Study of Mechanism of Ring-Like Vortex Formation in Late Flow Transition

2010 ◽  
Author(s):  
Chaoqun Liu ◽  
Lin Chen
Keyword(s):  
Vortex Formation ◽  
Flow Transition

scholarly journals New Findings by High-Order DNS for Late Flow Transition in a Boundary Layer

2011 ◽  
Vol 2011 ◽  
pp. 1-16 ◽  
Author(s):  
Chaoqun Liu ◽  
Lin Chen ◽  
Ping Lu
Keyword(s):  
Boundary Layer ◽  
Vortex Breakdown ◽  
Solid Wall ◽  
Vortex Formation ◽  
Ring Structure ◽  
Flow Transition ◽  
New Findings ◽  
Coherent Vortex ◽  
Coherent Vortex Structure ◽  
Multiple Ring

This paper serves as a summary of new discoveries by DNS for late stages of flow transition in a boundary layer. The widely spread concept “vortex breakdown” is found theoretically impossible and never happened in practice. The ring-like vortex is found the only form existing inside the flow field. The ring-like vortex formation is the result of the interaction between two pairs of counter-rotating primary and secondary streamwise vortices. Following the first Helmholtz vortex conservation law, the primary vortex tube rolls up and is stretched due to the velocity gradient. In order to maintain vorticity conservation, a bridge must be formed to link two Λ-vortex legs. The bridge finally develops as a new ring. This process keeps going on to form a multiple ring structure. The U-shaped vortices are not new but existing coherent vortex structure. Actually, the U-shaped vortex, which is a third level vortex, serves as a second neck to supply vorticity to the multiple rings. The small vortices can be found on the bottom of the boundary layer near the wall surface. It is believed that the small vortices, and thus turbulence, are generated by the interaction of positive spikes and other higher level vortices with the solid wall. The mechanism of formation of secondary vortex, second sweep, positive spike, high shear distribution, downdraft and updraft motion, and multiple ring-circle overlapping is also investigated.

Liutex core line and POD analysis on hairpin vortex formation in natural flow transition

2020 ◽  
Vol 32 (6) ◽  
pp. 1109-1121
Author(s):  
Sita Charkrit ◽  
Pushpa Shrestha ◽  
Chaoqun Liu
Keyword(s):  
Vortex Formation ◽  
Flow Transition ◽  
Hairpin Vortex ◽  
Natural Flow ◽  
Core Line ◽  
Pod Analysis

Intensification of Open Gutters Operation

2020 ◽  
pp. 66-70
Keyword(s):  
Water Flow ◽  
Vortex Formation ◽  
Hydraulic Testing ◽  
Polymer Materials ◽  
Bottom Surface ◽  
Artificial Roughness ◽  
Transport Capacity ◽  
Corrugated Surfaces ◽  
Inner Surface ◽  
Dispersed Inclusions

The intensification of the work of open gutter by applying textured shells to their bottom surface, forming an artificial roughness, is considered. It is shown that the presence of corrugated surfaces contributes to vortex formation during water flow and improves the separation and transportation of mineral impurities previously dropped into the bottom of the gutters. The implementation of operations to improve the structure of the gutters is possible during the repair and restoration works with the use of modern polymer materials. The design of a small-sized hydraulic stand, which makes it possible to study the transport capacity of flows containing solid inclusions, is presented. The method of research is hydraulic testing, accompanied by the use of chiaroscuro effect, as well as photo and film equipment. The optimal structure of the inner surface of the gutters and pipes providing vortex formation, which will improve the ability of the flow to carry out and transport foreign dispersed inclusions (sand) of different granulometric compositions, is determined.

DTNS3D Computer Code Simulation of Tip-Vortex Formation: RANS Code Validation

1997 ◽  
Author(s):  
John G. Telste ◽  
Roderick M. Coleman ◽  
Joseph J. Gorski
Keyword(s):  
Vortex Formation ◽  
Computer Code ◽  
Tip Vortex ◽  
Code Validation

Closed-Loop Control of Vortex Formation in Separated Flows with Application to Micro Air Vehicles

2010 ◽  
Author(s):  
Tim Colonius ◽  
Morteza Gharib ◽  
Clarence W. Rowley ◽  
Gilead Tadmor ◽  
David R. Williams
Keyword(s):  
Closed Loop ◽  
Vortex Formation ◽  
Micro Air Vehicles ◽  
Separated Flows ◽  
Closed Loop Control ◽  
Loop Control ◽  
Air Vehicles

scholarly journals Circulation derived from 4D flow MRI correlates with right ventricular dysfunction in patients with tetralogy of Fallot

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Nanae Tsuchiya ◽  
Michinobu Nagao ◽  
Yumi Shiina ◽  
Shohei Miyazaki ◽  
Kei Inai ◽  
...  
Keyword(s):  
Right Ventricular ◽  
Tetralogy Of Fallot ◽  
Main Pulmonary Artery ◽  
Vortex Formation ◽  
Cine Mri ◽  
Short Axis ◽  
4D Flow Mri ◽  
4D Flow ◽  
Flow Mri ◽  
Rv Function

AbstractWe used 4D-flow MRI to investigate circulation, an area integral of vorticity, in the main pulmonary artery (MPA) as a new hemodynamic parameter for assessing patients with a repaired Tetralogy of Fallot (TOF). We evaluated the relationship between circulation, right ventricular (RV) function and the pulmonary regurgitant fraction (PRF). Twenty patients with a repaired TOF underwent cardiac MRI. Flow-sensitive 3D-gradient sequences were used to obtain 4D-flow images. Vortex formation in the MPA was visualized, with short-axis and longitudinal vorticities calculated by software specialized for 4D flow. The RV indexed end-diastolic/end-systolic volumes (RVEDVi/RVESVi) and RV ejection fraction (RVEF) were measured by cine MRI. The PR fraction (PRF) and MPA area were measured by 2D phase-contrast MRI. Spearman ρ values were determined to assess the relationships between circulation, RV function, and PRF. Vortex formation in the MPA occurred in 15 of 20 patients (75%). The longitudinal circulation (11.7 ± 5.1 m2/s) was correlated with the RVEF (ρ = − 0.85, p = 0.0002), RVEDVi (ρ = 0.62, p = 0.03), and RVESVi (ρ = 0.76, p = 0.003) after adjusting for the MPA size. The short-axis circulation (9.4 ± 3.4 m2/s) in the proximal MPA was positively correlated with the MPA area (ρ = 0.61, p = 0.004). The relationships between the PRF and circulation or RV function were not significant. Increased longitudinal circulation in the MPA, as demonstrated by circulation analysis using 4D flow MRI, was related to RV dysfunction in patients with a repaired TOF.

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