scholarly journals A Generalized Hybrid RANSE/BEM Approach for the Analysis of Hull–Propeller Interaction in Off-Design Conditions

2021 ◽  
Vol 9 (5) ◽  
pp. 482
Author(s):  
Danilo Calcagni ◽  
Giulio Dubbioso ◽  
Alessandro Capone ◽  
Fabrizio Ortolani ◽  
Riccardo Broglia
Keyword(s):  
Complex Flow ◽  
Flow Solver ◽  
Wake Field ◽  
Hybrid Approaches ◽  
Twin Screw ◽  
Blade Loads ◽  
Fully Coupled ◽  
Straight Ahead ◽  
Accurate Experimental Data ◽  
Early Design Phase

During maneuvers, propellers’ operation differs from their design due to strong modification of the wake field with respect to the straight-ahead motion. The consequent modification of the loads overstresses the mechanical components of the shaftline, exacerbates propeller side effects and worsens overall efficiency. Therefore, the analysis of these situations in the early design phase is pivotal to increase the operation capabilities and safety at sea. This task relies on novel tools capable to accurately predict the complex flow field that develops past the hull and the propeller loads. Since the solution of the fully coupled problem with the rotating propeller by viscous flow solver is impractical for routine applications, hybrid approaches are a viable alternative. In this paper, an interactive RANSE/BEM methodology is presented, where the propeller is replaced by rotating body forces that map the actual loading state of the blades, allowing a fully unsteady analysis of hull–propeller interaction. The methodology is applied to the straight ahead and 8.4° pure drift motions of a twin screw propulsive configuration. Last, but not least, the study presents a validation study with accurate experimental data of the nominal wake field and single blade loads.

Predicting the Powering Performance of Different Vessel Types using an Open-Source CFD Propulsion Framework

2021 ◽  
Author(s):  
Björn Windén
Keyword(s):  
Energy Saving ◽  
Open Source ◽  
Fuel Efficiency ◽  
Computational Effort ◽  
The Body ◽  
Cfd Simulations ◽  
Local Flow ◽  
Flow Solver ◽  
Twin Screw ◽  
Coupled Solvers

CFD is a useful tool for ship designers looking for accurate predictions of the fuel efficiency achieved by a certain combination of hull, propeller and Energy Saving Devices (ESDs). Such predictions are key to meeting ever-increasing demands for reductions in emissions. However, CFD simulations of propeller-hull interaction can be very costly in terms of computational effort due to the need to resolve the unsteady flow around the rotating propeller. A popular approach to alleviate this cost, that has seen much practical use in industry, is the use of body forces (momentum sources) to represent the rotating propeller. There are many ways to describe the body force distribution in the fluid for a certain propeller and there are many options for what flow solver to use. In a previous meeting of the Society, an open-source framework for easily creating coupled solvers using an arbitrary combination of models was presented. Here, one of these coupled solvers is used to predict the local flow behind the propeller, as well as integral coefficients indicating performance, of four different vessels: a bulk carrier fitted with an Energy Saving Device, a fast container ship, a tanker and a fully appended twin-screw navy destroyer. All simulations are compared to available experimental data. Conclusions are drawn based on the success of the coupled solver to predict the local flow behind the propeller for each individual hull and how this relates to the vessel type and the local stern geometry.

A Study on the Influence of the Suction Arrangement on the Performance of Twin Screw Compressors

2013 ◽  
Author(s):  
Maria Pascu ◽  
Manoj Heiyanthuduwage ◽  
Sebastien Mounoury ◽  
Graeme Cook ◽  
Ahmed Kovacevic
Keyword(s):  
Screw Compressor ◽  
Complex Flow ◽  
Positive Displacement ◽  
Complex Shapes ◽  
Twin Screw ◽  
Profiling Techniques ◽  
Compressor Performance ◽  
Manufacturing Tolerances ◽  
Area Of Concern ◽  
Angle Of Rotation

Screw compressors are complex flow systems, but operate upon simple considerations: they are positive displacement machines consisting of meshing rotors contained in a casing to form a working chamber, whose volume depends only on the angle of rotation. Their performance is highly affected by leakages, which is dependent on various clearances and the pressure differences across these clearances. Nowadays, the manufacturing and profiling techniques have matured so much, that rotors of even the most complex shapes can be manufactured to tolerances in the order of few microns, resulting in high efficiencies. With manufacturing tolerances this tight, there is only small amount of improvement expected from further exploration of this venue, and a rather different direction for analysis may be more rewarding, i.e. other components of the screw compressor, like the suction and discharge areas. While the available literature includes several references on improvements of the compressor performance based on the analysis of the discharge port and discharge chamber, the investigation of the suction arrangement and inlet port remains fairly unexplored. This is the area of concern for the present paper, where the influence of the port shape and suction arrangement on the overall compressor performance is investigated. Two suction models were investigated for a standard screw compressor by means of CFD, which allowed in-depth analyses and flow visualizations, confirmed by the experimental investigation carried out on the actual compressor.

A study on the influence of hull wake on model scale cavitation and noise tests for a fast twin screw vessel with inclined shaft

2017 ◽  
Vol 232 (3) ◽  
pp. 307-330
Author(s):  
Giorgio Tani ◽  
Michele Viviani ◽  
Diego Villa ◽  
Marco Ferrando
Keyword(s):  
Scale Effects ◽  
Full Scale ◽  
Ship Wake ◽  
Radiated Noise ◽  
Wake Field ◽  
Model Scale ◽  
Propeller Noise ◽  
Twin Screw ◽  
Long Time ◽  
The Impact

The study of ship underwater radiated noise is nowadays a topic of great and largely recognized importance. This is due to the fact that in the last decades, the problem of the impact of anthropogenic noise on marine life has been addressed with higher emphasis, giving rise to different efforts aimed to the analysis of its effects on different organisms and, in parallel, to means for the reduction of shipping noise. In this context, attention is focused on the propeller noise, which, in cavitating conditions, may represent the most important noise source of the ship. The propeller noise has been studied for long time with different approaches. One of the most effective approaches is represented by model scale testing in cavitation tunnels or similar facilities. Despite having been adopted for several years, radiated noise experiments in model scale are usually affected by significant scale effects and technical issues. One of these aspects is represented by the correct modelling of the propeller inflow; different techniques are adopted, depending on the facility, in order to reproduce a certain target wake. One of the main problems is to define this target wake, which should in principle coincide with the ship wake; as it is well known, it is usually derived from model scale towing tank measurements, with the necessity for the prediction of the full-scale wake field. Starting from the outcomes of a previous work on the influence of different approaches for the prediction of the full-scale wake field for a single screw ship, in this work, attention is focused on the case of a fast twin screw vessel, analysing the different issues which may be connected to this hull form.

Fully-Coupled Simulation of Low Temperature Ablator and Hypersonic Flow Solver

2022 ◽  
Author(s):  
Aleksander L. Zibitsker ◽  
Joel McQuaid ◽  
Christoph Brehm ◽  
Alexandre Martin
Keyword(s):  
Low Temperature ◽  
Hypersonic Flow ◽  
Coupled Simulation ◽  
Flow Solver ◽  
Fully Coupled

CFD Simulation of a Twin-Screw Ship Self-Propulsion Using DDES-Overset Method

2019 ◽  
Author(s):  
Jianhua Wang ◽  
Decheng Wan
Keyword(s):  
Cfd Simulation ◽  
Ship Hull ◽  
The Self ◽  
Detached Eddy Simulation ◽  
Complex Flow ◽  
Ship Model ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Twin Screw ◽  
Cfd Method

Abstract Rotating propellers and moving rudders are necessary for the simulation of free running ship with the purpose of resolving detailed flow interaction. In the present work, CFD method is used to numerically investigate self-propulsion behavior for a twin-screw fully appended ship. The simulation conditions are following the experiment performed at IIHR. The benchmark ship model ONR Tumblehome is used for all the numerical computations. Overset grids are used to fully discretize the ship hull, twin propellers and rudders. Self-propulsion simulation is carried out using a PI controller to achieve target ship speed of Fr = 0.20 in calm water and the ship model is free to trim and sinkage. All the numerical calculations are carried out by the in-house CFD solver naoe-FOAM-SJTU. Unlike most previous studies based on RANS method, the present self-propulsion simulations adopt the Delayed Detached-Eddy-Simulation (DDES) approach to resolve the complex flow around ship hull, propeller and rudder. The main parameters of the self-propulsion as well as flow visualizations are presented. The predicted results are compared with previous RANS data and the available experimental data. The comparison with the experiment is satisfactory and the flow field shows that the present DDES-overset method can give more flow details for the self-propulsion condition.

Numerical Unsteady Flow Analysis of a Turbine Stage With Extremely Large Blade Loads

2001 ◽  
Author(s):  
Markus Jöcker ◽  
Francois X. Hillion ◽  
Torsten H. Fransson ◽  
Ulf Wåhlén
Keyword(s):  
Rocket Engine ◽  
Flow Analysis ◽  
Vortical Flow ◽  
Navier Stokes ◽  
Design Parameters ◽  
Turbine Stage ◽  
Flow Solver ◽  
Flow Disturbances ◽  
Excitation Mechanisms ◽  
Blade Loads

This paper presents the detailed numerical analysis including parametric studies on the aerodynamic excitation mechanisms in a turbine stage due to the unsteady stator-rotor interaction. The work is part of the pre-design study of a high pressure subsonic turbine for a rocket engine turbopump. The pressure level in such turbines can be remarkably high (in this case 54 MPa inlet total pressure). Hence, large unsteady rotor blade loads can be expected, which impose difficult design requirements. The parameter studies are performed at midspan with the numerical flow solver UNSFLO, a 2D/Q3D unsteady hybrid Euler/Navier-Stokes solver. Comparisons to 2D and steady 3D results obtained with a fully viscous solver, VOLSOL, are made. The investigated design parameters are the axial gap (∼8%–29% of rotor axial chord length) and the stator vane size and count (stator-rotor pitch ratio ∼1–2.75). For the nominal case the numerical solution is analyzed regarding the contributions of potential and vortical flow disturbances at the rotor inlet using rotor gust computations. It was found that gust calculations were not capable to capture the complexity of the detected excitation mechanisms, but the possibility to reduce excitations by enforcing cancellation of the vortical and potential effects has been elaborated. The potential excitation mechanism in the present turbine stage is found dominant compared to relatively small and local wake excitation effects. The parameter studies indicate design recommendations for the axial gap and the stator size regarding the unsteady rotor load.

Numerical Unsteady Flow Analysis of a Turbine Stage With Extremely Large Blade Loads

2002 ◽  
Vol 124 (3) ◽  
pp. 429-438 ◽  
Author(s):  
Markus Jo¨cker ◽  
Francois X. Hillion ◽  
Torsten H. Fransson ◽  
Ulf Wa˚hle´n
Keyword(s):  
Rocket Engine ◽  
Flow Analysis ◽  
Vortical Flow ◽  
Navier Stokes ◽  
Design Parameters ◽  
Turbine Stage ◽  
Flow Solver ◽  
Flow Disturbances ◽  
Excitation Mechanisms ◽  
Blade Loads

This paper presents the detailed numerical analysis including parametric studies on the aerodynamic excitation mechanisms in a turbine stage due to the unsteady stator-rotor interaction. The work is part of the predesign study of a high-pressure subsonic turbine for a rocket engine turbopump. The pressure level in such turbines can be remarkably high (in this case 54 MPa inlet total pressure). Hence, large unsteady rotor blade loads can be expected, which impose difficult design requirements. The parameter studies are performed at midspan with the numerical flow solver UNSFLO, a 2-D/Q3-D unsteady hybrid Euler/Navier-Stokes solver. Comparisons to 2-D and steady 3-D results obtained with a fully viscous solver, VOLSOL, are made. The investigated design parameters are the axial gap (∼8–29 percent of rotor axial chord length) and the stator vane size and count (stator-rotor pitch ratio ∼1–2.75). For the nominal case the numerical solution is analyzed regarding the contributions of potential and vortical flow disturbances at the rotor inlet using rotor gust computations. It was found that gust calculations were not capable to capture the complexity of the detected excitation mechanisms, but the possibility to reduce excitations by enforcing cancellation of the vortical and potential effects has been elaborated. The potential excitation mechanism in the present turbine stage is found dominant compared to relatively small and local wake excitation effects. The parameter studies indicate design recommendations for the axial gap and the stator size regarding the unsteady rotor load.

A Numerical Algorithm Based on a Tree Data for an Anisotropically Adaptive Cartesian Mesh

2003 ◽  
Author(s):  
Takanobu Ogawa
Keyword(s):  
Data Structure ◽  
Numerical Algorithm ◽  
Complex Flow ◽  
Flow Solver ◽  
Boundary Layer Problem ◽  
Cartesian Mesh ◽  
Rectangular Mesh ◽  
Tree Data ◽  
Anisotropic Mesh Refinement ◽  
Tree Data Structure

In an adaptive Cartesian mesh approach, a rectangular mesh is recursively and locally refined and mesh can be automatically generated for complex flow geometry. In this study, a numerical algorithm is developed for an adaptive Cartesian mesh. The tree data is employed to organize the adaptively refined meshes. With this data structure, mesh adaptation becomes very flexible and the algorithm developed for a conventional flow solver can be adapted with less modification. The algorithm can be extended for the anisotropic mesh refinement which is efficient for a boundary layer problem. Parallelization of the developed algorithm is also done in the SPMD paradigm. The domain decomposition technique is used and a tree data structure is split so that computational load should be balanced. Parallel efficiency is examined on a PC cluster.

scholarly journals A Well-Balanced and Fully Coupled Noncapacity Model for Dam-Break Flooding

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
Zhiyuan Yue ◽  
Huaihan Liu ◽  
Youwei Li ◽  
Peng Hu ◽  
Yanyan Zhang
Keyword(s):  
Sediment Transport ◽  
Momentum Conservation ◽  
Dam Break ◽  
Governing Equations ◽  
Complex Flow ◽  
Flow Phenomena ◽  
Dam Break Flow ◽  
Flow And Sediment Transport ◽  
Volume Method ◽  
Fully Coupled

The last two decades have seen great progress in mathematical modeling of fluvial processes and flooding in terms of either approximation of the physical processes or dealing with the numerical difficulties. Yet attention to simultaneously taking advancements of both aspects is rarely paid. Here a well-balanced and fully coupled noncapacity model is presented of dam-break flooding over erodible beds. The governing equations are based on the complete mass and momentum conservation laws, implying fully coupled interactions between the dam-break flow and sediment transport. A well-balanced Godunov-type finite volume method is used to solve the governing equations, facilitating satisfactory representation of the complex flow phenomena. The well-balanced property is attained by using the divergence form of matrix related to the static force for the bottom slope source term. Existing classical tests, including idealized dam-break flooding over irregular topography and experimental dam-break flooding with/without sediment transport, are numerically simulated, showing a satisfactory quantitative performance of this model.

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