some experiments on thermo - acoustics of rijke tube with geometric modifications and forced...
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Some Experiments on Some Experiments on Thermo - Acoustics of RIJKE Tube Thermo - Acoustics of RIJKE Tube with Geometric Modifications and with Geometric Modifications and
Forced VorticityForced Vorticity
S.D. SharmaS.D. SharmaAerospace Engineering DepartmentAerospace Engineering Department
IIT BombayIIT Bombay
Scope of StudyScope of Study
To develop a test setup consisting of a horizontal To develop a test setup consisting of a horizontal Rijke tube driven by a Rijke tube driven by a flameflame for experimental for experimental investigation of the thermo-acoustics.investigation of the thermo-acoustics.
To study the effects of introduction of streamwise To study the effects of introduction of streamwise vorticity and certain geometric modifications vorticity and certain geometric modifications including concentric tubes on thermo-acoustic including concentric tubes on thermo-acoustic behavior of the Rijke tube.behavior of the Rijke tube.
PreamblePreamble
Thermo-acoustic instability appears inside Thermo-acoustic instability appears inside chambers with heat source and mean flow when chambers with heat source and mean flow when unsteady heat release is coupled in phase with unsteady heat release is coupled in phase with pressure fluctuations. Such instability gives rise pressure fluctuations. Such instability gives rise to excitation of acoustic modes resulting in to excitation of acoustic modes resulting in noise.noise.
Typical examples include Rocket Motors, Pulsed Typical examples include Rocket Motors, Pulsed Combustors, Noisy Industrial Burners and Heat Combustors, Noisy Industrial Burners and Heat Exchangers.Exchangers.
Rijke TubeRijke Tube
Rijke tube is the simplest possible device that Rijke tube is the simplest possible device that demonstrates the thermo-acoustics instability. It demonstrates the thermo-acoustics instability. It is a vertical tube with open ends having its is a vertical tube with open ends having its length to diameter ratio of about 10. When a wire length to diameter ratio of about 10. When a wire gauge placed inside at about one fourth the tube gauge placed inside at about one fourth the tube length from its lower end is sufficiently heated length from its lower end is sufficiently heated with flame, a loud noise is produced. The reason with flame, a loud noise is produced. The reason for this noise is excitation of acoustic mode due for this noise is excitation of acoustic mode due to the coupling between the unsteady heat to the coupling between the unsteady heat release and the pressure fluctuations that is release and the pressure fluctuations that is enabled by the low speed flow driven by the enabled by the low speed flow driven by the convective currents. convective currents.
Schematics of Rijke TubeSchematics of Rijke Tube
Present Test Setup
Rijke Model
Heated metal mesh / wire gauze
Rijke Tube DemonstrationRijke Tube Demonstration
Rijke Tubes: Two Different Frequencies Rijke Tubes: Two Different Frequencies with Phase Differencewith Phase Difference
Development of Test SetupDevelopment of Test Setup Various Tube Configurations Used:Various Tube Configurations Used:
L/D=9.23
Port with optical window for viewing flame and LDV measurements
L = 705 mm
100 Φ 75 Φ 65 Φ 50 Φ 40 Φ L /D: 7.05 9.4 10.85 14.1 17.6
Concentric tubes arrangement: 40 mm Φ and 65 mm Φ tubes each with L=200 mm and 300 mm inside the 75 mm Φ tube.
10.5 mm
31 mm
72o sweep
Delta Fin Vortex Generatorat 30 degree angle of attack
Stepped collar for fixing vortex generators
6 Contra-rotating 6 Co-rotating 8 Contra-rotating 8 Co-rotating vortex generators vortex generators vortex generators vortex generators
Vortex GeneratorsVortex Generators
Preliminary DesignPreliminary Design
Improved DesignImproved Design
Interior Details of Plenum ChamberInterior Details of Plenum Chamber
Improved Design with Insulated TubeImproved Design with Insulated Tube
Plenum Chamber with CoolingPlenum Chamber with Cooling
Suction-end of the Plenum ChamberSuction-end of the Plenum Chamber
ThermocoupleTwin Blowers
Cooling air
Flow
Orifice meter
InstrumentationInstrumentation
Pressure Transducers
K Type Thermocouple
Rotameter
Visualization of Vortex FlowVisualization of Vortex Flow
Flow Through Vortex GeneratorsFlow Through Vortex Generators
Some Observations from Some Observations from Preliminary ExperimentsPreliminary Experiments
A certain flow velocity for a fixed fuel mass flow A certain flow velocity for a fixed fuel mass flow rate triggers the acoustic instability that results in rate triggers the acoustic instability that results in intense noise.intense noise.
Hysteresis effects on flame position inside the Hysteresis effects on flame position inside the tube.tube.
Introduction of vorticity advances the instability Introduction of vorticity advances the instability even when the flame is lean and closer to the even when the flame is lean and closer to the entry of the tube.entry of the tube.
With increase in the equivalance ratio marginal With increase in the equivalance ratio marginal increase in peak pressure and frequency was increase in peak pressure and frequency was observed.observed.
Temperature Profile at Various Axial LocationsTemperature Profile at Various Axial Locations
Wall Pressure Distribution (improved setup)Wall Pressure Distribution (improved setup)
Wall Pressures with Vortex GeneratorsWall Pressures with Vortex Generators
Wall Pressures with Vortex GeneratorsWall Pressures with Vortex Generators
Wall Pressures ComparisonWall Pressures Comparison
Wall Pressure SpectraWall Pressure Spectra
Wall Pressure SpectraWall Pressure Spectra
Vorticity Effect on TemperatureVorticity Effect on Temperature
0
10
20
30
40
50
60
70
80
90
0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800
TE
MP
ER
AT
UR
E IN
DE
GR
EE
CE
LS
IUS
AXIAL DISTANCE FROM INLET OF RIJKE TUBE (IN MM)
AXIAL TEMPERATURE DISTRIBUTION ALONG RIJKE TUBE FOR EQUIVALENCE RATIO 0.047
COLLAR
6CO
6CONTRA
8CO
8CONTRABU
RN
ER
PO
SIT
ION
Vorticity Effect on TemperatureVorticity Effect on Temperature
0
20
40
60
80
100
120
140
160
0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800
TE
MP
ER
AT
UR
E IN
DE
GR
EE
CE
LS
IUS
AXIAL DISTANCE FROM INLET SIDE IN MM
AXIAL TEMPERTURE DISTRIBUTION ALONG RIJKE TUBE AT EQUIVALENCE RATIO 0.068
COLLAR
6CO
6CONTRA
8CO
8CONTRA
BU
RN
ER
PO
SIT
ION
Frequency Spectra of PressuresFrequency Spectra of Pressures
Tube=40 Φ, A/F=220, Burner x/L=0.128
P1
P7
P1
P7
Tube=40 Φ, A/F=220, Burner x/L=0.624
Burner x/L=0.128
Burner x/L=0.624
Tube=75 Φ, A/F=530
Burner x/L=0.128
Burner x/L=0.624
Frequency Spectra of PressuresFrequency Spectra of Pressures
Tube=75 Φ, A/F=280
Burner x/L=0.128
Burner x/L=0.624
Frequency Spectra of PressuresFrequency Spectra of Pressures
Tube=100 Φ, A/F=530 at P1
Burner x/L=0.128
Burner x/L=0.624
Tube=100 Φ, A/F=280 at P1
Burner x/L=0.128
Burner x/L=0.624
Frequency Spectra for Concentric TubesFrequency Spectra for Concentric Tubes
40 Φ, Longer
40 Φ, Shorter
A/F=530, Burner x/L=0.128
50 Φ, Longer
50 Φ, Shorter
A/F=530, Burner x/L=0.128
Wall Pressure DistributionWall Pressure Distribution
Tube = 40 Φ, A/F=220 Tube = 50 Φ, Burner x/L=0.128
Tube = 50 Φ, Burner x/L=0.624 Tube = 65 Φ, Burner x/L=0.128
Wall Pressure DistributionWall Pressure Distribution
Tube = 65 Φ, Burner x/L=0.624 Tube = 75 Φ, Burner x/L=0.128
Tube = 75 Φ, Burner x/L=0.624 Tube = 100 Φ, Burner x/L=0.128
Pressure and Temperature Distributions in Pressure and Temperature Distributions in Concentric TubesConcentric Tubes
Axial Pressure Distribution: A/F ratio = 530, Burner x/L=0.128
Radial temperature profile at T3, A/F = 530, Burner x/L=0.128
Hysteresis Effect: Vortex Generators on BurnerHysteresis Effect: Vortex Generators on Burner
Hysteresis Effect: Vortex Generators on BurnerHysteresis Effect: Vortex Generators on Burner
Hysteresis Effects: Vortex Generators on BurnerHysteresis Effects: Vortex Generators on Burner
Hysteresis Effect: Vortex Generators on BurnerHysteresis Effect: Vortex Generators on Burner
Effect of Vortex Ring over FlameEffect of Vortex Ring over Flame
Some RemarksSome Remarks 40 and 50 mm diameter tubes had long spatial range of 40 and 50 mm diameter tubes had long spatial range of
instability for burner positions up to x/L=7.instability for burner positions up to x/L=7. This range was found to reduce for increasing diameter of This range was found to reduce for increasing diameter of
the tube.the tube. Concentric tubes tend to produce thermo-acoustics earlier Concentric tubes tend to produce thermo-acoustics earlier
compared to the plain Rijke tube.compared to the plain Rijke tube. In concentric tube, the flame was always blue and the noise In concentric tube, the flame was always blue and the noise
levels were amplified for all the cases when burner was levels were amplified for all the cases when burner was inside up to x/L=0.5.inside up to x/L=0.5.