2.8.1 Drag Coefficient

The following options for drag coefficients are available in the fiber model to compute the drag due to flow moving parallel to the fibers:

const-drag   A constant value for the drag can be specified.

kase-matsuo   A drag coefficient using the model taken from Kase and Matsuo [ 3], see Equation  2.8-1.

gampert   A drag coefficient using the model from Gampert [ 2].

Gampert provided analytical and numerical solutions for laminar axisymmetric flow of a moving cylinder in stationary air including strong curvature effects in the boundary layer, [ 2]. The drag coefficient and the Nusselt number are shown as dimensionless groups in Figure  2.8.1. Note that the curvature $k$ is defined as the abscissa in Figure  2.8.1. This correlation is recommended in laminar flows.

Figure 2.8.1: Dimensionless Groups of Drag Coefficient and Nusselt Number [ 2]

user-defined   A drag coefficient that you specify in a user-defined function (UDF). See Section  3.7 for more information on using UDFs in the fiber model.

In Figure  2.8.1 and Equation  2.8-1, the Reynolds number is computed based on the relative velocity of the surrounding flow parallel to the fibers $Re_d = \frac{\rho d (u_f - u_{par})}{\eta}$.

Lateral drag due to flow of the surrounding fluid perpendicular to the fibers is computed by a correlation from Schlichting [ 7]

In Equation  2.8-2 the Reynolds number is computed based on the relative velocity of the surrounding flow perpendicular to the fibers $Re_{d,lat} = \frac{\rho d u_{lat}}{\eta}$.