Large Eddy Simulation of a Shear-Coaxial LOX-H2 Jet at Supercritical Pressure

2002 ◽  
Author(s):  
Joseph Oefelein
Keyword(s):  
Large Eddy Simulation ◽  
Supercritical Pressure ◽  
Eddy Simulation ◽  
Large Eddy

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 Supercritical-Pressure Round Jets

AIAA Journal ◽  
2010 ◽  
Vol 48 (9) ◽  
pp. 2133-2144 ◽  
Author(s):  
Thomas Schmitt ◽  
Laurent Selle ◽  
Anthony Ruiz ◽  
Bénédicte Cuenot
Keyword(s):  
Large Eddy Simulation ◽  
Supercritical Pressure ◽  
Round Jets ◽  
Eddy Simulation ◽  
Large Eddy

scholarly journals Large Eddy Simulation Study on Forced Convection Heat Transfer to Water at Supercritical Pressure in a Trapezoid Annulus

2017 ◽  
Vol 4 (1) ◽  
Author(s):  
Muhsin Mohd Amin ◽  
Yu Duan ◽  
Shuisheng He
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Forced Convection ◽  
Supercritical Water ◽  
Supercritical Pressure ◽  
Working Fluid ◽  
Flow Structures ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Large Flow

It is now well known that heat transfer to fluid at supercritical pressure in a confined channel shows complex behaviors. This is due to the strong variations of the thermal–physical properties resulting from the changes of pressure and temperature. To improve the reliability and efficiency of the supercritical water-cooled reactors (SCWRs) to be designed, the understanding of supercritical fluid flow in the fuel assemblies is very important. The study reported here reconsiders a simplified geometry made of a trapezoid channel enclosing an inner rod to simulate the triangular arrangement of a fuel assembly. Large eddy simulation (LES) with the wall adapting local eddy viscosity (WALE) model is used to simulate the forced convection flow in the channel. Supercritical water at 25 MPa is used as the working fluid. The Reynolds number of flow based on the hydraulic diameter and the bulk velocity is 10,540, while the heat flux from the inner rod wall has been varied from 10 kW/m2 to 75 kW/m2. Large unsteady flow structures are observed to be present due to the nonuniformity of the cross section of the flow channel. The characteristics of the flow structures and their effect on the local heat transfer are analyzed using instantaneous velocities, spectrum analysis, and correlation analysis. The swinging flow structures in the wide gap are much weaker than those in the narrow gap. The behaviors of such large flow structures are influenced by the strong spatial and temporal variations of the properties. When the temperature distribution follows Tb < Tpc < Tw, the mixing parameters due to the large flow structures, including mixing coefficient and effective mixing velocity in the gap, are also significantly influenced.

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