在斜向非定常流动中由层流向湍流转变对模型尺度螺旋桨性能和压力脉动的影响

In this paper,after the successful applications to open water propeller performance estimations,the influence of transition sensitive and modified mass transfer models tuned to account for the laminar flow in the prediction of the cavitation inception of marine propulsors is investigated from the point of view of the unsteady functioning and induced pressure pulses.The VP1304(also known as PPTC)test case,for which dedicated data were collected during several workshops,is considered first.After preliminary analyses using RANS,also Detached Eddy Simulations(DES)are included to better account for the vortex dynamics and its influence on pressure pulses.Similarly to what observed in uniform inflow,results show a better agreement with the available measurements of propeller performances and confirm the reliability of the proposed approaches for unsteady,non-cavitating,model scale propeller predictions.The overall cavitation pattern is improved too by the application of the transition sensitive correction to the mass transfer model,but the complex dynamics of bubble cavitation observed in experiments prevents quantitatively better predictions in terms of thrust/torque breakdown and induced pressure pulses levels regardless the use of RANS or DES methods.

Cavitating Propeller Performance in Inclined Shaft Conditions with OpenFOAM:PPTC 2015 Test Case

In this paper,we present our analysis of the non-cavitating and cavitating unsteady performances of the Potsdam Propeller Test Case(PPTC)in oblique flow.For our calculations,we used the Reynolds-averaged Navier-Stokes equation(RANSE)solver from the open-source OpenFOAM libraries.We selected the homogeneous mixture approach to solve for multiphase flow with phase change,using the volume of fluid(VoF)approach to solve the multiphase flow and modeling the mass transfer between vapor and water with the Schnerr-Sauer model.Comparing the model results with the experimental measurements collected during the SecondWorkshop on Cavitation and Propeller Performance– SMP’15 enabled our assessment of the reliability of the open-source calculations.Comparisons with the numerical data collected during the workshop enabled further analysis of the reliability of different flow solvers from which we produced an overview of recommended guidelines(mesh arrangements and solver setups)for accurate numerical prediction even in off-design conditions.Lastly,we propose a number of calculations using the boundary element method developed at the University of Genoa for assessing the reliability of this dated but still widely adopted approach for design and optimization in the preliminary stages of very demanding test cases.

Numerical Evaluation of Rudder Performance Behind a Propeller in Bollard Pull Condition

Correct evaluation of rudder performance is a key issue in assessing ship maneuverability.This paper presents a simplified approach based on a viscous flow solver to address propeller and rudder interactions.Viscous flow solvers have been applied to this type of problems,but the large computational requests limit(or even prevent)their application at a preliminary ship design stage.Based on this idea,a simplified approach to include the propeller effect in front of the rudder is considered to speed up the solution.Based on the concept of body forces,this approach enables sufficiently fast computation for a preliminary ship design stage,therebymaintaining its reliability.To define the limitations of the proposed procedure,an extensive analysis of the simplified method is performed and the results are compared with experimental data presented in the literature.Initially,the reported results show the capability of the body-force approach to represent the inflow field to the rudder without the full description of the propeller,also with regard to the complex bollard pull condition.Consequently,the rudder forces are satisfactorily predicted at least with regard to the lift force.However,the drag force evaluation ismore problematic and causes higher discrepancies.Nevertheless,these discrepancies may be accepted due to their lower influence on the overall ship maneuverability performance.