Trouble with Error: ambiguous flow-through subsurface detected
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Jasper
Apr 1, 2026, 7:17:12 AMApr 1
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Dear OpenVSP Team,
I am trying to use the wave drag tool, however my engine ducts (inlet and outlet) are giving an error when doing the wave drag analysis: Error: ambiguous flow-through subsurface detected. I have done the line subsurface for the inlet face and the same for the outlet, as was highlighted in the workshop tutorial and in previous threads. So I am not sure what im doing wrong, perhaps the geometry is too aggressive and thus not water tight or because the inlets are intersecting with the fuselage, but im not at all sure. It was highlighted in the Integrated Flowpath Modeling workshop that the wave drag tool does not yet work with the engine definition in the fuselage geometry, hence why im adding the subsurfaces.
I have attached the design below. While it still meshes the engine duct geometry, it unfortunately does not subtract it and give the errror message.
I am trying to use the wave drag tool, however my engine ducts (inlet and outlet) are giving an error when doing the wave drag analysis: Error: ambiguous flow-through subsurface detected. I have done the line subsurface for the inlet face and the same for the outlet, as was highlighted in the workshop tutorial and in previous threads. So I am not sure what im doing wrong, perhaps the geometry is too aggressive and thus not water tight or because the inlets are intersecting with the fuselage, but im not at all sure. It was highlighted in the Integrated Flowpath Modeling workshop that the wave drag tool does not yet work with the engine definition in the fuselage geometry, hence why im adding the subsurfaces.
I have attached the design below. While it still meshes the engine duct geometry, it unfortunately does not subtract it and give the errror message.
Brandon Litherland
Apr 2, 2026, 2:36:10 PMApr 2
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I'm having trouble opening this model and pulling up Wave Drag. No error messages are popping up but when this model and wave drag are open at the same time, VSP crashes without fail. Not sure what's going on. Let me step back a few versions and see if I can find where it breaks.
Brandon Litherland
Apr 2, 2026, 2:38:18 PMApr 2
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Model fails to open in 3.47 or 3.46. I'll keep looking.
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Brandon Litherland
Apr 2, 2026, 2:51:08 PMApr 2
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Got it to work by inserting the VSP3 file into a fresh 3.48.2 version new model. Weird.
Anyway, as you note, Wave Drag doesn't work with the engine definitions. If you turn your mode back to None (Geom Type) you'll see a lot of self intersecting loops and bends in the surface. My suggestion is to first recreate your engine ducts from scratch without using engine definition parameters. Once you have that, then try using the subsurface method to identify inlet and outlet regions which should extend fore and aft to cut the intersected surfaces.
Jasper
Apr 6, 2026, 7:11:13 AMApr 6
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Thank you Brandon for having a look!
I made the model in 3.48.0 and upgraded to 3.48.2 which i should have mentioned, and indeed for me it also crashes upon startup, however, i found that when i run an analysis on another file/model, (keeping the wave drag analysis open) then switch to that model and run wave drag, there is no crash. However, the flow-through error persist.
I have done as you said and made a brand new inlet from scratch without the engine definition parameters, however, the error also occurs here unfortunately, perhaps I am sitll doing something wrong? I have made a new inlet on another model of mine, which should not crash the application when starting the wave drag analysis. I have made this in 3.48.2. I still get the error and it removes the inlet from the model in the mesh so my assumption is that it is the inlet that is still the problem.
I have attached the new model with the new inlet below.
I made the model in 3.48.0 and upgraded to 3.48.2 which i should have mentioned, and indeed for me it also crashes upon startup, however, i found that when i run an analysis on another file/model, (keeping the wave drag analysis open) then switch to that model and run wave drag, there is no crash. However, the flow-through error persist.
I have done as you said and made a brand new inlet from scratch without the engine definition parameters, however, the error also occurs here unfortunately, perhaps I am sitll doing something wrong? I have made a new inlet on another model of mine, which should not crash the application when starting the wave drag analysis. I have made this in 3.48.2. I still get the error and it removes the inlet from the model in the mesh so my assumption is that it is the inlet that is still the problem.
I have attached the new model with the new inlet below.
Rob McDonald
Apr 6, 2026, 11:35:34 AMApr 6
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The crash when loading Wave Drag should be fixed in 3.49.0.
The flat end caps were giving some trouble. I replaced them with point end caps and made the required adjustments to skinning etc.
Also, as I recommended in my other message. You should use Stack instead of Fuselage. Stack is an easier component to work with.
Rob
Also, as I recommended in my other message. You should use Stack instead of Fuselage. Stack is an easier component to work with.
Rob
Jasper
Apr 7, 2026, 12:09:26 PMApr 7
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Dear Rob,
I have upgraded to 3.49 and replicated the changes you have made so I could learn how you did it. It now all works like a charm. I will also now remake the inlets in a stack as recommended in the future.
Thank you very much Rob and Brandon for the help!
Cheers,
Jasper
I have upgraded to 3.49 and replicated the changes you have made so I could learn how you did it. It now all works like a charm. I will also now remake the inlets in a stack as recommended in the future.
Thank you very much Rob and Brandon for the help!
Cheers,
Jasper
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