Hypersonic speed is achieved when an aircraft or other object reaches speeds above Mach 5. Most commercial aircraft travel around Mach 0.8-0.9, which is below the speed of sound or transonic speed. As aircraft begin to travel above Mach 1, there starts to be a difference in the behavior of the fluid flow, with the formation of shock waves being the most evident manifestation of these physical changes. These differences increase even more when traveling at hypersonic speeds. At hypersonic speeds, many challenges may arise that need to be examined, and because there are so few wind tunnels in the world capable of testing these hypersonic prototypes, and flight testing is extremely expensive and lengthy, simulation offers the best and most cost-effective way to look at this flight regime. ANSYS simulation tools can be used to examine all the challenges one may face while traveling at hypersonic speed, such as:
- Very strong shocks — These very strong shocks cause discontinuous temperatures, pressures and densities across the shock waves. These strong compressibility effects will cause extreme thermal loads that can damage the structure of the vehicle.
- Chemical and thermodynamic nonequilibrium —as the Mach number rises, phenomena such as vibrational excitation of air, dissociation and ionization occur.
- Plasma —The above phenomena will generate a plasma layer that will degrade radio communications and eventually will generate the so-called “blackout” effect.
- Ablation —This is the conversion of solid materials to gas, due to pyrolysis and surface reactions as temperatures become extremely high.
- Structural deformation — The extreme temperatures and heat fluxes created by the hypersonic flowfield will deform the structure of the vehicle, altering its performance and putting its structural integrity at risk.