Volume 1: Fluid Mechanics最新文献

{"title":"Coupled Blowing and Suction for Flow Separation Control","authors":"M. Tadjfar, D. Kamari","doi":"10.1115/ajkfluids2019-5384","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5384","url":null,"abstract":"\u0000 The effects of applying a coupled unsteady blowing and suction combination over SD7003 airfoil at Reynolds number of 60,000 at an angle of attack of 13°, where a large separation on the suction side of the airfoil existed, was considered to investigate active flow control (AFC) mechanism. URANS equations were employed to solve the flow field and k–ω SST was used as the turbulence model. The unsteady blowing and suction were implemented at an angle to the surface crossing the boundary layer (CBL). The influence of location and frequency of the blowing/suction jets were examined.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122360494","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":"Flying Spiders: Effects of the Dragline Length and the Spider Mass in Free-Fall","authors":"Tessa Stevens, Longhua Zhao, R. Courtney, Wei Zhang, L. Miller","doi":"10.1115/ajkfluids2019-5083","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5083","url":null,"abstract":"\u0000 Many species of spiders move from one location to another using a remarkable aerial dispersal “ballooning”. By ballooning, spiders can reach distances as far as 3200 km and heights of up to 5 km. Though a large number of observations of spider ballooning have been reported, it remains a mysterious phenomenon due to the limited scientific observation of spider ballooning in the field, high uncertainties of the meteorological conditions and insufficient controlled laboratory experiments. Most of the ballooning spiders are spiderlings and spiders under 3 mm in length and 0.2 to 2 mg in mass with a few exceptions of large spiders (over 3 mm in length, over 5 mg in mass). What physical mechanism dominates the three stages of spider ballooning — take-off, flight, and settling? Many factors have been identified to influence the physical mechanism, including a spider’s mass, morphology, posture, the silken dragline properties, and local meteorological conditions (e.g., turbulence level, temperature and humidity). A thorough understanding of the roles of key parameters is not only of ecological significance but also critical to advanced bio-inspired technologies of airborne robotic devices.\u0000 This work aims to determine how the dragline length and spider mass affect the interaction of the spider-dragline system in the free-fall scenario. Experiments using a thread of different lengths and a sphere of different masses to mimic the spider-dragline were carried out. The first sets of tests focused on the spider-dragline system, rather than the fluid flow. High-speed images of a spider-dragline falling in a closed container of air were recorded with 1500 frames per second at Reynolds numbers of several thousand, based on the spider dragline and the local relative velocity. Image data allow for tracking the vertical velocities and acceleration of the spider-dragline, as well as the drag force acting on the spider-dragline. Terminal velocities in the settling stage are compared with estimates using various fluid dynamics models in previous work. Such results under controlled laboratory conditions are expected to shed lights on the intriguing flow physics of spider ballooning at the settling stage and to inform future experiments and numerical models.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"101 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114460475","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":"High Speed Transient Flow in Manifolds","authors":"N. Findanis","doi":"10.1115/ajkfluids2019-5577","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5577","url":null,"abstract":"\u0000 Flows in manifolds is a ubiquitous and important area to implement flow improvements. In almost all applications of industrial pipe flows, there is the requirement to distribute the flow of fluid. There is a deficiency of studies in the area of flow distribution in manifolds with high speed flows. The present work is aimed at providing a further understanding of transient high speed flow distribution in manifolds. The different manifold configurations were analysed computationally. A comparison was focused between through the different aspect ratio manifolds. The velocity field and the eddy viscosity parameters where compared between the simulated flow models to ascertain the key features in the distributed flow field and especially, to determine the areas that showed greater flow recirculation or flow eddies and the separated flow regions. The CFD study was conducted as a high speed flow/ compressible flow regime accounting for the ideal gas dynamic model being air as the working fluid. The study showed that the transient behaviour of flow field can significantly affect distribution of the flow depending on the aspect ratio and number of branches on the manifold. Efficiency gains can be achieved in high speed flows that can be of benefit in industrial and other engineered flow applications.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123863836","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":"Prediction of Drag Reduction Effect of Pulsating Control in Turbulent Pipe Flow by Machine Learning","authors":"W. Kobayashi, Takaaki Shimura, A. Mitsuishi, K. Iwamoto, A. Murata","doi":"10.1115/ajkfluids2019-5681","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5681","url":null,"abstract":"\u0000 It has been widely expected that the pulsating control can reduce friction drag in various fluid systems. In order to maximize its effect, a prediction tool of drag reduction using pulsating control is required. The present study aims at the prediction of the drag reduction rate by machine learning. Multilayer perceptron (MLP) was applied as the machine learning method. Water was used as the working fluid. First, an automatic measurement system was constructed and drag reduction effect was evaluated by an experiment with various pulsation waveforms. The flow pulsation was generated by giving periodical acceleration and deceleration by a centrifugal pump in a closed circulation system. The bulk Reynolds number Reb ranges between 3400 and 3800. Next, the experiments were performed with over 5000 kinds of waveforms to make training and validation data for MLP. Within the data, the maximum drag reduction rate of 38.6% was observed. The friction coefficient Cf decreased during the acceleration period and increased during deceleration period. Finally, the drag reduction rate was predicted in three cases with different input parameters of MLP. The relationship between pulsation waveforms and the drag reduction effect was successfully predicted.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124530470","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":"Modelling and Validation of Tooth Tip Leakages in Gerotor Pumps","authors":"Fnu Rituraj, A. Vacca","doi":"10.1115/ajkfluids2019-5531","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5531","url":null,"abstract":"\u0000 Gerotor pumps are commonly used as charge pumps in hydrostatic transmission systems as well as in fuel injection and automotive lubrication systems. For high pressure applications, Gerotors suffer from internal leakages which are one of the main sources of volumetric loss. The curvature of typical gear profiles for Gerotors prevents the usage of simple analytical relations to describe this leakage flow.\u0000 In this paper, a non-dimensional functional relationship is developed between geometric and flow parameters to model this leakage flow. A set of CFD simulations are conducted on the tooth tip geometry to establish this relationship. Then, an experimental setup is designed to reproduce the flow conditions at tooth tip of Gerotor. Experiments are conducted for a range of geometric and flow parameters and results from experiments are used to validate the proposed non-dimensional model.\u0000 The tooth tip leakage model developed and validated in this work is valuable for pump designers in determining the impact of gear geometry and clearances on volumetric performance of the pump. Moreover, the model can be readily used in any lumped parameter based simulation tool permitting a fast and accurate prediction of the tooth tip leakage flow and hence the volumetric efficiency of the unit.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"34 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132006502","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 Fineness Ratio of 0.5 - 2.0 on the Wake Structure Around a Circular Cylinder Measured Using Time-Resolved PIV","authors":"S. Yokota, T. Ochiai, Takumi Ambo, Y. Ozawa, T. Nonomura, K. Asai","doi":"10.1115/ajkfluids2019-5530","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5530","url":null,"abstract":"\u0000 In this study, the wake structure around freestream-aligned cylinder is investigated and its aerodynamic characteristics are discussed. A magnetic suspension and balance system (MSBS) was used to support a model without interference from a mechanical support device. Seven models with the fineness ratio (length to diameter, L/D) of 0.5, 1.0, 1.25, 1.5, 1.75, 2.0, and 2.25 were used. Reynolds number based on the cylinder diameter were 3.2 × 104 and 6.3 × 104. The velocity field was obtained by particle image velocimetry (PIV) in the center plane of the cylinder. In the case of fineness ratio over 1.5, the reattachment of shear layer was observed from the mean velocity field. The characteristic fluctuation of velocity was confirmed in power spectral density of streamwise component and vertical component. The length of the recirculation region is different depending on fineness ratio. The characteristic frequencies of the velocity fluctuation which seems to be due to recirculation bubble pumping and large-scale structure are observed from power spectrum density.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131714836","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 Simulations of the Rheological Behavior of Aqueous Foam Flow Through a Half-Sudden Expansion","authors":"H. Dallagi, Ahmad Al Saabi, C. Faille, T. Benezech, W. Augustin, F. Aloui","doi":"10.1115/ajkfluids2019-4650","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4650","url":null,"abstract":"\u0000 Aqueous foam is a non-Newtonian complex fluid. Its flow through the singularities presents many fundamental aspects. The rheological character of the foams flowing in this kind of geometries can create important disturbance on its behavior, according to the flow rate set and therefore a modification in its texture and in the nature of its established regime. During this study, numerical simulation for the case of a half-sudden expansion was developed using the Herschel-Bulkley rheological model. The model is used to describe the response of foams during under flowing conditions through this type of singularity. Obtained CFD results are focused on the pressure losses, velocity fields of the foam flow in various positions of the channel using different qualities (variation of void fraction) for lower velocities’ case (one-dimensional regime) and for the three-dimensional regime. Firstly, we validated the use of this type of non-Newtonian foam flow fluid to describe the flow reorganization through a half-sudden. In a second step, we used an experimental database to validate our CFD pressure losses and velocity fields. The comparison of these results with those obtained experimentally by Chovet shows a good agreement for lower speed foam flow, but with some uncertainty for higher foam flow velocities.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116937152","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":"Experimental Study on the Friction Drag Reduction of Hydrogel Paint in a Boundary Layer on Flat Plate","authors":"Y. Takagi, T. Hino, Nishimura Masanari, H. Aso","doi":"10.1115/ajkfluids2019-4746","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4746","url":null,"abstract":"\u0000 The drag reduction effect of hydrogel paint was experimentally investigated with the resistance test in a circular water tank. The hydrogel and non-hydrogel paints were coated on the 1.7-meters flat plate and the total drag force was measured with a one-component force meter up to the middle Reynolds number of 1.5 × 106. The attachment of turbulence stimulator at the leading edge on the plate was also considered. The remarkable drag reduction was observed at the low Reynolds number of laminar-turbulent transition region and the hydrodynamic mechanism of its drag reduction was discussed.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115994392","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":"Locomotive Capabilities of a Free-Swimming Robotic Tuna","authors":"Nicholas Noviasky, Alexander Matta, J. Bayandor","doi":"10.1115/ajkfluids2019-5557","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5557","url":null,"abstract":"\u0000 As we try and understand more about the oceans and the creatures that inhabit them, the need for effective modes of aquatic transportation becomes abundantly clear. Taking a step back from traditional propeller-based systems, we look toward nature and the millions of years of natural selection to find inspiration. The successful designs that have prospered vary greatly from creature to creature depending on their lifestyle. From rays to jellyfish, the propulsion methods used are tailored for a specific purpose. Considering the vastness of the oceans and our desire to explore them, a quick and efficient mode of locomotion would be well suited for this task. A great example of this type of swimmer can be found within the genus Thunnus.\u0000 Tuna rely on a lift-based propulsion system classified as thunniform swimming. The majority of thrust from this propulsion method is derived from the caudal fin and part of the tail. As the tail sweeps through the water, interesting vortex structures are shed from the trailing edge of the lunate fin. Along with velocity components that travel parallel to the movement of the fish, two separate vortices are shed from the top and bottom inner surfaces of the caudal fin and meet at the lengthwise center axis of the fish. These can be best visualized from the flow velocity components analyzed within a plane just behind the caudal fin and perpendicular to the body length axis. Over time, a reverse Karman vortex street is formed from the combination of vortices from multiple tail beats. A robotic tuna and CFD model were created with the minimum number of joints to approximate thunniform swimming.\u0000 A modified scotch yoke mechanism was used to convert uniform rotation of a brushless DC motor to oscillatory motion that mimics the tail of a tuna. A servo is mounted on the tail to provide an adjustable angle of attack for the caudal fin. The dynamic CFD model of the tuna employs overset meshing techniques created in ICEM CFD 18.2 and is simulated within ANSYS Fluent 18.2. The model is actuated at the start of the tail and the base of the fin to represent thunniform swimming. The body of the tuna is held static as steady flow is passed around the model. The flow velocity was chosen as an approximation of the speed of a tuna of comparable size and tail-beat frequency.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"115 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123458964","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":"Heat Transfer and Fluid Flow in Arc-Based Additive Manufacturing","authors":"Jun Zhou","doi":"10.1115/ajkfluids2019-4828","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4828","url":null,"abstract":"\u0000 Additive manufacturing (AM) is gaining rapid popularity in many industries like automotive, medical, electronics and aerospace due to its flexibility to build parts with complex geometry. Nowadays, laser/electron-beam/arc melting or deposition are commonly used for AM of metallic parts. Melting-solidification and melt flow repeatedly occur in the AM process, which are critical in determining the final shape, precision, and quality of the AM products. In this study, melt flow and heat transfer in arc-based metallic additive manufacturing process are discussed. The key parameters affecting the fluid flow; heat transfer; defect formation; and surface topology of the AM parts are investigated.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"42 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130000153","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}