A three component dual beam laser-Doppler-anemometer to be operated in large wind tunnels

A number of problems arose in connection with the employment of a two-component dual-beam laser Doppler anemometer (LDA) which was operated in backscatter mode in a 3 m x 3 m low speed wind tunnel. An approach to overcome certain difficulties involves a change from an on-axis concept to an off-axis concept. The implementation of this approach includes a separation of the emitting and receiving functions of the optical arrangement. This requirement is automatically satisfied if a three-component LDA is designed. In the considered case, the new design was implemented by using, in addition to the previously employed green and blue lines of an argon-ion laser, also the violet line. The obtained three-component LDA, running automatically under computer control, satisfies the requirements presented by a 3m x 3m low wind speed tunnel.