RE: PSV Tailpipe, 45 Degree Cut?

Paul,

I forwarded your remarks onto Hans Bos, and he returned the following:

"Any break of the rotational symmetry will definitely create a lateral momentum flux for a jet engine. There is a balance between jet momentum flux and the reaction force on the jet nozzle, but the lateral momentum flux creating lift is a loss for thrust force. If the flight is ballistic no lift is required. If lift is required it is energetically much more efficient to create lateral momentum with the smallest amount of kinetic energy. This is what wings do. Possibly a jet could generate the same lateral momentum (the same lift) but definitely at the cost of much more kinetic energy.

As for noise reduction. Breaking the toroidal vortex formation has proven to be effective in commercial jetliners. Large bypass jet engines have less intense shear layers and have proven to be less noisy.

Paul's question seems very intuitive to me. Hope this is a sufficient answer.

Hans Bos"

From: <a href="/group/PipingDesign/post?postID=Gk7mZ100bUWiQjiDNYCjwSdzyjvsm4FjLZLXv6TJL6t09hRHpVwER8ky5ei1ixkBJXYgJXneqJn2-ImBq3aKCwli">PipingDesign@yahoogroups.com</a> [mailto:<a href="/group/PipingDesign/post?postID=Gk7mZ100bUWiQjiDNYCjwSdzyjvsm4FjLZLXv6TJL6t09hRHpVwER8ky5ei1ixkBJXYgJXneqJn2-ImBq3aKCwli">PipingDesign@yahoogroups.com</a>] On Behalf Of Paul Bowers
Sent: Thursday, February 15, 2007 10:18 PM To: <a href="/group/PipingDesign/post?postID=Gk7mZ100bUWiQjiDNYCjwSdzyjvsm4FjLZLXv6TJL6t09hRHpVwER8ky5ei1ixkBJXYgJXneqJn2-ImBq3aKCwli">PipingDesign@yahoogroups.com</a> Subject: Re: [PipingDesign] PSV Tailpipe, 45 Degree Cut?

Tony Paulin sent:

> Dr. Hans Bos (author of BOS Fluids) added the following, which I
thought
> might be useful, and so wanted to pass along:

> 2) The lateral load component at the tail pipe exit is equal to
> the normal thrust force multiplied by the sine of one half of the
bevel
> angle.
> 4) Beveled ends break the flow symmetry at the exit, disturbing
> the periodic shedding of stable torus type vortices that contribute to
> noise strength. Rotational symmetry in the diamond shaped shock
> wave/expansion pattern downstream of the tail pipe, in combination
with
> the convection of vortices is considered the origin of the screeching
> noise in jet exhausts.

So if a bevel is placed on the outlet of a jet engine could it simultaneously reduce noise and re-direct thrust advantageously?

That's probably a dumb question.

Paul

[Non-text portions of this message have been removed] Received on Fri Feb 16 09:40:00 2007