The Initiation Of Gaseous Microbubble Growth In Laminar Separation Bubbles

1981 ◽  
Vol 103 (4) ◽  
pp. 543-549 ◽  
Author(s):  
B. R. Parkin
Keyword(s):  
Cavitation Bubble ◽  
Separation Zone ◽  
Separation Bubble ◽  
Practical Interest ◽  
The Body ◽  
Laminar Separation Bubble ◽  
Flow Conditions ◽  
Laminar Separation ◽  
Cavitation Inception ◽  
Air Diffusion

Flow conditions surrounding bubble-ring cavitation inception on hemispherical headforms are analyzed with respect to the initiation of air diffusion into microbubbles as is observed to occur at fixed positions in the boundary layer. Fairly recent observations have shown this phenomenon to occur in the laminar separation bubble on the body. The analysis shows, in agreement with the body of experimental evidence now available, that gaseous growth must be preceded by a period of vaporous growth starting in regions of low pressure upstream of the laminar separation bubble. It also appears that the most favorable condition for the initiation of gaseous growth should occur when a typical vapor bubble reaches its maximum radius as it enters the laminar separation bubble. The conditions for the initiation of subsequent gaseous growth, once the cavitation bubble is stabilized in the laminar separation zone, are more demanding. Nevertheless, it is found that the liquid in the water surrounding the bubble in the separation zone is definitely supersaturated for most flows of experimental or practical interest. Therefore, gaseous growth, as well as vaporous growth, is definitely to be associated with the onset of bubble-ring cavitation on both theoretical and experimental grounds.

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.

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.

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.

Loss Production Mechanisms in a Laminar Separation Bubble

2012 ◽  
Vol 89 (4) ◽  
pp. 547-562 ◽  
Author(s):  
Daniele Simoni ◽  
Marina Ubaldi ◽  
Pietro Zunino
Keyword(s):  
Separation Bubble ◽  
Laminar Separation Bubble ◽  
Laminar Separation ◽  
Production Mechanisms

Transition Mechanisms in Laminar Separated Flow Under Simulated Low Pressure Turbine Aerofoil Conditions

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Jerrit Dähnert ◽  
Christoph Lyko ◽  
Dieter Peitsch
Keyword(s):  
Reynolds Number ◽  
Separation Bubble ◽  
Separated Flow ◽  
Low Pressure ◽  
Main Flow ◽  
Test Facility ◽  
Flow Conditions ◽  
Laminar Separation ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine

Based on detailed experimental work conducted at a low speed test facility, this paper describes the transition process in the presence of a separation bubble with low Reynolds number, low free-stream turbulence, and steady main flow conditions. A pressure distribution has been created on a long flat plate by means of a contoured wall opposite of the plate, matching the suction side of a modern low-pressure turbine aerofoil. The main flow conditions for four Reynolds numbers, based on suction surface length and nominal exit velocity, were varied from 80,000 to 300,000, which covers the typical range of flight conditions. Velocity profiles and the overall flow field were acquired in the boundary layer at several streamwise locations using hot-wire anemometry. The data given is in the form of contours for velocity, turbulence intensity, and turbulent intermittency. The results highlight the effects of Reynolds number, the mechanisms of separation, transition, and reattachment, which feature laminar separation-long bubble and laminar separation-short bubble modes. For each Reynolds number, the onset of transition, the transition length, and the general characteristics of separated flow are determined. These findings are compared to the measurement results found in the literature. Furthermore, the experimental data is compared with two categories of correlation functions also given in the literature: (1) correlations predicting the onset of transition and (2) correlations predicting the mode of separated flow transition. Moreover, it is shown that the type of instability involved corresponds to the inviscid Kelvin-Helmholtz instability mode at a dominant frequency that is in agreement with the typical ranges occurring in published studies of separated and free-shear layers.

Sign in / Sign up

Export Citation Format

Share Document