Sonic boom propagation over real topography

Area of Science:

• Acoustics
• Computational Fluid Dynamics
• Geophysics

Background:

• Sonic booms generated by supersonic aircraft can be affected by ground topography.
• Understanding these effects is crucial for predicting noise impact and public acceptance.

Purpose of the Study:

• To investigate how elevation variations in real terrain influence sonic boom reflection.
• To quantify the impact of topography on sonic boom characteristics and noise levels.

Main Methods:

• Solving the two-dimensional Euler equations using finite-difference time-domain techniques.
• Performing numerical simulations on 10 km-long ground profiles from hilly regions.
• Analyzing two types of boom waves: classical N-wave and low-boom wave.

Main Results:

• Topography significantly alters reflected sonic booms for both mild and steep slopes.
• Wavefront folding due to terrain depressions was a key observed phenomenon.
• Steep slopes led to noise level amplification, with a 3 dB increase at 1% of positions and up to 5-6 dB near depressions.

Conclusions:

• Terrain elevation variations, particularly steep slopes and depressions, substantially affect sonic boom reflection and increase noise levels.
• Wavefront folding is a critical mechanism for this amplification.
• These findings apply to both N-waves and low-boom waves, informing future supersonic flight noise predictions.