Investigation of a High-Mach-Number Overexpanded Jet Using Large-Eddy Simulation

Abstract

An initially laminar overexpanded round jet at an exit Mach number of 3.30 and a Reynolds number of 10 5 is calculated by compressible large-eddy simulation. The near field obtained by large-eddy simulation is also propagated to the acoustic far field by solving the full Euler equations to take into account the nonlinear propagation effects. Both computations are performed using low-dissipation finite differences in combination with an adaptive shock-capturing method. The jet originates from a straight pipe nozzle of radius r e , including lips of thickness 0:05r e . At the pipe exit, Blasius mean flow profiles are imposed, and static pressure and temperature are equal to 0:5 10 5 Pa and 360 K, resulting in fully adapted and acoustic Mach numbers, respectively, of 2.83 and 3.47. The jet flowfields, as well as the acoustic near and far fields, are described in detail and compared with data of the literature. The turbulent mechanisms developing in the jet are investigated, using spectral and azimuthal decompositions of the velocity fluctuations along the shear layers. Same analyses are applied to the acoustic fields, in order to discuss the properties of jet noise components. In this way, Mach waves, shock-associated noise, screech tones, and turbulent mixing noise are identified. = first shock location on the jet axis = specific heat ratio r = mesh size in the radial direction z = mesh size in the axial direction = boundary-layer thickness in the pipe nozzle 0:5 = jet half-width e = exit molecular viscosity e = exit density = radiation angle measured according to the flow direction

Study on Acoustic Prediction and Reduction of Epsilon Launch Vehicle at Liftoff

“…According to past CFD studies on the free jet, numerical results tend to show higher level than the microphone measurements especially at the major acoustic emission direction. [41][42][43] If the resolution of numerical method and computational grid are insufficient, turbulent structure of the jet shear layer contains higher energy at low frequencies than the physics, and obtained acoustic level results in the overestimation. According to Cacqueray et al [41], simulation of a high-Mach number hot jet should be taken into account the non-linearity in calculating acoustic propagation.…”

Toward Active Control of Noise from Hot Supersonic Jets

“…While a simplified illustration of the formation of Mach waves from a high speed jet flow is shown in figure 1, the complexity is well visualized in, for example, the experiments of Clemens &; Paul (1993) on a perfectly expanded Mach 2 helium jet or the direct numerical simulation of a perfectly expanded Mach 1.92 jet flow by Freund et al (2000). Insightful snapshots of the far-field pressure produced by Mach waves can be seen in the recent simulations by de Cacqueray et al (2011a).…”

“…This eliminates screech and the noise produced by turbulence interactions with shock cells. Aside from the rocket engine noise studies of Mclnerny (1996), and de Cacqueray et al (2011a), the Mach number chosen for this study is not typical of commercial or military aircraft engines, and bears little relevance to most practical systems of engineering interest. However, the high Mach number results in a convective and acoustic Mach number around 1.4 and 1.8, respectively, which ensures the strong formation of Mach waves.…”

“…This last model was described in more detail by Baars et al (2011), including a discussion of the adaptations of the Witze (1974) model by other authors attempting to account for supersonic heated jets. A recent large-eddy simulation of a slightly overexpanded and slightly heated (Tj = 360 K) Mach 3.30 jet by de Cacqueray et al (2011a) found L c = 10 (based on locating the point where U = 0.90 Uj), L p = 12.5 and L s = 18. These numbers fall short of the empirical models previously mentioned and may be attributed to both the elevated temperature used in the simulation (this is known to reduce L c ; see Baars et al 2011) and, the first set of overexpansion shocks (causing the flow to deflect towards the jet axis and further shortening the core length).…”

Computational Study of Hydrogen Direct Injection for Internal Combustion Engines

“…The authors specifically concluded that the resolution that they employed was not adequate to resolve these details. Under-expanded jets have been studied for air and gaseous fuels (primarily natural gas), experimentally [31][32][33][34][35] and by LES [36][37][38][39]. In a recent publication on under-expanded jets, Scarcelli et al [40] validated RANS predictions of a sonic argon jet, injected at a flow rate corresponding to 100 bar nominal injection pressure into atmospheric environment, against experimental data obtained by means of X-ray radiography.…”