scholarly journals Shock Capturing in Large Eddy Simulations by Adaptive Filtering

Fluids ◽  
2019 ◽  
Vol 4 (3) ◽  
pp. 132 ◽  
Author(s):  
Sumit Kumar Patel ◽  
Joseph Mathew
Keyword(s):  
Adaptive Filtering ◽  
Low Frequency ◽  
Quantitative Agreement ◽  
Large Eddy Simulations ◽  
Shock Capturing ◽  
Shock Propagation ◽  
High Order Schemes ◽  
Large Eddy ◽  
Propagation Of Waves ◽  
Monotonic Extension

A method for shock capturing by adaptive filtering for use with high-resolution, high-order schemes for Large Eddy Simulations (LES) is presented. The LES method used in all the examples here employs the Explicit Filtering approach and the spatial derivatives are obtained with sixth-order, compact, finite differences. The adaptation is to drop the order of the explicit filter to two at gridpoints where a shock is detected, and to then increase the order from 2 to 10 in steps at successive gridpoints away from the shock. The method is found to be effective in a series of tests of common inviscid 1D and 2D problems of shock propagation and propagation of waves through shocks. As a prelude to LES, the 3D Taylor–Green problem for the inviscid and a finite viscosity case were simulated. An assessment of the overall performance of the method for LES was carried out by simulating an underexpanded round jet at a Reynolds number of 6.09 million, based in centerline velocity and diameter at nozzle exit plane. Very close quantitative agreement was found for the development of centerline mean pressure when compared to experiment. Simulations on several increasingly finer grids showed a monotonic extension of the computed part of the inertial range, with little change to low frequency content. Amplitudes and locations of large changes in pressure through several cells were captured accurately. A similar performance was observed for LES of an impinging jet containing normal and curved shocks.

Large Eddy Simulations of Flow and Heat Transfer in Rotating Ribbed Duct Flows

2005 ◽  
Vol 127 (5) ◽  
pp. 486-498 ◽  
Author(s):  
Mayank Tyagi ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Large Scale ◽  
Density Ratio ◽  
Low Frequency ◽  
Turbulent Energy ◽  
Large Eddy Simulations ◽  
Temperature Fields ◽  
Periodic Domain ◽  
Large Eddy

Large eddy simulations are performed in a periodic domain of a rotating square duct with normal rib turbulators. Both the Coriolis force as well as the centrifugal buoyancy forces are included in this study. A direct approach is presented for the unsteady calculation of the nondimensional temperature field in the periodic domain. The calculations are performed at a Reynolds number (Re) of 12,500, a rotation number (Ro) of 0.12, and an inlet coolant-to-wall density ratio Δρ/ρ of 0.13. The predicted time and space-averaged Nusselt numbers are shown to compare satisfactorily with the published experimental data. Time sequences of the vorticity components and the temperature fields are presented to understand the flow physics and the unsteady heat transfer behavior. Large scale coherent structures are seen to play an important role in the mixing and heat transfer. The temperature field appears to contain a low frequency mode that extends beyond a single inter-rib geometric module, and indicates the necessity of using at least two inter-rib modules for streamwise periodicity to be satisfied. Proper orthogonal decomposition (POD) of the flowfield indicates a low dimensionality of this system with almost 99% of turbulent energy in the first 80 POD modes.

Large Eddy Simulations of Flow and Heat Transfer in Rotating Ribbed Duct Flows

2004 ◽  
Author(s):  
Mayank Tyagi ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Large Scale ◽  
Density Ratio ◽  
Low Frequency ◽  
Turbulent Energy ◽  
Large Eddy Simulations ◽  
Temperature Fields ◽  
Periodic Domain ◽  
Large Eddy

Large eddy simulations are performed in a periodic domain of a rotating square duct with normal rib turbulators. Both the Coriolis force as well as the centrifugal buoyancy force are included in this study. A direct approach is presented for the unsteady calculation of the non-dimensional temperature field in the periodic domain. The calculations are performed at a Reynolds number (Re) of 12, 500, a Rotation number (Ro) of 0.12 and an inlet coolant-to-wall density ratio (Δρ/ρ) of 0.13. The time-averaged Nusselt numbers compare satisfactorily with the data of Wagner et al. (J. Turbomachinery, Vol. 114, pp. 847–857). Time-sequences of the vorticity components and the temperature fields are presented to understand the flow physics and the unsteady heat transfer processes. Large scale coherent structures are seen to play an important role in the mixing and heat transfer. The temperature field appears to contain a low frequency mode that extends beyond a single inter-rib geometric module, and indicates the necessity of using at least two inter-rib modules for streamwise periodicity to be satisfied. Proper orthogonal decomposition (POD) of 200 snapshots indicates a low dimensionality of this system with almost 99% of turbulent energy in the first 80 POD modes.

Numerical Analysis of Macro-Instability Characteristic in a Stirred Tank by Means of Large Eddy Simulations: Off-Bottom Clearance Effect

2008 ◽  
Vol 3 (1) ◽  
Author(s):  
Tantular Nurtono ◽  
Heru Setyawan ◽  
Ali Altway ◽  
Sugeng Winardi
Keyword(s):  
Flow Velocity ◽  
Flow Pattern ◽  
Dynamic Pressure ◽  
Low Frequency ◽  
Large Eddy Simulations ◽  
Bulk Flow ◽  
Stirred Tank ◽  
Series Data ◽  
Numerical Predictions ◽  
Large Eddy

Low frequency and large scale flow variations, often called macro-instability (MI) phenomena, were studied by means of a combination of large eddy simulations (LES) and sliding mesh (SM) models. Numerical predictions of MI characterictic in a six-bladed Rushton turbine stirred tank were performed by varying the off-bottom clearance at constant impeller rotational speed. The occurrence of MI in this study was identified by two methods: observing visually the flow velocity vector field and analyzing the time-series data of both velocity in the bulk flow and dynamic pressure on the vessel wall. The transient flow field visualization revealed the secondary circulation flow and the asymmetrical flow pattern beside of the mean flow pattern. The high variation intensity of flow pattern variation was clearly identified in the region with smaller space. The flow pattern variation was corroborated with the presence of high amplitude peaks in the low frequency part of the frequency spectrum of flow velocity. The distinct peak that was usually designated as the frequency of MI revealed the characteristic of MI. The physical meaning of the frequency of MI was the periodical appearance of the pronounced flow pattern. The numerical predictions of the frequency of MI in the region below and above impeller studied in this paper were confirmed well with the experimental results reported by Matsuda et al. (2004). The numerical prediction of the dynamic pressure monitored on the tank wall was also in agreement with the flow velocity monitored in the bulk flow for indicating the MI phenomena. This way of monitoring will be useful for the study of MI in multiphase agitated tank in the near future and in the practical application.

scholarly journals On state instability of the bi-stable flow past a notchback bluff body

2021 ◽  
Vol 931 ◽  
Author(s):  
Kan He ◽  
Guglielmo Minelli ◽  
Xinchao Su ◽  
Guangjun Gao ◽  
Siniša Krajnović
Keyword(s):  
Bluff Body ◽  
Low Frequency ◽  
Large Eddy Simulations ◽  
Turbulence Level ◽  
Wind Tunnel Experiments ◽  
Symmetric State ◽  
Large Eddy ◽  
Proper Orthogonal ◽  
Stable Flow ◽  
Wake State

The wake of a notchback Ahmed body presenting a bi-stable nature is investigated by performing wind tunnel experiments and large-eddy simulations. Attention is confined to the Reynolds number ( $Re$ ) influence on the wake state instability within $5\times 10^{4}\leq Re \leq 25\times 10^{4}$ . Experimental observations suggest a wake bi-stability with low-frequency switches under low $Re$ . The wake becomes ‘tri-stable’ with the increase of $Re$ with the introduction of a new symmetric state. The higher presence of the symmetric state can be considered as a symmetrization of the wake bi-stability with an increasing $Re$ . The wake symmetry under high $Re$ attributed to the highly frequent switches of the wake is extremely sensitive to small yaw angles, showing the feature of bi-stable flows. The wake asymmetry is confirmed in numerical simulations with both low and high $Re$ . The wake asymmetries are indicated by the wake separation, the reattachment and the wake dynamics identified by the proper orthogonal decomposition. However, the turbulence level is found to be significantly higher with a higher $Re$ . This leads to a higher possibility to break the asymmetric state, resulting in highly frequent switches showing symmetry.

Large Eddy Simulation of Evaporating Spray Jets

2015 ◽  
Author(s):  
Sri Vallabha Deevi ◽  
Joseph Mathew
Keyword(s):  
Carrier Phase ◽  
Quantitative Agreement ◽  
Large Eddy Simulations ◽  
The Self ◽  
Representative Point ◽  
Point Particles ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Evaporating Spray ◽  
Filtering Approach

Large Eddy Simulations (LES) of an evaporating spray jet is performed using an explicit filtering approach for carrier phase equations. Droplets are treated as representative point particles without any modeling of particle sub-grid-scale (SGS) evolution. The simulation of a recent benchmark dilute acetone spray experiment showed that close quantitative agreement could be obtained of the downstream self-preserving turbulent state. Several other simulations are performed to understand the effect of inflow fluctuation level, evaporation and droplet size on the relaxation to the self-preserving state.

scholarly journals Computing combustion noise by combining large eddy simulations with analytical models for the propagation of waves through turbine blades

2013 ◽  
Vol 341 (1-2) ◽  
pp. 131-140 ◽  
Author(s):  
Ignacio Duran ◽  
Matthieu Leyko ◽  
Stéphane Moreau ◽  
Franck Nicoud ◽  
Thierry Poinsot
Keyword(s):  
Turbine Blades ◽  
Large Eddy Simulations ◽  
Combustion Noise ◽  
Analytical Models ◽  
Large Eddy ◽  
Propagation Of Waves

scholarly journals How does turbulence change approaching a rotor?

2017 ◽  
Author(s):  
Jakob Mann ◽  
Alfredo Peña ◽  
Niels Troldborg ◽  
Søren J. Andersen
Keyword(s):  
Wind Speed ◽  
Wind Turbines ◽  
Low Frequency ◽  
Large Eddy Simulations ◽  
Thrust Coefficient ◽  
Disk Model ◽  
Actuator Disk ◽  
Large Eddy ◽  
Rotor Support ◽  
Induction Zone

Abstract. For load calculations on wind turbines it is usually assumed that the turbulence approaching the rotor does not change its statistics as it goes through the induction zone. We investigate this assumption using a nacelle-mounted forward-looking pulsed lidar that measures low frequency wind fluctuations simultaneous at distances between one half and three rotor diameters upstream. The measurements show that below rated wind speed the low-frequency wind variance is reduced by up to 10 % at one half rotor diameter upstream and above rated enhanced by up to 20 %. A quasi-steady model that takes into account the change of thrust coefficient with wind speed explains these variations partly. Large-eddy simulations of turbulence approaching an actuator disk model of a rotor support the finding that the slope of the thrust curve influences the low-frequency fluctuations.

Development of compressible large-eddy simulations combining high-order schemes and wall modeling

2015 ◽  
Author(s):  
Sophie Le Bras ◽  
Hugues Deniau ◽  
Christophe Bogey ◽  
Guillaume Daviller
Keyword(s):  
High Order ◽  
Large Eddy Simulations ◽  
High Order Schemes ◽  
Large Eddy

scholarly journals How does turbulence change approaching a rotor?

2018 ◽  
Vol 3 (1) ◽  
pp. 293-300 ◽  
Author(s):  
Jakob Mann ◽  
Alfredo Peña ◽  
Niels Troldborg ◽  
Søren J. Andersen
Keyword(s):  
Wind Speed ◽  
Wind Turbines ◽  
Low Frequency ◽  
Large Eddy Simulations ◽  
Thrust Coefficient ◽  
Disk Model ◽  
Actuator Disk ◽  
Large Eddy ◽  
Rotor Support ◽  
Induction Zone

Abstract. For load calculations on wind turbines it is usually assumed that the turbulence approaching the rotor does not change its statistics as it goes through the induction zone. We investigate this assumption using a nacelle-mounted forward-looking pulsed lidar that measures low-frequency wind fluctuations simultaneously at distances between 0.5 and 3 rotor diameters upstream. The measurements show that below rated wind speed the low-frequency wind variance is reduced by up to 10 % at 0.5 rotor diameters upstream and above rated enhanced by up to 20 %. A quasi-steady model that takes into account the change in thrust coefficient with wind speed explains these variations partly. Large eddy simulations of turbulence approaching an actuator disk model of a rotor support the finding that the slope of the thrust curve influences the low-frequency fluctuations.

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