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Preliminary control of the air entrainment in bow wave based on the Liutex force method

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Journal of Hydrodynamics 2022年第3期34卷 483-490页

作者： Yi-ding Hu Jian-wei Wu De-cheng Wan Guo Wang Yi-qian Wang Computational Marine Hydrodynamics Lab(CMHL) School of Naval ArchitectureOcean and Civil EngineeringShanghai Jiao Tong UniversityShanghai200240China Wuhan Second Ship Design and Research Institute Wuhan430205China Marine Design and Research Institute of China Shanghai200011China School of Mathematical Science Soochow UniversitySuzhou215006China

Trails induced by air entrainment of bow wave breaking can be observed clearly around an advancing ship,making it prong to be detected and causing reduction in hydrodynamic performance.In breaking bow wave region,different scale of coherent vortex structures related closely to the air entrainment are generated.The formation and evolution of bubble clouds can be accounted partly by the swirling vortex flow of the jet plunging.In this work,high-fidelity simulation of the bow wave breaking around a rectangular thin plate is performed with the in-house code BAMR-SJTU.A Liutex force model is constructed to investigate the interaction between the free surface and vortices,and to explore the possibility of alleviating or controlling the air entrainment.This study is the first attempt to manipulate vortices corresponding to the air entrainment of the bow wave breaking.Some typical vortex structures based on the Liutex vortex identification method and the distribution of the vortex force are presented.Comparison of the vortex structures and the entrapped bubbles is conducted to illustrate the efficiency of Liutex force model in air entrainment control.

关键词： Bow wave breaking air entrainment coherent vortex structures Liutex force field model

Inception point of air entrainment over stepped spillways

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Journal of Hydrodynamics 2013年第1期25卷 91-96页

作者： WU Jian-hua ZHANG Bin MA Fei College of Water Conservancy and Hydropower Engineering Hohai University

The location of the inception point of the air entrainment directly affects the energy dissipation ratio, the cavitation damage control, and the training wall height designs for a stepped spillway and a stilling basin. In this paper, the boundary layer theory of plates is used to predict the location of the inception point of the air entrainment over the stepped spillways by assuming the steps on the spillways as a kind of roughness. An empirical formula is presented based on the physical model experiments, with the maximum error less than 1% except at one point where the error is 1.6%, as compared to the experimental data. Meanwhile, it is shown that the location of the inception point of the air entrainment for the stepped spillway is much nearer to the top of the spillway than that for a smooth spillways, which explains why the high ratio of the energy dissipation is provided for the stepped spillway.

关键词： air entrainment cavitation energy dissipation inception point stepped spillway unit discharge

INCEPTION OF air entrainment ON STEEP SLOPE

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Journal of Hydrodynamics 1993年第3期5卷 9-15页

作者： Ning, Lizhong Wang, Changjiang Shaanxi Inst of Mechanical Engineering Xi'an China

Based on the momentum integral equation of boundary layer on the steep slope and the equation of water depth deduced form both the equation of continuity including the effect of the boundary layer and the energy equation outside the boundary layer on the steep slope, and with the aid of the function of velocity profile in the boundary layer, the water depth and boundary layer were numerically computed by Runge-Kutta method. The method determine parameters in the preceding equation were also discussed in detail for the laminar and turbulent flows. The water depth boundary layer and point of inception of air entrainment calculated by above method agree well with the data obtained by prototype.

关键词： air entrainment Boundary layers Spillways

A method of determining flame radiation fraction induced by interaction burning of tri-symmetric propane fires in open space based on weighted multi-point source model

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Frontiers in Energy 2022年第6期16卷 1017-1026页

作者： Jie JI Junrui DUAN Huaxian WAN State Key Laboratory of Fire Science University of Science and Technology of ChinaHefei 230026China Institute of Advanced Technology University of Science and Technology of ChinaHefei 230088China

The interaction of multiple fires may lead to a higher flame height and more intense radiation flux than a single fire,which increases the possibility of flame spread and risks to the surroundings.Experiments were conducted using three burners with identical heat release rates(HRRs)and propane as the fuel at various spacings.The results show that flames change from non-merging to merging as the spacing decreases,which result in a complex evolution of flame height and merging point height.To facilitate the analysis,a novel merging criterion based on the dimensionless spacing S/z_(c) was proposed.For non-merging flames(S/z_(c)>0.368),the flame height is almost identical to a single fire;for merging flames(S/z_(c)≤0.368),based on the relationship between thermal buoyancy B and thrust P(the pressure difference between the inside and outside of the flame),a quantitative analysis of the flame height,merging point height,and air entrainment was formed,and the calculated merging flame heights show a good agreement with the measured experimental values.Moreover,the multi-point source model was further improved,and radiation fraction of propane was calculated.The data obtained in this study would play an important role in calculating the external radiation of propane fire.

关键词： flame interaction air entrainment flame height multi-point source model thermal radiation

Two-phase air-water flows: Scale effects in physical modeling

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Journal of Hydrodynamics 2014年第2期26卷 291-298页

作者： PFISTER Michael CHANSON Hubert Ecole Polytechnique Fédérale de Lausanne (EPFL) Laboratory of Hydraulic Constructions (LCH) The University of Queensland School of Civil Engineering

Physical modeling represents probably the oldest design tool in hydraulic engineering together with analytical approaches. In free surface flows, the similitude based upon a Froude similarity allows for a correct representation of the dominant forces, namely gravity and inertia. As a result fluid flow properties such as the capillary forces and the viscous forces might be incorrectly reproduced, affecting the air entrainment and transport capacity of a high-speed model flow. Small physical models operating under a Froude similitude systematically underestimate the air entrainment rate and air-water interfacial properties. To limit scale effects, minimal values of Reynolds or Weber number have to be respected. The present article summarizes the physical background of such limitations and their combination in terms of the Morton number. Based upon a literature review, the existing limits are presented and discussed, resulting in a series of more conservative recommendations in terms of air concentration scaling. For other air-water flow parameters, the selection of the criteria to assess scale effects is critical because some parameters （e.g., bubble sizes, turbulent scales） can be affected by scale effects, even in relatively large laboratory models.

关键词： air entrainment hydraulic structures physical modeling scale effects two-phase flow Morton number

Inverse problem of bottom slope design for aerator devices

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Journal of Hydrodynamics 2013年第5期25卷 805-808页

作者：吴建华樊博许唯临 College of Water Conservancy and Hydropower Engineering Hohai University State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan University

air entrainment is an effective approach to protect release works from cavitation damage. The traditional method of aerator device designs is that, for given flow conditions, the geometries of the aerator device are designed and then the effec（s are experimentally tested for cavitation damage control. The present paper proposes an inverse problem method of determining the bottom slopes in front of and behind an aerator if the requirements of air entrainment, flow conditions and some of aerator geometric parameters are given. An RBF neural network model is developed and the relevant bottom slopes are calculated in different conditions of flow and geometry on the basis of the data of 19 aerator devices from different discharge tunnels with safe operation. The case study shows that the methodology provides an effective way to design aerator devices under given target conditions.

关键词： air entrainment bottom slope inverse problem neural network discharge ttmnel

EFFECTS OF ENTRAINED air MANNER ON CAVITATION DAMAGE

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Journal of Hydrodynamics 2011年第3期23卷 333-338页

作者： WU Jian-hua LUO Chao College of Water Conservancy and Hydropwer Engineering Hohai University Nanjing 210098 China

Early in 1953 the experiments by Peterka proved that air entrainment has effects on decreasing cavitation damage. This technology has been widely used in the release works of high dams since the inception of air entrainment in the Grand Goulee Dam in 1960. Behavior, mechanism and application of air entrainment for cavitation damage control have been investigated for over half century. However, severe cavitation damage happened due to complex mechanism of air entrainment. The effects of air entrainment are related to many factors, including geometric parameters, hydraulic parameters and entrained air manners. In the present work an experimental set-up for air entrainment was specially designed, the behavior of reducing cavitation damage was experimentally investigated in the three aspects of entrained air pressure, air tube aera and air tube number. The results show that magnitude of reduction of cavitation damage is closely related to the entrained air tube number as well as entrained air pressure, air tube aera, and that the effect through three air tubes is larger than that through single air tube although the entrained air tubes have the same sum of tube aera, that is, 1 ＋ 1 ＋ 1 〉 3. Therefore, it is important to design an effective manner of air entrainment.

关键词： air entrainment air pressure air tube area cavitation damage entrained air manner

Solution of analytical model for fuel spray penetration via homotopy perturbation method

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Propulsion and Power Research 2016年第3期5卷 202-210页

作者： B.Jalilpour S.Jafarmadar D.D.Ganji M.M.Rashidi Department of Mechanical Engineering Faculty of EngineeringUrmia UniversityUrmiaWest Azerbaijan 57561-15311Iran Babol University of Technology Department of Mechanical EngineeringP.O.Box 484BabolIran Shanghai Key Lab of Vehicle Aerodynamics and Vehicle Thermal Management Systems Tongji UniversityShanghai 201804China ENN-Tongji Clean Energy Institute of Advanced Studies ShanghaiChina

The present paper attempts to solve equations in the initial stage and the two-phase flow regime of fuel spray penetration using the HPM-Padétechnique,which is a combination of the homotopy perturbation method(HPM)and Padéapproximation.At the initial stage,the effects of the droplet drag and the air entrainment were explained while in the two-phase flow stage,the spray droplets had the same velocities as the entrained air.The results for various injection pressures and ambient densities are presented graphically and then discussed upon.The obtained results for these two stages show a good agreement with previously obtained expressions via successive approximations in the available literature.The numerical result indicates that the proposed method is straight forward to implement,efficient and accurate for solving nonlinear equations of fuel spray.

关键词： Spray air entrainment Initial stage Two-phase flow Homotopy perturbation method(HPM)

PARALLEL ADAPTIVE SIMULATION OF A PLUNGING LIQUID JET

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Acta Mathematica Scientia 2010年第2期30卷 522-538页

作者： Azat Yu.Galimov Onkar Sahni Richard T.Lahey Jr. Mark S.Shephard Donald A.Drew Kenneth E.Jansen Rensselaer Polytechnic Institute

This paper is concerned with three-dimensional numerical simulation of a plunging liquid jet. The transient processes of forming an air cavity around the jet, capturing an initially large air bubble, and the break-up of this large toroidal-shaped bubble into smaller bubbles were analyzed. A stabilized finite element method （FEM） was employed under parallel numerical simulations based on adaptive, unstructured grid and coupled with a level-set method to track the interface between air and liquid. These simulations show that the inertia of the liquid jet initially depresses the pool＇s surface, forming an annular air cavity which surrounds the liquid jet. A toroidal liquid eddy which is subse- quently formed in the liquid pool results in air cavity collapse, and in turn entrains air into the liquid pool from the unstable annular air gap region around the liquid jet.

关键词： plunging liquid jet air entrainment two-phase flows level set method parallel adaptive simulation