Numerical simulation of vortex evolution based on adaptive wavelet method

The application of the wavelet method to vortex motion prediction is investigated. First, the wavelet method is used to solve two initial boundary problems so as to verify its abilities of controlling numerical errors and capturing local structures. Then, the adaptive wavelet method is used to simulate the vortex emerging process. The results show that the wavelet method can control numerical errors easily, can capture local structures adaptively, and can predict the vortex fluctuation evolution. Therefore, the application of the wavelet method to turbulence is suggested.

Topology transition description of horseshoe vortex system in junctureflows with velocity characteristic lines

Particle image velocimetry and numerical simulation results of juncture flows were analyzed to parametricallyinvestigate topology transition.The vortex system evolutions from non-vortex to multi-vortex with variations inobstacle bluntness,obstacle width,flow velocity,and boundary layer thickness are discussed from the perspectiveof velocity characteristic lines.The velocity characteristic lines of u=0,v=0,and△↓^(2)v=0 are adopted to describe the vortex system evolution.The motions of the characteristic lines with juncture flow parameters are described indetail,and the corresponding reflections of the vortex system patterns are illustrated.A panoramic picture of thedevelopment of velocity characteristic lines corresponding to the HSV topology transition from a non-vortex to amulti-vortex system with variations in the juncture flow parameter is established.Two methods for determiningthe attachment/separation pattern of the most upstream singularity are proposed.One method is based on thenumber of intersections of the u=0 and v=0 velocity characteristic curve lines,and the other is based on the relative positions of the most upstream feet of the u=0 and v=0 loop curves with both feet attached to the wall.

Detached eddy simulation on the structure of swirling jet flow field

The improved delayed detached eddy simulation method with shear stress transport model was used to analyze the evolution of vortex structure,velocity and pressure fields of swirling jet.The influence of nozzle pressure drop on vortex structure development and turbulence pulsation was investigated.The development of vortex structure could be divided into three stages:Kelvin-Helmholtz(K-H)instability,transition stage and swirling flow instability.Swirling flow could significantly enhance radial turbulence pulsation and increase diffusion angle.At the downstream of the jet flow,turbulence pulsation dissipation was the main reason for jet velocity attenuation.With the increase of pressure drop,the jet velocity,pulsation amplitude and the symmetry of velocity distribution increased correspondingly.Meanwhile the pressure pulsation along with the axis and vortex transport intensity also increased significantly.When the jet distance exceeded about 9 times the dimensionless jet distance,the impact distance of swirling jet could not be improved effectively by increasing the pressure drop.However,it could effectively increase the swirl intensity and jet diffusion angle.The swirling jet is more suitable for radial horizontal drilling with large hole size,coalbed methane horizontal well cavity completion and roadway drilling and pressure relief,etc.

A decomposition method of vortex identification and its application in side channel pumps

This research utilizes theΩvortex identification method to address the turbulent flows in a single-stage side channel pump,to comprehensively characterize the three types of dynamic vortex structures classified based on directions.Premised on the Galilean invariance,the work employs coordinate rotation and transformation.Thus,the indistinguishable 3-D vortex can be simplified to 2-D vortex on typical research planes.When juxtaposing the overall performance,it was revealed that a diversity of areas with high values yielded enhanced reflection of the vortex intensity,as measured by velocity distribution.The axial vortex structure with high intensity exists at the outer radius under all conditions largely.While the longitudinal vortex usually shows high intensity between the middle and outer radius.Simultaneously,the radial vortex is more likely to be at the inner radius near the suction face.Finally,this paper introduces a specific valueξ,which represents the ratio of decomposition to the total of the manifestation of the fluid rotational pattern.From the fluctuation and mean value,it can be realized that the development of the specific vortex in three directions at different positions.For example,the specific valueξ2 refers to the typical longitudinal vortex as dynamic vortex are almost from 20%to 50%,which illustrates that the longitudinal vortex only occupies a minor percentage in the total vortex.This phenomenon is one of the main reasons for the low efficiency.The present work could provide some suggestions and references for in-depth studies in fluid engineering with intense swirling flows.

Study on S-shaped region of pump turbine based on Omega vortex analysis method and entropy production theory

In order to comprehensively analyze the operation instability of the pump turbine S-shaped region,this paper uses DDES turbulence model to calculate the model pump turbine from the perspective of the evolution law of runner vortex and draft tube vortex rope and entropy production rate,combined with experiments.The results show that the numerical simulation is in good agreement with the experiment.Omega vortex analysis method is more accurate than other vortex recognition methods because it is not affected by the threshold value.The vortices at the runner region under the runaway condition and the turbine brake condition develop towards the vaneless space and the blade pressure surface respectively,which will cause the flow obstruction and blade separation.The overall vorticity of the reverse pump condition is the largest.The vortex rope of the draft tube under runaway and turbine brake conditions is columnar in shape and has very high rotational strength.The vortex rope under reverse pump conditions is prone to fracture and form scattered vortices,impeding the normal movement of the fluid.The entropy production rate of the spanwise surface near the upper ring and the lower crown is greater than the middle spanwise surface due to the boundary layer effect.And the energy dissipation in the runner under reverse pump conditions is characterized by high at both ends of the runner and low in the middle.The energy dissipation near the wall of the straight cone section of the draft tube is large due to the squeezing effect of the vortex rope on the flow.