High-fidelity simulations of the aeroacoustic environment of the VEGA launch vehicle at lift-off

Posta, Giacomo Della; Martelli, Emanuele; Stella, F.; Barbagallo, D.; Neri, Agostino; Salvadore, Francesco; Bernardini, Matteo

doi:10.1016/j.compfluid.2023.105945

Cited by 4 publications

References 42 publications

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High-fidelity simulations of microramp-controlled shock wave/boundary layer interaction

Della Posta,

Martelli,

Salvadore

et al. 2024

J. Fluid Mech.

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Microvortex generators (MVGs) are a promising solution to control shock wave/turbulent boundary layer interactions (SBLIs), especially in supersonic inlets. In this study, we examine the effects of a microramp vortex generator on an SBLI generated by an oblique shock wave and a turbulent boundary layer using direct numerical simulations (DNSs). Two cases, with and without the presence of a microramp, are compared in terms of their mean and unsteady flow features at free-stream Mach number equal to 2 and friction Reynolds number at the inviscid shock impingement equal to 600. The long integration period allows us to assess how microramps affect the typical low-frequency unsteadiness observed in SBLIs, and the data generated may serve as a reference for simulations of lower fidelity or reduced order models. The analysis shows that the three-dimensional microramp wake alters the interaction region dramatically, inducing a significant spanwise modulation and topology change of the separation. For example, tornado-like structures redistribute the flow in both the spanwise and wall-normal directions inside the recirculation region. The increase in momentum close to the wall by the ramp vortices effectively delays the onset of the separation and, thus, the separation length, but at the same time leads to a significant increase in the intensity of the wall-pressure fluctuations. We then characterise the mutual interaction between the arch-like vortices around the ramp wake and the SBLI. The specific spanwise vorticity shows that these vortices follow the edge of the separation and their intensity, apart from mean compressibility effects, is not affected by the shocks. The shocks, instead, are deformed in shape by the periodic impingement of the vortices, although the spectral analysis did not reveal any significant trace of their shedding frequency in the separation region. These Kelvin–Helmholtz vortices, however, may be relevant in the closure of the separation bubble. Fourier analysis also shows a constant increase, in both value and magnitude, in the low-frequency peak all along the span, suggesting that the motion of the separation shock remains coherent while being disturbed by the arch-like vortices and oscillating at a higher frequency in absolute terms.

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High-fidelity simulations of microramp-controlled shock wave/boundary layer interaction

Della Posta,

Martelli,

Salvadore

et al. 2024

J. Fluid Mech.

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Designing jet deflector configuration for a semi-cryogenic rocket engine

Sandeep,

Sharma,

Krishna

2023

Physics of Fluids

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This study deals with the design of a suitable configuration of jet deflector for supersonic exhaust gases from a semi-cryogenic launch vehicle engine using computational fluid dynamics. Computational model of combustion in semi-cryogenic engine, with kerosene as fuel and liquid oxygen as oxidizer, was developed in which exhaust gases from engine were impinged on the deflector surface. Different design configurations of deflector structure, obtained by the combination of various impingement angles of 15°, 20°, 25°, 30°, and 45°, and different exit radii of 5000, 10 000, and 20 000 mm, were used in the developed computational models to analyze impingement, deflection, and associated flow properties of exhaust gases, such as acoustics, force on deflector imparted by jet, temperature, and Mach number of flow field. A new ablation model was developed based on Vieille's law to determine the amount of refractory material ablated from deflector structure for different configurations. The developed models of ablation, combustion, and flow impingement were also validated with existing literature. It was found that the configuration with 20° impingement angle and 10 000 mm exit radius had ablation, acoustics, force, and flow properties in desired limit. Furthermore, to find the optimum uplift angle for designing jet deflector, configurations with uplift angles of 0°, 5°, 15°, and 25° were studied using the computational models developed in the study. It was observed that the configuration with 20° impingement angle, 10 000 mm exit radius, and 15° uplift angle was best suited for impingement and deflection of exhaust jet from the specified semi-cryogenic engine.

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Direct Numerical Simulation of Boundary Layers over Microramps: Mach Number Effects

Della Posta,

Fratini,

Salvadore

et al. 2024

AIAA Journal

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Microvortex generators are passive control devices with heights below the boundary-layer thickness that have been proposed to mitigate the detrimental effects of shock-wave/boundary-layer interaction. Despite their demonstrated control effectiveness, several aspects of the flow induced in turbulent boundary layers still need to be characterized thoroughly. In this work, we present a campaign of direct numerical simulations of a turbulent boundary layer on a microramp, to investigate the effect of the Mach number, from subsonic to supersonic regime. We show that the flow topology changes significantly because of compressibility effects, and that typical wake features do not scale linearly with the geometry dimensions but rather depend on the incoming flow conditions. Moreover, we investigate the spectral content in time and space of the wake, which is dominated by the Kelvin–Helmholtz instability developing along the shear layer. For larger Mach numbers, the shedding onset is postponed and exhibits a lower peak frequency that evolves in space. Finally, we extract the spatially coherent structures convected in the wake by means of a dynamic mode decomposition along the characteristics, which represents effectively and efficiently the evolution of the entire field, despite the convective nature of the flow under consideration.

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High-fidelity simulations of the aeroacoustic environment of the VEGA launch vehicle at lift-off

Cited by 4 publications

References 42 publications

High-fidelity simulations of microramp-controlled shock wave/boundary layer interaction

High-fidelity simulations of microramp-controlled shock wave/boundary layer interaction

Designing jet deflector configuration for a semi-cryogenic rocket engine

Direct Numerical Simulation of Boundary Layers over Microramps: Mach Number Effects

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