scholarly journals Numerical Analysis of the Primary Gas Boundary Layer Flow Structure in Laser Fusion Cutting in Context to the Striation Characteristics of Cut Edges

Fluids ◽  
2021 ◽  
Vol 7 (1) ◽  
pp. 17
Author(s):  
Madlen Borkmann ◽  
Achim Mahrle
Keyword(s):  
Boundary Layer ◽  
Gas Flow ◽  
Cfd Simulation ◽  
Flow Characteristics ◽  
Laser Fusion ◽  
Formation Mechanisms ◽  
Momentum Exchange ◽  
Edge Structure ◽  
Laser Fusion Cutting ◽  
Comparison Of The Results

In cutting metals with solid-state lasers, a characteristic cutting edge structure is generated whose formation mechanisms still elude a consistent explanation. Several studies suggest a major contribution of the pressurized gas flow. Particular emphasis must be devoted to the gas boundary layer and its developing flow characteristics, since they determine the heat and momentum exchange between the cutting gas and the highly heated melt surface and thus the expulsion of the molten material from the kerf. The present study applies a CFD simulation model to analyze the gas flow during laser cutting with appropriate boundary conditions. Specifically, the gas boundary layer development is considered with a high spatial discretization of this zone in combination with a transition turbulence model. The results of the calculation reveal for the first time that the boundary layer is characterized by a quasi-stationary vortex structure composed of nearly horizontal geometry- and shock-induced separation zones and vertical vortices, which contribute to the transition to turbulent flow. Comparison of the results with the striation structure of experimental cut edges reveals a high agreement of the location, orientation, and size of the characteristic vortices with particular features of the striation structure of cut edges.

Evolution of the streamwise vortices generated between leading edge tubercles

2016 ◽  
Vol 788 ◽  
pp. 730-766 ◽  
Author(s):  
Kristy L. Hansen ◽  
Nikan Rostamzadeh ◽  
Richard M. Kelso ◽  
Bassam B. Dally
Keyword(s):  
Boundary Layer ◽  
Performance Enhancement ◽  
Numerical Study ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Surface Flux ◽  
Flow Visualisation ◽  
Streamwise Vortices ◽  
Momentum Exchange

Sinusoidal modifications to the leading edge of a foil, or tubercles, have been shown to improve aerodynamic performance under certain flow conditions. One of the mechanisms of performance enhancement is believed to be the generation of streamwise vortices, which improve the momentum exchange in the boundary layer. This experimental and numerical study investigates the formation and evolution of these streamwise vortices at a low Reynolds number of $Re=2230$, providing insight into both the averaged and time-dependent flow patterns. Furthermore, the strength of the vortices is quantified through calculation of the vorticity and circulation, and it is found that the circulation increases in the downstream direction. There is strong agreement between the experimental and numerical observations, and this allows close examination of the flow structure. The results demonstrate that the presence of strong pressure gradients near the leading edge gives rise to a significant surface flux of vorticity in this region. As soon as this vorticity is created, it is stretched, tilted and diffused in a highly three-dimensional manner. These processes lead to the generation of a pair of streamwise vortices between the tubercle peaks. A horseshoe-shaped separation zone is shown to initiate behind a tubercle trough, and this region of separation is bounded by a canopy of boundary-layer vorticity. Along the sides of this shear layer canopy, a continued influx of boundary-layer vorticity occurs, resulting in an increase in circulation of the primary streamwise vortices in the downstream direction. Flow visualisation and particle image velocimetry studies support these observations and demonstrate that the flow characteristics vary with time, particularly near the trailing edge and at a higher angle of attack. Numerical evaluation of the lift and drag coefficients reveals that, for this particular flow regime, the performance of a foil with tubercles is slightly better than that of an unmodified foil.

scholarly journals Numerical simulation of the mixing and flow characteristics in lobed mixers

2014 ◽  
Vol 18 (4) ◽  
pp. 1203-1212 ◽  
Author(s):  
Wang Zhi-Wu ◽  
Zhang Kun ◽  
Zheng Longxi ◽  
Chen Xing-Gu ◽  
Li Ping ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Gas Flow ◽  
Cfd Simulation ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Recirculation Region ◽  
Mixing Length ◽  
Mixing Performance ◽  
Gas Ratio ◽  
Better Than

This paper focused on the mixer optimization by numerical simulation. The mixing and flow characteristics inside two different lobed mixers with/without centrum were obtained by three-dimensional CFD simulation. The core flow was the hot rich-methane/O2?l?burnt gas, while the cold air flew by the by-pass. The air/burnt gas flow ratio was improved from 7 to 9 in order to confirm the effect of air/burnt gas ratio on the mixing and flow characteristics. The simulation results indicated that no matter which mixer was used, there were a pair of symmetrical recirculation regions in the mixers, and the total temperature and species distribution turned to be more uniform at the increased mixing length. The mixing performance in the lobed mixer with centrum was slightly better than that of the lobed mixer without centrum, and the length of recirculation region in the lobed mixer with centrum was slightly shorter than that of the lobed mixer without centrum. The air/burnt gas ratio had considerable effect on the mixing and flow characteristics. The mixing performance with air/burnt gas ratio of 9 was much better than that of air/burnt gas ratio 7. Similar mixing performance would attain in the case of air/burnt gas ratio 9 with only half of the mixing length in the case ofair/burnt gas ratio 7. The recirculation region in the case of air/burnt gas ratio 9 occurred ahead of that of air/burnt gas ratio 7, and the former was longer than the latter.

scholarly journals Laser fusion cutting: evaluation of gas boundary layer flow state, momentum and heat transfer

2021 ◽  
Author(s):  
Madlen Borkmann ◽  
Achim Mahrle ◽  
Eckhard Beyer ◽  
Christoph Leyens
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Laser Fusion ◽  
Flow State ◽  
Momentum And Heat Transfer ◽  
Laser Fusion Cutting ◽  
Layer Flow

TO THE THEORY OF UNSTEADY SEPARATION AND INTERACTION OF BOUNDARY LAYER WITH SUPERSONIC GAS FLOW

2018 ◽  
Vol 49 (4) ◽  
pp. 415-427
Author(s):  
Igor Ivanovich Lipatov ◽  
Vladimir Yakovlevich Neiland
Keyword(s):  
Boundary Layer ◽  
Gas Flow ◽  
Unsteady Separation ◽  
Supersonic Gas Flow

Gas flow characteristics in shale fractures after supercritical CO2 soaking

2021 ◽  
Vol 88 ◽  
pp. 103826
Author(s):  
Yiyu Lu ◽  
Jiankun Zhou ◽  
Honglian Li ◽  
Jiren Tang ◽  
Lei Zhou ◽  
...  
Keyword(s):  
Supercritical Co2 ◽  
Gas Flow ◽  
Flow Characteristics

scholarly journals Presence of Longitudinal Roll Structures during Synoptic Forced Conditions in Complex Terrain

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 737
Author(s):  
Cory M. Payne ◽  
Jeffrey E. Passner ◽  
Robert E. Dumais ◽  
Abdessattar Abdelkefi ◽  
Christopher M. Hocut
Keyword(s):  
Boundary Layer ◽  
Agricultural Research ◽  
Wrf Model ◽  
Flow Characteristics ◽  
Critical Threshold ◽  
Department Of Agriculture ◽  
Synoptic Conditions ◽  
Lee Waves ◽  
Lee Wave ◽  
Usda Agricultural Research

To investigate synoptic interactions with the San Andres Mountains in southern New Mexico, the Weather Research and Forecasting (WRF) model was used to simulate several days in the period 2018–2020. The study domain was centered on the U.S. Department of Agriculture (USDA) Agricultural Research Service’s Jornada Experimental Range (JER) and the emphasis was on synoptic conditions that favor strong to moderate winds aloft from the southwest, boundary layer shear, a lack of moisture (cloud coverage), and modest warming of the surface. The WRF simulations on these synoptic days revealed two distinct regimes: lee waves aloft and SW-to-NE oriented Longitudinal Roll Structures (LRS) that have typical length scales of the width of the mountain basin in the horizontal and the height of the boundary layer (BL) in the vertical. Analysis of the transitional periods indicate that the shift from the lee wave to LRS regime occurs when the surface heating and upwind flow characteristics reach a critical threshold. The existence of LRS is confirmed by satellite observations and the longitudinal streak patterns in the soil of the JER that indicate this is a climatologically present BL phenomenon.

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