DE 3.1: Final report on towing rank design, experimental setup, model construction, and preparation

Deliverable 3.1 contains the description of the experimental setups designed and constructed to perform PIV velocity measurements, wall pressure fluctuations measurements and vibro-acoustic tests devoted to the analysis of the response of plates, made of different materials, to turbulent boundary layer excitation. The characteristics of the Flame model built for towing tank measurements are also described. Moreover, some additional mean velocity and pressure measurements aim at characterising flow conditions about the Flame model, to be compared to those numerically reproduced, are presented. Some details are summarized below. Same size as the original Flame have been chosen in order to: i) be able to identify common test cases for towing tank and free field measurements and ii) obtain a thick, stationary turbulent boundary layer. This last is a fundamental requirement to perform accurate PIV measurements of the velocity field, close to the wall and to extend the correlation length range of measured wall pressure fluctuations. As a consequence, taking into account Flame size and the need to avoid free surface and floor effects, all test campaigns have been performed in the CNR-INSEAN largest towing tank, which is 470 m long, 13.5 m wide and 6.5 m deep, for carriage speeds of 2.5 and 5.1 m/s. Some additional data have been acquired for lower velocities starting from 0.5 m/s. The inner part of the Flame model is made of steel and contains an aluminum watertight box in correspondence of the test section for instrumentation placement. The box frontal area is 746 x 647 mm. The PIV setup has been designed with the aim to minimize the interaction between the laser light and the wall, making available data very close to the wall itself. Two PIV cameras have been placed inside the model, with two parallel points of view at about 120 mm of distance. The PIV field of view extends 40 mm in the streamwise direction and 45 mm spanwise for one camera and 35x42 for the other camera. Concerning wall pressure fluctuation measurements, a basic configuration has been designed for a number of 20 sensors that cover a maximum distance of 0.133 m is stream-wise direction and 0.025 m in cross-stream direction, respectively. Some additional points have been provided in order to have the possibility to investigate the evolution of the pressure field in stream-wise direction up to 0.25 m. An array of pitot tubes has been arranged to identify the turbulent boundary layer thickness and the flow behavior at the outer edge. Moreover, a couple of absolute pressure transducers have been installed upstream and downstream the measuring section in order to estimate the amplitude of the stream-wise pressure gradient. Five panels have been selected for the vibro-acoustic tests: the first one is a 5 mm thick aluminum bare panel, the second is a 3 mm thick aluminum panel ribbed by 3 stiffeners with al L section. The second set of panels consists of a 5 mm thick aluminum panels coated with two different kinds of polyurethane and a foam, respectively. To connect the plates to the rest of the system, an outer rigid frame fixed to the model and an inner rigid one, specific for each panel, have been designed and constructed. Panels are glued to the inner frame, the maximum dimensions in stream-wise and cross-stream direction are for all panels 0.6x0.5 m, the effective dimensions are 0.5x0.4 m. The instrumentation used includes 12 piezoelectric ICP accelerometers and 3 microphones placed inside the watertight box. Finally some information about the experimental modal analysis is provided.