Volume 2: Computational Fluid Dynamics最新文献

{"title":"Effect of Splitter Configurations on the Performance of a Sludge Pump","authors":"Jeong-Min Jin, H. Ji, Youn-J. Kim","doi":"10.1115/ajkfluids2019-5298","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5298","url":null,"abstract":"\u0000 Sludge pump, a type of centrifugal pump, is widely used to transport high-density sludge. The pump uses the impeller to generate a pressure difference for transporting the working fluid. The impeller is a crucial component of the pump. The internal pressure becomes higher with an increasing number of impeller blades, and this in turn results in an increased head. However, the increase in the number of blades interferes with the pump inlet flow, resulting in an efficiency loss due to an increase of surface friction. Therefore, in this study, numerical analysis was performed using ANSYS CFX ver. 17.1 to elucidate the effect of splitter configurations on the performance of sludge pump. The numerical results were compared with the efficiency and head according to the change of the splitter length, as 35%, 60%, and 80% of the reference blade shape.","PeriodicalId":346736,"journal":{"name":"Volume 2: Computational Fluid Dynamics","volume":"1 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":"129839930","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":"Mechanism of Wall Turbulence Modulation With Premixed Hydrogen Combustion","authors":"T. Ohta, Yuta Onishi, Yasuyuki Sakai","doi":"10.1115/ajkfluids2019-5075","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5075","url":null,"abstract":"\u0000 In order to clarify the mechanism of modulation of turbulence structures such as quasi-streamwise vortices affected by a flame propagating toward a wall, we perform a direct numerical simulation of wall turbulence with premixed hydrogen-air combustion using a detailed chemical reaction mechanism. As a result, existing quasi-streamwise vortices in turbulence near the wall are found to be suppressed, disappearing as the flame approaches. Hence, the turbulent flow tends to become laminar. Moreover, according to the analysis of the vorticity transport equation, it is found that the suppression is due to thermal expansion of the flame rather than an increase in viscosity. From the viewpoint of chemical reactions, it is revealed that thermal expansion inside turbulence vortices is mainly caused by reactions involving H2 and H2O2.","PeriodicalId":346736,"journal":{"name":"Volume 2: Computational Fluid Dynamics","volume":"153 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":"134348933","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":"Analysis of Angular Velocities, Surrounding Air Pressure and Velocities of Various Designed Micro Vertical Axis Savonius Wind Turbines by the Computational Fluid Dynamics (CFD) Method","authors":"W. Manosroi, T. Tangtrakool, C. Lhaosornthong","doi":"10.1115/ajkfluids2019-4911","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4911","url":null,"abstract":"\u0000 The objective of this study is to analyze angular velocities, surrounding air pressure and velocities of various micro vertical axis Savonius wind turbine prototypes by the Computational Fluid Dynamics (CFD) method. The angular velocities of turbines are the basic parameters for determining the major parameters of the wind turbines, such as efficiency, torque, power and electricity etc. Eight models of the micro vertical axis Savonius wind turbine made of acrylic were designed by varying three parameters including the turbine distance between the pivot point and the tip, the distance between the apex curvature and the center plane curvature and the cross section types (circular, square, triangular and trapezoid). The eight models were divided into three groups including two models (B1, B2) with two different cross section types (triangle and rectangular) in the first group, three models (C1, C2, C3) with three different distances from the curvature tip to the centerline of 110, 85 and 40 millimeters in the second group and three models (D1, D2, D3) with different distances between the pivot point and the tip in the third group. Then, the angular velocities, the surrounding air pressure and velocities of the micro vertical axis Savonius wind turbine at the five wind speeds at 5.59, 7.67, 9.76, 10.45 and 11.84 m/s were measured and evaluated by the ANSYS program. The simulation by the CFD method of the angular velocities of the designed wind turbines was compared with the experimental results. Some discrepancies due to the absence of friction in the CFD results were observed. However, discrepancies between the simulation and the experimental results were decreased when the wind speed was increased due to the increase of torque and force in the experimental results which has overcome the turbine core friction. It has indicated that at the highest wind speed (11.84 m/s), the designed micro vertical axis Savonius circular cross section wind turbine with the curvature of the distance from the apex curvature to the center plane at 110 millimeters gave the highest turbine angular velocity of 441 rpm. At this highest turbine velocity by the CFD simulation, the high surrounding air pressure was not the smallest and the low turbine surrounding air pressure area was not the largest. This might be due to the effect of the suitable apex curvature distance to the center plane causing the efficient air flow to overcome the effect of the surrounding air pressure. The wind turbine of the second group gave the highest angular velocities followed by the first and the third group. These designed micro vertical axis Savonius wind turbines can be used as a preliminary model for the design and construction of the micro wind turbine to generate electricity at low wind speed region, such as Thailand.","PeriodicalId":346736,"journal":{"name":"Volume 2: Computational Fluid Dynamics","volume":"116 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":"121284550","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":"Hybrid RANS-LES Simulation of Turbulent Heat Transfer in a Channel Flow With Imposed Spanwise and Streamwise Mean Temperature Gradient","authors":"Olalekan O. Shobayo, D. K. Walters","doi":"10.1115/ajkfluids2019-4920","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4920","url":null,"abstract":"\u0000 Computational fluid dynamics (CFD) results for turbulent flow and heat transfer in a plane channel are presented. This study presents an idealized fully-developed planar channel flow case for which the mean velocity gradient is non-zero only in the wall-normal direction, and the mean temperature gradient is imposed to be uniform and non-zero in the streamwise or spanwise direction. Previous studies have documented direct numerical simulation results for periodic channel flow with mean temperature gradient in both the streamwise and wall-normal directions, but limited investigations exist documenting the effect of imposed spanwise gradient. The objective of this study is to evaluate turbulent heat flux predictions for three different classes of modeling approach: Reynolds-averaged Navier-Stokes (RANS), large-eddy simulation (LES), and hybrid RANS-LES. Results are compared to available DNS data at Prandtl number of 0.71 and Reynolds number of 180 based on friction velocity and channel half-width. Specific models evaluated include the k-ω SST RANS model, monotonically integrated LES (MILES), improved delayed detached eddy simulation (IDDES), and dynamic hybrid RANS-LES (DHRL). The DHRL model includes both the standard formulation that has been previously documented in the literature as well as a modified version developed specifically to improve predictive capability for flows in which the primary mean velocity and mean temperature gradients are not closely aligned. The modification consists of using separate RANS-to-LES blending parameters in the momentum and energy equations. Results are interrogated to evaluate the performance of the three different model types and specifically to evaluate the performance of the new modified DHRL variant compared with the baseline version.","PeriodicalId":346736,"journal":{"name":"Volume 2: Computational Fluid Dynamics","volume":"14 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":"115452289","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":"The Effect of Mixing Promoters on the Performance of Forward Osmosis Membrane Systems: Computational Fluid Dynamics Simulations","authors":"Ahmed M. Alshwairekh, Abdullah A. Alghafis, Anas M. Alwatban, U. Alqsair, A. Oztekin","doi":"10.1115/ajkfluids2019-4862","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4862","url":null,"abstract":"\u0000 Computational fluid dynamics simulations are performed to study the desalination process in forward osmosis modules. Concentration polarization phenomenon is responsible for lowering the water flux permeation through the membrane. It is desired to mitigate the external concentrative and dilutive concentration polarizations by proper mixing of both the feed and the draw solutions. Chevron-type of corrugation with a single triangular shape is used for membrane corrugation. The peak of the corrugation is oriented toward the feed channel. This type of corrugations produces dips in the membrane in the draw side. The dips will not mix the draw solution properly. Net-type spacers of 45° will be placed in the middle of the draw channel. The spacers will work as mixing promoters and add extra support for the membrane. All configurations will have the same Reynold number of 1500 in both channels. k–ω SST turbulence model is used with modules containing mixing promoters, and the laminar model is used with the module without corrugation and spacers. The results indicate that a 14% increase in the water flux is attained with the presence of spacers and membrane corrugation compared with a flat membrane and no spacers. Also, the dilutive concentration polarization has been mitigated significantly compared with the empty case.","PeriodicalId":346736,"journal":{"name":"Volume 2: Computational Fluid Dynamics","volume":"3 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":"129638205","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":"Predictability Study of Viscoelastic Turbulent Channel Flow Using Deep Learning","authors":"Atsushi Nagamachi, T. Tsukahara","doi":"10.1115/ajkfluids2019-5261","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5261","url":null,"abstract":"\u0000 We tested Artificial Neural Networks (ANNs) to predict a fully-developed turbulent channel flow of a viscoelastic fluid in preparation for elucidating flow phenomenon and solving the difficulty in DNS (Direct Numerical Simulation) due to numerical instability of the viscoelastic fluid. Two kinds of ANNs (multi-layer perceptron (MLP) and U-Net) were trained using DNS data to predict conformation stress from given instantaneous field. The MLP showed accurate predictions and predictions got better with z-score normalization. ANN predicted accurately in near-wall region having coherent structures. In addition, we demonstrated that ANN get the nonlinear relationship between velocity gradient and viscoelastic stress partially.","PeriodicalId":346736,"journal":{"name":"Volume 2: Computational Fluid Dynamics","volume":"1 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":"129792137","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":"Numerical Investigation on Multiphase Reacting/Combusting Turbulent Flows: Aerodynamics, Kinetics, Heat and Mass Transfer Inside a Cement Kiln Precalciner","authors":"E. Cristea, P. Conti","doi":"10.1115/ajkfluids2019-5033","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5033","url":null,"abstract":"\u0000 This paper reports the modeling work to develop a computational fluid dynamics (CFD) engineering application, based on an appropriate 3D mathematical model able to perform the thermo-fluid dynamic numerical simulation of multiphase reacting/ combusting turbulent flows within a precalciner of an industrial four-stage cyclone preheater/precalciner cement kiln. In the precalciner furnace the hot micron-sized limestone (calcite/dolomite) meal, held in suspension, is quiet completely converted to quicklime (CaO(s)), and the CO2(g) by-product is driven-off during calcination process. Since, the thermal decomposition mechanism is a very endothermic reaction, the necessary heat is balanced by pulverized petcoke combustion.\u0000 These major physical and chemical processes inside the precalciner are properly described by the 3-D Favre-averaged Navier-Stokes equations with the species transport equations, the energy equation and the state equation, to be solved by an Eulerian-Lagrange approach. The CFD solver employed in this study is the commercial CFD code ANSYS Fluent R18.2. The used built-in models/sub-models include turbulence models and near-wall treatment, model of traditional air-pulverized petcoke combustion, pulverized-limestone calcination model, as well as the sub-models for radiation heat transfer and turbulence-chemistry interaction. They are used to formulate the closures of the unclosed terms in the PDEs system.\u0000 In summary, the trends of predicted results of limestone calcination and petcoke/TDF combustion processes in an industrial precalciner furnace are reasonable fair in confront to operation data measurable in the harsh environment conditions, typical for the pyroprocessing systems. The developed CFD engineering application can be used as an effective design tool for preliminary examination of the global effect of thermal-flow aerodynamics and turbulence on the precalciner processes.","PeriodicalId":346736,"journal":{"name":"Volume 2: Computational Fluid Dynamics","volume":"10 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":"126448443","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":"Impacts of Storm Surges on Hydrodynamics and Salinity of Sabine Lake and Sabine River Diversion Canal","authors":"Hairui Wang, Ning Zhang","doi":"10.1115/ajkfluids2019-4669","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4669","url":null,"abstract":"\u0000 In this study, a hydrodynamic and salinity transport model was developed for simulations of Sabine Lake water system located on the Texas-Louisiana border. The target simulation area ranges from Sabine River near Deweyville, TX as the north boundary to the Gulf of Mexico as the south boundary, and from Neches River near Beaumont, TX as the west boundary to part of Gulf Intracoastal Waterway (GIWW) and Sabine River Diversion Canal (SRDC) as the east boundary. The entire area includes several major water bodies, such as Sabine Lake, Sabine River, Sabine Pass, Sabine Neches Canal (Ship Channel), and part of GIWW and SRDC. The SRDC supplies fresh water to the area industry, mainly petrochemical. High salinity in SRDC could significantly affect the daily production of the industry. The major purposes of this study is to use the validated hydrodynamic and salinity transport model to assess and predict the salinity in SRDC under severe weather conditions such as hurricane storm surges. Measurement data from NOAA and USGS were used to calibrate the boundary conditions as well as to validate the model. Two different levels of storm surges each lasting for 24 hours were simulated, 0.5 and 1 meter, respectively, and the salinity in SRDC was monitored and compared to analyze the storm surge threats on SDRC water quality. The result shows that it took about 2 days for the salinity reaching SRDC under the 1m storm surge condition and about 3 days under 0.5m surge condition and the salinity value could reach as high as 5 to 10 ppt.","PeriodicalId":346736,"journal":{"name":"Volume 2: Computational Fluid Dynamics","volume":"109 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":"134403290","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":"Theoretical and Numerical Studies on the Performance of Shock Vector Control","authors":"Kexin Wu, H. Kim","doi":"10.1115/ajkfluids2019-4691","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4691","url":null,"abstract":"\u0000 The transverse injection into a supersonic flow is a significant application that appeared in numerous aerodynamic applications, such as drag reduction and fluidic thrust vectoring control. Nowadays, fluidic thrust vector control is gradually replacing mechanical thrust vector control to redirect various air vehicles. Shock vector control is very popular in fluidic thrust vector control field due to lots of advantages, such as simple structure, more integrated control effect, and quick vectoring response. In present works, numerical simulations and theoretical analyses were conducted to investigate the shock vectoring performance in a three-dimensional rectangular nozzle. To validate the reliability and accuracy of the present numerical methodology, static pressure distributions along upper and lower nozzle surfaces in the symmetry plane were compared with experimental data published by NASA. It was evident that present numerical results present great approximations with experimental data. Control variables of the slot injector were studied, which not only include slot length and slot width but also contain uniform mass flow ratio and injection pressure ratio. Performance variations were illustrated clearly, such as static pressure distributions along upper and lower nozzle surfaces, deflection angle, resultant thrust coefficient, and thrust efficiency. Useful conclusions were obtained for further investigations on shock vector control.","PeriodicalId":346736,"journal":{"name":"Volume 2: Computational Fluid Dynamics","volume":"33 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":"124933996","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":"Extra-Low Reynolds Number Vane Separation Using Immersed Boundary Method","authors":"P. Prapamonthon, B. Yin, Guowei Yang","doi":"10.1115/ajkfluids2019-5077","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5077","url":null,"abstract":"\u0000 Nowadays, mini unmanned aerial vehicles (MUAVs) and micro air vehicles (MAVs) are not only beneficially used as aviation models but also as modern drones for military missions and other civilian applications. Hence, research and development of propulsion sources for MUAVs and MAVs dynamically increase with a future trend of high performance, but low energy consumption. Certainly, using micro and ultra-small-size gas turbine is a good option for the propulsion source. To achieve ideal flight of MUAVs and MAVs powered by micro and ultra-small-size gas turbines under this trend, understanding of flow phenomena at wide ranges of Reynolds number is essential. This research presents a 2D numerical study of characteristics of laminar flow separation and the trailing-edge vortex on a turbine vane at extra-low Reynolds numbers (Res) i.e. Re = 1800 and 3600, and three rotational angles (α) i.e. α = 0°, 15° and 30° using immersed boundary method (IBM). With this method, the problem of incompressible flow is addressed by a sharp interface IBM. Numerical results indicate that IBM can characterize phenomena of laminar separation flow, which usually happens on the turbine airfoil when laminar boundary layer cannot overcome adverse pressure gradients and viscous effects. To our current knowledge, this may be the first research to study flow behavior at such low Res for gas turbine vanes using IBM. Even though it is now not common to operate micro and ultra-small-size gas turbines under these conditions, it is important to know how aerodynamic performance may be if micro and ultra-small-size gas turbines need to run under such conditions in the near future.","PeriodicalId":346736,"journal":{"name":"Volume 2: Computational Fluid Dynamics","volume":"14 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":"126619387","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}