[MBDyn-users] aerodynamic body element

Pierangelo Masarati pierangelo.masarati at polimi.it
Tue Mar 21 21:16:06 CET 2017

The local Mach number is computed according to the formula

Mach = V_tot * sqrt(cos(Gamma))

where V_tot is the norm of the local velocity 
sqrt(V(1)*V(1)+V(2)*V(2)+V(3)*V(3)), and Gamma is the sweep angle, 
defined as atan2(-V(3), |V(1)).

This should be in accordance with Harris et al., "Rotor High Speed 
Performance, Theory vs. Test", J. of the Am. Hel. Soc., 1970, which is 
not the perpendicular Mach number.

Sincerely, p.

On 03/21/2017 08:30 PM, Edoardo Codispoti wrote:
> Hi Mbdyn community,
> I have a problem with the aerodynamic body element.
> I don't understand how the local mach number is defined.
> I wrote a simple problem to check the behavior.
> I defined an aerodynamic body attached to a node.
> The panel has a sweep angle of 45° with respect to the asymptotic speed.
> The asymptotic mach number is 0.294. So the perpendicular mach of the 
> panel should be M_pan = M_inf * cos(45°) =  0.2079 ?
> As suggested in the input manual, the 4th column(standard output) of 
> the .aer file is the local mach number of the aero element, the value 
> printed is 0.2473.
> I misunderstood the manual?
> Thank you.
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Pierangelo Masarati
Dipartimento di Scienze e Tecnologie Aerospaziali
Politecnico di Milano

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