Volume 2: Computational Fluid Dynamics最新文献

{"title":"Numerical Simulation and Optimization of Blalock-Taussig Shunt","authors":"Thomas Hess, R. Agarwal, D. Hoganson","doi":"10.1115/AJKFLUIDS2019-4784","DOIUrl":"https://doi.org/10.1115/AJKFLUIDS2019-4784","url":null,"abstract":"\u0000 The goal of this study is to create an optimized Blalock-Taussig shunt used to temporarily repair pulmonary vascular blockages allowing a child time to grow so a more permanent surgical repair of the heart and vasculature can be performed. Blalock-Taussig or BT shunts are a surgical procedure performed on infants suffering from cyanosis or “Blue Baby Syndrome.” A BT shunt is an artificial vessel placed between the right ventricle and the pulmonary artery to increase blood flow in the lung and blood oxygen saturation levels. In a study of 96 patients with currently in use modified BT shunts, 32 patients (21%) had greater than 50% stenosis caused by myofibroblastic proliferation at the shunt lumen due to shunt geometry [1]. A 2007 study by the cardiac surgery division of Johns Hopkins Medical Institutions found an operative mortality rate of 14% (227 of 1,574) with patients undergoing BT surgery [2].\u0000 In this paper, the flow of blood through several different BT shunt configurations from actual patient data was analyzed using the commercial CFD software ANSYS Fluent. Results from each shunt’s analysis were then compared to determine the shunt parameters with optimal flow dynamics for use in infants suffering from pulmonary vascular blockage. It was found that the entrance boundary of current BT shunts caused blood flow hindrances due to high wall shear values and flow separation. A newly designed shunt was proven to partially fix this problem; however, a superior model could be optimized by using characteristics from currently used shunts and CFD results. Many iterations and designs of BT shunts were made using Solidworks, a solid modeling computer-aided design program, and were tested using Fluent to create a shunt optimized by smoothening the transition between areas of high and low wall shear stress, lowering the overall maximum wall shear stress, reducing flow separation, and equalizing the flow to the left and right lung. All these factors contribute to the chance of thrombosis and morbidity within patients. The resultant model shunt showed drastic improvement in lowering the average wall shear stress by more than 85% at the initial boundary with over 20% drop in overall average wall shear. It also achieved a decline of the maximum wall shear stress by over 25% while negating the possibility of any flow separation and improving the equality in flow to the left and right lung by more than 60%.","PeriodicalId":346736,"journal":{"name":"Volume 2: Computational Fluid Dynamics","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128242922","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of Microscopic Vortices Caused by Flow Interaction With Solid Obstacles on Heat Transfer in Turbulent Porous Media Flows","authors":"Ching-Wei Huang, V. Srikanth, Haoyang Li, A. Kuznetsov","doi":"10.1115/ajkfluids2019-4617","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4617","url":null,"abstract":"\u0000 Turbulent flow in a homogeneous porous medium was investigated through the use of numerical methods by employing the Reynolds Averaged Navier-Stokes (RANS) modeling technique. The focus of our research was to study how microscopic vortices in porous media flow influence the heat transfer from the solid obstacles comprising the porous medium to the fluid. A Representative Elementary Volume (REV) with 4 × 4 cylindrical obstacles and periodic boundary conditions was used to represent the infinite porous medium structure.\u0000 Our hypothesis is that the rate of heat transfer between the obstacle surface and the fluid (qavg) is strongly influenced by the size of the contact area between the vortices and the solid obstacles in the porous medium (Avc). This is because vortices are regions with low velocity that form an insulating layer on the surface of the obstacles. Factors such as the porosity (φ), Pore Scale Reynolds number (Rep), and obstacle shape of the porous medium were investigated. All three of these factors have different influences on the contact area Avc, and, by extension, the overall heat transfer rate qavg. Under the same Pore Scale Reynolds number (Rep), our results suggest that a higher overall heat transfer rate is exhibited for smaller contact areas between the vortices and the obstacle surface. Although the size of the contact area, Avc, is affected by Rep, the direct influence of Rep on the overall heat transfer rate qavg is much stronger, and exceeds the effect of Avc on qavg. The Pore Scale Reynolds number, Rep, and the mean Nusselt number, Num, have a seemingly logarithmic relationship.","PeriodicalId":346736,"journal":{"name":"Volume 2: Computational Fluid Dynamics","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126538598","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Three Dimensional Simulation of Ventilation Flow Through a Solar Windcatcher","authors":"P. Abdo, Rahil Taghipour, B. P. Huynh","doi":"10.1115/AJKFLUIDS2019-5383","DOIUrl":"https://doi.org/10.1115/AJKFLUIDS2019-5383","url":null,"abstract":"\u0000 Natural ventilation is the process of supplying and removing air through an indoor space by natural means. There are two types of natural ventilation occurring in buildings: winddriven ventilation and buoyancy driven or stack ventilation. The most efficient design for natural ventilation in buildings should implement both types of natural ventilation. Stack ventilation which is temperature induced is driven by buoyancy making it less dependent on wind and its direction. Heat emitted causes a temperature difference between two adjoining volumes of air, the warmer air will have lower density and be more buoyant thus will rise above the cold air creating an upward air stream. Combining the wind driven and the buoyancy driven ventilation will be investigated in this study through the use of a windcatcher natural ventilation system. Stack driven air rises as it leaves the windcatcher and it is replaced with fresh air from outside as it enters through the positively pressured windward side.\u0000 To achieve this, CFD (computational fluid dynamics) tool is used to simulate the air flow in a three dimensional room fitted with a windcatcher based on the winddriven ventilation alone, buoyancy driven ventilation alone, and combined buoyancy and winddriven ventilation. Different wind speeds between 0 up to 2.5 m/s are applied and the total air flow rate through the windcatcher is investigated with and without temperature of 350 K applied at the windcatcher’s outlet wall. As the wind speed increased the efficiency of the solar windcatcher decreased.","PeriodicalId":346736,"journal":{"name":"Volume 2: Computational Fluid Dynamics","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130423300","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Data-Driven Reduced Order Modeling of Flows Around Two-Dimensional Bluff Bodies of Various Shapes","authors":"K. Hasegawa, Kai Fukami, Takaaki Murata, K. Fukagata","doi":"10.1115/ajkfluids2019-5079","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5079","url":null,"abstract":"\u0000 We propose a reduced order model for predicting unsteady flows using a data-driven method. As preliminary tests, we use two-dimensional unsteady flow around bluff bodies with different shapes as the training datasets obtained by direct numerical simulation (DNS). Our machine-learned architecture consists of two parts: Convolutional Neural Network-based AutoEncoder (CNN-AE) and Long Short Term Memory (LSTM), respectively. First, CNN-AE is used to map into a low-dimensional space from the flow field data. Then, LSTM is employed to predict the temporal evolution of the low-dimensional data generated by CNN-AE. Proposed machine-learned reduced order model is applied to two-dimensional circular cylinder flows at various Reynolds numbers and flows around bluff bodies of various shapes. The flow fields reconstructed by the machine-learned architecture show reasonable agreement with the reference DNS data. Furthermore, it can be seen that our machine-learned reduced order model can successfully map the high-dimensional flow data into low-dimensional field and predict the flow fields against unknown Reynolds number fields and shapes of bluff body. As concluding remarks, we discuss the extension study of machine-learned reduced order modeling for various applications in experimental and computational fluid dynamics.","PeriodicalId":346736,"journal":{"name":"Volume 2: Computational Fluid Dynamics","volume":"128 5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123245158","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"CNN-SINDy Based Reduced Order Modeling of Unsteady Flow Fields","authors":"Takaaki Murata, Kai Fukami, K. Fukagata","doi":"10.1115/ajkfluids2019-5056","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5056","url":null,"abstract":"\u0000 We present a new framework of nonlinear reduced order model to extract low-dimensional modes and to predict their temporal evolutions. Autoencoder-type Convolutional Neural Network (CNN) which can learn nonlinearity of data is used to extract low-dimensional modes. For obtaining the temporal evolution of a mapped data by CNN, Sparse Identification of Nonlinear Dynamics (SINDy) is performed. The proposed method is applied to a circular cylinder wake at ReD = 100. The CNN trained using fluctuation components of velocity vector u, v shows better results than the snapshot Proper Orthogonal Decomposition in terms of the energy reconstruction rate. Although time-evolving flow fields reproduced by SINDy equation also show reasonable agreement with the reference direct numerical simulation, the errors of CNN and SINDy are accumulated through integral computation. The error of CNN can be reduced by devising a better network structure; however, the error of SINDy depends on the waveform of latent vector.","PeriodicalId":346736,"journal":{"name":"Volume 2: Computational Fluid Dynamics","volume":"105 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122737746","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"CFD Study of Implanted-Stent Impacts on Blood Flows in Left Coronary Artery Branch Models","authors":"Kazushi Fujimoto, T. Tsukahara, K. Yamamoto, M. Motosuke, H. Kawamoto, S. Tahara, Kentaro Tanaka, S. Nakamura","doi":"10.1115/ajkfluids2019-5250","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5250","url":null,"abstract":"\u0000 Percutaneous coronary intervention (PCI) is widely used as a treatment for ischemic heart disease. In particular, a high procedural precision of PCI for the left main coronary artery (LMCA), which supplies coronary artery blood to large amount of myocardium, is required. The restenosis after stent placement and target lesion revascularization of side branches (SB) is still a clinical issue. Regarding the stent implantation for bifurcation or trifurcation lesion, the stent struts should jail the inlets of SB. In such a situation, we clinically do the kissing balloon technique (KBT) to remove the struts existing at the opening of SB. As well as KBT, the proximal optimization technique (POT), which presses the stent against the wall, is also commonly used. However, merits of therapeutic strategies of KBT and POT for the branch are not confirmed from the fluid-dynamical viewpoint. In this study, we examined the influence of a stent in left main coronary artery on blood flow by employing CFD simulations. We investigated the influence of membrane position on the flow in bifurcation as well as of the stent position and shift on the flow in trifurcation. we confirmed that the effect of the stent position on the flow was bigger than that of the area occupied by the stent and that of KBT which moves the stent from the flow peak may be useful. However, it was also suggested that the intimal lining after KBT may cause serious flow inhibition.","PeriodicalId":346736,"journal":{"name":"Volume 2: Computational Fluid Dynamics","volume":"168 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122514200","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Computational Fluid Dynamic Analysis of a Marine Hydrokinetic Crossflow Turbine in Low Reynolds Number Flow","authors":"Minh N. Doan, Ivan H. Alayeto, Kana Kumazawa, S. Obi","doi":"10.1115/ajkfluids2019-4698","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4698","url":null,"abstract":"\u0000 This study focuses on surveying different turbulence models and dynamic mesh techniques to simulate a marine hydrokinetic (MHK) crossflow turbine at Rec ≈ 7,000. While several research projects have shown that studies of MHK devices in low Re flow could still yield interesting and significant results, existing computational fluid dynamic (CFD) simulations were conducted at the chord based Re of 105 ∼ 106. The wake and power production of a laboratory-scaled MHK crossflow turbine were numerically simulated and compared with relevant experimental data. The vertical axis turbine operated in a small flume with 20% blockage ratio and was fabricated by mounting three NACA0012 (2.54 cm chord length) straight blades at a radius of 3.41 cm and 15° pitch angle. Within OpenFOAM environment, blade-resolved models were built with Spalart-Allmaras, k-omega shear stress transport (SST), and k-kl-omega unsteady Reynolds-averaged Navier-Stokes simulation (URANS) in both two and three dimensions. Results from each model were compared with the experimental power measurement and flow field obtained by monoscopic particle image velocimetry (2D PIV). Additionally, four different techniques for moving the solid boundaries (turbine blades) in the unsteady simulation were presented and compared in terms of solution consistency and required computational power. Overset mesh, time-deforming mesh, and moving immersed boundary are all available in this open source environment, beside the common rotating mesh technique, and possess the potential to be applied to a more complicated configuration of turbines.","PeriodicalId":346736,"journal":{"name":"Volume 2: Computational Fluid Dynamics","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131766309","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}