Improvements in Lightly Loaded Rotor/Bearing and Rotor/Seal Models

1988 ◽  
Vol 110 (2) ◽  
pp. 129-136 ◽  
Author(s):  
A. Muszynska
Keyword(s):  
Stability Analysis ◽  
Fluid Dynamic ◽  
Velocity Ratio ◽  
Nonlinear Function ◽  
Circumferential Velocity ◽  
Rotating Shaft ◽  
Model Adequacy ◽  
Dynamic Forces ◽  
Key Factor ◽  
Lateral Mode

A model for lightly loaded steadily rotating shaft/bearing/seal systems is proposed in this paper. The model is based on modal characteristics for the rotor, and rotational characteristics for the fluid dynamic forces generated in bearings and/or seals. The fluid average circumferential velocity ratio as a nonlinear function of shaft eccentricity represents a key factor in the model. The model is extremely useful for rotor stability analysis. The model adequacy was proved for one and two lateral mode models of rotors.

Direct Measurement of Unsteady Fluid Dynamic Forces for a Hovering Dragonfly

AIAA Journal ◽  
2005 ◽  
Vol 43 (12) ◽  
pp. 2475-2480 ◽  
Author(s):  
Manabu Yamamoto ◽  
Koji Isogai
Keyword(s):  
Direct Measurement ◽  
Fluid Dynamic ◽  
Dynamic Forces ◽  
Unsteady Fluid

scholarly journals Flow reduces the amplitude and increases the frequency of lymphatic vasomotion: role of endothelial prostanoids

1999 ◽  
Vol 277 (6) ◽  
pp. R1683-R1689 ◽  
Author(s):  
Akos Koller ◽  
Risuke Mizuno ◽  
Gabor Kaley
Keyword(s):  
Fluid Dynamic ◽  
Intraluminal Pressure ◽  
Perfusate Flow ◽  
Intrinsic Mechanism ◽  
Dynamic Forces ◽  
The Difference ◽  
Induced Changes ◽  
Afferent Lymph ◽  
Oxide Synthase

Fluid dynamic forces have substantial effects on the movement of lymph and activity of lymph vessels. The effect of increases in intraluminal flow on spontaneous pumping activity of isolated collecting lymphatics has not yet been characterized in a condition in which the intraluminal pressure is constant. Thus, in afferent lymph microvessels isolated from rat iliac lymph nodes, changes in maximum (Dmax) and minimum (Dmin) diameter to increases in perfusate flow were investigated in the presence of a constant perfusion pressure of 6 cmH2O. Intraluminal flow was elicited by increases in the difference between outflow and inflow pressures (Pdiff, from 0 to 6 cmH2O). Diameters were measured by videomicroscopy. In response to increases in perfusate flow, Dmax and Dmin of lymphatics decreased from 157.5 ± 6.1 to 90.9 ± 5.6 μm and from 91.9 ± 5.3 to 66.3 ± 3.6 μm, respectively, whereas vasomotion frequency increased from 18.0 ± 0.7 min−1 to 23.4 ± 1.1 min−1 (at Pdiff of 4 cmH2O). Removal of extracellular Ca2+ abolished spontaneous diameter oscillations; under these conditions the passive diameter of lymphatics was 216.0 ± 7.1 μm and did not change in response to increases in perfusion. In the absence of endothelium, flow-induced changes in Dmax, Dmin, and oscillation frequency were eliminated. N ω-nitro-l-arginine methyl ester, an inhibitor of nitric oxide synthase, did not affect flow-induced changes in diameter of lymphatics. In contrast, indomethacin, an inhibitor of prostaglandin synthesis, or SQ-29,548, a PGH2/thromboxane A2(PGH2/TxA2) receptor blocker, inhibited the perfusion-induced reduction of Dmax and Dmin of lymphatics and also the increase in the frequency of vasomotion. These findings suggest that the sensitivity of lymphatic endothelium to increases in intraluminal flow could provide an important local intrinsic mechanism for the control of lymphatic resistance by release of constrictor prostanoids PGH2/TxA2.

Stability and dynamics of the laminar wake past a slender blunt-based axisymmetric body

2011 ◽  
Vol 676 ◽  
pp. 110-144 ◽  
Author(s):  
P. BOHORQUEZ ◽  
E. SANMIGUEL-ROJAS ◽  
A. SEVILLA ◽  
J. I. JIMÉNEZ-GONZÁLEZ ◽  
C. MARTÍNEZ-BAZÁN
Keyword(s):  
Stability Analysis ◽  
Numerical Simulations ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Velocity Ratio ◽  
Reynolds Numbers ◽  
Base Flow ◽  
Direct Numerical Simulations ◽  
The Body ◽  
Stream Velocity

We investigate the stability properties and flow regimes of laminar wakes behind slender cylindrical bodies, of diameter D and length L, with a blunt trailing edge at zero angle of attack, combining experiments, direct numerical simulations and local/global linear stability analyses. It has been found that the flow field is steady and axisymmetric for Reynolds numbers below a critical value, Recs (L/D), which depends on the length-to-diameter ratio of the body, L/D. However, in the range of Reynolds numbers Recs(L/D) < Re < Reco(L/D), although the flow is still steady, it is no longer axisymmetric but exhibits planar symmetry. Finally, for Re > Reco, the flow becomes unsteady due to a second oscillatory bifurcation which preserves the reflectional symmetry. In addition, as the Reynolds number increases, we report a new flow regime, characterized by the presence of a secondary, low frequency oscillation while keeping the reflectional symmetry. The results reported indicate that a global linear stability analysis is adequate to predict the first bifurcation, thereby providing values of Recs nearly identical to those given by the corresponding numerical simulations. On the other hand, experiments and direct numerical simulations give similar values of Reco for the second, oscillatory bifurcation, which are however overestimated by the linear stability analysis due to the use of an axisymmetric base flow. It is also shown that both bifurcations can be stabilized by injecting a certain amount of fluid through the base of the body, quantified here as the bleed-to-free-stream velocity ratio, Cb = Wb/W∞.

Experiments on the lift and drag of spheres suspended in a Poiseuille flow

1964 ◽  
Vol 20 (3) ◽  
pp. 513-527 ◽  
Author(s):  
R. Eichhorn ◽  
S. Small
Keyword(s):  
Reynolds Number ◽  
Poiseuille Flow ◽  
Rotation Speed ◽  
Fluid Dynamic ◽  
Particle Diameter ◽  
Dynamic Forces ◽  
Shear Parameter ◽  
Fluid Properties ◽  
Approach Velocity ◽  
Lift And Drag

An experimental investigation of the fluid dynamic forces on spheres suspended in a Poiseuille flow was performed. Small spheres of polystyrene, nylon, and Lucite, having diameters ranging from 0.061 in. to 0.126 in. were suspended in Poiseuille flows in a 0.419 in. diameter tube. Variations in particle size and density, the fluid properties, and the angle of inclination of the tube, resulted in a sphere Reynolds number (based on particle diameter and approach velocity) ranging from 80 to 250. The results are presented as curves which include the coefficients of lift and drag, and the dimensionless rotation speed plotted versus Reynolds number and a dimensionless shear parameter.

Effect of velocity on the filter feeding of dreissenid mussels (Dreissena polymorpha and Dreissena bugensis): implications for trophic dynamics

1999 ◽  
Vol 56 (9) ◽  
pp. 1551-1561 ◽  
Author(s):  
Josef Daniel Ackerman
Keyword(s):  
Dreissena Polymorpha ◽  
Fluid Dynamic ◽  
Flow Chamber ◽  
Freshwater Ecosystems ◽  
Trophic Dynamics ◽  
Clearance Rates ◽  
Dreissena Bugensis ◽  
Dreissenid Mussels ◽  
Marine Bivalves ◽  
Dynamic Forces

Fluid dynamic forces were found to significantly affect the ability of freshwater dreissenid mussels (Dreissena polymorpha and Dreissena bugensis) to clear plankton. Tests conducted in a flow chamber at <1 cm·s-1 were consistent with published clearance rates from standard tests involving unstirred containers (i.e., 60-70 mL· mussel-1·h-1 for 11-mm-long mussels). Increasing ambient velocity up to ~10 cm·s-1 led to clearance rates at least twice those of standard testing methods. Higher velocities (~20 cm·s-1) were inhibitory and resulted in reduced clearance rates. There were no detectable differences in the clearance rates of D. polymorpha and D. bugensis of equal size tested at ~10 cm·s-1, but large mussels had greater clearance rates than small ones. These results were found to be consistent with observations from marine bivalves and indicate that fluid dynamic issues are of importance in freshwater ecosystems, especially those that are shallow and (or) flowing. The trophic dynamics of these ecosystems will be better understood when the effects of fluid dynamics on the organism's ability to filter feed and the local delivery of seston through turbulent mixing are considered.

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