Critical Mach number

The critical Mach number, two different sizes are called.

Critical Mach number in aviation

The critical Mach number Makrit is both a term used in aviation. It is to those flight Mach number at which for the first time locally sonic conditions occur at a specific location of the aircraft. Sonically represents the transition from subsonic to supersonic flow, ie, Mach number = 1 Since the flow velocity at the upper side of the airfoil is higher than the air speed, contact areas of the supersonic flow at usually at the top of the wing.

In simple words said, even if the aircraft itself with fewer flies than the speed of sound, flows can occur with speed of sound at certain points in the flow around the aircraft. This airspeed is expressed by the critical Mach number Makrit.

With increasing Mach number from the local sonic territory a supersonic range. This is completed with a straight shock wave. The straight shock wave is formed at the transition of the flow from supersonic to subsonic. Exceeding the critical Mach number and the associated emergence of a straight shock wave can lead to a separation of the boundary layer behind the shock wave, the so-called Shock Stall come ( Coffin Corner).

The critical Mach number Makrit depends on the angle of attack of the wing sweep and the profile thickness.

Critical Mach number, Lavalzahl

As the critical Mach number M *, a similarity measure is referred to, in which the flow velocity U relative to the critical speed of sound c *. This ratio is also referred to as Lavalzahl.

The velocity of sound is dependent on temperature. In an accelerated flow, the temperature decreases.

The Mach number Ma is the ratio of local flow velocity u of the local sound velocity c, which is determined by the local temperature T.

In contrast, the critical Mach number M * is the ratio of local flow velocity u of the speed of sound c * which is present where the flow velocity is equal to sonic speed. There exists a critical temperature T *, which is in a fixed ratio to total temperature Tt.

In this case, set the isentropic exponent and the specific gas constant dar.

• Aerodynamics