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NASA NTRS1981

Analysis of a high-performance tubular solar collector

This article analyzes the thermal performance of a new vacuum tube solar collector. The assumptions and mathematical modeling are presented. The problem is reduced to the formulation of two simultaneous linear differential equations characterizing the collector thermal behavior. After applying the boundary conditions, a general solution is obtained which is found similar to the general Hottel, Whillier and Bliss form, but with a complex flow factor. The details of the two-dimensional thermal model of the solar collector at steady state is also presented to include the computer simulation and the performance parameterization. Comparison of the simulated performance with the manufacturer's test data showed good agreement at wide ranges of operating conditions.

Lansing, F. L.↗

NASA NTRS1981

Computerized symbolic manipulation in nonlinear finite element analysis

The potential of using computerized symbolic manipulation in the development of nonlinear finite elements is discussed. Three tasks which can be efficiently performed using computerized symbolic manipulation are identified: (1) generation of algebraic expressions for the stiffness coefficients of nonlinear finite elements, (2) generation of FORTRAN source code for numerical evaluation of stiffness coefficients, and (3) checking the correctness of the FORTRAN statements for the arrays of coefficients. The symbolic and algebraic manipulation system MACSYMA is used in the present study. Two sample MACSYMA programs are presented for the development of the nonlinear stiffness coefficients of two-dimensional, shear-flexible, doubly-curved deep shell elements. The first program is for displacement models and the second program is for mixed models with discontinuous stress-resultant fields at interelement boundaries.

Noor, A. K.↗

NASA NTRS1981

Thermal and stress analysis of thermal barrier coatings

An analysis has been performed that predicts the thermomechanical behavior of thermal barrier coated specimens. The analysis predicts the behavior during both plasma spray coating application and burner rig testing conditions simulating engine operation. The analysis was accomplished through utilization of one-dimensional through thickness and two-dimensional finite element calculations. The results of these calculations showed that specimens with a substrate control temperature between 300 F and 600 F would be optimum. Controlling substrate temperature was found to have a more dominant effect on the mechanical strains than the ceramic or substrate thicknesses. The predicted stresses and mechanical strains at the bond-coating interface are large enough to cause cracks in this region where post-test observations have determined coating failures originate.

Cassenti, B. N.↗

NASA NTRS1980

Model error estimation for large space systems

In-flight estimation of large structure model errors may have to be carried out in order to detect inevitable deficiencies in large structure controller/estimator models. These error estimates can most efficiently be obtained by the minimization of a quadratic functional of the model errors and on the subsequent analysis of the resulting optimal model error estimates. An integral operator approach to estimation leads to a geometrical interpretation of the model error estimation process. One of the significant insights gained with this interpretation is that the actual but unknown model errors can be decomposed as the sum of two distinct components that are orthogonal in some sense. One of these components is a so-called minimal error vector that retains many of the significant dynamics of the actual errors. The basic ideas in the model error estimation approach are first set forth with a two-dimensional analogy that has most of the essential features of the general estimation problem. The generalized results are then established and their application to a reference large structure model illustrated.

Rodriguez, G.↗

NASA NTRS1981

Transient thermal convection in microgravity

The unsteady two-dimensional thermal convection in a cylinder due to a transient acceleration solved for a step-function excitation. From this, the solution was obtained for an arbitrary time-dependent acceleration. The solutions are valied for sufficiently low Rayleigh numbers and therefore, relevant to microgravity fields. As an example, two graphs are presented for he convection resulting from the movement of an astronaut inside the Shuttle. The analysis can be applied to obtain any other convective flows such as those caused by g-jitter or variable rotation of the Shuttle.

Dressler, R. F.↗

NASA NTRS1982

Computation of blast wave-obstacle interactions

Numerical simulations of the interaction of a planar blast wave with various obstacles are presented. These obstacles are either ground structures or vehicles flying in the atmosphere. For a structure on the ground, the blast wave encounter is side-on, while for the flying vehicles the encounter is either head-on or oblique. Second-order accurate, finite-difference, and shock-capturing procedures are employed to solve the two-dimensional, axisymmetric, and three-dimensional unsteady Euler equations. Results are presented for the flow field consisting of blast wave striking obstacles that are at rest, moving subsonically and moving supersonically. Comparison of the numerical results with experimental data for a configuration at rest substantiates the validity of this approach and its potential as a flow analysis tool.

Champney, J. M.↗

NASA NTRS1982

Development of three-dimensional spatial displays using a geographically based information system

Procedures necessary for the development of a generalized three-dimensional perspective software capability in support of graphic, topographic, and color mapping of Landsat data are reviewed. The NASA Earth Resources Laboratory developed the procedures in order to facilitate the processing and analysis of disparate, geographically oriented base maps from aircraft and satellite sensors. Perspective displays are obtained through a translation of the space-viewed object to a vantage point coordinate system, followed by a rotation through two angles for alignment along the vantage line of sight, and finally a perspective transformation to yield two-dimensional displays with no hidden lines. Matrix equations for the transformations are reviewed, including scaling, and block diagrams are provided of the data and perspective software systems. The classification data plane may be mapped onto a topographic elevation data plane.

Junkin, B. G.↗

NASA NTRS1982

Application of a finite element algorithm for the solution of steady transonic Euler equations

A finite element algorithm for the solution of two-dimensional, steady Euler equations is presented which, through a Clebsch-type transformation for the velocity vector, solves the conservation of mass equation with one primary variable and two additional equations for the convection of two new variables. The accuracy and efficiency of this scheme is discussed, and the second-order accuracy attained in the analysis of the convection of the vorticity is demonstrated together with the efficient treatment of rotational and irrotational flow subregions. A sample problem is used to show the accuracy of the numerical scheme and its convergence characteristics.

Akay, H. U.↗

NASA NTRS1983

An aeroacoustic model for high-speed, unsteady blade-vortex interaction

A three-dimensional aeroacoustic model is developed to predict the sound pulse radiated by the passage of a helicopter blade over a potential vortex. The linearized analysis assumes that either the blade-vortex separation is small or that the blade-tip Mach number is close to 1, or both, so that an acoustically noncompact situation exists. The three-dimensional blade loading due to blade-vortex interaction is constructed through a spanwise superposition of two-dimensional solutions with strength linearly increasing from hub to tip. Such a loading overestimates somewhat the strength of tip region dipoles in the acoustic calculation that follows. The final expression for the predicted far-field signature is obtained in closed form, and thus permits a relatively inexpensive calculation of the directivity of peak acoustic pressures in three dimensions.

Martinez, R.↗

NASA NTRS1982

The Delta-K ocean wave spectrometer - Aircraft measurements and theoretical system analysis

Measurements of the relative strength of ocean surface wave spectral components have been made from an aircraft using the two-frequency microwave resonance technique. A coherent Ku-band radar was used to study the Bragg type resonance matching (at the difference frequency Delta-f) to the surface wave components. The spatial spectrum of the surface reflectivity modulation was then computed as the value of Delta-f was varied over a matching range of approximately 15 150 m in surface wavelength. This paper contains experimental results from flights conducted during the 1979 MARSEN project and the 1980 ARSLOE project, and the objective here is to present the radar results in terms of the variety of surface illumination geometries encountered. It will be shown that the MARSEN results, with the narrow footprint, are consistent with a one-dimensional theoretical approach and that the ARSLOE results, with a symmetric beam pattern, agree well with the existing two-dimensional theory.

Weissman, D. E.↗

NASA NTRS1984

Postprocessing for the UCLA climate model

Postprocessing programs written to analyze the results of a general circulation model are described. The model history data is interpolated to pressure surfaces, converted from 64-bit Cyber words to 32 bit IBM words, and transferred to tape for further analysis. The time average program reads the interpolation output tape and produces 15-day time averages. The model outputs a very detailed record for selected grid points. This data is sent to a tape in Cyber full words. The conversion program changes the format of the tape from 64 bit Cyber words to 32 bit IBM words, processing a month of data at a time. The grid-point history sorting program inputs the converted grid point history tape and sorts it by time. The end product is a tape with a time history of each field for every point. After the PBP data has been stored, it can be plotted. The plotting package is flexible, and allows the choice of fields and grid points. The one-dimensional fields are plotted as functions of time, and a daily summary is also produced. For the two-dimensional fields, time-height cross sections and daily summaries are produced. The model plotting package produces plots for all fields on the time average and pressure tapes. These plots include world maps, polar projections, zonal means, vectors, streamlines, and latitude-height plots.

Abeles, J.↗

NASA NTRS1984

Three-dimensional unsteady viscous flow analysis over airfoil sections

A three-dimensional solution procedure for the approximate form of the Navier-Stokes equation was exercised in the two- and three-dimensional modes to compute the unsteady turbulent boundary layer on a flat plate corresponding to the data of Karlsson. The procedure is based on the use of a consistently split Linearized Block Implicit technique in conjunction with a QR operator scheme. New time-dependent upstream boundary conditions were developed that yielded realistic solutions for the interior in the vicinity of the upstream boundary. Comparisons of the computation employing these boundary conditions with the data indicate that both qualitative and quantitative agreement was obtained for the mean velocity and the in phase and out of phase components of the first harmonic of the velocity. In addition, the calculation gave results for the skin friction phase angle that had expected physical behavior for large distances downstream of the inflow boundary. For the three-dimensional case, the two-dimensional data of Karlsson was considered, but in a coordinate system skewed at 45 deg to the free stream direction. The results of the calculations were in excellent agreement with the data and the two-dimensional computations.

Weinberg, B. C.↗

NASA NTRS1982

Transient and diffusion analysis of HgCdTe

Solute redistribution during directional solidification of HgCdTe is addressed. Both one-dimensional and two-dimensional models for solute redistribution are treated and model results compared to experiment. The central problem studied is the cause of radial inhomogeneities found in directionally solidified HgCdTe. A large scale gravity-driven interface instability, termed shape instability, is postulated to be the cause of radial inhomogeneities. Recommendations for future work, along with appropriate computer programs, are included.

Clayton, J. C.↗

NASA NTRS1984

Effects of boundary layer refraction and fuselage scattering on fuselage surface noise from advanced turboprop propellers

An acoustic disturbance's propagation through a boundary layer is discussed with a view to the analysis of the acoustic field generated by a propfan rotor incident to the fuselage of an aircraft. Applying the parallel flow assumption, the resulting partial differential equations are reduced to an ordinary acoustic pressure differential equation by means of the Fourier transform. The methods used for the solution of this equation include those of Frobenius and of analytic continuation; both yield exact solutions in series form. Two models of the aircraft fuselage-boundary layer system are considered, in the first of which the fuselage is replaced by a flat plate and the acoustic field is assumed to be two-dimensional, while in the second the fuselage is a cylinder in a fully three-dimensional acoustic field. It is shown that the boundary layer correction improves theory-data comparisons over simple application of a pressure-doubling rule at the fuselage.

Mcaninch, G. L.↗

NASA NTRS1984

Two-dimensional wind-tunnel interference from measurements on two contours

This paper describes how wall-induced velocities near a model in a two-dimensional wind tunnel can be estimated from upwash distributions measured along two contours surrounding a model. The method is applicable to flows that can be represented by linear theory. It was derived by applying the Schwarz Integral Formula separately to the two contours and by exploiting the free-air relationship between upwashes along the contours. Advantages of the method are that only one flow quantity need by measured and no representation of the model is required. A weakness of the method is that it assumes streamwise interference velocity vanishes far upstream of the model. This method was applied to a simple theoretical model of flow in a solid-wall wind tunnel. The theoretical interference velocities and the velocities computed using the method were in excellent agreement. The method was then used to analyze experimental data acquired during adaptive-wall experiments at Ames Research Center. This analysis confirmed that the wall adjustments reduced wall-induced velocities near the model.

Schairer, E. T.↗

NASA NTRS1984

Discrete models for the numerical analysis of time-dependent multidimensional gas dynamics

A possible technique is explored for extending to multidimensional flows some of the upwind-differencing methods that are highly successful in the one-dimensional case. Emphasis is on the two-dimensional case, and the flow domain is assumed to be divided into polygonal computational elements. Inside each element, the flow is represented by a local superposition of elementary solutions consisting of plane waves not necessarily aligned with the element boundaries.

Roe, P. L.↗

NASA NTRS1951

Flow through cascades in tandem

An exact treatment of the problem of finding the incompressible, inviscid two-dimensional flow around two cascades in tandem is presented. The analysis includes solutions of both the direct and the inverse problems. These problems are solved by conformally mapping the tandem cascade onto the region between two concentric circles in which region there are suitably placed flow singularities. Formulas for the velocity and the potential in the annular region are presented in a closed form by means of elliptic functions. The equations are presented in a form suitable for computation.

Spraglin, William E↗

NASA NTRS1948

Theoretical Analysis of Stationary Potential Flows and Boundary Layers at High Speed

The present report consists of two parts. The first part deals with the two-dimensional stationary flow in the presence of local supersonic zones. A numerical method of integration of the equation of gas dynamics is developed. Proceeding from solutions at great distance from the body the flow pattern is calculated step by step. Accordingly the related body form is obtained at the end of the calculation. The second part treats the relationship between the displacement thickness of laminar and turbulent boundary layers and the pressure distribution at high speeds. The stability of the boundary layer is investigated, resulting in basic differences in the behavior of subsonic and supersonic flows. Lastly, the decisive importance of the boundary layer for the pressure distribution, particularly for thin profiles, is demonstrated.

Oswaititsch, K.↗