## Fluids

#### Proper Vectors to Select. Simulating Hurricane forces on a home.

• jnelsen33
Subscriber

I am simulating hurricane force winds on a residential home and there is some discussion in my group over which vectors we should use. This is my first time using Fluent and I want to make sure I have all the right vectors selected for the following calculations/plots so that I'm not getting inaccurate values:

Lift force and lift coefficient.

Force definition plot.

Drag and Drag coefficient.

Pressure Coefficient.

Thank you.

• Rob
Ansys Employee
I'd be wary of using the coefficients unless you set the reference values correctly. Otherwise, pressure and force are mostly likely the values of interest.
• Karthik R
Hello:
I agree with Rob. I would definitely start with the reference values. Also, please check if you are getting a deep convergence in your simulation.
Karthik
• jnelsen33
Subscriber
We have all reference values plugged in and update velocity when we run a new simulation. Coefficient of lift is the main coefficient we actually have to worry about, pressure coefficient is also looked at, which is measured under forces, not Report Definitions, but our professor is more concerned with coefficient of lift. We are using transient flow (k-epsilon realizable) and using time step number and size to run our simulations, per our professor's instruction, so we are getting convergence almost immediately. There is just debate within the group about which vectors to use to find the values for the things I listed above. Lift acts perpendicular to any surface that the wind passes over and pressure can act in any direction, so I'm thinking all three vectors should be selected when finding force and coefficient for pressure and lift. I think we will have to manually find the coefficients since Fluent is subtracting forces in any negative direction from the net values.
But, if I find the coefficient for each face of the roof, would the overall coefficient of the roof be the average of all four??
And would you agree that all three vectors should be selected when getting lift and pressure from Fluent?
Thank you.
Josh
• Rob
Ansys Employee
This is why we said to be careful. The coefficients are calculated using the reference values, so you need to understand how these are related to the values your Prof wants. Force is reported in the vector you specify. Pressure is normal to the surface facet.