PowerPoint Presentation
ENME 489F
Fundamentals of
Atmospheric Flight
Dr. Dave Findlay
XXXXXXXXXX
mailto: XXXXXXXXXX
Course Goals…
• Basic knowledge & capability required to address the solution of
aerodynamic analysis associated with aircraft flight – considering low
to high (supersonic) speeds
• An understanding of first principles of flow physics involved in
atmospheric flight in the range of 0
• Mathematical formulation development as the classical theory of
airfoil/wing/vehicle aerodynamics
• Exposure to past, present, ~future~ state-of-the-art methods
employed by applied aerodynamicist (including an appreciation for
the inherent limitations of the techniques)
Course Content / Main Topics
• How Do Things Fly?
• Fundamentals of Fluid Dynamics
• Subsonic (Incompressible Aero)
• Compressibility
• Supersonic Aero
• Transonic Aero
Key Items of Interest
• First of two semester series toward introduction to fundamentals
of Air Vehicle Aeromechanics
• Prerequisite:
• Fluid Mechanics
• Differential Equations
• Thermodynamics (strongly recommended)
• Matla
• Numerical Methods (recommended)
• Required Textbook: Fundamentals of Aerodynamics, by J.D.
Anderson
• Recommended Textbook: Theory of Wing Sections: Including a
Summary of Airfoil Data, by A
ot& vonDoenhoff
Expected Student Learning Outcomes of
Course…
• an ability to apply knowledge of mathematics, science, and
engineering
• an ability to communicate effectively
• (k) an ability to use the techniques, skills, and modern
engineering tools necessary for engineering practice
Grading:
• Mid-term 30%
• Project 30%
• Homework 10%
• Final 30%
• Special consideration for class participation
…be sure to ask questions!
• A = 90-100
• B = 80-89
• C = 70-79
• D = 60-69
Other ME Dept Reg’s…
University Course Related Policies
• For further details on course related policies as specified by the
University, go to
http:
www.ugst.umd.edu/courserelatedpolicies.htm
l
http:
www.ugst.umd.edu/courserelatedpolicies.htm
Approximate Schedule:
• Week 6 - Review for Midterm
• Week 7 – Midterm
• Week 13 – Project (Wing analysis code) due
• Last Week – Review for Final
• TBD – Final
Why study fundamentals of aeromechanics?
• Navy sponsored students will obviously be working with aircraft.
• It is a vital / key special case of fluid dynamics.
• It is very cool!
• Flight sciences impact all of our lives…
Question: What are the top 5 news stories since 1900?
Top News Stories…
20th Century:
XXXXXXXXXXU.S. drops atomic bombs on Hiroshima, Nagasaki:
Japan su
enders to end World War II
XXXXXXXXXXAmerican astronaut Neil Armstrong becomes the
first human to walk on the moon
XXXXXXXXXXJapan bombs Pearl Ha
or: U.S. enters World War II
XXXXXXXXXXWilbur and Orville Wright fly the first powered airplane
21st Century:
XXXXXXXXXXBombing of World Trade Center, …9/11
What is the common denominator?
Course Content / Main Topics
• How Do Things Fly?
• Fundamentals of Fluid Dynamics
• Subsonic (Incompressible Aero)
• Compressibility
• Supersonic Aero
• Transonic Aero
The primary forces acting on an aircraft are…
…the question is: how are they created?
Note:
For straight &
level flight the
L=W & T=D.
Note:
Aero deals with L & D.
Structures deals with W.
Prop/power deals with
T & W.
What are some ways one can produce Lift?
Flapping…
Rotating…
Creating your own relative wind…or…
Can you produce your own lift?
Vectored Thrust…
However, Lift is usually produced by a wing moving forward
at an incidence…and the wing is built from a distribution of
Airfoils…
Note: The key is the “co
ect” shape of the airfoil.
a (deg.)
Set the airfoil (and eventually wing) at an angle of attack (aoa)…
the shape and aoa result in a pressure difference across the airfoil…
the integrated delta pressure results in lift force…
however, air resistance will also cause an integrated drag force.
Ultimately, the full configuration is important & complex…requiring detailed analysis/testing to ensure
safe & effective Flight!
However, it depends on the medium in which
you are flying…
• Vacuum (outerspace - e.g. Rockets / astrodynamics)
• Gas (atmosphere – e.g. air / aerodynamics)
• Liquid (the seas - e.g. submarines / hydrodynamics)
• What makes Gas & Liquid
mediums similar?
• and…some vehicles fly in all three…
Today’s fundaments of atmospheric flight are built
on the shoulders of a few scientific giants…
Atmospheric flight must abide by a few basic
physical laws…what are they?
• ~350 year ago Sir Isaac Newton made some clear observations of these
laws. Aircraft in flight are governed by them.
• These laws are basics of classical physics.
• Air is a fluid system that abides by the natural laws of thermodynamics.
• The laws of thermodynamics define fundamental physical quantities
(temperature, energy, and entropy) that characterize thermodynamic
systems.
• The laws describe how these quantities behave under various
circumstances.
Homework Assignment Number 1:
• List and discuss/explain Newton’s laws of classical
physics.
• List and discuss/explain the four basic laws of
thermodynamics.
Sources of Aerodynamic Forces & Moments:
• All aero forces are due to only two basic sources
(1) Pressure distributions
(2) Shear stress distributions
No Slip
Sources of Aerodynamic Forces & Moments:
• All aero forces are due to the integrated effects of these two basic sources
(1) N = Normal Force
(2) A = Axial Force
(3) L = Lift Force
(4) D = Drag Force
(5) R = single Resultant Force
(6) a = angle of attack
(7) Vinf = freestream speed
Inc.
L & D
Typical Forces…
• Define: Force Coefficient -> [ “Aero Force” / (qS) ]
where,
q = ½rVinf
2 = dynamic pressure
S = reference area (usually wing planform area)
= Chord X unit span (2D Airfoil)
then,
Vehicle Lift Coefficient = CL = L/(qS)
Sectional (Airfoil) Lift Coefficient = Cl = l/(qc)
similarly,
Vehicle Drag Coefficient = CD = D/(qS)
Sectional (Airfoil) Drag Coefficient = Cd = d/(qc)
Typical Forces…
where we also note that,
CL = CNcos(a) – CAsin(a)
CD = CNsin(a) + CAcos(a)
We can further define,
Moment Coefficient (in the pitch plane) = CM = M/(qSc)
where, c=reference length
M
Flow over a wing…
• Recall:
Lift is a result of
differential pressure…
Pressure Coefficient…Cp
• A common parameter for airfoil aerodynamics
• Used to represent how the pressure is distributed across the airfoil (wing)
surface
where,
p = local static pressure
pinf = fresstream static press.
−=
−
=
q
pp
V
pp
C p 2
2
1
Always plot w/ Neg. Up!!!!!!!
End of Week 1 - Review Notes:
Course Content / Main Topics
• How Do Things Fly?
• Fundamentals of Fluid Dynamics
• Subsonic (Incompressible Aero)
• Compressibility
• Supersonic Aero
• Transonic Aero
Some basic definitions
… assuming some background in fluids
• Fluid:
A substance that deforms continuously under action of shear forces.
A fluid is composed of a large number of molecules, each with a
certain position, velocity & energy which vary as a result of collisions
with other molecules.
In aerodynamics, we are concerned with describing fluid motion in
spaces which are very large compared to molecular dimensions (thus,
containing a large # of molecules.)
The fluid in aerodynamics is generally considered a continuous
material determined from statistical averaging in a unit volume.
The assumption is that the smallest volume of interest is much larger
than the molecular sizes. This is known as “Continuum theory.”
Physics of Air…
• Discrete molecules…transfe
ing momentum/energy…”flowing” to
egions of lower pressure…
Higher density Lower density
Some basic definitions
… assuming some background in fluids
• Fluid:
Properties used to represent a fluid continuum are:
T = Temperature
P = Pressure
= density
m = viscosity
a = speed of sound
These properties are observed on the macroscopic level.
Definitions (continued)
…in general, all are a function of position & time…
Temperature (T)
• Qualitative (ie, …it feels hot/cold…) – thus, an a
itrary scale is employed
Pressure (P)
• Force per unit area (due to rate of change of molecules rebounding from the
surface) - thus, it is dependent on the local properties of the medium
Density (r)
• Mass per unit volume (in general, a function of composition, T & P)
• Example: Equation of State: r = P/(RT) ; R = gas constant
Definitions (continued)
…in general, all are a function of position & time…
Viscosity (m)
• Constant (for given condition/time) of proportionality between shear stress &
gradient of velocity
• Shear Stress = m X (du/dy)
• Note: this assumes “Newtonian Fluid”
(ie, shear stress ~ rate of shear deformation)
• Example: For air at T< 3000o K,
m = 1.458X10-6 X (T1.5/(T+110.4))
with T in (oK) & m = [kg/(s-m)]
Definitions (continued)
…in general, all are a function of position & time…
Speed of Sound (a)
• Speed at which an infinitesimal distu
ance propagates through the fluid at
est
• For a perfect gas,
? = √γ??
• Note: g = ratio of specific heats
g = 1.4 for air (usually, ie, perfect gas / M< 4-ish)
Very High heat values can effect this property.
Definitions (continued)
…in general, all are a function of position & time…
Similarity Parameters…
What are similarity parameters / why are they important?
The main (non-dimensional) Similarity parameters of interest:
Mach Number = M = V/a XXXXXXXXXXindicates level of compressibility)
Reynolds Number = Re = (rVL)/m = ( inertial forces / viscous forces )
Equations of Fluid Motion
• Classical physics dictates conservation of mass, momentum & energy
• These laws are employed to mathematically describe fluid flow based
on the assumption of continuum mechanics for the medium of
concern (ie, air)
• We now seek to develop the basic equations that will represent these
laws…they are in turn refe
ed to as the…
Continuity equation (conservation of fluid mass)
Momentum equation (conservation of fluid momentum)
Energy equation (conservation of fluid energy)
Continuity Equation S = Control Surface
V = Control Volume
(Fixed in Space)
Moving
Fluid
Field
Physical Principle: Mass can neither be created or destroyed
Continuity Equation
• Say,
= r(x,y,z,t)
V = u(x,y,z,t)i + v(x,y,z,t)j + w(x,y,z,t)k
Then, with…
[Net mass flow out of V through S] = [time rate of decrease of mass inside V]
(LHS) = XXXXXXXXXXRHS)
Physical Principle: Mass can neither be created or destroyed
Eqn (1)
Velocity Field
Continuity Equation (continued)
→→
→→
→→
•=
=•
=•
S
dSV
dSV
dSV
(LHS)
S across V ofout mass ofelement
V ofout both when positive
Eqn (2)
dS
V
dV
V- (RHS)
V inside mass of increase V
Vin mass totalV
Vin element mass V
V
V
V
d
t
d
t
d
dd
=
=
=
=
Eqn (3)
The instantaneous
tangential vector field
quantity
V(x,y,z,t) = Velocity Vector Field
Continuity Equation (continued)
0V
...reordering & (1) into (3) & (2) Substuting
V
=•+
→→
S
dSVd
t
Eqn (4) dS
V
dV
Integral form of the continuity equation
Continuity Equation (continued)
0)(
have...must wea
itrary, is V since thus,
0 V})({
gives XXXXXXXXXXinto (6) gsubtitutin
V))((
have, then we(5) into substitute & XXXXXXXXXXlet,
V)(
)ˆ
z
ˆ
y
ˆ
x
:(note .Theorem".. Divergence" recall
V
V
V
=•+
=•+
••
=
••
+
+
=
→→
V
t
dV
t
dVSdV
VA
dAdSA
kji
S
S
Eqn (5)
dS
V
dV
Eqn (6)
Eqn (7)
Differential form of
the continuity equation
Continuity Equation (continued)
0)(
then,
0
and,
),,(
ie,
Flow"...Steady " of case Special aConsider
=•
=
=
V
t
zyx
f(t)
Eqn (8)
dS
V
dV
Differential form of steady flow continuity equation
0
then,
constant
Flow"... ibleIncompress"
of case Special aConsider
=•
=
V
Differential form of incomp.
continuity equation
Eqn (9)
Homework Number 2:
• Consider a low speed wind tunnel sketched below.
• If the motor diameter is