Navier-Stokes computations of a prolate spheroid at angle of attack

Vatsa, Veer N.; Thomas, James L.; Wedan, Bruce W.

doi:10.2514/3.45871

Cited by 48 publications

(5 citation statements)

References 11 publications

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“…A primary pair of streamwise counterrotating vortices are seen to form on the leeward side of the model. Similar flow fields have been observed over a wide range of Reynolds numbers by, for example, Han & Patel (1979) for a 4.3:1 spheroid and Vatsa, Thomas & Wedan (1989), Fu, Shekarriz & Huang (1994), Chesnakas & Simpson (1997), Karlsson & Fureby (2009) and Feymark et al (2012) for a 6:1 prolate spheroid. Werlé (1962), Hornung & Perry (1984) and Bippes (1987) described the separation topologies over similar bodies at low and moderate angles of attack, but here we are concerned with the evolution of the streamwise counter-rotating vortices which comprise the turbulent wake of such bodies in pitch.…”

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confidence: 55%

Asymmetries in the wake of a submarine model in pitch

2015

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Detailed velocity measurements in the wake of a body of revolution are reported for pitch angles up to 12 • , over an unprecedented range of Reynolds numbers (2.4 × 10 6 Re L 30 × 10 6 ). The body of revolution, an idealized submarine shape (DARPA SUBOFF), is mounted using a support that mimics a semi-infinite sail. The wake measurements at all pitch angles and Reynolds numbers reveal the presence of a pair of streamwise vortices of unequal strengths which tend to rotate around each other as they evolve downstream. Various attempts to perturb the upstream conditions on the body had no significant impact on the relative strength of the vortices. In addition, two different models, tested in two different wind tunnels, show similar asymmetries, and we propose that wake asymmetry appears to be a robust feature of this flow, a result previously only seen for sharp-nosed bodies at high angles of attack. It is also shown that the wake behaviour for x/D > 5, in terms of the streamwise mean velocity and turbulence intensity distributions, appears to become invariant with Reynolds number for Re L > 4.8 × 10 6 .

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confidence: 55%

Asymmetries in the wake of a submarine model in pitch

2015

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“…Two axis ratios of the prolate spheroid, namely, 6 : 1 and 4 : 1, were commonly investigated in past studies. For a 6 : 1 prolate spheroid, detailed surface shear stress, pressure, and oil flow pattern measurements have been performed by Kreplin et al [48], which provided a data set for validating the ability of turbulence modeling of Navier-Stokes solvers [49,50]. For a 4 : 1 spheroid, there are more flow visualization studies [46,47] than quantitative measurements.…”

Section: Steady Flow Past a 4 : 1 Prolate Spheroidmentioning

confidence: 99%

Comparison of Implicit Multigrid Schemes for Three-Dimensional Incompressible Flows

2002

Journal of Computational Physics

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To develop a robust and efficient computational flow simulation tool for incompressible flow applications, a number of different implicit multigrid schemes for solving the three-dimensional incompressible Navier-Stokes equations are compared in the current study. These schemes consist of a common full approximation storage (FAS) multigrid algorithm implemented in conjunction with three different implicit schemes, which include a modified point Gauss relaxation, a standard Gauss-Seidel line relaxation, and the Beam-Warming alternating direction implicit (ADI) scheme. The flow solver used in the study is based on artificial compressibility and uses a third-order upwind difference for the convective terms and a second-order central difference for the viscous terms. The efficiency of each implicit multigrid scheme is assessed in terms of the computing time required for two laminar flow problems: the entry flow through a 90• bent square duct, and the steady-state and unsteady flows past a prolate spheroid at incidence with an axis ratio of 4 : 1. It is found that implementation of Neumann boundary conditions on the coarse grid in terms of the flow variable correction rather than the flow variable itself is essential for obtaining good convergence in the collocated finite difference discretization. The results of steady-state flow computations show that all the implicit multigrid schemes yield more than 50% computational time savings over their single grid counterparts, and the point or line relaxation multigrid scheme outperforms the ADI multigrid scheme by at least a factor of 2. However, in unsteady flow computations, the computational time saving of the multigrid scheme is less than that in steady-state cases. The current study concludes that the FAS multigrid algorithm implemented with the modified point Gauss relaxation scheme is preferable for simulating both steady-state and time-dependent incompressible flows. c 2002 Elsevier Science (USA)

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“…Similar studies were performed by other authors. 8,26 In the case of airships, the 6:1 prolate spheroid was also employed to approximate the shape of the hull by Omari et al 18,19 To the best of the authors' knowledge, a CFD study of the complete configuration of an LTV or HAV has not been presented in the literature. Hence, after validating the employed CFD methods of Hybrid Air Vehicles Ltd., the present paper provides a study of the aerodynamics for an early variant of the Airlander HAV.…”

Section: Introductionmentioning

confidence: 99%

Analysis of Hybrid Air Vehicles Using Computational Fluid Dynamics

Carrion

Steijl

Barakos

et al. 2016

Journal of Aircraft

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This paper presents an aerodynamic study of bodies related to lighter than air vehicles, using Computational Fluid Dynamics. The work begins with the validation of the CFD method using a 6:1 prolate spheroid. The validated method is then employed for the study of the flow around a shape similar to the Airlander aircraft of Hybrid Air Vehicles Ltd. An overview of the flow around is presented, supported by pressure survey, flow visualisation and transitional flow effects. The sensitivity of the transition location to the Reynolds number is also demonstrated, and the role of each component of the vehicle is analysed in terms of its effect on the flow-field, the lift and drag, and stability in pitch. It was found that the fins contributed the most to increase the lift and drag coefficients.

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Navier-Stokes computations of a prolate spheroid at angle of attack

Cited by 48 publications

References 11 publications

Asymmetries in the wake of a submarine model in pitch

Asymmetries in the wake of a submarine model in pitch

Comparison of Implicit Multigrid Schemes for Three-Dimensional Incompressible Flows

Analysis of Hybrid Air Vehicles Using Computational Fluid Dynamics

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