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- Beko, G., et al.
(författare)
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The Indoor Chemical Human Emissions and Reactivity (ICHEAR) project: Overview of experimental methodology and preliminary results
- 2020
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Ingår i: Indoor Air. - : Hindawi Limited. - 1600-0668 .- 0905-6947. ; 30:6, s. 1213-1228
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Tidskriftsartikel (refereegranskat)abstract
- With the gradual reduction of emissions from building products, emissions from human occupants become more dominant indoors. The impact of human emissions on indoor air quality is inadequately understood. The aim of the Indoor Chemical Human Emissions and Reactivity (ICHEAR) project was to examine the impact on indoor air chemistry of whole-body, exhaled, and dermally emitted human bioeffluents under different conditions comprising human factors (t-shirts/shorts vs long-sleeve shirts/pants; age: teenagers, young adults, and seniors) and a variety of environmental factors (moderate vs high air temperature; low vs high relative humidity; presence vs absence of ozone). A series of human subject experiments were performed in a well-controlled stainless steel climate chamber. State-of-the-art measurement technologies were used to quantify the volatile organic compounds emitted by humans and their total OH reactivity; ammonia, nanoparticle, fluorescent biological aerosol particle (FBAP), and microbial emissions; and skin surface chemistry. This paper presents the design of the project, its methodologies, and preliminary results, comparing identical measurements performed with five groups, each composed of 4 volunteers (2 males and 2 females). The volunteers wore identical laundered new clothes and were asked to use the same set of fragrance-free personal care products. They occupied the ozone-free (<2 ppb) chamber for 3 hours (morning) and then left for a 10-min lunch break. Ozone (target concentration in occupied chamber ~35 ppb) was introduced 10 minutes after the volunteers returned to the chamber, and the measurements continued for another 2.5 hours. Under a given ozone condition, relatively small differences were observed in the steady-state concentrations of geranyl acetone, 6MHO, and 4OPA between the five groups. Larger variability was observed for acetone and isoprene. The absence or presence of ozone significantly influenced the steady-state concentrations of acetone, geranyl acetone, 6MHO, and 4OPA. Results of replicate experiments demonstrate the robustness of the experiments. Higher repeatability was achieved for dermally emitted compounds and their reaction products than for constituents of exhaled breath.
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| 2. |
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| 3. |
- Mamidala, Santhosh Babu
(författare)
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Effects of free-stream turbulence and three-dimensional roughness on boundary layer transition
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- External disturbances such as free-stream turbulence (FST), and isolated three-dimensional roughness are strong disturbance sources to the laminar boundary layers (BLs), which can lead to a rapid transition to turbulence. The transition process eventuates to increase in skin-friction coefficient and heat transfer rate and hence, both of the aforementioned disturbance sources have practical importance. The current thesis is an experimental work, with investigations carried out in low-turbulence wind-tunnels to study the influence of these disturbance sources on boundary layer transition. Today, in FST transition, it is known that the turbulence intensity and the streamwise integral length scale in the free stream are the two influential characteristics that decide the transition onset, location and the extent. Unsteady, elongated streaks in the streamwise direction dominate this scenario, whose amplitudes and spanwise scales are set by the FST conditions prevalent at the leading edge (LE). In reality, a LE is unavoidable and the influence of the inherent LE pressure gradient region on BL transition was always doubted and not investigated in detail. The first part of the current thesis explores the FST transition scenario for a wide range of FST conditions and pressure gradients providing an input to the future transition prediction models. An important result in this thesis is that the entire energy spectrum needs to be known if an accurate prediction of the transition onset is desired, i.e. the LE condition in terms of characteristic length scale and turbulence intensity is not sufficient. In the second part, isolated roughness-induced transition is investigated thoroughly by changing the roughness height in micrometer precision at various diameters. In the previous experimental studies, the investigations were performed by altering the free-stream velocity at a fixed aspect ratio and hence modifying the base flow. In contrast, here, the aspect ratio of the roughness element is altered in an extensive range and the influence of the aspect ratio on the roughness Reynolds number that causes transition is studied without affecting the base flow. Instabilities that occur prior to the transition onset were examined in detail by performing flow visualization experiments. Moreover, interaction of secondary disturbances like Tollmien-Schlichting waves with the roughness was investigated.
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| 4. |
- von Stillfried, Florian, 1980-
(författare)
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Computational fluid-dynamics investigations of vortex generators for flow-separation control
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many flow cases in fluid dynamics face undesirable flow separation due to ad-verse pressure gradients on wall boundaries. This occurs, for example, due togeometrical reasons as in a highly curved turbine-inlet duct or on flow-controlsurfaces such as wing trailing-edge flaps within a certain angle-of-attack range.Here, flow-control devices are often used in order to enhance the flow and delayor even totally eliminate flow separation. Flow control can e.g. be achieved byusing passive or active vortex generators (VGs) for momentum mixing in theboundary layer of such flows. This thesis focusses on such passive and activeVGs and their modelling for computational fluid dynamics investigations.First, a statistical VG model approach for passive vane vortex genera-tors (VVGs), developed at the Royal Institute of Technology Stockholm andthe Swedish Defence Research Agency, was evaluated and further improvedby means of experimental data and three-dimensional fully-resolved computa-tions. This statistical VVG model approach models those statistical vortexstresses that are generated at the VG by the detaching streamwise vortices.This is established by means of the Lamb-Oseen vortex model and the Prandtllifting-line theory for the determination of the vortex strength. Moreover, thisansatz adds the additional vortex stresses to the turbulence of a Reynolds-stresstransport model. Therefore, it removes the need to build fully-resolved three-dimensional geometries of VVGs in a computational fluid dynamics mesh. Usu-ally, the generation of these fully-resolved geometries is rather costly in termsof preprocessing and computations. By applying VVG models, the costs arereduced to that of computations without VVGs. The original and an improvedcalibrated passive VVG model show sensitivity for parameter variations suchas the modelled VVG geometry and the VVG model location on a flat plate inzero- and adverse-pressure-gradient flows, in a diffuser, and on an airfoil withits high-lift system extracted. It could be shown that the passive VG modelqualitatively and partly quantitatively describes correct trends and tendenciesfor these different applications.In a second step, active vortex-generator jets (VGJs) are considered. They were experimentally investigated in a zero-pressure-gradient flat-plate flow atTechnische Universitä̈t Braunschweig, Germany, and have been re-evaluated for our purposes and a parameterization of the generated vortices was conducted. Dependencies of the generated vortices and their characteristics on the VGJsetup parameters could be identified and quantified. These dependencies wereused as a basis for the development of a new statistical VGJ model. This modeluses the ansatz of the passive VVG model in terms of the vortex model, theadditional vortex-stress tensor, and its summation to the Reynolds stress ten-sor. Yet, it does not use the Prandtl lifting-line theory for the determinationof the circulation but an ansatz for the balance of the momentum impact thatthe VGJ has on the mean flow. This model is currently under developmentand first results have been evaluated against experimental and fully-resolvedcomputational results of a flat plate without pressure gradient.
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| 5. |
- Zannoni, Nora, et al.
(författare)
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Effect of Ozone, Clothing, Temperature, and Humidity on the Total OH Reactivity Emitted from Humans
- 2021
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 55:20, s. 13614-13624
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Tidskriftsartikel (refereegranskat)abstract
- People influence indoor air chemistry through theirchemical emissions via breath and skin. Previous studies showed thatdirect measurement of total OH reactivity of human emissionsmatched that calculated from parallel measurements of volatile organiccompounds (VOCs) from breath, skin, and the whole body.In thisstudy, we determined, with direct measurements from twoindependent groups of four adult volunteers, the effect of indoortemperature and humidity, clothing coverage (amount of exposedskin), and indoor ozone concentration on the total OH reactivity ofgaseous human emissions.The results show that the measuredconcentrations of VOCs and ammonia adequately account for themeasured total OH reactivity. The total OH reactivity of humanemissions was primarily affected by ozone reactions with organic skinoilconstituents and increased with exposed skin surface, higher temperature, and higher humidity. Humans emitted a comparabletotal mixing ratio of VOCs and ammonia at elevated temperature-low humidity and elevated temperature-high humidity, withrelatively low diversity in chemical classes.In contrast, the total OH reactivity increased with higher temperature and higherhumidity, with a larger diversity in chemical classes compared to the total mixing ratio. Ozone present, carbonyl compounds were thedominant reactive compounds in all of the reported conditions.
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