CFD_WIND_TUNNEL
CFD
Beta command
This command is in the beta stage and the format may change over time.
"Optional title"
fid${}_v$
Parameter definition
Description
This command is used to convert the CFD domain into a virtual wind tunnel. The ambient air conditions are assumed be at pressure $1 \mathrm{atm}$ and temperature $293 \mathrm{K}$. The flow inlet is at $x_0$ and the outlet is at $x_1$ (see CFD_DOMAIN).
Note that this command is only useful at supersonic speeds, as boundary layer and viscous drag effects are not accounted for.
Example
Retardation of an irregular object
In this example we start with the air inlet flow velocity $v_{inlet}(0) = v_0$. The drag force $F(t)$ acting on the object results in a virtual retardation $a(t) = -F(t)/m$, where $m$ is object mass. Instead of actually changing the velocity of the object, this retardation if used to dynamically adjust the air speed at the inlet:
$\displaystyle{\frac{\mathrm{d} v_{inlet}}{\mathrm{d} t} = a(t) = -\frac{F(t)}{m}}$
In this example the inlet velocity is defined through the FUNCTION with ID=12. The function uses the flag derivative=1, which means that the functional expression defines its time derivative and not its current value.
