Transition Point

Transition point may be defined as the end of the region at which the flow in the boundary layer on the surface ceases to be laminar and begins to become turbulent. It is essential to note that the transition from laminar to turbulent nature takes place over a length, and not at a single point. Thus the transition point marks the beginning of the transition process from laminar to turbulent nature.

2.7.2 Separation Point

Separation point is the position at which the boundary layer leaves the surface of a solid body. If the separation takes place while the boundary layer is still laminar, the phenomenon is termed laminar separation. If it takes place for a turbulent boundary layer it is called turbulent separation.

The boundary layer theory makes use of Navier-Stokes Equation (2.23) with the viscous terms in it but in a simplified form. On the basis of many assumptions such as, boundary layer thickness is small compared to the body length and similarity between velocity profiles in a laminar flow, the Navier-Stokes equation can be reduced to a nonlinear ordinary differential equation, for which special solutions exist. Some such problems for which Navier-Stokes equations can be reduced to boundary layer equations and closed form solutions can be obtained are: flow past a flat plate or Blassius problem; Hagen-Poiseuille flow through pipes; Couette flow between a stationary and moving parallel plates; and flow between rotating cylinders.