The value of the critical Reynolds number for the flow over a flat plate is 5 x10^5. The significance of the value is:

(a) The boundary layer will be turbulent where the Reynolds number is less than this value.

(b) At a position along the plate where the Reynolds number equals this value, transition from laminar to turbulent boundary layer gradually occurs.

(c) If the Reynolds number for the plate based on the length L is greater than this value, then the boundary layer is turbulent over the entire plate.

(d) Transition from laminar to turbulent boundary layer will occur immediately when this value is exceeded.

(e) None of the above represent a reasonable answer!

(c) If the Reynolds number for the plate based on the length L is greater than this value, then the boundary layer is turbulent over the entire plate.

Explanation:

The applicability of the Reynolds number differs depending on the specifications of the fluid flow such as the variation of density (compressibility), a variation of viscosity (Non-Newtonian), being internal - or external flow, etc. The critical Reynolds number is the expression of the value to specify transition among regimes which diversifies regarding type of flow and geometry as well. Whilst the critical Reynolds number for turbulent flow in a pipe is 2000, the critical Reynolds number for turbulent flow over a flat plate, when the flow velocity is the free-stream velocity, is in a range from 10 raised to power 5 to 10 raised to power 6,.4