scholarly journals Large-Eddy Simulations of Rim Seal Flow in a One-Stage Axial Turbine

2020 ◽  
Vol 4 ◽  
pp. 309-321
Author(s):  
Thomas Hösgen ◽  
Matthias Meinke ◽  
Wolfgang Schröder
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Level Set ◽  
Mass Flux ◽  
Acoustic Waves ◽  
Stokes Equations ◽  
Axial Flow ◽  
Cartesian Mesh ◽  
One Stage ◽  
Large Eddy

The flow field in a one-stage axial flow turbine with 30 stator and 62 rotor blades including the wheel space is investigated by large-eddy simulation (LES). The Navier-Stokes equations are solved using a massively parallel finite-volume solver based on a Cartesian mesh with immersed boundaries. The strict conservation of mass, momentum, and energy is ensured by an efficient cut-cell/level-set ansatz, where a separate level-set solver describes the motion of the rotor. Both solvers use individual subsets of a shared Cartesian mesh, which they can adapt independently. The focus of the analysis is on the flow field inside the rotor stator cavity between the stator and rotor disks. Two cooling gas mass flow rates are investigated for the same rim seal geometry. First, the time averaged flow field for both simulations is compared, followed by a detailed investigation of the unsteady flow field. The results for the cooling effectiveness are compared to experimental data. Both cases show good agreement with experimental data. It is shown that for the lower cooling gas mass flux several of the wheel space’s acoustic waves are excited. This is not observed for the higher cooling gas mass flux. The excited waves lead to stable, i.e., bounded, fluctuations inside the wheel space and result in a significantly higher hot gas ingestion.

Large-Eddy Simulation of Turbine Rim Seal Flow

2018 ◽  
Author(s):  
Alexej Pogorelov ◽  
Matthias Meinke ◽  
Wolfgang Schröder
Keyword(s):  
Flow Field ◽  
Large Eddy Simulation ◽  
Level Set ◽  
Large Scale ◽  
Stokes Equations ◽  
Axial Flow ◽  
Dominant Mode ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Impact

The flow field in a complete one-stage axial-flow turbine with 30 stator and 62 rotor blades is investigated by large-eddy simulation (LES). To solve the compressible Navier-Stokes equations, a massively parallelized finite-volume flow solver based on an efficient Cartesian cut-cell/level-set approach, which ensures a strict conservation of mass, momentum and energy, is used. This numerical method contains two adaptive Cartesian meshes, one mesh to track the embedded surface boundaries and a second mesh to resolve the fluid domain and to solve the conservation equations. The overall approach allows large scale simulations of turbomachinery applications with multiple relatively moving boundaries in a single frame of reference. The relative motion of the geometries is described by a kinematic motion level-set interface method. The focus of the numerical analysis is on the flow inside the cavity between the stator and the rotor disks. Full 360° computations of the turbine stage with a single lip rim seal geometry are conducted. First, the impact of the mesh resolution on the LES results is analyzed. Second, the LES results are compared to experimental data, followed by a detailed analysis of the flow field inside the rotor-stator wheel space. A dominant mode unrelated to the rotor frequency and its harmonics is identified, which shows a major impact on the ingress of the hot gas into the rotor-stator wheel space.

Investigation on hydrodynamic forces leading to coarse particle entrainment using Large-Eddy Simulations

2021 ◽  
Author(s):  
Gaston Latessa ◽  
Angela Busse ◽  
Manousos Valyrakis
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Large Scale ◽  
Large Eddy Simulations ◽  
Flow Conditions ◽  
Mean Flow ◽  
Protection Measures ◽  
Practical Applications ◽  
Particle Entrainment ◽  
Large Eddy

<p>The prediction of particle motion in a fluid flow environment presents several challenges from the quantification of the forces exerted by the fluid onto the solids -normally with fluctuating behaviour due to turbulence- and the definition of the potential particle entrainment from these actions. An accurate description of these phenomena has many practical applications in local scour definition and to the design of protection measures.</p><p>In the present work, the actions of different flow conditions on sediment particles is investigated with the aim to translate these effects into particle entrainment identification through analytical solid dynamic equations.</p><p>Large Eddy Simulations (LES) are an increasingly practical tool that provide an accurate representation of both the mean flow field and the large-scale turbulent fluctuations. For the present case, the forces exerted by the flow are integrated over the surface of a stationary particle in the streamwise (drag) and vertical (lift) directions, together with the torques around the particle’s centre of mass. These forces are validated against experimental data under the same bed and flow conditions.</p><p>The forces are then compared against threshold values, obtained through theoretical equations of simple motions such as rolling without sliding. Thus, the frequency of entrainment is related to the different flow conditions in good agreement with results from experimental sediment entrainment research.</p><p>A thorough monitoring of the velocity flow field on several locations is carried out to determine the relationships between velocity time series at several locations around the particle and the forces acting on its surface. These results a relevant to determine ideal locations for flow investigation both in numerical and physical experiments.</p><p>Through numerical experiments, a large number of flow conditions were simulated obtaining a full set of actions over a fixed particle sitting on a smooth bed. These actions were translated into potential particle entrainment events and validated against experimental data. Future work will present the coupling of these LES models with Discrete Element Method (DEM) models to verify the entrainment phenomena entirely from a numerical perspective.</p>

Large-Eddy and Unsteady Reynolds-Averaged Navier-Stokes Simulations of an Axial Flow Pump for Cardiac Support

2017 ◽  
Author(s):  
Benjamin Torner ◽  
Sebastian Hallier ◽  
Matthias Witte ◽  
Frank-Hendrik Wurm
Keyword(s):  
Flow Field ◽  
Axial Flow ◽  
Pressure Head ◽  
Damage Parameter ◽  
Ventricular Assist Devices ◽  
Navier Stokes ◽  
Mean Velocity ◽  
Blood Damage ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes

The use of implantable pumps for cardiac support (Ventricular Assist Devices) has proven to be a promising option for the treatment of advanced heart failure. Avoiding blood damage and achieving high efficiencies represent two main challenges in the optimization process. To improve VADs, it is important to understand the turbulent flow field in depth in order to minimize losses and blood damage. The application of the Large-eddy simulation (LES) is an appropriate approach to simulate the flow field because turbulent structures and flow patterns, which are connected to losses and blood damage, are directly resolved. The focus of this paper is the comparison between an LES and an Unsteady Reynolds-Averaged Navier-Stokes simulation (URANS) because the latter one is the most frequently used approach for simulating the flow in VADs. Integral quantities like pressure head and efficiency are in a good agreement between both methods. Additionally, the mean velocity fields show similar tendencies. However, LES and URANS show different results for the turbulent kinetic energy. Deviations of several tens of percent can be also observed for a blood damage parameter, which depend on velocity gradients. Possible reasons for the deviations will be investigated in future works.

scholarly journals Three-Dimensional Turbulent Vortex Shedding From a Surface-Mounted Square Cylinder: Predictions With Large-Eddy Simulations and URANS

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
B. A. Younis ◽  
A. Abrishamchi
Keyword(s):  
Experimental Data ◽  
Turbulence Model ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Navier Stokes Equations ◽  
Large Eddy

The paper reports on the prediction of the turbulent flow field around a three-dimensional, surface mounted, square-sectioned cylinder at Reynolds numbers in the range 104–105. The effects of turbulence are accounted for in two different ways: by performing large-eddy simulations (LES) with a Smagorinsky model for the subgrid-scale motions and by solving the unsteady form of the Reynolds-averaged Navier–Stokes equations (URANS) together with a turbulence model to determine the resulting Reynolds stresses. The turbulence model used is a two-equation, eddy-viscosity closure that incorporates a term designed to account for the interactions between the organized mean-flow periodicity and the random turbulent motions. Comparisons with experimental data show that the two approaches yield results that are generally comparable and in good accord with the experimental data. The main conclusion of this work is that the URANS approach, which is considerably less demanding in terms of computer resources than LES, can reliably be used for the prediction of unsteady separated flows provided that the effects of organized mean-flow unsteadiness on the turbulence are properly accounted for in the turbulence model.

An Average-Passage Empirical Closure Model for Centrifugal Compressors

2004 ◽  
Author(s):  
Limin Gao ◽  
Guang Xi ◽  
Shangjin Wang
Keyword(s):  
Experimental Data ◽  
Empirical Model ◽  
Stokes Equations ◽  
Computational Cost ◽  
Axial Flow ◽  
Equation System ◽  
Computational Grids ◽  
Navier Stokes ◽  
Sufficient Information ◽  
Centrifugal Compressors

Applying the novel time- and passage-averaging operators, a reduced average-passage equation system is derived to remove the bodyforce and the blockage factor in Adamczyk’s average-passage equations. Like the Reynolds-averaged Navier-Stokes equations the average-passage flow model does not contain sufficient information to determine its solution. Based on the rich throughflow analysis for axial-flow turbomachinery and numerous studies for centrifugal compressors, a semi-empirical model of the deterministic stress is developed for centrifugal compressors in the present study. Finally, the empirical model coupled with the interface approach is applied to predict the time-averaged flow field in a tested centrifugal compressor stage and the results are compared with experimental data. Using the same computational grids, the computational cost with the empirical model is slightly more than that with the mixing plane model, and a good agreement was obtained between the numerical results and experimental data.

scholarly journals Numerical Investigation of Fluid Flow and Performance Prediction in a Fluid Coupling Using Large Eddy Simulation

2017 ◽  
Vol 2017 ◽  
pp. 1-11
Author(s):  
Wei Cai ◽  
Yuan Li ◽  
Xingzhong Li ◽  
Chunbao Liu
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Large Eddy Simulation ◽  
Performance Prediction ◽  
Subgrid Scale ◽  
Eddy Simulation ◽  
Comparison Results ◽  
Large Eddy ◽  
Hydraulic Coupling ◽  
And Performance

Large eddy simulation (LES) with various subgrid-scale (SGS) models was introduced to numerically calculate the transient flow of the hydraulic coupling. By using LES, the study aimed to advance description ability of internal flow and performance prediction. The CFD results were verified by experimental data. For the purpose of the description of the flow field, six subgrid-scale models for LES were employed to depict the flow field; the distribution structure of flow field was legible. Moreover, the flow mechanism was analyzed using 3D vortex structures, and those showed that DSL and KET captured abundant vortex structures and provided a relatively moderate eddy viscosity in the chamber. The predicted values of the braking torque for hydraulic coupling were compared with experimental data. The comparison results were compared with several simulation models, such as SAS and RKE, and SSTKW models. Those comparison results showed that the SGS models, especially DSL and KET, were applicable to obtain the more accurate predicted results than SAS and RKE, and SSTKW models. Clearly, the predicted results of LES with DSL and KET were far more accurate than the previous studies. The performance prediction was significantly improved.

The Influence of Unsteady Rotor Response on a Distorted Flow Field

1982 ◽  
Vol 104 (3) ◽  
pp. 683-691 ◽  
Author(s):  
R. E. Henderson ◽  
I. C. Shen
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Axial Velocity ◽  
Axial Flow ◽  
Stagnation Pressure ◽  
Strong Function ◽  
Actuator Disk

The influence of the unsteady rotor response on the shape of stagnation pressure and axial velocity distortions passing through an axial flow rotor are investigated. Experimental data obtained with an isolated rotor in an incompressible, distorted inflow demonstrate that the magnitude of the distortion downstream of the rotor is a strong function of the ratio of the blade spacing s to the distortion wavelength ln. An existing actuator disk analysis based on a quasi-steady model of the rotor response and used extensively to predict the downstream distortion, has been extended to include the unsteady response of the rotor. By examining a series of sinusoidal distortions of varying wavelength, a semi-actuator disk analysis, which includes the unsteady rotor response, is shown to predict the same trend with s/ln as exhibited by the experimental data.

Numerical validation and back-pressure effect on internal compression flows of typical supersonic inlet

2015 ◽  
Vol 119 (1215) ◽  
pp. 631-645 ◽  
Author(s):  
F. Ding ◽  
C.-B. Shen ◽  
W. Huang ◽  
J. Liu
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Stokes Equations ◽  
Numerical Study ◽  
Pressure Ratio ◽  
Turbulence Models ◽  
Wave Pattern ◽  
Back Pressure ◽  
Freestream Turbulence ◽  
Supersonic Inlet

AbstractA numerical study was conducted to analyse the performance of different turbulence models and different turbulence intensities and turbulence length scales specified for the boundary condition of the inflow to the internal compression flow field of a typical supersonic inlet. The effect of the back-pressure ratio on the properties of the flow field was also investigated. Computational results obtained by the commercial software FLUENT, which is used to solve the full two-dimensional Reynolds-averaged Navier-Stokes equations, were validated through both graphical and quantitative comparisons with previously published experimental data. The two-equation models that were considered in this study are the RNGk-ε, realisablek-ε, standardk-ε, and SSTk-ω turbulence models. The RNGk-ε model had the best performance among the four models and predicted good wall pressure distributions. The best agreement between the predicted results and experimental data was obtained when either the default values of the freestream turbulence intensity and length scale in the FLUENT solver were used, or the empirical formula was used to calculate the two parameters of the freestream turbulence properties. The shock wave pattern varied between the oblique mode and the fully developed normal mode with increasing back-pressure ratio, and the unstart phenomenon occurred when the back-pressure ratio was sufficiently high.

Spectral Analysis of an Aeronautical Lean Direct Injection Burner Through Large Eddy Simulation

2020 ◽  
Author(s):  
M. Carreres ◽  
L. M. García-Cuevas ◽  
J. García-Tíscar ◽  
M. Belmar-Gil
Keyword(s):  
Experimental Data ◽  
Spectral Analysis ◽  
Flow Field ◽  
Large Eddy Simulation ◽  
Swirling Flow ◽  
Direct Injection ◽  
Flow Structures ◽  
Lean Direct Injection ◽  
Eddy Simulation ◽  
Large Eddy

Abstract During the last decades, many efforts have been invested by the scientific community in minimising exhaust emissions from aeronautical gas turbine engines. In this context, many advanced ultra-low NOx combustion concepts, such as the Lean Direct Injection treated in the present study, are being developed to abide by future regulations. Numerical simulations of these devices are usually computationally expensive since they imply a multi-scale problem. In this work, a non-reactive Large Eddy Simulation of a gaseous-fuelled, radial-swirled Lean-Direct Injection (LDI) combustor has been carried out through the OpenFOAM Computational Fluid Dynamics (CFD) code by solving the complete inlet flow path through the swirl vanes and the combustor. The geometry considered is the gaseous configuration of the CORIA LDI combustor, for which detailed measurements are available. Macroscopical analysis of the main turbulent features related to the swirling flow and the generated Central Recirculation Zone (CRZ) are well established in the literature. Nevertheless, a more in-depth characterization is still required in this area of active research since theory and experimental data are not yet able to predict which unstable mode dominates the flow. This work aims at using Large Eddy Simulation for a complete characterisation of the unsteady flow structures generated within the combustion chamber of a gaseous methane injection immersed in a strong non-reactive swirling flow field. To do so, a spectral analysis of the flow field is performed to identify the frequency, intensity and instabilities associated to the phenomena occurring at the swirler outlet region. A coherent structure known as Precessing Vortex Core (PVC) is identified both at the inner and the outer shear layers, resulting in a periodic disturbance of the pressure and velocity fields. The pressure and velocity fluctuations predicted by the CFD code are used to compute the spectral signatures through the Sound Pressure Level (SPL) amplitude at multiple locations. This allows investigating both the complex behaviour of the PVC and its associated acoustic phenomena. The acoustic characteristics computed by the numerical model are first validated qualitatively by comparing the spectrum with available experimental data. In this way, the use of dimensionless numbers to characterise the most energetic structures is coherent with the experimental observations and the characteristics of the PVC. Then, the numerical identification of the main acoustic modes in the chamber through Dynamic Mode Decomposition (DMD) allows overcoming the Fast Fourier Transform (FFT) shortcomings and better understanding the propagation of the hydrodynamic instability perturbations. This investigation on the main non-reacting swirling flow structures inside the combustor provides a suitable background for further studies on combustion instability mechanisms.

scholarly journals Study of Three-Dimensional Viscous Flow Field in Axial-Flow Fan

1996 ◽  
Author(s):  
Moming Su ◽  
Chuan-gang Gu ◽  
Yong-miao Miao
Keyword(s):  
Boundary Condition ◽  
Flow Field ◽  
Turbulent Flows ◽  
Stokes Equations ◽  
Interpolation Method ◽  
Three Dimensional ◽  
Axial Flow ◽  
Computational Procedure ◽  
Navier Stokes ◽  
Moving Wall

The complex three-dimensional flow field in an axial-flow impeller incorporating high-Reynolds-number k-ε turbulence model is studied in this paper. The fully three-dimensional Reynolds averaged Navier-Stokes equations are solved. A computational procedure has been developed for predicting three-dimensional incompressible separated turbulent flows in the impeller. The SIMPLE-like algorithm is used. Convective terms are approximated with higher-order upstream-weighted approximations and a TVD-type MUSCL scheme. Physical covariant velocity components are selected as dependent solving variables. The non-orthogonal boundary-fitted coordinate system and collocated grid arrangement are also employed. Rhie and Chow’s momentum interpolation method is adopted to eliminate the non-physical pressure and velocity oscillations. Periodic boundary condition and moving wall boundary condition are considered to simulate truthfully the turbulent flow field in impeller. Two types of axial-flow impellers are computed. The first one is designed by ordinary method and the other is a improved design that has been considered with eliminating flow separation and viscous vortex in the first design. The computed results show that the fully tree-dimensional turbulent flows computation can efficiently predict three-dimensional separated flows and viscous vortex in axial-flow impeller and vaneless clearance. Using the program, a designer can improve passage geometric design to enhance the performance of the fan.

Sign in / Sign up

Export Citation Format

Share Document