A research about cavitation.

1. Cavitation
&
super cavitation
INTERSTING PHENOMENTOMN

2. Presented By:
REZA HOSSEINI

3. What is cavitation?
What do water bottles, the mantis shrimp and propellers have in common?
They are both good way to see a phenomenon called cavitation in action.
Cavitation happens when the pressure in a liquid suddenly drops. The drop
in pressure is caused by pushing a liquid quicker than it can react, leaving
behind an area of low pressure often as a bubble of gas.

4. FOR EXAMPLE :
In the above example the glass bottle is hit from the top, the glass moves
down faster than the water, causing air bubbles and low pressure to form at
the bottom. Once the bubbles collapse a shock wave breaks the bottle of the
glass.
In general, objects like propellers are designed to avoid cavitation and the
damage it can cause. However there is one animal that exploits the effect. The
Mantis shrimp uses a punch strong enough to cause cavitation to stun prey. It
can also be used to break down kidney stones, sterilise water, or break up dirt.

http://www.physics.org/article

5. NOW LET’S TALK ABOUT
SUPERCVITATION THAT IT’S ONE OF
THE USES OF CAVITATION
PHENOMENON…….

6. Artist rendering of a supercavitating propeller in action
•////

7. A
ROCKET
TORPED
O THAT
SWIMS
IN AN
AIR
BUBBLE

8. supercavitating torpedo--a rocket-propelled weapon that speeds through the
water enveloped in a nearly frictionless air bubble may render obsolete the old
submarine strategy of sly maneuvering and silent running to evade the
enemy. The superfast torpedo could be outfitted with conventional explosive
warheads, nuclear tips or nothing at all--a 5,000-pound, 230-mph missile
could do enough damage on its own. The Russians invented the concept
during the Cold War, and their version of this underwater killer--dubbed the
Shkval ("Squall")--has recently been made available on the international
weapons market; the United States, of course, wants a new, improved version
of the original.

9. The hard part about building a rocket-propelled torpedo isn't so
much the propulsion as clearing a path through the ocean. Water
creates speed-sapping drag; the best way to overcome that drag
is to create a bubble that envelops the torpedo--a supercavity. A
gas ejected uniformly and with enough force through a cavitator
in the nose of the torpedo will provide such a bubble, permitting
speeds of more than 200 mph and a range of up to 5 miles
(traditional torpedoes have slightly longer ranges, but lumber at
only 30 to 40 mph).

10. Some of other using of supercavitation :

11. RAMICS
Rapid Airborne Mine Clearance System

12. RAMICS uses a gated electro-optic Laser Imaging Detection and
Ranging sensor for target re-acquisition and a 30mm MK44
Bushmaster II gun for neutralization.
The gun uses a MK 258 Mod 1 armor-piercing, fin-stabilized
round which is stable during flight, and after penetrating the water,
supercavitates to greatly reduce drag and improves underwater
flight performance. Supercavitation takes place when the tip of the
high velocity RAMICS projectile vaporizes the water to steam
allowing the projectile to travel through the resulting gas pocket in
the water column. The accuracy of the system will destroy the
with a minimum number of rounds.

13. SUPERCAVITATING AMMUNITION

14. Supercavitating ammunition that functions better in the underwater
environment has been developed by Defence & Security
Group (DSG), a Norwegian company. The Multi-Environment
Ammunition (MEA) series supercavitating rifle ammunition,
developed and marketed by DSG, is anticipated to be useful for
certain special operations, including underwater warfare. These
include defensive applications such as diver protection, as well as
offensive applications such as neutralization of enemy
divers, VBSS (Visit, Board, Search, and Seizure
Operations), MIO (Maritime Interception
Operations), GOPLATS (Gasoline and Oil
Platforms) boarding operations, speedboat interdiction and
neutralization, anti-submarine warfare, anti-torpedo operations.

15. CAVITATION IN VALVES
Cavitation is caused by low pressure areas in fluids. There are four causes of low
pressure areas

16. (1) Fluid is compressed, contraction flow exists, and flow velocity is increased. Then,
pressure reduces.
(2) Low pressure area inside vortexes at valve-outlet side.
(3) Low pressure area is produced at the boundary between the fluid flowing at high
velocity and objects such
as the protruding portion of the valve-moulded surface, heads of taper pins, and hubs,
etc.
(4) When the valve body or disc is vibrating at high frequency, the flow is disturbed and
air bubbles form in the
fluid.

19. The main causes of cavitation generation in butterfly valves are (1) and (2).
Thus, when the valve is nearly closed, the flow passes over the upper and
lower edges of the disc as shown in
figure. 1. The low pressure area can be caused when high flow velocity is
created.

20. Cavitation reduction treatment:
The following are the main methods for reducing or preventing cavitation
damage to control valves

21. (1) Install valves in series and control them. This method is for reducing the pressure load on
each valve.
In this case, space valves out at least 4D (4 times the pipe diameter). The total Kc or FL will be
improved. In
order to avoid full cavitation FL should satisfy the following condition:
In this case, however, valve control balance may be difficult.
Example:
When 507V and 508V types are nearly fully opened, FL is 0.72. When 507V and 508V types are
installed in series,
the combined FL is 0.72 = 0.84 and the permissible pressure difference across the valve is
increased by 36%.
However, both valves should be operated under exactly the same conditions.
(2) Use a resistance plate (perforated orifice for pressure reduction) at the same time. If the flow
rate fluctuates
heavily, a good result cannot be expected.
(3) Use a valve with higher Kc or FL .
(4) Lower the installation position of the valve; that is, lower the secondary pressure.
However, this method is hard to adopt in existing piping installations.
(5) Rectify the turbulent flow by using a rectifier grid.

22. SOME OF OBSERVATION IN CAVITATION
BY
RESEARCHER GROUP
IN
MINNESOTA UNIVERSITY
By DR Roger Ardnt

23. Axisymmetric ventilated supercavitation:
ventilation increases and cavitation index
decreases from top to bottom

24. A wedge-shaped fin partially piercing a supercavity. Note the
partial cavity forming from the leading edge of the fin.

25. Comparison of phase locked photos of cavitation (left column)
with numerical simulations of incondesable gas that come out of
solution as a result of cavitation.

26. Artificial supercavitation in a periodic, unsteady
gust

27. Refrence and help
The Minnesota UNI Research Group of Cavitation.
Phisics.org
CAVITATION (PHILLIP EISENBERG)’MIT UNI’.
SLIDE SHOW PRESENTATION FROM ‘MITESH NIKE’