44 research outputs found
The dynamics of active galactic nuclei
No full textSIGLEAvailable from British Library Document Supply Centre-DSC:D063502 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
Measurements and simulations of heat transfer in a Primix static mixer
No full textDuring tliis project tlie transfer of heat to a laminar flow inside a Primix static mixer has been investigated, using both experimental measurements and numerical simulations. This has been done for a high Prandtl number fiuid, in this case mineral oil. The Reynolds number of the flow in tlie mixer was between 7 and 18, while the Prandtl number of the fluid varied between 3200 and 5500. An experimental setup was designed and built using a heating circuit fliled with water and a separate circuit containing the oil. The temperature was measured at several positions inside and outside the mixer using PtlOO sensors. The measurements inside the mixer showed a strong dependency on the insertion depth of the sensors, a procedure to correct the measurements was developed. Because of the thin thermal boundary layers in the flow, special attention was given in the numerical simulations to the fluid layer close to the metal parts. Different options for modeUing this boundary layer were investigated, as well as the grid dependency of the results. The results of the simulations depend strongly on the boundary layer, while the bulk of the fluid can be modelled with a relatively coarse grid. The simulations predict the heat transfer of the mixer accurately, and can be used to further investigate the influence of design changes on heat transfer. Two mixers have been used: in one the mixing elements have been soldered to the wall, improving the conduction of heat from the outside to the mixing elements. In the second mixer the elements form a string which is inserted in the tube. A theoretical model has been developed to estimate the performance difference between both mixers for laminar flows. The experimental results agree with the theoretical model, while the simulations seem to result in a constant performance difference.Kramers Laboratorium voor Fysische TechnologieApplied Science
Author correction: Psychopathy
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Hydrodynamics of photoionized columns in the Eagle Nebula, M 16
No full textWe present hydrodynamical simulations of the formation, structure and evolution of photoionized columns, with parameters based on those observed in the Eagle Nebula. On the basis of these simulations we argue that there is no unequivocal evidence that the dense neutral clumps at heads of the columns were cores in the pre-existing molecular cloud. In our simulations, a variety of initial conditions leads to the formation and maintenance of near-equilibrium columns. Therefore, it is likely that narrow columns will often occur in regions with large-scale inhomogeneities, but that observations of such columns can tell us little about the processes by which they formed. The manner in which the columns in our simulations develop suggests that their evolution may result in extended sequences of radiation-induced star formation
Method and device for loading packed goods using an intermediate load unit
No full textThe invention relates to a device for loading packed goods into a transport unit (8b), the device comprising an orientation unit for orienting each packed good in a predetermined direction, means for transferring the packed goods in the order of a predetermined loading sequence to the orientation unit, a load module, provided with an intermediate load unit for temporarily loading the packed goods in their oriented state, and means (25,26) for transferring the contents (28) of the intermediate load unit into the transport unit (8b) in one stroke. The invention further relates to a method for loading packed goods into a transport unit (8b).Aerospace Engineerin
Implicit Large Eddy Simulation of Environmental Urban Flows
No full textMany environmental flows are turbulent flows. Depending on the physical aspects
of the wind and the urban topology, turbulence might result into unfavourable
or even dangerous conditions for the pedestrians. Turbulence can also play
a very important role in the transport of toxic pollutants from accidental or intentional
releases. Thus, it is vital to understand its complex characteristics so that its features
are accurately predicted when computational methods are used. Real urban environment
involving separation and reattachment regions provides an excellent testcase for
investigating such complex flows.
This thesis is focused on analysing the physics involved in flows around building models
pertinent to environmental flows in urban areas and to evaluate the applicability
of Implicit Large-Eddy Simulation in simulating the specific type of flows. For this
purpose, a number of high resolution schemes in the context of Implicit Large-Eddy
Simulation (each representing di erent degrees of spatial discretisation accuracy) was
assessed.
The evaluation of the schemes involved direct validation against experimental data as
well as comparisons with DNS and LES data regarding flows within roughness element
arrays in staggered arrangements. Initially, the flow within an uniform height
cubical matrix was simulated. Four numerical schemes were tested in three di erent
grid resolutions. The results were found in very good agreement with the Laser
Doppler Anemometry data and they even exhibit DNS-like characteristics in specific
locations of comparisons. Thus, it was concluded that high order spatial discretisation
schemes allow the accurate representation of reality even in relatively coarse computational
meshes.
The second case under investigation involved flows within a more realistic representation
of urban topology. Results obtained within an array of sixteen elements with five
di erent heights reveal that although the roughness of the area is increased, the wind’s
velocity profile above the obstacles shares almost the same slope as in the case of the
array of the four cubical element.
It is believed that this thesis has expanded the range of applications in the context
of Implicit Large Eddy Simulation using high resolution schemes and contributed in
persuading the scientific community for its potentials
Modeling X-ray Ionization of Grains with Cloudy
No full textIn this paper we discuss our recent efforts to update the X-ray
treatment of grains in the PDR modeling code Cloudy
