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11

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Flow with M/infinity/equals 1 past thin airfoils (1970)

Stahara, S. S. ; Spreiter, J. R.

In: Other Sources

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Publikationsdatum: 2019-06-27

Beschreibung: Pressure distribution on thin nonlifting airfoils in steady two dimensional flow with freestream Mach number at or near unity

Schlagwort(e): AERODYNAMICS

Materialart: ; UGREVUE(

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12

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Rapid approximate determination of nonlinear solutions - Application to aerodynamic flows and design/optimization problems (1982)

Stahara, S. S.

In: Other Sources

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Publikationsdatum: 2019-07-13

Beschreibung: Stahara et al. (1978) have considered the use of an approximation technique which employs two or more nonlinear base solutions determined by the full computational method to predict entire families of related nonlinear solutions. The present investigation provides results for several applications of that method which demonstrate both its accuracy and its utility for engineering applications. Attention is given to the perturbation concept and methods, aspects of coordinate straining, aspects of analytical formulation, and an application to surface properties. In a discussion of the results, single and multiple parameter perturbations are considered along with a combination of the approximation method with optimization procedures. The results show that it is possible to combine in certain cases large savings in computational cost with improved optimization.

Schlagwort(e): AERODYNAMICS

Materialart: Transonic aerodynamics; Transonic Perspective Symposium; Feb 18, 1981 - Feb 20, 1981; Moffett Field, CA

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13

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A rapid method for the approximate determination of nonlinear solutions Application to aerodynamic flows (1980)

Spreiter, J. R. ; Elliott, J. P. ; Stahara, S. S.

In: Other Sources

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Publikationsdatum: 2019-07-13

Beschreibung: A method for determining highly accurate approximations to families of strongly nonlinear solutions which are either continuous or discontinuous, and which represent variations in some arbitrary parameters, is developed and evaluated. The procedure consists of defining a unit perturbation by employing two or more nonlinear solutions which differ from one another by a nominal change in some geometric or flow parameter, and then using that unit perturbation to predict a family of related nonlinear solutions over a range of parameter variation. Coordinate straining is used in determining the unit perturbation to account for the movement of discontinuities and maxima of high-gradient regions due to the perturbation. Although the procedure is generally applicable, results are presented here for nonlinear aerodynamic applications. Attention is focused in particular on transonic flows which are strongly supercritical and exhibit large surface shock movement over the parametric range studied; and on subsonic flows which display large pressure variations in the stagnation and peak suction pressure regions. Flows past both isolated airfoils and compressor cascades involving a variety of flow and geometry parameter changes are considered. Comparisons with the corresponding 'exact' nonlinear solutions indicate a remarkable accuracy and range of validity of such a procedure. Computational time is trivial.

Schlagwort(e): AERODYNAMICS

Materialart: International Council of the Aeronautical Sciences, Congress; Oct 12, 1980 - Oct 17, 1980; Munich; Germany

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14

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Ingestion and dispersion of engine exhaust products by trailing vortices for supersonic flight in the stratosphere (1974)

Nielsen, J. N. ; Stahara, S. S. ; Woolley, J. P.

In: Other Sources

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Publikationsdatum: 2019-07-13

Beschreibung: Detailed analysis has been made of the ingestion and dispersion of engine exhaust products into the trailing-vortex system of a supersonic aircraft flying in the stratosphere. The rate of mixing between the supersonic jet and the coflowing supersonic stream was found to be an order of magnitude less than would be expected on the basis of subsonic eddy-viscosity results. Ingestion started at the end of the potential core, and all hot gas from the engine was ingested into the trailing vortex within two core lengths. The temperature rise in the wake of the supersonic aircraft was found to be much greater than that for a subsonic transport, since temperature rise varies directly as speed squared and inversely as aspect ratio. As a result, the final buoyancy phase started only ten seconds after leaving the trailing edge. Comparison between the buoyancy calculations for the supersonic case with nondimensionalized subsonic aircraft contrail data on wake spreading showed good agreement.

Schlagwort(e): AERODYNAMICS

Materialart: AIAA PAPER 74-42 , Aerospace Sciences Meeting; Jan 30, 1974 - Feb 01, 1974; Washington, DC

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15

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Perturbation solutions for blade-to-blade surfaces of a transonic compressor (1977)

Spreiter, J. R. ; Chaussee, D. S. ; Stahara, S. S.

In: Other Sources

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Publikationsdatum: 2019-07-13

Beschreibung: The paper describes a perturbation method for turbomachinery calculations, particularly where it is necessary to carry out a number of calculations for closely-related flows such as are needed in a parametric study. The method is applied for solving a model problem involving blade-to-blade surfaces of a transonic compressor. Basically, the method makes use of a previously calculated base solution to determine first-order changes in the flow field due to variations in one or more of a variety of geometrical or flow field parameters. The fundamental assumption associated with the perturbation solution is that the magnitude of the deviations from the base solution lies within the range of a linear perturbation analysis. Comparisons are made for results obtained, by varying the thickness ratio of an unstaggered nonlifting cascade composed of biconvex profiles in a flow with an oncoming freestream Mach number of 0.60.

Schlagwort(e): AERODYNAMICS

Materialart: Transonic flow problems in turbomachinery; Feb 11, 1976 - Feb 12, 1976; Monterey, CA

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16

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Unsteady transonic aerodynamics - An aeronautics challenge (1975)

Spreiter, J. R. ; Stahara, S. S.

In: Other Sources

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Publikationsdatum: 2019-07-13

Beschreibung: The paper presents a review of the historical development in unsteady transonic aerodynamics, along with the foundations and accomplishments of several approaches to solve the equations of unsteady transonic flow. The discussion covers the linearized unsteady flow theory, numerical solution of the exact equations for an inviscid compressible gas, nonlinear small disturbance theory of transonic flow and linearization of the unsteady component about the nonlinear solution for the steady state, local linearization solution for unsteady transonic flow, unsteady transonic flow theory for slender wings and bodies, and three-dimensional unsteady transonic flows. The relation between the calculated results and experiment is examined. It is shown that the newly emerging numerical methods are capable of solving the nonlinear equations for two-dimensional flow and can be extended to three-dimensional flows.

Schlagwort(e): AERODYNAMICS

Materialart: Unsteady aerodynamics; Mar 18, 1975 - Mar 20, 1975; Tucson, AZ

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