Computer aided evaluation of interferograms

Bartels-Lehnhoff, H. H.; Baumann, P.; Bretthauer, B.; Meier, G. E. A.

doi:10.1007/bf00188506

Cited by 9 publications

(3 citation statements)

References 14 publications

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“…In order to retrieve automatically the optical phase unsteady flow fields real-time phase-evaluation methods 9 [10][11][12][13] . If needed, the achieved optical phase maps can be later correlated with the respective pressure, temperature and density fields.…”

Section: $%675$and7mentioning

confidence: 99%

Laval nozzle flow characterization by Fourier-transform Mach-Zehnder interferometry

et al. 2005

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%675$&7The role of the assist gas blown by a nozzle during the laser cutting process of ceramics is very important as a complex flow field is created by the interaction with the material. Flow visualization provides valuable information related with the properties and characteristics of the process in order to clear up misconceptions and as a first step towards the nozzle optimization. Optical methods as Schlieren or interferometry are suitable techniques for this task as well-known nonintrusive full-field methods utilized for analysing fast transient flow phenomena. In this work a Mach-Zehnder interferometer is employed in order to characterize a Laval nozzle by studying the shock wave patterns in a free gas jet as a previous step in order to study the complex interaction of the gas flow against a transparent model of the processed material. The optical phase is extracted from the obtained high-frequency fringe pattern by the Fourier Transform Phase-Difference Method. Disturbing effects are cancelled by proper combination of high-frequency fringe patterns obtained with and without gas flow. The shock wave pattern is analyzed for different geometrical configurations and operating pressures..H\ZRUGV Shock wave, Mach-Zehnder interferometry, gas flow, Fourier Transform Method.,1752'8&7,21During the laser cutting process of ceramics the role of the assist gas is very important since the flow energy is related to the cutting velocity and quality cut kerf 1-2 . At the same time, energy efficient processes are directly related to the removal of the molten material due to friction and to the pressure gradient of the gas flow. These processes can be carried out by means of a Laval nozzle, perhaps the most important and essential engineering hardware tool related with propulsion of high speed flow of gasses. A Laval nozzle has a properly contoured wall of convergent-divergent configuration in order to achieve a uniform supersonic flow at its exit 3 . If the incoming pressure is suitable, the flow in the throat nozzle became choked and a uniformly supersonic jet is obtained. These ideal theoretical conditions can be relaxed if small amplitude shock waves are present in the jet. The laser cutting process would be more energy efficient if these optimal work conditions are obtained.Although sophisticated numerical methods are available in order to study flows and software capable of simulating an ample variety of fluid flows are accessible 4 , real measurements are necessary in order to increase the knowledge of the physical process, to optimize particular industrial practices and to validate design proposals. In particular, valuable qualitative information can be obtained by flow visualization as the unsteady three-dimensional flow fields need a visual display of experimental as well as theoretical results. Among other techniques, whole-field non-invasive optical techniques are the most important non-intrusive techniques in fluid mechanics as they offer bidimensional quantitative visualization of the refraction index field in...

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Section: $%675$and7mentioning

confidence: 99%

Laval nozzle flow characterization by Fourier-transform Mach-Zehnder interferometry

et al. 2005

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“…In the second part of the twentieth century, the development of coherent and stable light sources like lasers and the introduction of new mathematical tools, like Fourier Theory and Phase-Evaluation Methods, opened new perspectives in Optical Metrology [1,2]. Recently the notable improvement of the image acquisition systems coupled with the personal computer technology has increased the interest for these measurement techniques.…”

Section: Introductionmentioning

confidence: 98%

Evaluation of interferometric patterns of supersonic fluid flows by the differential Fourier transform method

2012

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The knowledge of the flow structure of fluids is essential in many industrial sectors as it determines the quality and success of processes like welding, cutting or material treatment. The employed fluid flow plays a fundamental role and in all cases to understand the complex pressure and shock waves patterns becomes necessary. The only way to absolutely ensure that the theoretical behavior predicted by numerical simulations fits with the real gas flow behavior is the experimental check. For such application, the optical techniques are very well suited resources due to their non invasive features. Schlieren, shadowgraph and interferometry are the typical techniques used for the study of the mass flow in fluids. In this work, we present the qualitative results obtained from a conventional interferometric technique combined with a new numerical approach used for analyzing the inner structure of supersonic flows provided by nozzles with Laval profile used in industrial oxy-fuel cutting processes. The extraction of the optical phase from the fringe patterns is performed through a Differential Fourier Transform Evaluation. We show that with further numerical processing we can obtain a complete qualitative description of the flow field including the first and second optical phase derivatives (Gradient and Lapacian phase maps).

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“…These techniques have gone on their development but it is in the second part of the twentieth century, that their use increased. Indeed the employment of coherent and stable light sources like lasers and the introduction of new mathematical tools, like Fourier Theory and Phase-Evaluation Methods [2,3], have opened new perspectives in Optical Metrology. Recently the notable improvement of the image acquisition systems coupled with the personal computer technology has increased the interest for these measurement techniques.…”

Section: Introductionmentioning

confidence: 99%

Fourier transform evaluation and numerical modeling of fluid flow in a Laval nozzle

Rodríguez¹,

Dorrio

Doval

2008

SPIE Proceedings

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A new system for characterizing the flow delivered by a Laval nozzle in different stream configurations has been designed, developed, settled and tested. An optical module (Mach-Zehnder interferometer), an acquisition module (CMOS camera) and a processing module (Fourier Transform Phase Difference Method) have been integrated and assembled in order to obtain the instantaneous optical phase distribution along the gas flow. An additional postprocessing numerical stage provides gradient and Laplacian information of the optical phase distribution and allows a complete modeling of the fluid flow. In this work the main results, advantages and limitations of the metrological protocol related with a detailed measurement campaign are presented. Also the analysis of the obtained optical phase difference distribution is compared with results given by a tailored processing numerical stage.

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Computer aided evaluation of interferograms

Cited by 9 publications

References 14 publications

Laval nozzle flow characterization by Fourier-transform Mach-Zehnder interferometry

Laval nozzle flow characterization by Fourier-transform Mach-Zehnder interferometry

Evaluation of interferometric patterns of supersonic fluid flows by the differential Fourier transform method

Fourier transform evaluation and numerical modeling of fluid flow in a Laval nozzle

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