Download or read book Numerical Simulation of Spiral Vortex Breakdown Above a Delta Wing written by Miguel R. Visbal and published by . This book was released on 1995 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Numerical Simulation of Transient Vortex Breakdown Above a Pitching Delta Wing written by and published by . This book was released on 1994 with total page 43 pages. Available in PDF, EPUB and Kindle. Book excerpt: Computational results are presented for transient vortex breakdown above a delta wing subject to a pitch-and-hold maneuver to high angle of attack. The flows are simulated by solving the full three-dimensional Navier-Stokes equations on a moving grid using the implicit Beam-Warming algorithm. An assessment of the effects of numerical resolution, and favorable comparison with experimental data suggest the computational approach captures the basic dynamics of this transient breakdown. The pressure gradient along the vortex axis is found to play a dominant role in the initiation of breakdown. A description of the three-dimensional instantaneous structure of the flow field is provided for the first time using critical-point theory. The reversed-flow region in the vortex core is associated with pairs of opposite spiral/saddle critical points. At its onset, the vortex breakdown is fairly axisymmetric; however, as it proceeds upstream and a stronger transition takes place along the axis, asymmetric effects become important and result in the formation of a bubble-type breakdown. This bubble structure is open and contains within itself a pair of stagnation points which are diametrically opposed and which rotate in the same sense as the base flow. Vortex breakdown, Delta wings, Unsteady aerodynamics, Computational fluid dynamics.
Download or read book A Digital Particle Image Velocimetry Investigation of Delta Wing Vortex Flow and Vortex Breakdown written by Jeremy David Wimer and published by . This book was released on 2003-01-01 with total page 128 pages. Available in PDF, EPUB and Kindle. Book excerpt: The vortical flow over the suction side of a 650 sweep delta wing at high angles of attack is investigated in the University of Washington water tunnel using digital particle image velocimetry (DPIV). The method is first validated and then used to qualitatively and quantitatively describe the development of the leading edge vortex (LEV) both upstream and downstream of vortex breakdown. The circulation and azimuthal velocity profile in the vortex are measured and reveal that the maximum circulation of the LEV increases nearly linearly in the downstream direction up to the point of vortex breakdown. Circulation and velocity measurements in the solid-body rotational part of the LEV core, however, reveal that once the core is formed near the apex of the wing, the circulation there remains constant until just prior to breakdown, and no further vorticity is added to the core from the shear layer. The secondary vortex is found to be the key player in separating the primary vortex core from the shear layer. This model of the flow field contradicts the generally accepted conical nature of delta wing flow. Current vortex breakdown suppression methods are analyzed in light of this new model. A numerical simulation based on the vortex filament method is also used to further the self-induction theory of vortex breakdown.
Download or read book Numerical Simulation of Vortex Breakdown by the Vortex filament Method written by Y. Nakamura and published by . This book was released on 1983 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: The vortex-filament method was applied to the simulation of vortex breakdown. The principal vortex region was represented by multiple filaments, and an axial velocity component was induced by a spiral winding of the filaments. First, an accuracy check was performed for a cylindrical swirling flow field that can be simulated to any accuracy by increasing the number of filaments. Second, an axisymmetric-type vortex breakdown was simulated, with experimental data serving asupstream conditions. The calculated axial- and theta-velocity contours show the breakdown of the vortex, including a rapid change in the vortex core, followed axially by a recovery zone and then a second breakdown. When three-dimensional initial data are used the second breakdown appears to be out of the spiral type in correspondence with experimental observations. The present method can easily be used to simulate other types of vortex breakdown or other vortex flows with axial velocity.
Download or read book Computational Fluid Dynamics Investigation of Vortex Breakdown for a Delta Wing at High Angle of Attack written by Jacob A. Freeman and published by . This book was released on 2003-03-01 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt: Using the commercially available FLUENT 3-D flow field solver, this research effort investigated vortex breakdown over a delta wing at high angle of attack (a) in preparation for investigation of active control of vortex breakdown using steady, along- core blowing A flat delta-shaped half-wing with sharp leading edge and sweep angle of 600 was modeled at a 180 in a wind tunnel at Mach 0,04 and Reynolds number of 3,4 x 10(sub 5). A hybrid (combination of structured and unstructured) numerical mesh was generated to accommodate blowing ports on the wing surface. Results for cases without and with along-core blowing included comparison of various turbulence models for predicting both flow field physics and quantitative flow characteristics, FLUENT turbulence models included Spalart-Allmaras (S-A), Renormalization Group k-e, Reynolds Stress (RSM), and Large Eddy Simulation (LES), as well as comparison with laminar and inviscid models. Mesh independence was also investigated, and solutions were compared with experimentally determined results and theoretical prediction, These research results show that, excepting the LES model for which the computational mesh was insufficiently refined and which was not extensively investigated, none of the turbulence models above, as implemented with the given numerical grid, generated a solution which was suitably comparable to the experimental data. Much more work is required to find a suitable combination of numerical grid and turbulence model.
Download or read book Numerical Simulation of Compressible Vortices written by Scott A. Morton and published by . This book was released on 1989 with total page 61 pages. Available in PDF, EPUB and Kindle. Book excerpt: A delta wing at a high angle of attack produces two vortices that generally undergo dramatic increases in core size, followed by the formation of regions of reversed flow. This phenomenon is called vortex breakdown and can have significant effects on the aircraft's lift, drag, and moment coefficients. The objective of this thesis is to provide a base line model of the compressible vortex, independent of the complex body interaction with the delta wing. The mathematical model is then used to simulate vortex breakdown for various vortex strengths, Reynolds numbers, and Mach numbers with particular attention given to the effects of compressibility. After running many simulations it was found that Mach number has a favorable effect by delaying vortex breakdown as defined above. Holding Reynolds number and vortex strength constant while increasing Mach number reduced the effective vortex strength while compressing the flow. Another important result of this compressible flow study was the disappearance of non-unique solutions at Re = 200 and V = 1.0 as Mach number was increased. No paths of non-unique solutions were found for M> 0.2. Keywords: Navier stokes solutions. (KR).
Download or read book Numerical Simulation of Vortex Breakdown written by Jasim Uddin Ahmad and published by . This book was released on 1989 with total page 318 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Direct Numerical Simulations of Highly Vortical Flows and Vortex Breakdown written by Wing Tsin Ma and published by . This book was released on 1995 with total page 348 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Vortical Flows Over Delta Wings and Numerical Prediction of Vortex Breakdown written by John A. Ekaterinaris and published by . This book was released on 1990 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Numerical Investigation of Vortex Breakdown Over A 70 Degree Delta Wing Using an Euler Code written by Magnus Tormalm and published by . This book was released on 1995 with total page 74 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Numerical Simulation of Complex Flow Around a 85 Degree Delta Wing written by H. Shan and published by . This book was released on 2001 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: The three-dimensional separated flow around a slender flat-plate delta wing with sharp leading-edge at a 12.5 deg angle of attack has been studied by solving the full compressible Navier-Stokes equations in the generalized curvilinear coordinates. The time integration is carried out by using the second-order LU-SGS implicit scheme. A fourth-order centered compact difference scheme is used for spatial derivatives. A sixth-order implicit filter is employed to reduce numerical oscillation. Non-reflecting boundary conditions are imposed at the far-field and outlet boundaries to avoid possible non-physical wave reflection. Parallel computing based on Message Passing Interface (MPI) has been utilized to improve the performance of the code. Two Reynolds numbers have been selected. At a lower Reynolds number of 50000 based on the chord length and the freestream velocity, the flow is stable and dominated by a pair of leading edge primary vortices. At a higher Reynolds number of 196000, the small-scale vortex shedding is observed near the leading-edge of the delta wing. The computational results are compared with the experimental work of Riley & Lowson (1998). The periodic shedding of small-scale vortical structures near the leading-edge has been studied in detail, and the vortex shedding is found to be associated with the Kelvin-Helmholtz-type instability and the secondary vortex. The period of vortex shedding is obtained from the time series of the three velocity components recorded near the leading-edge. The time-averaged features of the vortical structures are also discussed.
Download or read book Vortex flow and vortex breakdown above a delta wing in high supersonic flow written by Sharon Rose Donohoe and published by . This book was released on 1996 with total page 209 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book 27th AIAA Fluid Dynamics Conference written by and published by . This book was released on 1996 with total page 654 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Motion Effects on Leading Edge Vortex Behavior Over Delta Wings and Generalized Modeling written by and published by . This book was released on 2003 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book DESider A European Effort on Hybrid RANS LES Modelling written by Werner Haase and published by Springer Science & Business Media. This book was released on 2009-05-12 with total page 469 pages. Available in PDF, EPUB and Kindle. Book excerpt: Preface “In aircraft design, efficiency is determined by the ability to accurately and rel- bly predict the occurrence of, and to model the development of, turbulent flows. Hence, the main objective in industrial computational fluid dynamics (CFD) is to increase the capabilities for an improved predictive accuracy for both complex flows and complex geometries”. This text part taken from Haase et al (2006), - scribing the results of the DESider predecessor project “FLOMANIA” is still - and will be in future valid. With an ever-increasing demand for faster, more reliable and cleaner aircraft, flight envelopes are necessarily shifted into areas of the flow regimes exhibiting highly unsteady and, for military aircraft, unstable flow behaviour. This undou- edly poses major new challenges in CFD; generally stated as an increased pred- tive accuracy whist retaining “affordable” computation times. Together with highly resolved meshes employing millions of nodes, numerical methods must have the inherent capability to predict unsteady flows. Although at present, (U)RANS methods are likely to remain as the workhorses in industry, the DESider project focussed on the development and combination of these approaches with LES methods in order to “bridge” the gap between the much more expensive (due to high Reynolds numbers in flight), but more accurate (full) LES.
Download or read book Fluid Vortices written by Sheldon Green and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 905 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fluid Vortices is a comprehensive, up-to-date, research-level overview covering all salient flows in which fluid vortices play a significant role. The various chapters have been written by specialists from North America, Europe and Asia, making for unsurpassed depth and breadth of coverage. Topics addressed include fundamental vortex flows (mixing layer vortices, vortex rings, wake vortices, vortex stability, etc.), industrial and environmental vortex flows (aero-propulsion system vortices, vortex-structure interaction, atmospheric vortices, computational methods with vortices, etc.), and multiphase vortex flows (free-surface effects, vortex cavitation, and bubble and particle interactions with vortices). The book can also be recommended as an advanced graduate-level supplementary textbook. The first nine chapters of the book are suitable for a one-term course; chapters 10--19 form the basis for a second one-term course.
Download or read book Vortex Breakdown Over Slender Delta Wings written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The report contains a study of the phenomenon of leading-edge vortex breakdown over slender delta wings conducted by the NATO/RTO/AVT Task Group AVT-080. After an introduction and discussion of highlights, a chapter is devoted to a critical assessment of available experimental studies of the vortex breakdown phenomenon. Eight reliable experimental data sets are collected and compiled. These data sets are described in separate chapters and were obtained on more or less identical delta wing models tested in different wind tunnel test facilities. The datasets include time-average results at static model conditions, ensemble-average results at dynamic model conditions and unsteady results at static/dynamic model conditions. Based on the critical assessment, a benchmark test case is selected that provides sufficiently reliable data for validation of the numerical predictions. In separate chapters ten state-of-the-art numerical solutions from various research institutes are described that have been obtained for the benchmark test case configuration and test conditions. Studies of the effects of parameters like grid density, turbulence modeling, time scaling, etc., have been performed. In addition, for a special delta wing configuration, the effects of tunnel wall interference and of interactions between vortices have been calculated. In the final three chapters advanced analytical methods are described.
