Finally, at speeds comparable to that of planetary atmospheric entry from orbit, in the range of several km/s, the speed of sound is now comparatively so slow that it is once again mathematically ignored in the Hypervelocity regime.Īs an object accelerates from subsonic toward supersonic speed in a gas, different types of wave phenomena occur. Above about Mach 5, these wave angles grow so small that a different mathematical approach is required, defining the Hypersonic speed regime. ![]() ![]() In the supersonic regime the flow is dominated by wave motion at oblique angles similar to the Mach angle. Thus the transonic regime is described by a different (and much more difficult) mathematical treatment. Once the speed of the flow approaches the speed of sound, however, the Mach number becomes all-important, and shock waves begin to appear. At very slow flow speeds the speed of sound is so much faster that it is mathematically ignored, and the Mach number is irrelevant. ![]() These flow regimes are not chosen arbitrarily, but rather arise naturally from the strong mathematical background that underlies compressible flow (see the cited reference textbooks).
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