Numerical study of the flow over the modified simple frigate shape

2020 ◽  
pp. 095441002097775
Author(s):  
Tong Li ◽  
Yibin Wang ◽  
Ning Zhao
Keyword(s):  
Bluff Body ◽  
Recirculation Zone ◽  
Numerical Study ◽  
Reference Value ◽  
Flow Fields ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Simulation Results

The simple frigate shape (SFS) as defined by The Technical Co-operative Program (TTCP), is a simplified model of the frigate, which helps to investigate the basic flow fields of a frigate. In this paper, the flow fields of the different modified SFS models, consisting of a bluff body superstructure and the deck, were numerically studied. A parametric study was conducted by varying both the superstructure length L and width B to investigate the recirculation zone behind the hangar. The size and the position of the recirculation zones were compared between different models. The numerical simulation results show that the size and the location of the recirculation zone are significantly affected by the superstructure length and width. The results obtained by Reynolds-averaged Navier-Stokes method were also compared well with both the time averaged Improved Delayed Detached-Eddy Simulation results and the experimental data. In addition, by varying the model size and inflow velocity, various flow fields were numerically studied, which indicated that the changing of Reynolds number has tiny effect on the variation of the dimensionless size of the recirculation zone. The results in this study have certain reference value for the design of the frigate superstructure.

An investigation of ship airwake over the frigate afterbody

2020 ◽  
Vol 34 (14n16) ◽  
pp. 2040069
Author(s):  
Tong Li ◽  
Yi-Bin Wang ◽  
Ning Zhao ◽  
Ning Qin
Keyword(s):  
Turbulence Model ◽  
Parametric Study ◽  
Recirculation Zone ◽  
Flow Fields ◽  
Detached Eddy Simulation ◽  
Structured Grids ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Flight Deck

When air passes through the hangar of a frigate, the unstable airwake appears in the rear of the hangar, which may significantly increase the workload of the ship-borne helicopter pilot. Therefore, there must be a profound understanding of the characteristics of the airwake. In this paper, the airwake was numerically studied by using the Improved Delayed Detached-Eddy Simulation (IDDES) turbulence model on structured grids. The flow fields of the different simplified frigate afterbody models, consisting of hangar and flight deck, were compared regarding the size of the recirculation zone. A parametric study was conducted by varying the hangar length to find the optimal afterbody model with minimal recirculation zone behind the hangar. The results show that the size as well as the location of the recirculation zone are significantly affected by the hangar length, and the optimal afterbody model has been obtained.

Detached-Eddy Simulations Over a Simplified Landing Gear

2002 ◽  
Vol 124 (2) ◽  
pp. 413-423 ◽  
Author(s):  
L. S. Hedges ◽  
A. K. Travin ◽  
P. R. Spalart
Keyword(s):  
Stokes Equations ◽  
Separated Flow ◽  
Flow Fields ◽  
Equation Model ◽  
Landing Gear ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Navier Stokes Equations ◽  
Instantaneous Flow ◽  
Eddy Simulation

The flow around a generic airliner landing-gear truck is calculated using the methods of Detached-Eddy Simulation, and of Unsteady Reynolds-Averaged Navier-Stokes Equations, with the Spalart-Allmaras one-equation model. The two simulations have identical numerics, using a multi-block structured grid with about 2.5 million points. The Reynolds number is 6×105. Comparison to the experiment of Lazos shows that the simulations predict the pressure on the wheels accurately for such a massively separated flow with strong interference. DES performs somewhat better than URANS. Drag and lift are not predicted as well. The time-averaged and instantaneous flow fields are studied, particularly to determine their suitability for the physics-based prediction of noise. The two time-averaged flow fields are similar, though the DES shows more turbulence intensity overall. The instantaneous flow fields are very dissimilar. DES develops a much wider range of unsteady scales of motion and appears promising for noise prediction, up to some frequency limit.

A numerical study of snow accumulation on the bogies of high-speed trains based on coupling improved delayed detached eddy simulation and discrete phase model

2018 ◽  
Vol 233 (7) ◽  
pp. 715-730 ◽  
Author(s):  
Mingyang Liu ◽  
Jiabin Wang ◽  
Huifen Zhu ◽  
Sinisa Krajnovic ◽  
Guangjun Gao
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Snow Accumulation ◽  
Phase Model ◽  
Detached Eddy Simulation ◽  
Discrete Phase Model ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Flow Mechanisms ◽  
Discrete Phase

A numerical simulation method based on the improved delayed detached eddy simulation coupled with a discrete phase model is used to study the influence of the snow on the performance of bogies of a high-speed train running in snowy weather. The snow particle trajectories, mass of snow packing on the bogie, and thickness of snow accumulation have been analyzed to investigate the flow mechanisms of snow accumulation on different parts of the bogies. The results show that the snow accumulation on the first bogie of the head vehicle is almost the same as that of the second bogie, but the total accumulated snow on the top side of the second bogie is more than 74% higher than that of the first bogie. Among all the components of the bogies, the motors were found to be strongly influenced by the snow accumulation. The underlying flow mechanisms responsible for the snow accumulations are discussed.

LES and Hybrid RANS/LES of a Fundamental Trailing Edge Slot

2014 ◽  
Author(s):  
Elizaveta Ivanova ◽  
Gregory M. Laskowski
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Numerical Study ◽  
Mixing Layer ◽  
Detached Eddy Simulation ◽  
Trailing Edge ◽  
Adiabatic Wall ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation

This paper presents the results of a numerical study on the predictive capabilities of Large Eddy Simulation (LES) and hybrid RANS/LES methods for heat transfer, mean velocity, and turbulence in a fundamental trailing edge slot. The geometry represents a landless slot (two-dimensional wall jet) with adjustable slot lip thickness. The reference experimental data taken from the publications of Kacker and Whitelaw [1] [2] [3] [4] contains the adiabatic wall effectiveness together with the velocity and the Reynolds-stress profiles for various blowing ratios and slot lip thicknesses. The simulations were conducted at three different lip thickness and several blowing ratio values. The comparison with the experimental data shows a general advantage of LES and hybrid RANS/LES methods against unsteady RANS. The predictive capability of the tested LES models (dynamic ksgs-equation [5] and WALE [6]) was comparable. The Improved Delayed Detached Eddy Simulation (IDDES) hybrid method [7] also shows satisfactory agreement with the experimental data. In addition to the described baseline investigations, the influence of the inlet turbulence boundary conditions and their implication for the initial mixing layer and heat transfer development were studied for both LES and IDDES.

Assessment of LNG Pump Tower Loads

2019 ◽  
Author(s):  
Michael Thome ◽  
Jens Neugebauer ◽  
Ould el Moctar
Keyword(s):  
Structural Design ◽  
Numerical Study ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Impact Loads ◽  
Detached Eddy Simulation ◽  
Morison Equation ◽  
Field Methods ◽  
Delayed Detached Eddy Simulation ◽  
Tower Structure

Abstract The assessment of design loads acting on Liquefied Natural Gas (LNG) pump tower are widely based on Morison equation. However, the Morison equation lacks consideration of transverse flow, impact loads and the interaction between fluid and structure. Studies dealing with a direct simulation of LNG pump tower loads by means of Computational Fluid Dynamics (CFD), which can cover the aforementioned effects, are currently not available. A comparative numerical study on LNG pump tower loads is presented in this paper focusing on the following two questions: Are impact loads relevant for the structural design of LNG pump towers? In which way does the fluid-structure interaction influence the loads? Numerical simulations of the multiphase problem were conducted using field methods. Firstly, Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations, extended by the Volume of Fluid (VoF) approach were used to simulate the flow inside a three-dimensional LNG tank in model scale without tower structure. The results were used to validate the numerical model against model tests. Motion periods and amplitudes were systematically varied. Velocities and accelerations along the positions of the main structural members of the pump tower were extracted and used as input data for load approximations with the Morison equation. Morison equation, URANS and Delayed Detached Eddy Simulation (DDES) computed tower loads were compared. Time histories as well as statistically processed data were used. Global loads acting on the full (with tower structure) and simplified structure (no tower structure, but using Morison equation) are in the same order of magnitude. However, their time evolution is different, especially at peaks, which is considered significant for the structural design.

Numerical study of transonic cavity flows using large-eddy and detached-eddy simulation

2007 ◽  
Vol 111 (1117) ◽  
pp. 153-164 ◽  
Author(s):  
P. Nayyar ◽  
G. N. Barakos ◽  
K. J. Badcock
Keyword(s):  
Energy Content ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Complex Flow ◽  
Promising Alternative ◽  
Eddy Simulation ◽  
Massively Separated Flows ◽  
Large Eddy

Numerical analysis of the flow in weapon bays modelled as open rectangular cavities of length-to-depth (L/D) ratio of 5 and width-to-depth (W/D) ratio of 1 with doors-on and doors-off is presented. Flow conditions correspond to Mach and Reynolds numbers (based on cavity length) of 0·85 and 6·783m respectively. Results from unsteady Reynolds-averaged Navier-Stokes (URANS), large-eddy simulation (LES) and detached-eddy simulation (DES) are compared with the simulation methods demonstrating the best prediction of this complex flow. It was found that URANS was not able to predict the change of flow characteristics between the doors-on and doors-off configurations. In addition, the energy content of the cavity flow modes was much better resolved with DES and LES. Further, the DES was found to be quite capable for this problem giving accurate results (within 3dB of) experiments and appears to be a promising alternative to LES for modelling massively separated flows.

Aeroacoustics response of wind turbine blade profiles in normal and icing conditions

2018 ◽  
Vol 42 (3) ◽  
pp. 243-251 ◽  
Author(s):  
Edison H Caicedo ◽  
Muhammad S Virk
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Wind Turbine ◽  
Turbine Blade ◽  
Numerical Study ◽  
Turbulence Models ◽  
Wind Turbine Blade ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Eddy Simulation

This article describes a multiphase computational fluid dynamics–based numerical study of the aeroacoustics response of symmetric and asymmetric wind turbine blade profiles in both normal and icing conditions. Three different turbulence models (Reynolds-averaged Navier–Stokes, detached eddy simulation, and large eddy simulation) have been used to make a comparison of numerical results with the experimental data, where a good agreement is found between numerical and experimental results. Detached eddy simulation turbulence model is found suitable for this study. Later, an extended computational fluid dynamics–based aeroacoustics parametric study is carried out for both normal (clean) and iced airfoils, where the results indicate a significant change in sound levels for iced profiles as compared to clean.

Numerical Study on Ventilated Supercavitation Reaction to Gas Supply Rate

2011 ◽  
Vol 418-420 ◽  
pp. 1781-1785
Author(s):  
Guo Hua Gao ◽  
Jing Zhao ◽  
Fei Ma ◽  
Wei Dong Luo
Keyword(s):  
Process Simulation ◽  
Turbulence Modeling ◽  
Numerical Study ◽  
Detached Eddy Simulation ◽  
Supply Rate ◽  
Cavity Shape ◽  
Eddy Simulation ◽  
Natural Cavitation ◽  
Simulation Results ◽  
Gas Supply

In the present investigation, a computational fluid dynamics technique is used to investigate the ventilated supercavitation reaction to the change of gas supply rate. Detached eddy simulation, a hybrid RANS-LES method is used for turbulence modeling, and improved Singhal’s model is used to simulate cavitation process. Simulation results show that the change of cavity shape is lagging behind that of gas supply. When gas supply is shut, cavities experience a series fluctuation before reaching equilibrium state, if natural cavitation numbers are large; in contrast, they are monotone decreasing under small natural cavitation numbers.

Calculation of Manoeuvring Forces on Submarines Using Two Viscous-Flow Solvers

2010 ◽  
Author(s):  
Guilherme Vaz ◽  
Serge Toxopeus ◽  
Samuel Holmes
Keyword(s):  
Viscous Flow ◽  
Accurate Determination ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Empirical Methods ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Commercial Solver

Submersibles used for exploration, maintenance and naval warfare have to be both manoeuvrable and easy to control. Simulation of the trajectory for these vessels requires the accurate determination of the hydrodynamic forces and moments which are determined by model-testing, empirical methods or a combination of both. CFD can play a role here by permitting an easier and more accurate determination of these loads. In this paper we focus on the accurate prediction of the manoeuvring forces of free swimming streamlined submersibles (submarines) using CFD. We compare simulations of a standardised well-known submarine shape (DARPA SUBOFF) for two configurations, one bare hull (AFF-1) and one fully-appended hull (AFF-8), under different inflow angles. The viscous-flow solvers used are the finite volume solver ReFRESCO developed by MARIN, and the finite element commercial solver AcuSolve. Verification studies are performed and the numerical results are validated with the experimental data available in the literature. The influence of different turbulence models is investigated and results obtained with a RANS (Reynolds-Averaged-Navier-Stokes) approach are compared with the theoretically more realistic DDES (Delayed-Detached-Eddy-Simulation) results. The influence of the appendages on the forces and flow fields is also investigated and analysed. As a last example, results of a forced pitch motion including dynamic effects are presented.

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