Resonant Interaction of a Rectangular Jet with a Flat-plate

An experimental investigation of resonant interaction of a rectangular jet with a flat plate

Journal of Fluid Mechanics ◽

10.1017/jfm.2015.453 ◽

2015 ◽

Vol 779 ◽

pp. 751-775 ◽

Cited By ~ 14

Author(s):

K. B. M. Q. Zaman ◽

A. F. Fagan ◽

J. E. Bridges ◽

C. A. Brown

Keyword(s):

Mach Number ◽

Flat Plate ◽

Cross Section ◽

Leading Edge ◽

Resonant Interaction ◽

Trailing Edge ◽

Resonant Condition ◽

Direction Parallel ◽

Rectangular Jet ◽

Axis Switching

The interaction between an 8:1 aspect ratio rectangular jet and a flat plate, placed parallel to the jet, is addressed in this study. At high subsonic conditions and for certain relative locations of the plate, a resonance takes place with accompanying audible tones. Even when the tone is not audible the sound pressure level spectra are often marked by conspicuous peaks. The frequencies of these peaks, as functions of the plate’s length, its location relative to the jet as well as jet Mach number, are studied in an effort to understand the flow mechanism. It is demonstrated that the tones are not due to a simple feedback between the nozzle exit and the plate’s trailing edge; the leading edge also comes into play in determining the frequency. With parametric variation, it is found that there is an order in the most energetic spectral peaks; their frequencies cluster in distinct bands. The lowest frequency band is explained by an acoustic feedback involving diffraction at the plate’s leading edge. Under the resonant condition, a periodic flapping motion of the jet column is seen when viewed in a direction parallel to the plate. Phase-averaged Mach number data on a cross-stream plane near the plate’s trailing edge illustrate that the jet cross-section goes through large contortions within the period of the tone. Farther downstream a clear ‘axis switching’ takes place for the time-averaged cross-section of the jet that does not occur otherwise for a non-resonant condition.

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Numerical Investigation of a Rectangular Jet Exhausting over a Flat Plate with Periodic Surface Deformations at the Trailing Edge

Aerospace ◽

10.3390/aerospace8110314 ◽

2021 ◽

Vol 8 (11) ◽

pp. 314

Author(s):

Colby Niles Horner ◽

Adrian Sescu ◽

Mohammed Afsar ◽

Eric Collins

Keyword(s):

Flat Plate ◽

Experimental Studies ◽

Wing Surface ◽

Wave Number ◽

Noise Levels ◽

Trailing Edge ◽

Vehicle Performance ◽

Rectangular Jet ◽

Sound Levels ◽

Jet Interactions

Multiple competing factors are forcing aircraft designers to reconsider the underwing engine pod configuration typically seen on most modern commercial aircraft. One notable concern is increasing environmental regulations on noise emitted by aircraft. In an attempt to satisfy these constraints while maintaining or improving vehicle performance, engineers have been experimenting with some innovative aircraft designs which place the engines above the wings or embedded in the fuselage. In one configuration, a blended wing concept vehicle utilizes rectangular jet exhaust ports exiting from above the wing ahead of the trailing edge. While intuitively one would think that this design would reduce the noise levels transmitted to the ground due to the shielding provided by the wing, experimental studies have shown that this design can actually increase noise levels due to interactions of the jet exhaust with the aft wing surface and flat trailing edge. In this work, we take another look at this rectangular exhaust port configuration with some notional modifications to the geometry of the trailing edge to determine if the emitted noise levels due to jet interactions can be reduced with respect to a baseline configuration. We consider various horizontal and vertical offsets of the jet exit with respect to a flat plate standing in for the aft wing surface. We then introduce a series of sinusoidal deformations to the trailing edge of the plate of varying amplitude and wave number. Our results show that the emitted sound levels due to the jet–surface interactions can be significantly altered by the proposed geometry modifications. While sound levels remained fairly consistent over many configurations, there were some that showed both increased and decreased sound levels in specific directions. We present results here for the simulated configurations which showed the greatest decrease in overall sound levels with respect to the baseline. These results provide strong indications that such geometry modifications can potentially be tailored to optimize for further reductions in sound levels.

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Examination of Rabbit Fc Crystals

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100100445 ◽

1968 ◽

Vol 26 ◽

pp. 140-141

Author(s):

J. P. Robinson ◽

P. G. Lenhert

Keyword(s):

Molecular Weight ◽

Flat Plate ◽

Phosphate Buffer ◽

Asymmetric Unit ◽

X Ray Diffraction ◽

X Ray ◽

Neutral Ph ◽

Small Crystals ◽

Carbon Coated ◽

Diffraction Patterns

Crystallographic studies of rabbit Fc using X-ray diffraction patterns were recently reported. The unit cell constants were reported to be a = 69. 2 A°, b = 73. 1 A°, c = 60. 6 A°, B = 104° 30', space group P21, monoclinic, volume of asymmetric unit V = 148, 000 A°3. The molecular weight of the fragment was determined to be 55, 000 ± 2000 which is in agreement with earlier determinations by other methods.Fc crystals were formed in water or dilute phosphate buffer at neutral pH. The resulting crystal was a flat plate as previously described. Preparations of small crystals were negatively stained by mixing the suspension with equal volumes of 2% silicotungstate at neutral pH. A drop of the mixture was placed on a carbon coated grid and allowed to stand for a few minutes. The excess liquid was removed and the grid was immediately put in the microscope.

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