# Hovercraft Lift

Hi,
I’m working with a charity, Hoveraid to design a hovercraft for humanitarian work in remote communities. I’d like to analyse the flow of air from the lift fan round and down under the skirt and out the sides between the skirt and the ground.

I want to apply a velocity at the circular duct inlet which is where the fan will be. Longer term I’ll want to apply some swirl from the fan but a linear velocity will do for now. I can’t seem to work out how to do it as it’s in the middle of air volume and not at the boundary. I suspect I’m being a bit slow…

Any tips hive-mind?
thanks
Chris
https://www.simscale.com/projects/cjehover/lift_air_1/

Hi Sebastian here.

In my opinion you have a couple of options.

First You can apply a momentum source to your air region to simulate the air flow through the fan.

If you have the blade geometry of the fan, maybe an rotation zone can also be a solution. This would also give you the swirl of the fan.

But first would suggest you to reduce your simulation region with something like this, since you are only inside the hovercraft and through the small gaps.
The Simulation could look like this.

Where 1 is face with a velocity or pressure inlet and 2 are pressure outlets.

I hope that gives you some idea on how to approach your Simulation.

Best regards Sebastian

1 Like

Hi Sebastian, thanks again for the tips on how to set up the simulation run. However I’m completely failing to generate the air volume. I’ve created a box in Onshape which is the volume I’d like. But the right combination of seed face and boundary faces to turn it into a fluid volume is escaping me. Any help appreciated!

Hi Chris,

I think you are almost there. I would suggest to you to do the subtract operation in OnShape and just import one part which is the fluid volume. The other option would it be to simulate the external flow as well and using an momentum source.

Here a link on how to create an external volume.

Thanks Sebastian - doing the subtract in Onshape was a lot easier. Initial results look really interesting!

Hi Chris, it really does look great.

I have two thinks that you can maybe adjust to your Simulation setup.

First, I would suggest to implement a refinement region here.

Your gap right know has a resolution of only a few cells and also the boundary layer collapse here. For a even better converging Simulation refining this are will definitely help.

Second, you might want to increase the fluid volume around your hovercraft. For me it seems like the outlets are a bit to close to the hovercraft. Normally you will have something like a minimum distance 3*L to all boundaries.
(L = length of object in axis direction)

(Here an example of a different simulation)

With that your cell count will for sure increase, but since you are not interested in the fan swirl for now, you could use the symmetry along the y axis to reduce cell count.