2 Turbulent flow

• When the speed of the liquid exceeds a certain limit, the flow is no longer smooth: small circular eddies (vortices) appear.
• The same happens with gases (smoke rising from a cigarette or incense stick starts as steady streamlines and then becomes turbulent with eddies).
• Turbulence also results from violent change of flow or from the rapid motion of an object through the liquid, or when a gas diffuses from a narrow space to a larger one or from high to low pressure.

Turbulent flow is accompanied by noise: a doctor listens with a stethoscope to detect turbulent blood flow in an artery, which indicates illness.