CFD (Computational Fluid Dynamics) / Flow Simulation Questions

[Jeffrey Meyer]

Some other problems I would love to use CFD for:

- determine if fiberglass fairings are worth the effort to construct in several areas. For example a wingtip.
- cowl design, or some simplified version of this
- heat flow in engine compartment after shutdown
- ducts and airflow for cabin heater
- ducts and airflow for air conditioner (I'm trying to put one in a Zenith, but that is another topic!)
- determine drag with/without wheel pants a different speeds

From your last point, it sounds like even assuming no prop, flow over the entire airframe would be impractical. What would the limit be, could a wheel with/without fairing be possible? !

Yes, it would certainly be possible, and a wheel with or without a wheel spat would be a very good exercise on the learning curve. I suggest you try 4 CFD test runs:
1. Wheel only.
2. Wheel with spat - external geometry only.
3. Wheel with truncated spat - see attached images.
4. Shell the spat (2mm say) with an opening for the wheel.

After you run the above do a quick estimation of the actual drag using the following formula:

Drag = 1/2 * rho * V^2 * Cd * S

where rho is the density of air (about 1.25 Kg/cubic meter), V is the velocity in m/sec, Cd is the drag coefficient (0.25 for the wheel only, 0.15 for the wheel with spat), and S is the frontal area of the assembly in square meters. Using these units drag force is measured in Newtons. 1 Newton = 98.1 grams = 0.216 lb.

I think you will be surprised by the difference between the CFD and the actual (theoretical) results, especially when you complicate this relatively simple geometry as in CFD run #4.

Looking forward to your comments.