Laser-induced Thermal Acoustics
Author | : Eric B. Cummings |
Publisher | : |
Total Pages | : 176 |
Release | : 1995 |
Genre | : Gas dynamics |
ISBN | : |
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Author | : Eric B. Cummings |
Publisher | : |
Total Pages | : 176 |
Release | : 1995 |
Genre | : Gas dynamics |
ISBN | : |
Author | : |
Publisher | : |
Total Pages | : 11 |
Release | : 1994 |
Genre | : |
ISBN | : |
Laser-induced thermal acoustics (LITA) is a promising optical four- wave mixing technique for gasdynamic measurement. The X(3) nonlinear process is a sequence of two opto-acoustic effects, electrostriction and absorption/rapid- thermalization, and the acousto-optic effect. The evolution of the laser-induced acoustic structures temporally modulates X(3) and thereby the LITA signal. Time resolution of the signal provides the sound speed, thermal diffusivity, and acoustic damping rate, along with information about atomic or molecular energy transfer rates. LITA can also measure spectra of both the real and imaginary gas susceptibility. The physics of LITA is discussed and the derivation is sketched of a simple analytical expression that accurately describes both the magnitude and time history of the LITA signal. Early experimental results are presented. Sound speeds accurate to 0.5% and transport properties accurate to 30% have been measured in a single-shot without calibration. More realistic modeling should dramatically improve transport-property measurement. LITA spectra have been taken of weak spectral lines of NO2 in concentrations less than 50 ppb. Signal reflectivities as high as 0.0001 have been estimated. New applications of LITA, including velocimetry, are suggested. LITA, Four-wave mixing, Thermal grating, Single-shot measurement, Velocimetry.
Author | : Stefan Schlamp |
Publisher | : |
Total Pages | : |
Release | : 2003 |
Genre | : |
ISBN | : |
Author | : National Aeronautics and Space Adm Nasa |
Publisher | : Independently Published |
Total Pages | : 32 |
Release | : 2019-01-18 |
Genre | : Science |
ISBN | : 9781794248335 |
The relative signal strength of electrostriction-only (no thermal grating) laser-induced thermal acoustics (LITA) in gas-phase air is reported as a function of temperature T and pressure P. Measurements were made in the free stream of a variable Mach number supersonic wind tunnel, where T and P are varied simultaneously as Mach number is varied. Using optical heterodyning, the measured signal amplitude (related to the optical reflectivity of the acoustic grating) was averaged for each of 11 flow conditions and compared to the expected theoretical dependence of a pure-electrostriction LITA process, where the signal is proportional to the square root of [P*P /( T*T*T)]. Herring, Gregory C. Langley Research Center NASA/TM-2015-218762, L-20562, NF1676L-21439
Author | : Roger C. Hart |
Publisher | : |
Total Pages | : 14 |
Release | : 2001 |
Genre | : |
ISBN | : |
Author | : Felix Johannes Förster |
Publisher | : |
Total Pages | : |
Release | : 2016 |
Genre | : |
ISBN | : 9783843929738 |
Author | : National Aeronautics and Space Adm Nasa |
Publisher | : |
Total Pages | : 30 |
Release | : 2018-09-27 |
Genre | : |
ISBN | : 9781724080097 |
We demonstrate the use of a novel technique for the detection of heterodyne laser-induced thermal acoustics signals, which allows the construction of a highly stable seedless laser velocimeter. A common-path configuration is combined with quadrature detection to provide flow direction, greatly improve robustness to misalignment and vibration, and give reliable velocity measurement at low flow velocities. Comparison with Pitot tube measurements in the freestream of a wind tunnel shows root-mean-square errors of 0.67 m/s over the velocity range 0.55 m/s. Hart, Roger C. and Herring, G. C. and Balla, R. Jeffrey and Bushnell, Dennis M. (Technical Monitor) Langley Research Center NASA/CR-2001-211252, NAS 1.26:211252, ICASE-2001-37...
Author | : Christoph Steinhausen |
Publisher | : |
Total Pages | : 0 |
Release | : 2023 |
Genre | : |
ISBN | : 9783843952057 |
Author | : |
Publisher | : |
Total Pages | : 0 |
Release | : 2002 |
Genre | : |
ISBN | : |
The development of novel flow diagnostic techniques typically proceeds in certain stages from a proof of principle in a laboratory to a commercial product either for use in industry or as turn-key research tool. While the first usable versions are brought to market, further progress is made in the laboratory by improvements, refinements, and extensions of the technique. Consider Particle Image Velocimetry (PIV), which started by double-exposing a photographic film with the image of an illuminated particle-laden flow and where today turn-key, off-the-shelf CCD systems are available for purchase, which include the necessary data analysis software. At the same time, 3d PIV, dual-plane PIV, Doppler Global Velocimetry (DGV), etc. are being used in laboratories and will doubtless be available as integrated systems in the near future. In this paper, the origin, an overview over the current status and an outlook on the future potential of Laser-Induced Thermal Acoustics (LITA) will be given, where the focus will be on the possible technique extensions to other than the current applications. As such, it represents a collection of ideas and avenues for future research, which have not been applied as of yet, but are conceptually feasible.
Author | : Stefan Schlamp |
Publisher | : |
Total Pages | : |
Release | : 2000 |
Genre | : |
ISBN | : |