SEARCH · Engineering Papers

Results for “drag estimation”

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 631 records · Page 35

All sources NASA NTRS DOE OSTI

NASA NTRS1992

Venus lower thermosphere studies

Studies undertaken in this project have sought to understand lower thermospheric structure and dynamics (less than or equal to 145 km), particularly the processes responsible. This is a region just below the reach of in-situ instruments onboard PVO (Pioneer Venus Orbiter) during the first few diurnal cycles. PVO remote airglow observations (nitric oxide, O2, visible, O 1304A) have been coupled with ground-based observations (CO densities, winds, temperatures, O2 IR nightglow) to address the behavior of lower thermospheric winds and chemistry over 95 to 150 km. This interpretation of PVO and related data is accomplished by using the NCAR Venus thermospheric general circulation model (VTGCM) (Bougher et al., 1988; 1990). This model has been modified over the last two years to improve its ability to calculate O, CO, and O2 densities, temperatures, nightglow, and subsolar-to-antisolar and zonal winds over 95 to 150 km (Bougher and Borucki, 1992). Our VTGCM studies show that: (1) O2 visible and IR nightglow distributions can be used to trace lower thermosphere / upper mesosphere winds over 100-130 km. Typically, weak zonal winds (less than or equal to 25 m/sec) and nightglow maximum patches near 0100 LT prevail. Occasionally, strong zonal winds (30-60 m/sec) and airglow patches peaking near 0300 LT characterize the Venus lower thermosphere. (2) It is clear that the dynamics of the Venus 90-130 km region is highly variable on time scales as short as an hour. This is most likely due to the time variable nature of upward propagating gravity waves, which grow in amplitude and eventually break. The resulting turbulence gives rise to local time variable eddy diffusion and momentum drag, both of which strongly impact global density and nightglow distributions. (3) The oxygen chemistry (O, O2, etc.) over 90-120 km is strongly dependent on HO(x) and CLO(x) tracer species that must be properly included in any coupled chemical dynamical model. (4) The density profiles of light species (O, CO, N, He) are strongly affected by large-scale transport by the winds. Strong eddy diffusion is not a suitable model parameterization for approximating these light species, especially for extrapolation into the region below 140 km where PVO in-situ data is lacking. Instead, the fully coupled chemical dynamical VTGCM model should be used to improve estimates of densities within the VTS3 empirical model (Hedin et al., 1983) below 140 km.

Bougher, Stephen W.↗

NASA NTRS1997

The Interplay Between Transpiration and Runoff Formulations in Land Surface Schemes Used with Atmospheric Models

The Project for Intercomparison of Land-surface Parameterization Schemes (PILPS) has shown that different land surface models (LSMS) driven by the same meteorological forcing can produce markedly different surface energy and water budgets, even when certain critical aspects of the LSMs (vegetation cover, albedo, turbulent drag coefficient, and snow cover) are carefully controlled. To help explain these differences, the authors devised a monthly water balance model that successfully reproduces the annual and seasonal water balances of the different PILPS schemes. Analysis of this model leads to the identification of two quantities that characterize an LSM's formulation of soil water balance dynamics: (1) the efficiency of the soil's evaporation sink integrated over the active soil moisture range, and (2) the fraction of this range over which runoff is generated. Regardless of the LSM's complexity, the combination of these two derived parameters with rates of interception loss, potential evaporation, and precipitation provides a reasonable estimate for the LSM's simulated annual water balance. The two derived parameters shed light on how evaporation and runoff formulations interact in an LSM, and the analysis as a whole underscores the need for compatibility in these formulations.

Koster, Rindal D.↗

NASA NTRS1993

On the delivery of planetesimals to a protoplanet in the solar nebula

A planetesimal moving in the solar nebula experiences an aerodynamic drag which causes its orbit to circularize and shrink. However resonant perturbations from a protoplanet interior to the planetesimal's orbit can counteract both the orbital decay and the damping of the eccentricity: the planetesimal can be captured into an orbital resonance and its eccentricity pumped up to an equilibrium value. The resonance trapping phenomenon is sensitive to several factors and we elaborate on these below. Orbital resonances form (partial) barriers to the transport of planetesimals into the feeding zone of the protoplanet. Here we report on a systematic study of the idealized system of a single protoplanet of mass much larger than the masses of the planetesimals, comparing relevant analytic estimates with numerical simulations. Our principal conclusion is that in a gas-rich environment, the bulk of the solid material delivered to the feeding zone of the protoplanet is in the form of bodies of small radius.

Malhotra, Renu↗

NASA NTRS2022

Seasonal Variation of Thermospheric Composition Observed by NASA GOLD

We examine characteristics of the seasonal variation of thermospheric composition using column number density ratio ∑O/N(2) observed by the NASA Global Observations of Limb and Disk (GOLD) mission from low-mid to mid-high latitudes. We also use ∑O/N(2) derived from the Global Ultraviolet Imager (GUVI) limb measurements onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite and estimated by the NRLMSISE-00 empirical model to aid our investigation. We found that the ∑O/N(2) seasonal variation is hemispherically asymmetric: in the southern hemisphere, it exhibits the well-known annual and semiannual pattern, with highs near the equinoxes, and primary and secondary lows near the solstices. In the northern hemisphere, it is dominated by an annual variation, with a minor semiannual component with the highs shifting toward the wintertime. We also found that the durations of the December and June solstice seasons in terms of ∑O/N(2) are highly variable with longitude. Our hypothesis is that ion-neutral collisional heating in the equatorial ionization anomaly region, ion drag, and auroral Joule heating play substantial roles in this longitudinal dependency. Finally, the rate of change in ∑O/N(2) from one solstice season to the other is dependent on latitude, with more dramatic changes at higher latitudes.

thermosphere↗

NASA NTRS1983

Lorentz forces on the dust in Jupiter's ring

The paths of dust particles in the Jovian ring are investigated using a numerical integration program, including the acceleration due to gravity and the Lorentz and drag accelerations arising from the motions of the charged dust through the Jovian plasma. It is determined that the orbit of a 2.5 micron radius spherical dust particle with a density of 2 g/cu cm -10V will become significantly perturbed. The ring will tend to warp northwards near 130-160 deg longitude, with the maximum excursion of the Jupiter ring grains equalling about 0.1 deg (consistent with a distance of 220 km above the equatorial plane). It is found that either the particles are larger or the voltages on them less than what has been determined by previous investigators, while the plasma near the ring may be considerably cooler than was estimated. Calculations show that particles of 0.3 micron with -10 V potentials are spread from 1.68-1.98 of the radius of Jupiter and inclined up to 7 deg out of the equatorial plane. The paths of these particles do not follow Keplerian orbits, and the particle positions are not symmetric about the equatorial plane. Particles of 0.4 micron radius have less asymmetric orbits than 0.3 micron particles, while particles less than 0.2 micron are perturbed into Jupiter cloudtops within a few tens of hours.

Consolmagno, G. J.↗

NASA NTRS2017

The Impact Trajectory of Asteroid 2008 TC3

Asteroid 2008 TC3 was the rst asteroid ever discovered before reaching Earth. By using the almost 900 astrometric observations acquired prior to impact we estimate the trajectory of 2008 TC3 and the ground-track of the impact location as a function of altitude. For a reference altitude of 100 km the impact location 3- formal uncertainty is a 1.4 km 0.15 km ellipse with a semimajor axis azimuth of 105. We analyze the contribution of modeling errors and nd that the second-order zonal harmonics of the Earth gravity eld moves the ground-track by more than 1 km and the location along the ground-track by more than 2 km. Non-zonal and higher order harmonics only change the impact prediction by less than 20 m. The contribution of the atmospheric drag to the trajectory of 2008 TC3 is at the numerical integration error level, a few meters, down to an altitude of 50 km. Integrating forward to lower altitudes and ignoring the break-up of 2008 TC3, the atmospheric drag causes an along-track error that can be as large as a few kilometers at sea level. The locations of the recovered meteorites is consistent with the computed ground-track.

Trajectory↗

NASA NTRS2019

Sketch-To-Solution: An Exploration of Viscous CFD with Automatic Grids

Numerical simulation of the Reynolds-averaged Navier–Stokes (RANS) equations has become a critical tool for the design of aerospace vehicles. However, the issues that affect the grid convergence of three dimensional RANS solutions are not completely understood, as documented in the AIAA Drag Prediction Workshop series. Grid adaption methods have the potential for increasing the automation and discretization error control of RANS solutions to impact the aerospace design and certification process. The realization of the CFD Vision 2030 Study includes automated management of errors and uncertainties of physics-based, predictive modeling that can set the stage for ensuring a vehicle is in compliance with a regulation or specification by using analysis without demonstration in flight test (i.e., certification or qualification by analysis). For example, the Cart3D inviscid analysis package has automated Cartesian cut-cell gridding with output-based error control. Fueled by recent advances in the fields of anisotropic grid adaptation, error estimation, and geometry modeling, a similar work flow is explored for viscous CFD simulations; where a CFD application engineer provides geometry, boundary conditions, and flow parameters, and the sketch-to-solution process yields a CFD simulation through automatic, error-based, grid adaptation.

Kleb, William L.↗

NASA NTRS1993

The effect of high lift to drag ratio on aerobraking

This work reviews the use of aerodynamic forces to modify the velocity, and therefore, the orbital path of vehicles due to transit through planetary atmospheres, especially when high values of lift can be generated. The concepts of aerobraking and aerocapture are examined, and the limiting factors are discussed. The use of high L/D vehicles, such as hypersonic waveriders, is examined, and the advantages and disadvantages of their use for aerocapture are addressed. This preliminary study of non-optimized aerocapture trajectories suggests that entrance velocities at Mars can be 10 - 12 km/sec for a waverider while sustaining acceptable loads of about 3 - 4 Earth G's over a 3 minute period, diminishing to less than 1 G in about 15 minutes. The entrance velocities are greater than those for a more conventional biconic configuration with similar deceleration loads sustained. The convective heating rate on the waverider, increased due to the higher velocities and sharp leading edges, has an estimated upper bound of 14000 W/sq cm and a corresponding temperature of about 7500 degrees K.

Crouse, Patrick↗

NASA NTRS1985

Thermal design of AOTV heatshields for a conical drag brake

Results are presented from an on-going study of the thermal performance of thermal protection systems for a conical drag brake type AOTV. Three types of heatshield are considered: rigid ceramic insulation, flexible ceramic blankets, and ceramic cloths. The results for the rigid insulation apply to other types of AOTV as well. Charts are presented in parametric form so that they may be applied to a variety of missions and vehicle configurations. The parameters considered include: braking maneuver heat flux and total heat load, heatshield material and thickness, heatshield thermal mass and conductivity, absorptivity and emissivity of surfaces, thermal mass of support structure, and radiation transmission through thin heatshields. Results of temperature calculations presented show trends with and sensitivities to these parameters. The emphasis is on providing information that will be useful in estimating the minimum required mass of these heatshield materials.

Pitts, W. C.↗

NASA NTRSDate not supplied

Conceptual Integration Studies of Localized Active Flow Control on the Wing of a Commercial Aircraft

A study of conceptual integration and performance of localized active flow control technology onto wings of short-to-medium-range project passenger airplanes is summarized. Using predicted aerodynamic performance improvement opportunities on a computational fluid dynamics reference aircraft, this paper presents the estimated performance opportunities for conceptual implementation of studied wing localized active flow control technology for low-speed (takeoff and landing) application on a Project Research Aircraft configuration. Using conceptual active flow control systems and structural integration weight penalties for studied concepts, potential relevant net performance benefits can be obtained with reliable active flow control in takeoff and landing. The conceptual integration study identifies potential localized wing active flow control application opportunities for high-lift conditions using energy sources available on modern aircraft. Material benefits are estimated for takeoff and landing configurations for selected localized wing active flow control applications. The study concluded that substantial low-speed Maximum Lift and Lift/Drag related performance improvements may be possible with localized wing high-lift active flow control systems powered by auxiliary power unit, engine bleed, or electrical compressors - with due consideration of integration and weight impacts as well as availability requirements of such systems.

drag reduction↗

NASA NTRS1994

Toward Real Time Neural Net Flight Controllers

NASA Ames Research Center has an ongoing program in neural network control technology targeted toward real time flight demonstrations using a modified F-15 which permits direct inner loop control of actuators, rapid switching between alternative control designs, and substitutable processors. An important part of this program is the ACTIVE flight project which is examining the feasibility of using neural networks in the design, control, and system identification of new aircraft prototypes. This paper discusses two research applications initiated with this objective in mind: utilization of neural networks for wind tunnel aircraft model identification and rapid learning algorithms for on line reconfiguration and control. The first application involves the identification of aerodynamic flight characteristics from analysis of wind tunnel test data. This identification is important in the early stages of aircraft design because complete specification of control architecture's may not be possible even though concept models at varying scales are available for aerodynamic wind tunnel testing. Testing of this type is often a long and expensive process involving measurement of aircraft lift, drag, and moment of inertia at varying angles of attack and control surface configurations. This information in turn can be used in the design of the flight control systems by applying the derived lookup tables to generate piece wise linearized controllers. Thus, reduced costs in tunnel test times and the rapid transfer of wind tunnel insights into prototype controllers becomes an important factor in more efficient generation and testing of new flight systems. NASA Ames Research Center is successfully applying modular neural networks as one way of anticipating small scale aircraft model performances prior to testing, thus reducing the number of in tunnel test hours and potentially, the number of intermediate scaled models required for estimation of surface flow effects.

Jorgensen, C. C.↗

NASA NTRS1999

Sonic Boom Prediction and Minimization of the Douglas Reference OPT5 Configuration

Conventional CFD methods and grids do not yield adequate resolution of the complex shock flow pattern generated by a real aircraft geometry. As a result, a unique grid topology and supersonic flow solver was developed at Northrop Grumman based on the characteristic behavior of supersonic wave patterns emanating from the aircraft. Using this approach, it was possible to compute flow fields with adequate resolution several body lengths below the aircraft. In this region, three-dimensional effects are diminished and conventional two-dimensional modified linear theory (MLT) can be applied to estimate ground pressure signatures or sonic booms. To accommodate real aircraft geometries and alleviate the burdensome grid generation task, an implicit marching multi-block, multi-grid finite-volume Euler code was developed as the basis for the sonic boom prediction methodology. The Thomas two-dimensional extrapolation method is built into the Euler code so that ground signatures can be obtained quickly and efficiently with minimum computational effort suitable to the aircraft design environment. The loudness levels of these signatures can then be determined using a NASA generated noise code. Since the Euler code is a three-dimensional flow field solver, the complete circumferential region below the aircraft is computed. The extrapolation of all this field data from a cylinder of constant radius leads to the definition of the entire boom corridor occurring directly below and off to the side of the aircraft's flight path yielding an estimate for the entire noise "annoyance" corridor in miles as well as its magnitude. An automated multidisciplinary sonic boom design optimization software system was developed during the latter part of HSR Phase 1. Using this system, it was found that sonic boom signatures could be reduced through optimization of a variety of geometric aircraft parameters. This system uses a gradient based nonlinear optimizer as the driver in conjunction with a computationally efficient Euler CFD solver (NIIM3DSB) for computing the three-dimensional near-field characteristics of the aircraft. The intent of the design system is to identify and optimize geometric design variables that have a beneficial impact on the ground sonic boom. The system uses a simple wave drag data format to specify the aircraft geometry. The geometry is internally enhanced and analytic methods are used to generate marching grids suitable for the multi-block Euler solver. The Thomas extrapolation method is integrated into this system, and hence, the aircraft's centerline ground sonic boom signature is also automatically computed for a specified cruise altitude and yields the parameters necessary to evaluate the design function. The entire design system has been automated since the gradient based optimization software requires many flow analyses in order to obtain the required sensitivity derivatives for each design variable in order to converge on an optimal solution. Hence, once the problem is defined which includes defining the objective function and geometric and aerodynamic constraints, the system will automatically regenerate the perturbed geometry, the necessary grids, the Euler solution, and finally the ground sonic boom signature at the request of the optimizer.

Siclari, Michael J.↗

NASA NTRS2007

Inflatable Aerocapture Decelerators for Mars Orbiters

A multi-disciplinary research program was recently completed, sponsored by NASA Marshall Space Flight Center, on the subject of aerocapture of spacecraft weighing up to 5 metric tons at Mars. Heavier spacecraft will require deployable drag area beyond the dimensional limits of current and planned launch fairings. This research focuses on the approach of lightweight inflatable decelerators constructed with thin films, using fiber reinforcement and having a temperature limitation of 500 C. Trajectory analysis defines trajectories for a range of low ballistic coefficients for which convective heat flux is compatible with the material set. Fluid-Structure Interaction (FSI) tools are expanded to include the rarified flow regime. Several non-symmetrical configurations are evaluated for their capability to develop lift as part of the necessary trajectory control strategy. Manufacturing technology is developed for 3-D stretch forming of polyimide films and for tailored fiber reinforcement of thin films. Finally, the mass of the decelerator is estimated and compared to the mass of a traditional rigid aeroshell.

Brown, Glen J.↗

NASA NTRS1979

Recent theoretical developments and experimental studies pertinent to vortex flow aerodynamics, with a view towards design

Recent progress in a research program directed toward an improved vortex flow technology base was reviewed. Analysis methods for conical flow and analysis and design methods for nonconical flows are presented. Applications are made for a variety of planar, nonplanar, and interferring lifting surfaces. Several methods are shown to provide reasonable estimates of over-all forces and moments for simple wing planforms with the suction analogy method currently offering the most versatility for arbitrary configuration applications. For the prediction of surface loadings the free vortex sheet method being developed by Boeing is shown to have considerable promise and further development of this type of method is encouraged. A data base for ogee strake-wing configurations is summarized with an emphasis on the requirements for maximizing the interference lift. A strake planform design procedure is discussed and a first solution (gothic in planview) is integrated with a wing body. The data show the strake to exhibit expected stable vortex characteristics. It was found that, apart from increasing sweep, conically cambered delta wings developed drag levels approaching that of attached flow with increasing either the lift or the wing camber height, lastly, an approximate vortex flow design method, based on the suction analogy, is outlined and an example is given.

Lamar, J. E.↗

NASA NTRS2019

A Kuiper Belt Source for Solar Flare Track-Rich Interplanetary Dust Particles

The presence of solar flare particle tracks in mineral grains within interplanetary dust particles (IDPs) has long been accepted as proof of their extraterrestrial origin [e.g. 1]. The 10-20 micrometers diameter IDPs released by dust producing objects in the solar system (mainly comets and asteroids) spiral in towards the Sun under the influence of Poynting-Robertson (PR) drag forces [2] and accumulate solar flare energetic particle tracks during their journey. The number of IDPs with well-constrained track density measurements is small, owing to the difficulty in the measurements and the lack of appropriatelysized crystals in which to image them. In order to use track densities as a chronometer of space exposure, the track production rate must be known. All previous work relied on track production rates determined by chemical etching techniques [e.g. 3], but tracks in IDPs are measured using TEM imaging. Here we report measurements of track densities in IDPs from both the anhydrous and hydrated IDP groups. Using the track production calibration determined from TEM observations of anorthite and olivine in lunar rock 64455 [4] we estimate space exposure times for these IDPs to constrain their parent body sources.

Keller, L. P.↗

NASA NTRS1976

Tornadoes and other atmospheric vortices

The growth of random vortices in an atmosphere with buoyant instability and vertical wind shear is studied along with the velocities in a single gravity-driven vortex; a frictionless adiabatic model which is supported by laboratory experiments is first considered. The effects of axial drag, heat transfer, and precipitation-induced downdrafts are then calculated. Heat transfer and axial drag tend to have stabilizing effects; they reduce the downdrafts of updrafts due to buoyancy. It is found that downdrafts or tornadic magnitude might occur in negatively-buoyant columns. The radial-inflow velocity required to maintain a given maximum tangential velocity in a tornado is determined by using a turbulent vortex model. Conditions under which radial-inflow velocities become sufficiently large to produce tangential velocities of tornadic magnitude are determined. The radial velocities in the outer regions, as well as the tangential velocities in the inner regions may be large enough to cause damage. The surface boundary layer, which is a region where large radial inflows can occur, is studied, and the thickness of the radial-inflow friction layer is estimated. A tornado model which involves a rotating parent cloud, as well as buoyancy and precipitation effects, is discussed.

Deissler, R. G.↗

NASA NTRSDate not supplied

Hybrid Electric Aircraft with Unlike Engine Degradation

Control solutions are applied to uneven engine performance degradation on a conceptual twin-engine transport-class aircraft. Such degradation can lead to asymmetric thrust, which requires rudder trim to maintain desired aircraft heading. This will increase drag and fuel consumption. With the introduction of hybrid-electric aircraft powertrains, new solutions to unwanted asymmetric thrust can be derived. Four control strategies are demonstrated on the power and propulsion system of such an aircraft. Compared with existing strategies, the methodology proposed in this paper controls electromechanical actuators coupled to engine shafts and balances the thrust produced by both engines potentially leading to a decrease in fuel burn. The engine represented in this study is NASA’s conceptual dual-shaft Advanced Geared Turbofan 30,000 lbf thrust class engine. The conceptual engine is hybridized with electric machines attached to both shafts. Simulation results are presented with various levels of degradation. The control strategies are compared based on fuel burn, thrust symmetry, and estimated system weight.

control↗

NASA NTRSDate not supplied

Hybrid Electric Aircraft with Unlike Engine Degradation

control↗