Research On Vortex Evolution In The Main Channel Of Multiphase Pump Based On Q Criterion

The world is rich in marine oil resources,and more and more countries are beginning to explore and discover the oil and gas resources in deep sea areas.As a new type of oil and gas extraction equipment,the Helico-Axial multiphase pump has the advantages of simple structure,easy operation,anti-corrosion,anti-wear,and effective prevention of the separation of gas and liquid phases.The impeller is the core element of a multiphase pump,and the flow of its internal flow field is very complex during operation:the gas and liquid phases mix under the action of blade promotion powers and centrifugal forces;the vortex structure in the turbulent flow not only blocks the impeller channel but also destabilizes the flow field and generates abnormal pressure pulsations,thus reducing the impeller performance.Therefore,the study of the vortex structure can provide a certain theoretical basis for optimizing the design of multiphase pumps,which has great engineering application value.To reveal the evolution of the vortex structure in the impeller channel of a multiphase pump,this paper is based on numerical simulation,supplemented by experimental verification:The vortex in the impeller channel is captured based on the vortex volume and Q criterion identification method;the generation position and factors of the vortex structure are analyzed and discussed;the influence on the vortex structure under different working conditions,the vortex dynamics characteristics of the vortex structure,the three-dimensional spatial and temporal evolution characteristics of the vortex structure and the pressure pulsation characteristics are studied.The details are as follows.（1）Firstly,the article introduces the concepts of vortex volume and vortex,and compares the advantages and disadvantages of different vortex identification methods(Δ,λ₂,Q,λ_ci),mainly analyzes the three-dimensional structure on the isosurface,vortex field,and velocity vector distribution inside the impeller channel,captures the large-scale vortex structure,determines the location of vortex incipient,and explores the factors of vortex generation.It is found that the Q criterion identification method is widely used,simple,and effective,and combined with the vortex volume method can screen the vortex structure at different scales within the impeller channel.In addition,the vortex in the impeller channel is generated at the following locations:the leading edge of the blade,the second half of the suction surface,the middle section of the pressure surface,and the impeller wakes.Rotational speed,flow rate,and inlet gas void fraction are all causes of vortex generation.（2）Secondly,this article discusses the influence of rotational speed,inlet flow rate,and inlet gas void fraction on the vortex structure,analyzes the variation law of velocity and pressure with speed and inlet flow rate under pure water conditions,studies the distribution law of vortex volume and vorticity value curves under water conditions and gas-liquid conditions,and also investigates the relationship between the evolution of vortex structure and gas phase distribution.It is found that speed affects the vortices at the inlet and intermediate positions of the impeller.As the speed increases,the scale of the vortex structure in the inlet and intermediate regions of the impeller expands.The inlet flow rate affects the vortex in the main flow channel,a large number of vortices exist in the flow channel at low flow rates,and with the increase in the inlet flow rate vortex reduction,the flow field tends to stabilize.The inlet gas void fraction has a significant effect on the vortex at the impeller outlet position.The formation of gas masses produces entrainment;the complex flow structure of the two fluid media coexist.The vortex structure develops rapidly in these environments.As the gas phase increases,the vortex is born in the middle of the suction surface,followed by an extension downstream to form a vortex belt,which connects with the vortex on the trailing edge of the blade to form a large vortex region.（3）Finally,this paper analyzes the relationship between vortex structure and pressure pulsation intensity at different void fraction,and studies the trajectory and spatial and temporal evolution of vortices in the main flow path of the impeller,the time domain characteristics and frequency domain characteristics of pressure pulsation.It is found that the vortex structure in the impeller channel has different trajectories under the influence of the internal structure of the multiphase pump,the differential pressure force between the vanes,and the force of the impeller rotation.The vortex structure in the impeller channel changes in phase with spatial and temporal:The primary stage,extension stage,contraction stage,and dissipation stage.As the gas phase increases,the generation position of the vortex moves toward the suction surface,creating a larger vortex structure.In addition,the pressure pulsation time domain graph curves obtained from different pressure monitoring points have large waveform differences,especially the pressure pulsation at the impeller outlet is greatly influenced by the dynamic and static interference at the intersection of the impeller and guide vane,and the pressure pulsation amplitude at the wheel edge is stronger.From the frequency domain diagram,the pressure pulsation at the rim is not only affected by the dynamic interference,but also by the vortex structure.This paper identifies the vortex structure inside the impeller channel of multiphase pumps,studies the influence of external factors on the vortex structure,and explores the process of the vortex structure changing with time and space.The evolution law of the vortex structure in the impeller channel is gradually revealed to provide ideas for optimizing the structure of multiphase pumps and reducing the vortex in the flow channel.