| 21. |
- Marimon Giovannetti, Laura, et al.
(författare)
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Multi-wing sails interaction effects
- 2022
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Ingår i: SNAME 24th Chesapeake Sailing Yacht Symposium, CSYS 2022. - : The Society of Naval Architects and Marine Engineers.
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Konferensbidrag (refereegranskat)abstract
- The effects of multiple wings interacting and the change in efficiency due to those effects as well as optimal sheeting angles are becoming an important area of study with the advent of wind-propelled ships for goods transport. This research presents a first analysis of wind tunnel tests carried out at the University of Southampton R.J. Mitchell wind tunnel where three wings are subject to turbulent flow with Reynolds number in excess of 1 million. A range of possible variations of ship heading and apparent wind angles are tested taking into consideration the blockage effects and the geometrical characteristics of the working section. The forces and moments are captured on each individual wing as well as in the overall wind tunnel balance with 6-components dynamometers. Furthermore, pressure sensors and PIV data are recorded during the tests to provide the experimental campaign with results that can validate both qualitatively and quantitatively the numerical tools developed to aid the design stage of wind propelled vessels.
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| 22. |
- Niebles Atencio, Bercelay, 1979, et al.
(författare)
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An experimental study on laminar-turbulent transition at high free-stream turbulence in boundary layers with pressure gradients
- 2012
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Ingår i: The European Physical Journal Conferences. - : EDP Sciences. ; 25, s. Art. no. 01012-
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Konferensbidrag (refereegranskat)abstract
- We report here the results of a study on measurements and prediction of laminar-turbulenttransition at high free-stream turbulence in boundary layers of the airfoil-like geometries with presence of the external pressure gradient changeover. The experiments are performed for a number of flow cases with different flow Reynolds number, turbulence intensity and pressure gradient distributions. The results were then compared to numerical calculations for same geometries and flow conditions. The experiments and computations are performed for the flow parameters which are typical for turbomachinery applications and the major idea of the current study is the validation of the turbulencemodel which can be used for such engineering applications.
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| 23. |
- Ottersten, Martin, 1981, et al.
(författare)
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Inlet Gap Influence on Low-Frequency Flow Unsteadiness in a Centrifugal Fan
- 2022
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Ingår i: Aerospace. - : MDPI AG. - 2226-4310. ; 9:12
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Tidskriftsartikel (refereegranskat)abstract
- In this study, unsteady low-frequency characteristics in a voluteless low-speed centrifugal fan operating at a high mass flow rate are studied with improved delayed detached eddy simulation (IDDES). This study is motivated by a recent finding that the non-uniformly distributed pressure inside this type of fan could be alleviated by improving the gap geometry. The present simulation results show that the velocity magnitudes of the gap have distinct low and high regions. Intensive turbulent structures are developed in the low-velocity regions and are swept downstream along the intersection between the blade and shroud, on the pressure side of the blade. Eventually, the turbulence gives rise to a high-pressure region near the blade’s trailing edge. This unsteady flow behavior revolves around the fan rotation axis. Additionally, its period is 5% of the fan rotation speed, based on the analysis of the time history of the gap velocity magnitudes and the evolution of the high-pressure region. The same frequency of high pressure was also found in previous experimental measurements. To the authors’ knowledge, this is the first time that the trigger of the gap turbulence, i.e., the unsteady local low velocity, has been determined.
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| 24. |
- Ottersten, Martin, 1981
(författare)
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Numerical investigation of tonal noise sources from centrifugal fan
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Heating, ventilating, and air conditioning systems (HVAC) are today an important part of many people's life. They provide a sufficient amount of airflow with the correct temperature, quality, and humidity. The negative side is the noise it produces. Many improvements have been made in building development to reduce noise from the environment. When so, the noise from the HVAC system becomes clearer. The dominant tonal noise in an HVAC system is produced by the fan. In this work tonal noises produced by a centrifugal fan is investigated to be able to understand the generation mechanism and identify their sources. The approach is to use the hybrid computational aeroacoustics (CAA) method, that couples a computational fluid dynamics (CFD) method with the Ffowcs Williams and Hawkings (FW-H) acoustic analogy. Recirculating flows, which are responsible for reducing the fan efficiency and increasing the noise generation, are observed between the shroud and the blade trailing edges. It is found that the recirculating flows are associated with the gap between the shroud and the inlet duct. The recirculating flow causes large modeled turbulence kinetic energy (TKE). The TKE is unevenly distributed among the blades due to the unsteady recirculating flow. Moreover, the position of the largest TKE periodically varies among the blades. The period corresponds to approximately 4 times the fan rotation period, it was also found in acoustic measurements. Different pressure distributions among the blades are found and ascribed to the turbulence initializing from the inlet gap. The turbulence develops along the shroud wall and interacts with the blades at their leading edges. The interaction renders uneven surface pressure distributions among the blades as well as significant peak differences. As the distances to the inlet gap and the shroud increases, the difference of the pressure distributions among the blades decays. The wall-pressure fluctuations indicates that the locations of the tonal noise sources agree with the locations of the uneven surface pressure distributions and the significant pressure peaks, which are near the blade leading edges.
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| 25. |
- Wang, Chenglong, et al.
(författare)
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An Experimental Study of Heat Transfer on an Outlet Guide Vane
- 2014
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Ingår i: ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, GT 2014; Dusseldorf; Germany; 16 June 2014 through 20 June 2014. - 9780791845721 ; 5B, s. UNSP V05BT14A001-, s. 001-14
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Konferensbidrag (refereegranskat)abstract
- In the present study, the heat transfer characteristics on the suction and pressure sides of an outlet guide vane (OGV) are investigated by using liquid crystal thermography (LCT) method in a linear cascade. Because the OGV has a complex curved surface, it is necessary to calibrate the LCT by taking into account the effect of viewing angles of the camera. Based on the calibration results, heat transfer measurements of the OGV were conducted. Both on- and off-design conditions were tested, where the incidence angles of the OGV were 25 degrees and -25 degrees, respectively. The Reynolds numbers, based on the axial flow velocity and the chord length, were 300,000 and 450,000. In addition, heat transfer on suction side of the OGV with +40 degrees incidence angle was measured. The results indicate that the Reynolds number and incidence angle have considerable influences upon the heat transfer on both pressure and suction surfaces. For on-design conditions, laminarturbulent boundary layer transitions are on both sides, but no flow separation occurs; on the contrary, for off-design conditions, the position of laminar-turbulent boundary layer transition is significantly displaced downstream on the suction surface, and a separation occurs from the leading edge on the pressure surface. As expected, larger Reynolds number gives higher heat transfer coefficients on both sides of the OGV.
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| 26. |
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| 27. |
- Pradas Gómez, Alejandro, 1986, et al.
(författare)
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Design automation strategies for aerospace components during conceptual design phases
- 2023
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper explores the different design automation strategies used for the design of aerospace components. A literature review of the applicable strategies, together with the strategies used in the DEFAINE project are presented and compared. An opportunity to explore the combination of two strategies is presented (Enhanced Function-Mean and Knowledge Based Engineering), which has the potential to increase the discovery of novel design solutions while being able to assess their structural performance. The preliminary results of the combined strategy are presented, using a DEFAINE use case of a Turbine Rear Structure jet engine component.
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| 28. |
- Aghaali, Habib, 1981-, et al.
(författare)
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Turbocharged SI-Engine Simulation with Cold and Hot-Measured Turbocharger Performance Maps
- 2012
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Ingår i: Proceedings of ASME Turbo Expo 2012, Vol 5. - : ASME Press. - 9780791844717 ; , s. 671-679
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Konferensbidrag (refereegranskat)abstract
- Heat transfer within the turbocharger is an issue in engine simulation based on zero and one-dimensional gas dynamics. Turbocharged engine simulation is often done without taking into account the heat transfer in the turbocharger. In the simulation, using multipliers is the common way of adjusting turbocharger speed and parameters downstream of the compressor and upstream of the turbine. However, they do not represent the physical reality. The multipliers change the maps and need often to be different for different load points. The aim of this paper is to simulate a turbocharged engine and also consider heat transfer in the turbocharger. To be able to consider heat transfer in the turbine and compressor, heat is transferred from the turbine volute and into the compressor scroll. Additionally, the engine simulation was done by using two different turbocharger performance maps of a turbocharger measured under cold and hot conditions. The turbine inlet temperatures were 100 and 600°C, respectively. The turbocharged engine experiment was performed on a water-oil-cooled turbocharger (closed waste-gate), which was installed on a 2-liter gasoline direct-injected engine with variable valve timing, for different load points of the engine. In the work described in this paper, the difference between cold and hot-measured turbocharger performance maps is discussed and the quantified heat transfers from the turbine and to/from the compressor are interpreted and related to the maps.
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| 29. |
- Capitao Patrao, Alexandre, 1988, et al.
(författare)
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Numerical modeling of laminar-turbulent transition in an interconnecting compressor duct
- 2022
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Ingår i: 33rd Congress of the International Council of the Aeronautical Sciences, ICAS 2022. ; 2022:3, s. 2033-2044
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Konferensbidrag (refereegranskat)abstract
- Cryogenic hydrogen is being considered as a future aviation fuel since it eliminates CO2, CO, soot, sulphur, and unburnt hydrocarbons emissions. The storage temperature and high cooling capacity of cryogenic hydrogen also makes it a suitable coolant. In this paper a integrated heat exchanger in an interconnecting compressor duct (ICD) is analyzed with respect to heat transfer and transition.
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| 30. |
- Liefvendahl, Mattias, 1971, et al.
(författare)
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Wall-Modeled LES for Ship Hydrodynamics in Model Scale
- 2021
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Ingår i: Journal of Ship Research. - : Society of Naval Architects and Marine Engineers. - 1542-0604 .- 0022-4502. ; 65:1, s. 41-54
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Tidskriftsartikel (refereegranskat)abstract
- A complete approach for wall-modeled large-eddy simulation (WMLES) is demonstrated for the simulation of the flow around a bulk carrier in the model scale. Essential components of the method are an a-priori estimate of the thickness of the turbulent boundary layer (TBL) over the hull and to use an unstructured grid with the appropriate resolution relative to this thickness. Expressions from the literature for the scaling of the computational cost, in terms of the grid size, with Reynolds number, are adapted in this application. It is shown that WMLES is possible for model scale ship hydrodynamics, with similar to 10(8) grid cells, which is a gain of at least one order of magnitude as compared with wall-resolving LES. For the canonical case of a flat-plate TBL, the effects of wall model parameters and grid cell topology on the predictive accuracy of the method are investigated. For the flat-plate case, WMLES results are compared with results from direct numerical simulation, RANS (Reynolds-averaged Navier-Stokes), and semi-empirical formulas. For the bulk carrier flow, WMLES and RANS are compared, but further validation is needed to assess the predictive accuracy of the approach.
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