In order to test CPT symmetry between antihydrogen and its counterpart hydrogen, the ASACUSA collaboration plans to perform high precision microwave spectroscopy of ground-state hyperfine splitting of antihydrogen atom in-flight. We have developed an apparatus (“cusp trap”) which consists of a superconducting anti-Helmholtz coil and multiple ring electrodes. For the preparation of slow antiprotons and positrons, Penning-Malmberg type traps were utilized. The spectrometer line was positioned downstream of the cusp trap. At the end of the beamline, an antihydrogen beam detector was located, which comprises an inorganic Bismuth Germanium Oxide (BGO) single-crystal scintillator housed in a vacuum duct and surrounding plastic scintillators. A significant fraction of antihydrogen atoms flowing out the cusp trap were detected. 相似文献
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
CT
thrust coefficient (T/2R4)
-
M
magnification
-
rc
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)
-
Umax
maximum in-plane velocity component (m/s)
-
Wmax
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
For the design of hull forms with better resistance and propulsive performance, it is essential to understand flow characteristics, such as wave and wake development, around a ship. Experimental data detailing the local flow characteristics are invaluable for the validation of the physical and numerical modeling of computational fluid dynamics (CFD) codes, which are recently gaining attention as efficient tools for hull form evaluation. This paper describes velocity and wave profiles measured in the towing tank for the KRISO 138,000 m3 LNG carrier model with propeller and rudder. The effects of propeller and rudder on the wake and wave profiles in the stern region are clearly identified. The results contained in this paper can provide an opportunity to explore integrated flow phenomena around a model ship in the self-propelled condition, and can be added to the International Towing Tank Conference benchmark data for CFD validation as the previous KCS and KVLCC cases. 相似文献
Many machine elements in common engineering use exhibit the characteristic of “hysteresis springs”. Plain and rolling element bearings that are widely used in motion guidance of machine tools are typical examples. The study of the non-linear dynamics caused by such elements becomes imperative if we wish to achieve accurate control of such machines.
This paper outlines the properties of rate-independent hysteresis and shows that the calculation of the free response of a single-degree-of-freedom (SDOF) mass-hysteresis-spring system is amenable to an exact solution. The more important issue of forced response is not so, requiring other methods of treatment. We consider the approximate describing function method and compare its results with exact numerical simulations. Agreement is good for small excitation amplitudes, where the system approximates to a linear mass-spring-damper system, and for very large amplitudes, where some sort of mass-line is approached. Intermediate values however, show high sensitivity to amplitude variations, and no regular solution is obtained by either approach. This appears thus to be an inherent property of the system pointing to the need for developing further analysis methods. 相似文献
By means of a tripping wire turbulent spots are generated in a conditionally stable laminar boundary layer along a flat plate in a low-turbulence windtunnel. At several vertical and lateral positions the streamwise (U) and vertical (V) velocity components of the spot are measured using anX-shaped hot wire anemometer. The spot's leading edge (LE) and trailing edge (TE) are determined by a high frequency detection criterion.The derived ensemble averaged shear stress uv shows a remarkable plateau over the last 3/4 of the spot length and over about 1/2 of the spot width, approximately independent of the height above the plate. The measurements suggest that the velocities of the LE and the TE can be explained by simple advection of the active turbulent region. Other mechanisms seem to be responsible for the lateral spread of the spot, as is suggested by the measurements outside the plane of symmetry. 相似文献
Direct numerical simulation is a very powerful tool to evaluate the validity of new models and theories for turbulent combustion.
In this paper, direct numerical simulations of spherically expanding premixed turbulent flames in the thin reaction zone regime
and in the broken reaction zone regime are performed. The flamelet-generated manifold method is used in order to deal with
detailed reaction kinetics. The computational results are analyzed by using an extended flame stretch theory. It is investigated
whether this theory is able to describe the influence of flame stretch and curvature on the local burning velocity of the
flame. It is found that if the full profiles of flame stretch and curvature through the flame front are included in the theory,
the local mass burning rate is well predicted. The influence of several approximations, which are used in other existing theories,
is studied. When flame stretch is assumed constant through the flame front or when curvature of the flame front is neglected,
the theory fails to predict the local mass burning rate. The influence of using a reduced chemistry model is investigated
by comparing flamelet simulations with reduced and detailed chemistry. 相似文献
Results from an experimental study of flow behaviour at the inlet of a vaneless diffuser of a centrifugal compressor are presented. Measurements from a crossed hot-wire probe are given for operating points having inlet flow coefficients ranging from 0.006 to 0.019 at different Reynolds numbers. Instantaneous, time-averaged, and phase-averaged absolute velocity and flow angle at the diffuser inlet are deduced from the hot-wire signals after correction for mean density variations. These results show how flow behaviour varies in stable, rotating stall and surge regimes of compressor operation 相似文献