Module 2 Speed of Sound and Mach Number Flashcards
What is mach number?
The ratio of the airspeed v to the local speed of sound (a), indicates how close the air is to the speed of sound.
What is a mach line?
A common tangent line that can be drawn to represent the pressure wave front at any moment.
What represent μ in a mach cone?
The half apex angle
What happens when an object travels at the speed of sound?
Pressure waves propagate at the speed of sound sitting behind the object.
When does a shockwave form?
When the airflow becomes supersonic if there are compressive pressure disturbances.
Explain the wave front of a Normal shockwave?
The wave front is perpendicular to the direction of the relative airflow.
Explain the wave front of an oblique shockwave?
The wave front is not perpendicular to the direction of the relative airflow.
Explain the wave front of Bow shockwave?
A combination of the normal and oblique shockwave?
What occurs when a shockwaves propagates the air, and there are changes in the air property, in particular the pressure?
SONIC BOOOOOOOOMBACLAP
What is Mfs?
Free stream mach number, which is the ratio of the true airspeed (TAS) to the speed of sound in the free stream (afs)
What is Local Mach Number?
The ratio of a local airspeed (air particle speed) around an aircraft, to the local speed of sound.
What is the critical Mach number?
The free stream Mach number when a local mach number reaches 1, This marks the first local air particle speed becoming sonic.
During subsonic flight when Mfs < Mcrit, what happens to the airflow around the aircraft, and how can it be treated as?
The local airflow around the airflow is subsonic and is always less than the speed of sound. The airflow can be treated as incompressible, if the TAS of the a/c is below 250kts.
What happens around the aircraft when Mcrit < Mfs < 1.2?
The aircraft is in transonic flight.
The airflow around the aircraft can be sub sonic swell as supersonic, even if the Mfs is less than 1.
Air density is now compressible and shockwaves may be formed on aerofoils.
What happens to the aircraft when Mfs > 1.2?
The aircraft is in supersonic flight.
Airflow around the aircraft is supersonic, except behind the normal shockwave, and within the boundary layer.
Air is highly compressible and the kinetic heating is a significant concern due to the speed change of airflow around the supersonic aircraft.
