The cavitation noise from the propeller (only under full load) is not the only source of noise. The hull pushing through the water
is another source of longer wavelength noise. This includes turbulence and the deformation (vibration) of the hull. Nothing
the size of a submarine is a perfectly stiff object. It deforms in all sorts of ways. Long wavelength acoustic detection is
a real thing in naval warfare.
So conforming to hydrodynamic "aesthetics" is not superfluous but rather necessary. The US submarine tower is not only ugly,
it is noisy even if it is shaped like a fin in horizontal section. The sloping contour on the tower of the Russian submarine is not
a decoration. Also, pushing through water requires a shape that is not like a conic wedge with a taper to a leading point, but the
reverse with a nearly spherical frontal contact with a trailing shape like a tear drop. The US submarine in the graphic was
designed by someone barely aware of this detail and they were clearly going for a bullet penetrator shape, which is simply
the wrong approach. It may not look like much of a difference, but the Devil is in the details. The goal is to reduce the
disturbance of the flow contours and any transitions generate transients.
Pump jets are something every fanboi trots out a proof of their vicarious achievement credentials. Pump jets reduce
the propulsion efficiency and cavitation is only an issue at the limit of propeller rotational speed. Lots of effort is expended
designing propellers that push the cavitation regime to the high rotation limit. The decision to use a shroud only for the
missile carrier submarines makes perfect sense. Not hobbling the attack submarines with this feature is the right choice.
There is a trade off between speed under water and noise reduction. The Borei class has a pump jet and a tower that
is not shaped with the sort of streamlining as the Yasen class because it mostly crawls around under water and is not
intended for rapid maneuvers.
The Yasen-II pump jet is a whole new design that is supposed accommodate a much larger diameter propeller with a shorter
shroud length. That makes perfect sense to me. The propulsion efficiency goes up with such modifications since shroud
drag is reduced.
An example of the masturbation common in western coverage of Russia. Clowns teaching Russians about hydrodynamics.
Recall that Kolmogorov was from Russia and not the USA. To this day nobody has come up with any improvement on
his unstratified turbulent boundary layer theory. And the people working on coming up with an extension to stratified
boundary layers for geophysical applications are from Russia as well.