Enrico Nobile

Cavitating flows, which can occur in a variety of practical applications, can be modelled using a wide range of methods. One strategy consists of using the RANS (Reynolds Averaged Navier Stokes) approach along with an additional transport equation for the liquid volume fraction, where mass transfer rate due to cavitation is modelled by a mass transfer model. In this study, we verify the influence of three widespread mass transfer models, mainly on the numerical predictions of the propeller performances. The models in question share the common feature of employing some empirical coefficients to tune the models of condensation and evaporation processes, which can influence the accuracy and stability of the numerical predictions. For this reason, and for a fair and congruent comparison, the empirical coefficients of the different mass transfer models are first equally well tuned using an optimization strategy. The numerical predictions of the propeller performances based on the three d...

In this paper we present a comparison between hexa-structured and hybrid-unstructured meshing approaches for the numerical prediction of the flow around marine pro-pellers working in homogeneous flow (Open Water Con-ditions). The objective was to verify if the accuracy of the predictions based on structured meshes is significantly better than predictions based on hybrid meshes to justify the more difficult and time-consuming meshing strategy. The study was performed on two five-bladed propellers in model scale. Simulations were carried out with a com-mercial RANS solver, using a moving frame of reference approach and employing the SST (Shear Stress Transport) two equation turbulence model. Computational results from both meshing approaches were compared against ex-perimental data. The thrust and torque coefficients were used as global quantities. Circumferentially averaged ve-locity components and root-mean square values of the tur-bulent velocity fluctuations, avaiable for one of t...

Heat transfer augmentation is of paramount importance in many fields like, to name a few, fossil fuels, renewable energy production and conversion, thermal control of electronic equipment. The possibility to enhance the heat transfer process will eventually lead to energy savings, reduced size and cost of the equipment, and so on. Metal foams are considered good candidates to replace traditional heat transfer-augmentation strategies - i.e., extended and textured surfaces - in several applications: they might, in fact, guarantee increased heat transfer rate with a modest increase of pressure losses, with the added benefit of lighter and more compact equipments. However, for practical purposes, the estimation of the flow permeability and the thermal conductivity of the foam is fundamental, but far from simple. From this perspective, computational fluid dynamics (CFD) computations at the pore scale are becoming a challenging approach in addition to classical transport models. Moreover,...

ABSTRACT The numerical predictions of the cavitating flow around two model scale propellers in uniform inflow are presented and discussed. The simulations are carried out using a commercial CFD solver. The homogeneous model is used and the influence of three widespread mass transfer models, on the accuracy of the numerical predictions, is evaluated. The mass transfer models in question share the common feature of employing empirical coefficients to adjust mass transfer rate from water to vapour and back, which can affect the stability and accuracy of the predictions. Thus, for a fair and congruent comparison, the empirical coefficients of the different mass transfer models are first properly calibrated using an optimization strategy. The numerical results obtained, with the three different calibrated mass transfer models, are very similar to each other for two selected model scale propellers. Nevertheless, a tendency to overestimate the cavity extension is observed, and consequently the thrust, in the most severe operational conditions, is not properly predicted.

Enrico Nobile Sezione di Fisica Tecnica Dip. di Ingegneria Navale del Mare e per l'Ambiente University of Trieste, Trieste, 34127 ITALY Tel: +39 040-558-3507, Fax: +39 040 572-033 Email: nobile@units.it, WWW: http://www-dinma.univ.trieste.it/nirftc/

... Numerical simulation of heat transfer and fluid flow applied to exhaust manifold. ... Presented in this paper are the background of the new code, and an example of thermal conduction analysis for an exhaust manifold, a critical engine part in terms of coupling a heat flow with ...