Theoretical prediction of turbulent skin friction on geometrically complex surfaces

Peet, Yulia; Sagaut, Pierre

doi:10.1063/1.3241993

Cited by 67 publications

(57 citation statements)

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“…In particular, the impact of turbulence on skin friction can be clearly quantified and localized within the boundary layer thickness. This method has then been generalized to compressible flow [19] and to some complex wall surfaces [20]. The effect of riblets on each of the drag-contributing terms could shed more light on their drag-reducing mechanisms.…”

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Riblet Flow Model Based on an Extended FIK Identity

Bannier

Garnier

Sagaut

2015

Flow Turbulence Combust

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International audienceLarge Eddy Simulations of zero-pressure-gradient turbulent boundary layers over riblets have been conducted. All along the controlled domain, riblets maintain a significant 11 % drag reduction with respect to the flat plate at the same R e τ (from 250 to 450). To compare the flows above riblets and a reference smooth wall, an appropriate vertical shift between the two surfaces is required. In the present study, the “vertical origin” is set using the identity of Fukagata, Iwamoto and Kasagi (FIK) in Phys. Fluids, vol. 14, 2002, L73. This identity, which provides a physically meaningful decomposition of the skin friction, has been extended to complex wall surfaces and constitutes the basis for the derivation of a new virtual origin. Using this FIK-based origin, it is shown that the complex interactions between the riblets and the near-wall turbulent structures can be taken into account by a simple shift of the two axes of the mean and turbulent velocity profiles. The appropriate upward shift Δu +, typical for drag reduction, is directly dependent on the skin friction on the riblets and on the reference smooth plate at the same R e τ

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confidence: 99%

Riblet Flow Model Based on an Extended FIK Identity

Bannier

Garnier

Sagaut

2015

Flow Turbulence Combust

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“…Moreover, the shape and the size of these technological devices can impose severe constraints on the grid design. For example, riblets (thin slots manufactured on the blade wall) are known to be an effective solution to reduce losses [41,42] but their size is only a few dozen micrometres, compared to a few dozen millimetres for the blade span (figure 2).Steady RANS simulations are already used to partially address these challenges, but the lack of validation of turbulence models in complex configurations limits the predictive capability of CFD. Even the use of unsteady RANS has a limited impact on the flow prediction [3].…”

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confidence: 99%

Large eddy simulation of flows in industrial compressors: a path from 2015 to 2035

Gourdain

Sicot

Duchaine

et al. 2014

Phil. Trans. R. Soc. A.

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One contribution of 13 to a Theme Issue 'Aerodynamics, computers and the environment' . A better understanding of turbulent unsteady flows is a necessary step towards a breakthrough in the design of modern compressors. Owing to high Reynolds numbers and very complex geometry, the flow that develops in such industrial machines is extremely hard to predict. At this time, the most popular method to simulate these flows is still based on a Reynoldsaveraged Navier-Stokes approach. However, there is some evidence that this formalism is not accurate for these components, especially when a description of time-dependent turbulent flows is desired. With the increase in computing power, large eddy simulation (LES) emerges as a promising technique to improve both knowledge of complex physics and reliability of flow solver predictions. The objective of the paper is thus to give an overview of the current status of LES for industrial compressor flows as well as to propose future research axes regarding the use of LES for compressor design. While the use of wallresolved LES for industrial multistage compressors at realistic Reynolds number should not be ready before 2035, some possibilities exist to reduce the cost of LES, such as wall modelling and the adaptation of the phase-lag condition. This paper also points out the necessity to combine LES to techniques able to tackle complex geometries. Indeed LES alone, i.e. without prior knowledge of such flows for grid construction or the prohibitive yet ideal use of fully homogeneous meshes to predict compressor flows, is quite limited today. IntroductionThe aeronautic industry faces a formidable challenge by targeting in 2050 a reduction of CO 2 and NO x 2014 The Author(s) Published by the Royal Society. All rights reserved. emissions by 75% and 90% per kilometre and per passenger, respectively (compared to the 2000 level). Ultra-high bypass ratio (BR > 20) turbofan and ultra-high overall pressure ratio (OPR > 70) core engines have the potential for such significant reductions in fuel burn. However, after many years of optimization, the design of ever more efficient gas turbines now requires understanding of the complex unsteady flow appearing within each individual component and in an integrated fashion. Among all components, the compressor remains a critical part of a gas turbine, especially regarding its efficiency and stability. Owing to the adverse pressure gradients, compressors are naturally subjected to unstable flows such as surge and rotating stall [1], which can potentially lead to mechanical failure. These aerodynamic instabilities impose serious constraints on the design (the so-called 'surge margin') and thus on performance. In this context, maximizing the efficiency of compressors remains particularly complex and the improvement of the compressor robustness and performance thus requires good understanding of the flow physics.Complementary to experimental investigations, the numerical simulation of flows, commonly referred to as computational fluid dynamics (CFD), is...

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“…Because of the geometric complexity of our flow, the original FIK's formulation cannot be applied as is. Following Peet and Sagaut [17] who derived the equivalent of FIK's channel flow decomposition for three-dimensional complex wall shape, a similar formula can be obtained from FIK's boundary layer formulation:…”

Section: Analysis Of the Wall Frictionmentioning

confidence: 99%