Simulation of Flow Around Cylinder Actuated by DBD Plasma

The electric-static body force model is obtained by solving Maxwell＇s electromagnetic equations. Based on the electro-static model, numerical modeling of flow around a cylinder with a dielectric barrier discharge （DBD） plasma effect is also presented. The flow streamlines between the numerical simulation and the particle image velocimetry （PIV） experiment are consistent. According to the numerical simulation, DBD plasma can reduce the drag coefficient and change the vortex shedding frequencies of flow around tile cylinder.

Coupled CFD-DEM Numerical Simulation of the Interaction of a Flow-Transported Rag with a Solid Cylinder

A coupled Computational Fluid Dynamics-Discrete Element Method(CFD-DEM)approach is used to calculate the interaction of a flexible rag transported by a fluid current with a fixed solid cylinder.More specifically a hybrid Eulerian-Lagrangian approach is used with the rag being modeled as a set of interconnected particles.The influence of various parameters is considered,namely the inlet velocity(1.5,2.0,and 2.5 m/s,respectively),the angle formed by the initially straight rag with the flow direction(45°,60°and 90°,respectively),and the inlet position(90,100,and 110 mm,respectively).The results show that the flow rate has a significant impact on the permeability of the rag.The higher the flow rate,the higher the permeability and the rag speed difference.The angle has a minor effect on rag permeability,with 45°being the most favorable angle for permeability.The inlet position has a small impact on rag permeability,while reducing the initial distance between the rag an the cylinder makes it easier for rags to pass through.

Application of Optical Visualization Method in Observing Flow Field Around a Cylinder

In this paper, a free-surface synthetic schlieren(FS-SS) method was performed to detect the free surface disturbances. It is a purely optical method that uses refraction of light to reconstruct the height changes of water surface. The theory was developed based on Moisy's research, but has mainly been used in small-scale applications like painting and coating industry. Based on the methods and theories of the literature review, an in-depth investigation was conducted to optimize the FS-SS method and verify its feasibility on a relatively large-scale(e.g., wake region of shallow flow). The experimental setup was simplified which is approachable in most laboratories. Through proper experimental setting and an optimized post-processing routine, the quality of image was highly improved and ensured the accuracy of results. A drop test was performed proving the continuity of FS-SS method in the time domain. Also, a comparison test with flow around a cylinder at two speeds showed the ability of FS-SS method to reconstruct the irregular water surface in relative large-scale flow structures.

Stress boundary layers in the viscoelastic flow past a cylinder in a channel:limiting solutions

The flow past a cylinder in a channel with the aspect ratio of 2 ： 1 for the upper convected Maxwell （UCM） fluid and the Oldroyd-B fluid with the viscosity ratio of 0.59 is studied by using the Galerkin/Least-square finite element method and a p-adaptive refinement algorithm. A posteriori error estimation indicates that the stress-gradient error dominates the total error. As the Deborah number, De, approaches 0.8 for the UCM fluid and 0.9 for the Oldroyd-B fluid, strong stress boundary layers near the rear stagnation point are forming, which are characterized by jumps of the stress-profiles on the cylinder wall and plane of symmetry, huge stress gradients and rapid decay of the gradients across narrow thicknesses. The origin of the huge stress-gradients can be traced to the purely elongational flow behind the rear stagnation point, where the position at which the elongation rate is of 1/2De approaches the rear stagnation point as the Deborah number approaches the critical values. These observations imply that the cylinder problem for the UCM and Oldroyd-B fluids may have physical limiting Deborah numbers of 0.8 and 0.9, respectively.

The flow characteristics around bridge piers under the impact of a ship

The complicated flow structure around the pier threatens the safe navigation of ships.This paper studies the mechanism of the flow with a ship around the pier,passing or not passing and with consideration of the interval between the ship and the pier.The flow field model and the moving ship model are constructed by the six degrees of freedom(6DOF)solver combined with the virtual unit immersed boundary method and the level set method,both of which are based on the three-dimensional Navier-Stokes equations.The simulation results show that the ship significantly influences the flow around the pier,increasing the flow velocity by 50%to 140%.Away from the bridge pier,the cross-flow velocity decreases.The cross-flow velocity near the side of the pier also increases but in the opposite direction.The ship is affected by the negative yaw moment because of the reverse cross-flow between the pier and the ship.The size of the ship has an important impact on the extent of the affected flow areas but the velocity distribution is roughly in the same shape.The results show double impacts of ship and pier should be considered when determining the safe area of navigation.