Academic literature on the topic 'URANS/SAS'
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Journal articles on the topic "URANS/SAS"
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Yang, Xianglong, and Lei Yang. "An Elliptic Blending Turbulence Model-Based Scale-Adaptive Simulation Model Applied to Fluid Flows Separated from Curved Surfaces." Applied Sciences 12, no. 4 (February 16, 2022): 2058. http://dx.doi.org/10.3390/app12042058.
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On the basis of a previously developed elliptic blending turbulence model (SST–k–ω–φ–α model), a scale-adaptive simulation (SAS) model is developed by following Menter and Egorov’s SAS concept. An SAS source term, which is related to the ratio of the modeled turbulence scale to the von Kármán length scale, is introduced into the corresponding length-scale determining equation. The major motivation of this study is that the conventional unsteady Reynolds-averaged Navier–Stokes (URANS) models provide only large-scale unsteadiness. The introduction of the SAS term allows the proposed SAS model to dynamically adjust to resolved structures in a URANS framework because this term is sensitive to resolved fluctuations. The predictive capabilities of the proposed SAS model are demonstrated by computing the complex flow configurations in three cases with flow separation from curved surfaces, namely, three-dimensional (3D) diffuser flow, two-dimensional (2D) periodic hills flow, and 2D U-turn duct flow. For comparison, the results predicted by the SST–k–ω–φ–α model and the Menter and Egorov’s SAS model (SST–SAS) are provided. The results are also compared with the relevant experimental, direct numerical simulation, and large eddy simulation data. The results show that the SST–k–ω–φ–α model cannot capture the critical features for all three flows, and that the SST–SAS model is able to predict the results reasonably well. The proposed SAS model is capable of resolving more portions of the turbulence structures, and it yields the best results in all the cases.
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Kratzsch, Christoph, Amjad Asad, and Rüdiger Schwarze. "CFD of the MHD Mold Flow by Means of Hybrid LES/RANS Turbulence Modeling." Journal for Manufacturing Science and Production 15, no. 1 (March 31, 2015): 49–57. http://dx.doi.org/10.1515/jmsp-2014-0046.
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AbstractIn the last decades, electromagnetic braking (EMBr) systems become a powerful tool to dampen possible jet oscillations in the continuous casting mold. Further studies showed that if a EMBr is not positioned correctly, it can induce flow oscillations. Hence, the design of these braking systems can be promoted by adequate CFD simulations. In most cases, unsteady RANS simulations (URANS) are sufficient to resolve low-frequency, large-scale oscillations of these MHD flows. Alternatively, Large Eddy Simulations (LES) may also resolve important details of the turbulence. However, since they require much finer computational grids, the computational costs are much higher. A bridge between both approaches are hybrid methods like the Scale Adaptive Simulation (SAS). In this study, we compare the performance of SAS with URANS and LES. Results are validated in detail by comparison with data from a Ruler-EMBr model experiment.
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Jiménez-Varona, José, Gabriel Liaño, José L. Castillo, and Pedro L. García-Ybarra. "Roughness Effect on the Flow Past Axisymmetric Bodies at High Incidence." Aerospace 9, no. 11 (October 28, 2022): 668. http://dx.doi.org/10.3390/aerospace9110668.
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The flow at low Mach numbers and high angles of attack over axisymmetric configurations is not symmetric. The mechanism that triggers the asymmetry is a combination of a global (temporal) instability and a convective (spatial) instability. This latter instability is caused by roughness and other geometrical imperfections, which lead to roll angle dependent forces. The flow at these conditions has a complex vortex sheet structure, with two or three different flow regions. An accurate simulation by means of Computational Flow Dynamics (CFD) is thus very challenging, and many researchers have therefore employed Large Eddy Simulation (LES) codes. This study demonstrates that Unsteady Reynolds Averaged Navier-Stokes (URANS) methods are a suitable alternative, if Scale Adaptive Simulation (SAS) is used. This method is capable of capturing the main flow features, provided that fine meshes, which achieve geometrical similarity between the meshed geometry and the real object, and small-time steps are used. It is also demonstrated that, by using URANS methods in combination with SAS, strong differences in the global and local forces depending on the surface roughness of the model are obtained, a result which coincides with several wind tunnel tests.
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Higgins, R. J., G. N. Barakos, and E. Jinks. "Estimation of three-dimensional aerodynamic damping using CFD." Aeronautical Journal 124, no. 1271 (November 12, 2019): 24–43. http://dx.doi.org/10.1017/aer.2019.135.
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AbstractAeroelastic phenomena of stall flutter are the result of the negative aerodynamic damping associated with separated flow. From this basis, an investigation has been conducted to estimate the aerodynamic damping from a time-marching aeroelastic computation. An initial investigation is conducted on the NACA 0012 aerofoil section, before transition to 3D propellers and full aeroelastic calculations. Estimates of aerodynamic damping are presented, with a comparison made between URANS and SAS. Use of a suitable turbulence closure to allow for shedding of flow structures during stall is seen as critical in predicting negative damping estimations. From this investigation, it has been found that the SAS method is able to capture this for both the aerofoil and 3D test cases.
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Decaix, Jean, Vlad Hasmatuchi, Maximilian Titzschkau, and Cécile Münch-Alligné. "CFD Investigation of a High Head Francis Turbine at Speed No-Load Using Advanced URANS Models." Applied Sciences 8, no. 12 (December 5, 2018): 2505. http://dx.doi.org/10.3390/app8122505.
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Due to the integration of new renewable energies, the electrical grid undergoes instabilities. Hydroelectric power plants are key players for grid control thanks to pumped storage power plants. However, this objective requires extending the operating range of the machines and increasing the number of start-up, stand-by, and shut-down procedures, which reduces the lifespan of the machines. CFD based on standard URANS turbulence modeling is currently able to predict accurately the performances of the hydraulic turbines for operating points close to the Best Efficiency Point (BEP). However, far from the BEP, the standard URANS approach is less efficient to capture the dynamics of 3D flows. The current study focuses on a hydraulic turbine, which has been investigated at the BEP and at the Speed-No-Load (SNL) operating conditions. Several “advanced” URANS models such as the Scale-Adaptive Simulation (SAS) SST k - ω and the BSL- EARSM have been considered and compared with the SST k - ω model. The main conclusion of this study is that, at the SNL operating condition, the prediction of the topology and the dynamics of the flow on the suction side of the runner blade channels close to the trailing edge are influenced by the turbulence model.
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Wang, Shibo, James R. Bell, David Burton, Astrid H. Herbst, John Sheridan, and Mark C. Thompson. "The performance of different turbulence models (URANS, SAS and DES) for predicting high-speed train slipstream." Journal of Wind Engineering and Industrial Aerodynamics 165 (June 2017): 46–57. http://dx.doi.org/10.1016/j.jweia.2017.03.001.
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Wang, Guangxue, Shengye Wang, Hao Li, Xiang Fu, and Wei Liu. "Comparative assessment of SAS, IDDES and hybrid filtering RANS/LES models based on second-moment closure." Advances in Mechanical Engineering 13, no. 6 (June 2021): 168781402110284. http://dx.doi.org/10.1177/16878140211028447.
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The question of which turbulence model is better for a given class of applications is always confusing for the CFD researchers and users. Comparative assessments of scale-adaptive simulation (SAS), improved delay detached-eddy simulation (IDDES) and other hybrid RANS/LES models based on eddy-viscosity models (EVMs) are thoroughly investigated. But how well they perform based on a second-moment closure needs to be answered. In this paper, a widely acclaimed Reynolds-stress model (RSM) in aeronautical engineering, SSG/LRR-[Formula: see text] model, is carried out. The relevant test cases include the NACA0012 airfoil stalled flows and turret separated flow. In order to make a more reasonable comparison, a seventh-order scheme WCNS-E8T7 is adopted to reduce the influence of the numerical dissipation and a symmetrical conservative metric method is used to ensure the robustness. By comparing with the relevant experimental data and the solutions by original SSG/LRR-[Formula: see text] model (etc. URANS), it shows that all of the three hybrid methods (SAS, IDDES and hybrid filtering methods) based on the SSG/LRR-[Formula: see text] model have a good ability to simulate unsteady turbulence. Among them, the IDDES correction has the most potential.
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Shukla, S., S. N. Singh, S. S. Sinha, and R. Vijayakumar. "Comparative assessment of URANS, SAS and DES turbulence modeling in the predictions of massively separated ship airwake characteristics." Ocean Engineering 229 (June 2021): 108954. http://dx.doi.org/10.1016/j.oceaneng.2021.108954.
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Münsterjohann, Sven, Jens Grabinger, Stefan Becker, and Manfred Kaltenbacher. "CAA of an Air-Cooling System for Electronic Devices." Advances in Acoustics and Vibration 2016 (October 20, 2016): 1–17. http://dx.doi.org/10.1155/2016/4785389.
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This paper presents the workflow and the results of fluid dynamics and aeroacoustic simulations for an air-cooling system as used in electronic devices. The setup represents a generic electronic device with several electronic assemblies with forced convection cooling by two axial fans. The aeroacoustic performance is computed using a hybrid method. In a first step, two unsteady CFD simulations using the Unsteady Reynolds-Averaged Navier-Stokes simulation with Shear Stress Transport (URANS-SST) turbulence model and the Scale Adaptive Simulation with Shear Stress Transport (SAS-SST) models were performed. Based on the unsteady flow results, the acoustic source terms were calculated using Lighthill’s acoustic analogy. Propagation of the flow-induced sound was computed using the Finite Element Method. Finally, the results of the acoustic simulation are compared with measurements and show good agreement.
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Maleki, Siavash, David Burton, and Mark C. Thompson. "Assessment of various turbulence models (ELES, SAS, URANS and RANS) for predicting the aerodynamics of freight train container wagons." Journal of Wind Engineering and Industrial Aerodynamics 170 (November 2017): 68–80. http://dx.doi.org/10.1016/j.jweia.2017.07.008.
Full textDissertations / Theses on the topic "URANS/SAS"
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Decaix, Jean. "Modélisation et simulation de la turbulence compressible en milieu diphasique : application aux écoulements cavitants instationnaires." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00814309.
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La simulation des écoulements cavitants est confrontée à des difficultés de modélisation et de résolution numérique provenant des caractéristiques particulières de ces écoulements : changement de phase, gradient de masse volumique important, variation du nombre de Mach, turbulence diphasique, instationnarités. Dans cette thèse, nous nous sommes appliqués à dériver proprement le modèle de mélange homogène 1-fluide couplé à une modélisation RANS de la turbulence. A partir des termes contenus dans ces équations et de la nature des écoulements cavitants étudiés, plusieurs modèles de turbulence basés sur la notion de viscosité turbulente ont été testés : modèles faiblement non-linéaires (corrections SST et de réalisabilité), ajout des termes de turbulence compressible, application de la correction de Reboud, modèles hybrides RANS/LES (DES, SAS). Ces modèles ont été incorporés dans un code compressible qui fait appel à une résolution implicite en pas de temps dual des équations de conservation avec une technique de pré-conditionnement bas-Mach pour traiter les zones incompressibles. Les simulations 2D et 3D ont porté sur deux géométries de type Venturi caractérisées par la présence d'une poche de cavitation instationnaire due à l'existence d'un jet rentrant liquide/vapeur le long de la paroi. Elles montrent que l'ensemble des modèles sont capables de capturer le jet rentrant. En revanche, la dynamique de la poche varie entre les modèles et le manque de données expérimentales ne permet pas de discriminer les modèles entre eux. Il apparaît à la vue des résultats que les approches avec la correction de Reboud ou les modèles SAS améliorent la simulation des écoulements.
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ZUZUL, JOSIP. "Characterization of thunderstorm downburst winds through CFD techniques." Doctoral thesis, Università degli studi di Genova, 2022. http://hdl.handle.net/11567/1081542.
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The characteristic wind field of a certain region is mostly governed by the climatology of its larger scale area. In the case of mid-latitude regions (e.g. Europe), their climatology is determined by the extra-tropical cyclones at the larger synoptic scale. Atmospheric boundary layer (ABL) winds based on synoptic-scale structures are hence considered as the foundation for codes and standards used to assess the wind loading of structures and to design structures to prevent wind-related damage accordingly. In addition to the ABL winds, the mid-latitude regions are also prone to winds of a non-synoptic origin at the mesoscale level, with thunderstorm outflows or downbursts being the representative of such non-synoptic wind action. Since they are determined by a set of features that makes them fundamentally different from the ABL winds, downbursts can produce the corresponding wind action that is often fatal to low-rise and mid-rise structures. On these grounds, a comprehensive initiative to enable a better understanding of fundamental downburst flow features relevant for the structural loading was framed under the umbrella of the ERC THUNDERR Project. The present thesis, as the numerical modeling part of the THUNDERR Project framework, aims to address the physical characteristics of thunderstorm downbursts through the application of Computational Fluid Dynamics (CFD) technique. The focus of this work is placed on the CFD reconstruction of experimental tests of the reduced-scale thunderstorm downbursts carried out in the WindEEE Dome Research Institute (University of Western Ontario, Canada). Although they recreate the downburst flow field, the experimental analysis is restricted to the limited number of probe points. In that perspective, CFD allows expanding the analysis of experimental tests to the entire flow field, which can reveal phenomenological aspects that are either challenging or impossible to retrieve from experimental tests only. Two fundamental downburst scenarios were analyzed: (i) an isolated vertical downburst, and (ii) a downburst embedded inside the approaching ABL flow. For that purpose, three CFD approaches of a ranging complexity level were adopted. The unsteady Reynolds-Averaged Navier-Stokes (URANS), hybrid Scale-Adaptive Simulations (SAS), and Large-Eddy Simulations were used, and their overall reliability was examined. Theimplications of the WindEEE Dome specific geometrical features (i.e. bell-mouth inflow nozzle) on the downburst flow reconstruction by the facility were further discussed. The bulk of the thesis discusses the dominant flow features of the downburst with the particular emphasis on the dynamics of dominant vortex structures (i.e. primary vortex, secondary vortex, trailing ring vortices) and their spatio-temporal influence on the vertical profiles of radial velocity component. The non-dimensional flow characteristics of interest were evaluated such as the trajectory of the primary vortex and the spatial dependence of the velocity of primary vortex propagation. Analyses were further extended for the case of a joint downburst and ABL wind interaction to address the dynamics between two different wind fields, and the genesis of the worst condition in terms of the maximum radial velocity due to the ABL wind entrainment was discussed. The flow field was analyzed across various azimuth angles with respect to the ABL flow to report on the flow asymmetry, and general implications of such downburst configuration on spatio-temporal evolution of wind velocity profiles which can produce severe conditions for low-rise and mid-rise structures.
Conference papers on the topic "URANS/SAS"
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Ivanova, Elizaveta, Massimiliano Di Domenico, Berthold Noll, and Manfred Aigner. "Unsteady Simulations of Flow Field and Scalar Mixing in Transverse Jets." In ASME Turbo Expo 2009: Power for Land, Sea, and Air. ASMEDC, 2009. http://dx.doi.org/10.1115/gt2009-59147.
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This paper presents numerical simulations of flow and scalar mixing in two different jet in crossflow configurations. The testcases are chosen to resemble the dilution mixing processes in gas turbine combustion chambers. Unsteady simulations employing two different computational approaches are presented: unsteady Reynolds-Averaged Navier-Stokes (URANS) and Scale-Adaptive Simulations (SAS). The results obtained by each method are compared, analyzed, and validated against experimental data. The importance of the reproduction of the large-scale unsteady coherent vortical structures in the numerical simulation is demonstrated. Both URANS and SAS revealed the typical jet in crossflow vortical structures. The SAS method was able to resolve smaller structures than URANS on the same computational grid. The quantitative prediction accuracy of time-averaged velocities and temperatures is satisfactory for both methods. In contrast, the steady-state Reynolds-Averaged Navier-Stokes (RANS) computations failed for the present testcases.
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Marty, J., H. Gaible, and H. Bézard. "Assessment of Scale Adaptive Simulation of a Rotor of High Pressure Compressor." In ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/gt2018-76537.
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The main design objectives of a high pressure compressor are the aerodynamic efficiency and the operating range (e.g. the surge margin). Those quantities are impacted by secondary and leakage flows occurring in the blade passage such as corner separation or stall and tip leakage flows. The turbulence modeling influences strongly the prediction of the overall performances. The aims of the present study were (i) the validation of the combination of the SAS approach with the DRSM turbulence model by comparison to experimental data, especially to laser measurements in the tip of a rotor of a high pressure compressor and (ii) the discussion of the flow prediction improvements with respect to turbulence approaches classically used in CFD and industry: URANS simulations and standard SAS simulation i.e. combined with SST turbulence model. The SAS results are compared to experimental data and to URANS results (SST and DRSM). Only the simulations with IGV wakes predict the velocity fluctuations near tip gap, from the leading edge. Concerning the time-averaged performances, the stagnation pressure losses are slightly overestimated by SAS, especially with DRSM model. This is due to an amplification of the hub corner separation. Moreover, the isentropic efficiency is very sensitive to the SAS approach and to the turbulence model. The spectral analysis shows that the prediction of the amplitude and frequencies of the power spectral density of static pressure is improved using the SAS approach instead of URANS one. The SAS approach leads to PSD similar to ZDES, especially with the DRSM model. Thus, the SAS-DRSM is able to well predict the tip leakage flow with the fine mesh. Nevertheless, this approach amplifies the hub corner separation leading to a strong underestimation of overall performances.
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Volkmer, Silke, Markus Schatz, Michael Casey, and Matthew Montgomery. "Prediction of Flow in an Exhaust Gas Turbine Diffuser With a Scale-Adaptive Simulation Model." In ASME Turbo Expo 2013: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/gt2013-94954.
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The prediction of the flow in a gas turbine exhaust diffuser of a combined cycle power plant is particularly difficult as maximum performance is obtained with highly loaded diffusers, which operate close to boundary layer separation. CFD (computational fluid dynamics) simulations then need to cope with complex phenomena such as smooth wall separation, recirculation, reattachment, blockage and free shear layer mixing. Recent studies based on the RANS (Reynolds-Averaged-Navier-Stokes) approach demonstrate the challenge for two-equation turbulence models to predict separation and mixing of the flow correctly in such highly loaded diffusers and identify that more accurate methods are needed. Hence, the application of a hybrid Scale-Adaptive Simulation (SAS) is investigated and the CFD results are compared with experimental results from an in-house test rig. In the present study the flow in a model exhaust diffuser (for heavy-duty gas turbine diffuser applications typical Reynolds number 1.5×106 and inlet Mach number 0.6) is examined with unsteady RANS (URANS) simulations with the SST (Shear Stress Transport) model as well as a hybrid Scale-Adaptive Simulation (SAS) model. The SAS model switches from URANS to a mode similar to a Large Eddy Simulation (LES) in unsteady flow regions to resolve various scales of detached eddies. The current study shows that with the SST model similar results are obtained with RANS and URANS simulations, whereas the more complex SAS model leads to a much better resolution of the unsteady fluctuations. However, the time-averaged results of the SAS calculations overpredict the blockage of the separation and hub wake. This results in an underprediction of the pressure recovery and the mixing of the flow compared to the simpler two-equation models and also compared to experimental results.
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Wein, Lars, Joerg R. Seume, and Florian Herbst. "Improved Prediction of Labyrinth Seal Performance Through Scale Adaptive Simulation and Stream Aligned Grids." In ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/gt2017-64257.
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The accurate prediction of cavity flows is of importance to the turbomachinery design process. However, cavity flows are complex. It is known, that RANS models tend to struggle with the prediction of cavity flows and the flow phenomena associated with them. At the same time, scale-resolving methods are more accurate and give a more detailed view on the turbulent structure of the flow. This is accompanied by an inherent dependency on the computational grid, the timestep, and the size of the domain. Therefore, an experimentally validated comparison of RANS, URANS and SAS simulations for a stepped labyrinth seal is given in the paper at hand to demonstrate the individual methods capabilities, limitations, and requirements. It was shown that an alignment of the grid with the local flow direction can save about 40% of computational resources, while simultaneously reducing the discretization error by 25%. RANS and time averaged URANS results in comparison to measurements showed that the swirl development in the cavity is overpredicted and the cavity vortex is underpredicted. A distinct grid dependency was noticed for the SAS-SST turbulence model. The intermediate grid enhances the results in comparison to RANS and URANS. URANS-SST and SAS-SST simulations capture the same dominant frequencies of the velocity spectra, when the same sector size is used. Furthermore, the prediction of dominant frequencies depends strongly on the circumferential size of the domain. The time-averaged results are more sensitive to the grid refinement and turbulence model than to the size of the domain.
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Moëll, Daniel, Daniel Lörstad, Annika Lindholm, David Christensen, and Xue-Song Bai. "Numerical and Experimental Investigations of the Siemens SGT-800 Burner Fitted to a Water Rig." In ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/gt2017-64129.
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DLE (Dry Low Emission) technology is widely used in land based gas turbines due to the increasing demands on low NOx levels. One of the key aspects in DLE combustion is achieving a good fuel and air mixing where the desired flame temperature is achieved without too high levels of combustion instabilities. To experimentally study fuel and air mixing it is convenient to use water along with a tracer instead of air and fuel. In this study fuel and air mixing and flow field inside an industrial gas turbine burner fitted to a water rig has been studied experimentally and numerically. The Reynolds number is approximately 75000 and the amount of fuel tracer is scaled to represent real engine conditions. The fuel concentration in the rig is experimentally visualized using a fluorescing dye in the water passing through the fuel system of the burner and recorded using a laser along with a CCD (Charge Couple Device) camera. The flow and concentration field in the burner is numerically studied using both the scale resolving SAS (Scale Adaptive Simulation) method and the LES (Large Eddy Simulation) method as well as using a traditional two equation URANS (Unsteady Reynolds Average Navier Stokes) approach. The aim of this study is to explore the differences and similarities between the URANS, SAS and LES models when applied to industrial geometries as well as their capabilities to accurately predict relevant features of an industrial burner such as concentration and velocity profiles. Both steady and unsteady RANS along with a standard two equation turbulence model fail to accurately predict the concentration field within the burner, instead they predict a concentration field with too sharp gradients, regions with almost no fuel tracer as well as regions with far too high concentration of the fuel tracer. The SAS and LES approach both predict a more smooth time averaged concentration field with the main difference that the tracer profile predicted by the LES has smoother gradients as compared to the tracer profile predicted by the SAS. The concentration predictions by the SAS model is in reasonable agreement with the measured concentration fields while the agreement for the LES model is excellent. The LES shows stronger fluctuations in velocity over time as compared to both URANS and SAS which is due to the reduced amounts of eddy viscosity in the LES model as compared to both URANS and SAS. This study shows that numerical methods are capable of predicting both velocity and concentration in a gas turbine burner. It is clear that both time and scale resolved methods are required to accurately capture the flow features of this and probably most industrial DLE gas turbine burners.
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Voigt, Stefan, Berthold Noll, and Manfred Aigner. "Aerodynamic Comparison and Validation of RANS, URANS and SAS Simulations of Flat Plate Film-Cooling." In ASME Turbo Expo 2010: Power for Land, Sea, and Air. ASMEDC, 2010. http://dx.doi.org/10.1115/gt2010-22475.
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The present paper deals with the detailed numerical simulation of film cooling including conjugate heat transfer. Five different turbulence models are used to simulate a film cooling configuration. The models include three steady and two unsteady models. The steady RANS models are the Shear stress transport (SST) model of Menter, the Reynolds stress model of Speziale, Sarkar and Gatski and a k-ε explicit algebraic Reynolds stress model. The unsteady models are a URANS formulation of the SST model and a scale-adaptive simulation (SAS). The solver used in this study is the commercial code ANSYS CFX 11.0. The results are compared to available experimental data. These data include velocity and turbulence intensity fields in several planes. It is shown that the steady RANS approach has difficulties with predicting the flow field due to the high 3-dimensional unsteadiness. The URANS and SAS simulations on the other hand show good agreement with the experimental data. The deviation from the experimental data in velocity values in the steady cases is about 20% whereas the error in the unsteady cases is below 10%.
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Zamiri, Ali, and Jin Taek Chung. "Scale Adaptive Simulation of Transient Behavior in a Transonic Centrifugal Compressor With a Vaned Diffuser." In ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/gt2018-77264.
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Three-dimensional, compressible, unsteady Navier-Stokes equations are solved to investigate the unsteady flow behavior in a transonic centrifugal compressor. The computational model is a high compression ratio centrifugal compressor (4:1) consisted of an inlet duct, an impeller (15 main blades and 15 splitters) and a diffuser vane with 24 two-dimensional wedge vanes. The aim of this study is to conduct a comprehensive assessment of the ability of a hybrid scale-adaptive simulation (SAS) turbulent model to characterize the transient flow structures within the compressor passages. The main idea of SAS approach, an improved URANS (unsteady Reynold-averaged Navier-Stokes) model, is based on the introduction of von Karman length scale into the turbulent scale equation which results in LES-like behavior in unsteady regions of the flow field. A numerical sensitivity test is performed to validate the computational results in terms of pressure ratio and compressor efficiency. Instantaneous and mean flow field analyses are presented in the impeller and the vaned diffuser. Applying transient simulations, it is shown that the interaction between the pressure waves and the surface pressure of the diffuser blades leads to a pulsating behavior within the diffuser. Moreover, spectral analysis is evaluated to analyze the BPF tonal noise as the main noise source of centrifugal compressors. In addition, the current SAS results are compared with those of the URANS-SST (shear stress transport) approach to show the ability of SAS approach in the prediction of the turbulent structures where the SAS model leads to a much better resolution of the unsteady fluctuations. This study shows that the current SAS approach, as an alternative to the existing hybrid RANS/LES methods, is promising in terms of prediction of transient phenomena like LES, but with a substantially reduced turn-around time.
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Rulik, Sebastian, Slawomir Dykas, and Wlodzimierz Wroblewski. "Modeling of Aerodynamic Noise Using Hybrid SAS and DES Methods." In ASME Turbo Expo 2010: Power for Land, Sea, and Air. ASMEDC, 2010. http://dx.doi.org/10.1115/gt2010-22696.
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The purpose of the presented studies is to compare simple and fast CFD methods based on the unsteady Reynolds-Averaged Navier-Stokes equations (uRANS) with the so called hybrid uRANS/LES methods like Detached Eddy Simulation (DES) and Scale Adaptive Simulation (SAS) implemented in the commercial code ANSYS CFX. The goal of this comparison is to find an efficient and relatively fast method for both the flow dynamic and aerodynamic noise prediction in the near and far field, which would be suitable for engineering applications. The CFD calculations were carried out using the commercial code ANSYS CFX 11. The non-reflective boundary conditions and grid stretching were used to avoid the reflections of the acoustic waves from the outer boundaries. The different boundary conditions and turbulence models were used in the calculations. For the acoustic calculations the Fast Fourier Transformation (FFT) was applied to obtain the sound spectrum. The CFD results were compared with the experimental data obtained in references.
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Mahapatra, Debabrata, Jaydeep Basani, and Samir Rida. "Assessment of Scale Adaptive Simulation Model for Honeywell Combustor." In ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-43573.
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The complex flow phenomena inside a gas turbine combustor demands alternative simulation methods to the Reynolds Averaged Navier-Stokes (RANS) model, where a portion of turbulence scales is resolved inside the flow domain. Large Eddy Simulation (LES) is the most-widely acknowledged method for its attractive feature of resolving large turbulent structures down to the grid limit for the entire flow domain. However, for practical industrial problems where the Reynolds number is high and the flow domain is large, the grid resolution for LES becomes excessively high making it computationally very expensive. Scale Adaptive Simulation (SAS), on the other hand, adjusts to the resolved structures in an Unsteady RANS (URANS) simulation resulting in LES-like behavior in unsteady regions of the flow field. At the same time, it provides RANS capabilities in the stable flow regions. It allows a larger time step than LES resulting in the possibility of computation time advantage with LES-like solution fidelity. In the current paper, the SAS model is compared to the LES model for a Honeywell combustor using the commercial CFD code ANSYS FLUENT. Several time-steps are considered for SAS simulations. Results show that SAS is promising in terms of predicting combustor performance parameters like LES, but with a substantially reduced turn-around time.
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Ravelli, S., and G. Barigozzi. "Application of Unsteady CFD Methods to Trailing Edge Cutback Film Cooling." In ASME Turbo Expo 2014: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/gt2014-25435.
Full textAbstract:
The main purpose of this numerical investigation is to overcome the limitations of the steady modeling in predicting the cooling efficiency over the cutback surface in a high pressure turbine nozzle guide vane. Since discrepancy between Reynolds-averaged Navier–Stokes (RANS) predictions and measured thermal coverage at the trailing edge was attributable to unsteadiness, Unsteady RANS (URANS) modeling was implemented to evaluate improvements in simulating the mixing between the mainstream and the coolant exiting the cutback slot. With the aim of reducing the computation effort, only a portion of the airfoil along the span was simulated at an exit Mach number of Ma2is = 0.2. Three values of the coolant-to-mainstream mass flow ratio were considered: MFR = 0.66%, 1.05%, and 1.44%. Nevertheless the inherent vortex shedding from the cutback lip was somehow captured by the URANS method, the computed mixing was not enough to reproduce the measured drop in adiabatic effectiveness η along the streamwise direction, over the cutback surface. So modeling was taken a step further by using the Scale Adaptive Simulation (SAS) method at MFR = 1.05%. Results from the SAS approach were found to have potential to mimic the experimental measurements. Vortices shedding from the cutback lip were well predicted in shape and magnitude, but with a lower frequency, as compared to PIV data and flow visualizations. Moreover, the simulated reduction in film cooling effectiveness toward the trailing edge was similar to that observed experimentally.