LDA

A Laser Doppler Anemometry (LDA) system is available to optically measure fluid flow velocities. In LDA the flow velocities are measured by detecting the Doppler frequency shift of laser light that has been scattered by small particles moving with the fluid.

The available system is based on a 3D commercial LDA measurement system available from TSI. The flow is seeded with polydispersed liquid paraffin oil particles with a mean particle size of 0.4µm (particle generator, AGF2.0 and AGF10.0, Palas GmbH, Karlsruhe). The light source is an argon-ion laser (Coherent Innova 308 Ar-I).  A multicolor beam separator, with Bragg shift, is used to illuminate particles in two different directions (TSI ColorBurst). Collection of the scattered light and detection of Doppler frequency shift is accomplished with a multi channel receiver (TSI ColorLink) and signal processor (TSI IFA 755), respectively. Delivery and collection optics assure that the flow velocities are sampled (randomly), in a measurement volume (size of 100×100×500µm). High-precision positioning of the measurement volume is accomplished with a six-axis robot (Stäubli RX 60). Typically at a given point, 40,000 data points are stored together with a phase locking signal.