Large eddy simulations of a transcritical round jet submitted to transverse acoustic modulation

Abstract

This article reports numerical computations of a turbulent round jet of transcritical fluid (low temperature nitrogen injected under high pressure conditions) surrounded by the same fluid at rest under supercritical conditions (high temperature and high pressure) and submitted to transverse acoustic modulations. The numerical framework relies on large eddy simulation in combination with a real-gas description of thermodynamics and transport properties. A stationary acoustic field is obtained by modulating the normal acoustic velocity at the lateral boundaries of the computational domain. This study specifically focuses on the interaction of the jet with the acoustic field to investigate how the round transcritical jet changes its shape and mixes with the surrounding fluid. Different modulation amplitudes and frequencies are used to sweep a range of conditions. When the acoustic field is established in the domain, the jet length is notably reduced and the jet is flattened in the spanwise direction. Two regimes of oscillation are identified: for low Strouhal numbers a large amplitude motion is observed, while for higher Strouhal numbers the jet oscillates with a small amplitude around the injector axis. The minimum length is obtained for a Strouhal number of 0.3 and the jet length increases with increasing Strouhal numbers after reaching this minimum value. The mechanism of spanwise deformation is shown to be linked with dynamical effects resulting from reduction of the pressure in the transverse direction in relation with increased velocities on the two sides of the jet. A propagative wave is then introduced in the domain leading to similar effects on the jet, except that a bending is also observed in the acoustic propagation direction. A kinematic model, combining hydrodynamic and acoustic contributions, is derived in a second stage to represent the motion of the jet centerline. This model captures details of the numerical simulations quite well. These various results can serve to interpret observations made on more complex flow configurations such as coaxial jets or jet flames formed by coaxial injectors.

Large-eddy simulation of an air-assisted liquid jet under a high-frequency transverse acoustic forcing

“…The same kind of experiments have been carried out later for reactive jets (see Hardi et al (2014) for example) to understand how these acoustics/two-phase flow coupling mechanisms may impact the flame behaviour. In addition, complementary investigations have been successfully carried out by means of CFD, either in gas/gas (Selle et al 2014) or transcritical conditions (Hakim et al 2015a,b;Gonzalez-Flesca et al 2016;Urbano et al 2016). All these contributions have led to a better understanding of coupling mechanisms between acoustic perturbations and transcritical flames, which is essential to express general low-order models.…”

Reduced Order Modeling Approach to Combustion Instabilities of Liquid Rocket Engines

“…The BKD has 42 injectors which means that the average heat release rate per injector is around 2.07 MW. There are many possible mechanisms that may drive instabilities in rocket engines, among others, movement of the jet caused by transverse velocity variations that generate fluctuations of the heat release rate ( [16,18,20,48,54,55]) as well as pressure variations in front of the injectors ( [11,18,[48][49][50]). Therefore the combustion source terms chosen for the simulation of LP3 and LP4 are those defined by equations 33, 34 and 37.…”

Transverse Acoustic Forcing of Gaseous Hydrogen/Liquid Oxygen Turbulent Shear Coaxial Flames

“…Experimental and computational research on shear coaxial injectors using a gaseous annular propellant and a central cryogenic jet for liquid rocket engine applications were carried out by Poinsot et al [4], Rey et al [5], Richecoeur et al [6][7][8], Méry et al [9], Hakim et al [10,11], Urbano et al [12], Gonzalez-Flesca et al [13], Urbano et al [14], Hardi et al [15,16], Gröning et al [17], Armbruster et al [18], Mayer and Krülle [19], Mayer and Tamura [20], Mayer et al [21], Oefelein and Yang [22], Zong and Yang [23,24], Roa and Talley [25], Roa et al [26], Forliti et al [27], Hua et al [28], Graham et al [29], Levya et al [30,31], Rodriguez et al [32], Wegener et al [33], and Davis and Chehroudi [34]. Aspects of those studies that focused largely on characterizing and understanding the atomization, flame locations, and average global behavior for shear coaxial flows that are not experiencing combustion instabilities were reviewed by Roa and Talley.…”

“…Candel research group [4][5][6][7][8][9][10][11][12][13][14] performed both computational and experimental studies on acoustically forced shear coaxial flows. From large-eddy simulations, Candel research group [4][5][6][7][8][9][10][11][12][13][14] observed a flow effect that produced a physical change of the liquid oxygen (LOX) jet. When subjected to transverse acoustic modulations, the round cylindrical LOX jet flattened to a fan shape.…”

“…Experiments carried out in a flow modulated, windowed combustor showed a flow instability coupled to the acoustic forcing, where a vortex mode coupled to the acoustic field. By tracking changes in the OH emission, Candel research group [4][5][6][7][8][9][10][11][12][13][14] observed that the locations of high heat release were displaced in the direction of the transverse forcing and were in phase.…”