In observing the flow of air through an orifice plate using a CFD tool, it can be seen that there is a point in which air converges beyond the orifice plate, known as a vena contracta. This convergence leads to a restriction of air flow that is smaller than the orifice plate opening itself. Therefore, there is a need to guide the air into the restrictor, instead of creating a sudden step that would have been in the case of the orifice plate. Thus came the common design of a Convergent-Divergent Nozzle that replaces the orifice plate as an air intake restrictor.