EFD and CFD Characterization of a CLT Propeller

Abstract

In the present paper an experimental and numerical analysis of an unconventional CLT propeller is carried out. Two different numerical approaches, a potential panel method and an RANSE solver, are employed. Cavitation tunnel experiments are carried out in order to measure, as usual, thrust, torque, and cavity extension for different propeller working points. Moreover, LDV measurements are performed to have a deep insight into the complex wake behind the propeller and to analyze the dynamics of generated tip vortexes. The numerical/experimental analysis and comparison of results highlight the peculiarities of this kind of propellers, the possibility to increase efficiency and reduce cavitation risk, in order to exploit the design approaches already well proven for conventional propellers also in the case of these unconventional geometries.

EFD and CFD Design and Analysis of a Propeller in Decelerating Duct

“…In turn also continuity equation is modified, in order to take into account the effect of cavitation through a source term, modeled by the Sauer and Schnerr [23] approach. The numerical solutions have been computed on appropriate meshes (e.g., Figures 3 and 5), whose reliability has been verified similarly to Bertetta et al [4][5][6]. As it is well known, the quality of the mesh is a decisive factor for the overall reliability of the computed solution.…”

“…Despite the lifting surface corrections that can be adopted for the definition of the blade geometry (through the empirical corrections proposed by VanOossanen [19] or by a dedicated lifting surface code), the influence of the blade and of the duct thickness, the nonlinearities linked with the cavitation, and the effects of the flow in the gap between the blade tip and the inner duct surface strongly affect the optimal propeller geometry. An alternative and successful way to improve the propeller performances is represented by optimization [4][5][6]. The design of the ducted propeller can be improved, in fact, adopting an optimization strategy, namely, testing thousands of different geometries, automatically generated by a parametric definition of the main geometrical characteristics of the propeller (eventually also of the duct), and selecting only those able to improve the performances of the initial configuration (e.g., in terms of efficiency and cavity extension) together with the satisfaction of defined design constraints (thrust identity, first of all).…”

“…Force measurement is performed by means of strain gauges directly applied on the hollow bar. This instrumentation was successfully tested against towing tank results, as reported in Bertetta et al [4][5][6], where further details about its development and calibration may be also found.…”

“…A more robust approach is thus required at least for their preliminary design, as well as improved analysis tools, capable to assess the complex viscous interactions that take place on the gap region between the propeller tip and the duct inner surface. This first step geometry is successively refined by means of a panel method coupled 2 International Journal of Rotating Machinery with an optimization algorithm, adopting an approach which already demonstrated successful results in the case of conventional CP propellers [4][5][6] with multiple design points. In the present case, the use of the panel code in the second design phase (geometry optimization) allows a more accurate evaluation of the cavity extension and of its influence on the propeller performances, thus leading to a better design.…”

Ship propeller side effects: pressure pulses and radiated noise

“…Once the propeller is solved by imposing appropriate boundary conditions, it is straightforward to evaluate the velocity field in any point of the computational domain and, via the unsteady formulation of the Bernoulli theorem, derives the unsteady pressure distribution on the surfaces of interest (the hull stern or the flat plate adopted during cavitation tunnel tests). The solution is calculated, following the guidelines developed and extensively tested in previous works [17][18][19], by using about 1250 hyperbolical panels on the key blade and 1600 panels to model the hull stern or the flat plate. A detailed descrip- Hull stern test tion of the coupling procedure and of the developed BEM may be found in [8,14].…”