Development and application of a point Doppler velocimeter featuring two-beam multiplexing for time-resolved measurements of high-speed flow

Ecker, Tobias; Brooks, Donald R.; Lowe, K. Todd; Ng, Wing F.

doi:10.1007/s00348-014-1819-0

Cited by 37 publications

(18 citation statements)

References 38 publications

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“…Indeed, except for the first three shock cells of the M j ¼ 1:15 jet, in the supersonic region maximum levels of u sc rms occur barely in the middle of the shock cells with respect to the streamwise direction, whereas they are aligned with the shock tips in the low-speed region. This behavior is similar with the experimental observations by Ecker et al 39 in a M j ¼ 1:4 overexpended jet, or by Edgington-Mitchell et al 22 in a M j ¼ 1:45 jet, even though the maximum is found shifted toward the center of the shock cells in the present case in comparison with the two latter studies. This difference possibly arises from the difference in screech mode between these two studies in which helical mode is observed, whereas A1 and A2 modes of the present study are axisymmetric.…”

Section: Coherent Velocitiessupporting

confidence: 93%

Experimental study of the coherent vorticity in slightly under-expanded supersonic screeching jets

Mercier

Castelain

Bailly

2019

International Journal of Aeroacoustics

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The noise generation mechanism of screech tone by shock leakage in underexpended round jets is experimentally investigated by means of phase-averaged velocity fields. Two jet flows at Mach numbers 1.10 and 1.15 are measured by a particle image velocimetry apparatus simultaneously with their near acoustic fields and sorted according to their phase with respect to a screech period. The coherent vorticity fields are then computed and analyzed. They depict two distinct regions of high level of vorticity fluctuations. Thanks to the knowledge about shock leakage gathered in previous studies, the role of both regions in the acoustic generation process is identified and a region of the flow is recognized as suitable for emitting acoustic waves. Phase-averaged schlieren visualizations are also computed and used to determine the motion of the first five shocks over a screech period. For both jets, the peak shock motion is found at the fourth shock tip. This shock is also located in the region recognized as favorable for the shock leakage to be observed.

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Section: Coherent Velocitiessupporting

confidence: 93%

Experimental study of the coherent vorticity in slightly under-expanded supersonic screeching jets

Mercier

Castelain

Bailly

2019

International Journal of Aeroacoustics

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“…For planar operation, two laser sheets of equal width and thickness need to be consecutively illuminate the measurement plane. For a receiver system with a measurement plane parallel to the streamwise axis the maximal sheet width is dictated by the 45 deg angle position which was also found as the angle with the lowest overall uncertainty by Ecker et al 2 for this type of sensor geometry. A schematic of this configuration is shown in figure 4.…”

Section: A Multipoint Dgv Systemmentioning

confidence: 97%

“…In a first step Ecker et al 2 have demonstrated the fundamental developments for the Doppler-based technique capable of very high temporal resolution three-velocity component particle measurements in supersonic jets. The technique is a modification of the Doppler Global Velocimetry/Planar Doppler Velocimetry technique, but with improvements of using high sensitivity photodetectors, FPGA-based signal processors and a continuous wave laser.…”

Section: Introductionmentioning

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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“…For more details on the PIV setup and instrumentation, the reader is referred to the article by Henderson and Wernet (2016). Convection velocities were measured using the DGV instrument previously developed (Ecker et al (2014)), discussed further to follow.…”

Section: Experimental Methodsmentioning

confidence: 99%

Synthesis of convection velocity and turbulence measurements in three-stream jets

Stuber

Lowe

2019

Exp Fluids

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Key flow regions linked to jet noise sources are investigated through comparison of convection velocity and turbulence measurements in high speed threestream nozzles. A time-resolved Doppler global velocimetry (DGV) instrument was applied in the Nozzle Acoustic Test Rig (NATR) at NASAs Aero-Acoustic Propulsion Lab to measure 250 kHz repetition laser scattering signals arising from seeding particles at 32 points in high speed flow. Particle image velocimetry (PIV) measurements previously reported by NASA provided mean velocity and turbulence intensity. Results for convection velocity of the particle concentration field were obtained from the DGV data for three-stream nozzle configurations using a cross-correlation approach. The three-stream cases included an axisymmetric and an asymmetric, offset nozzle configuration. For the axisymmetric case, areas of high convection velocity and turbulence intensity were found to occur 4 to 6 area-equivalent nozzle diameters downstream from the nozzle exit. Comparison of convection velocity between the axisymmetric and offset cases show this same region as having the greatest reduction in convection velocity due to the offset, up to 20% reduction for the offset case compared to the axisymmetric case. These findings suggest this region along the centerline near the end of the potential core is an important area for noise generation with jets and contributes to the noise reductions seen from three-stream offset nozzles.

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Development and application of a point Doppler velocimeter featuring two-beam multiplexing for time-resolved measurements of high-speed flow

Cited by 37 publications

References 38 publications

Experimental study of the coherent vorticity in slightly under-expanded supersonic screeching jets

Experimental study of the coherent vorticity in slightly under-expanded supersonic screeching jets

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

Synthesis of convection velocity and turbulence measurements in three-stream jets

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