Large Eddy Simulation of Wingtip Vortex Evolution in an Adverse Pressure Gradient

2021 ◽  
Author(s):  
Elizabeth Wood-Bowyer ◽  
Alastair West ◽  
Joel Ho Mun Onn ◽  
Chris Cantwell
Keyword(s):  
Large Eddy Simulation ◽  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Eddy Simulation ◽  
Wingtip Vortex ◽  
Large Eddy

Large-eddy simulation of turbulent flow over a parametric set of bumps

2019 ◽  
Vol 866 ◽  
pp. 503-525 ◽  
Author(s):  
Racheet Matai ◽  
Paul Durbin
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Pressure Gradient ◽  
Separation Bubble ◽  
Adverse Pressure Gradient ◽  
Windward Side ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy

Turbulent flow over a series of increasingly high, two-dimensional bumps is studied by well-resolved large-eddy simulation. The mean flow and Reynolds stresses for the lowest bump are in good agreement with experimental data. The flow encounters a favourable pressure gradient over the windward side of the bump, but does not relaminarize, as is evident from near-wall fluctuations. A patch of high turbulent kinetic energy forms in the lee of the bump and extends into the wake. It originates near the surface, before flow separation, and has a significant influence on flow development. The highest bumps create a small separation bubble, whereas flow over the lowest bump does not separate. The log law is absent over the entire bump, evidencing strong disequilibrium. This dataset was created for data-driven modelling. An optimization method is used to extract fields of variables that are used in turbulence closure models. From this, it is shown how these models fail to correctly predict the behaviour of these variables near to the surface. The discrepancies extend further away from the wall in the adverse pressure gradient and recovery regions than in the favourable pressure gradient region.

scholarly journals Large-eddy simulation of the zero-pressure-gradient turbulent boundary layer up to Reθ = O(1012)

2011 ◽  
Vol 686 ◽  
pp. 507-533 ◽  
Author(s):  
M. Inoue ◽  
D. I. Pullin
Keyword(s):  
Boundary Layer ◽  
Friction Coefficient ◽  
Turbulent Boundary Layer ◽  
Large Eddy Simulation ◽  
Pressure Gradient ◽  
Skin Friction Coefficient ◽  
Smooth Wall ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Near Wall

AbstractA near-wall subgrid-scale (SGS) model is used to perform large-eddy simulation (LES) of the developing, smooth-wall, zero-pressure-gradient flat-plate turbulent boundary layer. In this model, the stretched-vortex, SGS closure is utilized in conjunction with a tailored, near-wall model designed to incorporate anisotropic vorticity scales in the presence of the wall. Large-eddy simulations of the turbulent boundary layer are reported at Reynolds numbers ${\mathit{Re}}_{\theta } $ based on the free-stream velocity and the momentum thickness in the range ${\mathit{Re}}_{\theta } = 1{0}^{3} \text{{\ndash}} 1{0}^{12} $. Results include the inverse square-root skin-friction coefficient, $ \sqrt{2/ {C}_{f} } $, velocity profiles, the shape factor $H$, the von Kármán ‘constant’ and the Coles wake factor as functions of ${\mathit{Re}}_{\theta } $. Comparisons with some direct numerical simulation (DNS) and experiment are made including turbulent intensity data from atmospheric-layer measurements at ${\mathit{Re}}_{\theta } = O(1{0}^{6} )$. At extremely large ${\mathit{Re}}_{\theta } $, the empirical Coles–Fernholz relation for skin-friction coefficient provides a reasonable representation of the LES predictions. While the present LES methodology cannot probe the structure of the near-wall region, the present results show turbulence intensities that scale on the wall-friction velocity and on the Clauser length scale over almost all of the outer boundary layer. It is argued that LES is suggestive of the asymptotic, infinite Reynolds number limit for the smooth-wall turbulent boundary layer and different ways in which this limit can be approached are discussed. The maximum ${\mathit{Re}}_{\theta } $ of the present simulations appears to be limited by machine precision and it is speculated, but not demonstrated, that even larger ${\mathit{Re}}_{\theta } $ could be achieved with quad- or higher-precision arithmetic.

scholarly journals A New Wall Model for Large Eddy Simulation of Separated Flows

Fluids ◽  
2019 ◽  
Vol 4 (4) ◽  
pp. 197 ◽  
Author(s):  
Ahmad Fakhari
Keyword(s):  
Large Eddy Simulation ◽  
Pressure Gradient ◽  
Separated Flows ◽  
Two Dimensional ◽  
Wall Model ◽  
Law Of The Wall ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Immersed Boundaries ◽  
Near Wall

The aim of this work is to propose a new wall model for separated flows which is combined with large eddy simulation (LES) of the flow field in the whole domain. The model is designed to give reasonably good results for engineering applications where the grid resolution is generally coarse. Since in practical applications a geometry can share body fitted and immersed boundaries, two different methodologies are introduced, one for body fitted grids, and one designed for immersed boundaries. The starting point of the models is the well known equilibrium stress model. The model for body fitted grid uses the dynamic evaluation of the von Kármán constant κ of Cabot and Moin (Flow, Turbulence and Combustion, 2000, 63, pp. 269–291) in a new fashion to modify the computation of shear velocity which is needed for evaluation of the wall shear stress and the near-wall velocity gradients based on the law of the wall to obtain strain rate tensors. The wall layer model for immersed boundaries is an extension of the work of Roman et al. (Physics of Fluids, 2009, 21, p. 101701) and uses a criteria based on the sign of the pressure gradient, instead of one based on the friction velocity at the projection point, to construct the velocity under an adverse pressure gradient and where the near-wall computational node is in the log region, in order to capture flow separation. The performance of the models is tested over two well-studied geometries, the isolated two-dimensional hill and the periodic two-dimensional hill, respectively. Sensitivity analysis of the models is also performed. Overall, the models are able to predict the first and second order statistics in a reasonable way, including the position and extension of the downward separation region.

Leading Edge Contamination of a C-D Compressor Blade Using Large Eddy Simulation

2020 ◽  
Author(s):  
S. Katiyar ◽  
S. Sarkar
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Separation Bubble ◽  
Leading Edge ◽  
Adverse Pressure Gradient ◽  
Suction Surface ◽  
Local Flow ◽  
Flow Acceleration ◽  
Eddy Simulation ◽  
Large Eddy

Abstract A large-eddy simulation (LES) is employed here to predict the flow field over the suction surface of a controlled-diffusion (C-D) compressor stator blade following the experiment of Hobson et al. [1]. When compared with the experiment, LES depicts a separation bubble (SB) in the mid-chord region of the suction surface, although discrepancies exist in Cp. Further, the LES resolves the growth of boundary layer over the mid-chord and levels of turbulence intensity with an acceptable limit. What is noteworthy that LES also resolves a tiny SB near the leading-edge at the designed inflow angle of 38.3°. The objective of the present study is to assess how this leading-edge bubble influences the transition and development of boundary layer on the suction surface before the mid-chord. It appears that the separation at leading-edge suddenly enhances the perturbation levels exciting development of boundary layer downstream. The boundary layer becomes pre-transitional followed by a decay of fluctuations up to 30% of chord attributing to the local flow acceleration. Further, the boundary layer appears like laminar after being relaxed from the leading edge excitation near the mid-chord. It separates again because of the adverse pressure gradient, depicting augmentation of turbulence followed by the breakdown at about 70% of chord.

scholarly journals On the Equivalence of Two Schemes for Convective Momentum Transport

2012 ◽  
Vol 69 (12) ◽  
pp. 3491-3500 ◽  
Author(s):  
David M. Romps
Keyword(s):  
Large Eddy Simulation ◽  
Pressure Gradient ◽  
Mass Flux ◽  
Deep Convection ◽  
Momentum Transport ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Convective Momentum Transport

Abstract The Gregory–Kershaw–Inness (GKI) parameterization of convective momentum transport, which has a tunable parameter C, is shown to be identical to a parameterization with no pressure gradient force and a mass flux smaller by a factor of 1 − C. Using cloud-resolving simulations, the transilient matrix for momentum is diagnosed for deep convection in radiative–convective equilibrium. Using this transilient matrix, it is shown that the GKI scheme underestimates the compensating subsidence of momentum by a factor of 1 − C, as predicted. This result is confirmed using a large-eddy simulation.

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