AAE 3710
Fundamentals of Aerodynamics
Lecture 14 Compressible FLow
03/15/2006
Thermodynamics reviews
By definition
Sound traveling at different Mach numbers
The point source stationary emits sound
Waves at different times
incompressible
Symmetric wave pattern occupies the whole
field symmetrically and unrestricted
The point source moving at a constant speed V (<c)
emits sound waves at different times
compressible, subsonic
Asymmetric wave pattern occupies the whole
field unrestricted
Sound traveling at different Mach numbers
The point source moving at speed of sound (V=c)
emits sound waves at different times
compressible, sonic
Communication of pressure info is restricted to the
Region of flow dowstream of the Machwave
Pressure
concentration
The point source moving at speed of sound (V=c)
emits sound waves at different times
compressible, sonic
Communication of pressure info is restricted to the
region of flow within the Machcone
>1
It can be shown that the total enthalpy is constant along
a steamline. If all the streamlines originate from a
common uniform freestream, then h0 is the same for each
streamline. h0=constant valid throughout the entire flow
for steady, adiabatic flow.
Detailed derivation see
attached handout
The definition of stagnation
is conceptual. We can slow
down the fluid element down
to zero velocity isentropically
anywhere in any flow field
If the general flow field is
Isentropic throughout, then
Both p0 and rho0 are constant
Throughout the flow
Assume isentropic throughout.
Effect of variations in flow cross-sectional area
For subsonic flows (Ma<1), density and area changes
are in the same direction;
For supersonic flows (Ma>1), density and area changes
are in the opposite direction
If Ma = 1, dA/dV = 0
Throat area
The area associated with Ma=1 is either
a minimum or a maximum amount