Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “control layers”

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.

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

At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Supersonic laminar flow control research

The objective of this research is to understand supersonic laminar flow stability, transition and active control. Some prediction techniques will be developed or modified to analyze laminar flow stability. The effects of distributed heating and cooling as an active boundary layer control technique will be studied. The primary tasks of the research apply to the NASA/Ames PoC and LFSWT's nozzle design with laminar flow control and are listed as follows: (1) predictions of supersonic laminar boundary layer stability and transition; (2) effects of wall heating and cooling on supersonic laminar flow control; (3) performance evaluation of the PoC and LFSWT nozzle designs with wall heating and cooling applied at different locations and various lengths; and (4) effects of a conducted -vs- pulse wall temperature distribution for the LFSWT.

Lo, Ching F.↗
NASA NTRS1995

Supersonic laminar flow control research

The objective is to understand supersonic laminar flow stability, transition, and active control. Some prediction techniques will be developed or modified to analyze laminar flow stability. The effects of distributed heating and cooling as an active boundary layer control technique will be studied. The primary tasks of the research apply to the NASA/Ames Proof of Concept (PoC) and Laminar Flow Supersonic Wind Tunnel's (LFSWT's) nozzle design with laminar flow control and are listed as follows: (1) predictions of supersonic laminar boundary layer stability and transition, (2) effects of wall heating and cooling on supersonic laminar flow control, (3) performance evaluation of the PoC and LFSWT nozzle designs with wall heating and cooling applied at different locations and various lengths, and (4) effects of a conducted versus pulse wall temperature distribution for the LFSWT.

Lo, Ching F.↗
NASA NTRS1993

System identification of the JPL micro-precision interferometer truss - Test-analysis reconciliation

The JPL Micro-Precision Interferometer (MPI) is a testbed for studying the use of control-structure interaction technology in the design of space-based interferometers. A layered control architecture will be employed to regulate the interferometer optical system to tolerances in the nanometer range. An important aspect of designing and implementing the control schemes for such a system is the need for high fidelity, test-verified analytical structural models. This paper focuses on one aspect of the effort to produce such a model for the MPI structure, test-analysis model reconciliation. Pretest analysis, modal testing, and model refinement results are summarized for a series of tests at both the component and full system levels.

Red-Horse, J. R.↗
NASA NTRS1997

Near-Surface Geologic Units Exposed Along Ares Vallis and in Adjacent Areas: A Potential Source of Sediment at the Mars Pathfinder Landing Site

A sequence of layers, bright and dark, is exposed on the walls of canyons, impact craters and mesas throughout the Ares Vallis region, Chryse Planitia, and Xanthe Terra, Mars. Four layers can be seen: two pairs of alternating dark and bright albedo. The upper dark layer forms the top surface of many walls and mesas. The upper dark-bright pair was stripped as a unit from many streamlined mesas and from the walls of Ares Valles, leaving a bench at the top of the lower dark layer, approximately 250 m below the highland surface on streamlined islands and on the walls of Ares Vallis itself. Along Ares Vallis, the scarp between the highlands surface and this bench is commonly angular in plan view (not smoothly curving), suggesting that erosion of the upper dark-bright pair of layers controlled by planes of weakness, like fractures or joints. These near-surface layers in the Ares Vallis area have similar thicknesses, colors, and resistances to erosion to layers exposed near the tops of walls in Valles Marineris (Treiman et al.) and may represent the same pedogenic hardpan units. From this correlation, and from analogies with hardpans on Earth, the light-color layers may be cemented by calcite or gypsum. The dark layers are likely cemented by an iron-bearing mineral. Mars Pathfinder instruments should permit recognition and useful analyses of hardpan fragments, provided that clean uncoated surfaces are accessible. Even in hardpan-cemented materials, it should be possible to determine the broad types of lithologies in the Martian highlands. However, detailed geochemical modeling of highland rocks and soils may be compromised by the presence of hardpan cement minerals.

Treiman, Allan H.↗
NASA NTRS1929

Wind tunnel tests on airfoil boundary control using a backward opening slot

This report presents the results of an investigation to determine the effect of boundary layer control on the lift and drag of an airfoil equipped with a backward opening slot. Various slot locations, widths of opening, and pressures, were used. The tests were conducted in the Five-Foot Atmospheric Wind Tunnel of the Langley Memorial Aeronautical Laboratory. The greatest increase in maximum lift was 96 per cent, the greatest decrease in minimum drag was 27 per cent, and the greatest increase in the ratio, maximum lift coefficient/minimum drag coefficient, was 151 per cent.

Knight, Montgomery↗
NASA NTRS1996

Features Of Cavity Flow And Acoustics Of Stratospheric Observatory For Infrared Astronomy

The stratospheric observatory for infrared astronomy (SOFIA) is a 2.5 meter aperture Cassegrain telescope with a Nasmyth focus that will be housed in an open cavity in the Boeing 747-SP aircraft and operated at altitudes around 41,000 feet for infrared (IR) viewing of celestial events of astronomical nature. At these altitudes the IR viewing capability of SOFIA far exceeds that of any ground based system. To minimize IR transmission losses, SOFIA will operate with an open cavity. Such an open cavity during flight creates several challenging aerodynamic and aeroacoustic design problems. Foremost of these are: the shear layer over the cavity may cause unwanted resonance if the cavity is untreated; this might give rise to excessive sound pressure levels (SPL) in the cavity and thus affect the unsteady loads on the telescope; the unsteady flow within the cavity produces large dynamic loads and moments that will impact the pointing accuracy of the telescope; the open cavity and the shear layer control devices produce additional drag that will affect directly the time of flight of the mission; the aft location of the cavity down stream of port wing will affect the the flow on the aircraft control surfaces and thus the stability of the aircraft. Also, the highly turbulent shear layer over the cavity and the temperature gradients and 'hot spots' within the cavity can produce a wave front error of the image when it reaches the focal plane of the recorder.

Srinivasan, G. R.↗
NASA NTRS1986

Aircraft drag prediction and reduction. Addendum 1: Computational drag analyses and minimization; mission impossible?

The Special Course on Aircraft Drag Prediction was sponsored by the AGARD Fluid Dynamics Panel and the von Karman Institute and presented at the von Karman Institute, Rhode-Saint-Genese, Belgium, on 20 to 23 May 1985 and at the NASA Langley Research Center, Hampton, Virginia, USA, 5 to 6 August 1985. The course began with a general review of drag reduction technology. Then the possibility of reduction of skin friction through control of laminar flow and through modification of the structure of the turbulence in the boundary layer were discussed. Methods for predicting and reducing the drag of external stores, of nacelles, of fuselage protuberances, and of fuselage afterbodies were then presented followed by discussion of transonic drag rise. The prediction of viscous and wave drag by a method matching inviscid flow calculations and boundary layer integral calculations, and the reduction of transonic drag through boundary layer control are also discussed. This volume comprises Paper No. 9 Computational Drag Analyses and Minimization: Mission Impossible, which was not included in AGARD Report 723 (main volume).

Slooff, J. W.↗
NASA NTRS1974

Comparison of theoretical and experimental boundary-layer development in a Mach 2.5 mixed-compression inlet

An analytical investigation was made of the boundary layer flow in an axisymmetric Mach 2.5 mixed compression inlet, and the results were compared with experimental measurements. The inlet tests were conducted in the Lewis 10- by 10-foot supersonic wind tunnel at a unit Reynolds number of 8.2 million/m. The inlet incorporated porous bleed regions for boundary layer control, and the effect of this bleed was taken into account in the analysis. The experimental boundary layer data were analyzed by using similarity laws from which the skin friction coefficient was obtained. The boundary layer analysis included predictions of laminar and turbulent boundary layer growth, transition, and the effects of the shock boundary layer interactions. In addition, the surface static pressures were compared with those obtained from an inviscid characteristics program. The results of investigation showed that the analytical techniques gave satisfactory predictions of the boundary layer flow except in regions that were badly distorted by the terminal shock.

Hingst, W. R.↗
NASA NTRS1994

Wind Tunnel Testing for the Stratospheric Observatory for Infrared Astronomy

NASA Ames Research Center is pursuing the development of SOFIA, the Stratospheric Observatory For Infrared Astronomy. SOFIA will consist of a 2.5 meter telescope mounted aft of the wing of a Boeing 747 aircraft. Since a large portion of the infrared spectrum is not visible at ground level due to absorption by water vapor in the atmosphere below 40,000 feet, it is highly desirable to make observations above this altitude. SOFIA will provide the opportunity for astronomers to conduct high-altitude research for extended periods of time. Current study is focused on wind tunnel testing for the open cavity. If not controlled, air would create resonance and damage the telescope. For this reason, SOFIA will design a boundary layer control device to achieve laminar flow over the cavity. This also provides a clearer flow for seeing, thus improving resolution on infrared sources. Other effects being tested in the wind tunnel are aerodynamic torque loads on the telescope, and flutter loads on the tail.

Schenberger, Deborah↗
NASA NTRS1995

Experimental testing using a remotely operated flap with a 2D high lift model

The problem of efficient wind tunnel testing for multi-element airfoils was first addressed by the author during a previous ASEE fellowship. A modern three element model with internal actuators to position a flap in two degrees of freedom was designed and later built. Some preliminary testing proved that the approach was viable. The purpose of this summer's work was to fully develop experimental methods including efficient data acquisition. The final goal is to develop dense data sets for both lift and drag measurements as a function of flap position for both take-off and landing configurations. The model has a span of 36 in. and chord of 18 in. and is currently being fitted for a 3 ft. x 4 ft. low speed wind tunnel. The flap was reworked to allow all pressure taps to function after initial tests showed two blocked ports. The serial method of obtaining pressures from the surface taps was found to be exceedingly slow so a new method using 12 pressure transducers and a 12 port parallel scanning valve were developed. A new automated data acquisition and control algorithm was developed using LabView software and a PC platform. Flow two-dimensionality is currently under investigation with boundary layer control by blowing; this was previously omitted for initial testing. By the end of the summer a detailed data set (uncorrected) consisting of lift coefficient versus flap position for the landing configuration should be available.

Landman, Drew↗
NASA NTRS1993

Boundary layer receptivity and control

Receptivity processes initiate natural instabilities in a boundary layer. The instabilities grow and eventually break down to turbulence. Consequently, receptivity questions are a critical element of the analysis of the transition process. Success in modeling the physics of receptivity processes thus has a direct bearing on technological issues of drag reduction. The means by which transitional flows can be controlled is also a major concern: questions of control are tied inevitably to those of receptivity. Adjoint systems provide a highly effective mathematical method for approaching many of the questions associated with both receptivity and control. The long term objective is to develop adjoint methods to handle increasingly complex receptivity questions, and to find systematic procedures for deducing effective control strategies. The most elementary receptivity problem is that in which a parallel boundary layer is forced by time-harmonic sources of various types. The characteristics of the response to such forcing form the building blocks for more complex receptivity mechanisms. The first objective of this year's research effort was to investigate how a parallel Blasius boundary layer responds to general direct forcing. Acoustic disturbances in the freestream can be scattered by flow non-uniformities to produce Tollmien-Schlichting waves. For example, scattering by surface roughness is known to provide an efficient receptivity path. The present effort is directed towards finding a solution by a simple adjoint analysis, because adjoint methods can be extended to more complex problems. In practice, flows are non-parallel and often three-dimensional. Compressibility may also be significant in some cases. Recent developments in the use of Parabolized Stability Equations (PSE) offer a promising possibility. By formulating and solving a set of adjoint parabolized equations, a method for mapping the efficiency with which external forcing excites the three-dimensional motions of a non-parallel boundary layer was developed. The method makes use of the same computationally efficient formulation that makes the PSE currently so appealing. In the area of flow control, adjoint systems offer a powerful insight into the effect of control forces. One of the simplest control strategies for boundary layers involves the application of localized mean wall suction.

Hill, D. C.↗
NASA NTRS1995

Active Control of Boundary-Layer Instabilities: Use of Sensors and Spectral Controller

Full Navier-Stokes equations were conducted to determine the feasibility of automating the control of wave instabilities within a flat plate boundary layer with sensors, actuators, and a spectral controller. The results indicate that a measure of wave cancellation can be obtained for small and large amplitude instabilities without feedback; however, feedback is required to optimize the control amplitude and phase for exact wave cancellation.

Joslin, R. D.↗
NASA NTRS2004

NASA Tech Briefs, September 2004

Topics covered include: Brazing SiC/SiC Composites to Metals; Composite-Material Tanks with Chemically Resistant Liners; Thermally Conductive Metal-Tube/Carbon-Composite Joints; Improved BN Coatings on SiC Fibers in SiC Matrices; Iterative Demodulation and Decoding of Non-Square QAM; Measuring Radiation Patterns of Reconfigurable Patch Antennas on Wafers; Low-Cutoff, High-Pass Digital Filtering of Neural Signals; Further Improvement in 3DGRAPE; Ground Support Software for Spaceborne Instrumentation; MER SPICE Interface; Simulating Operation of a Planetary Rover; Analyzing Contents of a Computer Cache; Discrepancy Reporting Management System; Silicone-Rubber Microvalves Actuated by Paraffin; Hydraulic Apparatus for Mechanical Testing of Nuts; Heat Control via Torque Control in Friction Stir Welding; Manufacturing High-Quality Carbon Nanotubes at Lower Cost; Setup for Visual Observation of Carbon-Nanotube Arc Process; Solution Preserves Nucleic Acids in Body-Fluid Specimens; Oligodeoxynucleotide Probes for Detecting Intact Cells; Microwave-Spectral Signatures Would Reveal Concealed Objects; Digital Averaging Phasemeter for Heterodyne Interferometry; Optoelectronic Instrument Monitors pH in a Culture Medium; Imaging of gamma-Irradiated Regions of a Crystal; Photodiode-Based, Passive Ultraviolet Dosimeters; Discrete Wavelength-Locked External Cavity Laser; Flexible Shields for Protecting Spacecraft Against Debris; Part 2 of a Computational Study of a Drop-Laden Mixing Layer; Controllable Curved Mirrors Made from Single-Layer EAP Films; and Demonstration of a Pyrotechnic Bolt-Retractor System.

Source record↗
NASA NTRS1980

On the stabilization of three-dimensional boundary layers by suction and cooling

A significant reduction in the drag of transonic aircraft can be achieved by using an active method of boundary-layer control to maintain laminar flow on the aerodynamic surfaces. The stabilizing influence of suction for both favorable and adverse pressure gradients is demonstrated by means of the self-similar incompressible three-dimensional boundary layers on yawed wedges. Profile instability is measured by the maximum amplification rate of fixed-frequency disturbances computed according to linearized, locally parallel, spatial stability theory. Suction is found to be more effective in controlling Tollmien-Schlichting instability than stationary cross-flow disturbances. The effectiveness of surface cooling as a method of stabilization is compared with suction for the boundary layers on a transonic 35 deg swept wing of infinite span. It is found from compressible stability theory that when the surface is cooled to a uniform temperature such that the maximum cross-flow velocity is reduced by the same amount as with a uniform suction distribution, the stabilizing effect of cooling on cross-flow disturbances is less than with suction.

Mack, L. M.↗
NASA NTRS1985

The passive control of compressible boundary layer growth by boundary layer trips

The passive control of compressible boundary layer growth by boundary layer trips has been studied experimentally. Axisymmetric trips and three dimensional trips were used in this study. The nomial freestream Mach numbers are 1.5 and 4. The results show that trips are effective in promoting boundary layer growth. Trips are more effective for Mach 1.5 flows than for Mach 4 flows.

Chou, J. H.↗
NASA NTRS2006

Control of Supersonic Boundary Layers Using Steady Suction

Control of supersonic boundary layers using steady suction through a series of very small two-dimensional strips is numerically investigated at a free stream Mach number of 1.8. The mean flow induced by rows of suction holes is also computed. Both the steady and unsteady solutions are obtained by solving the full Navier-Stokes equations using the 5th-order accurate weighted essentially non-oscillatory (WENO) scheme for space discretization and using third-order total-variationdiminishing (TVD) Runge-Kutta scheme for time integration. Computations for the two-dimensional cases are performed at suction coefficients 0.001 and 0.002 to investigate the stabilizing effects of suction. The simulation showed that a series of shock waves are generated at the slots. The stability results showed that the total amplification is reduced up to the end of the computational domain. However, the growth rates become larger at downstream distances away from the suction region. The computations for the suction holes showed the generation of Mach waves from each hole and the formation of longitudinal vortices.

Balakumar, P.↗
NASA NTRS1994

Maneuver Performance Enhancement for an Advanced Fighter/Attack Aircraft

A small scale wind tunnel test of a realistic fighter configuration has been completed in NASA Ames' 7'x10' wind tunnel. This test was part of the Fighter Lift and Control (FLAC) program, a joint NASA - USAF research program, involving small and large-scale wind-tunnel tests and computational analysis of unique lift augmentation and control devices. The goal of this program is to enhance the maneuver and control capability of next-generation Air Force multi-role fighter aircraft with low-observables geometries. The principal objective of this test was to determine the effectiveness of passive boundary layer control devices at increasing L/D at sustained maneuver lift coefficients. Vortex generators (VGs) were used to energize the boundary layer to prevent or delay separation. Corotating vanes, counter-rotating vanes, and Wheeler Wishbone VGs were used in the vicinity of the leading and trailing edge flap hinge lines. Principle test parameters were leading and trailing edge flap deflections, and location, size, spacing, and orientation for each VG type. Gurney flaps were also tested. Data gathered include balance force and moment data, surface pressures, and flow visualization for characterizing flow behavior and locating separation lines. Results were quite different for the two best flap configurations tested. All VG types tested showed improvement (up to 5%) in maneuver L/D with flaps at LE=20 degrees, TE=0 degrees. The same VGs degraded performance, in all but a few cases, with flaps at LE=15 degrees, TE=10 degrees.

Samuels, Jeff↗
NASA NTRSDate not supplied

Controls for Electrified Aircraft Propulsion

Advanced electrified aircraft propulsion (EAP) concepts with integrated power, propulsion, and thermal systems require the development of equally sophisticated controllers to fly safe and efficient missions. Hybrid electric aircraft utilize electric machines mechanically coupled to the engine shafts to extract and insert power for a variety of purposes. Additionally, electric machines may drive propulsive fans pulling from a combination of on-board energy storage devices and engine extracted power. NASA’s investment in hybrid electric aircraft hardware-in-the-loop testing enables controls research on representative engine models using a novel emulation and scaling methodology. High-voltage, high-power electrical powertrain presents several technical risks at altitude. High-power requires high efficiency to minimize losses. Superconducting electric machines and power distribution research at NASA has identified key challenges with potential controls solutions. These risks necessitate the development of controllers robust to model uncertainty, disturbances, and fault conditions. System health management and fault detection schemes play an important role in a multi-layer controls approach that utilizes a supervisor which oversees inner loops for the highly coupled power, propulsion, and thermal systems. Such a supervisory controller enables coordinates energy transfer between engines, energy storage devices, electric machines, propulsors, and heat exchangers. Existing methods have shown an improvement in engine operability using the hybrid electric powertrain.

Halle E Buescher↗