共查询到20条相似文献,搜索用时 46 毫秒
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2.
G. H. Keetels W. Kramer H. J. H. Clercx G. J. F. van Heijst 《Theoretical and Computational Fluid Dynamics》2011,25(5):293-300
Recently, numerical studies revealed two different scaling regimes of the peak enstrophy Z and palinstrophy P during the collision of a dipole with a no-slip wall [Clercx and van Heijst, Phys. Rev. E 65, 066305, 2002]: Z μ Re0.8{Z\propto{\rm Re}^{0.8}} and P μ Re2.25{P\propto {\rm Re}^{2.25}} for 5 × 102 ≤ Re ≤ 2 × 104 and Z μ Re0.5{Z\propto{\rm Re}^{0.5}} and P μ Re1.5{P\propto{\rm Re}^{1.5}} for Re ≥ 2 × 104 (with Re based on the velocity and size of the dipole). A critical Reynolds number Re
c
(here, Rec ? 2×104{{\rm Re}_c\approx 2\times 10^4}) is identified below which the interaction time of the dipole with the boundary layer depends on the kinematic viscosity
ν. The oscillating plate as a boundary-layer problem can then be used to mimick the vortex-wall interaction and the following
scaling relations are obtained: Z μ Re3/4, P μ Re9/4{Z\propto{\rm Re}^{3/4}, P\propto {\rm Re}^{9/4}} , and dP/dt μ Re11/4{\propto {\rm Re}^{11/4}} in agreement with the numerically obtained scaling laws. For Re ≥ Re
c
the interaction time of the dipole with the boundary layer becomes independent of the kinematic viscosity and, applying flat-plate
boundary-layer theory, this yields: Z μ Re1/2{Z\propto{\rm Re}^{1/2}} and P μ Re3/2{P\propto {\rm Re}^{3/2}}. 相似文献
3.
Understanding turbulent wall-bounded flows remains an elusive goal. Most turbulent phenomena are non-linear, complex and have
broad range of scales that are difficult to completely resolve. Progress is made only in minute steps and enlightening models
are rare. Herein, we undertake the effort to bundle several experimental and numerical databases to overcome some of these
difficulties and to learn more about the kinematics of turbulent wall-bounded flows. The general scope of the present work
is to quantify the characteristics of wall-normal and spanwise Reynolds stresses, which might be different for confined (e.g.,
pipe) and semi-confined (e.g., boundary layer) flows. In particular, the peak position of wall-normal stress and a shoulder
in spanwise stress never described in detail before are investigated using select experimental and direct numerical simulation
databases available in the open literature. It is found that the positions of the
á v¢2
ñ + \left\langle {v'{^2} } \right\rangle^{ + } -peak in confined and semi-confined flow differ significantly above δ
+ ≈ 600. A similar behavior is found for the position of the
á u¢v¢
ñ + \left\langle {u'v'} \right\rangle^{ + } -peak. The upper end of the logarithmic region seems to be closely related to the position of the
á v¢2
ñ + \left\langle {v'{^2} } \right\rangle^{ + } -peak. The
á w¢2
ñ + \left\langle {w'{^2} } \right\rangle^{ + } -shoulder is found to be twice as far from the wall than the
á v¢2
ñ + \left\langle {v'{^2} } \right\rangle^{ + } -peak. It covers a significantly large portion of the typical zero-pressure-gradient turbulent boundary layer. 相似文献
4.
Masataka Sugimoto Hirokazu Hida Takashi Taniguchi Kiyohito Koyama Yuji Aoki 《Rheologica Acta》2007,46(7):957-964
Poly(vinyl chloride) (PVC)/di-isononyl phthalate systems with PVC content of 45.5 (PVC8) and 70.4 wt% (PVC6) were prepared
by a hot roller at 150 °C and press molded at 180 °C. The dynamic viscoelasticity and elongational viscosity of PVC8 and PVC6
were measured in the temperature range from 150 to 220 °C. We have found that the storage and loss shear moduli, G′ and G″, of PVC8 and PVC6 exhibited the power-law dependence on the angular frequency ω at 190 and 210 °C, respectively. Correspondingly, the tan δ values did not depend on ω. These temperatures indicate the critical gel temperature T
gel of each system. The critical relaxation exponent n obtained from these data was 0.75 irrespective of PVC content, which was in agreement with the n values reported previously for the low PVC concentration samples. These results suggest that the PVC gels of different plasticizer
content have a similar fractal structure. Below T
gel, the gradual melting of the PVC crystallites takes place with elevating temperature, and above T
gel, a densely connected network throughout the whole system disappears. Correspondingly, the elongational viscosity behavior
of PVC8 and PVC6 exhibited strong strain hardening below T
gel, although it did not show any strain hardening above T
gel. These changes in rheological behavior are attributed to the gradual melting of the PVC crystallites worked as the cross-linking
domains in this physical gel, thereby inapplicability of the of time–temperature superposition for PVC/plasticizer systems. 相似文献
5.
We establish the existence and uniqueness results over the semi-infinite interval [0,∞) for a class of nonlinear third order
ordinary differential equations of the form
lf"¢( h) + f( h)f"( h) - ( f¢( h) )2 - Mf¢( h) + C(C + M ) = 0,f( 0 ) = s , f¢( 0 ) = c, limh? ¥ f¢( h) = C.\begin{array}{l}f'( \eta) + f( \eta)f'( \eta) - ( f'( \eta) )^{2} - Mf'( \eta)\\[6pt]\quad {}+ C(C + M ) = 0,\\[6pt]f( 0 ) = s ,\qquad f'( 0 ) = \chi ,\qquad \displaystyle\lim\limits_{\eta \to \infty} f'( \eta) = C.\end{array} 相似文献
6.
Craig Cowan Pierpaolo Esposito Nassif Ghoussoub Amir Moradifam 《Archive for Rational Mechanics and Analysis》2010,198(3):763-787
We study the regularity of the extremal solution of the semilinear biharmonic equation ${{\Delta^2} u=\frac{\lambda}{(1-u)^2}}
7.
This article presents a nonlinear stability analysis of a rotating thermoconvective magnetized ferrofluid layer confined between
stress-free boundaries using a thermal non-equilibrium model by the energy method. The effect of interface heat transfer coefficient
( H¢){( {{\mathcal H}^{\prime}})}, magnetic parameter (M
3), Darcy–Brinkman number ( [^(D)]a){( {\hat{{\rm D}}{\rm a}})}, and porosity modified conductivity ratio (γ′) on the onset of convection in the presence of rotation (TA1){({T_{{\rm A}_1}})} have been analyzed. The critical Rayleigh numbers predicted by energy method are smaller than those calculated by linear
stability analysis and thus indicate the possibility of existence of subcritical instability region for ferrofluids. However,
for non-ferrofluids stability and instability boundaries coincide. Asymptotic analysis for both small and large values of
interface heat transfer coefficient (H¢){({{\mathcal H}^{\prime}})} is also presented. A good agreement is found between the exact solutions and asymptotic solutions. 相似文献
8.
We prove a regularity result for the anisotropic linear elasticity equation ${P u := {\rm div} \left( \boldmath\mathsf{C} \cdot \nabla u\right) = f}
9.
We prove that, if ${u : \Omega \subset \mathbb{R}^n \to \mathbb{R}^N}
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