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M. Raffel H. Richard K. Ehrenfried B. Van der Wall C. Burley P. Beaumier K. McAlister K. Pengel 《Experiments in fluids》2004,36(1):146-156
Three-component particle image velocimetry measurements at moderate speeds and observation distances can now be accomplished on a routine basis. This article discusses the experiment performed on a 4 m-diameter model rotor in the 6-m×8-m open test section of the Large Low Speed Facility of the German–Dutch Wind Tunnels. More than half a terabyte of raw data were recorded at various positions on the advancing and retreating sides of the rotor in order to obtain detailed measurements of the trailing vortex in the frame of an international project. This paper addresses measuring techniques and possible sources of errors and presents a limited number of cases for the purpose of illustrating the solutions to numerous technical challenges relating to the acquisition and analysis of vortical flows.List of symbols
C
T
thrust coefficient (T/2
R
4)
-
M
magnification
-
r
c
radius of vortex core (mm)
-
R
rotor radius (m)
-
T
thrust (N)
-
u,v,w
velocity components in x, y and z coordinates (m/s)
- (u,v,w)wt
velocity components in wind tunnel coordinates (m/s)
-
U
max
maximum in-plane velocity component (m/s)
-
W
max
maximum out-of-plane velocity component (m/s)
-
x,y,z
particle image velocimetry (PIV) frame coordinates (m)
- (x,y,z)wt
wind tunnel coordinates (m)
- t
time delay (s)
- Z
light sheet thickness (mm)
- Z
light sheet thickness (mm)
-
rotor rotation frequency (rad/s)
-
rotor azimuth angle during recording (deg) vortex age
-
rotor shaft angle (deg)
-
x
displacement measurement error
-
advance ratio (V/R)
-
air density (kg/m3)
-
circulation (m2/s)
-
z
vorticity (s–1)
Abbreviations AFDD
Aeroflightdynamics Directorate
- BVI
blade–vortex interaction
- DLR
Deutches zentrum für Luft- und Raumfahrt
- DNW
German–Dutch Wind tunnel
- HART
HHC aeroacoustic rotor test
- LLF
large low speed facility
- NASA
National Aeronautics and Space Administration
- ONERA
Office National dEtudes e de Recherches Aerospatiales
- RANS
Reynolds-averaged Navier–Stokes
- SPR
stereo pattern recognition
- 3C-PIV
three-component particle image velocimetry 相似文献
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M. Hietschold F. Müller A.-D. Müller H. J. Engelmann E. Zschech 《Analytical and bioanalytical chemistry》1999,365(1-3):96-98
A technique is presented that allows to obtain information about sample surface topography and local electrical surface properties simultaneously. A scanning electrical force microscope is used for that purpose which is based on an atomic force microscope (AFM) working in the dynamical mode. Different information channels contained in the cantilever excitation spectrum are separated by a lock-in technique. The physical content of the technique is discussed in detail and the influence of surface topography on the non-topographic imaging is demonstrated. Finally, the real advantages of cross-sectional sample preparation (as known from electron microscopy) for this kind of scanning probe microscopy with respect to various applications is presented. 相似文献
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In the temperature range from 950 to 1200 K Kp-values result from 5 · 10−5 to 6,9 · 10−3 for the heterogeneous reversible reaction Ge(s) + H2O(g) ⇋ GeO(g) + H2O(g), the average reaction enthalpy being 46,5 ± 05 kcal/mol. Etching rates calculated with these equilibrium constants for closed systems are 20-25% larger than the experimental etching rates for (110)-Ge in the sandwich device. The ratio of the etching rates is for (111)-, (100)- and (110)-Ge 1:1,4:1,8; the average reaction enthalpy calculated experimentally is 46 ± 1 kcal/mol for the temperature range 1000-1200 K. The dependence of transport rate on distance between source and substrate characterizes the sandwich device as a quasi-closed system with the diffusion as the rate controlling step of the material transport. 相似文献
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Dr. Qiudi Yue Dr. Kristina Kutukova Ang Li Prof. Jiří Čejka Prof. Ehrenfried Zschech Dr. Maksym Opanasenko 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(35):e202200590
Crystal growth mechanisms govern a wide range of properties of crystalline materials. Reversed crystal growth is one of the nonclassical mechanisms observed in many materials. However, the reversed crystallization starting from amorphous aggregates and the key factors driving this growth remain elusive. Here, we describe a characteristic model of reversed crystal growth representing the inner structure and crystallinity development of aggregates studied by microscopy and nano X-ray computed tomography. By adjusting the synthesis conditions, the fundamental function of the structure-directing agent, which determines the crystallization pathway, was revealed. As a result, the crystal growth mode can be “switched” from the classical route at a low ratio of SDA/framework elements to reversed growth at a high ratio. Our findings provide further insights into crystal growth control, which is crucial for improving synthesis protocols and designing various forms of crystalline materials. 相似文献
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Ehrenfried Petras 《Colloid and polymer science》1967,218(2):136-139
Zusammenfassung Die Filtrationswirksamkeit von insgesamt 17 Sartorius-Membran-, Millipore- und Gelman-Filtern für in 4%iger wäßriger NaCl-Lösung suspendierte Testpartikel unterschiedlicher Form und Größe (Latex, Colanylgrün, Bakterienzellen) wurde experimentell untersucht. Dies erfolgte mittels elektronischer und mikrobiologischer Filtratanalysen. Die wichtigsten Untersuchungsergebnisse sind in Tabellenform zusammengestellt und werden kurz diskutiert.
Herrn G. König danke ich für seine außerordentlich gewissenhafte experimentelle Mitarbeit. Zugleich danke ich den Herren Dr. D. Thon und R. Gröpl von der Sartorius Membranfilter GmbH., Göttingen, sowie meinem Kollegen Dr. H.-J. Preußer für Diskussionen und Anregungen, letzterem darüber hinaus für die elektronenmikroskopische Untersuchung der Bakterien-Hemmformen. 相似文献
Summary Efficiencies of 17 different types of membrane filters (products of the Sartorius Membranfilter GmbH., Göttingen, the Millipore Filter Corporation, Bedford, Massachusetts, and the Gelman Instrument Co., Chelsea, Michigan) have been tested by electronic and microbiological analysis of the filtrates of particle suspensions. The test particles (polystyrene latex, colanyl green, bacterial cells — in all cases suspended in 4% saline) were representatives of different types with respect to their size and shape. The most essential results are presented by 2 tables. A short discussion is included.
Herrn G. König danke ich für seine außerordentlich gewissenhafte experimentelle Mitarbeit. Zugleich danke ich den Herren Dr. D. Thon und R. Gröpl von der Sartorius Membranfilter GmbH., Göttingen, sowie meinem Kollegen Dr. H.-J. Preußer für Diskussionen und Anregungen, letzterem darüber hinaus für die elektronenmikroskopische Untersuchung der Bakterien-Hemmformen. 相似文献
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Pascoal AC Ehrenfried CA Eberline MN Stefanello ME Salvador MJ 《Natural product communications》2011,6(7):969-972
Numerous diseases are induced by free radicals via lipid peroxidation, protein peroxidation and DNA damage. It has been known that a variety of plant extracts have antioxidant activity to scavenge free radicals. Campomanesia adamantium (Myrtaceae) is a small tree with edible fruit, commonly known as "guavira" or "guabiroba-branca" that has been used in popular medicine as depurative anti-diarrhoeic, antiinflammatory, anti-rheumatic and to liver diseases. In this study, the antiradical activities of ethanol crude extract of the leaves from C. adamantium and the ethyl acetate and butanol fractions obtained by partition, were determined using DPPH (2,2-Diphenyl-1-picrylhydrazyl radical) and ORAC-FL (Oxygen Radical Absorbance Capacity) assays. The total phenol content in the samples was estimated by Folin Ciocalteau method (FCR). In an initial evaluation the ethanolic extract and the fractions ethyl acetate and butanol have shown levels of phenolic compounds between 15- 74 mg GAE/g in FCR assay, showed DPPH free-radical scavenging activity with SC50 in the range of 7.77-13.35 microg/mL and demonstrated antioxidant capacity between 2648-3502 micromol TE/g of extract and fractions in the ORAC-FL assay. HPLC-DAD and ESI-MS analysis revealed were that the extract of the leaves of C. adamantium studied appears to contain flavonoids as major constituents, including isoquercetrin and quercetin that exhibit proven antioxidant activity. 相似文献