In the past 30 years, there has been considerable progress in the development of large-eddy simulation (LES) for turbulent flows, which has been greatly facilitated by the substantial increase in computer power. In this paper, we raise some fundamental questions concerning the conceptual foundations of LES and about the methodologies and protocols used in its application. The 10 questions addressed are stated at the end of the introduction. Several of these questions highlight the importance of recognizing the dependence of LES calculations on the artificial parameter Δ (i.e. the filter width or, more generally, the turbulence resolution length scale). The principle that LES predictions of turbulence statistics should depend minimally on Δ provides an alternative justification for the dynamic procedure.

https://robots.iopscience.iop.org/article/10.1088/1367-2630/6/1/035/pdf

Ten questions concerning the large-eddy simulation of turbulent flows

The paper presents large-eddy simulation (LES) formalism, along with the various subgrid-scale models developed since Smagorinsky’s model. We show how Kraichnan’s spectral eddy viscosity may be implemented in physical space, yielding the structure-function model. Recent developments of this model that allow the eddy viscosity to be inhibited in transitional regions are discussed. We present a dynamic procedure, where a double filtering allows one to dynamically determine the subgrid-scale model constants. The importance of backscatter effects is discussed. Alternatives to the eddy-viscosity assumption, such as scale- similarity models, are considered. Pseudo-direct simulations in which numerical diffusion replaces subgrid transfers are mentioned. Various applications of LES to incompressible and compressible turbulent flows are given, with an emphasis on the generation of coherent vortices

New Trends in Large-Eddy Simulations of Turbulence

Dynamics and stability of lean-premixed swirl-stabilized combustion

https://iopscience.iop.org/article/10.1016/0169-5983(92)90023-P/pdf

New Insights into Large Eddy Simulation

Fluid dynamic turbulence is one of the most challenging computational physics problems because of the extremely wide range of time and space scales involved, the strong nonlinearity of the governing equations, and the many practical and important applications. While most linear fluid instabilities are well understood, the nonlinear interactions among them makes even the relatively simple limit of homogeneous isotropic turbulence difficult to treat physically, mathematically, and computationally. Turbulence is modeled computationally by a two-stage bootstrap process. The first stage, direct numerical simulation, attempts to resolve the relevant physical time and space scales but its application is limited to diffusive flows with a relatively small Reynolds number (Re). Using direct numerical simulation to provide a database, in turn, allows calibration of phenomenological turbulence models for engineering applications. Large eddy simulation incorporates a form of turbulence modeling applicable when the large-scale flows of interest are intrinsically time dependent, thus throwing common statistical models into question. A promising approach to large eddy simulation involves the use of high-resolution monotone computational fluid dynamics algorithms such as flux-corrected transport or the piecewise parabolic method which have intrinsic subgrid turbulence models coupled naturally to the resolved scales in the computed flow. The physical considerations underlying and evidence supporting this monotone integrated large eddy simulation approach are discussed.

New insights into large eddy simulation

Numerical simulations have been performed to study the flowfield and near-field noise of a supersonic rectangular jet with two paddles inserted into the flow. The paddles cause a strong flapping motion to develop that enhances mixing of the jet with the surroundings. These simulations have been used to determine the flapping motion's frequency, the mixing enhancement, the near-field noise, and the thrust loss associated with the paddles and to study the acoustic feedback mechanism that modulates the flapping motion. The flapping frequency has been estimated using the pitot pressure distributions at a sequence of times and Fourier analysis of the local pressure and z component of velocity. For paddles located x/h = 7.3 from the nozzle, where h is the narrow dimension of the nozzle, a frequency of 4700 Hz [St(h) = 0.136] with an amplitude of 157.5 dB at the nozzle lip has been predicted and is in agreement with experimental results. The pitot pressure drop, the mass, and the x-momentum fluxes along the flow direction have been used as a measure of jet mixing for jets with and without paddles inserted into the flow. In our numerical simulations, a control volume approach was used to estimate the thrust loss caused by the insertion of the paddles. The computational value of 13% is close to the experimental value of 14.4%, considering that the physical support for the paddles in the experiments is not included in the simulations. A special sequence of local pressure distribution plots, which highlight the acoustic waves, has been used to study the feedback mechanism that modulates the flapping motion.

Ronald Kolbe

Papers

New Insights into Large Eddy Simulation

New insights into large eddy simulation

Numerical Simulations of Flow Modification of Supersonic Rectangular Jets

Three dimensional large eddy simulations with realistic boundary conditions performed on a connection machine

Numerical simulations of flow modification of supersonic rectangular jets