Mach Number :-

• Mach number is an important quantity to compare the speed of any object with a speed of sound. It is a parameter to denote the speed of a flying object in air medium.
• Mach number is heavily studied to have a proper idea on the motion of aeroplanes and rockets.
• It is a dimensionless quantity expressing the ratio of the velocity of an object in a medium to speed of sound.
• The Mach number is represented with the symbol ‘M’.

$$Mach\ Number\ =\ \frac{Speed\ of\ Object}{Speed\ of\ sound}$$

$$M\ =\ \frac{v}{c}$$

Where, v= Speed of the object in a medium with respect to some boundary either internal or external.

And c =Speed of sound in the local medium.

Stagnation Density:-

• Stagnation Density is the Static Density at a stagnation point, At a stagnation point the fluid velocity is zero.
• Stagnation pressure can be calculated in a fluid (water) by using the static pressure formula which is equal to the density of the fluid (water) multiplied by the acceleration of gravity and the depth of the fluid.
• The stagnation properties at a point are defined as those which are to be obtained if the local flow were imagined to cease to zero velocity is entropically. As we will see in the later part of the text, stagnation values are useful reference conditions in a compressible flow.
• The thermodynamic state which would exist at a point in a fluid stream (stagnation point) if the flow at that point was brought is entropically to rest.

Stagnation Temperature :-

• The stagnation temperature is the temperature measured at the stagnation point, where the velocity is zero.
• The thermodynamic state which would exist at a point in a fluid stream (stagnation point) if the flow at that point was brought isentropically to rest.
• Air at a stagnation temperature of 22°C enters the impeller of a centrifugal compressor in the axial direction. The rotor, which has 17 radial vanes, rotates at 15,000 rev/min. The stagnation pressure ratio between diffuser outlet and impeller inlet is 4.2 and the overall efficiency (total-to-total) is 83%.