Results for “single layer” — Page 80

NASA NTRS1974

Heat transfer and film cooling following injection through inclined circular tubes

Film cooling effectiveness and heat transfer are measured downstream of injection through discrete holes into a turbulent mainstream boundary layer. Air is injected through both a single hole and a row of holes spaced at three-diameter intervals and inclined at an angle of 35 deg to the main flow. There is little difference between the heat transfer coefficient with blowing and without blowing at low blowing rates (mass flux ratios). In fact, at low blowing rates, injection is found to decrease somewhat the heat transfer coefficient from that measured without blowing. As the mass flux ratio increases past unity, the heat transfer coefficient increases, especially with injection through a row of holes. The peak heat transfer is usually found at the edge of the spreading jets (i.e., between two holes). At a blowing rate near two, the lateral average of the heat transfer is as much as 27 percent higher than the heat transfer with no blowing. The increase in heat transfer is attributed to the interaction between the jets and the free stream, causing high levels of turbulence.

Eriksen, V. L.↗

NASA NTRS1975

Cadmium stannate selective optical films for solar energy applications

Efforts concentrated on reducing the electrical sheet resistance of sputtered cadmium stannate films, installing and testing equipment for spray coating experiments, and sputter deposition of thin cadmium sulfide layers onto cadmium stannate electrodes. In addition, single crystal silicon wafers were coated with cadmium stannate. Work also continued on the development of the backwall CdS solar cell.

Haacke, G.↗

NASA NTRS1977

Flow separation detector

An arrangement for sensing the fluid separation along a surface which employs a thermally insulating element having a continuous surface blending into and forming a part of the fluid flow surface is described. A sudden decrease in the temperature of the downstream sensor conductor and concomitant increase in the temperature of the upstream sensor conductor is an indication of the separation. When the temperatures are returned to the state achieved during normal flow, the indicator thereby indicates the normal, attached fluid flow. The conductors may be, for example, wires or thin films, and should be within the viscous sub-layer of the expected fluid flow. A single heater and several pairs of sensors and corresponding sensor conductors may be used to detect not only the fluid flow and the separation, but the direction of the fluid flow, over the fluid flow surface.

Mateer, G. C.↗

NASA NTRS1978

A combined potential and viscous flow solution for V/STOL engine inlets

A potential flow routine and a viscous boundary layer routine have been combined into a single routine for estimating the flow in and around subsonic inlets. In this combined routine, the viscous flow solution about the inlet body is obtained by adding the viscous displacement thickness to the inlet geometry. Combination of the two flow solutions has resulted in cost savings, both in preparation time and in computer time. This routine is a useful tool in optimizing lip shapes for V/STOL inlets. The method of combining the routine, comparison with NASA test data, and utilization of the routine for V/STOL inlet design are presented.

Ybarra, A. H.↗

NASA NTRS1982

Solution of viscous internal flows on curvilinear grids generated by the Schwarz-Christoffel transformation

The combination of an orthogonal, curvilinear coordinate generation procedure with a stable forward marching viscous flow solution technique is presently employed in the solution of flow fields for arbitrary, axisymmetric ducts. Coordinate generation is accomplished by means of both potential lines and plane potential flow streamlines. Since the coordinate streamlines approximate actual ones, the equations of motion for viscous compressible flow can be parabolized in order to solve for both the boundary layer and the core flow in a single streamwise pass. The method's versatility is demonstrated by two examples of viscous compressible swirling flow through complex radial gas turbine passages.

Anderson, O. L.↗

NASA NTRS1986

Low-loss optical waveguides made with molecular beam epitaxial In(0.012)Ga(0.988)As and In(0.2)Ga(0.8)As-GaAs superlattices

Low-loss optical guiding in In-doped GaAs is demonstrated for the first time. Ridge waveguides are made with single In(0.012)Ga(0.988)As ternary layers and In(0.2)Ga(0.8)As-GaAs superlattices. Attenuation constants of about 1.3 dB/cm are measured and the principal loss mechanism is identified to be scattering at the ridge walls. It is expected that improved fabrication techniques will lead to guides with attenuation less than or equal to 0.5 dB/cm.

Das, U.↗

NASA NTRS1987

Electrokinetic properties of particles in concentrated suspensions

The electrokinetic behavior of concentrated suspensions is studied under conditions where the double layer is thin. Bulk electrical conductivity and single particle electrophoretic mobilities were studied as functions of the particle concentration in the suspension. It is found that the interactions between particles affect the conduction processes.

Zukoski, C. F.↗

NASA NTRS1988

A low-drag nose-body

In the present investigation of the application of convex-curvature viscous drag reduction to an axisymmetric body, the qualification of a modified mixing-length formulation in several complex two-dimensional and axisymmetric turbulent boundary layers that are primarily curved is followed by the design of a low-drag nose-body for low drag at high subsonic speeds. The longitudinal distribution of the cross-sectional area ratio is found to be critical to boundary layer separation, requiring implementation not over a single long span of curvature but over three short spans. The possibility of a 'net' drag reduction is examined in relation to 'equivalent' nose-bodies.

Bandyopadhyay, P. R.↗

NASA NTRS1988

Absolute gain measurement of microstrip antennas under mismatched conditions

The gain of a single microstrip patch and a two-layer parasitic array is measured using the image method under mismatched conditions. This method produces accurate results, even in the case of low-gain microstrip antennas. The advantages of this method over the gain comparison technique are discussed.

Lee, R. Q.↗

NASA NTRS1988

Variable property analysis - Is there anything to it?

It is shown that the inclusion of variable thermodynamic and transport properties in the analysis of combusting flows qualitatively and quantitatively alters the results. Consideration is given to the following results: single droplet combustion, forced convective turbulent boundary layer combustion, and free convective combustion. In the case of the turbulent boundary layer combustion of solid/liquid fuels, it is shown that the fuel significantly influences the regression rate as it is found in the experiments.

Mukunda, H. S.↗

NASA NTRS1991

Growing Cobalt Silicide Columns In Silicon

Codeposition by molecular-beam epitaxy yields variety of structures. Proposed fabrication process produces three-dimensional nanometer-sized structures on silicon wafers. Enables control of dimensions of metal and semiconductor epitaxial layers in three dimensions instead of usual single dimension (perpendicular to the plane of the substrate). Process used to make arrays of highly efficient infrared sensors, high-speed transistors, and quantum wires. For fabrication of electronic devices, both shapes and locations of columns controlled. One possible technique for doing this electron-beam lithography, see "Making Submicron CoSi2 Structures on Silicon Substrates" (NPO-17736).

Fathauer, Obert W.↗

NASA NTRS1998

Shock Wave Boundary Layer Interactions in High Mach Number Flows: A Critical Survey of Current Numerical Prediction Capabilities

The report assesses the capability for numerical simulation of 2-D and 3-D shock wave laminar and turbulent boundary layer interactions Three fundamental configurations are considered: single fin, double fin, and hollow cylinder flare. Thirteen separate cases were examined by a distinguished international group of researchers using the Reynolds-averaged Navier-Stokes (RANS) equations with a wide range of turbulence models from zero equation to full Reynolds Stress Equation formulations. The report presents an extensive comparison of computations and experimental data, summarizes the results, and makes recommendations for future research.

Doyle D. Knight↗

NASA NTRS2008

Schottky barrier diode and method thereof

Pt/n.sup.-GaN Schottky barrier diodes are disclosed that are particularly suited to serve as ultra-violet sensors operating at wavelengths below 200 nm. The Pt/n.sup.-GaN Schottky barrier diodes have very large active areas, up to 1 cm.sup.2, which exhibit extremely low leakage current at low reverse biases. Very large area Pt/n.sup.-GaN Schottky diodes of sizes 0.25 cm.sup.2 and 1 cm.sup.2 have been fabricated from n.sup.-/n.sup.+ GaN epitaxial layers grown by vapor phase epitaxy on single crystal c-plane sapphire, which showed leakage currents of 14 pA and 2.7 nA, respectively for the 0.25 cm.sup.2 and 1 cm.sup.2 diodes both configured at a 0.5V reverse bias.

Aslam, Shahid↗

NASA NTRS2009

A Critical Study of Agglomerated Multigrid Methods for Diffusion

Agglomerated multigrid techniques used in unstructured-grid methods are studied critically for a model problem representative of laminar diffusion in the incompressible limit. The studied target-grid discretizations and discretizations used on agglomerated grids are typical of current node-centered formulations. Agglomerated multigrid convergence rates are presented using a range of two- and three-dimensional randomly perturbed unstructured grids for simple geometries with isotropic and highly stretched grids. Two agglomeration techniques are used within an overall topology-preserving agglomeration framework. The results show that multigrid with an inconsistent coarse-grid scheme using only the edge terms (also referred to in the literature as a thin-layer formulation) provides considerable speedup over single-grid methods but its convergence deteriorates on finer grids. Multigrid with a Galerkin coarse-grid discretization using piecewise-constant prolongation and a heuristic correction factor is slower and also grid-dependent. In contrast, grid-independent convergence rates are demonstrated for multigrid with consistent coarse-grid discretizations. Actual cycle results are verified using quantitative analysis methods in which parts of the cycle are replaced by their idealized counterparts.

Thomas, James L.↗

NASA NTRS2011

A Critical Study of Agglomerated Multigrid Methods for Diffusion

Agglomerated multigrid techniques used in unstructured-grid methods are studied critically for a model problem representative of laminar diffusion in the incompressible limit. The studied target-grid discretizations and discretizations used on agglomerated grids are typical of current node-centered formulations. Agglomerated multigrid convergence rates are presented using a range of two- and three-dimensional randomly perturbed unstructured grids for simple geometries with isotropic and stretched grids. Two agglomeration techniques are used within an overall topology-preserving agglomeration framework. The results show that multigrid with an inconsistent coarse-grid scheme using only the edge terms (also referred to in the literature as a thin-layer formulation) provides considerable speedup over single-grid methods but its convergence deteriorates on finer grids. Multigrid with a Galerkin coarse-grid discretization using piecewise-constant prolongation and a heuristic correction factor is slower and also grid-dependent. In contrast, grid-independent convergence rates are demonstrated for multigrid with consistent coarse-grid discretizations. Convergence rates of multigrid cycles are verified with quantitative analysis methods in which parts of the two-grid cycle are replaced by their idealized counterparts.

Nishikawa, Hiroaki↗

NASA NTRS2019

Dynamic Analysis of the STARC-ABL Propulsion System

In the pursuit of Electrified Aircraft Propulsion (EAP), much of the attention is on the development of hybrid electric concept vehicles and their propulsion systems from a steady state performance perspective. While it is steady-state performance that largely determines the efficiency of civil air transports, engine operability and transient performance define constraints for the steady state design that impact efficiency and system viability. Neglecting dynamics and control technologies can result in an over-designed, sub optimal propulsion system or a concept that is not feasible. Thus, dynamic system studies were conducted on the propulsion system of the conceptual aircraft design known as the Single-aisle Turboelectric AiRCraft with Aft Boundary Layer propulsor (STARC-ABL). This paper describes the development of a controller to verify the baseline concept's feasibility from an operability perspective. Further, studies were conducted to identify excessive stability margin in the baseline design that could be traded for potential benefits in efficiency through an engine re design. This study revealed the potential to reduce the high pressure compressor (HPC) stall margin by 3%. Finally, a study was conducted to investigate the potential benefit of adding energy storage to the STARC-ABL concept that further improves operability and enables more gains in engine efficiency and performance. The energy storage provided an additional 0.5% stall margin can be removed from the HPC.

STARC-ABL↗

NASA NTRS2019

Dynamic Analysis of the STARC-ABL Propulsion System

In the pursuit of Electrified Aircraft Propulsion (EAP), much of the attention is on the development of hybrid electric concept vehicles and their propulsion systems from a steady state performance perspective. While it is steady-state performance that largely determines the efficiency of civil air transports, engine operability and transient performance define constraints for the steady state design that impact efficiency and system viability. Neglecting dynamics and control technologies can result in an over-designed, sub optimal propulsion system or a concept that is not feasible. Thus, dynamic system studies were conducted on the propulsion system of the conceptual aircraft design known as the Single-aisle Turboelectric AiRCraft with Aft Boundary Layer propulsor (STARC-ABL). This paper describes the development of a controller to verify the baseline concept's feasibility from an operability perspective. Further, studies were conducted to identify excessive stability margin in the baseline design that could be traded for potential benefits in efficiency through an engine re design. This study revealed the potential to reduce the high pressure compressor (HPC) stall margin by 3%. Finally, a study was conducted to investigate the potential benefit of adding energy storage to the STARC-ABL concept that further improves operability and enables more gains in engine efficiency and performance. The energy storage provided an additional 0.5% stall margin can be removed from the HPC.

STARC-ABL↗

NASA NTRS2019

Dynamic Analysis of the STARC-ABL Propulsion System

In the pursuit of Electrified Aircraft Propulsion (EAP), much of the attention is on the development of hybrid electric concept vehicles and their propulsion systems from a steady state performance perspective. While it is steady-state performance that largely determines the efficiency of civil air transports, engine operability and transient performance define constraints for the steady state design that impact efficiency and system viability. Neglecting dynamics and control technologies can result in an over-designed, sub optimal propulsion system or a concept that is not feasible. Thus, dynamic system studies were conducted on the propulsion system of the conceptual aircraft design known as the Single-aisle Turboelectric AiRCraft with Aft Boundary Layer propulsor (STARC-ABL). This paper describes the development of a controller to verify the baseline concept's feasibility from an operability perspective. Further, studies were conducted to identify excessive stability margin in the baseline design that could be traded for potential benefits in efficiency through an engine re design. This study revealed the potential to reduce the high pressure compressor (HPC) stall margin by 3%. Finally, a study was conducted to investigate the potential benefit of adding energy storage to the STARC-ABL concept that further improves operability and enables more gains in engine efficiency and performance. The energy storage provided an additional 0.5% stall margin can be removed from the HPC.

dynamic systems analysis↗