[MBDyn-users] 2-D look-up table for bluff body aerodynamics ..also suitable for wind turbines ?

Rix, Patrick Patrick.Rix at repower.de
Wed Jul 21 08:22:29 CEST 2010


Hi,

I guess that the "generic aerodynamic force"-element is also the right candidate for modelling longitudinal and transversal aerodyn.drag effects of the nacelle housing and the rotor hub on a horizontal axis wind turbine, right ?

Regards, Patrick.


-----Ursprüngliche Nachricht-----
Von: mbdyn-users-bounces at mbdyn.org [mailto:mbdyn-users-bounces at mbdyn.org] Im Auftrag von masarati at aero.polimi.it
Gesendet: Dienstag, 20. Juli 2010 15:54
An: Hoff, Stefan van 't
Cc: mbdyn-users at mbdyn.org
Betreff: Re: [MBDyn-users] 2-D look-up table for bluff body aerodynamics

> LS,
>
> I want to achieve helicopter fuselage aerodynamics in MBDyn based on 2-D
> look-up tables. I require 6 outputs (3 force coefficients and 3 moment
> coefficients), as a function of two inputs (angle of attack and angle of
> sideslip). Multiplied by the dynamic pressure (density and velocity
> dependent), this should give the forces and moments.
>
> As far as I can tell there is currently no aerodynamic component that can
> do this. The aircraft instruments element could provide the two inputs
> required. Performing the 2-D table lookup required to derive the forces
> and moments should then be straightforward (similar to the aerodynamic
> body component, substituting the Mach number dependency by another angle).

As discussed in a private conversation, there is one, experimental and
undocumented.  It's called "generic aerodynamic force", and seems to do
exactly what you need.  It has been available since the beginning of
release 1.3.  The syntax is something like

generic aerodynamic force: <label>,
    <node_label> ,
    <offset> ,
    <orientation> ,
    [ reference surface , <reference_surface> , ]
    [ reference length , <reference_length> , ]
    " <data_file> " ;

The data file contains

% comments
% one row containing
n_alpha n_beta
% comments
% n_alpha * n_beta rows containing
alpha beta Kx/q Ky/q Kz/q Kl/q Km/q Kn/q

sorted by alpha (AoA), then beta (sideslip); if the coefficients are
normalized according to the dynamic pressure, then they're dimensional
(forces are forces per unit pressure, thus surfaces; moments are moments
per unit pressure, thus volumes).  Otherwise, if they're non-dimensional,
you need to provide the reference surface and length used in the
non-dimensionalization.

The angles are computed from the absolute velocity of the reference point
(the velocity of the body at the offset) projected in the local reference
frame of the body; alpha is the angle between v(3) and v(1), while beta is
the angle between -v(2) and v(1).

The output consists in:

label alpha beta fx fy fz mx my mz

where f, m refer to the forces and moments actually computed by the
element, namely dimensionalized using the dynamic pressure and the
reference surface and length.

Note that the syntax may change as soon as the element is "validated" and
exposed, to conform with the rest of the syntax and to be as general as
possible.  For example, I intend to separate reading data files and
elements, so that more than one element can use the same data.  If you
plan to use it, your feedback would be greatly appreciated.

Cheers, p.

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