Improved flow visualization by use of resonant refractivity

Bershader, D.; Prakash, Subbalakshmi; Huhn, G.

doi:10.2514/6.1976-71

Cited by 6 publications

(8 citation statements)

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“…2 Since the resonance transitions of air and other diatomic gases lie in the far ultraviolet, the work just referred to as well as the present Note deals with the resonance refractivity of sodium vapor. In a laboratory application of this method, the working fluid would be seeded with small quantities of sodium vapor or other suitable material, probably in the range 10 ~4 to 10 ~3 mole fraction.…”

Section: R Efractive Methods Pioneered By the Studies Of Machmentioning

confidence: 99%

Resonance refractivity studies of sodium vapor for enhanced flow visualization

1978

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Section: R Efractive Methods Pioneered By the Studies Of Machmentioning

confidence: 99%

Resonance refractivity studies of sodium vapor for enhanced flow visualization

1978

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“…The refractive index gradients comprising an acoustic wave can also be visualised with a Schlieren imager. [35] derive the relationship between the deflection of an electromagnetic wave, the sound pressure level (SPL) and the frequency of an acoustic wave. This relationship is plotted in Figure 3.…”

Section: Schlieren Imaging and Acoustic Wavesmentioning

confidence: 99%

“…As noted by several papers (eg. [35,36]) for a reasonable custom Schlieren imaging system, any acoustic wave at audible frequencies would need to be at a volume that is painful for humans to be clearly imaged. However, when considering ultrasonic frequencies, the amplitude of the sound wave does not need to be as large, as reflected in Figure 3.…”

Section: Schlieren Imaging and Acoustic Wavesmentioning

confidence: 99%

“…From literature such as [35,[39][40][41] it is evident that imaging audible acoustic waves with a Schlieren imaging system is difficult due the explained challenges. However, imaging ultrasonic signals in air is feasible and has been achieved in numerous situations such as by [37] who examined 5 MHz ultrasonic waves using a pulsed laser.…”

Section: Schlieren Imaging and Acoustic Wavesmentioning

confidence: 99%

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Using Schlieren Imaging and Radar Acoustic Sounding System for the Detection and Characterization of Close-in Air Turbulence

Gordon,

Brooker

2023

Preprint

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This paper presents a novel sensor for the detection and characterization of regions of air turbulence that would be of use to improve UAV stability in bad weather. It consists of a combined Schlieren imager and a Radar Acoustic Sounding System (RASS) to produce dual modality “images” of air movement within the measurement volume. The ultrasound modulated Schlieren imager consists of a strobed point light source, parabolic mirror, light-block and camera which are controlled by two laptops. It provides a fine scale projection of the acoustic pulse modulated air turbulence through the measurement volume. The narrow beam 40 kHz/ 17 GHz RASS produces spectra based on Bragg enhanced Doppler radar reflections from the acoustic pulse as it travels. Tests using artificially generated air vortices showed some disruption of the Schlieren image and of the RASS spectrogram. This should allow the higher resolution Schlieren images to identify the turbulence mechanisms that are disrupting the RASS spectra.

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“…The tunable dye lasers only operated efficiently in the visible portion of the spectrum where the air is highly transparent, so for these new applications, flow seeding became important. Initially seeding with sodium provided planar imaging of flow cross sections (Miles, 1975) and enhanced schileren (Bershader et al, 1976). These advances were accomplished by tuning the laser either onto a resonance or near a resonance and utilizing the laser induced fluorescence for imaging planar cross sections or the enhanced index of refraction for higher sensitivity schlieren.…”

Section: Introduction and Retrospectivementioning

confidence: 99%

Optical Diagnostics for High-Speed Flows

Miles

2013

43rd Fluid Dynamics Conference

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Since the year 2000 there has been a revolution in diagnostics of high-speed air flows. The foundations for this revolution were laid over the previous few decades, but with the development of new short pulse and pulse burst laser technologies, higher laser powers and higher pulse energies, new high speed cameras, better laser control and improved detection and laser delivery methodologies, many very effective new capabilities have been developed. Newly developed methods for molecular tagging velocimetry provide high fidelity visualization of transport properties and may be extended to simultaneous temperature measurements. Rapid field imaging with frequency tunable pulse burst lasers show instantaneous flow structure and complex boundary and mixing interactions. Extending these pulse burst concepts to swept volumetric imaging is very promising for full volumetric data collection. Fast wavelength modulation spectroscopy follows real time flow variation, and three dimensional particle imaging extends particle imaging velocimetry to volumetric data acquisition.

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Improved flow visualization by use of resonant refractivity

Cited by 6 publications

References 0 publications

Resonance refractivity studies of sodium vapor for enhanced flow visualization

Resonance refractivity studies of sodium vapor for enhanced flow visualization

Using Schlieren Imaging and Radar Acoustic Sounding System for the Detection and Characterization of Close-in Air Turbulence

Optical Diagnostics for High-Speed Flows

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