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.

scholarly journals Subgrid-scale models and large-eddy simulation of oxygen stream disintegration and mixing with a hydrogen or helium stream at supercritical pressure

2011 ◽  
Vol 679 ◽  
pp. 156-193 ◽  
Author(s):  
EZGI S. TAŞKINOĞLU ◽  
JOSETTE BELLAN
Keyword(s):  
Heat Flux ◽  
Flow Field ◽  
Large Eddy Simulation ◽  
Correction Term ◽  
A Priori ◽  
Supercritical Pressure ◽  
Subgrid Scale ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Impact

For flows at supercritical pressure, p, the large-eddy simulation (LES) equations consist of the differential conservation equations coupled with a real-gas equation of state, and the equations utilize transport properties depending on the thermodynamic variables. Compared to previous LES models, the differential equations contain not only the subgrid-scale (SGS) fluxes but also new SGS terms, each denoted as a ‘correction’. These additional terms, typically assumed null for atmospheric pressure flows, stem from filtering the differential governing equations and represent differences, other than contributed by the convection terms, between a filtered term and the same term computed as a function of the filtered flow field. In particular, the energy equation contains a heat-flux correction (q-correction) which is the difference between the filtered divergence of the molecular heat flux and the divergence of the molecular heat flux computed as a function of the filtered flow field. We revisit here a previous a priori study where we only had partial success in modelling the q-correction term and show that success can be achieved using a different modelling approach. This a priori analysis, based on a temporal mixing-layer direct numerical simulation database, shows that the focus in modelling the q-correction should be on reconstructing the primitive variable gradients rather than their coefficients, and proposes the approximate deconvolution model (ADM) as an effective means of flow field reconstruction for LES molecular heat-flux calculation. Furthermore, an a posteriori study is conducted for temporal mixing layers initially containing oxygen (O) in the lower stream and hydrogen (H) or helium (He) in the upper stream to examine the benefit of the new model. Results show that for any LES including SGS-flux models (constant-coefficient gradient or scale-similarity models; dynamic-coefficient Smagorinsky/Yoshizawa or mixed Smagorinsky/Yoshizawa/gradient models), the inclusion of the q-correction in LES leads to the theoretical maximum reduction of the SGS molecular heat-flux difference; the remaining error in modelling this new subgrid term is thus irreducible. The impact of the q-correction model first on the molecular heat flux and then on the mean, fluctuations, second-order correlations and spatial distribution of dependent variables is also demonstrated. Discussions on the utilization of the models in general LES are presented.

Large Eddy Simulation of Turbulent Axial Flow Along an Array of Rods

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
F. Abbasian ◽  
S. D. Yu ◽  
J. Cao
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Large Scale ◽  
Axial Flow ◽  
Dominant Frequency ◽  
Turbulence Structure ◽  
Circular Array ◽  
Central Difference ◽  
Eddy Simulation ◽  
Large Eddy

Large eddy simulation (LES) is employed in this paper to model the axial flow along a circular array of rods with a focus on anisotropic large-scale turbulence. The circular array consists of four whole rods and eight half rods, with a pitch-to-diameter ratio of 1.08. A dynamic Smagorinsky model with SIMPLE coupling method and a bounded central difference scheme are used to reduce numerical errors. The high demands for computations of the three-dimensional turbulent flows are afforded through parallel processing and utilization of 20 processors. The numerical results obtained using LES are compared with independent experimental data available in the literature; good agreement is achieved. The LES model was developed to accurately predict (i) the dependence of turbulence intensity and dominant frequency on the gap size and (ii) the turbulence structure in different directions.

Large-Eddy Simulation for Turbine Heat Transfer

2013 ◽  
Author(s):  
Gorazd Medic ◽  
Jongwook Joo ◽  
Ivana Milanovic ◽  
Om Sharma
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Large Scale ◽  
Leading Edge ◽  
Pressure Side ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Large Eddy ◽  
The Impact ◽  
Side Flow

Heat transfer in a high-pressure turbine configuration (from an experiment documented in [1–2]) has been analyzed by means of large-eddy simulation. Blair’s large-scale rotating rig consists of a first stator, a rotor and an exit stator. Flow and heat transfer in the first stator are assessed for two configurations — with and without the presence of turbulence generating grid. A particular challenge here is that turbulence grid generates fairly high levels of inlet turbulence with turbulence intensity (TU) of about 10% just upstream of leading edge; this in turn moves the transition location upstream in a dramatic fashion. As far as the rotor blade is concerned, the flow and heat transfer is also analyzed experimentally for a range of incidence angles assessing the pressure side heat transfer increase at negative incidence angles. Several challenging aspects relevant to flow in the rotor are also considered — the three-dimensionality of pressure side flow separation at negative incidence, the impact of upstream stator wakes, as well as the role of surface roughness.

Turbulence: the filtering approach

1992 ◽  
Vol 238 ◽  
pp. 325-336 ◽  
Author(s):  
M. Germano
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Large Scale ◽  
Stokes Equations ◽  
Small Scale ◽  
Mean Values ◽  
Eddy Simulation ◽  
Turbulent Field ◽  
Large Eddy ◽  
Different Levels

Explicit or implicit filtered representations of chaotic fields like spectral cut-offs or numerical discretizations are commonly used in the study of turbulence and particularly in the so-called large-eddy simulations. Peculiar to these representations is that they are produced by different filtering operators at different levels of resolution, and they can be hierarchically organized in terms of a characteristic parameter like a grid length or a spectral truncation mode. Unfortunately, in the case of a general implicit or explicit filtering operator the Reynolds rules of the mean are no longer valid, and the classical analysis of the turbulence in terms of mean values and fluctuations is not so simple.In this paper a new operatorial approach to the study of turbulence based on the general algebraic properties of the filtered representations of a turbulence field at different levels is presented. The main results of this analysis are the averaging invariance of the filtered Navier—Stokes equations in terms of the generalized central moments, and an algebraic identity that relates the turbulent stresses at different levels. The statistical approach uses the idea of a decomposition in mean values and fluctuations, and the original turbulent field is seen as the sum of different contributions. On the other hand this operatorial approach is based on the comparison of different representations of the turbulent field at different levels, and, in the opinion of the author, it is particularly fitted to study the similarity between the turbulence at different filtering levels. The best field of application of this approach is the numerical large-eddy simulation of turbulent flows where the large scale of the turbulent field is captured and the residual small scale is modelled. It is natural to define and to extract from the resolved field the resolved turbulence and to use the information that it contains to adapt the subgrid model to the real turbulent field. Following these ideas the application of this approach to the large-eddy simulation of the turbulent flow has been produced (Germano et al. 1991). It consists in a dynamic subgrid-scale eddy viscosity model that samples the resolved scale and uses this information to adjust locally the Smagorinsky constant to the local turbulence.

On Homogenization-Based Methods for Large-Eddy Simulation

2002 ◽  
Vol 124 (4) ◽  
pp. 892-903 ◽  
Author(s):  
L. Persson ◽  
C. Fureby ◽  
N. Svanstedt
Keyword(s):  
Large Eddy Simulation ◽  
Large Scale ◽  
Stokes Equations ◽  
Multiple Scales ◽  
Practical Importance ◽  
Small Scale ◽  
Homogeneous Material ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy

The ability to predict complex engineering flows is limited by the available turbulence models and the present-day computer capacity. In Reynolds averaged numerical simulations (RANS), which is the most prevalent approach today, equations for the mean flow are solved in conjunction with a model for the statistical properties of the turbulence. Considering the limitations of RANS and the desire to study more complex flows, more sophisticated methods are called for. An approach that fulfills these requirements is large-eddy simulation (LES) which attempts to resolve the dynamics of the large-scale flow, while modeling only the effects of the small-scale fluctuations. The limitations of LES are, however, closely tied to the subgrid model, which invariably relies on the use of eddy-viscosity models. Turbulent flows of practical importance involve inherently three-dimensional unsteady features, often subjected to strong inhomogeneous effects and rapid deformation that cannot be captured by isotropic models. As an alternative to the filtering approach fundamental to LES, we here consider the homogenization method, which consists of finding a so-called homogenized problem, i.e. finding a homogeneous “material” whose overall response is close to that of the heterogeneous “material” when the size of the inhomogeneity is small. Here, we develop a homogenization-based LES-model using a multiple-scales expansion technique and taking advantage of the scaling properties of the Navier-Stokes equations. To study the model simulations of forced homogeneous isotropic turbulence and channel flow are carried out, and comparisons are made with LES, direct numerical simulation and experimental data.

Large Eddy Simulation and Acoustical Analysis for Prediction of Aeroacoustics Noise Radiated From an Axial-Flow Fan

2006 ◽  
Author(s):  
Yoshinobu Yamade ◽  
Chisachi Kato ◽  
Hayato Shimizu ◽  
Takahiro Nishioka
Keyword(s):  
Flow Field ◽  
Large Eddy Simulation ◽  
Unsteady Flow ◽  
Axial Flow ◽  
Rotor Blades ◽  
Coarse Mesh ◽  
Axial Flow Fan ◽  
Eddy Simulation ◽  
Fine Mesh ◽  
Large Eddy

A final objective of this study is to develop a tool to predict aeroacoustics noise radiated from a low-speed fan, and its reduction. Aeroacoustics noise that is radiated from a low-speed axial flow fan, with a six-blades rotor installed in a casing duct, is predicted by an one-way coupled analysis of the computation of the unsteady flow in the ducted fan and computation of the sound radiated to the ambient air. The former is performed by our original code, FrontFlow/blue, which is based on Large Eddy Simulation (LES). The latter is performed by using a commercial code, SYSNOISE, which computes the sound fields in the frequency domain. The following three cases of computations are performed for LES with different flow field configurations and/or grid resolutions: a coarse mesh without the struts located, in the actual fan, upstream of the rotor blades, a fine mesh without the struts, and a coarse mesh with the struts. The first two test cases are intended to investigate the effects of the mesh resolution on the prediction accuracy of the unsteady flow field, especially we intended to capture unsteadiness in turbulent boundary layer (TBL) in the second test case with the computational mesh composed of about 30 millions hexahedral elements. The fine mesh LES successfully reproduced the transition to TBL on the suction surface of the rotor blades and gives better, when compared with the results from the coarse mesh LES, agreements with measurements in terms of Euler’s. The final case is used for providing acoustical input data of the sound source. A reasonable agreement is obtained between the predicted and measured sound pressure level evaluated at 1.5 m upstream of the blade center.

On the modelling of the subgrid-scale and filtered-scale stress tensors in large-eddy simulation

2001 ◽  
Vol 441 ◽  
pp. 119-138 ◽  
Author(s):  
DANIELE CARATI ◽  
GRÉGOIRE S. WINCKELMANS ◽  
HERVÉ JEANMART
Keyword(s):  
Large Eddy Simulation ◽  
Stress Tensor ◽  
Large Scale ◽  
Stokes Equations ◽  
Exact Result ◽  
Navier Stokes ◽  
Exact Nature ◽  
Subgrid Scale ◽  
Eddy Simulation ◽  
Large Eddy

The large-eddy simulation (LES) equations are obtained from the application of two operators to the Navier-Stokes equations: a smooth filter and a discretization operator. The introduction ab initio of the discretization influences the structure of the unknown stress in the LES equations, which now contain a subgrid-scale stress tensor mainly due to discretization, and a filtered-scale stress tensor mainly due to filtering. Theoretical arguments are proposed supporting eddy viscosity models for the subgrid-scale stress tensor. However, no exact result can be derived for this term because the discretization is responsible for a loss of information and because its exact nature is usually unknown. The situation is different for the filtered-scale stress tensor for which an exact expansion in terms of the large-scale velocity and its derivatives is derived for a wide class of filters including the Gaussian, the tophat and all discrete filters. As a consequence of this generalized result, the filtered-scale stress tensor is shown to be invariant under the change of sign of the large-scale velocity. This implies that the filtered-scale stress tensor should lead to reversible dynamics in the limit of zero molecular viscosity when the discretization effects are neglected. Numerical results that illustrate this effect are presented together with a discussion on other approaches leading to reversible dynamics like the scale similarity based models and, surprisingly, the dynamic procedure.

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.

Sign in / Sign up

Export Citation Format

Share Document