Fluid Mechanics
(18AS33): Video Lectures
Prof. Ashish Kumar Gupta
1
,Fluid Mechanics
Flow over aircrafts, engines, nacelles, rockets/ missiles, launch vehicles,
locomotive engines/ trains, cars, ships, bridges and buildings are being studied
today with the help of CFD which a solution method for fluid flow and can be
considered as outgrowth of fluid mechanics.
Definition of fluid
Fluid is a substance that undergoes continuous deformation under the application of
shear stress, however small it may be.
States of matter- Solids Liquids Gases Plasma
Intermolecular distances are small hence large force
of attraction- only vibrations degree of freedom.
Intermolecular distances are relative more and intermolecular forces are small compared
to solids, hence they are free to move about.
Intermolecular distances are much larger and intermolecular forces are very small or
negligible, hence they are free to move about anywhere. 2
,Fluid Mechanics
Aerodynamics is study of fluid mechanics limited to aircrafts, missiles launch vehicles
and ground vehicles applications and their movement through surrounding air. In other
words, aerodynamics is subset of fluid mechanics.
3
, Continuum Concept
10-9 mm3 is sufficiently small volume, and hence the density of fluid at STP can be
considered as point function, which means they can be defined at every point in the
domain. This argument can be extended to other fluid properties such as pressure,
temperature and velocity etc. This is more true since the dimensions of objects are much
larger than the mean free path, λ.
Thus the important fluid parameter which decide whether fluid behavior is continuum or not
is mean free path λ. It is defined as average of the distances of collision travelled by a
molecule in small time. At sea level λ=6.25x10-8 m. AT 96 km, λ= 0.1 m and at 160 km.
λ=50 m. Thus we can say that continuum concept is valid up to 50 km. altitude. Flow is
continuum flow if Kn<0.01. Knudsen number is defined as kn= λ/L, where L is body
4
dimension.
(18AS33): Video Lectures
Prof. Ashish Kumar Gupta
1
,Fluid Mechanics
Flow over aircrafts, engines, nacelles, rockets/ missiles, launch vehicles,
locomotive engines/ trains, cars, ships, bridges and buildings are being studied
today with the help of CFD which a solution method for fluid flow and can be
considered as outgrowth of fluid mechanics.
Definition of fluid
Fluid is a substance that undergoes continuous deformation under the application of
shear stress, however small it may be.
States of matter- Solids Liquids Gases Plasma
Intermolecular distances are small hence large force
of attraction- only vibrations degree of freedom.
Intermolecular distances are relative more and intermolecular forces are small compared
to solids, hence they are free to move about.
Intermolecular distances are much larger and intermolecular forces are very small or
negligible, hence they are free to move about anywhere. 2
,Fluid Mechanics
Aerodynamics is study of fluid mechanics limited to aircrafts, missiles launch vehicles
and ground vehicles applications and their movement through surrounding air. In other
words, aerodynamics is subset of fluid mechanics.
3
, Continuum Concept
10-9 mm3 is sufficiently small volume, and hence the density of fluid at STP can be
considered as point function, which means they can be defined at every point in the
domain. This argument can be extended to other fluid properties such as pressure,
temperature and velocity etc. This is more true since the dimensions of objects are much
larger than the mean free path, λ.
Thus the important fluid parameter which decide whether fluid behavior is continuum or not
is mean free path λ. It is defined as average of the distances of collision travelled by a
molecule in small time. At sea level λ=6.25x10-8 m. AT 96 km, λ= 0.1 m and at 160 km.
λ=50 m. Thus we can say that continuum concept is valid up to 50 km. altitude. Flow is
continuum flow if Kn<0.01. Knudsen number is defined as kn= λ/L, where L is body
4
dimension.
