Showing papers on "Rarefaction published in 1968"

Nonlinear shallow fluid flow over an isolated ridge

Abstract: The shallow water theory is applied to the study of one dimensional fluid flows over an isolated ridge. The work was motivated by the desire to investigate the phenomenon called the chinook which occurs on the eastern side of the Rockies and is characterized by extremely strong winds which blow from the mountains. The motion that arises from an initially uniform flow involves the formation of hydraulic jumps both on the windward and leeward sides of a ridge. Special emphasis is put on determining analytically the asymptotic structure of such flows with jumps by solving the appropriate "steady" state equations. The presence of the hydraulic jumps and a rarefaction wave was revealed by preliminary numerical solutions of the time dependent problems. These numerical results demonstrate the evolution in time of the various features of the flow found in the asymptotic solutions.

The structure of normal shock waves in a binary gas mixture

Abstract: A previous study of normal shock waves through numerical experiments with a simulated gas on a digital computer is extended to binary gas mixtures. The mixture is simulated by two sets of rigid elastic sphere molecules with the appropriate mass and diameter ratios. Velocity profile results for medium strength waves in a mixture of equal parts argon and helium are in qualitative agreement with the continuum calculations of Sherman (1960), but there is no initial acceleration of the argon in mixtures containing a very small initial mole fraction of this gas. The temperature profiles are similar to those for the velocity in that the argon profile lags behind the helium profile. However, when there is a small proportion of heavy gas, the profiles cross-over and the temperature of the heavy gas overshoots the Rankine-Hugoniot downstream value. For very strong shock waves, the overall shock thickness expressed in upstream mean free paths becomes larger, but the profiles are generally similar to those for the medium strength waves.

Calculations of expanding shock waves and late-stage equivalence

Abstract: : A numerical scheme based on the method of characteristics is developed and applied to the flow field of the expansion of a high pressure sphere into atmosphere. It is shown that this method is very accurate, involving errors of less than 1%. In calculating the expanding sphere, two rather challenging problems, namely, the initial singularity and the formation of a second shock, are successfully solved through special techniques. The formation of an inward traveling shock, in addition to the main shock, is found to exist at the tail of the left traveling rarefaction wave. The strength of the second shock remains rather weak at the early stage of its development, it becomes very strong just before reaching the center of the sphere. It is shown that 'late-stage equivalence' exists in the expansion of high pressure spheres into atmosphere, provided the initial total energy in each of the spheres is held constant. Late-stage equivalence is assumed to exist if the peak pressure distribution for different expanding spheres are the same for long times.

Area waves in a theta pinch.

Abstract: Measurements made in the mid-plane of a theta pinch plasma indicate a sudden decrease in line density. This is interpreted as the arrival of a rarefaction wave due to axial plasma loss. Detailed predictions of density, and β given by an axial MHD computation, are in good agreement with the observations.

Electromagnetic production of shock waves

Abstract: When a force is suddenly exerted within a confined region of a flow channel on a gas at rest, a shock wave and a rarefaction wave are set up in opposite directions. This situation arises, with heat being generated in addition, when crossed electric and magnetic fields E and B are suddenly applied to an electrically conductive gas at rest. In dependence on the total force P and the total energy input W per second, the asymptotic solutions are investigated toward which the state of flow converges as force and energy input become stationary. For strong shocks the Mach number is proportional to P1/2 and W2/3. If the power W is supplied by a battery with fixed data, M as a function of the applied magnetic field B has a maximum. It is supposed that some of the results are also approximately valid for T-tubes at times immediately following the discharge.

An Aluminum Splash Generated by Impact of a Detonation Wave

Abstract: Experimental observations are presented of two‐dimensional flow attending the impact of a detonation wave with an aluminum target plate. A time sequence of flash radiographs of the events provides a means for measuring the formation and growth of the resulting splash. Space‐time histories of various features of the splash are presented. The radiographs also display the course of the reflected shock in the explosive products, the shock transmitted into the target, the rarefaction wave which arises when this latter shock strikes the free surface of the target, the spalling resulting from this rarefaction wave, and the flow of the gases expanding from the burned explosive. Adequate equation of state data exist for both the gaseous products of the high explosive and the aluminum whereby the gross features that are observed can be replicated by today's computer techniques. However, viscosity and dynamic shear and tensile strengths, as functions of local conditions, are needed before a complete computer represe...

Aerosol Rarefaction Studies

Abstract: An experimental study was carried out to study the relative stabilities of charged and uncharged aerosols. The clouds differed in that charged aerosol had been passed through a DC corona. The aerosol was continuously generated at a point in a low-velocity wind tunnel in which relative cloud and tunnel dimensions practically eliminated wall effects. Aerosol cloud dimensions were determined at several distances downwind from the point of generation for both charged and uncharged aerosols. The rarefaction phenomenon produced as a result of the unipolar charging was measured for both positive and negative corona. The relative effects are noted. The point at which aerodynamic effects predominate over electrostatic effects is noted. The several forces affecting the interparticle spacing are considered in explaining the phenomena noted in these experiments.