Small Flow Velocities Research Articles

Relationship between energetic particles and plasmas in the distant plasma sheet

Measurements of ions from three different instruments on the IMP‐7 and 8 spacecraft are combined to yield the differential energy spectra of ions over the entire energy range of ∼ 100 eV to 4 MeV in the earth’s distant (∼ 30 to ∼ 40 Re) plasma sheet. These spectra, obtained during times of relatively small bulk flow velocities, span the intensity range from ∼ 10−5 to 105 (cm²sec sr keV)−1, varying smoothly over the entire energy range both when the plasma is cold (∼ 1 keV) and hot (∼ 9 keV). Overall, the shape of the spectrum resembles a Maxwellian but with a high energy (≳ 50 keV) tail described well by a power law (⧜E−γ). The high energy tail is displaced in a parallel fashion to higher or lower intensities when the plasma is hot or cold, respectively. The transition between the Maxwellian and the power law occurs at E ≃ (γ + 1)kT. It is found that the energetic particle populations in the plasma sheet appear to be directly related to the mean thermal energies of the corresponding plasmas.

Optical Doppler instrument for measuring small turbulent flow velocities

7. L. A. Dushin et al., in: Retunable Gas Lasers [in Russian], Kiev (1973). 8. G. P. Arnautov, Avtometriya, No. 5 (1972). 9. N. B. Koshelyaevskii et al., Pis'ma v Zh. Eks. Teor. Fiz., 13, No. Ii (1971). i0. S. P. Borisovskii et al., Abstract of Papers Read at the Third All-Union Conference on "Physical foundations in transmitting information by means of laser radiations," Kiev (1973). Ii. M. I. Vol'nov et al., Abstracts of Papers Read at the Third All-Union Scientific-Technical Seminar on "Metrology and Radioelectronics ," Moscow (1975).

Dynamics of cylindrical structures subjected to axial flow

A general theory is presented for the dynamics of slender cylindrical beams immersed in purely axial, uniform and steady flow. The cylinders may be either isolated or be part of a cluster of identical cylinders. Gravity and pressurization effects are taken into account. It is shown that small flow velocities damp free motions, but that at sufficiently high flow velocities hydroelastic instabilities are possible. Typically, pinned-pinned (simply supported) cylinders are subject to buckling in their first mode, and then at higher flow velocities in their second mode; at slightly higher flow velocities, coupled-mode flutter is shown to occur. Close spacing in a cluster severely destabilizes the system. Cantilevered cylinders, on the other hand, may be subject to buckling in their first mode and to flutter in their higher modes. Finally, the case of cylinders in axial flow subjected to an arbitrary force field is discussed, and a method is developed by which the response may be obtained.

Numerical solution of the Navier-Stokes equations for flow of gas around a rectangle

A difference scheme of the Lax-Wendroff type was used to solve the Navier-Stokes equations for the problem of flow of a perfect gas around a rectangle (cylinder of rectangular cross section) with and without a front plate for subsonic, transonic, and small supersonic flow velocities (Mach numbers 0.3≤M≤2 and Reynolds numbers 1≤R≤250). The occurrence and development of front, lateral, and rear separation of the flow are discussed, and the aerodynamic characteristics of the considered bodies are determined.

Bidirectional blood flow velocity in the cardiac chambers and great vessels studied with the Doppler ultrasonic flowmeter

Utilizing the bidirectional Doppler flowmeter catheter system, phasic forward and reverse flow velocity was measured in the cardiac chambers and great vessels of man. Recordings of right atrial, right ventricular and aortic flow velocity are characterized by a small reverse flow velocity component, usually occurring during early diastole, followed by a large forward systolic wave. Blood flow velocity in the left ventricular outflow tract and pulmonary artery is forward with negligible or no reverse flow. Ventricular extrasystoles and ventricular tachycardia result in diminished systolic and enhanced retrograde aortic and right ventricular flow velocity, possibly based on valvular incompetence. Aortic regurgitation and tricuspid insufficiency can be identified by their characteristic diastolic and systolic reverse flow velocity patterns. Patients with an increase in right atrial pressure, regardless of its etiology, manifest significant reverse flow velocity toward the caval system. We conclude that this technic is a valuable method for measuring bidirectional flow velocity under normal and pathologic conditions.

Numerical study of viscous gas flow in the wake of a plane body

The gas flow in the wake behind a plate of finite thickness is considered using the Navier-Stokes equations, at subsonic, near-sonic and small supersonic flow velocities (0.3 \< M ,< 2, Re = 100) and Pr = 0.71 and 1 ,< Re,< 1000 (at M = 0.3). The problem is solved by the establishment method, using explicit twostep difference scheme of the Lax-Wendroff type. The influence of the Re and M numbers, the temperature factor, the thickness of the open viscous layer and the nature of the gas, on the flow parameters in the wake, is considered. The appearance and development of bottom separation in the flow are investigated. The paper is an extension and development of [l].

Numerical Simulation of Coning Using Implicit Production Terms

Abstract This paper describes the use of a multiphase, multidimensional mathematical model to predict two- and three-phase coning behavior. Severe computational instability in the form of saturation oscillations in grid blocks near the wellbore is commonly encountered in the mathematical simulation of coning. This instability is due to the explicit (dated at the beginning of a time step and held constant for that time step) handling of saturation - dependent transmissibilities and production terms in the finite-difference solution of production terms in the finite-difference solution of the flow equations. An analysis of stability with respect to explicit handling of saturation-dependent transmissibilities is presented in this paper. This analysis shows why explicit transmissibilities can result in a severe time-step restriction for coning simulation. The use of implicit production terms in the difference equations to reduce instabilities is discussed and examples are given. These examples show that the implicit handling of production terms alone can result in a fivefold increase and permissible time step for a coning simulation with virtually no increase in computing time per time step. A laboratory water-coning experiment was simulated and excellent agreement was obtained between computed and observed results. A three-phase coning example for a gravity-segregation reservoir is also presented. Introduction Simulation of coning behavior is normally done by numerically solving the flow equations expressed in cylindrical (r, z, theta) coordinates with symmetry in the theta direction. The finite-difference technique of numerical solution of differential equations requires that the portion of the reservoir being simulated be divided into grid blocks as shown in Fig. 1. Since coning is a well phenomenon and not a gross reservoir phenomenon, the grid blocks must necessarily be relatively small in the vicinity of the wellbore because both pressures and saturations vary rapidly in this region. Severe computational instability is commonly encountered in the simulation of coning due to the relatively small grid-block sizes and high flow velocities in the vicinity of the wellbore. During a time step that would be considered normal for most reservoir simulation problems, a block near the wellbore is required to pass a volume of fluid many times its pore volume. SPEJ P. 257

Measurement of low speed gas flows by particle trajectories: A new determination of free convection velocity profiles

The development of a method for the measurement of small flow velocities and the application of this method to the measurement of free convection velocity profiles in air is described. The method employed uses photographic techniques to measure the trajectories of small dust particles ( d < 6-6 μ) carried along with the flow. Factors affecting the measurement technique and the results of the measurement of two laminar free convection velocity profiles on a vertical flat plate are presented.

On Hydromagnetic Stability of Stationary Equilibria

Bernstein et al., showed that the stability of a hydromagnetic fluid in static equilibrium could be determined by an energy principle formalism. Those methods are extended to the consideration of the stability of stationary equilibria. The considerations lack the powerful theorems available for systems governed by Hermitian operators, but it has been possible to obtain some general results for this case. Linearized equations of motion and the boundary conditions in a Lagrangian representation are discussed. Some properties of the equations and a general sufficient condition for stability are given. A general perturbation theory for small flow velocities is presented. A reformulation of the equations in hamiltonian form, and an application of the theory, calculated by Pytte, to a rotating stabilized pinch configuration are appended. (B.O.G.)