Extremely interesting footage shows the bow shock wave around an F-104 Starfighter flying supersonic.
As already explained in a previous article, Piercarlo “Capone” Ciacchi is the Director of Flight Operations at Starfighters Aerospace. A former Italian Air Force F-104 and Frecce Tricolori display team pilot, he regularly flies the F-104s owned by Starfighters Aerospace out of NASA’s Kennedy Space Center, Florida.
Such flights, carried out for research and development purposes as well as pilot/test pilot training, provide Ciacchi an opportunity to shoot some really cool footage. The last one he’s just posted to Youtube, is particularly interesting as it shows the bow shock wave created by the Starfighter flying supersonic over Florida.
In particular, what you can see in the video is the bow shock wave, a shock wave that forms in front of a supersonic object as it travels through a fluid medium: the supersonic object pushes its way through the fluid medium, creating a sudden increase in pressure and a corresponding drop in temperature: when a supersonic flow encounters a body, around which the necessary deviation angle of the flow is higher than the maximum achievable deviation angle for an attached oblique shock.
Then, the oblique shock moves ahead of the object and transforms in a curved detached shock wave. As bow shocks occur for high flow deflection angles, they are often seen forming around blunt bodies, because of the high deflection angle that the body impose to the flow around it.
Why does it become visible? Where the density of the air changes (as a consequence of shock waves) there is a change in its refractive index, resulting in light distortion (as mentioned by Ciacchi, it’s the same phenomena you can observe when a spoon looks bent in water) and this is something we have already discussed here.