摘要:

Measurements of radiated noise and wall‐pressure fluctuations in a turbulent boundary layer in water are described. A comparison is made between results obtained in pure water and in dilute solutions of drag‐reducing polymers. A new experimental geometry was developed to obtain these measurements. The experiment consisted of a spiral‐shaped plate which was rotated about its central axis in a stationary fluid, generating a turbulent boundary layer upon its inner surface. This boundary layer is shown to resemble that upon a flat plate in a uniform free stream. Wall‐pressure fluctuations under the boundary layer were measured with piezoelectric transducers mounted flush in the wall of the spiral plate. Noise radiated from the boundary layer was measured with a stationary transducer located outside of the boundary layer. All measurements were made as a comparison between water and dilute polymer solutions. It is shown that polymer additives cause significant reductions in both the radiated noise and wall pressure spectra. These reductions are greatest at high frequencies, corresponding to Strouhal numbers greater than one.

ISSN:0031-9171    

DOI:10.1063/1.1694530

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The time evolution integrodifferential equation for the ensemble mean of an advected passive scalar is derived for a general ensemble of compressible flows. Eulerian one‐point,n‐time velocity correlation functions and their spatial derivatives are required in the equation. The equation is applied to a case for which an exact solution is already known, and the validity of certain formal operator manipulations is demonstrated. A simple closure is discussed and the results are compared with other established results. Suggestions for further studies are made.

ISSN:0031-9171    

DOI:10.1063/1.1694531

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Memory times are smaller for transverse velocity components than for longitudinal components. For the former less downstream‐upstream asymmetries are apparent in the optimal space‐time isocorrelation contours.

ISSN:0031-9171    

DOI:10.1063/1.1694532

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A nonlinear analysis of the inviscid stability of a cylindrical vortex enclosing a central jet of light or dense fluid is presented. A uniformly valid second‐order expansion is obtained using the method of multiple time scales. For a stagnant core surrounded by a potential vortex, the axisymmetric mode remains stable to various scales of disturbances independent of core density. For asymmetric modes, the nonlinear effects make the stagnant core vortex sheet more unstable in second order for a given value of the core density. A central jet of any finite density always has a destabilizing effect on the jet‐vortex system undergoing any mode of deformation. A jet of any velocity tends to increase the unstable growth rates with increasing order of perturbations. The surface tension has a stabilizing effect with increasing order of perturbations. The frequency of oscillation becomes amplitude dependent in various orders of perturbations. The cylindrical surface departs significantly from its initially perturbed sinusoidal form and assumes an asinusoidal form.

ISSN:0031-9171    

DOI:10.1063/1.1694533

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

An initial value investigation is made of the motion of an incompressible, homogeneous, viscous fluid bounded by a porous plate with uniform suction or blowing. Both the plate and the fluid are in a state of solid body rotation with constant angular velocity about thezaxis normal to the plate, and additionally a nontorsional oscillation of a given frequency is superimposed on the plate for the generation of an unsteady flow in the rotating system. By using the Laplace transform technique, an exact solution of the three dimensional Navier‐Stokes equations for unsteady flow is obtained. The structure of the associated multiple boundary layers is determined. Effects of uniform suction (or blowing) and rotation on the flow phenomena are analyzed. Several known results of interest are found to follow as particular cases of the solution of the problem considered.

ISSN:0031-9171    

DOI:10.1063/1.1694534

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A boundary layer whose thickness is of the order of the mean free path squared divided by the radius of the curvature of the boundary is proposed to exist at the bottom of the kinetic boundary layer (or Knudsen layer) when the boundary is convex in shape.

ISSN:0031-9171    

DOI:10.1063/1.1694535

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The self‐diffusion coefficient of neon has been measured from 77° to 1400°K. The experimental values of the self‐diffusion coefficients are mutually consistent with experimental data for the viscosity and thermal conductivity of pure neon. The self‐diffusion data have been used to estimate values of the isotope thermal diffusion factor for neon and these estimated values are generally consistent with recent direct measurements of the thermal diffusion factor.

ISSN:0031-9171    

DOI:10.1063/1.1694536

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Observations of a highly structured discharge and current instability in unseeded shock heated argon flowing through a region of large transverse magnetic field are presented and analyzed. The experimental results are related to an extension of the theory of electrothermal (ionization) instability in partially ionized gases in which the presence of multiply charged ions is taken into account.

ISSN:0031-9171    

DOI:10.1063/1.1694537

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A model is developed for the momentum transferred to a solid from a laser‐supported gaseous detonation wave initiated in air above the surface. One‐dimensional gasdynamic analysis is used for the detonation wave moving away from the surface and cylindrical blast‐wave theory is employed to partially account for two dimensional effects. Momentum transfer coupling coefficients (impulse/laser energy) are calculated which are functions of the laser energy flux, pulse duration, and the beam and target surface areas. Results are compared with recent experimental data obtained using a high‐power CO2laser.

ISSN:0031-9171    

DOI:10.1063/1.1694538

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The effect of a cold wall on a hot plasma with initial uniform temperature and strong magnetic field parallel to the wall is studied. For physical values of thermal conductivity, resistivity, and electron‐ion equilibration coefficients, the full set of one‐fluid, two‐temperature equations is solved numerically. These results are then compared with analytic self‐similar solutions. The dynamic behavior of the plasma is presented. The total energy loss to the wall per unit area is evaluated and may be approximated rather well by an analytical expression derived from the fundamental equations.

ISSN:0031-9171    

DOI:10.1063/1.1694539

出版商:AIP    

年代:1973

数据来源: AIP