Fluid property definition

@FLUID_PROPERTY_DEFINITION {
@FLUID_PROPERTY_NAME {FldpropName} {
@FLUID_DENSITY {ρ}
@SPEED_OF_SOUND {a}
@DEFAULT_COEFFICIENTS {
@SLOPE_OF_LIFT_CURVE {a0}
@DRAG_COEFFICIENTS {cd}
@MOMENT_COEFFICIENTS {cm0, c}
@LIFT_CURVE_INTERCEPT {cℓ0}
}
@DEFAULT_COEFFICIENTS {
@DRAG_COEFFICIENTS {cd}
@FRICTION_COEFFICIENT {cf}
@APPARENT_MASS_COEFFICIENT {ca}
}
@FAR_FIELD_FLOW {
@FAR_FIELD_FLOW_VELOCITY {U∞1, U∞2, U∞3}
@TIME_FUNCTION_NAME {TimFunNameU}
@GUST_VELOCITY {Ug1, Ug2, Ug3}
@TIME_FUNCTION_NAME {TimFunNameG}
}
@MACH_NUMBER {M}
@REYNOLDS_NUMBER {Re}
@REFERENCE_LENGTH {Lref}
@REFERENCE_CHORD_LENGTH {cref}
@PERIOD {Period}
@COMMENTS {CommentText}
}
}

NOTES

  1. This section describes the physical properties of the fluid to be used in aerodynamic or hydrodynamics loads computation. The following physical properties can be defined: the free stream air density, ρ, the free stream speed of sound, a, the free stream Mach number, M, the free stream Reynolds number Re, the reference length, Lref, and the reference chord length, cref.
  2. In some case, aeroelastic simulations will fail at an early stage because it takes a certain amount of time for the wake to develop. In such cases, it is useful to build up aerodynamic loads in time by artificially building up the value of the air density. If the entry Period is not zero, the air density is computed as ρ (t) = 1/2 (1 - cos π t/T) ρ if t < T and ρ (t) = ρ if t ≥ T. After the period Period = T, the air density becomes equal to its nominal value, ρ.
  3. It is possible to attach comments to the definition of the object; these comments have no effect on its definition.

The default coefficients

Default coefficients can be defined for an airfoil or for a cylinder.

  1. In the case of an airfoil, the following coefficient are defined.
    • The slope of the lift curve a0 = ∂C/∂α.
    • The drag coefficient cd.
    • The camber pitching moment coefficient cm0.
    • The quarter-chord pitching moment curve slope c = ∂Cm/∂α
    • The lift curve intercept at zero angle of attack, cℓ0 (Default value: cℓ0 = 0).
    More details about the meaning of these coefficients is found in the description of unsteady aerodynamic theories.
  2. In the case of a cylinder, the following coefficient are defined.
    • The drag coefficient cd.
    • The frictional coefficient cf.
    • The apparent mass effect coefficient ca.
    More details about the meaning of these coefficients is found in the description of unsteady hydrodynamics theories.

The far-field flow velocity

The far-field flow velocity is defined as the superposition of the far-field flow velocity, denoted U(t), and of gust velocity, denoted Ug(t), such that U = U(t) + Ug(t).

  1. The components of the far field velocity vector, U resolved in the inertial system are denoted U∞1, U∞2, and U∞3.
  2. An optional time function, TimFunNameU, is associated with the far field flow velocity vector. This time function will modify the value of the far field velocity which becomes time dependent.
  3. The components of the optional gust velocity vector, Ug, resolved in the inertial system are denoted Ug1, Ug2, Ug3. The time history of the gust velocity is described by the time function, TimFunNameG, which must be defined if the gust velocity is present.