Transcript
Page 1: Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL Instructor:

Measurements in Fluid Mechanics058:180:001 (ME:5180:0001)

Time & Location: 2:30P - 3:20P MWF 218 MLH

Office Hours: 4:00P – 5:00P MWF 223B-5 HL

Instructor: Lichuan [email protected]

http://lcgui.net

Page 2: Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL Instructor:

2

Lecture 8. Optical experimentation: Illumination

Page 3: Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL Instructor:

3

Background for optical experimentation: Illumination

Point light source

- idealized source of electromagnetic radiation

- concentrated at a point in space

- radiates uniformly in all directions

Plane light source - emits energy uniformly from all pints on a plane surface

Radiance Le: A – plane source area

– angle of solid angle axis

Spectral radiance Le : – wave length

Irradiance Ee :

Radiant intensity Ie : – solid angle,

e – radiation power

units: steradian (sr)

Page 4: Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL Instructor:

Background for optical experimentation: Illumination

Luminous power (flux) v

- power of visible radiation sensed by standard human eye measured by lumens (lm)

Luminous intensity Iv : unit: candela (cd , 1 cd=1 lm/sr)

Luminance (brightness) Lv :

Spectral luminance Lv :

Illuminance Ev :

Human eye

- 3 membranes: cornea-sclera, choroid, and retina

4

- a lens images received radiation onto retina

- 7 million cones on retina respond to bright light and are sensitive to colors. (photopic or bright-adapted vision)

- 100 million rods on retina are sensitive to dim light but cannot separate different colors. (scotopic or dark-adapted vision)

Page 5: Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL Instructor:

5

Background for optical experimentation: Illumination

Luminous efficacy - ratio of luminous power to radiant power v / e (lm/W)

Solid curve: photopic vision Dashed curve: scotopic vision

Luminous efficacies of standard human eye

Page 6: Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL Instructor:

6

Background for optical experimentation: Illumination

Thermal radiation

Wien’s radiation law:

for infrared-visible-ultraviolet & T<104K

Wien’s displacement law:

Plank’s radiation law: Le – spectral radianceh – plank’s constantKB – Boltzmann’s constant (=1.3804210-23J/K)

for blackbody

Radiation power emitted by blackbody:

– Stefan-Boltzmann constant (=5.6703310-8 W/m2K)

Radiation power emitted by other than blackbody:

– total emissivity, e.g. 0.02-0.03 for shiny metallic surface, 0.95 for black flat surface

Page 7: Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL Instructor:

7

Background for optical experimentation: Illumination

Thermal light sources - emit electromagnetic radiation when heated to high temperature

- available in visible, ultraviolet and infrared ranges- line source: one or more narrow spectral bands continuum source: wideband radiation

Incandescent lamps- contain electrically heated tungsten filament in evacuated container - smooth continuous spectrum across visible range

- peak at =900 nm with T=2854 K

- filled with halogen for longer life and higher T

Electric discharge lamps- filled with mercury vapor at low pressure

- produce ultraviolet range light by electric discharge- convert to visible range through fluorescence

- e.g. mercury lamp:

sodium lamp:

- continuous spectrum & spectral lines

Page 8: Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL Instructor:

8

Flash lamps

Background for optical experimentation: Illumination

- single-flash or stroboscopic devices

- light pulse typically between 1 s – 1 ms xenon flashtube1909 flash-lamp

- tubes containing noble gas, e.g. xenon, krypton, or argon

- high voltage discharge

Lasers - Light amplification by stimulated emission of radiation

Page 9: Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL Instructor:

9

Background for optical experimentation: Illumination

Helium-Neon lasers– Continuous wave laser

– Extremely monochromatic with wave length of =632.8 nm

– High temporal coherence (typical coherence length of 1030 cm)

– Spatially coherent

– Unidirectional, parallel to the body of the laser

– Beam of Gaussian intensity distribution

– Low cost but not very powerful

– Used for flow visualization

– Traditionally used for evaluation of PIV images

Page 10: Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL Instructor:

10

Background for optical experimentation: Illumination

Argon-ion lasers– Gas laser

– Continuous wave

– Multiple wavelengths with very narrow bandwidths

– two dominant wavelengths, 514nm and 488nm, make up about 67% of the total beam output power

– Single line operation possible by inserting prisms, diffraction gratings and other optical devices to "filter out" the unwanted wavelengths

– Powerful enough to illuminate particles in PIV tests

Page 11: Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL Instructor:

11

Background for optical experimentation: Illumination

Copper-vapor lasers (Cu lasers)

– High pulse speed, can be considered either CW or individual pulses for PIV particle illumination

– Wavelength within the yellow and green spectrum

– High average power (Typically 130 W)

– Properties of a commercial Cu laser

Wavelength: 510.6 nm and 578.2 nmAverage power: 50 WPulse energy: 10 mJPulse duration: 15 ns – 60 nsPeak power: <300 kWPulse frequency: 5 kHz – 15 kHzBeam diameter: 40 mmBeam divergence: 0.6·10-3 rad

Page 12: Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL Instructor:

12

Background for optical experimentation: Illumination

Nd:YAG laser

– Most popular solid-state laser for PIV

– Available wavelengths: 1064, 532, 355, 266 nm etc.

– Short laser pulses (~5 ns)

– Slow repeat rate (10-15 Hz)

– Operated in triggered mode with quality switch (Q-switch)

– Dual-cavity configuration enables short time interval between laser pulses

Page 13: Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL Instructor:

13

Background for optical experimentation: Illumination

Illumination with white light

Front & back lighting

- view direction perpendicular to seeded flow

- front & back lighting inclined by 120

Collimators- combinations of lenses and mirrors

- cylindrical or slightly diverging light beam

- backlighting for high-speed imaging

- sheet of white light

Page 14: Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL Instructor:

14

Background for optical experimentation: Illumination

Illumination with lasers

- Laser beam diameter 1mm

Laser light sheet

- created with cylindrical lenses

Laser wide beam

- created with lens group

- for volume illumination e.g. MPIV, HPIV

- for PIV etc.

- created with rotation mirror

- for PIV etc.

Page 15: Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL Instructor:

15

Background for optical experimentation: Illumination

Light scattering behavior

MIE’s scattering (dp>) for spherical particles

Light scattering by a 1 m oil particle in air with 532 nm laser

Back scattering Forward scatteringSide scattering

Factors influencing the scattered light power - Light source power - Ratio of refractive index of particles to that of surrounding medium- Particle size- Particle shape and orientation- Polarization and observation angle- Others

Page 16: Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL Instructor:

16

Background for optical experimentation: Illumination

Light scattering behavior

MIE’s scattering (dp>) for spherical particles

1 m glass particle in water

10 m glass particle in water

30 m glass particle in water

Page 17: Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL Instructor:

17

Background for optical experimentation: Illumination

Light scattering behavior

Rayleigh scattering (dp</10) for spherical particles

Page 18: Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL Instructor:

18

Homework

- Questions and Problems: 11 on page 143

- Read textbook 5.3-5.4 on page 107-128

- Due on 09/12

(optional, but may add credit to midterm examination )


Recommended