Search NASA⌕ Search

SEARCH · Search NASA

Results for “High Aspect-Ratio”

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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Pulsed radio frequency power modulation for profile control in cryogenic reactive ion etching of silicon gratings

Cryogenic silicon etching with SF 6 /O 2 plasmas enables vertical sidewalls and smooth surfaces for high–aspect-ratio structures, yet precise control of etched profiles (sidewall angle, lateral etching, and linewidth retention) remains challenging under continuous-wave excitation due to coupling among radical fluxes, ion energy distributions, and in situ passivation dynamics. In this work, we investigated pulsed radio frequency bias delivery as a process knob for profile control during cryogenic silicon etching. Systematic experiments on 500 nm-wide, 1 μm-pitch gratings etched to 0.8–1.1 μm depth at 0.5–2 kHz pulsing frequency and 25%–75% duty cycle revealed strong dependencies of etch rate, linewidth, and sidewall angle on modulation conditions. We proposed a conceptual kinetic picture combined with feature-scale electrostatic analysis to understand the alternation of ion-driven etching and passivation recovery between on/off segments and local electric field shaping and modulation of ion trajectories within the trench. Moderate duty cycles (50%–75%) near 1 kHz achieved a balance between anisotropy and etch rate. These results demonstrate pulsed-bias modulation can be utilized to tune directionality and sidewall preservation in cryogenic SF 6 /O 2 etching, which are relevant to photonic, metrology, and quantum device fabrication.

36 MATERIALS SCIENCE↗
NASA NTRS1959

The Effect of Moment of Area Rule Modifications on the Drag, Lift and Pitching Moment Characteristics of an Unswept Aspect Ratio 6 Wing and Body Combination

An experimental investigation was conducted to determine the effect of moment-of-area-rule modifications on the drag, lift, and pitching-moment characteristics of a wing-body combination with a relatively high aspect-ratio unswept wing. The basic configuration consisted of an aspect-ratio-6 wing with a sharp leading edge and a thickness ratio of 0.06 mounted on a cut-off Sears-Haack body. The model with full moment-of-area-rule modifications had four contoured pods mounted on the wing and indentations in the body to improve the longitudinal distributions of area and moments of area. Also investigated were modifications employing pods and indentations that were only half the size of the full modifications and modifications with partial body indentations. The models were tested at angles of attack from -2 deg to +12 deg at Mach numbers from 0.6 to 1.4. In general, the moment-of-area-rule modifications had a large effect on the drag characteristics of the models but only a small effect on their lift and pitching-moment characteristics. The modifications provided substantial reductions in the zero-lift drag at transonic and low supersonic speeds, but at subsonic speeds the drag was increased. Near Mach number 1.0, the model with full modification provided the greatest reduction in drag, but at the highest test Mach numbers the half modification gave the largest drag reduction. In general, the percent reductions of zero- lift drag obtained with the aspect-ratio-6 wing were as great or greater than those previously obtained with aspect-ratio-3 wings. The effect of the modifications on the drag due to lift was small except at Mach num- bers below 0.9 where the modified models had higher drag-rise factors. Above Mach number 0.9, the modified models had higher lift-drag ratios than the basic model. The modified models also had higher lift curve slopes and generally were slightly more stable than the basic configuration.

Dickey, Robert R.↗
NASA NTRS1959

Effects of Forebody Deflection on the Stability and Control Characteristics of a Canard Airplane Configuration with a High Trapezoidal Wing at a Mach Number of 2.01

An investigation has been conducted in the Langley 4- by 4-foot supersonic pressure tunnel at a Mach number of 2.01 to determine the effects of forebody deflection on the stability and control characteristics of a canard airplane configuration. The configuration had a high trapezoidal aspect-ratio-3 wing, a trapezoidal canard surface, and a single swept vertical tail. Forebody deflection angles of 0 deg, 2 deg and deg were investigated. The results indicated that nose-up deflections of the forebody provided positive increments of pitching moment with little increase in drag and hence would be useful in reducing the pitch-control requirements and the attendant losses in lift-drag ratio due to trimming. Deflection of the forebody, however, aggravated the decrease in directional stability with increasing angle of attack by causing a loss in tail contribution and by increasing the instability of the wing-body combination.

Spearman, M. Leroy↗
NASA NTRS1955

An Experimental Investigation of the Hinge-moment Characteristics of a Constant-chord Control Surface Oscillating at High Frequency

The results of an experimental investigation of the hinge-moment characteristics of a constant-chord control surface oscillating at high frequency is presented. The control surface was mounted on an aspect-ratio-2 triangular wing. The aerodynamic restoring-moment coefficient and damping-moment coefficient were determined at a frequency of 260 cycles per second for a Mach number range of 0.6 to 0.8 and 1.3 to 1.9 at angles of attack of 5 degrees and 10 degrees. The test results showed linear theory to be a reliable guide to the prediction of the trend of the restoring-moment coefficient with Mach number for the supersonic speed range of the investigation but overestimated the magnitude of the coefficient. The experimental values of the damping-moment coefficient were, for the most part, more positive than those indicated by the theory and, for some conditions, could lead to instability of the control surface. Comparison of the results of this investigation with those of previous investigations at 0 and 50 cycles per second showed that frequency had little effect on the restoring-moment coefficient. The damping-moment coefficient was similarly insensitive to frequency at an oscillation amplitude of plus-or-minus 1.0 degrees but at an amplitude ofplus-or-minus 2.5 degrees the results showed a destabilizing shift with increasing frequency.

Reese, David E JR↗
NASA NTRS1957

Hydrodynamic characteristics over a range of speeds up to 80 feet per second of a rectangular modified flat plate having an aspect ratio of 0.25 and operating at several depths of submersion

Results of an investigation of the hydrodynamic characteristics over an extended speed range of a rectangular modified flat plate having an aspect ratio of 0.25 and operating at several depths of submersion are presented. Comparisons between these data and data over a lower speed range on a similar aspect-ratio-0.25 flat plate but having one-half the thickness are presented. These comparisons show no significant differences at the low speeds. At high speeds and high angles of attack, where extensive cavitation was present, the lift coefficients were lower than would have been indicated by the results of the previous investigations and the present investigation at the lower angles of attack. A brief discussion and comparison of ventilation are presented which shows two types of planing bubble formation and the effect of increasing the thickness of the model on the ventilation boundary.

REYNOLDS NUMBER EFFECTS - COMPLETE WINGS↗
NASA NTRS1958

Large-Scale Wind-Tunnel Tests of an Airplane Model with an Unswept, Aspect-Ratio-10 Wing, Two Propellers, and Blowing Flaps

An investigation was made to determine the lifting effectiveness and flow requirements of blowing over the trailing-edge flaps and ailerons on a large-scale model of a twin-engine, propeller-driven airplane having a high-aspect-ratio, thick, straight wing. With sufficient blowing jet momentum to prevent flow separation on the flap, the lift increment increased for flap deflections up to 80 deg (the maximum tested). This lift increment also increased with increasing propeller thrust coefficient. The blowing jet momentum coefficient required for attached flow on the flaps was not significantly affected by thrust coefficient, angle of attack, or blowing nozzle height.

Griffin, Roy N., Jr.↗
DOE OSTI2025

Competing conduction mechanisms in high performance carbon nanotube fibers

The performance of carbon nanotube (CNT) cables, a contender for copper-wire replacement, is tied to its metallic and semi-conducting-like conductivity responses with temperature; the origin of the semi-conducting-like response however is an underappreciated incongruity in literature. With controlled aspect-ratio and doping-degree, over 61 unique cryogenic experiments including anisotropy and Hall measurements, CNT cable performance is explored at extreme temperatures (65 mK) and magnetic-fields (60 T). A semi-conducting-like conductivity response with temperature becomes temperature-independent approaching absolute-zero, uniquely demonstrating for the first time the necessity of heterogeneous fluctuation induced tunneling; complete de-doping leads to localized hopping, contrasting graphite's pure metallic-like response. High-field magneto-resistance (including novel +22 % longitudinal magneto-resistance near room-temperature) is analyzed with hopping and classical two-band models, both yielding a similar parameter useful for conductor development. Varying field-orientation angle uncovers significant two- and four-fold symmetries that are shown to be from Aharonov-Bohm-like corrections to the curvature-induced bandgap, a first for macroscale CNT fibers. Tight-binding calculations using Green's Function formalism model the largest, coherent transport to-date in commensurate CNT bundles in magnetic-field, revealing non-uniform transmission across bundle cross-sections with doping restoring uniformity; independent of doping, transport in bundle-junction-bundle systems are predominantly from CNTs adjacent to the other bundle—demonstrating that smaller bundles are more efficient for electronic transport. The final impact is predicting the ultimate conductivity of heterogeneous CNT cables using temperature and field-dependent transport, surpassing conductivity of traditional metals.

36 MATERIALS SCIENCE↗
NASA NTRS1960

Low-Speed Investigation of a Full-Span Internal-Flow Jet-Augmented Flap on a High-Wing Model with a 35 deg Swept Wing of Aspect Ratio 7.0

An investigation of a full-span 17-percent-chord internal-flow jet-augmented flap on an aspect-ratio-7.0 wing with 35 deg of sweepback has been made in the Langley 300-MPH 7- by 10-foot tunnel. Blowing over the conventional elevator and blowing down from a nose jet were investigated as a means of trimming the large diving moments at the high momentum and high lift coefficients. The results of the investigation showed that the model with the horizontal tail 0.928 mean aerodynamic chord above the wing-chord plane was stable to the maximum lift coefficient. The large diving-moment coefficients could be trimmed either with a downward blowing nose jet or by blowing over the elevator. Neither the downward blowing nose jet nor blowing over the elevator greatly affected the static longitudinal stability of the model. Trimmed lift coefficients up to 8.8 with blowing over the elevator and up to 11.4 with blowing down at the nose were obtained when the flap was deflected 70 deg and the total momentum coefficients were 3.26 and 4.69.

Turner, Thomas R.↗
DOE OSTI2026

Disruption modelling for engineering and physics design of ST-E1 fusion power plant

Plasma disruptions represent a critical challenge for high-performance tokamak operations, as they can compromise machine integrity and reduce operational availability. Although future fusion devices essentially need to incorporate strategies to minimise disruption occurrence, complete avoidance remains unattainable. Consequently, assessing and characterising unmitigated disruption consequences is fundamental for the design and qualification of next-generation fusion power plants. This work supports the pre-conceptual design of ST-E1, a low aspect-ratio Tokamak Fusion Power Plant developed by Tokamak Energy Ltd., by presenting a comprehensive disruption modelling approach applied across different design stages. The methodology integrates both physics and engineering considerations to evaluate the impact of disruptions on machine performance and structural integrity. From an engineering perspective, several ST-E1 layout options were analysed to investigate the electromagnetic response of key components under disruption-induced loads, enabling comparison between alternative design solutions. On the physics side, a broad set of disruption scenarios was explored, scanning operational space parameters, plasma-material interactions, and associated thermal loads. Furthermore, the study examined variations in disruption behaviour arising from different reference equilibria, focusing on a range starting from Double Null to Single Null configurations, reflecting the increasing up-down asymmetry consequences. The results reveal significant contrasts in plasma dynamics and structures electromagnetic behaviour between configurations, highlighting the importance of disruption modelling in guiding design choices. These analyses have proven instrumental in shaping ST-E1 development, offering critical insights for mitigating risks and optimising future fusion power plant designs.

Borowiec, Katarzyna [ORNL] (ORCID:0000000335911739↗
DOE OSTI2026

The impact of kinetic and global effects on ideal ballooning 2nd stable pedestals of conventional and low aspect-ratio tokamaks

The EPED model (Snyder et al 2011 Nucl. Fusion 51 103016) has had success in describing the pedestal structure of Type-I ELM and QH-mode plasmas in tokamaks, by combining kinetic ballooning mode (KBM) and peeling–ballooning (PB) constraints. Within EPED, the KBM constraint is often approximated by a technique using calculated ideal ballooning mode (IBM) thresholds, fit to a functional form designed to capture non-local effects. It has been noted that quantitative differences between local ideal MHD and gyro-kinetic (GK) ballooning stability can be larger at low aspect ratio. KBM critical pedestals are consistent with observations in initial studies on conventional and spherical tokamaks. In this work, the application of a reduced model for the calculation of the kinetic ballooning stability boundary is presented based on a novel and newly developed gyro-fluid system (GFS) code (Staebler et al 2023 Phys. Plasmas 30 102501). GFS is observed to capture KBMs in DIII-D as well as the NSTX pedestals, opening a route to integrating this model into EPED. Finally, high but finite $n$ global ballooning modes are observed to limit the access to the local 2nd stability and thus provide a transport mechanism that constrains the pedestal evolution with $β_{p,\textrm{ped}}$. The high $n$ global ballooning stability is approximated by its ideal MHD analog using ELITE. It is shown that nearly-local high $n$ modes with $k_yρ_s$ ~ $0.25 - 0.5$ can provide a proxy for the critical $β_{p,\textrm{ped}}$ when a 2nd stable access exists on DIII-D plasmas. The use of GFS and ELITE scaling in EPED provides improved agreement to EPED1 in an initial comparison with DIII-D pedestal data.

Anastopoulos Tzanis, Michail Savvas [Oak Ridge Nat↗
NASA NTRS1959

An Experimental Investigation of the Effect of a Canard Control on the Lift, Drag, and Pitching Moment of an Aspect-Ratio 2.0 Triangular Wing Incorporating a Form of Conical Camber

The results of an experimental investigation to determine the effect of a canard control on the lift, drag, and pitching-moment characteristics of an aspect-ratio-2.0 triangular wing incorporating a form of conical camber are presented. The canard had a triangular plan form of aspect ratio 2.0 and was mounted in the extended chord plane of the wing. The ratio of the area of the exposed canard panels to the total wing area was 6.9 percent, and the ratio of the total areas was 12.9 percent. Data were obtained at Mach numbers from 0.70 to 2.22 through an angle-of-attack range from -6 deg to +18 deg with the canard on, and with the canard off. To provide a basis for comparison, the canard was also tested with a symmetrical wing having the same plan form, aspect ratio, and thickness distribution as the cambered wing. The results of the investigation showed that at the high subsonic speeds the gain in maximum lift-drag ratio achieved by camber was considerably reduced by the addition of a canard. At the supersonic speeds, the addition of the canard did not change the effect of camber on the maximum lift-drag ratios.

Menees, Gene P.↗
NASA NTRS1958

Lift, Drag, and Pitching Moment of an Aspect-Ratio-2 Triangular Wing with Leading-Edge Flaps Designed to Simulate Conical Camber

An investigation was conducted to determine the effectiveness of leading-edge flaps in reducing the drag at lifting conditions of a triangular wing of aspect ratio 2.0. The flaps, deflected to simulate conically cambered wings having a wide range of design lift coefficients, were tested over a Mach number range of 0.70 to 2.22 through an angle-of-attack variation from -6 deg to +18 deg at a constant Reynolds number of 3.68 million based on the wing mean aerodynamic chord. A symmetrical wing of the same plan form and aspect ratio was also tested to provide a basis for comparison. The experimental results showed that with the flaps in the undeflected position, a small amount of fixed leading-edge droop incorporated over the outboard 5 percent of the wing semispan was as effective at high subsonic speeds as conical camber in improving the maximum lift-drag ratio above that of the symmetrical wing. At supersonic speeds, the penalty in minimum drag above that of the symmetrical wing was less than that incurred by conical camber. Deflecting the leading-edge flaps about the hinge line through 80 percent of the wing semispan resulted in further improvements of the drag characteristics at lift coefficients above 0.20 throughout the Mach number range investigated. The lift and pitching-moment characteristics were not significantly affected by the leading-edge flaps.

Menees, Gene P.↗