Turbulent statistics of flow fields using large eddy simulations in batch high shear mixers

Large-eddy simulations (LES) of wall bounded, low Mach number turbulent flows are conducted using an unstructured finite-volume solver of the compressible flow equations. The numerical method employs linear reconstructions of the primitive variables based on the least-squares approach of Barth. The standard Smagorinsky model is adopted as the subgrid term. The artificial viscosity inherent to the spatial discretization is maintained as low as possible reducing the dissipative contribution embedded in the approximate Riemann solver to the minimum necessary. Comparisons are also discussed with the results obtained using the implicit LES (ILES) procedure. Two canonical test-cases are described: a fully developed pipe flow at a bulk Reynolds number Reb = 44 × 103 based on the pipe diameter, and a confined rotor–stator flow at the rotational Reynolds number ReΩ = 4 × 105 based on the outer radius. In both cases, the mean flow and the turbulent statistics agree well with existing direct numerical simulations (DNS) or experimental data.

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Hybrid RANS/ILES for Aero Engine Intake

Volume 1A: Aircraft Engine; Fans and Blowers ◽

10.1115/gt2014-26472 ◽

2014 ◽

Author(s):

Ugochukwu R. Oriji ◽

Xiaoyu Yang ◽

Paul G. Tucker

Keyword(s):

Large Eddy Simulations ◽

Navier Stokes ◽

Model Simulations ◽

Rans Model ◽

Acceleration Parameter ◽

Separated Shear Layer ◽

Turbulent Statistics ◽

Large Eddy ◽

Aero Engine ◽

Aero Engines

Hybrid, Implicit Large Eddy Simulations (ILES) for an idealized aero engine intake in a crosswind is performed. The ILES zone is smoothly blended to a near wall Reynolds Averaged Navier-Stokes (RANS) zone. The flow has a region of high favourable pressure gradient (FPG) where the streamwise acceleration parameter (KS) is found to be greater than 3×10−6. This is sufficient to laminarize the boundary layer (BL). As a consequence, the turbulence in the boundary is severely suppressed and this interacts with a shock causing separation and distortion at the engine fan face. This is known to be undesirable for aero engines. The separated shear layer reenergizes turbulence and this promotes reattachment. The calculation in the RANS zone has been enhanced with a novel three-component RANS model and this is used in the hybrid RANS/ILES framework. Simulations also consider the modelling of roughness. The turbulent statistics and the engineering relevance of these are also discussed in this work. Broadly, encouraging agreement is found with measurements. Substantial accuracy improvements are found relative to standard RANS model simulations. The accuracy of the hybrid simulations is also contrasted with pure ILES and the critical need for the RANS layer shown for modest grids.

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Large Eddy Simulations of Film Cooling Flow Fields From Cylindrical and Shaped Holes

Volume 4: Heat Transfer, Parts A and B ◽

10.1115/gt2008-51009 ◽

2008 ◽

Cited By ~ 9

Author(s):

D. H. Leedom ◽

S. Acharya

Keyword(s):

Film Cooling ◽

Flow Characteristics ◽

Flow Fields ◽

Large Eddy Simulations ◽

Delivery Tube ◽

Asymmetric Flow ◽

Specific Mass ◽

Cooling Flow ◽

Large Eddy ◽

Coolant Delivery

Large Eddy Simulations (LES) of cylindrical, laterally diffused, and console holes are performed, and the resulting flow field data is presented. The motivation for performing LES is to enable more accurate simulations and to obtain a better understanding of the flow physics associated with complex hole shapes. The simulations include the coolant delivery tube and the feeding plenum chamber, and are performed for a specific mass flow rate of coolant per unit width of blade. A crossflow inlet is used on the plenum, and the resulting asymmetric flow characteristics are investigated. Coolant delivery tube flow fields are investigated in detail. Results show qualitative agreement with reported trends of improved film coverage with diffused and console holes.

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Large-Eddy Simulation With Zonal Near Wall Treatment of Flow and Heat Transfer in a Ribbed Duct for the Internal Cooling of Turbine Blades

Journal of Turbomachinery ◽

10.1115/1.4006640 ◽

2013 ◽

Vol 135 (3) ◽

Cited By ~ 10

Author(s):

Sunil Patil ◽

Danesh Tafti

Keyword(s):

Heat Transfer ◽

Turbine Blades ◽

Reynolds Numbers ◽

Large Eddy Simulations ◽

Internal Cooling ◽

Mean Flow ◽

Flow And Heat Transfer ◽

Turbulent Statistics ◽

Large Eddy ◽

Near Wall

Large eddy simulations of flow and heat transfer in a square ribbed duct with rib height to hydraulic diameter of 0.1 and 0.05 and rib pitch to rib height ratio of 10 and 20 are carried out with the near wall region being modeled with a zonal two layer model. A novel formulation is used for solving the turbulent boundary layer equation for the effective tangential velocity in a generalized co-ordinate system in the near wall zonal treatment. A methodology to model the heat transfer in the zonal near wall layer in the large eddy simulations (LES) framework is presented. This general approach is explained for both Dirichlet and Neumann wall boundary conditions. Reynolds numbers of 20,000 and 60,000 are investigated. Predictions with wall modeled LES are compared with the hydrodynamic and heat transfer experimental data of (Rau et al. 1998, “The Effect of Periodic Ribs on the Local Aerodynamic and Heat Transfer Performance of a Straight Cooling Channel,”ASME J. Turbomach., 120, pp. 368–375). and (Han et al. 1986, “Measurement of Heat Transfer and Pressure Drop in Rectangular Channels With Turbulence Promoters,” NASA Report No. 4015), and wall resolved LES data of Tafti (Tafti, 2004, “Evaluating the Role of Subgrid Stress Modeling in a Ribbed Duct for the Internal Cooling of Turbine Blades,” Int. J. Heat Fluid Flow 26, pp. 92–104). Friction factor, heat transfer coefficient, mean flow as well as turbulent statistics match available data closely with very good accuracy. Wall modeled LES at high Reynolds numbers as presented in this paper reduces the overall computational complexity by factors of 60–140 compared to resolved LES, without any significant loss in accuracy.

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Turbulent Flow Fields Over a 3D Hill Covered by Vegetation Canopy Through Large Eddy Simulations

Energies ◽

10.3390/en12193624 ◽

2019 ◽

Vol 12 (19) ◽

pp. 3624 ◽

Cited By ~ 2

Author(s):

Zhenqing Liu ◽

Yiran Hu ◽

Yichen Fan ◽

Wei Wang ◽

Qingsong Zhou

Keyword(s):

Three Dimensional ◽

Flow Fields ◽

Large Eddy Simulations ◽

Wind Tunnel Experiments ◽

Turbulence Structures ◽

Large Eddy ◽

Turbulence Kinetic Energy Budget ◽

The Mean ◽

Spanwise Rotation ◽

The Hill

The flow fields over a simplified 3D hill covered by vegetation have been examined by many researchers. However, there is scarce research giving the three-dimensional characteristics of the flow fields over a rough 3D hill. In this study, large eddy simulations were performed to examine the coherent turbulence structures of the flow fields over a vegetation-covered 3D hill. The numerical simulations were validated by the comparison with the wind-tunnel experiments. Besides, the flow fields were systematically investigated, including the examinations of the mean velocities and root means square of the fluctuating velocities. The distributions of the parameters are shown in a three-dimensional way, i.e., plotting the parameters on a series of spanwise slices. Some noteworthy three-dimensional features were found, and the mechanisms were further revealed by assessing the turbulence kinetic energy budget and the spectrum energy. Subsequently, the instantaneous flow fields were illustrated, from which the coherent turbulence structures were clearly identified. Ejection-sweep motion was intensified just behind the hill crest, leading to a spanwise rotation. A group of vertical rotations were generated by the shedding of the vortex from the lateral sides of the hill.

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Reynolds Stress Transport Model Predictions and Large Eddy Simulations for Film Coolant Jet in Crossflow

Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/2000-gt-0249 ◽

2000 ◽

Cited By ~ 5

Author(s):

Asif Hoda ◽

Sumanta Acharya ◽

Mayank Tyagi

Keyword(s):

Flow Field ◽

Reynolds Stress ◽

Transport Model ◽

Large Eddy Simulations ◽

Complex Flow ◽

Navier Stokes Equation ◽

Reynolds Stress Transport Model ◽

Jet In Crossflow ◽

Turbulent Statistics ◽

Large Eddy

Predictions of a film coolant jet in a crossflow for turbine blade cooling applications have traditionally employed k-ε and k-ω closure models of turbulence. An evaluation of several such models (Hoda and Acharya, 1999) revealed that the existing two equation models fail to resolve the highly complex flow field in the vicinity of the jet created by the jet-crossflow interaction. The eddy viscosity approximation used to obtain closure for the Reynolds stress terms in the time-averaged Navier Stokes equation is unable to represent the anisotropy of the flow and does not model the wake region created behind the jet adequately. A more accurate prediction of the stress field can be obtained by the Reynolds stress transport (RST) equations, which represent a higher level of closure for the turbulent stresses. In this paper, two formulations of the RST model have been employed to predict the flow behind a row of jets discharging normally into a crossflow. The flow field predictions and turbulent statistics are compared with the experimental data of Ajersch et al. (1995) and with k-ε predictions using the model of Lam and Bremhorst (1981). Predictions using Large Eddy Simulations (LES) are also presented to show the predictive capability of LES.

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Large-eddy simulations of a round jet in crossflow

Journal of Fluid Mechanics ◽

10.1017/s0022112098003346 ◽

1999 ◽

Vol 379 ◽

pp. 71-104 ◽

Cited By ~ 261

Author(s):

LESTER L. YUAN ◽

ROBERT L. STREET ◽

JOEL H. FERZIGER

Keyword(s):

Coherent Structures ◽

Vortex Pair ◽

Large Eddy Simulations ◽

Back Side ◽

Round Jet ◽

Turbulent Statistics ◽

Jet Trajectory ◽

Large Eddy ◽

Crossflow Velocity ◽

Counter Rotating Vortex Pair

This paper reports on a series of large-eddy simulations of a round jet issuing normally into a crossflow. Simulations were performed at two jet-to-crossflow velocity ratios, 2.0 and 3.3, and two Reynolds numbers, 1050 and 2100, based on crossflow velocity and jet diameter. Mean and turbulent statistics computed from the simulations match experimental measurements reasonably well. Large-scale coherent structures observed in experimental flow visualizations are reproduced by the simulations, and the mechanisms by which these structures form are described. The effects of coherent structures upon the evolution of mean velocities, resolved Reynolds stresses, and turbulent kinetic energy along the centreplane are discussed. In this paper, the ubiquitous far-field counter-rotating vortex pair is shown to originate from a pair of quasi-steady ‘hanging’ vortices. These vortices form in the skewed mixing layer that develops between jet and crossflow fluid on the lateral edges of the jet. Axial flow through the hanging vortex transports vortical fluid from the near-wall boundary layer of the incoming pipe flow to the back side of the jet. There, the hanging vortex encounters an adverse pressure gradient and breaks down. As this breakdown occurs, the vortex diameter expands dramatically, and a weak counter-rotating vortex pair is formed that is aligned with the jet trajectory.

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Large Eddy Simulations of the Flow Fields over Simplified Hills with Different Roughness Conditions, Slopes, and Hill Shapes: A Systematical Study

Energies ◽

10.3390/en12183413 ◽

2019 ◽

Vol 12 (18) ◽

pp. 3413 ◽

Cited By ~ 2

Author(s):

Liu ◽

Hu ◽

Wang

Keyword(s):

Turbulent Flow ◽

Flow Fields ◽

Large Eddy Simulations ◽

International Electrotechnical Commission ◽

Roughness Effects ◽

Turbulence Structures ◽

Hill Slope ◽

Large Eddy ◽

Speed Up ◽

The Hill

Turbulent flow fields over topographies are important in the area of wind energy. The roughness, slope, and shape of a hill are important parameters affecting the flow fields over topographies. However, these effects are always examined separately. The systematic investigations of these effects are limited, the coupling between these effects is still unrevealed, and the turbulence structures as a function of these effects are still unclear. Therefore, in the present study, the flow fields over twelve simplified isolated hills with different roughness conditions, slopes, and hill shapes are examined using large eddy simulations. The mean velocities, velocity fluctuations, fractional speed-up ratios, and visualizations of the turbulent flow fields are presented. It is found that as the hill slope increases, the roughness effects become weaker, and the roughness effects will further weaken as the hill changes from 3D to 2D. In addition, the fractional speed-up ratio at the summit of rough hills can even reach to three times as large as that over the corresponding smooth hills. Furthermore, the underestimation of the ratios of spanwise fluctuation to the streamwise fluctuation by International Electrotechnical Commission (IEC) 61400-1 is quite obvious when the hill shape is 3D. Finally, coherent turbulence structures can be identified for smooth hills, and as the hill slope increases, the coherent turbulence structures will experience clear evolutions. After introducing the ground roughness, the coherent turbulence structures break into small eddies.

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