The instability of planar free shear layers is an important consideration in a broad range of applications, such as heat exchangers, chemical reactors, building wakes, and aerofoils. A planar free shear layer is primarily unstable through an inviscid Kelvin-Helmholtz mode that exists due to the inflectional shape of the shear-layer velocity profile. The OKCFD Lab performs detailed numerical research analyzing the effect of wall-proximity and external forcing on the instability of planar free shear layers.