The fluid domain associated with a solid CAD model, or the region in which the fluid flows in or around the geometry, is the starting point for performing a computational fluid dynamics (CFD) analysis. Quite often, CFD engineers are provided with only solid CAD geometries, and it is their responsibility to extract respective fluid domains for given solid models. Ansys Fluent Meshing’s watertight geometry workflow provides the tools needed to let the user extract the required fluid region. In this lesson, we will learn how to use the Extract Fluid Regions subtask of the Describe Geometry task to create capping surfaces, close any openings, and define the boundaries of the fluid domain. We will then learn about how to extract the fluid domain using the Create Regions subtask of the Describe Geometry task.