The Particle-Image-Velocity-System of the ISMT

Projektbetreuung: Dipl.-Ing. Jens Neugebauer

Description

The ISMT operates a stereoscopic Particle-Image-Velocimetry System (PIV-System) for the non-intrusive measurement of velocities in three components within a measurement plane. The advantage of using PIV compared to a 5-Hole-Sensor or Laser-Doppler-Anemometry (LDA) is the simultaneous acquisition of velocities in the desired plane, while the other techniques require a repositioning of the measurement device. Furthermore, compared to the 5-Hole-Sensor, the advantage of PIV is also its non-intrusiveness.

In order to perform PIV measurements, the fluid first needs to be seeded with tracer particles. A pulsed laser is expanded to a light-sheet which is then positioned in the flow via an optical access. The laser produces two laser pulses within a short period of time (separation time) and the light scattered by the tracer particles is recorded by two digital high-speed cameras mounted in different viewing angles.

In each camera, a pair of images is recorded, showing the motion of the tracer particles within the separation time. These double-frames are subdivided into a number of interrogation windows and processed by cross-correlation and additional pre and post-processing algorithms. Via stereo reconstruction, the results of both cameras are used to compute the fluid velocities in and perpendicular to the measurement plane, resulting in one velocity-vector per interrogation window. The results can also be processed in order to obtain derived quantities, such as vorticity and turbulent energy.

The PIV-System of the ISMT is working with a double-frame rate of up to 100 Hz and can therefore be used to measure unsteady flow. For the suppression of laser reflections due to boundaries of the tank cavity or the two-phase system, fluorescent tracer particles are used. The PIV-System has been purchased in the context of the Sloshing Laboratory and is suitable for being used at the hexapod.

Technical Data

Software

• Operation and Post-processing  - DaVis 7, DaVis 8