Improved Delayed Detached-Eddy Simulation on a Swept Hybrid Model in IRT

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.

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

Applied Sciences ◽

10.3390/app11020784 ◽

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.

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Delayed Detached-Eddy Simulation and Particle Image Velocimetry Investigation of S-Duct Flow Distortion

AIAA Journal ◽

10.2514/1.j055468 ◽

2017 ◽

Vol 55 (6) ◽

pp. 1893-1908 ◽

Cited By ~ 12

Author(s):

Daniel Gil-Prieto ◽

David G. MacManus ◽

Pavlos K. Zachos ◽

Geoffrey Tanguy ◽

François Wilson ◽

...

Keyword(s):

Particle Image Velocimetry ◽

Particle Image ◽

Duct Flow ◽

Detached Eddy Simulation ◽

Flow Distortion ◽

Eddy Simulation ◽

Delayed Detached Eddy Simulation ◽

Image Velocimetry

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Numerical Analysis of Side-loads Reduction in a Sub-scale Dual-bell Rocket Nozzle

Flow Turbulence and Combustion ◽

10.1007/s10494-021-00243-4 ◽

2021 ◽

Author(s):

M. Cimini ◽

E. Martelli ◽

M. Bernardini

Keyword(s):

Inflection Point ◽

Pressure Ratio ◽

Mean Value ◽

Detached Eddy Simulation ◽

Turbulent Structures ◽

Eddy Simulation ◽

Separation Shock ◽

Delayed Detached Eddy Simulation ◽

Controlled Flow ◽

Dual Bell

AbstractA calibrated delayed detached eddy simulation of a sub-scale cold-gas dual-bell nozzle flow at high Reynolds number and in sea-level mode is carried out at nozzle pressure ratio NPR = 45.7. In this regime the over-expanded flow exhibits a symmetric and controlled flow separation at the inflection point, that is the junction between the two bells, leading to the generation of a low content of aerodynamic side loads with respect to conventional bell nozzles. The nozzle wall-pressure signature is analyzed in the frequency domain and compared with the experimental data available in the literature for the same geometry and flow conditions. The Fourier spectra in time and space (azimuthal wavenumber) show the presence of a persistent tone associated to the symmetric shock movement. Asymmetric modes are only slightly excited by the shock and the turbulent structures. The low mean value of the side-loads magnitude is in good agreement with the experiments and confirms that the inflection point dampens the aero-acoustic interaction between the separation-shock and the detached shear layer.

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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

Proceedings of the Institution of Mechanical Engineers Part F Journal of Rail and Rapid Transit ◽

10.1177/0954409718805817 ◽

2018 ◽

Vol 233 (7) ◽

pp. 715-730 ◽

Cited By ~ 3

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.

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DDES Analysis of Wake Vortex Related Unsteadiness and Losses in the Environment of High-Pressure Turbine Stage

Volume 2D: Turbomachinery ◽

10.1115/gt2017-64152 ◽

2017 ◽

Author(s):

Dun Lin ◽

Xinrong Su ◽

Xin Yuan

Keyword(s):

High Pressure ◽

Boundary Layer Transition ◽

Wake Vortex ◽

High Fidelity ◽

Strong Impact ◽

Detached Eddy Simulation ◽

High Pressure Turbine ◽

Layer Transition ◽

Eddy Simulation ◽

Delayed Detached Eddy Simulation

In this work, the flows inside the high pressure turbine (HPT) vane and stage are studied with the help of a high-fidelity delayed detached eddy simulation (DDES) code. This work intends to study the fundamental nozzle/blade interaction with special attention paid to the development and transportation of the vane wake vortex. There are two motivations for this work. On the one hand, the high pressure turbine operates at both transonic Mach numbers and high Reynolds numbers, which imposes a great challenge to modern computational fluid dynamics (CFD), especially for scale-resolved simulation methods. An accurate and efficient high-fidelity CFD solver is very important for a thorough understanding of the flow physics and the design of more efficient HPT. On the other hand, the periodic wake vortex shedding is an important origin of turbine losses and unsteadiness. The wake and vortex not only cause losses themselves, but also interact with the shock wave (under transonic working condition), pressure waves, and have a strong impact on the downstream blade surface (affecting boundary layer transition and heat transfer). Built on one of our previous DDES simulations of a HPT vane VKI LS89, this work further investigates the development and length characteristics of the wake vortex, provides explanations of the length characteristics and reveals the transportation of the wake vortex into the downstream rotor passage along with its impact on the downstream aero-thermal performance.

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