Volume 1: Fluid Mechanics最新文献

{"title":"Pulsatile Flow Characteristics in a Stenotic Aortic Valve Model: An In Vitro Experimental Study","authors":"Ruihang Zhang, Yan Zhang","doi":"10.1115/ajkfluids2019-4978","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4978","url":null,"abstract":"\u0000 Aortic stenosis (AS) is one of the most common valvular heart diseases around the globe. The accurate assessment of AS severity is important and strongly associated with accurate interpretation of the hemodynamic parameters across the stenotic valve. In this study, we conducted in vitro fluid dynamic experiments to investigate the pulsatile flow characteristics of a stenotic aortic valve as a function of heart rate. An in vitro cardiovascular flow simulator was used to generate pulsatile flow with a prescribed waveform (40% systolic period and 4L/min cardiac output) under varied heart rates (50 bpm, 75 bpm and 100 bpm). The stenotic valve was constructed by molding silicone into three-leaflet aortic valve geometries wrapping around thin fabrics which increases its stiffness and tensile strength. Two-dimensional phase-locked particle image velocimetry (PIV) was employed to quantify the flow field characteristics of the stenotic valve. Pressure waveforms were recorded to evaluate the severity of the stenosis via the Gorlin and Hakki equations. Results suggest that as the heart rate increases, the peak pressure gradient across the stenotic aortic valve increases significantly under the same cardiac output. Analysis also shows the estimated aortic valve area (AVA) decreases as the heart rate increases under the same cardiac output using Gorlin equation estimation, while the trend is reversed using Hakki equation estimation. Under phase-locked conditions, quantitative flow characteristics, such as phase-averaged flow velocity, turbulence kinetic energy (TKE) for the stenotic aortic valve were analyzed based on the PIV data. Results suggest that the peak systolic jet velocity downstream of the valve increases as the heart rate increases, implying a longer pressure recovery distance as heart rate increases. While the turbulence at peak systole is higher under the slower heart rate, the faster heart rate contributes to a higher turbulence during the late systole and early diastole phases. Based on the comparison with no-valve cases, the differences in TKE was mainly related to the dynamics of leaflets under different heart rates. Overall, the results obtained in this study demonstrate that the hemodynamics of a stenotic aortic valve is complex and the assessment of AS could be significantly affected by the pulsating rate of the flow.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"19 25-26 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":"116704910","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":"A Validation Experiment for Turbulent Mixing in a Collated Jet","authors":"I. Craig, Coleman D. Hoff, Paul J. Kristo, M. Kimber","doi":"10.1115/ajkfluids2019-4981","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4981","url":null,"abstract":"\u0000 Numerical modeling of turbulent mixing is complicated not only by the natural complexity of the flow physics, but by the model sensitivity to the user specified conditions. When aiming to quantify the level of trust in a given model, a validation experiment is often performed to provide data against which confidence comparisons can be made, ultimately evaluating the adequacy of the model assumptions. In the nuclear community, a number of promising Generation IV reactor concepts have been proposed, each requiring high fidelity modeling capabilities to accurately assess safety related issues. The experiment described in this paper is intended to provide a much needed validation data set to assess the use of computational fluid dynamics (CFD) in a complex turbulent mixing scenario relevant to the prismatic very high temperature reactor (VHTR) concept. Over the course of the VHTR’s operation, the reactor’s graphite moderated hexagonal fuel blocks shrink from neutron damage, forming interstitial gaps between adjacent blocks. A significant percentage of the coolant can flow through these gaps, having a substantial impact on the thermal-hydraulic conditions in the core. An experimental facility is presented that uses air as a simulant fluid and includes a unit cell representation of the hexagonal blocks, which accounts for both the intended circular channels and secondary rectangular slot features induced by the bypass gaps. The outlet of the unit cell consists of a collated jet consisting of a central round jet surrounded by three slot jets at relative 120° angles to one another issuing into a stagnant domain. A preliminary test case is proposed in which the collated jet is set to an isothermal and iso-velocity condition. Constant temperature anemometry (CTA) and constant current anemometry (CCA) measurements serve to capture the velocity and temperature inlet quantities (IQs). Particle image velocimetry (PIV) measurements provide the appropriate system response quantities (SRQs), yielding insight into the mean and fluctuating components of the 2-D velocity field. Results are presented in the range of 0–8 diameters downstream of the inlet to the test section. The collated jet inlet region yields velocity profiles that are heavily influenced by opposing pressure gradients between the neighboring round and slot regions. As a result, the velocity peaks found in this area are neither in the centerline of the round jet nor that of the slot, but are towards the outer edge of each. With increasing downstream distance, the collated jet is found to exhibit a more classical round jet profile. The inlet region of the collated jet is thus of particular interest to future modeling efforts to more accurately depict the lower plenum behavior and transition to a self-similar profile downstream. Proper uncertainty quantification is also presented, and aids in assessing the integrity of the experimental results for future CFD validation.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"106 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":"132987980","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":"Wake Behavior Around Flapping Wings of Model Hawkmoth Moving Sideways","authors":"Jong-Seob Han, Jae-Hung Han","doi":"10.1115/ajkfluids2019-4808","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4808","url":null,"abstract":"\u0000 This study investigated nearwake behaviors around flapping wings moving sideways. A dynamically scaled-up flapping manipulator was installed on a servo-driven towing carriage to give the sideways movement. In the single wing configuration, the wing in the windward side did not encounter any noticeable effects on the aerodynamic characteristics. The wing in the leeward side, on the other hand, experienced a substantial lift augmentation. We found a stretched leading-edge vortex (LEV) on the wing in the leeward side, implying the additional feeding flux into the LEV. In this case, the moving sideways gave a continuous lateral wind, which became the source to maintain the lift augmentation with the less downward component. We also found that the moving sideways rather intensified the interaction between the wake of the wing in the windward side and the contralateral wing, i.e., the wing-wake interaction. Accordingly, the lift augmentation on the wing in the leeward side practically disappeared by the wing-wake interaction. A digital particle image velocimetry for nearwake behaviors found the less developed trailing-edge shear layer and wingroot vortex traces. This implied that the massive downwash induced by the wing in the windward side was the main source to neutralize the lift augmentation on the contralateral wing.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"160 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":"134338833","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":"On the Low and High Speed Flow of Gases Through Pillow Plate Channels","authors":"Maximilian Passmann, S. Wiesche, E. Kenig","doi":"10.1115/ajkfluids2019-4933","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4933","url":null,"abstract":"\u0000 Low speed and high speed flow phenomena in pillow plate channels are considered. High speed flows were investigated by means of analytical methods and fully three-dimensional computational fluid dynamics (CFD) simulations. The theoretical analysis indicated that a Fanno-type flow model described high speed flow behavior in pillow plate channels reasonably well. Since only wavy walls with smooth profiles were involved, linearized gas dynamics was applied in order to derive similarity laws for the high speed flows. The detailed CFD analysis was used to support the assumption of a Fanno-type flow. The effects of the wavy wall structures on pressure drop and Mach number distribution within the flow path were investigated in detail. The present analysis demonstrates that pillow plate heat exchangers represent promising candidates for high speed turbo machinery applications.","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":"115655361","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 Bionic Groove Surface Blade on Cavitation Characteristics of Centrifugal Pump","authors":"Zhang Zicheng, Yun Dai, Yunqing Gu, Shi Zhengzan, J. Mou","doi":"10.1115/ajkfluids2019-5119","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5119","url":null,"abstract":"\u0000 In order to improve the cavitation resistance of centrifugal pump, bionic groove surface structure was arranged on the suction surface of centrifugal pump blade which is the most prone to cavitation. Numerical simulation method was used to study the influence of different-shape groove blade on cavitation performance of centrifugal pump. The results showed that the head and efficiency of the centrifugal pump with circular grooved surface blades were close to the smooth surface blade centrifugal pump and higher than those with triangular grooved surface blades and rectangular grooved surface blades. The low pressure area of the circular groove blade was the smallest and the cavitation resistance was the best. At the critical cavitation margin point, circular groove blade can effectively reduce the probability of negative incidence, and the cavitation inhibition effect was the most obvious.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"47 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":"115019144","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":"PIV and POD Investigations of Coherent Vortices Downstream Circular or Rectangular Obstacles Located Between Two Parallel Plates","authors":"F. Aloui, A. Elawady, K. Hammad","doi":"10.1115/ajkfluids2019-4651","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4651","url":null,"abstract":"\u0000 The study is an experimental investigations using PIV. The measurements were obtained by PIV for an unsteady laminar flow across a rectangular channel with a cross-section 300 × 30mm2, in the middle of which is located a cylindrical or a square obstacle. In the case of the cylindrical configuration and due to the confinement, PIV measurements in the range of 40 < Re < 200 clearly show that the von Karman vortex shedding appears at a critical Reynolds number which is about 66. A post-processing of these PIV measurements using the Proper Orthogonal Decomposition (POD) technique is by keeping only the first most energetic six modes, can be used as a filtering process to remove noise from instantaneous velocity signals. In the case of the square obstacle, PIV measurements obtained in the range of 30 < Re < 350 show the absence of vortex detachments and the chaotic behavior of the wake behind the obstacle beyond a certain Reynolds number. By examining the POD post-possessing results, the existence of a dynamic detachments’ regime (instantaneous breaking and coalescence of vortices), can be clearly observed. Given the chaotic behavior of the wake behind the obstacle, the application of the POD filtering process to only the first most energetic modes, cannot lead to good results.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"3 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":"128569624","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":"Effects of Coriolis Force on Turbulence Structure in Rotating Channels With High and Low Aspect Ratios","authors":"H. Koyama, Shoichiro Tatsuta, E. Tamura, H. Nigim","doi":"10.1115/ajkfluids2019-4778","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4778","url":null,"abstract":"\u0000 To clarify the stabilization, destabilization and secondary flow effects of the Coriolis force on the turbulence structure in rotating channels with high and low aspect ratios, experimental investigations were undertaken by using a rotating wind tunnel about 2 meters in diameter. A hot-wire anemometer and more than 6 hot-wire probes with fine resistance wire, each inclined at a known angle to the main flow, were used for the measurements of time-mean velocities and 6 components of Reynolds normal and shear stresses. An optical transmission system of electrical signals from a rotating apparatus to the stationary system was used to immunize the electrical noise. The hot-wire probe was traversed with sufficient accuracy. Phenomena of the stratification, Taylor-Görtler type vortices in the destabilized nominal two-dimensional turbulent boundary layer, relaminarization from turbulent to laminar boundary layer in the high aspect ratio channel and a pair of longitudinal flat vortices in the low aspect ratio channel were observed, and discussed in detail by using the low of conservation of angular momentum, the vorticity transport equation and the Reynolds stress transport equations in a rotating frame.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"40 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":"124609672","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 Investigation of Nozzle Orientation Effects on Mixing Characteristics of Elliptic Triple Free Jets","authors":"Ella M. Morris, Seyed Sobhan Aleyasin, Neelakash Biswas, M. Tachie","doi":"10.1115/ajkfluids2019-5463","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5463","url":null,"abstract":"\u0000 An experimental investigation of nozzle orientation effects on turbulent characteristics of elliptic triple free jets was carried out for three nozzle configurations. The first configuration had all three nozzles oriented along the minor plane (3_Minor), the next had two nozzles oriented along the minor plane and one along the major plane (2_Minor_1_Major) and the last configuration had one nozzle oriented along the minor plane and two along the major plane (1_Minor_2_Major). The experiments were conducted using modified contoured nozzles with a sharp linear contraction for a nozzle-to-nozzle distance of 4.1, a nozzle equivalent diameter of 9 mm and a Reynolds number of 10,000. The effects of nozzle orientation on the mean velocity, turbulence intensity and Reynolds shear stress were discussed. The velocity decay, jet spread, merging point, combined point and potential core length were used to characterize the effects of nozzle orientation on the mixing performance. The results show that the 3_Minor configuration had shorter potential core length and closer merging point location which are indicative of a faster mixing in the converging region. Two-point correlation, skewness and flatness factors were used to provide insight into the effects of nozzle orientation on turbulence structure and higher order turbulence statistics.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"76 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":"129273731","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 and Numerical Analysis of an Axial Piston Pump: A Comparison Between Lumped Parameter and 3D CFD Approaches","authors":"E. Frosina, G. Marinaro, A. Senatore","doi":"10.1115/ajkfluids2019-5406","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5406","url":null,"abstract":"\u0000 In this paper an axial piston pump is studied using numerical and experimental approaches. The pump, manufactured by the company Continental Hydraulic Inc., has a maximum operating pressure limit of 280 bar and a displacement of 65.9 cm3/rev; it is a variable swashplate design with nine-piston, suitable for open circuit application, medium to high pressure.\u0000 Two numerical approaches have been compared to simulate the pump units. First of all, an accurate 3D -CFD model has been built up putting emphasis on the description of the detailed features of the flow through the unit. Specific attention has been reserved to the flow losses due to cavitation. Then a fast-lumped parameter approach has been built up focusing the attention on the valve plate geometry. Using the proposed numerical approaches, it is possible to fully understand the unit operation with, obviously, different assumptions and level of result details.\u0000 Numerical models have been validated with an experimental data performed by the pump manufactured on their test ring with high agreement.\u0000 As results, the proposed analysis permit to gain a high level of understanding of the operation of the unit finding the critical aspects and giving important information to the designer in order to improve the pump performance.\u0000 By the end a new valve plate has been designed to improve the pump volumetric efficiency and to reduce the flow ripples and the reverse flow.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"93 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":"126210649","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":"Global Stability Analysis on the Spiral-Vortex Mode in the Confined Cavity Flow Between Rotating and Stationary Disks","authors":"K. Okabayashi, Y. Kodera, S. Takeuchi, T. Kajishima, B. An, M. Nohmi, M. Obuchi","doi":"10.1115/ajkfluids2019-4785","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4785","url":null,"abstract":"\u0000 Global stability analysis (GSA) is applied to a 3D confined cavity flow between rotating and stationary disks (viz., rotor and stator). The Arnoldi method extended for incompressible viscous flow is used together with the eigenvalue spectrum conversion to solve the eigenvalue problem of the GSA. As a first step, the GSA is conducted in an axisymmetric flow, and circular vortices are obtained as eigen modes. Then, the GSA is applied to a flow with circular vortex at a higher Reynolds number, and eigen vectors of spiral vortex are obtained. The result suggests that the GSA shows unstable flows after transition of the baseflow. However, it is necessary to reconsider the convergence of the eigenvalues for the parameters of Arnoldi method.","PeriodicalId":314304,"journal":{"name":"Volume 1: Fluid Mechanics","volume":"340 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":"123399344","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}