Experimental studies of turbulent helicity and its spectrum in the atmospheric boundary layer

Koprov, B. M.; Koprov, V. M.; Пономарев, В. М.; Chkhetiani, О. G.

doi:10.1134/1.2039983

Cited by 52 publications

(36 citation statements)

References 8 publications

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“…10 for the same ABC flows (note that the absolute value of helicity is displayed). Similarly to the total 063007-10 [35]. The arrows highlight a sharp break in the spectra discussed in the text.…”

Section: Energy and Helicity Spectramentioning

confidence: 92%

“…Note that cyclostrophic balance implies curvature of trajectories that is not due to rotation (which is neglected here), as is also the case at low latitudes or at small scales, for example, in tornadoes [34]. Helicity spectra have also been measured in the planetary boundary layer [35]. The large scale balance that arises in the presence of both rotation and stratification is considered in Ref.…”

Section: Introductionmentioning

confidence: 99%

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Helicity dynamics in stratified turbulence in the absence of forcing

et al. 2013

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A numerical study of decaying stably stratified flows is performed. Relatively high stratification (Froude number ≈ 10 −2 -10 −1 ) and moderate Reynolds (Re) numbers (Re ≈ 3-6 × 10 3 ) are considered and a particular emphasis is placed on the role of helicity (velocity-vorticity correlations), which is not an invariant of the nondissipative equations. The problem is tackled by integrating the Boussinesq equations in a periodic cubical domain using different initial conditions: a nonhelical Taylor-Green (TG) flow, a fully helical Beltrami [ArnoldBeltrami-Childress (ABC)] flow, and random flows with a tunable helicity. We show that for stratified ABC flows helicity undergoes a substantially slower decay than for unstratified ABC flows. This fact is likely associated to the combined effect of stratification and large-scale coherent structures. Indeed, when the latter are missing, as in random flows, helicity is rapidly destroyed by the onset of gravitational waves. A type of large-scale dissipative "cyclostrophic" balance can be invoked to explain this behavior. No production of helicity is observed, contrary to the case of rotating and stratified flows. When helicity survives in the system, it strongly affects the temporal energy decay and the energy distribution among Fourier modes. We discover in fact that the decay rate of energy for stratified helical flows is much slower than for stratified nonhelical flows and can be considered with a phenomenological model in a way similar to what is done for unstratified rotating flows. We also show that helicity, when strong, has a measurable effect on the Fourier spectra, in particular at scales larger than the buoyancy scale, for which it displays a rather flat scaling associated with vertical shear, as observed in the planetary boundary layer.

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Section: Energy and Helicity Spectramentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Helicity dynamics in stratified turbulence in the absence of forcing

et al. 2013

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“…The joint or parallel cascade of the energy and helicity is supported by evidence from both direct numerical simulations [20][21][22] and experimental measurements of the atmospheric boundary layer flow [23]. It was shown through dimensional arguments and by using a shell model that there exists an inner scale ξ for helicity dissipation, which is always greater than the Kolmogorov scale η (characterizing the energy dissipation), and is increasingly so for helical turbulence with growing Reynolds number [24].…”

Section: Introductionmentioning

confidence: 67%

Joint-constraint model for large-eddy simulation of helical turbulence

Xiao

Shi

et al. 2014

Phys. Rev. E

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A three-term mixed subgrid-scale (SGS) stress model is proposed for large-eddy simulation (LES) of helical turbulence. The new model includes a Smagorinsky-Lilly term, a velocity gradient term, and a symmetric vorticity gradient term. The model coefficients are determined by minimizing the mean square error between the realistic and modeled Leonard stresses under a joint constraint of kinetic energy and helicity fluxes. The model formulated as such is referred to as joint-constraint dynamic three-term model (JCD3TM). First, the new model is evaluated a priori using the direct numerical simulation (DNS) data of homogeneous isotropic turbulence with helical forcing. It is shown that the SGS dissipation fractions from all three terms in JCD3TM have the properties of length-scale invariance in inertial subrange. JCD3TM can predict the SGS stresses, energy flux, and helicity flux more accurately than the dynamic Smagorinsky model (DSM) and dynamic mixed helical model (DMHM) in both pointwise and statistical senses. Then, the performance of JCD3TM is tested a posteriori in LESs of both forced and freely decaying helical isotropic turbulence. It is found that JCD3TM possesses certain features of superiority over the other two models in predicting the energy spectrum, helicity spectrum, high-order statistics, etc. It is also noteworthy that JCD3TM is capable of simulating the evolutions of both energy and helicity spectra more precisely than other models in decaying helical turbulence. We claim that the present SGS model can capture the main helical features of turbulent motions and may serve as a useful tool for LES of helical turbulent flows.

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“…Helicity in MHD turbulence can be detected indirectly by measurements of magnetic field induction [13]. As far as we know there is only one successful attempt to measure the helicity power spectrum [14]. Modern optical techniques such as dual-plane or tomographic PIV (particle image velocimetry) make possible the reconstruction of helicity density distribution in a plane [15] or even in a volume [16].…”

Section: Introductionmentioning

confidence: 99%

Analysis of mean and fluctuating helicity measured by TomoPIV in swirling jet

et al. 2018

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Abstract. Important role of helicity was theoretically predicted for the generation of large-scale magnetic fields and atmospheric vortices. Helicity can lead to a reduction of turbulent dissipation in the atmosphere or in a specific constrained flow, e.g. in pipe. We use the TomoPIV data (42 cube of grid points, resolution 0.84 mm) to measure 3D velocity field of turbulent swirling flows. We study spatial distribution of the mean and fluctuating components of energy and helicity. We find that helical turbulence excitation and decay along stream of the jet strongly depend on the inflow swirl. We observe spatial separation of turbulent flow with different sign of helicity while integrated values are conserves. It is shown that large scale swirling flow induces helicity at the small scales. Our results bring valuable materials for benchmark the modern numerical simulations with turbulent closure technique.

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Experimental studies of turbulent helicity and its spectrum in the atmospheric boundary layer

Cited by 52 publications

References 8 publications

Helicity dynamics in stratified turbulence in the absence of forcing

Helicity dynamics in stratified turbulence in the absence of forcing

Joint-constraint model for large-eddy simulation of helical turbulence

Analysis of mean and fluctuating helicity measured by TomoPIV in swirling jet

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