1,721,197 research outputs found
On the error-sensitivity of calibration procedures for normal hot-wire probes
No full textThe results of an investigation on the sensitivity of various hot-wire calibration procedures to errors in probe positioning are described. The analysis was carried out by means of a computer simulation procedure and regarded, in particular, methods for the evaluation of the direction sensitivity coefficients. It is shown that the classical calibration procedures are characterized by a high sensitivity to experimental errors, and this may explain both the large scatter usually found in the values of the direction sensitivity coefficients and, at least partially, their variation with yaw and pitch angle. New calibration procedures are also described which appear to be significantly less sensitive to errors in probe positioning and velocity setting. The practical application of the various procedures to the calibration of a typical commercial probe seems to confirm the results of the computer simulation analysis
Progress in Turbulence V: Proceedings of the ITi Conference in Turbulence 2012
No full textThis volume collects the edited and reviewed contributions presented in the 5th iTi Conference in Bertinoro. covering fundamental aspects in turbulent flows. In the spirit of the iTi initiative, the volume is produced after the conference so that the authors had the possibility to incorporate comments and discussions raised during the meeting.
Turbulence presents a large number of aspects and problems, which are still unsolved and which challenge research communities in engineering and physical sciences both in basic and applied research. The book presents recent advances in theory related to new statistical approaches, effect of non-linearities and presence of symmetries. This edition presents new contributions related to the physics and control of laminar-turbulent transition in wall-bounded flows, which may have a significant impact on drag reduction applications. Turbulent boundary layers, at increasing Reynolds number, are the main subject of both computational and experimental long research programs aimed at improving our knowledge on scaling, energy distribution at different scales, structure eduction, roughness effects to name only a few. Like previous editions several numerical and experimental analysis of complex flows, mostly related to applications, are presented.
The structure of the present book is as such that contributions have been bundled according to covering topics i.e. I Theory, II Stability, III Wall bounded flows, IV, Complex flows, V Acoustic, VI Numerical methods.
The volume is dedicated to the memory of Prof. Rudolf Friedrich who prematurely died in Münster/Germany on the 16th of August 2012. In his honor the conference has started with a special session dedicated to his work
Experimental characterization of the velocity field of a coaxial jet configuration
No full textThe mean and fluctuating flow fields of a coaxial jet configuration, with ratios between inner and outer diameters and velocities Di/Do = 0.485 and Ui/Uo = 0.67, turbulent exit boundary layers, and high turbulence levels in the exit cores are studied by means of LDA and hot-wire measurements, using an experimental facility designed for the purpose. The profiles of the mean axial velocity, of the axial and radial turbulence intensities, and of the shear stress are described for the initial and intermediate zones of the near field. The lenghts of the potential cores are in good agreement with available data obtained with lower exit turbulence levels and laminar boundary layers. It is shown that the prevailing frequencies of the flow fluctuations may be better recognized if the hot-wire spectra of both the axial and the radial velocities are analyzed. These frequencies show significant radial differences in the initial and intermediate mixing zones but become progressively more uniform with increasing distance from the exit. In the near-exit region of the inner mixing layer evidence is also found of a probable alternate vortex shedding from the inner duct wall. This phenomenon is shown to exist for Ui/Uo ≥ 0.44, with a constant Strouhal number St = 0.24, based on the thickness of the wall and on the average velocity of the two streams
The influence of temperature fluctuations on hot-wire measurements in wall-bounded turbulence
No full textThere are no measurement techniques for turbulent flows capable of reaching the versatility of hot-wire probes and their frequency response. Nevertheless, the issue of their spatial resolution is still a matter of debate when it comes to high Reynolds number near-wall turbulence. Another, so far unattended, issue is the effect of temperature fluctuations - as they are, e.g. encountered in non-isothermal flows - on the low and higher-order moments in wall-bounded turbulent flows obtained through hot-wire anemometry. The present investigation is dedicated to document, understand, and ultimately correct these effects. For this purpose, the response of a hot-wire is simulated through the use of velocity and temperature data from a turbulent channel flow generated by means of direct numerical simulations. Results show that ignoring the effect of temperature fluctuations, caused by temperature gradients along the wall-normal direction, introduces - despite a local mean temperature compensation of the velocity reading - significant errors. The results serve as a note of caution for hot-wire measurements in wall-bounded turbulence, and also where temperature gradients are more prevalent, such as heat transfer measurements or high Mach number flows. A simple correction scheme involving only mean temperature quantities (besides the streamwise velocity information) is finally proposed that leads to a substantial bias error reduction. © 2014 Springer-Verlag Berlin Heidelberg
Apparecchiatura e metodo per la determinazione di parametri caratterizzanti il moto relativo di un corpo rispetto ad un fluido
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Progress in Turbulence III. Proceedings of the iTi Conference in Turbulence 2008
No full textThis third issue on "progress in turbulence" is based on a meeting in which researchers from the engineering and physical sciences gathered to present latest results on the rather notorious difficult and essentially unsolved problem of turbulence. This challenge is driving us in doing basic as well as applied research. Clear progress can be seen from these contributions in different aspects. New sophisticated methods achieve more and more insights into the underlying complexity of turbulence. The increasing power of computational methods allows studying flows in more details. Increasing demands of high precision large turbulence experiments become aware. In further applications turbulence seem to play a central issue. As such a new field this time the impact of turbulence on the wind energy conversion process has been chosen
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