Journal of Applied Fluid Mechanics最新文献

{"title":"A Numerical Study on the Energy Dissipation Mechanisms of a Two-Stage Vertical Pump as Turbine Using Entropy Generation Theory","authors":"T. P. Chen, X. Z. Wei, R. S. Bie, Y. Li, T. Zhang, Y. X. Liu","doi":"10.47176/jafm.17.1.2010","DOIUrl":"https://doi.org/10.47176/jafm.17.1.2010","url":null,"abstract":"Utilizing a two-stage vertical pump as turbine (TVPAT) is an economically method for constructing small-scale pumping and storage hydropower stations at high head-low discharge sites, such as underground coal mines. The energy dissipation mechanisms in flow passages are theoretically important for performance prediction and geometric parameter optimization. In this paper, the energy dissipation within the TVPAT has been studied using entropy generation theory, which can be applied to visual, locate and quantify energy dissipation. The numerical solution of entropy dissipation components was extracted on turbine modes in different flow rates using the steady-state single-phase SST k-ω turbulence model. The numerical results show that the energy dissipation in TVPAT mainly comes from turbulent fluctuation (43.6%-72.1%) and blade surface friction (27.8%-58.2%). The runners are the main source of turbulent entropy (SD′ ) generation (47.2%-83.3%). The contribution of the return channel and spiral case to the generation under overload conditions is significant, accounting for 33.6% and 14.3 at 1.3QBEP, respectively. Flow field analysis reveals that high generation within a runner are located in the striking flow region of the leading edge, the flow squeezing region in the blade channel, and the wake region of tailing edge. The mismatch between the placement angle of the blades or guide vanes and the liquid flow angle is an important incentive for SD′ generation. Moreover, hydraulic energy is consumed through the interaction between mainstream and local inferior flows such as separation and vortices, as well as the striking and friction between local fluid and wall surfaces.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":"16 2","pages":""},"PeriodicalIF":1.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139126233","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"3D Numerical Modeling and Geometry Optimization of an Oscillating Water Column Device in Sloshing Conditions Using Openfoam and Genetic Algorithms","authors":"†. S.S.Razavi, R. Shafaghat, B. A. Kharkeshi, J. Eskandari","doi":"10.47176/jafm.17.1.1867","DOIUrl":"https://doi.org/10.47176/jafm.17.1.1867","url":null,"abstract":"Among various types of wave energy converters, the oscillating water column (OWC) has attracted significant research attention. In this paper, a 1:10 scale OWC with dimensions of 100×100×160 cm, variable inlet height and draft was numerically studied. Based on the tests conducted, it was found that the wave amplitude in the range of Caspian Sea waves decreased with the increase of wave frequency, to the extent that at the sloshing frequency, the system efficiency dropped significantly. To solve this problem, changes in the geometry of the device were studied, and numerical simulations were performed at the highest frequency using OpenFOAM software. Using Reynolds-averaged Navier-Stokes (RANS) equations, numerical simulations were performed in 3D, two-phase, and turbulent flow conditions. Changing the geometry was initially investigated by adjusting the height of the OWC inlet duct, and then by adding an inlet at the different angles of 0, 20, and 40 degrees. The results showed that by increasing the height of the inlet by 10 cm while keeping the water depth and wave conditions constant, the maximum output power of the system increased by 54%. However, after the optimization of the inlet duct, it was found that the best angle for an inlet duct is 30°, compared to the case without an inlet, which increased the maximum output power by up to 13% and slightly reduced the sloshing by more than 50%.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":"12 11","pages":""},"PeriodicalIF":1.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139127754","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A Methodology for Designing a Fish-Friendly Turbine Rotor Applied to High-Power Generation","authors":"G. E. Niño, †. DelRío, R. G. R. Camacho, N. M. Filho, W. D. Oliveira, T. M. A. Angulo","doi":"10.47176/jafm.17.1.1927","DOIUrl":"https://doi.org/10.47176/jafm.17.1.1927","url":null,"abstract":"Most large hydropower facilities employing conventional hydraulic turbines, e.g., Francis, Kaplan, or Bulb turbines, etc., cause significant harm to fish, resulting in high mortality rates, during turbine operation. This results from strong injury-inducing mechanisms at the rotor, including shear stresses, pressure variations, and pressure drop through the rotor. The study outlines a methodology for designing a fish-friendly turbine that is suitable for high-power generation applications. This methodology for a hydraulic channel design within the turbine rotor was derived based on classical fundamental applications of a rotor design, supplemented by subsequent assessments that incorporate fish-friendly design parameters that have been documented in the existing literature. A spiral curve characterized by a linear angle variation between the rotor's inlet and outlet was employed to project the blade geometry. Here, the Göttingen hydrofoil series was used, while a second-order polynomial function guided the hub design. Both of these parametrizations sought to enhance the turbine's hydraulic efficiency. Minimum Absolute Pressure, Strain Rate, and Pressure Variation Rate intervals were established as assessment criteria for fish survival for certain species, as has also been previously explored in the literature. The findings were outlined in terms of hydrodynamic performance and flow behavior within the rotor. An improvement in hydraulic efficiency was observed, transitioning from a Preliminary Turbine geometry design to an Optimized Turbine Geometry design. The turbine rotor was optimized using Computational Fluid Dynamics (CFD) simulations, generated from a Design of Experiments (DOE). Modifications to the hydrofoil type, the sweep angle, and the trailing edge angle of the blades were all made, coupled with integrations of assessments considering fish-friendly parameters.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":"39 10","pages":""},"PeriodicalIF":1.0,"publicationDate":"2024-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139129442","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of Personalized Ventilation in Seat Armrest on Diffusion Characteristics of Respiratory Pollutants in Train Carriages","authors":"X. Liu, †. T.Li, S. Wu, J. Zhang","doi":"10.47176/jafm.16.12.1953","DOIUrl":"https://doi.org/10.47176/jafm.16.12.1953","url":null,"abstract":"As one of the most important means of transportation, high-speed trains have a large capacity for carrying passengers. However, their narrow carriages can easily exacerbate the spread of respiratory diseases. Just like personalized ventilation in an airplane, ventilation in seat armrests of high-speed trains may increase comfort for passengers, but also influence the diffusion characteristics of respiratory pollutants. In this study, the effect of personalized ventilation in seat armrests, on the diffusion characteristics of respiratory pollutants in train carriages, is studied by means of the tracer gas method. Taking the ceiling air supply as the original ventilation system, comfortable temperature and pollutant diffusion characteristics of the personalized ventilation system, with 4 different air supply angles, are investigated. The 4 angles are 0°, 30°, 45° and 60°. When the personalized ventilation with the above 4 angles is adopted, the fluctuation amplitudes of pollutants in the passenger breathing zone are reduced by 15.84%, 19.27%, 19.76% and 19.68%, respectively, compared with the original ventilation system. It indicates that the sensible use of personalized ventilation can effectively reduce the passengers’ contaminant concentrations in the breathing zone, thereby reducing the possibility of cross-contamination between passengers. In addition, the use of the personalized ventilation system leads to a slight improvement in the thermal comfort and flow uniformity in the carriage. Based on the results, personalized air supply with an angle of 45° is advised for use in high-speed trains.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":" 12","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138615559","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Temporal Flow Characteristics of Three-Dimensional Centrifugal Impeller Suction System at Vacuum Conditions","authors":"Y. Li, B. Zhang, Y. Chen, Z. Wang, H. Yang, Y. Wei","doi":"10.47176/jafm.16.12.1875","DOIUrl":"https://doi.org/10.47176/jafm.16.12.1875","url":null,"abstract":"Temporal flow characteristics of a 3D centrifugal impeller suction system were numerically studied in vacuum conditions. The blockage of the high-speed rotating impeller appeared, which greatly dropped the suction of the layer suction device. The temporal flow characteristics of the 3D centrifugal impeller suction system were worthy of attention in vacuum conditions. Separation vortices were generated near the blade suction surface. The blocking mechanism of the passage was further analyzed at different extremely low flow rates through the time-space evolution of the streamline. The Q-criteria was introduced to analyze the vortex evolution within the fluid domain of the impeller. Vortex evolution law was captured—the vortices always generated near the suction surface of the blade and moved to the pressure surface of the adjacent blade in the same passage and disappeared. The uniform distribution of three stall cells was captured through the diagram of turbulent kinetic energy. The flow rate increased, and the vortex evolution period gradually decreased. The comparison of pressure fluctuations in different conditions further demonstrated the flow mechanism at the vacuum flow rate was different from that at low flow rates. The sharp increase of pressure fluctuations near the blade pressure surface was consistent with the phenomenon near the suction surface. The pressure fluctuation at extremely low flow was mainly composed of scattered fluctuations caused by fluid separation. The steady and unsteady characteristics described the internal flow characteristics of this suction system at vacuum-flow rates. Theresults provide a profound design for vacuum cleaners.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":" 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138616665","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Computational Analysis of Rheological Secondary Flow in a Pipe-Manifold Containing In-Plane Double Bends","authors":"A. Banerjee, S. Sengupta, S. Pramanik","doi":"10.47176/jafm.16.12.1966","DOIUrl":"https://doi.org/10.47176/jafm.16.12.1966","url":null,"abstract":"Non-Newtonian fluid flow in pipe bends is inevitable in industrial applications. Previous researchers have extensively explored Newtonian flow through curved ducts. However, the non-Newtonian counterpart gets little attention. We study the turbulent flow of shear-dependent fluids obeying the Power-Law model in a pipe manifold containing an in-plane double bend. Ostwald–de Waele's power law is used to model the fluid's rheology. We utilize computational fluid dynamics (CFD) to solve Reynolds-averaged Navier–Stokes (RANS) equations with the k-ε turbulence model. We validate our numerical results with previous experimental results. The in-plane double bend perturbs the flow in the pipe manifold to develop a Prandtl's secondary flow of the first kind. A fully developed flow at the bend upstream is disturbed due to the bend's curvature and regains its fully developed characteristics upon a certain downstream length after the exit of the bend. We study the rheological characteristics of the secondary flow within the bend and the evolution of fluid flow at the bend downstream. We demonstrate that the centrifugal force-dominated secondary flow increases with a decrease of the non-Newtonian power-law index. We capture the camel's-back-shaped velocity profiles within the bend due to accelerating-decelerating flow. The study reveals that the average flow velocity increases along the bend with a corresponding pressure head loss. We quantify this velocity rise by a newly introduced non-dimensional number, viz. enhancement ratio. The double bend's enhancement ratio decreases with an increase in n.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":" 42","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138617793","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of Different Types of External Guide Vanes on the Performance of High-Pressure Centrifugal Compressor","authors":"†. P.Niveditha, B. S. Gopi","doi":"10.47176/jafm.16.12.1814","DOIUrl":"https://doi.org/10.47176/jafm.16.12.1814","url":null,"abstract":"In order to reduce exit swirl and obtain the desired Mach number, axial exit guide vanes (EGV) are often employed in a centrifugal compressor. NASA CC3 compressor, with wedge vane diffuser and without EGV, is considered as the base model for the analysis and validation. An axial flow domain with exit guide vane is added to this base model after the diffuser outlet to study the effect on the compressor performance. The performance of exit guide vane with different profiles: flat plate, symmetric wedge, circular arc, and airfoil vane profiles by maintaining the same chord, number of vanes, and flow angle of the vanes are studied. Numerical simulations are carried out with 60 number of exit guide vanes for all four types of vanes. Among several combinations, when the centrifugal compressor is equipped with 60 circular arc vanes as EGV, the efficiency and pressure recovery values at the design point have increased by 6.5% and 8.9%, respectively.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":" 3","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138618015","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Emission Characteristics of Heavy-Duty Vehicle Diesel Engines at High Altitudes","authors":"Y. M. Zheng, †. L.B.Xie, D. Y. Liu, J. Ji, S. F. Li, L. L. Zhao, X. H. Zen","doi":"10.47176/jafm.16.12.1981","DOIUrl":"https://doi.org/10.47176/jafm.16.12.1981","url":null,"abstract":"The aim of this study was to accurately quantify the emission characteristics of pollutants at different altitudes. We used an intake and exhaust altitude simulation system that could simulate the intake and exhaust pressures of a national sixth vehicle diesel engine at different altitudes. Experimental research was conducted on the World Harmonized Transient Cycle (WHTC) and World Harmonized Steady State Cycle (WHSC) of the diesel engine. The results showed that carbon monoxide (CO) emissions increased with the altitude at full load, but their rates were significantly reduced at low speed (800 rpm), increasing by 0.0084–0.665 ppm/m. Hydrocarbon (HC) emissions showed an initial decreasing and then increasing trend, with a rise of up to 30%. Nitrogen oxides (NOx) showed a linear decreasing trend, especially at low speed. With the increase in altitude, the cycle work of the diesel engine decreased in a non-linear manner, and the decrease became more pronounced above 3000 m. The raw emission results of the WHTC and WHSC tests also revealed that CO increased exponentially, NOx decreased slightly and then increased rapidly, HC increased linearly, and the emissions of all pollutants deteriorated significantly above 3000 m. The exhaust emission results of the WHTC and WHSC tests showed that the CO emission showed an initial decreasing and then increasing trend with the elevation of the altitude, approximately 15 ± 5 mg/kWh. HC emissions showed an increasing trend, with HC emissions of 3 – 6 mg/kWh for the WHTC and 1 – 2 mg/kWh for the WHSC. NOx emissions did not follow any obvious rule, while the particulate matter (PM) tended to increase and then decrease with the elevation of the altitude. In relation to the current emission standards, the limit value margin for CO and HC exhaust emissions is greater than 95% and the limit value margin for PM emissions is greater than 88% at an altitude of 4000 m. The NOx emission limit is greater than 87% (within 3000 m), but there is a risk of exceeding the limit above 3000 m. The second sampling data from the WHTC and WHSC showed that the raw emissions of the engine were higher in the high-altitude area than in the low-altitude area, but the change law of the exhaust emissions was not obvious, and the levels of both emissions were low.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":"101 4","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138622413","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Supersonic Flow over Elliptic Cone with Different Ellipticity Ratio","authors":"†. V.Kotebavi, S. G. Rakesh","doi":"10.47176/jafm.16.12.1865","DOIUrl":"https://doi.org/10.47176/jafm.16.12.1865","url":null,"abstract":"This study investigates supersonic flow characteristics over circular and elliptic cones at various angles of attack. Simulations were conducted on the cones with the same base area and length-to-diameter ratio. The elliptic cones considered had axis ratios of 1.5 and 3. The angle of attack varied from 0o to 50o, with two different Mach numbers (1.97 and 2.94) employed for the analysis. The numerical results were compared with the experimental and theoretical findings from existing literature. The results revealed that increasing the ellipticity ratio of the cones resulted in higher lift generation. The pressure distributions on the windward and leeward sides of the cones were also examined. The results demonstrated that elliptic cones outperformed circular cones in terms of lift production, and this advantage increased with higher ellipticity ratios. Specifically, when the ellipticity ratio was increased from 1 to 3, the maximum increase in lift coefficient was 96% and 100% at Mach numbers 2.94 and 1.97, respectively. Additionally, by changing the ellipticity ratio from 1 to 1.5, the maximum gain in the lift-drag ratio was 16% and 22% at Mach numbers 1.97 and 2.94, respectively. Notably, an elliptic cone with an ellipticity ratio of 3 achieved a remarkable 46% gain in lift-to-drag ratio compared to a circular cone. However, as the angle of attack increased, a primary bow shock formed on the windward side of the cone, with an embedded shock appearing on the leeward side.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":" 783","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138610608","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Aerodynamic and RSM Analysis of Wingsuit Stability","authors":"M. Nazemian, M. S. Valipour","doi":"10.47176/jafm.16.12.2032","DOIUrl":"https://doi.org/10.47176/jafm.16.12.2032","url":null,"abstract":"A Wingsuit is a Skydiving Jumpsuit that generates more lift for longer flights. This study examined the effects of side slip angles on a beginner wingsuit at 106 Reynolds number. Experimental tests were determined by using the length of the model scale at angles of attack ranging from 0° to 40° and sideslip angles of up to 20°. Force and moment coefficients were analyzed using variations in angles of attack and sideslip. Despite the absence of significant effects of sideslip angles on the lift and drag coefficients, side force and rolling/yawing moments were highly nonlinear. Flow structure visualization and numerical simulation show that surface stalls only occur on the lower side when slip angles are lower. In individual aviation sports, wingsuits are more advantageous when they have less sideslip. With Tuft visualization on the wingsuit model, the best aerodynamic coefficient under different flight conditions was determined by comparing the Response Surface Methodology performance under different flight conditions.","PeriodicalId":49041,"journal":{"name":"Journal of Applied Fluid Mechanics","volume":" 55","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138620358","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}