A DDES study of the flow past a prolate spheroid using a high-order U-MUSCL scheme

2020 ◽  
Vol 34 (14n16) ◽  
pp. 2040075
Author(s):  
Yu-Chen Yang ◽  
Zhen-Ming Wang ◽  
Ning Zhao
Keyword(s):  
Flow Separation ◽  
Vortex Structure ◽  
Prolate Spheroid ◽  
High Order ◽  
Detached Eddy Simulation ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Flow Past ◽  
Delayed Detached Eddy Simulation ◽  
Flow Phenomena

Flow past a prolate spheroid, which is a representative simplified configuration for vehicles such as maneuvering ships, submarines and missiles, comprises a series of complex flow phenomena including pressure-induced flow separation, which results in unsteady forces and movements that may be detrimental to vehicles’ performance. In this paper, a Delayed Detached Eddy Simulation (DDES) method combined with a new high-order U-MUSCL scheme is proposed to more precisely and accurately capture the flow separation and vortex structure. This method is applied to simulate the aerodynamic performance of the 6:1 prolate spheroid at an AOA of [Formula: see text] with the Reynolds number of [Formula: see text]. Axial pressure distribution of five individual chord wise sections and flow field structure of the aft body are analyzed. Numerical results agree well with the experimental data. It can be concluded that DDES combined with three-order U-MUSCL scheme demonstrates reliable performance since it captures the vortex structure of aft body distinctly and predicts the separation and reattachment points of the secondary vortex precisely.

scholarly journals Numerical Investigation on the Influence of the Streamlined Structures of the High-Speed Train’s Nose on Aerodynamic Performances

2021 ◽  
Vol 11 (2) ◽  
pp. 784
Author(s):  
Zhenxu Sun ◽  
Shuanbao Yao ◽  
Lianyi Wei ◽  
Yongfang Yao ◽  
Guowei Yang
Keyword(s):  
Drag Reduction ◽  
Pressure Distribution ◽  
Flow Separation ◽  
High Speed ◽  
Leeward Side ◽  
Detached Eddy Simulation ◽  
Side Force ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Asymmetrical Design

The structural design of the streamlined shape is the basis for high-speed train aerodynamic design. With use of the delayed detached-eddy simulation (DDES) method, the influence of four different structural types of the streamlined shape on aerodynamic performance and flow mechanism was investigated. These four designs were chosen elaborately, including a double-arch ellipsoid shape, a single-arch ellipsoid shape, a spindle shape with a front cowcatcher and a double-arch wide-flat shape. Two different running scenes, trains running in the open air or in crosswind conditions, were considered. Results reveal that when dealing with drag reduction of the whole train running in the open air, it needs to take into account how air resistance is distributed on both noses and then deal with them both rather than adjust only the head or the tail. An asymmetrical design is feasible with the head being a single-arch ellipsoid and the tail being a spindle with a front cowcatcher to achieve the minimum drag reduction. The single-arch ellipsoid design on both noses could aid in moderating the transverse amplitude of the side force on the tail resulting from the asymmetrical vortex structures in the flow field behind the tail. When crosswind is considered, the pressure distribution on the train surface becomes more disturbed, resulting in the increase of the side force and lift. The current study reveals that the double-arch wide-flat streamlined design helps to alleviate the side force and lift on both noses. The magnitude of side force on the head is 10 times as large as that on the tail while the lift on the head is slightly above that on the tail. Change of positions where flow separation takes place on the streamlined part is the main cause that leads to the opposite behaviors of pressure distribution on the head and on the tail. Under the influence of the ambient wind, flow separation occurs about distinct positions on the train surface and intricate vortices are generated at the leeward side, which add to the aerodynamic loads on the train in crosswind conditions. These results could help gain insight on choosing a most suitable streamlined shape under specific running conditions and acquiring a universal optimum nose shape as well.

scholarly journals Delayed detached Eddy simulation of wing flutter boundary using high order schemes

2017 ◽  
Vol 71 ◽  
pp. 199-216 ◽  
Author(s):  
Jia-ye Gan ◽  
Hong-Sik Im ◽  
Xiang-ying Chen ◽  
Ge-Cheng Zha ◽  
Crystal L. Pasiliao
Keyword(s):  
High Order ◽  
Detached Eddy Simulation ◽  
High Order Schemes ◽  
Wing Flutter ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Flutter Boundary

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.

scholarly journals RANS and Hybrid RANS-LES Simulations of an H-Type Darrieus Vertical Axis Water Turbine

Energies ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 2348 ◽  
Author(s):  
Omar Mejia ◽  
Jhon Quiñones ◽  
Santiago Laín
Keyword(s):  
Turbulence Models ◽  
Vertical Axis ◽  
Navier Stokes ◽  
Speed Ratio ◽  
Small Scale ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Flow Phenomena ◽  
Water Turbine

Nowadays, the global energy crisis has encouraged the use of alternative sources like the energy available in the water currents of seas and rivers. The vertical axis water turbine (VAWT) is an interesting option to harness this energy due to its advantages of facile installation, maintenance and operation. However, it is known that its efficiency is lower than that of other types of turbines due to the unsteady effects present in its flow physics. This work aims to analyse through Computational Fluid Dynamics (CFD) the turbulent flow dynamics around a small scale VAWT confined in a hydrodynamic tunnel. The simulations were developed using the Unsteady Reynolds Averaged Navier Stokes (URANS), Detached Eddy Simulation (DES) and Delayed Detached Eddy Simulation (DDES) turbulence models, all of them based on k-ω Shear Stress Transport (SST). The results and analysis of the simulations are presented, illustrating the influence of the tip speed ratio. The numerical results of the URANS model show a similar behaviour with respect to the experimental power curve of the turbine using a lower number of elements than those used in the DES and DDES models. Finally, with the help of both the Q-criterion and field contours it is observed that the refinements made in the mesh adaptation process for the DES and DDES models improve the identification of the scales of the vorticity structures and the flow phenomena present on the near and far wake of the turbine.

scholarly journals Enhanced Delayed Detached Eddy Simulation for Cavities and Labyrinth Seals

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Richard J. Jefferson-Loveday
Keyword(s):  
Labyrinth Seal ◽  
High Order ◽  
Experimental Measurements ◽  
Detached Eddy Simulation ◽  
Specific Flow ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
New Variant ◽  
Wide Range ◽  
Original Definition

Abstract A range of popular hybrid Reynolds-averaged Navier–Stokes -large eddy simulation (RANS-LES) methods are tested for a cavity and two labyrinth seal geometries using an in-house high-order computational fluid dynamics (CFD) code and a commercial CFD code. The models include the standard Spalart–Allmaras (SA) and Menter shear stress transport (SST) versions of delayed detached eddy simulation (DDES) and the Menter scale adaptive simulation (SAS) model. A recently formulated, enhanced, variant of SA-DDES presented in the literature and a new variant using the Menter SST model are also investigated. The latter modify the original definition of the subgrid length scale used in standard DDES based on local vorticity and strain. For all geometries, the meshes are considered to be hybrid RANS-LES adequate. Very low levels of resolved turbulence and quasi-two-dimensional flow fields are observed for the standard DDES and SAS models even for the test cases here that contain obstacles, sharp edges, and swirling flow. Similar findings are observed for both the commercial and in-house high-order CFD codes. For the cavity simulations, when using standard DDES and SAS, there is a significant under prediction of turbulent statistics compared with experimental measurements. The enhanced versions of DDES, on the other hand, show a significant improvement and resolve turbulent content over a wide range of scales. Improved agreement with experimental measurements is also observed for profiles of the vertical velocity component. For the first labyrinth seal geometry swirl velocities are more accurately captured by the enhanced DDES versions. For the second labyrinth seal geometry, the mass flow coefficient prediction using the enhanced models is significantly improved (up to 30%). Standard, industrially available hybrid RANS-LES models, when applied to the present canonical cases can produce little to no resolved turbulent content. The standard SA- and Menter-based DDES models can yield lower levels of eddy viscosity when compared to equivilent steady RANS simulations which means that they are not operating as RANS or LES. It is recommended that hybrid RANS-LES models should be extensively tested for specific flow configurations and that special care is exercised by CFD practitioners when using many of the popular hybrid RANS-LES models that are currently available in commercial CFD packages.

Numerical Investigation of Flow Around a Multi-Element Airfoil with Hybrid RANS-LES Approaches Based on SST Model

2017 ◽  
Vol 34 (2) ◽  
pp. 123-134 ◽  
Author(s):  
L. Zhang ◽  
J. Li ◽  
Y. F. Mou ◽  
H. Zhang ◽  
W. B. Shi ◽  
...  
Keyword(s):  
Turbulence Modeling ◽  
Experimental Result ◽  
Numerical Dissipation ◽  
Small Scale ◽  
Detached Eddy Simulation ◽  
Complex Flow ◽  
Third Order ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation

AbstractAccurate prediction of the flow around multi-element airfoil is a prerequisite for improving aerodynamic performance, but its complex flow features impose high demands on turbulence modeling. In this work, delayed detached-eddy-simulation (DDES) and zonal detached-eddy-simulation (ZDES) was applied to simulate the flow past a three-element airfoil. To investigate the effects of numerical dissipation of spatial schemes, the third-order MUSCL and the fifth-order interpolation based on modified Roe scheme were implemented. From the comparisons between the calculations and the available experimental result, third-order MUSCL-Roe can provide satisfactory mean velocity profiles, but the excessive dissipation suppresses the velocity fluctuations level and eliminates the small-scale structures; DDES cannot reproduce the separation near the trailing edge of the flap which lead to the discrepancy in mean pressure coefficients, while ZDES result has better tally with the experiment.

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