Question

Critical Mach number of the airfoil is

• A. Free stream Mach number
• B. Local Mach number over the airfoil
• C. Mach number at trailing edge
• D. Mach number at the leading edge

Hint:

Definitions of Mach numbers: \[ \boxed{ \begin{aligned} M_\infty &\rightarrow \text{Free-stream Mach number} M_{cr} &\rightarrow \text{Free-stream Mach number at first local sonic point} \end{aligned} } \] At \(M=M_{cr}\), the local Mach number on the airfoil first becomes \[ \boxed{1.} \]

Answer 1

The Correct Option is A

Step 1: Recall the definition of Critical Mach Number. The Critical Mach Number (\(M_{cr}\)) is defined as the \[ \boxed{\text{free-stream Mach number}} \] at which the local airflow over some point on the airfoil first reaches Mach 1.

Step 2: Identify the correct statement. Thus, \[ \boxed{ M_{cr} = \text{Free-stream Mach number when the first sonic point appears.} } \] Therefore, \[ \boxed{\text{Free stream Mach number}} \] is the correct answer. Thus, \[ \boxed{(A)} \] is the correct answer.