Direct drag measurements in a turbulent flat-plate boundary layer with turbulence manipulators

High-order discontinuous Galerkin methods have become a popular technique in computational fluid dynamics because their accuracy increases spectrally in smooth solutions with the order of the approximation. However, their main drawback is that increasing the order also increases the computational cost. Several techniques have been introduced in the past to reduce this cost. On the one hand, local mesh adaptation strategies based on error estimation have been proposed to reduce the number of degrees of freedom while keeping a similar accuracy. On the other hand, multigrid solvers may accelerate time marching computations for a fixed number of degrees of freedom.In this paper, we combine both methods and present a novel anisotropic p-adaptation multigrid algorithm for steady-state problems that uses the multigrid scheme both as a solver and as an anisotropic error estimator. To achieve this, we show that a recently developed anisotropic truncation error estimator [1, A. M. Rueda-Ramírez, G. Rubio, E. Ferrer, E. Valero, Truncation Error Estimation in the p-Anisotropic Discontinuous Galerkin Spectral Element Method, Journal of Scientific Computing] is perfectly suited to be performed inside the multigrid cycle with negligible extra cost. Furthermore, we introduce a multi-stage p-adaptation procedure which reduces the computational time when very accurate results are required.The proposed methods are tested for the compressible Navier-Stokes equations, where we investigate two cases. First, the 2D boundary layer flow on a flat plate is studied to assess accuracy and computational cost of the algorithm, where a speed-up of 816 is achieved compared to the traditional explicit method. Second, the 3D flow around a sphere is simulated and used to test the anisotropic properties of the proposed method, where a speed-up of 152 is achieved compared to the explicit method. The proposed multi-stage procedure achieved a speed-up of 2.6 in comparison to the single-stage method in highly accurate simulations.

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“…where C N =15 d = 0.211, a value that is comparable to results in the literatute [65] for a flat plate at Re ∞ = 6000.…”

Section: Single-stage Adaptationsupporting

confidence: 74%

A p-multigrid strategy with anisotropic p-adaptation based on truncation errors for high-order discontinuous Galerkin methods

Rueda-Ramírez

Manzanero

Ferrer

et al. 2019

Journal of Computational Physics

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“…[15] analyses the effect on the total drag. Also in that case no net drag reduction is obtained thereby confirming the direct drag measurements in towing tanks [14, 32] and in a wind tunnel [22]. …”

Section: Introductionsupporting

confidence: 76%

“…” A spanwise non-homogeneous distribution of the effects of LEBUs may very well exist as was also shown in Ref. [22]. It should also be noted that even in standard turbulent boundary layers on flat plates in wind tunnels three-dimensionalities develop (with both smooth and rough surfaces) even if care is taken to make the flow two-dimensional [39].…”

Section: Discussionmentioning

confidence: 84%

“…It is also well known that the skin-friction in a nominally two-dimensional boundary layer may not be homogeneous in the spanwise direction and that introducing a manipulator may severely affect the spanwise distribution (see figures 6 and 8 in Ref. [ 22 ]).…”

Section: How To Determine Drag?mentioning

confidence: 99%

“…Similar experiments in a towing tank at NASA with an axisymmetric body were later made and reported by Anders [21] in 1989 and these experiments also showed no drag reduction. The very detailed and accurate measurements by Lynn et al [22] made in Germany in a wind tunnel reported in 1995, where both the plate drag and the LEBU drag were measured, also investigated many different parameter combinations, including single and tandem manipulators. Also those experiments showed the same result, i.e.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Large-Eddy BreakUp Devices – a 40 Years Perspective from a Stockholm Horizon

Alfredsson

2018

Flow Turbulence Combust

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In the beginning of the 1980’s Large Eddy BreakUp (LEBU) devices, thin plates or airfoils mounted in the outer part of turbulent boundary layers, were shown to be able to change the turbulent structure and intermittency as well as reduce turbulent skin friction. In some wind-tunnel studies it was also claimed that a net drag reduction was obtained, i.e. the reduction in skin-friction drag was larger than the drag on the devices. However, towing-tank experiments with a flat plate at high Reynolds numbers as well as with an axisymmetric body showed no net reduction, but instead an increase in total drag. Recent large-eddy simulations have explored the effect of LEBUs on the turbulent boundary layer and evaluations of the total drag show similar results as in the towing tank experiments. Despite these negative results in terms of net drag reduction, LEBUs manipulate the boundary layer in an interesting way which explains why they still attract some interest. The reason for the positive results in the wind-tunnel studies as compared to drag measurements are discussed here, although no definite answer for the differences can be given.

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Simulation of a Large-Eddy-Break-up Device (LEBU) in a Moderate Reynolds Number Turbulent Boundary Layer

Chin

Monty

Hutchins

et al. 2016

Flow Turbulence Combust

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A well-resolved large eddy simulation (LES) of a large-eddy breakup (LEBU) device in a spatially evolving turbulent boundary layer is performed with, Reynolds number, based on free-stream velocity and momentumloss thickness, of Re θ ≈ 4300. The implementation of the LEBU is via an immersed boundary method. The LEBU is positioned at a wall-normal distance of 0.8δ (δ denoting the local boundary layer thickness at the location of the LEBU) from the wall. The LEBU acts to delay the growth of the turbulent boundary layer and produces global skin friction reduction beyond 180δ downstream of the LEBU, with a peak local skin friction reduction of approximately 12%. However, no net drag reduction is found when accounting for the device drag of the LEBU in accordance with the towing tank experiments by Sahlin et al. (Phys. Fluids 31, 2814. Further investigation is performed on the interactions of high and low momentum bulges with the LEBU and the corresponding output is analysed, showing a 'break-up' of these large momentum bulges downstream of the LEBU. In addition, results from the spanwise energy spectra show consistent reduction in energy at spanwise length scales for λ + z > 1000 independent of streamwise and wall-normal location when compared to the corresponding turbulent boundary layer without LEBU.

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Direct drag measurements in a turbulent flat-plate boundary layer with turbulence manipulators

Cited by 7 publications

References 19 publications

A p-multigrid strategy with anisotropic p-adaptation based on truncation errors for high-order discontinuous Galerkin methods

A p-multigrid strategy with anisotropic p-adaptation based on truncation errors for high-order discontinuous Galerkin methods

Large-Eddy BreakUp Devices – a 40 Years Perspective from a Stockholm Horizon

Simulation of a Large-Eddy-Break-up Device (LEBU) in a Moderate Reynolds Number Turbulent Boundary Layer

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