An Assessment of the Influence of Environmental Factors on Cavitation Instabilities

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Damien T. Kawakami ◽  
A. Fuji ◽  
Y. Tsujimoto ◽  
R. E. A. Arndt
Keyword(s):  
Surface Effects ◽  
Dominant Frequency ◽  
Gas Content ◽  
Numerical Code ◽  
Repetitive Nature ◽  
Composite Parameter ◽  
Induced Flow ◽  
Cavity Shedding ◽  
Cavitation Behavior

Cavitation induced flow instabilities are of interest in numerous applications. Experimental and numerical investigations of this phenomenon are taking place at several institutions around the world. Although there is qualitative agreement among the numerous recent papers on the subject, there is a lack of agreement with regard to important details, such as the spectral content of unsteady lift oscillations. This paper summarizes observations of a cavitating NACA0015 foil in three different tunnels that revealed remarkably different cavity shedding appearances and behaviors. Some of the differences were attributed to system instabilities. However, in addition to a different cavitation behavior attributed to system instabilities, it was found that differences in gas content could significantly alter the lift spectrum of a cavitating foil. For a certain range of the composite parameter σ∕2α near 4, the dominant frequency appears to double when the gas content is reduced by a half. It is also argued that surface effects can have a significant influence on fully wetted time during cavity shedding. Normally, surface effects are assumed to play an important role in the initial inception of a fully wetted hydrofoil with gas content being the primary factor governing developed cavitation behavior. However, the repetitive nature of the process implies that each shedding cycle is an individual inception process. Hence, the unexpected role of surface effects in partially cavitating hydrofoils. The conclusions reached have important ramifications concerning numerical code verification that is a topic of major concern.

scholarly journals The role of thermal diffusion, particle clusters, hydrodynamic and magnetic forces on the flow behaviour of magneto-polymer composites

2021 ◽  
Vol 379 (2205) ◽  
pp. 20200302 ◽  
Author(s):  
William R. Suarez-Fernandez ◽  
Juan D. G. Duran ◽  
Modesto T. Lopez-Lopez
Keyword(s):  
Polymer Composites ◽  
Magnetic Particles ◽  
Hydrodynamic Forces ◽  
Particle Movement ◽  
Dimensionless Numbers ◽  
Anionic Polymer ◽  
Experimental Conditions ◽  
Magnetic Attraction ◽  
Induced Flow

In this paper, we study the shear-induced flow of magneto-polymer composites, consisting of dispersions of magnetic particles in solutions of polymers, as a competition between the colloidal forces amid particles and their bulk transport induced by the hydrodynamic forces. For this aim, we analyse the role of different experimental parameters. Firstly, by using only solutions of a well-known anionic polymer (sodium alginate), we provoke a moderate hindering of particle movement, but keeping the liquid-like state of the samples. On the contrary, a gel-like behaviour is conferred to the samples when a cationic polymer (chitosan) is additionally added, which further reduces the particle movement. We analyse the effect of an applied magnetic field, which is opposed to particle transport by hydrodynamic forces, by inducing magnetic attraction between the particles. We perform the analysis under both stationary and oscillatory shear. We show that by using dimensionless numbers the differences between samples and experimental conditions are emphasized. In all cases, as expected, the transport of particles driven by bulk hydrodynamic forces dominates at high values of the shear rate. This article is part of the theme issue ‘Transport phenomena in complex systems (part 1)’.

Effects of Dissolved Gas on Unsteady Cavitating Flow Around a Clark Y-11.7% Hydrofoil

2015 ◽  
Author(s):  
Haruki Daido ◽  
Satoshi Watanabe ◽  
Shin-ichi Tsuda
Keyword(s):  
High Speed ◽  
Cavitating Flow ◽  
Gas Content ◽  
Dissolved Gas ◽  
Drag Forces ◽  
Cavitation Behavior ◽  
Lift And Drag ◽  
Super Cavity ◽  
Unsteady Cavitating Flow ◽  
Low Do

In the present study, the effects of dissolved gas content on the unsteady cavitating flow around a Clark Y-11.7% hydrofoil are investigated in a cavitation tunnel. Lift and drag forces in various cavitating conditions are directly measured by strain gauges attached on the cantilever supporting the hydrofoil. In addition, the cavitating flow is filmed from the top and the side simultaneously using two high speed video cameras. The high (roughly 6–8ppm) and low (1–2ppm) DO conditions are examined to obtain the qualitative tendencies of the effects of dissolved gas on unsteady cavitation behavior and lift/drag characteristics. It is found that that the relationship between the cavitation behavior and the lift/drag fluctuations does not qualitatively differ in the two different DO conditions, while the amplitude is slightly larger in the low DO condition. At transitional cavity oscillation, in the both DO conditions, the lift/drag coefficients increase during the growth stage of sheet/bubble cavities on the hydrofoil and they decrease when the developed super-cavity disappears. Moreover, it seems that the amplitude of the lift/drag forces in the low DO condition is larger than in the high DO condition but the frequency of lift force fluctuation is not very different.

Role of surface effects on silicon carbide polytype stability

2012 ◽  
Vol 360 ◽  
pp. 189-192 ◽  
Author(s):  
Frédéric Mercier ◽  
Shin-ichi Nishizawa
Keyword(s):  
Silicon Carbide ◽  
Surface Effects ◽  
Silicon Carbide Polytype

Effects of Dissolved Gas Content on Pool Boiling of a Highly Wetting Fluid

1995 ◽  
Vol 117 (3) ◽  
pp. 687-692 ◽  
Author(s):  
S. M. You ◽  
T. W. Simon ◽  
A. Bar-Cohen ◽  
Y. S. Hong
Keyword(s):  
Heat Transfer ◽  
Pool Boiling ◽  
Electronics Cooling ◽  
Horizontal Cylinder ◽  
Gas Content ◽  
Free Fluid ◽  
Dissolved Gas ◽  
Boiling Incipience ◽  
Wetting Fluid

Experimental results on pool boiling heat transfer from a horizontal cylinder in an electronic cooling fluid (FC-72) are presented. The effects on the boiling curve of having air dissolved in the fluid are documented, showing that fluid in the vicinity of the heating element is apparently liberated of dissolved gas during boiling. Dissolved gas was found to influence boiling incipience only with high gas concentrations (>0.005 moles/mole). For low-to-moderate concentrations, a larger superheat is required to initiate boiling and a hysteresis is observed between boiling curves taken with increasing and decreasing heat flux steps. Boiling, a very effective mode of heat transfer, is attractive for electronics cooling. The present experiment provides further documentation of the role of dissolved gas on the incipience process and shows similarities with subcooled boiling of a gas-free fluid.

Responses To Conspecific Advertisement Calls in the Green Frog (Rana Clamitans) and Their Role in Male-Male Communication

Behaviour ◽  
1996 ◽  
Vol 133 (3-4) ◽  
pp. 283-301 ◽  
Author(s):  
Stephen A. Perrill ◽  
Mark A. Bee
Keyword(s):  
Sound Pressure ◽  
Vocal Communication ◽  
Dominant Frequency ◽  
Advertisement Call ◽  
Rana Clamitans ◽  
Green Frog ◽  
Playback Experiments ◽  
The Third ◽  
Altered Response

AbstractWe investigated vocal communication between males in a central Indiana population of the green frog, Rana clamitans. Three playback experiments were conducted. In the first test, we broadcasted a single-note and a multiple-note conspecific advertisement call and a control call (Acris crepitans) to calling males. In response to the conspecific stimuli, males increased the number of calls made per minute, increased note duration, lowered the dominant frequency in the call, and often approached the speaker platform. In a second playback test, designed to examine changes in the sound pressure levels of response calls, we broadcasted a conspecific single-note advertisement call and the control call to calling males. Males in this test lowered the intensity of their responses to the conspecific stimulus. We take these altered response calls to be encounter calls used in the vocal defense of a territory during agonistic male-male interactions. We examine the function of these calls and discuss their possible role in communication between males. In the third test, we broadcasted a second type of conspecific multiple-note call and the control call. In their responses, males increased the number of the second multiple-note calls. The multiple-note stimulus used in this test failed to elicit the agonistic responses of the first two conspecific calls. The role of this second type of multiple-note call in male-male communication remains unclear.

scholarly journals Multidecadal polynya formation in a conceptual (box) model

Ocean Science ◽  
2021 ◽  
Vol 17 (1) ◽  
pp. 335-350
Author(s):  
Daan Boot ◽  
René M. van Westen ◽  
Henk A. Dijkstra
Keyword(s):  
Deep Convection ◽  
Subsurface Layer ◽  
Dominant Frequency ◽  
Box Model ◽  
System Model ◽  
Freshwater Flux ◽  
Heat Accumulation ◽  
Community Earth System Model ◽  
Maud Rise

Abstract. Maud Rise polynyas (MRPs) form due to deep convection, which is caused by static instabilities of the water column. Recent studies with the Community Earth System Model (CESM) have indicated that a multidecadal varying heat accumulation in the subsurface layer occurs prior to MRP formation due to the heat transport over the Weddell Gyre. In this study, a conceptual MRP box model, forced with CESM data, is used to investigate the role of this subsurface heat accumulation in MRP formation. Cases excluding and including multidecadal varying subsurface heat and salt fluxes are considered, and multiple polynya events are only simulated in the cases where subsurface fluxes are included. The dominant frequency for MRP events in these results, approximately the frequency of the subsurface heat and salt accumulation, is still visible in cases where white noise is added to the freshwater flux. This indicates the importance and dominance of the subsurface heat accumulation in MRP formation.

PACAP-(1-38) as neurotransmitter in pig pancreas: receptor activation revealed by the antagonist PACAP-(6-38)

1997 ◽  
Vol 273 (2) ◽  
pp. G436-G446 ◽  
Author(s):  
K. Tornoe ◽  
J. Hannibal ◽  
J. Fahrenkrug ◽  
J. J. Holst
Keyword(s):  
Glucagon Secretion ◽  
Receptor Activation ◽  
Immunohistochemical Localization ◽  
Nerve Fibers ◽  
Relative Importance ◽  
Vagus Stimulation ◽  
Porcine Pancreas ◽  
Endocrine Secretion ◽  
Induced Flow

The pituitary adenylyl cyclase-activating polypeptide PACAP-(1-38) has potent pancreatic secretory effects. We studied its immunohistochemical localization, release, and contribution to secretion induced by electrical vagus stimulation using isolated perfused porcine pancreas and the PACAP receptor antagonist PACAP-(6-38) (10(-7) M). PACAP was found in nerve fibers throughout the pancreas but, in particular, encircling ganglionic vasoactive intestinal polypeptide (VIP)-positive nerve cell bodies and, mostly, colocalized with VIP. Vagus stimulation caused its release. PACAP-(1-38)(4 x 10(-9) M) stimulated exocrine and endocrine secretion and released VIP. PACAP-(6-38) decreased PACAP-induced flow of juice to 59 +/- 7.8% and insulin secretion and VIP release to 12 +/- 6.8 and 57 +/- 13%, respectively. Glucagon secretion was unaffected. PACAP-(6-38) reduced vagus-stimulated flow rate to 63 +/- 7.6%, insulin and glucagon responses to 31.8 +/- 13 and 6 +/- 4%, respectively, and VIP release to 23 +/- 8.4% and reduced VIP-induced (2 x 10(-9) M) juice and insulin (but not glucagon) outputs to 8.3 +/- 4.2 and 67 +/- 14%, respectively. In conclusion, 1) pancreatic PACAP fibers seem to activate intrapancreatic VIPergic neurons, 2) PACAP-(6-38) antagonism documents the role of VIP/PACAP for neural regulation but cannot distinguish their relative importance, and 3) a PACAP receptor with low affinity for PACAP-(6-38), associated with glucagon cells, may exist.

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