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| 3. |
- Nilsson, Johan, et al.
(författare)
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Passive load control in backward-facing step flow by using chevrons
- 2016
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Ingår i: Proceedings of the 5th International Conference on Jets, Wakes and Separated Flows, ICJWSF 2015. - Cham : Springer International Publishing. - 9783319306001 ; 185, s. 223-239
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Konferensbidrag (refereegranskat)abstract
- The ability of chevrons at the top edge of a backward-facing step to reduce downstream surface pressure fluctuations is investigated numerically. Three different chevron configurations are compared against a baseline case without chevrons. Low frequency reduction in the surface pressure fluctuations is observed for two of the configurations. The chevrons do not appear to have a significant effect on the flow as the mean reattachment length for all configurations is nearly constant and there is only a small increase in streamwise turbulence for one configuration with the other configurations unchanged.
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| 4. |
- Mihaescu, Mihai, et al.
(författare)
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Coaxial jet noise prediction: Grid resolution effect on the numerical solution
- 2005
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Ingår i: Collection of Technical Papers - 11th AIAA/CEAS Aeroacoustics Conference. - : AIAA. - 1563477300 ; 5, s. 3586-3595, s. 3586-3595
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Konferensbidrag (refereegranskat)abstract
- The flow and acoustic fields that are generated by two coaxial jets are considered. The problem is handled by solving the flow field using Large Eddy Simulation (LES) and the acoustics by a wave equation with source terms provided by the instantaneous LES. The paper is focused on the influence of the grid resolution on the solution accuracy.
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| 5. |
- Mihaescu, Mihai, 1976-, et al.
(författare)
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Computational Aeroacoustics of a Separate Flow Exhaust System with Eccentric Inner Nozzle
- 2007
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Ingår i: 45th AIAA Aerospace Sciences Meeting 2007. - 9781563478901 ; , s. 28-39
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Konferensbidrag (refereegranskat)abstract
- A major issue related to our modern way of life is the noise caused by jet engine powered airliners. Methods to reduce the jet noise were proposed in the last decades starting with the introduction of high bypass turbofan engines. A numerical investigation of flow and acoustics of a separate flow exhaust system is performed in the present paper. The goal is to investigate how the noise generated by a separate flow jet engine exhaust is influenced if the symmetry of the jet exhaust geometry is broken by having the inner nozzle and the center body off the center line axis of the fan nozzle. A decomposition of flow variables is used that allows separation of flow and acoustic computations. Large Eddy Simulation approach is employed to compute the flow field and the acoustic sources. The inhomogeneous wave equation is used to compute the acoustic near- and far-fields. Using this method, previous numerical studies of the symmetric (baseline) configuration showed good agreement between the computed data and the experimental results. Comparisons between the near- and far-field baseline concentric case and the computations obtained using the eccentric configuration are performed showing an acoustic benefit for the offset case.
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| 6. |
- Mihaescu, Mihai, et al.
(författare)
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Numerical investigations of the acoustics of a coaxial nozzle
- 2005
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Ingår i: 43rd AIAA Aerospace Sciences Meeting and Exhibit - Meeting Papers. - : AIAA. - 9781563477577 ; , s. 12601-12610
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Konferensbidrag (refereegranskat)abstract
- The acoustic field generated by two coaxial jets is studied numerically. The turbulent non-isothermal flow is handled by Large Eddy Simulations (LES) and the acoustical perturbations are treated by solving an inhomogeneous wave equation. The acoustical source is obtained from the instantaneous LES flow field. The computed flow and acoustical fields are compared to measured data. Good agreement between the computed and the measured results has been found.
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| 8. |
- Grosshans, Holger, et al.
(författare)
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Influence of the rotor configuration on the electrostatic charging of helicopters
- 2018
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Ingår i: AIAA Journal. - 0001-1452. ; 56:1, s. 368-375
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Tidskriftsartikel (refereegranskat)abstract
- A helicopter flying through an atmosphere containing particulates may accumulate high electrostatic charges that can challenge its operational safety. In this paper the influence of the helicopter configuration on its electrification is reported. The current study is based on a recently developed numerical approach in which the turbulent airflow around the rotorcraft is estimated via large-eddy simulations, whereas the particulate flow is computed via Lagrangian particle tracking. Also, this approach incorporates a model for the triboelectric charge transfer during particle-helicopter collisions that is briefly described herein. The configurations examined in the study include rotor systems equipped with two, three, or four blades. Also investigated are the effects of the rotor size and its rotational frequency. The current results predict that a helicopter with fewer blades accumulates less electric current, even though the charge on each individual blade is higher. Furthermore, the location of the charge buildup on the rotor disk depends strongly on the number of blades. Also, according to current computations, a reduction of the rotor size leads to a reduction of its electrification, even if the blade tip velocity is kept constant.
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| 9. |
- Grosshans, Holger, et al.
(författare)
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Modeling the electrostatic charging of a helicopter during hovering in dusty atmosphere
- 2017
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Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638. ; 64, s. 31-38
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Tidskriftsartikel (refereegranskat)abstract
- A helicopter flying through an atmosphere containing particulates may accumulate high electrostatic charges which can challenge its operational safety. In this paper we elaborate and validate a triboelectric charging model to predict the electrification experienced by a helicopter while hovering in dusty air. We employed Large Eddy simulations to describe the turbulent structures inherent in the flow around the rotorcraft. The dust particles were tracked individually in a Lagrangian framework. A model accounting for the triboelectric charge transfer when a particle hits the helicopter was introduced. The results demonstrate the accuracy of the proposed approach and allow a detailed analysis of the location of the charge accumulation.
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