**Abstract**

The flow transit from laminar to turbulent over the surface due to adverse pressure gradient, that the region in between the laminar separation and turbulent reattachment is called Laminar separation bubble. It experiences on the many engineering devices as well as controls the aerodynamic and heat transfer characteristics. The way of transition formation differs based on geometry, flow configuration and method of transition initiations by a wide range of possible background disturbance as free stream turbulence, pressure gradient, acoustic noise, wall roughness and obstructions, periodic unsteady disturbance so on. This chapter discusses about the flow transition on airfoil and nozzle in general and focuses more on the transition process in the free shear layer of separation bubbles, free stream turbulence, and identification of separation point with the help of the CFD method.

**Keywords:** laminar separation bubble, turbulence intensity, turbulence separation, reattachment
