Can I set Relative North?

No, Ventus does not implement Relative North as defined in ContamW. Ventus supports Wind direction adjustments differently than ContamW; remember, in Ventus the user models actual geometry. From the relevant section of the Ventus User Manual:

The Ventus global coordinate system has x-y-z axes in the lower left corner of the 2D/3D Workspace. Wind directions are defined relative to the global coordinate system. North is aligned with the positive Y-axis; East is aligned with the positive X-axis.

In keeping with this approach, rotate the model geometry to match its intended build orientation.

Use the Rotate tool as described in the Ventus User Manual

The orientation of the model relative to the Ventus global coordinate system is input to ContamX when modeling wind.

We hope that this system meets your needs, and we remain open to feedback. For more information, please contact Thunderhead Engineering for support: support@thunderheadeng.com.