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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.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Development of improved analytical models for mesh reflector surfaces

Several methods for computing the reflection coefficients from mesh surfaces are discussed. Some methods mentioned have severe limitations, and the spectral approach appears to be the most attractive alternative. In spite of some inherent problems, the solutions obtained with this method will offer not only the reflection coefficients but also the currents carried on the mesh. This would allow separation of the power lost to resistive terms from that due to transmission loss. Overall, good results and rapid convergence should be obtained from this method when proper care is applied.

Brand, J. C.↗
NASA NTRS1983

Analytical Modeling of Operating Characteristics of Premixing-prevaporizing Fuel-air Mixing Passages

A model for predicting the distribution of liquid fuel droplets and fuel vapor in premixing-prevaporizing fuel-air mixing passages of the direct injection type is described. This model consists of three computer programs: a calculation of the two dimensional or axisymmetric air flow field neglecting the effects of fuel; a calculation of the three dimensional fuel droplet trajectories and evaporation rates in a known, moving air flow; and a calculation of fuel vapor diffusing into a moving three dimensional air flow with source terms dependent on the droplet evaporation rates. The air flow calculation can treat compressible swirling flows in arbitrary ducts with arbitrary distributions of temperature and velocity as initial conditions. The fuel droplets are treated as initial conditions. The fuel droplets are treated as individual particle classes each satisfying Newton's law, a heat transfer, and a mass transfer equation. The vapor diffusion calculation treats three dimensional, gas phase, turbulent diffusion processes with the turbulence level determined by the air flow calculations and the source terms determined by the droplet evaporation rates.

Anderson, O. L.↗
NASA NTRS1983

Analytical model of rotor wake aerodynamics in ground effect

The model and the computer program developed provides the velocity, location, and circulation of the tip vortices of a two-blade helicopter in and out of the ground effect. Comparison of the theoretical results with some experimental measurements for the location of the wake indicate that there is excellent accuracy in the vicinity of the rotor and fair amount of accuracy far from it. Having the location of the wake at all times enables us to compute the history of the velocity and the location of any point in the flow. The main goal of out study, induced velocity at the rotor, can also be calculated in addition to stream lines and streak lines. Since the wake location close to the rotor is known more accurately than at other places, the calculated induced velocity over the disc should be a good estimate of the real induced velocity, with the exception of the blade location, because each blade was replaced only by a vortex line. Because no experimental measurements of the wake close to the ground were available to us, quantitative evaluation of the theoretical wake was not possible. But qualitatively we have been able to show excellent agreement. Comparison of flow visualization with out results has indicated the location of the ground vortex is estimated excellently. Also the flow field in hover is well represented.

Saberi, H. A.↗
NASA NTRS1984

Retardation analytical model to extend service life

A fatigue crack growth model that incorporates crack growth retardation effects and is applicable to the materials characteristics and service environments of high performance LH2/LO2 engine systems was developed and tested.

Matejczyk, D.↗
NASA NTRS1984

Analytic modeling of a spray diffusion flame

A detailed model for a spray diffusion flame is described. The model is based on the boundary layer form of the equations of motion, with droplet transport accounted for using a discretized droplet size distribution function. Interphase transport of mass and energy are accounted for, with a flame-sheet model used to describe the combustion process on a droplet scale. Near dynamic equilibrium is assumed for the description of droplet transport; droplets can diffuse relative to the gas phase. Gas-phase mixing is accounted for using a two-equation turbulence model; buoyancy effects are included, with a temperature fluctuation equation used to account for buoyancy effects on turbulence structure. Thermal radiation from gas-phase CO2 and H2O is included. Gas-phase chemical kinetics are modeled using a 20-reaction, 10-species version of the advanced quasi-global chemical kinetics formulation. Results are compared with data for a vaporizing Freon spray and a pentane spray flame. It is shown that the computational approach provides a reasonably valid picture of the overall development of a spray diffusion flame, and, furthermore, provides a useful tool for the parametric examination of the spray combustion process.

Harsha, P. T.↗
NASA NTRS1984

An analytical model for the vorticity associated with a transverse jet

A two dimensional model is developed for a turbulent jet injected normally into a uniform crossflow, in which particular emphasis is placed on the contra-rotating vortex pair associated with the jet. By approximating the forces acting on each of the viscous vortices, equations governing the vortex spacing and downstream jet velocity are evolved. No empirical information is incorporated into this model. A description of the variation in total vortex strength is utilized in which vorticity generated by the jet's impulse dominates the farfield. Numerical solution of the governing equations yields results for the vortex trajectory, half spacing, varying circulation, and viscous core size that correlate quite well with experimental data and asymptotic relations. Based on these findings, we conclude that vortex separation and other important characteristics of the jet cross-section are two dimensional and viscous in nature. Hence it becomes possible to predict, on purely theoretical grounds, the behavior of the vortex pair and of the jet itself.

Karagozian, A. R.↗
NASA NTRS1984

Retardation analytical model to extend service life

A fatigue crack growth model that incorporates crack growth retardation effects and is applicable to the materials characteristics and service environments of high performance LH2/LO2 engine systems is discussed. Future Research plans are outlined.

Matejczyk, J.↗
NASA NTRS1984

Analytical Modeling of Spacecraft Power Systems

During the 25 years of space flight with unmanned Earth orbiting satellites, there has been an evolution of power systems in three general areas. The size of power system in terms of power demand at the bus has increased frorm a few watts in the early 1960s to a few hundred watts during the 1970s. Today, the bus power requirements are typically in the .5 to 1 kw range with some mission requirements exceeding the 1 kw size. Power grounding and user isolation are major design considerations when high fidelity power is required by a user.

Ford, F. E.↗
NASA NTRS1984

Analytical Models

A system-level design and analysis model was developed. This model was conceived to have several key elements: a solar pond thermodynamic performance model, a power generation subsystem model, and an economic analysis element. The basic approach was to create these elements or modules and refine them on an individual basis yet retain the capability to easily couple them into a full system design model. This building block approach allows for maximum flexibility and substitution of refined descriptions as the technology develops. A general overview of interconnecting these subsystem models is presented. The primary program control element will perform the administrative functions of data input, data output, information storage and transfer, and sequential calling of the subsystem models. From the point of view of the requirements of a system design model, a power conversion subsystem model was developed. The goal of the effort was a preliminary subsystem model compatible with the solar pond subsystem model so that a first order system simulation analysis could be performed.

Source record↗
NASA NTRS1987

Zonal winds near Venus' cloud top level - An analytic model of the equatorial wind speed

A consequence of the presently hypothesized maintenance of the equatorial wind speed near the cloud top level of Venus by a balance between the semidiurnal tide's pumping and the Hadley circulation's vertical advection (both integrated across the thermal driving region) is that the maximum equatorial zonal wind speed is proportional to the product of the buoyancy frequency and the magnitude of the driving region's thickness. The proportionality constant is characterized as a weakly increasing function of the heating rate, and a decreasing function of the product of an inverse length, expressing the mean zonal wind shear, and the driving region thickness. For the class of solutions thus treated, there is a threshold heating rate value below which no equilibrium satisfies the prescribed balance.

Leovy, Conway B.↗
NASA NTRS1987

Verification of an analytic modeler for capillary pump loop thermal control systems

A number of computer programs have been written to model two-phase heat transfer systems for space use. These programs support the design of thermal control systems and provide a method of predicting their performance in the wide range of thermal environments of space. Predicting the performance of one such system known as the capillary pump loop (CPL) is the intent of the CPL Modeler. By modeling two developed CPL systems and comparing the results with actual test data, the CPL Modeler has proven useful in simulating CPL operation. Results of the modeling effort are discussed, together with plans for refinements to the modeler.

Schweickart, R. B.↗
NASA NTRS1987

Analytical modeling of helium II in forced flow conditions

A numerical model was developed to examine the flow behavior of He II under forced flow conditions. The model basically solves the governing equations in the two-fluid model of He II, and can be used to assess the pump requirement for transferring He II in spaceborne systems. Predictions of liquid temperature and pressure drop agree well with empirical data obtained from small scale tests. At high transfer rates, the model predicts that the forced convection dominates the Gorter-Mellink conduction in heat transfer, and the classical turbulent flow correlation is sufficient for calculating the pressure drop across the transfer line.

Ng, Y. S.↗
NASA NTRS1987

Analytical modeling of helicopter static and dynamic induced velocity in GRASP

The methodology used by the General Rotorcraft Aeromechanical Stability Program (GRASP) to model the characteristics of the flow through a helicopter rotor in hovering or axial flight is described. Since the induced flow plays a significant role in determining the aeroelastic properties of rotorcraft, the computation of the induced flow is an important aspect of the program. Because of the combined finite-element/multibody methodology used as the basis for GRASP, the implementation of induced velocity calculations presented an unusual challenge to the developers. To preserve the modelling flexibility and generality of the code, it was necessary to depart from the traditional methods of computing the induced velocity. This is accomplished by calculating the actuator disc contributions to the rotor loads in a separate element called the air mass element, and then performing the calculations of the aerodynamic forces on individual blade elements within the aeroelastic beam element.

Kunz, Donald L.↗
NASA NTRS1988

Analytical modeling of the structureborne noise path on a small twin-engine aircraft

The structureborne noise path of a six passenger twin-engine aircraft is analyzed. Models of the wing and fuselage structures as well as the interior acoustic space of the cabin are developed and used to evaluate sensitivity to structural and acoustic parameters. Different modeling approaches are used to examine aspects of the structureborne path. These approaches are guided by a number of considerations including the geometry of the structures, the frequency range of interest, and the tractability of the computations. Results of these approaches are compared with experimental data.

Cole, J. E., III↗