# Unexpected Upward Velocity Vectors in Drone Hover Simulation 

**URL:** <https://www.simscale.com/forum/t/unexpected-upward-velocity-vectors-in-drone-hover-simulation/100105>\
**Category:** CAD & Meshing\
**Created:** [May 28, 2025, 8:04am UTC](https://www.simscale.com/forum/t/unexpected-upward-velocity-vectors-in-drone-hover-simulation/100105 "2025-05-28T08:04:49Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![ceckert](https://www.simscale.com/forum/user_avatar/www.simscale.com/ceckert/32/66271_2.png) [@ceckert](https://www.simscale.com/forum/u/ceckert)\
**Post date:** [May 28, 2025, 8:04am UTC](https://www.simscale.com/forum/t/unexpected-upward-velocity-vectors-in-drone-hover-simulation/100105/1 "2025-05-28T08:04:49Z")

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![Capture](https://www.simscale.com/forum/uploads/default/original/3X/1/0/10accdd07676d4371333e48758642e27e6cde213.jpeg)

**Hi,**  
[https://www.simscale.com/workbench/?pid=3923271815672441018](https://www.simscale.com/workbench/?pid=3923271815672441018)

I’m trying to simulate the velocity fields of multi-copter drones in a hover state, out of ground effect. I’ve followed all the relevant tutorials I could find on the topic. I double-checked the rotation directions of the propellers, using negative values for counterclockwise rotation and positive values for clockwise.

Unfortunately, the results show the velocity vectors going **upwards** instead of **downwards** , which is not what I expected. As a SimScale newbie, I’m not sure where I went wrong. I’ve already double-checked all the small tweaks I’m aware of that could potentially cause this upside-down behaviour.

I’d really appreciate any help or advice from community members with more experience in airflow simulations for drones.

Thanks in advance!  
Christian

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**Author:** ![shenoy](https://www.simscale.com/forum/letter_avatar/shenoy/32/5_5575768a8748004e209b776fc1b2916d.png) [@shenoy](https://www.simscale.com/forum/u/shenoy)\
**Post date:** [May 28, 2025, 11:10am UTC](https://www.simscale.com/forum/t/unexpected-upward-velocity-vectors-in-drone-hover-simulation/100105/2 "2025-05-28T11:10:48Z")

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Hey @ceckert ,

Some observations comparing to a [similar tutorial](https://www.simscale.com/docs/tutorials/drone-simulation-rotating-zones/) we have,  
The atmosphere boundary condition would be set up differently with zero gradient to visualize results purely from blade rotation. The following settings that are currently being used would not mean a zero-gradient flow through the domain.

 ![image](https://www.simscale.com/forum/uploads/default/original/3X/5/f/5ff2d662d914793f5e4b5db2582db34e39bda742.png)  
Since you are not using Symmetry boundary condition, you would have to assign all outer faces to this [custom boundary condition](https://www.simscale.com/docs/simulation-setup/boundary-conditions/custom/) as follows:  
 ![image](https://www.simscale.com/forum/uploads/default/original/3X/6/a/6aa3bb2b723f55acbfdd13e8c9a7c64ddfa961f9.png)

For the direction of blades, I suggest you try to reverse the direction of the blades and check if that gives you the results you want. Everything from a solver and boundary condition perspective looks good other than the previous point I made. Let us know how it works out. 🙂

Best,  
Satvik