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Advances in vortical flow prediction methods for design of delta-winged aircraft
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
2008 (English)Doctoral 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.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , viii, 38 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2008:30
Keyword [en]
delta wing, slender wing, aircraft, vortex, VFE-2, CAWAPI, HISAC
National Category
Vehicle Engineering
Identifiers
URN: urn:nbn:se:kth:diva-4761ISBN: 978-91-7178-970-9 (print)OAI: oai:DiVA.org:kth-4761DiVA: diva2:13817
Public defence
2008-06-09, F3, KTH, Lindstedtsvägen 26, Stockholm, 10:15
Opponent
Supervisors
Note
QC 20100713Available from: 2008-05-16 Created: 2008-05-16 Last updated: 2010-07-13Bibliographically approved
List of papers
1. Numerical investigation of Reynolds number effects on a blunt leading-edge delta wing
Open this publication in new window or tab >>Numerical investigation of Reynolds number effects on a blunt leading-edge delta wing
2006 (English)In: 24th AIAA Applied Aerodynamics Conference: San Francisco, CA : 5 June 2006 through 8 June 2006, 2006, 708-726 p.Conference paper, Published 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.

Series
Collection of Technical Papers : AIAA Applied Aerodynamics Conference, ISSN 1048-5953
Keyword
Angle measurement; Computational fluid dynamics; Delta wing aircraft; Numerical methods; Vortex flow; Wind tunnels; Mach numbers; Secondary separation; Vortex strength
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-8476 (URN)2-s2.0-33845409766 (Scopus ID)978-156347812-3 (ISBN)
Note
QC 20100713Available from: 2008-05-16 Created: 2008-05-16 Last updated: 2010-07-13Bibliographically approved
2. Initial steady/unsteady CFD analysis of vortex flow over the VFE-2 delta wing
Open this publication in new window or tab >>Initial steady/unsteady CFD analysis of vortex flow over the VFE-2 delta wing
2006 (English)In: 25th Congress of the International Council of the Aeronautical Sciences, 3-8 September 2006, Hamburg, Germany, 2006, 883-892 p.Conference paper, Published 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.

National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-8477 (URN)2-s2.0-84878435922 (Scopus ID)978-160423227-1 (ISBN)
Conference
25th Congress of the International Council of the Aeronautical Sciences 2006; Hamburg; Germany
Note

QC 20100713

Available from: 2008-05-16 Created: 2008-05-16 Last updated: 2014-10-30Bibliographically approved
3. Steady, subsonic CFD analysis of the VFE-2 configuration and comparison to wind tunnel data
Open this publication in new window or tab >>Steady, subsonic CFD analysis of the VFE-2 configuration and comparison to wind tunnel data
2008 (English)In: 46th AIAA Aerospace Sciences Meeting and Exhibit, 2008Conference paper, Published 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.

Keyword
CFD analysis, Computational results, Delta wings, Experimental data, Flow experiments, Leading edge, Numerical results, Subsonic speed, Suction side, Surface flow patterns, Surface pressure coefficients, Time-accurate, Vortical structures, Wind-tunnel data
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-8478 (URN)2-s2.0-78149456322 (Scopus ID)9781563479373 (ISBN)
Conference
46th AIAA Aerospace Sciences Meeting and Exhibit; Reno, NV; United States; 7 January 2008 through 10 January 2008
Note

QC 20100713

Available from: 2008-05-16 Created: 2008-05-16 Last updated: 2014-10-13Bibliographically approved
4. Shock effects on delta wing vortex breakdown
Open this publication in new window or tab >>Shock effects on delta wing vortex breakdown
Show others...
2009 (English)In: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 46, no 3, 903-914 p.Article in journal (Refereed) Published
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.

Keyword
Angle of Incidence, Delta wing vortices, Delta wings, Experimental data, Free-stream, Shock strength, Vortex breakdown location, Vortex strength, Delta wing aircraft, Fluid dynamics
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-8479 (URN)10.2514/1.38792 (DOI)000266894200017 ()2-s2.0-67651065245 (Scopus ID)
Note

QC 20100713. Uppdaterad från konferensbidrag till artikel (20100713).

Available from: 2008-05-16 Created: 2008-05-16 Last updated: 2014-10-13Bibliographically approved
5. Reynolds number effects on blunt leading edge delta wings
Open this publication in new window or tab >>Reynolds number effects on blunt leading edge delta wings
2007 (English)In: 1st CEAS European Air and Space Conference: September 2007, Berlin, Germany, 2007Conference paper, Published paper (Refereed)
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-8480 (URN)
Note
QC 20100713Available from: 2008-05-16 Created: 2008-05-16 Last updated: 2010-07-13Bibliographically approved
6. Lessons learned from numerical simulations of the F-16XL at flight conditions
Open this publication in new window or tab >>Lessons learned from numerical simulations of the F-16XL at flight conditions
Show others...
2009 (English)In: Journal of Aircraft, ISSN 0021-8669, Vol. 46, no 2, 423-441 p.Article in journal (Refereed) Published
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.

Keyword
Aircraft; Computational fluid dynamics; Flight dynamics; Fluid dynamics; Friction; Gas dynamics; Models; Transonic aerodynamics; Turbulence models; Wings
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-8481 (URN)10.2514/1.35698 (DOI)000264858800007 ()2-s2.0-63349099579 (Scopus ID)
Note
QC 20100713. Uppdaterad från in press till published (20100713).Available from: 2008-05-16 Created: 2008-05-16 Last updated: 2010-07-13Bibliographically approved

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