Wing-propeller interaction (Velocity fields) and geometrical interaction in VSP

[Paul Dintilhac]

Hello, We are writing to you because we would like to have some details about the operation of VSP aero. We are currently working on a motor-glider with a pusher motor located at the trailing edge. On the one hand, we would like to know if VSP takes into account the viscous phenomena and if the rotor ingests the good velocity field at the level of the trailing edge (finally if it takes into account the Wing-Propeller interaction). On the other hand we would like to know how VSPaero manages the geometrical interactions. E.g.: If we place an engine very close over the wing (or even closer : in contact with the extrados surface). Thank you a lot for your help. Best regards, Tarek and Paul

[Rob McDonald]

VSPAERO does not do any viscous analysis.

So, if by 'if the rotor ingests the good velocity field', you meant -- does a rotor ingest an upstream boundary layer?  Then No -- VSPAERO doesn't ever model a boundary layer.

VSPAERO's actuator disk model superimposes the velocity field from an isolated actuator disk on the 3D flowfield -- consequently, the disk influences the rest of the model (wings, body, etc) but the rest of the model does not influence the disk.  The interaction is strictly one-way.

If your actuator disk trails behind a wing, then you will see an area of increased velocity on the wing in front of the actuator disk.  This model will probably be quite good.

VSPAERO is a potential flow code -- it operates in either vortex lattice (thin surface) or panel (thick surface) modes.  The interaction of different components is exactly what you'd expect from this kind of theory.

The VLM method represents everything (including fuselages and bodies) as thin cambered plates.  For a flow system dominated by lifting surfaces, this is a reasonable simplification and it will yield very fast results.

The Panel method represents everything as its true shape.  Consequently, the thickness of bodies (and wings) is correctly modeled.  The mesh grows by a factor of 2 and the solution becomes more complex, so solution time gets longer.

It is worth working back and forth with both solution types as you work to understand your system.  If you become comfortable with the VLM simplification, it may be a great way to then run large numbers of cases for performance surveys, flight sim results, or design studies. 

Rob

--
You received this message because you are subscribed to the Google Groups "OpenVSP" group.
To unsubscribe from this group and stop receiving emails from it, send an email to openvsp+unsubscribe@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[Paul Dintilhac]

Hello,

Thanks for this information.

We would also like to know if it was possible to enter a given velocity field uphill to the objet studied in VSP. Or is it possible to change the source code in order to get it ?

Best regards,

Tarek and Paul

--
You received this message because you are subscribed to a topic in the Google Groups "OpenVSP" group.
To unsubscribe from this topic, visit https://groups.google.com/d/topic/openvsp/obI81VrRDNg/unsubscribe.
To unsubscribe from this group and all its topics, send an email to openvsp+unsubscribe@googlegroups.com.

[Rob McDonald]

Yes and no...

In addition to propellers, rolling and pitching derivatives are computed by superimposing a 'nonuniform' freestream velocity field.  The source code could be modified to use other fields.

However, the current version of VSPAERO only does steady computations, so you couldn't use this to compute a gust response.

In the not-distant future, a new version of VSPAERO will be released that can do unsteady computations.

What kind of velocity fields are you interested in?

Rob

[Paul Dintilhac]

Hello,

Thanks for this information.

The kind of velocity field we're interested in, is the velocity field witch is downstream a glider wing. We would take it from another software (for example Xfoil) and directly put this field into VSPaero upstream of a propeller or actuator disk.

What we want to study there, is the aerodynamic impact of a wing on a pusher propeller downstream, depending on the position of the propeller.

Best regards,

Paul and Tarek

[Rob McDonald]

The best way to model the effect of a wing in VSPAERO is to put the wing in the model and let it take care of the rest.

I suspect you are concerned about the boundary layer and viscous wake from the wing (why you mentioned XFoil, a 2D tool -- but one that can model a boundary layer).

However, that really doesn't make sense because of the way VSPAERO's actuator disk model works.  VSPAERO's actuator disk influences everything else in the VSPAERO model.  Nothing influences the actuator disk.  It is a one-way interaction.

XRotor is a propeller blade element code written by Prof. Drela (like XFoil).  I believe it may be able to model the influence of a non-uniform inflow -- but I'm not sure how that works.  If you want to model a propeller in depth, XRotor, QProp, JavaProp, or other similar tools are a better place to start.

Rob

[Emre KARA]

Is VSPAERO capable of doing unsteady computations now? I need to perform a discrete gust analysis on a non-planar aircraft. Is there a new update for gust or should I try Matlab API (maybe it will take too much time)?

Best Regards,

Emre

23 Şubat 2017 Perşembe tarihinde saat 19:18:45 UTC+3 itibarıyla Rob McDonald şunları yazdı:

To unsubscribe from this group and stop receiving emails from it, send an email to openvsp+u...@googlegroups.com.

For more options, visit https://groups.google.com/d/optout.

--
You received this message because you are subscribed to a topic in the Google Groups "OpenVSP" group.
To unsubscribe from this topic, visit https://groups.google.com/d/topic/openvsp/obI81VrRDNg/unsubscribe.

To unsubscribe from this group and all its topics, send an email to openvsp+u...@googlegroups.com.

For more options, visit https://groups.google.com/d/optout.

--
You received this message because you are subscribed to the Google Groups "OpenVSP" group.

To unsubscribe from this group and stop receiving emails from it, send an email to openvsp+u...@googlegroups.com.

[Rob McDonald]

Yes VSPAERO has had the ability to do unsteady physics for some time.  However, it does not have unlimited ways of specifying the unsteadiness...

It can support rotating rigid blades.  There is some support for building up more complex motions.  It can support a roll, pitch, and yaw pulse in each axis to calculate unsteady derivatives.  It actually has a 6DOF mode where it will integrate a body's motion.

To my knowledge, it does not yet have the ability to model flight through an arbitrary (space, time) gust profile).

I do not know if this is on the development plan - or if it will be done soon.  So, if you need this, you may need to dig into the source and figure out how to specify a gust yourself.

Rob

To view this discussion on the web visit https://groups.google.com/d/msgid/openvsp/bff1594f-5096-4869-bba9-764e9e2dccaen%40googlegroups.com.