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  • 1
    facet.materialart.
    Unknown
    In:  Other Sources
    Publication Date: 2019-06-28
    Description: The feasibility of designing propellers by an optimization procedure is investigated. A scheme, which solves the full potential flow equation about a propeller by line relaxation, is modified so that the iterative solutions of the flow equation and the design parameters are updated simultaneously. Some technical problems in using optimization for designing propellers with maximum efficiency are identified. Approaches for overcoming these problems are presented.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: AIAA PAPER 86-0081
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  • 2
    Publication Date: 2019-06-28
    Description: A description of the emerging field of direct numerical simulations of turbulent, chemically reacting flows is presented. The types of direct numerical simulations, physical issues related to implementing the simulations, as well as the various numerical methods used are described. Examples are presented of recent applications of direct numerical simulations to a variety of problems, displaying both the potential of the method and also some of its limitations. Finally, our view of the potential role of direct numerical simulations in future research on turbulent, chemically reacting flows is presented.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 87-1324
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  • 3
    Publication Date: 2019-06-28
    Description: The so-called H-type mesh is used in a finite-element (or finite-volume) calculation of the potential flow past an airfoil. Due to coordinate singularity at the leading edge, a special singular trial function is used for the elements neighboring the leading edge. The results using the special singular elements are compared to those using the regular elements. It is found that the unreasonable pressure distribution obtained by the latter is removed by the embedding of the singular element. Suggestions to extend the present method to transonic cases are given.
    Keywords: AERODYNAMICS
    Type: NASA-CR-166387 , NAS 1.26:166387
    Format: application/pdf
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  • 4
    Publication Date: 2019-06-28
    Description: A fully conservative finite-volume algorithm is used to calculate transonic potential flows past isolated airfoils and through two-dimensional channels. The difference equations are solved by a multigrid technique which uses an alternating direction implicit method as a smoothing algorithm. The finite-volume formulation provides a framework within which to treat flows past complicated geometries, while the multigrid/alternating direction scheme provides rapid convergence of the solution to very small residuals.
    Keywords: AERODYNAMICS
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  • 5
    Publication Date: 2019-06-28
    Description: Previously cited in issue 15, p. 2344, Accession A82-31933
    Keywords: AERODYNAMICS
    Type: (ISSN 0001-1452)
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  • 6
    Publication Date: 2019-06-28
    Description: In order to study the coupling between chemical heat release and fluid dynamics, direct numerical simulations of a chemically reacting mixing layer with heat release are performed. The fully compressible equations as well as an approximate set of equations that is asymptotically valid for low-Mach-number flows are treated. These latter equations have the computational advantage that high-frequency acoustic waves have been filtered out, allowing much larger time steps to be taken in the numerical solution procedure. A detailed derivation of these equations along with an outline of the numerical solution technique is given. Simulation results indicate that the rate of chemical product formed, the thickness of the mixing layer, and the amount of mass entrained into the layer all decrease with increasing rates of heat release.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: AIAA PAPER 85-0143
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  • 7
    Publication Date: 2019-06-27
    Description: The sound field due to a propeller operating at supersonic tip speed in a uniform flow was investigated. Using the fact that the wave front in a uniform stream is a convected sphere, the fundamental solution to the convected wave equation was easily obtained. The Fourier coefficients of the pressure signature were obtained by a far field approximation, and are expressed as an integral over the blade platform. It is shown that cones of silence exist fore and aft the propeller plane. The semiapex angles are shown. These angles are independent of the individual Mach components such as the flight Mach number and the rotation Mach number. The result is confirmed by the computation of the ray path of the emitted Mach waves. The Doppler amplification factor strengthens the signal behind the propeller while it weakens that upstream.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA-CR-3080 , REPT-119
    Format: application/pdf
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  • 8
    Publication Date: 2019-07-13
    Description: An attempt is made to develop a three-dimensional, finite volume computational code for highly swept, twisted, small aspect ratio propeller blades with supersonic tip speeds, in a way that accounts for cascade effects, hub-induced flow, and nonlinear transonic effects. Attention is presently given to the generation of a computational mesh for such a complex propeller configuration, with the aim of sharing developmental process experience. The problem treated is unique, in that blade chord, blade length, hub length and blade-to-blade distance represent several characteristic length scales among which there is considerable disparity. An ad hoc mesh-generation scheme is accordingly developed.
    Keywords: AERODYNAMICS
    Type: Numerical grid generation; Symposium on Numerical Generation of Curvilinear Coordinate Systems and Their Use in the Numerical Solution of Partial Differential Equations; Apr 13, 1982 - Apr 16, 1982; Nashville, TN
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  • 9
    facet.materialart.
    Unknown
    In:  CASI
    Publication Date: 2019-06-28
    Description: Transonic flow through a cascade was studied by using the full potential equation and the finite volume method of Jameson and Caughey. The C-type computational grid is generated by an electrostatic analogy and simple shearing transformation. The solution algorithm includes an option of using either an artificial density or an artificial viscosity formulation of the dissipative term. Using the developed code, flows through a cascade of NACA 0012 airfoils and flows through a cascade of shockless blades were computed. It is found that the designed flow through the shockless blade is accurately predicted, the artificial density formulation shows more tolerance to the mesh irregularity, and the C-type mesh does not extend very far upstream for a small pitch-cord ratio.
    Keywords: AERODYNAMICS
    Type: NASA-CR-165471 , FRR-182
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  • 10
    Publication Date: 2019-07-12
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 27; 1543-155
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