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

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.

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

Journal of Fluid Mechanics ◽

10.1017/jfm.2011.130 ◽

2011 ◽

Vol 679 ◽

pp. 156-193 ◽

Cited By ~ 22

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.

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

Volume 2C: Turbomachinery ◽

10.1115/gt2020-14998 ◽

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.

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Revisiting the subgrid-scale Prandtl number for large-eddy simulation

Journal of Fluid Mechanics ◽

10.1017/jfm.2016.472 ◽

2016 ◽

Vol 802 ◽

Cited By ~ 8

Author(s):

Dan Li

Keyword(s):

Experimental Data ◽

Large Eddy Simulation ◽

Prandtl Number ◽

Subgrid Scale ◽

Budget Model ◽

Eddy Simulation ◽

Large Eddy ◽

Flux Transfer ◽

Neutral Conditions ◽

Transfer Term

The subgrid-scale (SGS) Prandtl number ($Pr$) is an important parameter in large-eddy simulation. Prior models often assume that the ‘$-5/3$’ inertial subrange scaling applies to the wavenumber range from 0 to $k_{\unicode[STIX]{x1D6E5}}$ (the wavenumber corresponding to the filter scale $\unicode[STIX]{x1D6E5}$) and yield a $Pr$ that is stability-independent and scale-invariant, which is inconsistent with experimental data and the results of dynamic models. In this study, the SGS Prandtl number is revisited by solving the co-spectral budgets of momentum and heat fluxes in an idealized but thermally stratified atmospheric surface layer. The SGS Prandtl number from the co-spectral budget model shows a strong dependence on the atmospheric stability and increases (decreases) as the atmosphere becomes stable (unstable), which is in good agreement with recent field experimental data. The dependence of $Pr$ on the filter scale is also captured by the co-spectral budget model: as the filter scale becomes smaller, the SGS Prandtl number decreases. Finally, the value of SGS Prandtl number under neutral conditions is shown to be caused by the dissimilarity between momentum and heat in the pressure decorrelation term and the flux transfer term. When the dissimilarity exists only in the flux transfer term, the fact that under neutral conditions the SGS Prandtl number is usually smaller than the turbulent Prandtl number for Reynolds-averaged Navier–Stokes simulations is an indication of a stronger spectral transfer coefficient for heat than for momentum. The model proposed in this study can be readily implemented.

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