Development of an experimental device for a pod fitted with contra-rotating propellers

In present paper the development of a device for testing a pod fitted with contra-rotating propellers is presented. The device was realized in order to be mounted on the University of Genoa Cavitation Tunnel to investigate both global performances and cavitation phenomena. Although standard cavitation tunnels have in some cases the capability of testing contra-rotating propellers, the whole propulsive efficiency of the pod is rarely determined. This was one of the objectives of the developed device, designed in the framework of a research project in cooperation with Zf Marine, whose final aim is to develop a design procedure for contra-rotating propellers. One of the objectives of present study was the simplicity of the device, in order to minimise costs, searching for a compromise between testing accuracy and device complexity, as described in the paper. A first application of the testing equipment is then described, showing results obtained for a couple of propellers, which were tested alone and in contra-rotating configuration. Despite the practical problems which had to be overcome to keep the measuring system as simple as possible, results were rather satisfactory, allowing to measure usual propeller coefficients and to have an insight into the complex cavitating behaviour of this kind of propulsors

Chapter 60. Effects of seat and handgrips adjustments on a Hand Bike vehicle. An ergonomic and aerodynamic study for a quantitative assessment of Paralympics athlete’s performance

The aim of this paper is to present a research study on a Handbike vehicle assessment for London 2012 Paralympics competition. The main assumption of this study is that the athlete’s posture can affect directly both the ergonomics and the aerodynamics of the performance, and the objective is to determine a method to perform a quantitative analysis to understand the way in which these important factors should be considered for the optimal performance of the athlete. To investigate this hypothesis, an Italian Paralympics athletes has been experimentally evaluated at LyPhE (Laboratory of Physical Ergonomics) and at GVPM (the Wind Tunnel) of Politecnico di Milano. The methodology proposed in this study requires a first ergonomic evaluation conducted through a kinematic to understand how specific vehicle adjustment could affect the performance. The Aerodynamic assessments is based on the measurement for each selected condition, of the aerodynamic resistance coefficient in a wind tunnel. Results of this work demonstrate that the ergonomics benefits and the aerodynamics improvements present an opposite behavior. In the ergonomics analysis there are two important evidences: the first one is that the increase of the handgrip length influences negatively the ergonomic scores in all the different postures; the second one regards the inclination of the backseat; the more the athlete posture is vertical, the more the ergonomic index present a decrease in the discomfort perception. On the contrary, the vertical position of the trunk affects negatively the aerodynamic resistance coefficient, and this result is coherent with the observation that, an increasing of the wind exposed surface produces higher values of the aerodynamic resistance coefficient. Also results about the length of the handgrip are in contrast with the ergonomic analysis. In fact, the longer handgrips seem to be more efficient for the aerodynamic analysis. Results about the seat adjustment are coherent with the initial hypothesis that ergonomics and aerodynamics present opposite impacts. The vertical position of the trunk requires less anti­gravity movements that are not recommended for human performance and increase the effort level and consequently the resistance in races. The most surprising result is the high relevance of the handgrip impact to the whole performances for both the analysis. As a conclusion, the optimal setup of the handbike seems to be related to the type of each single race; for longer races the ergonomics adjustments seems to be preferable while for races with high speed, the aerodynamics factors are definitely more important