A Study of Convective Velocity in Supersonic Jets Using MHz Rate Imaging

Blohm, M.; Lempert, Walter R.; Samimy, Mo; Thurow, Brain

doi:10.2514/6.2006-45

Cited by 9 publications

(3 citation statements)

References 22 publications

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“…Bias errors in the jet's shear layer due to flow seeding gradients as found by Blohm et al 40 were minimized by co-flow seeding via entrainment from a smoke generator. The Stokes relaxation time can be estimated as:…”

Section: Facilitymentioning

confidence: 99%

Fourth-order Spectral Statistics in the Developing Shear Layers of Hot Supersonic Jets

Ecker¹,

Lowe²,

Ng³

et al. 2014

50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference

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Novel non-intrusive measurements are presented to lend insight into behavior of 4 th order velocity fluctuation spectral statistics and space-time correlations in the developing shear layer of hot supersonic jets. Fourth-order statistics are dominated by the chaotic motion of large-scale coherent structures, which appear largely as the 'skirts' of probity density. Due to the interest in predicting the power spectral spectral density of acoustic density fluctuations, a mean-square quantity, 4 th order statistics hold direct application in acoustic analogies. Despite this, limited data exist for fourth-order spectral correlations of velocity, particularly in hot supersonic jets. A Doppler-based measurement technique with a frequency resolution of 125kHz is employed to obtain time-resolved measurements and used to determine 2 nd and 4 th order space-time correlations, integral timescales, convection velocities and auto-spectra on the lip line of a hot (TTR=1.6 and TTR=2) supersonic perfectly expanded jet at M d =1.65. Comparator data obtained in the same facility using laser Doppler velocimetry is analyzed with respect to 4 th order terms indicating the importance of the 4 th order correlation in the region of immediate interface between the potential core and the shear layer.

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Section: Facilitymentioning

confidence: 99%

Fourth-order Spectral Statistics in the Developing Shear Layers of Hot Supersonic Jets

Ecker¹,

Lowe²,

Ng³

et al. 2014

50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference

View full text Add to dashboard Cite

show abstract

“…The experimental arrangement for PDV is more complex due to the need to acquire two images (a signal and a reference) along the same optical path. Figure 8 shows the experimental arrangement employed by Blohm et al (2006) to measure the velocity of Mach 1.3 and Mach 2.0 rectangular jets. It should be noted that the technique is only sensitive to a single component of velocity (see equation ( 3)); three-component velocity measurements would require two additional measurements viewing the flow from separate angles.…”

Section: Filtered Rayleigh Scattering and Planar Doppler Velocimetrymentioning

confidence: 99%

Review of ultra-high repetition rate laser diagnostics for fluid dynamic measurements

Thurow

Jiang

Lempert

2012

Meas. Sci. Technol.

117

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Recent advances in ultra-high repetition rate (100 kHz and above) laser diagnostics for fluid dynamic measurements are reviewed. The development of the pulse burst laser system, which enabled several of these advances, is described. The pulse burst laser system produces high repetition rate output by slicing the output of a low power continuous wave laser and passing the resulting burst of pulses through a series of pulsed Nd:YAG amplifiers. Several systems have been built with output approaching 1.0 J/pulse over bursts of up to 100 pulses generated at between 50 and 1000 kHz. Combined with the capabilities of several types of commercially available high-speed cameras, these systems have been used to make a wide variety of high repetition rate and 3D flow measurements. Several examples of various high repetition rate laser diagnostics are described, including flow visualization, filtered Rayleigh scattering, planar Doppler velocimetry, particle image velocimetry, planar laser induced fluorescence, molecular tagging velocimetry and 3D flow visualization.

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“…echniques available for laser-based flow diagnostics have witnessed a revolution in recent years due to drastic improvements in imaging speed and resolution. CCD sensors and high-energy laser pulse generation methods, both capable of operation at 100s of kHz, have expanded traditional laser flow diagnostics such as two-dimensional flow visualization 1,2,3 , particle image velocimetry (PIV), and planar laser induced fluorescence (PLIF) 4 to high-speed flow regimes, and have made possible the development of entirely new measurement techniques.…”

Section: Introductionmentioning

confidence: 99%

Investigation of Image Processing Steps for Reconstruction of Three-Dimensional Flow Visualization Images

Lynch

Thurow

2008

26th AIAA Aerodynamic Measurement Technology and Ground Testing Conference

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The process of reconstructing and correcting three-dimensional flow visualization images created using a high-speed laser sheet scanning technique is explored. 3-D images are formed from a sequence of 2-D images obtained using laser sheet illumination with a MHz rate pulse burst laser system, a scanning mirror and a high-speed intensified camera capable of framing rates of 500,000 fps. Due to some unique properties of the high-speed camera, special image processing steps are required in order to form high quality 3-D images. Image processing steps described here include flat-field correction, dark field image subtraction, correction for non-uniform laser sheet intensity and image normalization. In addition, consideration is given to calibration of the 3-D image in 3-D physical space and correction of a ghosting phenomenon associated with the high-speed camera.Examples of visualizations compiled from sets of corrected image data are presented, the sources of remaining distortions are considered, and future system upgrades are described.

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A Study of Convective Velocity in Supersonic Jets Using MHz Rate Imaging

Cited by 9 publications

References 22 publications

Fourth-order Spectral Statistics in the Developing Shear Layers of Hot Supersonic Jets

Fourth-order Spectral Statistics in the Developing Shear Layers of Hot Supersonic Jets

Review of ultra-high repetition rate laser diagnostics for fluid dynamic measurements

Investigation of Image Processing Steps for Reconstruction of Three-Dimensional Flow Visualization Images

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