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Laminar flow is a smooth looking flow - the flow appears glassy when flowing out of the tap
- all the water particles have the same direction
- flow can be considered one directional/dimensional
Turbulent flow is turbid or not very clear
- the water particles have different directions superimposed on the mean flow. If you are close you can catch an occasional spray. The particle reached you because it had a velocity in your direction.
- flow is 3D and unsteady (function of time)
Same tap, similar water. The cause of the different flow is that you increased the flow rate or the velocity to cause the flow to become turbulent. In practice the classification of the laminar and turbulent flow is done through the Reynolds number. This is called the critical Reynolds number (Recr). Below the critical Re the flow is (considered) laminar and above the critical Re the flow is (considered) turbulent
Laminar and Turbulent Flow over a Flat Plate - Boundary Layer Difference
Growth of Boundary Layer Boundary Layer Profiles
The boundary layer development over a flat plate at SL conditions and U = 100 ft/s is illustrated below. The transition between Reynolds number of 300,000 and 600,000 is also shown. There is a big difference in the BL thickness (feet). The above figures represents the comparison of the velocity profiles. Nevertheless the Turbulent profile is flatter near the wall making the slope of the velocity profile at the wall is significantly higher with greater skin friction drag
Some observations on the two type of flows
- turbulent boundary layer is thicker than laminar boundary layer
- turbulent boundary layer is flatter near the wall
- velocity gradient for the turbulent layer is much higher than the laminar layer at the wall (this is related directly to the shear stress or skinfriction)
- turbulent boundary layer has more momentum/energy near the surface - hence has better resistance to separation (example of the dimpled golf ball)
- Calculations
Some Formula for Calculations:
A reference figure for the formula:
BL Thickness
Cf (l)
Cf (L)
Laminar Flow
Turbulent Flow
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