Free Surface Vortex Formation Research Articles

Formation of free-surface vortex and vortex suppression by rotating stopper-rod at end of tundish casting

Formation of free-surface vortex and vortex suppression by rotating stopper-rod at end of tundish casting

EFFECT OF SUMP GEOMETRY AND SUBMERGENCE DEPTH ON FREE SURFACE VORTEX FORMATION OF PUMP INFLOW

This paper examines and discusses pump sump design as it affects unsteady pump inflow. It is shown that an improvement of the unsteady inflow characteristics can be accomplished by introducing some modifications to the pump sump design. The paper introduces a 3D numerical computation of unsteady flow through a water sump into the intake of a large vertical pump. The numerical simulation is performed using ANSYS CFX. Numerical simulations performed use the shear stress transport model to account for the effect of turbulence. The results obtained were verified by comparison with published experimental data. The effect of the sump geometry and water level on the internal flow in pump sump is presented. Four sump geometries were studied: a rectangular sump, a sump with inclined edge at 30°, a sump with inclined edge at 45°, and a half-circle-ended sump. Also, three submergence levels were studied: S/D = 1.015, 0.771, and 0.54. It is concluded that sumps of rectangular geometry are the best to avoid surface and floor vortex formation.

An analytical model for vortex at vertical intakes

Abstract In the present paper, free surface vortex formation at intakes is investigated analytically. By assuming a spiral form for vortex streamlines, continuity and momentum equations were integrated and solved in a vortex flow domain. From this solution, velocity and pressure distributions were found above the intake under vortex action. An equation for the water surface profile was also found and compared with another research. By considering that in an air core vortex, pressure at the intake entrance drops to zero, a relationship was found for critical submerged depth and verified by experimental data and another analytical equation. It was concluded that the results of the proposed spiral analytical model had good agreement with the experimental data.

Free-surface vortex formation and aeration by a submerged rotating disk

We investigate the characteristics of free-surface vortex (FSV) formation and aeration processes in a self-ingested reactor. A disk with a protruded ridge rotating in a water tank is used as a simplified model. First, flow velocity fields on the FSV surface and the disk are obtained analytically using a semi-empirical method. From the bottom view of the impeller, we observe bubbles separated from two air pockets formed behind the ridge as the interface of the air pockets becomes fluctuated. Then, void fraction distribution along the vertical direction by rising bubbles is established theoretically and confirmed by experimental measurements. These results and the measured total void fraction data of the tank are used to show that the turbulence cascade energy near the disk is converted into the surface tension energy of bubbles and is responsible for aeration.

Numerical Simulation of an Air-Core Vortex and Its Suppression at an Intake Using OpenFOAM

A common challenge faced by engineers in the hydraulic industry is the formation of free surface vortices at pump and power intakes. This undesirable phenomenon which sometimes entrains air could result in several operational problems: noise, vibration, cavitation, surging, structural damage to turbines and pumps, energy losses, efficiency losses, etc. This paper investigates the numerical simulation of an experimentally observed air-core vortex at an intake using the LTSInterFoam solver in OpenFOAM. The solver uses local time-stepping integration. In simulating the air-core vortex, the standard k − ε, realizable k − ε, renormalization group (RNG) k − ε and the shear stress transport (SST) k − ω models were used. The free surface was modelled using the volume of fluid (VOF) model. The simulation was validated using a set of analytical models and experimental data. The SST k − ω model provided the best results compared to the other turbulence models. The study was extended to simulate the effect of installing an anti-vortex device on the formation of a free surface vortex. The LTSInterFoam solver proved to be a reliable solver for the steady state simulation of a free surface vortex in OpenFOAM.

Elimination of vortices by wave generation as a hydraulic anti-vortex method

Free-surface vortex formation is one of the undesirable hydraulic phenomena that may occur at intakes during the dewatering reservoir. This research is meant to investigate the effect of waves on formed vortices in vertical intakes numerically by applying STAR-CCM + software. The simulation was conducted to model the free surface and turbulence by volume of fluid and large eddy simulation methods, respectively. Sensitivity analysis was undertaken on different mesh sizes to select appropriate mesh dimensions. Then, verification was performed by Sun and Liu (J Hydraul Res 53:787–796, 2015) experimental data. Results showed that waves reduce or eliminate hydraulic parameters of the formed vortices such as vortex strength, tangential, radial, and axial velocity components. The reduction appeared by average values of 32%, 30%, 22%, and 25% in vortex strength, tangential, radial, and axial velocity components, respectively. Waves also led to decrement in the length and diameter of air-core of vortices about 45% for the former and more than 50% for the latter. In addition, it was concluded that the smaller the waves, the greater their effects would appear on the elimination of the vortex phenomenon. Finally, a relationship between the wave properties, as a hydraulic approach to anti-vortex, and vortex parameters was developed.

Physical and Mathematical Simulation of Surface‐Free Vortex Formation and Vortex Prevention Design during the End of Casting in Tundish

Herein, the formation of the vortex and slag entrainment in tundish is studied by using mathematical and physical simulation. This article aims at contributing to the understanding of the free surface vortex formation in continuous casting tundish at the end of casting. A 3D multiphase mathematical model using the renormalization group (RNG) k–ε turbulence model is developed to predict the vortex formation and slag layer behavior on the scale of the 1:4 water model of a two‐strand slab tundish. The Eulerian volume of fluid model is adopted to track the steel–slag–air free surface and vortex, and the effect of Coriolis force is considered in this simulation. An improved vortex prevention design is also proposed by changing the position of the diversion hole on the dam of the tundish, which is compared with the original scheme using numerical and physical simulation. The predicted results of the vortex structure and the critical height of the vortex formation agree well with the water modeling results. It is demonstrated that the critical height of the vortex formation is reduced significantly by regulating the position of the diversion hole on the dam near the outlet of the tundish.

Numerical analysis of free surface vortices behavior in a pump sump

Recently, designers and engineers of pump stations realized that the efficiency and performance of a pumping station does not depend only on the performance of selected pumps but also on proper design of intake sumps. Most recurring problems faced in a pumping station are related to the sump design or intake design rather than pump design. Swirl angle parameter and free surface vortex formation are important parameters that determine the quality of flow ingested by sump. For swirl angle parameter, the hydraulic institute prescribes the method that needs to be employed for estimating this parameter. On the other hand, the free surface vortex formation also leads to a decrease in the efficiency of pump intake and pump especially when the vortex rope rotates opposite to impeller rotation. In this study, both numerical and experimental analysis of a rectangular pump sump was carried out to predict swirl angle and free surface vortices formation. The swirl angle experimentally was obtained using a traditional swirl meter installed at the suction pipe in rectangular single pump intake. The objective was to obtain the average tangential velocity at different suction pipe diameter. For free surface vortices the objective was to observe the different vortex formation, air entrance and location. The swirl angle and average tangential velocity estimated by CFD simulation was in agreement with experimental results. The four types of free surface vortices (Surface swirl, Surface dimple, air bubbles and full air core to intake) was also observed clearly in ANSYS CFX.

Vortex Dissipation Using a Hydraulic-Based Anti-Vortex Device at Intakes

In the present research, dissipating free surface vortices over the intakes by designing a hydraulic anti-vortex method is studied experimentally. In this method, an up-stream submerged water jet is used as a hydraulic-based anti-vortex mechanism. The imposed jet acts as a point source of external momentum to the formed free surface area. The added momentum changes the hydrodynamic balance of the vortex zone, and leads to instability and disability of the vortex to form and develop. Experiments were conducted on a projected horizontal pipe intake to investigate the efficiency of the proposed anti-vortex hydraulic device on dissipating and preventing formation of free surface vortices. Results show that the efficiency of the imposed jet is dependent on the jet linear momentum and vertical distance between the nozzle and intake positions. Moreover, the critical submergence of the intake can potentially reduce up to the nozzle submergence in which less than 10% of the jet momentum is required by decreasing nozzle submergence about 50%. Finally, an empirical equation is suggested to predict the critical submergence of the intake with respect to the jet linear momentum and the nozzle submergence.

New idea of suppressing free surface vortex during tapping liquid steel from converter

During tapping liquid steel from a converter to a ladle, slag may carry over due to a formation of free surface vortex. Such vortex should be suppressed in order to minimize contamination of the steel by slag. In the present study, a new idea is proposed to minimize the vortex formation by applying dual tapping hole system. The idea was tested using a rectangular shape water vessel with dual tapping holes, supplemented by a numerical simulations, in order to evaluate feasibility of the dual tapping hole system. Both the water model experiment and the numerical simulation showed similar tendencies that the dual tapping hole system is promising to prevent the vortex formation. Experimental results showed that the free surface vortex formation is highly sensitive to shape and configuration of the nozzle. From the numerical simulation, flow characteristics were obtained, and vortex canceling between two nozzles is confirmed. Effect of dual tapping hole increased with increasing distance between two holes in the present experimental condition. Finally, a 1/7.8 scale-down water vessel simulating a real converter was employed in order to confirm the validity of the above findings. The result showed almost the same tendencies with the previous findings.

Analysis of Factors Affecting Free Surface Vortex Formation during Steel Teeming

Analysis of Factors Affecting Free Surface Vortex Formation during Steel Teeming

Mechanism Analysis of Free-Surface Vortex Formation during Steel Teeming

To develop an effective technology to prevent vortex forming in ladles, the mechanism underlying vortex formation during steel teeming must be studied. For simulations using the numerical simulation software Fluent, a geometric model of the ladle was generated, and initially water teeming in the ladle was simulated for different initial tangential velocities. The results obtained help to verify the validity of the numerical computations. Similar simulation conducted for steel showed that the tangential velocity increases from the liquid level to the bottom of the ladle, and the flow at the bottom is related to vortex formation. The inference is that vortex formation begins from the ladle bottom. Causes for vortex formation during teeming are discussed to help lay a theoretical basis for ladle design in preventing vortex formation during steel teeming.

A study on the two-phase flow in a stirred tank reactor agitated by a gas-inducing turbine

Experimental and numerical studies of a gas–liquid two-phase flow have been applied to a non-baffled laboratory-scale stirred tank reactor, mechanically agitated by a gas-inducing turbine. The dispersion of air as gas phase into isopropanol as liquid phase at room temperature under different stirrer speeds was investigated. The X-ray cone beam computed tomography (CBCT) measurements have been taken at five different stirrer speeds starting from 1000 rpm at which the gas inducement occurs for the given operating conditions. The considerable difficulties in acquiring the phase distribution due to beam hardening and radiation scattering effects have been overcome by developing a suitable measurement setup as well as by calibration and software correction methods to achieve high accuracy. The computational fluid dynamics analyses of the stirred tank reactor have been performed in 3D with CFX 10.0 numerical software. The simplified numerical setup of mono-dispersed bubbles, constant drag coefficient and the k– ɛ turbulence model was able to capture both the bubble induction and dispersion and the free surface vortex formation. Despite the assumed simplifications, the numerical predictions exhibit a good agreement with the experimental data.

Discussion of “Similitude in Free-Surface Vortex Formation”

Discussion of “Similitude in Free-Surface Vortex Formation”