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
|
|
rankine
|
OR
|
492
|
672
|
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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