The document explains laminar and turbulent flow in fluid mechanics, highlighting that laminar flow is characterized by smooth, parallel movement of fluid layers with Reynolds numbers less than 2000, whereas turbulent flow involves chaotic mixing of layers with Reynolds numbers greater than 4000. Laminar flow occurs at low velocities and in small diameter pipes, while turbulent flow is present at high velocities and larger diameters. The Reynolds number is a crucial parameter for determining the flow regime and is influenced by fluid density, velocity, and viscosity.

1. BIOMECHANICS
UNIT 2
TOPIC: Laminar and Turbulent flow

2. Laminar Flow
• The fluid flow in which the adjacent layers of the fluid do not
mix with each other and moves parallel to each other is
called laminar flow.
• In the laminar flow, the fluid layer moves in straight line.
• The laminar flow always occurs when the fluid flow with low
velocity and in small diameter pipes.
• The fluid flow having Reynolds number less than 2000 is
called laminar flow.
• The fluid flow is very orderly i.e. there is no mixing of
adjacent layers of the fluid and they move parallel to each
other and also with the walls of the pipe.

3. • Shear stress in laminar flow depends only on
the viscosity of the fluid and independent of the
density.
• Example: Consider running water through a hose.
You may observe the water flowing in a straight line
while the amount and rate of flow remain low. This
smooth and streamlined nature of fluid motion is
considered a laminar flow.

4. Turbulent Flow
• The fluid flow in which the adjacent layers of the fluid
cross each other and do not move parallel to each other
is called turbulent flow.
• In turbulent flow the fluid layers do not move in a
straight line. They move randomly in a zigzag manner.
• The turbulent flow occurs when the velocity of the fluid
is high and it flows through larger diameter pipes.
• The fluid flow having Reynolds number greater than
4000 is called turbulent flow.

5. • The fluid does not flow in a definite order. There is a mixing
of different layers and they do not move parallel to each
other but cross each other.
• The shear stress in turbulent flow depends upon its density.
• Example: Turbulent flow is a common occurrence and can
be observed in the flow of rivers, smoke coming out of
exhaust pipes, or even experienced during turbulence in
aircraft

6. Laminar and turbulent flow

7. Laminar and Turbulent Flow
• Laminar flow
– Streamlined
– Outermost layer
moving slowest and
center moving fastest
• Turbulent flow
– Interrupted
– Rate of flow exceeds
critical velocity
– Fluid passes a
constriction, sharp
turn, rough surface

8. • Reynolds number is an important dimensionless
parameter that identifies the behavior of fluid based on
attributes like viscosity or velocity of the fluid. Accordingly,
the value of Reynolds number (Re) can be expressed as:
Note that:
• ρ is the density of the fluid
• V is the fluid velocity
• D is the hydraulic diameter (of pipe, tube, or duct).
• μ is the fluid viscosity
Reynolds Number

9. • Important takeaways from the Reynolds number
calculation include:
• A flow is considered laminar if the Reynolds
number is up to 2300. Viscous force is more
prominent due to the slower flow rate.
• A flow is considered turbulent if the Reynolds
number is greater than 3500. A faster and
irregular flow path maximizes the inertial force in
the system.
• Flow regime for the Reynolds number between
2300 to 3500 is considered transitional flow.