Vanselow, Christoph
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Vanselow, Christoph
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Vanselow, Christoph
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Item-typ:Veröffentlichung, Revealing the impact of laser-induced breakdown on a gas flow(IOP Publishing, 2019-11-15); ; ; Laser-induced breakdown spectroscopy (LIBS) is an optical, and thus non-contact, but not non-invasive, measurement technique. Investigating the impact of laser-induced breakdown on a gas flow, combined LIBS and particle image velocimetry (PIV) measurements are performed. In the considered laminar air flow, the induced velocity field disturbance has an extent of about 0.7 cm with magnitudes up to 0.9 ms−1. As a further result, the combination of LIBS with other measurement techniques or high-speed LIBS measurements are found to require a minimal time delay of about 500 s in order to ensure influence of the preceding LIBS pulse on the considered gas flow of about 10 % relative velocity deviation. For a reduction to 0 % relative velocity deviation a time delay of about 20 ms is estimated for the investigated flow. Smaller time delays may occur in turbulent flows or flows with higher velocities.Wissenschaftlicher ArtikelBand:31Heft:2109 113 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Particle image velocimetry in refractive index fields of combustion flowsOptical measurements inside reacting flows are often disturbed by refractive index fields, e.g., due to the strong density gradients in flames. Although occurring measurement errors due to light refraction are a known problem for certain particle image velocimetry (PIV) applications, only a qualitative analysis of the resulting measurement uncertainty inside flame flows has been carried out to date. As an important step forward, a measurement approach is proposed, which enables a quantification of the resulting measurement uncertainties due to light refraction. As an example, the measurement approach is applied to a premixed propane flame. The uncertainty analysis is based on the determination of occurring particle position errors due to light refraction inside the flame. For three different measurement planes, the velocity field is measured with PIV and the particle position errors are experimentally measured and verified by ray-tracing simulation based on the measured refractive index field, which is determined by the background-oriented Schlieren method. In the examined flow, maximal position errors amount up to 14 μm and yield significant systematic velocity errors of up to 4% and random velocity errors of up to 6%. In contrast to the systematic velocity error, the random velocity error varies significantly for the analyzed measurement planes inside the flame flow.Wissenschaftlicher ArtikelBand:60106 72 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Influence of inhomogeneous refractive index fields on particle image velocimetryThe influence of inhomogeneous refractive index fields on particle image velocimetry (PIV) measurements is a well known problem, which leads to an unknown measurement uncertainty in, e.g., flame flows, shock waves and super sonic flows. Previous studies give only rough estimations of the measurement error due to inhomogeneous refractive index fields, and quantitative information is only available for special conditions such as a gradient of the refractive index independent of the viewing direction. Hence, the assessment of the spatial distribution of the quantitative measurement errors inside inhomogeneous refractive index distributions especially for stereoscopic and tomographic PIV is an open question. For this purpose, the flow measurement inside a hot jet flow is considered as an example, and a general analytic description of the error of the measured particle positions inside the hot jet flow is derived, numerically evaluated and finally validated by experiments. In particular, the determination of the particle position with triangulation is investigated, which is performed in stereoscopic and tomographic PIV. As a result, the measurement error is generally larger than for standard PIV without triangulation. The theoretically predicted errors of the measured particle position are validated with experiments and here amount to 11.7 µm for standard PIV and 17.3 µm for triangulation at the same distance from the center of the flow, respectively. Note that the error estimation requires the knowledge of the refractive index field that was determined by temperature measurements in the flow. Furthermore, the error analysis shows that for triangulation the measured particle position depends on the gradient and the curvature of the refractive index field, whereas for standard PIV the measured particle position only depends on the gradient of the refractive index. For the given temperature profile with a maximum temperature of 191 °C, the resulting flow velocity error is maximally 0.8 % with standard PIV, 1.7 % for the in plane and 2.9 % for the out of plane direction with stereoscopic PIV and 1.1 % with triangulation which is performed in tomographic PIV.Wissenschaftlicher ArtikelBand:10771 102