| 1. |
- Hörteborn, Erica, 1987, et al.
(författare)
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Architectural Knitted Windbreaks for Improved Wind Comfort in the City: A Wind Tunnel Study of Custom-Designed Porous Textile Screens
- 2023
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Ingår i: Buildings. - : MDPI AG. - 2075-5309. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- There is a need to shield from the wind to improve pedestrian comfort in urban environments. Perforated windbreaks, such as fences, vegetation or textile nets, have proven to be an efficient solution, whereas knitted textiles have not yet been explored. The purpose of this study was to evaluate the capacity of knitted textile windbreaks to reduce wind velocities, to inform further research and promote wider architectural applications. Five custom-knitted textile prototypes, representing fragments of textile windbreaks, were tested in a wind tunnel and compared against a perforated and a nonperforated solid board. Forces on the models, as well as upstream and downstream velocities, were measured. The results indicate that the optimal optical porosity of knitted windbreaks should be around 10%, which differs from the porosity for perforated windbreaks recommended by prior studies. Moreover, it was observed that a textile windbreak knitted using the drop-stitch technique efficiently reduces the wind, while not generating a large drag force. Furthermore, the drag coefficient for the knitted windbreak is reduced with increased windspeed. With this, the presented study demonstrates that knitted structures exposed to wind influence have the functional potential of becoming efficient windbreaks, thus improving wind comfort and aesthetic user experience in the urban space.
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| 2. |
- Jonsson, Isak, 1990, et al.
(författare)
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Experimental and Numerical Study of Laminar-Turbulent Transition on a Low-Pressure Turbine Outlet Guide Vane
- 2020
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Ingår i: Proceedings of the ASME Turbo Expo. ; 2B
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Konferensbidrag (refereegranskat)abstract
- In modern commercial aviation engines, the low-pressure turbine (LPT) has a high outlet swirl to maximize turbine power to weight ratio. Downstream of the last LPT rotor is the turbine rear structure (TRS) that with relatively few low-aspect-ratio outlet guide vanes (OGV) de-swirls the flow to maximize the thrust. The performance of the TRS is strongly connected to secondary flow structures, which in turn are strongly influenced by the laminar-turbulent transition. Transition can be challenging to predict in turbomachinery due to the highly complex flow present. At the design point the TRS can have both by-pass transition and laminar separation with transition and a following turbulent reattachment. In addition, a TRS needs to perform well in a large off-design envelope, with large variations of the inlet swirl angle. Accurately predicting transition, both at the design point and in important off-design points, is critical for the development of future TRS modules. In modern geared and ultra-high by-pass engines the TRS swirl angle off-design requirements are also increasing. There are several available transition models in RANS simulations and most of them need parameter tuning when introduced to new conditions. Evaluation of these models for different turbomachinery components is relatively well covered in the literature even though the model specifics often is a classified property of engine manufacturers. However, there are no cases in the literature of transition prediction with experimental verification in the TRS at engine-realistic conditions. This work presents the first experimental verification of laminar-turbulent transition in a TRS module tested in the LPT-OGV experimental facility at Chalmers Laboratory of Thermal and Fluid Science. The facility is a semi-closed rig using a rotating 1.5 stage shrouded low-pressure turbine stage to create engine representative inlet conditions for the TRS downstream of the LPT stage. Transition was measured using differential IR-thermography (DIT) which is a non-intrusive two-dimensional measurement technique. The technique was specially developed at Chalmers for this particular purpose and validated by boundary layer hot-wire measurements. The numerical analysis was done using commercially available transition models in Fluent and Ansys CFX. Gamma-theta transition model was used with the k-omega SST turbulence model. Experiments and numerical simulations were performed at a chord Reynold number of 235000 and with LPT outlet swirl angles covering both the design point (ADP) and relevant off-design points. Numerical and experimental results show that agreement between transition models and experiments can be achieved at these conditions. Boundary layers on the pressure side and suction side undergo laminar-turbulent transition for the selected test range. At decreased OGV aerodynamic load, the boundary layer on the pressure side near the leading edge is laminar along most of the span. At higher OGV loads the secondary flow is influencing the region near the shroud on the pressure side as well as near the hub on the suction side. The transition on the suction side midspan is significantly influenced by the vane load. The numerical analysis was used to better understand the involved flow mechanisms.
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| 3. |
- Jonsson, Isak, 1990, et al.
(författare)
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Experimental and Numerical Study of Laminar-Turbulent Transition on a Low-Pressure Turbine Outlet Guide Vane
- 2021
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Ingår i: Journal of Turbomachinery. - : ASME International. - 1528-8900 .- 0889-504X. ; 143:10
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Tidskriftsartikel (refereegranskat)abstract
- This work presents an experimental and numerical investigation on the laminar-turbulent transition and secondary flow structures in a Turbine Rear Structure (TRS). The study was executed at engine representative Reynolds number and inlet conditions at three different turbine load cases. Experiments were performed in an annular rotating rig with a shrouded low-pressure turbine upstream of a TRS test section. The numerical results were obtained using the SST k–ω turbulence model and the Langtry- Menter γ–θ transition model. The boundary layer transition location at the entire vane suction side is investigated. The location of the onset and the transition length are measured using IR thermography along the entire vane span. The IR-thermography approach was validated using hot-wire boundary layer measurements. Both experiments and CFD show large variations of transition location along the vane span with strong influences from endwalls and turbine outlet conditions. Both correlate well with traditional transition onset correlations near midspan and show that the transition onset Reynolds number is independent of the acceleration parameter. However, CFD tends to predict an early transition onset in the midspan vane region and a late transition in the hub region. Furthermore, in the hub region, CFD is shown to overpredict the transverse flow and related losses. Disclaimer: The content of this article reflects only the authors’ view. The Clean Sky 2 Joint Undertaking is not responsible for any use that may be made of the information it contains.
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| 4. |
- Jonsson, Isak, 1990, et al.
(författare)
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Experimental Study of Transition in a Turbine Rear Structure
- 2020
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In modern commercial aviation engines, the low-pressure turbine (LPT) has a high outlet swirl to maximize turbine power to weight ratio. Downstream of the last LPT rotor is the turbine rear structure (TRS) that with relatively few low-aspect-ratio outlet guide vanes (OGV), de-swirls the flow to maximize the thrust. In the wide operational envelope of the TRS, both transition location and mode can change during a normal operating cycle. Hence, accurately predicting transition is critical for the development of future TRS modules. This work discusses the experimental method and results of laminar-turbulent transition in a TRS module at engine representative conditions at Reynolds Number of 235,000. This was done in Chalmers 1.5 stage LPT-OGV facility. The transition was measured on the entire span using IR-thermography. The technique was specially developed at Chalmers for this particular purpose and validated by boundary layer hot-wire measurements. The technique provides both steady-state heat transfer with high confidence of 2-8% and time-resolved temperature fluctuations. This paper describes a collection of how this data can be used for transition detection, how it compares to fundamental correlations and as a tool for flow visualization. The facility was built thanks to the financial support of Energimyndigheten, Nationella flygtekniska forskningsprogrammet, the EU Commission, GKN Aerospace Sweden AB and the department of Mechanics and Maritime Sciences at Chalmers. The aerosurface of the LPT and TRS is designed by GKN Aerospace solely for the experimental rig and is not related to any GKN Aerospace product characteristics.
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| 5. |
- Jonsson, Isak, 1990, et al.
(författare)
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Infrared Thermography Investigation of Heat Transfer on Outlet Guide Vanes in a Turbine Rear Structure
- 2020
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Ingår i: International Journal of Turbomachinery, Propulsion and Power. - : MDPI AG. - 2504-186X. ; 5:3
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Tidskriftsartikel (refereegranskat)abstract
- Aerothermal heat transfer measurements in fluid dynamics have a relatively high acceptance of uncertainty due to the intricate nature of the experiments. The large velocity and pressure gradients present in turbomachinery application add further complexity to the measurement procedure. Recent method and manufacturing development has addressed some of the primary sources of uncertainty in these heat transfer measurements. However, new methods have so far not been applied in a holistic approach for heat transfer studies. This gap is bridged in the present study where a cost-effective and highly accurate method for heat transfer measurements is implemented, utilising infrared thermography technique (IRT) for surface temperature measurement. Novel heat transfer results are obtained for the turbine rear sturcture (TRS), at engine representative conditions for three different outlet guide vane (OGV) blade loading and at Reynolds Number of 235000. In addition to that, an extensive description of the implementation and error mitigation is presented.
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| 6. |
- Maccioni, Lorenzo, et al.
(författare)
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Fluxes in a full-flooded lubricated Tapered Roller Bearing: Particle Image Velocimetry measurements and Computational Fluid Dynamics simulations
- 2023
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Ingår i: Tribology International. - 0301-679X. ; 188
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Tidskriftsartikel (refereegranskat)abstract
- The acquisition of complex fluxes inside a Tapered Roller Bearing (TRB) via Particle Image Velocimetry (PIV) is an experimental challenge. This can be successfully performed by exploiting a special test rig having the outer ring manufactured with sapphire. In the present paper, the velocity field in the region between cage, rollers and outer race have been captured via PIV in a fully flooded lubricated TRB. The experimental conditions have been reproduced numerically via Computational Fluid Dynamics (CFD). The comparison of PIV results with CFD ones showed excellent consistency. It has been observed that, in the target domain, the tangential velocity of the lubricant is greater than those of the cage. In addition, in the proximity of the edges of the rollers, squeezing effects due to high gradients of pressure have been recorded. The distribution of flow rates due to the pumping effect in different regions of the TRB have been estimated.
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| 7. |
- Maccioni, Lorenzo, et al.
(författare)
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Particle Image Velocimetry measurements inside a tapered roller bearing with an outer ring made of sapphire: Design and operation of an innovative test rig
- 2022
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X. ; 165
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Tidskriftsartikel (refereegranskat)abstract
- Experimental studies on rolling-element bearing lubrication represent an ambitious engineering challenge. In the present study, the design of a dedicated test rig to perform Particle Image Velocimetry (PIV) measurements on the lubricant inside a tapered roller bearing is presented. Through the usage of a sapphire outer ring, it has been possible to optically access the inside of a bearing without compromising its kinematics. PIV measurements allowed the reconstruction of the lubricant velocity field in the cavity between the cage and the outer ring at different rotational speeds. Results show that as the speed of rotation increases, bubbles due to aeration phenomena tend to appear and modify the behavior of the lubricant considerably.
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| 8. |
- Maccioni, Lorenzo, et al.
(författare)
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Study of the impact of aeration on the lubricant behavior in a tapered roller bearing: Innovative numerical modelling and validation via particle image velocimetry
- 2022
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X. ; 165
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Tidskriftsartikel (refereegranskat)abstract
- The air-lubricant interaction causes aeration which influences lubrication mechanisms in rolling-element-bearings. The goal of this paper is to develop a Computational Fluid Dynamics (CFD) model capable to take into consideration aeration. A new solver was implemented in the open-source environment OpenFOAM®. A dip lubricated tapered-roller-bearing was simulated with the new and a standard solver. The numerical predictions were compared with experimental data acquired on a dedicated test rig exploiting Particle Image Velocimetry (PIV). The comparison of the standard predictions and the experimental data for high shaft rotational speeds (higher level of aeration) shows discrepant results. On the other hand, the solver that takes aeration into account leads to results which are comparable to the experimental ones in all rotational ranges investigated via PIV.
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| 9. |
- Mastrone, Marco Nicola, et al.
(författare)
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Oil distribution and churning losses of gearboxes: Experimental and numerical analysis
- 2020
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Ingår i: Tribology International. - : Elsevier BV. - 0301-679X. ; 151
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Tidskriftsartikel (refereegranskat)abstract
- Currently, energy efficiency represents one of the main requisites in mechanical design. Gearboxes play an important role in several industrial applications and, even if they are already characterized by high efficiency, their performance can still be improved, leading to energy saving and the reduction of pollutant emissions. The possibility to investigate different gearbox geometries and operating conditions in the preliminary stages of design represents a clear advantage for engineers and can significantly contribute to the achievement of these objectives. However, analytical formulations that are able to accurately describe gear losses, especially those due to the interaction with the lubricant, are not available or are not accurate enough. Furthermore, the analytical models are typically not suitable for novel gearbox designs. In the present work, a numerical approach based on Computational Fluid Dynamics (CFD) for the prediction of lubricant fluxes and power losses of gearboxes is presented. The presented methodology utilizes a meshing strategy that reduces the computational effort of the simulations and enables parametrical studies. The numerical approach is validated both with torque measurements and data regarding the oil flow obtained by the Particle Image Velocimetry (PIV). Thus, the validation of the numerical approach is performed not only qualitatively with respect to the oil distribution but also quantitatively with respect to the torque and velocity field in the oil sump. Good agreement of the CFD and experimental data was observed for the torque, oil distribution and fine flow details including the vorticial structures and recirculation areas.
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| 10. |
- Niebles Atencio, Bercelay, 1979, et al.
(författare)
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Experiments and Lattice-Boltzmann Simulation of Flow in a Vertically Aligned Gearbox
- 2023
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Ingår i: Journal of Tribology. - 0742-4787 .- 1528-8897. ; 145:11
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a study of the oil flow in a vertically arranged FZG gearbox. The splash and churning losses are experimentally evaluated using measurements of the resistance torque. Using high speed imaging, the instantaneous oil splashing inside the gearbox is also presented and compared with Computational Fluid Dynamics (CFD) results from the Lattice-Boltzmann method (LBM), instead of the traditional grid-based finite volume method. Four different configurations, including a spur gear based on the standard FZG geometry and a disc pair wheel-pinion with the same tip diameters of the standard geometries are used. The experiments cover a range from 500 to 3000 rpm and three oil levels are studied. For the CFD simulations, the same oil levels and rotational speeds are used. The experimental results indicate torque differences depending on the oil level and the configuration. The splashing pattern is also different from the standard horizontal FZG case, which is typically studied in the literature. On the other hand, the CFD simulations and flow visualization experiments are in relative agreement with one another. The similarities and differences in the torque values for the different configurations and the splashing pattern for both experiments and CFD simulations are analyzed and discussed.
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