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  • 1.
    Crippa, Simone
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Accurate physical and numerical modeling of complex vortex phenomena over delta wings2006Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    With this contribution to the AVT-113/VFE-2 task group it was possible to prove the feasibility of high Reynolds number CFD computations to resolve and thus better understand the peculiar dual vortex system encountered on the VFE-2 blunt leading edge delta wing. Initial investigations into this phenomenon seemed to undermine the hypothesis, that the formation of the inner vortex system relies on the laminar state of the boundary layer at separation onset. As a result of this research, this initial hypothesis had to be expanded to account also for high Reynolds number cases, where a laminar boundary layer status at separation onset could be excluded. Furthermore, the data published in the same context shows evidence of secondary separation under the inner primary vortex. This further supports the supposition of a different generation mechanism of the inner vortical system other than a pure development out of a possibly laminar separation bubble. The unsteady computations performed on numerical grids with different levels of refinement led furthermore to the establishment of internal guidelines specific to the DES approach.

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  • 2.
    Crippa, Simone
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Advances in vortical flow prediction methods for design of delta-winged aircraft2008Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis covers the field of vortex-flow dominated external aerodynamics. As part of the contribution to the AVT-113 task group it was possible to prove the feasibility of high Reynolds number CFD computations to resolve and thus better understand the peculiar dual vortex system encountered on the VFE-2 blunt leading edge delta wing at low to moderate incidences. Initial investigations into this phenomenon seemed to undermine the hypothesis, that the formation of the inner vortex system depends on the laminar/turbulent state of the boundary layer at separation onset. As a result of this research, the initial hypothesis had to be expanded to account also for high Reynolds number cases, where a laminar boundary layer at separation onset can be excluded.

    In addition, unsteady transonic computations are used to shed light on a highly non-linear phenomenon encountered at high angles of incidence. At certain conditions, the increase of the incidence by a single degree leads to a sudden movement of the vortex breakdown location from the trailing edge to mid-chord.

    The lessons learned from the contribution to the VFE-2 facet are furthermore used to prove the technology readiness level of the tools within the second facet of AVT-113, the Cranked Arrow Wing Aerodynamics Project International (CAWAPI). The platform for this investigation, the F-16XL aircraft, experiences at high transonic speeds and low incidence a complex interaction between the leading edge vortex and a strong, mid-chord shock wave.

    A synergetic effect of VFE-2 with a further project, the Environmentally friendly High Speed Aircraft (HISAC), is also presented in this thesis. Reynolds number dependence is documented in respect to leading edge vortex formation of the wing planform for a reference HISAC configuration. Furthermore, proof is found for a similar dual vortex system as for the VFE-2 blunt leading edge configuration.

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  • 3.
    Crippa, Simone
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Initial Steady and Unsteady CFD Analysis of a Half-span Delta Wing2006In: Proceedings of the 25th Congress of the International Council of the Aeronautical Sciences 2006, 2006Conference paper (Refereed)
  • 4.
    Crippa, Simone
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Initial steady/unsteady CFD analysis of vortex flow over the VFE-2 delta wing2006In: 25th Congress of the International Council of the Aeronautical Sciences, 3-8 September 2006, Hamburg, Germany, 2006, p. 883-892Conference paper (Refereed)
    Abstract [en]

    This study is aimed at assessing the application of the latest unstationary CFD method, Detached- Eddy Simulation (DES), to simulate the flowfield around blunt leading edge delta wings. For this purpose, the Second International Vortex Flow Experiment (VFE-2) 65° sweep delta wing model was used to perform numerical investigations at a Reynolds number of 6 million, Mach number of 0.4 and angles of attack of 18.5° and 23°. As the nature of this study is mainly exploratory, various numerical grids have been used. The results confirm the maturity of Reynolds averaged Navier-Stokes (RANS) methods but also the problems of DES to predict free separation and the grid sensitivity of this model.

  • 5.
    Crippa, Simone
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Numerical investigation of Reynolds number effects on a blunt leading-edge delta wing2006In: 24th AIAA Applied Aerodynamics Conference: San Francisco, CA : 5 June 2006 through 8 June 2006, 2006, p. 708-726Conference paper (Refereed)
    Abstract [en]

    Numerical results are presented and discussed in this paper allowing a deeper and more precise characterization of the unique double vortex system, which develops on the second International Vortex Flow Experiment (VFE-2) blunt leading edge delta wing of 65° sweep. Computational fluid dynamic (CFD) computations have been performed for three Reynolds numbers (2, 6 and 60 million) at three angles of attack (13.3°, 18.5° and 23.0°) for a fixed Mach number of 0.4. Leading edge primary separation onset is shown to match best the available wind tunnel data at the highest investigated Reynolds number of 60 million and at an angle of attack of 23.0°. At this condition, the coupling between outer primary vortex attachment line with the inner primary vortex separation line is clearly recognizable. Only if the inner primary vortex strength is predicted well, the attached flow passing under the inner primary vortex core is accelerated sufficiently to trigger (inner) secondary separation.

  • 6.
    Crippa, Simone
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Reynolds number effects on blunt leading edge delta wings2007In: 1st CEAS European Air and Space Conference: September 2007, Berlin, Germany, 2007Conference paper (Refereed)
  • 7.
    Crippa, Simone
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Rizzi, Arthur
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Steady, subsonic CFD analysis of the VFE-2 configuration and comparison to wind tunnel data2008In: 46th AIAA Aerospace Sciences Meeting and Exhibit, 2008Conference paper (Refereed)
    Abstract [en]

    A steady computational fluid dynamic (CFD) study is performed over a wide range of Reynolds numbers at low incidence and subsonic speeds on the Second International Vortex Flow Experiment (VFE-2) blunt leading-edge delta wing of 65° sweep. The numerical results are presented and compared to experimental data and are further used to understand the formation of a weak, thin vortical structure that develops upstream of primary leading-edge separation onset. Comparisons between computational results and experiments are presented with regard to surface pressure coefficient and surface flow patterns for the suction side of the delta wing. Inviscid computations displaying a similar vortical pattern as the viscous results raise the doubt that time-accurate computations might be necessary to correctly predict the formation of the weak apex vortex.

  • 8.
    Melin, Tomas
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Crippa, Simone
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Holl, Martin
    Smid, Miroslav
    Investigating Active Vortex Generators As A 2006In: ICAS 2006, Hamburg, Germany, 2006., 2006Conference paper (Refereed)
  • 9.
    Melin, Tomas
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Crippa, Simone
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Holly, M.
    Smid, M.
    Investigating active vortex generators as a novel high lift device2006In: ICAS-Secretariat - 25th Congress of the International Council of the Aeronautical Sciences 2006, Curran Associates, Inc., 2006, Vol. 3, p. 1472-1483Conference paper (Refereed)
    Abstract [en]

    Within the framework of the HELIX programme [1], a study using experimental and numerical tools was employed to simulate the aerodynamic behavior of a transport aircraft wing profile when equipped with deployable Active Vortex Generators (AVGs). The geometry of the investigated concept consists of a single row array of delta wings positioned above the main airfoil, close to the leading edge, see figure 1. The operational hypothesis of this concept is that the vortex pair generated by the shear layer roll-up at the leading edge of the delta wing will translate downwards. Previous wind tunnel results, obtained for a different wing profile, were promising [5], indicating a possible gain in maximum lift coefficient CLmax of about 0.3 with only small increment in drag and beneficiary stall characteristics. The numerical simulations performed were divided into three different cases: cruise, takeoff and landing configurations. The numerical simulation set-up was a 2.5 dimensional workspace, extruding the profile to a width of one vortex generator. An experimental validation was performed at VZLU:s three meter open low speed tunnel facility. The wind tunnel measurements were performed at a Reynold's number of 1.65.106: The results of the investigation showed that the baseline profile, without the AVGs mounted, produced a higher CLmax and a lower drag than the concept investigated. Possibly, the stall behavior of the AVG concept could be said to have better characteristics than the baseline. The conclusion is that the AVG cannot replace the slat on a late generation wing profile.

  • 10.
    Pettersson, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Crippa, Simone
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Implementation and Verification of a Correlation Based Transition Prediction Method2008In: 38th Fluid Dynamics Conference and Exhibit, American Institute of Aeronautics and Astronautics, 2008Conference paper (Refereed)
    Abstract [en]

    In many applications such as turbine and aircraft design, boundary layer transition prediction is an important topic. This paper deals with the implementation and verification of a correlation based transition prediction method previously presented by Menter and Langtry. The two additional transport equations used for predicting transition and a novel set of equations for the production terms are implemented into the CFD code Edge. The results are compared to the well-known Ercoftac wind tunnel results.

  • 11.
    Rizzi, Arthur
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Jirásek, Adam
    Swedish Def Res Agcy, Div Syst Technol.
    Lamar, John
    NASA, Langley Res Ctr.
    Crippa, Simone
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Badcock, Ken
    Univ Liverpool, Dept Engn.
    Boelens, Okko
    NLR, Natl Aerosp Lab, Dept Flight Phys & Loads, Aerosp Vehicles Div.
    Lessons learned from numerical simulations of the F-16XL at flight conditions2009In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 46, no 2, p. 423-441Article in journal (Refereed)
    Abstract [en]

    Nine organizations participated in the Cranked-Arrow Wing Aerodynamics Project International study and have contributed steady and unsteady viscous simulations of a full-scale semispan model of the F-16XL aircraft. Three different categories of flight Reynolds/Mach number combinations are computed and compared with flight-test measurements for the purpose of code validation and improved understanding of the flight physics. Steady-state simulations are done with several turbulence models (of different complexity, with no topology information required) that overcome Boussinesq-assumption problems in vortical flows. Detached-eddy simulation and its successor, delayed detached-eddy simulation, are used to compute the time-accurate flow development. Common structured and unstructured grids as well as individually adapted unstructured grids were used. Although discrepancies are observed in the comparisons, overall reasonable agreement is demonstrated for surface pressure distribution, local skin friction, and boundary velocity profiles at subsonic speeds. The physical modeling, be it steady or unsteady flow, and the grid resolution both contribute to the discrepancies observed in the comparisons with flight data, but at this time, how much each part contributes to the whole cannot be determined. Overall, it can be said that the technology readiness of computational fluid dynamics simulation technology for the study of vehicle performance has matured since 2001, such that it can be used today with a reasonable level of confidence for complex configurations.

  • 12. Schiavetta, Lucy
    et al.
    Boelens, Okko
    Crippa, Simone
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Cummings, Russel
    Fritz, Willy
    Badcock, Ken
    Shock effects on delta wing vortex breakdown2008In: 46th AIAA Aerospace Sciences Meeting and Exhibit, 2008Conference paper (Refereed)
    Abstract [en]

    It has been observed that delta wings placed in a transonic freestream can experience a sudden movement of the vortex breakdown location as the angle of incidence is increased. The current paper uses Computational Fluid Dynamics (CFD) to examine this behaviour in detail. The study shows that a shock-vortex interaction is responsible. The balance of the vortex strength and axial flow, and the shock strength, is examined to provide an explanation of the sensitivity of the breakdown location. Limited experimental data is available to supplement the CFD results in certain key respects, and the ideal synergy between CFD and experiments for this problem is considered.

  • 13.
    Schiavetta, Lucy
    et al.
    Univ Glasgow, Dept Aerosp Engn.
    Boelens, Okko
    NLR, Natl Aerosp Lab, Dept Flight Phys & Loads, Aerosp Vehicles Div.
    Crippa, Simone
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Cummings, Russel
    USAF Acad, Dept Aeronaut, Colorado Springs.
    Fritz, Willy
    EADS Mil Air Sys.
    Badcock, Ken
    Univ Liverpool, Dept Engn.
    Shock effects on delta wing vortex breakdown2009In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 46, no 3, p. 903-914Article in journal (Refereed)
    Abstract [en]

    It has been observed that delta wings placed in a transonic freestream can experience a sudden movement of the vortex breakdown location as the angle of incidence is increased. The current paper uses computational fluid dynamics to examine this behavior in detail. The study shows that a shock/vortex interaction is responsible. The balance of the vortex strength and axial flow and the shock strength are examined to provide an explanation of the sensitivity of the breakdown location. Limited experimental data are available to supplement the computational fluid dynamics results in certain key respects, and the ideal synergy between computational fluid dynamics and experiments for this problem is considered.

1 - 13 of 13
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