Working Principle

Image based spray diagnostic system developed by LaVision. This technique is based on the following optical techniques:

Particle Image Velocimetry (PIV) measures whole velocity fields by taking two images shortly after each other and calculating the distance individual particles travelled within this time. From the known time difference and the measured displacement the velocity is calculated. Since the flow can be quite fast one has to avoid blurred images and that's one reason to use laser pulses. They are only 6-10 ns long and freeze any motion. The other reason is that only laser light can be focused into a thin enough light sheet so that only particles in that plane are imaged. Otherwise the scattered light from particles in other planes would make this measurement impossible. A special camera is utilized so that it can store the first image (frame) fast enough to be ready for the second exposure. The "dead" time between the frames when the camera is "blind" is very short down to 100 ns.

LaVision FlowMaster systems measure instantaneously two and three dimensional velocity vector fields from scattered light patterns of particles or droplets seeded into the flo w(liquid or gas). Techniques like Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV) are supported.

The shadowgraphy technique (backlighting) is used to visualize particles (e.g. droplets from a spray or bubbles in liquid). Shadowgraph employs an expanded collimated beam of light from a laser that traverses the field of disturbance. If the disturbance is one of varying refractive index, the individual light rays passing through the test section are refracted and bent out of their original path. This causes a spatial modulation of the light-intensity distribution with respect to the original intensity on the screen. The resulting pattern is a shadow of the refractive index field prevailing in the region of the disturbance. A He-Ne laser is expanded and collimated to a suitable diameter by a beam expander. The collimated beam passes through the test section being investigated. The beam emerging from the exit window falls on a screen resulting in the shadowgraph image. The images may be recorded as individual frames or a video sequence by a suitable camera..

Features

1. High speed LIF systems
2. unable Nd:YAG laser module for OH-LIF imaging
3. High speed spectral analysis of transient processes
4. Complete hardware control using DaVis software
5. Flexible beam delivery and sheet forming optics
6. Most efficient LIF excitation technique for each application and flame radical
7. Combination of techniques, multi-parameter laser imaging
8. Accurate hardware and size calibration
9. Comprehensive on-line image evaluation and data processing
10. Hardware compatible with LaVision's PIV systems
11. High efficient diffuser for speckle-free illumination
12. Flexible definition of image acquisition sequences including delays, trigger bursts and synchronizing to external events
13. 2D and 3D visualization of image data, combination of vector data and images, extraction of profiles, user defined color lookup tables, variable color resolution and zoom function
14. Smoothing and many other filter operations for image and vector data (Gauss, Laplace, Sobel, Erosion, customizable filters ...)
15. Data import / export to TecPlot, ASCII, BMP, JPG, TIFF, VI, PS, FTS, ...

Technical Specifications

• DaVis 8.1 Software Packages & Integrated Command Language :
  1. LaVision flow master
  2. LaVision particle master
• Quantel EverGreen Integrated Cooling and Electronics (Laser Power Supply) :
  1. Operational temperature range: 18oC - 28oC
  2. Storage temperature range: 5oC - 50oC
  3. Laser Head mass15.5 lb [7.0 kg]
  4. ICE weight: Empty: 35 lb [15.9 kg]
  5. Full: 40 lb [18.1 kg]
  6. Laser wavelength: 532 nm
  7. Output energy: EVG00145 ≤145 mJ per pulse
  8. Beam near field profile: Flat-top, Uniform
  9. Polarization: linearly polarized
  10. Maximum repetition rate: up to 15 Hz
  11. Laser pulse width: (FWHM) less than or equal to 10 nanoseconds at nominal energy
  12. Coolant: distilled water
  13. Power requirements: 100-240 VAC, 50-60 Hz
  14. Laser Head sealing: sealed to IP 67 specification
  15. Power supply sealing sealed to IP 21 specification
  16. Laser vibration compliance: MIL-STD-810F Procedure 1 Category 10
• Laser Source :
  1. Nd:YAG laser by the LaVision Programmable Timing Unit (PTU)
  2. Laser material is a crystal where Nd3+ ions are incorporated in a YAG (Yttrium, Aluminum, Garnet) crystal.
  3. Pump usually is a krypton flashlamp or a smaller semiconductor laser.
  4. Dual oscillator i.e double pulse
• Charged Couple Device Camera Unit (ImagerProSX 5M) with IRO (Intensified Relay Optics) :
  1. Double shutter two images with 600 ns min. interframing time
  2. Resolution (hXv): 2448 pixel X 2050 pixel
  3. Sensor type: Sony ICX625
  4. Optical size: 2/3"
  5. Pixel size: 3.45 µm X 3.45 µm
  6. Spectral range: 400 - 850 nm
  7. Max. frame rate: (at full resolution) 14.2 fps
  8. Partial scan: yes
  9. Data output type: Gigabit Ethernet (1000 Mbits/s)
  10. Power requirements: +12 to +24 VDC, ≤1% ripple ≤5 W @ 12 V
  11. Operating temperature: 5 - 40 °C
  12. Size (l x w x h): 100 mmX57 mmX45 mm (without lens adapter or connectors)
  13. Weight: 380 g
• High Efficiency Diffuser :
  1. Allows incoming beam diameters of max. 8mm
  2. Calibration target 5 mm/ 200 lines
  3. Min. recommended laser power: 15 mJ, 527-532 nm
     1. Light output diameter: 120 mm
     2. Light output wavelength: 574-580 nm
  4. Light output pulse duration (@ 5 ns laser): 20 ns
• Long Distance Microscope (LDM) :
  1. Model: QM100
  2. Type: Maksutov Cassegrain Catadioptric
  3. Working Range: 150 mm (6 ") to 35 mm (14 "), subject plane to front element
  4. Clear Aperture: 63 mm (2.5 ")
  5. Back focal length: 70 mm (2.75 ") minimum measured from back plate
• Sheet Optics :
  1. Sheet thickness: 0.5 mm - 2.5 mm (adjustable, but dependant on M2 and size of Laser beam).
  2. Divergence lenses: f = -20 mm and -10 mm. 1108406 and 1108516 additionally with f=-50mm.
  3. Working distance: 300 mm - 2000 mm.
  4. Dimensions: approx. Ø43 mm X 90 mm.