Noise, turbulence, and thrust of subsonic free jets from lobed nozzles

Zaman, K. B. M. Q.; Wang, F. Y.

doi:10.2514/6.2002-569

Cited by 12 publications

(16 citation statements)

References 18 publications

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“…In fact, the authors observed that the distance of the first peak from the jet exit, scales on the width of the lobes (a1), with 4 ≤ Z/a1 ≤ 6. In our case, the first peak in the CO/P nozzle jet occurred at Z/a1 =5.2, which falls within the reported range [13].…”

Section: Flow Characteristicssupporting

confidence: 71%

“…Whereas the second peak is believed to be related to the wall damping effect [60], the occurrence of the first peak is not fully understood. From the study of Zaman et al [13] on a free rectangular lobed jet, the appearance of a sharp peak on the axial turbulence intensity near the jet exit could be related to the merging of the shear layers shed from an individual lobe. In fact, the authors observed that the distance of the first peak from the jet exit, scales on the width of the lobes (a1), with 4 ≤ Z/a1 ≤ 6.…”

Section: Flow Characteristicsmentioning

confidence: 99%

“…Active [7][8][9] or passive [10][11][12][13] alteration of the initial conditions causes considerable modifications of the large-scale vortices in both their shape and convection velocities. These techniques are commonly used to improve jet self-induction, which is useful in mixing processes such as those occurring in combustion chambers [6].…”

Section: Introductionmentioning

confidence: 99%

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Impinging cross-shaped submerged jet on a flat plate: a comparison of plane and hemispherical orifice nozzles

et al. 2015

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To cite this version:Kodjovi Sodjavi, Brice Montagné, Pierre Bragança, Amina Meslem, Florin Bode, et al.. Impinging cross-shaped submerged jet on a flat plate: a comparison of plane and hemispherical orifice nozzles. Meccanica, Springer Verlag, 2015, pp.1-21. 10 AbstractIt is well known that the transfer of heat, mass and momentum to a wall by an impinging jet is partially linked to the way in which jet generation is realized. The organization of the vortices at the jet exit depends on the upstream conditions and on the geometry of the nozzle. Particle Image Velocimetry (PIV) and electrodiffusion techniques were used to investigate the characteristics of different impinging jets and the resulting wall shear rates and mass transfer. Two Cross-Shaped orifice jets, one produced by a plane orifice nozzle (i.e. a Cross-Shaped Orifice made on a flat Plate, CO/P) and the second by a hemispherical orifice nozzle (i.e. a Cross-Shaped Orifice made on a Hemisphere, CO/H), were compared to a reference round jet produced by a convergent nozzle. The distance between the jet exit and the target wall was equal to two nozzle equivalent diameters (De), based on the free orifice area. The Reynolds number, based on De and on the exit bulk-velocity, was 5620 for each flow. PIV measurements give an overall view of the flow characteristics in their free and wall regions. The switching-over phenomena observed in the CO/P nozzle case, and already described in the literature with similar nozzles, did not occur in the jet from the CO/H nozzle. Electrodiffusion measurements showed differences in the shape and level of radial distribution of the wall shear rates and mass transfer. One of the most important observations is the large difference in wall shear stress between the three jets. For the same exit bulk-velocity, the maximum wall shear rate in the CO/P and CO/H nozzle jets was almost two and three times higher, respectively, than that of the reference convergent jet. This higher wall shear rate is accompanied

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Section: Flow Characteristicssupporting

confidence: 71%

Section: Flow Characteristicsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Impinging cross-shaped submerged jet on a flat plate: a comparison of plane and hemispherical orifice nozzles

et al. 2015

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“…This relatively slow speed case was selected in order to avoid any significant compressibility effects. Comparison of PIV data from this Mach 0.5 jet case with hot-wire measurements from a Mach 0.3 round jet investigated in reference [12] indicated very similar normalized mean flow and turbulence statistics, which verifies that the current Mach 0.5 case under consideration will not be noticeably biased by compressibility effects. In addition to the baseline Chien k-model and the modified k-model using the Var-D correction, we also examine the Menter Shear-Stress Transport (SST) model (Refs.…”

Section: Evaluation Of Var-d Correction For Jet Sp#3mentioning

confidence: 73%

Investigation of Variable-Diffusion Turbulence Model Correction for Round Jets

Engblom

Georgiadis

Khavaran³

et al. 2005

11th AIAA/CEAS Aeroacoustics Conference

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A Reynolds-Averaged Navier-Stokes (RANS) correction is described to account for a key effect of acoustic interaction near the end of the potential core for axisymmetric jets. Specifically, the Variable-Diffusion (Var-D) correction is formulated to mimic the effect of increased shear layer instability/motion near the end of the potential core by adjusting the local diffusion of k and . The proposed Var-D correction is initially evaluated for an unheated axisymmetric jet with a perfectly expanded jet Mach number of 0.5. Results for centerline velocity distribution and turbulent kinetic energy contours using commonly employed turbulence models (i.e. SST and k-) and k-with the Var-D correction are compared. Substantial improvement for prediction of potential core length, centerline velocity decay, and k field is demonstrated with the Var-D correction. The sensitivity of the proposed model to the closure coefficients associated with the correction is also examined using this cold subsonic jet case. Similar turbulence model performance comparisons are made for three other jets to evaluate the sensitivity of the correction to increased jet exhaust compressibility and heated jet flow conditions. The effect of the improved mean and turbulence field predictions obtained using the Var-D correction on farfield noise prediction is also evaluated using the JeNo acoustic analogy code, and shown to be negligible. Although the approach holds promise, the applicability of the Var-D correction is currently limited to round jets. I. Nomenclature= decay rate exponent = diffusion factor limit = dissipation of turbulent kinetic energy k = turbulent kinetic energy II. IntroductionDespite the routine use Reynolds-averaged Navier-Stokes (RANS) techniques for analysis of aerospace systems, the accurate prediction of nozzle and jet flows remains an area of needed improvement. Turbulence modeling remains the pacing item limiting the accuracy of jet flow predictions. Further, for aeroacoustics analysis, both the mean flow and turbulence state are important for assessment of noise emitted by jets under consideration. While Large-Eddy Simulation (LES) offers promise for the future by resolving the large-scale unsteady turbulent motion, this technique is currently prohibitively expensive computationally for realistic, high Reynolds number flows. Hence, RANS approaches will be required for the foreseeable future. As a result, there is still a need for work in the area of RANS turbulence modeling for jets, including turbulence model development to more accurately calculate developing jet flow features, as well as for comprehensive assessment of modeling advances to determine capabilities and limitations.Effective use of RANS computational fluid dynamics (CFD) in nozzle aeroacoustics investigations requires accurate simulation of both the mean flow and turbulent kinetic energy fields. Capturing the initial jet growth region remains a difficulty. There are many examples of subsonic jet potential core length underprediction in the literature. For ...

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“…It is to be noted that, since the sixties, much before the findings of Liepmann and Gharib (Liepmann, 1991;Liepmann and Gharib, 1992) on the important part played by the streamwise structures in mixing, artificial streamwise vorticity generation methods are used in aeronautics and combustion in order to improve mixing (Kuchar and Chamberlin, 1980;Paterson, 1984;Presz et al, 1986Presz et al, , 1994Presz et al, and 2002Zaman, et al, 1994;Zaman, 1996aZaman, , 1996bZaman, , 1999Zaman, and 2003Ramesh et al, 2006). The currently used passive generators of streamwise vortices are small tabs or chevrons placed at the nozzle exit.…”

Section: Introductionmentioning

confidence: 99%

Vortex dynamics and entrainment mechanisms in low Reynolds orifice jets

Năstase

Meslem

2008

J Vis

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Classical planar 2D-PIV measurements and time-resolved visualizations enriched by low-level processing are used for the reconstruction of the Kelvin-Helmholtz vortex passing in the near field of a circular and a 6-lobed orifice jet flow. In the circular jet, the entrainment is produced in the braid region, being interrupted in the presence of the Kelvin-Helmholtz ring. The latter compresses the streamwise vortices and alters their self-induction role. Conversely, the 6-lobed orifice geometry allows the cutting of the Kelvin-Helmholtz structures into discontinuous ring segments. Consequently, into these discontinuity regions streamwise large scale structures are developing. These streamwise structures are permanent thus controlling and enhancing the jet entrainment which is not altered by the Kelvin-Helmholtz structures passing.

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Noise, turbulence, and thrust of subsonic free jets from lobed nozzles

Cited by 12 publications

References 18 publications

Impinging cross-shaped submerged jet on a flat plate: a comparison of plane and hemispherical orifice nozzles

Impinging cross-shaped submerged jet on a flat plate: a comparison of plane and hemispherical orifice nozzles

Investigation of Variable-Diffusion Turbulence Model Correction for Round Jets

Vortex dynamics and entrainment mechanisms in low Reynolds orifice jets

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