Best approach for engine nacelle & duct

[Bob Pasque]

I've been reading up on the many approaches to making an engine nacelle/duct. Most of them though seem to be for older versions of openVSP. Is there a generally accepted best approach with the latest version?

A thought I had would be to make it using a single, fuselage component and have some sections double-back to form the duct inner surface. Would that work?

[Fred Bacon]

I've been thinking about a similar problem as well.  In my case, I'm interested in being able to model the variable area nozzle of an afterburner.  So doubling back to form the inner surface will be necessary to form the variable throat region as well as the turkey feathers.  The best solution is probably to build a custom component.  So, I'm thinking about what parameters we use to define the geometry of our current faceted models.  The throat position and area and the exit plane position and area.  Those are a couple of the important parameters we'd like to specify.  A custom component should make those parameters visible to the user.

You might want to consider the same thing for the nacelles and ducts.  What are the key parameters you want to specify?  Then start building a script which specifies the geometry from those parameters.

On Wed, Sep 7, 2016 at 10:34 AM, Bob Pasque <hardh...@gmail.com> wrote:

I've been reading up on the many approaches to making an engine nacelle/duct. Most of them though seem to be for older versions of openVSP. Is there a generally accepted best approach with the latest version?

A thought I had would be to make it using a single, fuselage component and have some sections double-back to form the duct inner surface. Would that work?

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[Rob McDonald]

There are probably two or three recommended ways to model an engine.

The first is as you've described, turning a fuselage component on
itself to make a flow-through duct. On the 'Design' tab, there is a
pull-down option to let you change the cross section ordering policy
(monotonic, loop, or free). The default is monotonic. If you change
it to loop, you force engine-nacelle type behavior.

There is an example of this in the generic transport model on the
OpenVSP hangar.

http://hangar.openvsp.org/vspfiles/268

There is also a 'duct' custom component that is distributed with
OpenVSP. For very simple shapes, it may suffice -- it is basically a
NACA 4-digit airfoil rotated about an axis. It could provide a
starting point for a more complex custom component.

Both of these are generally good approaches if the nacelle is largely
independent of the rest of the airframe.

On the other hand, if you're looking to model a fighter-type
configuration where the body and wing may be made of several
overlapping components -- and you want the engine flowpath to pass
through multiple components -- this approach probably won't work.

In that case, (and this only works for generating a CFDMesh), you can
explicitly model the flowpath using a component -- and then flip a
flag on the Gen tab to make it a 'negative volume'. This will cause
it to poke a hole when you generate a CFDMesh.

Hope this helps,

Rob

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[Brandon Litherland]

In addition to Rob's comments, I would also recommend using user defined parameters and links to make the fuselage component you design make more sense from an engine viewpoint.

If you place cross-sections at each engine station (inside the engine) and define whatever outer nacelle shape, you have control points to play with.  From here, you can define UserParms under a different name than Fuselage XSec_3 such as Combuster_Inlet_Diameter.  Using simple links, one can make the new Parm a 1:1 match to that dimension.  This allows you to quickly adjust the parameters important to your design without hashing through the individual sections or components.

Furthermore, if you choose to use Advanced Linking, you can adjust the engine dimensions based on your ratio equations.  So in Fred's example, the AB nozzle exit area could be the independent variable (along with however many other D.O.F. he chooses) and the engine dimensions could be found using the equations and links.

Hope this makes sense and helps in your design!