Investigation of tone generation in ideally expanded supersonic planar impinging jets using large-eddy simulation

The generation of tones in a supersonic planar jet impinging on a flat plate normally has been investigated by performing compressible large-eddy simulations using low-dissipation and low-dispersion finite differences. At the exit of a straight nozzle of height $h$ , the jet is ideally expanded, and has a Mach number of 1.28 and a Reynolds number of 50000. Four distances between the nozzle and the plate between 3.94h and 9.1h have been considered. Flow snapshots and mean velocity fields are first presented. The variations of turbulence intensities and of the convection velocity in the jet shear layers are then examined. The properties of the jet near fields are subsequently described, in particular by applying Fourier decomposition to the pressure fields. Several coexisting tones appear to be generated by aeroacoustic feedback loops establishing between the nozzle lip and the flat plate, which also lead to the presence of hydrodynamic–acoustic standing waves. The tone frequencies are consistent with those given by the aeroacoustic feedback model and with measurements for high-aspect-ratio rectangular jets. The jet oscillation modes at these frequencies are characterized, and found to agree with experimental data. Their symmetric or antisymmetric natures are shown to be well predicted by a wave analysis carried out using a vortex sheet model of the jet, providing the allowable frequency ranges for the upstream-propagating acoustic waves. Thus, it is possible, for an ideally expanded impinging planar jet to predict both the frequencies of the tones and the symmetric or antisymmetric nature of the corresponding oscillation modes by combining the aeroacoustic feedback model and the wave analysis

Large-eddy simulation of underexpanded round jets impinging on a flat plate 4 to 9 radii downstream from the nozzle

Supersonic round jets have been computed by compressible Large Eddy Simulation(LES) using low-dispersion and low-dissipation schemes. The jets are underexpanded, and are characterized by a Nozzle Pressure Ratio of NPR = Pr/Pamb = 4.03, where Pr is the stagnation pressure and Pamb is the ambient pressure. They have a fully expanded Mach number of Mj = 1.56, an exit Mach number of Me = 1, and a Reynolds number of Rej = ujD/mu = 5 × 104, where uj and D are the jet fully expanded exit velocity and the nozzle diameter, respectively. A free jet is first considered. Four jets impinging on a flat plate normally are then examined. The distance L between the nozzle lip and the flat plate varies from L = 4.16r0 up to L = 9.32r0 where r0 = D/2, for the impinging jets. The effects of the plate on the aerodynamic and acoustic properties of the jets are thus studied. For the free jet, snapshots of density, pressure and vorticity are presented. Mean velocity fields are displayed, they are in good agreement with experimental data. The near pressure field of the jet is investigated using Fourier decomposition. A screech tone component is found, at a frequency comparing well with experimental data and theoretical models. For the four impinging jets, similarly, flow snapshots and mean flow fields are shown. The results obtained are similar to the corresponding measurements. The convection velocity of large-scale structures in the jet shear layers is then evaluated and an expression giving the average convection velocity between the nozzle lips and the flat plate is proposed. The near pressure fields are then explored, and the main properties of the aeroacoustic feedback mechanism occurring between the nozzle lip and the flat plate are presented. The results are consistent with theoretical models and experimental data

Large-eddy simulation of supersonic planar jets impinging on a flat plate at an angle of 60 to 90 degrees

Six planar supersonic jets are computed by compressible large-eddy simulations (LES) using low-dissipation schemes. At the exit of a nozzle of height h, they are ideally expanded and have an exit velocity ue, yielding a Mach number of Me = 1.28, and a Reynolds number of Reh = ueh/mu = 5 × 10^4. Four jets impinging on a flat plate at distances L from the nozzle lips ranging from 3.94h up to 9.1h, with an angle between the jet direction and the plate of 90 degrees, are first considered. Two other jets with L = 5.5h and angles of 60 and 75 degrees are also examined. In this way, the effects of both the nozzle-to-plate distance and the angle of impact on the flow and acoustic fields of the jet are studied. Mean velocity flows and snapshots of density, pressure and vorticity are shown. The pressure fields are also described by computing sound pressure levels and using Fourier decomposition. Several tones are obtained in certain cases and their corresponding Strouhal numbers and symmetric or antisymmetric natures are in agreement with experimental data and theoretical models. They are due to an aeroacoustic feedback mechanism occurring between the nozzle lips and the flat plate. This mechanism generates an hydrodynamic-acoustic standing wave revealed by using Fourier decomposition

Direct noise computation of adaptive control applied to a cavity flow

The Large Eddy Simulation of closed-loop active flow control applied to a 3D cavity excited by a compressible airflow with a Mach number of 0.6 is presented. The control actuator is an idealized synthetic jet located at the upstream cavity edge, and the control function is supplied by a feedback LMS-type algorithm whose input is a pressure signal measured inside the cavity. The radiated sound, provided directly by the LES simulation, was shown to decrease substantially when active control was applied. A simultaneous reduction of the vertical velocity fluctuations in the shear layer was observed. The intensity of vortical structures inside the cavity was also reduced, although the general aspect of the recirculation zone was not modified. The direct noise computation technique, which supplies the pressure field by solving the fluid mechanics equations, is shown to constitute a powerful tool for studying active aeroacoustic noise control. To cite this article: O. Marsden et al., C. R. Mecanique 331 (2003). 2003 Académie des sciences. Published by Éditions scientifiques et médicales Elsevier SAS. All rights reserved

Numerical simulation of infrasound propagation in a realistic atmosphere : nonlinear and viscous effects

Des simulations numériques directes des équations de Navier-Stokes bidimensionnelles sont effectuées pour déterminer le champ de pression produit par une source infrasonore dans une atmosphère réaliste. L'algorithme numérique repose sur une méthode aux différences finies dans le domaine temporel développée pour des applications en aéroacoustique. La distorsion de la signature acoustique due aux non linéarités ainsi que les effets de dissipation visqueuse sont analysés et discutés

Réflexion d'ondes de choc acoustiques faibles

Des expériences à l'échelle du laboratoire ont été mises en place pour l'étude de la propagation de choc faibles à proximité de parois rigides. Ces ondes sont générées par une source à arc électrique et une méthode optique de type Schlieren est mise en place afin de visualiser les fronts d'ondes incidents ainsi que les schémas de réflexion. Les résultats expérimentaux sont comparés aux résultats issus de simulations numériques basées sur la résolution des équations complètes de Navier-Stokes

Geometric Generalisations of SHAKE and RATTLE

A geometric analysis of the Shake and Rattle methods for constrained Hamiltonian problems is carried out. The study reveals the underlying differential geometric foundation of the two methods, and the exact relation between them. In addition, the geometric insight naturally generalises Shake and Rattle to allow for a strictly larger class of constrained Hamiltonian systems than in the classical setting. In order for Shake and Rattle to be well defined, two basic assumptions are needed. First, a nondegeneracy assumption, which is a condition on the Hamiltonian, i.e., on the dynamics of the system. Second, a coisotropy assumption, which is a condition on the geometry of the constrained phase space. Non-trivial examples of systems fulfilling, and failing to fulfill, these assumptions are given

The redshift evolution of the distribution of star formation among dark matter halos as seen in the infrared

Recent studies revealed a strong correlation between the star formation rate (SFR) and stellar mass of star-forming galaxies, the so-called star-forming main sequence. An empirical modeling approach (2-SFM) which distinguishes between the main sequence and rarer starburst galaxies is capable of reproducing most statistical properties of infrared galaxies. In this paper, we extend this approach by establishing a connection between stellar mass and halo mass with the technique of abundance matching. Based on a few, simple assumptions and a physically motivated formalism, our model successfully predicts the (cross-)power spectra of the cosmic infrared background (CIB), the cross-correlation between CIB and cosmic microwave background (CMB) lensing, and the correlation functions of bright, resolved infrared galaxies measured by Herschel, Planck, ACT and SPT. We use this model to infer the redshift distribution these observables, as well as the level of correlation between CIB-anisotropies at different wavelengths. We also predict that more than 90% of cosmic star formation activity occurs in halos with masses between 10^11.5 and 10^13.5 Msun. Taking into account subsequent mass growth of halos, this implies that the majority of stars were initially (at z>3) formed in the progenitors of clusters, then in groups at 0.5<z<3 and finally in Milky-Way-like halos at z<0.5. At all redshifts, the dominant contribution to the star formation rate density stems from halos of mass ~10^12 Msun, in which the instantaneous star formation efficiency is maximal (~70%). The strong redshift-evolution of SFR in the galaxies that dominate the CIB is thus plausibly driven by increased accretion from the cosmic web onto halos of this characteristic mass scale