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1
Guan, Lixian, e Dan Zhao. "Numerical prediction nonlinear heat-driven acoustics behaviours in standing-wave thermoacoustic engines using stress-blended Eddy simulation method". Journal of the Acoustical Society of America 153, n. 3_supplement (1 marzo 2023): A38. http://dx.doi.org/10.1121/10.0018072.
Abstract (sommario):
The present work investigated a standing-wave heat-driven thermoacoustic engine (SWTAE) system by capturing its nonlinear thermoacoustic features with three-dimensional (3D) unsteady Reynolds-Averaged Navier-Stokes (URANS) and hybrid URANS/LES (large Eddy simulation) models such as detached-Eddy simulations (DES) and stress-blended Eddy simulation (SBES) models. The comparison studies show that the prediction of the acoustic power of SWTAE using URANS is about 21.0% lower than that using LES, while the results from SBES and DES are relatively in good agreement with LES. Comparative studies of nonlinear hydrodynamics in the flow fields show that the results from SBES are closer to LES than DES, which can be attributed to the SBES model providing a faster transition to an explicit LES model outside the wall boundary layer. Furthermore, the heat transfer characteristics are compared by analyzing heat leaks and transversal heat flux, and it is found that the URANS model over-estimates the heat transfer characteristics, while the results of the other three models are relatively smaller than those obtained by URANS. In conclusion, the SBES model has great potential to be applied in simulating thermoacoustic nonlinear, heat transfer and flow behaviors of heat-driven SWTAEs.
2
Giri Ajay, Adhyanth, Laurence Morgan, Yan Wu, David Bretos, Aurelio Cascales, Oscar Pires e Carlos Ferreira. "Aerodynamic model comparison for an X-shaped vertical-axis wind turbine". Wind Energy Science 9, n. 2 (27 febbraio 2024): 453–70. http://dx.doi.org/10.5194/wes-9-453-2024.
Abstract (sommario):
Abstract. This article presents a comparison study of different aerodynamic models for an X-shaped vertical-axis wind turbine and offers insight into the 3D aerodynamics of this rotor at fixed pitch offsets. The study compares six different numerical models: a double-multiple streamtube (DMS) model, a 2D actuator cylinder (2DAC) model, an inviscid free vortex wake model (from CACTUS), a free vortex wake model with turbulent vorticity (from QBlade), a blade-resolved unsteady Reynolds-averaged Navier–Stokes (URANS) model, and a lattice Boltzmann method (from PowerFLOW). All models, except URANS and PowerFLOW use the same blade element characteristics other than the number of blade elements. This comparison covers the present rotor configuration for several tip-speed ratios and fixed blade pitch offsets without unsteady corrections, except for the URANS and PowerFLOW which cover a single case. The results show that DMS and 2DAC models are inaccurate – especially at highly loaded conditions, are unable to predict the downwind blade vortex interaction, and do not capture the vertical/axial induction this rotor exhibits. The vortex models are consistent with each other, and the differences when compared against the URANS and PowerFLOW mostly arise due to the unsteady and flow curvature effects. Furthermore, the influence of vertical induction is very prominent for this rotor, and this effect becomes more significant with fixed pitch offsets where the flow at the blade root is considerably altered.
3
Baungaard, M., M. P. Van Der Laan, M. Kelly e E. L. Hodgson. "Simulation of a conventionally neutral boundary layer with two-equation URANS". Journal of Physics: Conference Series 2767, n. 5 (1 giugno 2024): 052013. http://dx.doi.org/10.1088/1742-6596/2767/5/052013.
Abstract (sommario):
Abstract Simulating conventionally neutral boundary layers (CNBLs) with the unsteady Reynolds-Averaged Navier-Stokes (URANS) technique is investigated in this paper using a modified two-equation linear eddy viscosity turbulence model. For CNBLs over a flat and uniform surface, as typically used as the inflow to wind farm simulations, the governing equations of URANS can be solved with a one-dimensional solver, which makes the simulation of a typical CNBL five to six orders of magnitude faster than with large-eddy simulation (LES) approaches. However, URANS on the other hand requires more modelling than LES, and its accuracy is heavily dependent on the turbulence model employed. Through a cross-code study of a CNBL case with data from five different LES codes, it is found that the length-scale limiter of the employed turbulence model should be removed to correctly predict the atmospheric boundary layer (ABL) height evolution and the qualitative shape of various atmospheric profiles. A parametric study of simulations with varying initial ABL height further demonstrates the prediction capabilities of URANS, although a comparison with LES data shows that modelling of turbulence anisotropy and near-surface turbulence could be improved.
4
Klimczyk, Witold, e Adam Sieradzki. "Airofil Tonal Noise Prediction Using Urans". Transactions on Aerospace Research 2023, n. 4 (1 dicembre 2023): 1–17. http://dx.doi.org/10.2478/tar-2023-0019.
Abstract (sommario):
Abstract To examine the feasibility of the laminar boundary layer (LBL), vortex shedding (VS) tonal noise modelling using unsteady Reynolds-averaged Navier–Stokes (URANS) was investigated for the non-symmetric S834 airfoil. A transition SST turbulence model was used to model the laminar-turbulent transition and its vital influence on the laminar bubble and hydrodynamic instabilities generation. The influence of turbulence on the unsteady vortex patterns was investigated. Hence, the hybrid aeroacoustic analysis with Lighthill analogy was conducted to obtain the acoustic pressure field. The approach allowed us to model hydrodynamic instabilities and the resulting VS tonal noise. The frequency of VS matched the experimental data, giving the same 1/3 octave tonal peak only for a limited freestream turbulence regime. The simplification of the present method did not allow us to model the aeroacoustic feedback loop, and resulted in lack of instabilities for higher freestream turbulence.
5
Saha, A. K., e Sumanta Acharya. "Flow and Heat Transfer in an Internally Ribbed Duct With Rotation: An Assessment of Large Eddy Simulations and Unsteady Reynolds-Averaged Navier-Stokes Simulations". Journal of Turbomachinery 127, n. 2 (7 dicembre 2004): 306–20. http://dx.doi.org/10.1115/1.1861917.
Abstract (sommario):
Large eddy simulations (LES) and unsteady Reynolds averaged Navier-Stokes (URANS) simulations have been performed for flow and heat transfer in a rotating ribbed duct. The ribs are oriented normal to the flow and arranged in a staggered configuration on the leading and trailing surfaces. The LES results are based on a higher-order accurate finite difference scheme with a dynamic Smagorinsky model for the subgrid stresses. The URANS procedure utilizes a two equation k-ε model for the turbulent stresses. Both Coriolis and centrifugal buoyancy effects are included in the simulations. The URANS computations have been carried out for a wide range of Reynolds number (Re=12,500-100,000), rotation number (Ro=0-0.5) and density ratio (Δρ∕ρ=0-0.5), while LES results are reported for a single Reynolds number of 12,500 without and with rotation (Ro=0.12,Δρ∕ρ=0.13). Comparison is made between the LES and URANS results, and the effects of various parameters on the flow field and surface heat transfer are explored. The LES results clearly reflect the importance of coherent structures in the flow, and the unsteady dynamics associated with these structures. The heat transfer results from both LES and URANS are found to be in reasonable agreement with measurements. LES is found to give higher heat transfer predictions (5–10% higher) than URANS. The Nusselt number ratio (Nu∕Nu0) is found to decrease with increasing Reynolds number on all walls, while they increase with the density ratio along the leading and trailing walls. The Nusselt number ratio on the trailing and sidewalls also increases with rotation. However, the leading wall Nusselt number ratio shows an initial decrease with rotation (till Ro=0.12) due to the stabilizing effect of rotation on the leading wall. However, beyond Ro=0.12, the Nusselt number ratio increases with rotation due to the importance of centrifugal-buoyancy at high rotation.
6
Wu, Huajie, e Shanwen Zhang. "Flow field analysis of Ahmed model based on URANS". Journal of Physics: Conference Series 1983, n. 1 (1 luglio 2021): 012021. http://dx.doi.org/10.1088/1742-6596/1983/1/012021.
7
Kamalov, Bagdaulet, Sagidolla Batay, Dinmukhamed Zhangaskhanov, Yong Zhao e Eddie Yin Kwee Ng. "Arbitrary Hybrid Turbulence Modeling Approach for High-Fidelity NREL Phase VI Wind Turbine CFD Simulation". Fluids 7, n. 7 (12 luglio 2022): 236. http://dx.doi.org/10.3390/fluids7070236.
Abstract (sommario):
Today, growth in renewable energy is increasing, and wind energy is one of the key renewable energy sources which is helping to reduce carbon emissions and build a more sustainable world. Developed countries and worldwide organizations are investing in technology and industrial application development. However, extensive experiments using wind turbines are expensive, and numerical simulations are a cheaper alternative for advanced analysis of wind turbines. The aerodynamic properties of wind turbines can be analyzed and optimized using CFD tools. Currently, there is a general lack of available high-fidelity analysis for the wind turbine design community. This study aims to fill this urgent gap. In this paper, an arbitrary hybrid turbulence model (AHTM) was implemented in the open-source code OpenFOAM and compared with the traditional URANS model using the NREL Phase VI wind turbine as a benchmark case. It was found that the AHTM model gives more accurate results than the traditional URANS model. Furthermore, the results of the VLES and URANS models can be improved by improving the mesh quality for usage of higher-order schemes and taking into consideration aeroelastic properties of the wind turbine, which will pave the way for high-fidelity concurrent multidisciplinary design optimization of wind turbines.
8
Gavrilov, Andrey, e Yaroslav Ignatenko. "Numerical Simulation of Taylor—Couette—Poiseuille Flow at Re = 10,000". Fluids 8, n. 10 (19 ottobre 2023): 280. http://dx.doi.org/10.3390/fluids8100280.
Abstract (sommario):
A fully developed turbulent flow in a concentric annulus, Re =10,000, ri/ro=0.5, with an inner rotating cylinder in the velocity range N=Uω/Ub=0÷4, is studied via a large-eddy simulation. Also, for comparison, simulations by steady-state, unstatiounary RANS k-ω SST (URANS), and Elliptic Blending Model (EBM) were made. The main focus of this study is on the effect of high rotation on the mean flow, turbulence statistics, and vortex structure. Distribution of the tangential velocity and the Reynolds stress tensor change their behaviour at N>0.5∼1. With rotation increases, the production of tangential fluctuation becomes dominant over axial ones and the position of turbulent kinetic energy maximum shifts towards the wall into the buffer zone. URANS and EBM approaches show good agreement with LES in mean flow, turbulent statistics, and integral parameters. The difference in pressure loss prediction between LES and URANS does not exceed 20%, but the average difference is about 11%. The EBM approach underestimates pressure losses up to 9% and on average not more than 5%. Vortex structures are described well by URANS.
9
Ehrle, Maximilian, Andreas Waldmann, Thorsten Lutz e Ewald Krämer. "Simulation of transonic buffet with an automated zonal DES approach". CEAS Aeronautical Journal 11, n. 4 (1 settembre 2020): 1025–36. http://dx.doi.org/10.1007/s13272-020-00466-7.
Abstract (sommario):
Abstract A study of transonic buffet on the NASA Common Research Model at flight Reynolds numbers is presented. The ability of two different hybrid RANS/LES models as well as the URANS approach for resolving three-dimensional buffet motion was evaluated by means of spectral analysis. Automated Zonal DES and URANS simulations show similar results in terms of buffet frequency and spanwise propagation of buffet cells, whereas the Delayed Detached Eddy Simulation results indicate a strong interaction between flow separation and shock motion. The extracted characteristic frequencies which are associated with transonic buffet are located in a range of Sr = 0.2–0.65 for URANS and AZDES and are therefore in accordance with findings from related recent research. Furthermore, the simulation time series were investigated and a structure of spanwise moving buffet cells with varying convection speed and wavelength could be observed.
10
Hakim, Samhuddin. "Analisa numerik karakteristik aliran di sekitar struktur bentuk menyilang menggunakan model uRANS". Dinamika : Jurnal Ilmiah Teknik Mesin 13, n. 1 (10 dicembre 2021): 69. http://dx.doi.org/10.33772/djitm.v13i1.21645.
Abstract (sommario):
Karakteristik aerostatik penampang struktur berbentuk menyilang diteliti secara numerik menggunakan model unsteady Reynold Average Navier-Stokes (uRANS) dua dimensi dengan model turbulensi SST k-w. Sudut aliran masuk yang berbeda digunakan untuk menyelidiki fitur aliran di sekitar struktur tersebut. Hasil penelitian menunjukkan bahwa tekanan dasar maksimum dicapai pada sudut serang (a) = 30 derajat di mana vortisitas negatif menggulung di belakang struktur relatif jauh dari benda. Gaya aerodinamika model dengan a= 30 derajat adalah kesepakatan yang masuk akal untuk hasil eksperimen. Frekuensi strouhal menunjukkan prediksi yang kurang tepat untuk model dengan a≥20 derajat aliran masuk dibandingkan dengan hasil eksperimen. Tekanan dasar yang paling negatif ditunjukkan pada sudut serang a =15°. Gaya aerodinamis hasil simulasi berbeda dari model tiga dimensi dari penelitian eksperimental. Hal ini menunjukkan bahwa struktur dua dimensi dari model uRANS dalam penelitian ini memberikan nilai yang besar untuk fitur aliran tiga dimensi dari hasil eksperimen. Vortex street dibelakang struktur menunjukkan model single-pair (S+P) untuk semua kasus perlakuan.
11
Purohit, Shantanu, Ijaz Fazil Syed Ahmed Kabir e E. Y. K. Ng. "On the Accuracy of uRANS and LES-Based CFD Modeling Approaches for Rotor and Wake Aerodynamics of the (New) MEXICO Wind Turbine Rotor Phase-III". Energies 14, n. 16 (23 agosto 2021): 5198. http://dx.doi.org/10.3390/en14165198.
Abstract (sommario):
This work presents a comparison study of the CFD modeling with two different turbulence modeling approaches viz. unsteady RANS and LES, on a full-scale model of the (New) MEXICO rotor wind turbine. The main emphasis of the paper is on the rotor and wake aerodynamics. Simulations are carried out for the three wind speeds considered in the MEXICO experiment (10, 15, and 24 ms−1). The results of uRANS and LES are compared against the (New) MEXICO experimental measurements of pressure distributions, axial, radial, and azimuth traverse of three velocity components. The near wake characteristics and vorticity are also analyzed. The pressure distribution results show that the LES can predict the onset of flow separation more accurately than uRANS when the turbine operates in the stall condition. The LES can compute the flow structures in wake significantly better than the uRANS for the stall condition of the blade. For the design condition, the mean absolute error in axial and radial velocity components along radial traverse is less than 10% for both the modeling approaches, whereas tangential component error is less than 2% from the LES approach. The results also reveal that wake recovers faster in the uRANS approach, requiring further research of the far wake region using both CFD modeling approaches.
12
Decaix, Jean, Vlad Hasmatuchi, Maximilian Titzschkau e Cécile Münch-Alligné. "CFD Investigation of a High Head Francis Turbine at Speed No-Load Using Advanced URANS Models". Applied Sciences 8, n. 12 (5 dicembre 2018): 2505. http://dx.doi.org/10.3390/app8122505.
Abstract (sommario):
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.
13
Krastev, Vesselin Krassimirov, Giovanni Di Ilio, Clara Iacovano, Alessandro d’Adamo e Stefano Fontanesi. "Standard and consistent Detached-Eddy Simulation for turbulent engine flow modeling: an application to the TCC-III engine". E3S Web of Conferences 197 (2020): 06021. http://dx.doi.org/10.1051/e3sconf/202019706021.
Abstract (sommario):
Multidimensional modeling of Cycle-to-Cycle Variability (CCV) has become a crucial support for the development and optimization of modern direct-injection turbocharged engines. In that sense, the only viable modeling options is represented by scale-resolving approaches such as Large Eddy Simulation (LES) or hybrid URANS/LES methods. Among other hybrid approaches, Detached-Eddy Simulation (DES) has the longest development story and is therefore commonly regarded as the most reliable choice for engineering-grade simulation. As such, in the last decade DESbased methods have found their way through the engine modeling community, showing a good potential in describing turbulence-related CCV in realistic engine configurations and at reasonable computational costs. In the present work we investigate the in-cylinder modeling capabilites of a standard two-equation DES formulation, compared to a more recent one which we call DESx. The DESx form differs from standard DES in the turbulent viscosity switch from URANS to LES-like behavior, which for DESx is fully consistent with Yoshizawa’s one-equation sub-grid scale model. The two formulations are part of a more general Zonal-DES (ZDES) methodology, developed and validated by the authors in a series of previous publications. Both variants are applied to the multi-cycle simulation of the TCC-III experimental engine setup, using sub-optimal grid refinement levels in order to stress the model limitations in URANS-like numerical resolution scenarios. Outcomes from this study show that, although both alternatives are able to ouperform URANS even in coarse grid arrangements, DESx emerges as sligthly superior and thus it can be recommended as the default option for in-cylinder flow simulation.
14
Viswanathan, Aroon K., e Danesh K. Tafti. "A Comparative Study of DES and URANS for Flow Prediction in a Two-Pass Internal Cooling Duct". Journal of Fluids Engineering 128, n. 6 (14 aprile 2006): 1336–45. http://dx.doi.org/10.1115/1.2353279.
Abstract (sommario):
The capabilities of the detached eddy simulation (DES) and the unsteady Reynolds averaged Navier-Stokes (URANS) versions of the 1988 k-ω model in predicting the turbulent flow field in a two-pass internal cooling duct with normal ribs is presented. The flow is dominated by the separation and reattachment of shear layers; unsteady vorticity induced secondary flows and strong streamline curvature. The techniques are evaluated in predicting the developing flow at the entrance to the duct and downstream of the 180deg bend, fully developed regime in the first pass, and in the 180deg bend. Results of mean flow quantities, secondary flows, and the average friction factor are compared to experiments and large-eddy simulations (LES). DES predicts a slower flow development than LES, whereas URANS predicts it much earlier than LES computations and experiments. However, it is observed that as fully developed conditions are established, the capability of the base model in predicting the flow is enhanced by the DES formulation. DES accurately predicts the flow both in the fully developed region as well as the 180deg bend of the duct. URANS fails to predict the secondary flows in the fully developed region of the duct and is clearly inferior to DES in the 180deg bend.
15
Benim, Ali Cemal, Sohail Iqbal, Franz Joos e Alexander Wiedermann. "Numerical Analysis of Turbulent Combustion in a Model Swirl Gas Turbine Combustor". Journal of Combustion 2016 (2016): 1–12. http://dx.doi.org/10.1155/2016/2572035.
Abstract (sommario):
Turbulent reacting flows in a generic swirl gas turbine combustor are investigated numerically. Turbulence is modelled by a URANS formulation in combination with the SST turbulence model, as the basic modelling approach. For comparison, URANS is applied also in combination with the RSM turbulence model to one of the investigated cases. For this case, LES is also used for turbulence modelling. For modelling turbulence-chemistry interaction, a laminar flamelet model is used, which is based on the mixture fraction and the reaction progress variable. This model is implemented in the open source CFD code OpenFOAM, which has been used as the basis for the present investigation. For validation purposes, predictions are compared with the measurements for a natural gas flame with external flue gas recirculation. A good agreement with the experimental data is observed. Subsequently, the numerical study is extended to syngas, for comparing its combustion behavior with that of natural gas. Here, the analysis is carried out for cases without external flue gas recirculation. The computational model is observed to provide a fair prediction of the experimental data and predict the increased flashback propensity of syngas.
16
Avila, Matias, O. Lehmkuhl, J. Navarro, J. F. González-Rouco, D. Paredes, G. Diaz-Marta e H. Owen. "Microscale simulations of extreme events in complex terrain driven by mesoscalar budget components". Journal of Physics: Conference Series 2265, n. 2 (1 maggio 2022): 022021. http://dx.doi.org/10.1088/1742-6596/2265/2/022021.
Abstract (sommario):
Abstract In this work, we apply a downscaling strategy to analyze extreme weather events that may impact wind farm operation. The coupling applies mesoscale momentum budget components (tendencies) from the WRF model as forcing terms to the governing microscale equations. Our study focuses on flow over complex terrain during specific days to reproduce extreme weather events that produced wind turbine damage. The interaction of the meso- and micro-scale features are relevant in the simulation of extreme conditions. The simulation results are compared with observations from nacelle anemometers of the wind turbines in two different wind farms by analyzing time series and wind profiles. The microscale code Alya, developed at the Barcelona Supercomputing Center (BSC), is closed with URANS and LES closures to solve the momentum and energy equations. Both closures use the same mesoscalar to microscalar coupling methodology and are used in this work to simulate the wind flow. We present the implementation of the mesoscalar coupling to the microscale solver when using URANS and LES closures. We show that the coupling via tendencies has excellent potential for understanding transient events under extreme weather conditions in very complex terrain. The wind industry can use such simulations to enhance forensic analysis in cases of wind turbine accidents or any other event that may impact turbine operation, such as high turbulence phenomena. We test the ability of the meso- to microscale coupling model to reproduce extreme events with regard to quantities of interest in wind energy. Simulation results using URANS and LES closures agree reasonably well with observations. In some scenarios, the LES provides results that are closer to measurements. LES models have the advantage of providing wind gusts. We compare the accuracy and performance (CPU-time) of the URANS vs. LES approaches.
17
Yang, Xianglong, e Lei Yang. "An Elliptic Blending Turbulence Model-Based Scale-Adaptive Simulation Model Applied to Fluid Flows Separated from Curved Surfaces". Applied Sciences 12, n. 4 (16 febbraio 2022): 2058. http://dx.doi.org/10.3390/app12042058.
Abstract (sommario):
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.
18
el Moctar, Ould, Udo Lantermann, Vladimir Shigunov e Thomas E. Schellin. "Experimental and numerical investigations of effects of ship superstructures on wind-induced loads for benchmarking". Physics of Fluids 35, n. 4 (aprile 2023): 045124. http://dx.doi.org/10.1063/5.0146778.
Abstract (sommario):
For a representative large modern containership, the effects of a deck container arrangement on the wind-induced loads were systematically investigated using physical model tests and numerical computations. Numerical simulations based on various turbulence models were performed to validate our predictions against comparative wind tunnel measurements. Not only standard two-equation turbulence models of the unsteady Reynolds-Averaged Navier–Stokes (URANS) equations solver but also the improved delayed detached eddy simulation (IDDES) and large eddy simulation (LES) turbulence models were used to determine their limits in the prediction of aerodynamic loads. Systematic discretization studies ensured adequate discretization independent predictions. With URANS, numerically predicted wind forces and moments in near-head and near-tail winds were compared favorably with the measured data. However, in oblique winds, URANS predictions deviated from measurements. In oblique winds, flow separations were pronounced; therefore, the flow was strongly transient. Consequently, a two-equation turbulence model was inappropriate. With IDDES, more accurate predictions were achieved, especially in oblique winds. With LES, although the computational effort was high, the agreement of the computed forces and moments with the measured values was superior. Flow details were also presented and discussed. The container arrangement on deck showed major effects on aerodynamic forces and moments. A tarpaulin covering the containers on deck reduced wind resistance by up to 70%.
19
Zhang, Xin, Heng Zhang e Jie Li. "Numerical Investigation of Stall Characteristics of Common Research Model Configuration Based on Zonal Detached Eddy Simulation Method". Aerospace 10, n. 9 (18 settembre 2023): 817. http://dx.doi.org/10.3390/aerospace10090817.
Abstract (sommario):
A zonal detached eddy simulation (ZDES) method, based on the two-equation k-ω SST turbulence model, was employed to predict stall characteristics and capture small-scale vortex structures in the wake region of the main wing under the post-stall condition of the Common Research Model (CRM) configuration. Additionally, the unsteady Reynolds-averaged Navier–Stokes (URANS) method was utilized for performance comparison in resolving small-scale vortices with ZDES. The results revealed a pronounced lateral flow on the wing, induced by the low-pressure region of the inner wing at post-stall angles of attack. Due to the downwash effect, the horizontal tail was influenced by the vortices in the wake region of the main wing, which the URANS method did not capture adequately. As the angle of attack increased, the separation area on the main wing expanded from the middle of the wing towards the inner wing. Consequently, the vortex structures in the wake region of the main wing became more intricate, and the primary peak of the lift coefficient spectrum shifted to the low-frequency region.
20
Stalewski, Wieńczysław, e Katarzyna Surmacz. "Helicopter Flight Simulation based on URANS Solver and Virtual Blade Model". Journal of KONES 26, n. 3 (1 settembre 2019): 211–17. http://dx.doi.org/10.2478/kones-2019-0075.
Abstract (sommario):
Abstract The methodology of simulation of a rotorcraft flight has been developed and applied to simulate several stages of flight of light helicopter. The methodology is based on coupling of several computational models of Computational Fluid Dynamics, Flight Dynamic. The essence of the methodology consists in calculation of aerodynamic forces acting on the flying rotorcraft by solving during the simulation the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. In this approach, the rotorcraft is flying inside the computational 3D mesh modelling the space filled with the air. The flight simulation procedure is completely embedded in the URANS solver ANSYS FLUENT. Flow effects caused by rotating blades of main or tail rotor are modelled by application of the developed Virtual Blade Model (VBM). In this approach, real rotors are replaced by volume discs influencing the flow field similarly as rotating blades. Time-averaged aerodynamic effects of rotating blades are modelled using momentum source terms placed inside the volume-disc zones. The momentum sources are evaluated based on the Blade Element Theory, which associates local flow parameters in the blade sections with databases of 2D-aerodynamic characteristics of these sections. Apart of the VBM module, two additional UDF modules support the simulation of helicopter flight: the module responsible for modelling of all kinematic aspects of the flight and the module gathering the momentary aerodynamic loads and solves 6 DOF-Equations describing a motion of the helicopter seen as solid body. Exemplary simulation of helicopter flight, starting from a hover, through an acceleration and fast flight until a deceleration and steep descent, has been discussed.
21
INOUE, Rintaroh, Ichirou KIMURA e Yasuyuki SHIMIZU. "COMPUTATIONS ON MEANDERING COMPOUND OPEN CHANNEL FLOWS USING 3D URANS MODEL". Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 67, n. 4 (2011): I_1015—I_1020. http://dx.doi.org/10.2208/jscejhe.67.i_1015.
22
Richardson, G. A., W. N. Dawes e A. M. Savill. "An unsteady, moving mesh CFD simulation for Harrier hot-gas ingestion control analysis". Aeronautical Journal 111, n. 1117 (marzo 2007): 133–44. http://dx.doi.org/10.1017/s0001924000004395.
Abstract (sommario):
Hot gas ingestion (HGI) can be a problematic feature of short take-off vertical landing (STOVL) aircraft during the descent phase of landing, or while on the ground. The hot exhaust gases from the downwards pointing nozzles can be re-ingested into the engine intakes, causing power degradation or reduced engine surge margin. The flow-fields that characterise this phenomenon are complex, with supersonic impinging jets and cross-flows creating large ground vortices and fountain up-wash flows. A flow solver has been developed to include a suitable linear mesh deformation technique for the descending aircraft configuration. The code has been applied to predict the occurrence of HGI, by simulating experimental results from a 1/15th scale model of a descending Harrier. This has enabled an understanding of the aerodynamic mechanisms that govern HGI, in terms of the near-field and far-field effects and their impact on the magnitude of temperatures at the engine intake. This paper presents three sets of CFD results. First a validation exercise shows predicted results from the twin-jet with intake in crossflow test-case. This is an unsteady Reynolds averaged Navier Stokes (URANS) solution for a static geometry (there is no moving mesh). This allows comparison with experiment. Secondly, a full descent phase URANS Spalart-Allmaras (SA) turbulence model calculation is done on an 8·5m cell mesh for half the flow domain of the Harrier model and test-rig without dams/strakes. This shows how the HGI flow mechanisms affect the engine intake temperature profiles, for the case where there are no flow control methods on the underside of the aircraft. Thirdly, the full descent phase URANS SA turbulence model calculation is done on a 22·4m cell mesh for the full flow domain of the Harrier model and test-rig, with the dam/strake geometry included in the structured mesh region.
23
Murugu, Sakthi Prakash, A. R. Srikrishnan, Bharath Kumar Krishnaraj., Anguraj Jayaraj, Akram Mohammad e Ratna Kishore Velamati. "Acoustic Modeling of Compressible Jet from Chevron Nozzle: A Comparison of URANS, LES and DES Models". Symmetry 14, n. 10 (21 settembre 2022): 1975. http://dx.doi.org/10.3390/sym14101975.
Abstract (sommario):
Chevron nozzles, which are characterized by the serrations at the nozzle exit, are widely used for suppressing jet noise in aircraft engines. The noise suppression is accomplished by the enhanced mixing of the exhaust streams, which, in turn, is a result of the streamwise vorticity induced by the serrations. The present study focuses on the numerical modeling of the acoustic field in a compressible jet issuing from a chevron nozzle at a Mach number of 0.8. The study evaluates the effectiveness of turbulence modeling approaches of Large Eddy Simulation and Detached Eddy Simulation methods and compares them with the less computationally intensive Unsteady Reynolds Averaged Navier–Stokes (URANS) formulation. The Ffowcs Williams–Hawkings noise model was used to predict the overall sound pressure level in the far field. The LES predictions of the acoustic signature were found to match well with the experimental data, whereas the URANS model grossly underpredicted the sound pressure levels in the compressible jet flow field.
24
Zhang, Yang, Laiping Zhang, Xin He, Xiaogang Deng e Haisheng Sun. "Detached Eddy Simulation of Complex Separation Flows Over a Modern Fighter Model at High Angle of Attack". Communications in Computational Physics 22, n. 5 (31 ottobre 2017): 1309–32. http://dx.doi.org/10.4208/cicp.oa-2016-0132.
Abstract (sommario):
AbstractThis paper presents the simulation of complex separation flows over a modern fighter model at high angle of attack by using an unstructured/hybrid grid based Detached Eddy Simulation (DES) solver with an adaptive dissipation second-order hybrid scheme. Simulation results, including the complex vortex structures, as well as vortex breakdown phenomenon and the overall aerodynamic performance, are analyzed and compared with experimental data and unsteady Reynolds-Averaged Navier-Stokes (URANS) results, which indicates that with the DES solver, clearer vortical flow structures are captured and more accurate aerodynamic coefficients are obtained. The unsteady properties of DES flow field are investigated in detail by correlation coefficient analysis, power spectral density (PSD) analysis and proper orthogonal decomposition (POD) analysis, which indicates that the spiral motion of the primary vortex on the leeward side of the aircraft model is highly nonlinear and dominates the flow field. Through the comparisons of flow topology and pressure distributions with URANS results, the reason why higher and more accurate lift can be obtained by DES is discussed. Overall, these results show the potential capability of present DES solver in industrial applications.
25
Krastev, Vesselin Krassimirov, Alessandro d’Adamo, Fabio Berni e Stefano Fontanesi. "Validation of a zonal hybrid URANS/LES turbulence modeling method for multi-cycle engine flow simulation". International Journal of Engine Research 21, n. 4 (12 giugno 2019): 632–48. http://dx.doi.org/10.1177/1468087419851905.
Abstract (sommario):
A zonal hybridization of the RNG [Formula: see text]-[Formula: see text] URANS model is proposed for the simulation of turbulent flows in internal combustion engines. The hybrid formulation is able to act as URANS, DES or LES in different zones of the computational domain, which are explicitly set by the user. The resulting model has been implemented in a commercial computational fluid dynamics code and the LES branch of the modified RNG [Formula: see text]-[Formula: see text] closure has been initially calibrated on a standard homogeneous turbulence box case. Subsequently, the full zonal formulation has been tested on a fixed intake valve geometry, including comparisons with third-party experimental data. The core of the work is represented by a multi-cycle analysis of the TCC-III experimental engine configuration, which has been compared with the experiments and with prior full-LES computational studies. The applicability of the hybrid turbulence model to internal combustion engine flows is demonstrated, and PIV-like flow statistics quantitatively validate the model performance. This study shows a pioneering application of zonal hybrid models in engine-relevant simulation campaigns, emphasizing the relevance of hybrid models for turbulent engine flows.
26
Martineau Rousseau, Philippe, Azzeddine Soulaïmani e Michel Sabourin. "Efficiency Assessment for Rehabilitated Francis Turbines Using URANS Simulations". Water 13, n. 14 (7 luglio 2021): 1883. http://dx.doi.org/10.3390/w13141883.
Abstract (sommario):
Due to the large number of aging hydraulic turbines in North America, rehabilitation is a growing market as these turbines have low efficiency compared to modern ones. Computational Fluid Dynamics identifies components with poor hydraulic performance. The models often used in industry are based on individually analyzing the sub-components of a turbine instead of full turbine simulations due to computational and time limitations. An industrial case has shown that such analyses may lead to underestimating the efficiency increases by modifying the stay vane. The unsteady full turbine simulation proposes to simulate all components simultaneously to assess this efficiency augmentation due to stay vane rehabilitation. The developed simulation methodology is used to evaluate the efficiency increase and the flow of two rehabilitated turbines with stay vane modifications. Comparison with model tests shows the accuracy of the simulations. However, the methodology used shows imprecision in predicting the efficiency increase compared to model tests. Further works should consider the use of more complex flow modeling methods to measure the efficiency increase by the stay vane modifications.
27
García, J., J. Muñoz-Paniagua, L. Xu e E. Baglietto. "A second-generation URANS model (STRUCT-ε) applied to simplified freight trains". Journal of Wind Engineering and Industrial Aerodynamics 205 (ottobre 2020): 104327. http://dx.doi.org/10.1016/j.jweia.2020.104327.
28
Chang, Kyoungsik, George Constantinescu e Seung-O. Park. "Assessment of Predictive Capabilities of Detached Eddy Simulation to Simulate Flow and Mass Transport Past Open Cavities". Journal of Fluids Engineering 129, n. 11 (5 giugno 2007): 1372–83. http://dx.doi.org/10.1115/1.2786529.
Abstract (sommario):
The three-dimensional (3D) incompressible flow past an open cavity in a channel is predicted using the Spalart–Almaras (SA) and the shear-stress-transport model (SST) based versions of detached eddy simulation (DES). The flow upstream of the cavity is fully turbulent. In the baseline case the length to depth (L∕D) ratio of the cavity is 2 and the Reynolds number ReD=3360. Unsteady RANS (URANS) is performed to better estimate the performance of DES using the same code and meshes employed in DES. The capabilities of DES and URANS to predict the mean flow, velocity spectra, Reynolds stresses, and the temporal decay of the mass of a passive contaminant introduced instantaneously inside the cavity are assessed based on comparisons with results from a well resolved large eddy simulation (LES) simulation of the same flow conducted on a very fine mesh and with experimental data. It is found that the SA-DES simulation with turbulent fluctuations at the inlet gives the best overall predictions for the flow statistics and mass exchange coefficient characterizing the decay of scalar mass inside the cavity. The presence of inflow fluctuations in DES is found to break the large coherence of the vortices shed in the separated shear layer that are present in the simulations with steady inflow conditions and to generate a wider range of 3D eddies inside the cavity, similar to LES. The predictions of the mean velocity field from URANS and DES are similar. However, URANS predictions show poorer agreement with LES and experiment compared to DES for the turbulence quantities. Additionally, simulations with a higher Reynolds number (ReD=33,600) and with a larger length to depth ratio (L∕D=4) are conducted to study the changes in the flow and shear-layer characteristics, and their influence on the ejection of the passive contaminant from the cavity.
29
Kratzsch, Christoph, Amjad Asad e Rüdiger Schwarze. "CFD of the MHD Mold Flow by Means of Hybrid LES/RANS Turbulence Modeling". Journal for Manufacturing Science and Production 15, n. 1 (31 marzo 2015): 49–57. http://dx.doi.org/10.1515/jmsp-2014-0046.
Abstract (sommario):
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.
30
Ja’fari, Mohammad, Artur J. Jaworski e Aldo Rona. "Numerical study of flow separation control over a circular hump using synthetic jet actuators". AIP Advances 12, n. 9 (1 settembre 2022): 095205. http://dx.doi.org/10.1063/5.0099926.
Abstract (sommario):
This study deals with the wall resolved Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulation of boundary layer flow separation over a circular hump model and its active control. An array of Synthetic Jet Actuators (SJAs) is implemented in the hump model to introduce a train of vortex rings into the boundary layer to control flow separation. The OpenFOAM solver is used to numerically simulate and analyze the fluid flow using the k– ω shear stress transport model. Hot wire anemometry and particle image velocimetry measurements are carried out to evaluate the accuracy of the URANS technique as well as the effectiveness of SJAs by comparing numerical predictions to experimental data. The time-averaged results are in a good agreement with experimental results and demonstrate a successful application of SJAs to delay the flow separation by the interactions of vortical structures with the separated shear flow. The three-dimensional simulation also reveals that near wall coherent flow structures (streamwise and spanwise vortices) are responsible for the wall shear stress components. The results can be used to better understand the performance of SJAs and to further improve future actuator configurations.
31
Zahn, Rebecca, e Christian Breitsamter. "Neuro-Fuzzy Network-Based Reduced-Order Modeling of Transonic Aileron Buzz". Aerospace 7, n. 11 (13 novembre 2020): 162. http://dx.doi.org/10.3390/aerospace7110162.
Abstract (sommario):
In the present work, a reduced-order modeling (ROM) framework based on a recurrent neuro-fuzzy model (NFM) that is serial connected with a multilayer perceptron (MLP) neural network is applied for the computation of transonic aileron buzz. The training data set for the specified ROM is obtained by performing forced-motion unsteady Reynolds-averaged Navier Stokes (URANS) simulations. Further, a Monte Carlo-based training procedure is applied in order to estimate statistical errors. In order to demonstrate the method’s fidelity, a two-dimensional aeroelastic model based on the NACA651213 airfoil is investigated at different flow conditions, while the aileron deflection and the hinge moment are considered in particular. The aileron is integrated in the wing section without a gap and is modeled as rigid. The dynamic equations of the rigid aileron rotation are coupled with the URANS-based flow model. For ROM training purposes, the aileron is excited via a forced motion and the respective aerodynamic and aeroelastic response is computed using a computational fluid dynamics (CFD) solver. A comparison with the high-fidelity reference CFD solutions shows that the essential characteristics of the nonlinear buzz phenomenon are captured by the selected ROM method.
32
Oz, Furkan, e Kursat Kara. "Jet Oscillation Frequency Characterization of a Sweeping Jet Actuator". Fluids 5, n. 2 (14 maggio 2020): 72. http://dx.doi.org/10.3390/fluids5020072.
Abstract (sommario):
The time-resolved flow field of a spatially oscillating jet emitted by a sweeping jet (SWJ) actuator is investigated numerically using three-dimensional Reynolds-averaged Navier–Stokes (3D-URANS) equations. Numerical simulations are performed for a range of mass flow rates providing flow conditions varying from incompressible to subsonic compressible flows. After a detailed mesh study, the computational domain is represented using two million hexagonal control volumes. The jet oscillation frequency is predicted by analyzing velocity time histories at the actuator exit, and a linear relationship between the jet oscillation frequency and time-averaged exit nozzle Mach number is found ( f = 511.22 M + 46.618 , R² = 0.97). The results of our numerical model are compared with data from the literature, and a good agreement is found. In addition, we confirmed that the Strouhal number is almost constant with the Mach number for the subsonic oscillating jet and has an average value of St = 0.0131. The 3D-URANS model that we presented here provides a computationally inexpensive yet accurate alternative to the researchers to investigate jet oscillation characteristics.
33
Girimaji, Sharath S., Eunhwan Jeong e Ravi Srinivasan. "Partially Averaged Navier-Stokes Method for Turbulence: Fixed Point Analysis and Comparison With Unsteady Partially Averaged Navier-Stokes". Journal of Applied Mechanics 73, n. 3 (8 novembre 2005): 422–29. http://dx.doi.org/10.1115/1.2173677.
Abstract (sommario):
Hybrid/bridging models that combine the advantages of Reynolds averaged Navier Stokes (RANS) method and large-eddy simulations are being increasingly used for simulating turbulent flows with large-scale unsteadiness. The objective is to obtain accurate estimates of important large-scale fluctuations at a reasonable cost. In order to be effective, these bridging methods must posses the correct “energetics”: that is, the right balance between production (P) and dissipation (ε). If the model production-to-dissipation ratio (P∕ε) is inconsistent with turbulence physics at that cutoff, the computations will be unsuccessful. In this paper, we perform fixed-point analyses of two bridging models—partially-averaged Navier Stokes (PANS) and unsteady RANS (URANS)—to examine the behavior of production-to-dissipation ratio. It is shown that the URANS-(P∕ε) ratio is too high rendering it incapable of resolving much of the fluctuations. On the other hand, the PANS-(P∕ε) ratio allows the model to vary smoothly from RANS to DNS depending upon the values of its resolution control parameters.
34
Bazdidi-Tehrani, Farzad, e Mehdi Jahromi. "ANALYSIS OF SYNTHETIC JET FLOW FIELD: APPLICATION OF URANS APPROACH". Transactions of the Canadian Society for Mechanical Engineering 35, n. 3 (settembre 2011): 337–53. http://dx.doi.org/10.1139/tcsme-2011-0019.
Abstract (sommario):
The present paper reports the time dependent simulation of a turbulent plane synthetic jet using an unsteady Reynolds averaged Navier-Stokes approach on the basis of the first and second moment closure turbulence models. All the applied turbulence models can capture a global feature of the long time averaged flow field quite well. However, the standard k – ε model yields a disappointing prediction of the turbulence field with inaccurately high levels of turbulence kinetic energy and normal Reynolds stress distributions. The second moment closure model with quadratic nonlinear pressure strain approximation shows the most reasonable prediction of the phase averaged flow and turbulence fields.
35
Ma, Lun, Pierre-Luc Delafin, Panagiotis Tsoutsanis, Antonis Antoniadis e Takafumi Nishino. "Blade-Resolved CFD Simulations of a Periodic Array of NREL 5 MW Rotors with and without Towers". Wind 2, n. 1 (14 gennaio 2022): 51–67. http://dx.doi.org/10.3390/wind2010004.
Abstract (sommario):
A fully resolved (FR) NREL 5 MW turbine model is employed in two unsteady Reynolds-averaged Navier–Stokes (URANS) simulations (one with and one without the turbine tower) of a periodic atmospheric boundary layer (ABL) to study the performance of an infinitely large wind farm. The results show that the power reduction due to the tower drag is about 5% under the assumption that the driving force of the ABL is unchanged. Two additional simulations using an actuator disc (AD) model are also conducted. The AD and FR results show nearly identical tower-induced reductions of the wind speed above the wind farm, supporting the argument that the AD model is sufficient to predict the wind farm blockage effect. We also investigate the feasibility of performing delayed-detached-eddy simulations (DDES) using the same FR turbine model and periodic domain setup. The results show complex turbulent flow characteristics within the farm, such as the interaction of large-scale hairpin-like vortices with smaller-scale blade-tip vortices. The computational cost of the DDES required for a given number of rotor revolutions is found to be similar to the corresponding URANS simulation, but the sampling period required to obtain meaningful time-averaged results seems much longer due to the existence of long-timescale fluctuations.
36
Meng, Qingjie, e Decheng Wan. "URANS Studies of Effect of Eccentricity on Ship–Lock Interactions". International Journal of Computational Methods 13, n. 04 (4 luglio 2016): 1641012. http://dx.doi.org/10.1142/s0219876216410127.
Abstract (sommario):
The unsteady viscous flow around a 12000TEU ship model entering the Third Set of Panama Locks with different eccentricity is simulated by solving the unsteady Reynolds averaged Navier–Stokes (RANS) equations in combination with the [Formula: see text]SST turbulence model. Overset grid technology is utilized to maintain grid orthogonality and the effects of the free surface are taken into account. The hydrodynamic forces, vertical displacement as well as surface pressure distribution are predicted and analyzed. First, a benchmark test case is designed to validate the capability of the present methods in the prediction of the viscous flow around the ship when maneuvering into the lock. The accumulation of water in front of the ship during entry into a lock is noticed. A set of systematic computations with different eccentricity are then carried out to examine the effect of eccentricity on the ship–lock hydrodynamic interaction.
37
Zbavitel, Jan, e Simona Fialová. "A numerical study of hemodynamic effects on the bileaflet mechanical heart valve". EPJ Web of Conferences 213 (2019): 02103. http://dx.doi.org/10.1051/epjconf/201921302103.
Abstract (sommario):
The work is focused on calculating hemodynamically negative effects of a flow through bileaflet mechanical heart valves (BMHV). Open-source FOAM-extend and cfMesh libraries were used for numerical simulation, the leaflet movement was solved as a fluid-structure interaction. A real model of the Sorin Bicarbon heart valve was employed as the default geometry for the following shape improvement. The unsteady boundary conditions correspond to physiological data of a cardiac cycle. It is shown how the modification of the shape of the original valve geometry positively affected the size of backflow areas. Based on numerical results, a significant reduction of shear stress magnitude is shown. The outcome of a direct numerical simulation (DNS) of transient flow was compared with results of low-Reynolds URANS model k-ω SST. Despite the limits of the two-dimensional solution and Newtonian fluid model, the suitability of models frequently used in literature was reviewed. Use of URANS models can suppress the formation of some relevant vortex structures which may affect the BMHV’s dynamics. The results of this analysis can find use in optimizing the design of the mechanical valve that would cause less damage to the blood cells and lower risk of thrombus formation.
38
Balashov, Vladislav Aleksandrovich, Vitaly Evgenyevich Borisov e Yana Vladislavovna Khankhasaeva. "An implicit scheme based on the LU-SGS method for URANS equations with SST turbulence model". Keldysh Institute Preprints, n. 31 (2018): 1–20. http://dx.doi.org/10.20948/prepr-2018-31.
39
Chen, X., L. W. Liu, Z. G. Zhang, X. Z. Wang e D. K. Feng. "URANS assessment of ship extreme roll event in irregular stern quartering sea". IOP Conference Series: Materials Science and Engineering 1288, n. 1 (1 agosto 2023): 012004. http://dx.doi.org/10.1088/1757-899x/1288/1/012004.
Abstract (sommario):
Abstract In this study, the extreme roll events of a free-running ONR Tumblehome model in stern quartering seas are predicted by an unsteady Reynolds-averaged Navier–Stokes (URANS) solver coupled with a dynamic overset grid approach. The validation study is first performed for the prediction of ship extreme roll amplitude in regular waves, indicating satisfactory agreement with an average difference of less than 3% between the simulation and experimental results. The URANS approach is then applied to the assessment of the extreme roll events as the ship is sailing in irregular seas. The ship is free to 6 degrees of freedom (DOF) motions with a course-keeping control. It is concluded that the ship’s yaw motion plays an important role in the occurrence of ship extreme roll events in an irregular stern quartering sea. A rapid increase of yaw angle is observed for the ship coupled with the occurrence of the extreme roll, even leading to the capsizing.
40
Holman, Jiří. "Unsteady Flow past a Circular Cylinder Using Advanced Turbulence Models". Applied Mechanics and Materials 821 (gennaio 2016): 23–30. http://dx.doi.org/10.4028/www.scientific.net/amm.821.23.
Abstract (sommario):
This work deals with the numerical simulation of unsteady compressible turbulent flow past a circular cylinder. Turbulent flow is modeled by two different methods. The first method is based on the system of URANS equations closed by the two equation TNT model or modified EARSM model. Second method is based on the X-LES model, which is a hybrid RANS-LES method. Numerical solution is obtained by the finite volume method. Presented results are for the sub-critical turbulent flow characterized by Re=3900.
41
Sereez, Mohamed, Nikolay Abramov e Mikhail Goman. "CFD Simulations and Phenomenological Modelling of Aerodynamic Stall Hysteresis of NACA 0018 Wing". Aerospace 11, n. 5 (29 aprile 2024): 354. http://dx.doi.org/10.3390/aerospace11050354.
Abstract (sommario):
Computational simulations of three-dimensional flow around a NACA 0018 wing with an aspect ratio of AR=5 were carried out by using the Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations with the Shear-Stress Transport turbulence model closure. Simulations were performed to capture aerodynamic stall hysteresis by using the developed pseudo-transient continuation (PTC) method based on a dual-time step approach in CFD OpenFOAM code. The flow was characterized by incompressible Mach number M=0.12 and moderate Reynolds number Re=0.67×106. The results obtained indicate the presence of noticeable aerodynamic hysteresis in the static dependencies of the force and moment coefficients, as well as the manifestation of bi-stable flow separation patterns, accompanied by the development of asymmetry in the stall zone. The URANS simulation results are in good agreement with the experimental data obtained for the NACA 0018 finite-aspect-ratio wing in the low-speed wind tunnel under the same test conditions. A new phenomenological bifurcation model of aerodynamic stall hysteresis under static and dynamic conditions is formulated and is proven to be able to closely match the experimental data.
42
Cornelius, Jason, Sven Schmitz, Jose Palacios, Bernadine Juliano e Richard Heisler. "Rotor Performance Predictions for Urban Air Mobility: Single vs. Coaxial Rigid Rotors". Aerospace 11, n. 3 (20 marzo 2024): 244. http://dx.doi.org/10.3390/aerospace11030244.
Abstract (sommario):
This work details the development and validation of a methodology for high-resolution rotor models used in hybrid Blade Element Momentum Theory Unsteady Reynolds Averaged Navier–Stokes (BEMT-URANS) CFD. The methodology is shown to accurately predict single and coaxial rotor performance in a fraction of the time required by conventional CFD methods. The methodology has three key features: (1) a high-resolution BEMT rotor model enabling large reductions in grid size, (2) a discretized set of momentum sources to interface between the BEMT rotor model and the structured URANS flow solver, and (3) leveraging of the first two features to enable highly parallelized GPU-accelerated multirotor CFD simulations. The hybrid approach retains high-fidelity rotor inflow, wake propagation, and rotor–rotor interactional effects at a several orders of magnitude lower computational cost compared to conventional blade-resolved CFD while retaining high accuracy on steady rotor performance metrics. Rotor performance predictions of thrust and torque for both single and coaxial rotor configurations are compared to test the data that the authors obtained at the NASA Langley 14- by 22-ft. Subsonic Tunnel Facility. Simulations were run with both fully turbulent and free-transition airfoil performance tables to quantify the associated uncertainty. Single rotor thrust and torque were predicted on average within 4%. Coaxial thrust and power were predicted within an average of 5%. A vortex ring state (VRS) shielding phenomenon for coaxial rotor systems is also presented and discussed. The results support that this hybrid BEMT-URANS CFD methodology can be highly parallelized on GPU machines to obtain accurate rotor performance predictions across the full spectrum of possible UAM flight conditions in a fraction of the time required by conventional higher-fidelity methods. This strategy can be used to rapidly create look-up tables with hundreds to thousands of flight conditions using a three-dimensional multirotor CFD for UAM.
43
Rui, Xiaocheng, Limin Lin, Junkui Wang, Xinxue Ye, Haijiang He, Wei Zhang e Zuchao Zhu. "Experimental and Comparative RANS/URANS Investigations on the Effect of Radius of Volute Tongue on the Aerodynamics and Aeroacoustics of a Sirocco Fan". Processes 8, n. 11 (11 novembre 2020): 1442. http://dx.doi.org/10.3390/pr8111442.
Abstract (sommario):
The geometry of volute tongue is crucial in the design of Sirocco fans. The size of the volute tongue determines its relative position and distance from the impeller which affects the local flow characteristics and thus the aerodynamic and aeroacoustic performances of the fan. In this work, we performed experimental and numerical investigations on the effect of volute tongue radius on the aerodynamic and aeroacoustic characteristics of a Sirocco fan. The internal flow characteristics are analyzed and discussed in terms of the spatial distribution and temporal variation of pressure and streamlines, the pulsating behaviors of pressure both in the impeller and on the volute surface with emphasis in the volute tongue region, the variation of passage flow with the rotation of impeller and the aeroacoustic features of the fan. We conducted numerical simulations using both steady Reynolds-Averaged Navier-Stokes (RANS) and unsteady Reynolds-Averaged Navier-Stokes (URANS) approaches with realizable k-ε turbulence model with rotation effect correction and the results are compared against the experimental data to assess the prediction capability and accuracy in qualitative and quantitative manners. Experimental and numerical results show that as the volute tongue radius increases, the static pressure rises as well as the far-field noise of the fan and pronounced fluctuation of flow is observed within the whole impeller and volute; the reversed flow in the passage of the impeller is reduced and the high-pressure region is found to be moving towards the outlet of the volute. The decreasing radius also enlarges the size of the adverse pressure gradient (APG) region on the volute tongue which contributes to the formation of recirculating flow. The comparative RANS and URANS simulations reveal that both approaches produce generally consistent results regarding the time-averaged flow although the URANS data are much closer to those of the experimental ones. However, the fluctuating flow which is not capable to be modeled by RANS still dominates for the present configuration and thus URANS is necessary for the accurate prediction of the flow details.
44
Shahi, Mina, Jim B. W. Kok, J. C. Roman Casado e Artur K. Pozarlik. "Assessment of thermoacoustic instabilities in a partially premixed model combustor using URANS approach". Applied Thermal Engineering 71, n. 1 (ottobre 2014): 276–90. http://dx.doi.org/10.1016/j.applthermaleng.2014.06.068.
45
Corrêa, Rafaela Gomide, João Rodrigo Andrade e Francisco José de Souza. "Improving Separation Prediction of Cyclone Separators with a Hybrid URANS-LES Turbulence Model". Powders 2, n. 3 (15 agosto 2023): 607–23. http://dx.doi.org/10.3390/powders2030038.
Abstract (sommario):
The CFD simulation of cyclone separators has remarkably evolved over the past decades. Nowadays, computational models are essential for designing, analyzing, and optimizing these devices. Due to the intrinsic anisotropy of the flow inside these separators, the Reynolds stress model (RSM) has been mostly employed. However, RSM models fail to solve most time and space scales, including those relevant to particle behavior. Consequently, the prediction of the grade collection efficiency may be hindered, particularly for low-Stokes-number particles. For example, the precessing vortex core phenomenon (PVC), a well-known phenomenon that is relevant for particle motion, is not usually captured in Reynolds-averaged Navier–Stokes (RANS) simulations. Alternatively, the large-eddy simulation (LES) has been proven to be a superior approach since it captures many time and space scales that would have been otherwise dissipated, allowing for more accurate predictions of particle collection. However, this accuracy comes at a considerable computational cost. To combine the advantages of these two models, the main objective of this research was to evaluate a new hybrid RSM-LES model applied to the cyclone’s flow. The results were compared to experimental data and with RSM model results. It showed that, compared to a RANS model given by the RSM closure model, the grade collection efficiency curve obtained by the hybrid model is closer to the experimental one, even for the coarser mesh. Beyond that, the results showed that while the improvement in results was not proportional to mesh refinement for RANS modeling, the hybrid model showed significant improvement with mesh refinement.
46
Escartí-Guillem, Mara S., Luis M. García-Raffi e Sergio Hoyas. "URANS Analysis of a Launch Vehicle Aero-Acoustic Environment". Applied Sciences 12, n. 7 (25 marzo 2022): 3356. http://dx.doi.org/10.3390/app12073356.
Abstract (sommario):
Predicting and mitigating acoustic levels become critical because of the harsh acoustic environment during space vehicle lift-off. This paper aimed to study the aero-acoustic environment during a rocket lift-off. The sound propagation within a launch event was studied using dedicated computational fluid dynamics (CFD). The resolution of all the phenomena that occur is unfeasible. We discuss the turbulence simplification and propose a feasible simulation through an unsteady Reynolds-averaged Navier–Stokes (URANS) model. The results were validated with experimental data showing a good correlation near the fairing surface and an improvable accuracy in the far field. To assess noise generation, the main shock waves were identified, and the evolution of the generated sound pressure was assessed. Moreover, vertical directivity was revealed by data analysis of the pressure field surrounding the fairing.
47
Grecu, I. S., G. Dunca, D. M. Bucur e M. J. Cervantes. "URANS numerical simulations of pulsating flows considering streamwise pressure gradient on asymmetric diffuser". IOP Conference Series: Earth and Environmental Science 1079, n. 1 (1 settembre 2022): 012087. http://dx.doi.org/10.1088/1755-1315/1079/1/012087.
Abstract (sommario):
Abstract The paper focuses on implementing the wall model developed by Manhart, in Reynolds Averaged Navier - Stokes (RANS) turbulence models used in the field of Computational Fluid Dynamics (CFD). This wall model considers the influence of the streamwise pressure gradient in addition to the existing wall models used in the usual CFD codes. In the present work, two RANS numerical simulations are carried out using the k-ω Shear Stress Transport (SST) turbulence model on an asymmetric diffuser geometry. One numerical simulation is carried out using the implementation of the Manhart wall model in the k-ω SST turbulence model, and the other numerical simulation is performed using the standard formulation of the k-ω SST turbulence model. The numerical simulations carried out using the Manhart wall model and the standard formulation of the k-ω SST are compared with experimental measurements made on the asymmetric diffuser experimental installation. The numerical simulations are carried out using a free, open-source CFD tool, Code_Saturne. The comparisons between numerical simulations and the experimental data are in good agreement in the boundary layer of the flow inside the diffuser. The Manhart wall model had a faster convergence resulting in a shorter simulation time.
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LUCHTENBURG, DIRK M., BERT GÜNTHER, BERND R. NOACK, RUDIBERT KING e GILEAD TADMOR. "A generalized mean-field model of the natural and high-frequency actuated flow around a high-lift configuration". Journal of Fluid Mechanics 623 (6 marzo 2009): 283–316. http://dx.doi.org/10.1017/s0022112008004965.
Abstract (sommario):
A low-dimensional Galerkin model is proposed for the flow around a high-lift configuration, describing natural vortex shedding, the high-frequency actuated flow with increased lift and transients between both states. The form of the dynamical system has been derived from a generalized mean-field consideration. Steady state and transient URANS (unsteady Reynolds-averaged Navier–Stokes) simulation data are employed to derive the expansion modes and to calibrate the system parameters. The model identifies the mean field as the mediator between the high-frequency actuation and the low-frequency natural shedding instability.
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Huang, Guofeng, Heng Wang, Sheng Tian e Wei Tan. "Research on the Aerodynamic Noise Characteristics of Heat Exchanger Tube Bundles Based on a Hybrid URANS-FWH Method". International Journal of Chemical Engineering 2024 (31 gennaio 2024): 1–15. http://dx.doi.org/10.1155/2024/5100871.
Abstract (sommario):
This paper examines the aerodynamic noise characteristics of heat exchanger tube bundles, with the objective of exploring the frequency and directional features of noise under nonacoustic resonance conditions, to provide assistance in determining acoustic resonance. To predict the flow-induced noise of tube bundles, this study employs a hybrid URANS-FWH method. The transition SST model of URANS is used to accurately simulate the turbulent flow field and obtain precise statistical data on turbulence. The FWH equation is utilized to predict and evaluate the intensity and spectral characteristics of the tube bundle noise. The research findings indicate that the noise generated by the heat exchanger tube bundle is affected by pressure pulsations resulting from vortex motion in the deeper regions of the tube bundles. Notably, within specific frequency ranges, the noise intensity experiences a significant enhancement, potentially triggering complex modes of acoustic resonance. This resonance phenomenon poses safety concerns for equipment and threatens the wellbeing of personnel. Consequently, this study provides a solid theoretical foundation for predicting and controlling noise in heat exchanger tube bundles, offering valuable guidance for practical applications.
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Sagimbayev, Sagi, Yestay Kylyshbek, Sagidolla Batay, Yong Zhao, Sai Fok e Teh Soo Lee. "3D Multidisciplinary Automated Design Optimization Toolbox for Wind Turbine Blades". Processes 9, n. 4 (26 marzo 2021): 581. http://dx.doi.org/10.3390/pr9040581.
Abstract (sommario):
This paper presents two novel automated optimization approaches. The first one proposes a framework to optimize wind turbine blades by integrating multidisciplinary 3D parametric modeling, a physics-based optimization scheme, the Inverse Blade Element Momentum (IBEM) method, and 3D Reynolds-averaged Navier–Stokes (RANS) simulation; the second method introduces a framework combining 3D parametric modeling and an integrated goal-driven optimization together with a 4D Unsteady Reynolds-averaged Navier–Stokes (URANS) solver. In the first approach, the optimization toolbox operates concurrently with the other software packages through scripts. The automated optimization process modifies the parametric model of the blade by decreasing the twist angle and increasing the local angle of attack (AoA) across the blade at locations with lower than maximum 3D lift/drag ratio until a maximum mean lift/drag ratio for the whole blade is found. This process exploits the 3D stall delay, which is often ignored in the regular 2D BEM approach. The second approach focuses on the shape optimization of individual cross-sections where the shape near the trailing edge is adjusted to achieve high power output, using a goal-driven optimization toolbox verified by 4D URANS Computational Fluid Dynamics (CFD) simulation for the whole rotor. The results obtained from the case study indicate that (1) the 4D URANS whole rotor simulation in the second approach generates more accurate results than the 3D RANS single blade simulation with periodic boundary conditions; (2) the second approach of the framework can automatically produce the blade geometry that satisfies the optimization objective, while the first approach is less desirable as the 3D stall delay is not prominent enough to be fruitfully exploited for this particular case study.