摘要:

An asymptotic method based upon the principles of geometrical optics, which has been used for linear problems, is extended to nonlinear wave propagation in a rotating fluid of variable depth. It yields the same modes, the same phase function, and the same rays as does the linear theory. However along each ray the amplitude satisfies a nonlinear equation of Korteweg‐DeVries form. Thus, the theory combines certain features of the linear theory of short waves and the nonlinear theory of long waves. The theory is developed for a layer of fluid with a free surface or for an atmosphere which extends upward to infinity, and also for fluid in a channel or a waveguide. It may be useful in dealing with problems of geophysical interest.

ISSN:0031-9171    

DOI:10.1063/1.1694181

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

In the simplified case considered, particles decrease the critical temperature difference for the onset of convection by increasing the heat capacity of the fluid. A proof of exchange of stabilities shows that there is no effect of particle drag when instability sets in, although the rate at which unstable perturbations grow is affected by this factor. Thermal force alone can, in principle, give rise to instability in layers heated from above or below. The results are discussed with reference to experiments in gas‐particle mixtures which show “columnar instabilities” at unusually low‐temperature differences.

ISSN:0031-9171    

DOI:10.1063/1.1694182

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The effects of foreign gas mass addition of classical boundary layer magnitude on the compressible flow past a hot (cold) flat plate in a high‐speed uniform air flow are studied. In the case of a wall injection distributionm = C (2 x Re)−1/2, it is shown that there is a critical value ofCdepending upon the injected species properties, for which classical boundary layer theory fails. An interaction theory is developed which is uniformly valid in the limitRe→∞. The analysis is based on a three layer model consisting of inviscid rotational injectant regionO (Re−1/3)in thickness, a free viscous shear layerOO(Re−1/2), and the potential external flow. It is shown that the displacement effect of the thick injectant layer causes a correction to the external flow which results in a weak interaction favorable pressure gradient. The formulas for the pressure interaction and the wall shear indicate that the injection of a warm, low molecular weight gas has the most dramatic influence on the flow configuration. It is also shown that heat transfer to the wall is considerably reduced from the value predicted by classical boundary layer theory.

ISSN:0031-9171    

DOI:10.1063/1.1694183

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Strong temperature mixing in subsonic air turbulence is studied in an open‐circuit wind tunnel with a 0.5 m cross section. The specially constructed heating grid consumes up to 300 kW of electric power at a mean flow velocity of 11 m/sec. The highest mean absolute temperature⟨T⟩reaches 370°K, while the rms temperature fluctuation&thgr;′at midtunnel is typically 6°K. Basic statistics of the temperature field are measured and discussed. It is found, in particular, that (i) the streamwise decay of the normalized mean‐square temperature fluctuation(&thgr;′ / < T >)2is not sensitive to the applied heating rates, suggesting that so far buoyancy contributes little to the dynamics of the turbulence; (ii) the observed decay rates are much higher than those reported by others in the literature and are consistent with the higher drag characteristics of the present grid; (iii) the temperature fluctuation spectrum, when normalized by local fluid properties and dissipation rates, retains a universal form and show an inertial‐convection subrange of limited extent; (iv) the one‐dimensional universal scalar inertial Kolmogoroff constant,&bgr;1, determined from such subrange has a value of 0.60±0.06.

ISSN:0031-9171    

DOI:10.1063/1.1694184

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The Krook kinetic equation is used as the governing equation in an investigation of a class of exterior flow problems involving flow past an elliptic cylinder. A numerical method for solving the integral equation form of the Krook equation for this class of problems is described, and several sets of solutions are presented.

ISSN:0031-9171    

DOI:10.1063/1.1694185

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The conventional problem of linear transport theory is to find the distribution function given the various scattering functions. Here, the inverse question is asked. Given the results of some simple experiment how can one construct the kernels? First, the simple problem of one velocity neutron diffusion is considered, and it is found that the methods and solution are quite similar to that for the problem of deducing a potential given the scattering data. The solution given is constructive and seems to be efficient.

ISSN:0031-9171    

DOI:10.1063/1.1694186

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The gas dynamic structures of the transport shock and the downstream collisional relaxation layer are evaluated for partially ionized monatomic gases. Elastic and inelastic collisional nonequilibrium effects are taken into consideration. In the microscopic model of the atom, three electronic levels are accounted for. By using an asymtpotic technique, the shock morphology is found on a continuum flow basis. This procedure gives two distinct layers in which the nonequilibrium effects to be considered are different. A transport shock appears as the inner solution to an outer collisional relaxation layer. The results show four main interesting points: (i) On structuring the transport shock, ionization and excitation rates must be included in the formulation, since the flow is not frozen with respect to the population of the different electronic levels; (ii) an electron temperature precursor appears at the beginning of the transport shock; (iii) the collisional layer is rationally reduced to quadrature for special initial conditions, which (iv) are obtained from new Rankine‐Hugoniot relations for the inner shock.

ISSN:0031-9171    

DOI:10.1063/1.1694187

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Time‐resolved electron temperature measurements were taken behind incident normal shock waves in an arc‐driven shock tube using xenon as the test gas at an initial driven tube pressure of 0.1 Torr. At shock wave velocities from 6 to 10 km/sec, the two‐line intensity ratio technique involving the spectral lines of XeII was used to determine the electron temperature. The data indicate an electron temperature peak almost immediately behind the shock front which is well above the predicted equilibrium temperature. This peak temperature decays rapidly(∼ 1 &mgr;sec)to a plateau temperature well below the predicted equilibrium temperature. The importance of both radiative energy loss and ionizing collisions on the electron temperature decay is considered in the interpretation of the data.

ISSN:0031-9171    

DOI:10.1063/1.1694188

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Electron temperature measurements in the ionized xenon gas downstream of a shock front are obtained using brightness observations of the XeII 5292‐Å line. The results show good agreement with previous measurements obtained using a two line intensity ratio technique. A theoretical model of the shock structure is developed which considers nonequilibrium collisional and continuum radiative transitions. The theoretical calculations agree qualitatively with the experimental observations and indicate the paramount importance of radiative heating of the electron gas within that portion of the shock structure which is otherwise dominated by elastic and inelastic electron‐heavy particle collisions. The theoretical calculations also provide a detailed time history of the populations of the first four excited levels of XeII and indicate that the higher excited levels may justifiably be assumed in equilibrium with each other in a Boltzmann sense at the local electron temperature. Considered are shock velocities between 6.0 and 10.0 km/sec at an upstream pressure of 0.1 Torr.

ISSN:0031-9171    

DOI:10.1063/1.1694189

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A set of numerical computations of the thermal structure and optical luminosity of strong shock waves in air is described. The model includes radiation transport coupled with hydrodynamics under assumed conditions of steady flow. With shock velocities above 10 km/sec a thermal precursor develops ahead of the shock front, and increases in prominence with increasing shock strength. For velocities above 50 km/sec the precursor is partially opaque to visible light and the computed brightness is smaller than that of a blackbody at the shock temperature. At higher velocities the brightness decreases with increasing shock strength. Steady solutions could not be found for velocities above 80 km/sec.

ISSN:0031-9171    

DOI:10.1063/1.1694190

出版商:AIP    

年代:1973

数据来源: AIP