Acoustics from a Rectangular C-D Nozzle Exhausting Over a Flat Surface

Mora, Pablo; Baier, Florian; Gutmark, Ephraim; Kailasanath, K.

doi:10.2514/6.2016-1884

Cited by 20 publications

(17 citation statements)

References 19 publications

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“…The current work is a continuation of our previous works [10,22,23], where the detailed grid convergence study, validation of the numerical method with experimental data of low-temperature jets with and without a plate are carried out and presented. Good agreements with the data from the experimental campaign at the University of Cincinnati [3,28] have been achieved for the low-temperature jets investigated.…”

Section: B Computational Domain and Boundary Conditionssupporting

confidence: 58%

Effect of an Adjacent Flat Plate on a Highly-Heated Rectangular Supersonic Jet

Chen

Gojon

Mihăescu

2020

AIAA Scitech 2020 Forum

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Solid surfaces located in the vicinity of a supersonic jet may affect its flow dynamics and greatly change its aeroacoustic characteristics. Large-eddy simulations (LES) are performed to investigate the effects of a plate on a highly-heated rectangular supersonic jet. The rectangular nozzle has an aspect ratio of 2.0 and is operated at overexpanded conditions with a nozzle pressure ratio of 3.0 and a nozzle temperature ratio of 7.0. Four cases with a plate-to-nozzle distance ranging from 0 to 3 times of the jet equivalent nozzle diameter are investigated. The large-scale implicit LES computations are performed by a well-validated in-house finite-volume based CFD code, which uses an artificial dissipation mechanism to represent the effects of small-scale turbulence structures and to damp the numerical oscillations near shocks. The temperature-dependent thermal properties of air in the highly-heated jets are considered by the chemical equilibrium assumption. Numerical results show that among the four jets, the case with the plate directly attached at the nozzle lip shows significant different flow and acoustic fields from the others. It exhibits a longer jet potential core length but without forming a series of well-structured shock diamonds. The other cases show similar shock/expansion wave structures as observed in the free jet but their jet plumes bend towards the plate. This bending leads to one jet to scrub over the plate in the downstream. The scrubbing effect, together with the unaffected shock-shear layer interactions and high plate pressure loading, leads to a stronger acoustic power in the near acoustic fields for this jet as compared to the others. The spectrum analysis in the nozzle upstream direction shows that the plate removes or mitigates the screech tone observed in the free jet and slightly amplifies the acoustic amplitudes in the low-frequency range.

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Section: B Computational Domain and Boundary Conditionssupporting

confidence: 58%

Effect of an Adjacent Flat Plate on a Highly-Heated Rectangular Supersonic Jet

Chen

Gojon

Mihăescu

2020

AIAA Scitech 2020 Forum

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“…Cases tested include the acoustic pulse, shock propagation, and shock-vortex interaction. The numerical method has also been used to study the supersonic jet with relatively low temperature ratios, and results match rather well with the experiments conducted at the University of Cincinnati [10,29]. Interested readers can refer to [20] for details.…”

Section: Verification and Validationsupporting

confidence: 53%

“…More detailed information about the nozzle geometry and operating conditions can be found in Ref. [10,[28][29][30].…”

Section: Nozzle Geometry and Operating Conditionsmentioning

confidence: 99%

High-Temperature Effects on Aerodynamic and Acoustic Characteristics of a Rectangular Supersonic Jet

Gojon²,

Mihăescu

2018

2018 AIAA/CEAS Aeroacoustics Conference

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Implicit large-eddy simulations (LES) are performed in this work to study the flow field and acoustic characteristics of a rectangular supersonic jet. The focus is to investigate the high-temperature effects, i.e. when the jet total temperature is as high as 2100 K. Four cases with a jet temperature ratio(TR) of 1.0, 2.0, 4.0 and 7.0 are investigated. The rectangular nozzle selected for this study has an aspect ratio of 2. The jets are overexpanded, with a series of shock cells in the jet core region. An artificial dissipation mechanism is used to damp the numerical oscillation and to represent the effect of small-scale turbulence. The temperature-dependent thermal properties of air within the high-temperature regime are also considered by using the chemical equilibrium assumption. The numerical results show that the high temperature significantly increases the jet velocity and acoustic Mach number, although the jet Mach number is maintained roughly the same. Meanwhile, the length of the jet core region of the hot jet (TR = 7.0) is found to be reduced by around 30 %, compared to the cold jet. The convection velocity and acoustic convection Mach number in the shear layer are also observed to be increased when the jet temperature is high. The elevated acoustic convection Mach number directly leads to a strong Mach wave radiation, and the crackle noise component has been identified by the pressure skewness and kurtosis factors. The Strouhal number of the screech tone is found to be decreased slightly, and good agreements between the numerical results and the theoretical analysis are observed. Moreover, the sound pressure levels (SPL) associated with turbulent mixing, screech, Mach wave radiation, and Broadband shock associated noise are all found to be amplified in different levels for the hot jets. In the far field, the SPL are strongly affected and increased by the high-temperature effect. Higher levels are notably observed in the side, downstream, and especially the Mach wave radiation directions.

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“…Sutherland's law is used to compute the viscosity. The geometry and the operating conditions match those in the experimental study by Mora et al [20] Please note that the experiments have been performed on two different occasions with different operating points. First, a PIV setup has been used in order to have access to the aerodynamic fields in the minor and major axis planes for three operating conditions at N P R = 3 and T R = 1, T R = 2 and T R = 2.5.…”

Section: Iiia Jet Parametersmentioning

confidence: 98%

“…The impact of the jet temperature on the flow and the acoustic fields associated with such configurations is targeted. An experimental study of a similar jet is conducted at the University of Cincinnati [20]. The spectral and hydrodynamic properties of the jet are described and compared with experimental data and models.…”

Section: Introductionmentioning

confidence: 99%

Antisymmetric Oscillation Modes in Rectangular Screeching Jets

2019

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In this paper, the origin and the properties of the oscillation modes in screeching nonideally expanded rectangular jets are investigated using compressible implicit LES of rectangular supersonic jets. At the exit of a converging diverging rectangular nozzle of aspect ratio 2 and of design Mach number 1.5, the jets are under-and over-expanded. Seven simulations with four different temperature ratios ranging from 1 to 3 and two different nozzle pressure ratios are performed. The geometry of the nozzle and the exit conditions are chosen such that to match the experimental study conducted at the University of Cincinnati. First, the over-expanded jets are studied. It is shown that the total number of shock cells decreases with increased temperature ratio. However, the temperature does not influence the size of the first shock cell and the linear decrease of the shock cell size in the downstream direction. The spreading of the jet is observed to be higher along the minor axis plane than along the major axis plane. The intensity of the screech noise increases with the temperature ratio in the present study although the opposite is observed in the experiments. Moreover, for jet temperature ratios of 2.5 and 3, the strong flapping motion of the jet along the minor axis plane due to the screech feedback mechanism yields to an antisymmetric organization of the Mach wave radiation. Thereafter, the near-and far-field acoustic are studied. In the near-field, screech tones are captured, whose frequencies are consistent with both experimental data and theoretical models. In the far-field, four acoustic components typical of non-ideally expanded supersonic jets are observed, namely the screech noise, the broadband shock-associated noise, the mixing noise and the Mach wave noise. Their directivities and frequencies are in agreement with experimental results and models. The mechanism of the screech noise generation is studied by using a Fourier decomposition of the pressure field. For the four over-expanded jets, a flapping motion along the diagonal or along the minor axis plane of the jet is noted. Finally, the hypothesis that the acoustic waves completing the feedback loop in these jets are linked to the upstreampropagating acoustic wave modes of the equivalent ideally expanded jets is tested. Using a jet vortex sheet model to describe the dispersion relations of these modes, it is found that this hypothesis allows us to explain the antisymmetric jet oscillation observed at the screech frequencies. Based on frequency-wavenumber decomposition of the pressure fluctuations in the jets, it is shown that at the screech frequencies, acoustic waves propagating in the upstream direction at the ambient speed of sound exist also in the jet flow, additionally

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Acoustics from a Rectangular C-D Nozzle Exhausting Over a Flat Surface

Cited by 20 publications

References 19 publications

Effect of an Adjacent Flat Plate on a Highly-Heated Rectangular Supersonic Jet

Effect of an Adjacent Flat Plate on a Highly-Heated Rectangular Supersonic Jet

High-Temperature Effects on Aerodynamic and Acoustic Characteristics of a Rectangular Supersonic Jet

Antisymmetric Oscillation Modes in Rectangular Screeching Jets

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