scholarly journals The decay of turbulence generated by a class of multiscale grids

2011 ◽  
Vol 687 ◽  
pp. 300-340 ◽  
Author(s):  
P. C. Valente ◽  
J. C. Vassilicos
Keyword(s):  
Reynolds Number ◽  
Dissipation Rate ◽  
High Reynolds Number ◽  
Transverse Energy ◽  
Mean Flow ◽  
Integral Scale ◽  
Square Grid ◽  
Turbulence Decay ◽  
Classical Behaviour ◽  
High Reynolds

AbstractA new experimental investigation of decaying turbulence generated by a low-blockage space-filling fractal square grid is presented. We find agreement with previous works by Seoud & Vassilicos (Phys. Fluids, vol. 19, 2007, 105108) and Mazellier & Vassilicos (Phys. Fluids, vol. 22, 2010, 075101) but also extend the length of the assessed decay region and consolidate the results by repeating the experiments with different probes of increased spatial resolution. It is confirmed that this moderately high Reynolds number${\mathit{Re}}_{\lambda } $turbulence (up to${\mathit{Re}}_{\lambda } \simeq 350$here) does not follow the classical high Reynolds number scaling of the dissipation rate$\varepsilon \ensuremath{\sim} {u{}^{\ensuremath{\prime} } }^{3} / L$and does not obey the equivalent proportionality between the Taylor-based Reynolds number${\mathit{Re}}_{\lambda } $and the ratio of integral scale$L$to the Taylor microscale$\lambda $. Instead we observe an approximate proportionality between$L$and$\lambda $during decay. This non-classical behaviour is investigated by studying how the energy spectra evolve during decay and examining how well they can be described by self-preserving single-length-scale forms. A detailed study of homogeneity and isotropy is also presented which reveals the presence of transverse energy transport and pressure transport in the part of the turbulence decay region where we take data (even though previous studies found mean flow and turbulence intensity profiles to be approximately homogeneous in much of the decay region). The exceptionally fast turbulence decay observed in the part of the decay region where we take data is consistent with the non-classical behaviour of the dissipation rate. Measurements with a regular square mesh grid as well as comparisons with active-grid experiments by Mydlarski & Warhaft (J. Fluid Mech., vol. 320, 1996, pp. 331–368) and Kang, Chester & Meveneau (J. Fluid Mech., vol. 480, 2003, pp. 129–160) are also presented to highlight the similarities and differences between these turbulent flows and the turbulence generated by our fractal square grid.

scholarly journals The streamwise turbulence intensity in the intermediate layer of turbulent pipe flow

2015 ◽  
Vol 774 ◽  
pp. 324-341 ◽  
Author(s):  
J. C. Vassilicos ◽  
J.-P. Laval ◽  
J.-M. Foucaut ◽  
M. Stanislas
Keyword(s):  
Reynolds Number ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Intermediate Layer ◽  
High Reynolds Number ◽  
Logarithmic Derivative ◽  
Turbulent Pipe Flow ◽  
Mean Flow ◽  
The Mean ◽  
High Reynolds

The spectral model of Perryet al. (J. Fluid Mech., vol. 165, 1986, pp. 163–199) predicts that the integral length scale varies very slowly with distance to the wall in the intermediate layer. The only way for the integral length scale’s variation to be more realistic while keeping with the Townsend–Perry attached eddy spectrum is to add a new wavenumber range to the model at wavenumbers smaller than that spectrum. This necessary addition can also account for the high-Reynolds-number outer peak of the turbulent kinetic energy in the intermediate layer. An analytic expression is obtained for this outer peak in agreement with extremely high-Reynolds-number data by Hultmarket al. (Phys. Rev. Lett., vol. 108, 2012, 094501;J. Fluid Mech., vol. 728, 2013, pp. 376–395). Townsend’s (The Structure of Turbulent Shear Flows, 1976, Cambridge University Press) production–dissipation balance and the finding of Dallaset al. (Phys. Rev. E, vol. 80, 2009, 046306) that, in the intermediate layer, the eddy turnover time scales with skin friction velocity and distance to the wall implies that the logarithmic derivative of the mean flow has an outer peak at the same location as the turbulent kinetic energy. This is seen in the data of Hultmarket al. (Phys. Rev. Lett., vol. 108, 2012, 094501;J. Fluid Mech., vol. 728, 2013, pp. 376–395). The same approach also predicts that the logarithmic derivative of the mean flow has a logarithmic decay at distances to the wall larger than the position of the outer peak. This qualitative prediction is also supported by the aforementioned data.

On the theory of unsteady high Reynolds number flow through a circular aperture

1979 ◽  
Vol 366 (1725) ◽  
pp. 205-223 ◽  
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
High Reynolds Number ◽  
Circular Aperture ◽  
Mean Flow ◽  
Reynolds Number Flow ◽  
Contraction Ratio ◽  
Number Flow ◽  
Flow Through ◽  
High Reynolds

This paper examines the theory of the unsteady motion caused by fluctuations in the driving pressure of a high Reynolds number mean flow through a circular aperture in a thin rigid plate. A theoretical model is proposed which is amenable to exact analytical treatment, and involves the shedding of vorticity from the rim of the aperture. The theory determines the dependence of the Rayleigh conductivity of the aperture on the Strouhal number, and provides quantitative estimates for the rate of dissipation of large scale ordered structures as a result of the generation of turbulence at the apertures in a perforated liner. The limit of zero Strouhal number yields a description of steady high Reynolds number flow, the contraction ratio of the emerging jet being predicted to be equal to the minimum theoretical value of ½. Application is made to the problem of sound trans­mission through a uniformly perforated screen in the presence of a low Mach number bias flow.

A Modified Form of the k-ε Model for Predicting Wall Turbulence

1981 ◽  
Vol 103 (3) ◽  
pp. 456-460 ◽  
Author(s):  
C. K. G. Lam ◽  
K. Bremhorst
Keyword(s):  
Reynolds Number ◽  
Pipe Flow ◽  
Dissipation Rate ◽  
High Reynolds Number ◽  
Present Form ◽  
Wall Turbulence ◽  
Wall Region ◽  
Wall Function ◽  
High Reynolds ◽  
Number Form

The high Reynolds number form of the k-ε model is extended and tested by application to fully developed pipe flow. It is established that the model is valid throughout the fully turbulent, semilaminar and laminar regions of the flow. Unlike many previously proposed forms of the k-ε model, the present form does not have to be used in conjunction with empirical wall function formulas and does not include additional terms in the k and ε equations. Comparison between predicted and measured dissipation rate in the important wall region is also possible.

scholarly journals The Spatial Structure of Homogeneous Turbulence at High Reynolds Number

1991 ◽  
Vol 130 ◽  
pp. 75-79
Author(s):  
A. Vincent ◽  
M. Meneguzzi
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
High Reynolds Number ◽  
Three Dimensional ◽  
Physical Space ◽  
Inertial Subrange ◽  
Integral Scale ◽  
Turbulent Field ◽  
High Reynolds ◽  
Typical Length

AbstractA direct numerical simulation at resolution 2403 is used to obtain a statistically stationary three-dimensional homogeneous and isotropic turbulent field at a Reynolds number around 1000 (Rλ ≈ 150). The energy spectrum displays an inertial subrange extending over more than one decade. In the physical space, the strongest vorticity is organized in very elongated thin tubes. The typical length of a tube is around the integral scale of the flow and its thickness is a few dissipation scales.

Reynolds Number Effects in Wall-Bounded Turbulent Flows

1994 ◽  
Vol 47 (8) ◽  
pp. 307-365 ◽  
Author(s):  
Mohamed Gad-el-Hak ◽  
Promode R. Bandyopadhyay
Keyword(s):  
Reynolds Number ◽  
Coherent Structures ◽  
High Reynolds Number ◽  
Stokes Equations ◽  
Reynolds Numbers ◽  
Mean Flow ◽  
Reynolds Number Effects ◽  
The Mean ◽  
Low Reynolds ◽  
High Reynolds

This paper reviews the state of the art of Reynolds number effects in wall-bounded shear-flow turbulence, with particular emphasis on the canonical zero-pressure-gradient boundary layer and two-dimensional channel flow problems. The Reynolds numbers encountered in many practical situations are typically orders of magnitude higher than those studied computationally or even experimentally. High-Reynolds number research facilities are expensive to build and operate and the few existing are heavily scheduled with mostly developmental work. For wind tunnels, additional complications due to compressibility effects are introduced at high speeds. Full computational simulation of high-Reynolds number flows is beyond the reach of current capabilities. Understanding of turbulence and modeling will continue to play vital roles in the computation of high-Reynolds number practical flows using the Reynolds-averaged Navier-Stokes equations. Since the existing knowledge base, accumulated mostly through physical as well as numerical experiments, is skewed towards the low Reynolds numbers, the key question in such high-Reynolds number modeling as well as in devising novel flow control strategies is: what are the Reynolds number effects on the mean and statistical turbulence quantities and on the organized motions? Since the mean flow review of Coles (1962), the coherent structures, in low-Reynolds number wall-bounded flows, have been reviewed several times. However, the Reynolds number effects on the higher-order statistical turbulence quantities and on the coherent structures have not been reviewed thus far, and there are some unresolved aspects of the effects on even the mean flow at very high Reynolds numbers. Furthermore, a considerable volume of experimental and full-simulation data have been accumulated since 1962. The present article aims at further assimilation of those data, pointing to obvious gaps in the present state of knowledge and highlighting the misunderstood as well as the ill-understood aspects of Reynolds number effects.

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