Download AE 2350 Lecture Notes #5

yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

Drag (physics) wikipedia, lookup

Fluid dynamics wikipedia, lookup

Lattice Boltzmann methods wikipedia, lookup

Computational fluid dynamics wikipedia, lookup

Flow conditioning wikipedia, lookup

Turbulence wikipedia, lookup

Reynolds number wikipedia, lookup

Aerodynamics wikipedia, lookup

Compressible flow wikipedia, lookup

Derivation of the Navier–Stokes equations wikipedia, lookup

Rheology wikipedia, lookup

Navier–Stokes equations wikipedia, lookup

Bernoulli's principle wikipedia, lookup

Hydraulic machinery wikipedia, lookup

Airy wave theory wikipedia, lookup

Lift (force) wikipedia, lookup

Flow measurement wikipedia, lookup

Wind-turbine aerodynamics wikipedia, lookup

Boundary layer wikipedia, lookup

Stokes wave wikipedia, lookup

Cyclorotor wikipedia, lookup

AE 1350
Lecture Notes #5
• Why should we study properties of
• Ideal Gas Law: p = rRT
• Variation of Temperature with Altitude
• Variation of Pressure with Altitude
• Variation of Density with Altitude
• Tables of Standard Atmosphere
• Incompressible flow
• Streamlines and stream tubes
• Conservation of Mass (Continuity)
Incompressible Flow
• Air is a compressible fluid.
• Its density WILL change if temperature changes,
or if some external force is applied.
– Example: A child squeezing a balloon
• A flow is said to be incompressible if there are no
changes in density attributable to (or caused by)
the velocity or speed of the flow.
• Theory and observations in wind tunnels suggest
that most flows may be treated as incompressible
(I.e. constant density) until the Mach number is
sufficiently high (>0.4 or so.)
What has flow speed got to do with
Fluid particles send out signals in the form of acoustic
waves to the surrounding fluid, indicating their motion.
If there is sufficient time for the sound waves to travel before the
fluid particle arrives, the fluid particles downstream will “hear”
the message and clear out.
Otherwise, there will be a crush (compression), or even a stampede
(shock wave).
Shocks form when the acoustic waves
generated by the air particles
in front of the body
can not outrun the body.
Streamlines in Steady Flow
Inviscid (ideal) flow
Viscous flow
•Streamlines describe the path the
fluid particles will take.
•At any point on the streamline,
the flow velocity is tangential to
the streamline.
•Viscosity alters the shape of streamlines
around bluff bodies.
•Scientists inject smoke particles into
streamlines to make them visible to
the naked eye.
Streamlines over a Cylinder
(Low Reynolds Number of 10)
Reynolds Number 
where D  Cylinder dia.
Streamlines over a Cylinder
(High Reynolds Number of 2000)
Reynolds Number 
where D  Cylinder dia.
Streamlines over an Airfoil
High Angles of Attack
• Consider a stream tube, i.e. a collection of
streamlines that form a tube-like shape.
• Within this tube mass can not be created or
• The mass that enters the stream tube from the left
(e.g. at the rate of 1 kg/sec) must leave on the right
at the same rate (1 kg/sec).
Rate at which mass enters=r1A1V1
Area A1
Density r1
Velocity V1
Rate at which mass leaves=r2A2V2
Area A2
Density r2
Velocity V2
In compressible flow through a “tube”
rAV= constant
In incompressible flow, r does not change. Thus,
AV = constant
Continuity (Continued..)
AV = constant
If Area between streamlines
is high, the velocity is low
and vice versa.
Low Velocity
High Velocity
Continuity (Continued..)
High Velocity
AV = constant
If Area between streamlines
is high, the velocity is low
and vice versa.
In regions where the
streamlines squeeze together,
velocity is high.
Low Velocity
Venturi Tube is a Device
Measuring Flow Rate
we will study later.
Low velocity
High velocity