Variable density turbulence tunnel facility

Bodenschatz, Eberhard; Bewley, Gregory P.; Nobach, Holger; Sinhuber, Michael; Xu, Haitao

doi:10.1063/1.4896138

Cited by 58 publications

(87 citation statements)

References 64 publications

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“…We note in this respect that the high resolution of our runs, h » k 6 max , effectively allows us to calculate increments over a very small distance (r≈η/2). A benefit of using velocity increments is that their 1D surrogates can be also obtained and verified using experiments [40]. Figure 5(a) shows the PDF of δu r , normalized by the Kolmogorov velocity scale u K , for h » r 0.5, at various Reynolds numbers.…”

Section: Pdfs Of Velocity Incrementsmentioning

confidence: 94%

Extreme velocity gradients in turbulent flows

et al. 2019

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Fully turbulent flows are characterized by intermittent formation of very localized and intense velocity gradients. These gradients can be orders of magnitude larger than their typical value and lead to many unique properties of turbulence. Using direct numerical simulations of the Navier-Stokes equations with unprecedented small-scale resolution, we characterize such extreme events over a significant range of turbulence intensities, parameterized by the Taylor-scale Reynolds number ( l R ). Remarkably, we find the strongest velocity gradients to empirically scale as t l

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Section: Pdfs Of Velocity Incrementsmentioning

confidence: 94%

Extreme velocity gradients in turbulent flows

et al. 2019

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“…The grid consists of 20 horizontal bars and 30 vertical bars, oriented as two layers of a 10 × 15 mesh, with a mesh length of M = 80 mm. The only grid with greater variability is that of Bodenschatz et al (2014), although the present grid has nearly twice the number of bars, which reduces the confinement effect of the tunnel size on the turbulence. Low friction cylindrical supports (diameter 12.7 mm) hold the various meshes of the grid apart, and help maintain overall rigidity.…”

Section: Active Grid Designmentioning

confidence: 99%

“…A recent advancement by Bodenschatz et al (2014) has introduced a 129 degree-of-freedom, 9M × 9M active grid in a 1.5 m × 1.5 m wind tunnel. Each wing of this grid is mechanically independent, unlike previous grids where all wings along a single axis were rigidly connected and moved together.…”

Section: Introductionmentioning

confidence: 99%

The effect of active grid initial conditions on high Reynolds number turbulence

Hearst

Lavoie

2015

Exp Fluids

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The most expansive active grid parametric study to date is conducted in order to ascertain the relative importance of the various grid parameters. It is identified that the three most important parameters are the Rossby number, Ro, the grid Reynolds number, Re M , and the wing geometry. For Ro > 50, an asymptotic state in turbulence intensity is reached where increasing Ro further does not change the turbulence intensity while other parameters continue to vary. Three wing geometries are used: solid square wings, solid circular wings, and square wings with holes. It is shown that the wings with the greatest blockage produce the highest turbulence intensities and Re λ , but that parameters such as the Kolmogorov, Taylor and integral scales are not significantly influenced by wing geometry. Finally, it is demonstrated that for several different sets of initial conditions that produce the same Re λ , the spectra are collapsed everywhere but at the largest scales. This result suggests that regardless of the very different origins of the turbulence, the shape of the spectra at high wavenumbers is dependent only on Re λ when normalized by Kolmogorov variables, hence demonstrating a degree of independence from the initial conditions.

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“…That is, we fixed the BCs so that the large-scale structure of the flow was approximately fixed. We then changed Re by varying the viscosity of the fluid [30]. The ability to do this was almost unique among turbulence decay experiments, and made it possible both to cover a wider range and to reach higher Re than ever before.…”

mentioning

confidence: 99%

“…We performed the experiments in the Variable Density Turbulence Tunnel (the VDTT) [30]. The VDTT circulated both air and pressurized sulfur-hexafluoride.…”

mentioning

confidence: 99%

Decay of Turbulence at High Reynolds Numbers

2015

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Turbulent motions in a fluid relax at a certain rate once stirring has stopped. The role of the most basic parameter in fluid mechanics, the Reynolds number, in setting the relaxation rate is not generally known. This paper concerns the high-Reynolds-number limit of the process. In a classical grid-turbulence wind-tunnel experiment that both reached higher Reynolds numbers than ever before and covered a wide range of them (10 4 < Re = U M ν < 5 × 10 6 ), we measured the relaxation rate with the unprecedented precision of about 2%. Here U is the mean speed of the flow, M the forcing scale, and ν the kinematic viscosity of the fluid. We observed that the relaxation rate was Reynolds-number independent, which contradicts some models and supports others.PACS numbers: 47.27. Gs, 47.27.Jv Turbulence dissipates kinetic energy, and the easiest way to see this is to let turbulence relax, or freely decay, by removing the agitation that initially set the fluid in motion. In so doing, one observes qualitatively that the fluid comes to rest. The rate at which that happens is the subject at hand, and underlies general turbulence phenomena and modeling. To simplify the problem, the statistics of the turbulent fluctuations are often arranged to be spatially homogeneous and isotropic [1,2]. Even under these conditions, it is not possible quantitatively to predict the decay rate; it is even difficult precisely to measure the decay rate [3][4][5][6]. Yet empirical constraints on the properties of decaying turbulence are what is needed to advance the knowledge of the subject.The physics that control the decay are not fully understood, to the extent that the role of the most basic parameter in fluid mechanics, the Reynolds number, is not clear. What is known is that toward very low Reynolds numbers, the decay rate increases [7,8], as it also does when the spatial structure of the turbulence grows to the size of its container [4,9]. Here, we study the rate of decay in the limit of large Reynolds numbers for turbulence free from boundary effects, a rate which cannot be determined from the previous data.One theoretical framework predicts that the decay rate depends on the large-scale structure of the flow, and not on the Reynolds number once turbulence is fully developed [2, 10-13]. As the Reynolds numbers diverge to infinity, the scale at which energy is dissipated grows arbitrarily small, but these scales continue to dissipate energy as quickly as it is transferred to them by the large scales. This picture is compatible with an emerging consensus that the initial structure of the turbulence sets its decay rate, even when the flow is homogeneous [14][15][16][17].There is also, however, a line of thinking that an elegant and fully self-similar decay emerges in the limit of high Reynolds number [14,15,[18][19][20][21][22][23]. In this description, turbulence tends to become statistically similar to itself, when appropriately rescaled, even as it decays. Observation of a tendency toward slower decay with increasing Reynolds numbers wo...

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Variable density turbulence tunnel facility

Cited by 58 publications

References 64 publications

Extreme velocity gradients in turbulent flows

Extreme velocity gradients in turbulent flows

The effect of active grid initial conditions on high Reynolds number turbulence

Decay of Turbulence at High Reynolds Numbers

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