ATPL Airframe Practice Test

In subsonic airflow, when air passes through a divergent duct, the velocity decreases and the pressure increases. This behavior is founded on the principle of conservation of mass and Bernoulli's equation.

As the duct expands, the cross-sectional area increases, allowing the same mass of air to occupy a larger volume. Since the mass flow rate must remain constant in a closed system, the air slows down, leading to decreased velocity. According to Bernoulli's principle, as the velocity of the fluid decreases, the static pressure must increase to satisfy the balance of energy. Thus, in a divergent duct for subsonic airflow, the air will experience a reduction in speed accompanied by a rise in pressure.

This phenomenon contrasts with what occurs in convergent ducts or in supersonic conditions, where opposite dynamics take place. The understanding of how air behaves in these different duct shapes is crucial for various applications in aerodynamics and aircraft design.