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- 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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| 2. |
- Jonsson, Isak, 1990, et al.
(författare)
-
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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| 3. |
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| 4. |
- Zetterström, Oskar, et al.
(författare)
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A 28-port MIMO Cube for Micro Base Station Applications
- 2020
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Ingår i: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers Inc.. - 0018-926X .- 1558-2221. ; 68:5, s. 3443-3452
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Tidskriftsartikel (refereegranskat)abstract
- A novel multi-band, dual-polarized, 28-port multiple-input multiple-output (MIMO) cube is presented. The cube structure enables dense placement of the antennas, whilst still allowing for low correlation between the individual antenna ports. The total size of the cube is roughly 2×2×7 λ30, where λ0 is the wavelength at the lowest used frequency. The novelty of the design lies in the use of a combination of orthogonally polarized endfire and broadside radiating antenna elements. Full use of all facets of the cube is achieved without the need to sacrifice bottom or top facets for mounting. Therefore, full azimuthal coverage for communication in two orthogonal polarizations is readily achieved. The system operates in both cellular and Wi-Fi 2:4, 5:5 GHz bands, with a targeted |S11| below –10 dB. The MIMO performance of the system is evaluated in two environments: the Rich Isotropic Multipath environment and the Random Line-of-Sight environment. These two scenarios represent the edge environments of any real-life propagation scenario in terms of the directional distribution of outgoing or incoming waves at a MIMO transceiver. The intended application of the system is micro base stations and repeaters, with possible extension to massive MIMO.
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