A Simulation and Optimization Study of the Swirling Nozzle for Eccentric Flow Fields of Round Molds

In continuous casting, the nozzle position may deviate from the center under actual operating conditions, which may cause periodic fluctuation of the steel-slag interface and easily lead to slag entrapment and gas absorption. Swirling nozzles can reduce these negative effects. A mathematical simulation method based on a round mold of steel components with a 600 mm diameter is applied to study the flow field of molten steel in a mold. The swirling nozzle is optimized through the establishment of a fluid dynamics model. Meanwhile, a 1:2 hydraulic model is established for validation experiments. The results show that, when the submerged entry nozzle (SEN) is eccentric in the mold, it results in serious bias flow, increasing the drift index in the mold up to 0.46 at the eccentric distance of 50 mm. The impact depth of liquid steel and turbulent kinetic energy can be decreased by increasing the rotation angle of the nozzle. The nozzle with one bottom hole, which significantly decreases the bottom pressure and turbulent kinetic energy, greatly weakens the scour on nozzle and surface fluctuation. In the eccentric casting condition, using the optimized swirling nozzle that employs a 5-fractional structure, in which the rotation angle of 4 side holes is 30° and there is one bottom outlet, can effectively restrain bias flow and reduce the drift index to 0.28, a decline of more than 39%.

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A New Method to Determine the Impact of Individual Field Quantities on Cycle-to-Cycle Variations in a Spark-Ignited Gas Engine

Energies ◽

10.3390/en14144136 ◽

2021 ◽

Vol 14 (14) ◽

pp. 4136

Author(s):

Clemens Gößnitzer ◽

Shawn Givler

Keyword(s):

Kinetic Energy ◽

Flow Field ◽

Turbulent Kinetic Energy ◽

Negative Impact ◽

Operating Conditions ◽

Engine Operation ◽

Gas Engine ◽

Cycle Simulation ◽

Simulation Results ◽

The Impact

Cycle-to-cycle variations (CCV) in spark-ignited (SI) engines impose performance limitations and in the extreme limit can lead to very strong, potentially damaging cycles. Thus, CCV force sub-optimal engine operating conditions. A deeper understanding of CCV is key to enabling control strategies, improving engine design and reducing the negative impact of CCV on engine operation. This paper presents a new simulation strategy which allows investigation of the impact of individual physical quantities (e.g., flow field or turbulence quantities) on CCV separately. As a first step, multi-cycle unsteady Reynolds-averaged Navier–Stokes (uRANS) computational fluid dynamics (CFD) simulations of a spark-ignited natural gas engine are performed. For each cycle, simulation results just prior to each spark timing are taken. Next, simulation results from different cycles are combined: one quantity, e.g., the flow field, is extracted from a snapshot of one given cycle, and all other quantities are taken from a snapshot from a different cycle. Such a combination yields a new snapshot. With the combined snapshot, the simulation is continued until the end of combustion. The results obtained with combined snapshots show that the velocity field seems to have the highest impact on CCV. Turbulence intensity, quantified by the turbulent kinetic energy and turbulent kinetic energy dissipation rate, has a similar value for all snapshots. Thus, their impact on CCV is small compared to the flow field. This novel methodology is very flexible and allows investigation of the sources of CCV which have been difficult to investigate in the past.

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Uncertainty analysis of CFD and performance prediction for an pumpjet propulsor

Modern Physics Letters B ◽

10.1142/s0217984921500834 ◽

2020 ◽

pp. 2150083

Author(s):

Chao Liu ◽

Hongxun Chen ◽

Zhengchuan Zhang ◽

Zheng Ma

Keyword(s):

Numerical Simulation ◽

Kinetic Energy ◽

Uncertainty Analysis ◽

Turbulent Kinetic Energy ◽

Guide Vane ◽

Outer Region ◽

Turbulence Models ◽

Operating Conditions ◽

Operating Characteristics ◽

Standard Formula

In order to reveal the operating characteristics of the pumpjet propulsor, standard [Formula: see text]–[Formula: see text], standard [Formula: see text]–[Formula: see text], RNG [Formula: see text]–[Formula: see text] and SST [Formula: see text]–[Formula: see text] turbulence models were used to conduct steady calculation for the whole flow channels. By comparing the calculation results with experimental data, it was found that the calculation errors were very large in some operating conditions. Therefore, the uncertainty analysis was carried out at all operating conditions of the pumpjet propulsor and the error source was finally determined that it is mainly derived from the model error. Then, the applicability of different turbulence models was analyzed to numerical simulation for the pumpjet propulsor by comparing the internal and external characteristics. It can be seen that the strong turbulent kinetic energy in the guide vane will inevitably cause energy loss, but not necessarily in the impeller. In this area, the increase of turbulent kinetic energy will enhance the mixing and transport of fluids, and the impeller makes the fluids get more energy. In addition, a modified hybrid Reynolds Average Numerical Simulation/Large Eddy Simulation (RANS/LES) model was proposed for unsteady calculation, and the performances, internal flow states and the interaction between the pump and the outer region were further revealed under various conditions of the pumpjet propulsor, which provides some references for predicting accurately and selecting conditions optimally in the future.

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Turbulent Kinetic Energy in Bolt Fishway

AgriEngineering ◽

10.3390/agriengineering1020020 ◽

2019 ◽

Vol 1 (2) ◽

pp. 265-282

Author(s):

Marta Puzdrowska ◽

Tomasz Heese

Keyword(s):

Spatial Distribution ◽

Kinetic Energy ◽

Turbulent Kinetic Energy ◽

Laboratory Tests ◽

Flow Structures ◽

3D Flow ◽

Velocity Magnitude ◽

Biological Development ◽

The Impact ◽

Channel Development

The paper presents an analysis the spatial distribution of turbulent kinetic energy (TKE) for bolt fishways, including the impact of additional spillway slots and fixed channel development. The research was done for two models, each containing a different arrangement of slots. The presented results of research for bolt fishways were obtained as an effect of laboratory tests. The measurements were done for three components of instant flow velocity magnitude (speed). Analysis of the results was done for a 3D flow structure using Matlab software. In the case of bolt fishways, significant differences were noted for the method of velocity and TKE distribution, in reference to research comprising channels with biological development. It was stated that a reason for this is the flexible development of the channel. The occurrence of extreme TKE values in the chamber (pool) is strictly associated with the characteristics of interaction zones between various flow structures. It was also stated that the lower the parapet of the slot’s spillway shelf is in the fishway’s partition, the higher TKE could be expected just downstream of the section. These establishments may be important for the designing process in the case of fish passes of various types of construction.

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A Statistical Evaluation of WRF-LES Trace Gas Dispersion Using Project Prairie Grass Measurements

Monthly Weather Review ◽

10.1175/mwr-d-20-0233.1 ◽

2021 ◽

Author(s):

Alex Rybchuk ◽

Caroline B. Alden ◽

Julie K. Lundquist ◽

Gregory B. Rieker

Keyword(s):

Kinetic Energy ◽

Natural Gas ◽

Turbulent Kinetic Energy ◽

Similarity Theory ◽

Trace Gas ◽

Near Surface ◽

Gas Dispersion ◽

Prairie Grass ◽

Strong Convection ◽

The Impact

AbstractIn recent years, new measurement systems have been deployed to monitor and quantify methane emissions from the natural gas sector. Large-eddy simulation (LES) has complemented measurement campaigns by serving as a controlled environment in which to study plume dynamics and sampling strategies. However, with few comparisons to controlled-release experiments, the accuracy of LES for modeling natural gas emissions is poorly characterized. In this paper, we evaluate LES from the Weather Research and Forecasting (WRF) model against Project Prairie Grass campaign measurements and surface layer similarity theory. Using WRF-LES, we simulate continuous emissions from 30 near-surface trace gas sources in two stability regimes: strong and weak convection. We examine the impact of grid resolutions ranging from 6.25 m to 52 m in the horizontal dimension on model results. We evaluate performance in a statistical framework, calculating fractional bias and conducting Welch’s t-tests. WRF-LES accurately simulates observed surface concentrations at 100 m and beyond under strong convection; simulated concentrations pass t-tests in this region irrespective of grid resolution. However, in weakly convective conditions with strong winds, WRF-LES substantially overpredicts concentrations – the magnitude of fractional bias often exceeds 30%, and all but one C-test fails. The good performance of WRF-LES under strong convection correlates with agreement with local free convection theory and a minimal amount of parameterized turbulent kinetic energy. The poor performance under weak convection corresponds to misalignment with Monin-Obukhov similarity theory and a significant amount of parameterized turbulent kinetic energy.

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Analysis of Turbulent Flow Structure with Its Fluvial Processes around Mid-Channel Bar

Sustainability ◽

10.3390/su14010392 ◽

2021 ◽

Vol 14 (1) ◽

pp. 392

Author(s):

Md. Amir Khan ◽

Nayan Sharma ◽

Jaan Pu ◽

Faisal M. Alfaisal ◽

Shamshad Alam ◽

...

Keyword(s):

Kinetic Energy ◽

Turbulent Flow ◽

Flow Velocity ◽

Turbulent Kinetic Energy ◽

Production Rate ◽

Energy Transport ◽

Vertical Distance ◽

Scour Hole ◽

The Impact ◽

Channel Bar

Researchers have recognized that the successive growth of mid-channel bar deposits can be entertained as the raison d’être for the initiation of the braiding process, which is closely interlinked with the growth, decay, and vertical distribution of fluvial turbulent kinetic energy (TKE). Thus, focused analysis on the underlying mechanics of turbulent flow structures in the proximity of a bar deposit occurring in the middle of the channel can afford crucial scientific clues for insight into the initiating fluvial processes that give rise to braiding. In the study reported herein, a physical model of a mid-channel bar is constructed in an experimental flume to analyze the turbulence parameters in a region close to the bar. Notably, the flow velocity plays an important role in understanding the flow behavior in the scour-hole location in the upstream flow divergence zone as well as near the downstream zone of flow convergence in a mid-channel bar. Therefore, the fluctuating components of turbulent flow velocity are herein discussed and analyzed for the regions located close to the bar. In the present study, the impact of the mid-channel bar, as well as its growth in turbulent flow, on higher-order velocity fluctuation moments are investigated. For near-bed locations, the results show the dominance of ejection events in upstream zones and the dominance of sweep events at locations downstream of the mid-channel bar. In scour-hole sections, the negative value of the stream-wise flux of turbulent kinetic energy and the positive value of the vertical flux of turbulent kinetic energy indicate energy transport in downward and forward directions, respectively. The downward and forward energy transport processes lead to scouring at these locations. The maximum turbulent production rate occurs in the wake region of the bar. The high rate of turbulence production has occurred in that region, which can be ascribed to the process of shedding turbulent vortices. The results show that the impact of the presence of the bar is mainly restricted to the lower layers of flow. The turbulent dissipation rate monotonically decreases with an increase in the vertical distance from the bed. The turbulent production rate first increases and then decreases with successive increases in the vertical distance from the bed. The paper concludes with suggestions for the future potential use of the present research for the practical purpose of examining braid bar occurrences in alluvial rivers to develop an appropriate response through training measures.

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On the Impact of Trees on Ventilation in a Real Street in Pamplona, Spain

Atmosphere ◽

10.3390/atmos10110697 ◽

2019 ◽

Vol 10 (11) ◽

pp. 697 ◽

Cited By ~ 4

Author(s):

Jose-Luis Santiago ◽

Riccardo Buccolieri ◽

Esther Rivas ◽

Beatriz Sanchez ◽

Alberto Martilli ◽

...

Keyword(s):

Wind Speed ◽

Kinetic Energy ◽

Turbulent Kinetic Energy ◽

Wind Velocity ◽

Flow Direction ◽

Pollutant Dispersion ◽

Average Concentration ◽

Pollutant Concentration ◽

Prevailing Wind Direction ◽

The Impact

This paper is devoted to the quantification of changes in ventilation of a real neighborhood located in Pamplona, Spain, due to the presence of street trees Pollutant dispersion in this urban zone was previously studied by means of computational fluid dynamic (CFD) simulations. In the present work, that research is extended to analyze the ventilation in the whole neighborhood and in a tree-free street. Several scenarios are investigated including new trees in the tree-free street, and different leaf area density (LAD) in the whole neighborhood. Changes between the scenarios are evaluated through changes in average concentration, wind speed, flow rates and total pollutant fluxes. Additionally, wind flow patterns and the vertical profiles of flow properties (e.g., wind velocity, turbulent kinetic energy) and concentration, horizontally-averaged over one particular street, are analyzed. The approach-flow direction is almost perpendicular to the street under study (prevailing wind direction is only deviated 4º from the perpendicular direction). For these conditions, as LAD increases, average concentration in the whole neighborhood increases due to the decrease of wind speed. On the other hand, the inclusion of trees in the street produces an increase of averaged pollutant concentration only within this street, in particular for the scenario with the highest LAD value. In fact, the new trees in the street analyzed with the highest LAD value notably change the ventilation producing an increase of total pollutant fluxes inward the street. Additionally, pollutant dispersion within the street is also influenced by the reduction of the wind velocity along the street axis and the decrease of turbulent kinetic energy within the vegetation canopy caused by the new trees. Therefore, the inclusion of new trees in a tree-free street should be done by considering ventilation changes and traffic emissions should be consequently controlled in order to keep pollutant concentration within healthy levels.

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Comparison and Analysis on the Impact of Two Typical Rearview Mirrors on Aerodynamic Performance

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1023.150 ◽

2014 ◽

Vol 1023 ◽

pp. 150-153

Author(s):

Xin Chen ◽

Wu Zhang ◽

Yuan Qiang Wu ◽

Huai Yu Wang ◽

Hou Yu Ning

Keyword(s):

Kinetic Energy ◽

Turbulent Kinetic Energy ◽

Static Pressure ◽

Flow Line ◽

Great Influence ◽

Aerodynamic Performance ◽

Computational Fluid Mechanics ◽

Monitoring Point ◽

Rearview Mirror ◽

The Impact

This paper aims to study the impact of the rearview mirror shape on aerodynamic performance. Two typical rearview mirrors were selected to conduct the wind tunnel test, and the test result showed that the noise on the rear monitoring point of the mirror 1 was lower than that of the mirror 2. This paper then conducted simulating computation through computational fluid mechanics (CFD) theory and Fluent software, and obtained the size of the monitoring points of the two typical rearview mirrors, static pressure chart, motion pattern and turbulent kinetic energy distribution diagram, and sequentially analyzed the reason for more noise of the mirror 2. The study shows that different mirror cover structures have a great influence on the flow line flowing through the rearview mirror cover, and significantly influenced the rear flow field of the rearview mirror and the static pressure and the turbulent kinetic energy of the monitoring point.

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A Numerical Study of the Effect of Dissipative Heating on Tropical Cyclone Intensity

Weather and Forecasting ◽

10.1175/waf1028.1 ◽

2007 ◽

Vol 22 (5) ◽

pp. 950-966 ◽

Cited By ~ 34

Author(s):

Yi Jin ◽

William T. Thompson ◽

Shouping Wang ◽

Chi-Sann Liou

Keyword(s):

Energy Dissipation ◽

Tropical Cyclone ◽

Kinetic Energy ◽

Turbulent Kinetic Energy ◽

Mesoscale Model ◽

Dissipative Heating ◽

Northwest Pacific ◽

Forecast Errors ◽

Maximum Wind ◽

The Impact

Abstract The impact of dissipative heating on tropical cyclone (TC) intensity forecasts is investigated using the U.S. Navy’s operational mesoscale model (the Coupled Ocean/Atmosphere Mesoscale Prediction System). A physically consistent method of including dissipative heating is developed based on turbulent kinetic energy dissipation to ensure energy conservation. Mean absolute forecast errors of track and surface maximum winds are calculated for eighteen 48-h simulations of 10 selected TC cases over both the Atlantic basin and the northwest Pacific. Simulation results suggest that the inclusion of dissipative heating improves surface maximum wind forecasts by 10%–20% at 15-km resolution, while it has little impact on the track forecasts. The resultant improvement from the inclusion of the dissipative heating increases to 29% for the surface maximum winds at 5-km resolution for Hurricane Isabel (2003), where dissipative heating produces an unstable layer at low levels and warms a deep layer of the troposphere. While previous studies depicted a 65 m s−1 threshold for the dissipative heating to impact the TC intensity, it is found that dissipative heating has an effect on the TC intensity when the TC is of moderate strength with the surface maximum wind speed at 45 m s−1. Sensitivity tests reveal that there is significant nonlinear interaction between the dissipative heating from the surface friction and that from the turbulent kinetic energy dissipation in the interior atmosphere. A conceptualized description is given for the positive feedback mechanism between the two processes. The results presented here suggest that it is necessary to include both processes in a mesoscale model to better forecast the TC structure and intensity.

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Data Assimilation of Steam Flow Through a Control Valve Using Ensemble Kalman Filter

Journal of Fluids Engineering ◽

10.1115/1.4050799 ◽

2021 ◽

Author(s):

Peixun Fang ◽

Chuangxin He ◽

Peng Wang ◽

Sihua Xu ◽

YingZheng Liu

Keyword(s):

Kalman Filter ◽

Kinetic Energy ◽

Data Assimilation ◽

Turbulent Kinetic Energy ◽

Flow Rate ◽

Ensemble Kalman Filter ◽

Control Valve ◽

Operating Conditions ◽

Constant Matrix ◽

Flow Through

Abstract The present work concentrates on the simulation enhancement of steam flow through a control valve using novel data assimilation (DA) approach. Ensemble Kalman filter (EnKF) is applied to improve the performance of k-? shear stress transport (SST) model by optimizing its turbulence model constants. The selected measurement data at different operating conditions are used as observation, while the rest data are involved for validation. Firstly, four flow patterns, which arise on their respective operating conditions, are identified and analyzed to illustrate the basic characteristics of flow in the control valve. Then DA is performed based on the sample computation by perturbing the model constants and the EnKF process to determine the optimal constant matrix. This optimized constant matrix is subsequently used for the precomputation of the valve flow with significant improvement on the flow rate prediction. The velocity and turbulent kinetic energy fields with default and optimal model constants are also compared to illustrate the effect of DA. The results show that the DA enhanced model constants can significantly reduce the predicted volume flow rate error at all opening ratios presently concerned. With updated model constants, the velocity and turbulent kinetic energy distributions are greatly modified in the valve seat between main valve and control valve.

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Transient Process and Micro-mechanism of Hydrofoil Cavitation Collapse

Processes ◽

10.3390/pr8111387 ◽

2020 ◽

Vol 8 (11) ◽

pp. 1387

Author(s):

Yuanyuan Zhao ◽

Qiang Fu ◽

Rongsheng Zhu ◽

Guoyu Zhang ◽

Chuan Wang ◽

...

Keyword(s):

Kinetic Energy ◽

Turbulent Kinetic Energy ◽

Attack Angle ◽

Solid Surfaces ◽

Underwater Robots ◽

Factors Affecting ◽

Cavity Collapse ◽

Hydraulic Machinery ◽

Pressure Peak ◽

The Impact

Cavitation will cause abnormal flow, causing a series of problems such as vibration, noise, and erosion of solid surfaces. In severe cases, it may even destroy the entire system. Cavitation is a key problem to be solved for hydraulic machinery and underwater robots, and the attack angle is one of the most important factors affecting the cavitation. In order to systematically study the impact of the attack angle on the hydrofoil cavitation, the hydrofoils of NACA 4412 with different attack angles were selected to study the collapse process and hydraulic characteristics such as pressure, velocity, vortex, and turbulent kinetic energy during cavitation. The results showed that when the cavitation number was the same, the process of cavity collapse was greatly affected by the attack angle. The length of the cavity collapse area was positively correlated with the attack angle. As the attack angle increased, the volume of the falling bubbles increased, resulting in a larger pressure peak caused by the collapse of bubbles. Moreover, the pressure gradient near the collapse point changed more drastically, thereby affecting the growth of attached cavitation. The fluctuation range of vortex core and turbulent kinetic energy also increased with increasing the attack angle.

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