摘要:

Recent experiments have disclosed electrical effects well ahead of an advancing shock front. Certain of these effects have been attributed to the diffusion of electrons through the shock front from the ionized region behind it. The diffusion hypothesis is examined in terms of a simple heuristic model, in which the diffusion is assumed to take place from a plane electron source moving with the shock velocity. According to this model, there is no true electron ``front,'' as has been suggested by some experiments with ionizing shocks. However, a transient in the electron distribution may give rise to a virtual front in certain experimental situations. Under reasonable assumptions, the existing observations of precursor fronts by Weymann are found to be consistent with the predictions of the model.

ISSN:0031-9171    

DOI:10.1063/1.1724453

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The natural generalization of the snowplow equation in two‐dimensional axisymmetric or Cartesian geometries is a Newtonian approximation in which the possibility of surface deformation is admitted. Such a general Newtonian approximation has been derived from the Lagrangian fluid equations, using an ideal‐gas model in the limit of strong shock and high density ratio across the shock front. In one dimension the result reduces properly to the snowplow equation. In two dimensions, if the surface is constrained and the motion steady, the result consists of the ``Newtonian plus Busemann'' terms. The general result contains in addition a Coriolis term. The general theory is applied to the evaluation of the pressure on the surface of a conical plasma whose vertex angle is decreasing uniformly with time. Although the results are derived for an ideal‐gas model, they are applicable whenever dissociation and ionization are taking place behind a strong shock front.

ISSN:0031-9171    

DOI:10.1063/1.1724454

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

``Steady extension'' is a flow possible in every incompressible simple fluid (Newtonian, non‐Newtonian, or viscoelastic) without neglect of inertia. A special example of this flow is realized by considering a cylindrical fluid mass which is being continually elongated (or shortened) at a rate proportional to its length. The behavior of a general simple fluid in steady extension is determined by material functions other than the viscosity and normal‐stress functions which govern viscometric flows.

ISSN:0031-9171    

DOI:10.1063/1.1724455

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The equilibrium‐interface technique has been suggested as a possible shock‐tunnel driver method. If this technique is workable, reservoir enthalpy levels can be increased substantially over those obtainable with the tailored‐interface technique without any physical modification of the shock tube. In order to determine the feasibility of the equilibrium‐interface technique as a shock‐tunnel driver method, experiments were performed in a shock tube, utilizing a cold helium driver over the shock Mach number range 3.29 to 7.26.Pressure histories were measured at the end of the driven tube; this pressure was found to reach an equilibrium condition for the complete shock Mach number range investigated. From the pressure histories the equilibrium pressure, time to reach equilibrium, and test time were determined. Measured equilibrium pressures were compared with those predicted from the measured shock Mach number. From the measured equilibrium pressure the equilibrium enthalpy level was computed. The maximum equilibrium enthalpy was more than six times the reservoir enthalpy produced using the tailored‐interface technique.

ISSN:0031-9171    

DOI:10.1063/1.1724456

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The laminar‐turbulent transition behind 0.500‐in.‐diameter spheres at 8500 ft/sec and behind 12.5° half‐angle cones at 5500 ft/sec in air have been measured as a function of pressure. Schlieren motion‐picture techniques were used to analyze the turbulent motion and the results are described. Autocorrelation functions of the density fluctuations of the turbulence have been measured. From these values &Dgr;&rgr;/&rgr; has been calculated and the results are given for several positions in the turbulent trail at 30 mm Hg downstream air pressure. In addition the authors' previous measurements of the gross radial growth of the turbulent wake have been extended to pressures of 10 mm Hg for the case of 0.500‐in.‐diameter spheres and to the trail behind 12.5° half‐angle cones for two pressures.

ISSN:0031-9171    

DOI:10.1063/1.1724457

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Numerical solutions have been obtained for one‐dimensional fluid flow problems involving shock and rarefaction waves by fixing attention, for the first time, on the energy of the fluid and following the motion of constantenergy cells, each of which contains a time‐dependent quantity of mass. This is analogous to the usual method which consists of solving the Lagrangian hydrodynamic equations and following the motion of constant‐mass cells, each of which contains a time‐dependent amount of energy. The method has been applied to problems in which the total energy of the fluid is a constant. Solution by finite‐difference techniques leads to a stability criterion which can be less restrictive than that obtained from the Lagrangian equations and hence give shorter computational times.

ISSN:0031-9171    

DOI:10.1063/1.1724458

出版商:AIP    

年代:1962

数据来源: AIP

ISSN:0031-9171    

DOI:10.1063/1.1724459

出版商:AIP    

年代:1962

数据来源: AIP

ISSN:0031-9171    

DOI:10.1063/1.1724460

出版商:AIP    

年代:1962

数据来源: AIP

ISSN:0031-9171    

DOI:10.1063/1.1724461

出版商:AIP    

年代:1962

数据来源: AIP

ISSN:0031-9171    

DOI:10.1063/1.1724462

出版商:AIP    

年代:1962

数据来源: AIP