Gas-liquid two-phase flow in the axial clearance of liquid-ring pumps

Renhui Zhang,Lei Tian,Guangqiang Guo,Xuebing Chen 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.2

In this study, the leakage flow in the axial clearance of a 2BEA-203 liquid-ring pump has been modeled through numerical simulation using the renormalization group k-ε turbulence model and the multiphase volume of fluid method. Numerical results show that the axial leakage flow reduces the inlet vacuum and efficiency of the liquid-ring pump. The gasliquid two-phase flow within the axial clearance region is completely separated. Several droplets are scattered outside the suction region, some of which flow back into the low-pressure suction region along the wall of the suction port. Given the axial asymmetry of the flow passage, the phase distribution within the impeller region is non-uniform along the axial direction. The numerically simulated pressure distribution within the axial clearance region accords well with the vortex distribution caused by the leakage flow. The leakage flow interacts with the impeller flow, and forms a corner vortex near the pressure side and a leakage vortex near the blade suction side. As the relative coordinate of the cross planes to the blade (sc −1 ) decreases from tip to hub, the corner vortex near the blade pressure side gradually weakens while the leakage vortex near the suction side gradually strengthens. These vortices mostly form in the suction and compression zones of the clearance region and significantly affect the overall pump efficiency. Findings of this study reveal the flow structure in the axial clearance of the liquid-ring pump and the interaction between the leakage and main flow.

CFD/CAA 연계 해석을 이용한 누설 유동의 공력 소음 예측

강성우,김시진,마평식,서윤호,명노신,이학진 한국전산유체공학회 2024 한국전산유체공학회지 Vol.29 No.1

The high speed flow leaked from cracks in gas pipelines can lead to severe explosion accidents. Therefore, detecting the location of leakage flow early and precisely is important to reduce the damage from leakage flow. The three-dimensional probe array using the acoustic intensity signals is one of the useful leak detection technologies. In this study, the CFD/CAA hybrid method is used to investigate the flow and acoustic characteristics of leakage flow. The features of leakage flow, including turbulence scales, roll-up pheno- menon, strong shock waves, and Mach disk are predicted through the large eddy simulation (LES), and the far-field noise is calculated using the Ffowcs Williams-Hawkings (FW-H) acoustic analogy with permeable surfaces. The parametric study is performed in terms of the internal pressure condition in the pipe (10, 30, 50, 100 bar) and the size of leakage hole (5, 8, 10 mm) to analyze the flow and acoustics characteristics of the leakage flow. The strong Mack disk expands widely as the internal pressure and hole size increase while screech tone noise at specific frequency is observed as the internal pressure and hole size decrease. It turns out that overall sound pressure level (OASPL) of leakage flow increases about 15 dB when screech tone noise occurs.

슈라우드 축류압축기에서 누수접선방향속도가 블레이드 구간 유동에 미치는 영향

김진욱(Jin Wook Kim),손대웅(Dae Woong Sohn),김동범(Tongbeum Kim),송성진(Seung Jin Song) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-

Although compressor blades have long been shrouded for aerodynamic and structural reasons, the impact of the leakage flow in the shroud cavities on passage flows has only recently been investigated. Furthermore, the tangential velocity of the leakage flow, set by the blading and the relative motion between rotating and stationary surfaces, has a strong influence on the passage flow. Yet the influence of the tangential velocity variation on the main flow in the blade passage are unknown. Therefore, this paper reports on an experimental investigation of the axial evolution of loss generation in the blade passage in shrouded axial compressor cascades subject to the variation of leakage tangential velocity. The newly found results are as follows. First, increasing tangential velocity of the leakage flow reduces loss at 10% and 50% chordwise locations in the passage. However, most of the blockage and loss reductions occurs in the aft half chord and downstream of the blade passage. Second, the increasing tangential velocity spreads the loss core, which is originally concentrated in the suction side hub corner, in the pitchwise direction. Thus, the loss core becomes more two-dimensional, and the region's radial extent is reduced. Third, increasing tangential velocity of the leakage flow makes the near hub passage flow more radially uniform. Consequently, the shear and resultant mixing loss between the passage and leakage flows are reduced near the hub, reducing the overall loss.

Numerical and experimental study of the leakage flow in guide vanes with different hydrofoils

Sailesh Chitrakar,Biraj Singh Thapa,Ole Gunnar Dahlhaug,Hari Prasad Neopane 한국CDE학회 2017 Journal of computational design and engineering Vol.4 No.3

Clearance gaps between guide vanes and cover plates of Francis turbines tend to increase in size due to simultaneous effect of secondary flow and erosion in sediment affected hydropower plants. The pressure difference between the two sides of the guide vane induces leakage flow through the gap. This flow enters into the suction side with high acceleration, disturbing the primary flow and causing more erosion and losses in downstream turbine components. A cascade rig containing a single guide vane passage has been built to study the effect of the clearance gap using pressure sensors and PIV (Particle Image Velocimetry) technique. This study focuses on developing a numerical model of the test rig, validating the results with experiments and investigating the behavior of leakage flow numerically. It was observed from both CFD and experiment that the leakage flow forms a passage vortex, which shifts away from the wall while travelling downstream. The streamlines contributing to the formation of this vortex have been discussed. Furthermore, the reference guide vane with symmetrical hydrofoil has been compared with four cambered profiles, in terms of the guide vane loading and the consequent effect on the leakage flow. A dimensionless term called Leakage Flow Factor (Lff) has been introduced to compare the performances of hydrofoils. It is shown that the leakage flow and its effect on increasing losses and erosion can be minimized by changing the pressure distribution over the guide vane.

Numerical investigation of aerodynamic load on the impellers of centrifugal compressor with leakage flow

Jianchi Xin,Xiaofang Wang,Haitao Liu,Wang wei,Lusheng Zhou 한국유체기계학회 2020 International journal of fluid machinery and syste Vol.13 No.2

Based on computational fluid dynamics (CFD) simulation, this study investigates the effect of leakage flow on the performance of centrifugal compressor, which helps to showcase the flow phenomenon considering the leakage flow and the aerodynamic load on the impellers. We consider four types of compressor models including the normal stage with hub and shroud leakages (SWT), the normal stage with hub leakage (SWH), the normal stage with shroud leakage (SWS), and the normal stage without leakages (SOT)). The results indicate that the leakage flow obviously affects the compressor performance, especially the flow field around the leading/trailing edge of the impeller. The aerodynamic load at the leading/trailing edge of the impeller was obtained for the models through unsteady simulation. The dominant frequency and the pulse amplitude obtained by Fast Fourier transforms revealed that the main frequencies of the aerodynamic load present different distributions under different leakage flows.

천음속 원심압축기 내부 유동해석

성선모(Seon-Mo Seong),강신형(Shin-Hyoung Kang),최재호(Jae-Ho Choi),이진수(Jin-Soo Lee) 한국유체기계학회 2008 유체기계 연구개발 발표회 논문집 Vol.2008 No.-

A computational study was carried out to simulate the flow fields within a transonic centrifugal compressor and focused on the variations in the tip leakage flow structure at three operating conditions- near choke, design point and peak pressure rise. The tip leakage flow shows very complex structures composed of the impingement on the pressure surface of the adjacent splitter blade, the spillage ahead of the adjacent splitter blade and strong radially upward flow near the suction surface. The tip leakage flow mixes with the incoming flow and there is a high entropy gradient in the interface between these two flows. As mass flow rate decreased, the interface becomes more tangential and the position of the minimum pressure moves upstream. Therefore, the peak of the tip leakage velocity appears near the leading edge at low mass flow rate. The profile of the tip leakage velocity shows the core with approximately constant slope at 20~80% height of the distance from the blade tip to the casing.

Investigation of Leakage Characteristics of Straight and Stepped Labyrinth Seals

Kim, Tong-Seop,Kang, Soo-Young Korean Society for Fluid machinery 2010 International journal of fluid machinery and syste Vol.3 No.3

Leakage characteristics of two labyrinth seals with different configurations (straight vs stepped) were investigated. Leakage flows were predicted by computational fluid dynamics (CFD) for the two configurations and compared with test data. A semi-analytical leakage prediction tool was also tried to predict the leakage. It was confirmed that the CFD gives quite good agreements with test data. The analytical tool also yielded similar leakage behaviors with test results, but the overall agreement with test data was not as good as that of the CFD. The effect of flow direction in the stepped seal on leakage flow was examined. The dependence of leakage performance, in terms of flow function, on the seal clearance size was investigated. Flow function decreased with decreasing clearance in the straight seal, while the trend was reversed in the stepped seal.

원자로계통내 주요 기기/부품에서의 누설특성 연구

김연식,어동진,김우식,권태순 한국유체기계학회 2019 한국유체기계학회 논문집 Vol.22 No.6

To predict leakage flowrate from major equipment/component in reactor system, potential leakage points in reactor system were reviewed and models of critical flowrate were investigated. For predictions of leakage flow, three kinds of critical flow models, e.g., ideal gas flow model, Trapp-Ransom model, and Henry-Fauske model, were investigated. Using Henry-Fauske model, leakage flows were obtained for selected leakage points in reactor system and equivalent crack sizes were also estimated for 0.5 gpm leakage.

Plastics Material Flow Study to Prove Possible Land Based Leakage: a Case Study of Sarbagita Region, Bali, Indonesia

( Emenda Sembiring ),( Enri Damanhuri ),( I Made Wahyu Widyarsana ),( Elprida Agustina ) 한국폐기물자원순환학회(구 한국폐기물학회) 2019 ISSE 초록집 Vol.2019 No.-

Plastics marine pollution is a highlighted environmental problem. Most of studies show that land base plastics leakage is the culprit. This study show how material flows analysis (MFA) can be used to prove the possible plastics waste leakage from land area. A case study at Sarbagita region in Bali is chosen to highlight on how to improve solid waste management in order to combat plastics marine pollution. Sarbagita region consists of Denpasar city, Badung Regency, Gianyar Regency, and Tabanan Regency which are situated in Bali island, a well-known tourism area in Indonesia. In 2018, the population in Bali Province expand to 4.2 million local residents and also a destination of 6 million tourists per year. This number continues to increase every year. The increasing population and socioeconomic activities have a direct impact to the waste generation. In 2019, approximately 1,767 t/d waste is generated. Plastic waste, due to its characteristics and quantity, become an environmental problem in a tourism area since that environment quality and aesthetics decrease because of unmanage plastics waste. Around 16.39% or 289,6 t/d plastic is generated at the source of Sarbagita region. In its journey, plastic waste which is generated at source have gone through many stages of its life in waste management system. The material flow study was conducted to identify the number of plastics which are processed, recycled, disposed into landfill, and also unmanaged in which eventually, is discharged into the environment. Up to 3.63% or 64.2 t/d plastic waste is managed in the formal sector called TPS 3R and Waste Bank while 2.7% or 47.9 t/d plastic is managed in the informal sector. The residue of plastic waste, approximately 7.31% or 127.4 t/d is being dumped to Suwung landfill site and around 2.74% or 48.4 t/d plastic waste released improperly to the environment. The error of material balance is 0.6%. The unmanaged waste which is discharged into the environment is potentially the land base of plastics waste leakage into the ocean. The MFA shows which stages of plastics waste life can be the focus of measures to reduce leakage.

Experimental investigation of tip-leakage flow in an axial flow fan at various flow rates

이홍권,박근태,최해천 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.3

We investigate the evolution of tip-leakage vortex (TLV) in a low-pressure axial flow fan using digital particle image velocimetry. The blade rotational speed is fixed at 1000 rpm, and the Reynolds number is 547000 based on the blade tip radius and tip velocity. The evolution of TLV in downstream is highly influenced by the incoming flow rate. The TLV breakup occurs for the peak efficiency and stall conditions and sometimes for a higher flow rate, but does not occur for the highest flow rate considered. Thus, the migration speed of the TLV for the peak efficiency condition is faster due to the TLV breakup than those for higher flow rates. The scatter plot of the TLV center location indicates that the TLV wanders around its mean location and the region swept by the wandering motion increases as the TLV migrates downstream. High turbulent kinetic energy exists at the phase-averaged TLV center and its upstream location, respectively, owing to the wandering motion and the interaction between the TLV and main axial flow.