Insights into how turbulence forms could pave the way for more stable and efficient high-speed aircraft, according to research. 

As the cone-shaped nose of an aircraft or missile moves through the air, vortices form behind it. These swirling structures can become large and unstable, often behaving unpredictably. This can cause the aircraft to pull to one side or rotate unexpectedly. In high-stakes environments, particularly military operations, even a slight deviation off-course can mean missing a target or losing control entirely.

To better understand the transition from stable to asymmetric vortices, researchers at FAMU-FSU College of Engineering in Florida, US, examined how different angles of flight affect these vortices. They combined experimental testing with advanced computational simulations to model complex airflow and identify when and how instability develops.

“Aircraft in flight are subject to extreme forces and, as speed and manoeuvring increase, these forces only get stronger. This study helps to understand critical phenomena responsible for those forces so engineers can create efficient and more stable designs,” said study co-author Rajan Kumar, chair of the department of mechanical and aerospace engineering and director of the Florida Center for Advanced Aero-Propulsion.

The team simulated airflow over a cone-shaped object travelling just above the speed of sound at Mach 1.1 at three angles of incidence: 15°, 25° and 30°.

At a 15° angle, the main swirl of air breaks down into a complex pattern resembling two intertwined spirals, which then split into many thin, tangled strands of swirling air.

At 25° and 30°, the breakdown looks different. The swirl twists apart in a single spiral pattern, indicating even stronger instability.

As the angle of incidence increased, vortex asymmetry also increased. Airflow shifted from structured and predictable to unstable and erratic, illustrating how quickly control conditions can deteriorate in real-world flight.

The study showed that small vortices within airflow can grow and join together, forming larger disruptions. It also showed that vortex behaviour depends on several interacting factors, including the size of the vortices and their orientation relative to the aircraft. Together, these elements determine how much force is exerted on the vehicle and how difficult it becomes to control.

The researchers say that understanding the forces at work on aircraft in flight could help engineers design more stable high-speed aircraft and missiles. They are now expanding their research to explore vortex behaviour at higher speeds and investigating methods, including AI, to enable aircraft to respond to instability in real time.

Their study – Investigation of vortex asymmetry of a conical forebody at angles of incidence – has been published in the Journal of Aircraft.