attractive for crystal growth. Such flow control is a possibility if a non-uniform PNE field is utilized for this purpose. Although this idea has been proposed earlier, it has not been conclusively demonstrated so far. In this work, we derive the governing equations for the fluid dynamics for such a system and obtain solutions for a few important cases. Results from parallel experimental measurements of fluid flow in a mercury column subjected to non-uniform RMF will also be presented.

Large eddy simulation of orientation and rotation of ellipsoidal particles in isotropic turbulent flows

NASA Astrophysics Data System (ADS)

Chen, Jincai; Jin, Guodong; Zhang, Jian

2016-03-01

The rotational motion and orientational distribution of ellipsoidal particles in turbulent flows are of significance in environmental and engineering applications. Whereas the translational motion of an ellipsoidal particle is controlled by the turbulent motions at large scales, its rotational motion is determined by the fluid velocity gradient tensor at small scales, which raises a challenge when predicting the rotational dispersion of ellipsoidal particles using large eddy simulation (LES) method due to the lack of subgrid scale (SGS) fluid motions. We report the effects of the SGS fluid motions on the orientational and rotational statistics, such as the alignment between the long axis of ellipsoidal particles and the vorticity, the mean rotational energy at various aspect ratios against those obtained with direct numerical simulation (DNS) and filtered DNS. The performances of a stochastic differential equation (SDE) model for the SGS velocity gradient seen by the particles and the approximate deconvolution method (ADM) for LES are investigated. It is found that the missing SGS fluid motions in LES flow fields have significant effects on the rotational statistics of ellipsoidal particles. Alignment between the particles and the vorticity is weakened; and the rotational energy of the particles is reduced in LES. The SGS-SDE model leads to a large error in predicting the alignment between the particles and the vorticity and over-predicts the rotational energy of rod-like particles. The ADM significantly improves the rotational energy prediction of particles in LES.

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.

Steady flow in a rotating sphere with strong precession

NASA Astrophysics Data System (ADS)

Kida, Shigeo

2018-04-01

The steady flow in a rotating sphere is investigated by asymptotic analysis in the limit of strong precession. The whole spherical body is divided into three regions in terms of the flow characteristics: the critical band, which is the close vicinity surrounding the great circle perpendicular to the precession axis, the boundary layer, which is attached to the whole sphere surface and the inviscid region that occupies the majority of the sphere. The analytic expressions, in the leading order of the asymptotic expansion, of the velocity field are obtained in the former two, whereas partial differential equations for the velocity field are derived in the latter, which are solved numerically. This steady flow structure is confirmed by the corresponding direct numerical simulation.

Magnetic moment of solar plasma and the Kelvin force: -The driving force of plasma up-flow -

NASA Astrophysics Data System (ADS)

Shibasaki, Kiyoto

2017-04-01

Thermal plasma in the solar atmosphere is magnetized (diamagnetic). The magnetic moment does not disappear by collisions because complete gyration is not a necessary condition to have magnetic moment. Magnetized fluid is subjected to Kelvin force in non-uniform magnetic field. Generally, magnetic field strength decreases upwards in the solar atmosphere, hence the Kelvin force is directed upwards along the field. This force is not included in the fluid treatment of MHD. By adding the Kelvin force to the MHD equation of motion, we can expect temperature dependent plasma flows along the field which are reported by many observations. The temperature dependence of the flow speed is explained by temperature dependence of magnetic moment. From the observed parameters, we can infer physical parameters in the solar atmosphere such as scale length of the magnetic field strength and the friction force acting on the flowing plasma. In case of closed magnetic field lines, loop-top concentration of hot plasma is expected which is frequently observed.

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.

Wave propagation reversal for wavy vortices in wide-gap counter-rotating cylindrical Couette flow.

PubMed

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.

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

Counter Clockwise Rotation of Cylinder with Variable Position to Control Base Flows

NASA Astrophysics Data System (ADS)

Asadullah, Mohammed; Khan, S. A.; Asrar, Waqar; Sulaeman, E.

2018-05-01

Experimental study of supersonic base flow at Mach 2 has been carried out to see the effect of cylinder when rotated counter clockwise inside the dead zone at variable locations near its base to control base pressure for different level of expansion for area ratio 9. Active cylinder of 2 mm diameter rotating counter clockwise when seen from top, is mounted as a controller. Three locations are chosen from the side wall of square duct namely at 2, 4, 6 mm respectively and 8 mm from square nozzle exit in the base region to mount the controller. Base pressure in recirculation zone and wall pressure along the square duct length has been measured with and without control. The experiments were carried out for NPR 2, 3, 6, 7.8 and 8.5. Cylinder when rotated counter clockwise as an active controller were found to reduce the base drag as high as 62 percent at NPR 8.5 when located near to duct wall and 50 percent when located away from duct wall for the same NPR. For perfectly expanded flows at NPR 7.8 the reduction in base drag was 53 percent near duct wall and 44 percent near duct wall. The active controller was up to 19 percentage effective for over expanded flows near to duct wall and up to 12 percent when located away from duct wall. Also, the control did not adversely affect the flow field.

Coarsening dynamics of binary liquids with active rotation.

PubMed

Sabrina, Syeda; Spellings, Matthew; Glotzer, Sharon C; Bishop, Kyle J M

2015-11-21

Active matter comprised of many self-driven units can exhibit emergent collective behaviors such as pattern formation and phase separation in both biological (e.g., mussel beds) and synthetic (e.g., colloidal swimmers) systems. While these behaviors are increasingly well understood for ensembles of linearly self-propelled "particles", less is known about the collective behaviors of active rotating particles where energy input at the particle level gives rise to rotational particle motion. A recent simulation study revealed that active rotation can induce phase separation in mixtures of counter-rotating particles in 2D. In contrast to that of linearly self-propelled particles, the phase separation of counter-rotating fluids is accompanied by steady convective flows that originate at the fluid-fluid interface. Here, we investigate the influence of these flows on the coarsening dynamics of actively rotating binary liquids using a phenomenological, hydrodynamic model that combines a Cahn-Hilliard equation for the fluid composition with a Navier-Stokes equation for the fluid velocity. The effect of active rotation is introduced though an additional force within the Navier-Stokes equations that arises due to gradients in the concentrations of clockwise and counter-clockwise rotating particles. Depending on the strength of active rotation and that of frictional interactions with the stationary surroundings, we observe and explain new dynamical behaviors such as "active coarsening" via self-generated flows as well as the emergence of self-propelled "vortex doublets". We confirm that many of the qualitative behaviors identified by the continuum model can also be found in discrete, particle-based simulations of actively rotating liquids. Our results highlight further opportunities for achieving complex dissipative structures in active materials subject to distributed actuation.

Numerical analysis of rotating stall instabilities of a pump- turbine in pump mode

NASA Astrophysics Data System (ADS)

Xia, L. S.; Cheng, Y. G.; Zhang, X. X.; Yang, J. D.

2014-03-01

Rotating stall may occur at part load flow of a pump-turbine in pump mode. Unstable flow structures developing under stall condition can lead to a sudden drop of efficiency, high dynamic load and even cavitation. CFD simulations on a pump-turbine model in pump mode were carried out to reveal the onset and developed mechanisms of these unstable flow phenomena at part load. The simulation results of energy-discharge and efficiency characteristics are in good agreement with those obtained by experiments. The more deviate from design conditions with decreasing flow rate, the more flow separations within the vanes. Under specific conditions, four stationary separation zones begin to progress on the circumference, rotating at a fraction of the impeller rotation rate. Rotating stalls lead to the flow in the vane diffuser channels alternating between outward jet flow and blockage. Strong jets impact the spiral casing wall causing high pressure pulsations. Severe separations of the stall cells disturb the flow inducing periodical large amplitude pressure fluctuations, of which the intensity at different span wise of the guide vanes is different. The enforced rotating nonuniform pressure distributions on the circumference lead to dynamic uniform forces on the impeller and guide vanes. The results show that the CFD simulations are capable to gain the complicated flow structure information for analysing the unstable characteristics of the pump mode at part load.

Spectral element simulation of precession driven flows in the outer cores of spheroidal planets

NASA Astrophysics Data System (ADS)

Vormann, Jan; Hansen, Ulrich

2015-04-01

A common feature of the planets in the solar system is the precession of the rotation axes, driven by the gravitational influence of another body (e.g. the Earth's moon). In a precessing body, the rotation axis itself is rotating around another axis, describing a cone during one precession period. Similar to the coriolis and centrifugal force appearing from the transformation to a rotating system, the addition of precession adds another term to the Navier-Stokes equation, the so called Poincaré force. The main geophysical motivation in studying precession driven flows comes from their ability to act as magnetohydrodynamic dynamos in planets and moons. Precession may either act as the only driving force or operate together with other forces such as thermochemical convection. One of the challenges in direct numerical simulations of such flows lies in the spheroidal shape of the fluid volume, which should not be neglected since it contributes an additional forcing trough pressure torques. Codes developed for the simulation of flows in spheres mostly use efficient global spectral algorithms that converge fast, but lack geometric flexibility, while local methods are usable in more complex shapes, but often lack high accuracy. We therefore adapted the spectral element code Nek5000, developed at Argonne National Laboratory, to the problem. The spectral element method is capable of solving for the flow in arbitrary geometries while still offering spectral convergence. We present first results for the simulation of a purely hydrodynamic, precession-driven flow in a spheroid with no-slip boundaries and an inner core. The driving by the Poincaré force is in a range where theoretical work predicts multiple solutions for a laminar flow. Our simulations indicate a transition to turbulent flows for Ekman numbers of 10-6 and lower.

Dynamic self-assembly and directed flow of rotating colloids in microchannels

NASA Astrophysics Data System (ADS)

Götze, Ingo O.; Gompper, Gerhard

2011-09-01

Nonequilibrium structure formation and dynamics in suspensions of superparamagnetic colloids driven by an external rotating magnetic field are studied by particle-based mesoscale hydrodynamics simulations in confined geometry. We address the fundamental question how the rotation of the colloids about their own axes can be converted into a translational motion by breaking the symmetry of the confining geometry. We study a two-dimensional system of colloids with short-range repulsive interactions, which mimics flow in shallow microchannels. In straight channels, we observe a two-way traffic but—for symmetry reasons—no net transport. However, by keeping some colloids fixed near one of the two walls, net transport can be achieved. This approach allows the control and switchability of the flow in complex microchannel networks. A minimal geometry that fulfills the requirement of broken symmetry are ring channels. We determine the translational velocity of the spinning colloids and study its dependence on the channel width for various median radii. We conclude that spinning colloids present a promising alternative for flow generation and control in microfluidic devices.

Experimental investigation of the hydrodynamic forces on the shroud of a centrifugal pump impeller. Thesis

NASA Technical Reports Server (NTRS)

Zhuang, Fei

1989-01-01

Fluid-induced forces acting on a rotating impeller are known to cause rotor-dynamic problems in turbomachines. The forces generated by leakage flow along the front shroud surface of a centrifugal turbomachine impeller play an important role among these fluid-induced forces. The present research was aimed to gain a better understanding of these shroud forces. An experimental apparatus was designed and constructed to simulate the impeller shroud leakage flow. Hydrodynamic forces and steady and unsteady pressure distributions on the rotating shroud were measured as functions of eccentricity, width of shroud clearance, face seal clearance and shaft rotating speed. The forces measured from the dynamometer and manometers agreed well. The hydrodynamic force matrices were found skew-symmetric and statically unstable. This is qualitatively similar to the result of previous hydrodynamic volute force measurements. Nondimensionalized normal and tangential forces decrease slightly as Reynolds number increases. As the width of the shroud clearance decreases and/or the eccentricity increases, the hydrodynamic forces increase nonlinearly. There was some evidence found that increased front seal clearance could reduce the radial shroud forces and the relative magnitude of the destabilizing tangential force. Subharmonic pressure fluctuations were also observed which may adversely affect the behavior of the rotor system.

Acute Effects of Foot Rotation in Healthy Adults during Running on Knee Moments and Lateral-Medial Shear Force

PubMed Central

Valenzuela, Kevin A.; Lynn, Scott K.; Noffal, Guillermo J.; Brown, Lee E.

2016-01-01

As runners age, the likelihood of developing osteoarthritis (OA) significantly increases as 10% of people 55+ have symptomatic knee OA while 70% of people 65+ have radiographic signs of knee OA. The lateral-medial shear force (LMF) and knee adduction moment (KAM) during gait have been associated with cartilage loading which can lead to OA. Foot rotation during gait has been shown to alter the LMF and KAM, however it has not been investigated in running. The purpose of this study was to investigate changes in the KAM and LMF with foot rotation during running. Twenty participants volunteered and performed five running trials in three randomized conditions (normal foot position [NORM], external rotation [EXT], and internal rotation [INT]) at a running speed of 3.35m·s-1 on a 20 meter runway. Kinematic and kinetic data were gathered using a 9-camera motion capture system and a force plate, respectively. Repeated measures ANOVAs determined differences between conditions. The KAM and LMF were lower in both EXT and INT conditions compared to the NORM, but there were no differences between EXT and INT conditions. The decreases in KAM and LMF in the EXT condition were expected and concur with past research in other activities. The reductions in the INT condition were unexpected and contradict the literature. This may indicate that participants are making mechanical compensations at other joints to reduce the KAM and LMF in this abnormal internal foot rotation condition. Key points External rotation of the foot during running reduced the loads on the medial compartment of the knee Internal rotation of the foot also reduced the medial loads, but is a more unnatural intervention External and internal rotation reduced the shear forces on the knee, which may help slow the degeneration of knee joint cartilage PMID:26957926

Computer modeling of the stalled flow of a rotating cylinder and the reverse magnus effect

NASA Astrophysics Data System (ADS)

Belotserkovskii, S. M.; Kotovskii, V. N.; Nisht, M. I.; Fedorov, R. M.

1985-02-01

Unsteady stalled flow around a rotating cylinder is investigated in a numerical experiment. Attention is mostly given to the reverse Magnus effect which was discovered in tube experiments at some critical rotational speed of the cylinder.

Multiscale Analysis of Rapidly Rotating Dynamo Simulations

NASA Astrophysics Data System (ADS)

Orvedahl, R.; Calkins, M. A.; Featherstone, N. A.

2017-12-01

The magnetic field of the planets and stars are generated by dynamo action in their electrically conducting fluid interiors. Numerical models of this process solve the fundamental equations of magnetohydrodynamics driven by convection in a rotating spherical shell. Rotation plays an important role in modifying the resulting convective flows and the self-generated magnetic field. We present results of simulating rapidly rotating systems that are unstable to dynamo action. We use the pseudo-spectral code Rayleigh to generate a suite of direct numerical simulations. Each simulation uses the Boussinesq approximation and is characterized by an Ekman number (Ek=ν /Ω L2) of 10-5. We vary the degree of convective forcing to obtain a range of convective Rossby numbers. The resulting flows and magnetic structures are analyzed using a Reynolds decomposition. We determine the relative importance of each term in the scale-separated governing equations and estimate the relevant spatial scales responsible for generating the mean magnetic field.

Multiscale Analysis of Rapidly Rotating Dynamo Simulations

NASA Astrophysics Data System (ADS)

Orvedahl, Ryan; Calkins, Michael; Featherstone, Nicholas

2017-11-01

The magnetic field of the planets and stars are generated by dynamo action in their electrically conducting fluid interiors. Numerical models of this process solve the fundamental equations of magnetohydrodynamics driven by convection in a rotating spherical shell. Rotation plays an important role in modifying the resulting convective flows and the self-generated magnetic field. We present results of simulating rapidly rotating systems that are unstable to dynamo action. We use the pseudo-spectral code Rayleigh to generate a suite of direct numerical simulations. Each simulation uses the Boussinesq approximation and is characterized by an Ekman number (Ek = ν / ΩL2) of 10-5. We vary the degree of convective forcing to obtain a range of convective Rossby numbers. The resulting flows and magnetic structures are analyzed using a Reynolds decomposition. We determine the relative importance of each term in the scale-separated governing equations and estimate the relevant spatial scales responsible for generating the mean magnetic field.

Numerical study of magnetohydrodynamic viscous plasma flow in rotating porous media with Hall currents and inclined magnetic field influence

NASA Astrophysics Data System (ADS)

Bég, O. Anwar; Sim, Lik; Zueco, J.; Bhargava, R.

2010-02-01

A numerical solution is developed for the viscous, incompressible, magnetohydrodynamic flow in a rotating channel comprising two infinite parallel plates and containing a Darcian porous medium, the plates lying in the x-z plane, under constant pressure gradient. The system is subjected to a strong, inclined magnetic field orientated to the positive direction of the y-axis (rotational axis, normal to the x-z plane). The Navier-Stokes flow equations for a general rotating hydromagnetic flow are reduced to a pair of linear, viscous partial differential equations neglecting convective acceleration terms, for primary velocity (u‧) and secondary velocity (v‧) where these velocities are directed along the x and y axes. Only viscous terms are retained in the momenta equations. The model is non-dimensionalized and shown to be controlled by a number of dimensionless parameters. The resulting dimensionless ordinary differential equations are solved using a robust numerical method, Network Simulation Methodology. Full details of the numerics are provided. The present solutions are also benchmarked against the analytical solutions presented recently by Ghosh and Pop [Ghosh SK, Pop I. An analytical approach to MHD plasma behaviour of a rotating environment in the presence of an inclined magnetic field as compared to excitation frequency. Int J Appl Mech Eng 2006;11(4):845-856] for the case of a purely fluid medium (infinite permeability). We study graphically the influence of Hartmann number (Ha, magnetic field parameter), Ekman number (Ek, rotation parameter), Hall current parameter (Nh), Darcy number (Da, permeability parameter), pressure gradient (Np) and also magnetic field inclination (θ) on primary and secondary velocity fields. Additionally we investigate the effects of these multiphysical parameters on the dimensionless shear stresses at the plates. Both primary and secondary velocity are seen to be increased with a rise in Darcy number, owing to a simultaneous

Primate-inspired vehicle navigation using optic flow and mental rotations

NASA Astrophysics Data System (ADS)

Arkin, Ronald C.; Dellaert, Frank; Srinivasan, Natesh; Kerwin, Ryan

2013-05-01

Robot navigation already has many relatively efficient solutions: reactive control, simultaneous localization and mapping (SLAM), Rapidly-Exploring Random Trees (RRTs), etc. But many primates possess an additional inherent spatial reasoning capability: mental rotation. Our research addresses the question of what role, if any, mental rotations can play in enhancing existing robot navigational capabilities. To answer this question we explore the use of optical flow as a basis for extracting abstract representations of the world, comparing these representations with a goal state of similar format and then iteratively providing a control signal to a robot to allow it to move in a direction consistent with achieving that goal state. We study a range of transformation methods to implement the mental rotation component of the architecture, including correlation and matching based on cognitive studies. We also include a discussion of how mental rotations may play a key role in understanding spatial advice giving, particularly from other members of the species, whether in map-based format, gestures, or other means of communication. Results to date are presented on our robotic platform.

Analog and numerical experiments investigating force chain influences on bed conditions in granular flows

NASA Astrophysics Data System (ADS)

Estep, J.; Dufek, J.

2013-12-01

Granular flows are fundamental processes in several terrestrial and planetary natural events; including surficial flows on volcanic edifices, debris flows, landslides, dune formation, rock falls, sector collapses, and avalanches. Often granular flows can be two-phase, whereby interstitial fluids occupy void space within the particulates. The mobility of granular flows has received significant attention, however the physics that govern their internal behavior remain poorly understood. Here we extend upon previous research showing that force chains can transmit extreme localized forces to the substrates of free surface granular flows, and we combine experimental and computational approaches to further investigate the forces at the bed of simplified granular flows. Analog experiments resolve discrete bed forces via a photoelastic technique, while numerical experiments validate laboratory tests using discrete element model (DEM) simulations. The current work investigates (1) the role of distributed grain sizes on force transmission via force chains, and (2) how the inclusion of interstitial fluids effects force chain development. We also include 3D numerical simulations to apply observed 2D characteristics into real world perspective, and ascertain if the added dimension alters force chain behavior. Previous research showed that bed forces generated by force chain structures can transiently greatly exceed (by several 100%) the bed forces predicted from continuum approaches, and that natural materials are more prone to excessive bed forces than photoelastic materials due to their larger contact stiffnesses. This work suggests that force chain activity may play an important role in the bed physics of dense granular flows by influencing substrate entrainment. Photoelastic experiment image showing force chains in gravity driven granular flow.

Periodic perturbations with rotational symmetry of planar systems driven by a central force

NASA Astrophysics Data System (ADS)

Fonda, Alessandro; Gallo, Anna Chiara

2018-06-01

We consider periodic perturbations of a central force field having a rotational symmetry, and prove the existence of nearly circular periodic orbits. We thus generalize, in the planar case, some previous bifurcation results obtained by Ambrosetti and Coti Zelati in [1]. Our results apply, in particular, to the classical Kepler problem.

A model for origin of self-rotation in a protoplanetary cloud under action of exterior periodic force

NASA Astrophysics Data System (ADS)

Tkachova, P. P.; Krot, A. M.

2009-04-01

This work investigates condition for origin of increasing rotational disturbance in a gas-liquid protoplanetary cloud under action of a periodic force. The model (based on Reynolds equations [1]) describing self-organization of rotational disturbance of viscous gas-liquid substance into a protoplanetary cloud is proposed. The Reynolds equations as well as continuity equation in cylindrical frame of reference (r, e, z) as basis relations for this analytical model are used. The mean velocity is supposed to be equal to zero from the beginning action of an exterior periodic force. The Reynolds' tensor of turbulent strain of velocity disturbances in a becoming fluid flow is sought for (besides, z-component of velocity disturbance is supposed to be equal to zero). In assumption that z-components of turbulent strains are equal to zero, the (r, e)-turbulent strain components are found. After all considerations the Reynolds equations and continuity one (in the cylindrical coordinate system) are reduced to the system of two differential equations in partial derivatives relatively to (r, e)-cylindrical components of turbulent strain of velocity disturbance. A common solution of these two equations permits us to reduce this task to solution of one differential equation relatively to (r, e)-turbulent strain. This homogeneous differential equation is solved with usage of the variables separation method. As a result, a superposition of two cosine's and sine's waves gives us (r, e)-turbulent strain wave with an elliptic (or circular) polarization. Moreover, this paper shows that amplitude of cosine-wave as well as sine-wave is an increasing function as r**(n**2-2). This paper finds that oscillations are intensified with growing a frequency of becoming oscillations. The computational experiments based on STAR-CD package [2] confirm the main analytical statements of the proposed model for becoming self-rotation in a gas-liquid protoplanetary cloud. This work develops also the

Perspectives on continuum flow models for force-driven nano-channel liquid flows

NASA Astrophysics Data System (ADS)

Beskok, Ali; Ghorbanian, Jafar; Celebi, Alper

2017-11-01

A phenomenological continuum model is developed using systematic molecular dynamics (MD) simulations of force-driven liquid argon flows confined in gold nano-channels at a fixed thermodynamic state. Well known density layering near the walls leads to the definition of an effective channel height and a density deficit parameter. While the former defines the slip-plane, the latter parameter relates channel averaged density with the desired thermodynamic state value. Definitions of these new parameters require a single MD simulation performed for a specific liquid-solid pair at the desired thermodynamic state and used for calibration of model parameters. Combined with our observations of constant slip-length and kinematic viscosity, the model accurately predicts the velocity distribution and volumetric and mass flow rates for force-driven liquid flows in different height nano-channels. Model is verified for liquid argon flow at distinct thermodynamic states and using various argon-gold interaction strengths. Further verification is performed for water flow in silica and gold nano-channels, exhibiting slip lengths of 1.2 nm and 15.5 nm, respectively. Excellent agreements between the model and the MD simulations are reported for channel heights as small as 3 nm for various liquid-solid pairs.

Effects of composition of grains of debris flow on its impact force

NASA Astrophysics Data System (ADS)

Tang, jinbo; Hu, Kaiheng; Cui, Peng

2017-04-01

Debris flows compose of solid material with broad size distribution from fine sand to boulders. Impact force imposed by debris flows is a very important issue for protection engineering design and strongly influenced by their grain composition. However, this issue has not been studied in depth and the effects of grain composition not been considered in the calculation of the impact force. In this present study, the small-scale flume experiments with five kinds of compositions of grains for debris flow were carried out to study the effect of the composition of grains of debris flow on its impact force. The results show that the impact force of debris flow increases with the grain size, the hydrodynamic pressure of debris flow is calibrated based on the normalization parameter dmax/d50, in which dmax is the maximum size and d50 is the median size. Furthermore, a log-logistic statistic distribution could be used to describe the distribution of magnitude of impact force of debris flow, where the mean and the variance of the present distribution increase with grain size. This distribution proposed in the present study could be used to the reliability analysis of structures impacted by debris flow.

A novel approach of magnetorheological abrasive fluid finishing with swirling-assisted inlet flow

NASA Astrophysics Data System (ADS)

Kheradmand, Saeid; Esmailian, Mojtaba; Fatahy, A.

Abrasive flow machining has been the pioneer of new finishing processes. Rotating workpiece and imposing a magnetic field using magnetorheological working medium are some assisting manipulations to improve surface finishing, because they can increase the forces on the workpiece surface. Similarly, swirling the inlet flow using stationary swirler vanes, as a novel idea, may also increase forces on the surface, and then raise the material removal, with a lower expense and energy consumption compared with the case of workpiece rotation. Thus, in this paper, surface roughness improvement is studied in a pipe with rotating inlet flow of a magnetorheological finishing medium under imposing a magnetic field. The results are compared with the case of rotating workpiece, using 3D numerical simulation. The governing hydrodynamic parameters are investigated in both cases to monitor the flow variations. It is shown that surface roughness is improved by rotating inlet flow. However, it is found that finishing in the entrance length of swirling-assisted inlet flow can be so economical for short length workpieces, compared with the case of rotating workpiece, with very near Ra values. By comparison of the numerical results and published experimental data, current study also shows the ability of the numerical simulation, as an inexpensive and efficient tool, to predict the surface roughness changes in finishing processes.

A rapid rotation to an inverted seated posture inhibits muscle force, activation, heart rate and blood pressure.

PubMed

Johar, Pramod; Grover, Varun; DiSanto, Mario C; Button, Duane C; Behm, David G

2013-08-01

Although previous studies have demonstrated neuromuscular and cardiovascular changes with slow inversion rates, emergencies, such as overturned vehicles and helicopters can occur rapidly. The purpose of this study was to investigate changes in neuromuscular and cardiovascular responses with rapid (1 s) and slower (3 s) transitions from upright to inverted seated positions. Twenty-two subjects performed separate and concurrent unilateral elbow flexion and leg extension maximal voluntary contractions (MVCs) for 6 s in an upright seated position and when inverted with 1 and 3 s rotations. Elbow flexion and leg extension force; biceps, triceps, quadriceps and hamstrings electromyographic (EMG) activity, heart rate (HR), systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured. Whether the elbow flexion or leg extension contractions occurred concurrently or individually, significant (p < 0.05) decreases in MVC force and EMG activity were found when inverted within 1 and 3 s rotations as compared to upright. Triceps and hamstrings EMG activity (p < 0.05) decreased when inverted within 1 s rotation as compared to upright. Following rotation, the maintenance of the inverted position (3-6 s timepoint) resulted in a significant (p < 0.05) increase in leg extension MVC as compared to the initial second of rotation to inversion. HR, SBP and DBP demonstrated (p < 0.001) decreases when inverted within 1 and 3 s rotations as compared to upright. In conclusion, this is the first study to show that irrespective of rotation speed, inversion inhibited neuromuscular and cardiovascular responses, similar to the more deliberate, slower rotation of previous inversion studies.

Methods of measurement signal acquisition from the rotational flow meter for frequency analysis

NASA Astrophysics Data System (ADS)

Świsulski, Dariusz; Hanus, Robert; Zych, Marcin; Petryka, Leszek

One of the simplest and commonly used instruments for measuring the flow of homogeneous substances is the rotational flow meter. The main part of such a device is a rotor (vane or screw) rotating at a speed which is the function of the fluid or gas flow rate. A pulse signal with a frequency proportional to the speed of the rotor is obtained at the sensor output. For measurements in dynamic conditions, a variable interval between pulses prohibits the analysis of the measuring signal. Therefore, the authors of the article developed a method involving the determination of measured values on the basis of the last inter-pulse interval preceding the moment designated by the timing generator. For larger changes of the measured value at a predetermined time, the value can be determined by means of extrapolation of the two adjacent interpulse ranges, assuming a linear change in the flow. The proposed methods allow analysis which requires constant spacing between measurements, allowing for an analysis of the dynamics of changes in the test flow, eg. using a Fourier transform. To present the advantages of these methods simulations of flow measurement were carried out with a DRH-1140 rotor flow meter from the company Kobold.

The Inhibition of the Rayleigh-Taylor Instability by Rotation.

PubMed

Baldwin, Kyle A; Scase, Matthew M; Hill, Richard J A

2015-07-01

It is well-established that the Coriolis force that acts on fluid in a rotating system can act to stabilise otherwise unstable flows. Chandrasekhar considered theoretically the effect of the Coriolis force on the Rayleigh-Taylor instability, which occurs at the interface between a dense fluid lying on top of a lighter fluid under gravity, concluding that rotation alone could not stabilise this system indefinitely. Recent numerical work suggests that rotation may, nevertheless, slow the growth of the instability. Experimental verification of these results using standard techniques is problematic, owing to the practical difficulty in establishing the initial conditions. Here, we present a new experimental technique for studying the Rayleigh-Taylor instability under rotation that side-steps the problems encountered with standard techniques by using a strong magnetic field to destabilize an otherwise stable system. We find that rotation about an axis normal to the interface acts to retard the growth rate of the instability and stabilise long wavelength modes; the scale of the observed structures decreases with increasing rotation rate, asymptoting to a minimum wavelength controlled by viscosity. We present a critical rotation rate, dependent on Atwood number and the aspect ratio of the system, for stabilising the most unstable mode.

The Inhibition of the Rayleigh-Taylor Instability by Rotation

PubMed Central

Baldwin, Kyle A.; Scase, Matthew M.; Hill, Richard J. A.

2015-01-01

It is well-established that the Coriolis force that acts on fluid in a rotating system can act to stabilise otherwise unstable flows. Chandrasekhar considered theoretically the effect of the Coriolis force on the Rayleigh-Taylor instability, which occurs at the interface between a dense fluid lying on top of a lighter fluid under gravity, concluding that rotation alone could not stabilise this system indefinitely. Recent numerical work suggests that rotation may, nevertheless, slow the growth of the instability. Experimental verification of these results using standard techniques is problematic, owing to the practical difficulty in establishing the initial conditions. Here, we present a new experimental technique for studying the Rayleigh-Taylor instability under rotation that side-steps the problems encountered with standard techniques by using a strong magnetic field to destabilize an otherwise stable system. We find that rotation about an axis normal to the interface acts to retard the growth rate of the instability and stabilise long wavelength modes; the scale of the observed structures decreases with increasing rotation rate, asymptoting to a minimum wavelength controlled by viscosity. We present a critical rotation rate, dependent on Atwood number and the aspect ratio of the system, for stabilising the most unstable mode. PMID:26130005

Activation of biceps femoris long head reduces tibiofemoral anterior shear force and tibial internal rotation torque in healthy subjects

PubMed Central

Azmi, Nur Liyana; Ding, Ziyun; Xu, Rui

2018-01-01

The anterior cruciate ligament (ACL) provides resistance to tibial internal rotation torque and anterior shear at the knee. ACL deficiency results in knee instability. Optimisation of muscle contraction through functional electrical stimulation (FES) offers the prospect of mitigating the destabilising effects of ACL deficiency. The hypothesis of this study is that activation of the biceps femoris long head (BFLH) reduces the tibial internal rotation torque and the anterior shear force at the knee. Gait data of twelve healthy subjects were measured with and without the application of FES and taken as inputs to a computational musculoskeletal model. The model was used to investigate the optimum levels of BFLH activation during FES gait in reducing the anterior shear force to zero. This study found that FES significantly reduced the tibial internal rotation torque at the knee during the stance phase of gait (p = 0.0322) and the computational musculoskeletal modelling revealed that a mean BFLH activation of 20.8% (±8.4%) could reduce the anterior shear force to zero. At the time frame when the anterior shear force was zero, the internal rotation torque was reduced by 0.023 ± 0.0167 Nm/BW, with a mean 188% reduction across subjects (p = 0.0002). In conclusion, activation of the BFLH is able to reduce the tibial internal rotation torque and the anterior shear force at the knee in healthy control subjects. This should be tested on ACL deficient subject to consider its effect in mitigating instability due to ligament deficiency. In future clinical practice, activating the BFLH may be used to protect ACL reconstructions during post-operative rehabilitation, assist with residual instabilities post reconstruction, and reduce the need for ACL reconstruction surgery in some cases. PMID:29304102

Activation of biceps femoris long head reduces tibiofemoral anterior shear force and tibial internal rotation torque in healthy subjects.

PubMed

Azmi, Nur Liyana; Ding, Ziyun; Xu, Rui; Bull, Anthony M J

2018-01-01

The anterior cruciate ligament (ACL) provides resistance to tibial internal rotation torque and anterior shear at the knee. ACL deficiency results in knee instability. Optimisation of muscle contraction through functional electrical stimulation (FES) offers the prospect of mitigating the destabilising effects of ACL deficiency. The hypothesis of this study is that activation of the biceps femoris long head (BFLH) reduces the tibial internal rotation torque and the anterior shear force at the knee. Gait data of twelve healthy subjects were measured with and without the application of FES and taken as inputs to a computational musculoskeletal model. The model was used to investigate the optimum levels of BFLH activation during FES gait in reducing the anterior shear force to zero. This study found that FES significantly reduced the tibial internal rotation torque at the knee during the stance phase of gait (p = 0.0322) and the computational musculoskeletal modelling revealed that a mean BFLH activation of 20.8% (±8.4%) could reduce the anterior shear force to zero. At the time frame when the anterior shear force was zero, the internal rotation torque was reduced by 0.023 ± 0.0167 Nm/BW, with a mean 188% reduction across subjects (p = 0.0002). In conclusion, activation of the BFLH is able to reduce the tibial internal rotation torque and the anterior shear force at the knee in healthy control subjects. This should be tested on ACL deficient subject to consider its effect in mitigating instability due to ligament deficiency. In future clinical practice, activating the BFLH may be used to protect ACL reconstructions during post-operative rehabilitation, assist with residual instabilities post reconstruction, and reduce the need for ACL reconstruction surgery in some cases.

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.

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.

Time-Distance Helioseismology with f Modes as a Method for Measurement of Near-Surface Flows

NASA Technical Reports Server (NTRS)

Duvall, Thomas L., Jr.; Gizon, Laurent

1999-01-01

Travel times measured for the f mode have been used to study flows near the solar surface in conjunction with simultaneous measurements of the magnetic field. Previous flow measurements of doppler surface rotation, small magnetic feature rotation, supergranular pattern rotation, and surface meridional circulation have been confirmed. In addition, the flow in supergranules due to Coriolis forces has been measured. The spatial and temporal power spectra for a six-day observing sequence has been measured.

Negative Magnus lift on a rotating sphere at around the critical Reynolds number

NASA Astrophysics Data System (ADS)

Muto, Masaya; Tsubokura, Makoto; Oshima, Nobuyuki

2012-01-01

Negative Magnus lift acting on a sphere rotating about the axis perpendicular to an incoming flow was investigated using large-eddy simulation at three Reynolds numbers of 1.0 × 104, 2.0 × 105, and 1.14 × 106. The numerical methods used were first validated on a non-rotating sphere, and the spatial resolution around the sphere was determined so as to reproduce the laminar separation, reattachment, and turbulent transition of the boundary layer observed in the vicinity of the critical Reynolds number. The rotating sphere exhibited a positive or negative Magnus effect depending on the Reynolds number and the imposed rotating speed. At Reynolds numbers in the subcritical or supercritical regimes, the direction of the Magnus lift force was independent of the rotational speed. In contrast, the lift force was negative in the critical regime when particular rotating speeds were imposed. This negative Magnus effect was investigated in the context of suppression or promotion of boundary layer transition around the separation point.

LDV measurement of boundary layer on rotating blade surface in wind tunnel

NASA Astrophysics Data System (ADS)

Maeda, Takao; Kamada, Yasunari; Murata, Junsuke; Suzuki, Daiki; Kaga, Norimitsu; Kagisaki, Yosuke

2014-12-01

Wind turbines generate electricity due to extracting energy from the wind. The rotor aerodynamics strongly depends on the flow around blade. The surface flow on the rotating blade affects the sectional performance. The wind turbine surface flow has span-wise component due to span-wise change of airfoil section, chord length, twisted angle of blade and centrifugal force on the flow. These span-wise flow changes the boundary layer on the rotating blade and the sectional performance. Hence, the thorough understanding of blade surface flow is important to improve the rotor performance. For the purpose of clarification of the flow behaviour around the rotor blade, the velocity in the boundary layer on rotating blade surface of an experimental HAWT was measured in a wind tunnel. The velocity measurement on the blade surface was carried out by a laser Doppler velocimeter (LDV). As the results of the measurement, characteristics of surface flow are clarified. In optimum tip speed operation, the surface flow on leading edge and r/R=0.3 have large span-wise velocity which reaches 20% of sectional inflow velocity. The surface flow inboard have three dimensional flow patterns. On the other hand, the flow outboard is almost two dimensional in cross sectional plane.

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.

Doppler sonographic screening of the flow in the basilar artery during head rotation reduces the risk for sudden infant death.

PubMed

Deeg, K-H; Reisig, A

2010-10-01

Position-dependent hypoperfusion of the brain stem may be a risk factor of sudden infant death. From 1998 to 2009 we performed Doppler sonographic flow measurements in the basilar artery of 18 194 newborns, 9322 boys and 8872 girls, in five different positions: the neutral position with the head in the midline and during head rotation to the left and right in a supine or prone position. The peak systolic and the time average flow velocity were measured from the flow profile. The flow velocities during head rotation were converted to % of the flow in the neutral position. A decrease in the velocities during head rotation below 50 % was thought to be abnormal. Biphasic flow, flow oscillating around the zero line or retrograde flow during rotation was considered to be pathological. Head rotations, which had caused abnormal and pathological flow, were avoided. The incidence of SIDS in our study group was evaluated and compared with the incidence in a control group of 3 519 newborns. In 17 929 newborns (98.54 %) the blood flow in the basilar artery was independent of head rotation and body position. In 204 newborns (1.12 %) we found an abnormal decrease under 50 %. Pathological flow alterations could be found in 61 patients (0.33 %). The overall incidence rate of SIDS in the study group was 0.055 ‰ (1:18 194). The incidence rate of SIDS in the control group was 1.14 ‰ (4:3519). The comparison of both groups showed a statistically significant (p < 0.0030) lower incidence rate in the study group. Hypoperfusion of the brain stem may be a significant risk factor of SIDS. © Georg Thieme Verlag KG Stuttgart · New York.

Calculations of Alfven Wave Driving Forces, Plasma Flow and Current Drive in Tokamak Plasmas

NASA Astrophysics Data System (ADS)

Elfimov, Artur; Galvao, Ricardo; Amarante-Segundo, Gesil; Nascimento, Ivan

2000-10-01

A general form of time-averaged poloidal ponderomotive forces induced by fast and kinetic Alfvin waves by direct numerical calculations and in geometric optics approximation are analyzed on the basis of the collisionless two fluid (ions and electrons) magneto-hydrodynamics equation. Analytical approximations are used to clarify the effect of Larmour radius on radio-frequency (RF) ponderomotive forces and on poloidal flows induced by them in tokamak plasmas.The RF ponderomotive force is expressed as a sum of a gradient part and of a wave momentum transfer force, which is proportional to wave dissipation. The gradient electromagnetic stress force is combined with fluid dynamic (Reynolds) stress force. It is shown that accounting only Reynolds stress term can overestimate the plasma flow and it is found that the finite ion Larmor radius effect play fundamental role in ponderomotive forces that can drive a poloidal flow, which is larger than a flow driven by a wave momentum transfer force. Finally, balancing the RF forces by the electron-ion friction and viscous force the current and plasma flows driven by ponderomotive forces are calculated for tokamak plasmas, using a kinetic code [Phys. Plasmas, v.6 (1999) p.2437]. Strongly sheared current and plasma flow waves is found.

Two-dimensional models of fast rotating early-type stars

NASA Astrophysics Data System (ADS)

Rieutord, Michel

2015-08-01

Rotation has now become an unavoidable parameter of stellar models, but for most massive or intermediate-mass stars rotation is fast, at least of a significant fraction of the critical angular velocity. Current spherically symmetric models try to cope with this feature of the stars using various approximations, like for instance the so-called shellular rotation usually accompanied with a diffusion that is meant to represent the mixing induced by rotationally generated flows. Such approximations may be justified in the limit of slow rotation where anisotropies and associated flows are weak. However, when rotation is fast, say larger than 50% of the critical velocities the use of a spherically symmetric 1D-model is doubtful. This is not only because of the centrifugal flattening of the star, but also because of the flows that are induced by the baroclinic torque that naturally appears in the radiative envelope of an early-type (rotating) star. These flows face the cylindrical symmetry of the Coriolis force and the spheroidal symmetry of the effective gravity.In this talk I shall present the latest results of the ESTER project that has taken up the challenge of making two-dimensional (axisymmetric) models of stars rotating at any rotation rate. In particular, I will focus on main sequence massive and intermediate-mass stars. I'll show what should be expected in such stars as far as the differential rotation and the associated meridional circulation are concerned, notably the emergence of a Stewartson layer along the tangential cylinder of the core. I'll also indicate what may be inferred about the evolution of an intermediate-mass star at constant angular momentum and how Be stars may form. I shall finally give some comparisons between models and observations of the gravity darkening on some nearby fast rotators as it has been derived from interferometric observations. In passing, I'll also discuss how 2D models can help to recover the fundamental parameters of a star.

Development and Testing of an Integrated Rotating Dynamometer Based on Fiber Bragg Grating for Four-Component Cutting Force Measurement.

PubMed

Liu, Mingyao; Bing, Junjun; Xiao, Li; Yun, Kang; Wan, Liang

2018-04-18

Cutting force measurement is of great importance in machining processes. Hence, various methods of measuring the cutting force have been proposed by many researchers. In this work, a novel integrated rotating dynamometer based on fiber Bragg grating (FBG) was designed, constructed, and tested to measure four-component cutting force. The dynamometer consists of FBGs that are pasted on the newly designed elastic structure which is then mounted on the rotating spindle. The elastic structure is designed as two mutual-perpendicular semi-octagonal rings. The signals of the FBGs are transmitted to FBG interrogator via fiber optic rotary joints and optical fiber, and the wavelength values are displayed on a computer. In order to determine the static and dynamic characteristics, many tests have been done. The results show that it is suitable for measuring cutting force.

Differential rotation in solar-like stars from global simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guerrero, G.; Kosovichev, A. G.; Smolarkiewicz, P. K.

2013-12-20

To explore the physics of large-scale flows in solar-like stars, we perform three-dimensional anelastic simulations of rotating convection for global models with stratification resembling the solar interior. The numerical method is based on an implicit large-eddy simulation approach designed to capture effects from non-resolved small scales. We obtain two regimes of differential rotation, with equatorial zonal flows accelerated either in the direction of rotation (solar-like) or in the opposite direction (anti-solar). While the models with the solar-like differential rotation tend to produce multiple cells of meridional circulation, the models with anti-solar differential rotation result in only one or two meridionalmore » cells. Our simulations indicate that the rotation and large-scale flow patterns critically depend on the ratio between buoyancy and Coriolis forces. By including a sub-adiabatic layer at the bottom of the domain, corresponding to the stratification of a radiative zone, we reproduce a layer of strong radial shear similar to the solar tachocline. Similarly, enhanced super-adiabaticity at the top results in a near-surface shear layer located mainly at lower latitudes. The models reveal a latitudinal entropy gradient localized at the base of the convection zone and in the stable region, which, however, does not propagate across the convection zone. In consequence, baroclinicity effects remain small, and the rotation isocontours align in cylinders along the rotation axis. Our results confirm the alignment of large convective cells along the rotation axis in the deep convection zone and suggest that such 'banana-cell' pattern can be hidden beneath the supergranulation layer.« less

Three-dimensional numerical investigation of vortex-induced vibration of a rotating circular cylinder in uniform flow

NASA Astrophysics Data System (ADS)

Munir, Adnan; Zhao, Ming; Wu, Helen; Lu, Lin; Ning, Dezhi

2018-05-01

The vortex-induced vibration (VIV) of an elastically mounted rotating circular cylinder vibrating in a uniform flow is studied numerically. The cylinder is allowed to vibrate only in the cross-flow direction. In the numerical simulations, the Reynolds number, the mass ratio, and the damping ratio are kept constants to 500, 11.5, and 0, respectively. Simulations are performed for rotation rates of α = 0, 0.5, and 1 and a range of reduced velocities from 1 to 13, which covers the entire lock-in regime. It is found that the lock-in regime of a rotating cylinder is wider than that of a non-rotating cylinder for α = 0, 0.5, and 1. The vortex shedding pattern of a rotating cylinder is found to be similar to that of a non-rotating cylinder. Next, simulations are performed for three typical reduced velocities inside the lock-in regime and a range of higher rotation rates from α = 1.5 to 3.5 to investigate the effect of the rotation rate on the suppression of VIV. It is found that the VIV is suppressed when the rotation rate exceeds a critical value, which is dependent on the reduced velocity. For a constant reduced velocity, the amplitude of the vibration is found to increase with increasing rotation rate until the latter reaches its critical value for VIV suppression, beyond which the vibration amplitude becomes extremely small. If the rotation rate is greater than its critical value, vortex shedding ceases and hairpin vortices are observed due to the rotation of the cylinder.

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.

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

Film stability in a vertical rotating tube with a core-gas flow.

NASA Technical Reports Server (NTRS)

Sarma, G. S. R.; Lu, P. C.; Ostrach, S.

1971-01-01

The linear hydrodynamic stability of a thin-liquid layer flowing along the inside wall of a vertical tube rotating about its axis in the presence of a core-gas flow is examined. The stability problem is formulated under the conditions that the liquid film is thin, the density and viscosity ratios of gas to liquid are small and the relative (axial) pressure gradient in the gas is of the same order as gravity. The resulting eigenvalue problem is first solved by a perturbation method appropriate to axisymmetric long-wave disturbances. The damped nature (to within the thin-film and other approximations made) of the nonaxisymmetric and short-wave disturbances is noted. In view of the limitations on a truncated perturbation solution when the disturbance wavenumber is not small, an initial value method using digital computer is presented. Stability characteristics of neutral, growing, and damped modes are presented showing the influences of rotation, surface tension, and the core-gas flow. Energy balance in a neutral mode is also illustrated.

Rotation of a spheroid in a Couette flow at moderate Reynolds numbers.

PubMed

Yu, Zhaosheng; Phan-Thien, Nhan; Tanner, Roger I

2007-08-01

The rotation of a single spheroid in a planar Couette flow as a model for simple shear flow is numerically simulated with the distributed Lagrangian multiplier based fictitious domain method. The study is focused on the effects of inertia on the orbital behavior of prolate and oblate spheroids. The numerical orbits are found to be well described by a simple empirical model, which states that the rate of the spheroid rotation about the vorticity axis is a sinusoidal function of the corresponding projection angle in the flow-gradient plane, and that the exponential growth rate of the orbit function is a constant. The following transitions in the steady state with increasing Reynolds number are identified: Jeffery orbit, tumbling, quasi-Jeffery orbit, log rolling, and inclined rolling for a prolate spheroid; and Jeffery orbit, log rolling, inclined rolling, and motionless state for an oblate spheroid. In addition, it is shown that the orbit behavior is sensitive to the initial orientation in the case of strong inertia and there exist different steady states for certain shear Reynolds number regimes.

Counter-rotating type tidal stream power unit boarded on pillar (performances and flow conditions of tandem propellers)

NASA Astrophysics Data System (ADS)

Usui, Yuta; Kanemoto, Toshiaki; Hiraki, Koju

2013-12-01

The authors have invented the unique counter-rotating type tidal stream power unit composed of the tandem propellers and the double rotational armature type peculiar generator without the traditional stator. The front and the rear propellers counter-drive the inner and the outer armatures of the peculiar generator, respectively. The unit has the fruitful advantages that not only the output is sufficiently higher without supplementary equipment such as a gearbox, but also the rotational moment hardly act on the pillar because the rotational torque of both propellers/armatures are counter-balanced in the unit. This paper discusses experimentally the performances of the power unit and the effects of the propeller rotation on the sea surface. The axial force acting on the pillar increases naturally with the increase of not only the stream velocity but also the drag of the tandem propellers. Besides, the force vertical to the stream also acts on the pillar, which is induced from the Karman vortex street and the dominant frequencies appear owing to the front and the rear propeller rotations. The propeller rotating in close to the sea surface brings the abnormal wave and the amplitude increases as the stream velocity is faster and/or the drag is stronger.

The Geophysical Fluid Flow Cell Experiment

NASA Technical Reports Server (NTRS)

Hart, J. E.; Ohlsen, D.; Kittleman, S.; Borhani, N.; Leslie, F.; Miller, T.

1999-01-01

The Geophysical Fluid Flow Cell (GFFC) experiment performed visualizations of thermal convection in a rotating differentially heated spherical shell of fluid. In these experiments dielectric polarization forces are used to generate a radially directed buoyancy force. This enables the laboratory simulation of a number of geophysically and astrophysically important situations in which sphericity and rotation both impose strong constraints on global scale fluid motions. During USML-2 a large set of experiments with spherically symmetric heating were carried out. These enabled the determination of critical points for the transition to various forms of nonaxisymmetric convection and, for highly turbulent flows, the transition latitudes separating the different modes of motion. This paper presents a first analysis of these experiments as well as data on the general performance of the instrument during the USML-2 flight.

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.

Electric force on plasma ions and the momentum of the ion-neutrals flow

NASA Astrophysics Data System (ADS)

Makrinich, G.; Fruchtman, A.; Zoler, D.; Boxman, R. L.

2018-05-01

The electric force on ions in plasma and the momentum flux carried by the mixed ion-neutral flow were measured and found to be equal. The experiment was performed in a direct-current gas discharge of cylindrical geometry with applied radial electric field and axial magnetic field. The unmagnetized plasma ions, neutralized by magnetized electrons, were accelerated radially outward transferring part of the gained momentum to neutrals. Measurements were taken for various argon gas flow rates between 13 and 100 Standard Cubic Centimeter per Minute, for a discharge current of 1.9 A and a magnetic field intensity of 136 G. The plasma density, electron temperature, and plasma potential were measured at various locations along the flow. These measurements were used to determine the local electric force on the ions. The total electric force on the plasma ions was then determined by integrating radially the local electric force. In parallel, the momentum flux of the mixed ion-neutral flow was determined by measuring the force exerted by the flow on a balance force meter (BFM). The maximal plasma density was between 6 × 1010 cm-3 and 5 × 1011 cm-3, the maximal electron temperature was between 8 eV and 25 eV, and the deduced maximal electric field was between 2200 V/m and 5800 V/m. The force exerted by the mixed ion-neutral flow on the BFM agreed with the total electric force on the plasma ions. This agreement showed that it is the electric force on the plasma ions that is the source of the momentum acquired by the mixed ion-neutral flow.

Design and Flight Evaluation of a New Force-Based Flow Angle Probe

NASA Technical Reports Server (NTRS)

Corda, Stephen; Vachon, Michael Jacob

2006-01-01

A novel force-based flow angle probe was designed and flight tested on the NASA F-15B Research Testbed aircraft at NASA Dryden Flight Research Center. The prototype flow angle probe is a small, aerodynamic fin that has no moving parts. Forces on the prototype flow angle probe are measured with strain gages and correlated with the local flow angle. The flow angle probe may provide greater simplicity, greater robustness, and better access to flow measurements in confined areas relative to conventional moving vane-type flow angle probes. Flight test data were obtained at subsonic, transonic, and supersonic Mach numbers to a maximum of Mach 1.70. Flight conditions included takeoff, landing, straight and level flight, flight at higher aircraft angles of attack, and flight at elevated g-loadings. Flight test maneuvers included angle-of-attack and angle-of-sideslip sweeps. The flow angle probe-derived flow angles are compared with those obtained with a conventional moving vane probe. The flight tests validated the feasibility of a force-based flow angle measurement system.

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

Nonlinear dynamics near the stability margin in rotating pipe flow

NASA Technical Reports Server (NTRS)

Yang, Z.; Leibovich, S.

1991-01-01

The nonlinear evolution of marginally unstable wave packets in rotating pipe flow is studied. These flows depend on two control parameters, which may be taken to be the axial Reynolds number R and a Rossby number, q. Marginal stability is realized on a curve in the (R, q)-plane, and the entire marginal stability boundary is explored. As the flow passes through any point on the marginal stability curve, it undergoes a supercritical Hopf bifurcation and the steady base flow is replaced by a traveling wave. The envelope of the wave system is governed by a complex Ginzburg-Landau equation. The Ginzburg-Landau equation admits Stokes waves, which correspond to standing modulations of the linear traveling wavetrain, as well as traveling wave modulations of the linear wavetrain. Bands of wavenumbers are identified in which the nonlinear modulated waves are subject to a sideband instability.

Vertical and Horizontal Impact Force Comparison During Jump Landings With and Without Rotation in NCAA Division I Male Soccer Players.

PubMed

Harry, John R; Barker, Leland A; Mercer, John A; Dufek, Janet S

2017-07-01

Harry, JR, Barker, LA, Mercer, JA, and Dufek, JS. Vertical and horizontal impact force comparison during jump landings with and without rotation in NCAA Division I male soccer players. J Strength Cond Res 31(7): 1780-1786, 2017-There is a wealth of research on impact force characteristics when landing from a jump. However, there are no data on impact forces during landing from a jump with an airborne rotation about the vertical axis. We examined impact force parameters in the vertical and horizontal axes during vertical jump (VJ) landings and VJ landings with a 180° rotation (VJR). Twenty-four Division I male soccer players performed 3 VJ and VJR landings on a dual-force platform system. Paired-samples t-tests (α = 0.05) compared differences in the first (F1) and second (F2) peak vertical ground reaction forces, times to F1 (tF1), F2 (tF2), and the end of the impact phase, vertical impulse, and anterior-posterior and medial-lateral force couples. Effect sizes (ES; large >0.8) were computed to determine the magnitude of the differences. Lower jump height (41.60 ± 4.03 cm, VJ landings; 39.40 ± 4.05 cm, VJR landings; p = 0.002; ES = 0.39), greater F2 (55.71 ± 11.95 N·kg, VJ; 68.16 ± 14.82 N·kg; p < 0.001; ES = 0.94), faster tF2 (0.057 ± 0.012 seconds, VJ; 0.047 ± 0.011 seconds, VJR; p = 0.001; ES = 0.89), greater anterior-posterior (0.06 ± 0.03 N·s·kg, VJ; 0.56 ± 0.15 N·s·kg, VJR; p < 0.001; ES = 1.83) and medial-lateral force couples (0.29 ± 0.11 N·s·kg, VJ; 0.56 ± 0.14 N·s·kg, VJR; p < 0.001; ES = 1.46) occurred during VJR landings. No other differences were identified. This kinetic analysis determined that landing from a jump with 180° airborne rotation is different than landing from a jump without an airborne rotation. Male Division I soccer players could benefit from increasing the volume of VJR landings during training to address the differences in jump height and force parameters compared with VJ landings.

Development and Testing of an Integrated Rotating Dynamometer Based on Fiber Bragg Grating for Four-Component Cutting Force Measurement

PubMed Central

Liu, Mingyao; Bing, Junjun; Xiao, Li; Yun, Kang; Wan, Liang

2018-01-01

Cutting force measurement is of great importance in machining processes. Hence, various methods of measuring the cutting force have been proposed by many researchers. In this work, a novel integrated rotating dynamometer based on fiber Bragg grating (FBG) was designed, constructed, and tested to measure four-component cutting force. The dynamometer consists of FBGs that are pasted on the newly designed elastic structure which is then mounted on the rotating spindle. The elastic structure is designed as two mutual-perpendicular semi-octagonal rings. The signals of the FBGs are transmitted to FBG interrogator via fiber optic rotary joints and optical fiber, and the wavelength values are displayed on a computer. In order to determine the static and dynamic characteristics, many tests have been done. The results show that it is suitable for measuring cutting force. PMID:29670062

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.

Approaching a realistic force balance in geodynamo simulations

PubMed Central

Yadav, Rakesh K.; Gastine, Thomas; Christensen, Ulrich R.; Wolk, Scott J.; Poppenhaeger, Katja

2016-01-01

Earth sustains its magnetic field by a dynamo process driven by convection in the liquid outer core. Geodynamo simulations have been successful in reproducing many observed properties of the geomagnetic field. However, although theoretical considerations suggest that flow in the core is governed by a balance between Lorentz force, rotational force, and buoyancy (called MAC balance for Magnetic, Archimedean, Coriolis) with only minute roles for viscous and inertial forces, dynamo simulations must use viscosity values that are many orders of magnitude larger than in the core, due to computational constraints. In typical geodynamo models, viscous and inertial forces are not much smaller than the Coriolis force, and the Lorentz force plays a subdominant role; this has led to conclusions that these simulations are viscously controlled and do not represent the physics of the geodynamo. Here we show, by a direct analysis of the relevant forces, that a MAC balance can be achieved when the viscosity is reduced to values close to the current practical limit. Lorentz force, buoyancy, and the uncompensated (by pressure) part of the Coriolis force are of very similar strength, whereas viscous and inertial forces are smaller by a factor of at least 20 in the bulk of the fluid volume. Compared with nonmagnetic convection at otherwise identical parameters, the dynamo flow is of larger scale and is less invariant parallel to the rotation axis (less geostrophic), and convection transports twice as much heat, all of which is expected when the Lorentz force strongly influences the convection properties. PMID:27790991

On the phase lag of turbulent dissipation in rotating tidal flows

NASA Astrophysics Data System (ADS)

Zhang, Qianjiang; Wu, Jiaxue

2018-03-01

Field observations of rotating tidal flows in a shallow tidally swept sea reveal that a notable phase lag of both shear production and turbulent dissipation increases with height above the seafloor. These vertical delays of turbulent quantities are approximately equivalent in magnitude to that of squared mean shear. The shear production approximately equals turbulent dissipation over the phase-lag column, and thus a main mechanism of phase lag of dissipation is mean shear, rather than vertical diffusion of turbulent kinetic energy. By relating the phase lag of dissipation to that of the mean shear, a simple formulation with constant eddy viscosity is developed to describe the phase lag in rotating tidal flows. An analytical solution indicates that the phase lag increases linearly with height subjected to a combined effect of tidal frequency, Coriolis parameter and eddy viscosity. The vertical diffusion of momentum associated with eddy viscosity produces the phase lag of squared mean shear, and resultant delay of turbulent quantities. Its magnitude is inhibited by Earth's rotation. Furthermore, a theoretical formulation of the phase lag with a parabolic eddy viscosity profile can be constructed. A first-order approximation of this formulation is still a linear function of height, and its magnitude is approximately 0.8 times that with constant viscosity. Finally, the theoretical solutions of phase lag with realistic viscosity can be satisfactorily justified by realistic phase lags of dissipation.

The Effects of Rotation on Boundary Layers in Turbomachine Rotors

NASA Technical Reports Server (NTRS)

Johnston, J. P.

1974-01-01

The boundary layers in turbomachine rotors are subject to Coriolis forces which can (1) contribute directly to the development of secondary flows and (2) indirectly influence the behavior of boundary layers by augmentation and/or suppression of turbulence production in the boundary layers on blades. Both these rotation-induced phenomena are particularly important in the development of understanding of flow and loss mechanisms in centrifugal and mixed flow machines. The primary objective of this paper is to review the information available on these effects.

Notes on aerodynamic forces on airship hulls

NASA Technical Reports Server (NTRS)

Tuckerman, L B

1923-01-01

For a first approximation the air flow around the airship hull is assumed to obey the laws of perfect (i.e. free from viscosity) incompressible fluid. The flow is further assumed to be free from vortices (or rotational motion of the fluid). These assumptions lead to very great simplifications of the formulae used but necessarily imply an imperfect picture of the actual conditions. The value of the results depends therefore upon the magnitude of the forces produced by the disturbances in the flow caused by viscosity with the consequent production of vortices in the fluid. If these are small in comparison with the forces due to the assumed irrotational perfect fluid flow the results will give a good picture of the actual conditions of an airship in flight.

Instability of counter-rotating stellar disks

NASA Astrophysics Data System (ADS)

Hohlfeld, R. G.; Lovelace, R. V. E.

2015-09-01

We use an N-body simulation, constructed using GADGET-2, to investigate an accretion flow onto an astrophysical disk that is in the opposite sense to the disk's rotation. In order to separate dynamics intrinsic to the counter-rotating flow from the impact of the flow onto the disk, we consider an initial condition in which the counter-rotating flow is in an annular region immediately exterior the main portion of the astrophysical disk. Such counter-rotating flows are seen in systems such as NGC 4826 (known as the "Evil Eye Galaxy"). Interaction between the rotating and counter-rotating components is due to two-stream instability in the boundary region. A multi-armed spiral density wave is excited in the astrophysical disk and a density distribution with high azimuthal mode number is excited in the counter-rotating flow. Density fluctuations in the counter-rotating flow aggregate into larger clumps and some of the material in the counter-rotating flow is scattered to large radii. Accretion flow processes such as this are increasingly seen to be of importance in the evolution of multi-component galactic disks.

Piloted Ignition of Polypropylene/Glass Composites in a Forced Air Flow

NASA Technical Reports Server (NTRS)

Fernandez-Pello, A. C.; Rich, D.; Lautenberger, C.; Stefanovich, A.; Metha, S.; Torero, J.; Yuan, Z.; Ross, H.

2003-01-01

The Forced Ignition and Spread Test (FIST) is being used to study the flammability characteristics of combustible materials in forced convective flows. The FIST methodology is based on the ASTM E-1321, Lateral Ignition and Flame Spread Test (LIFT) which is used to determine the ignition and flame spread characteristics of materials, and to produce 'Flammability Diagrams' of materials. The LIFT apparatus, however, relies on natural convection to bring air to the combustion zone and the fuel vapor to the pilot flame, and thus cannot describe conditions where the oxidizer flow velocity may change. The FIST on the other hand, by relying on a forced flow as the dominant transport mechanism, can be used to examine variable oxidizer flow characteristics, such as velocity, oxygen concentration, and turbulence intensity, and consequently has a wider applicability. Particularly important is its ability to determine the flammability characteristics of materials used in spacecraft since in the absence of gravity the only flow present is that forced by the HVAC of the space facility. In this paper, we report work on the use of the FIST approach on the piloted ignition of a blended polypropylene fiberglass (PP/GL) composite material exposed to an external radiant flux in a forced convective flow of air. The effect of glass concentration under varying external radiant fluxes is examined and compared qualitatively with theoretical predictions of the ignition process. The results are used to infer the effect of glass content on the fire safety characteristics of composites.

Mode- and plasma rotation in a resistive shell reversed-field pinch

NASA Astrophysics Data System (ADS)

Malmberg, J.-A.; Brzozowski, J.; Brunsell, P. R.; Cecconello, M.; Drake, J. R.

2004-02-01

Mode rotation studies in a resistive shell reversed-field pinch, EXTRAP T2R [P. R. Brunsell et al., Plasma Phys. Control. Fusion 43, 1 (2001)] are presented. The phase relations and nonlinear coupling of the resonant modes are characterized and compared with that expected from modeling based on the hypothesis that mode dynamics can be described by a quasi stationary force balance including electromagnetic and viscous forces. Both m=0 and m=1 resonant modes are studied. The m=1 modes have rotation velocities corresponding to the plasma flow velocity (20-60 km/s) in the core region. The rotation velocity decreases towards the end of the discharge, although the plasma flow velocity does not decrease. A rotating phase locked m=1 structure is observed with a velocity of about 60 km/s. The m=0 modes accelerate throughout the discharges and reach velocities as high as 150-250 km/s. The observed m=0 phase locking is consistent with theory for certain conditions, but there are several conditions when the dynamics are not described. This is not unexpected because the assumption of quasi stationarity for the mode spectra is not fulfilled for many conditions. Localized m=0 perturbations are formed in correlation with highly transient discrete dynamo events. These perturbations form at the location of the m=1 phase locked structure, but rotate with a different velocity as they spread out in the toroidal direction.

Effect of rotating magnetic field on thermocapillary flow stability and the FZ crystal growth on the ground and in space

NASA Astrophysics Data System (ADS)

Feonychev, A. I.

It is well known that numerous experiments on crystal growth by the Bridgman method in space had met with only limited success. Because of this, only floating zone method is promising at present. However, realization of this method demands solution of some problems, in particular reduction of dopant micro- and macrosegregation. Rotating magnetic field is efficient method for control of flow in electrically conducting fluid and transfer processes. Investigation of rotating magnetic field had initiated in RIAME MAI in 1994 /3/. Results of the last investigations had been presented in /4/. Mathematical model of flow generated by rotating magnetic field and computer program were verified by comparison with experiment in area of developed oscillatory flow. Nonlinear analysis of flow stability under combination of thermocapillary convection and secondary flow generated by rotating magnetic field shows that boundary of transition from laminar to oscillatory flow is nonmonotone function in the plane of Marangoni number (Ma) - combined parameter Reω Ha2 (Ha is Hartman number, Reω is dimensionless velocity of magnetic field rotation). These data give additional knowledge of mechanism of onset of oscillations. In this case, there is reason to believe that the cause is Eckman's viscous stresses in rotating fluid on solid end-walls. It was shown that there is a possibility to increase stability of thermocapillary convection and in doing so to remove the main cause of dopant microsegregation. In doing so, if parameters of rotating magnetic field had been incorrectly chosen the dangerous pulsating oscillations are to develop. Radial macrosegregation of dopant can result from correct choosing of parameters of rotating magnetic field. As example, optimization of rotating magnetic field had been carried out for Ge(Ga) under three values of Marangoni number in weightlessness conditions. In the case when rotating magnetic field is used in terrestrial conditions, under combination of

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.

Flow field and thermal characteristics induced by a rotationally oscillating heated flat plate

NASA Astrophysics Data System (ADS)

Koffi, Moise

The objective of this dissertation is the study the flow and heat transfer in the vicinity of a rectangular flat heated plate of subject to rotational oscillations. Of interest is the effect of the flow field on the thermal characteristics of the plate's surface. A constant heat flux is applied to both sides while the plate is rotated about a fixed edge at a frequency of 2 rad/s in an infinite domain at atmospheric pressure. A computational simulation of the flow with FLUENT reveals a hooked-shape vortex tube around the free edges of the plate, which is confirmed by the flow visualization with smoke particles. During the flapping cycle, vortices form and grow progressively on one face while they shed from the opposite, until they are completely detached from both surfaces at stroke reversal. A data acquisition system uses a numerical computing and programming software (MATLAB) to track the surface temperature recorded by J- type thermocouples at desired locations on the plate. Both experimental and computational results agree with local surface temperature profiles characterized by a transient unsteady periodic variation followed by a steady periodic phase. These characteristics are symmetrical about the median plane of the plate, which is normal to its axis of rotation. The cooling rate of the surface, proportional to the frequency of rotation, depends on the angular position of the plate and the spatial location on the plate's surface. However, the highest heat transfer coefficient is recorded at free edges, especially in the corners swept by strong tip vortices shedding in two orthogonal directions. Conclusions of the present study are used to explain the role of ear flapping in the metabolic heat regulation of large mammals such as elephants. Flow visualization and surface temperature measurements of full size rigid and flexible elephant ear-shape models were carried out. Results indicate improved interaction between the shedding vortex and the model's boundary

Local-area simulations of rotating compressible convection and associated mean flows

NASA Technical Reports Server (NTRS)

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

1995-01-01

The dynamics of compressible convection within a curved local segment of a rotating spherical shell are considered in relation to the turbulent redistribution of angular momentum within the solar convection zone. Current supercomputers permit fully turbulent flows to be considered within the restricted geometry of local area models. By considering motions in a curvilinear geometry in which the Coriolos parameters vary with latitude, Rossby waves which couple with the turbulent convection are thought of as being possible. Simulations of rotating convection are presented in such a curved local segment of a spherical shell using a newly developed, sixth-order accurate code based on compact finite differences.

Simulations of turbulent rotating flows using a subfilter scale stress model derived from the partially integrated transport modeling method

NASA Astrophysics Data System (ADS)

Chaouat, Bruno

2012-04-01

The partially integrated transport modeling (PITM) method [B. Chaouat and R. Schiestel, "A new partially integrated transport model for subgrid-scale stresses and dissipation rate for turbulent developing flows," Phys. Fluids 17, 065106 (2005), 10.1063/1.1928607; R. Schiestel and A. Dejoan, "Towards a new partially integrated transport model for coarse grid and unsteady turbulent flow simulations," Theor. Comput. Fluid Dyn. 18, 443 (2005), 10.1007/s00162-004-0155-z; B. Chaouat and R. Schiestel, "From single-scale turbulence models to multiple-scale and subgridscale models by Fourier transform," Theor. Comput. Fluid Dyn. 21, 201 (2007), 10.1007/s00162-007-0044-3; B. Chaouat and R. Schiestel, "Progress in subgrid-scale transport modelling for continuous hybrid non-zonal RANS/LES simulations," Int. J. Heat Fluid Flow 30, 602 (2009), 10.1016/j.ijheatfluidflow.2009.02.021] viewed as a continuous approach for hybrid RANS/LES (Reynolds averaged Navier-Stoke equations/large eddy simulations) simulations with seamless coupling between RANS and LES regions is used to derive a subfilter scale stress model in the framework of second-moment closure applicable in a rotating frame of reference. This present subfilter scale model is based on the transport equations for the subfilter stresses and the dissipation rate and appears well appropriate for simulating unsteady flows on relatively coarse grids or flows with strong departure from spectral equilibrium because the cutoff wave number can be located almost anywhere inside the spectrum energy. According to the spectral theory developed in the wave number space [B. Chaouat and R. Schiestel, "From single-scale turbulence models to multiple-scale and subgrid-scale models by Fourier transform," Theor. Comput. Fluid Dyn. 21, 201 (2007), 10.1007/s00162-007-0044-3], the coefficients used in this model are no longer constants but they are some analytical functions of a dimensionless parameter controlling the spectral distribution of

Forces and torques on rigid inclusions in an elastic environment: Resulting matrix-mediated interactions, displacements, and rotations

NASA Astrophysics Data System (ADS)

Puljiz, Mate; Menzel, Andreas M.

2017-05-01

Embedding rigid inclusions into elastic matrix materials is a procedure of high practical relevance, for instance, for the fabrication of elastic composite materials. We theoretically analyze the following situation. Rigid spherical inclusions are enclosed by a homogeneous elastic medium under stick boundary conditions. Forces and torques are directly imposed from outside onto the inclusions or are externally induced between them. The inclusions respond to these forces and torques by translations and rotations against the surrounding elastic matrix. This leads to elastic matrix deformations, and in turn results in mutual long-ranged matrix-mediated interactions between the inclusions. Adapting a well-known approach from low-Reynolds-number hydrodynamics, we explicitly calculate the displacements and rotations of the inclusions from the externally imposed or induced forces and torques. Analytical expressions are presented as a function of the inclusion configuration in terms of displaceability and rotateability matrices. The role of the elastic environment is implicitly included in these relations. That is, the resulting expressions allow a calculation of the induced displacements and rotations directly from the inclusion configuration, without having to explicitly determine the deformations of the elastic environment. In contrast to the hydrodynamic case, compressibility of the surrounding medium is readily taken into account. We present the complete derivation based on the underlying equations of linear elasticity theory. In the future, the method will, for example, be helpful to characterize the behavior of externally tunable elastic composite materials, to accelerate numerical approaches, as well as to improve the quantitative interpretation of microrheological results.

Self-oscillations of a two-dimensional shear flow with forcing and dissipation

NASA Astrophysics Data System (ADS)

López Zazueta, A.; Zavala Sansón, L.

2018-04-01

Two-dimensional shear flows continuously forced in the presence of dissipative effects are studied by means of numerical simulations. In contrast with most previous studies, the forcing is confined in a finite region, so the behavior of the system is characterized by the long-term evolution of the global kinetic energy. We consider regimes with 1 < Reλ << Re, where Reλ is the Reynolds number associated with an external friction (such as bottom friction in quasi-two-dimensional flows), and Re is the traditional Reynolds number associated with Laplacian viscosity. Depending on Reλ, the flow may develop Kelvin-Helmholtz instabilities that exhibit either regular or irregular oscillations. The results are discussed in two parts. First, the flow is limited to develop only one vortical instability by choosing an appropriate width of the forcing band. The most relevant regime is found for Reλ > 36, in which the energy maintains a regular oscillation around a reference value. The flow configuration is an elliptical vortex tilted with respect to the forcing axis, which oscillates steadily also. Second, the flow is allowed to develop two Kelvin-Helmholtz billows and eventually more complicated structures. The regimes of the one-vortex case are observed again, except for Reλ > 135. At these values, the energy oscillates chaotically as the two vortices merge, form dipolar structures, and split again, with irregular periodicity. The self-oscillations are explained as a result of the alternate competition between forcing and dissipation, which is verified by calculating the budget terms in the energy equation. The relevance of the forcing-vs.-dissipation competition is discussed for more general flow systems.

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

Lithospheric "corner flow" via extensional faulting and tectonic rotation at non-volcanic, slow-spreading ridges

NASA Astrophysics Data System (ADS)

Schroeder, T.; Cheadle, M. J.; Dick, H. J.; Faul, U.

2005-12-01

Large degrees (up to 90°) of tectonic rotation may be the norm at slow-spreading, non-volcanic ridges. Vertically upwelling mantle beneath all mid-ocean ridges must undergo corner flow to move horizontally with the spreading plate. Because little or no volcanic crust is produced at some slow-spreading ridges, the uppermost lithospheric mantle must undergo this rotation in the regime of localized, rather than distributed deformation. Anomalous paleomagnetic inclinations in peridotite and gabbro cores drilled near the 15-20 Fracture Zone (Mid-Atlantic Ridge, ODP Leg 209) support such large rotations, with sub-Curie-temperature rotations up to 90° (Garces et al., 2004). Here, we present two end-member tectonic mechanisms, with supporting data from Leg 209 cores and bathymetry, to show how rotation is accomplished via extensional faults and shear zones: 1) long-lived detachment faults, and 2) multiple generations of high-angle normal faults. Detachment faults accommodate rotation by having a moderate to steep dip at depth, and rotating to horizontal through a rolling hinge as the footwall is tectonically denuded. Multiple generations of high-angle normal faults accommodate large rotations in a domino fashion; early faults become inactive when rotated to inopportune slip angles, and are cut by younger high-angle faults. Thus, each generation of high-angle faults accommodates part of the total rotation. There is likely a gradation between the domino and detachment mechanisms; transition from domino to detachment faulting occurs when a single domino fault remains active at inopportune slip angles and evolves into a detachment that accommodates all corner flow for that region. In both cases, the original attitude of layering within mantle-emplaced gabbro bodies must be significantly different than present day observed attitudes; sub-horizontal bodies may have been formed sub-vertically and vice-versa. Leg 209 cores record an average major brittle fault spacing of

The effect of gas and fluid flows on nonlinear lateral vibrations of rotating drill strings

NASA Astrophysics Data System (ADS)

Khajiyeva, Lelya; Kudaibergenov, Askar; Kudaibergenov, Askat

2018-06-01

In this work we develop nonlinear mathematical models describing coupled lateral vibrations of a rotating drill string under the effect of external supersonic gas and internal fluid flows. An axial compressive load and a torque also affect the drill string. The mathematical models are derived by the use of Novozhilov's nonlinear theory of elasticity with implementation of Hamilton's variation principle. Expressions for the gas flow pressure are determined according to the piston theory. The fluid flow is considered as added mass inside the curved tube of the drill string. Using an algorithm developed in the Mathematica computation program on the basis of the Galerkin approach and the stiffness switching method the numerical solution of the obtained approximate differential equations is found. Influences of the external loads, drill string angular speed of rotation, parameters of the gas and fluid flows on the drill string vibrations are shown.

Generalization of Boundary-Layer Momentum-Integral Equations to Three-Dimensional Flows Including Those of Rotating System

NASA Technical Reports Server (NTRS)

Mager, Arthur

1952-01-01

The Navier-Stokes equations of motion and the equation of continuity are transformed so as to apply to an orthogonal curvilinear coordinate system rotating with a uniform angular velocity about an arbitrary axis in space. A usual simplification of these equations as consistent with the accepted boundary-layer theory and an integration of these equations through the boundary layer result in boundary-layer momentum-integral equations for three-dimensional flows that are applicable to either rotating or nonrotating fluid boundaries. These equations are simplified and an approximate solution in closed integral form is obtained for a generalized boundary-layer momentum-loss thickness and flow deflection at the wall in the turbulent case. A numerical evaluation of this solution carried out for data obtained in a curving nonrotating duct shows a fair quantitative agreement with the measures values. The form in which the equations are presented is readily adaptable to cases of steady, three-dimensional, incompressible boundary-layer flow like that over curved ducts or yawed wings; and it also may be used to describe the boundary-layer flow over various rotating surfaces, thus applying to turbomachinery, propellers, and helicopter blades.

Forces on stationary particles in near-bed turbulent flows

NASA Astrophysics Data System (ADS)

Schmeeckle, Mark W.; Nelson, Jonathan M.; Shreve, Ronald L.

2007-06-01

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

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

Investigation of flow mechanism of a robotic fish swimming by using flow visualization synchronized with hydrodynamic force measurement

NASA Astrophysics Data System (ADS)

Tan, Guang-Kun; Shen, Gong-Xin; Huang, Shuo-Qiao; Su, Wen-Han; Ke, Yu

2007-11-01

When swimming in water by flapping its tail, a fish can overcome the drag from uniform flow and propel its body. The involved flow mechanism concerns 3-D and unsteady effects. This paper presents the investigation of the flow mechanism on the basis of a 3-D robotic fish model which has the typical geometry of body and tail with periodic flapping 2-freedom kinematical motion testing in the case of St = 0.78, Re = 6,600 and phase delay mode ( φ = -75°), in which may have a greater or maximum propulsion (without consideration of the optimal efficiency). Using a special technique of dye visualization which can clearly show vortex sheet and vortices in detail and using the inner 3-component force balance and cable supporting system with the phase-lock technique, the 3-D flow structure visualized in the wake of fish and the hydrodynamic force measurement were synchronized and obtained. Under the mentioned flapping parameters, we found the key flow structure and its evolution, a pair of complex 3-D chain-shape vortex (S-H vortex-rings, S1-H1 and S2-H2, and their legs L1 and L2) flow structures, which attach the leading edge and the trailing edge, then shed, move downstream and outwards and distribute two anti-symmetric staggering arrays along with the wake of the fish model in different phase stages during the flapping period. It is different with in the case of St = 0.25-0.35. Its typical flow structure and evolution are described and the results prove that they are different from the viewpoints based on the investigation of 2-D cases. For precision of the dynamic force measurement, in this paper it was provided with the method and techniques by subtracting the inertial forces and the forces induced by buoyancy and gravity effect in water, etc. from original data measured. The evolution of the synchronized measuring forces directly matching with the flow structure was also described in this paper.

Investigation of flow mechanism of a robotic fish swimming by using flow visualization synchronized with hydrodynamic force measurement

NASA Astrophysics Data System (ADS)

Tan, Guang-Kun; Shen, Gong-Xin; Huang, Shuo-Qiao; Su, Wen-Han; Ke, Yu

When swimming in water by flapping its tail, a fish can overcome the drag from uniform flow and propel its body. The involved flow mechanism concerns 3-D and unsteady effects. This paper presents the investigation of the flow mechanism on the basis of a 3-D robotic fish model which has the typical geometry of body and tail with periodic flapping 2-freedom kinematical motion testing in the case of St = 0.78, Re = 6,600 and phase delay mode (φ = - 75°), in which may have a greater or maximum propulsion (without consideration of the optimal efficiency). Using a special technique of dye visualization which can clearly show vortex sheet and vortices in detail and using the inner 3-component force balance and cable supporting system with the phase-lock technique, the 3-D flow structure visualized in the wake of fish and the hydrodynamic force measurement were synchronized and obtained. Under the mentioned flapping parameters, we found the key flow structure and its evolution, a pair of complex 3-D chain-shape vortex (S-H vortex-rings, S1 - H1 and S2 - H2, and their legs L1 and L2) flow structures, which attach the leading edge and the trailing edge, then shed, move downstream and outwards and distribute two antisymmetric staggering arrays along with the wake of the fish model in different phase stages during the flapping period. It is different with in the case of St = 0.25-0.35. Its typical flow structure and evolution are described and the results prove that they are different from the viewpoints based on the investigation of 2-D cases. For precision of the dynamic force measurement, in this paper it was provided with the method and techniques by subtracting the inertial forces and the forces induced by buoyancy and gravity effect in water, etc. from original data measured. The evolution of the synchronized measuring forces directly matching with the flow structure was also described in this paper.

Vibration-rotation-tunneling spectroscopy of the van der Waals Bond: A new look at intermolecular forces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cohen, R.C.; Saykally, R.J.

Measurements of the low-frequency van der Waals vibrations in weakly bound complexes by high-resolution laser spectroscopy provide a means to probe intermolecular forces at unprecedented levels of detail and precision. Several new methods are presently being used to record vibration/rotation-tunneling (VRT) transitions associated with the motions of the weak bonds in van der Waals clusters. The most direct measurements are those probing only the van der Waals modes themselves, which occur at far-infrared wavelengths. This article presents a review of the information on both intramolecular forces and intramolecular dynamics that has been obtained from far-infrared VRT spectra of 18 complexesmore » during the past several years. Some rotationally resolved measurements of van der Waals modes observed in combination with electronic or vibrational excitation are also discussed. 185 refs., 15 figs., 1 tab.« less

A Experimental Investigation of Hydrodynamic Forces on Circular Cylinders in Sinusoidal and Random Oscillating Flow

NASA Astrophysics Data System (ADS)

Longoria, Raul Gilberto

An experimental apparatus has been developed which can be used to generate a general time-dependent planar flow across a cylinder. A mass of water enclosed with no free surface within a square cross-section tank and two spring pre-loaded pistons is oscillated using a hydraulic actuator. A circular cylinder is suspended horizontally in the tank by two X-Y force transducers used to simultaneously measure the total in-line and transverse forces. Fluid motion is measured using a differential pressure transducer for instantaneous acceleration and an LVDT for displacement. This investigation provides measurement of forces on cylinders subjected to planar fluid flow velocity with a time (and frequency) dependence which more accurately represent the random conditions encountered in a natural ocean environment. The use of the same apparatus for both sinusoidal and random experiments provides a quantified assessment of the applicability of sinusoidal planar oscillatory flow data in offshore structure design methods. The drag and inertia coefficients for a Morison equation representation of the inline force are presented for both sinusoidal and random flow. Comparison of the sinusoidal results is favorable with those of previous investigations. The results from random experiments illustrates the difference in the force mechanism by contrasting the force transfer coefficients for the inline and transverse forces. It is found that application of sinusoidal results to random hydrodynamic inline force prediction using the Morison equation wrongly weighs the drag and inertia components, and the transverse force is overpredicted. The use of random planar oscillatory flow in the laboratory, contrasted with sinusoidal planar oscillatory flow, quantifies the accepted belief that the force transfer coefficients from sinusoidal flow experiments are conservative for prediction of forces on cylindrical structures subjected to random sea waves and the ensuing forces. Further analysis of

Importance of body rotation during the flight of a butterfly.

PubMed

Fei, Yueh-Han John; Yang, Jing-Tang

2016-03-01

In nature the body motion of a butterfly is clearly observed to involve periodic rotation and varied flight modes. The maneuvers of a butterfly in flight are unique. Based on the flight motion of butterflies (Kallima inachus) recorded in free flight, a numerical model of a butterfly is created to study how its flight relates to body pose; the body motion in a simulation is prescribed and tested with varied initial body angle and rotational amplitude. A butterfly rotates its body to control the direction of the vortex rings generated during flapping flight; the flight modes are found to be closely related to the body motion of a butterfly. When the initial body angle increases, the forward displacement decreases, but the upward displacement increases within a stroke. With increased rotational amplitudes, the jet flows generated by a butterfly eject more downward and further enhance the generation of upward force, according to which a butterfly executes a vertical jump at the end of the downstroke. During this jumping stage, the air relative to the butterfly is moving downward; the butterfly pitches up its body to be parallel to the flow and to decrease the projected area so as to avoid further downward force generated. Our results indicate the importance of the body motion of a butterfly in flight. The inspiration of flight controlled with body motion from the flight of a butterfly might yield an alternative way to control future flight vehicles.

Multi-scale modeling of tsunami flows and tsunami-induced forces

NASA Astrophysics Data System (ADS)

Qin, X.; Motley, M. R.; LeVeque, R. J.; Gonzalez, F. I.

2016-12-01

The modeling of tsunami flows and tsunami-induced forces in coastal communities with the incorporation of the constructed environment is challenging for many numerical modelers because of the scale and complexity of the physical problem. A two-dimensional (2D) depth-averaged model can be efficient for modeling of waves offshore but may not be accurate enough to predict the complex flow with transient variance in vertical direction around constructed environments on land. On the other hand, using a more complex three-dimensional model is much more computational expensive and can become impractical due to the size of the problem and the meshing requirements near the built environment. In this study, a 2D depth-integrated model and a 3D Reynolds Averaged Navier-Stokes (RANS) model are built to model a 1:50 model-scale, idealized community, representative of Seaside, OR, USA, for which existing experimental data is available for comparison. Numerical results from the two numerical models are compared with each other as well as experimental measurement. Both models predict the flow parameters (water level, velocity, and momentum flux in the vicinity of the buildings) accurately, in general, except for time period near the initial impact, where the depth-averaged models can fail to capture the complexities in the flow. Forces predicted using direct integration of predicted pressure on structural surfaces from the 3D model and using momentum flux from the 2D model with constructed environment are compared, which indicates that force prediction from the 2D model is not always reliable in such a complicated case. Force predictions from integration of the pressure are also compared with forces predicted from bare earth momentum flux calculations to reveal the importance of incorporating the constructed environment in force prediction models.

An infinitely-stiff elastic system via a tuned negative-stiffness component stabilized by rotation-produced gyroscopic forces

NASA Astrophysics Data System (ADS)

Kochmann, D. M.; Drugan, W. J.

2016-06-01

An elastic system containing a negative-stiffness element tuned to produce positive-infinite system stiffness, although statically unstable as is any such elastic system if unconstrained, is proved to be stabilized by rotation-produced gyroscopic forces at sufficiently high rotation rates. This is accomplished in possibly the simplest model of a composite structure (or solid) containing a negative-stiffness component that exhibits all these features, facilitating a conceptually and mathematically transparent, completely closed-form analysis.

Liquid Hydrogen Recirculation System for Forced Flow Cooling Test of Superconducting Conductors

NASA Astrophysics Data System (ADS)

Shirai, Y.; Kainuma, T.; Shigeta, H.; Shiotsu, M.; Tatsumoto, H.; Naruo, Y.; Kobayashi, H.; Nonaka, S.; Inatani, Y.; Yoshinaga, S.

2017-12-01

The knowledge of forced flow heat transfer characteristics of liquid hydrogen (LH2) is important and necessary for design and cooling analysis of high critical temperature superconducting devices. However, there are few test facilities available for LH2 forced flow cooling for superconductors. A test system to provide a LH2 forced flow (∼10 m/s) of a short period (less than 100 s) has been developed. The test system was composed of two LH2 tanks connected by a transfer line with a controllable valve, in which the forced flow rate and its period were limited by the storage capacity of tanks. In this paper, a liquid hydrogen recirculation system, which was designed and fabricated in order to study characteristics of superconducting cables in a stable forced flow of liquid hydrogen for longer period, was described. This LH2 loop system consists of a centrifugal pump with dynamic gas bearings, a heat exchanger which is immersed in a liquid hydrogen tank, and a buffer tank where a test section (superconducting wires or cables) is set. The buffer tank has LHe cooled superconducting magnet which can produce an external magnetic field (up to 7T) at the test section. A performance test was conducted. The maximum flow rate was 43.7 g/s. The lowest temperature was 22.5 K. It was confirmed that the liquid hydrogen can stably circulate for 7 hours.

Parallel Computing of Upwelling in a Rotating Stratified Flow

NASA Astrophysics Data System (ADS)

Cui, A.; Street, R. L.

1997-11-01

A code for the three-dimensional, unsteady, incompressible, and turbulent flow has been implemented on the IBM SP2, using message passing. The effects of rotation and variable density are included. A finite volume method is used to discretize the Navier-Stokes equations in general curvilinear coordinates on a non-staggered grid. All the spatial derivatives are approximated using second-order central differences with the exception of the convection terms, which are handled with special upwind-difference schemes. The semi-implicit, second-order accurate, time-advancement scheme employs the Adams-Bashforth method for the explicit terms and Crank-Nicolson for the implicit terms. A multigrid method, with the four-color ZEBRA as smoother, is used to solve the Poisson equation for pressure, while the momentum equations are solved with an approximate factorization technique. The code was successfully validated for a variety test cases. Simulations of a laboratory model of coastal upwelling in a rotating annulus are in progress and will be presented.

Semidiurnal thermal tides in asynchronously rotating hot Jupiters

NASA Astrophysics Data System (ADS)

Auclair-Desrotour, P.; Leconte, J.

2018-05-01

Context. Thermal tides can torque the atmosphere of hot Jupiters into asynchronous rotation, while these planets are usually assumed to be locked into spin-orbit synchronization with their host star. Aims: In this work, our goal is to characterize the tidal response of a rotating hot Jupiter to the tidal semidiurnal thermal forcing of its host star by identifying the structure of tidal waves responsible for variation of mass distribution, their dependence on the tidal frequency, and their ability to generate strong zonal flows. Methods: We develop an ab initio global modelling that generalizes the early approach of Arras & Socrates (2010, ApJ, 714, 1) to rotating and non-adiabatic planets. We analytically derive the torque exerted on the body and the associated timescales of evolution, as well as the equilibrium tidal response of the atmosphere in the zero-frequency limit. Finally, we numerically integrate the equations of thermal tides for three cases, including dissipation and rotation step by step. Results: The resonances associated with tidally generated gravito-inertial waves significantly amplify the resulting tidal torque in the range 1-30 days. This torque can globally drive the atmosphere into asynchronous rotation, as its sign depends on the tidal frequency. The resonant behaviour of the tidal response is enhanced by rotation, which couples the forcing to several Hough modes in the general case, while the radiative cooling tends to regularize it and diminish its amplitude.

Global simulation of the induction heating TSSG process of SiC for the effects of Marangoni convection, free surface deformation and seed rotation

NASA Astrophysics Data System (ADS)

Yamamoto, Takuya; Okano, Yasunori; Ujihara, Toru; Dost, Sadik

2017-07-01

A global numerical simulation was performed for the induction heating Top-Seeded Solution Growth (TSSG) process of SiC. Analysis included the furnace and growth melt. The effects of interfacial force due to free surface tension gradient, the RF coil-induced electromagnetic body force, buoyancy, melt free surface deformation, and seed rotation were examined. The simulation results showed that the contributions of free surface tension gradient and the electromagnetic body force to the melt flow are significant. Marangoni convection affects the growth process adversely by making the melt flow downward in the region under the seed crystal. This downward flow reduces carbon flux into the seed and consequently lowers growth rate. The effects of free surface deformation and seed rotation, although positive, are not so significant compared with those of free surface tension gradient and the electromagnetic body force. Due to the small size of the melt the contribution of buoyancy is also small.

Measurements of Shear Lift Force on a Bubble in Channel Flow in Microgravity

NASA Technical Reports Server (NTRS)

Nahra, Henry K.; Motil, Brian J.; Skor, Mark

2003-01-01

Under microgravity conditions, the shear lift force acting on bubbles, droplets or solid particles in multiphase flows becomes important because under normal gravity, this hydrodynamic force is masked by buoyancy. This force plays an important role in furnishing the detachment process of bubbles in a setting where a bubble suspension is needed in microgravity. In this work, measurements of the shear lift force acting on a bubble in channel flow are performed. The shear lift force is deduced from the bubble kinematics using scaling and then compared with predictions from models in literature that address different asymptotic and numerical solutions. Basic trajectory calculations are then performed and the results are compared with experimental data of position of the bubble in the channel. A direct comparison of the lateral velocity of the bubbles is also made with the lateral velocity prediction from investigators, whose work addressed the shear lift on a sphere in different two-dimensional shear flows including Poiseuille flow.

Elongational flow of polymer melts at constant strain rate, constant stress and constant force

NASA Astrophysics Data System (ADS)

Wagner, Manfred H.; Rolón-Garrido, Víctor H.

2013-04-01

Characterization of polymer melts in elongational flow is typically performed at constant elongational rate or rarely at constant tensile stress conditions. One of the disadvantages of these deformation modes is that they are hampered by the onset of "necking" instabilities according to the Considère criterion. Experiments at constant tensile force have been performed even more rarely, in spite of the fact that this deformation mode is free from necking instabilities and is of considerable industrial relevance as it is the correct analogue of steady fiber spinning. It is the objective of the present contribution to present for the first time a full experimental characterization of a long-chain branched polyethylene melt in elongational flow. Experiments were performed at constant elongation rate, constant tensile stress and constant tensile force by use of a Sentmanat Extensional Rheometer (SER) in combination with an Anton Paar MCR301 rotational rheometer. The accessible experimental window and experimental limitations are discussed. The experimental data are modelled by using the Wagner I model. Predictions of the steady-start elongational viscosity in constant strain rate and creep experiments are found to be identical, albeit only by extrapolation of the experimental data to Hencky strains of the order of 6. For constant stress experiments, a minimum in the strain rate and a corresponding maximum in the elongational viscosity is found at a Hencky strain of the order of 3, which, although larger than the steady-state value, follows roughly the general trend of the steady-state elongational viscosity. The constitutive analysis also reveals that constant tensile force experiments indicate a larger strain hardening potential than seen in constant elongation rate or constant tensile stress experiments. This may be indicative of the effect of necking under constant elongation rate or constant tensile stress conditions according to the Considère criterion.

Derivation of Inviscid Quasi-geostrophic Equation from Rotational Compressible Magnetohydrodynamic Flows

NASA Astrophysics Data System (ADS)

Kwon, Young-Sam; Lin, Ying-Chieh; Su, Cheng-Fang

2018-04-01

In this paper, we consider the compressible models of magnetohydrodynamic flows giving rise to a variety of mathematical problems in many areas. We derive a rigorous quasi-geostrophic equation governed by magnetic field from the rotational compressible magnetohydrodynamic flows with the well-prepared initial data. It is a first derivation of quasi-geostrophic equation governed by the magnetic field, and the tool is based on the relative entropy method. This paper covers two results: the existence of the unique local strong solution of quasi-geostrophic equation with the good regularity and the derivation of a quasi-geostrophic equation.

Theoretical and experimental studies in support of the geophysical fluid flow experiment

NASA Technical Reports Server (NTRS)

Hart, J.; Toomre, J.

1985-01-01

Meteorologists and astrophysicists interested in large scale planetary and solar circulations have come to recognize the importance of rotation and stratification in determining the character of these flows. In particular, the effect of latitude-dependent Coriolis force on nonlinear convection is thought to play a crucial role in such phenomena as differential rotation on the Sun, cloud band orientation on Jupiter, and the generation of magnetic fields in thermally driven dynamos. The continuous low-gravity environment of the orbiting space shuttle offers a unique opportunity to make laboratory studies of such large-scale thermally driven flows under the constraint imposed by rotation and sphericity. This is possible because polarization forces in a dielectric liquid, which are linearly dependent on fluid temperature, give rise to an effectively radial buoyancy force when a radial electrostatic field is imposed. The Geophysical Fluid Flow Cell (GFFC) is an implementation of this ideal in which fluid is contained between two rotating hemispheres that are differentially heated and stressed with a large a-c voltage. The experiment, to be flown on Spacelab III (currently set for launch April 29, 1985), will explore non-linear mode selection and high Rayleigh number turbulence in a rotating convecting spherical shell of liquid. Experiments will be carried out in a low driving parameter range where some limited numerical experimentation is currently feasible, as well as in a parameter range significantly beyond numerical computation for many years.

Correlating Lagrangian structures with forcing in two-dimensional flow

NASA Astrophysics Data System (ADS)

Ouellette, Nicholas; Hogg, Charlie; Liao, Yang

2015-11-01

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. Here, we instead take a first step toward controlling the presence or locations of LCSs by studying 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 backwards in time, with forward-time (repelling) LCSs showing much more correlation with the forcing than backwards-time (attracting) LCSs.

Direct numerical simulation of Taylor-Couette flow subjected to a radial temperature gradient

DOE Office of Scientific and Technical Information (OSTI.GOV)

Teng, Hao; Liu, Nansheng, E-mail: lns@ustc.edu.cn; Lu, Xiyun

Direct numerical simulations have been performed to study the Taylor-Couette (TC) flow between two rotating, coaxial cylinders in the presence of a radial temperature gradient. Specifically, the influence of the buoyant force and the outer cylinder rotation on the turbulent TC flow system with the radius ratio η = 0.912 was examined. For the co-rotating TC flows with Re{sub i} (inner cylinder) =1000 and Re{sub o} (outer cylinder) =100, a transition pathway to highly turbulent flows is realized by increasing σ, a parameter signifying the ratio of buoyant to inertial force. This nonlinear flow transition involves four intriguing states thatmore » emerge in sequence as chaotic wavy vortex flow for σ = 0, wavy interpenetrating spiral flows for σ = 0.02 and 0.05, intermittent turbulent spirals for σ = 0.1 and 0.2, and turbulent spirals for σ = 0.4. Overall, the fluid motion changes from a centrifugally driven flow regime characterized by large-scale wavy Taylor vortices (TVs) to a buoyancy-dominated flow regime characterized by small-scale turbulent vortices. Commensurate changes in turbulence statistics and heat transfer are seen as a result of the weakening of large-scale TV circulations and enhancement of turbulent motions. Additionally, the influence of variation of the outer cylinder rotation, −500 < Re{sub o} < 500 in presence of buoyancy (σ = 0.1) with Re{sub i} = 1000, has been considered. Specifically, it is demonstrated that this variation strongly influences the azimuthal and axial mean flows with a weaker influence on the fluctuating fluid motions. Of special interest, here are the turbulent dynamics near the outer wall where a marked decrease of turbulence intensity and a sign inversion of the Reynolds stress R{sub rz} are observed for the strongly counter-rotating regimes (Re{sub o} = − 300 and −500). To this end, it has been shown that the underlying flow physics for this drastic modification are associated with the modification of the

Rotating thermal convection at very large Rayleigh numbers

NASA Astrophysics Data System (ADS)

Weiss, Stephan; van Gils, Dennis; Ahlers, Guenter; Bodenschatz, Eberhard

2016-11-01

The large scale thermal convection systems in geo- and astrophysics are usually influenced by Coriolis forces caused by the rotation of their celestial bodies. To better understand the influence of rotation on the convective flow field and the heat transport at these conditions, we study Rayleigh-Bénard convection, using pressurized sulfur hexaflouride (SF6) at up to 19 bars in a cylinder of diameter D=1.12 m and a height of L=2.24 m. The gas is heated from below and cooled from above and the convection cell sits on a rotating table inside a large pressure vessel (the "Uboot of Göttingen"). With this setup Rayleigh numbers of up to Ra =1015 can be reached, while Ekman numbers as low as Ek =10-8 are possible. The Prandtl number in these experiment is kept constant at Pr = 0 . 8 . We report on heat flux measurements (expressed by the Nusselt number Nu) as well as measurements from more than 150 temperature probes inside the flow. We thank the Deutsche Forschungsgemeinschaft (DFG) for financial support through SFB963: "Astrophysical Flow Instabilities and Turbulence". The work of GA was supported in part by the US National Science Foundation through Grant DMR11-58514.

In-flight investigation of a rotating cylinder-based structural excitation system for flutter testing

NASA Technical Reports Server (NTRS)

Vernon, Lura

1993-01-01

A research excitation system was test flown at the NASA Dryden Flight Research Facility on the two-seat F-16XL aircraft. The excitation system is a wingtip-mounted vane with a rotating slotted cylinder at the trailing edge. As the cylinder rotates during flight, the flow is alternately deflected upward and downward through the slot, resulting in a periodic lift force at twice the cylinder's rotational frequency. Flight testing was conducted to determine the excitation system's effectiveness in the subsonic and transonic flight regimes. Primary research objectives were to determine the system's ability to develop adequate force levels to excite the aircraft's structure and to determine the frequency range over which the system could excite structural modes of the aircraft. The results from the exciter were compared with results from atmospheric turbulence excitation at the same flight conditions. The results from the forced excitation were of higher quality and had less variation than the results from atmospheric turbulence. The forced excitation data also invariably yielded higher structural damping values than those from the atmospheric turbulence data.

On a class of unsteady three-dimensional Navier Stokes solutions relevant to rotating disc flows: Threshold amplitudes and finite time singularities

NASA Technical Reports Server (NTRS)

Hall, Philip; Balakumar, P.

1990-01-01

A class of exact steady and unsteady solutions of the Navier Stokes equations in cylindrical polar coordinates is given. The flows correspond to the motion induced by an infinite disc rotating with constant angular velocity about the z-axis in a fluid occupying a semi-infinite region which, at large distances from the disc, has velocity field proportional to (x,-y,O) with respect to a Cartesian coordinate system. It is shown that when the rate of rotation is large, Karman's exact solution for a disc rotating in an otherwise motionless fluid is recovered. In the limit of zero rotation rate a particular form of Howarth's exact solution for three-dimensional stagnation point flow is obtained. The unsteady form of the partial differential system describing this class of flow may be generalized to time-periodic equilibrium flows. In addition the unsteady equations are shown to describe a strongly nonlinear instability of Karman's rotating disc flow. It is shown that sufficiently large perturbations lead to a finite time breakdown of that flow whilst smaller disturbances decay to zero. If the stagnation point flow at infinity is sufficiently strong, the steady basic states become linearly unstable. In fact there is then a continuous spectrum of unstable eigenvalues of the stability equations but, if the initial value problem is considered, it is found that, at large values of time, the continuous spectrum leads to a velocity field growing exponentially in time with an amplitude decaying algebraically in time.

Effect of Processing Parameters on Plastic Flow and Defect Formation in Friction-Stir-Welded Aluminum Alloy

NASA Astrophysics Data System (ADS)

Zeng, X. H.; Xue, P.; Wang, D.; Ni, D. R.; Xiao, B. L.; Ma, Z. Y.

2018-07-01

The effect of processing parameters on material flow and defect formation during friction stir welding (FSW) was investigated on 6.0-mm-thick 2014Al-T6 rolled plates with an artificially thickened oxide layer on the butt surface as the marker material. It was found that the "S" line in the stir zone (SZ) rotated with the pin and stayed on the retreating side (RS) and advancing side (AS) at low and high heat inputs, respectively. When the tool rotation rate was extremely low, the oxide layer under the pin moved to the RS first and then to the AS perpendicular to the welding direction, rather than rotating with the pin. The material flow was driven by the shear stresses produced by the forces at the pin-workpiece interface. With increases of the rotation rate, the depth of the shoulder-affected zone (SAZ) first decreased and then increased due to the decreasing shoulder friction force and increasing heat input. Insufficient material flow appeared in the whole of the SZ at low rotation rates and in the bottom of the SZ at high rotation rates, resulting in the formation of the "S" line. The extremely inadequate material flow is the reason for the lack of penetration and the kissing bonds in the bottom of the SZ at extremely low and low rotation rates, respectively.

Effect of Processing Parameters on Plastic Flow and Defect Formation in Friction-Stir-Welded Aluminum Alloy

NASA Astrophysics Data System (ADS)

Zeng, X. H.; Xue, P.; Wang, D.; Ni, D. R.; Xiao, B. L.; Ma, Z. Y.

2018-04-01

The effect of processing parameters on material flow and defect formation during friction stir welding (FSW) was investigated on 6.0-mm-thick 2014Al-T6 rolled plates with an artificially thickened oxide layer on the butt surface as the marker material. It was found that the "S" line in the stir zone (SZ) rotated with the pin and stayed on the retreating side (RS) and advancing side (AS) at low and high heat inputs, respectively. When the tool rotation rate was extremely low, the oxide layer under the pin moved to the RS first and then to the AS perpendicular to the welding direction, rather than rotating with the pin. The material flow was driven by the shear stresses produced by the forces at the pin-workpiece interface. With increases of the rotation rate, the depth of the shoulder-affected zone (SAZ) first decreased and then increased due to the decreasing shoulder friction force and increasing heat input. Insufficient material flow appeared in the whole of the SZ at low rotation rates and in the bottom of the SZ at high rotation rates, resulting in the formation of the "S" line. The extremely inadequate material flow is the reason for the lack of penetration and the kissing bonds in the bottom of the SZ at extremely low and low rotation rates, respectively.

Technology of forced flow and once-through boiling: A survey. [pressure distribution

NASA Technical Reports Server (NTRS)

Poppendieck, H. F.; Sabin, C. M.

1975-01-01

Representative boiling heat transfer and pressure drop information obtained primarily from past NASA and AEC programs is presented which is applicable to forced flow and once-through boiler systems. The forced convection boiler has a number of advantages: little possibility of flow mal-distribution; heat transfer characteristics are usually consistent; and conductances are predictable, so that higher heat fluxes may be employed with safety (which leads to more compact, lighter weight equipment). It was found that in gas-fired systems particularly, the controlling heat transfer resistance may be on the hot side, so that increased fluxes would require extended surfaces. If in a power generation system the working fluid is very expensive, a forced flow boiler can be designed especially for small holdup volume. If the fluid is temperature sensitive, the boiling side wall temperatures can be tailored to maintain maximum heat transfer rates without overheating the fluid. The forced flow and once-through configurations may be the only type which can satisfy a specific need (such as the automotive Rankine cycle power plant design having a very short time-response boiler).

The Influence of Swirl Brakes and a Tip Discharge Orifice on the Rotordynamic Forces Generated by Discharge-to-Suction Leakage Flows in Shrouded Centrifugal Pumps

NASA Technical Reports Server (NTRS)

Sivo, Joseph M.; Acosta, A. J.; Brennen, C. E.; Caughey, T. K.

1993-01-01

Recent experiments conducted in the Rotor Force Test Facility at the California Institute of Technology have examined the effects of a tip leakage restriction and swirl brakes on the rotordynamic forces due to leakage flows on an impeller undergoing a prescribed circular whirl. The experiments simulate the leakage flow conditions and geometry of the Alternate Turbopump Design (ATD) of the Space Shuttle High Pressure Oxygen Turbopump and are critical to evaluating the pump's rotordynamic instability problems. Previous experimental and analytical results have shown that discharge-to-suction leakage flows in the annulus of a shrouded centrifugal pump contribute substantially to the fluid induced rotordynamic forces. Also, previous experiments have shown that leakage inlet (pump discharge) swirl can increase the cross-coupled stiffness coefficient and hence increase the range of positive whirl for which the tangential force is destabilizing. In recent experimental work, the present authors demonstrated that when the swirl velocity within the leakage path is reduced by the introduction of ribs or swirl brakes, then a substantial decrease in both the destabilizing normal and tangential forces could be achieved. Motivation for the present research is that previous experiments have shown that restrictions such as wear rings or orifices at pump inlets affect the leakage forces. Recent pump designs such as the Space Shuttle Alternate Turbopump Design (ATD) utilize tip orifices at discharge for the purpose of establishing axial thrust balance. The ATD has experienced rotordynamic instability problems and one may surmise that these tip discharge orifices may also have an important effect on the normal and tangential forces in the plane of impeller rotation. The present study determines if such tip leakage restrictions contribute to undesirable rotordynamic forces. Additional motivation for the present study is that the widening of the leakage path annular clearance and the

Unsteady flow simulations around complex geometries using stationary or rotating unstructured grids

NASA Astrophysics Data System (ADS)

Sezer-Uzol, Nilay

In this research, the computational analysis of three-dimensional, unsteady, separated, vortical flows around complex geometries is studied by using stationary or moving unstructured grids. Two main engineering problems are investigated. The first problem is the unsteady simulation of a ship airwake, where helicopter operations become even more challenging, by using stationary unstructured grids. The second problem is the unsteady simulation of wind turbine rotor flow fields by using moving unstructured grids which are rotating with the whole three-dimensional rigid rotor geometry. The three dimensional, unsteady, parallel, unstructured, finite volume flow solver, PUMA2, is used for the computational fluid dynamics (CFD) simulations considered in this research. The code is modified to have a moving grid capability to perform three-dimensional, time-dependent rotor simulations. An instantaneous log-law wall model for Large Eddy Simulations is also implemented in PUMA2 to investigate the very large Reynolds number flow fields of rotating blades. To verify the code modifications, several sample test cases are also considered. In addition, interdisciplinary studies, which are aiming to provide new tools and insights to the aerospace and wind energy scientific communities, are done during this research by focusing on the coupling of ship airwake CFD simulations with the helicopter flight dynamics and control analysis, the coupling of wind turbine rotor CFD simulations with the aeroacoustic analysis, and the analysis of these time-dependent and large-scale CFD simulations with the help of a computational monitoring, steering and visualization tool, POSSE.

Generalized derivation of the added-mass and circulatory forces for viscous flows

NASA Astrophysics Data System (ADS)

Limacher, Eric; Morton, Chris; Wood, David

2018-01-01

The concept of added mass arises from potential flow analysis and is associated with the acceleration of a body in an inviscid irrotational fluid. When shed vorticity is modeled as vortex singularities embedded in this irrotational flow, the associated force can be superimposed onto the added-mass force due to the linearity of the governing Laplace equation. This decomposition of force into added-mass and circulatory components remains common in modern aerodynamic models, but its applicability to viscous separated flows remains unclear. The present work addresses this knowledge gap by presenting a generalized derivation of the added-mass and circulatory force decomposition which is valid for a body of arbitrary shape in an unbounded, incompressible fluid domain, in both two and three dimensions, undergoing arbitrary motions amid continuous distributions of vorticity. From the general expression, the classical added-mass force is rederived for well-known canonical cases and is seen to be additive to the circulatory force for any flow. The formulation is shown to be equivalent to existing theoretical work under the specific conditions and assumptions of previous studies. It is also validated using a numerical simulation of a pitching plate in a steady freestream flow, conducted by Wang and Eldredge [Theor. Comput. Fluid Dyn. 27, 577 (2013), 10.1007/s00162-012-0279-5]. In response to persistent confusion in the literature, a discussion of the most appropriate physical interpretation of added mass is included, informed by inspection of the derived equations. The added-mass force is seen to account for the dynamic effect of near-body vorticity and is not (as is commonly claimed) associated with the acceleration of near-body fluid which "must" somehow move with the body. Various other consequences of the derivation are discussed, including a concept which has been labeled the conservation of image-vorticity impulse.

Ion flow measurements during the rotating kink behavior of the central column in the HIST device

NASA Astrophysics Data System (ADS)

Yamada, S.; Yoshikawa, T.; Hashimoto, S.; Nishioka, T.; Kikuchi, Y.; Fukumoto, N.; Nagata, M.

2007-11-01

Plasma flow is essentially driven in self-organization and magnetic reconnection process of compact spherical torus (ST) and spheromak in the helicity-driven systems. For example, when reversing the external toroidal field of ST, the direction not only of the plasma current but also of the toroidal ion flow is self-reversed during the formation of the flipped ST relaxed states. Mach probe measurement shows that the velocity of the ion flow reversed after the flip increases to about 20 km/s. We have been newly developing an ion Doppler spectrometer (IDS) system using a compact 16 or 64 channel photomultiplier tube (PMT) in order to measure the spatial profile of ion temperature and rotation velocity in the HIST device. The IDS system consists of a light collection system including optical fibers, 1 m-spectrometer and the PMT detector. The optical fibers covered with glass tubes are inserted into the plasma. The glass tubes can be rotated in the poloidal and the toroidal directions. The new IDS system will be applied to observations of ion temperature and plasma rotation in the flipped ST formation and in the MHD control of kinking behaviors of the central column by using the rotating magnetic field (RMF). Preliminary IDS results will be compared to those from Mach probe measurements in space.

Two dimensional numerical analysis of aerodynamic characteristics for rotating cylinder on concentrated air flow

NASA Astrophysics Data System (ADS)

Alias, M. S.; Rafie, A. S. Mohd; Marzuki, O. F.; Hamid, M. F. Abdul; Chia, C. C.

2017-12-01

Over the years, many studies have demonstrated the feasibility of the Magnus effect on spinning cylinder to improve lift production, which can be much higher than the traditional airfoil shape. With this characteristic, spinning cylinder might be used as a lifting device for short take-off distance aircraft or unmanned aerial vehicle (UAV). Nonetheless, there is still a gap in research to explain the use of spinning cylinder as a good lifting device. Computational method is used for this study to analyse the Magnus effect, in which two-dimensional finite element numerical analysis method is applied using ANSYS FLUENT software to examine the coefficients of lift and drag, and to investigate the flow field around the rotating cylinder surface body. Cylinder size of 30mm is chosen and several configurations in steady and concentrated air flows have been evaluated. All in all, it can be concluded that, with the right configuration of the concentrated air flow setup, the rotating cylinder can be used as a lifting device for very short take-off since it can produce very high coefficient of lift (2.5 times higher) compared with steady air flow configuration.

Nucleation of rotating crystals by Thiovulum majus bacteria

NASA Astrophysics Data System (ADS)

Petroff, A. P.; Libchaber, A.

2018-01-01

Thiovulum majus self-organize on glass surfaces into active two-dimensional crystals of rotating cells. Unlike classical crystals, these bacterial crystallites continuously rotate and reorganize as the power of rotating cells is dissipated by the surrounding flow. In this article, we describe the earliest stage of crystallization, the attraction of two bacteria into a hydrodynamically-bound dimer. This process occurs in three steps. First a free-swimming cell collides with the wall and becomes hydrodynamically bound to the two-dimensional surface. We present a simple model to understand how viscous forces localize cells near the chamber walls. Next, the cell diffuses over the surface for an average of 63+/- 6 s before escaping to the bulk fluid. The diffusion coefficient {D}{{eff}}=7.98 +/- 0.1 μ {{{m}}}2 {{{s}}}-1 of these 8.5 μ {{m}} diameter cells corresponds to a temperature of (4.16+/- 0.05)× {10}4 K, and thus cannot be explained by equilibrium fluctuations. Finally, two cells coalesce into a rotating dimer when the convergent flow created by each cell overwhelms their active Brownian motion. This occurs when cells diffuse to within a distance of 13.3 ± 0.2 μm of each other.

Inverse cascades and resonant triads in rotating and stratified turbulence

NASA Astrophysics Data System (ADS)

Oks, D.; Mininni, P. D.; Marino, R.; Pouquet, A.

2017-11-01

Kraichnan's seminal ideas on inverse cascades yielded new tools to study common phenomena in geophysical turbulent flows. In the atmosphere and the oceans, rotation and stratification result in a flow that can be approximated as two-dimensional at very large scales but which requires considering three-dimensional effects to fully describe turbulent transport processes and non-linear phenomena. Motions can thus be classified into two classes: fast modes consisting of inertia-gravity waves and slow quasi-geostrophic modes for which the Coriolis force and horizontal pressure gradients are close to balance. In this paper, we review previous results on the strength of the inverse cascade in rotating and stratified flows and then present new results on the effect of varying the strength of rotation and stratification (measured by the inverse Prandtl ratio N/f, of the Coriolis frequency to the Brunt-Väisäla frequency) on the amplitude of the waves and on the flow quasi-geostrophic behavior. We show that the inverse cascade is more efficient in the range of N/f for which resonant triads do not exist, 1 /2 ≤N /f ≤2 . We then use the spatio-temporal spectrum to show that in this range slow modes dominate the dynamics, while the strength of the waves (and their relevance in the flow dynamics) is weaker.

Dawn-dusk asymmetries in rotating magnetospheres: Lessons from modeling Saturn

NASA Astrophysics Data System (ADS)

Jia, Xianzhe; Kivelson, Margaret G.

2016-02-01

Spacecraft measurements reveal perplexing dawn-dusk asymmetries of field and plasma properties in the magnetospheres of Saturn and Jupiter. Here we describe a previously unrecognized source of dawn-dusk asymmetry in a rapidly rotating magnetosphere. We analyze two magnetohydrodynamic simulations, focusing on how flows along and across the field vary with local time in Saturn's dayside magnetosphere. As plasma rotates from dawn to noon on a dipolarizing flux tube, it flows away from the equator along the flux tube at roughly half of the sound speed (Cs), the maximum speed at which a bulk plasma can flow along a flux tube into a lower pressure region. As plasma rotates from noon to dusk on a stretching flux tube, the field-aligned component of its centripetal acceleration decreases and it flows back toward the equator at speeds typically smaller than 1/2 Cs. Correspondingly, the plasma sheet remains far thicker and the field less stretched in the afternoon than in the morning. Different radial force balance in the morning and afternoon sectors produce asymmetry in the plasma sheet thickness and a net dusk-to-dawn flow inside of L = 15 or equivalently, a large-scale electric field (E) oriented from postnoon to premidnight, as reported from observations. Morning-afternoon asymmetry analogous to that found at Saturn has been observed at Jupiter, and a noon-midnight component of E cannot be ruled out.

Noise induced aperiodic rotations of particles trapped by a non-conservative force

NASA Astrophysics Data System (ADS)

Ortega-Piwonka, Ignacio; Angstmann, Christopher N.; Henry, Bruce I.; Reece, Peter J.

2018-04-01

We describe a mechanism whereby random noise can play a constructive role in the manifestation of a pattern, aperiodic rotations, that would otherwise be damped by internal dynamics. The mechanism is described physically in a theoretical model of overdamped particle motion in two dimensions with symmetric damping and a non-conservative force field driven by noise. Cyclic motion only occurs as a result of stochastic noise in this system. However, the persistence of the cyclic motion is quantified by parameters associated with the non-conservative forcing. Unlike stochastic resonance or coherence resonance, where noise can play a constructive role in amplifying a signal that is otherwise below the threshold for detection, in the mechanism considered here, the signal that is detected does not exist without the noise. Moreover, the system described here is a linear system.

In-flight investigation of a rotating cylinder-based structural excitation system for flutter testing

NASA Technical Reports Server (NTRS)

Vernon, Lura

1993-01-01

A research excitation system was test flown at the NASA Dryden Flight Research Facility on the two-seat F-16XL aircraft. The excitation system is a wingtip-mounted vane with a rotating slotted cylinder at the trailing edge. As the cylinder rotates during flight, the flow is alternately deflected upward and downward through the slot, resulting in a periodic lift force at twice the cylinder's rotational frequency. Flight testing was conducted to determine the excitation system's effectiveness in the subsonic, transonic, and supersonic flight regimes. Primary research objectives were to determine the system's ability to develop adequate force levels to excite the aircraft's structure and to determine the frequency range over which the system could excite structural modes of the aircraft. In addition, studies were conducted to determine optimal excitation parameters, such as sweep duration, sweep type, and energy levels. The results from the exciter were compared with results from atmospheric turbulence excitation at the same flight conditions. The comparison indicated that the vane with a rotating slotted cylinder provides superior results. The results from the forced excitation were of higher quality and had less variation than the results from atmospheric turbulence. The forced excitation data also invariably yielded higher structural damping values than those from the atmospheric turbulence data.

Variable Viscosity Effects on Time Dependent Magnetic Nanofluid Flow past a Stretchable Rotating Plate

NASA Astrophysics Data System (ADS)

Ram, Paras; Joshi, Vimal Kumar; Sharma, Kushal; Walia, Mittu; Yadav, Nisha

2016-01-01

An attempt has been made to describe the effects of geothermal viscosity with viscous dissipation on the three dimensional time dependent boundary layer flow of magnetic nanofluids due to a stretchable rotating plate in the presence of a porous medium. The modelled governing time dependent equations are transformed a from boundary value problem to an initial value problem, and thereafter solved by a fourth order Runge-Kutta method in MATLAB with a shooting technique for the initial guess. The influences of mixed temperature, depth dependent viscosity, and the rotation strength parameter on the flow field and temperature field generated on the plate surface are investigated. The derived results show direct impact in the problems of heat transfer in high speed computer disks (Herrero et al. [1]) and turbine rotor systems (Owen and Rogers [2]).

Inertial modes and their transition to turbulence in a differentially rotating spherical gap flow

NASA Astrophysics Data System (ADS)

Hoff, Michael; Harlander, Uwe; Andrés Triana, Santiago; Egbers, Christoph

2016-04-01

We present a study of inertial modes in a spherical shell experiment. Inertial modes are Coriolis-restored linear wave modes, often arise in rapidly-rotating fluids (e.g. in the Earth's liquid outer core [1]). Recent experimental works showed that inertial modes exist in differentially rotating spherical shells. A set of particular inertial modes, characterized by (l,m,ˆω), where l, m is the polar and azimuthal wavenumber and ˆω = ω/Ωout the dimensionless frequency [2], has been found. It is known that they arise due to eruptions in the Ekman boundary layer of the outer shell. But it is an open issue why only a few modes develop and how they get enhanced. Kelley et al. 2010 [3] showed that some modes draw their energy from detached shear layers (e.g. Stewartson layers) via over-reflection. Additionally, Rieutord et al. (2012) [4] found critical layers within the shear layers below which most of the modes cannot exist. In contrast to other spherical shell experiments, we have a full optical access to the flow. Therefore, we present an experimental study of inertial modes, based on Particle-Image-Velocimetry (PIV) data, in a differentially rotating spherical gap flow where the inner sphere is subrotating or counter-rotating at Ωin with respect to the outer spherical shell at Ωout, characterized by the Rossby number Ro = (Ωin - Ωout)/Ωout. The radius ratio of η = 1/3, with rin = 40mm and rout = 120mm, is close to that of the Earth's core. Our apparatus is running at Ekman numbers (E ≈ 10-5, with E = ν/(Ωoutrout2), two orders of magnitude higher than most of the other experiments. Based on a frequency-Rossby number spectrogram, we can partly confirm previous considerations with respect to the onset of inertial modes. In contrast, the behavior of the modes in the counter-rotation regime is different. We found a triad interaction between three dominant inertial modes, where one is a slow axisymmetric Rossby mode [5]. We show that the amplitude of the most

On the Evolution of Pulsatile Flow Subject to a Transverse Impulse Body Force

NASA Astrophysics Data System (ADS)

di Labbio, Giuseppe; Keshavarz-Motamed, Zahra; Kadem, Lyes

2014-11-01

In the event of an unexpected abrupt traffic stop or car accident, automotive passengers will experience an abrupt body deceleration. This may lead to tearing or dissection of the aortic wall known as Blunt Traumatic Aortic Rupture (BTAR). BTAR is the second leading cause of death in automotive accidents and, although quite frequent, the mechanisms leading to BTAR are still not clearly identified, particularly the contribution of the flow field. As such, this work is intended to provide a fundamental framework for the investigation of the flow contribution to BTAR. In this fundamental study, pulsatile flow in a three-dimensional, straight pipe of circular cross-section is subjected to a unidirectional, transverse, impulse body force applied on a strictly bounded volume of fluid. These models were simulated using the Computational Fluid Dynamics (CFD) software FLUENT. The evolution of fluid field characteristics was investigated during and after the application of the force. The application of the force significantly modified the flow field. The force induces a transverse pressure gradient causing the development of secondary flow structures that dissipate the energy added by the acceleration. Once the force ceases to act, these structures are carried downstream and gradually dissipate their excess energy.

Rotation profile flattening and toroidal flow shear reversal due to the coupling of magnetic islands in tokamaks

DOE PAGES

Tobias, B.; Chen, M.; Classen, I. G. J.; ...

2016-04-15

The electromagnetic coupling of helical modes, including those having different toroidal mode numbers, modifies the distribution of toroidal angular momentum in tokamak discharges. This can have deleterious effects on other transport channels as well as on magnetohydrodynamic (MHD) stability and disruptivity. At low levels of externally injected momentum, the coupling of core-localized modes initiates a chain of events, whereby flattening of the core rotation profile inside successive rational surfaces leads to the onset of a large m/n = 2/1 tearing mode and locked-mode disruption. Furthermore, with increased torque from neutral beam injection, neoclassical tearing modes in the core may phase-lockmore » to each other without locking to external fields or structures that are stationary in the laboratory frame. The dynamic processes observed in these cases are in general agreement with theory, and detailed diagnosis allows for momentum transport analysis to be performed, revealing a significant torque density that peaks near the 2/1 rational surface. However, as the coupled rational surfaces are brought closer together by reducing q95, additional momentum transport in excess of that required to attain a phase-locked state is sometimes observed. Rather than maintaining zero differential rotation (as is predicted to be dynamically stable by single-fluid, resistive MHD theory), these discharges develop hollow toroidal plasma fluid rotation profiles with reversed plasma flow shear in the region between the m/n = 3/2 and 2/1 islands. Additional forces expressed in this state are not readily accounted for, and therefore, analysis of these data highlights the impact of mode coupling on torque balance and the challenges associated with predicting the rotation dynamics of a fusion reactor-a key issue for ITER. Published by AIP Publishing.« less

Rotation profile flattening and toroidal flow shear reversal due to the coupling of magnetic islands in tokamaks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tobias, B.; Grierson, B. A.; Okabayashi, M.

2016-05-15

The electromagnetic coupling of helical modes, even those having different toroidal mode numbers, modifies the distribution of toroidal angular momentum in tokamak discharges. This can have deleterious effects on other transport channels as well as on magnetohydrodynamic (MHD) stability and disruptivity. At low levels of externally injected momentum, the coupling of core-localized modes initiates a chain of events, whereby flattening of the core rotation profile inside successive rational surfaces leads to the onset of a large m/n = 2/1 tearing mode and locked-mode disruption. With increased torque from neutral beam injection, neoclassical tearing modes in the core may phase-lock to each othermore » without locking to external fields or structures that are stationary in the laboratory frame. The dynamic processes observed in these cases are in general agreement with theory, and detailed diagnosis allows for momentum transport analysis to be performed, revealing a significant torque density that peaks near the 2/1 rational surface. However, as the coupled rational surfaces are brought closer together by reducing q{sub 95}, additional momentum transport in excess of that required to attain a phase-locked state is sometimes observed. Rather than maintaining zero differential rotation (as is predicted to be dynamically stable by single-fluid, resistive MHD theory), these discharges develop hollow toroidal plasma fluid rotation profiles with reversed plasma flow shear in the region between the m/n = 3/2 and 2/1 islands. The additional forces expressed in this state are not readily accounted for, and therefore, analysis of these data highlights the impact of mode coupling on torque balance and the challenges associated with predicting the rotation dynamics of a fusion reactor—a key issue for ITER.« less

The lift force on a drop in unbounded plane Poiseuille flow

NASA Technical Reports Server (NTRS)

Wohl, P. R.

1976-01-01

The lift force on a deformable liquid sphere moving in steady, plane Poiseuille-Stokes flow and subjected to an external body force is calculated. The results are obtained by seeking a solution to Stokes' equations for the motion of the liquids inside and outside the slightly perturbed sphere surface, as expansions valid for small values of the ratio of the Weber number to the Reynolds number. When the ratio of the drop and external fluid viscosities is small, the lift exerted on a neutrally buoyant drop is found to be approximately one-tenth of the magnitude of the force reported by Wohl and Rubinow acting on the same drop in unbounded Poiseuille flow in a tube. The resultant trajectory of the drop is calculated and displayed as a function of the external body force.

Investigation of Body Force Effects on Flow Boiling Critical Heat Flux

NASA Technical Reports Server (NTRS)

Zhang, Hui; Mudawar, Issam; Hasan, Mohammad M.

2002-01-01

The bubble coalescence and interfacial instabilities that are important to modeling critical heat flux (CHF) in reduced-gravity systems can be sensitive to even minute body forces. Understanding these complex phenomena is vital to the design and safe implementation of two-phase thermal management loops proposed for space and planetary-based thermal systems. While reduced gravity conditions cannot be accurately simulated in 1g ground-based experiments, such experiments can help isolate the effects of the various forces (body force, surface tension force and inertia) which influence flow boiling CHF. In this project, the effects of the component of body force perpendicular to a heated wall were examined by conducting 1g flow boiling experiments at different orientations. FC-72 liquid was boiled along one wall of a transparent rectangular flow channel that permitted photographic study of the vapor-liquid interface at conditions approaching CHF. High-speed video imaging was employed to capture dominant CHF mechanisms. Six different CHF regimes were identified: Wavy Vapor Layer, Pool Boiling, Stratification, Vapor Counterflow, Vapor Stagnation, and Separated Concurrent Vapor Flow. CHF showed great sensitivity to orientation for flow velocities below 0.2 m/s, where very small CHF values where measured, especially with downflow and downward-facing heated wall orientations. High flow velocities dampened the effects of orientation considerably. Figure I shows representative images for the different CHF regimes. The Wavy Vapor Layer regime was dominant for all high velocities and most orientations, while all other regimes were encountered at low velocities, in the downflow and/or downward-facing heated wall orientations. The Interfacial Lift-off model was modified to predict the effects of orientation on CHF for the dominant Wavy Vapor Layer regime. The photographic study captured a fairly continuous wavy vapor layer travelling along the heated wall while permitting liquid

Gravitoinertial force background level affects adaptation to coriolis force perturbations of reaching movements

NASA Technical Reports Server (NTRS)

Lackner, J. R.; Dizio, P.

1998-01-01

We evaluated the combined effects on reaching movements of the transient, movement-dependent Coriolis forces and the static centrifugal forces generated in a rotating environment. Specifically, we assessed the effects of comparable Coriolis force perturbations in different static force backgrounds. Two groups of subjects made reaching movements toward a just-extinguished visual target before rotation began, during 10 rpm counterclockwise rotation, and after rotation ceased. One group was seated on the axis of rotation, the other 2.23 m away. The resultant of gravity and centrifugal force on the hand was 1.0 g for the on-center group during 10 rpm rotation, and 1.031 g for the off-center group because of the 0.25 g centrifugal force present. For both groups, rightward Coriolis forces, approximately 0.2 g peak, were generated during voluntary arm movements. The endpoints and paths of the initial per-rotation movements were deviated rightward for both groups by comparable amounts. Within 10 subsequent reaches, the on-center group regained baseline accuracy and straight-line paths; however, even after 40 movements the off-center group had not resumed baseline endpoint accuracy. Mirror-image aftereffects occurred when rotation stopped. These findings demonstrate that manual control is disrupted by transient Coriolis force perturbations and that adaptation can occur even in the absence of visual feedback. An increase, even a small one, in background force level above normal gravity does not affect the size of the reaching errors induced by Coriolis forces nor does it affect the rate of reacquiring straight reaching paths; however, it does hinder restoration of reaching accuracy.