Intrinsic equations of rotational gas flows

Considering a vortex line as aC ³ curve inE ³, equations governing the flow of a steady, compressible gas are expressed in the intrinsic form. These intrinsic relations are applied to derive some geometric properties of rotational motions, and to study a class of flows whose vortex lines form a family of helices on right circular cylinders.     

On rotational viscous flow through a tube

Zusammenfassung Für die Eigenwerte und Eigenfunktionen eines Eigenwertproblems, auf dasL. Collatz undH. Görtler im Zusammenhang mit einer kürzlichen Untersuchung [3] über Rohrströmung mit schwachem Drall geführt worden sind, werden asymptotische Näherungsformeln angegeben, die insbesondere die höhern Eigenwerte mit grösserer Genauigkeit als in [3] zu berechnen gestatten. Auch zur Ermittlung der niedrigen Eigenwerte wird ein einfaches Verfahren vorgeschlagen. Die Ergebnisse werden numerisch mit denen von [3] verglichen.

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This paper was prepared under a National Bureau of Standards contract with American University and was supported by the Office of Naval Research.     

Vibrational and rotational relaxation in a moderately dense gas. II

Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 78, No. 1, pp. 81–93, January, 1989.     

On the two-dimensional rotational body of maximal Newtonian resistance

We investigate, by means of computer simulations, shapes of nonconvex bodies that maximize resistance to their motion through a rarefied medium, considering that the bodies are moving forward and at the same time slowly rotating. A two-dimensional geometric shape that confers to the body a resistance very close to the theoretical supremum value is obtained, which improves previous results.     

On wave propagation in elastic tubes conducting rotational flows

The propagation of perturbations in liquid filled elastic tubes depends on the stream velocity of the basic flow. This phenomenon is currently analyzed with the method of the characteristics which relies upon a basic flow with a rectangular velocity profile. It seems that this one-dimensional flow approximation has not been convincingly validated, which justifies to consider other, more general velocity profiles.In the present analytical study the velocity profile is a quadratic function of the radial coordinate. Small amplitude perturbations are superposed on this inviscid, basic state in which the mean velocity is arbitrarily large. A normal mode analysis shows that the velocity profile and therefore the vorticity of the basic flow influence the more the phenomenon the larger is. For example, a parabolic profile allows countercurrent wave propagation regardless of.This questions the one-dimensional wave propagation theory in compliant tubes and, consequently, the interpretation of several physiological and medical problems mainly in the respiratory and cardio-vascular systems.

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Resumé La propagation de perturbations dans un tube élastique conduisant un écoulement fluide dépend de la vitesse de l'écoulement de base. Ce phénomène est habituellement étudié avec la méthode des caractéristiques, où l'on suppose que le profil de vitesse de l'écoulement est rectangulaire. Comme cette simplification ne semble pas avoir été bien validée, il paraît indiqué d'étudier l'impact d'autres profils.Dans la présente étude analytique, ce profil de vitesse est une fonction quadratique de la coordonée radiale. A cet écoulement non visqueux, dont la vitesse moyenne est arbitraire, l'on superpose des perturbations de faible amplitude. Une analyse linéarisée montre que le profil de vitesse et donc le rotationel de l'écoulement de base influencent d'autant plus ce phénomène d'ondes que est élévée.Ceci met en question la théorie uni-dimensionelle de la propagation d'ondes dans des tubes compliants et, par là-même, l'interpretation de divers problèmes physiologiques et médicaux, avant tout des systèmes respiratoires et cardio-vasculaires.

     

On the aerodynamic heating of blunt bodies

Zusammenfassung Die Berechnung der Erw?rmung stumpfer Flugk?rper wird für grosse Geschwindigkeiten in Berücksichtigung der übergangserscheinungen er?rtert. Im besondern wird auf das Problem der Abkühlung durch Massentranspiration eingegangen.

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This research was supported by the United States Air Force, through the Air Force Office of Scientific Research of the Air Research and Development Command, under contract AF 18(600)-786.     

A submodel of the rotational motions of a gas in a uniform force field

An invariant submodel, constructed using a subalgebra of the sum of the rotation, time transfer and Galilean transfer is considered within the framework of the Podmodeli program [1]. A group classification is constructed and simple solutions are obtained. The submodel is reduced to symmetrical form. Assertions are made on the hyperbolicity, characteristics and force discontinuities. The necessary conditions far solutions to exist without discontinuities on the axis of symmetry are derived and their asymptotic submodel is investigated.     

On the error estimates for the rotational pressure-correction projection methods

In this paper we study the rotational form of the pressure-correction method that was proposed by Timmermans, Minev, and Van De Vosse. We show that the rotational form of the algorithm provides better accuracy in terms of the -norm of the velocity and of the -norm of the pressure than the standard form.

     

On the maximal operator associated with certain rotational invariant measures

The aim of this work is to investigate the integrability properties of the maximal operator Mu,associated with a non-doubling measure μ defined on Rn. We start by establishing for a wide class of radial and increasing measures μ that Mu is bounded on all the spaces Lu^p（R^n）,P〉1.Also,we show that there is a radial and increasing measure p for which Mμ does not map Lμ^p（R^n） into weak Lμ^p（R^n）,1≤p〈∞.     

On a phase-change problem arising from inductive heating

In this paper we study a phase-change problem arising from induction heating. The mathematical model consists of time-harmonic Maxwell’s system in a quasi-stationary field coupled with nonlinear heat conduction. The enthalpy form is used to characterize the phase-change in the material. It is shown that the problem has a global solution. Moreover, it is shown that the solution is unique and regular in one-space dimension even with an unbounded resistivity. This work is supported in part by a NSF grant: DMS-0102261     

Kinetic model of the Boltzmann equation for a diatomic gas with rotational degrees of freedom

A system of model kinetic equations is proposed to describe flows of a diatomic rarefied gas (nitrogen). A conservative numerical method is developed for its solution. A shock wave structure in nitrogen is computed, and the results are compared with experimental data in a wide range of Mach numbers. The system of model kinetic equations is intended to compute complex-geometry three-dimensional flows of a diatomic gas with rotational degrees of freedom.     

Analytic solution to the problem of the temperature jump in a gas with rotational degrees of freedom

An exact solution is obtained for the first time for the problem of the temperature jump in a gas with allowance for internal (rotational) degrees of freedom. The treatment is based on a model collision integral proposed by the authors. The problem reduces to the solution of a boundary-value problem for a linear vector transport equation with matrix kernel. Separation of the variable leads to a characteristic equation for which eigenvectors are found in a space of generalized functions and the eigenvalue spectrum is investigated. An expansion of the solution to the problem with respect to eigenvectors of the continuous and discrete spectra is established. On the basis of the conditions of solvability of the vector Riemann-Hilbert boundary-value problem which arises in the process of the proof, an exact (in closed form) expression is obtained for the temperature jump.Moscow Pedagogical University. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 95, No. 3, pp. 530–540, June, 1993.     

On a nonlocal problem modelling Ohmic heating in planar domains

In this paper, we consider the nonlocal problem of the form ut-Δu = (λe-u)/(∫Ωe-udx)2,x ∈Ω, t0 and the associated nonlocal stationary problem -Δv = (λe-v)/(∫Ωe-vdx)2, x ∈Ω,where λ is a positive parameter. For Ω to be an annulus, we prove that the nonlocal stationary problemhas a unique solution if and only if λ 2| Ω| 2 , and for λ = 2|Ω|2, the solution of the nonlocal parabolic problem grows up globally to infinity as t →∞.     

On a nonideal Bose gas model

We consider a polynomial generalization of the Huang-Davies model in the nonideal Bose gas theory. We prove that the Gaussian dominance condition is fulfilled for all values of the chemical potential. We show that the lower bound for the critical temperature in the Huang-Davies model obtained by the infrared bound method coincides with the exact value of this quantity in the Davies theory. Using the large deviation principle, we prove a possibility of a generalized Bose condensation in the polynomial model. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 120, No. 1, pp. 130–143, July, 1999.