Machnumero

Machnumero is the dimensionless quantity used in aerodynamics to express the ratio between an object's speed and the local speed of sound in the surrounding fluid. It is a central parameter in compressible flow analysis and helps describe how air or other gases respond to moving bodies.

The Machnumero, usually denoted Ma, is defined by Ma = v / a, where v is the flow speed relative to the fluid and a is the local speed of sound. The speed of sound depends on the medium’s temperature, composition, and phase; for an ideal gas, a = sqrt(gamma * R * T). Because a varies with altitude and environment, the same physical velocity can correspond to different Machnumbers in different situations.

Machnumero values categorize flow regimes: subsonic when Ma < 1, transonic near Ma ≈ 1, supersonic when Ma > 1, and often, though with varying definitions, hypersonic at Ma ≈ 5 or higher. These regimes influence wave formation, shock behavior, and drag, and they are fundamental to the design and analysis of aircraft, missiles, rockets, and wind tunnel experiments.

Historically, the concept is named after Ernst Mach, whose studies of shock waves and high-speed gas dynamics led to its adoption in aerodynamics. In English-language literature the term Mach number is standard, while some languages render it as Machnumero. See also Mach number, compressibility, sonic boom, and speed of sound.