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The drag-divergence Mach number (not to be confused with critical Mach number) is the Mach number at which the aerodynamic drag on an airfoil or airframe begins to increase rapidly as the Mach number continues to increase. [1] This increase can cause the drag coefficient to rise to more than ten times its low-speed value.
Mach number in transonic airflow around an airfoil; M < 1 (a) and M > 1 (b). When an aircraft exceeds Mach 1 (i.e. the sound barrier ), a large pressure difference is created just in front of the aircraft .
Supercritical airfoils feature four main benefits: they have a higher drag-divergence Mach number, [21] they develop shock waves farther aft than traditional airfoils, [22] they greatly reduce shock-induced boundary layer separation, and their geometry allows more efficient wing design (e.g., a thicker wing and/or reduced wing sweep, each of which may allow a lighter wing).
Transonic flow patterns on an aircraft wing, showing the effects at and above the critical Mach number. In aerodynamics, the critical Mach number (Mcr or M*) of an aircraft is the lowest Mach number at which the airflow over some point of the aircraft reaches the speed of sound, but does not exceed it. [1]
Transonic (or transsonic) flow is air flowing around an object at a speed that generates regions of both subsonic and supersonic airflow around that object. [1] The exact range of speeds depends on the object's critical Mach number, but transonic flow is seen at flight speeds close to the speed of sound (343 m/s at sea level), typically between Mach 0.8 and 1.2.
This assumption is commonly made in engineering practice when the Mach number is less than about 0.3. C p {\displaystyle C_{p}} of zero indicates the pressure is the same as the freestream pressure. C p {\displaystyle C_{p}} of one corresponds to the stagnation pressure and indicates a stagnation point .
Drag curve for the NACA 63 3 618 airfoil, colour-coded as opposite plot. The significant aerodynamic properties of aircraft wings are summarised by two dimensionless quantities, the lift and drag coefficients C L and C D. Like other such aerodynamic quantities, they are functions only of the angle of attack α, the Reynolds number R e and the ...
Therefore, the Drag coefficient on a supersonic airfoil is described by the following expression: C D = C D,friction + C D,thickness + C D,lift. Experimental data allow us to reduce this expression to: C D = C D,O + KC L 2 Where C DO is the sum of C (D,friction) and C D,thickness, and k for supersonic flow is a function of the Mach number. [3]