In Week 1, we'll explore flow in a channel with a semi-circular obstacle on the bottom wall is used to introduce the basic flow models (Euler, Navier-Stokes, and Reynolds-averaged Navier-Stokes equations), the basic features of most flows in engineering applications (boundary layer, shear layer, flow separation, recirculation zone), and the approaches to simulate flows including these phenomena. The distinction between inviscid, laminar, and turbulent flows is explained, as well as how the flow features can be visualized and analyzed and how the knowledge of the flow regime affects the design of the computational grid and the choice of physics models and simulation parameters. Finally, the ways of increasing the efficiency of simulation and the estimation of discretization errors are presented.