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  • 1
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    Asymptotic analysis of numerical wave propagation in finite difference equations (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An asymptotic technique is developed for analyzing the propagation and dissipation of wave-like solutions to finite difference equations. It is shown that for each fixed complex frequency there are usually several wave solutions with different wavenumbers and the slowly varying amplitude of each satisfies an asymptotic amplitude equation which includes the effects of smoothly varying coefficients in the finite difference equations. The local group velocity appears in this equation as the velocity of convection of the amplitude. Asymptotic boundary conditions coupling the amplitudes of the different wave solutions are also derived. A wavepacket theory is developed which predicts the motion, and interaction at boundaries, of wavepackets, wave-like disturbances of finite length. Comparison with numerical experiments demonstrates the success and limitations of the theory. Finally an asymptotic global stability analysis is developed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-175323 , NAS 1.26:175323 , GT/PDL-171
    Format: application/pdf
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  • 2
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    Researched applied to transonic compressors in numerical fluid mechanics of inviscid flow and viscous flow (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A streamline Euler solver which combines high accuracy and good convergence rates with capabilities for inverse or direct mode solution modes and an analysis technique for finite difference models of hyperbolic partial difference equations were developed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-174353 , NAS 1.26:174353
    Format: application/pdf
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  • 3
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    Boundary treatments for implicit solutions to Euler and Navier-Stokes equations (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: It seems apparent that for inviscid calculations the differences between the explicit and implicit boundary formulations tested are far smaller than anticipated. New work should focus on understanding of how the convergence rate is limited or affected by boundary formulations. Since the inflow/outflow boundary treatments tested were simple extrapolations, it may be the case that treatments more closely representing the differential equations will prove to have superior convergence properties. However, several such improved boundary treatments were attempted with disappointing results.
    Keywords: NUMERICAL ANALYSIS
    Type: NASA. Ames Research Center Numerical Boundary Condition Procedures; p 353-366
    Format: text
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  • 4
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    Exit flow from a transonic compressor rotor (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The three dimensional unsteady flow field behind a transonic compressor rotor with a design pressure ratio of 1.6 at a tip Mach number of 1.2 has been resolved on the blade passing time scale. Quantities determined were total and static pressures, tangential flow angle, and radial flow angle. The spatial and temporal resolution achieved was sufficient to determine velocity components inside individual blade wakes and in the surrounding flow. From these measurements the flow structure is described at stations immediately behind the rotor and one chord downstream. Some dominant features of the flow just behind the rotor are large radial velocity components, large static pressure fluctuations near the blade wakes, and definite unsteadiness (in rotor coordinates) of the wakes. The wake behavior one chord downstream is described in terms of the effect of the strong mean swirl on the behavior of shear disturbances. In the outer portion of the annulus, where the mean flow approximates a solid body rotation, a strong, persistent oscillatory flow is found with 16 periods in the circumference as roughly predicted by theory. In the inner portion of the annulus the disturbances attenuate axially.
    Keywords: AERODYNAMICS
    Type: AGARD Unsteady Phenomena in Turbomachinery; 23 p
    Format: text
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  • 5
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    A study of non-unique solutions of the two-dimensional boundary layer equations at laminar separation and reattachment points (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Nonunique laminar boundary layer equation solutions in direct problem calculations are identified for the case of accelerating flow. As a separation or reattachment point is approached, the multiple solutions approach each other and become identical. The computer code used to generate these results was developed for the solution of compressible, laminar or turbulent boundary layer, and free wake problems, in either direct or inverse mode. Similarity solutions in either a primitive variable or a stream function form are possible, and the resulting equations are solved by means of a modified Keller's Box scheme in which the energy equation and turbulence modeling equations are solved simultaneously with the continuity and momentum equations. Examples illustrating the nature of the solutions at the separation and reattachment points are presented.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 6
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    Time resolved measurements in a low aspect ratio transonic compressor stage (1982)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The time resolved flowfield in a low aspect ratio transonic compressor stage has been studied using a high frequency response sphere probe with a bandpass of D.C. to 20 kHz in a blowdown compressor facility. Averaged over the compressor annulus, the data agree well with those measured with standard pitot type probes on the same stage in a conventional test rig. Not all the spanwise distributions agree, however. These differences are explained as errors in the pitot probe readings due to fluctuations in the flow. The experimental data are compared to the results of a three-dimensional inviscid Euler calculation.
    Keywords: AERODYNAMICS
    Type: ASME PAPER 82-GT-201 , International Gas Turbine Conference and Exhibit; Apr 18, 1982 - Apr 22, 1982; London
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  • 7
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    A quasi-three-dimensional blade surface boundary layer analysis for rotating blade rows (1981)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A quasi-three-dimensional approximation has been developed for a blade boundary layer which involves the calculation of the effect of nonzero pressure gradients, turbulent flow, and blade twist, but includes only a simple coupling between streamlines. The resulting set of equations is solved using Keller's box scheme. The solution scheme is checked against available incompressible flow solutions and then applied to a NASA low aspect ratio transonic compressor stage for which extensive experimental and computational data are available. It is found that the three-dimensional boundary layer separates significantly sooner and has a much larger influence on rotor performance than would be expected from a two-dimensional analysis.
    Keywords: AERODYNAMICS
    Type: ASME PAPER 81-GT-126 , Gas Turbine Conference and Products Show; Mar 09, 1981 - Mar 12, 1981; Houston, TX
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  • 8
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    A miniature high frequency sphere probe (1980)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A spherical probe having five surface mounted silicon pressure sensors is described. The probe is 0.2 inches in diameter yielding a frequency response above 30 kHz. A scheme is described for retrieving from the five pressure signals the stagnation and static pressures, Mach number and flow angles in two planes. The calibrations forming the base for this procedure, obtained from steady state tests, are given in the form of polynomials in the two flow angles. A method for compensating the silicon pressure sensors for thermal effects is given. Typical data obtained in the MIT Blowdown Compressor are presented in raw form and after reduction to flow angles, Mach number and stagnation pressure.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Measurement methods in rotating components of turbomachinery; Mar 10, 1980 - Mar 13, 1980; New Orleans, LA
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  • 9
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    A comparison of the computed and experimental three dimensional flow in a transonic compressor rotor (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The three dimensional inviscid flow in a transonic compressor rotor; total pressure ratio of 1.65, has been numerically computed using MacCormack's time-marching method. This solution is compared to intra-blade static density measurements obtained by gas fluorescence. These results and comparisons illustrate the importance of three dimensional flow phenomena in determining the rotor flow field and show that while the viscous phenomena have an important influence, particularly on the outflow, the inviscid computation properly models the flow in the inlet portion of the rotor passages.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 76-368 , Fluid and Plasma Dynamics Conference; Jul 14, 1976 - Jul 16, 1976; San Diego, CA
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  • 10
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    Shock structure in transonic compressor rotors (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The inadequacy of axisymmetric theory in modeling the structure of the shock system in a transonic compressor rotor is shown with a simple model. A more accurate model for the flow near the sonic radius is proposed, which is supported by some flow visualization data and three-dimensional computations.
    Keywords: AERODYNAMICS
    Type: AIAA Journal; 17; Apr. 197
    Format: text
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