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  • 1
    Electronic Resource
    Electronic Resource
    Separation-bubble flow solution using Euler/Navier-Stokes zonal approach with downstream compatibility conditions (1988)
    Springer
    Journal of scientific computing 3 (1988), S. 121-137 
    Details
    ISSN: 1573-7691
    Keywords: Computational fluid dynamics ; compressible Navier-Stokes equations ; zonal method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract An Euler/Navier-Stokes zonal scheme is developed to numerically simulate the two-dimensional flow over a blunt leading-edge plate. The computational domain has been divided into inner and outer regions where the Navier-Stokes and Euler equations are used, respectively. On the downstream boundary, compatibility conditions derived from the boundary-layer equations are used. The grid is generated by using conformal mapping and the problem is solved by using a compressible Navier-Stokes code, which has been modified to treat Euler and Navier-Stokes regions. The accuracy of the solution is determined by the reattachment location. Bench-mark solutions have been obtained using the Navier-Stokes equations throughout the optimum computational domain and size. The problem is recalculated with sucessive decrease of the computational domain from the downstream side where the compatibility conditions are used, and with successive decrease of the Navier-Stokes computational region. The results of the zonal scheme are in excellent agreement with those of the benchmark solutions and the experimental data. The CPU time saving is about 15%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01061253
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    Paper (German National Licenses)
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  • 2
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    Steady and unsteady incompressible free-wake analysis (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The flows around highly sweptback wings and bodies of revolution at high angle of attack are described, and inviscid model approximations and mathematical formulation of the problem are given to steady and unsteady incompressible flows. A general presentation of the methods of solution is given, with emphasis on current computational techniques. Detailed descriptions of the nonlinear vortex-lattice and vortex-panel techniques are presented to show how the boundary conditions are enforced using iteration. Typical numerical results are compared with the available experimental data.
    Keywords: AERODYNAMICS
    Format: text
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  • 3
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    Application of the nonlinear vortex-lattice concept to aircraft-interference problems (1976)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A discrete-vortex model was developed to account for the hazardous effects of the vortex trail issued from the edges of separation of a large leading wing on a small trailing wing. The model is divided into three main parts: the leading wing and its near wake, the near and far wakes of the leading wing, and the trailing wing and the portion of the far wake in its vicinity. The normal force, pitching moment, and rolling moment coefficients for the trailing wing are calculated. The circulation distribution in the vortex trail is calculated in the first part of the model where the leading wing is far upstream and hence is considered isolated. A numerical example is solved to demonstrate the feasibility of using this method to study interference between aircraft. The numerical results show the correct trends: The following wing experiences a loss in lift between the wing-tip vortex systems of the leading wing, a gain outside this region, and strong rolling moments which can change sign as the lateral relative position changes. All the results are strongly dependent on the vertical relative position.
    Keywords: AERODYNAMICS
    Type: NASA. Langley Res. Center Advan. in Eng. Sci., Vol. 4; p 1321-1330
    Format: application/pdf
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  • 4
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    Unsteady flow past wings having sharp-edge separation (1976)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A vortex-lattice technique is developed to model unsteady, incompressible flow past thin wings. This technique predicts the shape of the wake as a function of time; thus, it is not restricted by planform, aspect ratio, or angle of attack as long as vortex bursting does not occur and the flow does not separate from the wing surface. Moreover, the technique can be applied to wings of arbitrary curvature undergoing general motion; thus, it can treat rigid-body motion, arbitrary wing deformation, gusts in the freestream, and periodic motions. Numerical results are presented for low-aspect rectangular wings undergoing a constant-rate, rigid-body rotation about the trailing edge. The results for the unsteady motion are compared with those predicted by assuming quasi-steady motion. The present results exhibit hysteretic behavior.
    Keywords: AERODYNAMICS
    Type: NASA. Langley Res. Center Vortex-Lattice Utilization; p 407-421
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  • 5
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    Thin-layer and full Navier-Stokes, locally-conical and three-dimensional asymmetric solutions (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The unsteady, compressible thin-layer and full Navier-Stokes equations are used to numerically simulate steady and unsteady asymmetric, supersonic, locally-conical flows around a 5-deg-semiapex angle circular cone. The main computational scheme used for the present computations is the implicit, upwind, flux-difference splitting, finite-volume scheme. Comparisons of the solutions using the two sets of equations are presented for the flow asymmetry and its control. Computational studies are also presented to investigate the effects of the freestream Reynolds number and the locally-scaled Reynolds number on the flow asymmetry. These studies are carried out using the full Navier-Stokes equations. Three-dimensional, asymmetric flow solutions are also presented for a 5-deg-semiapex angle cone of unit length and a cone-cylinder configuration. The three-dimensional solutions are obtained by using the thin-layer equations and short-duration transient side-slip disturbances along with a very fine grid.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 91-0547
    Format: text
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  • 6
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    Influence of numerical dissipation in computing supersonic vortex-dominated flows (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Steady supersonic vortex-dominated flows are solved using the unsteady Euler equations for conical and three-dimensional flows around sharp- and round-edged delta wings. The computational method is a finite-volume scheme which uses a four-stage Runge-Kutta time stepping with explicit second- and fourth-order dissipation terms. The grid is generated by a modified Joukowski transformation. The steady flow solution is obtained through time-stepping with initial conditions corresponding to the freestream conditions, and the bow shock is captured as a part of the solution. The scheme is applied to flat-plate and elliptic-section wings with a leading edge sweep of 70 deg at an angle of attack of 10 deg and a freestream Mach number of 2.0. Three grid sizes of 29 x 39, 65 x 65 and 100 x 100 have been used. The results for sharp-edged wings show that they are consistent with all grid sizes and variation of the artificial viscosity coefficients. The results for round-edged wings show that separated and attached flow solutions can be obtained by varying the artificial viscosity coefficients. They also show that the solutions are independent of the way time stepping is done. Local time-stepping and global minimum time-steeping produce same solutions.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 86-1073
    Format: text
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  • 7
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    Finite-volume and integral-equation techniques for transonic and supersonic vortex-dominated flows (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Two computational techniques are developed to calculate the compressible vortex-dominated flows. The first technique is a finite-volume Euler Solver which uses four-Stage Runge-Kutta time stepping with second- and fourth-order dissipation terms. The technique is applied to supersonic conical and three-dimensional flows about sharp- and round-edged delta wings. Attached and separated-flow solutions have been obtained depending on the values of damping coefficients. The second technique is an integral-equation solver of the full potential equation which uses a volume-integral term in addition to the classical surface-integral terms. The technique is applied to transonic three-dimensional flows about sharp-edged delta wings. A hybrid technique which combines the finite-volume and the integral-equation solvers is also presented.
    Keywords: AERODYNAMICS
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  • 8
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    Applications of perturbation techniques (1982)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Two perturbation techniques were applied to two singular perturbation problems in heat transfer to obtain uniformly valid solutions which can serve as benchmarks for finite difference and finite element techniques. In the first problem, the method of strained parameters coupled with the application of a solvability condition is used to obtain a uniform solution for the problem of unsteady heat conduction in a long nearly circular cylinder. In the second problem, the method of matched asymptotic expansion coupled with Van Dyke's matching principle is used to obtain a uniform solution for the problem of one dimensional conduction-convection heat transfer of a uniform fluid flow.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Langley Research Center Computational Aspects of Heat Transfer in Struct.; p 147-160
    Format: application/pdf
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  • 9
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    Computational technique for compressible vortex flows past wings at large incidence (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 750-755
    Format: text
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  • 10
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    Computational technique for three-dimensional compressible flow past wings at high angles of attack (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A computational technique, based on the integral solution of the full potential equation, has been developed for the solution of three-dimensional high-subsonic flows past wings at high angles of attack. The problem includes two sources of nonlinearities: a boundary oriented nonlinearity (separated flow roll up) and a region oriented nonlinearity (flow compressibility). The former is represented by a nonlinear vortex lattice while the latter is represented by a source distribution inside a finite volume. The solution is obtained by using double iteration cycles; a separated flow (wake) iteration cycle and a compressibility iteration cycle. The computational technique is applied to a delta wing. The results show that the technique is very promising and efficient.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 83-2078
    Format: text
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