Noise Prediction of a Transonic Cavity Flow via Shear-Layer-Adapted Delayed Detached-Eddy Simulation

2018 ◽  
Author(s):  
Ozgur Yalcin ◽  
Kenan Cengiz ◽  
Yusuf Ozyoruk
Keyword(s):  
Shear Layer ◽  
Cavity Flow ◽  
Noise Prediction ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation

Numerical Study of Impulse Actuation for Stall Control

2011 ◽  
Author(s):  
SolKeun Jee ◽  
Omar D. Lopez Mejia ◽  
Robert D. Moser
Keyword(s):  
Shear Layer ◽  
Numerical Study ◽  
Separation Point ◽  
Detached Eddy Simulation ◽  
Airfoil Surface ◽  
Vortical Structures ◽  
Eddy Simulation ◽  
Separated Shear Layer ◽  
Delayed Detached Eddy Simulation ◽  
Stall Control

The response of a stalled flow to a single impulse actuation is examined numerically to investigate the mechanism by which this actuation affects the flow. Delayed detached eddy simulation is used on a stalled NACA 4415 airfoil at an angle of attack of 20 degrees and Reynolds number Re = 570,000. A brief strong jet issues normal to the airfoil surface upstream of the nominal flow separation point of the airfoil, causing the boundary layer temporally reattached. This computation shows the detailed evolution of vortical structures generated by both the baseline flow and the impulse actuation. Initial vortices from the actuation convect downstream, interact with the separated shear layer, and dismantle the layer. After the collapse of the separated shear layer, the separation point moves aft and remains delayed for a much longer period than the actuation time, similar to experimental observation [1]. The jet is simply represented as a Dirichlet velocity boundary condition, which is found to be sufficient to represent the global effects of impulse actuation on the stalled flow.

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.

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.

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