DRDO, PSU and Private Defence Sector News

[amit6371]

btw, I had read about why cavitation happens-

it is because when propellers rotate, low pressure areas are created in the water flowing through the propeller,

so the water gets boiled off in lp areas, due to which bubbles are created and when those bubbles burst, noise is created.

(very simplified version)

To be more technical,
As the fluid(water) flows around the blade, due to the inherent airfoil shape of blade crosssection, the water velocity increases which leads to a decrease in pressure. If the absolute pressure of the water on the blade surface becomes lower than the saturation pressure of water, it starts boiling or the formation of bubbles starts. Now when these bubbles strike the blade surface, they burst and produce weak shocks and a pitting sound (Sonar are used to detect these sounds to find submarines). It also causes damage to the blade over the time and hence decreases its efficiency. No doubt propeller design is one of the closest guarded secrets.

 

[Lonewolf]

rim driven pumpjet, the last one shown in video

this will be used by smx 31 (french)

looks something like this

Add a Straightener to it and your noise levels will fall further

 

[THESIS THORON]

Add a Straightener to it and your noise levels will fall further

hain ji ??

 

[Lonewolf]

hain ji ??

To straighten the flow , in axis to the blade rotor so those bubbles created in video can be further reduced in the shroud itself

 

[ShouvikGhosh]

Now when these bubbles strike the blade surface, they burst and produce weak shocks and a pitting sound (Sonar are used to detect these sounds to find submarines). It also causes damage to the blade over the time and hence decreases its efficiency.

The physics is right but, there is an issue. The bubbles are mainly formed on the surface of the blade where velocity is high & the pressure is low. And are moved behind the blades. ( How would they colide with the blades & burst. Because the water velocity is still high & the pressure is low around the blades, they would bounce back from the blade)

They collapse under the water pressure when the pressure around the bubbles become normal. And produces mini shocks.

The shock waves which carry these mini bubbles may produce constructive interference & destructive interference at certain intervals & amplify the noise. Mainly seen in double propeller designs. Very minimal in single propeller designs though. That's why Soviet Typhoon class submarines are completely obsolete.

 

[THESIS THORON]

The physics is right but, there is an issue. The bubbles are mainly formed on the surface of the blade where velocity is high & the pressure is low. And are moved behind the blades. ( How would they colide with the blades & burst. Because the water velocity is still high & the pressure is low around the blades, they would bounce back from the blade)

They collapse under the water pressure when the pressure around the bubbles becomes normal. And produces mini shocks.

The shock waves which carry these mini bubbles may produce constructive interference & destructive interference at certain intervals & amplify the noise. Mainly seen in double propeller designs. Very minimal in single propeller designs though. That's why Soviet Typhoon class submarines are completely obsolete.

which branch ??

 

[indiatester]

@Indx TechStyle or @indiatester ..i forgot

Definitely not me.

 

[MonaLazy]

Some more links to understand the phenomenon of cavitation

 

[ShouvikGhosh]

How would they colide with the blades & burst. Because the water velocity is still high & the pressure is low around the blades, they would bounce back from the blade

OK the bubble collision produces considerable damage to the propeller.
Bubble cavitation usually occurs at mid chord and is usually associated with too high a curvature or camber of the blade sections. It can be eliminated, if its presence can be suspected, in the design stage.

The low pressure zone may not extend to the end tip of the blade if the fluid velocity is too high (which follows a gradient) & so the bubble may collapse on the rear end of the fin itself which is out of the low pressure zone causing the damage.

This is rectified by introducing variable pitch propellers.

 

[Chinmoy]

What is this?

Aero Engine shaft.

 

[Haldilal]

Ya'll Nibbiars Ajan Lens meim Maine apply kiya tha Digital marketing ke post ke liye bolte hai 1 saal ka experience mangta hai fresher ke liye. Are abh ke kis type ka joke hai fresher ks liye bhi expert to phir non experience wale Mar dobe kya?.

Abhi inko bhi bhaut chada hai kya?. In private sectors no bhi kya?.

 

[karn]

Ya'll Nibbiars Ajan Lens meim Maine apply kiya tha Digital marketing ke post ke liye bolte hai 1 saal ka experience mangta hai fresher ke liye. Are abh ke kis type ka joke hai fresher ks liye bhi expert to phir non experience wale Mar dobe kya?.

Abhi inko bhi bhau chada hai kya?. In private sectors no bhi kya?.

Try for internships .. get experience on your resume that way .. it's what I did .

 

[Haldilal]

Try for internships .. get experience on your resume that way .. it's what I did .

Ya'll Nibbiars kiya hai lekin unko 1 saal ka premanenet experience chaiye. Not the internship or part time job wala.

 

[EthanHunt]

 

[Love Charger]

Naaaaaaaaaaaaaaaaaaaaaaaaaacho saaaaaaaaaaaaaaaaab ke saaaaaaaaaaaaaaaab

 

[Love Charger]

So it flew , finally

 

[SavageKing456]

This is neuron ffs

 

[THESIS THORON]

This is neuron ffs

yeah, I am also thinking where is the eo assembly, which was on top

 

[Love Charger]

This is neuron ffs

Kya garm karke thanda kardiya aapne

 

[EthanHunt]

It is Dassault neuron first flight 2012 photo