mach number by suman

8/7/2019 mach number by suman

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MACH NUMBER

Presented by

SUMAN


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Definition

Mach number (Ma orM) is the speed of an objectmoving through air, or any other fluid substance,divided by the speed of sound as it is in thatsubstance.

where

M is the Mach number V is the relative velocity of the source to the

medium and

a is the speed of sound in the medium


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HISTORY BEHIND THE TERM MACH

The term is named in honor of Ernst Mach, aAustrian scientist .

Mach was actually the first person in history to

develop a method for visualizing the flowpassing over an object at supersonic speeds.

He was also the first to understand the

fundamental principles that govern supersonic

flow and their impact on aerodynamics.


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Ernst Mach


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Mach published the very first photograph ofthe shock waves formed by a bullet traveling

faster than the speed of sound.

The photo shown , illustrates the strong shock

wave formed by the nose of the bullet, theweaker shock wave created at the at end ofthe bullet.

Also visible in the photo are two vertical linesmade by the trip wires that triggered thecamera as the projectile passed by.


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Ernst Mach's photo of a bullet in

supersonic flight


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How a shadowgraph works

Light is passed through an airflow and

reflected onto a screen or film plate.

Since shock waves create changes in the

temperature and density of the airflow, thelight waves are bent, or refracted, as they pass

through the shock waves.

These refracted light patterns createshadows that can be seen on the screen.


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How a shadowgraph works


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Basic Definitions

Speed of sound: It defines the velocity at

which sound waves travel through a

substance, such as air.

subsonic: A vehicle that is traveling slower

than the speed of sound (M1) is said to beflying at supersonic speeds.


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Speed ofSound

The speed of sound, also known as Mach 1,

changes throughout the atmosphere based on

the temperature at any given altitude.

1,116.4 ft/s

340.3 m/s

761.2 mph 1,225.1 km/h

661.5 knots


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Speed of sound varies?

the speed of sound through the standardatmosphere is 761.2 mph (1,223 km/h) at sea

level, Mach 2 then follows as 1,522 mph

(2,447 km/h).

At an altitude of 30,000 Ft (9,150 m) it is only

1,356 mph (2,180 km/h) ,because the speed

of sound generally decreases as altitude

increases.

a is the speed of sound


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Significance of MachNumber

Vehicle traveling at a given Mach number willexperience similar aerodynamic properties,

regardless of its altitude or dimensional

airspeed.

In addition, similarity parameters make it

possible to measure the aerodynamic

properties of a subscale model in a wind

tunnel rather than having to test a full scale

vehicle in free flight.


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Shock wave

When an aircraft exceeds Mach 1 a largepressure difference is created just in front of

the aircraft. This abrupt pressure difference,

called a shock wave, spreads backward and

outward from the aircraft in a cone shape (a

so-called Mach cone).

The higher the speed, the more narrow the

cone; at just overM=1 it is hardly a cone at all,but closer to a slightly concave plane.


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Calculating Mach number

An aircraft Machmeter or electronic flightinformation system (EFIS) can display Mach

number derived from stagnation pressure

(pitot tube) and static pressure.


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