F. Di Felice

Experimental testing of Taylor's hypothesis by L.D.A. in highly turbulent flow

A new configuration for the transmitting optics of a laser Doppler anemometer has been developed in order to measure the velocity at two different points at the same time. From the simultaneous measurements at two points along the mean flow direction it is possible to evaluate the spatial correlations and to compare them with the temporal correlation to verify the validity limits of Taylors hypothesis also known as the frozen turbulence hypothesis. The transfer function between the velocity signals at two different points has been introduced to better explain the differences between Taylors hypothesis and non frozen flow. The analysis is carried out in a flow with high turbulence levels.

Analysis of the Propeller-hull Interaction by LDV Phase Sampling Techniques

In the present paper the results of the wake survey in two stern sections of a twin screw ship model, located just upstream the propeller disk and behind the directional rudder, are presented. Experiments have been performed in a large towing tank by using a Laser Doppler Velocimeter and phase sampling techniques, in order to analyse wake evolution with the propeller angular position. The main features of the propeller installation are highlighted as well as the strong and complex interaction of the propeller with the hull wake, especially in the brackets region and down stream the directional rudder.