Bernouilli's Law. In a flow field a high speed is associated with a low pressure. If that pressure is lower that the boiling point at that temperature a bubble is formed. And when the speed is reduced the bubble collapses.
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09III/09IV (093/094) Nuclear Submarine Thread
- Thread starter SinoSoldier
- Start date
Hendrik_2000
Lieutenant General
I don't ask for that I ask your Theory that by diving deeper it will eliminate cavitation. It doesn't it make it worse
BTW your theory about duct is also incorrect
The reason duct is better for cavitation because it increase the pressure therefore reduce tendency for cavitation It doesn't eliminate cavitation
Types
There are two types of ducts; accelerating and decelerating. With accelerating ducts, the inflow velocity and efficiency of the propeller is increased. This is the type that is used on heavily loaded propellers or propellers with limited diameter. As Ludwig Kort performed extensive research on this type, it is often called a "Kort nozzle".
With the second type, the inflow velocity is reduced, whereby pressure is increased, reducing cavitation. This is called a pump-jet, especially in combination with fixed blades or stators.
NACA 4415.
MARIN has done extensive research on ducted propellers. Many of the used profiles are based on the NACA airfoils of which the NACA 4415 has very good characteristics. Most commonly used are nozzle 19A and 37 of the MARIN series. These have a rounded trailing edge to ease fabrication and increase efficiency sailing astern. Initially, the propellers of the Wageningen B-series were used, later the Kaplan-type with a wider blade tip.
Physics
Circulation around accelerating and decelerating nozzle Circulation around nozzles.svg
dT = Thrust
dL = Lift
pu: Negative pressure
po: Positive pressure
In a Kort nozzle, the inflow velocity is increased, reducing pressure. This lowers thrust and torque of the propeller. At the same time, a circulation occurs, resulting in an inward aimed force, that has a forward component. The duct therefore has a positive thrust. This is normally larger than the thrust reduction of the propeller. The small clearance between the propeller and duct reduces tip vortex, increasing efficiency.
As drag increases with increasing speed, eventually this will become larger than the added thrust. Vessels that normally operate above this speed are therefore normally not fitted with ducts. When towing, tugboats sail with low speed and heavily loaded propellers, and are often fitted with ducts. Bollard pull can increase up to 30% with ducts.
With decelerating ducts, the circulation opposite of the Kort nozzle, resulting in a negative thrust of the duct. This type is used for high speed vessels with increased exposure to cavitation and vessels that want to reduce noise levels, such as warships.
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Thank you for the clear explanation of the ducted propellers. I remember reading about these things fifty years ago and I see that you understand them better than I do.I don't ask for that I ask your Theory that by diving deeper it will eliminate cavitation. It doesn't it make it worse
BTW your theory about duct is also incorrect
The reason duct is better for cavitation because it increase the pressure therefore reduce tendency for cavitation It doesn't eliminate cavitation
Types
There are two types of ducts; accelerating and decelerating. With accelerating ducts, the inflow velocity and efficiency of the propeller is increased. This is the type that is used on heavily loaded propellers or propellers with limited diameter. As Ludwig Kort performed extensive research on this type, it is often called a "Kort nozzle".
With the second type, the inflow velocity is reduced, whereby pressure is increased, reducing cavitation. This is called a pump-jet, especially in combination with fixed blades or stators.
NACA 4415.
MARIN has done extensive research on ducted propellers. Many of the used profiles are based on the NACA airfoils of which the NACA 4415 has very good characteristics. Most commonly used are nozzle 19A and 37 of the MARIN series. These have a rounded trailing edge to ease fabrication and increase efficiency sailing astern. Initially, the propellers of the Wageningen B-series were used, later the Kaplan-type with a wider blade tip.
Physics
Circulation around accelerating and decelerating nozzle Circulation around nozzles.svg
dT = Thrust
dL = Lift
pu: Negative pressure
po: Positive pressure
In a Kort nozzle, the inflow velocity is increased, reducing pressure. This lowers thrust and torque of the propeller. At the same time, a circulation occurs, resulting in an inward aimed force, that has a forward component. The duct therefore has a positive thrust. This is normally larger than the thrust reduction of the propeller. The small clearance between the propeller and duct reduces tip vortex, increasing efficiency.
As drag increases with increasing speed, eventually this will become larger than the added thrust. Vessels that normally operate above this speed are therefore normally not fitted with ducts. When towing, tugboats sail with low speed and heavily loaded propellers, and are often fitted with ducts. Bollard pull can increase up to 30% with ducts.
With decelerating ducts, the circulation opposite of the Kort nozzle, resulting in a negative thrust of the duct. This type is used for high speed vessels with increased exposure to cavitation and vessels that want to reduce noise levels, such as warships.
As for Bernoulli the decrease of the pressure is proportional to the square of the speed and the density. Bubbles form when the pressure falls to the level at which the liquid boils at that temperature. I well remember seeing the physics teacher fitting an air pump to a glass vessel with water at room temperature and seeing that water boil until it froze.
I see that the wiki describes it as I understand it. How is your view different?
The Australian Short Fin Barracudas would be equipped with the MESMA AIP. I don't know how much they are different from the Sterling AIP but the impression I have is, it uses the subs main Diesel engines instead of an auxiliary engine. Maybe Masieur Forbin can add more light to it
I think the PLAN would be perfectly happy with a 095 that is in between 688i and Seawolf/Virginia, which is probably where the 095 will end up IMO.
Isn't the "news" on the last page saying that it may be 09III that had natural circulation cooled reactor rather than 09V?
https://www.sinodefenceforum.com/pl...r-submarine-thread.t6883/page-100#post-450375
How do you know all these stuff Hendrik ? Despite completing my Masters in mechanical engineering , I forgot every thing by now .I don't ask for that I ask your Theory that by diving deeper it will eliminate cavitation. It doesn't it make it worse
BTW your theory about duct is also incorrect
The reason duct is better for cavitation because it increase the pressure therefore reduce tendency for cavitation It doesn't eliminate cavitation
Types
There are two types of ducts; accelerating and decelerating. With accelerating ducts, the inflow velocity and efficiency of the propeller is increased. This is the type that is used on heavily loaded propellers or propellers with limited diameter. As Ludwig Kort performed extensive research on this type, it is often called a "Kort nozzle".
With the second type, the inflow velocity is reduced, whereby pressure is increased, reducing cavitation. This is called a pump-jet, especially in combination with fixed blades or stators.
NACA 4415.
MARIN has done extensive research on ducted propellers. Many of the used profiles are based on the NACA airfoils of which the NACA 4415 has very good characteristics. Most commonly used are nozzle 19A and 37 of the MARIN series. These have a rounded trailing edge to ease fabrication and increase efficiency sailing astern. Initially, the propellers of the Wageningen B-series were used, later the Kaplan-type with a wider blade tip.
Physics
Circulation around accelerating and decelerating nozzle Circulation around nozzles.svg
dT = Thrust
dL = Lift
pu: Negative pressure
po: Positive pressure
In a Kort nozzle, the inflow velocity is increased, reducing pressure. This lowers thrust and torque of the propeller. At the same time, a circulation occurs, resulting in an inward aimed force, that has a forward component. The duct therefore has a positive thrust. This is normally larger than the thrust reduction of the propeller. The small clearance between the propeller and duct reduces tip vortex, increasing efficiency.
As drag increases with increasing speed, eventually this will become larger than the added thrust. Vessels that normally operate above this speed are therefore normally not fitted with ducts. When towing, tugboats sail with low speed and heavily loaded propellers, and are often fitted with ducts. Bollard pull can increase up to 30% with ducts.
With decelerating ducts, the circulation opposite of the Kort nozzle, resulting in a negative thrust of the duct. This type is used for high speed vessels with increased exposure to cavitation and vessels that want to reduce noise levels, such as warships.
It won't. Only wastly increased battery capacity, through both volume and efficiency(Li-ion).
part of modern trend against AIP systems, especially on larger subs.
Problem with you how applied the theory. Static pressure is not the same thing as dynamic pressure.
Monsieur hehe
make sense he use this AIP but i am not sure also planned for Scorpene but right now no Scorpene in sevice equiped for soon/later 6 Indians don' t have, Brazil i don' t think.Pakistanese Agosta 90B have.
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