Can we run a CHTv2 simulation with just a fluid?

Yes, the new CHTv2 analysis type can be used to simulate a fluid only case.
See below for an example:

Here is a sample project where the CHTv2 is used to simulation a fluid only problem.
Cold Storage Analysis

As an extension to Conjugate Heat Transfer SimScale recently released an upgraded version Conjugate Heat Transfer v2.0 (referred to as CHT v2) which is more stable and provides faster convergence as the energy equation is strongly coupled between the solid and fluid regions.
Both incompressible and compressible flows can be modeled involving the impact of solar load.

To know more about the CHTv2 analysis type please take a look at this page.

With Regards,