Position of the fan inside a convergent nozzle

[T C]

TL;DR Summary

What's the best position to set a fan/blower inside a convergent nozzle?

I want to present two scenarios here. First, there is a convergent nozzle shaped structure having a fan/blower fitted inside. In this case, the fan/blower is fitted at the throat of the nozzle. The inlet to throat ratio isn't important here. And the second scenario, the same nozzle is used but the blower is now fitted at the inlet. Just to mention that velocity of fluid is subsonic in both cases at every point. I want to know what's the best position of the fan/blower? The first one or the second one?

 

[russ_watters]

I want to present two scenarios here. First, there is a convergent nozzle shaped structure having a fan/blower fitted inside. In this case, the fan/blower is fitted at the throat of the nozzle. The inlet to throat ratio isn't important here. And the second scenario, the same nozzle is used but the blower is now fitted at the inlet. Just to mention that velocity of fluid is subsonic in both cases at every point. I want to know what's the best position of the fan/blower? The first one or the second one?

It depends on many factors, such as what your goals are (highest flow rate, highest velocity, highest pressure?) and other constraints, such as is this the same nozzle/fan in both scenarios, type of fan, structural support issues, space constraints, flow smoothness/uniformity requirements, etc. There is no general answer to the question.

 

[T C]

Correct! I just forgot to mention that in both cases the fan/blower power is the same too. And I have already mentioned that the velocity is subsonic in both cases, therefore no question of increase in pressure. And, to be precise, as you have asked, I want maximum velocity at the throat. And in my thread, I have clearly mentioned that the nozzle is the same in both cases.

 

[russ_watters]

Correct! I just forgot to mention that in both cases the fan/blower power is the same too.

Ok...

And I have already mentioned that the velocity is subsonic in both cases, therefore no question of increase in pressure.

That isn't true. The whole point of a fan/blower is to move air by creating a pressure difference. But I guess what you are after is a just an axial fan in a nozzle, with nothing else attached (no ductwork system)? In that case, the static pressure requirement is close to zero, and the type of fan fits that requirement.

And in my thread, I have clearly mentioned that the nozzle is the same in both cases.

I see now...

So you want to know how two different fans that you haven't selected or specified will perform under conditions you also haven't specified. Well, ok, just to throw something at the wall and see if it sticks:

An otherwise uncased axial fan should at least have an inlet bell because the inlet side of the fan has to pull air from all directions and converge it into a coherent stream, which creates turbulence if there is an abrupt entry. This will make it operate more efficiently than the same fan with no inlet bell.

https://www.thefanguy.ca/wp-content/uploads/2017/01/Inlet-Bell-Brochure-Motion-Canada-2017.pdf

 

[T C]

From the link, it seems that the best position is at the inlet.

 

[russ_watters]

From the link, it seems that the best position is at the inlet.

No, that isn't what the link is describing. It's an "inlet bell", which is a nozzle providing an inlet to a fan.

More:
https://www.google.com/search?q=inl...iw=1536&bih=711&dpr=1.25#imgrc=zOyMh5D4EFnByM: