piv study of heated rectangular jets
TRANSCRIPT
PIV OF HEATED RECTANGULAR JETS
AATRESH KARNAM
GUIDED BY – EPHRIAM GUTMARKPABLO MORA SANCHEZ; FLORIAN BAER
Flow Visualization Techniques
• Surface Flow Visualization• Optical Methods
– Shadowgraph – Schlieren– Laser Induced FluorescenceParticle Tracer Method
• Laser Doppler Velocimetry • Particle Image Velocimetry
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
Methodology Hardware Component : Tracer/seed particles
Light source
Light sheet optics
Camera
Software component: Interrogation area
Post-processing
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
Methodology • Application of correlation function to find
average particle displacement• Repeat to find best estimate
Important Considerations• Type of seed • Sizing of seed • Density & distribution of seed• Definition of interrogation regions
Interrogation region too large or too small
Important Considerations• Definition of co-relation function• Post processing
– Vector analysis– Scalar calculation
Components of Jet Noise
• Three major components
Tam . Christopher. K. W., Supersonic Jet Noise, Annu. Rev. Fluid Mech. 1995, 27:17-43
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
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
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
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
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
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
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
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
High Pressure Tank
Laser
Camera Mixing Tank
Alumina Tank
Olive oil tank
Olive oil tank
Nozzle
Experimental Setup
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
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
• 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
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
• 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
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
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
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
• 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
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
Thank you