Introduction to Aerospace Engineering - The Open Academy · Fundamentals of aerodynamics 16...
Transcript of Introduction to Aerospace Engineering - The Open Academy · Fundamentals of aerodynamics 16...
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1 Challenge the future
Introduction to Aerospace Engineering
Lecture slides
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1Fundamentals of aerodynamics
Introduction to Aerospace EngineeringAerodynamics 1&2
Prof. H. Bijl ir. N. Timmer
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2Fundamentals of aerodynamics
1 & 2.Fundamentals of aerodynamics Anderson chapters 2.1 – 2.5 and 4.1 – 4.4
Leonard Euler Daniel Bernoulli
1700-17821707-1783
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3Fundamentals of aerodynamics
Subjects
Fundamental quantities
• pressure• density• temperature• velocity
Equation of state
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4Fundamentals of aerodynamics
Pressure is the normal force per unit
area on a surface
0,lim →
= dAdA
dFp
Dimension of pressure = [N/m2]
The pressure in point B is:
Pressure is force per unit area
dF
dA
dA = element surface around B
dF = force on 1 side of dA
B
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5Fundamentals of aerodynamics
0lim →
= ,dvdv
dmρ
Density of a substance is its mass
per volume
Dimension of density = [kg/m3]
The density in point B is:
Density is mass per volumedv = element volume around B
dm = mass of gas in dv
Bdv
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6Fundamentals of aerodynamics
Temperature is a measure of the
average kinetic energy of the
particles in the gas
Temperature is a measure of the average kinetic energy of the particles in the gas:
kT,KE2
3=
with k = Boltzmann constant ( 1.38x10-23 J/K )
Dimension of temperature : K (Kelvin)°C (degree Celsius),
C273.15K +=with
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7Fundamentals of aerodynamics
A perfect gas is a gas in which intermolecular forces are negligible
The equation of state for a perfect gas is:
ρRTp =
Relation among pressure, density
and temperature is the equation
of state
With gas constant R:
287,05 J/(kg)(K)R =
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8Fundamentals of aerodynamics
31
T
bp
T
ap
RT
p −+=ρ
For an actual gas the equation of state is approximated by theBerthelot equation:
The difference with the equation of state for a perfect gas becomes smaller as p decreases or T increases( The distance between the molecules Inc r e a s e s)
The equation of state for a non-
perfect or actual gas
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9Fundamentals of aerodynamics
( )2 3 6 3 2 2
00 0 2 2
1 1 1 1 1 11 exp
CRT cp B RT A bRT a a
v T v v v T v v vα γ γ
= + − − + − + + + −
where A0, B0, C0, a, b, c, α, γ — gas constants for the equation
A0 = 0.313 kg m5 s-2 mol-2
B0 = 5.1953×10-5 m3 mol-1
C0 = 1.289×104 kg m5 K2 s-2 mol-2
a = 1.109 ×10-5 kg m8 s-2 mol-3
b = 3.775×10-9 m6 mol-2
c = 1.398 kg m8 K2 s-2 mol-3
α = 9.377×10-14 m9 mol-3
γ = 5.301×10-9 m6 mol-2
The Benedict-Webb-Rubin (BWR) equation of state [2,3] within temperature range from -30 to 150°C, for densities up to 900kg/m3, and maximum pressure of 200bar:
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10Fundamentals of aerodynamics
Ex 2.1 Compute the temperature in a point on a wing of a Boeing 747,
where pressure and density are given to be: 0.7 x 105 N/m2 and 0.91 kg/m3
T = 268.0 K
= -5.2 oC
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11Fundamentals of aerodynamics
Pressure, density and temperature
under standard conditions
Ps = 1.01325 * 105 N/m2
ρs = 1.225 kg/m3
Ts = 288.15 K
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12Fundamentals of aerodynamics
Ex. Compute the total weight of air in a room of 30 m x 15 m x 5 m under standard atmospheric conditions at sea level.
Volume=2250 m2
ρ=1.225 kg/m3
Weight = 2756 kg
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13Fundamentals of aerodynamics
ρv
1=
Definition of specific volume
pv RT=
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14Fundamentals of aerodynamics
Ex 2.3 Compute the density and specific volume of air in a wind tunnel at
P = 0.3 atm, and -100O C.
pρ
RT= ρ= 0.3X105/(287.05 x 173.15)
= 0.60 kg/m3
ν = 1.66 m3/kg
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15Fundamentals of aerodynamics
Velocity and streamlines
dx
dydt
dsv =�
[m/s]v�
streamlineB
The velocity in point B is the velocity of an infinitesimally small fluid element as it sweeps through B
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16Fundamentals of aerodynamics
Visualisation of the velocity and streamlines
Smoke traces in air
Aluminum Particles in water
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17Fundamentals of aerodynamics
Filmpje alfa=25 gr.
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18Fundamentals of aerodynamics
Velocity and streamlines
V0
V
Stagnation point (stuwpunt, V = 0 )
streamline
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19Fundamentals of aerodynamics
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20Fundamentals of aerodynamics
Aerodynamic forces
Shear stress or friction force
Pressure distribution
wτ
p
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21Fundamentals of aerodynamics
Homework:
Problems 2.1, 2.7 and 2.8 from
Anderson, page 102 (sixth edition)
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22Fundamentals of aerodynamics
Fundamental equations
• Continuity equation: Conservation of mass
• Momentum equation (Euler eqn.): Conservation of momentum
• Bernouilli’s law for incompressible flow
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23Fundamentals of aerodynamics
Continuity equation: Time rate of change
of the mass of a material region is
zero (mass is conserved)
in outm = mɺ ɺ
12
For 1-directional
incompressible flow:
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24Fundamentals of aerodynamics
Continuity equation for 1-dimensional incompressible flow
(assumption: ρ and V uniformly distributed over A, or:
ρ and V are mean values)
dmm
dt=ɺ AVQ (Qdt), ρdm ==
222111 VAρVAρ
constant ρAV
==
dmm
dt
AVdtAV
dt
ρ ρ= = =ɺ
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25Fundamentals of aerodynamics
Example 4.1: Consider a convergent duct with an inlet
area A1 = 5 [m2]. Air enters this duct with a velocity
V1 = 10 [m/s] and leaves the duct exit with a
velocity V2 = 30 [m/s]. What is the area of the duct
exit?
Assume a steady, incompressible 1-directional flow
1 1 2 2
1 1 12 1
2 2
105 * 1 .6 7
3 0
A V A V
A V VA A
V V
ρ ρρρ
=
= = = = [m2]
Application of the continuity law:……………….. e.g. wind tunnels
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26Fundamentals of aerodynamics
1.80
1.25
2.90
3.66
4.50
3.64
17.825.69
5.17
10.94 9.102.60 1.38
φ 2.90
0.55
A
C
B
D
E
A B C D E
Sizes in meters
6.50
5.70
2.60
2.10
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27Fundamentals of aerodynamics
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28Fundamentals of aerodynamics
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29Fundamentals of aerodynamics
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30Fundamentals of aerodynamics
Circuit layout of Delft University Open-jet Facility
Test section
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31Fundamentals of aerodynamics
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32Fundamentals of aerodynamics
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33Fundamentals of aerodynamics
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34Fundamentals of aerodynamics
Euler equation
Newton’s Second Law:
F = m.a ( Force = mass * acceleration)
Applied to a flowing gas :
dx
dy
p dxdxdp
p
+
x
z
y
dz
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35Fundamentals of aerodynamics
Euler equation, left hand part of
F=m*a
In reality 3 forces act on this element:• Pressure force
• Friction force
• Gravity force
In the derivation we neglect 2 forces:• Neglect the gravity force (small)
• Neglect the viscosity No friction forces
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36Fundamentals of aerodynamics
Euler equation, left hand part
(F=m*a)
The force in x-direction:
dpF = pdydz - p dx dydz
dx +
dxdydz dx
dp = F −Hence: = force on fluid element due to
pressure
dx
dy
pdp
p dxdx
+
dz
dp
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37Fundamentals of aerodynamics
Euler equation, right hand part
(F=m*a) and resulting equation
The mass (m) of the fluid element is : m = ρ.Vol = ρdxdydz
Acceleration (a) of the fluid element is:
Substitution in F = m*a
V dx
dV =
dt
dx
dx
dV
dt
dV = a =
dxdV
V)dxdydz()dxdydz(dxdp ρ=−
Or: ρVdVdp −=
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38Fundamentals of aerodynamics
Resulting equation:
1. It is a relation between Force and
Momentum
2. Also called the momentum equation
ρVdVdp −=
Euler (1707 - 1783)
Swiss MathematicianEuler equation
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39Fundamentals of aerodynamics
Euler equation
Keep in mind for this equation:
� Gravity forces are neglected� Viscosity is neglected (inviscid flow)� Steady flow� Flow may be compressible!
The Euler equation is a Differential equation
ρVdVdp −=
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40Fundamentals of aerodynamics
Bernoulli’s law for inviscid and
incompressible flow, gravity forces
neglected
2
1
2
1
p V
Vp
dp + VdV = 0ρ∫ ∫1 2
Integrate Euler equation (dp + ρVdV = 0) along streamline
between point 1 and 2:
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41Fundamentals of aerodynamics
Bernoulli’s law for inviscid and
incompressible flow, gravity forces
neglected
2
1
2 21 1 2 2
1 1
2 2
2
1
p V
2 22 12 1
Vp
1 1 dp + VdV = 0 ( - ) + - = 0p p V V
2 2
p V p V
ρ ρ
ρ ρ
→
+ = +
∫ ∫
1 2
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42Fundamentals of aerodynamics
Dynamic pressure
Static pressure
Bernoulli’s law for inviscid and
incompressible flow, gravity forces
neglected
2 21 1 2 2
1 1
2 2p V p Vρ ρ+ = +
=+ Vρ 2
1 p 2 constant along a streamline
Total
pressure
pt
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43Fundamentals of aerodynamics
Bernoulli’s law for inviscid and
incompressible flow, gravity forces
neglected
Daniel Bernoulli (1700-1782)Dutch born (Groningen, 29 jan. 1700),
Swiss Mathematician
constant along a streamline
Bernoulli’s law:
=+ Vρ 2
1 p 2
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44Fundamentals of aerodynamics
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45Fundamentals of aerodynamics
1738
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46Fundamentals of aerodynamics
Application of Bernoulli’s principle
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47Fundamentals of aerodynamics
NACA 0018Re=0.7x106
-4.0
-3.0
-2.0
-1.0
0.0
1.0
Cp
Application of Bernoulli’s principle
The pressure distribution over an aerofoil
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48Fundamentals of aerodynamics
Remember
• Bernoulli equation only for inviscid = frictionless, incompressible flow
• Bernoulli equation is valid along a streamline
• For compressible flow => Euler equation !
• Momentum equation, Euler equation and Bernoulli equation is in
fact F = m⋅⋅⋅⋅ a (Newton) applied to fluid dynamics.
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49Fundamentals of aerodynamics
Ex 4.4. Consider the same convergent duct as in example 4.1. If
the air pressure and temperature at the inlet are p1 = 1.2
x 105 N/m2 and T1=330K, respectively, calculate the
pressure at the exit.
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50Fundamentals of aerodynamics
Example: Consider the same convergent duct as in the previous
example. If the air pressure and temperature at the inlet
are p1 = 1.2 x 105 [N/m2] and T1=330 [K] respectively,
calculate the pressure at the exit
�Assume inviscid, incompressible flow
�Neglect the gravity forces
�On a streamline in the duct: Apply Bernoulli’s law!
( )
( )
( ) ( )
2 2 2 21 1 2 2 2 1 1 2
51
1 11
2 2 5 2 2 52 1 1 2
1 1 1
2 2 21.2*10
1.266287.15*330
1 11.2*10 *1.266* 10 30 1.19*10
2 2
p V p V p p V V
pp RT
RT
p p V V
ρ ρ ρ
ρ ρ
ρ
+ = + → = + −
= → = = =
= + − = + − =
[kg/m3]
[N/m2]
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51Fundamentals of aerodynamics
Example: Consider an airfoil in a flow of air, where far ahead
(upstream) of the airfoil, the pressure, velocity and
density are: 1.01 x 105 [N/m2], 150 [km/h] and 1.225
[kg/m3] respectively. At a given point A on the airfoil the
pressure is 9.95 x 104 [N/m2]. What is the velocity in
point A?
�Assume inviscid, incompressible flow
�Neglect the gravity forces
�On a streamline near the airfoil: Apply Bernoulli’s law!
∞ A
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52Fundamentals of aerodynamics
Example: Consider an airfoil in a flow of air, where far ahead
(upstream) of the airfoil, the pressure, velocity and
density are: 1.01 x 105 [N/m2], 150 [km/h] and 1.225
[kg/m3] respectively. At a given point A on the airfoil the
pressure is 9.95 x 104 [N/m2]. What is the velocity in
point A?
Assume that point A and ∞ are on the same streamline. Bernoulli then gives:
( )
( ) ( )
2
2 2
5 4 22
11 1 2
12 22
2 1.01*10 9.95*102 15064.7
1.225 3.6
A
A A A
AA
p p Vp V p V V
p pV V
ρρ ρ
ρ
ρ
∞ ∞ ∞
∞ ∞ ∞ ∞
∞
∞∞
∞
− ++ = + → =
−− = + = + =
[m/s]
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53Fundamentals of aerodynamics
• Problems 4.3 and 4.5