SEARCH · Engineering Papers

Results for “different”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,567 records · Page 87

All sources NASA NTRS DOE OSTI

NASA NTRS1980

An experimental study of the effects of swirl and density difference on mixing in shear flow

Experiments were carried out on the mixing of streams with and without swirl and with and without density differences in a coannular geometry. Three variations of flow visualization techniques were used: direct excitation, collisional excitation, and quenching of the tracer. The axial variation of the flow for the case with swirl in the inner annulus is investigated in some detail. From the flow visualization pictures, it is concluded that the initial Helmholtz instability of the tangential shear layer gives rise to small scale peripheral strucutres, then it is possible that the inner swirling stream drives an instability which turns these small scale peripheral structures into ones of larger scale, thereby rearranging the initial vorticity distribution of the flow field. The pictures also indicate the occurrence of interchange of fluid between the annuli. It is also concluded that the interaction of density field with the resulting radial pressure gradient may have influenced the evolution of the flow structures.

Tan, C. S.↗

NASA NTRS1981

Comparison of different plate treatments and designs, an update

Nine packs of cells of different designs were put on test at Crane. They were run through their initial evaluation tests and then put into a cycling test. These were GE 12A h cells. The temperature was 20 C, the orbit was 90 minutes, the depth of discharge was 40%, the discharge rate was 9.6A and the initial charge rate was 9.6A to a voltage limit where it went into a taper. The goal was to get 100% return. The voltage limit was 1.453V through most of the testing, although recently it became necessary to lower some packs and raise some to hold 115% return. After one year, one cell from each pack was removed and the initial evaluation tests were repeated.

Baer, D.↗

NASA NTRS1981

Investigation of aerodynamic characteristics of wings having vortex flow using different numerical codes

The aerodynamic characteristics of highly sweptback wings having separation-induced vortex flow were investigated by employing different numerical codes with a view to determining some of the capabilities and limitations of these codes. Flat wings of various configurations-strake wing models, cropped, diamond, arrow and double delta wings, were studied. Cambered and cranked planforms have also been tested. The theoretical results predicted by the codes were compared with the experimental data, wherever possible, and found to agree favorably for most of the configurations investigated. However, large cambered wings could not be successfully modeled by the codes. It appears that the final solution in the free vortex sheet method is affected by the selection of the initial solution. Accumulated span loadings estimated for delta and diamond wings were found to be unusual in comparison with attached flow results in that the slopes of these load curves near the leading edge do not tend to infinity as they do in the case of attached flow.

Reddy, C. S.↗

NASA NTRS1981

Cumulative annoyance due to multiple aircraft flyover with differing peak noise levels

A laboratory study in which 160 subjects judged the annoyance of 30 minute sessions of aircraft noise is described. Each session contained nine flyovers consisting of various combinations of three takeoff recordings of Boeing 727. The subjects were asked to judge their annoyance in the simulated living room environment of the laboratory and also to assess how annoyed they would be if they heard the noise in their home during the day, evening, and night periods. The standard deviation of the sound level did not improve the predictive ability of L sub eq (equivalent continuous sound level) which performed as well or better than other noise measured. Differences were found between the projected home responses for the day, evening, and nighttime periods. Time of day penalties derived from these results showed reasonable agreement with those currently used in community noise indices.

Shepherd, K. P.↗

NASA NTRS1981

The chromospheric and transition layer emission of stars with different metal abundances

Preliminary results on observations of chromospheric and transition layer emission of stars with different metal abundances are reported. Metal deficient stars generally show reduced emission in the Mg II resonance lines and also in the other chromospheric and transition layer emission lines. This is interpreted as showing that energy fluxes other than acoustic fluxes must at least be coresponsible for the coronal and transition layer heating.

Boehm-Vitense, E.↗

NASA NTRS1981

Influence of exit impedance on finite difference solutions of transient acoustic mode propagation in ducts

The time-dependent governing acoustic-difference equations and boundary conditions are developed and solved for sound propagation in an axisymmetric (cylindrical) hard-wall duct without flow and with spinning acoustic modes. The analysis begins with a harmonic sound source radiating into a quiescent duct. This explicit iteration method then calculates stepwise in real time to obtain the steady solutions of the acoustic field. The transient method did not converge to the steady-state solution for cutoff acoustic duct modes. This has implications as to its use in a variable-area duct, where modes may become cutoff in the smal-area portion of the duct. For single cutoff mode propagation the steady-state impedance boundary condition produced acoustic reflections during the initial transient that caused finite instabilities in the numerical calculations. The stability problem is resolved by reformulating the exit boundary condition. Example calculations show good agreement with exact analytical and numerical results for forcing frequencies above, below, and nearly at the cutoff frequency.

Baumeister, K. J.↗

NASA NTRS1981

Stability analysis of numerical boundary conditions and implicit difference approximations for hyperbolic equations

Implicit, noniterative, finite difference schemes were recently developed by several authors for multidimensional systems of nonlinear hyperbolic partial differential equations. When applied to linear model equations with periodic boundary conditions those schemes are unconditionally stable (A-stable). As applied in practice the algorithms often face a severe time step restriction. A major source of the difficulty is the treatment of the numerical boundary conditions. One conjecture was that unconditional stability requires implicit numerical boundary conditions. An apparent counter example was the space time extrapolation considered by Gustafsson, Kreiss, and Sunstrom. Spatial (implicit) and space time (explicit) extrapolation using normal mode analysis for a finite and infinite number of spatial mesh intervals are examined. The results indicate that for unconditional stability with a finite number of spatial mesh intervals, the numerical boundary conditions must be implicit.

Beam, R. M.↗

NASA NTRS1981

Unconditional instability of inflow dependent boundary conditions in difference approximations to hyperbolic systems

The stability of finite difference approximations to initial boundary hyperbolic systems is studied. As is well known, a proper specification of boundary conditions for such systems is essential for their solutions to be well defined. A discrete analogue of the above is proved - if the numerical boundary conditions are consistent with an inflow part of the problem, they render the overall computation unstable. An example of the inviscid gasdynamics equations is considered.

Tadmor, E.↗

NASA NTRS1979

Implicit finite-difference simulations of steady and unsteady transonic flows

Implicit methods for several fluid dynamic formulations have been developed and applied to steady-state and low-frequency transonic flows. The basic steps involved in the construction of implicit schemes include: selection of linearly stable accurate implicit difference operators, time-linearization of nonlinear terms, and approximate factorization of the implicit operators into easily solved systems of equations. The proposed schemes are found very efficient for the simpler formulations.

Ballhaus, W. F.↗

NASA NTRS1981

Some modifications to, and operational experiences with, the two-dimensional, finite-difference, boundary-layer code, STAN5

The two-dimensional, finite-difference boundary-layer code, STAN5, is the primary tool used at the NASA-Lewis Research Center for predicting turbine blade gas-side heat-transfer coefficients. A number of modifications have been made to the program to enhance its usefulness for these calculations. Experience in using STAN5 has identified some problems in the program that can be treated through program input, without modifying the program. These include the presence of a small separation bubble near the leading edge, and the effect of full-coverage film cooling on transition to turbulence. Some of the techniques used to treat these problems are described.

Gaugler, R. E.↗

NASA NTRS1980

The solution of variable-step implicit difference equations for dynamic systems analysis

A semi-implicit iterative technique is given for the solution of implicit matrix difference equations which arise in variable-step direct time integration of dynamic systems equations. For all practical purposes, the technique avoids repeated refactoring of the stepsize-dependent solution matrix and achieves the solution convergence for engineering accuracy requirements within a permissible number of iterations. Extension of the present method to nonlinear problems treated by the pseudo-force procedure is straightforward. For nonlinear solution procedures based on the tangent modulus formulation, the technique requires modification to make use of the tangent stiffness matrix. It is noted that the question of whether to include the nonlinear terms within the iteration loop has not yet been resolved.

Park, K. C.↗

NASA NTRS1981

On a fourth order accurate implicit finite difference scheme for hyperbolic conservation laws. I - Nonstiff strongly dynamic problems

An implicit finite difference method of fourth order accuracy in space and time is introduced for the numerical solution of one-dimensional systems of hyperbolic conservation laws. The basic form of the method is a two-level scheme which is unconditionally stable and nondissipative. The scheme uses only three mesh points at level t and three mesh points at level t + delta t. The dissipative version of the basic method given is conditionally stable under the CFL (Courant-Friedrichs-Lewy) condition. This version is particularly useful for the numerical solution of problems with strong but nonstiff dynamic features, where the CFL restriction is reasonable on accuracy grounds. Numerical results are provided to illustrate properties of the proposed method.

Harten, A.↗

NASA NTRS1981

Direct measurement of lower atmospheric vertical potential differences

A high impedance system has been developed to make direct measurements of the atmospheric potential difference up to several thousand feet. A tethered balloon flown from Wallops Island, Virginia was used to loft a high voltage, insulated wire and a conducting collector in a test flight to 550 meters for two days of experiments in October 1980. The balloon was equipped with a payload to measure exact altitude, wind speed and direction, and other meteorological parameters. Electric potentials of 170,000 volts at 550 meters were measured. The collected currents which could be drawn through the wire by grounding the lower end were in the 10 microamp range indicating a system impedance of about 10 to the 10th ohms. This paper describes the apparatus and details of these measurements.

Holzworth, R. H.↗

NASA NTRS1981

Computation of wing-vortex interaction in transonic flow using implicit finite difference algorithm

An implicit delta form finite difference algorithm for Euler equations in conservation law form was used in preliminary calculations of three dimensional wing vortex interaction. Both steady and unsteady transonic flow wing vortex interactions are computed. The computations themselves are meant to guide upcoming wind tunnel experiments of the same flow field. Various modifications to the numerical method that are intended to improve computational efficiency are also described and tested in both two and three dimensions. Combination of these methods can reduce the overall computational time by a factor of 4.

Srinivasan, G.↗

NASA NTRS1982

Behavioral study of ultradian activity periods of mice enclosed in experimental cages of different dimensions

Male mice are enclosed in cages of different dimensions (cage A - 23x8x8 cm., cage B - 36x27x17 cm.), in an alternating light/dark regimen, at an ambient temperature of 22 to 23 C. The successions of the behavioral sequences of ultradian activity periods are noticed by direct observation during 11 consecutive hours in light. The experimental situation modifies the mean duration time and the behavioral organization of each activity period. However, the comparison of the overall activity time lengths and the comparison of the overall behavioral frequencies suggest that the energy spent per mouse is constant.

Guillot, A.↗

NASA NTRS1982

A comparison of the finite difference and finite element methods for heat transfer calculations

The finite difference method and finite element method for heat transfer calculations are compared by describing their bases and their application to some common heat transfer problems. In general it is noted that neither method is clearly superior, and in many instances, the choice is quite arbitrary and depends more upon the codes available and upon the personal preference of the analyst than upon any well defined advantages of one method. Classes of problems for which one method or the other is better suited are defined.

Emery, A. F.↗

NASA NTRS1981

Evaluating software development characteristics: A comparison of software errors in different environments

Error data obtained from two different software development environments are compared. To obtain data that was complete, accurate, and meaningful, a goal-directed data collection methodology was used. Changes made to software were monitored concurrently with its development. Similarities common to both environments are included: (1) the principal error was in the design and implementation of single routines; (2) few errors were the result of changes, required more than one attempt to correct, and resulted in other errors; (3) relatively few errors took more than a day to correct.

Weiss, D. M.↗

NASA NTRS1982

Finite difference methods for the solution of unsteady potential flows

Various problems which are confronted in the development of an unsteady finite difference potential code are reviewed mainly in the context of what is done for a typical small disturbance and full potential method. The issues discussed include choice of equations, linearization and conservation, differencing schemes, and algorithm development. A number of applications, including unsteady three dimensional rotor calculations, are demonstrated.

Caradonna, F. X.↗