An Investigation of Heat Transfer Characteristics of Swirling Flow in a 180$^{\circ}$ Circular Section Bend with Uniform Heat Flux

Chang, Tae-Hyun The Korean Society of Mechanical Engineers 2003 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.17 No.10

An experiment was performed to obtain the local heat transfer coefficient and Nusselt number in a circular duct with a 180$^{\circ}$ bend for Re=6 x 10$^4$, 8 x 10$^4$ and 1 x 10$\^$5/ under swirling flow and non-swirling flow conditions. The test tube with a circular section was made from stainless steel having a curvature ration of 9.4. Current heat flux of 5.11 kW/㎡ was applied to the test tube by electrical power and the swirling motion of air was produced by a tangential inlet to the pipe axis at 180$^{\circ}$. Measurements of local wall temperatures and the bulk mean temperatures of air were made at four circumferential positions at 16 stations. The wall temperatures showed a reduced distribution curve at the bend for the non-swirling flow, but this effect did not appear for the swirling flow. The Nusselt number distributions for the swirling flow, which was calculated from the measured wall and the bulk temperatures, were higher than that of the non-swirling flow. The average Nusselt number of the swirling flow increased by about 90-100%, compared to that of the non-swirling flow. The Nu/Nu$\_$DB/ values at the 90$^{\circ}$ station for non-swirling flow and swirling flow were approximately 2.5 and 4.8 at Re=6x10$^4$ respectively. The values agree well with Said's results for non-swirling flow.

Experimental study of bubbly swirling flow in a vertical tube using ultrasonic velocity profiler (UVP) and wire mesh sensor (WMS)

Ari Hamdani,Tomonori Ihara,Nobuyoshi Tsuzuki,Hiroshige Kikura 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.9

Two-phase air-water bubbly swirling flow through a pipe is a complex turbulent flow and its prediction is still challenging. The present paper describes the experimental investigation of the air-water bubbly swirling flow in vertical co-current flow. Swirling flow is induced by a twisted tape in a 20 mm inner diameter pipe. The flow is investigated using Ultrasonic velocity profiler (UVP), which allows the measurement of liquid and gas velocities simultaneously. Furthermore, simultaneous measurement of void fraction is performed using Wire mesh sensor (WMS). The experimental results reveal that swirling flow has significant impact on bubbles’ distribution. In low liquid flow rate, the average bubble velocity is fairly uniform along the radial position and void fraction increases in the near wall region. However, increasing liquid flow rate at constant gas flow rate leads to increase in void fraction in the core region, this is mainly due to drift velocity which is affected by centrifugal force. Experimental findings and parametric trends based on the effects of swirling flow are summarized and discussed.

Effect of swirling blood flow on vortex formation at post-stenosis

Ha, Hojin,Choi, Woorak,Park, Hanwook,Lee, Sang Joon Professional Engineering Publishing Ltd. 2015 Proceedings of the Institution of Mechanical Engin Vol. No.

<P>Various clinical observations reported that swirling blood flow is a normal physiological flow pattern in various vasculatures. The swirling flow has beneficial effects on blood circulation through the blood vessels. It enhances oxygen transfer and reduces low-density lipoprotein concentration in the blood vessel by enhancing cross-plane mixing of the blood. However, the fluid-dynamic roles of the swirling flow are not yet fully understood. In this study, inhibition of material deposition at the post-stenosis region by the swirling flow was observed. To reveal the underlying fluid-dynamic characteristics, pathline flow visualization and time-resolved particle image velocimetry measurements were conducted. Results showed that the swirling inlet flow increased the development of vortices at near wall region of the post-stenosis, which can suppress further development of stenosis by enhancing transport and mixing of the blood flow. The fluid-dynamic characteristics obtained in this study would be useful for improving hemodynamic characteristics of vascular grafts and stents in which the stenosis frequently occurred. Moreover, the time-resolved particle image velocimetry measurement technique and vortex identification method employed in this study would be useful for investigating the fluid-dynamic effects of the swirling flow on various vascular environments.</P>

THE INFLUENCES OF SWIRL FLOW ON FRACTIONAL FLOW RESERVE IN MILD/MODERATE/SEVERE STENOTIC CORONARY ARTERIAL MODELS

이경은,김국태,류아진,심은보 한국전산유체공학회 2017 한국전산유체공학회지 Vol.22 No.1

Swirl flow is often found in proximal coronary arteries, because the aortic valves can induce swirl flows in the coronary artery due to vortex formation. In addition, the curvature and tortuosity of arterial configurations can also produce swirl flows. The present study was performed to investigate fractional flow reserve alterations in a post-stenotic distal part due to the presence of pre-stenotic swirl flow by computational fluid dynamics analysis for virtual stenotic models by quantifying fractional flow reserve(FFR). Simplified stenotic coronary models were divided into those with and without pre-stenotic swirl flow. Various degrees of virtual stenosis were grouped into three grades: mild, moderate, and severe, with degree of stenosis of 0 ~ 40%, 50 ~ 60%, and 70 ~ 90%, respectively. In this study, three-dimensional computational hemodynamic simulations were performed under hyperemic conditions in virtual stenotic coronary models by coupling with a zero-dimensional lumped parameter model. The results showed that the influence of pre-stenotic swirl inflow is dominant on FFR alteration in mild stenosis, whereas stenosis is dominant on FFR alteration in moderate/severe stenosis. The decrease in FFR caused by swirl flow is more significant in mild stenosis than moderate/severe stenosis. Biomechanical modeling is useful for clinicians to provide insight for medical intervention strategies. This hemodynamic-based parameter study could play a critical role in the development of a non-invasive imaging-based strategy-support system for percutaneous transluminal angioplasty in cases of mild/moderate stenosis.

Suppression of flow instability in the Francis hydro turbine draft tube by J-groove shape optimization at a partial flow rate

Ujjwal Shrestha,최영도 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.6

Flow instability and pressure fluctuation are common problems in hydro turbines, especially in partial flow conditions. When Francis hydro turbine operates at partial flow rate, swirl flow occurs at the runner outlet, which is the cause of pressure pulsations, vortex core, noise and vibration in the draft tube. Among various methods, J-groove was selected and mounted in the draft tube to suppress the swirl flow. The study focuses on the Jgroove incorporation in a draft tube from the design process to optimization. The optimization focused on the suppression of swirl flow with minimum efficiency drop. The turbine efficiency and swirl number were selected for the optimization, which encounters global and local effects of J-groove installation on the Francis hydro turbine. J-groove shape optimization was performed by response surface methodology (RSM) and multi-objective genetic algorithm (MOGA). The flow behavior in the draft tube was compared without and with the initial and optimal J-groove shapes. The optimal J-groove shape is more effective in swirl flow suppression than the initial J-groove shape. Additionally, the installation of the J-groove did not hinder turbine performance. Therefore, the optimal J-groove shape improved flow behavior in the draft tube at the partial flow rate.

THE INFLUENCES OF SWIRL FLOW ON FRACTIONAL FLOW RESERVE IN MILD/MODERATE/SEVERE STENOTIC CORONARY ARTERIAL MODELS

Kyung Eun Lee(이경은),Gook Tae Kim(김국태),Ah-Jin Ryu(류아진),Eun Bo Shim(심은보) 한국전산유체공학회 2017 한국전산유체공학회지 Vol.22 No.1

Swirl flow is often found in proximal coronary arteries, because the aortic valves can induce swirl flows in the coronary artery due to vortex formation. In addition, the curvature and tortuosity of arterial configurations can also produce swirl flows. The present study was performed to investigate fractional flow reserve alterations in a post-stenotic distal part due to the presence of pre-stenotic swirl flow by computational fluid dynamics analysis for virtual stenotic models by quantifying fractional flow reserve(FFR). Simplified stenotic coronary models were divided into those with and without pre-stenotic swirl flow. Various degrees of virtual stenosis were grouped into three grades: mild, moderate, and severe, with degree of stenosis of 0 ~ 40%, 50 ~ 60%, and 70 ~ 90%, respectively. In this study, three-dimensional computational hemodynamic simulations were performed under hyperemic conditions in virtual stenotic coronary models by coupling with a zero-dimensional lumped parameter model. The results showed that the influence of pre-stenotic swirl inflow is dominant on FFR alteration in mild stenosis, whereas stenosis is dominant on FFR alteration in moderate/severe stenosis. The decrease in FFR caused by swirl flow is more significant in mild stenosis than moderate/severe stenosis. Biomechanical modeling is useful for clinicians to provide insight for medical intervention strategies. This hemodynamic-based parameter study could play a critical role in the development of a non-invasive imaging-based strategy-support system for percutaneous transluminal angioplasty in cases of mild/moderate stenosis.

압축성 스월유동에 관한 이론적 및 수치 해석적 연구

이재혁(Jaehyeok Lee),조양명(Yangmyeong Jo),Fanshi Kong,김희동(Heuydong Kim) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11

Although compressible swirling flows are often encountered in many diverse engineering applications, the related flow physics is seldom known. Thus, almost all of fluid machinery with the swirling flow are so far designed neglecting the compressibility effects that can lead to mal-operation or performance deterioration of the device. In the present study, theoretical and computational analyses have been carried out to investigate the planar, isentropic, axisymmetric compressible swirling flow. A series of governing equations have derived to disclose the compressibility effects in the swirling flow. The present theoretical results show the choking phenomena which are discussed in terms with the swirl angle and pressure ratio. A computational work has been performed to reveal the complicated flow involved in the compressible swirl flow. It is expected that the present results would be very helpful in designing the flow devices operated at high pressure ratios.

Numerical analysis of multi-parallelized swirling flow inside a circular pipe

Akimasa Takayama,Koki Kitagawa,Toru Shimada 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.3

The flow field of multi-parallelized swirling flow inside a circular pipe was investigated numerically. Two types of swirling flow configurationare considered. One type is the co-rotating type. Four co-rotating swirls are arranged at the vertex position of square in thistype. The other type is the counter-rotating type which consists of two pairs of swirls having opposite swirl rotations. Each pair is arrangeddiagonally at the vertex position of a square. By coupling the discrete vortex method and boundary element method, unsteadyflow simulation is performed. Swirl modeling with vortex elements is used in this simulation and its validity is confirmed. From thesimulation results, in the co-rotating type, the four swirls interact and their shape is deformed. Each vortex motion vanishes rapidly in thedownstream region. Finally, they are turned into a single swirling flow. In counter-rotating type, each vortex motion is maintained a littlebit longer than co-rotating type, and their shape is not so deformed. However, the flow patterns are changed completely in the downstreamregion. The swirling velocity of each swirl mostly vanishes. Finally, they are turned into an axial flow. For the investigation of themixing promoting effect due to parallelizing swirls, particle tracking simulations are performed in the co-rotating type and the counterrotatingtype. As a comparison, the simulation for single swirl flow is also performed. In these simulations, the particles are introduced inthe vicinity of pipe inner wall. In addition, the assumption that particles follow the flow motion absolutely is used. From the results, themotion of particles in these three cases is completely different. For the co-rotating and counter-rotating type, the particle entrainment intothe main axial flow is clearly observed. This indicates the mixing is improved compared to single swirl flow. The difference of particleentrainment motion between co-rotating and counter-rotating type is slight.

Fluid Dynamic Efficiency of an Anatomically Correct Total Cavopulmonary Connection: Flow Visualizations and Computational Fluid Dynamic Studies

Yun, S.H.,Kim, S.Y.,Kim, Y.H. Biomedical Engineering Society for Circulation 2003 International Journal of Vascular Biomedical Engin Vol.1 No.2

Both flow visualizations and computational fluid dynamics were performed to determine hemodynamics in a total cavopulmonary connection (TCPC) model for surgically correcting congenital heart defects. From magnetic resonance images, an anatomically correct glass model was fabricated to visualize steady flow. The total flow rates were 4, 6 and 8L/min and flow rates from SVC and IVC were 40:60. The flow split ratio between LPA and RPA was varied by 70:30, 60:40 and 50:50. A pressure-based finite-volume software was used to solve steady flow dynamics in TCPC models. Results showed that superior vena cava(SVC) and inferior vena cava(IVC) flow merged directly to the intra-atrial conduit, creating two large vortices. Significant swirl motions were observed in the intra-atrial conduit and pulmonary arteries. Flow collision or swirling flow resulted in energy loss in TCPC models. In addition, a large intra-atrial channel or a sharp bend in TCPC geometries could influence on energy losses. Energy conservation was efficient when flow rates in pulmonary branches were balanced. In order to increase energy efficiency in Fontan operations, it is necessary to remove a flow collision in the intra-atrial channel and a sharp bend in the pulmonary bifurcation.

Fluid Dynamic Efficiency of an Anatomically Correct Total Cavopulmonary Connection: Flow Visualizations and Computational Fluid Dynamic Studies

Yun, S.H.,Kim, S.Y.,Kim, Y.H. Biomedical Engineering Society for Circulation 2004 International Journal of Vascular Biomedical Engin Vol.2 No.1

Both flow visualizations and computational fluid dynamics were performed to determine hemodynamics in a total cavopulmonary connection (TCPC) model for surgically correcting congenital heart defects. From magnetic resonance images, an anatomically correct glass model was fabricated to visualize steady flow. The total flow rates were 4, 6 and 8L/min and flow rates from SVC and IVC were 40:60. The flow split ratio between LPA and RPA was varied by 70:30, 60:40 and 50:50. A pressure-based finite-volume software was used to solve steady flow dynamics in TCPC models. Results showed that superior vena cava(SVC) and inferior vena cava(IVC) flow merged directly to the intra-atrial conduit, creating two large vortices. Significant swirl motions were observed in the intra-atrial conduit and pulmonary arteries. Flow collision or swirling flow resulted in energy loss in TCPC models. In addition, a large intra-atrial channel or a sharp bend in TCPC geometries could influence on energy losses. Energy conservation was efficient when flow rates in pulmonary branches were balanced. In order to increase energy efficiency in Fontan operations, it is necessary to remove a flow collision in the intra-atrial channel and a sharp bend in the pulmonary bifurcation.