Inhomogeneous Velocity Field Research Articles

The relativistic fermi gas in a nonuniform velocity field

Abstract We review the relativistic Fermi gas in an inhomogeneous velocity field and calculate components of the current vector and the energy-momentum tensor in a comoving frame. We derive quantum corrections to the classical distribution function in the framework of the grand canonical ensemble.

Comparison of CARS Measurements and Calculations of the Structure of Laminar Methane‐Air Counterflow Diffusion Flames

AbstractInformation on the structure of laminar diffusion flames under the influence of the strain of an inhomogeneous velocity field is essential for the understanding of turbulent diffusion flames.—To simulate the structure of the stagnation‐point flame the corresponding governing equations for enthalpy, momentum, and chemical species are to be solved. By boundary layer approximations and a coordinate transformation these equations are transformed into a one dimensional form, which is integrated with a finite differences method. Transport is described by a simplified multicomponent model. The detailed reaction mechanism consists of more than 250 elementary steps and 39 chemical species.—For comparison with the numerical results Coherent Anti‐Stokes Raman Scattering (CARS) is used to determine temperature and concentration profiles in an atmospheric pressure CH4/air counterflow diffusion flame. First a comparison between thermocouple and CARS measurements is done in a high temperature furnace up to 2000 K. The temperature dependent CARS spectra of N2 and O2 are evaluated by a computer program. Agreement between both techniques is obtained within 40 K over the complete temperature range. The same procedure is done with oxygen CARS spectra giving a temperature uncertainty of ± 80 K.—The comparison between the experimental and simulated temperature profiles shows satisfactory agreement on the fuel rich side but deviates significantly on the fuel lean side of the mixing layer. This discrepancy is ascribed to shortcomings in the model underlying the numerical simulation. Further ejaculations should therefore replace the use of boundary layer approximations by true two‐dimensional representations of the flow field.

Directional depth migration

Complicated geologic structures such as folds, overthrusts, and salt domes can produce reflectors with dips as great as 90 degrees. Because oil and gas accumulations are often associated with these steeply dipping interfaces, accurate processing of reflection seismic information from such areas becomes an important though challenging task. The proper imaging of steeply dipping reflectors requires accurate knowledge of the velocity field through which the wavefronts propagate. Thus, velocity analysis becomes extremely important. In addition to this problem, most migration algorithms have serious difficulties when dip is greater than about 50 degrees. In this discussion, we assume the velocity field is known, the data may be stacked correctly before migration, and the chief concern is migration accuracy. We describe a method for depth migration of very steeply inclined wavefronts through inhomogeneous velocity fields. The extension of the proposed technique to migration before stack is obvious.