optical measurement techniques - clarkson … measurement techniques • turbulent flows are the...
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ME637 -Particle Transport, Deposition and Removal II
Jeffrey A. Taylor
ME637 -Particle Transport, Deposition and Removal II
Jeffrey A. Taylor
Optical Measurement Techniques
Optical Measurement Techniques
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• Turbulent flows are the rule, not the exception. • Practical turbulent flows are VERY difficult to
simulate using DNS. • Verification of turbulent flow models.
• Turbulent flows are the rule, not the exception. • Practical turbulent flows are VERY difficult to
simulate using DNS. • Verification of turbulent flow models.
Why Make Measurements?Why Make Measurements?
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• Non-intrusive (seed, but no probes in the flow field)
• Robust (no particle collection on probe)• High accuracy (accuracy is predictable)• High precision (Very little drift)• Small measurement volume
• Non-intrusive (seed, but no probes in the flow field)
• Robust (no particle collection on probe)• High accuracy (accuracy is predictable)• High precision (Very little drift)• Small measurement volume
Optical Techniques: Advantages
Optical Techniques: Advantages
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• Expensive!!• Fragile optics.• Seeding... Seeding... Seeding...
• Expensive!!• Fragile optics.• Seeding... Seeding... Seeding...
Optical Techniques: Disadvantages
Optical Techniques: Disadvantages
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• DANTEC -- LDA, PDA, PIV, PLIF, IPI• TSI -- LDA, PDA, PIV• VioSense -- LDA, Shear Stress, PIV• LAVision -- PIV, PLIF, IPI
• DANTEC -- LDA, PDA, PIV, PLIF, IPI• TSI -- LDA, PDA, PIV• VioSense -- LDA, Shear Stress, PIV• LAVision -- PIV, PLIF, IPI
What Are My Options and Who Sells Them?
What Are My Options and Who Sells Them?
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• A pair of coherent laser beams intersect, forming a fringe pattern in the measurement volume.
• As a seed particle passes through the fringe pattern, the light reflected from the particle pulsates.
• The pulsating light is measured by a photodetector.
• The frequency of the pulsating light and the fringe spacing is used to compute a velocity.
• A pair of coherent laser beams intersect, forming a fringe pattern in the measurement volume.
• As a seed particle passes through the fringe pattern, the light reflected from the particle pulsates.
• The pulsating light is measured by a photodetector.
• The frequency of the pulsating light and the fringe spacing is used to compute a velocity.
How do LDA & PDA Systems Work?
How do LDA & PDA Systems Work?
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LDA: u = d/tLDA: u = d/t
Figure courtesy of DANTEC Measurement TechnologyFigure courtesy of DANTEC Measurement Technology
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LDA: EquationsLDA: Equations
Fringe SpacingFringe Spacing Frequency of PulseFrequency of Pulse
VelocityVelocity
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LDA: System ConfigurationsLDA: System Configurations
Forward ScatterDifficult to alignLower power requirements
Forward ScatterDifficult to alignLower power requirements
Back ScatterFiber optic LDA systems
make alignment a non-issueLarger power requirements
Back ScatterFiber optic LDA systems
make alignment a non-issueLarger power requirements
Figure courtesy of DANTEC Measurement TechnologyFigure courtesy of DANTEC Measurement Technology
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• Particles moving forward or backwards will produce a pulsating wave with identical frequencies.
• An accousto-optical modulator (Bragg Cell) can be used to oscillate the fringes in the measurement volume.
• Velocity is calculated by subtracting the modulator frequency from the measured frequency.
• Particles moving forward or backwards will produce a pulsating wave with identical frequencies.
• An accousto-optical modulator (Bragg Cell) can be used to oscillate the fringes in the measurement volume.
• Velocity is calculated by subtracting the modulator frequency from the measured frequency.
LDA: Directional AmbiguityLDA: Directional Ambiguity
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• A different color, λ, is used for measuring each velocity component. • Each beam is then separated into three
colors: green: λ = 514.5 nmblue: λ = 488 nmpurple: λ = 476.5 nm
• A single probe can be used for 2 components• A second probe is necessary for 3 components
• A different color, λ, is used for measuring each velocity component. • Each beam is then separated into three
colors: green: λ = 514.5 nmblue: λ = 488 nmpurple: λ = 476.5 nm
• A single probe can be used for 2 components• A second probe is necessary for 3 components
LDA: Multiple Components of Velocity?
LDA: Multiple Components of Velocity?
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LDA: Seed ParticlesLDA: Seed Particles
Table courtesy of DANTEC Measurement TechnologyTable courtesy of DANTEC Measurement Technology
Particle Frequency ResponseParticle Frequency Response
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• A particle scatters light from two incident laser beams
• Both scattered waves interfere in space and create a beat signal with a frequency which is proportional to the velocity of the particle
• Two detectors receive this signal with different phases
• The phase shift between these two signals is proportional to the diameter of the particle
• A particle scatters light from two incident laser beams
• Both scattered waves interfere in space and create a beat signal with a frequency which is proportional to the velocity of the particle
• Two detectors receive this signal with different phases
• The phase shift between these two signals is proportional to the diameter of the particle
Phase Dopper AnemometryPhase Dopper Anemometry
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PDA: Phase - Diameter Relationship
PDA: Phase - Diameter Relationship
Figure courtesy of DANTEC Measurement TechnologyFigure courtesy of DANTEC Measurement Technology
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• Beam intersection angle θ• Scattering angle ϕ• Elevation angle ψ• Polarization
(parallel or perpendicular to scattering plane)
• Shape and size of detector aperture
• Beam intersection angle θ• Scattering angle ϕ• Elevation angle ψ• Polarization
(parallel or perpendicular to scattering plane)
• Shape and size of detector aperture
PDA: General Set-upPDA: General Set-up
Figure courtesy of DANTEC Measurement TechnologyFigure courtesy of DANTEC Measurement Technology
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• Seed particles are uniformed dispersed throughout a flow.
• Two images are acquired, separated by a short period of time, t.
• Spatial correlation between image pair is used to determine a shift, s, in the particle locations.
• Velocity is computed as, v = s/t
• Seed particles are uniformed dispersed throughout a flow.
• Two images are acquired, separated by a short period of time, t.
• Spatial correlation between image pair is used to determine a shift, s, in the particle locations.
• Velocity is computed as, v = s/t
How does PIV Work?How does PIV Work?
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PIV: System ConfigurationPIV: System Configuration
Figure courtesy of DANTEC Measurement TechnologyFigure courtesy of DANTEC Measurement Technology
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Visualization vs. Measurement?
Visualization vs. Measurement?
Figure courtesy of DANTEC Measurement TechnologyFigure courtesy of DANTEC Measurement Technology
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PIV: Data FlowPIV: Data Flow
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Stereo PIV: Error ReductionStereo PIV: Error Reduction
Make measurements of flow through the measurement plane.
Make measurements of flow through the measurement plane.
Figure courtesy of DANTEC Measurement TechnologyFigure courtesy of DANTEC Measurement Technology