Improvement and validation of a flow model for conical vortices

Jihong Ye,Xin Dong 한국풍공학회 2014 Wind and Structures, An International Journal (WAS Vol.19 No.2

Separation bubble and conical vortices on a large-span flat roof were observed in this study through the use of flow visualization. The results indicated that separation bubble occurred when the flow was normal to the leading edge of the flat roof. Conical vortices that occur under the cornering flow were observed near the leading edge, and their appearance was influenced by the wind angle. When the wind changed from along the diagonal to deviating from the diagonal of the roof, the conical vortex close to the approaching flow changed from circular to be more oblong shaped. Based on the measured velocities in the conical vortices by flow visualization, a proposed two-dimensional vortex model was improved and validated by simplifying the velocity profile between the vortex and the potential flow region. Through measured velocities and parameters of vortices, the intensities of conical vortices and separation bubble on a large-span flat roof under different wind directions were provided. The quasi-steady theory was corrected by including the effect of vortices. With this improved two-dimensional vortex model and the correctedquasi-steady theory, the mean and peak suction beneath the cores of the conical vortices and separation bubble can be predicted, and these were verified by measured pressures on a larger-scale model of the flat roof.

Improvement and validation of a flow model for conical vortices

Ye, Jihong,Dong, Xin Techno-Press 2014 Wind and Structures, An International Journal (WAS Vol.19 No.2

Separation bubble and conical vortices on a large-span flat roof were observed in this study through the use of flow visualization. The results indicated that separation bubble occurred when the flow was normal to the leading edge of the flat roof. Conical vortices that occur under the cornering flow were observed near the leading edge, and their appearance was influenced by the wind angle. When the wind changed from along the diagonal to deviating from the diagonal of the roof, the conical vortex close to the approaching flow changed from circular to be more oblong shaped. Based on the measured velocities in the conical vortices by flow visualization, a proposed two-dimensional vortex model was improved and validated by simplifying the velocity profile between the vortex and the potential flow region. Through measured velocities and parameters of vortices, the intensities of conical vortices and separation bubble on a large-span flat roof under different wind directions were provided. The quasi-steady theory was corrected by including the effect of vortices. With this improved two-dimensional vortex model and the corrected quasi-steady theory, the mean and peak suction beneath the cores of the conical vortices and separation bubble can be predicted, and these were verified by measured pressures on a larger-scale model of the flat roof.

Axisymmetric Swirling Flow Simulation of the Draft Tube Vortex in Francis Turbines at Partial Discharge

Susan-Resiga, Romeo,Muntean, Sebastian,Stein, Peter,Avellan, Francois Korean Society for Fluid machinery 2009 International journal of fluid machinery and syste Vol.2 No.4

The flow in the draft tube cone of Francis turbines operated at partial discharge is a complex hydrodynamic phenomenon where an incoming steady axisymmetric swirling flow evolves into a three-dimensional unsteady flow field with precessing helical vortex (also called vortex rope) and associated pressure fluctuations. The paper addresses the following fundamental question: is it possible to compute the circumferentially averaged flow field induced by the precessing vortex rope by using an axisymmetric turbulent swirling flow model? In other words, instead of averaging the measured or computed 3D velocity and pressure fields we would like to solve directly the circumferentially averaged governing equations. As a result, one could use a 2D axi-symmetric model instead of the full 3D flow simulation, with huge savings in both computing time and resources. In order to answer this question we first compute the axisymmetric turbulent swirling flow using available solvers by introducing a stagnant region model (SRM), essentially enforcing a unidirectional circumferentially averaged meridian flow as suggested by the experimental data. Numerical results obtained with both models are compared against measured axial and circumferential velocity profiles, as well as for the vortex rope location. Although the circumferentially averaged flow field cannot capture the unsteadiness of the 3D flow, it can be reliably used for further stability analysis, as well as for assessing and optimizing various techniques to stabilize the swirling flow. In particular, the methodology presented and validated in this paper is particularly useful in optimizing the blade design in order to reduce the stagnant region extent, thus mitigating the vortex rope and expending the operating range for Francis turbines.

Numerical analysis study on the application of three-lobed vortex tube in low-production wells

Ruyi Gou,Chenchen Kang,Xun Luo 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.6

In order to solve the problem of fluid accumulation in horizontal gas wells and improve the fluid-carrying capacity and recovery efficiency of gas wells, this paper simulates three internal vortex tools using the commercial software ANSYS FLUENT, and analyzes the drainage recovery efficiency of the three vortex structures and the vortex characteristics of the downstream section vortex field. The results show that the axial velocity of the three-bladed spiral tube in the cyclonic field rotates quasi-periodically with the flow field compared with the internal vortex tube and the rifled tube, and the axial velocity, tangential velocity and vortex intensity of the three-bladed vortex tube guided flow field are the highest; meanwhile, the axial velocity, tangential velocity and vortex intensity of the three-bladed spiral tube guided flow field decay the fastest, and the line rifled tube decays the slowest. The liquid phase in the cyclonic field exhibits obvious spiral motion and maintains a long-distance cyclonic flow state under the action of cyclonic flow. The enhancement of the vortex intensity easily leads to the increase of liquid volume fraction and liquid film thickness at the tube wall. Through the analysis of the energy efficiency of the three structures, it is found that the three-leaf spiral tube is more suitable for the initial phase of drainage transport, while the internal vortex tube is more favorable for the stable phase of transport. The study of the gas-liquid swirl flow of the three swirl tools demonstrated the feasibility of the internal swirl tool for application in horizontal wells. It can provide theoretical guidance and practical basis for effective liquid filling with internal vortex tools in the future.

Numerical Analysis of the Three-Dimensional Wake Flow and Acoustic Field around a Circular Cylinder

Tae-Su Kim,Jae-Soo Kim 한국항공우주학회 2010 International Journal of Aeronautical and Space Sc Vol.11 No.4

For decades, researchers have rigorously studied the characteristics of flow traveling around blunt objects in order to gain greater understanding of the flow around aircraft, vehicles or vessels. Many different types of flow exist, such as boundary layer flow, flow separation, laminar and turbulent flow, vortex and vortex shedding; such types are especially observed around circular cylinders. Vortex shedding around a circular cylinder exhibits a two-dimensional flow structure possessing a Reynolds number within the range of 47 and 180. As the Reynolds number increases, the Karman vortex changes into a three-dimensional flow structure. In this paper, a numerical analysis was performed examining the flow and aero-acoustic field characteristics around a circular cylinder using an optimized high-order compact scheme, which is a high order scheme. The analysis was conducted with a Reynolds number ranging between 300 and 1,000, which belongs to B-mode flow around a circular cylinder. For a B-mode Reynolds number, a proper spanwise length is analyzed in order to obtain the characteristics of three-dimensional flow. The numerical results of the Strouhal number as well as the lift and drag coefficients according to Reynolds numbers are coincident with the other experimental results. Basic research has been conducted studying the effects an unstable three-dimensional wake flow on an aero-acoustic field.

Numerical Analysis of the Three-Dimensional Wake Flow and Acoustic Field around a Circular Cylinder

Kim, Tae-Su,Kim, Jae-Soo The Korean Society for Aeronautical and Space Scie 2010 International Journal of Aeronautical and Space Sc Vol.11 No.4

For decades, researchers have rigorously studied the characteristics of flow traveling around blunt objects in order to gain greater understanding of the flow around aircraft, vehicles or vessels. Many different types of flow exist, such as boundary layer flow, flow separation, laminar and turbulent flow, vortex and vortex shedding; such types are especially observed around circular cylinders. Vortex shedding around a circular cylinder exhibits a two-dimensional flow structure possessing a Reynolds number within the range of 47 and 180. As the Reynolds number increases, the Karman vortex changes into a three-dimensional flow structure. In this paper, a numerical analysis was performed examining the flow and aero-acoustic field characteristics around a circular cylinder using an optimized high-order compact scheme, which is a high order scheme. The analysis was conducted with a Reynolds number ranging between 300 and 1,000, which belongs to B-mode flow around a circular cylinder. For a B-mode Reynolds number, a proper spanwise length is analyzed in order to obtain the characteristics of three-dimensional flow. The numerical results of the Strouhal number as well as the lift and drag coefficients according to Reynolds numbers are coincident with the other experimental results. Basic research has been conducted studying the effects an unstable three-dimensional wake flow on an aero-acoustic field.

Vortex generation by viscoelastic sheath flow in flow-focusing microchannel

김동영,김주민 한국화학공학회 2019 Korean Journal of Chemical Engineering Vol.36 No.6

Microfluidics-based technologies have attracted much attention since the fluid flow can be controlled precisely and only small sample volumes are required. Viscoelastic non-Newtonian fluids such as polymer solution and biofluids are frequently used in microfluidic analyses, and it is essential to understand the small-scale flow dynamics of such viscoelastic fluids. In this work, we report on vortex generation at the junction region of a flow-focusing microchannel, where a central flow stream of a Newtonian fluid meets two sheath flows of a non-Newtonian poly (ethylene oxide) aqueous solution. We elucidated the vortex-generation mechanism by the backward-flow component induced by the first normal stress difference in the viscoelastic sheath fluid. We systematically investigated the effects of polymer concentration, total flow rate, and total to central-stream flow-rate ratio, on the vortex generation. In addition, we demonstrated that this phenomenon can be engineered to enhance the mixing in the flow-focusing microchannel. We expect this work to be helpful for the understanding of viscoelastic flow dynamics in microscale flows and also for the development of microfluidic mixers.

Flow uniformity in a multi-intake pump sump model

최종웅,최영도,김창구,이영호 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.7

The head-capacity curves for pumps developed by the pump manufacturer are based on tests of a single pump operation in a semiinfinite basin with no close walls or floors and with no stray currents. Therefore, flow into the pump intake is with no vortices or swirling. However, pump station designers relying on these curves to define the operating conditions for the pump selected sometimes experience reductions of capacity and efficiency, as well as the increase of vibration and additional noise, which are caused by free air mixed with the pump inlet flow. Therefore, sump model test is necessary in order to examine the flow structure around pump intake. In this study,flow uniformity according to the flow distribution in the pump intake channel is examined to find out the cause of vortex occurrence in detail. A multi-intake pump sump model with 7 pump intakes and a single-intake pump sump model are adopted for the investigation. Furthermore, effectiveness of anti-submerged vortex device (AVD) for the suppression of the vortex occurrence in a single pump intake,as well as in a multi-intake pump sump model has been examined by the methods of experiment and numerical analysis. The results show that most high value of flow uniformity is found at the inlet of pump intakes #3 and 5 in the multi-intake pump sump with 7 pump intakes. Therefore, when the pump station is designed, the flow patterns at the upstream region of pump intake inlet in the forebay diffusing area should be to consider in detail because the unbalanced flow at the channel inlet region gives considerable influence on the vortex occurrence around bell-mouth. Strong submerged vortex can be successfully suppressed by AVD installation on the bottom of pump intake channel just below the bell mouth.

Coupling Effect Diagnoses of Quasi-Stationary Mesoscale Vortex in Guangxi Rainstorm Process of China

Jingjing Ge,Hancheng Lu,Wei Zhong 한국기상학회 2011 Asia-Pacific Journal of Atmospheric Sciences Vol.47 No.1

The mesoscale weather system which affected the Guangxi flash-flood-producing rainstorm of China in June 2008 is a quasistationary mesoscale vortex. Its genesis and development is closely related to the coupling effects of weather systems in different scales and different latitudes. On the one hand, the coupling of synoptic scale high- and low-level jets provides the environmental conditions for development of vortices and vertical circulations in the mesoscale vortex; On the other hand, the coupling of waves in mid-latitude westerlies and perturbations in low-latitude warm-moist flow under the influence of complex terrain makes the mesoscale vortex circulations strengthened. With the piecewise potential vorticity (PV) inversion method, PV anomalies in different regions are analyzed; also the vortex-vortex interactions and vortex-background flow interactions are diagnosed. Thus, the reasons why the mesoscale is quasi-stationary at first, while developing and deepening later are indicated. Under the condition of coupling effects, the vertical motions accompanied with the mesoscale vortex can be diagnosed with the PV-ω inversion system based on the analysis of quasi-balanced flow.

동축 실린더 내부 회전 유동 특성 해석

이승수,손현아 한국풍공학회 2013 한국풍공학회지 Vol.17 No.2

입자상 물질이 혼합된 유동장을 이용한 공학적 응용 분야에 있어서 미세먼지이나 침전물 분리 과정을 거친 청정 유동장의 생성은 중요한 핵심 요소 기술로서 친환경 에너지 활용이나 자원 활용에 다양하게 활용된다. 일반적으로 이용되는 화학적 처리나 막(Membrane) 분리와 같은 공정이 야기하는 유지 관리의 문제로 Vortex Separator를 이용한 방법이 이용되는 추세로서 유지 보수의 측면에서 매우 큰 장점을 갖는다. 이러한 Vortex Separator 적용에 있어서 가장 큰 문제점의 하나는 Taylor-Couette 유동으로 알려진 환형 와류의 형성에 의한 분리 효율 저하로 알려져 있다. 본연구에서는 Vortex Separator 내부 유동과 같이 밀폐된 영역 내에서 발생하는 회전 유동에 대한 유한 체적법 기반의 전산 유체 해석 기술의 적용을 통해 입자상 물질과 유체의 분리 특성에 대한 기술적 접근 방법을 도출하기 위하여, 동일한 축을 갖는 두 개의 실린더 사이의 회전 유동을 해석하고 기존의 연구 결과와 비교를 통하여 검증하였다. 유한체적법 기반의 3차원 점성 유동장의 비정상 해석을 수행하였으며 해석 결과를 이전의 선행 연구와 비교를 통하여 검증하였다. 본 연구의 결과로 고전적인 Taylor-Couette 유동을 재현함으로써 전산 유체 해석 기법을 이용한 Vortex Separator 내부의 회전 유동 해석이 가능함을 제시하였다. Separation of clean fluid out of granular flow including particulate or sediment is an essential process in the engineering for eco-friendly energy or resource. General process for the separation utilizes chemical treatments or membrane filtering, both of which always suffer from maintenance. As alternatives, mechanical processes such as vortex separator are recently applied since they require less attention during the operation. One of the primary concerns on the vortex separator is the possibility of development of vortex rings which are known as Taylor-Couette flow and will hinder the efficient separation of the particulate. This study was carried out to assess the computational technology based on finite-volume method to analyze the rotational flow, a fundamental flow regime in vortex separator technology. To achieve this goal, the rotational flow between co-axial cylinders was computationally analyzed, which successfully reproduced Taylor-Couette flow. The present approach was validated by comparison with the results of previous studies and shows the possibility of application to the rotating flow system such as vortex separator.