Because our primary aim has been to provide reliable experimental data to clients and scientists, research into new measurement techniques and data analysis tools have been an important activity within our group. Extensive efforts have been put into developing new measurement principles and we were among the first to manufacture and use pulsed hot-wire anemometers in wind tunnel experiments. This is a measurement principle very suitable for measurements in low speed recirculating flows and we were the first to introduce this system in room ventilation investigations. Our first prototype system was available in 1980 and has been steadily improved to become a reliable and highly accurate tool. (See Venås, Abrahamsson, Krogstad and Lofdahl for a documentation of the system and its capabilities).
We have also for a long time been actively working with non-intrusive measurement systems such as Laser-Doppler Anemometry and more a Particle-Image-Velocimetry system has been developed, allowing simultaneous measurements in a two-dimensional section of the flow field. This has been developed based on two Yag Lasers. Details may be found in the Ph.D. Thesis of Loland, 1998. The laboratory also uses comercial LDA and PIV systems from Dantec Dynamics
Equally important as being able to measure accurately is the analysis of the data. Since most of the research activity has been devoted to detecting small structural changes to the turbulence field for different flow conditions, it is essential to have advanced analysis tools to be able to make reliable detections. The method of using Wavelet analysis has been explored. This technique may be considered as a Fourier analysis tool which resolves the scale distribution in the flow without loosing the time information. This has allowed new methods of structure detections where the events which lead to sudden burst in turbulent energy may be identified. Our group has published a new detection method called "Wavelet peak energy method", based on this type of analysis (see Ph.D. Thesis of Kaspersen, 1996).
Methods to detect coherent structures; a comparisonP.-Å. Krogstad and J. H. Kaspersen
11th Australasian Fluid Mechanics Conference, Hobart, 1991
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Two-point space-time correlation measurements in an adverse pressure gradient boundary layerP.-Å. Krogstad, P .E. Skåre and J. H. Kaspersen
10th Turbulent Shear Flows Conference, Pennsylvania, 1995
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Pulsed Hot-Wire Measurements in Two- and Three-Dimensional Wall JetsB. Venås, H. Abrahamsson, P.-Å. Krogstad and L. Lofdahl
Experiments in Fluids, 1999
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A velocity dependent effective angle method for calibration of X-probes at low velocitiesO.M. Bakken and P.-Å. Krogstad Experiments in Fluids, Vol. 37, 2004
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J. H. Kaspersen, Ph.D. Thesis, NTNU, 1996
T. Loland, Ph.D. Thesis, NTNU, 1998