2nd International Symposium on Advanced Fluid/Solid Science and Technology in Experimental Mechanics, 23-25 Sept. 2007, Osaka, Japan

Phase-Averaged Mixing and Combustion Characteristics of Multiple Jets Perturbed by Cyclic Oscillation
Masaaki MIZUNO, Kazuya TATSUMI , Shinya OKANO and Kazuyoshi NAKABE
Department of Mechanical Engineering and Science, Kyoto University, Kyoto 606-8501, Japan

2. Experimental apparatus and conditions
Pulsating jet generating system
Flow Controller
Moter
GearboxPressure
Gauge Regulator||

Chamber

to atmosphereto Nozzle

|| ||
||

Valve
Flowmeter

Compressor

Pressure
Gauge||

Regulator

| |||
||

1. Introduction
Mixing between multiple jets is fundamental andimportant phenomena in fluid dynamics. It appears invarious industrial applications and is an essential factor
that significantly affects the device performances. For
example, poor mixing between jets of fuels and oxidation
in a combustor incurs a deterioration of the combustion
efficiency and emission of toxic substances such as
unburned hydrocarbons, soot and carbon monoxide.
Particularly, under low Reynolds number conditions, theflow becomes laminar, and a marked deterioration of themixing performance takes place among the jets due to thelack of turbulence mixing. These low Reynolds number jet
flows are found in small size applications (e.g. micro gas
turbine, chemical mixing devices and μ-TAS) owing to
the small characteristic length scale of the jet nozzles.
To tackle this problem, several techniques have beensuggested and studied in the past decades. Choi et al. [1]proposed a novel miniature-size can-type combustor
consisting of millimeter-scale confined multiple jets. In
this combustor, a baffle plate consisting of several nozzle
holes was introduced, and the fuel and air wererespectively supplied from the baffle plate through thenozzles to the combustion chamber. The mixing
performance was markedly improved in this system
mainly due to the interaction between each jet [2]. In order
to investigate the effects of such jet interactions upon thejet fluid mixing, the velocity distributions in triple jetsarrayed simply in line were measured by Nakabe et al. [3].
In this case, the interaction between the jets moved thelaminar-turbulent transition region upstream compared||

Key words
Multiple jet array, Jet flame, Pulsating flow, LaserDoppler velocimetry, Schlieren photographswith a single jet case. They also reported that an earliertransition of the jet flow from laminar to turbulent andalso a jet bifurcation were observed by applying a minimal
cyclic perturbation to the flow using acoustic waves.
Recently, Tatsumi et al. [4, 5] studied the effects ofpulsating the mass flow rate of the jets on the unsteadycharacteristics of the multi-jets under the conditions oflarge amplitudes and very low Strouhal number based on
the time-mean jet velocity. Although the effects were notso large compared with those produced by the acoustic
excitation [3], the large temporal fluctuation of jet flow
affected the time-mean mixing performance of the jets,
particularly in the area adjacent to the nozzle exit.
The above characteristics were discussed under theconditions without combustion reaction. The effects of theinteraction between the jets and flow-perturbation on thecharacteristics of the multi-jets can be more significant in
combustion state due to the existence of the physicalproperties variation in the flow, particularly at the flame
surface. In the present study, therefore, experiments wereconducted to evaluate the aforementioned effects on a
triple-jets arrayed in line. Visualization of the combustion
field applying the Schlieren method to the multi-jets was
conducted. Furthermore, flow velocity measurements
using laser Doppler velocimetry were carried out toevaluate the pulsating flow effects on the air jet mixing
characteristics in non-combustion state, to discriminate theinteraction effect between the pulsating jets and jet flamefrom the basic flow characteristics of the multi-jet.

||

Abstract
In the present study, flow and flame characteristics of a jetarray, which consists of three jets arranged in a row, were
evaluated. Methane and air were supplied from the centerand two side jets, respectively. The effects of periodicallypulsating the flow rate of the side air jets were examined
under very small Stouhal number based on the time-mean
jet velocity. Schlieren photographs were taken by a highspeed digital video camera in the cases when combustion
was accompanied. Flow velocity distributions in noncombustion cases were obtained using laser-Doppler
velocimetry. Small effects of the pulsating flow wereobserved in non-combustion state under such small
Stouhal number discussed in the present study. However,lager effect on the flow patterns was observed when
combustion reaction was accompanied, particularlychanging the location of the flow transition from laminar
to turbulent.

Valve

Flowmeter
Nozzles (test section)

Methane cylinder

Fig. 1: Experimental apparatus.
Figure 1 shows the experimental apparatus of the present
study. The triple jet nozzles aligned in the apparatus was
employed as the measuring object, which was the same as
the above mentioned experiments done by Tatsumi et al[4,5]. Figure 2 illustrates the magnified view of the nozzle
arrangement.. Three jets nozzles were aligned in a row,and the jets were blown into the stationary atmosphere,
which was an open, wide and calm space. The nozzles
were situated in parallel with the same inner diameter of d

2nd International Symposium on Advanced Fluid/Solid Science and Technology in Experimental Mechanics, 23-25 Sept. 2007, Osaka, Japanx
CylinderdyO

Chasiss

Flow direction

High - Speed Camera

Marker

L
S-jet

L

C-jet

S-jet

Laser Emitter
Laser Sheet

Laser ReceiverFig. 3: Schematic view of pulsating flow generating
unit.
High - Speed Camera

Fig. 2: Nozzle arrangement.
= 4mm, constituting a triple jet array. The nozzle tip was
sharpen and tapered by 45 degrees. As convenient for
further discussion, hereafter, the center jet will be referred
to as C-jet and the two other side jets will be referred to as
S-jets. The separation distance between the center of C-jet
and S-jets, L, was fixed at 6.0mm.
Air was supplied from a compressor to the S-jets. To
C-jet, methane gas and air were respectively supplied
under each condition of non-combustion and combustion
states. The flow rates of these gases were controlled by aflow meter located at the upstream of the nozzles.
The pulsating jet flow was generated by a pulsating
flow generating unit, which was installed upstream of thejets as indicated by the black frame in Fig. 1. Figure 3
shows the schematic view of this unit. The unit wascomposed of a cylinder and chassis. Through-holes weremade at the side walls of the cylinder and chassis, andtheir locations corresponded to each other. The cylinder
was connected to a DC electric motor (Oriental Motor,
MSD425-401D), and was rotated under constant angularspeed. The flow rate was, thus, changed periodicallydepending on the crossover area between the holes of thecylinder and chassies. Note that a bypass hole was drilledaside the main hole described above so that in the phasewhen the area of the main flow passage was decreased, thearea of the bypass hole was increased and large amount offlow was discharged to the atmosphere. This prevented anincrease of the upstream pressure which caused anundesired pulse in the velocity profiles of pulsating flow.
The frequency of jet perturbation was controlled by therotation speed of the cylinder.
As shown in Fig. 3, a laser motion detection sensor(KEYENCE, LV-51M) was employed on the pulsating
flow generating unit. A needle-shape marker was attachedto the rotating cylinder that intersected the aforementioned

laser sensor at each period of the cylinder rotation. The
trigger signal from the sensor was sent to the high-speed
digital camera used in the Shlieren method and to themechanical shutter placed at the exit of the laser unit usedin the laser Doppler velocimetry (LDV) measurements. In
each measurement, this trigger signal was used to start thedata recording, and to synchronize the data signals withthe phase of the pulsating flow.
Figure 4 shows the schematic view of the system of
the Schlieren method employed in the combustion
experiments. An Ar-ion laser (Spectra Physics,
model2017L-AR) was employed as the light source. The
laser beam was first lead through a converging lens andpinhole, by which a point light source was produced. The
light was then changed to a parallel light by a concave
mirror, as shown in Fig. 3 described as CM1. The
diameter and focal length of this mirror were 300mm and3,000mm, respectively. The parallel light passing the test
section was then converged by another concave mirror,
CM2, and was guided to the high speed camera. A knifeedge, KE, was placed at the focal point located at thecamera upstream to intensify the contrast produced by thegas density difference in the image. KE was made of a
glass plate, onto which a 2mm size square pattern was
printed as shown in Fig. 4 (b). The Schlieren photographs
were taken by a high speed camera (Vision Research,
Phantom V7.3). The exposure time of the camera was 2μs
and the frame rate was 1,000 frames per second. The
resolution of the captured images was approximately
1.3mm per pixel.
In non-combustion experiments, the flow velocity wasmeasured by the LDV system. In this system, two pairs oflaser beams (wave length = 488.0nm and 514.5nm)
emitted from the aforementioned Ar-ion laser were guided
to the test section. The Doppler burst signals of thescattering light from the tracer particles obtained by areceiver probe were recorded and analyzed by a signal
processor (DANTEC, BSA F50), which was linked to andcontrolled by a personal computer. To mix tracer particles
in the working fluids, a particle generator (TSI,2nd International Symposium on Advanced Fluid/Solid Science and Technology in Experimental Mechanics, 23-25 Sept. 2007, Osaka, Japan

Concave lens

Argon-ion laser
Convex lensCM1

KE
Convex lensx/dTest section

CM2

High-speed degital camera(a) Schematic of optical path.

(b) Schematicknife edge.

Fig. 4: Apparatus of Schlieren method.
model9306) was installed downstream of flow meters.
The particles used in the present study were oil mist of DiEthyl-Hexy-Sebacate (1.0μm in nominal diameter). As
mentioned before, the start of the LDV measurement wassynchronized with the pulsating jet by a mechanicalshutter (Suruga Seiki, F116), to which the trigger signal
was sent from the laser sensor.
Table 1 shows the experimental conditions discussed
in the present study. The characters “St” and “P” used inTable 1 indicate the flow conditions of the jets: steady andpulsating states. The titles “air” and “flame” indicate
respectively the jets under non-combustion andcombustion conditions. Largely grouped, three cases were
examined in the present study. The first one is a single jetblown out from the C-jet nozzle under steady state
condition (the case of 1S). The second one is triple jets
discharged from the nozzles of the C-jet and S-jets understeady state conditions (the case of 3S). The last one istriple jets (the case of 3P), in which a steady jet wasprovided from the nozzles of C-jet and pulsating jets were
supplied from S-jets.
The Reynolds number of the steady jet was fixed at aconstant value, Re = 1.5 × 103 . Re was calculated on thebasis of the nozzle diameter d and time-mean streamwise
velocity at the center of the C-jet nozzle outlet (x/d = 0.25
and y/d = 0). In the pulsating jet case, the mean Reynolds
number was 1.5 × 103 . In this case, the characteristic
velocity was the half value of the time-mean streamwise
velocity at the center of the S-jet nozzle outlet (x/d = 0.25
and y/d = ±1.5). The frequency of the pulsating jet, f, was
1Hz. The kinetic viscosity was calculated under thecondition of the atmosphere temperature.
Table 1: Experimental conditions.
Case
C-jet
S-jets

1S-F
3S-F
3P-F
St-flame St-flame St-flame
St-air
P-air
－

1S-A
St-air－

3S-A
St-airSt-air

60

60

50

50

40

40

x/d

Pine hole

30

30

20

20

10

10

0

0

(a) Case 1S-F(b) Case 3S-F
Fig. 5: Schlieren photographs in steady jet flame cases.
under steady state flow conditions (the cases of 1S-F and
3S-F). In the case of 1S-F, generation of large scale
periodical fluctuations are observed at the boundary surfaceof the fuel and surrounding air. This is believed to be
attributed to velocity increase of the jet fluid relative to theambient fluid due to the decrease of the fluid density
produced by the local temperature increase of the flame. On
the other hand, in the case of 3S-F, such fluctuations are notobserved. A smooth surface is formed along the streamwise
direction from the exit of the nozzles to the location of x/d ~40. This implies that in the multi-jet case, the suppressionof the flame surface fluctuating is attained by the assist of
air-supply jets along the sides of a fuel jet.
In Fig. 6, the time-sequential Schliren images obtainedin the case of 3P-F are shown. T described in the figure
presents the time period of one cycle of the pulsating flow.
T is estimated using the distribution of auto-correlation
function, C(τ), that is defined as the following equation
using the instantaneous streamwise velocity, U(t).
t2
1
C (τ ) =U (t )U (t + τ )dt
(1)
∫
1
t
t2 − t1
In Eq. (1), t2 − t1 indicates the time span of the LDV
measurement.
Figure 7 shows the distributions of the time history of
the phase-averaged streamwise velocity Ui monitored at
the center of the nozzle exit (x/d = 0.25, y/d = 0) of C-jet
and S-jet, respectively. Both values are obtained in thecase of 3P-A. The values in the figure are normalized by
U 0 that represents the time-mean streamwise velocity
obtained at the nozzle exit center of the C-jet under thesteady state case of 3S-A.
Although not shown here, according to the streamwise
turbulence intensity, u ′ , obtained at the nozzle exit, thejet was considered to be laminar during the period of
0.4 ≤ t / T ≤ 0.9 . On the contrary, during the periods of0 ≤ t / T ≤ 0.4 and 0.9 ≤ t / T ≤ 1.0 ,was markedlyu′increased, and, therefore, a turbulent jet was expected tobe discharged from the nozzle. The relation among Ui ,u’(t) and turbulence intensity, u ′ , and the definition ofu ′ used in the present study are described in Eqs. (2) and(3).
i + u ′(t )U (t ) = U + U ′(t ) = U
(2)
2

3P-A
St-airP-air

3. Results and discussion

22

3.1 Schlieren photographing in combustion
experiments
Figure 5 shows the Schlieren photographs of the flames
obtained in the cases of (a) single and (b) triple jet arrays2

2nd International Symposium on Advanced Fluid/Solid Science and Technology in Experimental Mechanics, 23-25 Sept. 2007, Osaka, Japant/T=0.30 0.47

60
50

1.4

x/d

40

1.2

30

1.0

U/U0

20

0.8

10

0.6

0

(a) t/T=0.1

0.4(b) t/T=0.2

60
50

x/d

0.70 0.80

0.2

U (C-jet)U (S-jets)

0.0
0.0

0.2

0.4

0.6

0.8

1.0

40

t/T

30

Fig. 7: Ui of C-jet and S-jets measured at the nozzle
center and x/d = 0.25 in the case of 3P-A.

20
10

Case-1S-A:

0(c) t/T=0.3

Case-3S-A:(d) t/T=0.4

2

U/U0

u' /U0U/U0

2

u' /U0

1.0

1.0

0.8

0.8

0.6

0.6

0.4

0.4

0.2

0.2

U/U0

x/d

40
30
20
10
0

(e) t/T=0.5

2

50

0.0

(f) t/T=0.6

u' /U0

60

0

10

20

30

0.0
40

x/d
Fig. 8: Streamwise distributions of Ui / U 0 andu ′ / U 0 at center of C-jet and S-jets.

60
50

2

x/d

40
30
20
10
0

(g) t/T=0.7(h) t/T=0.8

60
50

x/d

40
30
20
10
0

(j) t/T=1.0(i) t/T=0.9
Fig. 6: Time-sequential Schlieren images of jet flamewith pulsating air-jets (the case of 3P-F).

u ′2 =t2
1
i (t ))dt(U (t ) − U∫
t 2 − t1 t1(3)

At t/T = 0.1~0.4, which is the period that Ui is
relatively large and a turbulent jets is formed from thenozzle exit of S-jets, ripples appear at the boundary
between fuel and air from the area of x/d = 10~20 in spiteof unclearly visualized images in Fig. 6 (a) ~ (d). At thelocation further downstream of these jets, generation ofvarious length-scale vortices becomes recognizable, whichindicates that the jet flame is turbulent. During the period
when the S-jets are accelerating, i.e. at t/T = 0.7 and 0.8 ofFig. 6 (g) and (h), large scale fluctuations are observed at
the boundary surface of the flame in the area of0 ≤ x / d ≤ 30 . Production of such periodical fluctuation at
the flame surface is a common characteristic similar to thatobtained in the case of 1S-F shown in Fig. 5 (a). During theperiod when the S-jets are decelerating, i.e. at (e) t/T = 0.5
and (f) t/T = 0.6 of Fig. 6, the flame images appear a bit
different, compared to the ones in the accelerating period.
Some traces of typical turbulent flame’s feature remains inthis period, particularly in the region beyond half-way
downstream of the flame. More detail investigation shouldbe necessary in the near future. At t/T = 0.9, 1.0 shown in
Fig. 6 (i) and (j), the flame shows a common behavior thatobserved in the case of 3S-F shown in Fig. 5 (b). Namely, asmooth flame surface is developed at the nozzle
downstream to the region of 0 ≤ x / d ≤ 30 .
3.2 Comparison of the multi-jet flow characteristics
in combustion state with in non-combustion state
In this section, comparisons of the flow characteristics ofthe multi-jets obtained in the cases under the conditions ofcombustion and non-combustion states are conducted toU / U0x/d = 30

U / U0x/d = 20

U / U0x/d =10

U / U0U / U0x/d = 0.25

U / U0x/d = 40

U / U0Case-1S-A
t/T=0.70

U / U0

1.2
0.8
0.4
0.0
1.2
0.8
0.4
0.0
1.2
0.8
0.4
0.0
1.2
0.8
0.4
0.0
1.2
0.8
0.4
0.0

U / U0

2nd International Symposium on Advanced Fluid/Solid Science and Technology in Experimental Mechanics, 23-25 Sept. 2007, Osaka, Japan

-2

-1

0
y/d

1

U / U0

2

2

U / U0x/d = 30

U / U0x/d = 20

U / U0x/d =10

U / U0}U / U0x/d = 40

U / U0U / U0Case-3S-A
t/T=0.47
t/T=0.80

U / U0of 3S-P at t/T = 0.70.

U / U0U / U0x/d = 0.25

-2

-1

0
y/d

1

2

i / U 0 in the case(b) U / U 0 in the case of 3S-A and U

of 3S-P at t/T = 0.47, 0.80.
t/T=0.30

U / U0

1.2
0.8
0.4
0.0
1.2
0.8
0.4
0.0
1.2
0.8
0.4
0.0
1.2
0.8
0.4
0.0
1.2
0.8
0.4
0.0

2

2

i / U 0 in the case(a) U / U 0 in the case of 1S-A and U
1.2
0.8
0.4
0.0
1.2
0.8
0.4
0.0
1.2
0.8
0.4
0.0
1.2
0.8
0.4
0.0
1.2
0.8
0.4
0.0

evaluate the interaction effects of the flame and pulsating
jet flows.
Figure 8 shows the streamwise distributions of timemean streamwise velocity, U / U 0 , and turbulence intensity,u ′ / U 0 , obtained along the centerline of C-jet (y = 0) in
the cases of 1S-A and 3S-A. The solid square and triangle
symbols (■ and ▲) indicate respectively U / U 0 and u′ /U 0 obtained in the case of 1S-A. The solid circle andinverted triangles (● and ▼) represent respectively U / U 0
and u′ / U 0 in the case of 3S-A. Figure 9 shows thecomparison of the spanwise distributions of thestreamwise velocity at five streamwise locations, i.e., x/d= 0.25, 10, 20, 30 and 40. The time-mean streamwise
velocity, U / U 0 , of the cases of 1S-A and 3S-A are shownin Fig. 9 (a) and (b), respectively. The phase-averaged
velocity, Ui / U 0 , obtained in the case of 3P-A at the time
periods of t/T = 0.70, 0.47, 0.80 and 0.30 are plotted using
open symbols, ▽, △, ☆ and ○, in Fig. 9 (a), (b) and (c).
In Fig. 8, U / U 0 decreases markedly in the streamwise
locations of 15 ≤ x / d ≤ 25 in the cases of 1S-A and 3S-A.
u ′ / U 0 increases approximately at the same location andtakes a maximum value at x / d ≈ 20 . In Fig. 9 (b), themaximum peaks of U / U 0 distribution located downstreamof each jet center decreases in the area of 10 ≤ x / d ≤ 20 in
the case of 3S-A, and a relatively flat pattern in the
spanwise direction is obtained further downstream.
Transition of the jet from laminar to turbulent is, therefore,
expected in this region, and a larger diffusion effects is
obtained in the spanwise direction in the case of 3S-A. In
the results of triple jets in combustion state (the case of
3S-F), a smooth flame surface was produced in the regionof x / d ≤ 40 as represented in Fig. 5 (b), due to the effectsof the neighboring air-jets. Comparing the locations of thearea where the transition of the jet from laminar toturbulent, one can find that it is located downstream in thecase of 3S-F compared with the case of 3S-A. The main
reason for this is believed to be due to the variation of theproperties of the fluid owing to the temperature increaseof the flame. By this, the kinetic viscosity increased andthe reduction of the local Reynolds number was obtainedthat induced a laminarization of the flow. Therefore, theinteraction effects, and namely mixing, between theneighboring jets deteriorates in combustion state.
The effects of perturbation in non-combustion states
will be considered. Comparing the streamwise velocities
shown in Fig. 9 (a), the distributions of U / U 0 of the caseof 1S-A are nearly equivalent to those of Ui / U 0 obtainedin the case of 3P-A at t/T = 0.70. Comparing thestreamwise velocities shown in Fig. 9 (b), the distributionsof U / U 0 obtained in the case of 3P-A at t/T = 0.47 and0.80 are nearly equivalent to those obtained in the case of
3S-A. In the former case, the flow rate of S-jets isapproximately zero as shown in Fig. 7, i.e., only C-jet isdischarged. In the latter case, the instantaneous Reynolds
numbers of S-jets are identical with those of the case of
3S-A that can be estimated from Fig. 7. The instantaneous
flow characteristics of the triple jets are, therefore,roughly equivalent between the cases under steady andx/d = 40

U / U0x/d = 30

U / U0x/d = 20

U / U0x/d =10

U / U0x/d = 0.25

-2

-1

0
y/d

1

2

i / U 0 in the case of 3S-P at t/T = 0.30.
(c) U

Fig. 9: Spanwise distribution of thestreamwise velocity at each crosssection.

2

2nd International Symposium on Advanced Fluid/Solid Science and Technology in Experimental Mechanics, 23-25 Sept. 2007, Osaka, Japanpulsating conditions if the Reynolds numbers are the same.
These results suggest that the effects of perturbation on
the flow characteristics in the triple jet array under noncombustion conditions are small during the time phase of
0.4 ≤ t / T ≤ 0.9 when the Strouhal number is small with thepresent perturbation patterns. These results are different
from those obtained by Tatsumi [4, 5], one possible reasonof which will be due to the difference of pulsating pattern.
More detail investigation will be needed.
In combustion states, first, Fig. 6 (g) (the case of 3P-F
at t/T = 0.7) and Fig. 5 (a) (the case of 1S-F) are compared.
In both cases, the instantaneous flow rate of S-jets isnearly zero. As mentioned in the previous section, large
scale fluctuation is found at the fuel-air jets boundary inboth cases. However, while the large scale vortices wereperiodically observed from the nozzle exit to downstream
in Fig. 5 (a) (the case of 1S-F), such large scale vortices
are only partially observed in Fig. 6 (g) and the conditionsof flame were different in each region.
Next, the image of Fig. 6 (e) and (h) (the image of thecase of 3S-F at t/T = 0.5 and 0.8) are compared with Fig. 5(b) (the case of 3S-F). Although the instantaneous flow
rates of S-jets are approximately identical as is indicatedin Fig. 8, a difference in the flow characteristics between
these three photographs is observed. The transition
regions of the flow from laminar to turbulent shown in Fig.
6 (e) and (h) are located further upstream than that theregion shown in Fig. 5 (b). This result indicates thatduring the period even when the instantaneous flow rate isequivalent in the cases of 3P-F and 3S-F, a different flow
are obtained in the multi-jets when combustion isaccompanied. This differs to the results obtained in the
non-combustion case previously discussed. Therefore, theeffects on flow characteristics of the perturbation
produced by the side air-jets are believed to be moresignificant in combustion states.
4. Conclusions
The flow characteristics of a triple jet array accompanied bya pulsating neighboring jets in combustion and noncombustion state have been experimentally investigated.
The flow Reynolds number was fixed at 1.5 × 103 andpulsating frequency was f = 1Hz in the present study. The
major findings are summarized as follows:
1) In the steady triple jets cases, the region where thetransition of jet flow from laminar to turbulent occurs was
located further downstream under the condition withcombustions, compared with the case of non-combustion
air jet array. This is due to the increase of the local fluid
temperature gained by the combustion reaction.
2) The phase-averaged streamwise velocity distributions of
the jet array with pulsating jet in non-combusiton state were
nearly equivalent to those obtained in the steady jet caseduring the period when the instantaneous flow rate of thepulsating jet was identical with that of the steady jet cases.
Therefore, the effects of flow pulsation were considered tobe small in non-combustion states under very small Stouhal
number and the present pulsation pattern.
3) The instantaneous flame characteristics of the jet flame
array with pulsating jet were different from those obtainedin the steady jet flame array, even under the conditions of
the instantaneous flow rate of the pulsating jet to be thesame as that in the steady cases. The effects of the pulsating
flow were considered to be larger when a combustions
reaction is accompanied, compared with non-combustion
jet array. Acceleration and deceleration effects of theneighboring air jet pulsation might have additional
interesting influences on the combustion characteristics ofthe central fuel jet.
Nomenclatured nozzle diameter, mf
perturbation frequency, Hz
L separation distance between nozzles, m
Re jet Reynolds number, U m d / νU time-mean streamwise velocity of jet, m/s
u’ streamwise velocity fluctuation, m/s
V time-mean lateral velocity, m/sv’ lateral velocity fluctuation, m/s
xstreamwise distance, mylateral distance, mtinstantaneous time, sT time-period of jet perturbation, s
Subscripts
0 time-mean reference value at the jet center
Superscripts~ phase-averaged value
Acknowledgements
This research was partially supported through Grand-inaid for Scientific Research (B) by Ministry of Education,
Culture, Sports, Science and Technology. The authors
express their gratitude here.
References[1] Choi, H.-S., Katsumoto, Y., Nakabe, K. and Suzuki,
K., An Experimental Investigation of Mixing andCombustion Characteristics on the Can-Type Micro
Combustor sith a Multi-Jet Baffle Plate, Fluid
Mechanics and Its Applications – Turbulent, Mixing
and Combustion -, 70 (2002), 367-375, Kluwer
Academic Publisher.
[2] Woodfield, P.L., Nakabe, K. and Suzuki, K.,
Numerical Study for Enhancement of Laminar Flow
Mixing Using Multiple Confined Jets in a Micro-Can
Combustor, Int. Journal of Heat and Mass Transfer,
46(2003), pp. 2655-2663.
[3] Nakabe, K., Kitaoka, Y., H.S. Choi and Suzuki, K.,
Experimental Study on Flow Characteristics of a
Micro Jet Deformed by the Interaction with the
Neighboring Jets, Proc. of the 6th ASME-JSME
Thermal Eng. Conf., TED-AI03-637 (2003).
[4] Tatsumi, K., Shinohara, E., Mizuno, M., Nakabe, K.,phase-averaged Mixing Characteristics of Multi-Jets
Modified by Cyclic Perturbation, JSME Int. J., Ser. B,(2006), 49-4, 959-965.
[5] Tatsumi, K., Shinohara, E., Mizuno, M. and Nakabe,K., Phase-Averaged Mixing Characteristics of MultiJets Modified by Cyclic Perturbation, JapaneseSociety for Experimenatl Mechanics, (2007), 7, 6-11.