Sampat Kumar
Ansys Employee

Hi Mario Liebermann, 
Will you please tell me if it is a 2D model or a 3D model? Will you please check the fluid body creation again? 
I have attached the video and Asys helped documents link for the volume extraction and split of the geometry. This might help you to solve this issue. 

Volume Extract Tool (ansys.com)

Discovery SpaceClaim: Model Prep for CAE & MFG - Manual Fluid Body Creation - Ansys Knowledge

Discovery SpaceClaim: Model Prep for CAE & MFG - Splitting and Imprinting Faces - Ansys Knowledge

Regards, 
Sampat