ترغب بنشر مسار تعليمي؟ اضغط هنا

Depletion of nonlinearity in two-dimensional turbulence

143   0   0.0 ( 0 )
 نشر من قبل Wouter Bos
 تاريخ النشر 2014
  مجال البحث فيزياء
والبحث باللغة English
 تأليف Andrey Pushkarev




اسأل ChatGPT حول البحث

The strength of the nonlinearity is measured in decaying two-dimensional turbulence, by comparing its value to that found in a Gaussian field. It is shown how the nonlinearity drops following a two-step process. First a fast relaxation is observed on a timescale comparable to the time of for-mation of vortical structures, then at long times the nonlinearity relaxes further during the phase when the eddies merge to form the final dynamic state of decay. Both processes seem roughly independent of the value of the Reynolds number.



قيم البحث

اقرأ أيضاً

198 - Wouter Bos 2010
Two-dimensional statistically stationary isotropic turbulence with an imposed uniform scalar gradient is investigated. Dimensional arguments are presented to predict the inertial range scaling of the turbulent scalar flux spectrum in both the inverse cascade range and the enstrophy cascade range for small and unity Schmidt numbers. The scaling predictions are checked by direct numerical simulations and good agreement is observed.
We study the small-scale behavior of generalized two-dimensional turbulence governed by a family of model equations, in which the active scalar $theta=(-Delta)^{alpha/2}psi$ is advected by the incompressible flow $u=(-psi_y,psi_x)$. The dynamics of t his family are characterized by the material conservation of $theta$, whose variance $<theta^2>$ is preferentially transferred to high wave numbers. As this transfer proceeds to ever-smaller scales, the gradient $ ablatheta$ grows without bound. This growth is due to the stretching term $( ablathetacdot abla)u$ whose ``effective degree of nonlinearity differs from one member of the family to another. This degree depends on the relation between the advecting flow $u$ and the active scalar $theta$ and is wide ranging, from approximately linear to highly superlinear. Linear dynamics are realized when $ ablau$ is a quantity of no smaller scales than $theta$, so that it is insensitive to the direct transfer of the variance of $theta$, which is nearly passively advected. This case corresponds to $alphage2$, for which the growth of $ ablatheta$ is approximately exponential in time and non-accelerated. For $alpha<2$, superlinear dynamics are realized as the direct transfer of $<theta^2>$ entails a growth in $ ablau$, thereby enhancing the production of $ ablatheta$. This superlinearity reaches the familiar quadratic nonlinearity of three-dimensional turbulence at $alpha=1$ and surpasses that for $alpha<1$. The usual vorticity equation ($alpha=2$) is the border line, where $ ablau$ and $theta$ are of the same scale, separating the linear and nonlinear regimes of the small-scale dynamics. We discuss these regimes in detail, with an emphasis on the locality of the direct transfer.
Conflict between formation of a cyclonic vortex and isotropization in forced homogeneous rotating turbulence is numerically investigated. It is well known that a large rotation rate of the system induces columnar vortices to result in quasi-two-dimen sional (Q2D) flow, while a small rotation rate allows turbulence to be three-dimensional (3D). It is found that the transition from the Q2D turbulent flow to the 3D turbulent flow and the reverse transition occur at different values of the rotation rates. At the intermediate rotation rates, bistability of these two statistically steady states is observed. Such hysteretic behavior is also observed for the variation of the amplitude of an external force.
124 - Prasad Perlekar 2010
We present a natural framework for studying the persistence problem in two-dimensional fluid turbulence by using the Okubo-Weiss parameter $Lambda$ to distinguish between vortical and extensional regions. We then use a direct numerical simulation (DN S) of the two-dimensional, incompressible Navier--Stokes equation with Ekman friction to study probability distribution functions (PDFs) of the persistence times of vortical and extensional regions by employing both Eulerian and Lagrangian measurements. We find that, in the Eulerian case, the persistence-time PDFs have exponential tails; by contrast, this PDF for Lagrangian particles, in vortical regions, has a power-law tail with an exponent $theta=2.9pm0.2$.
We numerically investigate the spatial and temporal statistical properties of a dilute polymer solution in the elastic turbulence regime, i.e., in the chaotic flow state occurring at vanishing Reynolds and high Weissenberg numbers. We aim at elucidat ing the relations between measurements of flow properties performed in the spatial domain with the ones taken in the temporal domain, which is a key point for the interpretation of experimental results on elastic turbulence and to discuss the validity of Taylors hypothesis. To this end, we carry out extensive direct numerical simulations of the two-dimensional Kolmogorov flow of an Oldroyd-B viscoelastic fluid. Static point-like numerical probes are placed at different locations in the flow, particularly at the extrema of mean flow amplitude. The results in the fully developed elastic turbulence regime reveal large velocity fluctuations, as compared to the mean flow, leading to a partial breakdown of Taylors frozen-field hypothesis. While second-order statistics, probed by spectra and structure functions, display consistent scaling behaviors in the spatial and temporal domains, the third-order statistics highlight robust differences. In particular the temporal analysis fails to capture the skewness of streamwise longitudinal velocity increments. Finally, we assess both the degree of statistical inhomogeneity and isotropy of the flow turbulent fluctuations as a function of scale. While the system is only weakly non-homogenous in the cross-stream direction, it is found to be highly anisotropic at all scales.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا