1,721,074 research outputs found
RIM Driven propellers design using a Simulation Based Design Optimization approach
No full textA Simulation Based Design Optimization approach is proposed for the design of RIM driven
propellers operating in an accelerating duct. The tool relies on RANS analyses of parametrically described geometries
driven by an automatic, multi-objective optimization loop for the design of propellers with improved
performances simultaneously in terms of both propulsive efficiency and cavitation inception. Pareto convergence
is achieved by using a mix of fully resolved RANS analyses and surrogate models aimed at significantly
improving the computational efficiency of the procedure. The effectiveness of the design approach is verified by
comparing the devised RIM propellers with the performance of a reference ducted propeller at the same functioning
point while design trends and guidelines are extracted from the analysis of the amount of data collected
during the optimization process
Design of PBCF energy saving devices using optimization strategies: A step towards a complete viscous design approach
No full textThe need of improving propulsive efficiency continuously encourages the development of energy saving devices, the understanding of their underlying principles and the validation of their effectiveness. In this work, a design by optimization of Propeller Boss Cap Fin (PBCF) devices is carried out using Computational Fluid Dynamics analyses. RANS Equations, solved by using the OpenFOAM library, are applied in an automatic design approach involving a parametric description of the main characteristics of PBCFs and an optimization algorithm. The optimization is carried out with multiple purposes: identify a reliable design strategy necessary to customize the PBCF geometry based on the propeller functioning and, by exploiting the systematic calculations carried out in the framework of the optimization, evaluate the influence of alternative configurations and of main geometrical parameters in achieving higher efficiency. The use of high-fidelity RANS calculations allows confirming the decrease of the hub vortex strength, the reduction of the net torque and the influence of the additional fins on blades performance as the major contributors to the increase of efficiency. Results of detailed analyses of optimal PBCF configurations show model scale increases of efficiency of about 1%, which can reach the outstanding value of 4% in the case of a rather unrefined propeller design
Improving model scale propeller performance prediction using the k - kL - ω transition model in OpenFOAM
No full textThe effect of laminar to turbulent flow transition plays an important role for the prediction of model scale performance, which is of utmost interest for the development of scaling approaches entirely based on Computational Fluid Dynamics calculations. The recent inclusion of transition models (either based on local correlations, like the γ - Re θ, or on the concept of kinetic laminar energy, like the k - k L - ω) in many RANS codes fosters their application for improving the model scale prediction of propeller performance. In the present work the numerical results using the well-established SST k - ω and the k - k L - ω turbulence models available in OpenFOAM are presented and compared with towing tank experiments for three test case propellers. The influence of turbulence parameters (i.e. turbulence intensity and turbulent viscosity ratio at inlet) is discussed, at first for the ERCOFTAC T3A flat plate validation case, through which useful guidelines for propeller performance predictions using transition sensitive turbulence models are derived. By using these relationships, a significant improvement of numerical predictions of propeller forces is achieved, with discrepancies with respect to model scale measurements appreciably reduced if compared to usual fully turbulent calculations. At the same time the limitations of the adopted transitional model are discussed based on the systematic analyses carried out for three test cases
Steady cavitating propeller performance by using OpenFOAM, StarCCM+ and a boundary element method
No full textAccurate and reliable numerical predictions of propeller performance are a fundamental aspect for any analysis and design of a modern propeller. Prediction of cavitation and of cavity extension is another important task, since cavitation is one of the crucial aspects that influences efficiency in addition to propagated noise and blade vibration and erosion. The validation of the numerical tools that support the design process, including open-source codes, is, consequently, essential. The public availability of measurements and observations which cover not only usual thrust and torque in open water conditions (including cavitation) but also unsteady functioning with pressure pulse measurements in the case of
the Potsdam Propeller Test Case certainly represents an extremely useful source of information and an excellent chance for verification and validation purposes. In the present work, the prediction of the Potsdam Propeller Test Case propeller performance using the OpenFOAM computational fluid dynamics package is proposed. After a preliminary validation and calibration of the OpenFOAM native Schnerr–Sauer interphase mass transfer model for cavitating flow, based on the experimental results on a 2D NACA66Mod hydrofoil, open water propeller performance and cavitation predictions are carried out. The OpenFOAM results are finally compared both with the available experimental measurements and with calculations carried out with StarCCM+and with a proprietary boundary element method code, in order to assess
the accuracy and the overall capabilities of the open-source tools (from meshing to post-processing) available in the OpenFOAM package. The comparison, in addition to assessing the accuracy of the open-source approach, is aimed to verify its advantages and drawbacks with respect to widely used solvers and to further verify the reliability of traditional boundary element method approaches that are still widely adopted for design and optimization (thanks to their extremely higher computational efficiency) in a very demanding test case
A Potential Panel Method for the Analysis of Propellers in Unsteady Flow
No full textThe unsteady flow around an open marine propeller subject to a spatially non-uniform inflow is analyzed by utilizing a
time marching potential based panel method. An efficient algorithm is implemented in order to ensure an explicit Kutta
condition at the blade trailing edge at each time step. Numerical results are shown to be convergent with respect to the
size of the time step and the number of panels on the propeller and also to be consistent with existing analytic solutions
and experimental data
Silent Propellers with Unconventional Profile Shapes. Examples Obtained with a New Automatic Optimization Method
No full textThe CFD Potentiality on the AUV Hydrodynamic Design
No full textHydrodynamic aspects of autonomous underwater vehicles, even if of-
ten underestimated, play a crucial role in the overall vessel design. Over the past
few decades, computational fluid dynamics has become a widely used tool for in-
vestigating complex hydrodynamic problems in a fast and reliable way, often sub-
stituting the most expensive and time-consuming experimental campaigns. Nev-
ertheless, even if several researchers adopt these approaches to investigate some
specific aspect (i.e. vehicle resistance, PMM tests, etc.), from an industrial point
of view they are rarely used in the vehicle design stages (in particular during the
preliminary ones), because of vehicles designs are primary driven by control as-
pects (i.e. payload arrangements, propulsion layout, etc.). The present paper tries
to show possible research fields where these numerical tools can provide a valuable
contribution to their design. Different aspects are investigated, ranging from the
typical ones, such as the impact of the vehicle geometry on the resistance, to the
most complex ones, such as hull-propeller interactions in hovering conditions. This
activity demonstrates that a more deep knowledge of these hydrodynamic aspects
can better drive the vehicle design, obtaining a more effective and efficient design
CFD Prediction of the Asymmetrical Shaft Unbalance During Ship Maneuvers
No full textAbstract. The paper explores the accuracy of a low-cost CFD based approach to
evaluate the propeller load variation experienced during manoeuvring conditions.
The proposed procedure is based on the inclusion, in the ship hydrodynamic analyses by RANS, of the propeller effect through a body-force approach calibrated on
BEM calculation to realize a computationally efficient method. Numerical results
have been compared with the literature available experimental data performed on
the well-known DTMB5415 benchmark test case, where the thrusts experienced by
both of her propellers during dedicated Captive Model Tests were recorded. Both
pure drift and pure yaw tests have been considered in the numerical campaign to
cover the entire kinematic conditions involved during standard IMO manoeuvres.
To prove the effectiveness of the method, also a severe turning circle condition
is evaluated. The comparison shows the maturity of these numerical calculations,
even if based on a simplified approach, to correctly evaluate the propeller unbalance, opening the way to the application of the proposed method to investigate the
causes of load variations in manoeuvre conditions and directly in manoeuvre simulations
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