Space-Time Correlation Structure of Hypersonic Boundary Layers

AIAA Journal ◽  
1976 ◽  
Vol 14 (2) ◽  
pp. 256-257 ◽  
Author(s):  
Anthony Demetriades ◽  
A. J. Laderman
Keyword(s):  
Boundary Layers ◽  
Time Correlation ◽  
Space Time ◽  
Correlation Structure ◽  
Hypersonic Boundary Layers

Structure of a high-Reynolds-number turbulent wake in supersonic flow

1984 ◽  
Vol 143 ◽  
pp. 277-304 ◽  
Author(s):  
J. P. Bonnet ◽  
V. Jayaraman ◽  
T. Alziary De Roquefort
Keyword(s):  
Reynolds Number ◽  
Supersonic Flow ◽  
Boundary Layers ◽  
High Reynolds Number ◽  
Time Correlation ◽  
Turbulent Wake ◽  
Turbulent Boundary Layers ◽  
Space Time ◽  
Trailing Edge ◽  
High Reynolds

An experimental study of a high-Reynolds-number turbulent wake in supersonic flow is performed using space and space–time correlation measurements by means of hot-wire anemometry. The correlations for the streamwise component of the mass-flux fluctuations are given for six stations starting from the trailing edge down to the asymptotic part. The validity of the Taylor's hypothesis is tested, the convection velocities are determined and the downstream evolution of the optimum space–time correlation is given; the frequency spectra are discussed and the integral lengths are analysed. Finally, the three-dimensional isocorrelation surfaces are given at the six test stations and discussed in relation to classical incompressible-flow results. The downstream evolution of the correlations shows that the two sides of the wake are statistically independent near the trailing edge, and a statistical link is gradually established during the wake development. A three-zonal description of wakes generated by fully developed turbulent boundary layers applies as well for mean quantities (velocity, width) as for turbulence correlations. In the near-wake region the overall structure of the isocorrelation curves is close to that observed in turbulent boundary layers in incompressible flows; some low-frequency phenomena are observed in this region. In the latest part of the wake, an asymptotic state is reached for all the correlation characteristics; the final state reached is not explained by the double-roller-eddy model established for lower-Reynolds-number wakes; it appears that wakes generated by fully turbulent boundary layers behave quite differently from initially laminar wakes, and new turbulent structure models for high-Reynolds-number wakes are to be devised.

Mechanism of stabilization of porous coatings on unstable supersonic mode in hypersonic boundary layers

2021 ◽  
Vol 33 (5) ◽  
pp. 054105
Author(s):  
Tiehan Long ◽  
Ying Dong ◽  
Rui Zhao ◽  
Chihyung Wen
Keyword(s):  
Boundary Layers ◽  
Porous Coatings ◽  
Hypersonic Boundary Layers

scholarly journals Spatial and space-time correlations in systems of subpopulations with genetic drift and migration.

Genetics ◽  
1993 ◽  
Vol 133 (3) ◽  
pp. 711-727
Author(s):  
B K Epperson
Keyword(s):  
Population Genetics ◽  
Time Correlation ◽  
Space Time ◽  
Spatial Correlations ◽  
Gene Frequencies ◽  
Migration Patterns ◽  
Migration Rates ◽  
Space And Time ◽  
Time Correlations ◽  
And Migration

Abstract The geographic distribution of genetic variation is an important theoretical and experimental component of population genetics. Previous characterizations of genetic structure of populations have used measures of spatial variance and spatial correlations. Yet a full understanding of the causes and consequences of spatial structure requires complete characterization of the underlying space-time system. This paper examines important interactions between processes and spatial structure in systems of subpopulations with migration and drift, by analyzing correlations of gene frequencies over space and time. We develop methods for studying important features of the complete set of space-time correlations of gene frequencies for the first time in population genetics. These methods also provide a new alternative for studying the purely spatial correlations and the variance, for models with general spatial dimensionalities and migration patterns. These results are obtained by employing theorems, previously unused in population genetics, for space-time autoregressive (STAR) stochastic spatial time series. We include results on systems with subpopulation interactions that have time delay lags (temporal orders) greater than one. We use the space-time correlation structure to develop novel estimators for migration rates that are based on space-time data (samples collected over space and time) rather than on purely spatial data, for real systems. We examine the space-time and spatial correlations for some specific stepping stone migration models. One focus is on the effects of anisotropic migration rates. Partial space-time correlation coefficients can be used for identifying migration patterns. Using STAR models, the spatial, space-time, and partial space-time correlations together provide a framework with an unprecedented level of detail for characterizing, predicting and contrasting space-time theoretical distributions of gene frequencies, and for identifying features such as the pattern of migration and estimating migration rates in experimental studies of genetic variation over space and time.

scholarly journals Investigation of Gas Seeding for Planar Laser-Induced Fluorescence in Hypersonic Boundary Layers

AIAA Journal ◽  
2015 ◽  
Vol 53 (12) ◽  
pp. 3637-3651 ◽  
Author(s):  
C. J. Arisman ◽  
C. T. Johansen ◽  
B. F. Bathel ◽  
P. M. Danehy
Keyword(s):  
Boundary Layers ◽  
Laser Induced Fluorescence ◽  
Hypersonic Boundary Layers ◽  
Planar Laser Induced Fluorescence ◽  
Planar Laser

Turbulence functions useful for probes (space–time correlation) and for scattering (wave-number–frequency spectrum) analysis

1968 ◽  
Vol 46 (23) ◽  
pp. 2683-2702 ◽  
Author(s):  
I. P. Shkarofsky
Keyword(s):  
Characteristic Size ◽  
Time Correlation ◽  
Exponential Model ◽  
Time Correlation Function ◽  
Maximum Energy ◽  
Confluent Hypergeometric Function ◽  
Space Time ◽  
Wave Number ◽  
Taylor’S Hypothesis ◽  
Number Frequency

The wave-number–frequency dependent spectral function, S(k, ω), and the space–time correlation function, C(r, t), are considered in a turbulent flowing plasma. The decay mechanisms are associated with either velocity fluctuations about the mean convection velocity or diffusion effects or attachment, or combinations of these, including the Brownian motion model. The ψ(k, ω) function, which is the ratio of S(k, ω) to its frequency-integrated value, depends on the mechanism and exhibits a profile which can be Gaussian, Lorentzian, a Z function, a Hermite polynomial modification of the Gaussian, or a confluent hypergeometric function. Anisotropic forms are also considered.The function C(r, t), obtained by convolving ψ (r, t) with C(r), the space autocorrelation function, is next considered. Adopting a Gaussian or an exponential model (which may be anisotropic) for C(r), we illustrate C(r, t) forms, which can readily be manipulated. Furthermore, letting r = 0, we derive two conditions for the applicability of Taylor's hypothesis. The assumption of frozen flow is not necessary, only that the root-mean-square Lagrangian displacement in a given time, associated with the decay, be much smaller than both the flow distance and the characteristic size of blobs having maximum energy.

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