17 research outputs found
An improved \eps expansion for three-dimensional turbulence: summation of nearest dimensional singularities
An improved \eps expansion in the -dimensional () stochastic
theory of turbulence is constructed by taking into account pole singularities
at in coefficients of the \eps expansion of universal quantities.
Effectiveness of the method is illustrated by a two-loop calculation of the
Kolmogorov constant in three dimensions.Comment: 4 page
Anomalous scaling, nonlocality and anisotropy in a model of the passively advected vector field
A model of the passive vector quantity advected by a Gaussian
time-decorrelated self-similar velocity field is studied; the effects of
pressure and large-scale anisotropy are discussed. The inertial-range behavior
of the pair correlation function is described by an infinite family of scaling
exponents, which satisfy exact transcendental equations derived explicitly in d
dimensions. The exponents are organized in a hierarchical order according to
their degree of anisotropy, with the spectrum unbounded from above and the
leading exponent coming from the isotropic sector. For the higher-order
structure functions, the anomalous scaling behavior is a consequence of the
existence in the corresponding operator product expansions of ``dangerous''
composite operators, whose negative critical dimensions determine the
exponents. A close formal resemblance of the model with the stirred NS equation
reveals itself in the mixing of operators. Using the RG, the anomalous
exponents are calculated in the one-loop approximation for the even structure
functions up to the twelfth order.Comment: 37 pages, 4 figures, REVTe
Calculation of the anomalous exponents in the rapid-change model of passive scalar advection to order
The field theoretic renormalization group and operator product expansion are
applied to the model of a passive scalar advected by the Gaussian velocity
field with zero mean and correlation function \propto\delta(t-t')/k^{d+\eps}.
Inertial-range anomalous exponents, identified with the critical dimensions of
various scalar and tensor composite operators constructed of the scalar
gradients, are calculated within the expansion to order
(three-loop approximation), including the exponents in
anisotropic sectors. The main goal of the paper is to give the complete
derivation of this third-order result, and to present and explain in detail the
corresponding calculational techniques. The character and convergence
properties of the expansion are discussed; the improved
``inverse'' expansion is proposed and the comparison with the
existing nonperturbative results is given.Comment: 34 pages, 5 figures, REVTe
Stochastic magnetohydrodynamic turbulence in space dimensions
Interplay of kinematic and magnetic forcing in a model of a conducting fluid
with randomly driven magnetohydrodynamic equations has been studied in space
dimensions by means of the renormalization group. A perturbative
expansion scheme, parameters of which are the deviation of the spatial
dimension from two and the deviation of the exponent of the powerlike
correlation function of random forcing from its critical value, has been used
in one-loop approximation. Additional divergences have been taken into account
which arise at two dimensions and have been inconsistently treated in earlier
investigations of the model. It is shown that in spite of the additional
divergences the kinetic fixed point associated with the Kolmogorov scaling
regime remains stable for all space dimensions for rapidly enough
falling off correlations of the magnetic forcing. A scaling regime driven by
thermal fluctuations of the velocity field has been identified and analyzed.
The absence of a scaling regime near two dimensions driven by the fluctuations
of the magnetic field has been confirmed. A new renormalization scheme has been
put forward and numerically investigated to interpolate between the
expansion and the double expansion.Comment: 12 pages, 4 figure
Anomalous scaling of a passive scalar in the presence of strong anisotropy
Field theoretic renormalization group and the operator product expansion are
applied to a model of a passive scalar field, advected by the Gaussian strongly
anisotropic velocity field. Inertial-range anomalous scaling behavior is
established, and explicit asymptotic expressions for the n-th order structure
functions of scalar field are obtained; they are represented by superpositions
of power laws with nonuniversal (dependent on the anisotropy parameters)
anomalous exponents. In the limit of vanishing anisotropy, the exponents are
associated with tensor composite operators built of the scalar gradients, and
exhibit a kind of hierarchy related to the degree of anisotropy: the less is
the rank, the less is the dimension and, consequently, the more important is
the contribution to the inertial-range behavior. The leading terms of the even
(odd) structure functions are given by the scalar (vector) operators. For the
finite anisotropy, the exponents cannot be associated with individual operators
(which are essentially ``mixed'' in renormalization), but the aforementioned
hierarchy survives for all the cases studied. The second-order structure
function is studied in more detail using the renormalization group and
zero-mode techniques.Comment: REVTEX file with EPS figure
Anomalous exponents in the rapid-change model of the passive scalar advection in the order
Field theoretic renormalization group is applied to the Kraichnan model of a
passive scalar advected by the Gaussian velocity field with the covariance
. Inertial-range
anomalous exponents, related to the scaling dimensions of tensor composite
operators built of the scalar gradients, are calculated to the order
of the expansion. The nature and the convergence of
the expansion in the models of turbulence is are briefly discussed.Comment: 4 pages; REVTeX source with 3 postscript figure
Theory of the nonsteady diffusion growth of a gas bubble in a supersaturated solution of gas in liquid
Using a self-similar approach a general nonsteady theory is elaborated for
the case of the diffusion growth of a gas bubble in a supersaturated solution
of gas in liquid. Due to the fact that the solution and the bubble in it are
physically isolated, the self-similar approach accounts for the balance of the
number of gas molecules in the solution and in the bubble that expells
incompressible liquid solvent while growing. The rate of growth of the bubble
radius in its dependence from gas solubility and solution supersaturation is
obtained. There is a nonsteady effect of rapid increase of the rate of bubble
growth simultaneous with the growth of the product of gas solubility and
solution supersaturation. This product is supplied with a limitation from
above, which also stipulates isothermal conditions of bubble growth. The
smallness of gas solubility is not presupposed.Comment: 22 pages, 3 figure
Passive scalar turbulence in high dimensions
Exploiting a Lagrangian strategy we present a numerical study for both
perturbative and nonperturbative regions of the Kraichnan advection model. The
major result is the numerical assessment of the first-order -expansion by
M. Chertkov, G. Falkovich, I. Kolokolov and V. Lebedev ({\it Phys. Rev. E},
{\bf 52}, 4924 (1995)) for the fourth-order scalar structure function in the
limit of high dimensions 's. %Two values of the velocity scaling exponent
have been considered: % and . In the first case, the
perturbative regime %takes place at , while in the second at , %in agreement with the fact that the relevant small parameter %of the
theory is . In addition to the perturbative results, the
behavior of the anomaly for the sixth-order structure functions {\it vs} the
velocity scaling exponent, , is investigated and the resulting behavior
discussed.Comment: 4 pages, Latex, 4 figure
Field theoretic renormalization group for a nonlinear diffusion equation
The paper is an attempt to relate two vast areas of the applicability of the
renormalization group (RG): field theoretic models and partial differential
equations. It is shown that the Green function of a nonlinear diffusion
equation can be viewed as a correlation function in a field-theoretic model
with an ultralocal term, concentrated at a spacetime point. This field theory
is shown to be multiplicatively renormalizable, so that the RG equations can be
derived in a standard fashion, and the RG functions (the function and
anomalous dimensions) can be calculated within a controlled approximation. A
direct calculation carried out in the two-loop approximation for the
nonlinearity of the form , where is not necessarily
integer, confirms the validity and self-consistency of the approach. The
explicit self-similar solution is obtained for the infrared asymptotic region,
with exactly known exponents; its range of validity and relationship to
previous treatments are briefly discussed.Comment: 8 pages, 2 figures, RevTe
Theory of Developed Turbulence: Principle of Maximal Randomness and Spontaneous Parity Violation
A set of self-consistent equations in one-loop approximation in a statistical model of fully developed homogeneous isotropic turbulence, which is based on the principle of maximal randomness of the velocity field with a given energy spectral flux, is obtained. These equations do not possess both infrared and ultraviolet divergences near the Kolmogorov values of indices. The formal solution found of the system of equations yields Kolmogorov exponents, but this solution leads to negative Kolmogorov constant and negative viscosity. It has been shown, that the turbulent fluid becomes stable if spontaneous parity violation is achieved. Namely, the solution with the Kolmogorov indices and additional helical terms (which lead to positive both and effective viscosity) exists. This solution predicts a large, closed to limit value, helical coefficient in inertial range. The relationship obtained between and confirms this conclusion for the experimental value of