Supersonic Flight
Diana Mann
Feb 19, 2008
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Agenda
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Review Of Speed Regimes
Problems At High Speeds
Supersonic Engines
Special Materials
Aerodynamics
Special Shapes
Bonus Section – Hypersonic X-Plane
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Review of Speed Regimes (1 of 4)
Velocity, Force, and Temperature Increase
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Graphic courtesy of NASA Glenn Research Center
Review of Speed Regimes (2 of 4)
Low Subsonic
V < 250 mph
High Subsonic
V < 600 mph
General Aviation – Commuter
Airliners
Propeller Propulsion
Aluminum Skin
Straight Wings
Turbofan Engines
Aluminum Skin
Swept Wings
Graphics courtesy of NASA Glenn Research Center
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Review of Speed Regimes (3 of 4)
Low Supersonic
V < 1500 mph
High Supersonic
V < 2500 mph
Fighter Planes
Spy Planes
Afterburner Engines
Aluminum Skin
Swept Wings
Ramjet Engines
Titanium Skin
Small Wings
Graphics courtesy of NASA Glenn Research Center
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Review of Speed Regimes (4 of 4)
Low Hypersonic
V < 6000 mph
High Hypersonic
V < 17,500 mph
X - Planes
Space Shuttle
Scramjet or Rocket Engine
Cooled Titanium – Nickel Skin
Short Wings
Rocket Engines
Thermal Protection System
Short Blunt Wings
Graphics courtesy of NASA Glenn Research Center
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Operational Envelopes
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http://www.aircraftenginedesign.com/custom.html4.html
Problems at High Speeds
• Large Forces
– Forces increase as the square of velocity
• Need Bigger Engines
• Need Stronger Airframe
• Need Special Shapes
• High Temperatures
– Friction heating increases with velocity
• Need Special Materials
• Need Active Cooling
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Slide courtesy of NASA Glenn Research Center
Supersonic Engines
• Propeller Propulsion
• Turbofan Engines
• Ramjet Engines
As engines become
more powerful,
Thrust Increases
• Scramjet Engines
• Rocket Engines
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General Thrust Equation
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Graphic courtesy of NASA Glenn Research Center
Excess Thrust
(Thrust – Drag)
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Graphic courtesy of NASA Glenn Research Center
Ramjet Engines
• No moving parts
• Speed of the jet "rams" or forces air into the
engine
• The ramjet develops no static thrust and very
little thrust in general below the speed of sound
• Ramjet vehicles require some form of assisted
takeoff, such as another aircraft or booster
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http://www.ueet.nasa.gov/Engines101.html#types
Scramjet Engines
• Ramjets with supersonic combustion are known
as SCRAMJET (supersonic combustion ramjet)
engines
– Air-breathing engine in which the airflow through the
engine remains supersonic
• Another engine system is required to accelerate
the aircraft to ramjet velocities
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http://en.wikipedia.org/wiki/Scramjet
Rocket Engines
• Rocket engines are
reaction engines
– The basic principle driving
a rocket engine is Newton’s
3rd Law:
• “To every action there is
an equal and opposite
reaction"
– A rocket engine ejects
mass in one direction and
benefits from the reaction
that occurs in the other
direction as a result
http://science.howstuffworks.com/rocket.htm
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Special Materials
• Address larger forces
and increased
temperature at high
velocity
– Aluminum Skin
– Titanium Skin
– Cooled Titanium /
Nickel Skin
– Thermal Protection
System (TPS)
• Melting Points
– Al: 220 °F (660 °C)
– Ti: 3263 °F (1795 °C)
– TPS (Silicon): 2588 °F
(1420 °C)
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Space Shuttle Thermal Protection
System – Ceramic Tiles
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http://en.wikipedia.org/wiki/Space_Shuttle_thermal_protection_system
Aerodynamics
• A branch of dynamics
concerned with
studying the motion
of air, particularly
when it interacts with
a moving object
Designers match airframe and
propulsion system capabilities
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http://en.wikipedia.org/wiki/Aerodynamics
Aerodynamics Is Really
Fluid Dynamics
• When an object passes
through the air, it creates
a series of pressure
waves
– These waves travel at the
speed of sound
• As aircraft speed
increases, the waves
compress and merge into
a single shock wave
moving at the speed of
sound
– Speed of Sound 761 mph
(~1,225 kph) at sea level
– A.k.a. Mach 1
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http://en.wikipedia.org/wiki/Sonic_boom
Speed of Sound
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Graphic courtesy of NASA Glenn Research Center
Laminar Flow
• Laminar flow occurs when a fluid flows in parallel layers,
with no disruption between the layers
• It is the opposite of turbulent
• In nonscientific terms laminar flow is "smooth," while
turbulent flow is "rough"
Graphic courtesy of NASA Glenn Research Center
Text courtesy of http://en.wikipedia.org/wiki/Laminar_flow
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Shock Waves (1 of 3)
• The speed at which some
portion of the airflow over the
wing first equals Mach 1.0 is
termed the Critical Mach
Number
– This is also the speed at
which a shock wave first
appears on the airplane
• A shock wave is formed
where the airflow suddenly
returns to subsonic flow
• Shock wave becomes more
severe and moves aft on the
wing as speed of the wing is
increased
• Eventually flow separation
occurs behind the welldeveloped shock wave
Cross Section of a wing
http://en.wikipedia.org/wiki/Shock_wave
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Shock Waves (2 of 3)
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Shock Waves (3 of 3)
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Normal Shock Waves
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Graphic courtesy of NASA Glenn Research Center
Oblique Shock Waves
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Graphic courtesy of NASA Glenn Research Center
Crossed Shock Waves
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Graphic courtesy of NASA Glenn Research Center
Shock Wave Imaged at Mach 7
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Schlieren Photography
•
Schlieren photography is a visual
process used to photograph the
flow of fluids of varying densities
– Used to visualize airflow over an
aircraft traveling at supersonic
speeds
– Maps the variations of density in
fluids
• Since shock waves are regions of
higher pressure than normal air
pressure, their density is greater
than that of normal air pressure
• Pressure differential created by
the shock waves allows the shape
of the shock waves to be imaged
– Invented by the German physicist
August Toepler in 1864 to study
supersonic motion
•
Its role is changing due to the
increasing use of computational
fluid dynamics, where the same
principle is used to display the
computed results as flow images
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Computational Fluid Dynamics
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Computational fluid dynamics (CFD) is
one of the branches of fluid mechanics
that uses numerical methods and
algorithms to solve and analyze
problems involving fluid flow
During preprocessing
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The geometry (physical bounds) of the
problem is defined
The volume occupied by the fluid is
divided into discrete cells (the mesh)
•
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The physical model is defined
•
–
•
•
equations of motions + enthalpy +
radiation + species conservation
Boundary conditions are defined
•
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The mesh may be uniform or non
uniform
Specifies fluid behavior and properties
at the boundaries of the problem
For transient problems, the initial
conditions are also defined
The simulation is started and the
equations are solved iteratively as a
steady-state or transient
Finally a postprocessor is used for the
analysis and visualization of the
resulting solution
A computer simulation of high velocity air flow
around the Space Shuttle during re-entry.
http://en.wikipedia.org/wiki/Computational_fluid_dynamics
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Vapor Cones
• The condensation “cloud” marks the approximate location of the
shock wave
• It’s called the Prandtl-Glauert singularity
– The point at which a sudden drop in air pressure occur
– Generally accepted as the cause of the visible condensation cloud that
often surrounds an aircraft traveling at transonic speeds
http://en.wikipedia.org/wiki/Prandtl-Glauert_singularity
http://en.wikipedia.org/wiki/Image:FA-18_Hornet_breaking_sound_barrier_%287_July_1999%29.jpg
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Special Shapes (1 of 2)
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http://airwarrior.afkamm.co.uk/Aerodynamics/aero5.shtml
Special Shapes (2 of 2)
• NASA believes that aircraft of the
future can mimic the flight of birds,
flying more efficiently and safely
• This video shows what NASA has
observed in the flight of an eagle that
can be translated into a concept for a
future aircraft
• For example, just as a bird uses
different feathers on its wings to control
flight, aircraft wing shapes can be
designed to change and adapt to
constantly changing conditions of flight
• Or, an aircraft can mimic the way a bird
lands, greatly decreasing the amount
of fuel and runway space required
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http://www.hq.nasa.gov/office/aero/videos/eagle_morph.htm
Bonus Section – Hypersonic X-Plane
(1 of 4)
• The X-43A was a
small experimental
research aircraft
designed to flightdemonstrate the
technology of
airframe-integrated
scramjet propulsion
at hypersonic
speeds above
Mach 5
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http://www.nasa.gov/centers/dryden/history/pastprojects/HyperX/index.html
Bonus Section – Hypersonic X-Plane
(2 of 4)
• On June 2, 2001, the X-43A
"stack" -- a modified Orbital
Sciences Corporation’s
Pegasus XL booster topped
with the Hyper-X research
vehicle -- was released from a
B-52 carrier aircraft
• Booster ignition went as
planned, with the aircraft
accelerating on its
predetermined high-altitude
ascent
• Seconds later, however,
booster fins broke off and the
aircraft spun out of control
• The vehicle was then
destroyed by range control
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http://www.space.com/businesstechnology/technology/x43a_report_030718.html
Bonus Section – Hypersonic X-Plane
(3 of 4)
• NASA convened the X-43A
Mishap Investigation Board
(MIB) to look into the failure on
June 5, 2001 at NASA’s
Dryden Flight Research Center
at Edwards, CA
– Because of the increased
thermal loads predicted for the
flight trajectory, changes were
made in thermal protection to
the Hyper-X launch vehicle
wing, fins and body
• Additional thermal protection
was not taken into account in
preflight wind tunnel test
modeling
• Computer and wind tunnel
tests to help understand what
caused the failure showed the
new thermal protection
altered the booster’s
aerodynamic characteristics
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http://www.space.com/businesstechnology/technology/x43a_report_030718.html
Bonus Section – Hypersonic X-Plane
(4 of 4)
•
Enter the X-51
– The Air Force Research
Laboratory’s X-51 ScramjetWaverider is being built by Pratt &
Whitney and Boeing
– This scramjet demonstrator is to
fly by 2009 at target speeds close
to Mach 7 (around 8,050 km/h)
• Ground tests of the X-51A began
in late 2006
– For the flight demonstrations, a B52 will carry the vehicle to an
altitude of about 35,000 feet and
then release it.
– Initially propelled by an Army
Tactical Missile System (ATACMS)
solid rocket booster, the scramjet
will take over at approximately
Mach 4.5, and the vehicle will
accelerate to a flight speed near
Mach 7
412th TW tests X-51 antennas
An X-51 Scramjet-Waverider mock-up hangs inside the
Benefield Anechoic Facility here during the vehicle's
antenna testing. The 412th Test Wing Hypersonic Flight
Test Team, Electronic Warfare and Boeing began the
month-long testing Jan. 28. (Air Force photo by Mike
Cassidy)
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http://www.edwards.af.mil/news/story.asp?id=123084673
Selected Links
•
•
•
•
http://www.ueet.nasa.gov/Engines101.html
http://wings.avkids.com/Book/advanced.html
http://travel.howstuffworks.com/turbine6.htm
http://www.aircraftenginedesign.com/custom.htm
l4.html
• http://en.wikipedia.org/wiki/Aerodynamics#Super
sonic_aerodynamics
• http://www.wilk4.com/misc/soundbreak.htm
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EngineSim Exercises
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EngineSim Exercises (1 of 4)
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Set the following conditions in
EngineSim:
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Design Mode
English Units
Turbojet
Output: Graphs
Input Speed + Altitude
Set the Airspeed to 0 mph, the
Altitude 0 ft, and the Throttle 100.
– Record Net Thrust ___________
– Record Fuel Flow ____________
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•
What happens when you choose a
different engine?
– Choose a jet with afterburner
• Record Net Thrust ___________
• Record Fuel Flow ____________
– Choose a turbofan engine
• Record Net Thrust ___________
• Record Fuel Flow ____________
– Choose a ramjet engine
• Record Net Thrust ___________
• Record Fuel Flow ____________
Now change the Airspeed to 350,
and the Altitude to 10,000 ft.
– Record Net Thrust ___________
– Record Fuel Flow ____________
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EngineSim Exercises (2 of 4)
• What can you conclude about the effect of
an increase in altitude and airspeed on
thrust?
__________________________________
• On fuel flow?_______________________
• Which engine is most fuel efficient?
_______________________________
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EngineSim Exercises (3 of 4)
•
What happens when you increase speed?
– Select Turbojet, and set Airspeed to 1500 mph (Low Supersonic)
• Record Net Thrust ________
• Record Fuel Flow _________
– Select Afterburner, and set Airspeed to 1500 mph (Low Supersonic)
• Record Net Thrust ________
• Record Fuel Flow _________
– Select Turbofan, and Set Airspeed to 1500 mph (Low Supersonic)
• Record Net Thrust ________
• Record Fuel Flow _________
– Select Ramjet, and Set Airspeed to 1500 mph (Low Supersonic)
• Record Net Thrust ________
• Record Fuel Flow _________
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EngineSim Exercises (4 of 4)
• Examine the graph on the right. Where is
the pressure greatest for each engine?
_________________________________
• Bonus Question:
– How are pressure and temperature
related?____________________________
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