Large-eddy simulations of a round jet in crossflow

1999 ◽  
Vol 379 ◽  
pp. 71-104 ◽  
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.

Large-eddy simulations and lidar measurements of vortex-pair breakup in aircraft wakes

AIAA Journal ◽  
1998 ◽  
Vol 36 ◽  
pp. 1439-1445 ◽  
Author(s):  
D. C. Lewellen ◽  
W. S. Lewellen ◽  
L. R. Poole ◽  
C. A. Hostetler ◽  
R. J. DeCoursey ◽  
...  
Keyword(s):  
Vortex Pair ◽  
Large Eddy Simulations ◽  
Large Eddy ◽  
Lidar Measurements

Large Eddy Simulations of Film-Cooling Flows With a Micro-Ramp Vortex Generator

2011 ◽  
Author(s):  
Aaron F. Shinn ◽  
S. Pratap Vanka
Keyword(s):  
Film Cooling ◽  
Cross Flow ◽  
Vortex Generator ◽  
Vortex Pair ◽  
Large Eddy Simulations ◽  
Wind Tunnel Experiments ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Flows ◽  
Large Eddy

Large Eddy Simulations were performed to study the effect of a micro-ramp on an inclined turbulent jet interacting with a cross-flow in a film-cooling configuration. The micro-ramp vortex generator is placed downstream of the film-cooling jet. Changes in vortex structure and film-cooling effectiveness are evaluated and the genesis of the counter-rotating vortex pair in the jet is discussed. Results are reported with the jet modeled using a plenum/pipe configuration. This configuration was designed based on previous wind tunnel experiments at NASA Glenn Research Center, and the present results are meant to supplement those experiments. It is found that the micro-ramp improves film-cooling effectiveness by generating near-wall counter-rotating vortices which help entrain coolant from the jet and transport it to the surface. The pair of vortices generated by the micro-ramp are of opposite sense to the vortex pair embedded in the jet.

Large-Eddy Simulations of Wall Bounded Turbulent Flows Using Unstructured Linear Reconstruction Techniques

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Dario Amirante ◽  
Nicholas J. Hills
Keyword(s):  
Reynolds Number ◽  
Turbulent Flows ◽  
Outer Radius ◽  
Large Eddy Simulations ◽  
Test Cases ◽  
Mean Flow ◽  
Flow Equations ◽  
Turbulent Statistics ◽  
Large Eddy ◽  
Least Squares Approach

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.

Hybrid RANS/ILES for Aero Engine Intake

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.

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

2013 ◽  
Vol 135 (3) ◽  
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.

scholarly journals Contributions of the wall boundary layer to the formation of the counter-rotating vortex pair in transverse jets

2011 ◽  
Vol 676 ◽  
pp. 461-490 ◽  
Author(s):  
FABRICE SCHLEGEL ◽  
DAEHYUN WEE ◽  
YOUSSEF M. MARZOUK ◽  
AHMED F. GHONIEM
Keyword(s):  
Boundary Layer ◽  
Boundary Condition ◽  
Near Field ◽  
Vortex Pair ◽  
Transverse Jets ◽  
Vortical Structures ◽  
Wall Boundary Layer ◽  
Wall Boundary ◽  
Jet Trajectory ◽  
Counter Rotating Vortex Pair

Using high-resolution 3-D vortex simulations, this study seeks a mechanistic understanding of vorticity dynamics in transverse jets at a finite Reynolds number. A full no-slip boundary condition, rigorously formulated in terms of vorticity generation along the channel wall, captures unsteady interactions between the wall boundary layer and the jet – in particular, the separation of the wall boundary layer and its transport into the interior. For comparison, we also implement a reduced boundary condition that suppresses the separation of the wall boundary layer away from the jet nozzle. By contrasting results obtained with these two boundary conditions, we characterize near-field vortical structures formed as the wall boundary layer separates on the backside of the jet. Using various Eulerian and Lagrangian diagnostics, it is demonstrated that several near-wall vortical structures are formed as the wall boundary layer separates. The counter-rotating vortex pair, manifested by the presence of vortices aligned with the jet trajectory, is initiated closer to the jet exit. Moreover tornado-like wall-normal vortices originate from the separation of spanwise vorticity in the wall boundary layer at the side of the jet and from the entrainment of streamwise wall vortices in the recirculation zone on the lee side. These tornado-like vortices are absent in the case where separation is suppressed. Tornado-like vortices merge with counter-rotating vorticity originating in the jet shear layer, significantly increasing wall-normal circulation and causing deeper jet penetration into the crossflow stream.

Flow Dynamics and Heat Transfer of a Stranded Overhead Conductor Cable

2020 ◽  
Author(s):  
Mohamed Abdelhady ◽  
David H. Wood
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Circular Cylinder ◽  
Coherent Structures ◽  
Carrying Capacity ◽  
Orthogonal Decomposition ◽  
Flow Dynamics ◽  
Large Eddy Simulations ◽  
Large Eddy ◽  
Proper Orthogonal

Abstract Stranded overhead conductor cables are used to transfer electric power, often over large distances. Conductor geometry, as well as environmental conditions, affect the power carrying capacity. This paper studies the flow dynamics and heat transfer for one stranded conductor geometry in air at Reynolds number of 1,000, determined using dynamic Smagorinsky Large Eddy Simulations. Proper Orthogonal Decomposition was used to identify coherent structures. In comparison to a smooth circular cylinder, the conductor strands noticeably affect the flow dynamics and heat transfer, locally and globally.

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