| Zugriffsnummer | 39503 |
| Dokumenttyp | Konferenzartikel |
| Sprache | Englisch |
| Titel | Correction for the effective measuring position of LDA in circular cross-sections |
| Übersetzungstitel | Korrektur des effektiven Messortes für LDA in runden Strömungsquerschnitten |
| Autor(in); Institution |
Steinbock, Jonas; 7.5, Wärme und Vakuum, PTB-Berlin
Weissenbrunner, Andreas; 7.5, Wärme und Vakuum, PTB-Berlin
Juling, Markus; 7.5, Wärme und Vakuum, PTB-Berlin
Thamsen, P. U.; Technische Universität Berlin, Fachgebiet Fluidsystemdynamik, Berlin, GERMANY
|
| Quelle/Jahr | Experimentelle Strömungsmechanik: 25. Fachtagung, 5.-7. September 2017, Karlsruhe:(2017), 33-1 - 33-7 |
| ISSN | 2194-2447 |
| ISBN | 978-3-9816764-3-3 |
| URL | |
| Verlag | Karlsruhe: Deutsche Gesellschaft für Laser-Anemometrie GALA e.V. |
| Konferenzangaben | 25. Fachtagung "Experimentelle Strömungsmechanik", Karlsruhe, 05-07 September 2017, Deutschland |
| Zusammenfassung | Laser Doppler anemometry (LDA) systems for one velocity component (1C) are widely applied within flow diagnosis and more recently also for flow rate measurements, compare Mickan and Strunck (2014), Juling (2016) and Steinbock (2017). To obtain a spatially resolved velocity field, the intersection of two interfering laser beams, the so called measuring or probe volume, is positioned successively at different sample positions. In general, the geometric centre of the LDA measuring volume is coincident with the effective measuring position. However, for sample positions in proximity of the wall, there is an offset between the effective measuring position and the geometric centre of the measuring volume. The effect is most obvious when positioning the geometric centre of the measuring volume directly on the wall. A virtual velocity which contradicts the ‘no slip’ boundary condition is determined. This effect can also be used to determine the position of the wall, compare Durst et al. (1988). The offset can be explained by superposing the measuring volume with the wall: A part of the measuring volume is located inside the wall, as such, it does not contribute to the velocity measurement. The magnitude and the direction of the offset depend on the position, the geometry of the measuring volume and the optical path of the laser beams. In this paper a method is presented to calculate the individual geometric offset, thus allowing to correct the measuring positions for near wall 1C LDA measurements. The position of the geometric center of the measuring volume in the flow section is derived by a geometric ray-tracing method. The intensity distribution is modelled by a Gaussian shape. The effective measuring position for each sample point is given by the centroid for the intensity distribution of the measuring volume in the flow domain. Simulations with analytic velocity profiles exhibit a deviation in the order of up to 1 % for flow rate measurements. The correction method reduces this deviation at least to one third of ist original amount. For Reynolds numbers above 1 x 105 the remaining deviation is lower than 0.01 %. |
