Eddy viscosity distributions in a Mach 20 turbulent boundary layer
Shear stress and eddy viscosity distribution in Mach 20 compressible turbulent boundary layer, using mixing length flow theory
Bushnell, D. M.↗
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Effective eddy diffusion coefficient and atmospheric composition in the lower thermosphere
Lower thermosphere eddy diffusion coefficient effects on height variations in ionospheric composition
Shimazaki, T.↗
Laminarization model for turbulent eddy transport in highly accelerated nozzle turbulent boundary layers
A laminarization model which consists of a completely laminar sublayer region near the wall and a turbulent wake region is developed for the turbulent eddy transport in accelerated turbulent boundary layers. This laminarization model is used in a differential boundary layer calculation which was applied to nozzle flows. The resulting theoretical velocity profiles are in good agreement with the experimental nozzle data in the convergent region.
Schmidt, J. F.↗
Evaluation of eddy-current proximity devices for measuring thin potassium film thicknesses
Two eddy current proximity probe systems were tested over a range of 0 to 508 micrometers (0 to 20 mils) of simulated potassium film thicknesses for simulated temperatures of 66 C (150 F), 232 C (450 F), and 666 C (1230 F). The results of short time calibration tests are presented. Instrument drift was a problem throughout the testing and, without correction, may limit the use of such systems to short periods of time. Additional development will be required prior to their being usable as practical instrumentation systems.
Asadourian, A. S.↗
Turbulent-wake calculations with an eddy-viscosity model.
A simple eddy-viscosity model is shown to make it possible to calculate numerically the mean properties of a turbulent wake. Although the structure of the Reynolds stress terms is not resolved, the results obtained are adequate for predicting velocity profiles and displacement thicknesses.
Inouye, M.↗
Eddy-current testing
Eddy-current inspection is discussed as a method for locating subsurface flaws in electrically conductive materials. The physical principles and electrical circuitry are described along with the test equipment.
Pasley, R. L.↗
The effect of large-scale eddies on climatic change.
A parameterization for the fluxes of sensible heat by large-scale eddies developed in an earlier paper is incorporated into a model for the mean temperature structure of an atmosphere including only these fluxes and the radiative fluxes. The climatic changes in this simple model are then studied in order to assess the strength of the dynamical feedback and to gain insight into how dynamical parameters may change in more sophisticated climatic models. The model shows the following qualitative changes: (1) an increase in the solar constant leads to increased static stability, decreased dynamic stability, and stronger horizontal and vertical winds; (2) an increase in the amount of atmospheric absorption leads to decreased static and dynamic stability, and stronger horizontal and vertical winds; and (3) an increase in rotation rate leads to greater static and dynamic stability, weaker horizontal winds, and stronger vertical winds.
Stone, P. H.↗
Calculation of eddy viscosity in a compressible turbulent boundary layer with mass injection and chemical reaction, volume 2
As described in Vol. 1, the eddy viscosity is calculated through the turbulent kinetic energy, in order to include the history of the flow and the effect of chemical reaction on boundary layer characteristics. Calculations can be performed for two different cooling concepts; that is, transpiration and regeneratively cooled wall cases. For the regenerative cooling option, coolant and gas side wall temperature and coolant bulk temperature in a rocket engine can be computed along the nozzle axis. Thus, this computer program is useful in designing coolant flow rate and cooling tube geometry, including the tube wall thickness as well as in predicting the effects of boundary layers along the gas side wall on thrust performances.
Omori, S.↗
Initiation and structure of axisymmetric eddies in a rotating stream
Axisymmetric flow of a rotating stream is examined numerically to determine conditions under which an isolated eddy will form on the axis of rotation. An explicit finite difference procedure is used to integrate the time dependent transport equations. Solutions provide details of the flow structure and are presented for a range of Reynolds numbers and swirl ratios. Calculated results are interpreted in terms of recent physical experiments insofar as is possible.
Kopecky, R. M.↗
Calculation of eddy viscosity in a compressible turbulent boundary layer with mass injection and chemical reaction
The turbulent kinetic energy equation is coupled with boundary layer equations to solve the characteristics of compressible turbulent boundary layers with mass injection and combustion. The Reynolds stress is related to the turbulent kinetic energy using the Prandtl-Wieghardt formulation. When a lean mixture of hydrogen and nitrogen is injected through a porous plate into the subsonic turbulent boundary layer of air flow and ignited by external means, the turbulent kinetic energy increases twice as much as that of noncombusting flow with the same mass injection rate of nitrogen. The magnitudes of eddy viscosity between combusting and noncombusting flows with injection, however, are almost the same due to temperature effects, while the distributions are different. The velocity profiles are significantly affected by combustion. If pure hydrogen as a transpiration coolant is injected into a rocket nozzle boundary layer flow of combustion products, the temperature drops significantly across the boundary layer due to the high heat capacity of hydrogen. At a certain distance from the wall hydrogen reacts with the combustion products, liberating an extensive amount of heat.
Omori, S.↗
Eddy-current measurements of thickness of high-temperature coatings
The eddy-current technique was applied to measuring the thickness of a fused silicide coating on a refractory alloy slab. Phase and magnitude of the test signal were measured at four places in 13 different samples, and thickness of coating was computed on the basis of each of these quantities. These results were then compared with those obtained by conventional metallographic methods. Phase-based measurements were most reliable, and the maximum error between the metallographically determined thickness and the thickness as determined by the least squares fit to the phase measurements was less than 0.01 mm (about 1%). Photomicrography of a typical sample shows that a large source of error resides in the fact that two regions - an outer rough region and an inner uniform region - of the coating layer exist rather than the single region upon which the calculations were based.
Dodd, C. V.↗
Foam-machining tool with eddy-current transducer
Three-cutter machining system for foam-covered tanks incorporates eddy-current sensor. Sensor feeds signal to numerical controller which programs rotational and vertical axes of sensor travel, enabling cutterhead to profile around tank protrusions.
Copper, W. P.↗
On the development of noise-producing large-scale wavelike eddies in a turbulent jet
The development of large-scale wavelike eddies in a two-dimensional turbulent jet was studied. The basic mean flow develops from a mixing region type with an initial specified boundary layer thickness into a fully developed jet. The role of the varicose and sinuous modes as these develop in a growing mean flow is brought out. In general, it was found, for a given frequency parameter, the varicose mode has a shorter streamwise lifetime than the sinuous mode. The latter, for lower frequency ranges, persists past the end of the potential core only to be subject to dissolution by the more enhanced fine scale turbulent activity in that region.
Merkine, L. O.↗
Energy cascade in large-eddy simulations of turbulent fluid flows
The derivation of smoothed or filtered momentum and continuity equations for large-scale, energy-containing eddies is considered. Questions regarding the energy loss of large-scale turbulence are discussed along with aspects of turbulent diffusion of a passive scalar. It is found that the large-scale fluctuations satisfy filtered or averaged momentum and continuity equations. An averaging of the nonlinear advection term yields two terms.
Leonard, A.↗
On the development of noise-producing large-scale wavelike eddies in a plane turbulent jet
The paper studies the development of large-scale wavelike eddies in a two-dimensional turbulent jet, extending earlier work on the mixing region (Liu, 1974). The basic mean flow developes from one of mixing-region type with an initially specified boundary-layer thickness into a fully developed jet. This study brings out the role of the varicose and sinuous modes as they develop in a growing mean flow. In general, it is found that, for a given frequency parameter, the varicose mode has a shorter streamwise lifetime than the sinuous mode. For lower frequencies, the latter persists past the end of the potential core only to become subject to dissipation by the enhanced fine-scale turbulent activity in that region.
Merkine, L.-O.↗
Large eddy numerical simulations of turbulent flows
Large eddy simulations are a numerical technique in which large scale turbulent structures are explicitly computed and the small structures are modelled. Arguments for believing this method to be superior to more conventional approaches are given, the basis of the method is given, and some typical results displayed. The results show that the method does have enormous promise, but much further development is required.
Ferziger, J. H.↗
Improved methods for large-eddy simulations of turbulence
By using Fourier transforms for evaluating spatial derivatives, the accuracy of the large-eddy simulation of homogeneous isotropic turbulence is improved. Especially, the treatment of certain terms that arise in filtering the equations is considerably improved in both speed and accuracy. Use of vorticity as the principal variable is shown to be a viable and potentially useful alternative to the primitive variables. A method of deriving conservation properties of numerical schemes is given which is much simpler than previous methods and is widely applicable. The methods are applied to the computation of homogeneous isotropic turbulence, and it is found that the subgrid scale model is improved by using finite differences in place of 'exact' derivatives.
Mansour, N. N.↗
Extraction of the large eddy structure of a turbulent boundary layer
Much attention is currently being focused on turbulence modeling by separation of large-scale and small-scale turbulence. One major difficulty with this method is the problem of separating and defining the large-scale structure. In this paper, a method is presented which does this separation by analyzing time-averaged, two-point double velocity correlation measurements. The basis of the method is a maximization of the inner product of a candidate velocity field with the measured turbulent velocity field. An eigenvalue problem results, whose solution provides a set of orthogonal eigenfunctions associated with specific modes of turbulent motion. The large-scale eddy, containing most of the turbulent energy, is associated with the first (largest) mode. The turbulent velocity field is then represented as a sum of the eigenfunctions. A short description of the equations is given, the methods of solution are discussed, and some results for a two-dimensional fully developed turbulent boundary layer are presented.
Lemmerman, L. A.↗