# Virtual Wind Tunnel Drag and Lift

Hi,
I’m new in Palabos and I’m trying to simulate a complex geometry in a 3D wind tunnel for a final degree project. I’ve found the example of “externalFlowAroundObstacle” and I think that it’s the most useful example for me.
I’ve changed my geometry and variate some parameters and it works.

So the problem is that the code provides me with resulting force values. I need drag and lift coeficients. Can anybody help me? I’ve seen how implementate drag in 2D but not in 3D.

Many thanks!

Marc

The drag coefficient can be computed from the drag force, right? See:

http://en.wikipedia.org/wiki/Drag_coefficient

Many thanks, sorry for my ingnorance.

Do you know if Palabos work in SI units (wind tunnel velocity, wind tunnel measures, kinematic viscosity)? The first lines of the xml say that all are physical units. But I’ve had problems with implement my geometry in the example of “externalFlowAroundObstacle”. The geometry of the example is very small of the order of milimeters and it can’t be that the wind tunnel measures work in meters. Probably i make a mistake with Rhinoceros.

Many thanks again! And sorry for my bad English

The LBM generaly works in Lattice Boltzmann units. LBM requires that viscosity is around the value of 0.1 and the maximum velocity is 0.3. You use this knowledge to rescale real units to LBM units to satisfy these requirements.

Many thanks @czb!

obstacle.stl problem solved. However, the simulation still doesn’t work…

hello my friend I want to simulate the problem as same as you. I want to simulate a wind tunnel around the cylinder obstacle which is place at the ground of my domain with dx=dy=dz=1. Cylinder’s height is 20 and mu scale is one. I also determine czLB=1, but the problem that I encounter is when I analyze the outputs, part of the obstacle bottom is removed and the velocity magnitude is really high.