Analysis of the Sutton Model for Aero-Optical Properties of Compressible Boundary Layers

2005 ◽  
Vol 128 (2) ◽  
pp. 239-246 ◽  
Author(s):  
Eric Tromeur ◽  
Eric Garnier ◽  
Pierre Sagaut
Keyword(s):  
Boundary Layer ◽  
Density Field ◽  
The Other ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Compressible Boundary Layers ◽  
Optical Effects ◽  
Large Eddy ◽  
The One ◽  
Reference Tool

In order to assess the capability of the Sutton model to evaluate aero-optical effects in a turbulent boundary layer, large-eddy simulation (LES) evolving spatially and Reynolds averaged Navier-Stokes (RANS) computations are carried out at Mach number equal to 0.9. First aerodynamic fields are proved to compare favorably with theoretical and experimental results. Once validated, the characteristics of the boundary layer allow us to obtain information concerning optical beam degradation. On the one hand, the density field is used to compute phase distortion directly and, on the other hand, by means of the Sutton model. Therefore, LES and RANS simulations allow us to study optical models and the validity of their assumptions. Finally, LES is proved to be considered as a reference tool to evaluate aero-optical effects.

scholarly journals The Collection Efficiency of Shielded and Unshielded Precipitation Gauges. Part II: Modeling Particle Trajectories

2015 ◽  
Vol 17 (1) ◽  
pp. 245-255 ◽  
Author(s):  
Matteo Colli ◽  
Luca G. Lanza ◽  
Roy Rasmussen ◽  
Julie M. Thériault
Keyword(s):  
Collection Efficiency ◽  
Time Dependent ◽  
Navier Stokes ◽  
Turbulent Structures ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Efficiency Comparison ◽  
The One ◽  
The Impact

Abstract The use of windshields to reduce the impact of wind on snow measurements is common. This paper investigates the catching performance of shielded and unshielded gauges using numerical simulations. In Part II, the role of the windshield and gauge aerodynamics, as well as the varying flow field due to the turbulence generated by the shield–gauge configuration, in reducing the catch efficiency is investigated. This builds on the computational fluid dynamics results obtained in Part I, where the airflow patterns in the proximity of an unshielded and single Alter shielded Geonor T-200B gauge are obtained using both time-independent [Reynolds-averaged Navier–Stokes (RANS)] and time-dependent [large-eddy simulation (LES)] approaches. A Lagrangian trajectory model is used to track different types of snowflakes (wet and dry snow) and to assess the variation of the resulting gauge catching performance with the wind speed. The collection efficiency obtained with the LES approach is generally lower than the one obtained with the RANS approach. This is because of the impact of the LES-resolved turbulence above the gauge orifice rim. The comparison between the collection efficiency values obtained in case of shielded and unshielded gauge validates the choice of installing a single Alter shield in a windy environment. However, time-dependent simulations show that the propagating turbulent structures produced by the aerodynamic response of the upwind single Alter blades have an impact on the collection efficiency. Comparison with field observations provides the validation background for the model results.

scholarly journals Testing the Accuracy of the Cell-Set Model Applied on Vane-Type Sub-Boundary Layer Vortex Generators

Processes ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 503
Author(s):  
Koldo Portal-Porras ◽  
Unai Fernandez-Gamiz ◽  
Iñigo Aramendia ◽  
Daniel Teso-Fz-Betoño ◽  
Ekaitz Zulueta
Keyword(s):  
Boundary Layer ◽  
Vortical Structure ◽  
Gradient Flow ◽  
Vortex Generators ◽  
Navier Stokes ◽  
Computational Time ◽  
Eddy Simulation ◽  
Mesh Model ◽  
Large Eddy ◽  
Modelling Techniques

Vortex Generators (VGs) are applied before the expected region of separation of the boundary layer in order to delay or remove the flow separation. Although their height is usually similar to that of the boundary layer, in some applications, lower VGs are used, Sub-Boundary Layer Vortex Generators (SBVGs), since this reduces the drag coefficient. Numerical simulations of sub-boundary layer vane-type vortex generators on a flat plate in a negligible pressure gradient flow were conducted using the fully resolved mesh model and the cell-set model, with the aim on assessing the accuracy of the cell-set model with Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) turbulence modelling techniques. The implementation of the cell-set model has supposed savings of the 40% in terms of computational time. The vortexes generated on the wake behind the VG; vortical structure of the primary vortex; and its path, size, strength, and produced wall shear stress have been studied. The results show good agreements between meshing models in the higher VGs, but slight discrepancies on the lower ones. These disparities are more pronounced with LES. Further study of the cell-set model is proposed, since its implementation entails great computational time and resources savings.

Large-Eddy simulation of rim seal ingestion

2011 ◽  
Vol 225 (12) ◽  
pp. 2881-2891 ◽  
Author(s):  
T S D O'Mahoney ◽  
N J Hills ◽  
J W Chew ◽  
T Scanlon
Keyword(s):  
Reynolds Number ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Rans Turbulence Models ◽  
Unsteady Rans ◽  
Rans Simulations ◽  
Secondary Air ◽  
The One

Unsteady flow dynamics in turbine rim seals are known to be complex and attempts accurately to predict the interaction of the mainstream flow with the secondary air system cooling flows using computational fluid dynamics (CFD) with Reynolds-averaged Navier–Stokes (RANS) turbulence models have proved difficult. In particular, published results from RANS models have over-predicted the sealing effectiveness of the rim seal, although their use in this context continues to be common. Previous studies have ascribed this discrepancy to the failure to model flow structures with a scale greater than the one which can be captured in the small-sector models typically used. This article presents results from a series of Large-Eddy Simulations (LES) of a turbine stage including a rim seal and rim cavity for, it is believed by the authors, the first time. The simulations were run at a rotational Reynolds number Reθ = 2.2 × 106 and a main annulus axial Reynolds number Rex = 1.3 × 106 and with varying levels of coolant mass flow. Comparison is made with previously published experimental data and with unsteady RANS simulations. The LES models are shown to be in closer agreement with the experimental sealing effectiveness than the unsteady RANS simulations. The result indicates that the previous failure to predict rim seal effectiveness was due to turbulence model limitations in the turbine rim seal flow. Consideration is given to the flow structure in this region.

A modified blending function for zonal hybrid Reynolds-averaged Navier—Stokes/large-eddy simulation methodology

2009 ◽  
Vol 223 (8) ◽  
pp. 1067-1081 ◽  
Author(s):  
M B Sun ◽  
J H Liang ◽  
Z G Wang
Keyword(s):  
Boundary Layer ◽  
Supersonic Flow ◽  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Navier Stokes ◽  
Empirical Constant ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes ◽  
Blending Function

A modified blending function for zonal hybrid Reynolds averaged Navier—Stokes/large eddy simulation (RANS/LES) methodology was developed using an empirical analogy from Menter k—ω shear stress transport (SST) turbulent model (Menter, 1994) to predict complex turbulent flows. Tests of slot jet in supersonic flow and supersonic flow over compression—expansion ramp was conducted and prediction of separations was well improved when certain model constant was forced on the traditional blending function (Baurle et al., 2003). Analysis based on calculations of flat plate boundary layer demonstrated that an efficient empirical constant could be used in blending function and boundary layer could be well calculated without heavy contamination of RANS on wake region. Validation of the modified zonal hybrid RANS/LES approach for slot jet in supersonic flow, supersonic flow over compression—expansion ramp, supersonic flow over backward facing step, and supersonic cavity flow was conducted. The simulated results showed that the modified blending function performs well on complex turbulent flows. Deficiencies of traditional hybrid zonal RANS/LES method in over-prediction of separations associated with adverse pressure gradient flows were favourably improved.

Cost-effective hybrid RANS-LES type method for jet turbulence and noise prediction

2017 ◽  
Vol 16 (1-2) ◽  
pp. 97-111 ◽  
Author(s):  
M Mahak ◽  
IZ Naqavi ◽  
PG Tucker
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Cost Effective ◽  
Wall Turbulence ◽  
Scale Model ◽  
Navier Stokes ◽  
High Concentration ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Layer Region

Jets at higher Reynolds numbers have a high concentration of energy in small scales in the nozzle vicinity. This is challenging for large-eddy simulation, potentially placing severe demands on grid density. To circumvent this, we propose a novel procedure based on well-known Reynolds number (Re) independent of jets. We reduce the jet Re while rescaling the boundary layer properties to maintain incoming boundary layer thickness consistent with high Re jet. The simulations are carried out using hybrid large-eddy simulation type of approach which is incorporated by using near-wall turbulence model with modified properties. No subgrid scale model is used in these simulations. Hence, they effectively become numerical large-eddy simulation with Reynolds-averaged Navier–Stokes covering the full boundary layer region. The noise post-processing is carried out using the Ffowcs-Williams-Hawking approach. The simulations are made for Mach numbers (M) of 0.75 and 0.875 (cold and hot). The results for the overall sound pressure level are observed to be within 2–3% of the measurements, and directivity of sound is also captured accurately for both the cases. Hence, the low Re simulations can be more beneficial in saving time and cost while providing reasonably accurate results.

Direct numerical simulation, large eddy simulation and unsteady Reynolds-averaged Navier—Stokes simulations of periodic unsteady flow in a low-pressure turbine cascade: A comparison

2003 ◽  
Vol 217 (4) ◽  
pp. 403-411 ◽  
Author(s):  
V Michelassi ◽  
J. G. Wissink ◽  
W Rodi
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Direct Numerical Simulation ◽  
Low Pressure ◽  
Navier Stokes ◽  
Stagnation Region ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes

The unsteady periodic flow in a low-pressure (LP) prismatic turbine vane with incoming wakes is computed by direct numerical simulation (DNS), large eddy simulation (LES) and unsteady Reynolds-averaged Navier—Stokes simulations (URANSs). The results are compared with existing measurements at a Reynolds number Re = 5.18 × 104 which reveal the presence of a large unsteady stalled region on the suction side. Both DNS and LES suggest that the boundary layer separates while being still laminar, with subsequent turbulent reattachment. Several URANSs with and without a transition model and a constraint on the turbulence time-scale designed to prevent excessive production in the stagnation region are analysed and compared with the DNS and LES. The useful information provided by DNS and LES has made it possible to improve the results of the URANSs, which ensure a fair reproduction of the flow, especially in terms of blade load and losses, although they partly fail to detail the complex wake—boundary layer interaction in the separated flow region.

Cost-Effective Hybrid RANS-NLES Method for Jet Turbulence and Noise Prediction

2012 ◽  
Author(s):  
M. Mahak ◽  
Paul G. Tucker ◽  
Prasun K. Ray
Keyword(s):  
Boundary Layer ◽  
Cost Effective ◽  
Reynolds Numbers ◽  
Wall Turbulence ◽  
Navier Stokes ◽  
High Concentration ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Layer Region ◽  
Near Wall Turbulence

Jets at higher Reynolds numbers have a high concentration of energy in the small scales in the nozzle vicinity. This is challenging for LES, potentially placing severe demands on grid density. To circumvent this, we propose a novel procedure based on well known Reynolds number (Re) independence of jets. We reduce the jet Re whilst rescaling the boundary layer properties to maintain incoming boundary layer thickness consistent with high Re jet. The simulations are carried out using hybrid largeeddy simulation type of approach which is incorporated by using near wall turbulence model with modified properties. No Subgrid Scale (SGS) model is used in these simulations. Hence, they effectively become Numerical Large Eddy Simulation (NLES) with Reynolds-averaged Navier-Stokes (RANS) covering the full boundary layer region. The noise post processing is carried out using Ffowcs-Williams-Hawking (FWH) approach. The simulations are made for Mach numbers (M) of 0.75 and 0.875. The results for Overall Sound Pressure Level (OASPL) are observed to be within 2–3% accuracy range and directivity of sound is also captured accurately for both the cases. The low Re simulations hence, can be more beneficial in saving time and cost of the simulation while providing reasonably accurate results.

Large-Eddy Simulation of Supersonic Flat-Plate Boundary Layers Using the Monotonically Integrated Large-Eddy Simulation (MILES) Technique

2002 ◽  
Vol 124 (4) ◽  
pp. 868-875 ◽  
Author(s):  
H. Yan ◽  
D. Knight ◽  
A. A. Zheltovodov
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Transfer Coefficient ◽  
Large Eddy Simulation ◽  
Flat Plate ◽  
Boundary Layers ◽  
Plate Boundary ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy

A supersonic flat-plate boundary layer at a Reynolds number of 2×104 based on the inflow boundary layer thickness is investigated at different Mach numbers (M=2.88 and 4) using the monotonically integrated large-eddy simulation (MILES) technique. The inherent numerical dissipation is taken as an implicit subgrid scales (SGS) model to close the Favre-filtered compressible Navier-Stokes (NS) equations. A finite volume method with second-order accuracy in time and space is implemented for the solution of the Navier-Stokes equations on an unstructured grid of tetrahedra. The heat transfer coefficient is predicted by simulating both adiabatic and isothermal cases. The mean flowfield and turbulent stresses are in good agreement with experiment. The relationship between the predicted skin friction coefficient and heat transfer coefficient is in close agreement with the Reynolds analogy factor. The variation of turbulent Prandtl number cross the boundary layer falls within the experimental envelope. These are the first LES predictions of adiabatic and isothermal supersonic flat plate boundary layers using the MILES technique.

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