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981.
Experimental results on the reaction of the near wall turbulence and drag to a localized time periodical blowing are reported.
The injection velocity is periodical and dissymmetric in time, with a rapid acceleration phase followed by a slow deceleration
one. The flow is relaminarized during 70% of the oscillation period mainly during the deceleration phase. The latter maintains
stable the vorticity layer induced by the blowing and prevents its roll-up contrarily to a sinusoidal time periodical blowing.
Thus, a time mean drag reduction of 50% is obtained in the region recovering 200 wall units downstream of the blowing slot
and this is 40% larger than the drag reduction obtained by a steady blowing with the same time mean severity parameter. The
dissymmetric blowing annihilates considerably the wall turbulence activity and gives better results in terms of drag reduction
compared with steady and sinusoidal blowing.
相似文献
Sedat F. TarduEmail: |
982.
A modified cold gas-dynamic spray technique is under development by using shock tunnel technology, which can enhance the coating
quality by increasing the solid particle velocity up to 1,500 m/s. The particle diameter typically amounts to 10 μm. A theoretical
model based on gas-particle flows is employed to describe the behaviour of the flow and the solid particles. This quasi-1D
model is capable to consider non-equilibrium effects of the gas phase due to high reservoir temperatures, and the influence
of wall friction and heat transfer averaged over the nozzle cross section. This model is used for the design and optimization
of the nozzle geometry by a parametric study, which results in a conical nozzle with a half opening angle of 2.8° and a length
of 325 mm. Particles for coating are injected at about 55 mm downstream of the throat. A shock tunnel facility has been set
up at the Shock Wave Laboratory for performing an experimental study of this new technique. The theoretical performance of
this setup is evaluated by the KASIMIR simulation software and the quasi-1D method described in this paper. The high reservoir
conditions required to achieve particle velocities of 1,500 m/s can be realized by using either a very high driver pressure
of about 600 bar for air as driver gas or a relatively low driver pressure of about 200 bar for helium as driver gas.
相似文献
983.
Eugene Tyrtyshnikov 《高等学校计算数学学报(英文版)》2009,2(4):421-426
For an arbitrary tensor (multi-index array) with linear constraints at each direction, it is proved that the factors of any minimal canonical tensor approximation to this tensor satisfy the same linear constraints for the corresponding directions. 相似文献
984.
Experimental results on the dynamics of a vortex dipole evolving in a shallow fluid layer are presented. In particular, the
generation of a spanwise vortex at the front of the dipole is observed in agreement with previous experiments at larger Reynolds
numbers. The results show that this secondary vortex is of comparable strength to the dipole. The present physical analysis
suggests that the origin of this structure involves the stretching induced by the dipole of the boundary-layer vorticity generated
by the dipole’s advection over the no-slip bottom. 相似文献
985.
It is well known that the flow-field over blunt and pointed bodies is sensitive to the non-equilibrium phenomena characteristic
of high enthalpy hypersonic flows. Till date, most experiments and modelling were related to flows essentially dominated by
the dissociation rate. However, in practical cases of a re-entry low density flow, the aerodynamic quantities such as the
shock shape and location may also be strongly influenced by vibrational relaxation coupled with dissociation and chemical
reactions. Thus, the flow about various bodies such as spheres, hemisphere–cylinders and cones is recomputed using a chemical
model recently proposed by the authors and by taking into account the coupling between the vibrational relaxation and the
chemical kinetics. Then, the computed shock shapes in air flow are compared to recent experimental results obtained in a ballistic
range for flight velocities between 2,500 and 4,000 m/s, and in a shock tunnel for enthalpies close to 5 and 10 MJ/kg. The
computed density field around hemispherical bodies is also compared to the experimental one. A good agreement, within 5%,
between computed and measured results is observed. A few comparisons are also proposed with the results obtained with another
well-known (empirical) model. A comparison is also made between the flow quantities along the stagnation line obtained over
cylindrical and spherical bodies using the present model and those coming from a quasi-one-dimensional model recently developed,
showing also a satisfactory agreement. 相似文献
986.
We study doubly-periodic instantons, i.e. instantons on the product of a 1-dimensional complex torus T with a complex line ℂ, with quadratic curvature decay. We determine the asymptotic behaviour of these instantons, constructing
new asymptotic invariants. We show that the underlying holomorphic bundle extends to T×ℙ1. The converse statement is also true, namely a holomorphic bundle on T×ℙ1 which is flat on the torus at infinity, and satisfies a stability condition, comes from a doubly-periodic instanton. Finally,
we study the hyperk?hler geometry of the moduli space of doubly-periodic instantons, and prove that the Nahm transform previously
defined by the second author is a hyperk?hler isometry with the moduli space of certain meromorphic Higgs bundles on the dual
torus.
Received June 8, 2000 / final version received February 1, 2001?Published online April 3, 2001 相似文献
987.
Olivier Teulié 《Monatshefte für Mathematik》2001,134(2):169-176
In this paper, we prove that for any real number ξ, which is not an algebraic number of degree , there exist infinitely many real algebraic units α of degree n + 1 such that . We also show how the flexibility of H. Davenport and W. M. Schmidt’s method allows to replace, with the same exponent of
approximation, units of degree over Z (i.e. elements α with both α and integral over Z) by units of degree over a finite intersection .
(Received 14 March 2000; in revised form 16 November 2000) 相似文献
988.
JPC – Journal of Planar Chromatography – Modern TLC - A quantitative thin layer chromatographic (TLC) method on silica gel, with ethyl acetate–acetone–alcohol, 62 + 40 + 3... 相似文献
989.
Summary Lopinavir is a new specific and potent HIV-1 protease inhibitor. A rapid high-performance liquid chromatographic method using
UV detection, has been developed and validated for the analysis of lopinavir in plasma. This involved a single liquid-solid
extraction on an OASIS? HLB column in the presence of an internal standard. Separation was achieved on a Xterra?, C8 (150×3.9 mm I.D.) column with a mobile phase consisting of acetonitrile and water (41∶59, v/v). The detection wavelength
was 210 nm. The assay was linear from 0.187 to 10.0 μg.mL−1 and the limit of quantification was 0.187 μg.mL−1. Mean recovery was ranged from 90.7% to 97.8% for lopinavir and 97.1% for the internal standard. Day to day precision and
accuracy were less than 9.6% and 7.3% respectively. This rapid and simple method can readily be used for drug monitoring of
lopinavir, in HIV-1 infected patients. 相似文献
990.
Olivier Quinet Benoît Champagne Bernard Kirtman 《Journal of computational chemistry》2001,22(16):1920-1932
Analytical calculation of second derivatives of the dynamic electronic polarizability with respect to vibrational normal coordinates has been implemented at the TDHF level of approximation. Important simplifications are obtained by using the 2n+1 rule and interchange relations. In application to small molecules the first‐order ZPVA correction is found to have greater frequency dispersion than the electronic polarizability, but the former remains small in comparison. For the linear polyenes, C2nH2n+2 (n=1–3), the percentage ZPVA correction decreases with chain length for all ?ω<0.10 a.u. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1920–1932, 2001 相似文献