REALIZATION OF THE FULL-POTENTIAL OF THE LASER-DOPPLER ANEMOMETER IN THE ANALYSIS OF COMPLEX FLOWS

An improved method of alignment for the laser doppler anemometer has b een developed which greatly enhances its capabilities for the examinat ion of the often very small scale complexities of three-dimensional fl ows. Unlike the alignment methods normally employed, which are subject ive, this method is quantitative, using a pin-hole device to measure l aser light intensity. This 'pin-hole meter' also enables the geometry of the laser beam configuration to be defined in situ and with greater facility and precision than previous methods. Examples are given whic h illustrate the enhanced capability of the system, the greatest impro vement coming from the ability to operate in the difficult to achieve and sustain, off-axis mode of signal collection. With this mode, the i mproved procedures enable very small measurement volumes, typically 50 micron diameter, while maintaining high data rates, in measurements t aken from distances compatible with accessing the flow from outside th e windtunnel.