%

Final Report

NAS8-36955 D.O. 77

Study of Basic Physical Processes

in Liquid Rocket Engines

Period of Performance: February 23, 1990 - February 21, 1992

N

_4

.0 _n ,0

,..., _ a"

I ,=" U_

O_ C

b-

_O

_O_

>-.JN E

0

u_ O_

_DLU N

I _"

Z_Z O

o

e4

O

by

S. T. Wu

Department of Mechanical Engineering

and

C. P. Chen

Department of Chemical Engineering

The University of Alabama in Huntsville

Huntsville, AL 35899

Submitted to:

Mr. Klaus Gross

EP 5_

NASA/Marshall Space Flight Center

Huntsville, AL 35812

September 1992
II.

III.

IV.

Table of Contents

VII.

I ,

II.

III.

Summary ....................................................

I. Introduction ...........................................

Gibbsian Thermodynamics ................................

Alternative Theory: Straub Method .....................

Derivation of Equivalent Navier-Stokes Equations

on the Basis of the Boltzmann Equation .................

V. Prigogine's Non-Equilibrium Thermodynamics:

Conservation Laws ......................................

VI. Truesdell's Rational Thermodynamics:

A Classical Reproach ...................................

Discussion and Concluding Remarks ......................

Tables

Comparison between Classical N-S and Straub's AT .......

Comparsion between Falk-Ruppel and Straub ..............

Comparison between Wu's Formalism and

Classical Navier-Stokes Equation .......................

IV. Comparison between Prigogine Non-Equilibrium

Thermodynamics and Straub's A-T ........................

Acknowledgement ............................................

References .................................................

Appendices ................... ;.............................

I. Conclusion from Ref[4] .................................

II. Conclusion from Ref[5] .................................

i
_._._ _ SUMMARY

!

Inconsistencies between analytical results and measurements for

liquid rocket thrust chamber performance, which escape suitable

explanations, have motivated the examination of the basic

physical modeling formulations as to their unlimited application.

The publication of Prof. D. Straub's book, "Thermofluid-dynamics

of Optimized Rocket Propulsions", further stimulated the interest

of understanding the gas dynamic relationships in chemically

reacting mixtures. A review of other concepts proposed by FalkRuppel (Gibbsian Thermodynamics), Straub (Alternative Theory,

AT), Prigogine (Non-Equilibrium Thermodynamics), Boltzmann

(Kinetic Theory), and Truesdell (Rational Mechanism) has been

made to obtain a better understanding of the Navier-Stokes

equation, which is now used extensively for chemically reacting

flow treatment in combustion chambers.

In addition to the study of the different concepts, two workshops

were conducted to clarify some of the issues. The first workshop

centered on Falk-Ruppel's new "dynamics" concept, while the

second one concentrated on Straub's AT.

In this report brief summaries of the reviewed philosophies are

presented and compared with the classical Navier-Stokes

formulation in a tabular arrangement. Also the highlights of

both workshops are addressed. _i _

The primary conclusions are as follows:

i. The new thermodynamics theory by Faulk-Ruppel provides

an indepth approach to formulate thermo-fluid equations.

However, the connection with the conventional Navier-Stokes

equation is not apparent. Further investigation of this issue is

necessary for the assessment of the governing equations in

combustion chamber flows for CFD simulations.

2. Both, NASA's ODE program and the Munich Method Code for

thermodynamic equilibrium calculations of rocket engines now

carry an option to consider finite area combustion effects. The

solution process in both approaches is based on the Lagrangian

multiplier scheme. The results from these two programs are

practically identical for two demonstrated sample cases.

However, the ODE program contains many more chemical elements and

species and is equipped with several practical calculation

options.

3. The derivation of a new "Navier-Saint Venant" equation

as a result of Prof. Straub's "Alternative Theory" was not

presented. Hence, the equation was not accepted as a preferred

scheme over the Navier-Stokes Equation at this time. Some

interesting results should be surveyed.

4. The comparison of Navier-Stokes equation with other

formulations from Boltzmann, Prigogine, and Truesdell have
_r

revealed certain limitltions, when this equation is used for

combustion chamber flow modeling.

5. This review process is an initial attempt to establish a

sound foundation for the analytical simulation of rocket engine

flow processes. Further re-evaluations are in order and should

be supported by a group of experts from the academic profession

to assist the engineering community in solving their problems

with a high degree of confidence.
I. INTRODUCTION

Since the introduction of the maximization of entropy for

equilibrium in rocket engine combustion processes by Prozan [i]

in 1969, this scheme has induced considerable different opinions

in the JANNAF community. In 1982, NASA/MSFC awarded a contract

(NAS8-34946) to Continuum Inc. to program this entropy

maximization concept and provide quantitative evidence. The

results led to a workshop at Continuum Inc., where Prozan's

proposed concept was reviewed and debated. In the meantime,

some new developments appeared in Europe. The introduction of a

"Dynamics" concept by Falk and Ruppel [2,3] forms the basis for a

new look at the currently used thermodynamic and fluid dynamic

laws. Building on their concept, Prof. Straub formulated an

"Alternative Theory (AT)" which is characterized in a recently

published book entitled "Thermofluid-Dynamics of Optimized Rocket

Propulsions". The contents of the book became strongly

controversial. To gain further understanding of these

differences, MSFC awarded a contract to The University of Alabama

in Huntsville (UAH) to investigate the fundamental analytical

formulations, which are currently used to simulate the physical

processes in liquid rocket combustion chambers and nozzles.

To accomplish these goals, two workshops were organized, and

their proceedings have been published [4,5]. Brief information

about both workshops and the conclusions are included in Appendix

I and II of this report. The foundation of the "Gibbsian

Thermodynamics" and one important application is described in

Section II. Information about Prof. Straub's (AT) is included in

Section III. Section IV discusses the derivation of conservation

laws via Boltzmann equations, and the ones based on Prigogine's

non-equilibrium thermodynamics are presented in Section V.

Truesdell's rational mechanics theory is displayed in Section

VI. A comparison of these concepts and theories with concluding

remarks are presented in Section VII.

The motivation to select the classical theorems (Gibbsian,

Boltzmann, Prigogine and Truesdell}-to be included in this study

is because in one way or another they attempt to formulate the

non-equilibrium chemically and radiatively acting flow. These

are being compared with the current Navier Stokes Equation used

in the present Computational Fluid Dynamics (CFD) for the

combustion chamber flow simulation.

3
li.'%IBSSIA T E OOY ICS

Professors Gottfried Falk and Wolfgang Ruppel are the originators

of a new concept, called "Gibbsian Thermodynamics", which is

presented in the following two books [2,3], written in German and

printed by the Springer Publishing Company:

i. Mechnik, Relativitat, Gravitation - (1977)

2. Energie und Entropie - (1976)

Some important chapters of these books have been summarized and

translated, and they are included as Appendix C in [4]. This

section provides only excerpts from [4], relating to the

justification of the new concept and one notable application.

comprehensive document showing the derivation of the novel

equation and its advantage should be prepared in English to

assure proper attention and relevant studies.

A

In the book "Energy and Entropy" the mass character of

energy, the various forms in which energy is exchanged, energy

fluxes, and the spatial distribution of energy or energy flux

concentration are addressed. The mass character of energy

permits the summation of all energy forms. The energy which is

connected with an energy transport during a process appears in

specific energy forms. Please note that only the transported

energy relates to an energy form and not the stored energy.

Energy forms are: energy of rotation, energy of motion, energy

of compression, surface energy, chemical energy, heat energy, and

others. All energy forms can be represented with the following

mathematical description f dX, where X is the extensive variable

specifying the energy form and f is the intensive variable,

identifying the quantity of energy which is exchanged in this

form.

Energy Form = (intensive variable f) . d(extensive variable X)

There are as many different energy-forms as there are extensive

variables, however, they do not have to be independent of each

other. The number of independent energy forms reflect the number

of degrees of freedom in a system. The general validity of this

energy form convention cannot be proven, like no assertion about

nature can be confirmed.

One of the great achievements in physics has been the

identification of "standard variables", which permit the

description of an untold number of processes in nature. A

special simple treatment of such processes can be accomplished

with variables which satisfy conservation laws. They are

especially favored as standard variables.
Since energy is a mass guantity, which is distributed in

space and can flow, the following Gibbs Fundamental Form is

introduced. The terminology "form" is used because the equation

is composed of differentials of the first order (linear), also

known as Pfaff's form.

dE = fldXl+f2dX2 + ...+fndX_ (ii.l)

Distinct energy forms are presented below with bold letters

identifying vector quantities:

Energy of:

ROTATION: _dL

TRANSLATION: -Fdr

MOTION: vdP

COMPRESSION: -pdV

SURFACE: _dA

ELECTRICAL: _dQ

CHEMICAL: _dN

HEAT: TdS

POLARIZATION: Edv

MAGNETISM: Hdm

(Angular Velocity) * L (Rot. Momentum)

(-Force) * r (Position Vector)

(Velocity) * P (Momentum)

(-Pressure) * V (Volume)

(Surface Tension) * A (Surface Area)

(Electrical Potential) * Q (Charge)

(Chemical Potential) * N (Partical No.)

(Temperature) * S (Entropy)

(El. Field Strength) * v (Dipole Moment)

(Mag. Field Strength) * m (Dipole Moment)

Gibbs Fundamental Form

dE=_fndX n (11.2)

In this equation dE is the received or produced energy. It

is important that each energy form is independent of the other

ones, which means that the energy flux of each energy form must

be possible regardless of the other fluxes.

If all extensive variables have a constant value, then all

differentials are zero, which in turn requires dE = 0 or E =

constant. The corresponding Gibbs Function reads:

E = f (P,r,L,S,V,A,N) (II.3)

(The electrical, polarization, and magnetic energy forms are not

considered here)
This function describes systems which are physically equal

when the same extensive variables are involved. However, they do

not need to be the same in reality.

Gibbs functions are also called Thermodynamic Potentials.

Statement

The identification of the energy E of a system as a function

of the independent extensive variables is a very difficult task,

which can only be solved by approximations in the end. Large

disciplines of physics, such as statistical mechanics, are used

primarily to find these functions.

The intensive variables are obtained by differentiating the

Gibbs function E = E ( ..... ) with respect to the extensive

variables.

dE -

0E 0E 0E 0E 0E

dP - m dr + -- dS + m dV + -- dN

0P ar 0S 0V ON

(II.4)

where the partial derivatives represent the velocity v = 0E/aP,

the force F = 0E/0r, the temperature T = 0E/aS, the pressure -p =

0E/0V, and the chemical potential _ = 0E/aN respectively. These

results give

dE = vdP + Fdr + TdS + pdV + _dN

The specific features of this equation are:

(ii.5)

O

The fundamental equation reflects an energy change and not

its conservation.

O All energy terms are portrayed by the same mathematical

structure.

o All terms have quantity charaeter and become additive.

o Each term represents a specific energy form.

o

Each energy form is presented by two conjugate physical

parameters of an intensive and extensive variable.

o Each variable can appear in the equation only once.

o A system can be subdivided if the variables in one subsystem

do not affect the variables in the other one.

The identified "Gibbs Fundamental Form" and its identified

features form the basis of Gibbsian Thermodynamics. In order to

show the connection with the classical mechanics (i.e. Newton's

Second Law) we shall discuss the derivation of Newton's Second

Law from the Gibbs Fundamental Equation. Recall the Gibbs

6
f

fundamental equation.

dE = Z/idX i

E = E(L,r,P,V,A,Q,Ni,S,7,m) (II.6)

Separating the energy into two parts which represent the motion

and the internal character, neglecting the energy forms of

polarization and magnetism results in:

E(P,r,L,S,V,A,Ni) = EI(P,r ) + E0(L,S,V,A,Ni) (II.7)

Reducing this equation to hold only the energy of motion (vdP)

and energy of translation (Fdr) requires that the dynamic

variables of the internal energy subsystem have: (i) constant

values and, therefore, their differentials are zero, (2) their

differentials are not zero, but the summation of the associated

energy forms are zero, (3) the independent variables

representing the internal energy have no influence, or perhaps

only a weak one on the other subsystem.

/idXl = vdP; Velocity . d (Impulse)

/2dX2 = Fdr; -Force . d (Position) (Ii.8)

With a further assumption that the system does not exchange

energy with another system finally results in the equation:

dE = vdP - Fdr = 0

or (II.9)

E = E(P,r) = const.

In a static field where the force is only a function of the

position, F = F(r), which postulates that the velocity is only a

function of the impulse, v = v(P), the differentials of the

extensive variables become total differentials. The energy of

motion is now representing the kinetic energy, and the energy of

translation the potential energy. --

If the system is subject to a change in time and postulating

that P and r are functions of time, then differentiation with

respect to time yields:

dP dr

v-- - F - 0

dt dt

(II.10)

Recognizing that the change of position with time is equivalent

to the kinematic velocity, v = dr/dt, which can be equated for

point particle motion with the dynamic velocity v = 8E/SP, and

substituting the proper term in the equation leads to:

7
dP

v-- -Fv = 0

dt

'dP 'i

v -- - F I = 0

[dt )

(II. Ii)

This equation is satisfied when

v = 0

!---- F ]= 0

and the scalar vector product is Zero.

The second requirement leads to the equation below

dP

- F

dt

(II.12)

Please note that there are two equations of motion which are

valid in general when only the energy of motion and energy of

translation are present, where F = F(P,r) and v = v(P,r).

Separation into two independent subsystems requires that they

cannot share independent variables, and total derivatives can be

used.

dP

-- = F

dt

dr

_ V

dt

(II.13)

Now, the intensive variables F and v are only functions of either

P and r respectively.

For Newton's condition (v << c) the two equations translate

into a better known form. With the assumption that a field of

the first type is present, the force F is only a function of r,

which requires that the velocity v is only a function of P. The

latter condition can be obtained in the following approach. In

Einstein's important relationship the impulse is related to the

energy in the following way:

E

P - v (II. 14)

2

C
In this equation E represents the total transport energy which

itself depends on v and increases with growing velocity. For

transport velocities v _ 0 the energy approaches a finite value

which is known as the internal energy E 0 = M c 2 . Substituting

this term in the previous equation results in

P = Mv (II.15)

This is just the relationship we are looking for, where v is a

function of P. In this equation M represents the inert mass,

which is normally a function of the velocity, but here M is

equivalent to the velocity independent rest energy or internal

energy EQ for v = 0 and P = 0.

Substituting the impulse value for Newton's condition (v << c) in

the bracket term (II.ll), and taking M out of the differential

expression, since it is a constant and therefore independent of

time, yields the following equation:

dP

- F

dt

d (Mv)

- F

dt

dv

M - F

dt

(II.16)

d2r

M--= F

dt 2

The last equation is Newton's famous law:

MASS * ACCELERATION = FORCE

During this derivation the following assumptions have been made:

o The motion of the system is virtually independent of the

internal energy of the system with v << c or clP 1 << E.

o The energy of motion and translation of a system remain

when:

(i) The fixed values of the extensive variables L

(Rotational Momentum), S (Entropy), V (Volume), N (Particle

Numbers) and therefore, also their conjugated intensive

variables _ (Angular Velocity), T (Temperature), p

(Pressure), a (Chemical Potential), state that the internal

energy does not change. This relates to the motion of rigid

9
bodies or mass particles.

(2) The sum of the energy forms representing _he internal

energy is zero, but the individual terms are not. Here the

motion is independent of the internal energy.

<3) The independent variables portraying the internal

energy do not affect the other subsystem or have only a weak

impact on it.

o The mass M is independent of time.

O Only two forms of energy are considered which are

independent of each other.

The transitional energy Fdr is restricted even to a static

field, where F = F(r) and not of v.

Please note: If fields of the second type (non-conservative

fields) with F = F(P,r) and v = v(P,r) are present, the

relationship P = Mv is not possible. Therefore, equation (II.16)

cannot result for such a condition.

10
III. ALTERNATIVE THEORY: STRAUBMETHOD*

Straub has deduced his so-called "Alternative Theory" (AT),

[6], on the basis of the _dynamics' theory by Falk and Ruppel,

[2,3], combined with Progogine's new micro-theory [7]. The

Navier-Saint Venant equation is a principle result of the AT and

leads to a confrontation with the Navier-Stokes equation of

motion. Subsequently, Straub's description of the AT from [6] is

presented.

III.l. The Navier-Saint Venant Equation of Motion

In order to offer a quantitative presentation of the

numerous important results of the AT, the equation of motion of a

compressible multicomponent single-phase fluid mixture is

compared to the Navier-Stokes equation of motion. The basic

relationship representing the momentum conservation law is a

Cauchy-type equation of motion.

pDv = pf- 7 . _ + 1/2 at p# , (III.l)

whereas D is a differential operator called the substantial or

material time derivative

D: : a t + V ' 7 (III.2)

in this definition a t denotes the partial time derivatives and

is the gradient vector operator (nabla-operator).

The local flow velocity v involved has a double definition:

the original _dynamic' establishment

aE(P,r,s,V,N k)

v = (III.3)

aP

is obtained with the Gibbs Fundamental Equation [6] of the

multicomponent single-phase fluid mixture. Identification of v

with the kinematic velocity v,: = dr/dt guarantees conservation

of the particle number of all baryons. This invariance

generalizes the Newtonian mechanics of finite systems of masspoints, called 'bodies'. At every given instant the body is

located at some place and assigned real numbers denoting the

properties of state. In field theories the continuity equation

controls the time behavior of such a body by considering the

baryons constancy (see Straub 1988, pp. 53 f).

*The content of this section is directly transposed form ref. [6] .

ii
The properties _ and # appearing in equation (III.l) along

with mass density p and the specific field force f (for example,

gravity), are defined as follows in the AT:

_: = p_ -- 7 pressure tensor (III.4)

#: = v - i dissipation velocity (III.5)

Here _ stands for the unity tensor and p is the thermodynamic

pressure established with the equation for the hypothetical state

of rest [6]. This pressure is permitted to be calculated only

with the thermal equation of state

p = R T p Z (III.6)

where p denotes the density and T is the temperature defined for

hypothetical state of rest [6]; the compressibility factor Z =

Z(T,p) is identical to one only with ideal gases.

The viscous stress tensor T typical for individual classes

of flowing fluids is related to the AT's characteristic

dissipation velocity through the dyadic product

T: = 1/2 pv# viscous stress tensor (III.7)

The quantity # equals the vector difference between the local

flow velocity v and the specific (linear) impulse i; the limiting

case "

lim¢ = 0

¢_0 (III.8)

disappears only for vanishing dissipation, expressed by the local

values of the entropy production density ¢.

A

For # = #(_ # 0) _ O, equation (III.l) formally corresponds

to the classical Cauchy equation of motion.

The following Navier-Saint V_nant equation of motion for a

defined class of compressible fluids and their mixture is taken

from the AT and is comprised of equations (III.l) and (III.4).

For the viscous stress tensor T the expression

12
S / i _

T = t, Z-I p- iD-- (V, v) 8[ -

R . 2 I

1

- -- t_ T(Ots + 7 . Js)

2

- t T (ZR)-I PiVSV - -- (v . sv)

\ 2

- t T (ZR)-I Pi[Vs x v] x

(iii.9)

is theoretically derived.

For simplification, the abbreviation

t T pTs: = 2B = t T Z -l

s

p --

R

(III.10)

is introduced.

Before equation (III.9) is discussed in greater detail, its

corresponding traditional continuum mechanics relationship should

be offered for comparison. These Navier-Stokes equation_, as

generali_ed notations of the set of field equations for v (r,t),

T(r,t), p(r,t) and p(r,t), are defined by its viscous stress

tensor:

T: = 2u.D + I"0v - --21_:

3

v . v (Ill.ll)

Perhaps the clearest interpretation of this equation is found in

Truesdell (1984, pp. 426-427 & 409-410). In this case, D is the

deviator which is the symmetrical share of the (tensorial)

velocity gradient vv in symmetrical stress tensors; _ and _v are

the fluid's shear or volume viscosity respectively. C.

Truesdell offers convincing reasons why the known Stokes relation

(i.e. nv E 0) is valid.

At first glance one notes that the expression (III.9) for

the compressible fluid's viscous stress tensor T is considerably

more complicated than the formulation - equation (III.ll) - for a

Navier-Stokes fluid. The structure of equation (III.9), with its

characteristic Nabla operators (which have multiple effects on

the local specific entropy s of the fluid), contains the

13
asymptotic limiting case

lim T = 0

_0 (III.12)

allowing a physially satisfactory transition from frictionaffected motion to a dissipation-free Euler flow. A serious and

historically explicable defect of the Navier-Stokes equation of

motion is its lack of this limit for each infinitesimal local

entropy production density ¢. The demand for such an asymptotic

behaviour is closely related to Maxwell's principle of kinetic

equilibrium. On the level of the Maxwell-Boltzmann gas kinetics,

a flow field with gradients results as a solution to the

Boltzmann equation when the collision operator disappears

identically for all r and t. This case of kinetic equilibrium is

asymptotically possible only for reversible processes in which

all transfer current densities equal zero (see Truesdell, (ed.),

p. 414).

Equation (III.9) contains not only one term (which cannot be

generally neglected: see Straub, 1988, p. 123) for the unsteady

changes of the specific entropy s. In addition, the divergence

of the entropy flow vector Js also appears, which through

Js = T-I q + _ sk J_

k

- (RZ p)v (III.13)

is related not only to the heat flow density q and a convective

term, but to the diffusion flow density Jk as well. The latter

is weighted by the partial specific entropy s k of all the

polynary single-phase system's components. This divergence term

in an expression for a second order tensor 7 apparently

contradicts the Curie principle. It is a constitutive part of

the linear Irreversible Thermodynamics and postulates without

proof: even and odd order tensors may not appear together in an

equation for continuum mechanics. C. Truesdell vehemently

polemicized against this "principle" (Truesdell, 1984, pp 387-

391). He not only traced its rather dubious origin, but

criticized above all its mathematl-cal ambiguity. Equation

(III.9) offers an example of the problems encountered with the

principle: from divergence of vectors q and Jk (k = I(1)K)

follow two scalars. They are tensors of even order zero, whose

occurrence together with the viscous stress tensor by no means

contradicts the Curie principle. Otherwise the coupling of all

transfer processes conforms with all physical experiences; this

is not reflected, however, in the Navier-Stokes equation of

motion (see Moore, 1964, p. 192).

This is probably because its "deduction" fails to take

simultaneously occuring transfer processes into consideration.

Such a restriction is consequent, however, for an artificial

construction such as an incompressible model fluid. If one

accepts the known incompatibility of this theoretical fluid with

14
the thermodynamics of real materials, one is compelled to

acknowledge that concepts such as temperature, entropy, heat flow

density, etc. are not, strictly speaking, compatible. Taking

this circumstance into consideration and assuming S = _ for the

shear viscosity s, it is notable that the Navier-Saint Venant

motion equation (III.9) for an incompressible model fluid (_ . v

0) contains the Navier-Stokes motion equation as a

"pathological" limiting case (see Straub, 1988, pp. 141-144).

Seen from the standpoint of the AT, a notable conclusion can

be made: for an incompressible fluid with constant shear

viscosity _, the Navier-Stokes equation of motion, together with

the incompressibility condition

7 . v- 0 (III. 14)

and the compatible initial boundary constraints, represent a

complete set of equations. The solution - flow velocity v and

pressure p dependent on location r and time t - is parametrically

dependent only on the kinematic viscosity v = u/p = constant

(and, additionally, on the parameters fixed by the initial and

boundary constraints); to a certain extent individualizes the

incompressible fluid with a number for comparison.

In reality things look completely different: for all

compressible fluids the new quantity 6 (a physically

corresponding function of _) - equation (III.10) - is normally a

function of state, provided the proportionality coefficient t T is

either a constant or a known function of the density p, the mass

fraction wk and temperature T. In the latter case this

characteristic time t T is a property of state like the pressure

p, the compressibility factor Z and the absolute specific entropy

s of the polynary single-phase system.

Even simple examples, however, lead one to expect that this

coefficient B is more likely to be dependent on the class of

given flows (for example, a shear flow under certain constraints

such as constant shear and isothermal fluid) than on the material

properties (see Straub 1988, section 5.2). It is evident that

this difficulty raises questions about conventional viscosity

concepts. This is not the place, however to present an answer to

this problem, particularly since other authors have already made

some pertinent attempts (see, for example, Nettleton 1987). If

necessary, there are no theoretical objections against accepting

t 7 as an empirical coefficient for the present.

Generally speaking, one arrives at an interesting

conclusion: the Navier-Stokes equation of motion can be

substantiated only for incompressible model fluids; for real

compressible materials, one can only define it as addressed by

Truesdell [9].

It is understandable that the Navier-Saint Venant equation

of motion at present cannot be used for actual projects.

15
Currently available numerical procedures and computers are still

too inefficient to handle the work. Therefore it is appropriate

to search for a first non-trivial approximation of equation

(III.9). The answer naturally depends on which approximations

one can agree upon.

The gas kinetics fundamentals of non-uniform and thermallyperfect gases lead one to the conclusion that the most important

prerequisite for a decisive simplification of the problem, the

inequation

vT/T << I, (III.15)

may be valid for the profiles of local temperatures.

(III.15) vT relates to the absolute value of the local

temperature gradients. If one ignores extreme cases,the

condition (III.15) is still fulfilled within the linear

dimensions of the order of magnitude (Vm/N_) I/3 : 33 _ [6].

means that in most practical cases there are no relevant

limitations.

In equation

This

In these cases, both Navier-Saint Venant equation of motion

(III.9) and the energy field equation can be simplified further

in the form:

cvpDT =- pv . v- v . qF + 1/2 _M(v . v)2 (III.16)

pDv = pf - vp v (III.17)

Pv: =P- i/2_, v . v (III.18)

_M: = tTP (III. 19)

p = RTp (III.20)

The same can be done with the field equations of the mass

fractions not shown here.

Equation (III.17) agrees formally with the Euler equation of

motion. Yet the pressure Pv by no means corresponds with the

thermodynamic pressure p according to equation (III.20).

Equation (III.17) describes dissipative processes and can, like

the Navier-Stokes equation of motion, fulfill no-slip boundary

conditions. Analogies due to numerical viscosity effects

obviously are the reason why the Euler equations of motions have

recently been so successfully applied in industry for simulating

real flows.

An equation of motion of the Euler type (and not the Navier

Stokes equation of motion!) is thus a first step toward

describing real flow fields of compressible fluids. All field

properties such as velocity v, specific field force f, mass

density p, pressure p, and temperature T are clearly defined by

the Gibbs Fundamental Equation and related to one another.

16
If one accepts for q_ the known proportionality to vT

according to the First law of Fourier

qF : = - k 7T = - 7 . [Cv _M f 7T]. (III.21)

that is equivalent to assume steady transfer processes (see

Straub et al. 1987) in connection with the Fourier heat flow

vector qF. The coupling of heat conductivity _ with the Max_4ell

viscosity (analog to the known gas kinetic relationship _ = f cvn

between _ and the dynamic viscosity _ of non-uniform gases [6]

allows further simplification of equations (III.16) and (III.17),

assuming continued constant material data. If one adds the wellknown relations

cv/R = (_ - l)-l; B: = p/p = RT (III.22)

for perfect gases and ignores the quadratic v . v term in

equation (III.16) as well as the field force term in equation

(III.17), then these two equations are immediately transformed -

taking equation (III.15) into account (see Straub, 1988, p.148) -

into the forms

Df_ = - (_ - i) Ill v . v - I/2v M 7 . 7 _] _: = cp/c v (III.23)

D v = - v_ + 1/2 YM V(V . V) ; vM: = UM/P (III.24)

They are of particular interest because they contain only two

dependent variables - flow velocity v and the scalar potential _,

which with constant material data can also be easily connected

with the special enthalpy of a perfect gas - as well as two

parameters _ and _M" To solve them, one needs suitable initial

and boundary conditions, but not the continuity equations: the

latter can subsequently be used, when fields _(r, t) and v(r,t)

are established to calculate the density field p(r,t).

17
v_

IV. DERIVATION OF EQUIVALENT NAVIER-STOKES EQUATION

ON THE BASIS OF THE BOLTZMANN EQUATION

In this section, we shall summarize the classical kinetic

theory of transport properties developed by Chapman and Enskog

[8]. Particularly, we shall demonstrate that the first order

approximation is equivalent to the Navier-Stokes equation of

fluid flow as well as gasdynamics.

IV.l. Th_ee Boltzmann Equation and the E_ of Transport

Let us define the local distribution function for the gas,

f(v,r,t), such that

f(v,r,t) dv dr (zv.l)

represent9 t_e number of particles having velocity v, v + dv at

position r, r + dr at time t. The local distribution function is

a function of the macroscopic properties such as number density,

mean velocity and temperature. Thus, the rate of change of the

distribution function f(v,r,t) at a specific position r and time

t by considering a ga9 is subject to an 9xternal force mF, which

may be a function of r an_ t but not of v. Between the time t

and t + dt, the velocity y of any molecule which does not 9ollide

with anothgr , 9hanges to v + Fdt 4 9nd i_s_position-vector r will

change to r + vdt. There are f(v_r,_)dvdr molecules which at

time t lie in the volume-element r,dr, and have velocities in the

range v, dv. After the interval dt, if the effect of collisions

could be neglected, the same molecules, and no others, would

compose the set that occupy _he volume r + vdt, dr, and have

velocities in the range v + Fdt, dv, the number in this set is:

f(v + Fdt, r + vdt, t + dt) dvdr.

On dividing by dvdrdt, and making dt tend to zero, Boltzmann's

equation for the distribution function f is obtained.

@f _ af _ of @e f

-- + V , -- + F ' - (IV.2)

at ar av at

8e f

The quantitiy of -- defined above is equal to the rate of the

at

change, owing to encounters in the velocity-distribution function

@fe

of f at a fixed point. It will appear that -- is expressible as

at

an integral involving the unknown function f:

18
2

with k12dk the collision parameters.

Another important equation may be derived from Boltzmann's

equation which give the connection between the molecular velocity

distribution and conservation laws of fluid dynamic equations.

Let # be any molecular property as defined by:

7 = -- _fdv

n

(IV.4)

with n being the number density of molecules and mass the density

given by nm, with m being the mass of a molecule.

Multiply Boltzmann's equation by _dv and integrate

throughout velocity-space; it is assumed that all the integrals

obtained @re convergent, and that products such as _f tend to be

zero and v tends to infinity in any direction (i.e., -_, +_).

The result may be written as,

c_

+ V ' --%- + _ ' -- dv = nit (iv.5)

where

-- _ 8ef

na_ _ I _ dv 8t

(IV. 6)

and the integration limits are from_-m to +m. The physical

significance of a# is the measure of the rate of ch_nge_in the

molecular property with velocities in the range of v, dv per unit

volume at r, t, owing to encounters.

From Eq. (IV.5), we obtain

I 8f-- dv -

at

- 9ddv - f -- dv - -- n --

8t at at at

(zv.7)

ar 8r

-- . _vfdv- Ifv . -7

8r

dvar_ . n# -nv . --/

aroo

(IV.8)

19
F¢ -- dv = II[¢f] uodvdw - i00 f -- dv = -n -- (IV.9)

Substituting these results into Eq. (IV.5) we obtain the

transport equation:

-- + -- . nCv - n -- + v . -- + F . = na¢

at 8r _St ar

(IV. lO)

This equation could be expressed in terms of a peculiar velocity,

C = v - co, with c o being the center of mass velocity. With

proper mathematical manipulation, we obtain the transport

equation in terms of the peculiar velocity:

n¢ + n¢ -- . c +- • n¢6 - n _--+ 6- +

Dt ar 0 ar [ Dt 0r Dt ) 0C

a¢ c c0 = n_,¢

a6 ar

(IV. ii)

D

with -- being the substantial derivative, which is given by

Dt

D 8 O

-- + C 0 '

Dt 8t O/"

(IV.12)

The transport equation (IV.II) is used for the bridge to

connect the microscopic theory to the continuum (fluid) theory.

IV.2. Conservation Law____ssof Fluid Flow.- Special Forms of the

E_uation of Chanqe of Molecular properties.

The conventional form of the governing equations of fluid

flow could be obtained from the transport equation by assigning

the proper form of the molecular property ¢.

Case I. Let ¢ = i, #c = 0,

a¢ De 8¢

- 0, - O, - 0, a¢ = 0.

ac Dt

Thus Eq. (IV. ll) becomes

Dn 0

-- + n -- . 6

Dt O_"

= 0

0 t (IV.13)

This is the equation of continuity.

2O
_L

w

Case II. Let _ mC; then # = 0, n_c = ncc = _ (i.e. pressure

tensor), - 0, - 0, - (m), - 0, _ = 0.

8r Dt 8c 8c

Hence, Eq. (IV. ll) becomes

Dc 0 8

p - . R - ... (zv.14)

Dt 8r

This momentum equation at the lowest order

corresponds to the Maxwellian distribution function

which will lead to the momentum equation for

inviscid flow. The next higher order will lead to

the Navier-Stokes equation for both compressible

and incompressible flow.

Case III.

1 3

Let _ = E =- mC 2, then =- nkT, n#c = (i.e.

2 2

heat flux),

a_ D_

- o,

ar Dt

- 0 and, since E depends on

c only through the contribution of the kinetic

energy of translation, - mc; thus - 0, and

ac ac

a_ -%.%

n -- C = pCC = [.

Oc

Since a# = 0, the transport

equation becomes,

DtDT 3nk2{ ra 0}

.... _ _ C + _ ,

8_ o ar-_ ,

(IV. 15)

this is the energy equation.

IV.3. Maxwellian Velocity Distribution

Consider a simple gas whose molecules are spherical,

possesses only energy of translation, and is subject to no

external forces. If its state is uniform:

21
- 0 = - kldkdc I

_t t

f_fl = ffl Detailed balancing (i.e. at statistical

equilibrium)

!

log f' + log f l = log f + log f l

This shows that log f is a summational invariant for

encounters. Thus, it must be a linear combination of the three

summational invariants (conservation laws):

log f = _ _[i) _(i)

1

(3) 2

= _[ I) + _(2) , mc - _ - mc

2

The form of the Maxwellian distribution is

(3) 2

f = e_0} e-_ i/2 mc ,

log f = _(1) + ml_(2)u +

X

/

(3)

m(u2+v2+w 2)

= logs{0) _ _(3)

C % = C

By definition

_(2)

(3)

%/

(2)

_x

(3)

(z

+ V

c c c

x y z

n

F

fdc = o_(0)

t

CO

= (0) 2 '_ --(_. c e

-(X, e

(3) i/2 mc

2 %

I/2 mc

2 _

2

dc_ I sin ede I d#

0 0

'2z 312

= ct(°)[_-_'_(3)

22
nc o =

cfd6

= +6' fd6'

(3)

_(2) I

= n + (0) e

_(3) t

(3) -(x, 1/2mc

0

,2 6'd6'

_(2)

C O --

_(3)

f = oL(0) (3}

-_ l/2mc

e

2 {m_(3)

= n L 2_

3/2

e-(X,

(3) 1/2me

(IV. 16)

Using,

3 1

-- kT = -- mc -_ -

2 2

m I c2fdc

2n

(3)

m Im_

2 2_

c 2 e-_

(3) 1/2mc' 2 d6

3

2c_( 3 )

1

we obtained _(3) - , thus Eq (IV.16) becomes

kT _

2

mc

f = n e -2kT

This is the Maxwellian distribution. It is well-known

[I0,Ii] that gas has Maxwellian distribution, it corresponds to a

non-dissipative state which is equivalent to the Euler equation

of motion of fluid dynamics.

IV.4. Remarks

It should be noted that this formalism for the derivation of

conservation laws is only valid for the dilute gas, because of

the limited treatment of the Boltzmann collisional integral, in

which only the binary collisions are considered. However, this

23
formalism does not give us a clear track to chase these physical

processes as expressed in kinetic theory. For example, the gas

behavior follows a Maxwellian distribution; with it lowest order

it leads to the Euler equation of motion, whereas the next higher

order behavior of the gas leads to the Navier-Stokes equation of

motion. A summary of these comments is depicted in the Table

below.

24
0

.,--I

0

<

0

>

.p

U

>

,H

r_

E

"0

r_

2

v

u

E

E

o

.+ E

.=.=.2

N _ _

U I_ II II I

I

E

I --

c

=o='_

I

=

.+

25

•- e-

"Z

= C,

=

_ N

llt ,_

>,

. _I,,<

ORI,_NAL P,_GE IS

OF POOR QUALITY
V, PRIGOGINE'S NON-EQUILIBRIUM THERMODYNAMICS:

CONSERVATION LAWS*

It has been understood that the description of a "mechanical

system" is in terms of the coordinates and momenta of the

molecules, or in ter_ns of its wave function. However, such a

description, when applied to systems of interests in chemical

physics and fluid dynamics such as combustion chamber flow, leads

to great practical and conceptual difficulties, because it is

impossible to say 1023 molecules in a macroscopic system. In

order to remedy these difficulties, the combined thermodynamic

and fluid dynamic methods are used to provide us with a "reduced

description," as pointed out by Prigogine, "simplified language"

with which to describe macroscopic systems. In this chapter, we

shall briefly summarize Prigogine's concept through the

derivation of conservation laws and balance equations which are

equivalent to the equation of motion of combustion chamber flows

being used for current CFD simulation.

Let us consider a system of volume V limited by the surface _.

_ge wish to follow the time change of the intergral

I (t) = IfdV (V.l)

This intergral is extended over the volume V of the system we are

interested in. The surface _ is assumed to be at rest. In the

terminology usually adopted in thermodynamics, I(t) is an

extensive quantity. For instance, it may be the mass or the

energy of the system. On the contrary, f(x, y, z, t)is an

intensive quantity, which does not depend on the system as a

whole. It corresponds to the volume density associated to I and

may be represented by the functional derivative

f - (V.2)

The change can be expressed by

8I

- P[I] +#[I]

8t (V.3)

*The materials presented in this chapter are based on a text book

entitled Thermodynamic Theory of Structure t Stability and

Fluctuations, by P. Glansd0rfF and I . Prig0gine; Wi leyInterscience, 1971.

26
The first term on the r.h.s, corresponds to the production per

unit time of the quanity I inside the volume V. It can be

written as a volume intergral

P[I] = I_[I]dV (V.4)

where _[I] denotes the source of I per unit time and unit volume.

The second term in the r.h.s, of (V.3) represents the flow of the

quantity I through the boundary surface _. It can be written as

a surface intergral

_[I] = ljn[I]dn (v.5)

This formula introduces the density of flow j[I] associcated with

I; Jn[I] is its projection along the inside normal to the

surface. For simplicity, we shall also use the term flow instead

of density flow (or current, or flux). From equations (V.4) and

(V.5) we obtain the so-called balance equation corresponding to

the extensive variable I as:

- _[I]dV + n[I]d_

8t ,

(V.6)

It is sometimes useful to write the balance equation (V.3) or

(V.6) in the symbolic form

dI = diI + deI (V.7)

where diI represents the source term and deI the flow term. One

may write as well

diI = dI + (-deI) -_ (v.8)

In this form, we see that the source diI contributes on one side

to the time change of I and on the other to the flow from the

system to the outside world (-deI) . It must be emphasized that

only dI is in general a total differential of the state

variables.

Equality (V.6) has to be valid whatever the volume V. Therefore,

the application of Green's formula gives us directly the balance

equation in local form

af

8t

- _[I] - div j[I] (v.9)

27
One of the advantages of this formulation is that all

conservation equations can be expressed by the statement that the

source term corresponding to a conserved quanity vanishes. For

example, if I represents the total mass system on has

I = M

f becomes the mass density p

f = p

and conservation of mass is expressed by the relation

= 0 (V.Z0)

The time change of the density p is then, apart from the sign,

equal to the divergence of the mass flow. Moreover, the mass

flow is clearly

j[M] = pv (V. ll)

where v is the velocity of matter. Using (V.10) and (V. II), we

therefore obtain the classical continuity equation

8p

i + div pv = 0

at

(V.12)

Likewise, conservation of total energy U (first law of

thermodynamics), and of total momentum Q (in the absence of

external forces), may be expressed as

¢[U] = 0; _[Q] = 0 (V. 13)

The source term for entropy S plays a special role as the second

principle of thermodydnamics and postulates the inequality:

_[S] _ 0 _ (V.14)

Entropy is not a conserved quanity, but increases as the

result of irreversible processes included in the source term.

is only for reversible processes that the change of entropy is

entirely due to entropy exchanges with the outside world.

It

Let us go back to the density of flow j[I] in the balance

equation (V.9). In general, we are concerned not only with a

convection flow such as (V. ll) but also with a conduction flow

Jc0nd (say), which occurs even in a system at rest. We have

therefore

J = Jc0nd + Jconv = J¢ond + fv (v.15)

28
For example, the heat flow W is the conduction current

associated with internal energy. We shall consider other

examples later on in this chapter.

In many cases, it is useful to introduce the so-called

substantial or hydrodynamic derivative

d 8 8

- + Z v i

dt 8t i 8x i

(v.16)

The continuity equation (1.12) leads then to the equalities:

d9 8# 8# 8(p_) 8

p - p -- + [ pV i -- + E _ (pvip) (V.17)

dt 8t i 8x i 8t i 8xi

This relation may be applied to an arbitrary intensive variable

_(x,y,z,t) H _(xl,x_,x_,t ) .

A summary of these results are shown in Table IV. Table IV

also provides a comparison with solutions from Straub's AT

method.

The details for the derivation of conservation laws can be

found in the book entitled "Thermodynamic Theory of Structure,

Stability and Fluctuation" by Glansdorff and Prigogine (1971)[7].

29
VI. TRUESDELL'S RATIONAL THERMODYNAMICS: A CLASSICAL REPROACH

The approach taken by rational thermodynamics researchers is

to seek concepts and principles sufficient to describe and

calculate temperature fields in bodies subject to deformation and

heating. Rational thermodynamics has pointed its attention at a

process occuring in time, as opposed to the classical approach of

Gibbs who has sought in statistical mechanics and from it has

constructed a rational foundation for the statics of hotness,

heat, and equilibrated forces. Recent applications of rational

thermodynamics were the propagation of stress waves, the effects

of severe deformation upon a body's ability to conduct heat and

of heating, upon a body's response to stress and strain, and the

nature of energetic and diffusive transfer, incident upon change

of shape. Because such effects notoriously differ in bodies of

different materials, an adequate theory must distinguish

materials by constitutive properties, openly and explicitly

stated. The constitutive function of a body must make it

impossible for that body ever to violate the fundamental axioms

of thermodynamics. The fundamental theory of rational

thermodynamics is to reproach that the concepts and assumptions

of the pioneers such as Kelvin, Clausius and Gibbs, selected and

refined and extended, can be made the basis of a treatment that

reflects simply the physics of heat and work and is not only

rigorous, but also broad enough to cover irreversible processes

in deformable continua.

The treatment of dissipative phenomena highlights the spirit of

rational thermodynamics of Truesdell. In terms of describing

fluid flows, rational thermodynamics rests upon some prior

concepts of mechanics which may mean the ordinary theory of a

deformable body. The concepts of mechanics were further extended

to allow for diffusion and chemical reactions as well.

In developing a thermodynamic theory for deformable bodies,

Truesdell starts with the classical theory of continua. Let a

body B occupy a domain of space at each time t. These domains

are its configurations. The mappin_ of one such domain or

reference configuration K onto the present configuration is

called the motion of B with respect to that configuration:

x = x K (X, t) , - _ < t < _. (VI. i)

Here x K is the mapping that carries the place X in the reference

configuration K into the place x at time t. The places X

identify the particles; thus we may speak of "the particle X"

without fear of confusion. The velocity x is the rate of change

of position of a particle:

H 8txK(X,t) = x(x,t). (vi.2)

A mass, which is a non-negative measure M, is defined once and

for all over measurable subsets of the body and is also assumed

to be an absolutely continuous function of volume. Hence a non30
negative mass-density p(.) exists almost everyw, here at each time,

and at points where it and the velocity field x(.) are

sufficiently smooth

p + p div x = O. (vl.3)

The linear momentum m and rotational momentum _x0 of B in its

present configuration are defined by

r

m _ | x dM,

_B]

_x0 -= I (x - x0) A x dM,

B

(VI. 4)

where x 0 is a fixed place and where the integration is based on

mass. Euler's laws of mechanics assert that for every body the

time rates of change m and _x0 of these quantities are equal to

the total force f and total torque Fx0 acting upon that body in

its present configuration:

m = f, hx0 = F×0. (VI.5)

In the simplest kind of continuum mechanics, the force f is

assumed to be the sum of two forces of special kinds: the total

body force fb and the total contact force fc. The total body

force is an absolutely continuous function of mass, while the

total contact force is an absolutely continuous function of

surface area:

f = = fb ,

= [ tdA + I bdM"

_SB B

(VI. 6)

The field b, defined in the interior of B, is the body force per

unit mass; it represents forces acting at a distance, e.g., those

of gravitation and electromagnetism. The traction t represents

the action of neighboring parts of material upon one another, or

any forces applied in any way to the boundary aB of the body B in

its present configuration. According to a theorem of Cauchy, the

traction is delivered by the stress tensor T:

t _ Tn, (VI.7)

n being the outward unit normal to aB. By combining (VI.4),

(VI.5), (VI.6), and (VI.7), on the assumption that the various

fields occurring in those equations must be sufficiently smooth ,

it is easy to derive a local equivalent to the principle of

linear momentum for continua:

31
div T + pb = px, (VI.8)

called Cauchy's first law of motion.

If we restrict attention to the case when all torques are

moments of forces, and so

Fx0 = [ (x- x0)\ t dA + [ (x - x0) \ b dM,

L 0B L 0B

(VI.9)

then another theorem of Cauchy asserts that the stress tensor T

is symmetric:

T = T T (VI. i0)

This is Cauchy's second law of motion.

The kinetic energy K of B in the present configuration is

defined by

K = i[x2 - dM,

2 _ B

(VI. Ii)

while the power P is the rate of working of all the forces acting

on B:

P _--[ t . x dA + [ b . x dM. (VI.12)

LOB _B

Now, according to a simple theorem-first proved by Stokes, the

net working W at a time T on the body B is given by the

difference of P, the mechanical power, and K, the kinetic energy,

thus:

W-P-K,

r

= | w dV,

LBI

(VI. 13 )

where

w = T . grad x, (VI. 14)

the dot indicating the inner product in the vector space of

second-order tensors (X . Y _ tr (XyT)). The scalar w is the net

32
_orking per unit volume; it is often called the stress power.

These few formulae provide a specfic mechanical framework upon

which a structure of thermodynamics may be raised. Here, of

course, all quantities are given in terms of time-dependent

spatial fields, not merely functions of time alone, and so we

cannot blindly apply the results of Lecture i, but we may proceed

in a parallel way. A number of things I shall say will be valid

equally in more general kinds of mechanics, where a result of the

form (VI.13) holds with a density w which is given by an

expression more complicated than (VI.14), allowing, for example,

for the action of couple stresses, but, so as to have a fully

definite and explicit mechanical background.

The first law of thermodynamics, expressing the balance of

energy is [9]:

E = W + Q

where E is the internal energy of a body, W is the net working on

it, and Q is its heating. This axiom we now set alongside

Euler's laws (VI.5) as basic for all theories relating forces and

energies to motions. Just as we have specialized Euler's laws by

assuming (VI.6) so as to obtain forms appropriate to continuum

mechanics, so also we may specialize the principle of balance of

energy in a corresponding way. First of all, we take the net

working W to be that calculated according to continuum mechanics

and hence given by (VI.13) as an absolutely continuous, additive

set function with density (VI.14). Parallel to the assumptions

(VI.6) and (VI.9) regarding the resultant force and resultant

torque, we lay down the assumption that the heating Q is the sum

of the two hearings of special kinds: the body heating Qb and

the contact heating Qc; the former being an absolutely continuous

funcntion of mass, and the latter, an absolutely continuous

function of surface area:

Q = Qc + Qb,

[ q dA + [ s dM.

J 8B _BI

(vi.15)

The volume density s is called the heating supply; the surface

density q, the influx of heating. The two kinds of heating, Qc

and Qb, are often said to describe conduction and radiation,

respectively, but no such specific connotation need be made in

general. Finally, the internal energy is assumed to be an

absolutely continuous, additive set function:

P

E = | _ dM,

tB|

(VI. 16)

33
_he density E being called the specific internal energy or, for

short, the energetic.

Under the assumption (VI.16), from [9] and (VI.15) Stokes

derived by Cauchy's method a result inferred earlier in a major

special case by Fourier, namely, the influx of heating is

delivered by the heating-flux vector h:

q = h . n, (VI. 17)

n being the outward unit normal to 8B. For sufficiently smooth

fields, by (VI.17), (VI.16), (VI.15), (VI.14), and [9] it is easy

to show by use of the divergence theorem and (VI.10) and (VI.8)

that

pc = w + div h + ps. (vI.18)

This differential equation is sometimes regarded as a local

statement of the "first law of thermodynamics", although in fact

it is a consequence of a rather subtle sequence of field

definitions along with Cauchy's laws of motion (VI.8) and (VI.10)

as well as the general balance of energy [9]. Major special

cases of this differential equation were derived, under various

special hypotheses, by Fourier, Kirchhoff, and C. Neumann.

In the thermodynamics of homogeneous processes the axiom of

irreversibility takes the form of the Clausius-Planck inequality

[9]:

eH __ Q,

where e is the absolute temperature and H is the calory. We must

now introduce the concepts of temperature and calory in continuum

mechanics. The former offers no difficulty. The temperature e

is given by a positive-valued temperature field,

e = e(x,t) > 0, (VI. 19 )

defined over the persent configuration of the body B. As in

statistical mechanics, also in continuum mechanics the reciprocal

of the temperature, which may be called the coldness J is often

more convenient for the mathematical theory:

i

j - _.

e

(VI.20)

It is natural to assume that the calory, like the internal

energy, is an absolutely continuous function of mass:

34
.r

H = J_ n dM (VI.21)

B

The density 4, which is usually called the specific entropy, I

prefer to name the coloric. This name has the virtue of dragging

a red herring across the path of those who lay down police-edicts

concerning when and how "entropy" is to be "defined". As they

back off in horror at revival of the long-dead caloric theory of

heat, we can return to our concrete, mathematical theory, safe

behind our two negations of authority.

Caloric is introduced to represent gross dissipation. While

coloric may flow from place to place and thus increase or

decrease locally, its total, the calory H, is subjected to a rule

favoring increase. We may regard this vague statement as

expressing the content of Clausius' assertion:

H _ 0 when Q = 0. (VI.22)

The pioneers of thermodynamics regarded this assertion as a

general axiom, not restricted to any special type of body or

process, but they were unable to implement it by mathematics such

as to give it a concrete form. Their various "second laws" sound

more like warnings or threats than principles of a rational

science. In modern continuum mechanics, because (VI.15) holds,

we may express Clausius' assertion thus: In a body B where

conditions are so balanced that

I dA + | dM = 0

r

q S

r

8B JB

(VI.23)

the calory cannot decrease:

I n dM __ O.

B

(vi.24)

(A body B is said to be in a "calorically isolated" or

"insulated" configuration if q = 0 on 8B while s = 0 in the

interior of B. For such a body, of course, (VI.23) holds.)

While this statement expresses some idea about irreversibility,

it does not lead to a unique generalization of the ClausiusPlanck inequality [9] to deformable bodies. In particular, since

temperature does not appear in it, it affords no connection

between the ideas of heat and temperature. In this lecture I

shall motivate the principle now regarded by most of the

presently productive theorists, though not by all, as being a

correct dissipation inequality. To this end I shall present some

35
simple aspects of dissipation in familiar examples.

The internal dissipation $ is defined as being the amount by

which the increase of caloric multiplied by the temperature

exceeds the local heating:

1

- 8n - - (div h + ps).

P

(VI. 25)

While _ is defined in terms of the quantities associated with

temperature and heat alone, the equation of energy balance

(VI.18) permits us to interpret $ also as the amount by which the

increase of caloric times temperature exceeds the increase of

energetic not produced by working:

w

P

(VI.26)

If we were to transfer to the local description the ideas that

motivate the Clausius-Planck inequality [9], we should require

that this increase be non-negative:

£ 0. (VI.27)

We shall name (VI.27) the Planck inequality. 4 For reasons to

appear later, we shall not impose it as an axiom. Instead, in

the remainder of this report, we shall first calculate _ for the

most familiar kinds of materials and then note some consequences

that follow when indeed _ £ 0.

First, for the ideal gas of the Euler-Hadamard theory,

T = -pl (VI. 28)

and also [9],

E = ECv,+), p = -avE, O = @hE,

where v -- i/p. Hence by (VI.14) and (VI.3)

w p

.... tr (grad x) = -pv,

P P

and so by (VI.26)

(VI. 29)

36
= 0. (VI. 30)

Thus the internal dissipation of the ideal gas is always null.

The same result holds for the general thermo-elastic material,

which includes as a special case the ideal gas.

Consider now the linearly viscous fluid of the Navier-Stokes

theory. For it, a viscous stress V is superposed on the Eulerian

pressure:

T = -pl + V. (VT.31)

and this V is assumed to be a homogeneous, linear, isotropic

function of the stretching D:

2D = grad x + (grad x)T, (VI.32)

and

V = k(trD) 1 + 2_D, (VI.33)

the pressure p still being related to the internal energy by [9].

Hence by (VI.26)

p_ = V . D,

= _(trD)2 + 2_ tr D 2, (VI.34)

Thus the internal dissipation of the Navier-Stokes fluid is the

working of the viscous stress V. The requirement _ £ 0 is

standard in this theory. Moreover, it is imposed identically in

D. That is, in the theory of viscous fluids we demand that the

viscous stress shall never give out work in any motion we might

imagine s , but it may use up work, and generally it will. It is

easy to show from (VI.34) that the condition _ £ 0 for all D is

equivalent to the classical inequalities of Duhem and Stokes:

>_ 0 3X + 2_ >_ 0. (VI.35)

The concept, described so far in Lecture 2 of [9] by Truesdell,

contains the important aspects of rational thermodynamics and its

application to fluid flows.

37
VII. Discussions and Concluding Remarks

In this study, we have surveyed a number of theories in

connection to the description of combustion chamber flows.

Particular attention was paid to the Falk-Ruppel theory of

'Gibbsian thermodynamics' and Straub's 'Alternative Theory' (AT)

in addition to Prigogine's theory of 'Non-eqilibrium

Thermodynamics', Truesdell's 'Rational Mechanics', and Boltzmann's _Kinetic Equation'. Whenever possible, comparisons were

made with the conventional Navier-Stokes equations and Straub's

AT. Table I shows side by side the equations of motion from

Navier-Stokes and Straub. Table II compares respective

formulations of Falk-Ruppel and Straub. Wu's formalism, deduced

from Boltzmann's kinetic equation, is compared with the classical

Navier-Stokes equation in Table III. Finally, the comparison

between Prigogine's non-equilibrium thermodynamics and Straub's

AT is shown in Table IV.

A direct correspondence between Falk-Ruppel's theory and the

Navier-Stokes equation could not be established at this time.

However, Boltzmann's kinetic equation with certain constraints,

extended by Wu's formalism, permitted the derivation of the

classical Navier-Stokes equation.

During this investigation, no conclusive results could be

established. However, some comments about the application of the

classical Navier-Stokes equation to combustion chamber flows can

be stated. Before addressing these comments, some important

characteristics, which are fundamental in combustion chamber

flows, are summarized below:

(i). Many species exist in the spray/combustion domain

under wide ranging pressure and temperature conditions. These

species could be present also in different phases. This

identifies the combustion chamber flow as a multi-flow and multiphase system.

(ii). During the combustion process the multi-species,

multi-phase flows go through states of non-equilibrium

thermodynamics, i.e. each species exhibits its own number

density, temperature, and velocity.

(iii). Since the flow conditions follow non-equilibrium

thermodynamic states, the associated chemical reactions will also

observe non-equilibrium behavior.

With these specific flow characterisics in the combustion

chamber, it is obvious that the classical Navier-Stokes equation

becomes theoretically inadequate to describe the complex flow

system. We realize that the modified Navier-Stokes equations are

being used currently for combustion chamber flow simulations.

But these modified equations have been derived on an _ad hoc'

basis. To illustrate the inadequacy of the present Navier-Stokes

38
equation for combustion chamber flow modeling, we offer the

following few comments without exhaustion:

(i). It is known that the Navier-Stokes (NS) equation is

derived for a single-fluid flow. Although the NS equation has

been extended to multi-fluids with multi-phases, the equation of

state for ideal gases is used to describe this fluid system,

which we all know is not the case.

(ii). As demonstrated by Wu [i0, ii], the radiative

gasdynamics flow under non-local thermodynamic equilibrium (nonLTE) conditions has led to a number of additional transport

coeficients. These additional transport coefficients will have

an effect on the momentum and energy transport. Such phenomena

should be expected for combustion chamber flows.

(iii). If the momentum and energy transport were modified,

the flow field will be changed also. Thus, it will affect the

design and performance parameters of the combustion chamber.

From these remarks, it is obvious that the governing equations

(usually called NS equations) deserve a great deal of attention

to better understand and model the physics of the combustion

chamber flow. Therefore, we conclude with the following

recommendations:

(i). Investigate the potential connection between FalkRuppel's theory of Gibbsian thermodynamics and the Navier-Stokes

equations.

(ii). Examine whether Straub's claim from his AT could

contribute to the improvement of the modeling of combustion

chamber flows.

(iii). Conduct a rigorous investigation for a conclusive

comparison of the NS equations with the respective governing

equations from the theories developed by Faulk-Ruppel, Straub,

Prigogine, Truesdell and Boltzmann_s extended and demonstrated

by Wu [i0, ii]. The outcome will establish a reliable foundation

for the modeling of combustion chamber flows.

39
J

Table I. Comparison Between Classical N-S and Straub's AT

N-S

Assuming start point is

Newton's law

I _=dp

dt

2 p = mv _ momentum

3 v Pdt

4 v = - -'p+ _.T + _

dv _ _

5 P dt _P + r +pf

I 6 No change

7 No change

I 8 No change

1 1 result

Dv

i P Dt _p _ 7 T _ pt

Assuming s_art point is Newton's

4O
Table II. Comparison Between Falk-Ruppel and Straub

1

2

3

4

5

6

Falk-Ruppel Theory

Gibbsian Thermodynamics

Momentum

p = m v

No difference with

Newton's Equation of

Motion under certain

assumptions.

Entropy production is

the central problem

Reference

G. Falk-W. Ruppel

Energy and Entropy(1976)

Mechanics, Relativity,

Gravitation (1977)

Straub

Alternative Theory (AT)

Momentum

p = mv + m# (3, s, p, wk)

There are differences with

Newton's Equation of Motion

a

i.e. an extra term -- (p#)

at

He got his "AT" from Falk's

dynamics.

He dealt with AT using the

entropy production

Reference

D. Straub (1989)

Thermofluiddynamics of Optimized

Rocket Propulsions

41
"3

r-

"3

E

'./1 0

.'3

OM

5_

_ eJ

,- !

mZ

OU

!

g

G'

E M

O

._ S3

I

g =

._ r'

M 0

''J ¢,1 O

'.1 0

_r..n O

0

> .la

M

1

e-

_ .,-to_t_

0 0 0

C_

I

P

.'N I

I

=Ix

I

i

: '1 1:° =o

_- o _

II ._" U

g :g ,-o ._ _"

._ r-' >a

,'_ tl I

+ M _

c_, L_ °L._ ,

ORIGINAL p;:_C.E _s

OF POOR QUALITY

;1

"3

O P"

0

,"_ C

• _1.C

0 ,_ I._ +

_ E E

_ It II

=-g--?

°

;.4

T

v

I

v

I

i -

I :1

=

0 ::_ -

U

glg

;I

+

I/1

_ L_ B

:5"

p.

v

I

G

P,.I I

I

+

g

I

I

>.

o

:_,_,

ii

g i:g

+

_L _

42
Table III-B. Comparison Between Wu's Formalism and

Classical Navier-Stokes Equation - Continuity

Wu's Formalism [i0, ii]

Wu's Formalism on the Basis of

the Boltzmann Equation

Continuity

Equation (6.4) of Wu

ap 0

-- + -- . (pc0) = 0

at a_

Eq. (2.22)

1

C0=- _ pj Uj

P j

(2.24a) uj = C O + /_j

If all the species have the same

velocity, namely at LTE.

=> 13j = 0

uj = Co

pco = l:j pj /Sj = (Zpj) L;= pLi

Op 0

-- +-- , (p/5)= o.

at a_

Classical Navier-Stokes

Classical N-S Equation

Continuity

ap a

-- +-- , (;u) = o.

at a_

ap (9

-- + -- ' (pU) = O.

at ap

43
Table IV. Comparison Between Prigogine's Non-Equilibrium

Thermodynamics and Straub's AT

1

2

3

41

-I

51

PRIGOGINE

D$

p --= pf --7 (ps --_)

Dt

Micro theory (nonequilibrium statistical)

(A) Starting at Liouville

Equation

(B) Parallel to quantum

Mechanical method

What remains unclear in

Boltzmann's derivation

is the range of validity

of his equation.

In chemical thermodynamics, he described the

entropy production.

References:

1. Prigogine (1962)

Non-equilibrium

Statistical Mechanics

2. Prigogine (1964)

Chemical Thermodynamics

3. Glansdorff and

Prigogine (1971)

Thermodynamic Theory of

Structure, Stability

and Fluxation

STRAUB

Dv 1 a

p - pf -- 7(p_--T) + -- --(pV--pl)

Dt 2 at

AT is based on Prigogine's micro

theory, but he referred only

to Prigogine's book "Chemical

Thermodynamics" in which the

micro-theory was not involved.

The macroscopic laws must be

throroughly revised according

to Prigogine's results.

Justifying them with the

Boltzmann equation is untenable.

He used the entropy products

in his AT.

Reference:

D. Straub (1989)

Thermofluiddynamics of

Optimized Rocket Propulsions

44
ACKNOWLEDGEMENT

The Principal Investigators appreciate the valuable comments

and suggestions of Mr. Klaus Gross (contract monitor) NASA/MSFC

in his review of this final report.

_r

95
REFERENCES

i. Maximization of Entropy for Equilibrium Processes with

Emphasis on Rocket Engine Combustion Phenomena, by R.J.

Prozan, Lockheed Missiles & Space Company, Inc.,

Huntsville, AL, 28 October, 1969.

2. Mechanik, Relativitat, Gravitation, by G. Falk and W.

Ruppel, Springer Verlag, 2nd Edition, 1977.

3. Energie und Entropie, by G. Falk and W. Ruppel, Springer

Verlag, 1976.

4. Gibbsian Thermodynamics, Meeting Minutes, January 9-14,

1991, University of Alabama, Huntsville, By K. W. Gross and

S. T. Wu.

.

.

,

,

•

10.

ii.

Thermo-Fluid-Dynamics Processes in Rocket Thrust Chambers,

Workshop Report, November 13-15, 1991, University of

Alabama, Huntsville, by K. W. Gross and S. T. Wu.

Thermofluiddynamics of Optimized Rocket Propulsions, by

Dieter Straub, Birkhauser Verlag, 1989.

Thermodynamic Theory of Structure, Stability, and

Fluctuations, by P. Glansdorff and I. Progigine, WileyInterscience, 1971.

The Mathematical Theory of Non-uniform Gases by Sydney

Chapman and T. G. Cowling, Cambridge at the University

Press, 1960.

Rational Thermodynamics, by C. Truesdell, Springer Verlag,

2nd Edition, 1984.

Kinetic Theory of Macroscopic Transport Phenomena in

in Multifluid Systems, by S° T. Wu, J. of the Phys. Soc.

of Japan, 27, No. i, pp 8-19, 1969.

Conservation Equations for the Non-Equilibrium Radiative

Flow, by S. T. Wu, J. of Phys. Soc. of Japan, 2__9, No. 3,

pp 778-788, 1970.

46
8-

APPENDIX I

Meeting Minutes

Gibbsian Thermodynamics

on January 9 to 14, 1991 Professor Wolfgang Ruppel from the

University in Karlsruhe/Germany visited UAH and MSFC to present

and discuss a new concept he defines as "Gibbsian

Thermodynamics." This concept has been proposed in two books

with Prof. Falk and Prof. Ruppel as authors, written in German

and entitled EnerqY a__nd EntroDv and Mechanics, Relativity,

Gravity.

Professor Ruppel familiarized us with the novel Gibbsian

Concept, and he pointed out the simplicity of the new concept as

well as many advantage associated with this approach.

The concept was accepted in its abstract formulation, but

questions with respect to some applications were not resolved.

Prof. Ruppel will give us his answer shortly, after he has looked

at the problems from the different points of view presented at

the meetings.

In general, the new concept appears to be superior to the

classical thermodynamics approach. The presentations and

discussions have only covered a limited number of topics due to

the limited time available. It also takes time to comprehend

this new approach. However, a dialog has been initiated and

should be continued. A translation of the two books in question

or a new report, which is oriented to the evaluation of existing

equations of motion, will be of advantage.

47
-i

APPENDIX II

Workshop Report

Thermo-Fluid-Dynamics Processes in Rocket Thrust Chambers

The workshop was held at the Mechanical Engineering

Department of The University of Alabama in Huntsville from

November Ii - 15, 1991 in Engineering Building Room 102. The

principal investigator for the MSFC contract is Prof. S. T. Wu.

This workshop addressed two topics: (a) thermodynamic

equilibrium calculation for rocket engines, and (b) critique of

the Navier-Stokes equation, which are discussed in reference (6)

by Prof. Straub.

(a) Both, the NASA ODE program and the Munich Method code

carry now an option to consider finite area combustion effects.

The solution process in both approaches is based on the

identified Lagrange function, and the predictions are close. The

claimed preference of the maximization of entropy over the

minimization of energy was not accepted. Although comments in

Ref. (6) relate to an earlier ODE program, documented in NASA SP

273, there are other specific harsh unjustified claims and

erroneous results from an inadequate earlier Munich method

program. To clear the ODE program from these allegations, the

appropriate steps shall be initiated by Prof. Straub to correct

this situation.

(b) Proof of a new 'Navier-Saint Venant' equation validity,

resulting from Prof. Straub's proposed Alternative theory, was

not presented and, therefore, the equation was not accepted as a

preferred scheme over the Navier-Stokes equation at this time.

Some interesting results, however, should be surveyed. A

document, showing the derivation of the novel equation, should be

prepared in English to assure a tention and relevant studies.

_T

48