Breaking the Sound Barrier: Shock Waves, Drag Rise, and the Physics of Transonic Flight

Why is it so difficult for aircraft to fly near Mach 1?

In this short video, I use Stallion 3D to look at transonic flow around an aircraft. The example starts with the Bell X-1, the first aircraft to break the sound barrier in 1947. The main idea is simple: as an aircraft approaches the speed of sound, the airflow does not change smoothly. The drag can rise sharply.

This speed range is called the transonic regime. In transonic flow, part of the air around the aircraft can still be subsonic, while another part has already become supersonic. This can happen directly on the surface of the aircraft. That is what makes the problem important for aircraft design.

When shocks form on the aircraft surface, the pressure distribution changes quickly. The forces on the airplane are found by adding up the pressure over the surface. If the pressure changes sharply before and after a shock, the aircraft can see a large increase in drag. This is one reason wave drag becomes important near the speed of sound.

The flow can also become unsteady. A shock wave may move back and forth on the aircraft surface. That motion can create unsteady aerodynamic forces. In some cases, those forces can contribute to structural vibration or other design problems.

One common way to reduce transonic drag is to sweep the wing. Wing sweep reduces the effective Mach number seen by the airfoil section and helps delay some of the strongest transonic effects. This is one of the reasons swept wings became common on fast aircraft. The video is a simple look at this problem using Stallion 3D CFD.

More information can be found at Hanley Innovations ➡️ https://www.hanleyinnovations.com 

Thanks for watching

Patrick