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.

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.

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.

Prediction of Unsteady Loading on a Circular Cylinder in High Reynolds Number Flows Using Large Eddy Simulation

2005 ◽  
Author(s):  
Sung-Eun Kim ◽  
L. Srinivasa Mohan
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Turbulent Viscosity ◽  
Reynolds Numbers ◽  
Unstructured Meshes ◽  
Navier Stokes ◽  
Step Method ◽  
Fractional Step Method ◽  
Eddy Simulation ◽  
Large Eddy

Large eddy simulations were carried out for the flow around a hydrodynamically smooth, fixed circular cylinder at two Reynolds numbers, one at a subcritical Reynolds number (Re = 1.4 × 105) and the other at a supercritical Reynolds number (Re = 1.0 × 106). The computations were made using a parallelized finite-volume Navier-Stokes solver based on a multidimensional linear reconstruction scheme that allows use of unstructured meshes. Central differencing was used for discretization of both convection and diffusion terms. Time-advancement scheme, based on an implicit, non-iterative fractional-step method, was adopted in conjunction with a three-level, backward second-order temporal discretization. Subgrid-scale turbulent viscosity was modeled by a dynamic Smagorinsky model adapted to arbitrary unstructured meshes with the aid of a test-filter applicable to arbitrary unstructured meshes. The present LES results closely reproduced the flow features observed in experiments at both Reynolds numbers. The time-averaged mean drag coefficient, root-mean-square force coefficients and the frequency content of fluctuating forces (vortex-shedding frequency) are predicted with a commendable accuracy.

Prediction of Profile Losses by Means of Large-Eddy Simulation Including Turbulence Modeling Assessment

2017 ◽  
Author(s):  
Karsten Hasselmann ◽  
Stefan aus der Wiesche
Keyword(s):  
Large Eddy Simulation ◽  
Turbulence Modeling ◽  
Flow Behavior ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Unsteady Separation ◽  
Power Spectral ◽  
Large Eddy ◽  
Experimental Values

In this contribution, a Large-Eddy Simulation (LES) analysis was carried out, to get detailed information about the unsteady flow behavior and loss generation in a turbine cascade at moderate Reynolds numbers. A comprehensive comparison study with experimental data was conducted to validate the LES results. Compared to Reynolds averaged Navier-Stokes (RANS) results, the LES shows a much better agreement with the measured values of the profile loss coefficient, downstream velocity profile, and blade pressure distribution. The unsteady separation and reattachment process was covered well by the LES approach. The power spectral density (PSD) profiles at several positions of the downstream wake were compared and analyzed. Although the results of the LES show mainly a good agreement with the experimental values, there are still some deviations at high frequency. In summery the present case study indicates the high potential of LES especially in case of moderate Reynolds numbers with flow separation.

scholarly journals Research on heat transfer characteristics of fractal-generated turbulence based on large eddy simulation

2019 ◽  
Vol 23 (6 Part B) ◽  
pp. 3993-4004
Author(s):  
Chengdong Duan ◽  
Yuncong Jiang ◽  
Nannan Wu ◽  
Qiwen Xu ◽  
Lijun Wang
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Flow Field ◽  
Large Eddy Simulation ◽  
Cross Section ◽  
Mesh Size ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Effective Mesh Size ◽  
Layer Region

Turbulence plays an important role in the fields of heat and mass transfer and enhanced chemical reaction. In order to explore the effect of grid-generated turbulence on flow heat transfer, in this paper, three different fractal grid structures with the same blocking ratio ?, effective mesh size Meff and thickness ratio tr= t max/t min (Case1: The grid cross-section is a triangle, Case2: the grid cross-section is an inverted triangle, Case3:the grid cross-section is square, Case4:no grid) and without the grid were simulated based on large eddy simulation. The aim of this simulation is to explain the evolution characteristics and heat transfer mechanism of turbulent flow field under the four cases. The results show that, in the same initial condition, Case 2 can generate the highest turbulence intensity and the feature of heat transfer on the cylindrical surface is more uniform. In Case 3, the boundary-layer in the flow field is separated earlier, and more vortices are excited to enhance the heat transfer than other cases in the boundary-layer region. The surface average Nusselt number is 1.3 times than that of Case 4.

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.

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