Observations of the Various Types of Limited Cavitation on Axisymmetric Bodies

1981 ◽  
Vol 103 (3) ◽  
pp. 415-424 ◽  
Author(s):  
J. W. Holl ◽  
J. A. Carroll
Keyword(s):  
Cavitation Number ◽  
Pressure Data ◽  
Roughness Effects ◽  
Laminar Separation ◽  
Fluctuating Pressure ◽  
Air Content ◽  
Speed Range ◽  
All Speeds ◽  
Axisymmetric Bodies ◽  
Flow States

Observations are presented of various types of limited cavitation on 5.1 cm diameter Schiebe, hemispherical, and DTNSRDC noses. These three noses were selected to give various flow states over the range of test speeds 6.1–21.3 m/s ranging from laminar separation for all speeds (hemispherical nose) to nonseparated flow for all speeds (Schiebe nose) with the DTNSRDC nose experiencing both separated and nonseparated flow over the speed range. The types of cavitation observed fall into two broad classes, namely transient and attached. Transient cavitation was observed in three forms, namely travelling-bubble, travelling-patch and bubble-ring. Three types of attached cavitation were observed, namely band, fixed-patch and developed. Bubble-ring and band cavitation are observed only on a body with laminar separation as noted previously by Arakeri and Acosta. Bubble-ring cavitation has been observed only on hemispherical and eighth caliber ogive noses. The desinent cavitation numbers for band and bubble-ring cavitation on the hemispherical nose are related to measured mean and fluctuating pressure data. Travelling cavitation was the most prevalent type of cavitation and the cavitation number decreased with speed and increased with air content. An analysis of travelling cavitation data from several investigations is presented. The cavitation number for fixed-patch cavitation increases with speed which suggests that surface roughness effects are involved.

The Onset of Bubble-Ring Cavitation on Hemispherical Headforms

1982 ◽  
Vol 104 (1) ◽  
pp. 115-122
Author(s):  
B. R. Parkin
Keyword(s):  
Pressure Coefficient ◽  
Reynolds Numbers ◽  
Present Theory ◽  
Cavitation Number ◽  
Approximate Theory ◽  
Freestream Velocity ◽  
Laminar Separation ◽  
Air Bubble ◽  
Air Content ◽  
Good Agreement

An approximate theory is developed to predict the onset of cavitation on hemispherical headforms for Reynolds numbers at which laminar separation is known to occur. Insofar as it is possible, the theory is based upon first principles. Fairly good agreement is obtained between the cavitation desinence trends recently measured by Holl and Carroll and the present theory. It is also found that the onset cavitation number should be less than the magnitude of the pressure coefficient at the laminar separation point and that the cavitation number increases with freestream velocity. As long as there is an appreciable concentration of dissolved air in the water, it is also found, in agreement with experiment, that the onset of bubblering cavitation is practically independent of air content. Moreover, the observed occurrence of a lowest speed for “bubble-ring” cavitation, which is the only cavitation form considered here, and the range of “cutoff” speeds predicted by the present asymptotic theory show very encouraging agreement. The present theory suggests that this cutoff speed and its accompanying cutoff cavitation number can also depend on the temperature of the water, provided that the initial size attributed to a “typical” spherical free-stream air bubble nucleus also varies with the temperature. At 80° F (26.6°C) it is estimated that the typical nucleus from which bubble-ring cavitation originates has a radius of about seven μm. At higher temperatures the nucleus radius decreases from this value while at lower temperatures the initial radius exceeds the value noted.

Occurrence of Bubbles in a Thin Wire at Low Reynolds Number

1992 ◽  
Vol 114 (2) ◽  
pp. 255-260 ◽  
Author(s):  
K. Sato
Keyword(s):  
Separation Zone ◽  
Reynolds Numbers ◽  
Cavitation Number ◽  
The Other ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Thin Wires ◽  
Different Types ◽  
Low Reynolds ◽  
Air Diffusion

Thin wires of various diameters from 0.07 to 0.7 mm are examined about appearances and characteristics of bubble occurrence behind them in the range of low Reynolds numbers. The appearance of bubbles is very dependent on diameters of wires. Two different types of bubbles can be observed in the present experiment. One is a streamer-type bubble for smaller wires and the other is a small unspherical bubble for larger wires. The incipient and the desinent values of cavitation number also change greatly with the bubble types. The streamer-type bubble is related to the presence of laminar separation zone and the growth due to air diffusion. The small unspherical bubble can be mainly attributed to the motion of rolled-up vortices and the growth due to vaporization.

An Effect of Air Content on the Occurrence of Cavitation

1960 ◽  
Vol 82 (4) ◽  
pp. 941-945 ◽  
Author(s):  
J. W. Holl
Keyword(s):  
Pressure Coefficient ◽  
Cavitation Number ◽  
Experimental Results ◽  
Simultaneous Occurrence ◽  
Minimum Pressure ◽  
Air Content ◽  
The Difference ◽  
Dissolved Air

The simultaneous occurrence of vaporous and gaseous cavitation on hydrofoils is considered. The experimental results show that gaseous cavitation occurs at much higher ambient pressures than that for the vaporous cavitation resulting in desinent-cavitation numbers twice the minimum-pressure coefficient of the hydrofoil. The analysis indicates that the difference between the desinent-cavitation number for the gaseous cavitation and that for the vaporous cavitation is proportional to the dissolved air content and inversely proportional to the square of the velocity.

scholarly journals Dynamics of Attached Cavities on Bodies of Revolution

1992 ◽  
Vol 114 (1) ◽  
pp. 93-99 ◽  
Author(s):  
S. L. Ceccio ◽  
C. E. Brennen
Keyword(s):  
Reynolds Numbers ◽  
Cavitation Number ◽  
The Body ◽  
Cavity Surface ◽  
Bodies Of Revolution ◽  
The Mean ◽  
Cavity Thickness ◽  
Cavity Closure ◽  
Axisymmetric Bodies ◽  
Single Cavity

Attached cavitation was generated on two axisymmetric bodies, a Schiebe body and a modified ellipsoidal body (the I. T. T. C. body), both with a 50.8 mm diameter. Tests were conducted for a range of cavitation numbers and for Reynolds numbers in the range of Re = 4.4 × 105 to 4.8 × 105. Partially stable cavities were observed. The steady and dynamic volume fluctuations of the cavities were recorded through measurements of the local fluid impedance near the cavitating surface suing a series of flush mounted electrodes. These data were combined with photographic observations. On the Schiebe body, the cavitation was observed to form a series of incipient spot cavities which developed into a single cavity as the cavitation number was lowered. The incipient cavities were observed to fluctuate at distinct frequencies. Cavities on the I. T. T. C. started as a single patch on the upper surface of the body which grew to envelope the entire circumference of the body as the cavitation number was lowered. These cavities also fluctuated at distinct frequencies associated with oscillations of the cavity closure region. The cavities fluctuated with Strouhal numbers (based on the mean cavity thickness) in the range of St = 0.002 to 0.02, which are approximately one tenth the value of Strouhal numbers associated with Ka´rma´n vortex shedding. The fluctuation of these stabilized partial cavities may be related to periodic break off and filling in the cavity closure region and to periodic entrainment of the cavity vapor. Cavities on both headforms exhibited surface striations in the streamwise direction near the point of cavity formation, and a frothy mixture of vapor and liquid was detected under the turbulent cavity surface. As the cavities became fully developed, the signal generated by the frothy mixture increased in magnitude with frequencies in the range of 0 to 50 Hz.

A Review of Surface Roughness Effects in Gas Turbines

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
J. P. Bons
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Surface Roughness ◽  
Gas Turbines ◽  
Engine Performance ◽  
Boundary Layer Transition ◽  
Roughness Effects ◽  
Layer Transition ◽  
Laminar Separation

The effects of surface roughness on gas turbine performance are reviewed based on publications in the open literature over the past 60 years. Empirical roughness correlations routinely employed for drag and heat transfer estimates are summarized and found wanting. No single correlation appears to capture all of the relevant physics for both engineered and service-related (e.g., wear or environmentally induced) roughness. Roughness influences engine performance by causing earlier boundary layer transition, increased boundary layer momentum loss (i.e., thickness), and/or flow separation. Roughness effects in the compressor and turbine are dependent on Reynolds number, roughness size, and to a lesser extent Mach number. At low Re, roughness can eliminate laminar separation bubbles (thus reducing loss) while at high Re (when the boundary layer is already turbulent), roughness can thicken the boundary layer to the point of separation (thus increasing loss). In the turbine, roughness has the added effect of augmenting convective heat transfer. While this is desirable in an internal turbine coolant channel, it is clearly undesirable on the external turbine surface. Recent advances in roughness modeling for computational fluid dynamics are also reviewed. The conclusion remains that considerable research is yet necessary to fully understand the role of roughness in gas turbines.

A Note on the Effect of Short and Long Laminar Separation Bubbles on Desinent Cavitation

1981 ◽  
Vol 103 (1) ◽  
pp. 28-32 ◽  
Author(s):  
V. H. Arakeri ◽  
J. A. Carroll ◽  
J. W. Holl
Keyword(s):  
Flow Visualization ◽  
Viscous Flow ◽  
Critical Velocity ◽  
Film Flow ◽  
Separation Bubble ◽  
Sudden Change ◽  
Cavitation Number ◽  
The Body ◽  
Laminar Separation Bubble ◽  
Laminar Separation

Earlier desinent cavitation studies on a 1/8 caliber ogive by one of the authors (J. W. H.) showed a sudden change in the magnitude of the desinent cavitation number at a critical velocity. In the present work it is shown by means of oil-film flow visualization that below the critical velocity a long laminar separation bubble exists whereas above the critical velocity the laminar separation bubble is short. Thus the desinent cavitation characteristics of a 1/8 caliber ogive are governed by the nature of the viscous flow around the body.

scholarly journals Cavitation Flow of Oil and Water Through the Nozzle

2020 ◽  
Vol 328 ◽  
pp. 03012
Author(s):  
Marian Bojko ◽  
Milada Kozubková ◽  
Jana Jablonská
Keyword(s):  
High Speed ◽  
Cavitation Number ◽  
Loss Coefficient ◽  
High Speed Camera ◽  
Cavitation Flow ◽  
Air Content ◽  
Hydraulic Equipment ◽  
Hydraulic Fluids ◽  
Different Types ◽  
Different Temperatures

The hydraulic equipment and elements are designed so that the flow is not significantly affected by the content of gases in the fluid. In the case of cavitation, there is a change in the volumetric amount of gas, which in water is due to the air and water vapour present, and in the case of oils, especially the air content. This phenomenon causes a significant change in the loss coefficient of the element. The problem of cavitation is solved in the literature for water flow, for other hydraulic fluids (e.g. hydraulic oils operated at different temperatures) the problem is still not solved to a sufficient extent. The article deals with the issue of cavitation in systems in which different types of liquids are used. In the introduction, the physical properties of the used liquids are evaluated, because they significantly influence the origin and development of cavitation. Subsequently, an experimental device with a transparent nozzle is described, on which the measurement. The dependence of the loss coefficient and the cavitation number on the Reynolds number is evaluated. Cavitation is evaluated by a high-speed camera, where it is possible to monitor the behaviour of the cavitation cloud.

Cavitation Inception Observations on Axisymmetric Bodies at Supercritical Reynolds Numbers

1976 ◽  
Vol 20 (01) ◽  
pp. 40-50
Author(s):  
V. H. Arakeri ◽  
A. J. Acosta
Keyword(s):  
Boundary Layer ◽  
Reynolds Numbers ◽  
The Body ◽  
Laminar Separation ◽  
Cavitation Inception ◽  
Minimum Pressure ◽  
Pressure Point ◽  
A Site ◽  
Axisymmetric Bodies

A laminar separation on a body provides a site for the inception of cavitation. The separated region disappears when the boundary layer upstream becomes turbulent; this may occur naturally or by stimulation. The consequences of this disappearance on the values of the cavitation inception index and the type and appearance of the cavitation at inception are investigated on three different axisymmetric bodies. On one of these bodies, a hemisphere-cylinder, a trip near the nose so energized the boundary layer that it was impossible for any form of cavitation to remain attached to the body even when a tension of about one half atm. existed at the minimum pressure point on the body.

Cavitation Inception on a Circular Cylinder at Critical and Supercritical Flow Range

1986 ◽  
Vol 108 (4) ◽  
pp. 421-427 ◽  
Author(s):  
A. Ihara ◽  
H. Murai
Keyword(s):  
Circular Cylinder ◽  
Separation Bubble ◽  
Circular Cylinders ◽  
Critical Flow ◽  
Laminar Separation Bubble ◽  
Supercritical Flow ◽  
Laminar Separation ◽  
Cavitation Inception ◽  
Rear Part ◽  
Axisymmetric Bodies

Cavitation tests were performed in the critical and supercritical flow range on circular cylinders with and without boundary layer trip. Mean and fluctuating static pressures were meausred on the smooth circular cylinder from θ = 0 to 180° and on the tripped surface at θ = 104 and 106° corresponding to tripping wire location α = 38 and 40 deg. Through these measurements it was found that cavitation that closely resembles bubble ring cavitation reported on axisymmetric bodies took palce in a reattachment region of the laminar separation bubble for the critical flow range where the laminar separation bubble was present. For the supercritical flow range where the laminar separation bubble disappeared, smooth cavitation with small irregular bubbles at its rear part took place at a location about 100° from the stagnation point.

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