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Transition Modelling with the k-Ω Turbulence Model and an Intermittency Transport Equation

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Journal of Thermal Science 2004年第3期13卷 220-225页

作者： Koen LODEFIER bart merci Chris De LANGHE Erik DICK Ghent University Dept. of Flow Heat and Combustion Mechanics Sint-Pietersnieuwstraat 41 B-9000 Gent BelgiumGhent University Dept. of Flow Heat and Combustion Mechanics Sint-Pietersnieuwstraat 41 B-9000 Gent BelgiumGhent University Dept. of Flow Heat and Combustion Mechanics Sint-Pietersnieuwstraat 41 B-9000 Gent BelgiumGhent University Dept. of Flow Heat and Combustion Mechanics Sint-Pietersnieuwstraat 41 B-9000 Gent Belgium

In gas turbine engines, laminar-turbulent transition occurs. However, generally, the turbulence models to describe such transition results in too early and too short transition. Combining a turbulence model with a description of intermittency, i.e. the fraction of time the flow is turbulent during the transition phase, can improve it. By letting grow the intermittency from zero to unity, start and evolution of transition can be imposed. In this paper, a method where a dynamic equation of intermittency combining with a two-equation k-ωturbulence model is described. This intermittency factor is a premultiplicator of the turbulent viscosity computed by the turbulence model. Following a suggestion by Menter et al.[1], the start of transition is computed based on local variables.

关键词： bypass transition intermittency SST turbulence model.

VLES Modelling with the Renormalization Group

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Journal of Thermal Science 2003年第4期12卷 328-331页

作者： Chris De Langhe rug.ac.be bart merci rug.ac.be Koen Lodefier rug.ac.be Erik Dick rug.ac.be Ghent University Dept. of Flow Heat and Combustion Mechanics Sint-Pietersnieuwstraat 41 B-9000 Gent Belgium

In a Very-Large-Eddy Simulation (VLES), the filterwidth-wavenumber can be outside the inertial range, and simple subgrid models have to be replaced by more complicated (''RANS-like'') models which can describe the transport of the biggest eddies. One could approach this by using a RANS model in these regions, and modify the lengthscale in the model for the LES-regions. The problem with these approaches is that these models are specifically calibrated for RANS computations, and therefore not suitable to describe inertial range quantities. We investigated the construction of subgfid viscosity and transport equations without any calibrated constants, but these are calculated directly form the Navier-Stokes equation by means of a Renormalization Group (RG) procedure. This leads to filterwidth dependent transport equations and effective viscosity with the right limiting behaviour (DNS and RANS limits).

关键词： very-large-eddy simulation subgrid modellig k-εmodel.

The free-electron laser FLASH

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High Power Laser Science and Engineering 2015年第3期3卷 28-40页

作者： Siegfried Schreiber bart Faatz Deutsches Elektronen-Synchrotron

FLASH at DESY, Hamburg, Germany is the first free-electron laser(FEL) operating in the extreme ultraviolet(EUV)and soft x-ray wavelength range. FLASH is a user facility providing femtosecond short pulses with an unprecedented peak and average brilliance, opening new scientific opportunities in many disciplines. The first call for user experiments has been launched in 2005. The FLASH linear accelerator is based on TESLA superconducting technology, providing several thousands of photon pulses per second to user experiments. Probing femtosecond-scale dynamics in atomic and molecular reactions using, for instance, a combination of x-ray and optical pulses in a pump and probe arrangement,as well as single-shot diffraction imaging of biological objects and molecules, are typical experiments performed at the facility. We give an overview of the FLASH facility, and describe the basic principles of the accelerator. Recently,FLASH has been extended by a second undulator beamline(FLASH2) operated in parallel to the first beamline, extending the capacity of the facility by a factor of two.

关键词： bunch compression free-electron laser high-gain FEL process photo injector SASE superconducting accelerator undulator

Airborne Measurements of the Impact of Ground-based Glaciogenic Cloud Seeding on Orographic Precipitation

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Advances in Atmospheric Sciences 2013年第4期30卷 1025-1038页

作者：缪群 bart GEERTS Department of Applied Mathematics Ningbo University Department of Atmospheric Science University of Wyoming

Data from in situ probes and a vertically-pointing ram-wave Doppler radar aboard a research aircraft are used to study the cloud microphysical effect of glaciogenic seeding of cold-season orographic clouds. A previous study （Geerts et al., 2010） has shown that radar reflectivity tends to be higher during seeding periods in a shallow layer above the ground downwind of ground-based silver iodide （AgI） nuclei generators. This finding is based on seven flights, conducted over a mountain in Wyoming （the Unites States）, each with a no-seeding period followed by a seeding period. In order to assess this impact, geographically fixed flight tracks were flown over a target mountain, both upwind and downwind of the AgI generators. This paper examines data from the same flights for further evidence of the cloud seeding impact. Com- posite radar data show that the low-level reflectivity increase is best defined upwind of the mountain crest and downwind of the point where the cloud base intersects the terrain. The main argument that this increase can be attributed to AgI seeding is that it is confined to a shallow layer near the ground where the flow is turbulent. Yet during two flights when clouds were cumuliform and coherent updrafts to flight level were recorded by the radar, the seeding impact was evident in the flight-level updrafts （about 610 m above the mountain peak） as a significant increase in the ice crystal appears short-lived as it is not apparent just downwind of concentration in all size bins. The seeding effect the crest.

关键词： glaciogenic cloud seeding orographic snowfall cloud radar

Promoting axon regeneration in the central nervous system by increasing PI3-kinase signaling

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Neural Regeneration Research 2022年第6期17卷 1172-1182页

作者： bart Nieuwenhuis Richard Eva John van Geest Center for Brain Repair Department of Clinical NeurosciencesUniversity of CambridgeCambridgeUK

Much research has focused on the PI3-kinase and PTEN signaling pathway with the aim to stimulate repair of the injured central nervous *** in the central nervous system fail to regenerate,meaning that injuries or diseases that cause loss of axonal connectivity have life-changing *** 2008,genetic deletion of PTEN was identified as a means of stimulating robust regeneration in the optic *** is a phosphatase that opposes the actions of PI3-kinase,a family of enzymes that function to generate the membrane phospholipid PIP_(3) from PIP_(2)(phosphatidylinositol(3,4,5)-trisphosphate from phosphatidylinositol(4,5)-bisphosphate).Deletion of PTEN therefore allows elevated signaling downstream of PI3-kinase,and was initially demonstrated to promote axon regeneration by signaling through *** recently,additional mechanisms have been identified that contribute to the neuron-intrinsic control of regenerative *** review describes neuronal signaling pathways downstream of PI3-kinase and PIP3,and considers them in relation to both developmental and regenerative axon *** briefly discuss the key neuron-intrinsic mechanisms that govern regenerative ability,and describe how these are affected by signaling through *** highlight the recent finding of a developmental decline in the generation of PIP_(3) as a key reason for regenerative failure,and summarize the studies that target an increase in signaling downstream of PI3-kinase to facilitate regeneration in the adult central nervous ***,we discuss obstacles that remain to be overcome in order to generate a robust strategy for repairing the injured central nervous system through manipulation of PI3-kinase signaling.

关键词： axon cytoskeleton axon regeneration axon transport cell signaling central nervous system growth cone neuroprotection PI3-kinase PI3K PTEN trafficking transcription translation

Generating synthetic as-built additive manufacturing surface topography using progressive growing generative adversarial networks

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Friction 2024年第6期12卷 1283-1298页

作者： Junhyeon SEO Prahalada RAO bart RAEYMAEKERS Department of Mechanical Engineering Virginia TechBlacksburgVA 24061USA Grado Department of Industrial and Systems Engineering Virginia TechBlacksburgVA 24061USA

Numerically generating synthetic surface topography that closely resembles the features and characteristics of experimental surface topography measurements reduces the need to perform these intricate and costly ***,existing algorithms to numerically generated surface topography are not well-suited to create the specific characteristics and geometric features of as-built surfaces that result from laser powder bed fusion(LPBF),such as partially melted metal particles,porosity,laser scan lines,and ***,we present a method to generate synthetic as-built LPBF surface topography maps using a progressively growing generative adversarial *** qualitatively and quantitatively demonstrate good agreement between synthetic and experimental as-built LPBF surface topography maps using areal and deterministic surface topography parameters,radially averaged power spectral density,and material ratio *** ability to accurately generate synthetic as-built LPBF surface topography maps reduces the experimental burden of performing a large number of surface topography ***,it facilitates combining experimental measurements with synthetic surface topography maps to create large data-sets that facilitate,*** as-built surface topography to LPBF process parameters,or implementing digital surface twins to monitor complex end-use LPBF parts,amongst other applications.

关键词： additive manufacturing surface topography synthetic surface topography generative adversarial networks

CFB cyclones at high temperature:Operational results and design assessment

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维普期刊数据库

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Particuology 2008年第3期6卷 149-156页

作者： Raf Dewil Jan Baeyens bart Caerts Department of Chemical Engineering Associated Faculty of Technology and Bio-sciencesCampus De NayerKatholieke Universiteit LeuvenJan De Nayerlaan 5B-2860 Sint-Katelijne-WaverBelgium Department of Chemical Engineering University of BirminghamEdgbastonBirmingham B15 2TTUnited Kingdom Department of Chemical Engineering Katholieke Universiteit LeuvenWillem De Croylaan 46B-3001 HeverleeBelgium

Pressure drop and cut size measurements are reported for a full scale cyclone operating within a 58 MWth CFB-combustor unit at 775 ℃. The paper reviews the vast number of equations to calculate the pressure drop and separation efficiency of cyclones, generally for operation at ambient temperature and at low Cs [〈0.5]. None of the literature correlations predicts the pressure drop with a fair accuracy within the range of experimental operating conditions. The cut size d50 can be estimated using direct empirical methods or using the Stokes number, Stk50. Both methods were used to compare measured and predicted values of d50. With the exception of Muschelknautz and Krambrock, none of the equations made accurate predictions. Finally, an alternative method to determine the friction factor of the pressure drop equation （Euler number, Eu） and of the cut size is proposed. The Eu number is determined from the geometry of common cyclones, and the derived value of Stk50 defines more accurate cut sizes. The remaining discrepancy of less than 5%, when compared with the measured values, is tentatively explained in terms of a reduced cyclone diameter due to the solids layer formed near its wall. Further measurements, mostly using positron emission particle tracking, elucidate the particle motion in the cyclone and both tracking results and the influence of the particle movement on Eu and Stk50 will be discussed in a follow-up paper.

关键词： Cyclone High loading High temperature Combustor

Newly Detected Hydroxyls in Zeolite Mordenite by^1H MAS Spin Echo NMR Spectroscopy

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催化学报 2001年第3期22卷 219-220页

作者：陈铁红 WOUTERS，bart 等 DepartmentofChemistry NankaiUniversityTianjing300071 CenterforSurfaceChemistryandCatalyssi Katholiek

The study of the acidic sites in zeolites is important to understand the nature of the acidic catalytic function.

关键词：丝光沸石羟基结构核磁共振催化剂

Linking axon transport to regeneration using in vitro laser axotomy

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Neural Regeneration Research 2018年第3期13卷 410-412页

作者： bart Nieuwenhuis Richard Eva John van Geest Centre for Brain Repair Department of Clinical Neurosciences University of Cambridge Cambridge UK Laboratory for Regeneration of Sensorimotor Systems Netherlands Institute for Neuroscience Royal Netherlands Academy of Arts and Sciences (KNAW) Amsterdam The Netherlands

Spinal cord injury has devastating consequences because adult central nervous system （CNS） neurons do not regenerate their axons after injury. Two key reasons for axon regeneration fail- ure are extrinsic inhibitory factors and a low intrinsic capacity for axon regrowth. Research has therefore focused on overcom- ing extrinsic growth inhibition, and enhancing intrinsic regeneration capacity. Both of these issues will need to be addressed to enable optimal repair of the injured sp＋inal cord.

关键词： CNS ARF Linking axon transport to regeneration using in vitro laser axotomy EFA