Explanation:
Consider a fluid of density, ρ moving with a velocity, U over a flat plate of length, L.
Let the Kinematic viscosity of the fluid be ν.
Let the flow over the fluid be laminar for a distance x from the leading edge.
Now this distance is called the critical distance.
Therefore, for a laminar flow, the critical distance can be defined as the distance from the leading edge of the plate where the Reynolds number is equal to 5 x [tex]10^{5}[/tex]
And Reynolds number is a dimensionless number which determines whether a flow is laminar or turbulent.
Mathematically, we can write,
Re = [tex]\frac{\rho .U.x}{\mu }[/tex]
or 5 x [tex]10^{5}[/tex] = [tex]\frac{\rho .U.x}{\mu }[/tex] ( for a laminar flow )
Therefore, critical distance
[tex]x=\frac{5\times 10^{5}\times \mu }{\rho \times U}[/tex]
So x is defined as the critical distance upto which the flow is laminar.
