# BOUNDARY LAYER SEPARATION

Posted by admin
On April 08, 2014

**BOUNDARY LAYER SEPARATION**

#### When fluid flows past a body (cylinder or an airplane), fluid is accelerated due to pressure drop and ∂p/∂x is negative. Pressure decreases as distance x increases. When ∂p/∂x becomes zero, velocity decreases and separation of flow occurs and back flow is just to start. At the point of separation, the following are observed.

#### (i) It is a point of stagnation.

#### (ii) ∂p/∂x becomes zero at this point.

#### (iii) ∂u/∂y = 0

#### (iv) U = 0 and v = 0

#### (v) Velocity profile has a point of inflexion at the point of separation i.e. there will be change in direction of the velocity after the point of separation.

#### (vi) Beyond the point of separation fluid starts flowing in the back direction of the main stream.

#### (vii) Eddies will be formed and there will be energy loss which is highly un-desirable.

#### (viii) This is also found in the divergent portion of the convergent-divergent portion of nozzles used before the steam turbine.

#### (ix) Flow patterns and flow nets are useful in finding the points (or regions)of separation

#### (x) Design should be such that back flow does not occur.