Density Field Measurements of a Supersonic Impinging Jet with Microjet Control

Venkatakrishnan, L.; Wiley, Alex; Kumar, Rajan; Alvi, Farrukh S.

doi:10.2514/1.j050511

Cited by 11 publications

(6 citation statements)

References 12 publications

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“…The SPL of the CFD results falls between the two experimental measurements for the dominant peak, L3, but is overall higher as expected. The CFD results show L3 to be the dominant tone in agreement with one of the experiments (Venkatakrishnan et al, 2011) but not the other (Krothapalli et al, 1999) which shows L1 to be the dominant tone with L3 very close in level. As pointed out in both experimental observations, the jet exhibited more unsteadiness in its oscillation at this separation distance.…”

Section: Comparisons To Experimental Datasupporting

confidence: 71%

“…This unsteadiness is believed to be attributed to the competition between the L1 and L3 tones. In the Venkatakrishnan et al (2011) results, a strong harmonic of the L3 tone is shown, whereas the CFD and Krothapalli et al's (1999) results show a much weaker harmonic. As mentioned above, an important observation made from Figure 4 is the difference shown between the two experimental results.…”

Section: Comparisons To Experimental Datamentioning

confidence: 74%

“…Results from the study showed that the lift loss increased as the separation distance between the nozzle exit and the ground plane decreased. Venkatakrishnan et al (2011) carried out similar experiments to that of Krothapalli et al (1999) with the addition of injection into the plume using microjets located on the lift plate around the circumference of the jet. Microjet injection was found to make the jet flow less unsteady.…”

Section: Introductionmentioning

confidence: 99%

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Flow structures and noise from a supersonic impinging jet

Frendi

Brown

2016

HFF

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Purpose The purpose of this paper is to carry out an extensive numerical study in order to understand the flow structures and the resulting noise generated by a supersonic impinging jet on a flat plate. One of the parameters varied in this study is the distance between the jet exit plane and the flat plate. Design/methodology/approach Because of the unsteady nature of the problem a time-dependent computation is carried out using the detached eddy simulation turbulence model. The OVERFLOW 2 CFD code was used with a highly resolved grid and small time steps. Findings The authors found that as the separation distance increases, the dominant frequencies in the noise spectrum decrease. In addition, the relative strength of the various frequencies to each other changes with changing distance, indicating the changing modes of the jet. The CFD results indicate a strong interaction between the acoustic waves emanating from the impingement plate and the jet plume. This feedback mechanism is responsible for destabilizing the jet shear layer leading to the jet changing modes. The computed near field spectra, convection velocities of the jet vortical structures and mean jet centerline velocity profile are in good agreement with experimental measurements. The results also show very high sound pressure levels all over the impingement plate but especially near the impingement point. These levels, if sustained, are detrimental to both human operators as well as the surrounding structures. Research limitations/implications Given the large-scale nature of the computations carried out, it is very costly to run the computations long enough to collect a good, statistically steady time sample to achieve a low frequency bandwidth resolution. Such a long time sample could actually improve the results in terms of frequency resolution and obtained an even better agreement with experiments. Off course there is always the issue of grid resolution as well, but given the good agreement with experiments that the authors obtained, the authors are confident in their results. Practical implications The practical implications of the results the authors obtained are significant in that, the authors now know that hybrid RANS-large eddy simulation methods can be used for this complex, unsteady engineering problems. In addition, the results also show the high noise level both on the impingement surface and in the surroundings of the jet. This could have a negative impact on the structural integrity of the flat surface. Social implications Noisy environments are never desirable anywhere especially in places where human operations take place. Therefore, given the high noise levels obtained in the simulations and confirmed by experiments, any human presence around the jet will be harmful to hearing and precautions need to be taken. Originality/value This is a physics-based study; i.e. understanding the physical phenomena involved in supersonic jet impingement. Of particular interest is the interaction of the jet shear layer with the acoustic waves emanating from the impingement area. This feedback loop is found to be responsible for intensifying the instability of the jet shear layer.

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Section: Comparisons To Experimental Datasupporting

confidence: 71%

Section: Comparisons To Experimental Datamentioning

confidence: 74%

Section: Introductionmentioning

confidence: 99%

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Flow structures and noise from a supersonic impinging jet

Frendi

Brown

2016

HFF

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Section: Introductionmentioning

confidence: 99%

“…Similar to the schlieren method, BOS is capable of measuring two in-plane, first-order gradients parallel to the background target and the image sensor, which are integrated along the line of sight [2,3,14,17]. Additional procedures can be followed to measure the gradients in the normal direction of the plane [3,12,14,17]. Besides providing quantitative measurements, the other advantages of BOS can be summarized as: the straightforward computation, no restriction on the measurement object size, reduced number of optical elements and simpler adjustment compared to traditional schlieren technique [2,4,9].…”

Section: Introductionmentioning

confidence: 99%

Temperature and velocity measurements in a fluid layer using background-oriented schlieren and PIV methods

Tokgöz

Geisler

Bokhoven

et al. 2012

Meas. Sci. Technol.

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In this paper, we discuss temperature and velocity measurements inside a thin fluid layer using background-oriented schlieren (BOS) and particle image velocimetry (PIV) methods. BOS is a suitable technique for quantitative temperature measurements, but so far it has been used in fully transparent systems only. Introducing a reflective surface inside the measurement geometry which is optically accessible from only one viewing direction, we measure the refractive index change of a flow provided by two elliptical jets by visualizing displacements on a background target. Relation between the refractive index change and the temperature gradients is used to compute 2D temperature fields. Measurements are carried out for various temperature differences between the jets for both steady and dynamic flow. The simultaneous implementation of BOS and PIV techniques provides instantaneous, two-dimensional temperature gradients and velocity vectors inside the thin fluid layer.

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