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再入大气动力学与热保护系统
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更新于2024-07-19
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"Re-Entry Aerodynamics" 是一本由Wilbur L. Hankey编写的书籍,专注于探讨在航天器重返地球大气层时所面临的空气动力学挑战。这本书由美国航空航天学会(AIAA)出版,并作为其教育系列的一部分。书中涵盖了地球大气层的描述、高超音速空气动力学的基本原理、再入飞行器轨迹预测,以及针对不同类型的再入配置(如可升力式如航天飞机和弹道式如阿波罗计划)的热转移和热保护系统。 在“Re-Entry Aerodynamics”中,作者深入讨论了高速气动热力学,这是理解再入阶段关键的一部分,因为航天器在高速穿越大气层时会面临极高的温度和压力。这个阶段涉及到复杂的流动现象,包括激波、边界层相互作用以及热流的计算。Hankey还分析了如何利用这些理论来估计再入配置的气动特性,这对于设计有效的热保护系统至关重要。 书中还详细介绍了用于航天器热保护的系统,这些系统旨在防止高温对飞行器结构造成破坏。对于可升力式再入飞行器(如航天飞机),需要考虑升力对热流分布的影响,而弹道式再入飞行器则主要关注减少热负荷的策略。此外,高温度材料的使用也在设计中起到关键作用,它们能承受再入过程中的极端环境。 书中的内容可能还包括了实际案例研究,比如航天飞机和阿波罗任务的再入过程,以及这些历史事件如何影响了再入技术的发展。通过这些例子,读者可以更好地理解理论概念在实际应用中的意义。 “Re-Entry Aerodynamics”为航空航天领域的工程师、学生和研究人员提供了全面的指导,帮助他们理解和解决再入大气层过程中遇到的关键问题。它不仅涉及了科学原理,还包含了工程实践,是该领域的重要参考资料。
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q
Btu
ft
2
sec.
RE-ENTRY
AERODYNAMICS
=10,000
20 sec
Fig.
1.3
Heating
rate
on the
noses
of
different
re-entry
vehicles.
This
constraint
greatly
limits
the use of a
rejection-type
thermal
protection
system.
Histograms
of the
heating
rate
on the
nose
of two
different
types
of
re-entry
vehicles
are
shown
in
Fig.
1.3.
A
ballistic
missile
has a
profile
of
short
duration
with
an
intense
heating
rate
peak.
On the
other
hand,
a
glide
vehicle
re-entry
is of a
long
duration
with
a
relatively
low
peak
heating
rate.
It
should
be
observed,
however,
that
the
total
heat
energy
can be
compara-
ble for
both
cases.
A map of the
domain
where
each
thermal
system
applies
for
different
applications
is
shown
in
Fig.
1.4 to
help
establish
a
better
perspective.
10,000
1,000
log
i
100
/JtyJV
\ft
2
sec/
©SPACE
SHUTTLE
©
X-15
10
log
t
(min)
100
Fig.
1.4
Thermal
system
domains.
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![](https://csdnimg.cn/release/download_crawler_static/9958889/bg11.jpg)
RE-ENTRY
FLIGHT
REGIMES
9
1.2
ATMOSPHERE
The
U.S.
Standard
Atmosphere
3
will
be
used
to
determine
the
upper
atmospheric
properties.
A
description
of the
primary
features
of the
atmo-
sphere
will
be
presented
in
this
section.
Air is
composed
of the
elements
shown
in
Table
1.4.
The
average
molecular
weight
of
this
mixture
of
perfect
gases
is
Af=
20^
=
28.
966
The
atmosphere
is
extremely
thin,
relative
to the
Earth
radius
(R =
3959
miles).
At a 60
mile
altitude,
p/p
sl
=
10~
6
and
A/z/jR
=
60/3959
=
0.015,
which
is
thinner
relatively
than
an
apple
peel,
compared
to its
core
size.
Air can be
analyzed
as a
long
column
that
must
obey
Archimedes'
principle
of
fluid
statics.
The
incremental
pressure
dp can be
expressed
in
terms
of the
density
p and the
gravitational
constant
g by the
equation
dp=-pgdh
(1.14)
The
pressure
p is
also
expressible
by
p
=
P
RT
(1.15)
where
R is the gas
constant
and T the
temperature.
Elimination
of p in
Eqs.
(1.14)
and
(1.15)
leads
to
dp=-p
1
j
T
dh
(1.16)
which
can be
integrated
to
give
where
p
sl
is the sea
level
pressure.
Thus,
for a
given
temperature
T as a
function
of the
altitude
h,
the
right-hand
side
of Eq.
(1.17)
can be
integrated.
Table
1.4
Properties
of Air
Element
N
2
0
2
Ar
CO
2
Mass
concentration
C
t
0.7809
0.2095
0.0093
0.0003
2C
1.0000
Molecular
weight
M
{
28.016
32.000
39.944
44.010
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![](https://csdnimg.cn/release/download_crawler_static/9958889/bg12.jpg)
10
RE-ENTRY
AERODYNAMICS
As
an
approximation,
an
isothermal
case
(T=T)
can be
considered
for
which
Eq.
(1.17)
becomes
-ah
(1.18)
where
a
=
g/RT=
4.4 X
10~
5
/ft
(1.19)
Also
from
Eq.
(1.15)
—
=
—
^
=
—
(1
20)
Psl
Hence,
e-«
h
(1.21)
Clearly,
the
isothermal
case
(T=
T) may be
used
as an
approximation
for
any
subsequent
re-entry
computations.
1.3
KINETIC
THEORY
OF
GASES
In
dealing
with
the
flow
of
air,
information
is
needed
concerning
the
thermodynamic
properties
of
density,
pressure,
and
temperature
(p,
/?,
T\
as
well
as the air
transport
properties
of
diffusivity,
viscosity,
and
thermal
conductivity
(D,
/A,
k).
The
basis
for the
understanding
of
these
air
proper-
ties,
produced
by
many
gas
molecules
in
random
motion,
is
contained
in
this
section.
The
approach
used
here
4
to
develop
the
concepts
is
classically
described
as
the
"Ultrasimplified
Kinetic
Theory
of
Gases."
In
this
theory,
one
should
appreciate
that,
although
appropriate
relationships
will
be
derived,
the
numerical
value
of
coefficients
will
be
only
approximate.
First,
consider
a
cube
of air
with
sides
of
length
L
containing
N
molecules.
The
velocity
distribution
is
known
to
Maxwellian,
in
which
all
speeds
are
possible
(see
Fig.
1.5).
Most
molecules,
however,
are
traveling
f
Fig.
1.5
Velocity
distribution
of
molecules
in a
cube
of
air.
IVI
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![](https://csdnimg.cn/release/download_crawler_static/9958889/bg13.jpg)
RE-ENTRY
FLIGHT
REGIMES
1
1
within
±
50%
of the
most
probable
speed.
Based
upon
this
observation,
a
simple
model
of
this
molecular
motion
can be
derived.
The
assumptions
are
1) All
molecules
are
identical
rigid
spheres
oj_
diameter
a and
mass
m.
2) All
molecules
possess
the
same
speed
V,
i.e.,
average
molecular
speed.
3)
The
molecules
move
equally
in
only
three
axes
(x,
y,
z),
i.e.,
1/6N
in
each
direction
(±x,
±y,
±z),
where
N is the
number
of
molecules.
Based
on
these
simplifying
assumptions,
relationships
for p,
/?,
and T
will
now be
derived.
The
mass
in the
cube
of air (or
gas)
is M = N X m and its
volume
is
V=
L
3
.
Hence,
the
density
p is
given
by
p
=
M/V=Nm/V
(1.22)
Newton's
second
law for the
collision
of all the
particles
on one
wall
is
given
by
FAf
=
MAu
(1.23)
where
F is the
total
force
acting
on one
wall
and
v
the
average
particle
velocity.
Equaling
the
impulse
to the
change
in
momentum
Hence,
F=(Nm/3L)v
2
(1.24)
The
pressure
p can be
expressed
as
p
=
F/L
2
(1.25)
Hence,
substituting
Eqs.
(1.22)
and
(1.24)
into
Eq.
(1.25)
results
in
(1.26)
The
equation
for the gas
temperature
T is
derived
from
the
equation
of
state
p
=
pRT and
Eqs.
(1.15)
and
(1.26),
i.e.,
Hence,
T=v
2
/3R
(1.27)
(A
more
precise
analysis
produces
a
result
that
T=
0.392v
2
/R.)
The
speed
of
sound
a is
related
to
temperature
by the
well-known
expression
a
=
JyRT
(1.28)
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![](https://csdnimg.cn/release/download_crawler_static/9958889/bg14.jpg)
12
RE-ENTRY
AERODYNAMICS
which
can be
used
to
determine
the
ratio
of v/a
from
Eq.
(1.27).
This
leads
to
=1.35
(1.29)
Therefore,
the
average
molecular
speed
is
approximately
equal
to the
speed
of
sound.
Collision
Frequency
To
obtain
the
transport
properties
for the
transport
of
mass,
momentum,
and
energy,
the
collision
frequency
of the
molecules
is
required.
It is
primarily
through
collisions
that
these
basic
quantities
may be
transported.
First,
only
collisions
between
molecules
moving
in the z
direction
will
be
considered,
as
depicted
in
Fig.
1.6.
Any
molecule
moving
inside
the
cylinder
of
radius
a at
velocity
+2v
will
collide
with
the
stationary
molecule.
All
others
moving
in the + z
direction
will
never
collide
with
this
molecule,
as
illustrated
in
Fig.
1.7.
The
number
of
molecules
in
this
cylinder
at any one
time
is
The
frequency
of
these
collisions
is
given
by
+ z
-z
2V
Fig.
1.6
Collisions
between
molecules
moving
in the z
direction.
Fig.
1.7
Molecules
moving
inside
the
cylinder
of
radius
a at
velocity
2tx
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