Free-stream Mach number

{
  "id": "MLC-T-MET-005763",
  "term": "Free-stream Mach number",
  "field": "Meteorology and atmospheric science",
  "definition": "The ratio of the speed of an object moving through a fluid, or the speed of the fluid itself, to the local speed of sound in the undisturbed fluid far away from the object. This dimensionless quantity, denoted M∞, characterizes the overall flow regime as subsonic (M∞ < 1), transonic (M∞ ≈ 1), supersonic (M∞ > 1), or hypersonic (M∞ > 5). It is a fundamental parameter in aerodynamics and compressible fluid dynamics, governing phenomena like shock wave formation and compressibility effects on airflow over terrain or aircraft.",
  "url": "https://mlchart.com/terminology/meteorology/free-stream-mach-number/"
}