Fluid Mechanics in

Aeronautics and Astronautics

Marc WilliamsSchool of Aeronautics and

Astronautics

Aeronautics = Airplanes

Astronautics = Spacecraft

Parts of Aero & AstroAerodynamics

Design Dynamics & Control Structures

Propulsion

Three forces from fluids

• LIFT - Force perpendicular to flight directionThe Air pushes the airplane “up”

• DRAG - Force opposite the flight directionThe Air pushes the airplane “back”

• THRUST - Force in the flight directionInternal pressure inside the engine pushes the

aircraft/rocket forward

LIFT

Newton say :

The air pushes the airplane up

So

The airplane pushes the air down

Cessna Citation

Boeing 777

Boeing 757

DRAG

•The air sticks to the airplane, pushing it back (Viscosity== Friction drag)

•The airplane imparts kinetic energy to the air behind it…. This energy comes from the engines, And shows up as a drag(Induced Drag, or Drag due to Lift)

Flight Regimes – A Vocabulary

00 1.0 2.0 3.0 6.0

Mach Number – M

Altitude(1000 ft.)

100

80

60

40

20

Subsonic Supersonic Hypersonic

Structural Limit(Dynamic pressure and heating) Aerodynamic

Limit

Transonic

V = flight speed

a = speed of sound

M = V / a

Wing Loading (N/m2)

All the Worlds Flyers

• Flyers meeting MAV requirements abound in nature

• Flyers with most remarkable performance leverage unsteady aerodynamics

• Flapping provides access to game-changing aerodynamic mechanisms for meeting MAV requirements

Conventional Aircraft(Steady)

Large Birds(Quasi-steady)Small Birds

(Transition)

Insects/Hummingbirds(Unsteady)

Cruising Speed (m/s)

Wei

ght (

N)

Micro Air Vehicles (MAVs)

• Unmanned aerial systems becoming for missions too dull, dirty, dangerous, or difficult for pilots– Persistent ISR– Chemical/biological sensing– “Over the hill”/“Around the

corner” scouting• Operation space is changing

– Urban canyons– Building interiors– Subterranean caverns/bunkers

• MAVs are new class of vehicle to fill new operational roles

Images from wikipedia.org, defense-update.com, delta.tudelft.nl

DYNAMICS AND CONTROL

http://www.grc.nasa.gov/WWW/K-12/airplane/alr.html

Mach Number Effects

•Mach Number = Speed / Speed of Sound

Speed of Sound = 340 m/s = 770 mph

•Mach squared = Kinetic Energy / Thermal Energy

An F/A-18 Hornet at transonic speed

F4 phantom ii breaking the sound barrier

Mars Exploration Rover (MER) aeroshell, artistic rendition

Thrust

• Thrust is produced by throwing something opposite to the direction you want to go (Newton again)

You can throw airYou can throw hot exhaust gases

You can throw rocks… but fluids are easier to work with

Air Thrower

http://www.youtube.com/watch?v=nSQzvimD3cc

Turbofan Engine

This throws air and hot exhaust gases

Turbofan Flowpath

Tomahawk Cruise Missile

Mi-24 Hind Military Aviation Helicopter

Air Thrower

Joint Strike Fighter- Marine Version

Lift Fan

Another Air Thrower

OSPREY- Tilt Rotor

And another… but you get to change the throw direction

Rockets – Pure Hot Gas Throwers

How a Rocket Produces Thrust

ROCKETS

BIG (SSME)

A micro-thruster array measuring one-quarter the size of a penny, designed by a TRW-led team for use on micro-, nano- and pico-satellites, has successfully demonstrated its functionality in a live fire test aboard a Scorpius sub-orbital sounding rocket. Individual micro-electromechanical system (MEMS) thrusters, each a poppy seed-sized cell fueled with lead styphnate propellant, fired more than 20 times at 1-second Intervals during the test staged at the White Sands Missile Range. Each thruster delivered 10(-4) Newton seconds of impulse.

ROCKETS: SMALL

SidewinderAir to Air supersonic missile

THE END

Have a great summer

Dynamic Stall on an Airfoil

Boeing 757

Vortex break-up on a delta wing at high incidence