Some Experiments on Thermo - Acoustics of RIJKE Tube with Geometric Modifications and Forced...

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.