piv study of heated rectangular jets

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


Turbulent Mixing Noise

• Stochastic wave model• Assumption : Equal turbulent statistics,

self similar flow

• Find to find flow & acoustic properties


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


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


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


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


Turbulent kinetic Energy NPR = 3.0; TR = 1; Major Axis



• Minor axis demonstrates larger noise levels• Higher turbulence – higher broadband

associated noise• Large velocity gradient – higher growth rate –

higher screech tone for minor axis


Comparison of acoustic signatureLarger velocity gradient for 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




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


• 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


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


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

piv study of heated rectangular jets

Engineering