1. Laminar flow, turbulent flow and Reynold’s number
Chan Wei
Lim Zhong Hui
Tan Hong You M4

2. Laminar flow Also known as streamline flow
Occurs when the fluid flows in parallel layers, with no disruption between the layers
The opposite of turbulent flow (rough)

3. Laminar flow
In fluid dynamics (scientific study of properties of moving fluids), laminar flow is:
A flow regime characterized by high momentum diffusion, low momentum convection, pressure and velocity independent from time.
*momentum diffusion refers to the spread of momentum (diffusion) between particles of substances, usually liquids

4. Laminar flow
Turbulent
Flow
Laminar flow over a flat and horizontal surface can be pictured as consisting of parallel and thin layers
Layers slide over each other, thus the name ‘streamline’ or smooth.
The paths are regular and there are no fluctuations
Laminar Flow

5. Laminar flow 3 Conditions
fluid moves slowly
viscosity is relatively high
flow channel is relatively small
Blood flow through capillaries is laminar flow, as it satisfies the 3 conditions
Most type of fluid flow is turbulent
There is poor transfer of heat energy!

6. Turbulent flow Usually occurs when the liquid is moving fast
The flow is ‘chaotic’ and there are irregular fluctuations
Includes:
Low momentum diffusion
high momentum convection
rapid variation of pressure and velocity of the fluid
Good way to transfer thermal energy

7. Turbulent Flow
The speed of the fluid at a point is continuously undergoing changes in both magnitude and direction.

8. Examples of turbulence
Oceanic and atmospheric layers and ocean currents
External flow of air/water over vehicles such as cars/ships/submarines
In racing cars, e.g. leading car causes understeer at fast corners
Turbulence during air-plane’s flight
Most of terrestrial atmospheric circulation
Flow of most liquids through pipes

9. Reynold’s number A dimensionless number in fluid mechanics
Dynamic Pressure : Shearing Stress
Thus, it quantifies the relative importance of these two types of forces for given flow conditions.
Arises when performing analysis of fluid dynamics
Can be used to determine dynamic similitude in such cases. Concept used in the testing of models, e.g. testing miniature airplanes/submarines

10. Dynamic Pressure + Shearing Stress
The pressure of a fluid which results from its motion
Formula:
Shearing Stress
Measure of the force of friction from a fluid acting on a body in the path of that fluid
Formula:
Fluid Density
Weight Density of Water
Fluid Velocity
Water
Surface
Slope
Average
water
depth

11. Reynold’s number Flow in a pipe or liquid
p is the density of the fluid
V is the mean fluid velocity
D is the diameter
Q is the volumetric flow rate
Dynamic Pressure
μ  is the dynamic viscosity of the fluid
v is the kinematic velocity of the fluid
A is the pipe cross-sectional area.
Shearing Stress

12. Reynold’s number
The Reynold’s number can be used to determine if a flow is laminar, transient or turbulent
Laminar when Re < 2300
Turbulent when Re > 4000
Transient when 2300 < Re < 4000
Spermatozoa
1×10−4
Blood flow in brain
1×102
Blood flow in aorta
1×103

13. Acknowledgements

14. Acknowledgements