According to the continuity equation for incompressible airflow, what happens to airflow velocity as stream tube area decreases?

The continuity equation for incompressible airflow states that the mass flow rate must remain constant along a streamline. This is expressed mathematically as the product of the cross-sectional area of a stream tube and the fluid velocity. Therefore, as the area of the stream tube decreases, the airflow velocity must increase to maintain that constant mass flow rate.

This relationship is a result of the conservation of mass principle: if the same amount of air must pass through a smaller area, then the air must move faster to get through in the same amount of time. Thus, the correct understanding here is that a reduction in stream tube area directly results in an increase in airflow velocity directly related to the need to conserve mass flow under incompressible conditions.