Direction cosine matrix in turbulence model

Hello,

I am trying to use the von Karman turbulence model in Simulink and I am having trouble understanding the utility of the Direction Cosine Matrix (DCM) needed as an input. As per my understanding, this is supposed to provide the user with the posibility of having the disturbance velocities in a reference frame of his choice. Intuitively, one has to provide the rotation matrix from whatever reference frame the model employs internally (to express the velocity disturbance) to a chosen reference frame. My questions are:

- What is the reference frame used internally by the turbulence model ? (or, With respect to what frame are the velocity disturbances provided if one supplies a unity DCM?)

- If the DCM has other utility, what would be it and what reference frames does it relate ?

Thanks!