Modifying MachUpX for simulating hydrofoils

Lev Chernyshev

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Nov 13, 2023, 5:21:39 PM11/13/23

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Simulating hydrofoils requires a way of modelling the effects of the free surface (air-water interface). With lifting line models, this is achieved by introducing an image of the wing being simulated, mirrored about the mean water level plane. There are two kinds of images that can be used: a standard mirror where the direction of circulation is reversed on the image wing; and one where the circulation direction does not change. To illustrate this, I have attached a few images below. The type of image needed depends on the Froude number the hydrofoil is operating at. The idea would be to switch between the formulations depending on the desired Froude number (freestream velocity and submergence depth).

I have tried scrolling through the MachUpX source code to understand your implementation and how I could introduce the aforementioned mirror images into the modelling, but am still struggling to figure out where/how this should be done. I was wondering if you could hint at what the best way to do this in MachUpX would be.

Conventional mirror image for wing-in-ground effect or hydrofoil operating at a low Froude number (left) and opposite mirror type for hydrofoils at high Froude numbers (right).

Cory Goates

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Nov 14, 2023, 4:04:08 PM11/14/23

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It's been too long since I've dived into the source code to say what may be the best way to go about this, but I do have some thoughts.

One is you should check out MachUp Pro. It's also on the AeroLab GitHub page and has ground effect/free-surface interactions implemented, albeit in Fortran. Looking at that source code may be useful.

For modeling ground effect, many have just put duplicate configurations into MachUpX, one above/below the other having been flipped around 90 degrees. This is not as computationally efficient as it could be but will give the correct results if set up properly.

Free surface interactions at high Froude numbers (opposite mirror) would require modifying the source code. This would likely be easiest inside of the Scene class. I'd recommend doing as little modification to the geometry classes as possible, since you aren't actually changing the geometry, just adding a flow effect. That would also be the most convenient place for enforcing the mirrored vortex strengths.

Baptiste Labat

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Mar 15, 2025, 9:23:53 AMMar 15

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Hi,

For those interested, I have seen that Lev Chenyshev has implemented the changes in a fork https://github.com/lev-chern/MachUpHydro