BOUNDARY LAYER INVESTIGATIONS WITH LDA NEW PROCESSING EQUIPMENTS

Experimental investigation of fluid velocity fields around ship model hulls, especially in the few millimeters near the wall is needed for performance optimisation, viscous drag component determination and appendix behaviour evaluation. Velocity fields measurements near a wall are difficult for both intrusive and optical methods. In LDA (laser Doppler anemometry) systems, the determination of the Doppler frequency from high noise levels signal has not usually been well performed by the more diffused processors. Two new instruments (BSA and IFA 550) make it possible to work also with low signal to noise ratio and hence very close to a wall. In order to test these new instruments, velocity measurements in a high turbulent flux near a wall have been performed. Mean values, standard deviations and power-spectra have been measured.