Academic literature on the topic 'Swirl turbine with counter-rotating runners'
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Journal articles on the topic "Swirl turbine with counter-rotating runners"
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Fahlbeck, Jonathan, Håkan Nilsson, and Saeed Salehi. "Flow Characteristics of Preliminary Shutdown and Startup Sequences for a Model Counter-Rotating Pump-Turbine." Energies 14, no. 12 (2021): 3593. http://dx.doi.org/10.3390/en14123593.
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Pumped Hydropower Storage (PHS) is the maturest and most economically viable technology for storing energy and regulating the electrical grid on a large scale. Due to the growing amount of intermittent renewable energy sources, the necessity of maintaining grid stability increases. Most PHS facilities today require a geographical topology with large differences in elevation. The ALPHEUS H2020 EU project has the aim to develop PHS for flat geographical topologies. The present study was concerned with the initial design of a low-head model counter-rotating pump-turbine. The machine was numerically analysed during the shutdown and startup sequences using computational fluid dynamics. The rotational speed of the individual runners was decreased from the design point to stand-still and increased back to the design point, in both pump and turbine modes. As the rotational speeds were close to zero, the flow field was chaotic, and a large flow separation occurred by the blades of the runners. Rapid load variations on the runner blades and reverse flow were encountered in pump mode as the machine lost the ability to produce head. The loads were less severe in the turbine mode sequence. Frequency analyses revealed that the blade passing frequencies and their linear combinations yielded the strongest pulsations in the system.
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WANG, SHANWU, VIGOR YANG, GEORGE HSIAO, SHIH-YANG HSIEH, and HUKAM C. MONGIA. "Large-eddy simulations of gas-turbine swirl injector flow dynamics." Journal of Fluid Mechanics 583 (July 4, 2007): 99–122. http://dx.doi.org/10.1017/s0022112007006155.
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A comprehensive study on confined swirling flows in an operational gas-turbine injector was performed by means of large-eddy simulations. The formulation was based on the Favre-filtered conservation equations and a modified Smagorinsky treatment of subgrid-scale motions. The model was then numerically solved by means of a preconditioned density-based finite-volume approach. Calculated mean velocities and turbulence properties show good agreement with experimental data obtained from the laser-Doppler velocimetry measurements. Various aspects of the swirling flow development (such as the central recirculating flow, precessing vortex core and Kelvin–Helmholtz instability) were explored in detail. Both co- and counter-rotating configurations were considered, and the effects of swirl direction on flow characteristics were examined. The flow evolution inside the injector is dictated mainly by the air delivered through the primary swirler. The impact of the secondary swirler appears to be limited.
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Andolfatto, L., E. Vagnoni, V. Hasmatuchi, C. Münch-Alligné, and F. Avellan. "Simulation of energy recovery on water utility networks by a micro-turbine with counter-rotating runners." IOP Conference Series: Earth and Environmental Science 49 (November 2016): 102012. http://dx.doi.org/10.1088/1755-1315/49/10/102012.
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Vagnoni, E., L. Andolfatto, S. Richard, C. Münch-Alligné, and F. Avellan. "Hydraulic performance evaluation of a micro-turbine with counter rotating runners by experimental investigation and numerical simulation." Renewable Energy 126 (October 2018): 943–53. http://dx.doi.org/10.1016/j.renene.2018.04.015.
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Hasmatuchi, Vlad, Alin Bosioc, Sébastien Luisier, and Cécile Münch-Alligné. "A Dynamic Approach for Faster Performance Measurements on Hydraulic Turbomachinery Model Testing." Applied Sciences 8, no. 9 (2018): 1426. http://dx.doi.org/10.3390/app8091426.
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During the design and optimization of hydraulic turbomachines, the experimental evaluation of hydraulic performances beyond the best efficiency point and for off-design conditions remains essential to validate the simulation process and to finalize the development. In this context, an alternative faster method to measure the efficiency of hydraulic turbomachines using a dynamic approach has been investigated. The so-called “sliding-gate” dynamic measurement method has been adapted and implemented on the hydraulic test rig of the HES-SO Valais//Wallis, Sion, Switzerland. This alternative approach, particularly gainful for small-hydro for which the investment devoted to development is limited, has been successfully assessed on two cases for drinking water networks energy recovery. A 2.65 kW double-regulated laboratory prototype of a tubular axial micro-turbine with two independent variable speed counter-rotating runners and a 11 kW multi-stage centrifugal pump-as-turbine (PAT) with variable speed have been selected. The hydraulic efficiency results obtained by dynamic measurements are compared to the ones obtained by the classical steady point-by-point method. This dynamic method, suitable not only for hydraulic machinery, allows: (i) reducing significantly (up to 10×) the time necessary to draw the complete efficiency characteristics of a hydraulic machine; (ii) rapidly detecting the hydrodynamic instabilities within the operating range of the machine.
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Houde, Sébastien, Guy Dumas, and Claire Deschênes. "Experimental and Numerical Investigations on the Origins of Rotating Stall in a Propeller Turbine Runner Operating in No-Load Conditions." Journal of Fluids Engineering 140, no. 11 (2018). http://dx.doi.org/10.1115/1.4039713.
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Hydraulic turbines are more frequently used for power regulation and thus spend more time providing spinning reserve for electrical grids. Spinning reserve requires the turbine to operate at its synchronous rotation speed, ready to be linked to the grid in what is termed the speed-no-load (SNL) condition. The turbine's runner flow in SNL is characterized by low discharge and high swirl leading to low-frequency high amplitude pressure fluctuations potentially leading to blade damage and more maintenance downtime. For low-head hydraulic turbines operating at SNL, the large pressure fluctuations in the runner are sometimes attributed to rotating stall. Using embedded pressure transducer measurements, mounted on runner blades of a model propeller turbine, and numerical flow simulations, this paper provides an insight into the inception mechanism associated with rotating stall in SNL conditions. The results offer evidence that the rotating stall is in fact associated with an unstable vorticity distribution not associated with the runner blades themselves.
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Skripkin, S. G., M. A. Tsoy, P. A. Kuibin, and S. I. Shtork. "Study of Pressure Shock Caused by a Vortex Ring Separated From a Vortex Rope in a Draft Tube Model." Journal of Fluids Engineering 139, no. 8 (2017). http://dx.doi.org/10.1115/1.4036264.
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Operating hydraulic turbines under part- or over-load conditions leads to the development of the precessing vortex rope downstream of the turbine runner. In a regime close to the best efficiency point (BEP), the vortex rope is very unstable because of the low residual swirl of the flow. However, strong pressure pulsations have been detected in the regime. These oscillations can be caused by self-merging and reconnection of a vortex helix with the formation of a vortex ring. The vortex ring moves along the wall of the draft tube and generates a sharp pressure pulse that is registered by pressure transducer. This phenomenon was investigated on a simplified draft tube model using a swirl generator consisting of a stationary swirler and a freely rotating runner. The experiments were performed at Reynolds number (Re) = 105. The measurements involved a high-speed visualization technique synchronized with pressure measurements on the draft tube wall, which enables an analysis of the key stages of vortex ring formation by comparing it with the pressure on the draft tube wall. Quantitative information regarding the average velocity distribution was obtained via the laser Doppler anemometer (LDA) technique.
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Javadi, A., A. Bosioc, H. Nilsson, S. Muntean, and R. Susan-Resiga. "Experimental and Numerical Investigation of the Precessing Helical Vortex in a Conical Diffuser, With Rotor–Stator Interaction." Journal of Fluids Engineering 138, no. 8 (2016). http://dx.doi.org/10.1115/1.4033416.
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The flow unsteadiness generated in a swirl apparatus is investigated experimentally and numerically. The swirl apparatus has two parts: a swirl generator and a test section. The swirl generator which includes two blade rows, one stationary and one rotating, is designed such that the emanating flow at free runner rotational speed resembles that of a Francis hydroturbine operated at partial discharge. The test section consists of a conical diffuser similar to the draft tube cone of a Francis turbine. Several swirling flow regimes are produced, and the laser Doppler anemometry (LDA) measurements are performed along three survey axes in the test section for different runner rotational speeds (400–920 rpm), with a constant flow rate, 30 l/s. The measured mean velocity components and its fluctuating parts are used to validate the results of unsteady numerical simulations, conducted using the foam-extend-3.0 CFD code. Furthermore, phase-averaged pressure measured at two positions in the draft tube is compared with those of numerical simulations. A dynamic mesh is used together with the sliding general grid interfaces (GGIs) to mimic the effect of the rotating runner. The delayed detached-eddy simulation method, conjugated with the Spalart–Allmaras turbulence model (DDES–SA), is applied to achieve a deep insight about the ability of this advanced modeling technique and the physics of the flow. The RNG k−ε model is also used to represent state-of-the-art of industrial turbulence modeling. Both models predict the mean velocity reasonably well while DDES–SA presents more realistic flow features at the highest and lowest rotational speeds. The highest level of turbulence occurs at the highest and lowest rotational speeds which DDES–SA is able to predict well in the conical diffuser. The special shape of the blade plays more prominent role at lower rotational speeds and creates coherent structures with opposite sign of vorticity. The vortex rope is captured by both turbulence models while DDES–SA presents more realistic one at higher rotational speeds.
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Sheoran, Yogi, Bruce Bouldin, and P. Murali Krishnan. "Compressor Performance and Operability in Swirl Distortion." Journal of Turbomachinery 134, no. 4 (2011). http://dx.doi.org/10.1115/1.4003657.
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Inlet swirl distortion has become a major area of concern in the gas turbine engine community. Gas turbine engines are increasingly installed with more complicated and tortuous inlet systems such as those found on embedded installations on unmanned aerial vehicles. These inlet systems can produce complex swirl patterns in addition to total pressure distortion. The effect of swirl distortion on engine or compressor performance and operability must be evaluated. The gas turbine community is developing methodologies to measure and characterize swirl distortion. There is a strong need to develop a database containing the impact of a range of swirl distortion patterns on a compressor performance and operability. A recent paper presented by the authors described a versatile swirl distortion generator system that produced a wide range of swirl distortion patterns of a prescribed strength, including bulk swirl, twin swirl, and offset swirl. The design of these swirl generators greatly improved the understanding of the formation of swirl. The next step of this process is to understand the effect of swirl on compressor performance. A previously published paper by the authors used parallel compressor analysis to map out different speed lines that resulted from different types of swirl distortion. For the study described in this paper, a computational fluid dynamics (CFD) model is used to couple upstream swirl generator geometry to a single stage of an axial compressor in order to generate a family of compressor speed lines. The complex geometry of the analyzed swirl generators requires that the full 360 deg compressor be included in the CFD model. A full compressor can be modeled several ways in a CFD analysis, including sliding mesh and frozen rotor techniques. For a single operating condition, a study was conducted using both of these techniques to determine the best method, given the large size of the CFD model and the number of data points that needed to be run to generate speed lines. This study compared the CFD results for the undistorted compressor at 100% speed to comparable test data. Results of this study indicated that the frozen rotor approach provided just as accurate results as the sliding mesh but with a greatly reduced cycle time. Once the CFD approach was calibrated, the same techniques were used to determine compressor performance and operability when a full range of swirl distortion patterns were generated by upstream swirl generators. The compressor speed line shift due to co-rotating and counter-rotating bulk swirl resulted in a predictable performance and operability shift. Of particular importance is the compressor performance and operability resulting from an exposure to a set of paired swirl distortions. The CFD generated speed lines follow similar trends to those produced by parallel compressor analysis.
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Johansson, Martin, Thomas Povey, Kam Chana, and Hans Abrahamsson. "Effect of Low-NOX Combustor Swirl Clocking on Intermediate Turbine Duct Vane Aerodynamics With an Upstream High Pressure Turbine Stage—An Experimental and Computational Study." Journal of Turbomachinery 139, no. 1 (2016). http://dx.doi.org/10.1115/1.4034311.
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Flow in an intermediate turbine duct (ITD) is highly complex, influenced by the upstream turbine stage flow structures, which include tip leakage flow and nonuniformities originating from the upstream high pressure turbine (HPT) vane and rotor. The complexity of the flow structures makes predicting them using numerical methods difficult, hence there exists a need for experimental validation. To evaluate the flow through an intermediate turbine duct including a turning vane, experiments were conducted in the Oxford Turbine Research Facility (OTRF). This is a short duration high speed test facility with a 3/4 engine-sized turbine, operating at the correct nondimensional parameters for aerodynamic and heat transfer measurements. The current configuration consists of a high pressure turbine stage and a downstream duct including a turning vane, for use in a counter-rotating turbine configuration. The facility has the ability to simulate low-NOx combustor swirl at the inlet to the turbine stage. This paper presents experimental aerodynamic results taken with three different turbine stage inlet conditions: a uniform inlet flow and two low-NOx swirl profiles (different clocking positions relative to the high pressure turbine vane). To further explain the flow through the 1.5 stage turbine, results from unsteady computational fluid dynamics (CFD) are included. The effect of varying the high pressure turbine vane inlet condition on the total pressure field through the 1.5 stage turbine, the intermediate turbine duct vane loading, and intermediate turbine duct exit condition are discussed and CFD results are compared with experimental data. The different inlet conditions are found to alter the flow exiting the high pressure turbine rotor. This is seen to have local effects on the intermediate turbine duct vane. With the current stator–stator vane count of 32-24, the effect of relative clocking between the two is found to have a larger effect on the aerodynamics in the intermediate turbine duct than the change in the high pressure turbine stage inlet condition. Given the severity of the low-NOx swirl profiles, this is perhaps surprising.
Dissertations / Theses on the topic "Swirl turbine with counter-rotating runners"
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Pokorný, Tomáš. "Konstrukční řešení vírové turbiny s protiběžnými koly." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2012. http://www.nusl.cz/ntk/nusl-230202.
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The construction of swirl turbine with counter-rotating runners. Master's thesis of master's studies of 2th years. This master's thesis is a technical report. The content of this technical report is engineering design of turbine, strength calculation of designed parts, design of bearings and development drawings for production.
Conference papers on the topic "Swirl turbine with counter-rotating runners"
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Biner, D., V. Hasmatuchi, F. Avellan, and C. Munch-Alligne. "Design & performance of a hydraulic micro-turbine with counter-rotating runners." In 2015 5th International Youth Conference on Energy (IYCE). IEEE, 2015. http://dx.doi.org/10.1109/iyce.2015.7180737.
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Hu, Shuzhen, Yanfeng Zhang, Xue Feng Zhang, and Edward Vlasic. "Influences of Inlet Swirl Distributions on an Inter-Turbine Duct: Part I—Casing Swirl Variation." In ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/gt2011-45554.
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The inter-turbine transition duct (ITD) of a gas turbine engine has significant potential for engine weight reduction and/or aerodynamic performance improvement. This potential arises because very little is understood of the flow behavior in the duct in relation to the hub and casing shapes and the flow entering the duct (e.g., swirl angle, turbulence intensity, periodic unsteadiness and blade tip vortices from upstream HP turbine blade rows). In this study, the flow development in an ITD with different inlet swirl distributions was investigated experimentally and numerically. The current paper, which is the first part of a two-part paper, presents the investigations of the influences of the casing swirl variations on the flow physics in the ITD. The results show a fair agreement between the predicted and experimental data. The radial pressure gradient at the first bend of ITD drives the low momentum hub boundary layer and wake flow radially, which results in a pair of hub counter-rotating vortices. Furthermore, the radially moving low momentum wake flow feeds into the casing region and causes 3D casing boundary layer. At the second bend, the reversed radial pressure gradient together with the 3D casing boundary layer generates a pair of casing counter-rotating vortices. Due to the local adverse pressure gradient, 3D boundary layer separation occurs on both the casing and hub at the second bend and the exit of the ITD, respectively. The casing 3D separation enhances the 3D features of the casing boundary layer as well as the existing casing counter-rotating vortices. With increasing casing swirl angle, the casing 3D boundary layer separation is delayed and the casing counter-rotating vortices are weakened. On the other hand, although the hub swirls are kept constant, the hub counter-rotating vortices get stronger with the increasing inlet swirl gradient. The total pressure coefficients within the ITD are significantly redistributed by the casing and hub counter-rotating vortices.
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Zhang, Yanfeng, Shuzhen Hu, Xue Feng Zhang, and Edward Vlasic. "Influences of Inlet Swirl Distributions on an Inter-Turbine Duct: Part II—Hub Swirl Variation." In ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/gt2011-45555.
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The inter-turbine transition duct (ITD) of a gas turbine engine has significant potential for engine weight reduction and/or aerodynamic performance improvement. This potential arises because very little is understood of the flow behavior in the duct in relation to the hub and casing shapes and the flow entering the duct (e.g., swirl angle, turbulence intensity, periodic unsteadiness and blade tip vortices from upstream HP turbine blade rows). In this study, the flow development in an ITD with different inlet swirl distributions was investigated experimentally and numerically. The current paper, which is the second part of a two-part paper, presents the investigations of the influences of the hub swirl variations on the flow physics of ITD. The results show that the radial movement of the low momentum hub boundary layer and wake flow induces a pair of hub counter-rotating vortices. This pair of counter-rotating vortices merges with the upstream vorticity, forming a pair of stronger vortices, which persist until ITD exit. Due to the hub streamwise adverse pressure gradient, the hub 3D separation occurs at the exit of the ITD. The hub counter-rotating vortices are strongest with the highest inlet swirl gradient. The hub boundary layer thickness is thickest with the largest inlet hub swirl angle. The hub 3D separation is reduced by the increased hub swirl angle. Based on the studies in both parts of this paper, a detailed loss mechanism has been described. The total pressure coefficient shows that the loss increases gradually at the first bend, and then increases more rapidly at the second bend. The total pressure coefficients within the ITD are significantly redistributed by the casing and hub counter-rotating vortices.
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Murakami, Tengen, Toshiaki Kanemoto, Gohki Takano, and Risa Kasahara. "Numerical Simulation in Turbine Mode of Counter-Rotating Type Axial Flow Pump (Preparation of Pump-Turbine Unit in Cooperation With Wind Power Unit)." In ASME 2012 Fluids Engineering Division Summer Meeting collocated with the ASME 2012 Heat Transfer Summer Conference and the ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/fedsm2012-72046.
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Pumped storage system contributes to adjust the electric power unbalance between day and night, in general. The pumping operation, however, may be unstable in the rising portion of the head characteristics, and/or bring the cavitation at the low suction head. To simultaneously overcome both weak points, the authors have proposed a superior pumping unit that is composed of counter-rotating type impellers and a peculiar motor with double rotational armatures. This paper discusses the operation at the turbine mode of the above unit. It is concluded with the numerical simulations that this type unit can be also operated acceptably at the turbine mode, because the unit works so as to coincide the angular momentum change through the front runners/impellers with that thorough the rear runners/impellers, namely to take the axial flow at not only the inlet but also the outlet without the guide vanes.
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Suzuki, Toshiaki, Gohki Takano, Yoshihiro Nakamura, and Toshiaki Kanemoto. "Counter-Rotating Type Hydroelectric Unit (Effects of Blade Numbers on On-Cam Operations)." In ASME-JSME-KSME 2011 Joint Fluids Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajk2011-07023.
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To cope with warming global environments, authors have proposed the counter-rotating type hydroelectric unit, which is composed of tandem runners and the peculiar generator with double rotational armatures. The unit can be provided for various water circumstances at not only the onshore but also the offshore. This paper discusses effects of setting angle and the number of runner blades on turbine performances and then optimum blade setting angles giving the maximum output and/or the maximum efficiency, namely the on-cam operation, are presented at various discharges/heads.
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Daniels, W. A., B. V. Johnson, and D. J. Graber. "Aerodynamic and Torque Characteristics of Enclosed Co/Counter Rotating Disks." In ASME 1989 International Gas Turbine and Aeroengine Congress and Exposition. American Society of Mechanical Engineers, 1989. http://dx.doi.org/10.1115/89-gt-177.
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Experiments were conducted to determine the aerodynamic and torque characteristics of adjacent rotating disks enclosed in a shroud. These experiments were performed to obtain an extended data base for advanced turbine designs such as the counter-rotating turbine. Torque measurements were obtained on both disks in the rotating frame of reference for co-rotating, counter-rotating and one-rotating/one-static disk conditions. The disk models used in the experiments included disks with typical smooth turbine geometry, disks with bolts, disks with bolts and partial bolt covers and flat disks. A windage diaphragm was installed at mid-cavity for some experiments. The experiments were conducted with various amounts of coolant throughflow injected into the disk cavity from the disk hub or from the disk OD with swirl. The experiments were conducted at disk tangential Reynolds number up to 1.6×107 with air as the working fluid. The results of this investigation indicated that the static shroud contributes a significant amount to the total friction within the disk system, the torque on counter-rotating disks is essentially independent of coolant flow total rate, flow direction and tangential Reynolds number over the range of conditions tested and a static windage diaphragm reduces disk friction in counter-rotating disk systems.
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Schmid, Gregor, and Heinz-Peter Schiffer. "Numerical Investigation of Inlet Swirl in a Turbine Cascade." In ASME Turbo Expo 2012: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/gt2012-69397.
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New combustion concepts towards lean burn aim at reducing peak temperatures and therefore emissions, especially nitrogen oxides. High swirl is required in order to enhance the mixing of fuel and air and thus, improve combustion and flame stability. In a numerical investigation of a turbine vane cascade the effect of such inlet swirl on aerodynamic losses, secondary flow pattern and heat transfer is investigated. The computations are conducted prior to particle image velocimetry and five-hole-probe measurements in a cascade of six vane passages and swirl generators upstream of each passage. The analysis covers three constituent parts: First, different swirl intensities are simulated which resemble the situation in a real combustion chamber. Second, different clocking positions are investigated — the swirl cores are either aligned with the vane leading edge or with midpassage — and finally, swirl orientation as clockwise, anticlockwise and counter rotating swirl is analysed. Two-dimensional inlet boundary conditions are applied to model the discrete swirl cores. Furthermore, a comparison with circumferentially averaged as well as with axial inflow conditions is made. Increasing the swirl number at the inlet boundary results in reduced heat transfer coefficient within the vane passage and higher pressure loss. Heat transfer through vanes and endwalls is maximal if the swirl generators are aligned with the vane leading edge and counter rotating swirl.
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Fu, Yongqiang, Jun Cai, San-Mou Jeng, and Hukam Mongia. "Confinement Effects on the Swirling Flow of a Counter-Rotating Swirl Cup." In ASME Turbo Expo 2005: Power for Land, Sea, and Air. ASMEDC, 2005. http://dx.doi.org/10.1115/gt2005-68622.
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Gas turbine combustor’s performance, emissions, operability, liner and dome temperature levels and gradients are affected by the degree of confinement expressed indirectly by the dome reference velocity. An experimental investigation was therefore undertaken to characterize the aerodynamic characteristics of non-reacting swirling flow generated by a counter-rotating swirl cup as affected by the test section dimensions. A two-component Laser Doppler Velocimetry (LDV) system was used to measure the mean velocity components and Reynolds stresses of the flowfield generated by the swirl cup installed in 8 square box test sections with width of 3.0, 4.0, 4.1, 4.3, 4.4, 4.5, 5.0, and 6.0 inch, in addition to unconfined flow. Measurements were carried out at fourteen axial distances ranging from 3 to 250 mm downstream of the flare exit, and the radial profiles are obtained through 2 mm intervals. Detailed experimental data are provided to improve mechanistic understanding of the swirl cup generated flowfield as impacted by the ratio of the test section cross-section to the mixer’s effective area. The benchmark quality data are planned for validating the state-of-the-art numerical models in addition more advanced LES approach.
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Zhao, Wei, Bing Wu, and Jianzhong Xu. "Aerodynamic Design and Analysis of a Multistage Vaneless Counter-Rotating Turbine." In ASME Turbo Expo 2014: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/gt2014-26335.
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Multistage vaneless counter-rotating turbines eliminate vanes between rotors, which reduces the weight of the turbine pronouncedly and avoids viscous losses associated with vanes. As a result, a gas turbine engine employing such a turbine would have greater thrust to weight ratio and smaller specific fuel consumption. This paper presents aerodynamic design and analysis for a multistage vaneless counter-rotating turbine, named as a 4*1/2 turbine, which consists of a rotating frame and four rotors without any vanes. The first rotor and the third rotor drive a single-shaft compressor with a pressure ratio of 11.8, and the second rotor and the forth rotor deliver a total shaft power of around 2MW. Stage loading and flow axial acceleration in blades and ducts are selected to provide sufficient inlet swirl for downstream vaneless rotor to produce required power output with acceptable performance. The stage work coefficients of each rotor are 0.95, 2.9, 1.4 and 1.0, respectively. Non-uniform radial circulation distributions and tapered blades are also used to maximize the turbine power output. Centrifugal forces in the outer rotor of the turbine are captured by carrying out a finite element analysis to validate the aerodynamic design results. Three dimensional viscous numerical results show that an adiabatic total-to-total efficiency of 91.5% with a pressure ratio of 9.8 at design condition is obtained and achieves the initial design objective very well. Entropy creation associated with the tip leakage and secondary flow in each rotor is also illustrated for understanding the origins and effects of losses in such turbines. Pressure ratios and efficiency at speed combinations of the 80% to 100% design speeds of the inner and outer rotors are discussed to reveal the turbine characteristics at off-design conditions.
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Nishida, Yoshifumi, Hideo Nishida, Hiromi Kobayashi, and Takahiro Nishioka. "Experimental and Numerical Study of Return Channel Flow Influence on Surge Margin of a Multi-Stage Centrifugal Compressor." In ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-42546.
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Experimental and numerical studies were performed to investigate influences of the return channel flow on the surge margin of a multistage centrifugal compressor. Two return channels, which were named RCH-A and RCH-B, were designed and evaluated in a two-stage centrifugal compressor. The measured performance of the compressor suggested that the surge margin of this compressor was dominated by the operating limit of the second stage and that the surge margin of RCH-B was 5% larger than that of RCH-A. The outlet flow of RCH-A and RCH-B swirled in a counter-rotating direction near the shroud region, and the flow angle at the outlet of RCH-A was larger than that of RCH-B. CFD was conducted to investigate the internal flow in the return channel. The CFD results of both RCH-A and RCH-B showed that the flow separation occurred on the suction surface of the return vanes near the operating limit. This separation induced the velocity difference between the suction and pressure sides, and the swirl flow in the counter-rotating direction was generated by this velocity difference. The swirl flow in the counter-rotating direction increased the blade loading of the second stage impeller at the operating limit. It was considered that the blade loading of RCH-B was lower than that of RCH-A at the operating limit, because the swirl flow in the counter-rotating direction of RCH-B was weaker than that of RCH-A. Therefore, the surge margin of the second impeller with RCH-B seemed to be larger than that with RCH-A. It was conclude from the experimental and numerical results that the locally swirl flow in the counter-rotating direction at the outlet of the return channels near the shroud side influenced the surge margins of the downstream impeller and the multi-stage centrifugal compressor.