| 1. |
- Alnegren, Patrik, 1988, et al.
(författare)
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Inhibiting chromium evaporation and oxide scale growth on SOFC metallic interconnects by nano coatings
- 2014
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Ingår i: 20th World Hydrogen Energy Conference, WHEC 2014. - 9780000000002 ; 1:2014
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Konferensbidrag (refereegranskat)abstract
- High chromium ferritic steel is today the most commonly considered material for SOFC interconnectors due to many desirable properties, such as matching thermal expansion coefficient with other cell components but most importantly better machinability and price compared to ceramic alternatives. Yet there are some obstacles that need to be addressed before long term stability of a ferritic steel interconnector based fuel cell stack can be realized. First of all the electrical conductivity needs to remain high throughout the fuel cell stack operating life time and thus the formed oxide layers need to be electrically conductive and thin. Secondly, volatilization of chromium from the oxide scale of metallic interconnects causes rapid degradation due cathode poisoning. In the current study both oxidation and chromium evaporation of ferritic steel substrates are investigated in controlled atmospheres that simulates the environments of an operating SOFC stack. Samples coated with nanometer scale dual coatings of Co and Ce were tested. The dual coating substantially increased the performance of the ferritic substrates by i) significantly reducing oxidation rate, ii) increasing scale adherence and iii) diminishing chromium evaporation by 90 % via the formation of a Co-Mn-spinel cap layer.
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| 2. |
- Bachinger, Angelika, et al.
(författare)
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Stiffness-modifiable composite for pedestrian protection
- 2014
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Ingår i: 16th European Conference on Composite Materials, ECCM 2014. - : European Conference on Composite Materials, ECCM. - 9780000000002
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Konferensbidrag (refereegranskat)abstract
- A novel functional material allowing stiffness-reduction upon external stimulation was developed. Implementation of such technology in the design of a car front has high potential to result in increased protection of vulnerable road users (VRUs). The composite material is obtained by coating carbon fibres with a thermoplastic polymer in a continuous process, followed by infusion with an epoxy resin. The process is scalable for industrial use. The coating process was optimized regarding coating efficiency, energy consumption, risks involved for operating personnel and environment, and tailored to gain the optimal coating thickness obtained from numerical calculations. A drastic decrease in transversal stiffness could be detected for the composite material by dynamic mechanical thermal analysis (DMTA), when the temperature was increased above the glass transition temperature of the thermoplastic interphase. The ability of the material to achieve such temperature and associated reduction in stiffness by the application of current was verified using a special 3-point bending setup developed for this task.
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| 3. |
- Berg, Jan, et al.
(författare)
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Adapting audio quality assessment procedures for engineering practice
- 2016
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Ingår i: 139th Audio Engineering Society International Convention. - New York : Audio Engineering Society, Inc.. - 9780000000002
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Konferensbidrag (refereegranskat)abstract
- Audio quality is of concern up and down the production chain from content creation to distribution. The technologies employed at each step - equipment, processors like codecs, downmix algorithms and loudspeakers - all are scrutinized for their impact. The now well-established field of audio quality research has developed robust methods for assessments. To form a basis for this work, research has investigated how perceptual dimensions are formed and expressed. The literature includes numerous sonic attributes that may be used to evaluate audio quality. All together, these findings have provided benchmarks and guidelines for improving audio technology, setting standards in the manufacture of sound and recording equipment, and furthering the design of reproduction systems and spaces. They are, however, by comparison rarely used to inform recording and mixing practice. In this paper quality evaluation and mixing practice are compared on selected counts and observations are made on what points these fields may mutually inform one another.
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| 4. |
- Brandt, L.uca, et al.
(författare)
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Numerical study of turbulent channel flow laden with finite-size non-spherical particles
- 2017
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Ingår i: 10th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2017. - : International Symposium on Turbulence and Shear Flow Phenomena, TSFP10. - 9780000000002
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Konferensbidrag (refereegranskat)abstract
- We present interface-resolved numerical simulations of turbulent channel flow laden with non-spherical rigid and neutrally-buoyant particles. We first focus on the case of oblate particles of aspect ratio 1/3 at volume fractions up to 15% and show that the turbulent drag is decreasing when increasing the particle volume fraction although the effective viscosity of the suspension actually increases. We relate the observed drag reduction to turbulence attenuation and to particle migration away from the near-wall region. Particles tend to align parallel to the wall with rotation rates significantly lower than those reported for spheres. In the second part of the study, we examine the effect of the particle slenderness on the observed drag reduction and show that the drag increases for flatter particles.
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| 5. |
- Brynjell-Rahkola, Mattias, 1986-, et al.
(författare)
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Modal analysis of roughness-induced crossflow vortices in a Falkner-Skan-Cooke boundary layer
- 2013
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Ingår i: International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2013. - : TSFP-8. - 9780000000002
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Konferensbidrag (refereegranskat)abstract
- A three-dimensional global stability analysis using high-order direct numerical simulations is performed to investigate the effect of surface roughness with Reynolds number (based on roughness height) Rek above and below the critical value for transition, on the eigenmodes of a Falkner-Skan-Cooke boundary layer. The surface roughness is introduced with the immersed boundary method and the eigenvalues and eigenfunctions are solved using an iterative time-stepper method. The study reveals a global instability for the case with higher Reynolds number that causes the flow in the non-linear simulations to break down to turbulence shortly downstream of the roughness. Examination of the unstable linear global modes show that these are the same modes that are observed in experiments immediately before breakdown due to secondary instability, which emphasizes the importance of these modes in transition.
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| 6. |
- Canton, Jacopo, et al.
(författare)
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Linear stability of the flow in a toroidal pipe
- 2015
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Ingår i: 9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015. - : TSFP-9. - 9780000000002
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Konferensbidrag (refereegranskat)abstract
- While hydrodynamic stability and transition to turbulence in straight pipes - being one of the most fundamental problems in fluid mechanics - has been studied extensively, the stability of curved pipes has received less attention. In the present work, the first (linear) instability of the canonical flow inside a toroidal pipe is investigated as a first step in the study of the related laminar-turbulent transition process. The impact of the curvature of the pipe, in the range 8 e [0.002,1], on the stability properties of the flow is studied in the framework of linear stability analysis. Results show that the flow is indeed modally unstable for all curvatures investigated and that the wave number corresponding to the critical mode depends on the curvature, as do several other features of this problem. The critical modes are mainly located in the region of the Dean vortices, and are characterised by oscillations which are symmetric or antisymmetric as a function of the curvature. The neutral curve associated with the first bifurcation is the result of a complex interaction between isolated modes and branches composed by several modes characterised by a common structure. This behaviour is in obvious contrast to that of straight pipes, which are linearly stable for all Reynolds numbers.
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| 7. |
- Caraeni, D., et al.
(författare)
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LES of spray in compressible flows on unstructured grids
- 1999
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Ingår i: 30th Fluid Dynamics Conference. - 9780000000002
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Konferensbidrag (refereegranskat)abstract
- In this paper we report some results of our numerical simulations of sprays in compressible flows using Large Eddy Simulation. The combined LES- and spray code has been applied to the computation of the flow and spray injection into a swirl generator of a gas-turbine. The interaction between the spray jet and the flow field has been investigated. A dynamic SGS model has been used and results have been compared with the experimental data.
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| 8. |
- Cataldi, A., et al.
(författare)
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Polymer composite with micro- and nanocellulose for artwork protection and restoration
- 2014
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Ingår i: 16th European Conference on Composite Materials, ECCM 2014. - 9780000000002
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Konferensbidrag (refereegranskat)abstract
- Micro- and nanocomposites were prepared using Aquazol® 500 as a polymeric matrix and a microcrystalline cellulose (MCC), and suspensions of cellulose nanocrystals (CNC), as reinforcing agents. After a preliminary thermo-mechanical characterization that highlighted a stabilizing effect due to the micro- and nanofiller introduction, with an increase of the elastic modulus and a decrease of the thermal expansion coefficient and the creep compliance [1], these materials were applied as canvas lining adhesives. Single-lap shear tests both in quasi-static and creep conditions confirmed the dimensional stability provided by cellulose micro- and nanoparticles, with an important reduction of the adhesives compliance proportional to the filler content. Interestingly, MCC and CNC introduction did not impair the fracture behavior of the neat matrix.
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| 9. |
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| 10. |
- Davidson, Lars, 1957
(författare)
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Backscatter from a scale-similarity model: embedded LES of channel flow, developing boundary layer flow and backstep flow
- 2013
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Ingår i: 8th International Symposium on turbulence and shear flow phenomena (TSFP8). - 9780000000002 ; 3
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Konferensbidrag (refereegranskat)abstract
- The scale-similarity model was proposed by Bardina et al. (1980) some 30 years ago. It was found not to be sufficiently dissipative. Much later, Davidson (2009) found a way to make it strictly dissipative. This was simply achieved by selecting those instants when the scale-similarity term in the momentum equation has the same sign as the viscous diffusive term (the latter term is indeed dissipative). In Davidson (2009) this technique was also used the other way around: by selecting time instants when the scale-similarity term has the opposite sign to the viscous diffusion term it acts as a backscatter term, which destabilizes the momentum equation. This feature is exploited in the present work to promote the generation of resolved turbulence. It is used to promote the creation of resolved turbulence in embedded LES of channel flow, and LES of developing boundary layer and backstep flow. The present method reduces the gray area problem described by Spalart (2009). The proposedmethod can also be used to promote transition from laminar to turbulent flow.
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