scholarly journals Calculation of Spotting Particles Maximum Distance in Idealised Forest Fire Scenarios

2015 ◽  
Vol 2015 ◽  
pp. 1-17 ◽  
Author(s):  
José C. F. Pereira ◽  
José M. C. Pereira ◽  
André L. A. Leite ◽  
Duarte M. S. Albuquerque
Keyword(s):  
Forest Fire ◽  
Particle Diameter ◽  
Moisture Loss ◽  
Spherical Particles ◽  
Eddy Simulation ◽  
Random Fashion ◽  
Wide Range ◽  
Large Eddy ◽  
Fire Scenarios ◽  
Particle Momentum

Large eddy simulation of the wind surface layer above and within vegetation was conducted in the presence of an idealised forest fire by using an equivalent volumetric heat source. Firebrand’s particles are represented as spherical particles with a wide range of sizes, which were located into the combustion volume in a random fashion and are convected in the ascending plume as Lagrangian points. The thermally thin particles undergo drag relative to the flow and moisture loss as they are dried and pyrolysis, char-combustion, and mass loss as they burn. The particle momentum, heat and mass transfer, and combustion governing equations were computed along particle trajectories in the unsteady 3D wind field until their deposition on the ground. The spotting distances are compared with the maximum spotting distance obtained with Albini model for several idealised line grass or torching trees fires scenarios. The prediction of the particle maximum spotting distance for a 2000 kW/m short grass fire compared satisfactorily with results from Albini model and underpredicted by 40% the results for a high intensity 50000 kW/m fire. For the cases of single and four torching trees the model predicts the maximum distances consistently but for slightly different particle diameter.

On LES Methods Applied to Seal Geometries

2012 ◽  
Author(s):  
James Tyacke ◽  
Richard Jefferson-Loveday ◽  
Paul Tucker
Keyword(s):  
Maximum Error ◽  
Labyrinth Seal ◽  
Navier Stokes ◽  
Final Solution ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Wide Range ◽  
Large Eddy ◽  
Rans Models ◽  
Flow Through

Nine Large Eddy Simulation (LES) methods are used to simulate flow through two labyrinth seal geometries and are compared with a wide range of Reynolds-Averaged Navier-Stokes (RANS) solutions. These involve one-equation, two-equation and Reynolds Stress RANS models. Also applied are linear and nonlinear pure LES models, hybrid RANS-Numerical-LES (RANS-NLES) and Numerical-LES (NLES). RANS is found to have a maximum error and a scatter of 20%. A similar level of scatter is also found among the same turbulence model implemented in different codes. In a design context, this makes RANS unusable as a final solution. Results show that LES and RANS-NLES is capable of accurately predicting flow behaviour of two seals with a scatter of less than 5%. The complex flow physics gives rise to both laminar and turbulent zones making most LES models inappropriate. Nonetheless, this is found to have minimal tangible results impact. In accord with experimental observations, the ability of LES to find multiple solutions due to solution non-uniqueness is also observed.

Large Eddy Simulation of Laminar and Turbulent Shock/Boundary Layer Interactions in a Transonic Passage

2020 ◽  
Author(s):  
Stephan Priebe ◽  
Daniel Wilkin ◽  
Andy Breeze-Stringfellow ◽  
Giridhar Jothiprasad ◽  
Lawrence C. Cheung
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Low Frequency ◽  
Boundary Layer Separation ◽  
Eddy Simulation ◽  
Turbulent Inflow ◽  
Wide Range ◽  
Large Eddy ◽  
Constant Radius ◽  
Structure Boundary

Abstract Shock/boundary layer interactions (SBLI) are a fundamental fluid mechanics problem relevant in a wide range of applications including transonic rotors in turbomachinery. This paper uses wall-resolved large eddy simulation (LES) to examine the interaction of normal shocks with laminar and turbulent inflow boundary layers in transonic flow. The calculations were performed using GENESIS, a high-order, unstructured LES solver. The geometry created for this study is a transonic passage with a convergent-divergent nozzle that expands the flow to the desired Mach number upstream of the shock and then introduces constant radius curvature to simulate local airfoil camber. The Mach numbers in the divergent section of the transonic passage simulate single stage commercial fan blades. The results predicted with the LES calculations show significant differences between laminar and turbulent SBLI in terms of shock structure, boundary layer separation and transition, and aerodynamic losses. For laminar flow into the shock, significant flow separation and low-frequency unsteadiness occur, while for turbulent flow into the shock, both the boundary layer loss and the low-frequency unsteadiness are reduced.

High-resolution atmospheric boundary layer simulations using WRF-LES

2020 ◽  
Author(s):  
Gokhan Kirkil
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Cross Sections ◽  
Wrf Model ◽  
Field Measurements ◽  
Mean Flow ◽  
Spatial And Temporal Scales ◽  
Eddy Simulation ◽  
Wide Range ◽  
Large Eddy

<p>WRF model provides a potentially powerful framework for coupled simulations of flow covering a wide range of<br>spatial and temporal scales via a successive grid nesting capability. Nesting can be repeated down to turbulence<br>solving large eddy simulation (LES) scales, providing a means for significant improvements of simulation of<br>turbulent atmospheric boundary layers. We will present the recent progress on our WRF-LES simulations of<br>the Perdigao Experiment performed over mountainous terrain. We performed multi-scale simulations using<br>WRF’s different Planetary Boundary Layer (PBL) parameterizations as well as Large Eddy Simulation (LES)<br>and compared the results with the detailed field measurements. WRF-LES model improved the mean flow field<br>as well as second-order flow statistics. Mean fluctuations and turbulent kinetic energy fields from WRF-LES<br>solution are investigated in several cross-sections around the hill which shows good agreement with measurements.</p>

Computation of the self-noise of a controlled-diffusion airfoil based on the acoustic analogy

2017 ◽  
Vol 16 (1-2) ◽  
pp. 44-64 ◽  
Author(s):  
P Martínez-Lera ◽  
J Christophe ◽  
C Schram
Keyword(s):  
Turbulent Flows ◽  
Sound Production ◽  
The Self ◽  
Acoustic Analogy ◽  
Trailing Edge Noise ◽  
Controlled Diffusion ◽  
Eddy Simulation ◽  
Wide Range ◽  
Large Eddy ◽  
Computational Fluid Dynamics Cfd

The self-noise of a controlled-diffusion airfoil is computed with several numerical techniques based on the acoustic analogy and involving different degrees of approximation. The flow solution is obtained through an incompressible large eddy simulation. The acoustic field as described by Lighthill’s analogy is computed with a finite element method applied to the exact airfoil geometry, and this solution is compared with results based on a half-plane Green’s function. This problem behaves as a classical trailing-edge noise problem for a wide range of frequencies; however, other mechanisms of sound production become significant at high frequencies. The results highlight the relative strengths and weaknesses of quadrupole- and dipole-based formulations of the acoustic analogy based on incompressible Computational Fluid Dynamics (CFD) results when applied to wall-bounded turbulent flows.

scholarly journals Large Eddy Simulations of Turbulent and Buoyant Flows in Urban and Complex Terrain Areas Using the Aeolus Model

Atmosphere ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1107
Author(s):  
Akshay A. Gowardhan ◽  
Dana L. McGuffin ◽  
Donald D. Lucas ◽  
Stephanie J. Neuscamman ◽  
Otto Alvarez ◽  
...  
Keyword(s):  
Urban Areas ◽  
Complex Terrain ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Buoyant Plumes ◽  
Flow And Transport ◽  
Eddy Simulation ◽  
Wide Range ◽  
Large Eddy ◽  
Radiological Dispersal

Fast and accurate predictions of the flow and transport of materials in urban and complex terrain areas are challenging because of the heterogeneity of buildings and land features of different shapes and sizes connected by canyons and channels, which results in complex patterns of turbulence that can enhance material concentrations in certain regions. To address this challenge, we have developed an efficient three-dimensional computational fluid dynamics (CFD) code called Aeolus that is based on first principles for predicting transport and dispersion of materials in complex terrain and urban areas. The model can be run in a very efficient Reynolds average Navier–Stokes (RANS) mode or a detailed large eddy simulation (LES) mode. The RANS version of Aeolus was previously validated against field data for tracer gas and radiological dispersal releases. As a part of this work, we have validated the Aeolus model in LES mode against two different sets of data: (1) turbulence quantities measured in complex terrain at Askervein Hill; and (2) wind and tracer data from the Joint Urban 2003 field campaign for urban topography. As a third set-up, we have applied Aeolus to simulate cloud rise dynamics for buoyant plumes from high-temperature explosions. For all three cases, Aeolus LES predictions compare well to observations and other models. These results indicate that Aeolus LES can be used to accurately simulate turbulent flow and transport for a wide range of applications and scales.

Prediction of Pressure Fluctuation on a Vehicle by Large Eddy Simulation

2015 ◽  
Author(s):  
Yoshinobu Yamade ◽  
Chisachi Kato ◽  
Akiyoshi Iida ◽  
Shinobu Yoshimura ◽  
Keiichiro Iida
Keyword(s):  
Structural Analysis ◽  
Large Eddy Simulation ◽  
Unsteady Flow ◽  
Pressure Fluctuation ◽  
Pressure Fluctuations ◽  
Sound Fields ◽  
Eddy Simulation ◽  
Acoustical Analysis ◽  
Wide Range ◽  
Large Eddy

The objective of this study is to predict accurately interior aeroacoustics noise of a car for a wide range of frequency between 100 Hz and 4 kHz. One-way coupled simulations of computational fluid dynamics (CFD), structural analysis and acoustical analysis were performed to predict interior aeroacoustics noise. We predicted pressure fluctuations on the outer surfaces of a test car by computing unsteady flow around the car as the first step. Secondary, the predicted pressure fluctuations were fed to the subsequent structural analysis to predict vibration accelerations on the inner surfaces of the test car. Finally, acoustical analysis was performed to predict sound fields in the test car by giving vibration accelerations computed by the structural analysis as the boundary conditions. In this paper, we focus on the unsteady flow computations, which is the first step of the coupled simulations. Large Eddy Simulation (LES) was performed to predict the pressure fluctuations on the outer surfaces of the test car. We used the computational mesh composed of approximately 5 billion hexahedral grids with a spatial resolution of 1.5 mm in the streamwise and spanwise directions to resolve the dynamics of the small vortices in the turbulence boundary layer. Predicted and measured pressure fluctuation at several sampling points on the surface of the test car were compared and they matched well in a wide range of frequency up to 2 kHz.

scholarly journals Large Eddy Simulations of Reactive Mixing in Jet Reactors of Varied Geometry and Size

Processes ◽  
2020 ◽  
Vol 8 (9) ◽  
pp. 1101 ◽  
Author(s):  
Krzysztof Wojtas ◽  
Wojciech Orciuch ◽  
Łukasz Makowski
Keyword(s):  
Scale Up ◽  
Operating Conditions ◽  
Mixing Efficiency ◽  
Chemical Test ◽  
Eddy Simulation ◽  
Wide Range ◽  
Large Eddy ◽  
Test Reactions ◽  
Reactive Mixing ◽  
Cfd Method

We applied large eddy simulation (LES) to predict the course of reactive mixing carried out in confined impinging jet reactors (CIJR). The reactive mixing process was studied in a wide range of flow rates both experimentally and numerically using computational fluid dynamics (CFD). We compared several different reactor geometries made in different sizes in terms of both reaction yields and mixing efficiency. Our LES model predictions were validated using experimental data for the tracer concentration distribution and fast parallel chemical test reactions, and compared with the k-ε model supplemented with the turbulent mixer model. We found that the mixing efficiency was not affected by the flow rate only at the highest tested Reynolds numbers. The experimental results and LES predictions were found to be in good agreement for all reactor geometries and operating conditions, while the k-ε model well predicted the trend of changes. The CFD method used, i.e., the modeling approach using closure hypothesis, was positively validated as a useful tool in reactor design. This method allowed us to distinguish the best reactors in terms of mixing efficiency (T-mixer III and V-mixer III) and could provide insights for scale-up and application in different processes.

Large Eddy Simulation for Turbines: Methodologies, Cost and Future Outlooks

2013 ◽  
Vol 136 (6) ◽  
Author(s):  
James Tyacke ◽  
Paul Tucker ◽  
Richard Jefferson-Loveday ◽  
Nagabushana Rao Vadlamani ◽  
Robert Watson ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Computational Cost ◽  
Quality Data ◽  
Real Surface ◽  
Internal Cooling ◽  
Design Environment ◽  
Roughness Effects ◽  
Eddy Simulation ◽  
Wide Range ◽  
Large Eddy

Flows throughout different zones of turbines have been investigated using large eddy simulation (LES) and hybrid Reynolds-averaged Navier–Stokes-LES (RANS-LES) methods and contrasted with RANS modeling, which is more typically used in the design environment. The studied cases include low and high-pressure turbine cascades, real surface roughness effects, internal cooling ducts, trailing edge cut-backs, and labyrinth and rim seals. Evidence is presented that shows that LES and hybrid RANS-LES produces higher quality data than RANS/URANS for a wide range of flows. The higher level of physics that is resolved allows for greater flow physics insight, which is valuable for improving designs and refining lower order models. Turbine zones are categorized by flow type to assist in choosing the appropriate eddy resolving method and to estimate the computational cost.

scholarly journals Comparative Studies of RANS Versus Large Eddy Simulation for Fan–Intake Interaction

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Yunfei Ma ◽  
Nagabhushana Rao Vadlamani ◽  
Jiahuan Cui ◽  
Paul Tucker
Keyword(s):  
Large Eddy Simulation ◽  
Turbulence Model ◽  
Immersed Boundary Method ◽  
Immersed Boundary ◽  
Flow Acceleration ◽  
Eddy Simulation ◽  
Boundary Method ◽  
Fan Effect ◽  
Wide Range ◽  
Large Eddy

The present research applied a mixed-fidelity approach to examine the fan–intake interaction. Flow separation induced by a distortion generator (DG) is either resolved using large eddy simulation (LES) or modeled using the standard k–ω model, Spalart–Allmaras (SA) model, etc. The immersed boundary method with smeared geometry (immersed boundary method with smeared geometry (IBMSG)) is employed to represent the effect of the fan and a wide range of test cases is studied by varying the (a) height of the DG and (b) proximity of the fan to the DG. Comparisons are drawn between the LES and the Reynolds-averaged Navier–Stokes (RANS) approaches with/without the fan effect. It is found that in the “absence of fan,” the discrepancies between RANS and LES are significant within the separation and reattachment region due to the well-known limitations of the standard RANS models. “With the fan installed,” the deviation between RANS and LES decreases substantially. It becomes minimal when the fan is closest to the DG. It implies that with an installed fan, the inaccuracies of the turbulence model are mitigated by the strong flow acceleration at the casing due to the fan. More precisely, the mass flow redistribution due to the fan has a dominant primary effect on the final predictions and the effect of turbulence model becomes secondary, thereby suggesting that high fidelity eddy resolving simulations provide marginal improvements to the accuracy for the installed cases, particularly for the short intake–fan strategies with fan getting closer to intake lip.

On the Combination of Large Eddy Simulation and Phenomenological Soot Modelling to Calculate the Smoke Index From Aero-Engines Over a Large Range of Operating Conditions

2017 ◽  
Author(s):  
Jean Lamouroux ◽  
Stéphane Richard ◽  
Quentin Malé ◽  
Gabriel Staffelbach ◽  
Antoine Dauptain ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Gas Turbines ◽  
Soot Formation ◽  
Operating Conditions ◽  
Extended Model ◽  
Eddy Simulation ◽  
Design Office ◽  
Wide Range ◽  
Large Eddy ◽  
Aero Engines

Nowadays, models predicting soot emissions are, neither able to describe correctly fine effects of technological changes on sooting trends nor sufficiently validated at relevant operating conditions to match design office quantification needs. Yet, phenomenological descriptions of soot formation, containing key ingredients for soot modeling exist in the literature, such as the well-known Leung et al. model (Combust Flame 1991). This approach indeed includes contributions of nucleation, surface growth, coagulation, oxidation and thermophoretic transport of soot. When blindly applied to aeronautical combustors for different operating conditions, this model fails to hierarchize operating points compared to experimental measurements. The objective of this work is to propose an extension of the Leung model, including an identification of its constants over a wide range of condition relevant of gas turbines operation. Today, the identification process can hardly be based on laboratory flames since few detailed experimental data are available for heavy-fuels at high pressure. Thus, it is decided to directly target smoke number values measured at the engine exhaust for a variety of combustors and operating conditions from idling to take-off. A Large Eddy Simulation approach is retained for its intrinsic ability to reproduce finely unsteady behavior, mixing and intermittency. In this framework, The Leung model for soot is coupled to the TFLES model for combustion. It is shown that pressure-sensitive laws for the modelling constant of the soot surface chemistry are sufficient to reproduce engine emissions. Grid convergence is carried out to verify the robustness of the proposed approach. Several cases are then computed blindly to assess the prediction capabilities of the extended model. This study paves the way for the systematic use of a high fidelity tool solution in design office constraints for combustion chamber development.

Sign in / Sign up

Export Citation Format

Share Document