scholarly journals A dual-grid hybrid RANS/LES model for under-resolved near-wall regions and its application to heated and separating flows

2018 ◽  
Author(s):  
P. Nguyen ◽  
Juan Uribe ◽  
I. Afgan ◽  
Dominique R. Laurence
Keyword(s):  
Separating Flows ◽  
Les Model ◽  
Near Wall

scholarly journals A Dual-Grid Hybrid RANS/LES Model for Under-Resolved Near-Wall Regions and its Application to Heated and Separating Flows

2019 ◽  
Vol 104 (4) ◽  
pp. 835-859
Author(s):  
Philipp T. L. Nguyen ◽  
Juan C. Uribe ◽  
Imran Afgan ◽  
Dominique R. Laurence
Keyword(s):  
Grid Point ◽  
Plane Channel ◽  
Boundary Layer Separation ◽  
Navier Stokes ◽  
Overlapping Grids ◽  
Eddy Viscosity Model ◽  
Logarithmic Layer ◽  
High Reynolds ◽  
Les Model ◽  
Near Wall

Abstract A hybrid RANS/LES model for high Reynolds number wall-bounded flows is presented, in which individual Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulations (LES) are computed in parallel on two fully overlapping grids. The instantaneous, fluctuating subgrid-scale stresses are blended with a statistical eddy viscosity model in regions where the LES grid is too coarse. In the present case, the hybrid model acts as a near-wall correction to the LES, while it retains the fluctuating nature of the flow field. The dual computation enables the LES to be run on isotropic grids with very low wall-normal and wall-parallel resolution, while the auxiliary RANS simulation is conducted on a wall-refined high-aspect ratio grid. Running distinct, progressively corrected simulations allows a clearer separation of the mean and instantaneous flow fields, compliant with the fundamentally dissimilar nature of RANS and LES. Even with the wall-nearest grid point lying far in the logarithmic layer, velocity and temperature predictions of a heated plane channel flow are corrected. For a periodic hill flow, the dual-grid system improves the boundary layer separation and velocity field prediction both for a constant-spaced and a wall-refined LES grid.

scholarly journals Development and validation of a hybrid temporal LES model in the perspective of applications to internal combustion engines

2019 ◽  
Vol 74 ◽  
pp. 56
Author(s):  
Al Hassan Afailal ◽  
Jérémy Galpin ◽  
Anthony Velghe ◽  
Rémi Manceau
Keyword(s):  
Steady Flow ◽  
Channel Flow ◽  
Internal Combustion Engines ◽  
Internal Combustion ◽  
Core Region ◽  
Wall Region ◽  
Combustion Engines ◽  
The Core ◽  
Les Model ◽  
Near Wall

CFD simulation tools are increasingly used nowadays to design more fuel-efficient and clean Internal Combustion Engines (ICE). Within this framework, there is a need to benefit from a turbulence model which offers the best compromise between prediction capabilities and computational cost. The Hybrid Temporal LES (HTLES) approach is here retained within the perspective of an application to ICE configurations. HTLES is a hybrid Reynolds-Averaged Navier Stokes/Large Eddy Simulation (RANS/LES) model based on a solid theoretical framework using temporal filtering. The concept is to model the near-wall region in RANS and to solve the turbulent structures in the core region if the temporal and spatial resolutions are fine enough. In this study, a dedicated sub-model called Elliptic Shielding (ES) is added to HTLES in order to ensure RANS in the near-wall region, regardless of the mesh resolution. A modification of the computation of the total kinetic energy and the dissipation rate was introduced as first adaptions of HTLES towards non-stationary ICE configurations. HTLES is a recent approach, which has not been validated in a wide range of applications. The present study intends to further validate HTLES implemented in CONVERGE code by examining three stationary test cases. The first validation consists of the periodic hill case, which is a standard benchmark case to assess hybrid turbulence models. Then, in order to come closer to real ICE simulations, i.e., with larger Reynolds numbers and coarser near-wall resolutions, the method is validated in the case of a channel flow using wall functions and in the steady flow rig case consisting in an open valve at a fixed lift. HTLES results are compared to RANS k-ω SST and wall-modeled LES σ simulations performed with the same grid and the same temporal resolution. Unlike RANS, satisfactory reproduction of the flow recirculation has been observed with HTLES in the case of periodic hills. The channel flow configuration has underlined the capability of HTLES to predict the wall friction properly. The steady flow rig shows that HTLES combines advantages of RANS and LES in one simulation. On the one hand, HTLES yields mean and rms velocities as accurate as LES since the scale-resolving simulation is triggered in the core region. On the other hand, hybrid RANS/LES at the wall provides accurate pressure drop in contrast with LES performed on the same mesh. Future work will be dedicated to the extension of HTLES to non-stationary flows with moving walls in order to be able to tackle realistic ICE flow configurations.

Hybrid RANS-LES Modeling of a Normal Jet in Crossflow for Film Cooling Applications

2013 ◽  
Author(s):  
Tej P. Dhakal ◽  
D. Keith Walters
Keyword(s):  
Film Cooling ◽  
Velocity Ratio ◽  
Mean Flow ◽  
Low Velocity ◽  
Lower Velocity ◽  
Jet In Crossflow ◽  
Wall Structures ◽  
Crossflow Velocity ◽  
Les Model ◽  
Near Wall

Numerical simulation of a normal jet in crossflow has been performed using a recently developed hybrid RANS-LES model. The model form utilizes a solution based parameter that dynamically determines the RANS and LES regions. Numerical simulations using commercially available DDES model and a RANS model have also been performed for comparison purposes. Three jet to crossflow velocity ratios (R = 2, 1, 0.5) have been investigated. Computational results obtained are compared with the experiment of Andreopoulos and Rodi (1984). The results highlight the predictive capabilities of hybrid RANS-LES model to reproduce the important vortical structures of a jet in crossflow case, which play a crucial role in the film cooling. The hybrid RANS-LES model results from the velocity ratio R = 2 case fare well with the experiment in comparison to RANS predictions. For lower velocity ratios, discrepancies in mean flow statistics have been observed at some measurement stations. The near wall statistics from the hybrid model resembles RANS predictions for the case with jet to crossflow velocity ratio R = 0.5. This observation can be attributed to the requirement of higher grid resolution necessary to capture the near wall structures for low velocity ratio cases.

NEAR-WALL CHARACTERISTICS OF AN IMPINGING GASOLINE SPRAY AT INCREASED AMBIENT PRESSURE AND WALL TEMPERATURE

2009 ◽  
Vol 19 (11) ◽  
pp. 997-1012 ◽  
Author(s):  
Jochen Stratmann ◽  
D. Martin ◽  
P. Unterlechner ◽  
R. Kneer
Keyword(s):  
Wall Temperature ◽  
Ambient Pressure ◽  
Near Wall

Nonisothermal Mixing of a Near-Wall Gas-Liquid Jet with a Flow in a Tube

2001 ◽  
Vol 32 (4-6) ◽  
pp. 7
Author(s):  
Viktor I. Terekhov ◽  
K. A. Sharov ◽  
N. E. Shishkin ◽  
V. P. Lebedev
Keyword(s):  
Liquid Jet ◽  
Near Wall

APPLICATION OF THE HIGH-RESOLUTION RANS/ILES TECHNOLOGY FOR FLOW SIMULATION AND THE NEARBY ACOUSTIC FIELD OF NEAR-WALL JETS AND MIXING LAYERS

2016 ◽  
Vol 47 (2) ◽  
pp. 159-183 ◽  
Author(s):  
Leonid Aleksandrovich Bendersky ◽  
Dmitriy Aleksandrovich Lyubimov ◽  
Irina Vasilevna Potekhina ◽  
Alena Eduardovna Fedorenko
Keyword(s):  
High Resolution ◽  
Acoustic Field ◽  
Flow Simulation ◽  
Mixing Layers ◽  
Wall Jets ◽  
Near Wall
Sign in / Sign up

Export Citation Format

Share Document