Thursday, April 19, 2012

Second try

I have scaled the spats to meters and remeshed it.

A longitudinal clip through the new mesh.

Detail of the mesh. Does this look good?
I had to adjust some geometry data in the snappyHexMeshDict too.

Every time I start Paraview from the terminal it tries to connect to servers that are non existent. This may take minutes!
This is what I get 4 times every time I start Paraview
I tried to find the default_servers.pvsc and server.pvsc files that are described in the Paraview wiki but can't find them. Who tackled this problem and is willing to help? I use the compiled OpenFoam 1.7 version of the ETH Zurich.

Below you see the results after 500 steps. What I find very hard to believe is that now I have scaled te body with 1/1000 the pressure distribution is almost the same. In the first simulation the body was in mm. and the pressure range -225 to 50 now the body is is meters and the pressure range -185 to 50.

These are the forces on the body:
# Time    forces(pressure, viscous)
506    (((1.6243 0.398176 -18.9121) (1.52785 -0.00296421 0.00193884))
The total drag would be something like 1.6+1.5 =3.1 N (vehicle speed 10m/s)
There is a large downwards force of -19 N!

Let's compare this with the experience of Miles kingsbury: His estimates for the Quattro:
Cd_A of 0.12, A 0.6 m^2. At 10m/s the drag would be 4.32 N ( F = rho/2*Cd*A*v^2 ).

Pressure p/rho [m^2s^-2]
Pressure p/rho [m^2s^-2]
Pressure p/rho [m^2s^-2]

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