PIV Study of Heated Rectangular Jets
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Transcript of PIV Study of Heated Rectangular Jets
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PIV OF HEATED RECTANGULAR JETS
AATRESH KARNAM
GUIDED BY – EPHRIAM GUTMARKPABLO MORA SANCHEZ; FLORIAN BAER
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Flow Visualization Techniques
• Surface Flow Visualization• Optical Methods
– Shadowgraph – Schlieren– Laser Induced FluorescenceParticle Tracer Method
• Laser Doppler Velocimetry • Particle Image Velocimetry
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PIV – Particle Image Velocimetry• State of the art Optical Analysis Technique• Non intrusive in nature• High planar accuracy• Large field of view data processing• Instantaneous & averaged flow field
measurement• Faster compared to other methods
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Methodology Hardware Component : Tracer/seed particles
Light source
Light sheet optics
Camera
Software component: Interrogation area
Post-processing
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Methodology • Particle identification• Estimation of trajectory• Intensity estimation
Sum of product intensities high resulting in good matching Sum of product intensities low
resulting in bad matching
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Methodology • Application of correlation function to find
average particle displacement• Repeat to find best estimate
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Important Considerations• Type of seed • Sizing of seed • Density & distribution of seed• Definition of interrogation regions
Interrogation region too large or too small
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Important Considerations• Definition of co-relation function• Post processing
– Vector analysis– Scalar calculation
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Components of Jet Noise
• Three major components
Tam . Christopher. K. W., Supersonic Jet Noise, Annu. Rev. Fluid Mech. 1995, 27:17-43
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Turbulent Mixing Noise • Source – large scale turbulent structures• Single large peak• Upstream independent of St• Downstream dependence on St • Increases with temperature• Consists of monopole & dipole sources
Tam . Christopher. K. W., Supersonic Jet Noise, Annu. Rev. Fluid Mech. 1995, 27:17-43
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Turbulent Mixing Noise
• Stochastic wave model• Assumption : Equal turbulent statistics,
self similar flow
• Find to find flow & acoustic properties
Tam . Christopher. K. W., Supersonic Jet Noise, Annu. Rev. Fluid Mech. 1995, 27:17-43
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Turbulent Mixing Noise
• Generation mechanism – based on wavy wall analogy
• Highest near nozzle exit • Thin mixing layer – large velocity gradient• Mach wave radiation• Damping downstream leads to zero
growth
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Broadband Shock Associated Noise
• Shocks assumed to be quasi periodic• Constructive scattering of large turbulent
structures of jet• The frequency of the associated noise was
found to be
• Represents superposition of different spectral fields
Tam . Christopher. K. W., Supersonic Jet Noise, Annu. Rev. Fluid Mech. 1995, 27:17-43
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Screech Tones• Generated due to feed back loop• Acoustic disturbances excite flow near nozzle lip• Instabilities propagate downstream• Energy extraction from mean flow• Rapid growth in amplitude
Tam . Christopher. K. W., Supersonic Jet Noise, Annu. Rev. Fluid Mech. 1995, 27:17-43
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Screech Tones
• For a given jet Mach number the tone frequency was found to be
• Tone intensity governed by instability wave• Inverse relation with temperature• Intensity decreases with decrease in
temperature
Tam . Christopher. K. W., Supersonic Jet Noise, Annu. Rev. Fluid Mech. 1995, 27:17-43
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Rectangular jets vs circular jets• Circular jets – symmetric in nature and spread• Rectangular jets – asymmetric spread• Jet plume spread varies with plane• Circular jet spreads earlier
Time averaged plume spread for M = 0.2, equivalent AR rectangular nozzle. TR = 1
Viswanath et.al ; Noise Characteristics of a Rectangular vs Circular Nozzle for Ideally Expanded Jet Flow
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Rectangular jets vs circular jets• At higher TR spreading similar for both
geometries • Initial spreading length decreases for
rectangular nozzle
Time averaged plume spread for M = 0.2, equivalent AR rectangular nozzle. TR = 3
Viswanath et.al ; Noise Characteristics of a Rectangular vs Circular Nozzle for Ideally Expanded Jet Flow
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High Pressure Tank
Laser
Camera Mixing Tank
Alumina Tank
Olive oil tank
Olive oil tank
Nozzle
Experimental Setup
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PIV Results for Rectangular jets
Avg. Velocity NPR = 3.0; TR = 1; Major Axis
Avg. Velocity NPR = 3.0; TR = 1; Minor Axis
Comparison of Major & Minor axes
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PIV Results for Rectangular jets
Turbulent kinetic Energy NPR = 3.0; TR = 1; Major Axis
Avg. Velocity NPR = 3.0; TR = 1; Minor Axis
Comparison of Major & Minor axes
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• Minor axis demonstrates larger noise levels• Higher turbulence – higher broadband
associated noise• Large velocity gradient – higher growth rate –
higher screech tone for minor axis
PIV Results for Rectangular jets
Comparison of acoustic signatureLarger velocity gradient for minor axis
Comparison of Major & Minor axes
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PIV Results for Rectangular jets
Avg. Velocity NPR = 3.0; TR = 1; Minor Axis
Avg. Velocity NPR = 3.67; TR = 1; Minor Axis
Avg. Velocity in y direction NPR = 3.0; TR = 1; Minor Axis
Avg. Velocity in y direction NPR = 3.67; TR = 1; Minor Axis
Comparison of Overexpanded & Ideally Expanded Jets
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• Jet spreading minimized at high NPR• Reduced screech tones, increased core length • Higher mixing noise levels
PIV Results for Rectangular jetsComparison of Overexpanded & Ideally Expanded Jets
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PIV Results for Rectangular jets
Avg. Velocity NPR = 3.67; TR = 1; Minor Axis
Avg. Velocity NPR = 4.5; TR = 1; Minor Axis
Comparison of Underexpanded & Ideally Expanded Jets
• Shock cell spacing increased at high NPR
• Increase in potential core length
• Higher mixing noise levels
• Lower screech
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PIV Results for Rectangular jetsComparison of Underexpanded & Ideally Expanded Jets
Turbulent kinetic Energy NPR = 3.6; TR = 1; Minor Axis
Turbulent kinetic Energy NPR = 4.5; TR = 1; Minor Axis Comparison of acoustic signature
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PIV Results for Rectangular jets
• Higher TR -Reduction in core length
• Spreading of jet is lesser
• Quicker shock cell decay
Avg. Velocity NPR = 3.67; TR = 2.6; Minor Axis
Avg. Velocity NPR = 3.67; TR = 1; Minor Axis
Comparison of Cold & Hot Jets
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• Overall increase in noise levels • Reduced shock associated noise at higher
temperatures• Complete absence of screech tones• Increase in mixing noise
PIV Results for Rectangular jets
TR = 1 TR = 2.6
Comparison of Cold & Hot Jets
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Conclusions • Variation of shock cell structure studied • Changes attributed to observed acoustic
patterns• Quantitative visualization achieved
through PIV• Further studies for high AR nozzles• Perform sizing studies to better estimate
real world effects
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Thank you