Theoretical study of turbulent channel flow: bulk properties, pressure fluctuations, and propagation of electromagnetic waves (original) (raw)

On the structure of turbulent channel flow

Journal of Fluid Mechanics, 1982

Hot-film measurements of the streamwise velocity component were carried out in a fully developed turbulent water-channel flow for three different Reynolds numbers (13 800, 34 600 and 48 900). The results for the first four statistical moments complement and extend the results from previous studies of turbulent channel flow. The VITA variance technique waa employed to detect deterministic events in the streamwise velocity. It waa demonstrated that the VITA technique has a band-pass-filter character. The number of events detected was found to decrerrae exponentially with the threshold level and the events occupy a wide range of timescales. This makes it impossible to define one unique frequency of occurrence or one unique duration of the events. However, by using this technique information was obtained on the amplitude and timescale distributions of the events. The chmacteristic features of the conditional iverages were found to be related to the skewness and flatness factors.

Behavior of uniform turbulence in channels of variable cross-sectional area

A system of equations for the rms components of the pulsation velocity vector and integral turbulence scales is derived on the basis of an equation describing the behavior of the spectral pulsation-velocity energy tensor for one-dimensional flow in a channel of variable cross-sectional area. For very low turbulence, the equations obtained lead to results of linear theory; for a constant cross-sectional area, they describe known empirical relations for the degeneration of turbulence behind cascades.

Fundamental Research in Turbulent Modeling, Part 1. Theory. Part 2. Experiment

Dataonthe mean and fluctuating velocity fields are presented for flow in a pipe with a central rod where the ratio of inner rod diameter to outer pipe diameter was .118. The measurements were taken at a downstream distance of 30 diameters and the turbulent intensities for the three fluctuating velocity components were obtained as a function of radius along with the Reynolds stress. Turbulent length scales were measured by use of time autocorrelation functions in conjunction with Taylor's hypothesis and by two-point correlation measurements using pure radial separations. The present results regarding the flow fields and length scales are compared with previous experimental results and our theoretical knowledge of such flows. p Unclassi fied SCueRITY CLASSIFICATION Of TuS PAOE(ftPn D.

Numerical investigation of turbulent channel flow

Journal of Fluid Mechanics, 1982

Fully developed turbulent channel flow has been simulated americally at. Reynolds number 19800, based on centerline velocity and channel half width. The large-scale flow field has been obtained by directly integrating the filtered, three-dimensional, tine-dependent, Davies-Stokes equations. The smallscale field motions were simulated through an eddy viscosity model. The calculations were carried out on the ILLIAC IV computer with up to 516,096 grid points. The computed flow field was used to study the statistical properties of the flow as well as its time-dependent features. The agreement of the computed mean velocity profile, turbulence statistics, and detailed flow structures with experimental data is good. The resolvable portion of the statistical correlations appearing in the Reynolds stress equations are calculated. Particular attention is given to the examination of the flow structure in the vicinity of the wall. I. Introduction Large-eddy simulation (LBS) is a relatively new approach to the calculation of turbulent flows. The basic idea stems from two experimental observations. First, the large-scale structure of turbulent flows varies greatly from flow to flow (e.g., jets vs. boundary layers) and consequently is difficult, if not impossible, to model in a general way. Second, the small-scale turbulence structures are nearly isotropic, very universal in character (Chapman, 1979) and hence such sore amenable to general modeling. In LBS, one actually calculates the large-scale notions in a time-dependent, three-*Portions of this work were carried out while the authors held NRC Research Associateships at Ames Research Center.

Model for propagation speed in turbulent channel flows

The propagation speed V c of the streamwise velocity fluctuations u in turbulent channel flows is calculated using direct numerical simulation (DNS) data at four Mach numbers (M = 0, 0.8, 2.0, and 3.0). The profiles of V c are shown to display remarkable similarity at different M. Quantitative models are developed based on a statistical structure called Velocity-Vorticity Correlation Structure (VVCS), defined as the vorticity region most correlated to velocity fluctuations at a fixed location. Good agreement with DNS-measured propagation velocities is obtained throughout the channel and for all M. The result confirms earlier speculation that the near-wall propagation is due to an advection by coherent vortex structures, and validates the concept of the VVCS.

Propagation velocity of perturbations in turbulent channel flow

Physics of Fluids A: Fluid Dynamics, 1993

Eigenmodes of averaged small-amplitude perturbations to a turbulent channel flow-which is one of the most fundamental canonical flows-are identified for the first time via an extensive set of high-fidelity graphics processing unit accelerated direct numerical simulations. While the system governing averaged small-amplitude perturbations to turbulent channel flow remains unknown, the fact such eigenmodes can be identified constitutes direct evidence that it is linear. Moreover, while the eigenvalue associated with the slowest-decaying anti-symmetric eigenmode mode is found to be real, the eigenvalue associated with the slowest-decaying symmetric eigenmode mode is found to be complex. This indicates that the unknown linear system governing the evolution of averaged small-amplitude perturbations cannot be self-adjoint, even for the case of a uni-directional flow. In addition to elucidating aspects of the flow physics, the findings provide guidance for development of new unsteady Reynolds-averaged Navier-Stokes turbulence models, and constitute a new and accessible benchmark problem for assessing the performance of existing models, which are used widely throughout industry.

Turbulence statistics in fully developed channel flow at low Reynolds number

Journal of Fluid Mechanics, 1987

A direct numerical simulation of a turbulent channel flow is performed. The unsteady Navier-Stokes equations are solved numerically at a Reynolds number of 3300, based on thc mean centreline velocity and channel half-width, with about 4 x los grid points (192 x 129 x 160 in 2, y, 2). All essential turbulence scales are resolved on the computational grid and no subgrid model is used. A large number of turbulence statistics are computed and compared with the existing experimental data at comparable Reynolds numbers. Agreements as well as discrepancies are discussed in detail. Particular attention is given to the behaviour of turbulence correlations near the wall. In addition, a number of statistical correlations which are complementary to the existing experimental data are reported for the first time. 10' 10' kz FIQURE 3. One-dimensional energy spectra: -, Euu; ----, Evv; ---, Eww. (a) Streamwise; ( b ) spanwise.

Scaling of the energy spectra of turbulent channels

Journal of Fluid Mechanics, 2004

The spectra and correlations of the velocity fluctuations in turbulent channels, especially above the buffer layer, are analysed using new direct numerical simulations with friction Reynolds numbers up to Re_{tau} {=} 1900. It is found, and explained, that their scaling is anomalous in several respects, including a square-root behaviour of their width with respect to their length, and a velocity scaling of the largest modes with the centreline velocity U_c. It is shown that this implies a logarithmic correction to the k(-1) energy spectrum, and that it leads to a scaling of the total fluctuation intensities away from the wall which agrees well with the mixed scaling of de Graaff & Eaton (2000) at intermediate Reynolds numbers, but which tends to a pure scaling with U_c at very large ones.

Low-Reynolds-number effects in a fully developed turbulent channel flow

Journal of Fluid Mechanics, 1992

Low-Reynolds-number effects are observed in the inner region of a fully developed turbulent channel flow, using data obtained either from experiments or by direct numerical simulations. The Reynolds-number influence is observed on the turbulence intensities and to a lesser degree on the average production and dissipation of the turbulent energy. In the near-wall region, the data confirm Wei & Willmarth's (1989) conclusion that the Reynolds stresses do not scale on wall variables. One of the reasons proposed by these authors to account for this behaviour, namely the 'geometry ' effect or direct interaction between inner regions on opposite walls, was investigated in some detail by introducing temperature at one of the walls, both in experiment and simulation. Although the extent of penetration of thermal excursions into the opposite side of the channel can be significant a t low Reynolds numbers, the contribution these excursions make to the Reynolds shear stress and the spanwise vorticity in the opposite wall region is negligible. In the inner region, spectra and cospectra of the velocity fluctuations u and v change rapidly with the Reynolds number, the variations being mainly confined to low wavenumbers in the u spectrum. These spectra, and the corresponding variances, are discussed in the context of the active/inactive motion concept and the possibility of increased vortex stretching a t the wall. A comparison is made between the channel and the boundary layer a t low Reynolds numbers.