F-314 TOC

Proceedings of ASME FEDSM’03
th
Proceedings
F-314 Forumon Fluidics:
4 thASME_JSME
Joint FluidsofEngineering
Conference
4 ASME, JSME Joint Fluids Engineering Conference
Honolulu, Hawaii, USA, July 6-10, 2003
July 6-10, 2003, Honolulu, Hawaii

FEDSM2003-45130
FEDSM2003-45130
THE EFFECT OF UPSTREAM FLOW CONDITIONS TO LAMINAR MIXING IN A MINIATURECOMBUSTION CHAMBERPeter L. Woodfield / Kyoto University

Kazuya Tatsumi / Kyoto University

Kazuyoshi Nakabe / Osaka Prefecture University

Kenjiro Suzuki / Kyoto University

ABSTRACTA three-dimensional unstructured finite-volume method isused to investigate laminar flow characteristics of a miniaturechamber with a possible application to micro gas turbine
combustor design. The chamber is cylindrical in shape and20mm in diameter with the fuel stream entering via a single jetin the center of one end of the can. Oxidizer jets are generated
by a circular baffle plate having six holes surrounding the fueljet. Attention is given to the effect of the inlet conditions on
the flow structure and mixing pattern inside the chamber.
Computations are carried out with the calculation domain inlet
being positioned at two different locations; (1) at the immediate
entrance to the combustion chamber (2) one combustor
diameter upstream of the baffle plate. Numerous inlet
conditions are considered including ‘top-hat’, fully-developed,
swirling, an annular backward facing step and someasymmetrically skewed profiles. The baffle plate is shown tohave a significant smoothing effect on the inlet conditions for a
Reynolds number of 100.
INTRODUCTION
The present study is part of an ongoing project to develop aminiature can-combustor for a micro gas turbine (MGT; 5 - 100kW) to be used in a hybrid MGT – solid oxide fuel cell (SOFC)
distributed energy system [1]. The device could ultimately be
used for electricity production in individual houses or for small
communities. Hence it is essential that each component in thesystem is compact, safe and reliable. To meet the first of theserequirements, the physical size of the combustion chamber is
expected to be restricted to the order of 20mm in diameter and
200 mm in length. Thus simulation of gas mixing in smallchambers is considered an important topic for investigation
within the overall framework of the project. The device itself
could be designed to operate under either laminar or turbulent
flow conditions.
Figure 1 shows the geometry under consideration. The
fuel enters the chamber as a single jet in the center of one end
and the oxidizer jets are produced by a circular baffle plate
having six holes surrounding the fuel jet.

Previously, the authors considered the effects of the sizeand positioning of the jets in the present design for laminarconditions [2]. The goal of the present study is to continue thestudy on the laminar flow case and in particular to focus on theeffects of the inlet conditions upstream of the baffle plate to themixing patterns in the chamber. To separate the effects ofchemical reaction and fluid dynamics, the results presented arefor isothermal constant density flow.

Baffle Plate
d2

Oxidizer
Fuel

Combustion
Chamberd3 d1

Coord.
Sys. Origin

D
R2

z

Lup
L
Fig. 1 Geometry for investigation.
NOMENCLATURE
bth
d1
d2
d3
D
L
Lup
L1
p
R1
R2
ReD
U
ui

1

thickness of baffle plate
inside diameter of fuel tube
diameter of oxidizer holes
outside diameter of fuel tube
diameter of canlength of domain downstream of baffle plate
length of domain upstream of baffle plate
distance upstream of baffle plate to back-steppressure
radius for top of annular step
radial position of center of oxidizer holes
Reynolds number, ρUD/µmean velocity over can cross-section‘i’th component of velocity

Copyright © 2003 by ASME

xi
x
y
z

computational grid on the surface of the domain. The view isfrom the upstream side of the baffle plate. Using finer grid
spacing produced little change to the results indicating that thechosen spacing was fine enough for the present study.

Cartesian coordinate
Cartesian coordinate (= x1)
Cartesian coordinate (= x2)
Cartesian coordinate (= x3)

Greek symbolsµ
dynamic viscosityξmixture fractionρ
densityσ
Schmidt numberφdependent variable
GOVERNING EQUATIONS
Three-dimensional incompressible continuity (Eq. (1)) andNavier-Stokes equations (Eq. (2)) are solved for steady state
conditions.
∂u j
(1)
=0
∂x j



∂
(ρu jui ) = − ∂p + ∂  µ ∂ui ∂x j∂xi ∂x j  ∂x j CODE VALIDATIONThe computer code used for this study was written by the
first author and has been tested and found to perform well [3]for a range of laminar flows including pipe flow, flow in an
eccentric annulus, backward facing step flow and flow for acompact fin and tube heat exchanger element. Low sensitivity
to grid arrangement and orientation also has been demonstrated
for practical grid spacing [3] at Reynolds numbers similar to
those used in the present study. Figure 3 shows the centerline
velocity distribution for a three-dimensional lid-driven cavity
flow against the benchmark finite-element results of Jiang et al.
[5]. The grid allocation was similar to that used in thebenchmark test. The good agreement shown is a further
example of the validity of the present numerical procedure.

(2)

1

The calculation is treated as a constant property, twostream mixing problem and Eq. (3) is solved for the mixture
fraction, ξ, (mass fraction of gas which originated in the fuelstream) under non-reacting (cold flow) conditions.


∂
(3)
(ρu jξ ) = ∂  µ ∂ξ 
∂x j
∂x j  σ ∂x j 

0.8

Jiang et. al.
(1994)(Finite Element)

Present
(UFV)

y/H

0.6
0.4
0.2

NUMERICAL METHOD

0
-1

-0.5

0

0.5

1

u/U
Fig. 3 Centerline velocity distribution for a lid-driven
cubic cavity flow.

Fig. 2 Computational mesh on surface of domain viewed
from the upstream side of the baffle plate.
A three-dimensional unstructured finite-volume procedure[3] is used to discretize the governing equations, Eq. (1) ~ (3).
A second-order upwind biased scheme is used for theconvection terms and the Rhie/Chow approach [4] is used toprevent checker-board oscillations in the pressure field. The
SIMPLE algorithm is employed to couple velocity and pressure
via the continuity equation. Median-dual control volumes
based on a hexahedral mesh are used for numerical integration.
Fig. 2 gives a close-up three-dimensional view of part of the

DOMAIN AND BOUNDARY CONDITIONS
Figure 1 shows the domain of the computation for thepresent study. Table 1 gives the specific details of thegeometry used in this study. All solid surfaces are treated with
the no-slip condition for velocity and the zero-flux condition
for the species conservation equation. The outlet which islocated at L = 15 diameters downstream of the baffle plate
utilizes a zero normal gradient boundary condition forcomponents of velocity and the mixture fraction. The locationof the inlet and the choice of inlet velocity profiles were varied
as the theme of this present study and thus are not given in
Table 1. In all cases however, the ratio of fuel to oxidizer mass
flow rate was kept constant at m1/m2 = 0.0488 whichcorresponds approximately to a methane/air combustor
operating with 18% excess air. Unless otherwise stated, theReynolds number, ReD, was set at 100 based on the diameter ofthe can, D, and the bulk velocity, U, on the downstream side of
the baffle plate. For these flow conditions, the authors
previously found that the specifications in Table 1 give close to
the optimum mixing rate for the present design [2].

2Copyright © 2003 by ASME

Table 1 Geometry for computation domain.
d1/D

d2/D

R2/D

bth/D

d3/D

L/D

0.182

0.182

0.341

0.05

0.282

15

OVERALL PERFORMANCE OF DESIGNPreviously, the authors considered the performance of thepresent design for a range of hole locations and sizes [2]. In
comparison to the confined co-axial jet with the same flow
rates of fuel and oxidizer, the present arrangement was found to
perform extremely well. Figure 4 reiterates this finding where
it is clear that the baffle plate contributes significantly to themixing compared with the case where no baffle plate is present.

the outlet positioned both at 10 and 20 can diameters
downstream of the baffle plate. Since the results shown for thetwo cases are almost identical it is considered that the length of
15 diameters is more than adequate for the present study.

EFFECT OF CALCULATION INLET LOCATION AND
VELOCITY PROFILETo test the importance of the choice of inlet location,
calculations are performed with the computational domain
beginning at the entrance to the combustion chamber (Figs. 6(a) and (b)) and with the inlet specified one diameter upstreamof the baffle plate (Figs. 6 (c) and (d)). For both cases two
different inlet velocity profiles are considered – the Poiseuilleprofile (Figs. 6 (b) and (d)) and the top-hat profile (Figs. 6 (a)and (c)).
start of comp. domain

0.4

0.5

y/D

y/D

0.2
0

0

-0.2

0.055

-0.4
-0.5

-0.5

0

0.5

1

1.5

2

-0.5

0

0.5

1

1.5

2

1.5

2

z/D

z/D

(a) with baffle plate-1(a) Top hat profiles at chamber inlet

start of comp. domain
0.5

0.4

y/D

y/D

0.2
0

0

0.055

-0.2

-0.5

-0.4
-0.5

0

0.5

z/D

1

1.5

-1

-0.5

0

0.5

1

z/D

2

(b) Fully developed profiles at chamber inlet
start of comp. domain(b) no baffle plate

0.5

y/D

Fig. 4 Overall effect of baffle plate - velocity vectors (x =0 plane). The solid line represents the mixture
fraction iso-surface, ξ = 0.055.

0

0.055
-0.5

SENSITIVITY TO OUTLET LOCATION

y/D

y/D

-0.25

-0.5
-0.5

-0.5
-0.5

z/D

(a) L/D = 10

0.5

1

1

1.5

2

0.5

0

-0.25
0

0.5

(c) Top hat profiles upstream of baffle plate
0.055

0.25

0

0

start of comp. domain

0.5

0.055

-0.5

z/D

y/D

0.5
0.25

-1

0

z/D

0.5

0

0.055

1

-0.5

(b) L/D = 20

-1

-0.5

0

0.5

1

1.5

2

z/D

(d) Fully developed profiles upstream of baffle plate

Fig. 5 Mixture fraction contours. Effect of choice ofdomain outlet location (x = 0 plane).
Before considering the sensitivity to the inlet velocity
profiles, it is useful to confirm that the computational domain
has been made long enough so that the outlet position has little
influence on the results. For the present study, the outlet was
positioned at 15 diameters downstream of the baffle plate.
Figure 5 shows mixture fraction contours in the x = 0 plane forFig. 6 Mixture fraction contours showing effect of choiceof inlet location for computational domain (ReD =100 and x = 0 plane).
As can be seen in Fig. 6, the results are reasonably
sensitive to the inlet velocity profile if it is specified at the inlet
to the combustion chamber (Figs. 6 (a) and (b)). However, if

3

Copyright © 2003 by ASME

the upstream region is included (Figs. 6 (c) and (d)) changing
the velocity profile from a top-hat profile to the Poiseuilleprofile has a negligible effect on the predicted mixture fraction
contours inside the chamber. Hence it is better to commence
the calculation upstream of the baffle plate and we may expectthat at one diameter upstream of the inlet a partially developed
or fully developed symmetrical profile will not have a major
effect on the mixing pattern inside the chamber for ReD = 100.
EFFECT OF INLET SWIRL
0.5

1.0

0.5
1.0

0.25

0

y/D

y/D

0.25

0

-0.25

-0.25

-0.5
-0.5
-0.25
0
0.25
x/D
(a) Inlet Vel. Profile; Swirl Number = 4

-0.5
-0.5
-0.25
0
0.25
x/D
(b) z/D = -0.25; Inlet Swirl Number = 4

0.5

0.5

0.25

0.25

y/D

1.0

y/D

1.0

0

Many practical combustors aim to make use of a swirling
flow field to enhance the mixing performance and achieve
stable combustion. Thus it is useful to consider the effect of aswirling inlet profile within the framework of the present study.
However, from the results shown above in Fig. 6 we might
expect that introducing swirl on the upstream side of the inlet
may not be so effective. This is confirmed in Figs. 7 and 8.
Figures 7 and 8 show velocity vectors at a number of axial
positions for swirling profiles introduced one diameter
upstream of the baffle plate. The length of the vector arrows
are scaled against the same reference vector so it is possible tosee how the swirl component diminishes with downstream
distance by comparing Figs. 7 (a), (b), (c) and (d).
Figure 7 shows results for an inlet swirl number of 4 where
the swirl number is defined as the maximum inlet tangential
component of velocity divided by the mean axial component ofvelocity. Figure 8 shows the same z – cross sections for a swirl
number of 8.
We can see from Figs. 7 and 8 that the baffle plate very
effectively damps out even a large component of swirl if
introduced one diameter upstream of the plate. The small
component of swirl that finally enters the combustion chamber
itself appears to contribute only a little towards enhancing themixing as is shown in Fig. 9.
0.5

0.5

0

0.055

-0.25

y/D

y/D

0.25
-0.25

0.25

0

-0.5
-0.5

-0.5
-0.5

-0.25

0
0.25
x/D
(c) z/D = 0.1; Inlet Swirl Number = 4

-0.5
-0.5

-0.25
0
0.25
x/D
(d) z/D = 0.25; Inlet Swirl Number = 4

0

0.5

z/D

1

(a) Inlet swirl number = 4

Fig. 7 Velocity vectors for swirl number = 4. The solidline is the mixture fraction contour for ξ = 0.055.
0.5

0.5

0.25

0.25

y/D

1.0

y/D

1.0

0

-0.25

-0.5
-0.5

0

-0.25

-0.25

0
0.25
x/D
(a) Inlet Vel. Profile; Swirl Number = 8

-0.5
-0.5

0

0.5

1

z/D

(b) Inlet swirl number = 8

Fig. 9 Mixture fraction contours (x = 0 plane).
Thus, the results of this section suggest that introducing
swirl on the upstream side of the baffle plate may not be thebest approach to create a strongly swirling flow field in the
combustor. Also, noting the observations made concerning Fig.
6, perhaps a more effective approach to introduce swirl would
be to change the angles of the jets as they enter the combustion
chamber by boring the holes in the baffle plate itself at angles
offset from the perpendicular.

-0.25
0
0.25
x/D
(b) z/D = -0.25; Inlet Swirl Number = 8
1.0

0.25

0.25

y/D

y/D

1.0

0

0.055

-0.5
-0.5

0.5

0.5

0

-0.25

-0.25

0

-0.25

-0.25

-0.5
-0.5
-0.25
0
0.25
x/D
(c) z/D = 0.1; Inlet Swirl Number = 8

-0.5
-0.5
-0.25
0
0.25
x/D
(d) z/D = 0.25; Inlet Swirl Number = 8

Fig. 8 Velocity vectors for swirl number = 8. The solidline is the mixture fraction contour for ξ = 0.055.

EFFECT OF INLET ASYMMETRY
While the baffle plate may have a tendency to damp out
some desirable inlet features such as swirl introduced on the
upstream side of the plate, we can also expect that it will reduce
the effects of undesirable inlet features such as asymmetry in
the inlet profile. This is an important consideration since thesize constraints on the practical design may make it difficult tocompletely smooth out the inlet velocity profile.
Figure 10 (a) shows the effect of specifying an inlet
velocity distribution which is tilted slightly about the x-axis sothat the velocity is 5% higher than the mean at y/D = 0.5 and
5% lower at y/D = -0.5. Figure 10 (b) shows the correspondingcase for a 20 percent departure from a uniform inlet velocity
profile.

4

Copyright © 2003 by ASME

y/D

0.5

desirable for a practical combustor. Hence from another aspect,
introducing a movable backward facing step on the upstreamside of the baffle plate could result in an adjustable device
capable of fine-tuning the mixing pattern.

5% higher than mean

0

0.055
-0.5

-1
-0.5
5% lower

0

0.5

1

L1
1.5

2

0.5

z/D

R1

0.5

y/D

(a) Inlet velocity profile skewed by 5%
20% higher than mean

0

0.055

y/D

-0.5

-0.5

0

0.5

1

1.5

2

1.5

2

1.5

2

(a) L1/D = 0.8; Re = 100

0.055
-1
-0.5
20% lower

0

0.5

1

1.5

0.5
2

z/D

y/D

-0.5

-1

z/D

0

(b) Inlet velocity profile skewed by 20%

0

0.055

-0.5

Fig. 10 Mixture fraction contours showing effect ofasymmetry in the inlet velocity profile (x = 0
plane).

-1

-0.5

0

0.5

1

z/D

(b) L1/D = 0.6; Re = 100
0.5

y/D

From Fig. 10 (a) it is apparent that for the case of a
Reynolds number of 100, a five percent departure from asymmetrical profile at one diameter upstream of baffle plateproduces only a very small effect on the symmetry of themixing pattern inside the combustion chamber. Figure 10 (b)indicates that an increase to 40 percent variation across the inlet
profile does have a noticeable effect on the mixture fraction
field. Thus, we can conclude that it is desirable to keep theflow pattern upstream of the baffle plate symmetrical but withthe present geometry and flow conditions, a small departurefrom symmetry at one diameter upstream of the inlet may beforgivable.

0

0.055

-0.5

-1

-0.5

0

0.5

1

z/D

(c) L1/D = 0.5; Re = 100

y/D

0.5
0

0.055
-0.5

-1

-0.5

0

0.5

1

1.5

2

z/D

(d) L1/D = 0.2; Re = 100

y/D

0.5

EFFECT OF PROXIMITY TO BAFFLE PLATE OF
UPSTREAM CHANGES IN GEOMETRY
In the above sections the effectiveness of the present
design in smoothing out a number of different profiles specified
at one diameter upstream of the baffle plate was demonstrated.
We will now examine how close to the baffle plate it is possible
to introduce a change in geometry before having a major effecton the flow field inside the chamber. This is an importantconsideration for the present application which, as mentioned
above, is likely to have restrictions placed on the maximum sizeof the inlet passage. For this test we have selected to introduce
an annular backward facing step upstream of the baffle plate.
The top of the step is specified by R1 in Fig. 11 (a) which
for the present study is set equal to R2 (cf. Fig. 1 and Table 1).
Figure 11 shows the effect of varying the upstream location of
the step denoted L1 as shown in Fig. 11 (a).
The similarity between Figs. 11 (a) ~ (c) and 5 (c) makes it
clear that for ReD = 100 the step has little influence on the
mixing pattern so long as it is positioned greater than about
0.5D upstream from the plate. On the other hand, if very close
to the plate as in Figs. 11 (d) and (e) the position of the step hasa significant effect on the mixing pattern. In both Figs. 11 (d)and (e) the mixing is evidently slower than in Figs. 11 (a) and(b). However, the fuel-rich region near the wall in Fig. 11 (a)has been reduced in size in Figs. 11 (d) and (e). This may be

0

0.055
-0.5

-1

-0.5

0

0.5

1

1.5

2

z/D

(e) L1/D = 0.1; Re = 100

Fig. 11 Mixture fraction contours – effect of adding anannular backward facing step upstream of thebaffle plate (Re = 100 and x = 0 plane).

EFFECT OF INCREASING REYNOLDS NUMBER
All the cases considered in the previous sections have been
for a Reynolds number of 100 based on the mean flow and candiameter. At higher Reynolds numbers we may expect that the
upstream inlet conditions will become more important forlaminar flow. To examine this effect, in Fig. 12 we haverepeated the cases shown in Fig. 11 but with ReD = 200. For allcases again we have maintained the same fuel/oxidizer ratio
and all inlet conditions are symmetrical.
It is apparent from Fig. 12 (a) that the mixing performanceof the present design is still very good at the higher Reynolds
number. Comparing Figs. 11 (a) and 12 (a) it is clear from thelocation of the iso-surface for ξ = 0.055 that the mixing field

5

Copyright © 2003 by ASME

generally expands in the downstream direction for an increaseof Reynolds number. However, unlike laminar coaxial jet flow
(cf. Ref. [2] for example), the expansion is not in direct
proportion to Re for every feature of the flow.

for clarity of the discussion it is easier to compare cases Fig.s
12 (b) and (d). Figure 13 shows the flow patterns in a z-crosssection located at z/D = 0.1 for the step positioned at L1/D =0.6 and at L1/D = 0.2.

0.5

0.5

y/D

0.055

1.0

0

0.055

-0.5

-1

-0.5

0

0.5

1

0.25

1.5

2

z/D
y/D

(a) L1/D = 0.8; Re = 200

y/D

0.5

0

0.055

0

-0.25
0.055

-0.5

-1

-0.5

0

0.5

1

1.5

2

-0.5
-0.5

z/D

0
x/D
(a) L1/D = 0.6; z/D = 0.1(b) L1/D = 0.6; Re = 200

y/D

0.5

-0.25

0.25

0.5

0

1.0

0.055
-0.5

-1

-0.5

0

0.5

1

1.5

2

0.25

z/D

(c) L1/D = 0.5; Re = 200

y/D

y/D

0.5

0

0

0.055
-0.5

-1

-0.5

0

0.5

1

1.5

-0.25
2

z/D

(d) L1/D = 0.2; Re = 200

-0.5
-0.5

0
x/D
(b) L1/D = 0.2; z/D = 0.1

y/D

0.5

-0.25

0.25

0

0.055
-0.5

-1

-0.5

0

0.5

1

1.5

Fig. 13 Velocity vectors for the cases shown in Fig. 12(b)and d. The sections are taken at z/D = 0.1. The
solid line represents the mixture fraction surface (ξ= 0.055 and ReD = 200).

2z/D(e) L1/D = 0.1; Re = 200

Fig. 12 Mixture fraction contours – effect of adding
annular backward facing step upstream of baffle
plate (ReD = 200 and x = 0 plane).
Another important observation from Fig. 12 is that at
higher Reynolds numbers, the position where the inlet
conditions start to become important is further upstream than atlower ReD. It should be noted here that the results for Fig. 12(a) are almost identical to the ReD = 200 case without the step
(not shown). Comparing Fig. 12 (a) with Fig. 12 (b), thepositioning the step at 0.6 diameters upstream of the baffle
plate in the case of ReD = 200 has a noticeable influence on the
mixing pattern in the chamber where almost no change isobserved for the same position with ReD = 100 (cf. Figs. 11 (a)and (b)).
It also should be noted that there is a dramatic difference inthe mixing pattern for Figs. 12 (b), (c) and (d). This in part canbe explained through an examination of the respective flow
fields. Before examining the non-symmetrical case Fig. 12 (c),In Fig. 13 (a), the solid lines corresponding to the mixture
fraction surface ξ = 0.055 show very clearly the locations of theoxidizer jets. In Fig. 13 (a) there is a strong flow of the fuelstream into the region between the jets. This is evidenced by
the large arrows in the positive radial direction in these regions.
For the case shown in Fig. 13 (b) where the overall mixing
performance is much poorer (cf. Fig. 12 (d)), the flow of thefuel stream into the regions between the jets is greatly reduced
and the fuel-rich region (given by ξ > 0.055) does not encircle
the oxidizer jets. A close examination of the velocity vectors in
the center of the oxidizer jets, for example at x/D = 0 and y/D =0.35 in Fig. 13, shows that there is a considerably greater
negative radial component of velocity at this location for Fig.
13 (b) than for Fig. 13 (a). It is not unreasonable to supposethat for the case of Fig. 13 (b) the oxidizer jets have been
deflected towards the center of the chamber due to thepositioning of the backward facing step on the upstream side of
the baffle plate shown in Fig. 12 (d). Thus the jet angle has

6

Copyright © 2003 by ASME

been altered and a rather different flow and mixing patterninside the chamber has resulted.

2.
3.

0.5
1.0

y/D

0.25

4.

0

5.

-0.25

-0.5
-0.5

-0.25

0
0.25
x/D
L1/D = 0.5; z/D = 0.25

Fig. 14 Velocity vectors for the non-symmetric case in Fig.
12. The cross section is taken at z/D = 0.25. The
solid line represents the mixture fraction isosurface, ξ = 0.055, Re = 200.
Moving on to the non-symmetrical case shown in Fig. 12(c), it should be noted that the final level of convergence forthis case was quite good suggesting that it is in fact a valid
solution to the governing equations. Figure 14 shows a z-crosssection for this case at a position z/D = 0.25. The results
indicate some degree of symmetry, but not the full symmetry
for the cases shown in Fig. 13.
While somewhat undesirable from an engineering design
point of view, the non-symmetrical result is fascinating fromthe perspective of fluid dynamics. It demonstrates that for
perfectly symmetrical geometry and boundary conditions a
non-symmetrical solution can arise. In this case the fuel jet,instead of being divided evenly among the surrounding oxidizer
jets, has taken a special ‘liking’ to one jet in the top left-handcorner of Fig. 14. This kind of non-symmetrical phenomenon,
although well known for cases such as the double-sided
backward facing step perhaps has not been reported as widelyfor multiple confined jet arrays. Thus, in modeling this kind of
combustor it is better to follow the present procedure to include
the whole domain in the calculation rather than employ
symmetry boundaries where the geometry is symmetrical.
In concluding this section on the case with ReD = 200, it isclear that for laminar flow, as Reynolds number is increased so
also is the need for consideration of the effects of upstream
flow conditions prior to the combustion chamber.

CONCLUSIONSIn summing up this investigation on the effects of upstream
conditions a number of conclusions can be drawn as follows:

1.

Using an unstructured finite-volume technique theproposed combustor design was simulated and shown toperform well in terms of flow mixing over a range of
upstream inlet conditions for laminar flow.

6.

7.

For practical calculation it is better to start thecomputational domain on the upstream side of the baffle
plate rather than directly at the inlet to the chamber.
The present baffle plate design was generally shown tohave a smoothing effect on the upstream conditions thus
reducing the influence on the mixing pattern in thechamber.
If introduced one diameter upstream of the baffle plate, alarge component of swirl is necessary in order to have a
noticeable effect on the mixing pattern inside the chamber.
For a Reynolds number of 100 while some degree ofasymmetry may be permissible in the flow at a distance of
one can diameter upstream of the baffle plate, it is highly
desirable that the upstream inlet conditions be symmetricalto increase the likelihood of a symmetrical mixing patterninside the chamber.
For at least one set of flow conditions it was found that a
non-symmetrical flow pattern could result inside thechamber in spite of the fact that the geometry andboundary conditions were symmetrical. Thus it is better toinclude the full domain in a computation rather thanassume symmetry boundaries at locations where thegeometry is symmetrical.
Finally, for laminar flow, the higher the Reynolds number
the more care is likely to be required in preparing the inlet
conditions for a practical combustor.

ACKNOWLEDGMENTS
This work was supported through the project “Micro Gas
Turbine / Fuel Cell Hybrid-Type Distributed Energy System”
by the Japan Science and Technology Corporation (JST) as
Core Research of Evolutional Science and Technology(CREST). The support of the Japan Society for the Promotionof Science (JSPS) for the first author is gratefully
acknowledged

REFERENCES
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2. Woodfield, P. L., Nakabe, K. and Suzuki, K., 2003,“Numerical study for enhancement of laminar flow mixing
using multiple confined jets in a micro can combustor”,
International Journal of Heat and Mass Transfer, (in press).
3. Woodfield, P. L., Nakabe, K. and Suzuki, K., 2003,“Performance of a three-dimensional pressure-based
unstructured finite-volume method for low Reynolds
number flow and wall heat transfer rate prediction”,
Numerical Heat Transfer, B (in press).
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separation”, AIAA Journal, 21, pp. 1525 - 1532.
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