Question

Explain how the compressibility and shock wave generation affects the design of fighter jets.

Answer 1

Compressiblity :

Fighter jets are designed to move at high speeds.At high speeds, the assumptions of incompressibility of the air used in low-speed aerodynamics no longer apply.Compressibility is of paramount importance at speeds approaching the speed of sound. In these transonic speed ranges, compressibility causes a change in the density of the air around an airplane. This result in the onset of compressibility effects such as shock wave formation, drag increase,buffeting, stability, and control difficulties.

Shock Waves :

Shock waves are formed when a pressure front moves at supersonic speeds and pushes on the surrounding air. This happens at the nose of fighter jets. At the region where this occurs, sound waves travelling against the flow reach a point where they cannot travel any further upstream and the pressure progressively builds in that region.

When an object (or disturbance) moves faster than the information can propagate into the surrounding fluid, then the fluid near the disturbance cannot react or "get out of the way" before the disturbance arrives. In a shock wave the properties of the fluid such as density, pressure, temperature, flow velocity, Mach number change almost instantaneously. This again leads to loss of controliblity and increase in drag.

In this way, compressiblity ans shock wave generation play a key role in design of air crafts that run at high speeds such as fighter jets