What is a critical Mach number?

Mach number at which wake formation does not exist

Mach number at which sonic flow is achieved on the surface

Mach number at which the coefficient of lift is minimum

Mach number at which transonic flow is achieved on the surface

Correct Answer : Mach number at which sonic flow is achieved on the surface

Explanation : When freestream air flows over an airfoil at suppose Mach number = 0.3, there’s a point on the top surface of the airfoil where the pressure is minimum and the Mach number is maximum such as 0.43. When this freestream velocity is increased, there’s a certain Mach number for which sonic flow is achieved at the top surface. This is known as the critical Mach number.

Recently Updated in Aerodynamics Questions

What happens to the coefficient of pressure in a supersonic flow for an increase in Mach number?

Increases

Decreases

Remains unaffected

First increases then decreases

Correct Answer : Option (B) : Decreases

Explanation : For linearized supersonic flow, the coefficient of pressure is inversely proportional to

Thus, when the Mach number increases, the coefficient of pressure decreases. This in contrast to the trend followed by the subsonic flow where an increasing Mach number results in decreasing coefficient of pressure.

What is the source of wave drag exerted on the supersonic airfoil?

Skin friction

Trailing vortex

Shock waves

Viscous boundary layer

Correct Answer : Option (C) : Shock waves

Explanation : Wave drag is a result of pressure distribution which is exerted over the airfoil. This is a consequence of formation of shock waves and expansion wave pattern due to the presence of supersonic flow.

What is the lift coefficient over a flat plate at an angle of attack of 3 degrees in a supersonic flow at Mach 4?

0.0512

0.0541

0.0628

0.0714

Correct Answer : Option (B) : 0.0541

Explanation :