Nobach, Holger, Dr.*
- 1997 Dr.-Ing., University of Rostock
- 1998-2000 Postdoctoral research at Dantec Dynamics A/S in Copenhagen, DK
- 2000-2005 Postdoctoral research at the Technical University of Darmstadt
- since 2005 Postdoctoral research at the Max Planck Institute for Dynamics and Self-Organization with stay at Cornell University, Ithaca, NY, USA
- 2007 Habilitation, Technical University of Darmstadt
- 1997 Joachim Jungius Award of the University of Rostock
- Ruhnau, P.; Kohlberger, T.; Schnörr, C.; Nobach H.: Variational optical flow estimation for particle image velocimetry, Experiments in Fluids, vol. 38 (2005), pp. 21–32.
- Damaschke N.; Nobach H.; Nonn T.I.; Semidetnov N.; Tropea C.:
Multi-dimensional particle sizing techniques, Experiments in Fluids, vol. 39 (2005), pp. 336–35.
- Honkanen M.; Nobach H.: Background extraction from double-frame PIV images, Experiments in Fluids, vol. 38 (2005), pp. 348–362.
- Nobach, H.: Gegen Wavelets & Co. — Vorteile klassischer Signal- und Datenverarbeitungsverfahren in der optischen Strömungsmesstechnik, Shaker Verlag Aachen, 2007, ISBN 978-3-8322-6564-9, (Zugl.: Darmstadt, Techn. Univ., Habil.- Schr., 2007).
- JNobach H.; Bodenschatz E.: Limitations of accuracy in PIV due to individual variations of particle image intensities, Experiments in Fluids, vol. 47 (2009), pp. 27–38.
- Nobach H.: Influence of individual variations of particle image intensities on high-resolution PIV, Experiments in Fluids (online first, 2010).
Major Research Interests
Modern turbulence and fluid dynamics research increasingly depends on the development of suitable measurement
techniques with the required precision, resolution and dynamic rage. Due to their non-intrusive principles, optical measurement techniques as laser Doppler velocimetry (LDV) or particle image velocimetry (PIV) have a high potential for obtaining statistical flow properties without disturbing the flow fields. Main research topics are the development and improvement of these measurement techniques and their effective use in flow investigation. In cooperation with the manufacturers, efficient methods have been developed for both the processing of LDV burst signals and the derivation of flow statistics from LDV velocity series. For PIV, new image processing methods have been developed to improve the accuracy and the spatial resolution, extending the applicability of PIV towards unstable and transient flows. In both cases, LDV and PIV, the main issue of the improvements are the highest possible efficiency of signal or image processing.
Other developments concern extensions of the basic methods to measure new flow quantities, such as the particle size in backscatter, the particle size and 3D tracking for non-stereoscopic PIV or the measurement of the particle size distribution with LDV. Recently, a commercial LDV system in back-scatter has been used additionally to measure particle accelerations. Knowledge of the Lagrangian or material acceleration is very valuable in fluid mechanics as the fundamental conservation equations are cast in terms of this acceleration, in particular the Navier-Stokes equations. Both the optical setup and the signal processing are critical components of the measurement system.
They must realize an enormous accuracy to allow reasonable resolution of acceleration measurements. However, due to its very small measurement volume the LDV “accelerometer” has a much better spatial resolution than competitive measurement techniques such as high-speed particle imaging and tracking. Therefore, it can be used to resolve smaller scale flow statistics.
With the development of the new turbulence wind tunnel at the Max Planck Institute for Dynamics and Self-organization in Göttingen, the resolution of very small flow scales becomes essential, since here Reynolds numbers will be achieved, that are close to the highest values on Earth. The measurements will provide new insights into turbulence that will be indispensable for understanding turbulent disper-sion and related problems in the atmospheric and environmental sciences, micrometeorology and engineering. The implementation of measurement techniques like LDV or high-speed optical particle tracking requires adequate modifications to allow the use in SF6 gas at a pressure of 15 bar.
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