Learning Forum

[andreannedum]

Hi all,  

I tried to do a basic drag and lift analysis on a kayak outrigger hull. The velocity of water is 5 m/s and it's turbulent. Part of the hull is immersed in the water (see pictures shown). The way I did it is by drawing a domain under my hull in SolidWorks to create my inlet/outlet and wall boundaries. I used Fluent, but when I print my forces acting on my hull, I have a negative y force (the y-axis is positive upward) which does not make any sense. The drag force I obtained was about 9 N. 

I am wondering if my analysis is valid or not since I was shown how to use Fluent quickly.

Also, ss the y force generated really a lift force ? If so, what could be causing it to be negative ? 

Here are some data from my simulation : 

- Models : Turbulent (standard k-epsilon)

- Inlet : Velocity magnitude of water 5 m/s, Outlet : Pressure (0) , the hull is a wall with a No slip condition, the rest of the domain is also a wall with Specific Shear (0,0,0). 

 

 

[Kalyan Goparaju]

Hello, 

The negative y force just means that the force is acting in the downward direction.When calculating the force, if you specify the vector as -1 for y, you will get a positive value. As for the setup of the problem, it appears reasonable to me. The only question I have is if there is any particular reason for deviating from the default SST k-omega turbulence model and using the standard k-epsilon model? 

Thanks,

Kalyan

[andreannedum]

Hi,

Tank you for your reply ! But if my force is acting downward, isn't it wrong ? I expected my hull to ''lift out of the water'' as the speed goes, and not be ''sucked'' in the water. Hopefully I am clear. 

As for the turbulence model, I was told to use the standard k-epsilon model, but would you recommend the SST k-omega model for turbulence ? With quick research I see that the SST might be more accurate. 

Thanks,