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51.
Ratnesh K. Shukla Jeff. D. Eldredge 《Theoretical and Computational Fluid Dynamics》2007,21(5):343-368
An inviscid vortex sheet model is developed in order to study the unsteady separated flow past a two-dimensional deforming
body which moves with a prescribed motion in an otherwise quiescent fluid. Following Jones (J Fluid Mech 496, 405–441, 2003)
the flow is assumed to comprise of a bound vortex sheet attached to the body and two separate vortex sheets originating at
the edges. The complex conjugate velocity potential is expressed explicitly in terms of the bound vortex sheet strength and
the edge circulations through a boundary integral representation. It is shown that Kelvin’s circulation theorem, along with
the conditions of continuity of the normal velocity across the body and the boundedness of the velocity field, yields a coupled
system of equations for the unknown bound vortex sheet strength and the edge circulations. A general numerical treatment is
developed for the singular principal value integrals arising in the solution procedure. The model is validated against the
results of Jones (J Fluid Mech 496, 405–441, 2003) for computations involving a rigid flat plate and is subsequently applied
to the flapping foil experiments of Heathcote et al. (AIAA J, 42, 2196–2204, 2004) in order to predict the thrust coefficient.
The utility of the model in simulating aquatic locomotion is also demonstrated, with vortex shedding suppressed at the leading
edge of the swimming body.
相似文献
52.
A turbulent boundary layer manipulated by outer-layer devices has been studied. Experiments have been conducted in the 0.70 by 0.50 m2 low speed wind tunnel of the Modesto Panetti Aeronautical Laboratory of the Politecnico di Torino. Mean values and turbulent quantities measured in the natural and manipulated boundary layers are shown for comparison. The mechanisms to explain the observed skin friction and turbulence reduction are discussed. The manipulator wake effect, consisting in decoupling the wall-region from the boundary layer outer-region, is stressed in the present results.
Sommario Viene studiato uno strato limite turbolento manipolato, utilizzando la tecnica degli outer-layer devices. Gli esperimenti sono stati condotti nella galleria del vento 0.70×0.50 m2 del Laboratorio di Aeronautica Modesto Panetti del Politecnico di Torino. Sono confrontati risultati relativi ai casi di flusso non manipolato e manipolato. Vengono discussi i meccanismi che conducono alla riduzione dello sforzo di attrito a parete e delle quantità turbolente; in particolare si punta l'attenzione sull'effetto decorrelante della scia del manipolatore.相似文献
53.
The thermal decomposition of nitric oxide (diluted in Argon) has been measured behind incident shock waves by means of IR diode laser absorption spectroscopy. In two independent runs the diode laser was tuned to the=0 =12
3/2
R(18.5)-rotational vibrational transition and the=1 =22
3/2
R(20.5)-rotational vibrational transition of nitric oxide, respectively. These two transitions originating from the vibrational ground state (=0) and the first excited vibrational state (=1) were selected in order to probe the homogeneity along the absorption path. The measured NO decomposition could satisfactorily be described by a chemical reaction mechanism after taking into account boundary layer corrections according to the theory of Mirels. The study forms a further proof of Mirels' theory including his prediction of the laminar-turbulent transition. It also shows, that the inhomogeneities from the boundary layer do not affect the IR linear absorption markedly.This article was processed using Springer-Verlag TEX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society. 相似文献
54.
A great number of experimental data indicating shock wave/boundary layer interactions in internal or external supersonic flows
were reviewed to make clear the mechanism of the interaction and to decide the onset of shock-induced separation. The interesting
conclusions were obtained for the considerably wide range of flow geometries that the onset of separation is independent of
the flow geometries and the boundary layer Reynolds number. It is found that the pressure rise necessary to separate the boundary
layer in supersonic external flows could be applied to such internal flows as overexpanded nozzles or diffusers. This is due
to the fact that the separation phenomenon caused by shock wave/boundary layer interactions is processed through a supersonic
deceleration. The shock-induced separation in almost all of interacting flow fields is governed by the concept of free interaction,
and the onset of shock-induced separation is only a function of the Mach number just upstream of shock wave. However, physical
scales of the produced separation are not independent of the downstream flow fields. 相似文献
55.
Intersonic crack propagation in homogeneous media under shear-dominated loading: theoretical analysis 总被引:1,自引:0,他引:1
Dhirendra V. Kubair Philippe H. Geubelle Yonggang Y. Huang 《Journal of the mechanics and physics of solids》2002,50(8):1547-1564
The mechanics of cohesive failure under mixed-mode loading is investigated for the case of a steadily propagating subsonic and intersonic dynamic crack subjected to a follower tensile and shear distributed load. The cohesive failure model chosen in this study is rate independent but accounts for the coupling between normal and tangential damage. Special emphasis is placed here on mixed-mode cases with predominantly shear loading. The analysis shows that the size of the mixed-mode cohesive zone is smaller than that obtained in the pure shear case. The relative extent of the shear and tensile cohesive damage zones depends on the crack speed and the mode mixity. In the intersonic regime, the failure process takes place exclusively in shear, even under remote mixed-mode loading conditions. 相似文献
56.
本文以调和函数的边值问题为例,探讨了边界积分方程的充要条件.文中首次提出了超定问题的概念,并建立了超定问题有解的一个充要条件,它也就是直接变量边界积分方程的一个充要条件.文中首次阐明了边界积分方程与变分原理的内在的联系,还指出了间接变量与直接变量两类边界积分方程之间存在着一一对应的关系.文中的慨念、思路和论点不难用于其它有变分原理的问题的边界积分方程. 相似文献
57.
58.
59.
A rectangular cell of known boundary conditions is cut out from a medium containing the doubly periodic array of inclusions. The stress and strain relationship of the rectangular cell is obtained by using the classical boundary element methods. By matching the boundary condition requirements, the effective elastic properties of the doubly periodic array of inclusions can then be calculated. Numerical examples from the sub-domain boundary element method and the single domain boundary element method are compared and discussed. However, the present method cannot be readily extended to domains having circular or curved boundary parts. 相似文献
60.
We formulate integral statements of force balance, energy balance, and entropy imbalance for an interface between a body and
its environment. These statements account for interfacial energy, entropy, and stress but neglect the inertia of the interface.
Our final results consist of boundary conditions describing thermomechanical interactions between the body and its environment.
In their most general forms, these results are partial differential equations that account for dissipation and encompass as
special cases Navier’s slip law, Newton’s law of cooling, and Kirchhoff’s law of radiation. When dissipation is neglected,
our results reduce to the well-known zero-slip, free-surface, zero-shear, prescribed temperature, and flux-free conditions.
Dedicated to James K. Knowles: teacher, colleague, friend 相似文献