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FUNDAMENTAL PHYSICAL QUANTITIES OF AERODYNAMICS(FLOWING GAS)

Fundamental Physical Quantities of Aerodynamics (Flowing gas)

  • The flow of air over the surface of an airplane is the basic source of the lifting or sustaining force that allows a heavier then air machine to fly
  • the science that deals with the flow of air or gas is called aerodynamics 
  • four fundamental physical quantities in the language aerodynamics are pressure, density, temperature and velocity of flow

PRESSURE   'P'

  • Pressure is the normal force per unit area exerted on a surface due to the time rate of change of momentum of the gas molecules impacting on the surface
p=F(normal)/a
  • units of pressure  N/m2  , pascal , bar , atm , lb/ft2 
  • Some conversations      
 1 ft = 30.48 cm
1 kg =2,205 ponds (Lbm)
1 slug = 32.3 Lbm
1 mile = 1609.3 m = 1.609 km

DENSITY  "ρ "

  •   the density of the substance is the mass of the substance per unit volume
  • units of density    Kg/m3 ,  slug/ft3   

TEMPERATURE

  • temperature is measure of coldness (or) hotness of a body
(or)
  • temperature is a measure of average kinetic energy of the particles in the gas/air
mean molecular kinetic energy is given as
where          k = boltzman constant
                       =1.38 X 10-23   j/k   
                    T = temperature


SCALES AND UNITS


  • different scales are used to determine temperature main of them are given below
SCALES
UNITS
LOWER LIMIT
UPPER LIMIT
NUMBER OF DIVISONS
celsius
oC
0
100
100
kelvin
K
273.15
373.15
100
fahrenheit
oF
32
212
180
rankine
OR
492
672
180


Relationship Between The Scale Reading Of Temperature

FLOW VELOCITY 'v'

  • the velocity at any fixed point in a flowing gas is the velocity of an infinitesimally small fluid element  as it sweeps through that point 
  • velocity is a vector quantity because it has both magnitude and direction
  • velocity is a point property and varies from point to point in flow

note 

streamlines

  • the path taken by a moving fluid element is called a streamline of the flow
  • streamlines are imaginary lines used to visualize the motion of the gas


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