Cavitation Bubble in a Heavy ...

[ Pobierz całość w formacie PDF ]
Combustion, Explosion, and Shock Waves, Vol. 36, No. 6, 2000
Cavitation Bubble
in a Heavy Viscous Liquid
V. N. Rodionov
1
UDC 532.528(527)
Translated from Fizika Goreniya i Vzryva, Vol. 36, No. 6, pp. 84{86, November{December, 2000.
Original article submitted June 29, 2000.
The motion of a cavitation bubble in a heavy viscous liquid is considered. The re-
sults of lming of the process are analyzed. A laboratory facility for modeling this
phenomenon is described.
The invention of a shaped charge was an impor-
tant event in military activity and changed qualita-
tively the ideas of hitting armored machines. How-
ever, hydrodynamic models that explained the pro-
cess of jet generation by explosive compression of a
conical metal shell and the mechanism of jet penetra-
tion into an armored plate were even more important
for science and technology.
These models were proposed by
M. A. Lavrent'ev in clear and explicit form,
which is typical of all classical models of natural
history. Based on the classical models, associative
thinking generates images, which are helpful in
studying natural phenomena in various situations.
Specially or incidentally, all naturalists seek in nature
something born in their imagination. An example of
scientic search of a physical object originating in
G. V. Belyakov's imagination under the inuence of
models developed by M. A. Lavrent'ev may be the
experiments on generation of a cavitation bubble in
a heavy viscous liquid.
G. V. Belyakov assumed that a fast short jet
penetrating into a liquid under pressure forms a cav-
ity collapsing in the backward part to form another
jet. If the velocity and thickness of the new jet are
not too dierent from the same characteristics of the
rst jet, the resultant bubble can exist autonomously
and move without exciting disturbances in the liquid.
The research experiment was successful: a rapidly
moving cavitation vortex actually appeared in some
experiments [1].
A laboratory facility was designed to nd the
conditions of bubble origination in a stationary liq-
uid with a jet penetrating into it. A pipe 50 cm long
with an internal diameter of 11 cm was located verti-
cally. The butt-end faces of the pipe were covered by
lids; there was a nozzle near the bottom and a branch
pipe for evacuation of air in the upper lid. The liq-
uid lled part of the volume up to a given level above
the nozzle. The jet was exhausted from the nozzle by
the piston under the action of the compressed spring.
1
Institute of Geosphere Dynamics, Russian
Academy of Sciences, Moscow 117334.
Fig. 1. Layout of the facility: 1) nozzle; 2) piston;
3) spring; 4) windows; 5) metal cylinder; 6) AKS-
4 camera; 7) lighter; 8) branch pipe.
0010-5082/00/3606-0751 $25.00
c
2000
Plenum Publishing Corporation
751
752
Rodionov
TABLE 1
x
1
, mm x
2
, mm v
1
, m/sec v
2
, m/sec l, mm
66
24.2
4.18
1.434
41.8
85.8
31.9
1.98
0.77
52.9
96.8
37.4
1.1
0.55
59.4
106.7
41.8
0.99
0.44
64.9
The length, diameter, and velocity of the jet could
be varied from one test to another. Optical registra-
tion of the bubble was performed through two long
windows located opposite each other along the pipe.
One window 2.5 cm wide was illuminated by scat-
tered light, and the lming was performed through
the other window 3.5 cm wide. Figure 1 shows the
working volume of the facility. (The cross section is
shown in the central part, in the brakes.)
The test conditions and results of one ex-
periment are presented below. Glycerin [density
1.26 g/cm
3
and viscosity 20 g/(cmsec)] lled the pipe
up to a level of 15 cm above the nozzle. A jet 1 cm in
diameter and 2.5 cm long was \shot" with a velocity
of 4.5 m/sec. The gas pressure above the glycerin
surface was about 10
4
atm. The lming frequency
was 100 frames per second. The experimental facil-
ity allows one to organize conditions necessary for a
cavitation bubble to appear and autonomously exist
for some time.
Figure 2 shows a stable shape of the cavitation
bubble ascending in a heavy liquid. The coordinates
and velocities of the bubble apex (v
1
) and backward
surface (v
2
) were measured. These data are listed in
Table 1. It is not possible to measure the jet diam-
eter in the photographs, since the refraction of light
beams in the bubble distorts the size of the jet and
objects located behind the bubble. The external con-
tours of the bubble itself on the background of the
illuminated window are not distorted (Fig. 3).
The energy of the bubble is proportional to the
product of its volume and the pressure in the ambi-
ent liquid. For a constant energy, the bubble volume
is inversely proportional to the pressure in the liquid.
The resistance to bubble motion is caused by the vis-
Fig. 2. Stable shape of the cavitation bubble in a heavy
liquid
Fig. 3. Photograph of the cavitation bubble.
Cavitation Bubble in a Heavy Viscous Liquid
753
cosity of the liquid, which is mainly manifested in
local zones of the forward and backward parts of the
bubble. Because of this, the energy losses of the bub-
ble are signicantly lower than the losses of a solid
body of the same size.
Ascending in the eld of gravity, the bubble may
increase its energy if energy losses are reduced. Sim-
ilarly, the bubble energy increases if it moves in the
direction of the accelerated motion of the vessel con-
taining the liquid. After losing its energy, the bubble
ceases to exist.
Under favorable conditions, the bubble may
cover a large distance and transfer some part of the
substance of the initiating jet, since the exchange of
substance between the bubble and the ambient liquid
is rather limited.
The experimental results presented demonstrate
the formation and autonomous motion of a cavitation
bubble inside the laboratory facility. The mechani-
cal image of the bubble is quite clear for construct-
ing models and studying them theoretically in detail.
This image may be realized in various natural phe-
nomena and in various media.
REFERENCES
1. M. A. Sadovskii, V. N. Rodionov, and G. V. Belyakov,
\Mechanics of origination of a cavitation bubble,"
Dokl. Ross. Akad. Nauk, 325, No. 1, 42{45 (1992).
[ Pobierz całość w formacie PDF ]