Large Eddy Simulation of the Wake Behind a Turning Ship

2002 ◽  
Author(s):  
Ibrahim Yavuz ◽  
Zeynep N. Cehreli ◽  
Ismail B. Celik ◽  
Shaoping Shi
Keyword(s):  
Large Eddy Simulation ◽  
Sensitivity Study ◽  
West Virginia University ◽  
Vortical Structures ◽  
Turbulence Structures ◽  
Eddy Simulation ◽  
Flow Generation ◽  
Large Eddy ◽  
Unsteady Inflow ◽  
Random Flow

This study examines the dynamics of turbulent flow in the wake of a turning ship using the large eddy simulation (LES) technique. LES is applied in conjunction with a random flow generation (RFG) technique originally developed at West Virginia University to provide unsteady inflow boundary conditions. As the ship is turning, the effects of the Coriolis and centrifugal forces on vortical structures are included. The effects of the Coriolis force on the flow-field are assessed and a grid sensitivity study is performed. The predicted turbulence structures are analyzed and compared with the wake of a non-turning ship.

Large Eddy Simulation of Round Impinging Jets With Large Stand-Off Distance

2014 ◽  
Author(s):  
Mehrdad Shademan ◽  
Vesselina Roussinova ◽  
Ron Barron ◽  
Ram Balachandar
Keyword(s):  
Large Eddy Simulation ◽  
Flow Characteristics ◽  
Impinging Jet ◽  
Impinging Jets ◽  
Vortical Structures ◽  
Nozzle Height ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean ◽  
Good Agreement

Large Eddy Simulation (LES) has been carried out to study the flow of a turbulent impinging jet with large nozzle height-to-diameter ratio. The dynamic Smagorinsky model was used to simulate the subgrid-scale stresses. The jet exit Reynolds number is 28,000. The study presents a detailed evaluation of the flow characteristics of an impinging jet with nozzle height of 20 diameters above the plate. Results of the mean normalized centerline velocity and wall shear stress show good agreement with previous experiments. Analysis of the flow field shows that vortical structures generated due to the Kelvin-Helmholtz instabilities in the shear flow close to the nozzle undergo break down or merging when moving towards the plate. Unlike impinging jets with small stand-off distance where the ring-like vortices keep their interconnected shape upon reaching the plate, no sign of interconnection was observed on the plate for this large stand-off distance. A large deflection of the jet axis was observed for this type of impinging jet when compared to the cases with small nozzle height-to-diameter ratios.

Overset Grid Method for Large Eddy Simulation of Turbulent Flows Around Bluff Bodies

2007 ◽  
Author(s):  
Y. Itoh ◽  
T. Tamura
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Grid Method ◽  
Side Surface ◽  
Mass Conservation ◽  
Overset Grid ◽  
Turbulence Structures ◽  
Eddy Simulation ◽  
Side Ratio ◽  
Large Eddy

The large eddy simulation of turbulent flow around a rectangular cylinder with side ratios of 1.0, 2.0, 2.67, and 3.0 at Re = 22000, is carried out using an overset grid system. In order to improve mass conservation along the boundary of computational domains, numerical procedures are proposed. The aerodynamic forces of rectangular cylinders can be predicted numerically. Details of pressure distributions along the side surface of the cylinder and turbulence structures in the wake is discussed, because there is a difference in accuracy of computational results in terms of the side ratio.

Large Eddy Simulation of a Vortex Ring Impacting a Bump

2014 ◽  
Vol 6 (3) ◽  
pp. 261-280
Author(s):  
Heng Ren ◽  
Ning Zhao ◽  
Xi-Yun Lu
Keyword(s):  
Large Eddy Simulation ◽  
Vortex Ring ◽  
Three Dimensional ◽  
Vortical Flow ◽  
Flow State ◽  
Vortical Structures ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Phenomena ◽  
Flow Evolution

AbstractA vortex ring impacting a three-dimensional bump is studied using large eddy simulation for a Reynolds number Re = 4 × 104 based on the initial diameter and translational speed of the vortex ring. The effects of bump height and vortex core thickness for thin and thick vortex rings on the vortical flow phenomena and the underlying physical mechanisms are investigated. Based on the analysis of the evolution of vortical structures, two typical kinds of vortical structures, i.e., the wrapping vortices and the hair-pin vortices, are identified and play an important role in the flow state evolution. The boundary vorticity flux is analyzed to reveal the mechanism of the vorticity generation on the bump surface. The circulation of the primary vortex ring reasonably elucidates some typical phases of flow evolution. Further, the analysis of turbulent kinetic energy reveals the transition from laminar to turbulent state. The results obtained in this study provide physical insight into the understanding of the mechanisms relevant to the flow evolution and the flow transition to turbulent state.

The Effects of the Wall-Layer Models on the Outer Turbulence Structures in Large Eddy Simulation of Pipe Flows

2007 ◽  
Author(s):  
Makoto Tsubokura ◽  
Yasuo Oto ◽  
Jun Etoh ◽  
Binghu Piao ◽  
Shigeaki Kuroda
Keyword(s):  
Large Eddy Simulation ◽  
Wall Layer ◽  
Detached Eddy Simulation ◽  
Layer Model ◽  
Turbulence Structures ◽  
Pipe Flows ◽  
Eddy Simulation ◽  
Streaky Structures ◽  
Large Eddy ◽  
Shed Light

Reproduction of the outer turbulence in Large Eddy Simulation (LES), when the wall-layer model is adopted in the inner layer, is investigated to validate the hybrid RANS/LES as an approximate near-wall treatment. Special emphasis is on the possibility of Detached Eddy Simulation (DES) for the reproduction of outer large (∼ R) and very large (∼ 10R) streaky structures typically observed in the pipe turbulence. LES and DES of fully developed turbulent pipe flows at the friction Reynolds number up to 5000 are conducted using a very long analysis region to capture entire outer scales. It is found that the outer scales are properly captured in DES independent on the unphysical super-streaks in the RANS region near the wall, as long as sufficient height for the DES buffer layer is maintained. Our results shed light on the origin of the outer structures, which are rather autonomous similar to the inner sublayer streaks, and these two structures with different scaling exists in the isolated manner.

scholarly journals Large eddy simulation of ship tracks in the collapsed marine boundary layer: a case study from the Monterey area ship track experiment

2015 ◽  
Vol 15 (10) ◽  
pp. 5851-5871 ◽  
Author(s):  
A. H. Berner ◽  
C. S. Bretherton ◽  
R. Wood
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Liquid Water ◽  
Satellite Images ◽  
Sensitivity Study ◽  
Liquid Water Path ◽  
Water Path ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Ship Tracks

Abstract. For the first time, a large eddy simulation (LES) coupled to a bulk aerosol scheme is used to simulate an aircraft-sampled ship track. The track was formed by the M/V Sanko Peace on 13 June 1994 in a shallow drizzling boundary layer with high winds but very low background aerosol concentrations (10 cm−3). A Lagrangian framework is used to simulate the evolution of a short segment of track as it is advected away from the ship for 8 h (a downwind distance exceeding 570 km). Using aircraft observations for initialization, good agreement is obtained between the simulated and observed features of the ambient boundary layer outside the track, including the organization of the cloud into mesoscale rolls. After 8 h, a line of aerosol is injected to start the ship track. The simulation successfully reproduces the significant albedo enhancement and suppression of drizzle observed within the track. The aerosol concentration within the track dilutes as it broadens due to turbulent mixing. A sensitivity study shows the broadening rate strongly depends on the alignment between the track and the wind-aligned boundary layer rolls, as satellite images of ship tracks suggest. Entrainment is enhanced within the simulated track, but the observed 100 m elevation of the ship track above the surrounding layer is not simulated, possibly because the LES quickly sharpens the rather weak observed inversion. Liquid water path within the simulated track increases with time even as the ambient liquid water path is decreasing. The albedo increase in the track from liquid water and cloud fraction enhancement (second indirect effect) eventually exceeds that from cloud droplet number increases (first indirect or Twomey effect). In a sensitivity study with a higher initial ambient aerosol concentration, stronger ship track aerosol source, and much weaker drizzle, there is less liquid water inside the track than outside for several hours downwind, consistent with satellite estimates for such situations. In that case, the Twomey effect dominates throughout, although, as seen in satellite images, the albedo enhancement of the track is much smaller.

scholarly journals Large-eddy simulation of ship tracks in the collapsed marine boundary layer: a case study from the Monterey Area Ship Track experiment

2014 ◽  
Vol 14 (17) ◽  
pp. 24387-24439
Author(s):  
A. H. Berner ◽  
C. S. Bretherton ◽  
R. Wood
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Liquid Water ◽  
Satellite Images ◽  
Sensitivity Study ◽  
Liquid Water Path ◽  
Water Path ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Ship Tracks

Abstract. For the first time, a large-eddy simulation (LES) coupled to a bulk aerosol scheme is used to simulate an aircraft-sampled ship track. The track was formed by the M/V Sanko Peace on 13 June 1994 in a shallow drizzling boundary layer with high winds but very low background aerosol concentrations (10 cm−3). A Lagrangian framework is used to simulate the evolution of a short segment of track as it is advected away from the ship for eight hours (a downwind distance exceeding 570 km). Using aircraft observations for initialization, good agreement is obtained between the simulated and observed features of the ambient boundary layer outside the track, including the organization of cloud into mesoscale rolls. After eight hours, a line of aerosol is injected to start the ship track. The simulation successfully reproduces the significant albedo enhancement and suppression of drizzle observed within the track. The aerosol concentration within the track dilutes as it broadens due to turbulent mixing. A sensitivity study shows the broadening rate strongly depends on the alignment between the track and the wind-aligned boundary layer rolls, as satellite images of ship tracks suggest. Entrainment is enhanced within the simulated track, but the observed 100 m elevation of the ship track above the surrounding layer is not simulated, possibly because the LES quickly sharpens the rather weak observed inversion. Liquid water path within the simulated track increases with time even as the ambient liquid water path is decreasing. The albedo increase in the track from liquid water and cloud fraction enhancement (second indirect effect) eventually exceeds that from cloud droplet number increases (first indirect or Twomey effect). In a sensitivity study with a higher initial ambient aerosol concentration, stronger ship track aerosol source, and much weaker drizzle, there is less liquid water inside the track than outside for several hours downwind, consistent with satellite estimates for such situations. In this case, the Twomey effect dominates throughout, although, as seen in satellite images, the albedo enhancement of the track is much smaller.

scholarly journals Large Eddy Simulation of a Bluff Body Stabilized Lean Premixed Flame

2014 ◽  
Vol 2014 ◽  
pp. 1-18 ◽  
Author(s):  
A. Andreini ◽  
C. Bianchini ◽  
A. Innocenti
Keyword(s):  
Large Eddy Simulation ◽  
Gas Turbine ◽  
Turbulent Combustion ◽  
Bluff Body ◽  
Sensitivity Study ◽  
Flame Stabilization ◽  
Combustion Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Lean Premixed

The present study is devoted to verify current capabilities of Large Eddy Simulation (LES) methodology in the modeling of lean premixed flames in the typical turbulent combustion regime of Dry LowNOxgas turbine combustors. A relatively simple reactive test case, presenting all main aspects of turbulent combustion interaction and flame stabilization of gas turbine lean premixed combustors, was chosen as an affordable test to evaluate the feasibility of the technique also in more complex test cases. A comparison between LES and RANS modeling approach is performed in order to discuss modeling requirements, possible gains, and computational overloads associated with the former. Such comparison comprehends a sensitivity study to mesh refinement and combustion model characteristic constants, computational costs, and robustness of the approach. In order to expand the overview on different methods simulations were performed with both commercial and open-source codes switching from quasi-2D to fully 3D computations.

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