Gale force for coastal areas, between and . The definition is very non-standard. A common alternative definition of the maximum is . The most common way of measuring wind force is with the Beaufort scale which defines a gale as wind from to . It is an empirical measure for describing wind speed based mainly on observed sea conditions. On the original 1810 Beaufort wind force scale, there were four different "gale" designations whereas generally today there are two gale forces, 8 and 9, and a near gale 7: The word "gale" is derived from the older "gail", but its origin
Subsonic and transonic wind tunnel interactions occur (such as shock waves or boundary layer interaction) both Mach and Reynolds number are important and must be properly simulated. Large-scale facilities and/or pressurized or cryogenic wind tunnels are used. With a sonic throat, the flow can be accelerated or slowed down. This follows from the 1D area–velocity equation. If an acceleration to supersonic flow is required, a convergent-divergent nozzle is required. Otherwise: Conclusion: The Mach number is controlled by the expansion ratio formula_11 Subsonic and transonic wind tunnel Low-speed wind tunnels are used for operations at very low Mach number, with speeds in the test section up