Particle shadow velocimetry (PSV) is a novel technique that shares many of the attributes of microPIV and Forward Scatter PIV (fsPIV). It utilizes low-power pulsed LED light sources to measure the displacement of seed particles in a flow. PSV images can also be used to characterize particle parameters such as size and shape. Since this is a volumetric illumination technique, it relies on the receiver optics to optimize the depth of field for the measurement. Any pulsed light system can be used as the light source; however, LEDs are particularly well suited since they can be over-driven in a short-pulse mode to produce intense sub-microsecond light pulses. Furthermore, the use of LEDs combined with a high speed camera results in a high-speed system with bandwidth of 10’s of kHz. Because the technique does not rely upon weak-particle light scattering, lasers are neither necessary nor recommended for use with this approach.
With the availability of off-the-shelf PIV systems, why is PSV of interest? PSV offers several advantages over traditional PIV systems.
• PSV is a low cost option. PSV utilizes LEDs rather than Lasers, and therefore, the cost of the equipment is significantly lower. It is also noted that the use of an LED rather than a Laser has significant safety advantages.
• LEDs can be pulsed at 10’s of kHz and therefore, data can be obtained at these high rates without the use of an expensive Laser.
• Finally, PSV uses volumetric illumination, this eliminates the strong scattering from the surface which can saturate the camera when using PIV. PSV, like every other experimental technique has limitations. The most significant issue for PSV is probe volume. As it is necessary to image individual particles the field of view is limited by a combination of the particle size and number of pixels on the camera.
ISSI CCD Color Camera
The PSP-CCD is a 2-megapixel CCD camera used for pressure sensitive paint data acquisition. The camera is small and lightweight allowing for an array of cameras to be mounted in a tight place for larger scale models and applications. Communication with the PSP-CCD is via Gigabit Ethernet.
The PSG-3 is a four channel pulse/delay generator used for controlling the timing of experiment parameters and can be used as an experiment master clock or externally triggered (or gated) by an external event. Pulse width, delay, repetition rate, and other timing parameters are controlled by a simple user interface.
3-Color RGB LED Light Source
The LM2X-DMHP-RGB is an LED light source that provides 3 color (Red, Green, and Blue) outputs from its LED head. This LED is used for Particle Shadow Velocimetry (PSV) to illuminate small seed particles in a flow field to measure velocity and particle density.
EF Lens Controller
The EF lens controller is designed to operate Canon® EF, EF-S and L series IS auto focus lenses as well as Sigma® and Tamron® EF lenses. The lens controller makes it possible to operate these lenses on non-Canon® cameras. The LC-2 gives precise control of lens focus and iris for sensitive optical systems like particle shadow velocimetry.
Between the camera and the lens, extension rings are used to move the lens away from the CCD sensor of the camera. This will reduce the amount of light coming into the camera, thus narrowing the depth of field. Ideally, the depth of field for PSV is 0.5 to 1.0 mm.