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TECH.

r

(HE

H

OL DElFT

VL'~GTUIGBOU KUNDE ~1ic U c' :J 10 - DElFT

TRAINING CENTER FOR EXPERIMENTAL AERODYNAMICS

TECHNICAL NOTE

5

ANALYSIS OF THE PROBLEM OF RE-ENTRY

AT SUPERCIRCULAR VELOCITY

by

Léopo1d MOULIN

RHODE-SAINT-GENESE, BELGIUM

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TCEA TN 5

ANALYSIS OF THE PROBLEM OF RE-ENTRY

AT SUPERCIRCULAR VELOCITY

b Y

rLéopo1d I10ULIN

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Acknowledgement

The au thor wishes to express his thanks to Dr. R.H. Korkegi

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SUMMARY

The problem of re-en try of a vehicle into the earth's atmosphere at supercircular velocity has been analyzed for the simplified case of shallow entry of a non lifting vehicle. The purpose of the analysis is to investigate the possibility of obtaining an approximate analytical solution which will give the trajectory with good accuracy and be convenient for evaluation of peak deceleration and heating conditions.

Two classical approaches have been used in an attempt to solve the system of dynamic equations :

1) by power series expansion of the variables about both entry and circular velocity conditions, and

2) by an iteration procedure starting with approximate solutions whose validity is limited to the neighborhood of either entry or circular velocity conditions.

The iteration process requires the use of power series expansion, becau,se of the non linearity of the differential equations.

It is concluded that the common mathematical procedures using power series expansions are not adequate to yield a prac-tical analyprac-tical solution of the problem.

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v

g s h h s

Po

r r o

z

f k v t a , b n n Subscripts E S LIST OF SYMBOLS velocity

gravitation constant of the earth atmospheric density

reference area of the vehicle vehicle weight

drag coefficient lift coefficient

angle between flight path and local horizon distance along the flight path

altitude above earth's surface scale height of the atmosphere

1.5 x reference density at sea level

distance from vehicle to the earth's center mean distance from vehicle to earth's center

2-e...,

V~ V2.

non dimensional density

velocity parameter

~~o:Po

Vs

2 density parameter

tCI-~

'l.e lift parameter

Cp hs

eft

inclination angle parameter

(~t

eu.

b

altitude parameter

coefficients of power series expansion

entry conditions

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TABLE OF CONTENTS

1. Introduction

2. Equations of motion

3. Solution about entry conditions

A. Series expansion

B. Iteration process

4. Solution about circular velocity conditions

A. Series Expansion B. Iteration process 5. Combination of solutions 6. Conc1usions Page 1 2 4 10 13 14

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1. INTRODUCTION

The problem of entry of a space vehicle into the earth's atmosphere at supercircular velocity has received much attention in the last few years. Although the solution for a given set of boundary condi-tions can always be obtained by direct integration of the equations of motion on a digital computer, there is sufficient interest in an analytical solution to warrant considerable effort spent to this end.

An approximate solution reasonably accurate over that part '):: i:ne atmospheric trajectory of interest would be extremely useful for a "first look" at a re-entry problem by showing the influence of the various parameters (entry angle, velocity, altitude, drag, lift) on peak dec elera-tions and overall heat rates.

Many useful results have been given in the literature,

which have shed much light on some aspects of the general problem of re-entry. However, in the case of shallow entry of a vehicle with supercircular velo-city, the validity of the results presented does not extend over the whole range of interest of the trajectory. H.J. Allen and A.J. Eggers derived an analytical solution for the entry of a ballistic missile at high angles

(ref.l). Nonweiler analyzed the re-entry phase of a non lifting vehicle at circular velocity (ref.2) while Lees, Hartwig and Cohen considered the case of shallow entry of a lifting vehicle at circular velocity (ref.3). Moe

(ref.4), Wang and Ting (refs.5 and 6) respectively treated the case of non lifting and lifting vehicles at supercircular velocity - on the basis of simplifying assumptions.

In the .present report, the case of shallow entry of a non lifting vehicle with constant drag coefficient is investigated as a first step of the general problem. This represents the simplest case of re-entry at supercircular velocity. Approximate analytical solutions of the simplified equations of motion have been obtained and compared for a specific case with the exact solution of these same equations by numerical integration.

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The analysis has been carried out by two different methods using conve~ient parametric expressions for velocity, altitude or air densi-ty, and inclination angle of the flight part to the local horizon. In the first method, two of the parameters are expres$ed as power series expansions of the third parameter about both the entry point and the point where circu-lar velocity is reached. It is possible in some cases to eliminate one of the parameters by combining the two dynamc equations and thus deal with.a single series expansion. In the second method, the differential equations are solved by an iteration procedure whereby a simplified expression from the expansion of one or the other of the parameters is taken as the starting point.

2. EQUATIONS OF MOTION

Using as reference axes the local tangent and normal to the flight path, the general equations of motion are

as

V

d V

=

~

E.wA

CL) 1/ 2 - $.M

e

-~M

. 2

-

~2~

::

t

f$-c;.v~

-

~e(A- ~2)

The law of variation of the density with altitude is taken

- hl"!>

P

=

Po

e

The following simplifying assumptions are made :

1) The inclination of the flight path to the local horizon is small; one may consequently write sin 9 ~ 9 cos 9 ~ 1

2) The value of the earth's gravity is constant with altitude

3) The distance b"etween the vehicle and the earth I s center is a1so taken to be a constant, equal to its mean va1ue rover the range of interest.

There-o

fore the value of the circular velocity is a constant for the problem and one has

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4) The component of gravity along the flight path is negligible compared with the drag force.

Using the non-dimensional parameters introduced by HilI (ref. 7)

with the assumptions made above~ the simplified equations of motion are

dz _

f_

d.o - ~

'r.o

~

+

kt

+

-t -

ez-

=0

3.

The variable 5 can be eliminated by use of the density altitude relation and the parameter f, and if one restricts the analysis to the case of a non Iifting vehicle (k

=

0) and defines an inclination angle parameter by

one obtains simply

and

Eliminating ~ between the two equations, one obtains

f

4.

+

-t -

e.

Z =0

clz~

(2.1)

(2.2)

(2.3)

Equations (2.1) and (2.2) have been integrated numerically for a vehicle

W

characterized by cp~

=

1003 entering the atmosphere at 400,000 ft with a

velocity of 35,000 ft/sec and an inclination angle of 6°. This case is similar to one of those which have been treated numerically by Lees, Hartwig and Cohen in ref.3.

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4.

In part of the analysis, it was found more convenient to use the non-dimensional parameters

wherebyequations (2.1) and (2.2) become respectively

(2.4)

(2.5)

3. SOLUTION ABOUT ENTRY CONDITIONS

A. Series Expansion

The expansion about entry conditions is based on the system of differential equatións (2.4) and (2.5). The variables v and

't'

are expanded in power series of t :

(3.1)

(3.2)

The coefficients a and b of the above series are given by the boundary

o 0

conditions of the problem, i.e. v

E and ~E respectively at t = O.

The values of the remaining coefficients are obtained by substituting the expressions for v and

lY

into the differential equations, and equating to zero the coefficients of like powers of t. The values of ao(=v

E) and b 0 (=:\1' E) remain arbitrary and one obtains for the coefficients a

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s.

Cl :: I

or in general

Similarly for the coefficients b

The general recursion formula is '\'\-1

b_

= :

bo

[C~"'-I

-

&.

k 6

K

b"_k)

The expressionsfor these coefficients in terms of a and o bare particularly involved and will not be given here.

o

It is very difficult to find a criterion to determine whether or not the series converge. However, numerical calculations show

that the number of terms which have to be retained in order to keep a rea-sonable accuracy becomes overwhelming if one departs from the center of expansion. Consequently, a direct application of the series expansions would be so unwieldly that one cannot justify their use in comparison with numerical integration of the differential equations.

One may next attempt to solve the equation by an iteration process starting with simplified expressions for v or~.

B. Iteration Process

As a first approximation, only the first term v

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6.

series expansion for v is retained in Eq (2.5). This approximation has been used by Wang and Ting in Rei. 5.

The approximate value of v is substituted in Eq (2.5) whieh ean be direetly integrated and yields

(3.3)

This expression for ~ is in turn substituted in the equation (2.4) for v. One obtains

(3.4)

where

It is readily seen that the proeess of iteration cannot be eontinued beyond this point since the next expression for

't'

cannot be integrated. The above results for the velocity parameter and the inclination angle are compared with the exact solution on Figs 1 and 3 respectively. There is good agreement only in the vicinity of the center of expansion.

Since one cannot proceed very far with the iteration, an

improvement of the technique has been sought by starting with a bet ter

expression for the velocity parameter. An inspection of the numerical values

of each of the factors which are involved in the expressions of the coef-ficient shows that the most important ones are of the type

A more accurate expression for v is thus obtained by retaining these terms only in the series expansion. Consequently, putting

in Eq {3.l) one obtains directly

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7.

This expression is substituted in Eq (2.5). The corresponding value of

<t'

is

obtained by direct integration

'i/I:

o/E~

+-.t{U&-IJ.t -

24e~

t

(3.6)

The results obtained by this first step for v and o/are shown on Figs. 2 and 3 respectively. The improvement with respect to the previous solution is not significant.

The iteration requires substitution of the expression for

~ in the equation

It is readily seen that the integration is only possible if the denominator

is expanded iri seriès. Generally speaking, the relationship giving

't'

in

terms of t can always be written in the form

~

=

V~-À(f=)

0/&

where

À

(t) is a given function of t. The inclination angle decreases.

con-tinuously from its value at entry until circular velocity is reached; beyond this point, the angle increases again. If the range is limited to that point

where the.angle reaches again its initial value, the function ) (t) lies

in the interval 0

<

.x

(t) L , •

The series expansion of

(3. 7)

required for the integra.tion, is then fulty justified. Unfortunately, the

inc1ination ang1e decreases very sharply in the vicinity of entry so that

th~ ratio 'P/'f'.: becomes a rather smalt quantLty. The value of ) (t) is con"

sequently close to unity and the series expansion (3.7) must be performed

near the edge of the domain of convergence • . One·can again expect that a

large number of terms must be retained in the series to ensure a sufficient accuracy.

To illustrate this, tbe next step of the iteration has been carried out by expanding the expression (3.7) in series, retaioing 6n1y the terms up to the second power in t. One obtains the result

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lT

=

l!é

~lA (e~-I)

-1-

B[e..t"(t-,)

+11

+ C

[e/;[t~2t+2-)-2

]

+

f

(el~,)

+

~ (e3~1)

+

f

[ett{k--±)+i:]

J

(3.8)

where the coefficientsare given by

with

The result is shown on Fig. lp where the iterations are compared with the exact soiution. It is clear that the iteration process becomes less effieient because of the series expansionD for the reason which has been stated above.

It is worth to remark that if one makes all the coeffi-cients b equal to zeroD except b o » in the reeursion formula for a n D the series expansion ean be easily reeombined to yield the simple result.

(3.9)

This solution ean alternatively be derived by putting ~

=

~ë into Eq

(204)0

The latter assumption was made by Allen and Eggers (refoi) for the study of

the ballistic trajeetory at large entry angles. They obtained the above equation

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for the velocity parameter whieh is shown on Fig. 2 for eomparison with the previous approximations. This relationship has been used as starting point of an iteration process by Wang and Ting (ref.6). If one starts with the Alien-Eggers relationship for the velocity parameter,

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the value of ~ can be derived from the differential equation (2.5) written as

if the expression for the velocity parameter is transformed into Z ::: Z

-k

+

L_

E

'+'e

%

The integration yields

9.

~vhere Ei denotes an exponential integrale It is worth to note incidentally that the integration can equaily weil he carried out if lift is taken into account. To proceed further with the solution requires again series expansion.

A further improvement of the situation has been sought by

keeping the term b

l in the preceeding developments. In order to retain the possibility of direct integration, the expression fbr

an

has been simplified to

1

'ft

a.o

1I't-1

b.

Q

a-t\.': - I

bo -

-m:-

-b ~-,

/tI.. 0 0

\<lhich includes indeed the two factors which have the largest numerical value. The above expression for a , when substituted in Eq (3.1), leadsto the

dif-n

ferential equation

which yields upon

(3.10) By use of Eq (2.5) one obtains directly

b .

'fot::

%J.

+.t(Vë-,)1:; -

2~t:(et:.)

+.2-je

~:.!

e

-r.~+

~t)[E,

·

(I;+t7)

-

EI' ({;)]

(3.11) These relationships are represented on Figs 2 and 3 res-pectively and show very little improvement to the previous solutions.

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lO.

The coefficient b

2 could be taken into account. The

system can still be integrated although the calculations become more

elaborate and yield rather involved expressions. On the other hand, one does

not gain much by adding one more term in the expression for v. These results

are not given here.

Consequently, series expansion about entry conditions do

not appear to be a satisfactory way of obtaining the solution. The series

cannot be directly used and the iteration fails because non linearity of the

differential equations necessitate series expansions at the edge of their

domain of convergence. Starting with more accurate expressions for the velocity parameter does not yield significant improvement.

4. SOLUTION ABOUT CIRCULAR VELOCITY CONDITIONS

A. Series Expansion

The problem can be looked at from the other side, starting

from the point at which circular velocity is reached. A solution valid in this region should yield the peak deceleration and peak heating conditions with reasonable accuracy. To be of value, the solution must nevertheless

give sufficient accuracy when extended to the point of entry as the boundary

conditions for a given mission will generally be given at this point.

Alternatively, if conditions are prescribed in the vicinity of the point of

circular velocity near which peak deceleration and heat rates are expected,

th en it is also important to estimate entry conditions with good accuracy.

The condition of circular velocity is more easily expressed

with the variable Z, which is th en simply equal to zero. The latter parameter

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1l. The differentia1 equation (2.3) can be put in a suitab1e form for a series solution by writing

The parameter f is then expanded in a power series of Z

or in general A

a.,.,. :::

1

-m.tto

e>O _

P

= ~ Q", Z

T

1'1:0 The coefficients a

o and al are arbitrary and represent respective1y the values of f and ~ (by virtue of Eq 2.1) at circular velocity conditions. In the absence of lift, a

2 is equa1 to zero. No definite mathematical proof of convergence of the series has been found. But, as in the case of expansion about entry con-ditions, numerical calculations show that the series converge but so slowly that a very large number of terms must be taken into account if one departs

from the center of expansion. This solution by power series expansion is consequently rejected for the same reasons as stated earlier.

B. Iteration Process

An iteration process can be started by simp1ifying the series. If all the coefficients a are put equa1 to zero for n '7 2. , one

n

has simply

(4.1)

(4.2)

This first approximation is shown on Figs 4 and 5. It is a1ready apparent that the main difficulty will be to obtain a good agreement

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12.

in the region of entry. This approximation is similar to that made in ref. 3, whereby the difference between the gravitional force and the centrifu-gal force is negligible compared with the aerodynamic lift force. In the present non lifting case, on may expect that the same argument will be

justified in the close vicinity of the point of circular velocity, as

shown in fact by the curves of Figs 4 and 5.

The iteration f~om these simplified va lues is however

~asible. By substitution in the equations (2.1) and (2.2) one obtains the

following values (4.3)

t

=

~5"5

-

~f>

(e-Z _ Z - 1) -

~

$" -L

1

+-

~Cl.F [Ed~)-

Ei

(lt.)]

(4.4) with

a-

=

.h-\.f-"s

The latter result is shown in comparison on Figs 4 and 5.

Incidentally, it is wor th noting that the equations for

the iteration can be integrated just as easily for the case of a lifting

vehicle. Thus, the solution with lift represents a second approximation of

the results of Lees, Hartwig and Cohen (Ref. 3) with a somewhat extended

region of validity about the circular velocity point.

However, it appears from Figs 4 and 5 that the actual

iterated solution is far from being satisfactory in the region of entry.

Ta continue the iteration requires the integration of an equation like

~

_

e~-1

cfz -

T

where f is given by an expression which is similar to the above one. Direct

integration is no lon~er feasible and an expansion in series must be

considered. The expression for f can always be written as

A -i

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13.

is fully justified in the domain 0

<:

t.

<:

2. • The part f :? fs is

not of great interest since the actual solution may already be considered as a good approximation. The region of interest extends towards the entry

0<::

t

~

1, in which the function

~

(Z) is negative. However t as one approaches the entry conditions,

t/~s

becomes a small quantity 8S f is

proportional to the density. Consequently, the value of

'fez)

approaches unity and the series expansion is taken near the edge of the domain of convergence. Therefore, a very large number of terms of the series must be retained, thereby rendering the iteration process unwieldy.

If more terms of the series are included in the starting expression, a series expansion is already required for the first iteration. An approximate recombination of the series in terms of simple analytical

forms has been obtained but does not Yield a better result than the above mentioned iteration.

s.

COMBINATION OF SOLUTIONS ..

The possibility of matching two approximate solutions, one derived from the expansion about entry conditions and the other derived from expansion about circular velocity conditions has been considered next. A particular case is given on Fig. 6 which shows the inclination angle given as a function of the altitude parameter by the last solutions of section 3 and 4.

Unfortunately, no criterion. can.bè established to deter-mine the matching point of, both solutions. MoreQVer, .assuming that a

match-ing point could be defined, it would still be necessary-to use a trial and error process on that solution for which the boundary conditions are

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14.

6. CONCLUSIONS

The prob1em of entry of a non 1ifting vehicle with supercircular velocity is defined by two dynamic equations in terms of three variables.- the velocity, the altitude (or density) and the inclina-tion of the flight path to the local horizon - which are expressed in parametric form for convenience. It is possible to eliminate one of the variables between the two equations, resulting in a single higher order differential equation, or to treat them separately. Furthermore, the choice of the independent variable is arbitraryj however, the inclination angle is unsuitable as it is a double-valued function of both altitude and velocity--it decreases from entry to circular velocity conditions and increases beyond this point.

A solution of the prob1em has been sought by power series expansion about both entry and circular velocity conditions~ using respectively the altitude and velocity parameters as independent variables.

In both cases a very large number of terms has to be retained in·the series to.insure sufficient accuracy when one departs from the center óf

expansion, eventhough numerical calculations tend to show that the series

converge. The use of power series expansions presents no advantage over

a numerical integration of the differential equations.

The process of iteration of the differential equations, startj,ng with a simplified expression of the series, a1so fails, because the equations obtained in successive steps require the use of additional series expansions to be integrable.

If the ~unction f is selected as the independent variable, one has to integrate an equation of the type

t

A ohr

= )-

~

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15 .. where l/~ is given in general by

(6.1) when entry conditions are se1ected as the center of expansion. The va1ue of

1/~ is given by a series expansion which has been shown to converge, but which must be evaluated near the edge of the domain of convergence.

Similar1y, if Z is the independent variable, one has to integrate the equation

where l/f is given by an expression of the form

(6.2 ) when the center of expansion is the point of circu1ar velocity.

Again, l/f is given by a series expansion which is convergent, but which must be eva1uated near the edge of the domain of converge.

I f Z is se1ected as thè independent vari~ble for the solution about entry conditions, the series expansion of Eq (6.2) inay no.t converge in the whole range of interest. 11 f is·the iridependent variable for the solution about circu1ar velocity conditions, the series expansion Eq (6.1) may be divergent in some of the regioris of interest. These

arguments justify a posteriQri the:choice of the independent variables which has been made •• Consequent1y, all the possib1e combinations have

been investigated.

It has been shown that the failure of common mathematical methods is due to the use of power series expansions. It appears that the

portion of the trajectory of interest-which extends from entry to'peak deceleration conditions beyond circular velocity':"coversa 1a.rge par.t of the domain of convergence of the series. If one of the:two particular points is se1ected as the center of expansion, the other one lies in the

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16.

vicinity of the border of the domain of convergence.

It is a weil known property of the Taylor series that in order to keep a given constant accuracy, the number of terms which has to be retained in the series increases quite rapidly if one departs from the center of.

expansion tO\l7ards the extremity of the radius of convergence. Therefore, having in mind the requirements for the solution which have been stated earlier, it appears that power series expansions are not a suitable

mathematical tooi to ana~yze the problem, and one should look toward other mathematical procedures.

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R E F ERE N CES

1. H.J. Allen and A.J. Eggers : "A study of the motion and aerodynamic heating of ballistic missi1es entering the earth's atmosphere at high supersonic speeds", NACA Report 1381, 1958.

2. T. Nonweiler: "The motion of an earth sate11ite on re-entry to the atmosphere" Astronautica Acta Vol. V. Fase. 1 1959

17 ..

3. L. Lees, F.M. Hartwig and C.B. Cohen : uUse of aerodynamic lift during entry into the earth's atmosphere ft; ARS Journa1, September 1959. 4. M.M. Moe - "An approximation to the re-entry trajeetory"

ARS Journa1, January 1960

5. K. Wang and L. Ting : "Ana1ytic solutions of p1anar reentry trajectories with lift and drag", PIBAL Report n° 601, April 1960;

6. K. Wang and L. Ting : "Approximate solutions for re-entry trajectories with aerodynamic force", PIBAL Report n° 647, May 1961.

7. A.F. Hi11 : IIStudy of hypersonic aerodynamic dece1erators incorporating lift" MIT Nava1 supersonic Laboratory WADD Technica1 Report 60-706, August 1960.

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0.5 0.4 0.3 0.2 0.1 0 -0.1 -0.2 -0.3 -0.4 -0.5 -0.6 -0.7 Z / . , / , / , / , / ; ' ; ' , / , / , / / / , / / / / / / / I I /

--.--.

I I I I I Eq I I

-,--'

(3.4)

--.-' --.-'

exact lolution

--.---

_.-

Eq (3.8) ~ ,&.

_.-'

_.-'

--

.-'

-'

----~

• __ . _ . Eq (3.Sl

,---~_._.

__

._._._._._._._._._._._._._._._._._._._._._.---

_ _ _ _ _ v - v - - E --- ---0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1

Fig.1 - Series Expansion about entry conditions - Velocity parameter.

f 1.2

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exact solution 0.5 z 0.4 0.3 0.2 0.1 1 -0.1 -0.2 Eq (3.10) -0.3 -0.4 / ' ~All.n-Eggm q (3.5)

--0.5 -0.6 v vJ:: -0.7 f 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2

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9 0.12 0.1 0.08 0.06 0.04 0.02 ~~ Eq (3.U)

~

---

'q (3.6)

---~---

...

-

...

--

...

--

...

---

---"...

',Eq (3.3 ) exact solution f o 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2

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Z 0'.5 0.4 0.3 0.2 0.1 0 -0.1 -0.2 -0.3 -0.4 -0.5 -0.6 -0.7 0 1 exact solution 3 4 5 6 7

---

-

--_

... ----~ Eq (4.4) ... /

'"

Ij 'I 'I 'I / / / ... -"'Eq (4.2)

--_-c

I~! f E 8 9 10 11 12

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9 0.12 0.1 0.08 0.06 ...

...

Eq (4.l)- _ -'-.;; __ ..., exact so1ution

--- -::-::::::-::::=:====-=---====-==-====-======-==

Eq (4.1) 0.04 0.02 f o 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2

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CD

=

0

....

...

::l ... 0

.,

.... ö

....

0

=

0 ....

...

111 '" ö ....

=

I

~

I u I \Q I 11"\ bÖ I Ö

....

I>< I I I ~ I Ö I I I I ...., 0 N Ö ... Ö <I 0 N ~ \Q

g

a

... ... 0 ö ö ö ö ö ö

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"TCEA TN 5

Training Center for Experimenta1 Aerodynamics

ANALYSIS OF mE PROBLEM OF RE-ENTRY AT SUPERCIRCULAR VELOCITY

November 1961 L6opo1d Moulin

The prob1em of re-entry into the earth's atmosphere at 8upercircular ve10city has been analyzed for the simp1ified case of shal10w entry of a non lifting vehicle. Two classical mathematical methods have been used in anattempt to derive an approxi-mate analytical solution of dynamic equations :

TCEA TH 5

Training Center for Experimental Aerodynamic8

ANALYSIS OF THE PROBLEM OF RE-ENTRY AT SUPERCIRCULAR VELOCITY

November 1961 Léopo1d Moulin

The prob1em of re-entry into the

earth's atmosphere at supercircular

velocity bas been ana1yzed for the simp1ified case of sha110w entry of a non 1ifting vehic1e. Two c1sasica1 mathematical methods have been used

in an attempt to derive an approx

i-~te analytical solution of dynamic

equations :

I. MOULIN, Léopo1d

11. TCEA TN 5

CFAE TN 5

Centre de Formation en Aérodynamique

Expérimenta1e

ETUDE DU PROBLEME DU hETOUR DANS L'ATMOSPHERE A VITESSE SUPE~Or-BITALE

Novembre 1961 Léopo1d Houlin

Le problème du retour dans l'atmos-phère à vitesse superorbitale a été étudié dans le cas simplifié d'un engin non portant et d'une trajec-toire faib1ement inclinée sur l'hori-zontale. L'utllisation de deux méthodes classiques a été envisagée pour obtenir une so1ution ana1ytique approchée du problème :

CFAE TN 5

I. MOULIH.

Léopold Icentre de Formation en Aérodynamique

11.

TCEA

TH 5

Expérimenta1e

ETUDE DU PROBLEME DU RETOUR DANS L'AT}10SPHERE A VITESSE SUPERORBITALE

Novembre 1961 Léopo1d Moulin

Le prob1ème du retour dans

1'atmos-phère à vitesse superorbita1e a été

étudié dans 1e cas simp1ifié d'un engin non portant et d'une

trajec-toire faib1ement inc1inée sur 1'hori

-zonta1e. L'uti1isation de deux

méthodes c1assiques a été envisagée pour obtenir une so1ution ana1ytique

approchée du prob1ème :

I. MOULIN, Léopo1d

Il. TCEA TN 5

I. MOULIN, Léopold

(44)

1) By power series expansion about both entry and circular velocity conditions and

2) by an iteration procedure.

It is shown that the iteration process requires the use

of power series expansion.

It is concluded that common mathematical procedures using

power series expansions are not adequate to yield a practical analytical solution of the problem.

Copies available at TCEA, Rhode-St-Genèse, Belgium

'1) By power series expansion about both entry and circular velocity conditions and

2) by an iteration procedure.

It is shown that the iteration process requires the use

of power series expansion.

It is concluded that common ~ 'hematical procedures using

power series expansions are n01> adequate to yield a

practical analytical solution of the probl~

Copies available at TCEA, Rhode-at-Genèse, Belgium

1) Développements en séries de puissance autour du point

d'entrée ainsi que du point ou la vitesse orbitale est atteinte

2) Solution du système différentiel par itération. Le proces sus d'itération ne peut être développé que par

l'introduction de séries de puissance.

11 est conclu que les procédés mathématiques faisant

appel à des développements en séries de puissance ne

peuvent conduire à une solution satisfaisante.

Copies disponibles au CFAE, Rhode-St-Genèse,Belgique

1) Développements en séries de puissance au tour du point

d'entrée ainsi que du point ou la vitesse orbitale est atteinte

2) Solution du système différentiel par itération.

Le processus d'itération ne peut être développé que par l'introduction de séries de puissance.

11 est conclu que les procédés mathématiques faisant

appel à des développements en séries de puissance ne

peuvent conduire à une solution satisfaisante.

(45)

rTCEA TN 5

Training Center for Experimental

Aerodynamics

ANALYSIS OF THE PROBLEM OF RE-ENTRY AT SUPERCIRCULAR VELOCITY

November 1961 L4opo1d Moulin

The prob1em of re-en try tnto the earth's atmosphere at 8upercircular velocity has been analyzed for the

simplified case of shallow entry of a non lifting vehicle. Two classical mathematical methods have been used

in anattempt to derive an approxi-mate analytica1 solution of dynamic

equations :

TCEA TN 5

Training Center for Experimenta1 Aerodynamics

ANALYSIS OF THE PROBLEM OF RE-ENTRY AT SUPERCIRCULAR VELOCITY

November 1961 Léopold Moulin

The prob1em of re-entry into the

earth's atmosphere at supercircu1ar velocity has been ana1yzed for the simplified case of shallow entry of a non lifting vehicle. Two classical

~thematical methods have been used

in an attempt to derive an approxi -~te analytical 801ution of dynamic

equatlons :

I. MOULIN, Léopoid

11. TCEA TN 5

CFAE TN 5

Centre de Formation en Aérodynamique

Expérimentale

ETUDE DU PROBLEME DU hETOUR DANS

L'ATMOSPHERE A VITESSE SUPEr.Or.BITALE

Novembre 1961 Léopold Houlin

Le problème du retour dans

l'atmos-phère à vitesse superorbitale a été étudié dans Ie cas simpIifié d'un engin non portant et d'une trajec-toire faiblement incIinée sur I'hori-zonta1e. L'utilisation de deux

~éthode8 classiques a été envisagée pour obtenir une solution analytique approchée du problème :

CFAE TN 5

I. MOULIN. Léopold Icentre de Formation en Aérodynamique

11. TCEA TH 5 Expérimentaie

L

ETUDE DU PROBLEME DU RETOUR DANS

L'AT}10SPHERE A VITESSE SUPERORBITALE

Novembre 1961 Léopold Moulin

Le problème du retour dans I'atmos-phère à vitesse superorbitale a été étudié dans Ie cas simpIifié d'un

engin non portant et d'une trajec-toire faib1ement inclinée sur l'hori-zontale. L'uti1isation de deux

méthodes classiques a été envisagée

pour obtenir une solution analytique

approchée du problème :

I. MOULIN, Léopoid

Il. TCEA TN 5

I.

MOULIN, Léopold

(46)

1) By power series expansion about both entry and circu1ar velocity conditions and

2) by an iteration procedure.

It is shown that the iteration process requires the use

of power series expansion.

It is conc1uded that common mathematical procedures using

power series expansions are not adequate to yie1d a

practical analytica1 solution of the prob1em.

Copies available at TCEA, Rhode-St-Genèse, Belgium 1) By power series expansion about both entry and

circular velocity conditions and 2) by an iteration procedure.

It is shown that the iteration process requires the use of power series expansion.

It is concluded that common m.' hematical procedures using power series expansions are no" adequate to yield a

practical analytical solution of the probleD4

Copies available at TCEA, Rhode-st-Genèse, Belgium

1) Développements en séries de puissance au tour du point d'entrée ainsi que du point ou la vitesse orbitale est

atteinte

2) Solution du système différentiel par itération. Le processus d'itération ne peut être développé que par

l'introduction de séries de puissance.

11 est conclu que les procédés mathématiques faisant appel à des développements en séries de puissance ne peuvent conduire à une solution satisfaisante.

Copies disponibles au CFAE, Rhode-St-Genèse, Belgique 1) Développements en séries de puissance au tour du point

d'entrée ainsi que du point ou la vitesse orbitale est

atteinte

2) Solution du système différentiel par itétation. Le processus d'itération ne peut être développé que par

l'introduction de séries de puissance.

11 est conclu que les procédés mathématiques faisant appel à des développements en séries de puissance ne peuvent conduire à une solution satisfaisante.

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