Academic literature on the topic 'Velocity triangles'
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Journal articles on the topic "Velocity triangles"
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Rüger, Andreas, and Dave Hale. "Meshing for velocity modeling and ray tracing in complex velocity fields." GEOPHYSICS 71, no. 1 (2006): U1—U11. http://dx.doi.org/10.1190/1.2159061.
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In seismic processing, velocity fields are commonly represented on finely sampled Cartesian grids. Attractive alternatives are unstructured grids such as meshes composed of triangles or tetrahedra. Meshes provide a space-filling framework that enables editing of velocity models while facilitating numerical tasks such as seismic modeling and inversion. In this paper, we introduce an automated process to generate meshes of subsurface velocity structures for highly resolved velocity fields without providing additional external constraints such as horizons and faults. Our analysis shows that these new meshes can represent both smooth and discontinuous velocity profiles accurately and with less computer memory than grids.
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Avitzur, B., W. Gordon, and S. Talbert. "Analysis of Strip Rolling by the Upper Bound Approach." Journal of Engineering for Industry 109, no. 4 (1987): 338–46. http://dx.doi.org/10.1115/1.3187137.
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The process of strip rolling is analyzed using the upper bound technique. Two triangular velocity fields, one with triangles in linear rigid body motion and the other with triangles in rotational rigid body motion, are developed. The total power is determined as a function of the four independent process parameters (relative thickness, reduction, friction and net front-back tension). The results of these two velocity fields are compared with the established solution from Avitzur’s velocity field of continuous deformation. Upon establishing the validity of the triangular velocity field as an approach to the strip rolling problem, recommendations are suggested on how this approach can be used to study the split end or alligatoring defect.
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Gu, Yun Qing, Jing Ru, Zhao Gang, Zhao Yuan Li, Wen Bo Liu, and Muhammad Farid Khattak. "Influence of Jet Hole Configuration on Drag Reduction of Bionic Jet Surface." Applied Mechanics and Materials 461 (November 2013): 725–30. http://dx.doi.org/10.4028/www.scientific.net/amm.461.725.
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According to the jet hole configuration mode of bionic jet surface and its influence on the drag reduction, as the basic form of jet hole configuration is the isosceles triangle elements, so this was used to establish the computational model of jet hole configuration. In this case, the height and base of the triangles were considered as variable. The SST k-ω turbulence model was used to simulate and research the drag reduction characteristics of bionic jet surface in different configuration modes of jet holes at the main flow field velocity value of 20m/s and the jet velocity value of 0.4~2.0m/s. Also the influence of different configurations of height and base on drag reduction characteristics of bionic jet surface was studied, which got the optimum size of jet hole configuration. Results show that in triangle configuration elements, the drag reduction characteristics of bionic jet surface can be influenced by the jet hole of different configurations of height and base; the drag reduction of bionic jet surface reaches the peak of 32.74% at 8mm height, 11mm base, and the jet velocity value of 2.0m/s. At the same flow field velocity, the drag reduction rate results achieved by experimental tests and by numerical simulation were changing consistently and were found same, which verifies correctness of numerical simulation results.
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Averbeck, Bruno B., Matthew V. Chafee, David A. Crowe, and Apostolos P. Georgopoulos. "Parietal Representation of Hand Velocity in a Copy Task." Journal of Neurophysiology 93, no. 1 (2005): 508–18. http://dx.doi.org/10.1152/jn.00357.2004.
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We recorded neural activity from ensembles of neurons in areas 5 and 2 of parietal cortex, while two monkeys copied triangles, squares, trapezoids, and inverted triangles and used both linear and nonlinear models to predict the hand velocity from the neural activity of the ensembles. The linear model generally outperformed the nonlinear model, suggesting a reasonably linear relation between the neural activity and the hand velocity. We also found that the average transfer function of the linear model fit to individual cells was a low-pass filter because the neural response had considerable high-frequency power, whereas the hand velocity only had power at frequencies below ∼5 Hz. Increasing the width of the transfer function, up to a width of 700–800 ms, improved the fit of the model. Furthermore, the Rsqr of the linear model improved monotonically with the number of cells in the ensemble, saturating at 60–80% for a filter width of 700 ms. Finally, it was found that including an interaction term, which allowed the transfer function to shift with the eye position, did not improve the fit of the model. Thus ensemble neural responses in superior parietal cortex provide a high-fidelity, linear representation of hand kinematics within our task.
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Pennock, Gordon R., and Patrick J. Meehan. "Geometric Insight Into the Dynamics of a Rigid Body Using the Spatial Triangle of Screws." Journal of Mechanical Design 124, no. 4 (2002): 684–89. http://dx.doi.org/10.1115/1.1500340.
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Geometric relationships between the velocity screw and momentum screw are presented, and the dual angle between these two screws is shown to provide important insight into the kinetics of a rigid body. Then the centripetal screw is defined, and the significance of this screw in a study of the dynamics of a rigid body is explained. The dual-Euler equation, which is the dual form of the Newton-Euler equations of motion, is shown to be a spatial triangle. The vertices of the triangle are the centripetal screw, the time rate of change of momentum screw, and the force screw. The sides of the triangles are three dual angles between the three vertices. The spatial triangle provides valuable geometrical insight into the dynamics of a rigid body and is believed to be a meaningful alternative to existing analytical techniques. The authors believe that the work presented in this paper will prove useful in a dynamic analysis of closed-loop spatial mechanisms and multi-rigid body open-chain systems.
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Selzer, Philipp, and Olaf A. Cirpka. "Postprocessing of standard finite element velocity fields for accurate particle tracking applied to groundwater flow." Computational Geosciences 24, no. 4 (2020): 1605–24. http://dx.doi.org/10.1007/s10596-020-09969-y.
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Abstract Particle tracking is a computationally advantageous and fast scheme to determine travel times and trajectories in subsurface hydrology. Accurate particle tracking requires element-wise mass-conservative, conforming velocity fields. This condition is not fulfilled by the standard linear Galerkin finite element method (FEM). We present a projection, which maps a non-conforming, element-wise given velocity field, computed on triangles and tetrahedra, onto a conforming velocity field in lowest-order Raviart-Thomas-Nédélec ($\mathcal {RTN}_{0}$ R T N 0 ) space, which meets the requirements of accurate particle tracking. The projection is based on minimizing the difference in the hydraulic gradients at the element centroids between the standard FEM solution and the hydraulic gradients consistent with the $\mathcal {RTN}_{0}$ R T N 0 velocity field imposing element-wise mass conservation. Using the conforming velocity field in $\mathcal {RTN}_{0}$ R T N 0 space on triangles and tetrahedra, we present semi-analytical particle tracking methods for divergent and non-divergent flow. We compare the results with those obtained by a cell-centered finite volume method defined for the same elements, and a test case considering hydraulic anisotropy to an analytical solution. The velocity fields and associated particle trajectories based on the projection of the standard FEM solution are comparable to those resulting from the finite volume method, but the projected fields are smoother within zones of piecewise uniform hydraulic conductivity. While the $\mathcal {RTN}_{0}$ R T N 0 -projected standard FEM solution is thus more accurate, the computational costs of the cell-centered finite volume approach are considerably smaller.
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Liebold, Frank, Ali A. Heravi, Oliver Mosig, Manfred Curbach, Viktor Mechtcherine, and Hans-Gerd Maas. "Crack Propagation Velocity Determination by High-speed Camera Image Sequence Processing." Materials 13, no. 19 (2020): 4415. http://dx.doi.org/10.3390/ma13194415.
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The determination of crack propagation velocities can provide valuable information for a better understanding of damage processes of concrete. The spatio-temporal analysis of crack patterns developing at a speed of several hundred meters per second is a rather challenging task. In the paper, a photogrammetric procedure for the determination of crack propagation velocities in concrete specimens using high-speed camera image sequences is presented. A cascaded image sequence processing which starts with the computation of displacement vector fields for a dense pattern of points on the specimen’s surface between consecutive time steps of the image sequence chain has been developed. These surface points are triangulated into a mesh, and as representations of cracks, discontinuities in the displacement vector fields are found by a deformation analysis applied to all triangles of the mesh. Connected components of the deformed triangles are computed using region-growing techniques. Then, the crack tips are determined using the principal component analysis. The tips are tracked in the image sequence and the velocities between the time stamps of the images are derived. A major advantage of this method as compared to the established techniques is in the fact that it allows spatio-temporally resolved, full-field measurements rather than point-wise measurements. Furthermore, information on the crack width can be obtained simultaneously. To validate the experimentation, the authors processed image sequences of tests on four compact-tension specimens performed on a split-Hopkinson tension bar. The images were taken by a high-speed camera at a frame rate of 160,000 images per second. By applying the developed image sequence processing procedure to these datasets, crack propagation velocities of about 800 m/s were determined with a precision in the order of 50 m/s.
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Xing, Weiwei, Jian Zhang, Wei Lu, and Peng Bao. "An Improved Potential Field Based Method for Crowd Simulation." International Journal of Software Engineering and Knowledge Engineering 25, no. 03 (2015): 427–51. http://dx.doi.org/10.1142/s021819401540015x.
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Crowd simulation explores crowd behavior in virtual environments, which has been extensively studied in many areas, such as safety and civil engineering, transportation, social science, and entertainment industry. In this paper, an improved potential field method is proposed to achieve the real-time crowd simulation, which is composed of the global navigation with Dijkstra's algorithm and the potential field based local navigation. First, a region separation is performed to divide the environment into a set of triangles, and thus a topological graph can be built with the triangles as vertices. Then a velocity-density model is introduced for improving the speed controlling mechanism and solving the "maximum speed dilemma" which means the velocity of an individual derived by potential field will be stuck into the maximum due to the ill speed control. Since the movement of an individual in the crowd is influenced by the socio-psychological forces, the individuals' actions express the group attributes. In order to represent the group attributes in the crowd, the repulsive potential function is improved in this paper. Experiments have been carried out and the results show that the improved potential field based method can simulate the crowd in real time and avoid the "maximum speed dilemma".
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MULDER, W. A. "HIGHER-ORDER MASS-LUMPED FINITE ELEMENTS FOR THE WAVE EQUATION." Journal of Computational Acoustics 09, no. 02 (2001): 671–80. http://dx.doi.org/10.1142/s0218396x0100067x.
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The finite-element method (FEM) with mass lumping is an efficient scheme for modeling seismic wave propagation in the subsurface, especially in the presence of sharp velocity contrasts and rough topography. A number of numerical simulations for triangles are presented to illustrate the strength of the method. A comparison to the finite-difference method shows that the added complexity of the FEM is amply compensated by its superior accuracy, making the FEM the more efficient approach.
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Monen, Jos, and Eli Brenner. "Detecting Changes in One's Own Velocity from the Optic Flow." Perception 23, no. 6 (1994): 681–90. http://dx.doi.org/10.1068/p230681.
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Experiments were designed to establish whether we can use the optic flow to detect changes in our own velocity. Subjects were presented with simulations of forward motion across a flat surface. They were asked to respond as quickly as possible to a step increase in simulated ego-velocity. The smallest change for which subjects could respond within 500 ms was determined. At realistic simulated speeds of locomotion, the simulated ego-velocity had to increase by about 50%. The threshold for detecting changes in simulated ego-velocity was hardly better than the threshold for detecting other changes in the acceleration of the dots on the screen. It made little difference whether the surface across which the subject appeared to move was built up of dots, lines, or triangles; neither did it matter whether subjects saw the same image with both eyes, or whether the simulation was presented in stereoscopic depth. The results show that we are very poor at detecting changes in our own velocity on the basis of visual input alone.
Dissertations / Theses on the topic "Velocity triangles"
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Pavlíček, Jan. "Vliv délky lopatky virové turbíny na její charakteristiku." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231342.
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This thesis deals with the evaluation of swirl turbine measurement, which the length of the turbine blades was gradually reduced. The subject of the effect was influence of the length of the blades, especially the measured efficiency of the turbine, and the character assessment of the flow at the inlet and outlet of the impeller. The measured data were analysed using the computing workbook with macro support, which can be used to evaluate other measurements of similar character. The different behaviour of the turbine depending on the length of the blades of the impeller was shown in the characteristics of the turbine and velocity triangles. For the variant with the best efficiency achieved was constructed QH diagram used in the design of turbine parameters for a particular location.
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Pavlík, Jan. "Širokopásmová Francisova turbina." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2011. http://www.nusl.cz/ntk/nusl-229667.
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his diploma thesis deals with hydraulic design of vane wheel impeller of wide range Francis turbine; in addition to hydraulic calculation it consists overview of used theory, modelling in SolidWorks and computing in Fluent.
Books on the topic "Velocity triangles"
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Escudier, Marcel. Flow through axial-flow-turbomachinery blading. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198719878.003.0014.
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This chapter is concerned primarily with the flow of a compressible fluid through stationary and moving blading, for the most part using the analysis introduced in Chapter 11. The principles of dimensional analysis are applied to determine the appropriate non-dimensional parameters to characterise the performance of a turbomachine. The analysis of incompressible flow through a linear cascade of aerofoil-like blades is followed by the analysis of compressible flow. Velocity triangles for flow relative to blades, and Euler’s turbomachinery equation, are introduced to analyse flow through a rotor. The concepts introduced are applied to the analysis of an axial-turbomachine stage comprising a stator and a rotor, which applies to either a compressor or a turbine.
Conference papers on the topic "Velocity triangles"
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Lou, Fangyuan, and Nicole L. Key. "On Choosing the Optimal Impeller Exit Velocity Triangles in Preliminary Design." In ASME Turbo Expo 2021: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/gt2021-59210.
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Abstract Impeller discharge flow plays an important role in centrifugal compressor performance and operability for two reasons. First, it determines the work factor and relative diffusion for the impeller. Second, it sets the flow into the downstream stationary diffusion system. The choice made in the preliminary design phase for the impeller exit velocity triangle is crucial for a successful design. The state-of-the-art design approach for determining the impeller exit velocity triangle in the preliminary design phase relies on several empirical guidelines, i.e. maximum work factor and diffusion ratio for an impeller, the optimal range of absolute flow angle, etc. However, as modern compressors continue pushing toward higher efficiency and higher work factor, this design approach falls short in providing exact guidance for choosing an optimal impeller exit velocity triangles due to its empirical nature as well as the competing mechanism of the two trends. In light of this challenge, this paper introduces a reduced-dimension, deterministic approach for the design of the impeller exit velocity triangle. The method gauges the design of the impeller exit velocity triangle from a different design philosophy using a relative diffusion effectiveness parameter and is validated using 6 impeller designs, representative of applications in both turbochargers and aero engines. Furthermore, with the deterministic method in place, optimal impeller exit velocity triangles are explored over a broad design space, and a one-to-one mapping from a selection of impeller total-to-total pressure ratios and backsweep angles to a unique optimal impeller exit velocity triangle is provided. This new approach is demonstrated, and discussions regarding the influences of impeller total-to-total pressure ratio, isentropic efficiency, and backsweep angle on the optimal impeller exit velocity triangle are presented.
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Auchoybur, Kiran, and Robert J. Miller. "Design of Compressor Endwall Velocity Triangles." In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-57396.
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Near the endwalls of multi-stage compressor blade rows, there is a spanwise region of low momentum, high entropy fluid which develops due to the presence of annulus walls, leakage flows and corner separations. Off-design this region, known as the endwall flow region, often grows rapidly and in practice sets the compressor’s operating range. By contrast, over the operating range of the compressor, the freestream region of the flow is not usually close to its diffusion limit and has little effect on overall range. In light of these two distinct flow regions within a bladerow, this paper considers how velocity triangles in the endwall region should be designed to give a more balanced spanwise failure across the blade span. In the first part of the paper, the sensitivity of the operating flow range of a single blade row to variations in realistic multistage inlet conditions and endwall geometry is investigated. It is shown that the operating range of the blade row is largely controlled by the size and structure of the endwall ‘repeating stage’ inlet boundary layer and not the detailed local geometry within the blade row. In the second part of the paper the traditional design process is ‘flipped’. Instead of redesigning a blade’s endwall geometry to cope with a particular inlet profile into the blade row, the endwall region is redesigned in the multi-stage environment to ‘tailor’ the inlet profile into downstream blade rows. This is shown to allow an extra degree of freedom not usually open to the designer. This extra degree of freedom is exploited to balance freestream and endwall operating range, resulting in a compressor having an increased operating range of ∼20%. If this increased operating range is traded with reduced blade count, it is shown that a design efficiency improvement of Δη∼0.5% can be unlocked.
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Li, Shuo, Eric M. Krivitzky, and Xuwen Qiu. "Meanline Modeling of a Radial-Inflow Turbine Nozzle With Supersonic Expansion." In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-58077.
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High pressure ratio, radial-inflow turbines typically experience supersonic expansion in the nozzle section. Accurate estimation of the flow conditions and velocity triangle at the nozzle outlet is of critical importance in correctly predicting the overall turbine performance. The meanline modeling of such a nozzle requires special attention, due to the significantly altered flow field downstream of the throat. In this study, the flow field of a supersonic expansion nozzle is investigated, using a three-dimensional (3D) computational fluid dynamics (CFD) simulation calibrated with test data. Three different CFD configurations are explored: the nozzle alone, the nozzle plus rotor coupled with a mixing plane, and the nozzle plus rotor coupled with the nonlinear harmonic (NLH) method. These configurations are compared to each other to gauge the effect of the rotor and stator interaction and the potential for error in establishing the velocity triangles. The exit vane angle, number of vanes, and expansion ratio across the nozzle are systematically varied to provide the data as the base for nozzle modeling. Finally, a meanline method is proposed to calculate the pressure loss and flow deviation at the nozzle outlet and is compared with CFD results.
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Tsuboi, Kazuya, Shinnosuke Nishiki, and Tatsuya Hasegawa. "An Analysis of Local Quantities of Turbulent Premixed Flames Using DNS Databases." In ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference collocated with the ASME 2007 InterPACK Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/ht2007-32794.
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An analysis of local flame area was performed using DNS (Direct Numerical Simulation) databases of turbulent premixed flames with different density ratios and with different Lewis numbers. Firstly, a local flame surface at a prescribed progress variable was identified as a local three-dimensional polygon. And then the polygon was divided into some triangles and local flame area was evaluated. The turbulent burning velocity was evaluated using the ratio of the area of turbulent flame to that of planar flame and compared with the turbulent burning velocity obtained by the reaction rate.
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Sadeghi, Nader, Fred Barez, and Younes Shabany. "A New Approach to Model Axial Fans in Commercial CFD Tools." In ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems collocated with the ASME 2005 Heat Transfer Summer Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/ipack2005-73336.
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Most commercial CFD tools use fan curves to represent a fan. However, the presence of a blockage near inlet or exhaust of a fan and a restricted airflow direction will alter the fan performance, and the use of the original fan curve may result in erroneous results in these cases. A new approach to model fans will be presented in this paper. Using conservation of mass, momentum and energy, and the velocity triangles, this model relates velocity and pressure at fan exhaust to the corresponding values at fan inlet as well as fan geometry, rotational speed and fan blade lift and drag coefficients.
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Abraham, Santosh, Kapil Panchal, Srinath V. Ekkad, Wing Ng, Barry J. Brown, and Anthony Malandra. "Effect of Airfoil Shape and Turning Angle on Turbine Airfoil Aerodynamic Performance at Transonic Conditions." In ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-62167.
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Performance data for high turning gas turbine blades under transonic Mach numbers is significantly lacking in literature. Performance of three gas turbine airfoils with varying turning angles at transonic flow conditions was investigated in this study. Midspan total pressure loss, secondary flow field and static pressure measurements on the airfoil surface in a linear cascade setting were measured. Airfoil curvature and true chord were varied to change the loading vs. chord for each airfoil. Airfoils A, D and E are designed to operate at different velocity triangles. Velocity triangle requirements (inlet/exit Mach number and gas angles) come from 1D and 2D models that include calibrated loss systems. One of the goals of this study was to use the experimental data to confirm/refine loss predictions for the effect of various Mach numbers and gas turning angles. The cascade exit Mach numbers were varied within a range from 0.6 to 1.1. The airfoil turning angle ranges from 120° to 138°. A realistic inlet/exit Mach number ratio, that is representative of that seen in a real engine, was obtained by reducing the inlet span with respect to the exit span of the airfoil, thereby creating a quasi 2D cascade. In order to compare the experimental results and study the detailed flow characteristics, 3D viscous compressible CFD analysis was also carried out.
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Helmers, Lennard, and Jens Klingmann. "Unshrouded Rotor Tip Clearance Effects in Expander Cycle Turbines." In ASME Turbo Expo 2002: Power for Land, Sea, and Air. ASMEDC, 2002. http://dx.doi.org/10.1115/gt2002-30338.
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Steady flow in axial one-stage turbines is assessed numerically and experimentally. The simulations are performed on coarse meshes using a standard numerical approach (3D, steady state, kε-turbulence model, wall function at solid boundaries). In order to allow for conclusions drawn from these rapid numerical studies, the approach was compared with an explicit LDA (Laser Doppler anemometry) mapping of the velocity field downstream the rotor on a representative turbine stage. A two-component LDA system allowed for measurements of axial and tangential velocity components at varying depth (radius) in the flow channel, Measurements thus correspond to a full plane at constant axial position in the rotating frame of reference of the rotor. Comparison between LDA velocity mapping and CFD results shows good agreement. A series of subsequent simulations is thus used to judge the impact of varied blade/stage design parameters. Two turbine layouts are defined for identical operating conditions and shaft power. The flow in the unshrouded rotor blade row is analyzed for the influence of varying tip clearance size and the dependency on stage velocity triangles. – Known correlations for tip clearance losses (typically used in mean line predictions) are used, though the blade row geometry considered is beyond the limits the correlations are intended for. The absolute loss level found in CFD simulations differs significantly from what is expected when using loss correlations. Still the variation with tip gap size is predicted well by some of the investigated models. As dependency of tip clearance losses on stage velocity triangles is considered, none of the tested correlations gives results consistent with the numerical simulations. The use of standard correlations ‘beyond the limits’ is thus considered to introduce high uncertainty. Due to the good consistency between LDA and numerical results, the conclusions are considered to be valid for stage designs similar to the ones analyzed.
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Muppana, Sai, Kiran Siddappaji, Shaaban Abdallah, and Mark Turner. "Low Fidelity Design and Analysis Parametric Tool for General Centrifugal Compressors." In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-92002.
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Abstract Performance prediction and blade generation in a preliminary design stage of centrifugal compressors is critical to have a successful design. In this paper, a one-dimensional meanline design and analysis tool has been developed for single-rotor and novel multi-rotor centrifugal impellers. Loss models used for performance prediction of single stage compressors have been extended to single hub multi-rotor compressors to evaluate isentropic efficiency and pressure ratio. Stage conditions like work ratio and stator turning angle are given as input parameters and the tool computes flow properties along the meanline and also, generates velocity triangles, streamlines, smooth definition of blade angles at different spanwise sections. The tool acts a preprocessor for Tblade3 which is an in-house 3D parametric blade geometry generator to create blades. A 0D tool has been developed for multi-rotor impellers to provide an estimate of work ratio. 0D coupled with 1D tool can provide a good preliminary design point. The process of 0D to blade generation has been automated enabling it to connect with high-fidelity analysis. The motivation to create this tool is to calculate flow angles, metal angles, velocity triangles, ease of parametric modification and reduce aero-design cycle time. This tool is modular which adds the flexibility of capability extension. The code is validated with DLR centrifugal compressor experimental data. The 1D tool is also used to calculate performance and blade angles for the novel single hub multi-rotor centrifugal compressor demonstrating the versatility of the low fidelity tool. The tool suite is written in Python and is open source https://github.com/msaisiddhartha/CIMdes.
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Gill, Andrew, Theodor W. von Backström, Thomas M. Harms, and Dwain Dunn. "Flow Fields in an Axial Flow Compressor During Four-Quadrant Operation." In ASME Turbo Expo 2013: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/gt2013-95028.
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It has been shown in previous investigations that when all combinations of both positive and negative direction of rotation and flow direction are allowed in operating a multistage axial flow compressor, the operating point may be in any of the four quadrants of the pressure rise versus flow characteristic. The present paper is the first discussion of the flow field of all possible modes of operation of an axial flow compressor. During the present study interstage time dependent hot film velocity measurements and five hole pneumatic probe measurements were combined with steady and time dependent CFD solutions to investigate the flow fields in the three-stage axial compressor. Results are presented in terms of mean-line velocity triangles, mean stream surface plots, mid-span radial velocity contours right through the compressor, rotor-downstream radial distributions of axial and tangential velocity, stator-downstream axial velocity contours and mid-span entropy contours through the compressor. Main flow features are pointed out and discussed. The study was instigated in an effort to understand possible accident scenarios in a three-shaft closed cycle nuclear powered helium gas turbine.
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Willinger, Reinhard, and Michael Köhler. "Influence of Blade Loading Criteria and Design Limits on the Cordier-Line for Axial Flow Fans." In ASME Turbo Expo 2014: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/gt2014-25140.
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Volume flow rate, specific isentropic enthalpy difference, rotor outer diameter and rotational speed of a fan can be transformed to speed number and diameter number. These two non-dimensional numbers are related together in the so-called Cordier-diagram. For axial, radial and mixed flow fans, there is a single empirical relationship between both quantities and it is well accepted that this line represents “optimum” fan designs with high efficiency. Based on velocity triangles, a relationship between flow coefficient and pressure coefficient exists. This so-called performance curve captures off-design operating points as well as the design point of a fan. Therefore, the performance curve can be transformed to the Cordier-diagram to predict the relationship between speed number and diameter number. It is shown that the Cordier-line depends mainly on velocity triangles and the common argument of high efficiency, claimed in the majority of the literature, plays only a secondary role. Nevertheless, the requirement of high efficiency influences the fan design for a certain design point. This paper focuses mainly on axial flow fans. It gives a theoretical interpretation of the influence of blade loading criteria and design limits on the Cordier-line: (1) De Haller number, (2) cascade loading parameter, (3) Lieblein diffusion factor, (4) Strscheletzky swirl number. Criterion (1) reflects the minimum velocity ratio to avoid endwall separation in a linear compressor cascade. Criterion (2) is a combination of lift coefficient and cascade solidity. It reflects the aerodynamic loading of the suction side blade boundary layer. Criteria (1) and (2) are included in criterion (3). Finally, criterion (4) indicates the risk of hub separation due to strong swirl flow. The investigation shows that the transformation of these criteria to the Cordier-diagram gives very similar results. Furthermore, it is shown that the axial fan design limits in the Cordier-diagram are represented by certain hub-to-tip radius ratios.