Decay of a coherent scalar disturbance in a turbulent flow

  • 4.38 MB
  • English

National Aeronautics and Space Administration, Ames Research Center, For sale by the National Technical Information Service , Moffett Field, Calif, [Springfield, Va
StatementRobert M. Kerr, Tohru Nakano, Mark Nelkin.
SeriesNASA technical memorandum -- 86700.
ContributionsNakano, Tohru., Nelkin, Mark., Ames Research Center.
The Physical Object
Pagination1 v.
ID Numbers
Open LibraryOL15284372M

The decay of a single mode after the transition in the simulation best describes the experiment. The time evolution of an initially coherent, sinusoidal passive-scalar disturbance is considered when the wavelength q is less than the length scale of the surrounding isotropic turbulent : R.

Kerr, T. Nakano, M. Nelkin. Get this from a library. Decay of a coherent scalar disturbance in a turbulent flow. [Robert M Kerr; Tohru Nakano; Mark Nelkin; Ames Research Center.]. Decay of a coherent scalar disturbance in a turbulent flow.

Download Decay of a coherent scalar disturbance in a turbulent flow PDF

-scalar disturbance is considered when the wavelength q is less than the length scale of the surrounding isotropic turbulent flow. In 64 sup 3 direct numerical simulations a Gaussian prescription for the average scalar amplitude breaks down after a timescale associated with the Author: T.

Nakano, R. Kerr and M. Nelkin. particle diffusion. The decay of a single mode after the transition in the simulation best describes the experiment. Introduction In many experimental situations an initially coherent, passive-scalar disturbance, O(r,O), is added to a turbulent flow.

For example, a coherent disturbance. The corresponding conserved quantity J 2 (t) plays the same role in the turbulent decay of the magnetic field as played by the " Corrsin invariant " in the decay of the passive scalar [14, Decay of Scalar Turbulence Revisited M.

Chertkov1 and V. Lebedev1,2 1Theoretical Division, LANL, Los Alamos, New Mexico 2Landau Institute for Theoretical Physics, Moscow, Kosygina 2,Russia (Received 12 April ; published 23 January ) We demonstrate that at long times the rate of passive scalar decay in a turbulent, or simply chaotic.

The decay of scalar variance in isotropic turbulence in a bounded domain is investigated. Extending the study of Touil, Bertoglio and Shao (; Journal of Turbulence, 03, 49) to the case of a.

A simple extension of recent work by Larcheveque and Lesieur leads to a one parameter analytic expression for the decay of scalar variance in an isotropic homogeneous turbulent flow. The essential qualitative features of the Warhaft–Lumley experiment are by: 16 th Australasian Fluid Mechanics Conference Crown Plaza, Gold Coast, Australia December Effect of Initial Conditions on the Scalar Decay in Grid Turbulence at Low R A.

Benaissa 1, L. Djenidi 2, R. Antonia 2, R. Parker 2 1 Department of Mechanical Engineering, Royal Military College of Canada, Kingston Ontario, Canada 2 of Mechanical. The model approximates the scalar pdf in a general Decay of a coherent scalar disturbance in a turbulent flow book combusting flow by the pdf of reacting scalars decaying in homogeneous turbulence, parameterized by an appropriate set of lower moments.

The pdf construction model can be described by explaining the three major assumptions it is based by: Abstract The decay of homogeneous scalar fields in isotropic turbulence is addressed by considering the dispersion of particle pairs.

The evolution of the variance is studied by considering the dispersion backwards in time from the measurement time to the source by: The turbulent flow downstream of a single square grid is being experimentally investigated in a relatively small-sized wind tunnel.

2D LDV (Laser Doppler. Conversely, one may also study the diffusion in a turbulent flow whose velocity field is well documented experimentally.

This is done in the present section for a grid turbulence (see papers by Saetran et al., Gibson et al.), a turbulence submitted to a constant mean velocity (Stapountzis and Britter), and for the turbulent channel flow (Kim Author: M.

Lesieur. PDF approach for turbulent scalar field that the interaction between random turbulent advection and molecular diffusion distorts a Gaussian PDF to generate mild non-Gaussian tails (Gao et al.

), the clear exponential tails observed in these experiments cannot be explained within the frame of this interaction. The average kinetic energy (E ̂) is now considered splitting into a turbulent mean flow (1 2 m Γ u k u k ‾) and a contribution of asymmetry in the scalar field as shown in Fig.

Momentum conservation tells us that (1 2 m Γ u k u k ‾) 2 = - 1 2 u k ‾ (e → k ξ) 1 = ξ ∗, and eventually leading to the conservation of energy Author: S. Wattananusorn. Request PDF | Wall Turbulence and Its Coherent Structure | This chapter introduced fundamental concepts associated with the formation and evolution.

When the jet velocity is set to 20% of the uniform-flow velocity, a laminar-turbulent transition takes place, whereas in the 18% case, the disturbances created by the jet decay downstream. Budgets of the passive scalar variance and its dissipation rate are presented using the DNS data of a turbulent channel flow, with an imposed mean scalar gradient, by Wikström & Johansson [10].

Details Decay of a coherent scalar disturbance in a turbulent flow FB2

The Prandtl number is and the Reynolds number based on the wall friction velocity, uτ, and the channel half width is The advection of a passive substance by a turbulent flow is important in many natural and engineering settings.

The concentration of such a substance can exhibit complex dynamic behaviour that. This decomposition of a flow variable into a mean value and a turbulent fluctuation was originally proposed by Osborne Reynolds inand is considered to be the beginning of the systematic mathematical analysis of turbulent flow, as a sub-field of fluid dynamics.

While the mean values are taken as predictable variables determined by dynamics laws, the turbulent fluctuations. To realize the full potential of Direct Numerical Simulation in turbulent mixing studies, it is necessary to develop numerical schemes capable of sustaining the flow physics of turbulent scalar quantities.

In this work, a new scalar field forcing technique, termed “linear scalar forcing,” is presented and evaluated for passive scalars. It is compared to both the well-known mean scalar Cited by: Turbulent flow is s are complex multi-scale and chaotic motions that need to be classified into more elementary components, referred to coherent turbulent a structure must have temporal coherence, i.e.

it must persist in its form for long enough periods that the methods of time-averaged statistics can be applied. More recently, Mi et al.

Description Decay of a coherent scalar disturbance in a turbulent flow FB2

examined the flow field for two jets (one with a contraction nozzle, the other with a long pipe inlet) over 0 ≤ x / D ≤ 70 to verify the analytical results of George and confirmed that the turbulent scalar properties throughout the jet flow Cited by:   For stronger strain fields, but not strong enough to give persistent cat's eyes, the exponential decay of the disturbance varies: as time increases the decay slows down, because of the nonlinear feedback on the mean profile of the vortex.

This is confirmed by determining the decay rate given by the Landau pole for these modified by: 8. The flow is modeled with a direct numerical simulation, and the dispersion is modeled with Lagrangian methods based on Lagrangian scalar tracking (LST).

The LST technique allows the simulation of scalar sources that span a range of Prandtl or Schmidt numbers that cover orders of. Book contents Engineering Turbulence Modelling and Experiments 6 Procedings of the ERCOFTAC International Symposium on Engineering Turbulence Modelling and Measurements; ETMM6, Sardinia, Italy, 23–25 May, Cited by: 1.

SCALAR MIXING AND DISSIPATION RATE IN LARGE-EDDY SIMULATIONS OF NON-PREMIXED TURBULENT COMBUSTION HEINZ PITSCH and HELFRIED STEINER Center for Turbulence Research Flow Physics and Computation Division Stanford University Stanford, CAUSA Predictions of scalar mixing and the scalar dissipation rate from large-eddy.

In the second turbulent phase, the SBR core breaks down, turbulence starts to decay exponentially and the kinetic energy of the mean flow decays logarithmically.

Eventually, the flow relaminarises and the velocity profile of the analytical solution for purely laminar decay is recovered, albeit at an earlier temporal instant due to the net.

In a laminar flow the scalar dissipation rate is defined (units are 1/s) as where is the diffusion coefficient of the scalar.

In turbulent flows, the scalar dissipation is seen as a scalar energy dissipation} and its role is to destroy (dissipate) scalar variance (scalar energy) analogous to the dissipation of the turbulent energy. There is also reduced turbulent scalar transport and dissipation compared with active turbulence of similar total energy.

These ideas have been used by Gibson [] in his physical modeling of this problem to derive criteria for discriminating stably stratified turbulent flow which is buoyancy-dominated from inertially-dominated (active Cited by: 5. The ‘problems’ associated with analysing different kinds of turbulent flow and different methods of solution are classified and discussed with reference to how the turbulent structure in a flow domain depends on the scale and geometry of the domain's boundary, and on the information provided in the boundary by:   KHAKPOUR, HAMID R.

SHEN, LIAN and YUE, DICK K. P. Transport of passive scalar in turbulent shear flow under a clean or surfactant-contaminated free surface. Journal of Fluid Mechanics, Vol.p. CrossRef; Google ScholarCited by: Structure and Mechanisms of Turbulence II Experimental investigation of velocity disturbance features in turbulent MHD duct flows.

H. Branover. Structure boundary layer density diffusion heat mechanics noise pressure radiation stability turbulence turbulent flow. Bibliographic information.

DOI https.