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Stably stratified Taylor–Green vortex simulations are performed by lattice Boltzmann methods (LBM) and compared to other recent works using Navier–Stokes solvers. The density variation is modeled with a separate distribution function in addition to the particle distribution function modeling the flow physics. Different stencils, forcing schemes, and collision models are tested and assessed. The overall agreement of the lattice Boltzmann solutions with reference solutions from other works is very good, even when no explicit subgrid model is used, but the quality depends on the LBM setup. Although the LBM forcing scheme is not decisive for the quality of the solution, the choice of the collision model and of the stencil are crucial for adequate solutions in underresolved conditions. The LBM simulations confirm the suppression of vertical flow motion for decreasing initial Froude numbers. To gain further insight into buoyancy effects, energy decay, dissipation rates, and flux coefficients are evaluated using the LBM model for various Froude numbers.

A far-field solver based on the acoustic analogy of Ffowcs Williams and Hawkings for acoustic problems with convection and vortical waves was implemented in the open source package Overture. The numerical calculations of CAA test cases showed good agreement with analytical solutions or results from measurements and simulation data from the literature. This paper presents the implemented solver and its verification. In futher work, the developed framework will be used to investigate jet-flap interaction and the emitted sound field, numerically.

A round jet with \(Re=3600\) and \(M=0.9\) as well as two planar nozzle-wing flap configurations were simulated by using LES. An evaluation was proposed to predict the effect of the instantaneous Lighthill sources, S, their linear components, \(S^{\mathrm {l}}\), and non-linear components, \(S^{\mathrm {n}}\). The simulations indicate that conclusions can be made regarding the directional characteristic of the emitted sound field. These findings were used in investigations of a nozzle-wing-flap configuration. The wing-nozzle configuration showed increased values of the mean Lighthill source terms on the bottom of the wing and flap, contrary to the case of an isolated wing.

Turbulent compressible flows are traditionally simulated using explicit time integrators applied to discretized versions of the Navier-Stokes equations. However, the associated Courant-Friedrichs-Lewy condition severely restricts the maximum time-step size. Exploiting the Lagrangian nature of the Boltzmann equation’s material derivative, we now introduce a feasible three-dimensional semi-Lagrangian lattice Boltzmann method (SLLBM), which circumvents this restriction. While many lattice Boltzmann methods for compressible flows were restricted to two dimensions due to the enormous number of discrete velocities in three dimensions, the SLLBM uses only 45 discrete velocities. Based on compressible Taylor-Green vortex simulations we show that the new method accurately captures shocks or shocklets as well as turbulence in 3D without utilizing additional filtering or stabilizing techniques other than the filtering introduced by the interpolation, even when the time-step sizes are up to two orders of magnitude larger compared to simulations in the literature. Our new method therefore enables researchers to study compressible turbulent flows by a fully explicit scheme, whose range of admissible time-step sizes is dictated by physics rather than spatial discretization.

A new class of one-dimensional solar wind models is developed within the general polytropic, single-fluid hydrodynamic framework. The particular case of quasi-adiabatic radial expansion with a localized heating source is considered. We consider analytical solutions with continuous Mach number over the entire radial domain while allowing for jumps in the flow velocity, density, and temperature, provided that there exists an external source of energy in the vicinity of the critical point which supports such jumps in physical quantities. This is substantially distinct from both the standard Parker solar wind model and the original nozzle solutions, where such discontinuous solutions are not permissible. We obtain novel sample analytic solutions of the governing equations corresponding to both slow and fast wind., 13 pages, 3 figures, MNRAS, Accepted for publication

This work thoroughly investigates a semi-Lagrangian lattice Boltzmann (SLLBM) solver for compressible flows. In contrast to other LBM for compressible flows, the vertices are organized in cells, and interpolation polynomials up to fourth order are used to attain the off-vertex distribution function values. Differing from the recently introduced Particles on Demand (PoD) method [Dorschner, Bosch, and Karlin, Phys. Rev. Lett. 121, 130602 (2018)PRLTAO0031-900710.1103/PhysRevLett.121.130602], the method operates in a static, nonmoving reference frame. Yet the SLLBM in the present formulation grants supersonic flows and exhibits a high degree of Galilean invariance. The SLLBM solver allows for an independent time step size due to the integration along characteristics and for the use of unusual velocity sets, like the D2Q25, which is constructed by the roots of the fifth-order Hermite polynomial. The properties of the present model are shown in diverse example simulations of a two-dimensional Taylor-Green vortex, a Sod shock tube, a two-dimensional Riemann problem, and a shock-vortex interaction. It is shown that the cell-based interpolation and the use of Gauss-Lobatto-Chebyshev support points allow for spatially high-order solutions and minimize the mass loss caused by the interpolation. Transformed grids in the shock-vortex interaction show the general applicability to nonuniform grids.

The lattice Boltzmann method (LBM) facilitates efficient simulations of fluid turbulence based on advection and collision of local particle distribution functions. To ensure stable simulations on underresolved grids, the collision operator must prevent drastic deviations from local equilibrium. This can be achieved by various methods, such as the multirelaxation time, entropic, quasiequilibrium, regularized, and cumulant schemes. Complementing a part of a unified theoretical framework of these schemes, the present work presents a derivation of the regularized lattice Boltzmann method (RLBM), which follows a recently introduced entropic multirelaxation time LBM by Karlin, B\"osch, and Chikatamarla (KBC). It is shown that both methods can be derived by locally maximizing a quadratic Taylor expansion of the entropy function. While KBC expands around the local equilibrium distribution, the RLBM is recovered by expanding entropy around a global equilibrium. Numerical tests were performed to elucidate the role of pseudoentropy maximization in these models. Simulations of a two-dimensional shear layer show that the RLBM successfully reproduces the largest eddies even on a $16\ifmmode\times\else\texttimes\fi{}16$ grid, while the conventional LBM becomes unstable for grid resolutions of $128\ifmmode\times\else\texttimes\fi{}128$ and lower. The RLBM suppresses spurious vortices more effectively than KBC. In contrast, simulations of the three-dimensional Taylor-Green and Kida vortices show that KBC performs better in resolving small scale vortices, outperforming the RLBM by a factor of 1.8 in terms of the effective Reynolds number.

The admitted region of five joint irreducible invariants of the strain and rotation rate tensors calculated as the traces of the products of these tensors is determined.

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Pseudopotential-based lattice Boltzmann models are widely used for numerical simulations of multiphase flows. In the special case of multicomponent systems, the overall dynamics are characterized by the conservation equations for mass and momentum as well as an additional advection diffusion equation for each component. In the present study, we investigate how the latter is affected by the forcing scheme, i.e., by the way the underlying interparticle forces are incorporated into the lattice Boltzmann equation. By comparing two model formulations for pure multicomponent systems, namely the standard model [X. Shan and G. D. Doolen, J. Stat. Phys. 81, 379 (1995)JSTPBS0022-471510.1007/BF02179985] and the explicit forcing model [M. L. Porter et al., Phys. Rev. E 86, 036701 (2012)PLEEE81539-375510.1103/PhysRevE.86.036701], we reveal that the diffusion characteristics drastically change. We derive a generalized, potential function-dependent expression for the transition point from the miscible to the immiscible regime and demonstrate that it is shifted between the models. The theoretical predictions for both the transition point and the mutual diffusion coefficient are validated in simulations of static droplets and decaying sinusoidal concentration waves, respectively. To show the universality of our analysis, two common and one new potential function are investigated. As the shift in the diffusion characteristics directly affects the interfacial properties, we additionally show that phenomena related to the interfacial tension such as the modeling of contact angles are influenced as well.

Coaxial jets originating from a nozzle interacting with a two-element wing configuration consisting of a main wing and a flap are computed using large-eddy simulations (LES) to investigate in the long term the effect of the interaction on the sound field of this jet-wing-flap configuration. The secondary jet Mach number is \(M_s=0.37\) and the Reynolds number based on the secondary velocity and diameter is \(Re_{s}=1.32 \times 10^6\). The nozzle inlet boundary layers are modeled by Blasius velocity profiles with a boundary layer thicknesses of 20% of the nozzle channel half-width. The acoustic far-field is predicted by solving the linearized Euler equations (LEE) in a region attached to the LES domain. The jet streams interacts with the two-element wing configuration and lead to a significantly changed mean flow field in the wing-flap gap area and pressure at the wing surface. Additionally, a strong influence of the flap on the jet development is observed, especially in the case of a non-zero free stream velocity.

In forming processes of thermoplastic composites, the combined forming behaviour of matrix material and fibre reinforcement determines the resulting geometry and structure. These specific characteristics of the components and their interaction vary during the processing steps, especially for the matrix material with change in temperature. During the forming step, the molten thermoplastic polymer exhibits viscoelastic behaviour. Therefore, the fibres encounter resistance if a forming load is applied. The resulting fibre alignment is dependent on the forming temperature, the forming speed, and the time between the release of load and cooling. An investigation into the specific matrix characteristics during the forming step is presented. In the experiments a representing fibre is drawn through a molten polymer specimen under variation of speed and temperature and the resistance force is measured. The experimental findings are compared to numerical results obtained with a computational fluid dynamics (CFD) package using a finite volume approach and its ability for the prediction of fibre movement in molten matrix during forming processes is evaluated. In addition, a better understanding of the impact of forming speed and temperature during forming processes due to the characteristics of the molten matrix is obtained.

We propose and analyse a new strategy of shear flow turbulence control that can be realized by the following steps: (i) imposing specially designed seed velocity perturbations, which are non-symmetric in the spanwise direction, at the walls of a flow; (ii) the configuration of the latter ensures a gain of shear flow energy and the breaking of turbulence spanwise reflection symmetry: this leads to the generation of spanwise mean flow; (iii) that changes the self-sustained dynamics of turbulence and results in a considerable reduction of the turbulence level and the production of turbulent kinetic energy. In fact, by this strategy the shear flow transient growth mechanism is activated and the formed spanwise mean flow is an intrinsic, nonlinear composition of the controlled turbulence and not directly introduced in the system. In the present paper, a weak near-wall volume forcing is designed to impose the velocity perturbations with required characteristics in the flow. The efficiency of the proposed scheme has been demonstrated by direct numerical simulation using plane Couette flow as a representative example. A promising result was obtained: after a careful parameter selection, the forcing reduces the turbulence kinetic energy and its production by up to one-third. The strategy can be naturally applied to other wall-bounded flows, e.g. channel and boundary-layer flows. Of course, the considered volume force is theoretical and hypothetical. Nevertheless, it helps to gain knowledge concerning the design of the seed velocity field that is necessary to be imposed in the flow to achieve a significant reduction of the turbulent kinetic energy. This is convincing with regard to a new control strategy, which could be based on specially constructed blowing/suction or riblets, by employing the insight gained by the comprehension of the results obtained using the investigated methodology in this paper.

To understand the self-sustenance of subcritical turbulence in spectrally stable shear flows, we performed direct numerical simulations of homogeneous shear turbulence for different aspect ratios of the flow domain and analyzed the dynamical processes in Fourier space. There are no exponentially growing modes in such flows and the turbulence is energetically supported only by the linear growth of perturbation harmonics due to the shear flow non-normality. This non-normality-induced, or nonmodal growth is anisotropic in spectral space, which, in turn, leads to anisotropy of nonlinear processes in this space. As a result, a transverse (angular) redistribution of harmonics in Fourier space appears to be the main nonlinear process in these flows, rather than direct or inverse cascades. We refer to this type of nonlinear redistribution as the nonlinear transverse cascade. It is demonstrated that the turbulence is sustained by a subtle interplay between the linear nonmodal growth and the nonlinear transverse cascade that exemplifies a well-known bypass scenario of subcritical turbulence. These two basic processes mainly operate at large length scales, comparable to the domain size. Therefore, this central, small wave number area of Fourier space is crucial in the self-sustenance; we defined its size and labeled it as the vital area of turbulence. Outside the vital area, the nonmodal growth and the transverse cascade are of secondary importance. Although the cascades and the self-sustaining process of turbulence are qualitatively the same at different aspect ratios, the number of harmonics actively participating in this process varies, but always remains quite large. This implies that the self-sustenance of subcritical turbulence cannot be described by low-order models., 22 pages, 24 figures

Direct numerical simulation is used to investigate effects of heat release and compressibility on mixing-layer turbulence during a period of self-similarity. Temporally evolving mixing layers are analysed at convective Mach numbers between 0.15 and 1.1 and in a Reynolds number range of 15000 to 35000 based on vorticity thickness. The turbulence inhibiting effects of heat release are traced back to mean density variations using an analysis of the fluctuating pressure field based on a Green's function.

The article by M. Wacławczyk et al. [Phys. Rev. E 90, 013022 (2014)] proposes two new statistical symmetries in the classical theory for turbulent hydrodynamic flows. In this Comment, however, we show that both symmetries are unphysical due to violating the principle of causality. In addition, they must get broken in order to be consistent with all physical constraints naturally arising in the statistical Lundgren-Monin-Novikov (LMN) description of turbulence. As a result, we state that besides the well-known classical symmetries of the LMN equations no new statistical symmetries exist. Finally, we criticize the relation between intermittency and global symmetries as it is presented throughout that study.

A new model for large eddy simulation is derived by considering a formal extension to the deconvolution method of Stolz et al. [Stolz, S., Adams, N., 1999. An approximate deconvolution procedure for large-eddy simulation. Phys. Fluids 11, 1699–1701] as interpreted in Mathew et al. [Mathew, J., Lechner, R., Foysi, H., Sesterhenn, J., Friedrich, R., 2003. An explicit filtering method for LES of compressible flows. Phys. Fluids 15(8), 2279–2289]. The new model terms are shown to reduce the error in approximating the governing differential equations, and are evaluated with a simple, additional filtering step. This approach holds special promise for compressible flows, which have several kinds of nonlinearities besides convection, because all nonlinearities are treated in a uniform, mathematically consistent way without recourse to heuristic modeling. The method was assessed by computing supersonic channel flows with passive scalar transport at high Reynolds numbers and found to give excellent results.

We performed direct numerical simulations of homogeneous shear turbulence to study the mechanism of the self-sustenance of subcritical turbulence in spectrally stable (constant) shear flows. For this purpose, we analyzed the turbulence dynamics in Fourier/wavenumber/spectral space based on the simulation data for the domain aspect ratio 1 : 1 : 1. Specifically, we examined the interplay of linear transient growth of Fourier harmonics and nonlinear processes. The transient growth of harmonics is strongly anisotropic in spectral space. This, in turn, leads to anisotropy of nonlinear processes in spectral space and, as a result, the main nonlinear process appears to be not a direct/inverse, but rather a transverse/angular redistribution of harmonics in Fourier space referred to as the nonlinear transverse cascade. It is demonstrated that the turbulence is sustained by the interplay of the linear transient, or nonmodal growth and the transverse cascade. This course of events reliably exemplifies the wellknown bypass scenario of subcritical turbulence in spectrally stable shear flows. These processes mainly operate at large length scales, comparable to the box size. Consequently, the central, small wavenumber area of Fourier space (the size of which is determined below) is crucial in the self-sustenance and is labeled the vital area. Outside the vital area, the transient growth and the transverse cascade are of secondary importance - Fourier harmonics are transferred to dissipative scales by the nonlinear direct cascade. The number of harmonics actively participating in the self-sustaining process (i.e., the harmonics whose energies grow more than 10% of the maximum spectral energy at least once during evolution) is quite large - it is equal to 36 for the considered box aspect ratio - and obviously cannot be described by low-order models.

The quest to find new statistical symmetries in the theory of turbulence is an ongoing research endeavor which is still in its beginning and exploratory stage. In our comment we show that the recently performed study of Waclawczyk and Oberlack [J. Math. Phys. 54, 072901 (2013)] failed to present such new statistical symmetries. Despite their existence within a functional Fourier space of the statistical Burgers equation, they all can be reduced to the classical and well-known symmetries of the underlying deterministic Burgers equation itself, except for one symmetry, but which, as we will demonstrate, is only a mathematical artefact without any physical meaning. Moreover, we show that the proposed connection between the translation invariance of the multi-point moments and a symmetry transformation associated to a certain invariant solution of the inviscid functional Burgers equation is invalid. In general, their study constructs and discusses new particular solutions of the functional Burgers equation without referring them to the well-established general solution. Finally, we also see a shortcoming in the presented methodology as being too restricted to construct a complete set of Lie point symmetries for functional equations. In particular, for the considered Burgers equation essential symmetries are not captured.

The e ect of ltering on the sound spectrum in variable density jets is investigated. Prediction of aeroacoustics using large-eddy simulations is becoming increasingly popular. A direct evaluation of the sound eld is, however, often computationally too expensive. The sound in the near far eld of variable density jets was therefore computed using a hybrid method developed by Ewert & Schr oder. The power spectral density (PSD) and overall sound pressure levels (OASPL) of the reference direct numerical simulation (DNS) are compared to ltered DNS and large-eddy simulation (LES) of the variable density jet at a density ratio of s=0.14, relating the jet to the free-stream density. The jet develops under a global instability, which determines the low Strouhal number range of the PSD and results in similar shapes of the spectrum for di erent radiation angles. Unlike the pure LES, the ltered elds show only slightly reduced levels at all Strouhal numbers. Good agreement is found for low radiation angles, but an up to 10dB reduction is observed for sideline and backward radiation. The LES simulation showed higher values at low Strouhal numbers, which could be attributed to a non-universal side-jet phenomenon, which may be encountered in strongly heated jets. A further simulation using a reduced part of the available time series without this event lead to PSD values comparable to that of the DNS.

Large-eddy simulations (LES) of heated and cooled plane and round variable-density jets were conducted using a variety of density ratios s = ρ j / ρ co , which relates the jet nozzle density ρ j to the freestream density ρ co . The initial momentum flux was kept constant for better comparison of the resulting data. Both simulations confirm experimental results, in that the jet half-width grows linearly with streamwise coordinate x and the lighter jets decay much faster than the heavy ones. The centerline velocity decay is however different between the plane and round geometries. Whereas the round jets exhibits a decay with 1 / x for all density ratios s, there seem to be two self-similar scalings in plane jets, in the limit of small and large density ratios s. In the limit of small s or for incompressible flow, U c scales as U c ∼ 1 / x , for strongly heated jets on the other hand we find U c ∼ 1 / x . A mixed scaling is proposed and shown to work nicely for both small and large density ratios s. For the round jet simulations, on the other hand, scaling x and U c by s - 1 / 4 ( Chen and Rodi, 1980 ) collapses the round jet data. Furthermore, it is shown that the streamwise growth in the mean density or the decay of the velocity fluctuations in the quasi-self-similar region, is stronger for round jets. The round jet simulation with a density ratio of s = 0.14 is seen to develop under a global instability. To the author’s knowledge, this is the first LES of a globally unstable round jet at a density ratio of s = 0.14 . The frequency agrees excellently with experimental data and with the new scaling proposed by Hallberg and Strykowski (2006) .

Direct numerical (DNS) and large-eddy simulations (LES) of a strongly heated globally unstable round jet are juxtaposed with respect to aerodynamical mean characteristics and the sound being generated. The sound field is computed by a hybrid approach using the acoustic perturbation equations (APE). All used codes have been adopted to massive-parallel supercomputers. This way results can be obtained in a reasonable time frame. When compared to the DNS results, the LES is capable to capture the major characteristics of the emitted sound field in the forward direction. The sideline and backward direction that are dominated by small scale noise reveal larger discrepancies that are due to the inherent restrictions of large eddy simulations.

Direct numerical simulation (DNS) is used to explore similarities and differences between fully developed supersonic turbulent plane channel and axisymmetric non-swirling pipe flow bounded by isothermal walls. The comparison is based on equal friction Mach number, friction Reynolds number, Prandtl number, ratio of specific heats and viscosity exponent. The channel half-width and pipe radius are chosen to define the Reynolds numbers. To what extent and why mean flow quantities, second-order turbulence statistics and terms in the Reynolds stress equations coincide or diverge in both flows are investigated. The role of the fluctuating pressure in causing characteristic differences among correlations involving pressure fluctuations is identified via a Green-function-based analysis of the pressure field.

Direct numerical simulations of compressible turbulent channel flow including passive scalar transport have been performed at five Mach numbers, M, ranging from 0.3 to 3.5 and Reynolds numbers, Re, ranging from 181 to 1030. The Prandtl and Schmidt numbers are 0.7 and 1.0, respectively, in all cases. The passive scalar is added to the flow through one channel wall and removed through the other, leading to an S-shaped mean scalar profile with non-zero gradient in the channel centre. The paper describes the set of compressible flow equations, which is integrated using high-order numerical schemes in space and time. Statistical equations are presented for fully developed flow, including budgets for the Reynolds stresses, the turbulent scalar fluxes and the scalar variance. Results are presented for second order moments and the terms in the mentioned balance equations. Outer scalings are found suitable to collapse incompressible and compressible data. The reduction in the near-wall pressure-strain and pressure-scalar gradient correlations due to compressibility is explained using a Green-function-based analysis of the fluctuating pressure field.

Direct numerical simulations (DNS) of compressible supersonic channel flow of air at Reynolds numbers ranging from Re τ = 180 to Re τ = 560 and Mach numbers ranging from M = 0.3 to M = 3.0 have been performed. A Navier-Stokes solver of high order accuracy has been vectorized and parallelized to run efficiently on the Hitachi SR8000-F1. Budgets of the Reynolds stresses and the passive scalar fluxes are presented, as well as explanations concerning the reduction of the pressure-correlation terms, using a Green's function approach.

Direct numerical simulations (DNS) of turbulent supersonic channel flow of air at Reynolds numbers ranging from Re τ = 180 to 560 and Mach numbers ranging from M = 0.3 to 3.0 have been performed. The DNS data are used to explain the reduction of the pressure-correlation terms due to compressibility, using a Green’s function approach.

Direct numerical simulations of compressible supersonic turbulent channel flow with passive scalar transport are performed at the Reynolds numbers Re T of 455 and 544, at a Mach number of 1.5 and Prandtl and Schmidt numbers of 0.7 and 1.0, respectively. A mean scalar gradient is imposed across the mean flow. Budgets of the scalar variance and the scalar flux components are presented for both Reynolds numbers. A scaling of the Van-Driest transformed scalar similar to u VD + in the viscous is observed. Furthermore scalings of the Reynolds stress components and the pressure-rate-of-strain tensor that collapse both compressible and incompressible data in the outer layer are derived and investigated in more detail.

Direct numerical simulations of isothermal channel flow, with Mach numbers ranging from M = 0.3 to M = 3 and Reynolds numbers ranging from Re τ = 180 to Re τ = 560 have been performed. Their statistical analysis shows that changes in the turbulent stress peak values are linked to the changes in the corresponding pressure strain components. The strong attenuation of the pressure strain correlations relative to their incompressible values, is shown to be due to decreasing velocity derivative fluctuations for x 2 * < 35, as well as to the decreased mean density with respect to its wall value.

Turbulence in supersonic channel flow is studied using direct numerical simulation. The ability of outer and inner scalings to collapse profiles of turbulent stresses onto their incompressible counterparts is investigated. Such collapse is adequate with outer scaling when sufficiently far from the wall, but not with inner scaling. Compressibility effects on the turbulent stresses, their anisotropy, and their balance equations are identified. A reduction in the near-wall pressure-strain, found responsible for the changed Reynolds-stress profiles, is explained using a Green's-function-based analysis of the pressure field

A method for large eddy simulation (LES) is presented in which the sub-grid-scale modeling is achieved by filtering procedures alone. The procedure derives from a deconvolution model, and provides a mathematically consistent approximation of unresolved terms arising from any type of nonlinearity. The formal steps of primary filtering to obtain LES equations, approximate deconvolution to construct the subgrid model term and regularization are combined into an equivalent filter. This filter should be an almost perfect low pass filter below a cut-off wavenumber and then fall off smoothly. The procedure has been applied to a pressure-velocity-entropy formulation of the Navier–Stokes equations for compressible flow to perform LES of two fully developed, turbulent, supersonic channel flows and has been assessed by comparison against direct numerical simulation (DNS) data. Mach numbers are 1.5 and 3.0, and Reynolds numbers are 3000 and 6000, respectively. Effects of filter cut-off location, choice of differentiation scheme (a fifth-order compact upwind formula and a symmetric sixth-order compact formula were used), and grid refinement are examined. The effects are consistent with, and are readily understood by reference to, filtering characteristics of the differentiation and the LES filter. All simulations demonstrate a uniform convergence towards their respective DNS solutions.

A semi-implicit large-eddy simulation technique is used to predict transport and infinitely fast reaction processes of an / jet injected through a narrow spanwise slot into a subsonic turbulent air flow between isothermal channel walls. The large-eddy simulation (LES) technique is based on approximate deconvolution and explicit modelling of the filtered heat release term. Spatial derivatives are computed using sixth-order accurate central compact schemes. An explicit fourth-order Runge–Kutta algorithm serves for time-integration. Turbulent inflow conditions are generated by a separate LES of fully developed channel flow and are introduced well upstream of the injection station using characteristic boundary conditions. The complex transport processes in the vicinity of the injection region are highlighted by instantaneous and statistically averaged flow quantities by Reynolds stress and total enthalpy balances.

This article employs LES to simulate temporal mixing layers with Mach numbers ranging from M c = 0.3 to M c = 1.2. A form of approximate deconvolution together with a dynamic Smagorinsky subgrid model are employed as subgrid models. A large computational domain is used along with relatively good resolution. The LES results regarding growth rate, turbulence levels, turbulence anisotropy, and pressure–strain correlation show excellent agreement with those available from previous experimental and DNS results of the same flow configuration, underlining the effectiveness and accuracy of properly conducted LES. Coherent structures during the transitional stage change from spanwise aligned rollers to streamwise-aligned thinner vortices at high Mach number. In the quasi-self-similar turbulent stage, the resolved-scale vorticity is more isotropic at higher M c , and its vertical correlation length scale is smaller. The ratio of the vertical integral length scale of streamwise velocity fluctuation to a characteristic isotropic estimate is found to decrease with increasing M c . Thus, compressibility leads to increased spatial decorrelation of turbulence which is one reason for the reduction in pressure–strain correlation with increasing M c . The balance of the resolved-scale fluctuating vorticity is examined, and it is observed that the linear production by mean shear becomes less important compared to nonlinear vortex stretching at high M c . A spectral decomposition of the pressure fluctuations into low- and intermediate-to-high-wave numbers is performed. The low-wave number part of the pressure field is found not to correlate with the strain field, although it does have a significant contribution to the r.m.s of the fluctuating pressure. As a consequence, the pressure–strain correlation can be analyzed using a simplified Green’s function for the Poisson equation as is demonstrated here using the LES data.