A similar experiment may be conducted today using Hot Wire Anemometer, which measures instantaneous velocities at a point. The traces of velocity at the three regimes of flow are shown in Fig.7.3. It is clear that while the laminar flow has a predominant velocity in the main flow direction, turbulent flow has a significant component of velocity in the flow normal direction. While laminar flow is "orderly" turbulent flow is "Random" and "Chaotic".
Figure 7.3: Hot Wire Signals for Turbulent flow (top), Transitional flow (middle) and Laminar Flow (bottom)
It is also found that a flow in a pipe is laminar if the Reynolds Number (based on diameter of the pipe) is less than 2100 and is turbulent if it is greater than 4000. Transitional Flow prevails between these two limits. But it should be pointed out that people have preserved laminar flow at very high Reynolds number through carefully monitored conditions.
(c) Aerospace, Mechanical & Mechatronic Engg. 2005
University of Sydney