Sonic Boom Alleviation Using Keel Configurations

A detailed numerical investigation of the application of off-axis volume control for sonic boom mitigation is summarized. An 85-ft (25.9-m) aircraft flying at a Mach of 2.4 at an altitude of 57,000 ft (17.4 km) in a real atmosphere was studied. The off-axis volume was supplied by a keel system below the forward portion of the supersonic vehicle. The off-axis volume increased the fineness ratio of the vehicle by adding volume under the vehicle, thereby increasing its apparent length. A fully three-dimensional nonlinear Euler model was employed. The results presented proved that off-axis volume addition is effective and efficient for increasing the apparent length of the vehicle, thereby greatly alleviating sonic boom both on and off the flight-path axis. It was also shown that a keel swept forward normal to the Mach plane has a length efficiency factor equal to the freestream Mach number. It was further demonstrated that heat addition could be substituted for off-axis volume. Finally, nonlinear effects serve to minimize the keel size.