A typical use of CFD is to evaluate the aerodynamic performance of aerospace vehicles like rockets and airplanes. The first step in this process is to create a mesh of the vehicle geometry from a CAD definition. This essentially lets us break the problem down into thousands or millions of small cells in which we numerically simulate the physics that govern flow.
There are generally two lines of work mechanical engineers end up doing once they graduate: HVAC or aerospace. My undergrad was heavily based on mechanical design. I fell into my career by chance. It’s interesting to see that an aerospace engineer was one of lucky ones to get a review unit.