VisualSPHysics is integrated into Blender user interface. So objects imported from DualSPHysics simulations behave like regular Blender objects.
To add a DualSPHysics object to your scene, you simply need to open the add object menu with SHIFT A and then go to Mesh → DualSPHysics Object. A file dialog will be open. Here you can navigate to the folder where the VTK files are located. If you open a file that belongs to a sequence (e.g. Surface_0150.vtk), VisualSPHysics will detect first and last steps, and load automatically the file corresponding to the current time step.
Check the object properties before accepting. These properties are located in the bottom left of the dialog:
You can change the properties of the object by selecting the object, pressing n key to show the properties panel and scrolling down to DualSPHysics Object Properties.