scholarly journals A Numerical Investigation of a Winglet-Propeller using an LES Model

2019 ◽  
Vol 7 (10) ◽  
pp. 333 ◽  
Author(s):  
Zhu ◽  
Gao
Keyword(s):  
Volume Fraction ◽  
Mesh Size ◽  
Open Water ◽  
Tip Vortex ◽  
Vortex Wake ◽  
Time Step ◽  
Thrust Coefficient ◽  
Eddy Simulation ◽  
Water Characteristics ◽  
Les Model

The generation of tip vortex cavitation (TVC) is a common phenomenon in marine propellers. Therefore, it is important to find a way for the effective suppression of TVC. Based on the enlightenment of bionics, a propeller with winglets was numerically investigated by using a large eddy simulation (LES) model and the commercial software STAR-CCM+. Various variables, such as mesh size, number of prism layers, vapor properties and time step, were analyzed using the benchmark MAU5-80 propeller. The open water characteristics calculated for the benchmark propeller were compared with experimental data. The meshes in the region of the tip vortex wake were refined. The power spectral density (PSD) of the thrust coefficient and axial velocity were investigated. The comparison of TVC between the benchmark propeller and the propeller with winglets was studied with the Q-criterion, helicity and volume fraction of the vapor. The strength of the tip vortex wake is weakened by winglets; therefore, the presence of winglets leads to a reduction in vapor volume, which in turn alleviates TVC.

scholarly journals Interpolation of LES Cloud Surfaces for Use in Direct Calculations of Entrainment and Detrainment

2011 ◽  
Vol 139 (2) ◽  
pp. 444-456 ◽  
Author(s):  
Jordan T. Dawe ◽  
Philip H. Austin
Keyword(s):  
Numerical Model ◽  
Spatial Scales ◽  
Grid Cell ◽  
Time Step ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Temporal And Spatial ◽  
Les Model ◽  
Direct Calculations ◽  
Good Agreement

Abstract Direct calculations of the entrainment and detrainment of air into and out of clouds require knowledge of the relative velocity difference between the air and the cloud surface. However, a discrete numerical model grid forces the distance moved by a cloud surface over a time step to be either zero or the width of a model grid cell. Here a method for the subgrid interpolation of a cloud surface on a discrete numerical model grid is presented. This method is used to calculate entrainment and detrainment rates for a large-eddy simulation (LES) model, which are compared with rates calculated via the direct flux method of Romps. The comparison shows good agreement between the two methods as long as the model clouds are well resolved by the model grid spacing. This limitation of this technique is offset by the ability to resolve fluxes on much finer temporal and spatial scales, making it suitable for calculating entrainment and detrainment profiles for individual clouds.

Body Force Propeller Model for Unsteady Surge Motion

2018 ◽  
Author(s):  
Bradford G. Knight ◽  
Kevin J. Maki
Keyword(s):  
Body Force ◽  
Computational Cost ◽  
Mesh Size ◽  
Open Water ◽  
Time Step ◽  
Mesh Model ◽  
Water Test ◽  
Semi Empirical ◽  
Ship Propeller ◽  
Unsteady Conditions

Accurately modelling a self-propelled vessel in a large amplitude seaway with CFD is very expensive and practically out of reach. The expense is due to the very small numerical time-step required for the propeller rotation and the large mesh size. A method for accurately modelling a propeller while reducing computational cost is desirable. This paper describes the first step towards developing a body force propeller model for unsteady conditions. The purpose of this study is to train a semi-empirical algorithm to accurately prescribe the unsteady body force to model the propeller. The MOERI Container Ship propeller is analyzed with RANS CFD. Open water test data is compared to the RANS CFD results of a steady Moving Reference Frame approach. Harmonic surge is applied to a transient rotating mesh model in open water and the behind condition.

Numerical Study on the Performance Analysis and Vibration Characteristics of Flexible Marine Propeller

2020 ◽  
Author(s):  
Kumar S. Ashok ◽  
Subramanian V. Anantha ◽  
R. Vijayakumar
Keyword(s):  
Performance Analysis ◽  
Numerical Study ◽  
Open Water ◽  
Simulation Method ◽  
Mode Shapes ◽  
Thrust Coefficient ◽  
Fluid Structure ◽  
Marine Propellers ◽  
Water Characteristics ◽  
Wet Condition

Abstract This paper addresses the hydro-elastic performance of two composite marine propellers at operating condition and compares the results with conventional materials. The study involves three stages namely, design and development of a B series propeller, hydrodynamic and structural performance analysis in uniform flow and free vibration test both in dry and wet condition. In order to perform the hydro-elastic based fluid structure interaction (FSI), Co-Simulation method was adopted to couple Reynolds Averaged Navier-Strokes Equation (RANSE) based Computational Fluid Dynamics (CFD) solver and finite element method (FEM) solvers. The open water characteristics such as thrust coefficient (KT), torque coefficient (KQ), and open water efficiency (ηO) were analyzed as a function of advance velocity (J) of the propeller. A detailed study of the various blade materials by varying mechanical properties are presented. The results obtained show the variation of stress and deflection on the blade, along with the influence of the blade deformation on the performance of propeller. The vibration behaviour of the propellers were also analysed by Block-Lanczos method in FEM solver to obtain the natural frequencies and the mode shapes using Acoustic Fluid-Structure Coupling method for both dry and wet condition. Results showed that composite propeller have better hydro-dynamic property and lower vibration than metal propeller.

Research on the Improved Body-Force Method Based on Viscous Flow

2019 ◽  
Author(s):  
Zhiheng Li ◽  
Jiawei Yu ◽  
Dakui Feng ◽  
Kaijun Jiang ◽  
Yujie Zhou
Keyword(s):  
Drag Coefficient ◽  
Viscous Flow ◽  
Body Force ◽  
Lift Coefficient ◽  
Open Water ◽  
Viscous Effects ◽  
Thrust Coefficient ◽  
Force Method ◽  
Water Characteristics ◽  
Body Force Method

Abstract The virtual propeller model can achieve the rapid numerical prediction of the ship self-propulsion performance through viscous flow, which used the improved body-force method. The two-dimensional lift coefficient CL and the drag coefficient CD are very important parameters in this method, which are generally obtained by the potential flow methods and cannot incorporate viscous effects. This study will perform a fully nonlinear unsteady RANS (Reynolds Average Navier-Stokes) simulation to get the KP505 open-water characteristics and then divide its blade into several parts to get the lift coefficient CL and the drag coefficient CD on each one. Then fitting by multivariate regression method, the relationship between CL, CD and propeller parameters is obtained. The Unsteady Blade Element Theory (UBET) is coupled with RANS in house CFD code HUST-Ship (Hydrodynamic Unsteady Simulation Technology for Ship) to calculate the flow around the propeller. RANS equations are solved by the finite difference method and PISO arithmetic. have been made using structured grid with overset technology. The results show that comparing with the EFD data, the maximum differences of the result of the improved body-force method are 4.32% and 2.7% for the thrust coefficient and the torque coefficient respectively near the propeller operating point.

Prediction of Performance of Tip Loaded Propeller and its Induced Pressures on the Hull

2020 ◽  
Author(s):  
Seungnam Kim ◽  
Spyros A. Kinnas
Keyword(s):  
Open Water ◽  
Tip Vortex ◽  
Navier Stokes ◽  
Paper Briefly ◽  
Water Characteristics ◽  
Cavitation Performance ◽  
Numerical Predictions ◽  
Unsteady Wake ◽  
Wake Alignment ◽  
Initial Knowledge

Abstract In this paper, a boundary element method (BEM) is applied to a tip loaded propeller (TLP) to predict its open water characteristics and induced hull pressures under fully-wetted and uniform inflow. Tip of a TLP blade has a winglet-like tip plate on the pressure side to improve the overall propeller efficiency over the traditional open tip propellers by preventing circulation loss toward the tip region. TLPs are also used to reduce the tip vortex strength and thus free from the trade off the propeller efficiency against the cavitation performance; therefore, predicting their performance early in the designing stage via numerical applications can provide the initial knowledge on the loading distributions and cavitation performance. In the present method, the trailing wake is first aligned using the full wake alignment (FWA) scheme by aligning the wake surface to the local stream in order to satisfy the force free condition. The FWA is shown to improve the open water characteristics of the TLPs compared to the simplified alignment scheme that ignores the details of the flow behind the trailing edge due to the simplicity of the method. Afterwards, a pressure-BEM solver is used to solve for the diffraction potentials on the hull and estimate the propeller-induced hull pressures. In this case, both the FWA and the unsteady wake alignment scheme (UWA), which considers the time dependency of the problem, produce the same results as the testing flow is assumed to be uniform. This paper briefly introduces the model TLP, proper ways to consider the viscous effect on the blade surface, wake alignment scheme, and the pressure-BEM solver. Then, the predicted open water characteristics of the benchmark TLP and its induced hull pressures are compared to the experimental data, as well as the results from unsteady full-blown Reynolds-Averaged Navier-Stokes simulations for validations of the numerical predictions.

Numerical Investigation of Propeller Noise From Tip Vortex Cavitation

2017 ◽  
Author(s):  
Wencai Zhu ◽  
Hongtao Gao ◽  
Yuchao Song
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Flow Model ◽  
Open Water ◽  
Pressure Level ◽  
Tip Vortex ◽  
Cavitation Model ◽  
Tip Vortex Cavitation ◽  
Water Characteristics ◽  
Time Histories

In this paper, the Mixture multiphase flow model and the Schnerr-Sauer cavitation model are used to simulate the tip vortex cavitation of the propeller and then to predict the sound pressure level of the propeller. The structured and unstructured grids are adopted in stationary domain and rotating domain, respectively. The moving reference frame model is used in the rotating domain. The open water characteristics of the propeller are calculated by the SST k-ω turbulence model and the isosurface of vorticity magnitude is clearly presented. The results of the calculation are compared with the non-cavitating condition. It shows that the efficiency of the propeller is reduced when the tip vortex cavitation appears. The tip vortex cavitation will lead to increases both in the overall sound pressure in time histories and in the sound pressure level in the frequency domain.

Implicit LES Applied to Isothermal Swirling Coaxial Jets

2016 ◽  
Author(s):  
Teresa Parra-Santos ◽  
Robert Z. Szasz ◽  
J. Rubén Pérez ◽  
Ville Vuorinen ◽  
Francisco Castro
Keyword(s):  
Swirling Flow ◽  
Mesh Size ◽  
Good Precision ◽  
Hexahedral Mesh ◽  
Swirl Number ◽  
Eddy Simulation ◽  
Filter Width ◽  
Annular Jet ◽  
Les Model ◽  
The Impact

This work is devoted to the analysis of the interaction of two coaxial jet with swirling flow using Large Eddy Simulation methodology to reproduce the case of Roback and Johnson. The eight - flat - vanes in the annular nozzle are the precursor of the swirling annular jet with high swirl number. An implicit LES model was used, this model uses mesh size as filter width so no sub-grid model is required. It is the numerical error who plays the role of dissipative part of the stress tensor in the sub-mesh. Mesh prerequisites are Δy+ = 1 and uniform hexahedral mesh. The resolution scheme used is a Total Variation Diminishing (TVD) with coefficients looking for good precision. PISO is the pressure-velocity coupling used. Besides, multigrid resolution improves the performance towards the full convergence. Influence of the swirl number on the flow pattern is analyzed. Also the impact of conical diffuser on the mixing is presented.

Hybrid LES Approach for Practical Turbomachinery Flows—Part I: Hierarchy and Example Simulations

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Paul Tucker ◽  
Simon Eastwood ◽  
Christian Klostermeier ◽  
Richard Jefferson-Loveday ◽  
James Tyacke ◽  
...  
Keyword(s):  
Convex Surface ◽  
Computational Cost ◽  
Companion Paper ◽  
Navier Stokes ◽  
Computationally Efficient ◽  
Turbulent Structures ◽  
Hybrid Strategy ◽  
Eddy Simulation ◽  
Related Approach ◽  
Les Model

Unlike Reynolds-averaged Navier–Stokes (RANS) models that need calibration for different flow classes, LES (where larger turbulent structures are resolved by the grid and smaller modeled in a fashion reminiscent of RANS) offers the opportunity to resolve geometry dependent turbulence as found in complex internal flows—albeit at substantially higher computational cost. Based on the results for a broad range of studies involving different numerical schemes, large eddy simulation (LES) models and grid topologies, an LES hierarchy and hybrid LES related approach is proposed. With the latter, away from walls, no LES model is used, giving what can be termed numerical LES (NLES). This is relatively computationally efficient and makes use of the dissipation present in practical industrial computational fluid dynamics (CFD) programs. Near walls, RANS modeling is used to cover over numerous small structures, the LES resolution of which is generally intractable with current computational power. The linking of the RANS and NLES zones through a Hamilton–Jacobi equation is advocated. The RANS-NLES hybridization makes further sense for compressible flow solvers, where, as the Mach number tends to zero at walls, excessive dissipation can occur. The hybrid strategy is used to predict flow over a rib roughened surface and a jet impinging on a convex surface. These cases are important for blade cooling and show encouraging results. Further results are presented in a companion paper.

Larger-Eddy Simulation of Velocity Fluctuation in a Mixing T-Junction

2012 ◽  
Vol 152-154 ◽  
pp. 1313-1318
Author(s):  
Tao Lu ◽  
Su Mei Liu ◽  
Ping Wang ◽  
Wei Yyu Zhu
Keyword(s):  
Experimental Data ◽  
Velocity Fluctuation ◽  
Flow Model ◽  
Numerical Results ◽  
Mean Square ◽  
Main Duct ◽  
Velocity Fluctuations ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Les Model

Velocity fluctuations in a mixing T-junction were simulated in FLUENT using large-eddy simulation (LES) turbulent flow model with sub-grid scale (SGS) Smagorinsky–Lilly (SL) model. The normalized mean and root mean square velocities are used to describe the time-averaged velocities and the velocities fluctuation intensities. Comparison of the numerical results with experimental data shows that the LES model is valid for predicting the flow of mixing in a T-junction junction. The numerical results reveal the velocity distributions and fluctuations are basically symmetrical and the fluctuation at the upstream of the downstream of the main duct is stronger than that at the downstream of the downstream of the main duct.

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