Numerical study of mechanisms of air-core vortex evolution in an intake flow

Zi, Dan; Xuan, Anqing; Wang, Fujun; Shen, Lian

doi:10.1016/j.ijheatfluidflow.2019.108517

Cited by 24 publications

(5 citation statements)

References 51 publications

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“…The Q -criterion is the second matrix invariant of the characteristic equation of the velocity gradient tensor, which can display the vortex structure and its intensity. 30 Both the Q -criterion and velocity distribution reflect that the difference in the flow pattern mainly occurs in the descending segment, which is consistent with the distribution law of the hydraulic loss coefficient in Figure 18. In Figure 19(a), two elliptical areas with a high Q value appear in the descending segment of the original design, which indicates that two vortices appear, deteriorating the flow pattern and increasing the hydraulic loss.…”

Section: Results and Analysissupporting

confidence: 80%

Multi-objective shape optimization of siphon outlet in pumping station considering two-phase flow

Chen

et al. 2022

Proceedings of the Institution of Mechanical Engineers, Part A:

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The siphon outlet is widely used in pumping stations due to its reliable and convenient cut-off performance. Long siphoning time or high hydraulic loss caused by the inappropriate design of the siphon outlet can significantly affect the safety of stations. The air compressibility volume-of-fluid (VOF) method is conducted to simulate the two-phase flow in the siphoning formation process at the design points selected by the optimal Latin hypercube design (OLHD), the results of which show good agreement with the experimental data. In this work, the siphoning time and hydraulic loss coefficient are selected as the objective functions, and a multi-objective shape optimization strategy is proposed for the siphon outlet in conjunction with the response surface method (RSM). This optimization strategy can not only reconcile conflicting objective functions but also obtain the effect and interaction of design variables. Sensitivity analysis on the constructed response surface models indicates that among three design variables, the aspect ratio has the greatest effect on the objective functions, the descending angle has the second greatest effect, and the ascending angle has almost no effect. Compared with the original design, the hydraulic loss coefficient and siphoning time of the optimized design are reduced by 2.95% and 26.76%, respectively. A higher vorticity magnitude and more uniform outflow are created in the optimized design, which results in the improvement of hydraulic performance.

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Section: Results and Analysissupporting

confidence: 80%

Multi-objective shape optimization of siphon outlet in pumping station considering two-phase flow

Chen

et al. 2022

Proceedings of the Institution of Mechanical Engineers, Part A:

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“…Therefore, depending on the volume fraction of each phase, the properties in each control volume may belong to one phase or to the whole (combination) of phases. This model has been used in almost all numerical simulations [4,18,19,20,27,30]. The continuity equation for phase q is as follows [32].…”

Section: Governing Equationsmentioning

confidence: 99%

“…{ 𝑎 = −80𝑉 𝜃 𝑏 = 180𝑉 𝜃 𝑐 = −100𝑉 𝜃 (20) This method can be used for all the analytical relations presented for tangential velocity, i.e., Eqs 10, 11, 15, and 16. Accordingly, the modified tangential velocity diagrams are shown in Fig.…”

Section: The Near-wall Behavior Of Analytical Relationsmentioning

confidence: 99%

“…In parallel with analytical works, many attempts have been made through experiments as well as numerical simulations. In general, these studies investigate some phenomena and topics, such as the formation of vortices in specific geometries, for example, in tanks and turbines, the details of vortex formation, such as critical height, velocity components, and the structure of vortices [4,[19][20][21], improvement analytical relationships [17,18], the effects of important dimensionless numbers such as Reynolds, Weber, and Froude [22,23], the effect of the vortex breaker and its shape [8,9,23,24], the use of the vortex for thermal energy transfer [25], and sometimes a comparison between the performance of turbulence models [26,27,28]. Due to the complexity of the problem, almost all numerical simulations have been performed using commercial software such as Ansys Fluent [23], Ansys CFX [4,2926,29], Flow 3D [18,27,30], and open source CFD codes such as OpenFOAM [28].…”

Section: Introductionmentioning

confidence: 99%

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Numerical analysis of transient vortex formation at the outlet of a tank containing gas-liquid phases

Mohseni

Domfeh

2023

Preprint

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One of the basic phenomena when a liquid leaves a tank, is the formation of vortices. This phenomenon can significantly affect the remaining liquid mass in the tank and the penetration of air and bubbles into the system. As a result, system performance may be disrupted. This study numerically investigates the influence of parameters such as discharge time, gas pressure, liquid depth, and angular velocity of the reference frame on the vortex characteristics. In addition, the near-wall behavior of the analytical relations proposed for the tangential velocity has been revised based on the boundary layer theory. The "volume of fluid" model (VOF) and the SST k-ω turbulence model have been used to solve the two-phase turbulent flow. The results show that increasing the gas pressure from 1 to 5 bar and its direct impact on the liquid surface significantly accelerates the formation of the vortex and the critical height. This phenomenon causes, after the starting of liquid discharge, the air core to reach the inlet port of the outlet pipe about 7 seconds earlier. As a result, much more liquid mass remains in the tank. Also, the increase in the angular velocity of the reference frame from 0.1 to 1 rad/s causes the critical height to be formed much sooner and the remaining liquid mass to increase by 32 kg. Furthermore, the amount and the variations of turbulent viscosity significantly differ from the semi-empirical constant values, limiting their use to particular streams.

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“…The coupled level set/volume-of-fluid (CLSVOF) method, as developed in [63], is applied when the free surface is expected to be highly complex. Results of a very recent work which deals with mechanisms of air-core vortex evolution in an intake flow are reported in [64].…”

Section: Choice Of the Numerical Approachmentioning

confidence: 99%

Analysis of Polygonal Vortex Flows in a Cylinder with a Rotating Bottom

Rashkovan¹,

Amar

Bieder

et al. 2021

Applied Sciences

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The present paper provides a physically sound numerical modeling of liquid flows experimentally observed inside a vertical circular cylinder with a stationary envelope, rotating bottom and open top. In these flows, the resulting vortex depth may be such that the rotating bottom disk becomes partially exposed, and rather peculiar polygon shapes appear. The parameters and features of this work are chosen based on a careful analysis of the literature. Accordingly, the cylinder inner radius is 145 mm and the initial water height is 60 mm. The experiments with bottom disk rotation frequencies of 3.0, 3.4, 4.0 and 4.6 Hz are simulated. The chosen frequency range encompasses the regions of ellipse and triangle shapes as observed in the experimental studies reported in the literature. The free surface flow is expected to be turbulent, with the Reynolds number of O(105). The Large Eddy Simulation (LES) is adopted as the numerical approach, with a localized dynamic Subgrid-Scale Stresses (SGS) model including an energy equation. Since the flow obviously requires a surface tracking or capturing method, a volume-of-fluid (VOF) approach has been chosen based on the findings, where this method provided stable shapes in the ranges of parameters found in the corresponding experiments. Expected ellipse and triangle shapes are revealed and analyzed. A detailed character of the numerical results allows for an in-depth discussion and analysis of the mechanisms and features which accompany the characteristic shapes and their alterations. As a result, a unique insight into the polygon flow structures is provided.

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Numerical study of mechanisms of air-core vortex evolution in an intake flow

Cited by 24 publications

References 51 publications

Multi-objective shape optimization of siphon outlet in pumping station considering two-phase flow

Multi-objective shape optimization of siphon outlet in pumping station considering two-phase flow

Numerical analysis of transient vortex formation at the outlet of a tank containing gas-liquid phases

Analysis of Polygonal Vortex Flows in a Cylinder with a Rotating Bottom

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