Self-induced Sloshing Research Articles

Experimental Study and Prediction by Computational Fluid Dynamics on Self-induced Sloshing Due to Bubble Flow in a Rectangular Vessel

Experimental Study and Prediction by Computational Fluid Dynamics on Self-induced Sloshing Due to Bubble Flow in a Rectangular Vessel

Study of Self-Induced Sloshing in Model Test of a Water Retaining Weir

This paper presents for the first time observations of a self-induced sloshing phenomenon in the water-retaining weir model. Fast Fourier Transform method is used to detect the dominant frequency for the sloshing water. The characteristics of the sloshing water in terms of sloshing strength and frequency are experimentally studied for six different cases. Results show that both sloshing regions and sloshing strength depends on not only the water levels but also the inlet velocities, and the relationship between them is displayed in this paper. Different prediction models for sloshing frequencies are built and compared with the experimental results, with discussions of the differences between them. For higher water level sloshing region, a new factor is introduced to the Faltinsen’s prediction formula, leading to a better agreement between prediction and experimental results. The mechanism of the self-induced sloshing is also discussed in this paper.

Self-induced rotary sloshing caused by an upward round jet in a cylindrical container

Jet-induced rotary sloshing of a Newtonian fluid in a partially filled cylindrical container is numerically and experimentally visualized to investigate a flow pattern inside the rotary sloshing wave. Visualization techniques employed in this study include Computational Fluid Dynamics (CFD) and Particle Image Velocimetry (PIV). Result for the sloshing period is compared with the theoretical result of a small time-harmonic irrotational flow of an inviscid and incompressible fluid, and several results for 3D view of the rotary sloshing and the velocity vector in the vertical and horizontal cross-sections are given.

Self-induced sloshing excited by a horizontally injected plane jet

A self-induced free-surface oscillation termed ‘self-induced sloshing’ was observed in a rectangular tank with a submerged and horizontally injected water jet. Self-induced sloshing is excited by the flow itself without any external force. Its behaviour was examined by experiment. The dominant frequency was found to be close to the first or second eigenvalue of fluid in a tank. The conditions of sloshing excitation were obtained for four tank geometries. They were called the ‘sloshing condition’, and defined in terms of inlet velocity and water level. Sloshing conditions were found to be strongly dependent on inlet velocity and tank geometry. A two-dimensional numerical simulation code was developed to simulate self-induced sloshing. The code was based on the boundary-fitted coordinate (BFC) method with height function. The numerical results were qualitatively verified by the experimental results, and were found to correlate well in terms of flow pattern, free-surface shape and sloshing conditions. In this study, sloshing growth was evaluated quantitatively using the simulation results. Oscillation energy supplied for the sloshing motion during a sloshing period (Econ) was calculated from simulation results. Sloshing growth was found to be strongly related to the sign and magnitude of Econ. The distribution of Econ showed that jet flow had a strong correlation with the sloshing growth. It was clarified that sloshing growth was primarily dependent on the spatial phase state of jet fluctuation. A governing parameter of self-induced sloshing, the modified Strouhal number Sts, was proposed on the basis of numerical evaluations of oscillation energy. The value of Sts suggests that one or two large vortices generated by jet fluctuations exist between the inlet and outlet during a sloshing period. When Sts is approximately either 1 (first stage) or 2 (second stage), self-induced sloshing occurs consistently in all experimental cases. The dependence of sloshing on inlet velocity, water level and tank geometry was revealed using Sts. For several tank geometries, a sloshing mode shift or jet mode (stage) transition was found to occur due to changes in inlet jet velocity. The combination of sloshing mode and jet stage can determine the state of the self-induced sloshing. As a result of this study, we propose a new excitation mechanism of self-induced sloshing, represented by a simple feedback loop closed by sloshing motion and jet fluctuation. The overall physical oscillation mechanism of self-induced sloshing was clarified using this feedback loop.

Development and evaluation of an improved correlation based PTV method

An improved correlation based Particle Tracking Velocimetry (PTV) algorithm was proposed in the present paper. The path tracking of the tracer particles was achieved through a correlation operation of the small interrogation window around the studied tracer particles at two-time steps. The central positions of the tracer particles were determined by the correlation operation of the tracer particle image with a Gaussian particle mask in order to improve the accuracy to identify the central positions of particles up to sub-pixel level. The performance of the present improved correlation based Particle Tracking Velocimetry (PTV) algorithm was evaluated by using both synthetic VSJ standard PIV images and actual PIV images of a self-induced sloshing. Compared with other conventional PTV methods, the present improved correlation based PTV algorithm was found to be able to provide better solution and more robust for suppression the effect of background noise in the PIV images.

B102濃度相関ベースの粒子追跡法の改良

An improved correlation based Particle Tracking Velocimetry (PTV) algorithm was proposed in the present paper. The path tracking of the tracer particles was achieved through a recursive correlation operation of the small interrogation window at two-time steps. The central positions of the tracer particles were determined by the correlation operation of the tracer particle image with a gauss particle mask in order to improve the accuracy to identify the central positions of particles up to sub-pixel level. The performance of the present improved correlation based Particle Tracking Velocimetry (PTV) algorithm was evaluated by using both artifical VSJ standard PIV images and actual PIV images of a self-induced sloshing. Compared with other conventional PTV methods, the present improved correlation based PTV algorithm was found to be able to provide better solution.

Study on Growth Mechanism of Self-Induced Sloshing, Using Numerical Simulation. 2nd Report. Oscillation Energy Transformation System.

A self-induced sloshing is excited by the flow itself without any other external force. In a rectangular tank having a horizontal plane jet, the 1st mode sloshing grew in a certain condition of the inlet velocity and the water level. The self-induced sloshing in the rectangular tank was simulated, using a two-dimensional numerical simulation code. The simulated results agreed qualitatively with the experimental ones. In this study, a growth mechanism of self-induced sloshing in the numerical simulation was evaluated. The interaction between the free surface motion and the unsteady flow was modeled simply. The oscillation energy (En) supplied for sloshing motion was calculated from the pressure and velocity distributions in the tank. The oscillation growth was related to the sign, magnitude and distribution of supplied oscillation energy (En). Therefore, the excitation of the simulated self-induced sloshing was quantitatively explained by the present mechanism. The self-induced sloshing was considered to be caused by the nonlinear interaction between the jet and the sloshing motion without inlet-outlet flow. It was clarified that the excitation of self-induced sloshing was dependent on the distribution of the oscillation energy along the jet.

132 PIVを用いた自励振動におけるジェットの可視化

The self-induced sloshing is an oscillation phenomen on, which is excited by flow itself. In order to evaluate a self-induced sloshing, the flow with free surface in a rectangular tank having a horizontal plane jet was observed experimen tally. Under two separate conditions with respect to inlet velocity U0, the self-induced sloshing was found to be excited. The jet was observed to be oscillating only when the sloshing motion was excited. In this study, the jet fluctuation was measured using PIV under two separately excited conditions. The obtained unsteady velocity and vorticity distrib utions showed that the self-induced sloshing had different mode pattern s of the jet fluctuation, which was similar to simulated results. In order to clarify the sloshing growth, the distribution of oscillation energy supplied to s loshing motion was calculated from velocity distributions obtained using PIV, based on a feedback mechanism. The experimental energy distributions was observed to have different patterns under the different sloshing modes. Consequently, the validity of feedback mechanism was supported exp erimentally. It was experimentally clarified that the specific phase of jet fluctuation played an important role to sloshing growth.

Excitation Mechanism of Self-Induced Sloshing Caused by Horizontal Plane Jet.

A self-induced sloshing is excited by flow without any other external force. In a rectangular tank having a horizontal plane jet, the 1 st or 2 nd mode sloshing grow in a certain condition of the inlet velocity and the water level. In this study, the experiment of this phenomenon was conducted and physical characteristics were examined in detail. The new sloshing conditions, i.e. "1st Stage Sloshing" and "2 nd Stage Sloshing", were discovered in a tank. The governing parameter of the sloshing growth, i.e. the modified Strouhal Number Sts, was derived approximately. When Sts was nearly either 1.0 (1 st Stage) or 2.0 (2 nd Stage), the sloshing excitation was arranged consistently. The dependency of the inlet velocity and tank geometry was revealed using Sty. A sloshing mode shift or a jet mode (stage) transition was evaluated to give rise to, with varying the inlet jet velocity. Consequently, a feedback mechanism was considered to be validated, which was closed by the jet fluctuation and the sloshing motion. The overall physical oscillation mechanism of the self induced sloshing was clarified.

131 自由液面の自励振動を伴う2次元噴流の画像計測

This paper describes the results of PIV measurement of two-dimensional plane jet flow with self-induced sloshing, which are obtained by means of the so-called spatiotemporal derivative method. The research group for PIV measurement in Visualization Society in Japan has suggested this experiment for evaluating the performance of the analysis method. The results show the typical unsteady flow field owing to self-induced sloshing. PIV is a powerful tool for this experiment.

B202 PIVによる矩形容器内の自励振動流れ場の解析

The self-induced sloshing in a rectangular tank had been investigated experimentally by using Particle Imaging Velocimetry (PIV) technique. The instantaneous flow fields, time average results and phase average results of the PIV measurement were used to reveal the evolution of the vortical structures in the test tank. Based on the experimental result, resonated oscillation was suggested to be the mechanism of the self-induced sloshing, and the fluctuation of the inlet plane jet and the periodically shedding of the unsteady vortical structures were conjectured to be the excitation source of the self-induced sloshing.

Self-Induced Sloshing Caused by Plunging Jet.

A self-induced oscillation of a free-surface caused by plunging jet was discovered. Plane water jet flowed into a thin rectangular tank horizontally and fell to the water in the tank. The jet plunged into the water and flowed out through the outlet at the bottom. At a certain water level and flow rate, the free surface began to oscillate and the sloshing motion of water in the tank was excited. The occurrence of the oscillation was dependent on the jet velocity at the plunging point. The oscillating frequency almost agreed with the natural frequency of the liquid in the tank. Oscillation mode shift was observed with varying the tank width. The mode shift occurred so that the sloshing frequency fell in a certain range. Under oscillating conditions, Strouhal number, which represents the ratio of the travelng time of jet disturbance from the plunging point to the outlet to sloshing period, was in the range of 0.2 to 0.5.

Study on Growth Mechanism of Self-Induced Sloshing, Using Numerical Simulation. 1st Report. Numerical Simulation of Self-Induced Sloshing Caused by Horizontal Plane Jet.

A self-induced sloshing is excited by the flow without any other external force. In a rectangular tank having a horizontal plane jet, the first-mode sloshing grew in a certain condition of the inlet jet velocity and the water level. In this study, the self-induced sloshing was simulated, using a two dimensional numerical simulation code. The code was based on the Boundary Fitted Coordinate (BFC) method with the height function. The results of the simulation agreed qualitatively with the experimental results, e. g. the sloshing occurrence condition. In order to investigate the growth mechanism of the self-induced sloshing, the fluctuation of the jet streak line was calculated using the simulated results. The dependency of the jet fluctuation on the self-induced sloshing was clarified qualitatively using the numerical simulation.

Fluid dynamics of a free surface in liquid metal fast breeder reactors

In the Liquid Metal Fast Breeder Reactor, the coolant sodium has free surfaces in the vessel. The interaction between the high speed flow and the free surfaces could induce self-induced surface oscillations and bubble entrainment. Recently, several self-induced free surface oscillations caused by water jet were discovered, e.g., a self-induced sloshing, “Jet-Flutter” “Swell-Flapping” and a self-induced manometer oscillation. These self-induced oscillations were excited by the non-linear interaction between free surface and flow. In this paper, the characteristics and mechanism of these self-induced oscillations were investigated.

Growth Mechanism of Self-Induced Sloshing Caused by Jet in Rectangular Tank. 2nd Report. Multimode Sloshing Caused by Horizontal Rectangular Jet.

A jet under a free surface can induce sloshing in a tank without an oscillating external force. In the previous study, the authors proposed a new growth model of self-induced sloshing caused by a vertical plane jet. The model was based on a feedback loop which simply simulated the interaction between the jet and the free surface. The dependence of sloshing on the tank geometry, water depth and inlet velocity was qualitatively evaluated. In this study, the model was applied to self-induced sloshing caused by a horizontal rectangular jet. Under a certain geometric condition of a rectangular tank, 1st and 2nd mode sloshings were observed The growth of multimode sloshing was qualitatively explained by the model. The self-induced sloshing was considered to be excited by a jet-surface interaction regardless of the incident jet angle to the surface.

Growth Mechanism of Self-Induced Sloshing Caused by Jet in Rectangular Tank. 1st Report. Self-Induced Sloshing Caused by Vertical Plane Jet.

A sloshing can be induced by a jet without any external oscillatory force. In a rectangular tank having a vertical plane jet, the first-mode sloshing was observed under a certain condition of the inlet jet velocity and the water depth, i. e., a sloshing condition. In this study, a growth mechanism of the self-induced sloshing caused by the vertical plane jet was theoretically evaluated. A new growth model was proposed, which was based on a feedback loop between the sloshing and the jet. When an oscillation energy supplied for the sloshing was positive, the sloshing was able to grow. The calculated sloshing condition agreed qualitatively with the experimental sloshing condition for different tank geometries. Therefore, the validity of the sloshing growth model was confirmed. The sloshing was found to be caused by the feedback loop constituted by the jet and the free surface.

Self-Induced Sloshing Caused by Upward Jet Impinging on Upper-Inner-Structure.

New self-induced free-surface oscillations were discovered, which were caused by the interaction between a jet, a free surface and a structure. An upward round jet was injected into a cylindrical tank filed with water. The jet impinged on a cylindrical rod (UIS) which was set just beneath the free surface of the tank. Under a certain condition of jet velocity and UIS depth, two self-induced free surface oscillations with their natural frequency were observed. One had no diametric node and two nodal circles, (0, 2), and the other had one node in each direction, (1, 1). (0, 2) mode sloshing was classified into two modes according to their flow patterns. In the (0, 2) mode with outward surface velocity, (0, 2)OUT the oscillating frequency depended on the jet velocity. In the (0, 2) mode with inward surface velocity, (0, 2)IN, the mechanism was thought to be similar to that of self-induced sloshing in the previous study. (1, 1) mode oscillation with swelling of the free surface, (1, 1)α, is found to be the same as "Jet Flutter" in a cylindrical tank without UIS.

118 流動励起自励スロッシングにおける噴流挙動の可視化

A self-induced sloshing caused by an upward plane jet was recently discovered in a rectangular test tank. The submerged jet entered the tank from an inlet at the bottom center and impinged vertically on a free surface. Under a certain water depth and inlet velocity condition, the first mode sloshing was observed. At the sloshing, the visualized jet streakline had a peculiar oscillatory behavior. Based on the observation, a relation-between the sloshing period and a time was noticed, which was required for the jet fluctuation to travel from the inlet to the surface. As a result, the sloshing was found to occur when the traveling time of the jet fluctuation was about discrete constant times as long as the sloshing period.

Self-Induced Sloshing Caused by Upward Plane Jet Impinging on Free Surface.

Self-Induced Sloshing Caused by Upward Plane Jet Impinging on Free Surface.

Senf-Induced Oscillation of Free Surface in a Tank with Circulating Flow. 3rd Report. Ideal Fluid Model.

A new model explaining the energy supply mechanism to self-induced sloshing in a tank with circulating flow is proposed. The oscillation energy is considered to be supplied by pressure fluctuations caused by the interaction between the circulating flow and the sloshing motion. When the direction of the under-water-surface stream of sloshing motion coincides with the steady circulation, the dynamic pressure increases and the ensuing static pressure reduction causes an imbalance between the fluid and the atmosphere. If the static pressure reduces more in the region where the free surface is descending, the work done by the imbalance supplies energy to the sloshing oscillation.