Kushnerik Effect

Kushnerik Effect

Post by Jerry Irvin » Fri, 24 May 2002 02:01:11





Quote:

> >Krushnik Effect:

> >I never found a scientific explanation for the effect.  It seems to me that
> >the
> >exhaust gas velocity must be reduced by some kind of flow effect within the
> >tube.  That's my guess anyway.

>    My quasi-educated guess would be that the bodytube below the motor would
> behave as an extension to the nozzle.  The effect would be the same if you
> made a extra large nozzle for the motor.  The exhaust gasses become over
> expanded and thus their velocity drops, reducing thrust.

The inefficient exit shape (cylinder not cone) accounts for most of the
theoretical variation from a straingt nozzle.

The internal eddies cause the vectors to non-linearize and the resulting
loss of "impulse".

Just tech Jerry

Hey, lets make a 12" motor rocket with intentional gross Krushnik effect
to keep it under the 5000 foot waiver.

--
Jerry Irvine, Box 1242, Claremont, California 91711 USA

Please bring common sense back to rocketry administration.
Produce then publish.

 
 
 

Kushnerik Effect

Post by Leonard Fehsken » Fri, 24 May 2002 03:46:14




Quote:
> This raises an interesting question for me.  With the Estes Saturn V,
> the engine is recessed quite a bit up into the base.  As is, the rocket
> BARELY flies with a D12-3.

That's an impulse/mass issue.  The Saturn V is large enough diameter that
even recessed as far as the motor is, it is unlikely that the Krushnik
effect applies.  The behavior of the Saturn V is accurately predicted by
flight simulation software without resorting to thrust reduction.

Quote:
> I'm wondering if there are any programs (a la Rocksim)
> that would calculate the 'Kushnik effect' on a model rocket,

Krushnik.  Brant.  Arcas.  Stine.

There's no theoretical or empirical model available to base such
calculations on.

Quote:
> I have to admit (sheepishly) this is the first time I've heard of
> this effect.

It was first observed in the '60s.

len.

 
 
 

Kushnerik Effect

Post by Leonard Fehsken » Fri, 24 May 2002 03:47:46




Quote:
> The momentum of the ejecta forms a boundry layer and it is formed by
> the Bernoilli effect among others.

What?

Regardless, this has nothing to do with the assertion that the Krushnik
effect is due to increased drag rather than reduced thrust.

len.

 
 
 

Kushnerik Effect

Post by Glen Gardne » Fri, 24 May 2002 10:31:18


The Krusnhik effect is probably due to underexpanded exhaust gases exiting
an overexpanded nozzle skirt.

If the body tube extends past the nozzle of the motor , it may be analogous
to having a longer skirt on the motror nozzle.  This is called an
"overexpanded" nozzle. Since the expanding exhaust gases are allowed to
expand more than they need to for the given nozzle exit velocity,  pressure
inside the nozzle skirt becomes nonuniform and excessive turbulence is
introduced into the exhaust plume, which results in a loss of thrust.

Overexpanded nozzles don't work well at low altitudes, but are preferred in
motors for flight in the vacum of space.  Conversely, underexpanded nozzles
don't work well at high altitudes but are better at low altitudes. The trick
is to get the nozzle expansion ratio exactly right for the flight profile of
the rocket.

Glen Gardner (Your mileage may vary)

Quote:

>Can anyone point me to a good site that might help enlighten me on this
>phenomenon?

>Thanx
>Kevin C
>CAR S569 L2

 
 
 

Kushnerik Effect

Post by Doug Gonc » Sat, 25 May 2002 03:33:42


I remember an engine, I think made by Centauri, that had an extended graphite
nozzle with thin edges, to minimize the boat tail drag and rolling donut back
flow adjacent a normally positioned engine of the same rating. The effect
mentioned is an extension of the same thing.

You can see this in the rolling donut adjacent the face of an oxy/acetylene
torch when it's not lit, and there's a rolling donut in Schreckling's turbine
engine combustor. It's rolling like a *** on a bannana, not like a tire on
the road.

Yours,

Doug Goncz, Replikon Research, Seven Corners, VA (remove pee dot mil)
 http://www.FoundCollection.com/
 http://www.FoundCollection.com/
 "Function, Funding, Form, Fit, and Finish"

 
 
 

Kushnerik Effect

Post by Jonathan W. Mil » Sat, 25 May 2002 18:46:42




Quote:

>>Krushnik Effect:

>>I never found a scientific explanation for the effect.  It seems to me that the
>>exhaust gas velocity must be reduced by some kind of flow effect within the
>>tube.  That's my guess anyway.

>   My quasi-educated guess would be that the bodytube below the motor would
>behave as an extension to the nozzle.  The effect would be the same if you
>made a extra large nozzle for the motor.  The exhaust gasses become over
>expanded and thus their velocity drops, reducing thrust.

Hmmm...maybe the Coanda effect, that results in attachment of a flow
of liquid (i.e., exhaust) to a surface as it passes over a "step"?
I recall reading about this in Scientific American 30-40 years ago.
And as usual, this probably has to do with Bernoulli's principle. :-)

Jonathan Mills

 
 
 

Kushnerik Effect

Post by Kevin Crawfor » Mon, 27 May 2002 04:15:22


What I have is a 29mm PML tailcone modified to fit my Lil Nuke also
modified with a 38mm MMT.
The nozzle of the Pro 38 H110s is recessed 3.5 cm from the aft end of
the tailcone.Will the Krushnic effect be a factor?
And if so would drilling vent holes in the boattail be an effective way
to deal with it?
This rocket will be flown in an alt competition and any loss of thrust
would be a very bad thing. :)

Thanks
Kevin C
CAR S569 L2

Quote:

> Can anyone point me to a good site that might help enlighten me on this
> phenomenon?

> Thanx
> Kevin C
> CAR S569 L2

 
 
 

Kushnerik Effect

Post by Bob Kapl » Wed, 29 May 2002 10:10:08


Quote:

> Can anyone point me to a good site that might help enlighten me on this
> phenomenon?

Wasn't he an editor of an old newsletter? Spotter?

        Bob Kaplow      NAR # 18L       TRA # "Impeach the TRA BoD"

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