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Sample records for aerodynamic roughness lengths

  1. RELATIONSHIP BETWEEN THE AERODYNAMIC ROUGHNESS LENGTH AND THE ROUGHNESS DENSITY IN CASES OF LOW ROUGHNESS DENSITY

    EPA Science Inventory

    This paper presents measurements of roughness length performed in a wind tunnel for low roughness density. The experiments were performed with both compact and porous obstacles (clusters), in order to simulate the behavior of sparsely vegetated surfaces.

  2. Influence of aerodynamic roughness length on aeolian processes: Earth, Mars, Venus

    NASA Technical Reports Server (NTRS)

    Blumberg, Dan G.; Greeley, Ronald

    1992-01-01

    The aerodynamic roughness length (z sub 0) is the height at which a wind profile assumes a zero velocity. The lower part of the atmospheric boundary layer will be impeded by friction with the surface. An increase in surface roughness will also increase the shear stress required to initiate particle entrainment by the wind. Bagnold (1941) estimated z sub 0 as being 1/30 of the mean particle size. In Nature, surface roughness is composed of nonerodible elements as well as sand-size erodible particles. To assess z sub 0 values as a function of terrain, field experiments were conducted to obtain wind profiles monitored over natural surfaces at 15 sites in the Mojave Desert, Death Valley, and Nye County, Nevada. These sites span a variety of arid-land terrains, including smooth playas, alluvial fans, and lava flows; z sub 0 values ranged from 0.0001 cm to 1 cm. These values were incorporated in a threshold model and a flux model to assess transport efficiency over such terrains in three planetary environments (Venus, Earth, and Mars), and for particle sizes ranging from 60-500 micron. Threshold and flux are a function of planetary environment, particle density and size (Dp), and z sub 0, and the shear velocity of 1.2 x U sub *t (for Dp = 250 micron and z sub 0 = 0.84). Results show that flux on Mars is approximately 14 g/(cm x s), on Earth it is approximately 3 g/(cm x s), and on Venus 0.5 g/(cm x s). Under all planetary environments, the results also show a dramatic decrease in the flux for particles greater than 200 microns when z sub 0 increases above 0.0085 cm (corresponding to sites consisting of alluvium). When z sub 0 approaches 0.03 cm (corresponding to a mantled pahoehoe lava), the flux diminishes.

  3. Comparison of aerodynamically and model-derived roughness lengths (zo) over diverse surfaces, central Mojave Desert, California, USA

    USGS Publications Warehouse

    MacKinnon, D.J.; Clow, G.D.; Tigges, R.K.; Reynolds, R.L.; Chavez, P.S.

    2004-01-01

    The vulnerability of dryland surfaces to wind erosion depends importantly on the absence or the presence and character of surface roughness elements, such as plants, clasts, and topographic irregularities that diminish wind speed near the surface. A model for the friction velocity ratio has been developed to account for wind sheltering by many different types of co-existing roughness elements. Such conditions typify a monitored area in the central Mojave Desert, California, that experiences frequent sand movement and dust emission. Two additional models are used to convert the friction velocity ratio to the surface roughness length (zo) for momentum. To calculate roughness lengths from these models, measurements were made at 11 sites within the monitored area to characterize the surface roughness element. Measurements included (1) the number of roughness species (e.g., plants, small-scale topography, clasts), and their associated heights and widths, (2) spacing among species, and (3) vegetation porosity (a measurement of the spatial distribution of woody elements of a plant). Documented or estimated values of drag coefficients for different species were included in the modeling. At these sites, wind-speed profiles were measured during periods of neutral atmospheric stability using three 9-m towers with three or four calibrated anemometers on each. Modeled roughness lengths show a close correspondence (correlation coefficient, 0.84-0.86) to the aerodynamically determined values at the field sites. The geometric properties of the roughness elements in the model are amenable to measurement at much higher temporal and spatial resolutions using remote-sensing techniques than can be accomplished through laborious ground-based methods. A remote-sensing approach to acquire values of the modeled roughness length is particularly important for the development of linked surface/atmosphere wind-erosion models sensitive to climate variability and land-use changes in areas such

  4. Characterizing aerodynamic roughness length (z0) for a debris-covered glacier: aerodynamic inversion and SfM-derived microtopographic approaches

    NASA Astrophysics Data System (ADS)

    Miles, Evan; Steiner, Jakob; Brun, Fanny; Detert, Martin; Buri, Pascal; Pellicciotti, Francesca

    2016-04-01

    Aerodynamic surface roughness is an essential parameter in surface energy balance studies. While actual measurements on bare ice glaciers are rare, a wide range of literature values exist for ice and snow surfaces. There are very few values suggested for debris covered glaciers and actual measurements are even scarcer - studies instead optimize z0 or use a reference value. The increased use of photogrammetry on glaciers provides an opportunity to characterize the range of z0 values meaningful for debris-covered glaciers. We apply Agisoft's Structure-from-Motion process chain to produce high resolution DEMs for five 1m x 1m plots (1mm resolution) with differing grain-size distributions, as well as a large ~180m x ~180m depression (5cm) on Lirung Glacier in the Nepalese Himalayas. For each plot, we calculate z0 according to transect-based microtopographic parameterisations. We compare individual-transect z0 estimates based on profile position and direction, and develop a grid version of the algorithms aggregating height data from all bidirectional transects. This grid approach is applied to our larger DEM to characterize the variability of z0 across the study site for each algorithm. For the plot DEMs, z0 estimated by any algorithm varies by an order of magnitude based on transect position. Although the algorithms reproduce the same variability among transects and plots, z0 estimates vary by an order of magnitude between algorithms. For any algorithm, however, we find minimal difference between cross- and down-glacier profile directions. At the basin scale, results from different algorithms are strongly correlated and results are more closely clustered with the exception of the Rounce (2015) algorithm, while any algorithm's values range by two orders of magnitude across the study depression. The Rounce algorithm consistently produced the highest z0 values, while the Lettau (1969) and Munro (1989) methods produced the lowest values, and use of the Nield (2013

  5. Simulation of the mineral dust emission over Northern Africa and Middle East using an aerodynamic roughness length map derived from the ASCAT/PARASOL

    NASA Astrophysics Data System (ADS)

    Basart, Sara; Jorba, Oriol; Pérez García-Pando, Carlos; Prigent, Catherine; Baldasano, Jose M.

    2014-05-01

    Aeolian aerodynamic roughness length in arid regions is a key parameter to predict the vulnerability of the surface to wind erosion, and, as a consequence, the related production of mineral aerosol (e.g. Laurent et al., 2008). Recently, satellite-derived roughness length at the global scale have emerged and provide the opportunity to use them in advanced emission schemes in global and regional models (i.e. Menut et al., 2013). A global map of the aeolian aerodynamic roughness length at high resolution (6 km) is derived, for arid and semi-arid regions merging PARASOL and ASCAT data to estimate aeolian roughness length. It shows very good consistency with the existing information on the properties of these surfaces. The dataset is available to the community, for use in atmospheric dust transport models. The present contribution analyses the behaviour of the NMMB/BSC-Dust model (Pérez et al., 2011) when the ASCAT/PARASOL satellite-derived global roughness length (Prigent et al, 2012) and the State Soil Geographic database Food and Agriculture Organization of the United Nations (STATSGO-FAO) soil texture data set (based on wet techniques) is used. We explore the sensitivity of the drag partition scheme (a critical component of the dust emission scheme) and the dust vertical fluxes (intensity and spatial patterns) to the roughness length. An annual evaluation of NMMB/BSC-Dust (for the year 2011) over Northern Africa and the Middle East using observed aerosol optical depths (AODs) from Aerosol Robotic Network sites and aerosol satellite products (MODIS and MISR) will be discussed. Laurent, B., Marticorena, B., Bergametti, G., Leon, J. F., and Mahowald, N. M.: Modeling mineral dust emissions from the Sahara desert using new surface properties and soil database, J. Geophys. Res., 113, D14218, doi:10.1029/2007JD009484, 2008. Menut, L., C. Pérez, K. Haustein, B. Bessagnet, C. Prigent, and S. Alfaro, Impact of surface roughness and soil texture on mineral dust emission

  6. Intercomparison of Methods for the Simultaneous Estimation of Zero-Plane Displacement and Aerodynamic Roughness Length from Single-Level Eddy-Covariance Data

    NASA Astrophysics Data System (ADS)

    Graf, Alexander; van de Boer, Anneke; Moene, Arnold; Vereecken, Harry

    2014-05-01

    We applied three approaches to estimate the zero-plane displacement through the aerodynamic measurement height (with and being the measurement height above the surface), and the aerodynamic roughness length , from single-level eddy covariance data. Two approaches (one iterative and one regression-based) were based on the universal function in the logarithmic wind profile and yielded an inherently simultaneous estimation of both and . The third approach was based on flux-variance similarity, where estimation of and consecutive estimation of are independent steps. Each approach was further divided into two methods differing either with respect to the solution technique (profile approaches) or with respect to the variable (variance of vertical wind and temperature, respectively). All methods were applied to measurements above a large, growing wheat field where a uniform canopy height and its frequent monitoring provided plausibility limits for the resulting estimates of time-variant and . After applying, for each approach, a specific data filtering that accounted for the range of conditions (e.g. stability) for which it is valid, five of the six methods were able to describe the temporal changes of roughness parameters associated with crop growth and harvest, and four of them agreed on to within 0.3 m most of the time. Application of the same methods to measurements with a more heterogeneous footprint consisting of fully-grown sugarbeet and a varying contribution of adjacent harvested fields exhibited a plausible dependence of the roughness parameters on the sugarbeet fraction. It also revealed that the methods producing the largest outliers can differ between site conditions and stability. We therefore conclude that when determining for canopies with unknown properties from single-level measurements, as is increasingly done, it is important to compare the results of a number of methods rather than rely on a single one. An ensemble average or median of the results

  7. Upscaling analysis of aerodynamic roughness length based on in situ data at different spatial scales and remote sensing in north Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Sun, Genhou; Hu, Zeyong; Wang, Jiemin; Xie, Zhipeng; Lin, Yun; Huang, Fangfang

    2016-07-01

    The aerodynamic roughness length (z0m) is a crucial parameter in quantifying momentum, sensible and latent heat fluxes between land surface and atmosphere, and it depends greatly on spatial scales. This paper presents a tentative study on the upscaling analysis of z0m in the north Tibetan Plateau based on in situ data from eddy covariance (EC) and large aperture scintillometer (LAS) and leaf area index (LAI) of MODerate-resolution Imaging Spectroradiometer (MODIS) with 250 m and 2 km spatial resolutions. The comparison of z0m calculated from EC (z0m_EC) and LAS (z0m _LAS) data indicates that z0m at both scales has apparent seasonal variations and is in good agreement with the LAI result. However, z0m_LAS is higher than z0m_EC, which is attributed to the differences in roughness elements in their footprints. An upscaling relationship for z0m is developed with z0m_EC, z0m _LAS and LAI with 250 m spatial resolution of MODIS. In addition, an altitude correction factor is introduced into the vegetation height estimation equation because the cold environment in the north Tibetan Plateau, which is due to its high altitude, has a strong influence on vegetation height. The z0m retrieval with 250 m spatial resolution in the rain season is validated with z0m_EC at sites Nagqu/Amdo, Nagqu/MS3478 and Nagqu/NewD66, and the agreement is acceptable. The spatial distribution of z0m retrievals at small spatial scale in the north Tibetan Plateau from June to September 2012 shows that the z0m values are less than 0.015 m in most areas, with the exception of the area in the southeast part, where z0m reaches 0.025 m owing to low altitudes. The z0m retrievals at large spatial scale in the north Tibetan Plateau from June to September 2012 range from 0.015 to 0.065 m, and high values appear in the area with low altitudes. The spatial distribution and frequency statistics of z0m retrievals at both spatial scales reveal the influence of altitude and LAI on the z0m in the north Tibetan

  8. An Upscaling Analysis on Aerodynamic Roughness Length in North Tibetan Plateau based on Eddy Covariance, Large Aperture Scitillometer Data and Remote Sensing Product

    NASA Astrophysics Data System (ADS)

    SUN, G.; Hu, Z.; Fanglin, S.

    2015-12-01

    Abstract: Aerodynamic roughness length (z0m) is a crucial parameter in quantifying momentum, sensible heat, and latent heat fluxes between atmosphere and land surface, and depends greatly on spatial scales. This paper presents a tentative study in upscaling of z0m in North Tibetan Plateau, based on ground measurement data of different spatial scales from eddy covariance (EC) and large aperture scintillometer (LAS) and NDVI products from MODIS with 250m and 2km spatial resolutions. The comparison of z0m calculated from EC and LAS data indicates that the z0m values at both scales have apparent seasonal variations, and are in good agreement with that of NDVI. However, z0m_LAS is higher than z0m_EC, which is attributed to the differences of roughness elements in their footprints. An upscaling relationship about z0m was established with z0m observations and NDVI products of MODIS.In addition, an altitude correction factor was introduced into vegetation height estimation with NDVI, because the low temperature environment in North Tibetan Plateau due to its high altitude has strong influence on vegetation heights.The z0m retrievals with NDVI products with 250m spatial resolutions from June to September are validated with ground z0m results of Naqu/Amdo, Naqu/MS3478 and Naqu/NewD66 and the agreement is acceptable. The spatial distribution of z0m at 250m spatial resolutions in North Tibetan Plateau from June to September shows that z0m values are below 0.015m in most area, except the area in the southeast part where z0m values reach 0.025m due to lower altitudes. The z0m retrievals at 2km spatial resolutions of the same period range from 0.015 to 0.065m, and high values appear in the area with lower altitudes.The z0m retrievals at both spatial scales are affected by altitude, indicating the uniqueness of Tibetan Plateau. Frequency statistics on z0m retrievals at both spatial resolutions from June to September, 2012 shows obvious typical monthly changes in monsoon season.

  9. Parameterization of Vegetation Aerodynamic Roughness of Natural Regions Satellite Imagery

    NASA Technical Reports Server (NTRS)

    Jasinski, Michael F.; Crago, Richard; Stewart, Pamela

    1998-01-01

    Parameterizations of the frontal area index and canopy area index of natural or randomly distributed plants are developed, and applied to the estimation of local aerodynamic roughness using satellite imagery. The formulas are expressed in terms of the subpixel fractional vegetation cover and one non-dimensional geometric parameter that characterizes the plant's shape. Geometrically similar plants and Poisson distributed plant centers are assumed. An appropriate averaging technique to extend satellite pixel-scale estimates to larger scales is provided. The parameterization is applied to the estimation of aerodynamic roughness using satellite imagery for a 2.3 sq km coniferous portion of the Landes Forest near Lubbon, France, during the 1986 HAPEX-Mobilhy Experiment. The canopy area index is estimated first for each pixel in the scene based on previous estimates of fractional cover obtained using Landsat Thematic Mapper imagery. Next, the results are incorporated into Raupach's (1992, 1994) analytical formulas for momentum roughness and zero-plane displacement height. The estimates compare reasonably well to reference values determined from measurements taken during the experiment and to published literature values. The approach offers the potential for estimating regionally variable, vegetation aerodynamic roughness lengths over natural regions using satellite imagery when there exists only limited knowledge of the vegetated surface.

  10. Time Series Vegetation Aerodynamic Roughness Fields Estimated from MODIS Observations

    NASA Technical Reports Server (NTRS)

    Borak, Jordan S.; Jasinski, Michael F.; Crago, Richard D.

    2005-01-01

    Most land surface models used today require estimates of aerodynamic roughness length in order to characterize momentum transfer between the surface and atmosphere. The most common method of prescribing roughness is through the use of empirical look-up tables based solely on land cover class. Theoretical approaches that employ satellite-based estimates of canopy density present an attractive alternative to current look-up table approaches based on vegetation cover type that do not account for within-class variability and are oftentimes simplistic with respect to temporal variability. The current research applies Raupach s formulation of momentum aerodynamic roughness to MODIS data on a regional scale in order to estimate seasonally variable roughness and zero-plane displacement height fields using bulk land cover parameters estimated by [Jasinski, M.F., Borak, J., Crago, R., 2005. Bulk surface momentum parameters for satellite-derived vegetation fields. Agric. For. Meteorol. 133, 55-68]. Results indicate promising advances over look-up approaches with respect to characterization of vegetation roughness variability in land surface and atmospheric circulation models.

  11. Estimation of Vegetation Aerodynamic Roughness of Natural Regions Using Frontal Area Density Determined from Satellite Imagery

    NASA Technical Reports Server (NTRS)

    Jasinski, Michael F.; Crago, Richard

    1994-01-01

    Parameterizations of the frontal area index and canopy area index of natural or randomly distributed plants are developed, and applied to the estimation of local aerodynamic roughness using satellite imagery. The formulas are expressed in terms of the subpixel fractional vegetation cover and one non-dimensional geometric parameter that characterizes the plant's shape. Geometrically similar plants and Poisson distributed plant centers are assumed. An appropriate averaging technique to extend satellite pixel-scale estimates to larger scales is provided. ne parameterization is applied to the estimation of aerodynamic roughness using satellite imagery for a 2.3 sq km coniferous portion of the Landes Forest near Lubbon, France, during the 1986 HAPEX-Mobilhy Experiment. The canopy area index is estimated first for each pixel in the scene based on previous estimates of fractional cover obtained using Landsat Thematic Mapper imagery. Next, the results are incorporated into Raupach's (1992, 1994) analytical formulas for momentum roughness and zero-plane displacement height. The estimates compare reasonably well to reference values determined from measurements taken during the experiment and to published literature values. The approach offers the potential for estimating regionally variable, vegetation aerodynamic roughness lengths over natural regions using satellite imagery when there exists only limited knowledge of the vegetated surface.

  12. Analysis of microwave backscatter measured by radar altimeter on land to study surface aerodynamic roughness

    NASA Astrophysics Data System (ADS)

    Yang, Le; Liu, Qinhuo

    2012-10-01

    The aerodynamic surface roughness z0 is a key parameter for climate and land-surface models to study surfaceatmosphere exchanges of mass and energy. The roughness length is difficult to estimate without wind speed profile data, which is intractable at regional to global scale. Theoretical formulations of roughness have been developed in terms of canopy attributes such as frontal area, height, and drag coefficient. This paper discusses the potential of radar altimetry, which provides the backscatter coefficient of the land surface at nadir view, to characterise the surface roughness at km scale. The AIEM model and ProSARproSIM are employed to simulate the backscatter coefficient under different surface condition and different observation geometry at bare soil and at pine forest, respectively. The altimetry backscatter decreases with increase of geometric roughness. The microwave backscatter measured at the nadir view is more sensitive to the surface roughness than that at the oblique observation, especially for the smooth surface. The direct forest return is the dominated scattering mechanism for normal incidence at forest area. Since we failed to collect the z0 measurement at arid and semi-arid area with sparse vegetation, the backscatter measurements at Ku and C band of altimeter Jason1 were analyzed with the ground measured aerodynamic surface roughness at three vegetated sites (Da yekou, Yin ke, and Chang Baisan) of China. The relationships we found between Jason1 sigma0 and z0 is not significant, since Jason1 lost track seriously at the three sites. Further research using the altimeter data of Jason2 and Cryosat is possible to demonstrate the potential to map z0 from orbit using radar altimeters.

  13. ROUGHNESS LENGTHS FOR THE SAVANNAH RIVER SITE

    SciTech Connect

    Hunter, C.

    2012-03-28

    Surface roughness values for the areas surrounding the H, D and N-Area meteorological towers were computed from archived 2010 meteorological data. These 15-minute-averaged data were measured with cup anemometers and bidirectional wind vanes (bivanes) 61 m above the surface. The results of the roughness calculation using the standard deviation of elevation angle {sigma}{sub E}, and applying the simple formula based on tree canopy height, gave consistent estimates for roughness around the H-Area tower in the range of 1.76 to 1.86 m (95% confidence interval) with a mean value of 1.81 m. Application of the {sigma}{sub E} method for the 61-m level at D and N-Areas gave mean values of 1.71 and 1.81 with confidence ranges of 1.62-1.81 and 1.73-1.88 meters, respectively. Roughness results are azimuth dependent, and thus are presented as averages over compass sectors spanning 22.5 degrees. Calculated values were compared to other methods of determining roughness, including the standard deviation of the azimuth direction, {sigma}{sub A}, and standard deviation of the wind speed, {sigma}{sub U}. Additional data was obtained from a sonic anemometer at 61-m on the H-Area tower during a period of a few weeks in 2010. Results from the sonic anemometer support our use of {sigma}{sub E} to calculate roughness. Based on the H-Area tower results, a surface roughness of 1.8 m using is recommended for use in dispersion modeling applications that consider the impacts of a contaminant release to individuals along the Site boundary. The canopy surrounding the H-Area tower is relatively uniform (i.e., little variance in roughness by upwind direction), and data supplied by the U.S. Forest Service at Savannah River show that the canopy height and composition surrounding the H-Area tower is reasonably representative of forested areas throughout the SRS reservation. For dispersion modeling analyses requiring assessments of a co-located worker within the respective operations area, recommended

  14. Relationships between aerodynamic roughness and land use and land cover in Baltimore, Maryland

    USGS Publications Warehouse

    Nicholas, F.W.; Lewis, J.E.

    1980-01-01

    Urbanization changes the radiative, thermal, hydrologic, and aerodynamic properties of the Earth's surface. Knowledge of these surface characteristics, therefore, is essential to urban climate analysis. Aerodynamic or surface roughness of urban areas is not well documented, however, because of practical constraints in measuring the wind profile in the presence of large buildings. Using an empirical method designed by Lettau, and an analysis of variance of surface roughness values calculated for 324 samples averaging 0.8 hectare (ha) of land use and land cover sample in Baltimore, Md., a strong statistical relation was found between aerodynamic roughness and urban land use and land cover types. Assessment of three land use and land cover systems indicates that some of these types have significantly different surface roughness characteristics. The tests further indicate that statistically significant differences exist in estimated surface roughness values when categories (classes) from different land use and land cover classification systems are used as surrogates. A Level III extension of the U.S. Geological Survey Level II land use and land cover classification system provided the most reliable results. An evaluation of the physical association between the aerodynamic properties of land use and land cover and the surface climate by numerical simulation of the surface energy balance indicates that changes in surface roughness within the range of values typical of the Level III categories induce important changes in the surface climate.

  15. Mask roughness induced LER: geometric model at long correlation lengths

    SciTech Connect

    McClinton, Brittany M.; Naulleau, Patrick P.

    2011-02-11

    Collective understanding of how both the resist and line-edge roughness (LER) on the mask affect the final printed LER has made significant advances. What is poorly understood, however, is the extent to which mask surface roughness couples to image plane LER as a function of illumination conditions, NA, and defocus. Recently, progress has been made in formulating a simplified solution for mask roughness induced LER. Here, we investigate the LER behavior at long correlation lengths of surface roughness on the mask. We find that for correlation lengths greater than 3/NA in wafer dimensions and CDs greater than approximately 0.75/NA, the previously described simplified model, which remains based on physical optics, converges to a 'geometric regime' which is based on ray optics and is independent of partial coherence. In this 'geometric regime', the LER is proportional to the mask slope error as it propagates through focus, and provides a faster alternative to calculating LER in contrast to either full 2D aerial image simulation modeling or the newly proposed physical optics model. Data is presented for both an NA = 0.32 and an NA = 0.5 imaging system for CDs of 22-nm and 50-nm horizontal-line-dense structures.

  16. Friction velocity and aerodynamic roughness of conventional and undercutter tillage within the Columbia Plateau, USA

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Friction velocity and aerodynamic roughness are characteristics of the soil-plant-atmosphere interface which affect wind erosion. Although exchange of momentum at the interface can be altered by land management practices, no attempts have been made to quantify the effect of tillage on friction veloc...

  17. Aerodynamic forces acting on a rough rotating cylinder in a cross-flow

    NASA Astrophysics Data System (ADS)

    Bychkov, N. M.; Kovalenko, V. M.

    1981-06-01

    The forces are investigated experimentally for two values of the degree of turbulence. The experiments are carried out in a low-turbulence, subsonic wind tunnel; the Reynolds number varies between 100,000 and 600,000, and the rotation parameter, between 0 and 1 radian. The apparatus permits the registration of instantaneous forces with relatively high precision. The desired roughness is produced by covering the surface of the cylinder with emery paper. The magnitude and type of changes in the aerodynamic forces for the case of a rough cylinder are found to differ in a fundamental way from that of a smooth cylinder, a difference related to features of the flow near the wall and to the position of the separation points of the boundary layer. Increasing the degree of turbulence of the flow does not noticeably affect the aerodynamic forces of a rough cylinder in the supercritical region of Reynolds numbers.

  18. Experimental research of surface roughness effects on highly-loaded compressor cascade aerodynamics

    NASA Astrophysics Data System (ADS)

    Chen, Shao-wen; Xu, Hao; Wang, Song-tao; Wang, Zhong-qi

    2014-08-01

    Aircraft engines deteriorate during continuous operation under the action of external factors including fouling, corrosion, and abrasion. The increased surface roughness of compressor passage walls limits airflow and leads to flow loss. However, the partial increase of roughness may also restrain flow separation and reduce flow loss. It is necessary to explore methods that will lower compressor deterioration, thereby improving the overall performance. The experimental research on the effects of surface roughness on highly loaded compressor cascade aerodynamics has been conducted in a low-speed linear cascade wind tunnel. The different levels of roughness are arranged on the suction surface and pressure surface, respectively. Ink-trace flow visualization has been used to measure the flow field on the walls of cascades, and a five-hole probe has been traversed across one pitch at the outlet. By comparing the total pressure loss coefficient, the distributions of the secondary-flow speed vector, and flow fields of various cases, the effects of surface roughness on the aerodynamics of a highly loaded compressor cascade are analyzed and discussed. The results show that adding surface roughness on the suction surface and pressure surface make the loss decrease in most cases. Increasing the surface roughness on the suction surface causes reduced flow speed near the blade, which helps to decrease mixing loss at the cascades outlet. Meanwhile, adding surface roughness on the suction surface restrains flow separation, leading to less flow loss. Various levels of surface roughness mostly weaken the flow turning capacity to various degrees, except in specific cases.

  19. Parameterization of aerodynamic roughness of China's land surface vegetation from remote sensing data

    NASA Astrophysics Data System (ADS)

    Hu, Deyong; Xing, Liwei; Huang, Shengli; Deng, Lei; Xu, Yingjun

    2014-01-01

    Aerodynamic roughness length (z0) is one of the important parameters that influence energy exchange at the land-atmosphere interface in numerical models, so it is of significance to accurately parameterize the land surface. To parameterize the z0 values of China's land surface vegetation using remote sensing data, we parameterized the vegetation canopy area index using the leaf area index and land cover products of moderate resolution imaging spectroradiometer data. Then we mapped the z0 values of different land cover types based on canopy area index and vegetation canopy height data. Finally, we analyzed the intra-annual monthly z0 values. The conclusions are: (1) This approach has been developed to parameterize large scale regional z0 values from multisource remote sensing data, allowing one to better model the land-atmosphere flux exchange based on this feasible and operational scheme. (2) The variation of z0 values in the parametric model is affected by the vegetation canopy area index and its threshold had been calculated to quantify different vegetation types. In general, the z0 value will increase during the growing season. When the threshold in the dense vegetation area or in the growing season is exceeded, the z0 values will decrease but the zero-plane displacement heights will increase. This technical scheme to parameterize the z0 can be applied to large-scale regions at a spatial resolution of 1 km, and the dynamic products of z0 can be used in high resolution land or atmospheric models to provide a useful scheme for land surface parameterization.

  20. Aerodynamic roughness of ice surfaces derived from high resolution topographic data

    NASA Astrophysics Data System (ADS)

    Smith, Mark; Quincey, Duncan; Dixon, Timothy; Bingham, Robert; Carrivick, Jonathan; Irvine-Fynn, Tristram; Rippin, David

    2016-04-01

    The aerodynamic roughness of glacier surfaces is an important component of energy balance models and meltwater runoff estimates through its influence on turbulent fluxes of latent and sensible heat. In a warming climate these fluxes are predicted to become more significant in contributing to overall melt volumes. Ice aerodynamic roughness (z0) is commonly estimated from measurements of ice surface microtopography, typically from topographic profiles taken perpendicular to the prevailing wind direction. Recent advances in surveying permit rapid acquisition of high resolution topographic data allowing revision of assumptions underlying conventional topographic profile-based z0 measurement. This poster presents alternative methods of estimating z0 directly from Digital Elevation Models (DEMs) or three-dimensional point clouds, and examines the spatial and temporal variability of z0 across the ablation zone of a small Arctic glacier. Using Structure-from-Motion (SfM) photogrammetry to survey ice surfaces with millimeter-scale accuracy, z0 variation over three orders of magnitude was observed but was unrelated to large scale topographic variables such as elevation or slope. Different surface-types demonstrated different temporal trajectories in z0 through three days of intense melt, though the observed temporal z0 variability was lower than the spatial variability. A glacier-scale topographic model was obtained through Terrestrial Laser Scanning (TLS) and sub-grid roughness was significantly related to z0 calculated from a 2 m resolution DEM. Thus, glacier scale TLS or SfM surveys can characterize z0 variability over a glacier surface and allow distributed representations of z0 in surface energy balance models.

  1. Aerodynamic roughness of glacial ice surfaces derived from high-resolution topographic data

    NASA Astrophysics Data System (ADS)

    Smith, Mark W.; Quincey, Duncan J.; Dixon, Timothy; Bingham, Robert G.; Carrivick, Jonathan L.; Irvine-Fynn, Tristram D. L.; Rippin, David M.

    2016-04-01

    This paper presents new methods of estimating the aerodynamic roughness (z0) of glacier ice directly from three-dimensional point clouds and digital elevation models (DEMs), examines temporal variability of z0, and presents the first fully distributed map of z0 estimates across the ablation zone of an Arctic glacier. The aerodynamic roughness of glacier ice surfaces is an important component of energy balance models and meltwater runoff estimates through its influence on turbulent fluxes of latent and sensible heat. In a warming climate these fluxes are predicted to become more significant in contributing to overall melt volumes. Ice z0 is commonly estimated from measurements of ice surface microtopography, typically from topographic profiles taken perpendicular to the prevailing wind direction. Recent advances in surveying permit rapid acquisition of high-resolution topographic data allowing revision of assumptions underlying conventional z0 measurement. Using Structure from Motion (SfM) photogrammetry with Multi-View Stereo (MVS) to survey ice surfaces with millimeter-scale accuracy, z0 variation over 3 orders of magnitude was observed. Different surface types demonstrated different temporal trajectories in z0 through 3 days of intense melt. A glacier-scale 2 m resolution DEM was obtained through terrestrial laser scanning (TLS), and subgrid roughness was significantly related to plot-scale z0. Thus, we show for the first time that glacier-scale TLS or SfM-MVS surveys can characterize z0 variability over a glacier surface potentially leading to distributed representations of z0 in surface energy balance models.

  2. Aerodynamic performance of transonic and subsonic airfoils: Effects of surface roughness, turbulence intensity, Mach number, and streamline curvature-airfoil shape

    NASA Astrophysics Data System (ADS)

    Zhang, Qiang

    The effects of surface roughness, turbulence intensity, Mach number, and streamline curvature-airfoil shape on the aerodynamic performance of turbine airfoils are investigated in compressible, high speed flows. The University of Utah Transonic Wind Tunnel is employed for the experimental part of the study. Two different test sections are designed to produce Mach numbers, Reynolds numbers, passage mass flow rates, and physical dimensions, which match values along turbine blades in operating engines: (i) a nonturning test section with a symmetric airfoil, and (ii) a cascade test section with a cambered turbine vane. The nonuniform, irregular, three-dimensional surface roughness is characterized using the equivalent sand grain roughness size. Changing the airfoil surface roughness condition has a substantial effect on wake profiles of total pressure loss coefficients, normalized Mach number, normalized kinetic energy, and on the normalized and dimensional magnitudes of Integrated Aerodynamic Losses produced by the airfoils. Comparisons with results for a symmetric airfoil and a cambered vane show that roughness has more substantial effects on losses produced by the symmetric airfoil than the cambered vane. Data are also provided that illustrate the larger loss magnitudes are generally present with flow turning and cambered airfoils, than with symmetric airfoils. Wake turbulence structure of symmetric airfoils and cambered vanes are also studied experimentally. The effects of surface roughness and freestream turbulence levels on wake distributions of mean velocity, turbulence intensity, and power spectral density profiles and vortex shedding frequencies are quantified one axial chord length downstream of the test airfoils. As the level of surface roughness increases, all wake profile quantities broaden significantly and nondimensional vortex shedding frequencies decrease. Wake profiles produced by the symmetric airfoil are more sensitive to variations of surface

  3. Sensitivity of roughness length for heat transport (zoh) on evapotranspiration derived from SEBAL

    NASA Astrophysics Data System (ADS)

    Paul, G.; Gowda, P. H.; Prasad, V.; Howell, T. A.; Aiken, R. M.

    2012-12-01

    Thermal infrared remote sensing has greatly contributed to the development and improvement of remote sensing based evapotranspiration (RS-ET) mapping algorithms. The radiometric temperature derived from the thermal sensors were inherently different than the aerodynamic temperature required for solving the bulk formulation of sensible heat (H) based on the Monin-Obukhov similarity (MOS); this posed a critical problem. The TSM (Two Source Model), SEBS (Surface Energy Balance System) and SEBAL (Surface Energy Balance Algorithm) forms the three most widely applied RS-ET algorithm's differing in their conceptualization and parameterization of the soil-canopy-air heat exchange mechanism addressing the issue arising from aerodynamic-radiometric temperature differences. The scalar roughness length zoh, representing heat transport and described by the dimensionless parameter kB-1, was used as a correction factor to accommodate the discrepancy between radiometric and aerodynamic temperatures. In this study we looked into the sensitivity of zoh on the ET estimates using the SEBAL approach. ET estimates from four approaches namely, (i) zoh derived from constant kB-1 of 2.3, (ii) zoh=0.1, (iii) zoh=0.01, and (iv) zoh from kB-1 parameterization, were compared. SEBAL was executed for 10 high resolution airborne images acquired during BEAREX07-08 (Bushland Evapotranspiration and Agricultural Remote Sensing Experiment) field campaign and validated against large precision weighing lysimeters installed on two irrigated and two dryland fields. Statistical tests revealed no significant differences between the first three approaches, however, the fourth approach of kB-1 parameterization produced significantly different results. Model performance evaluation for all the components of the energy balance was conducted. Percent root mean square error (%RMSE) for instantaneous ET estimates from the four approaches were 33.7, 26.9, 27.7 and 23.2 respectively. Evaluation of the SEBAL

  4. Estimation of Aerodynamic Roughness and Zero Plane Displacement Using Medium Density of Airborne LIDAR Data

    NASA Astrophysics Data System (ADS)

    Mohd Salleh, M. R.; Rahman, M. Z. Abdul; Abu Bakar, M. A.; Rasib, A. W.; Omar, H.

    2016-09-01

    This paper presents a framework to estimate aerodynamic roughness over specific height (zo/H) and zero plane displacement (d/H) over various landscapes in Kelantan State using airborne LiDAR data. The study begins with the filtering of airborne LiDAR, which produced ground and non-ground points. The ground points were used to generate digital terrain model (DTM) while the non-ground points were used for digital surface model (DSM) generation. Canopy height model (CHM) was generated by subtracting DTM from DSM. Individual trees in the study area were delineated by applying the Inverse Watershed segmentation method on the CHM. Forest structural parameters including tree height, height to crown base (HCB) and diameter at breast height (DBH) were estimated using existing allometric equations. The airborne LiDAR data was divided into smaller areas, which correspond to the size of the zo/H and d/H maps i.e. 50 m and 100 m. For each area individual tree were reconstructed based on the tree properties, which accounts overlapping between crowns and trunks. The individual tree models were used to estimate individual tree frontal area and the total frontal area over a specific ground surface. Finally, three roughness models were used to estimate zo/H and d/H for different wind directions, which were assumed from North/South and East/West directions. The results were shows good agreements with previous studies that based on the wind tunnel experiments.

  5. Global Retrieval of Roughness Length from EOS-Terra Satellite Products and Limited Field Study Data

    NASA Astrophysics Data System (ADS)

    Schaudt, K. J.; Dickinson, R. E.

    2003-12-01

    Global and regional retrievals, which illustrate the seasonality, of roughness length will be presented. Roughness length is a key factor in estimating the sensible and latent heat fluxes in climate models. In the past the lack of observations made it necessary for most climate models to use relatively crude estimates for roughness length. Typically the roughness length was assigned a constant value for each of the land cover classifications. In reality roughness length depends upon the average height, shape, density and Leaf Area Index (LAI) of the vegetation present. The retrievals presented here depend on these four variables, and they represent a significant improvement over past approaches. The parameterization of roughness length in terms of the four variables (average height, shape, density and LAI) is based on the work of Raupach and Lindroth. The roughness length is formulated in such a way that roughness length can be found either by remote sensing or by variables used in climate models with interactive canopies. The EOS-Terra satellite products used are the overstory plant density and LAI for the seven treed IGBP land cover classes (evergreen and deciduous needle-leaf, evergreen and deciduous broad-leaf and mixed forests, savannah and woody savannah). The tree crown shape (the canopy height-to-width ratio) is based on field studies; it depends on the tree's basic shape (conical or elliptical) and on latitude. At present, the height is of all the vegetation is the average height for the various land cover classifications found in numerous field studies. Limitations of the current retrieval and future improvements will be discussed.

  6. Simultaneous measurement of the root-mean-square roughness and autocorrelation length by optical method

    NASA Astrophysics Data System (ADS)

    Kim, Dalwoo; Oh, Ki-Jang; Lim, Choong-Soo

    1998-12-01

    We developed an on-line measurement system for the simultaneous measurement of the root-mean-square roughness and autocorrelation length which are the parameters of surface roughness. The measurement is based on the scattering theory of light on the rough surface. Computer simulation shows that the measurement range depends on the wavelength of the light source, and this is verified with the experiment. We installed the measurement system at the finishing line of a cold-rolling steel work, and measured the two parameters in situ. The rms roughness and autocorrelation length are measured and transformed in the average surface roughness and then umber of peaks per inch, respectively. The measured data for both of the parameters are compared with those of stylus method, an the optical method is well coincided with the conventional stylus method.

  7. Turbulent transfer coefficient and roughness length in a high-altitude lake, Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Li, Zhaoguo; Lyu, Shihua; Zhao, Lin; Wen, Lijuan; Ao, Yinhuan; Wang, Shaoying

    2016-05-01

    A persistent unstable atmospheric boundary layer was observed over Lake Ngoring, caused by higher temperature on the water surface compared with the overlying air. Against this background, the eddy covariance flux data collected from Lake Ngoring were used to analyse the variation of transfer coefficients and roughness lengths for momentum, heat and moisture. Results are discussed and compared with parameterization schemes in a lake model. The drag coefficient and momentum roughness length rapidly decreased with increasing wind velocity, reached a minimum value in the moderate wind velocity and then increased slowly as wind velocity increased further. Under weak wind conditions, the surface tension or small scale capillary wave becomes more important and increases the surface roughness. The scalar roughness length ratio was much larger than unity under weak wind conditions, and it decreased to values near unity as wind velocity exceeded 4.0 m s-1. The lake model could not reproduce well the variation of drag coefficient, or momentum roughness length, versus wind velocity in Lake Ngoring, but it did simulate well the sensible heat and latent heat fluxes, as a result of complementary opposite errors.

  8. Topographic Roughness of Hawaiian Volcanic Terrains: Analysis of Multiple Datasets Indicates Length Scales are Critical

    NASA Astrophysics Data System (ADS)

    Morris, A. R.; Anderson, F. S.; Mouginis-Mark, P.; Haldemann, A.; Brooks, B.; Foster, J.

    2007-12-01

    The roughness of a natural surface is often defined by the topography of the surface at scales of a few tens of meters or less. To ensure the safety of rovers and scientific instruments on Mars, these scales are of critical importance during landing site selection and rover traverse operations. Published work on terrestrial and Martian topography datasets has demonstrated that statistical values such as the Hurst exponent can be used in conjunction with related statistical measures such as RMS slope or deviation to quantify the relationship between scale-dependent roughness values and the morphology of a surface. In our detailed studies of the statistical behavior of meter-scale surface roughness on Earth, we determine that the length scales used to calculate the surface roughness affect the resulting roughness statistics and must be taken into account when analyzing planetary surface roughness. Extensive airborne Light Detection and Ranging (a-LiDAR) coverage of the summit of Kilauea volcano on the Big Island of Hawaii (1 m DEM) provides an opportunity for simulating higher resolution Martian topography data such as will be obtained from photoclinometry and stereo imaging using the HiRISE camera on MRO. In addition to the a-LiDAR data, we use high-resolution topography (2 cm DEM) generated from a tripod-mounted scanning LiDAR system (t-LiDAR). Previous authors have described techniques for calculating roughness statistics in one dimension using topographic profiles. We adapt the 1D method for use with 2D topographic datasets to generate maps of the Hurst exponent of Martian analog flows in Hawaii. Results from the surface roughness analysis suggest that the calculated RMS deviation or slope and Hurst exponent exhibit systematic variations as the length of a profile segment (in 1D studies) or size of the cell (in 2D studies) changes. These new results, combined with previously described data, indicate that the length scales used to calculate roughness statistics

  9. Effect of milling machine roughness and wing dihedral on the supersonic aerodynamic characteristics of a highly swept wing

    NASA Technical Reports Server (NTRS)

    Darden, Christine M.

    1989-01-01

    An experimental investigation was conducted to assess the effect of surface finish on the longitudinal and lateral aerodynamic characteristics of a highly-swept wing at supersonic speeds. A study of the effects of wing dihedral was also made. Included in the tests were four wing models: three models having 22.5 degrees of outboard dihedral, identical except for surface finish, and a zero-dihedral, smooth model of the same planform for reference. Of the three dihedral models, two were taken directly from the milling machine without smoothing: one having a maximum scallop height of 0.002 inches and the other a maximum scallop height of 0.005 inches. The third dihedral model was handfinished to a smooth surface. Tests were conducted in Test Section 1 of the Unitary Plan Wind Tunnel at NASA-Langley over a range of Mach numbers from 1.8 to 2.8, a range of angle of attack from -5 to 8 degrees, and at a Reynolds numbers per foot of 2 x 10(6). Selected data were also taken at a Reynolds number per foot of 6 x 10(6). Drag coefficient increases, with corresponding lift-drag ratio decreases were the primary aerodynamic effects attributed to increased surface roughness due to milling machine grooves. These drag and lift-drag ratio increments due to roughness increased as Reynolds number increased.

  10. Roughness distribution of multiple hit and long surface diffusion length noise reduced discrete growth models

    NASA Astrophysics Data System (ADS)

    Disrattakit, P.; Chanphana, R.; Chatraphorn, P.

    2016-11-01

    Conventionally, the universality class of a discrete growth model is identified via the scaling of interface width. This method requires large-scale simulations to minimize finite-size effects on the results. The multiple hit noise reduction techniques (m > 1 NRT) and the long surface diffusion length noise reduction techniques (ℓ > 1 NRT) have been used to promote the asymptotic behaviors of the growth models. Lately, an alternative method involving comparison of roughness distribution in the steady state has been proposed. In this work, the roughness distribution of the (2 +1)-dimensional Das Sarma-Tamborenea (DT), Wolf-Villain (WV), and Larger Curvature (LC) models, with and without NRTs, are calculated in order to investigate effects of the NRTs on the roughness distribution. Additionally, effective growth exponents of the noise reduced (2 +1)-dimensional DT, WV and LC models are also calculated. Our results indicate that the NRTs affect the interface width both in the growth and the saturation regimes. In the steady state, the NRTs do not seem to have any impact on the roughness distribution of the DT model, but it significantly changes the roughness distribution of the WV and LC models to the normal distribution curves.

  11. The impacts of thermal roughness length on land surface climate in IPSL-CM

    NASA Astrophysics Data System (ADS)

    Wand, Fuxing; Cheruy, Frédérique; Vuichard, Nicolas; Sima, Adriana; Hourdin, Frederic

    2016-04-01

    The aerodynamic and thermal roughness lengths (z0m and z0h) are the two crucial parameters for bulk transfer equations to calculate turbulent flux. The exchange of momentum is usually different with scalars as heat (or water vapor, carbon dioxide, traces gas). In general, the transport of scalars (by molecular diffusion) is considered less efficient than momentum (by pressure fluctuations), owing to the absence of bluff-body forces for scalar exchange. However, the z0h and z0m are equal in the current IPSL-CM model. The objective of the study is to investigate the impacts of z0h parameterizations on the land surface climate. Several sensitivity experiments that accounting for different z0h and z0m are carried out with IPSL-CM: (1) z0h = z0m/10; (2) z0h = z0m/100; (3) a more physically based z0h parameterizations. A nudging approach is used in order to avoid the time-consuming long-term simulations required to account for the natural variability of the climate. The results show that the seasonal mean surface temperature (Ts) increases 0.5-1 K (for z0h = z0m/10) and 1-2 K (for z0h = z0m/100) over JJA due to the decrease of z0h. The most significant variation is over the Sahara. During the daytime, the increase of Ts (around 1-2 K) is higher than the air temperature (Tair, ~0.2 K) for z0h = z0m/10. During the night time, the increase of Ts and Tair are very close (around 0.3-0.6 K) for z0h = z0m/10. The asymmetric variation of Tair during night and day causes a decrease (~0.3 K for z0h = z0m/10; ~0.6 K for z0h = z0m/100) of diurnal temperature range (DTR). The seasonal mean sensible heat flux decreases by ~4-6 W/m2 (for z0h = z0m/10) with the decrease of z0h as well. The change of latent heat flux is the most significant over the tropics with the seasonal mean decrease of 4-8 W/m2 for z0h = z0m/10 over both JJA and DJF. Besides the change of mean climate, the human thermal comfort is also affected by z0h. A smaller z0h corresponds to a higher wet-bulb temperature

  12. Atmospheric sensitivity to roughness length in a regional atmospheric model over the Ohio-Tennessee River Valley

    NASA Astrophysics Data System (ADS)

    Quintanar, Arturo I.; Mahmood, Rezaul; Suarez, Astrid; Leeper, Ronnie

    2016-06-01

    The response of a regional atmospheric model to small changes in roughness length of two vegetation categories (crops and deciduous broadleaf forest) was analyzed for three synoptic events in June 2006. These were characterized by two convective events (June 11 and 22) and one prefrontal event (June 17). The responses of the model, for precipitation, equivalent potential temperature and wind field were notable in general. However, the response became muted as roughness lengths were increased or decreased. Atmospheric response to these changes varied for different convective events. A small dependence on roughness length was found for the sensible and latent heat fluxes and planetary boundary layer heights during the convective event of June 11. For the June 22 event, the model response was weaker for the crop-only and forest-only roughness length experiments compared to the response when both the crop and forest-only roughness length were changed in combination.

  13. The adverse aerodynamic impact of very small leading-edge ice (roughness) buildups on wings and tails

    NASA Technical Reports Server (NTRS)

    Lynch, Frank T.; Valarezo, Walter O.; Mcghee, Robert J.

    1991-01-01

    Systematic experimental studies were performed to establish the aerodynamic impact of very small leading-edge simulated ice (roughness) formations on lifting surfaces. The geometries studied include single element configurations (airfoil and 3-D tail) as well as multi-element high-lift airfoil geometries. Emphasis in these studies was placed on obtaining results at high Reynolds numbers to insure the applicability of the findings to full-scale situations. It was found that the well-known Brumby correlation for the adverse lift impact of discrete roughness elements at the leading edge is not appropriate for cases representative of initial ice build up (i.e., distributed roughness). It was also found that allowing initial ice formations of a size required for removal by presently proposed deicing systems could lead to maximum lift losses of approximately 40 percent for single-element airfoils. Losses in angle-of-attack margin to stall are equally substantial - as high as 6 degrees. Percentage losses for multi-element airfoils are not as severe as for single-element configurations, but degradations of the angle-of-attack-to-stall margin are the same for both.

  14. Estimates of bottom roughness length and bottom shear stress in South San Francisco Bay, California

    USGS Publications Warehouse

    Cheng, R.T.; Ling, C.-H.; Gartner, J.W.; Wang, P.-F.

    1999-01-01

    A field investigation of the hydrodynamics and the resuspension and transport of participate matter in a bottom boundary layer was carried out in South San Francisco Bay (South Bay), California, during March-April 1995. Using broadband acoustic Doppler current profilers, detailed measurements of turbulent mean velocity distribution within 1.5 m above bed have been obtained. A global method of data analysis was used for estimating bottom roughness length zo and bottom shear stress (or friction velocities u*). Field data have been examined by dividing the time series of velocity profiles into 24-hour periods and independently analyzing the velocity profile time series by flooding and ebbing periods. The global method of solution gives consistent properties of bottom roughness length zo and bottom shear stress values (or friction velocities u*) in South Bay. Estimated mean values of zo and u* for flooding and ebbing cycles are different. The differences in mean zo and u* are shown to be caused by tidal current flood-ebb inequality, rather than the flooding or ebbing of tidal currents. The bed shear stress correlates well with a reference velocity; the slope of the correlation defines a drag coefficient. Forty-three days of field data in South Bay show two regimes of zo (and drag coefficient) as a function of a reference velocity. When the mean velocity is >25-30 cm s-1, the ln zo (and thus the drag coefficient) is inversely proportional to the reference velocity. The cause for the reduction of roughness length is hypothesized as sediment erosion due to intensifying tidal currents thereby reducing bed roughness. When the mean velocity is <25-30 cm s-1, the correlation between zo and the reference velocity is less clear. A plausible explanation of scattered values of zo under this condition may be sediment deposition. Measured sediment data were inadequate to support this hypothesis, but the proposed hypothesis warrants further field investigation.

  15. Effects of surface roughness on the aerodynamic characteristics of the Space Shuttle Orbiter configuration

    NASA Technical Reports Server (NTRS)

    Ware, G. M.; Spencer, B., Jr.

    1986-01-01

    An investigation has been conducted to determine the effects of surface roughness on two Space Shuttle Orbiter models. The tests were conducted over a Mach number range from 0.2 to 6.0 in the Langley Low Turbulance Pressure Tunnel, 8-foot Transonic Pressure Tunnel, Unitary Plan Wind Tunnel, 20-Inch Mach 6 Tunnel, and the Vought High Speed Tunnel. Analytical estimates of the degradation of the subsonic performance resulting from the roughness were made and are presented. The investigation also included tests to explore the possibility of asymmetric flow separation or attachment over the wings during transition from high to low angles of attack that might cause roll divergence.

  16. Roughness of fault surfaces over a length-scale range from nano- to milimeters

    NASA Astrophysics Data System (ADS)

    Kishida, M.; Mizoguchi, K.; Takahashi, M.; Hirose, T.

    2014-12-01

    Fault-surface roughness is one of the primary factors affecting the mechanics of earthquakes and faulting. We report on the topographic roughness measurements on two natural fault surfaces with a continuous length-scale range from 1 nm to 3 mm. The fault surfaces observed in this study include (1) the Corona Heights fault in the Castro Area of San Francisco, detail microstructures reported by Kirkpatrick et al., (2013), and (2) the Itozawa fault in Fukushima prefecture, a fault moved just after the 2011 Off the Pacific Coast of Tohoku earthquake. To measure fault surface to we performed line-measurements both parallel and perpendicular to the slickenlines using two scanner devices; a confocal white-light scanning microscope (measurable range: 0.15 ˜ 3000 μm) and a scanning probe microscope (1 ˜ 50000 nm). The topographic properties of the measured surfaces were expressed either as a Hurst exponent (H) which are calculated from Power Spectrum Density (PSD) of topography data. The measurements revealed that the Corona Heights fault and the Itozawa fault exhibit a similar geometrical property, a linear behavior on a log-log plot where axes are PSD and spatial length scale. A slope of the log-log plot, H, of the Corona Heights fault and the Itozawa fault shows HN = 0.76 ± 0.01 perpendicular to the slickenslide and HP = 0.84 ± 0.01 parallel to it, and HN = 0.88 ± 0.01 and HP = 0.91 ± 0.01, respectively. The measurements on both faults show HP are higher than HN, which is inconsistent with previous results that HP is small compared to HN because surface roughness in the slip direction becomes less pronounced selectively with progressive displacement. (e.g., Sagy et al., 2007). There is a hypotheses that explain the difference that HP and HN are undifferentiated with displacement in the length-scale range from 1 nm to 3 mm. Candela et al., (2012) measured roughness of 13 earthquake fault surfaces and suggested that the fault geometry can be expressed as a single

  17. Predicting the roughness length of turbulent flows over landscapes with multi-scale microtopography

    NASA Astrophysics Data System (ADS)

    Pelletier, Jon D.; Field, Jason P.

    2016-05-01

    The fully rough form of the law of the wall is commonly used to quantify velocity profiles and associated bed shear stresses in fluvial, aeolian, and coastal environments. A key parameter in this law is the roughness length, z0. Here we propose a predictive formula for z0 that uses the amplitude and slope of each wavelength of microtopography within a discrete-Fourier-transform-based approach. Computational fluid dynamics (CFD) modeling is used to quantify the effective z0 value of sinusoidal microtopography as a function of the amplitude and slope. The effective z0 value of landscapes with multi-scale roughness is then given by the sum of contributions from each Fourier mode of the microtopography. Predictions of the equation are tested against z0 values measured in ˜ 105 wind-velocity profiles from southwestern US playa surfaces. Our equation is capable of predicting z0 values to 50 % accuracy, on average, across a 4 order of magnitude range. We also use our results to provide an alternative formula that, while somewhat less accurate than the one obtained from a full multi-scale analysis, has an advantage of being simpler and easier to apply.

  18. CFD Analysis Based Evaluation of Aerodynamic Characteristics for Supersonic Biplane with Finite Span Length

    NASA Astrophysics Data System (ADS)

    Yonezawa, Masahito; Obayashi, Shigeru

    The supersonic biplane is well known as the airfoil that has zero wave drag at the supersonic speed. This paper investigates aerodynamic characteristics of the supersonic biplane with the finite span length and effects of the aspect and taper ratios by comparing with the two-dimensional supersonic biplane which has the infinite span length using the computational fluid dynamics. The rectangular wing was employed to examine the effect of the aspect ratio and tapered wing was employed to inspect the effect of the taper ratio. Both the rectangular wing and the two-dimensional supersonic biplane choke at the high angle of attack. The drag of the three-dimensional wing becomes smaller when it has a higher aspect ratio. The drag polar curve of the three-dimensional wing approaches asymptotically to the drag polar curve of the two-dimensional supersonic biplane when it has a higher taper ratio. The drag of the tapered wing becomes smaller when it has an adequate taper ratio.

  19. Effect of Length-Beam Ratio on the Aerodynamic Characteristics of Flying-Boat Hulls without Wing Interference

    NASA Technical Reports Server (NTRS)

    Lowry, John G.; Riebe, John M.

    1948-01-01

    Contains experimental results of an investigation of the aerodynamic characteristics of a family of flying boat hulls of length beam ratios 6, 9, 12, and 15 without wing interference. The results are compared with those taken on the same family of hulls in the presence of a wing.

  20. Application of a roughness-length representation to parameterize energy loss in 3-D numerical simulations of large rivers

    NASA Astrophysics Data System (ADS)

    Sandbach, S. D.; Lane, S. N.; Hardy, R. J.; Amsler, M. L.; Ashworth, P. J.; Best, J. L.; Nicholas, A. P.; Orfeo, O.; Parsons, D. R.; Reesink, A. J. H.; Szupiany, R. N.

    2012-12-01

    Recent technological advances in remote sensing have enabled investigation of the morphodynamics and hydrodynamics of large rivers. However, measuring topography and flow in these very large rivers is time consuming and thus often constrains the spatial resolution and reach-length scales that can be monitored. Similar constraints exist for computational fluid dynamics (CFD) studies of large rivers, requiring maximization of mesh- or grid-cell dimensions and implying a reduction in the representation of bedform-roughness elements that are of the order of a model grid cell or less, even if they are represented in available topographic data. These "subgrid" elements must be parameterized, and this paper applies and considers the impact of roughness-length treatments that include the effect of bed roughness due to "unmeasured" topography. CFD predictions were found to be sensitive to the roughness-length specification. Model optimization was based on acoustic Doppler current profiler measurements and estimates of the water surface slope for a variety of roughness lengths. This proved difficult as the metrics used to assess optimal model performance diverged due to the effects of large bedforms that are not well parameterized in roughness-length treatments. However, the general spatial flow patterns are effectively predicted by the model. Changes in roughness length were shown to have a major impact upon flow routing at the channel scale. The results also indicate an absence of secondary flow circulation cells in the reached studied, and suggest simpler two-dimensional models may have great utility in the investigation of flow within large rivers.

  1. Aerodynamic Characteristics of a Flying-Boat Hull Having a Length-Beam Ratio of 15, TED No. NACA 2206

    NASA Technical Reports Server (NTRS)

    Riebe, John M.; Naeseth, Rodger L.

    1951-01-01

    An investigation was made in the Langley 300 MPH 7- by 10-foot tunnel to determine the aerodynamic characteristics of a flying-boat hull of a length-beam ratio of 15 in the presence of a wing. The investigation was an extension of previous tests made on hulls of length-beam ratios of 6, 9, and 12; these hulls were designed to have approximately the same hydrodynamic performance with respect to spray and resistance characteristics. Comparison with the previous investigation at lower length-beam ratios indicated a reduction in minimum drag coefficients of 0.0006 (10 peroent)with fixed transition when the length-beam ratio was extended from 12 to 15. As with the hulls of lower length-beam ratio, the drag reduction with a length-beam ratio of 15 occurred throughout the range of angle of attack tested and the angle of attack for minimum drag was in the range from 2deg to 3deg. Increasing the length-beam ratio from 12 to 15 reduced the hull longitudinal instability by an mount corresponding to an aerodynamic-center shift of about 1/2 percent of the mean aerodynamic chord of the hypothetical flying boat. At an angle of attack of 2deg, the value of the variation of yawing-moment coefficient with angle of yaw for a length-beam ratio of 15 was 0.00144, which was 0.00007 larger than the value for a length-beam ratio of 12.

  2. Effects of roughness size on the position of boundary-layer transition and on the aerodynamic characteristics of a 55 deg. swept delta wing at supersonic speeds

    NASA Technical Reports Server (NTRS)

    Stallings, R. L., Jr.; Lamb, M.

    1977-01-01

    An experimental investigation was conducted to determine the effects of roughness size on the position of boundary layer transition and on the aerodynamic characteristics of a 55 deg swept delta wing model. Results are presented and discussed for wind tunnel tests conducted at free stream Mach numbers from 1.50 to 4.63, Reynolds numbers per meter from 3,300,000 to 1.6 x 10 to the 7th power, angles of attack from -8 to 16 deg, and roughness sizes ranging from 0.027 cm sand grit to 0.127 cm high cylinders. Comparisons were made with existing flat plate data. An approximate method was derived for predicting the drag of roughness elements used in boundary layer trips.

  3. The Influence of Roughness Length on Simulated Surface air Temperature (2 m), Wind (10 m), Precipitation, and Energy and Water Fluxes in Eastern China

    NASA Astrophysics Data System (ADS)

    Zuo, J.; Lu, L.

    2012-12-01

    The heterogeneity of land cover characteristics has significant impact on the land-atmosphere water, energy, and momentum exchanges. The aerodynamic roughness length (z0) is an important surface parameter for estimating surface fluxes in numerical models. This study is to investigate the sensitivity of z0 on weather and climate in Eastern China, which has experienced dramatic growth in the urban areas over the past 30 years. Driven by ERA-40 reanalysis product as atmospheric lateral boundary conditions, Regional Atmospheric Modeling System (RAMS) was used to perform a series of one-year ensemble simulations over the eastern China. Ten sensitivity experiments were conducted by increasing and decreasing vegetation roughness length by 10%, 25%, 50%, 70%, 90%, as well as a control run by using the model's default parameterization of z0, which is derived from a look-up table based on vegetation type. Furthermore, a data assimilation run using the real time z0 map that is derived from MODIS product was carried out, which includes the heteorogenous z0 within the same vegetation type. The difference between the data assimilation run and the default run will help us to understand how remotely sensed land-surface information influences land-atmosphere interactions and mesoscale circulations. The preliminary results show that the bigger the magnitude of z0 changes, the larger the responses in surface air temperatures, wind speeds, and fluxes, except that these changes are opposite in sign with z0 changes. More localized changes occur in the Southeast China than Northeast China, as there are more vegetation cover variations in the south. In addition, z0 has larger effect on spring and summer surface air temperature, and summer sensible heat fluxes. The remote sensing product derived z0 map shows different spatial and temporal distribution when compare to the default z0 distribution, which in turn results in both spatial and seasonal differences in simulated climate variables.

  4. An estimate of the roughness length and displacement height of Sonoran Desert vegetation, south-central Arizona

    SciTech Connect

    Claassen, H.C.; Riggs, A.C.

    1993-12-01

    A somewhat unconventional technique using a tethered balloon was used to estimate the roughness length for momentum (z{sub m}) and displacement height (d) for typical Sonoran Desert vegetation. It has been suggested that measurements of the meteorological fluxes of momentum, sensible heat, and latent heat are best done at heights above ground level determined by either the roughness length (z{sub m}) or the size and shape of vegetation. Therefore, estimates of z{sub m} and vegetation characteristics are a desirable prerequisite to developing a flux-measurement protocol. Because the literature contains little information on z{sub m} for Sonoran Desert vegetation, it is desirable to measure z{sub m} and the displacement height (d) associated with Sonoran Desert vegetation.

  5. Low-subsonic aerodynamic characteristics of a shuttle-orbiter configuration designed for reduced length

    NASA Technical Reports Server (NTRS)

    Ware, G. M.; Spencer, B., Jr.

    1973-01-01

    An investigation has been made in a low-turbulence pressure tunnel to determine the low-subsonic aerodynamic characteristics of a 0.01875-scale model of a potential shuttle orbiter. The design has the rocket engines mounted in fairings on either side of the body on top of the wing. The wing had a leading-edge sweep of 50 and a trailing-edge sweep of minus 4. configurations investigated included engine-mounted twin dorsal tails at various rollout angles, a body-mounted center-line vertical tail, cylindrical and boattailed afterbody, and elevon and rudder at several deflections.

  6. Is a change in roughness length the cause of the recent decrease in Sahelian dust emission?

    NASA Astrophysics Data System (ADS)

    Cowie, S.; Knippertz, P.; Marsham, J.

    2012-04-01

    conditions in the Sahel through the following mechanisms: (A) Changes in Bowen ratio due to higher soil moisture levels reduce atmospheric turbulence, which has a larger negative impact on local wind-speed measurements than on grid box vector winds. (B) Increases in vegetation lead to increased surface roughness, which is not accounted for by ECMWF. This effect might have been enhanced by population increase around the measurement sites.

  7. Molecular dynamics study of the effect of atomic roughness on the slip length at the fluid-solid boundary during shear flow.

    PubMed

    Galea, T M; Attard, Phil

    2004-04-13

    A systematic study into the effect of solid roughness on the slip boundary condition during shear flow is presented. Atomic roughness is modeled by varying the size and spacing between solid atoms at constant packing fraction while the interaction parameters and the thermodynamic state of the fluid are kept constant. It is shown that the fluid structure as manifest in the amplitude of the density oscillations increases with increasing smoothness of the surfaces. The fluid-solid slip length is shown to exhibit nonmonotonic behavior as the solid structure is varied from smooth to rough. Slip occurs for both smooth and rough surfaces, and stick occurs only for surfaces commensurate with the fluid.

  8. Effects of Nanowire Length and Surface Roughness on the Electrochemical Sensor Properties of Nafion-Free, Vertically Aligned Pt Nanowire Array Electrodes.

    PubMed

    Li, Zhiyang; Leung, Calvin; Gao, Fan; Gu, Zhiyong

    2015-01-01

    In this paper, vertically aligned Pt nanowire arrays (PtNWA) with different lengths and surface roughnesses were fabricated and their electrochemical performance toward hydrogen peroxide (H₂O₂) detection was studied. The nanowire arrays were synthesized by electroplating Pt in nanopores of anodic aluminum oxide (AAO) template. Different parameters, such as current density and deposition time, were precisely controlled to synthesize nanowires with different surface roughnesses and various lengths from 3 μm to 12 μm. The PtNWA electrodes showed better performance than the conventional electrodes modified by Pt nanowires randomly dispersed on the electrode surface. The results indicate that both the length and surface roughness can affect the sensing performance of vertically aligned Pt nanowire array electrodes. Generally, longer nanowires with rougher surfaces showed better electrochemical sensing performance. The 12 μm rough surface PtNWA presented the largest sensitivity (654 μA·mM⁻¹·cm⁻²) among all the nanowires studied, and showed a limit of detection of 2.4 μM. The 12 μm rough surface PtNWA electrode also showed good anti-interference property from chemicals that are typically present in the biological samples such as ascorbic, uric acid, citric acid, and glucose. The sensing performance in real samples (river water) was tested and good recovery was observed. These Nafion-free, vertically aligned Pt nanowires with surface roughness control show great promise as versatile electrochemical sensors and biosensors. PMID:26404303

  9. Effects of Nanowire Length and Surface Roughness on the Electrochemical Sensor Properties of Nafion-Free, Vertically Aligned Pt Nanowire Array Electrodes

    PubMed Central

    Li, Zhiyang; Leung, Calvin; Gao, Fan; Gu, Zhiyong

    2015-01-01

    In this paper, vertically aligned Pt nanowire arrays (PtNWA) with different lengths and surface roughnesses were fabricated and their electrochemical performance toward hydrogen peroxide (H2O2) detection was studied. The nanowire arrays were synthesized by electroplating Pt in nanopores of anodic aluminum oxide (AAO) template. Different parameters, such as current density and deposition time, were precisely controlled to synthesize nanowires with different surface roughnesses and various lengths from 3 μm to 12 μm. The PtNWA electrodes showed better performance than the conventional electrodes modified by Pt nanowires randomly dispersed on the electrode surface. The results indicate that both the length and surface roughness can affect the sensing performance of vertically aligned Pt nanowire array electrodes. Generally, longer nanowires with rougher surfaces showed better electrochemical sensing performance. The 12 μm rough surface PtNWA presented the largest sensitivity (654 μA·mM−1·cm−2) among all the nanowires studied, and showed a limit of detection of 2.4 μM. The 12 μm rough surface PtNWA electrode also showed good anti-interference property from chemicals that are typically present in the biological samples such as ascorbic, uric acid, citric acid, and glucose. The sensing performance in real samples (river water) was tested and good recovery was observed. These Nafion-free, vertically aligned Pt nanowires with surface roughness control show great promise as versatile electrochemical sensors and biosensors. PMID:26404303

  10. Roughness Characterization of and Turbulent Boundary Layer Flow over flat Snow Surfaces

    NASA Astrophysics Data System (ADS)

    Gromke, C.; Guala, M.; Manes, C.; Walter, B.; Lehning, M.

    2009-12-01

    The surface roughness is essential for all turbulent exchange processes within the lower part of the atmospheric boundary layer. Consequently, a proper representation of the surfaces roughness is needed in every mathematical description of near surface mass-, energy- and momentum exchange processes. Considering the vertical mean velocity profile of turbulent boundary layer flow, this is done by assigning an aerodynamic roughness length z0 to the surface. We followed two procedures to describe the roughness of freshly fallen snow surfaces. First, photographs of snow surfaces have been taken and evaluated using digital image analysis giving snow surface contour line coordinates. Applying structure functions to the snow surface coordinates and statistical fitting procedures, resulted in classes of surface characteristic length scales and scaling exponents. These results allow to identify the deposition process of snow fall as scaling exponents corresponded to that of Ballistic Deposition. Moreover, the resulting characteristic length scales can be assigned to typical particle size and aggregation size length scales consistent with results found by Lowe et al. (2007) and Manes et al. (2008). Second, aerodynamic roughness lengths z0 have been estimated from log-law fitting of velocity profiles over the snow surfaces measured in the SLF cold atmospheric boundary layer wind tunnel. The aerodynamic roughness lengths found are in general agreement with available literature data and suggest the presence of aerodynamically rough regimes with flow independent z0. In the synthesis of both approaches, we found evidence for a linear relationship between one class of surface characteristic length scales, which is associated with typical snow particle sizes, and aerodynamic roughness lengths z0. The correlation with the aggregation length scale is weaker for the few (4) samples analyzed thus far. The relatively weak pronounced scale separation between particle and aggregation size

  11. Investigating the influence of roughness length for heat transport (zoh) on the performance of SEBAL in semi-arid irrigated and dryland agricultural systems

    NASA Astrophysics Data System (ADS)

    Paul, George; Gowda, Prasanna H.; Vara Prasad, P. V.; Howell, Terry A.; Aiken, Robert M.; Neale, Christopher M. U.

    2014-02-01

    Satellite-based thermal infrared remote sensing has greatly contributed to the development and improvement of remote sensing-based evapotranspiration (RS-ET) mapping algorithms. Radiometric temperature (Ts) derived from thermal sensors is inherently different from the aerodynamic temperature (To) required for solving the bulk formulation of sensible heat (H). The scalar roughness length (zoh) representing heat transport mechanism and described by the dimensionless parameter kB-1 was used to account for the discrepancy between Ts and To. Surface Energy Balance Algorithm for Land (SEBAL), with its indigenous approach of linearly relating dT (near-surface temperature gradient) with Ts across the imagery, maintained that this approach would absorb the impacts of differences between Ts and To. Therefore, it utilized a constant kB-1 value of 2.3 in its initial version, and later switched to a constant zoh (z1) value of 0.1. In this study, we investigated the influence of these changes in SEBAL by testing four different approaches: (i) zoh derived from a constant kB-1 of 2.3, (ii) constant zoh (z1) = 0.1 m, (iii) constant zoh (z1) = 0.01 m, and (iv) spatially variable zoh from kB-1 parameterization. SEBAL was applied on 10 high-resolution airborne images acquired during BEAREX07-08 (Bushland Evapotranspiration and Agricultural Remote Sensing Experiment) and validated against measurements from four large weighing lysimeters installed on two irrigated and two dryland fields. The spatially variable kB-1 produced statistically different and improved ET estimates compared to that with constant kB-1 and constant z1 (zoh) approaches. SEBAL performance for irrigated fields representing high ET and complete ground cover surfaces was markedly different from that for dryland fields representing greater soil water deficits with sparser vegetation cover. A variable kB-1 value derived from a physical model generated good overall estimates while delivering improved performance for

  12. Intercomparison of methods for the estimation of displacement height and roughness length from single-level eddy covariance data

    NASA Astrophysics Data System (ADS)

    Graf, Alexander; van de Boer, Anneke; Schüttemeyer, Dirk; Moene, Arnold; Vereecken, Harry

    2013-04-01

    The displacement height d and roughness length z0 are parameters of the logarithmic wind profile and as such these are characteristics of the surface, that are required in a multitude of meteorological modeling applications. Classically, both parameters are estimated from multi-level measurements of wind speed over a terrain sufficiently homogeneous to avoid footprint-induced differences between the levels. As a rule-of thumb, d of a dense, uniform crop or forest canopy is 2/3 to 3/4 of the canopy height h, and z0 about 10% of canopy height in absence of any d. However, the uncertainty of this rule-of-thumb becomes larger if the surface of interest is not "dense and uniform", in which case a site-specific determination is required again. By means of the eddy covariance method, alternative possibilities to determine z0 and d have become available. Various authors report robust results if either several levels of sonic anemometer measurements, or one such level combined with a classic wind profile is used to introduce direct knowledge on the friction velocity into the estimation procedure. At the same time, however, the eddy covariance method to measure various fluxes has superseded the profile method, leaving many current stations without a wind speed profile with enough levels sufficiently far above the canopy to enable the classic estimation of z0 and d. From single-level eddy covariance measurements at one point in time, only one parameter can be estimated, usually z0 while d is assumed to be known. Even so, results tend to scatter considerably. However, it has been pointed out, that the use of multiple points in time providing different stability conditions can enable the estimation of both parameters, if they are assumed constant over the time period regarded. These methods either rely on flux-variance similarity (Weaver 1990 and others following), or on the integrated universal function for momentum (Martano 2000 and others following). In both cases

  13. Aerodynamics of sports balls

    NASA Technical Reports Server (NTRS)

    Mehta, R. D.

    1985-01-01

    Research data on the aerodynamic behavior of baseballs and cricket and golf balls are summarized. Cricket balls and baseballs are roughly the same size and mass but have different stitch patterns. Both are thrown to follow paths that avoid a batter's swing, paths that can curve if aerodynamic forces on the balls' surfaces are asymmetric. Smoke tracer wind tunnel tests and pressure taps have revealed that the unbalanced side forces are induced by tripping the boundary layer on the seam side and producing turbulence. More particularly, the greater pressures are perpendicular to the seam plane and only appear when the balls travel at velocities high enough so that the roughness length matches the seam heigh. The side forces, once tripped, will increase with spin velocity up to a cut-off point. The enhanced lift coefficient is produced by the Magnus effect. The more complex stitching on a baseball permits greater variations in the flight path curve and, in the case of a knuckleball, the unsteady flow effects. For golf balls, the dimples trip the boundary layer and the high spin rate produces a lift coefficient maximum of 0.5, compared to a baseball's maximum of 0.3. Thus, a golf ball travels far enough for gravitational forces to become important.

  14. Aerodynamics of sports balls

    NASA Astrophysics Data System (ADS)

    Mehta, R. D.

    Research data on the aerodynamic behavior of baseballs and cricket and golf balls are summarized. Cricket balls and baseballs are roughly the same size and mass but have different stitch patterns. Both are thrown to follow paths that avoid a batter's swing, paths that can curve if aerodynamic forces on the balls' surfaces are asymmetric. Smoke tracer wind tunnel tests and pressure taps have revealed that the unbalanced side forces are induced by tripping the boundary layer on the seam side and producing turbulence. More particularly, the greater pressures are perpendicular to the seam plane and only appear when the balls travel at velocities high enough so that the roughness length matches the seam heigh. The side forces, once tripped, will increase with spin velocity up to a cut-off point. The enhanced lift coefficient is produced by the Magnus effect. The more complex stitching on a baseball permits greater variations in the flight path curve and, in the case of a knuckleball, the unsteady flow effects. For golf balls, the dimples trip the boundary layer and the high spin rate produces a lift coefficient maximum of 0.5, compared to a baseball's maximum of 0.3. Thus, a golf ball travels far enough for gravitational forces to become important.

  15. Diurnal Variations of Thermal Roughness Height over a Grassland

    NASA Astrophysics Data System (ADS)

    Sun, Jielun

    The thermal roughness height associated with the surface radiation temperature has been previously found to vary between different surface types. This study finds that the thermal roughness height varies diurnally even over a homogeneous senescent grassland. The corresponding roughness length for momentum is relatively constant.Both the aerodynamic temperature and the surface radiation temperature are found to be closely related to the air temperature in the middle of the grass canopy. However, the aerodynamic temperature is strongly influenced by the horizontally integrated heat transfer, while the surface radiation temperature represents the integrated thermal emission through the grass depth within the field of view of the radiometer. The aerodynamic temperature is less sensitive to variations and measurement errors in sensible heat flux, wind speed, and air temperature than the thermal roughness height. We find that formulating the aerodynamic temperature in terms of the surface radiation temperature is better posed for use in the bulk formula than using the surface radiation temperature directly and adjusting the thermal roughness length.

  16. Investigation of surface roughness and tool wear length with varying combination of depth of cut and feed rate of Aluminium alloy and P20 steel machining.

    NASA Astrophysics Data System (ADS)

    Varmma a/l Suparmaniam, Madan; Razlan Yusoff, Ahmad

    2016-02-01

    High-speed milling technique is often used in many industries to boost productivity of the manufacturing of high-technology components. The occurrence of wear highly limits the efficiency and accuracy of high- speed milling operations. In this paper, analysis of high-speed milling process parameters such as material removal rate, cutting speed, feed rate and depth of cut carried out by implemented to conventional milling. This experiment investigate the effects of varying combination of depth of cut and feed rate to tool wear rate length using metallurgical microscope and surface roughness using portable surface roughness tester after end milling of Aluminium and P20 steel. Results showed that feed rate significantly influences the surface roughness value while depth of cut does not as the surface roughness value keep increasing with the increase of feed rate and decreasing depth of cut. Whereas, tool wear rate almost remain unchanged indicates that material removal rate strongly contribute the wear rate. It believe that with no significant tool wear rate the results of this experiment are useful by showing that HSM technique is possible to be applied in conventional machine with extra benefits of high productivity, eliminating semi-finishing operation and reducing tool load for finishing.

  17. A global climatology of albedo, roughness length and stomatal resistance for atmospheric general circulation models as represented by the Simple Biosphere Model (SiB)

    NASA Technical Reports Server (NTRS)

    Dorman, J. L.; Sellers, P. J.

    1989-01-01

    Components of the Simple Biosphere Model (SiB) of Sellers et al. (1986) were used to generate global monthly fields of surface albedo (0.4-4.0 microns), roughness length and minimum surface (stomatal) resistance. SiB consists of three submodels which describe the roles of radiative transfer, turbulent transfer and surface resistance in determining the energy balance of the vegetated land surface. These three submodels were detached from SiB and used on the SiB parameter set (total and green leaf area index, leaf angle orientation, canopy dimensions, etc.) to calculate global monthly fields of albedo, roughness length and minimum stomatal resistance at 1 x 1 deg resolution. Time series of various parameters are also displayed for each vegetation type for specified grid points. The SiB results compare reasonably well with appropriate measurements obtained from the literature and have the additional merit of being mutually consistent; the three submodels use many common parameters, which ensures that, for each grid area, the calculated surface properties are closely interrelated as is the case in nature. The derived fields provide a check on the operation of the submodels and the correctness of the parameter set. They can also be used as prescribed fields for GCMs that do not have biophysically based land surface parameterizations.

  18. Effective roughness in meso-scale modeling.

    NASA Astrophysics Data System (ADS)

    Nielsen, Joakim R.

    2010-05-01

    Effective roughness in meso-scale modeling. J.R. Nielsen, E. Dellwik, A. Hahmann, A. Sogachev, C.B. Hasager, Wind Energy Division, Risø DTU National Laboratory, Denmark Accurate estimation of effective roughness lengths for use in meso-scale models in heterogeneous terrain requires assessment of highly non-linear processes. These non-linear effects are often neglected in meso-scale modeling where, typically, a simple logarithmic average or a dominant vegetation type provide crude estimates of the aggregated aerodynamical roughness length in each grid cell. Although the parameterizations are computationally efficient, improvements are needed since some regional-scale sensitivity studies indicate that grid cell roughnesses strongly influence model predictions (i.e. Hasager and Jensen, 1999). Effective roughness parameterizations can be provided through the use of microscale flow models, which simulate the he local scale effect of orography and roughness changes. Results from two linearized micro-scale models and a k-ω model (Sogachev and Panferov, 2006) are presented for an idealized terrain with roughness changes. Furthermore, sensitivity experiments are performed within the meso-scale model WRF (Weather Research and Forecasting) using the standard Community Noah Land Surface model. The same experiment will be performed with a new modified version with multi-physics options (Niu et al.,submitted 2009). The analysis is carried out using different roughness aggregation techniques in WRF and the influence on scalar fluxes such as temperature, humidity and CO2 is investigated. Based on the WRF sensitivity analysis and the results of micro-scale modeling, the potential improvement of using micro-scale models for parameterization of sub-grid scale variability is evaluated.

  19. Aerodynamic Performance and Static Stability at Mach Number 3.3 of an Aircraft Configuration Employing Three Triangular Wing Panels and a Body Equal Length

    NASA Technical Reports Server (NTRS)

    James, Carlton S.

    1960-01-01

    An aircraft configuration, previously conceived as a means to achieve favorable aerodynamic stability characteristics., high lift-drag ratio, and low heating rates at high supersonic speeds., was modified in an attempt to increase further the lift-drag ratio without adversely affecting the other desirable characteristics. The original configuration consisted of three identical triangular wing panels symmetrically disposed about an ogive-cylinder body equal in length to the root chord of the panels. This configuration was modified by altering the angular disposition of the wing panels, by reducing the area of the panel forming the vertical fin, and by reshaping the body to produce interference lift. Six-component force and moment tests of the modified configuration at combined angles of attack and sideslip were made at a Mach number of 3.3 and a Reynolds number of 5.46 million. A maximum lift-drag ratio of 6.65 (excluding base drag) was measured at a lift coefficient of 0.100 and an angle of attack of 3.60. The lift-drag ratio remained greater than 3 up to lift coefficient of 0.35. Performance estimates, which predicted a maximum lift-drag ratio for the modified configuration 27 percent greater than that of the original configuration, agreed well with experiment. The modified configuration exhibited favorable static stability characteristics within the test range. Longitudinal and directional centers of pressure were slightly aft of the respective centroids of projected plan-form and side area.

  20. Gliding swifts attain laminar flow over rough wings.

    PubMed

    Lentink, David; de Kat, Roeland

    2014-01-01

    Swifts are among the most aerodynamically refined gliding birds. However, the overlapping vanes and protruding shafts of their primary feathers make swift wings remarkably rough for their size. Wing roughness height is 1-2% of chord length on the upper surface--10,000 times rougher than sailplane wings. Sailplanes depend on extreme wing smoothness to increase the area of laminar flow on the wing surface and minimize drag for extended glides. To understand why the swift does not rely on smooth wings, we used a stethoscope to map laminar flow over preserved wings in a low-turbulence wind tunnel. By combining laminar area, lift, and drag measurements, we show that average area of laminar flow on swift wings is 69% (n = 3; std 13%) of their total area during glides that maximize flight distance and duration--similar to high-performance sailplanes. Our aerodynamic analysis indicates that swifts attain laminar flow over their rough wings because their wing size is comparable to the distance the air travels (after a roughness-induced perturbation) before it transitions from laminar to turbulent. To interpret the function of swift wing roughness, we simulated its effect on smooth model wings using physical models. This manipulation shows that laminar flow is reduced and drag increased at high speeds. At the speeds at which swifts cruise, however, swift-like roughness prolongs laminar flow and reduces drag. This feature gives small birds with rudimentary wings an edge during the evolution of glide performance. PMID:24964089

  1. Gliding Swifts Attain Laminar Flow over Rough Wings

    PubMed Central

    Lentink, David; de Kat, Roeland

    2014-01-01

    Swifts are among the most aerodynamically refined gliding birds. However, the overlapping vanes and protruding shafts of their primary feathers make swift wings remarkably rough for their size. Wing roughness height is 1–2% of chord length on the upper surface—10,000 times rougher than sailplane wings. Sailplanes depend on extreme wing smoothness to increase the area of laminar flow on the wing surface and minimize drag for extended glides. To understand why the swift does not rely on smooth wings, we used a stethoscope to map laminar flow over preserved wings in a low-turbulence wind tunnel. By combining laminar area, lift, and drag measurements, we show that average area of laminar flow on swift wings is 69% (n = 3; std 13%) of their total area during glides that maximize flight distance and duration—similar to high-performance sailplanes. Our aerodynamic analysis indicates that swifts attain laminar flow over their rough wings because their wing size is comparable to the distance the air travels (after a roughness-induced perturbation) before it transitions from laminar to turbulent. To interpret the function of swift wing roughness, we simulated its effect on smooth model wings using physical models. This manipulation shows that laminar flow is reduced and drag increased at high speeds. At the speeds at which swifts cruise, however, swift-like roughness prolongs laminar flow and reduces drag. This feature gives small birds with rudimentary wings an edge during the evolution of glide performance. PMID:24964089

  2. Investigating the influence of roughness length for heat transport (zoh) on the performance of SEBAL in semi-arid irrigated, and dryland agricultural systems

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Satellite-based thermal infrared remote sensing has greatly contributed to the development and improvement of remote sensing–based evapotranspiration (ET) mapping algorithms. Radiometric temperature (Ts) derived from thermal sensors is inherently different from the aerodynamic temperature (To) requi...

  3. Experimental study of noise emitted by circular cylinders with large roughness

    NASA Astrophysics Data System (ADS)

    Alomar, Antoni; Angland, David; Zhang, Xin; Molin, Nicolas

    2014-12-01

    The aerodynamic noise generated by high Reynolds number flow around a bluff body with large surface roughness was investigated. This is a relevant problem in many applications, in particular aircraft landing gear noise. A circular cylinder in cross-flow and a zero-pressure-gradient turbulent boundary layer with various types of roughness was tested in a series of wind tunnel experiments. It has been shown that distributed roughness covering a circular cylinder affects the spectra over the entire frequency range. Roughness noise is dominant at high frequencies, and the peak frequency is well described by Howe's roughness noise model when scaled with the maximum outer velocity. There are differences between hemispherical and cylindrical roughness elements for both the circular cylinder and the zero-pressure-gradient turbulent boundary layer cases, indicating a dependence on roughness shape, not described by the considered roughness noise models. Cylindrical roughness generates higher noise levels at the highest frequencies, especially for the zero-pressure-gradient turbulent boundary layer case. Cable-type roughness aligned with the mean flow does not generate roughness noise, and its spectrum has been found to collapse with the smooth cylinder at medium and high frequencies. At low and medium frequencies the noise spectra have the same features as the smooth cylinder, but with higher shedding peak levels and fall-off levels, despite the decrease in spanwise correlation length. Roughness induces early separation, and thus a shift of the spectra to lower frequencies.

  4. Feather roughness reduces flow separation during low Reynolds number glides of swifts.

    PubMed

    van Bokhorst, Evelien; de Kat, Roeland; Elsinga, Gerrit E; Lentink, David

    2015-10-01

    Swifts are aerodynamically sophisticated birds with a small arm and large hand wing that provides them with exquisite control over their glide performance. However, their hand wings have a seemingly unsophisticated surface roughness that is poised to disturb flow. This roughness of about 2% chord length is formed by the valleys and ridges of overlapping primary feathers with thick protruding rachides, which make the wing stiffer. An earlier flow study of laminar-turbulent boundary layer transition over prepared swift wings suggested that swifts can attain laminar flow at a low angle of attack. In contrast, aerodynamic design theory suggests that airfoils must be extremely smooth to attain such laminar flow. In hummingbirds, which have similarly rough wings, flow measurements on a 3D printed model suggest that the flow separates at the leading edge and becomes turbulent well above the rachis bumps in a detached shear layer. The aerodynamic function of wing roughness in small birds is, therefore, not fully understood. Here, we performed particle image velocimetry and force measurements to compare smooth versus rough 3D-printed models of the swift hand wing. The high-resolution boundary layer measurements show that the flow over rough wings is indeed laminar at a low angle of attack and a low Reynolds number, but becomes turbulent at higher values. In contrast, the boundary layer over the smooth wing forms open laminar separation bubbles that extend beyond the trailing edge. The boundary layer dynamics of the smooth surface varies non-linearly as a function of angle of attack and Reynolds number, whereas the rough surface boasts more consistent turbulent boundary layer dynamics. Comparison of the corresponding drag values, lift values and glide ratios suggests, however, that glide performance is equivalent. The increased structural performance, boundary layer robustness and equivalent aerodynamic performance of rough wings might have provided small (proto) birds with

  5. Feather roughness reduces flow separation during low Reynolds number glides of swifts.

    PubMed

    van Bokhorst, Evelien; de Kat, Roeland; Elsinga, Gerrit E; Lentink, David

    2015-10-01

    Swifts are aerodynamically sophisticated birds with a small arm and large hand wing that provides them with exquisite control over their glide performance. However, their hand wings have a seemingly unsophisticated surface roughness that is poised to disturb flow. This roughness of about 2% chord length is formed by the valleys and ridges of overlapping primary feathers with thick protruding rachides, which make the wing stiffer. An earlier flow study of laminar-turbulent boundary layer transition over prepared swift wings suggested that swifts can attain laminar flow at a low angle of attack. In contrast, aerodynamic design theory suggests that airfoils must be extremely smooth to attain such laminar flow. In hummingbirds, which have similarly rough wings, flow measurements on a 3D printed model suggest that the flow separates at the leading edge and becomes turbulent well above the rachis bumps in a detached shear layer. The aerodynamic function of wing roughness in small birds is, therefore, not fully understood. Here, we performed particle image velocimetry and force measurements to compare smooth versus rough 3D-printed models of the swift hand wing. The high-resolution boundary layer measurements show that the flow over rough wings is indeed laminar at a low angle of attack and a low Reynolds number, but becomes turbulent at higher values. In contrast, the boundary layer over the smooth wing forms open laminar separation bubbles that extend beyond the trailing edge. The boundary layer dynamics of the smooth surface varies non-linearly as a function of angle of attack and Reynolds number, whereas the rough surface boasts more consistent turbulent boundary layer dynamics. Comparison of the corresponding drag values, lift values and glide ratios suggests, however, that glide performance is equivalent. The increased structural performance, boundary layer robustness and equivalent aerodynamic performance of rough wings might have provided small (proto) birds with

  6. Experimental investigation of aerodynamic devices for wind turbine rotational speed control: Phase II

    SciTech Connect

    Miller, S L

    1996-02-01

    An experimental investigation was undertaken to further evaluate and enhance the performance of an aerodynamic device for wind turbine overspeed protection and power modulation applications. The trailing-edge device, known as the Spoiler-Flap, was examined in detail during wind tunnel tests. The impact of hp length, vent angle, pivot point and chord variations on aerodynamic and hinge moment characteristics were evaluated and a best overall configuration was identified. Based on this effort, a 40% chord device with a 1% hp length and 40 degree vent angle offers improved performance potential for wind turbine applications. This specific configuration appears to offer good suction coefficient performance for both turbine power modulation and overspeed (i.e., aerodynamic braking) applications. Device hinge moment loads improved (compared to other devices investigated) in magnitude and the impact of surface roughness was found to be minimal.

  7. Aerodynamic potpourri

    NASA Technical Reports Server (NTRS)

    Wilson, R. E.

    1981-01-01

    Aerodynamic developments for vertical axis and horizontal axis wind turbines are given that relate to the performance and aerodynamic loading of these machines. Included are: (1) a fixed wake aerodynamic model of the Darrieus vertical axis wind turbine; (2) experimental results that suggest the existence of a laminar flow Darrieus vertical axis turbine; (3) a simple aerodynamic model for the turbulent windmill/vortex ring state of horizontal axis rotors; and (4) a yawing moment of a rigid hub horizontal axis wind turbine that is related to blade coning.

  8. Aerodynamic potpourri

    NASA Astrophysics Data System (ADS)

    Wilson, R. E.

    1981-05-01

    Aerodynamic developments for vertical axis and horizontal axis wind turbines are given that relate to the performance and aerodynamic loading of these machines. Included are: (1) a fixed wake aerodynamic model of the Darrieus vertical axis wind turbine; (2) experimental results that suggest the existence of a laminar flow Darrieus vertical axis turbine; (3) a simple aerodynamic model for the turbulent windmill/vortex ring state of horizontal axis rotors; and (4) a yawing moment of a rigid hub horizontal axis wind turbine that is related to blade coning.

  9. Comparison of selected approaches for urban roughness determination based on voronoi cells

    NASA Astrophysics Data System (ADS)

    Ketterer, Christine; Gangwisch, Marcel; Fröhlich, Dominik; Matzarakis, Andreas

    2016-07-01

    Wind speed is reduced above urban areas due to their high aerodynamic roughness. This not only holds for above the urban canopy. The local vertical wind profile is modified. Aerodynamic roughness (both roughness length and displacement height) therefore is relevant for many fields within human biometeorology, e.g. for the identification of ventilation paths, the concentration and dispersion of air pollutants at street level or to simulate wind speed and direction in urban environments and everything depending on them. Roughness, thus, also shows strong influence on human thermal comfort. Currently, roughness parameters are mostly estimated using classifications. However, such classifications only provide limited assessment of roughness in urban areas. In order to calculate spatially resolved roughness on the micro-scale, three different approaches were implemented in the SkyHelios model. For all of them, the urban area is divided into reference areas for each of the obstacles using a voronoi diagram. The three approaches are based on building and [+one of them also on] vegetation (trees and forests) data. They were compared for the city of Stuttgart, Germany. Results show that the approach after Bottema and Mestayer (J Wind Eng Ind Aerodyn 74-76:163-173 1998) on the spatial basis of a voronoi diagram provides the most plausible results.

  10. Relationships between topographic roughness and aeolian processes

    NASA Technical Reports Server (NTRS)

    Greeley, Ronald; Lancaster, N.; Gaddis, L.; Rasmussen, K. R.; White, B. R.; Saunders, R. S.; Wall, S.; Dobrovolskis, Anthony R.; Iversen, J. D.

    1991-01-01

    The interaction between winds and desert surfaces has important implications for sediment transport on Earth, Mars, and Venus, and for understanding the relationships between radar backscatter and aerodynamic roughness as part of the NASA Shuttle Imaging radar (SIR-C) Mission. Here, researchers report results from measurements of boundary layer wind profiles and surface roughness at sites in Death Valley and discuss their implications. The sites included a flat to undulating gravel and sand reg, alluvial fans, and a playa. Estimates of average particle size composition of Death Valley sites and arithmetic mean values of aerodynamic roughness are given in tabular form.

  11. NASP aerodynamics

    NASA Technical Reports Server (NTRS)

    Whitehead, Allen H., Jr.

    1989-01-01

    This paper discusses the critical aerodynamic technologies needed to support the development of a class of aircraft represented by the National Aero-Space Plane (NASP). The air-breathing, single-stage-to-orbit mission presents a severe challenge to all of the aeronautical disciplines and demands an extension of the state-of-the-art in each technology area. While the largest risk areas are probably advanced materials and the development of the scramjet engine, there remains a host of design issues and technology problems in aerodynamics, aerothermodynamics, and propulsion integration. The paper presents an overview of the most significant propulsion integration problems, and defines the most critical fluid flow phenomena that must be evaluated, defined, and predicted for the class of aircraft represented by the Aero-Space Plane.

  12. Analysis of full-length sequences of two Citrus yellow mosaic badnavirus isolates infecting Citrus jambhiri (Rough Lemon) and Citrus sinensis L. Osbeck (Sweet Orange) from a nursery in India.

    PubMed

    Anthony Johnson, A M; Borah, B K; Sai Gopal, D V R; Dasgupta, I

    2012-12-01

    Citrus yellow mosaic badna virus (CMBV), a member of the Family Caulimoviridae, Genus Badnavirus is the causative agent of mosaic disease among Citrus species in southern India. Despite its reported prevalence in several citrus species, complete information on clear functional genomics or functional information of full-length genomes from all the CMBV isolates infecting citrus species are not available in publicly accessible databases. CMBV isolates from Rough Lemon and Sweet Orange collected from a nursery were cloned and sequenced. The analysis revealed high sequence homology of the two CMBV isolates with previously reported CMBV sequences implying that they represent new variants. Based on computational analysis of the predicted secondary structures, the possible functions of some CMBV proteins have been analyzed.

  13. The Effects of Highly Detailed Urban Roughness Parameters on a Sea-Breeze Numerical Simulation

    NASA Astrophysics Data System (ADS)

    Varquez, Alvin Christopher G.; Nakayoshi, Makoto; Kanda, Manabu

    2015-03-01

    We consider the effects of detailed urban roughness parameters on a sea-breeze simulation. An urban roughness database, constructed using a new aerodynamic parametrization derived from large-eddy simulations, was incorporated as a surface boundary condition in the advanced Weather Research and Forecasting model. The zero-plane displacement and aerodynamic roughness length at several densely built-up urban grids were three times larger than conventional values due to the consideration of building-height variability. A comparison between simulations from the modified model and its default version, which uses uniform roughness parameters within a conventional method, was conducted for a 2-month period during summer. Results showed a significant improvement in the simulation of surface wind speed but not with temperature. From the 2-month study period, a day with an evident sea-breeze penetration was selected and simulated at higher temporal resolution. Sea-breeze penetration weakened and was more delayed over urbanized areas. The slow sea-breeze penetration also lessened heat advection downwind allowing stronger turbulent mixing and a deeper boundary layer above urban areas. Horizontal wind-speed reduction due to the increased urban surface drag reached heights of several hundreds of metres due to the strong convection.

  14. Computational aerodynamics and supercomputers

    NASA Technical Reports Server (NTRS)

    Ballhaus, W. F., Jr.

    1984-01-01

    Some of the progress in computational aerodynamics over the last decade is reviewed. The Numerical Aerodynamic Simulation Program objectives, computational goals, and implementation plans are described.

  15. Determination of aerodynamic parameters of urban surfaces: methods and results revisited

    NASA Astrophysics Data System (ADS)

    Mohammad, A. F.; Zaki, S. A.; Hagishima, A.; Ali, M. S. M.

    2015-11-01

    Estimates of aerodynamic parameters, in particular roughness length z 0 and displacement height d, are important for the analysis of the roughness of an urban surface, which affects processes that occur within the urban boundary layer such as pollutant dispersion and urban ventilation. Findings regarding the aerodynamic effects of various configurations of urban arrays were compiled from various studies. Several experimental, numerical and semi-empirical studies to estimate z 0 and d were reviewed and compared with each other. The results can be summarized as follows: (1) the influence of the frontal area index ( λ f ) on z 0 is significant and their relationship has been confirmed by both experimental and numerical data; (2) compared to one-parameter and two-parameter fitting methods, the three-parameter fitting method is the least accurate; (3) the physical meaning of d remains vague because its definition as the height where surface drag acts may not be accurate for sharp-edged roughness blocks and (4) the peak values of z 0 for uniform and heterogeneous block heights indicate presence of skimming or wake-interference flow effects, which may influence surface roughness. Finally, the semi-empirical models were found to be limited to cases derived from available experimental data, which normally involve uniform arrays of cubes.

  16. Large-eddy simulations of surface roughness parameter sensitivity to canopy-structure characteristics

    DOE PAGES

    Maurer, K. D.; Bohrer, G.; Kenny, W. T.; Ivanov, V. Y.

    2015-04-30

    Surface roughness parameters, namely the roughness length and displacement height, are an integral input used to model surface fluxes. However, most models assume these parameters to be a fixed property of plant functional type and disregard the governing structural heterogeneity and dynamics. In this study, we use large-eddy simulations to explore, in silico, the effects of canopy-structure characteristics on surface roughness parameters. We performed a virtual experiment to test the sensitivity of resolved surface roughness to four axes of canopy structure: (1) leaf area index, (2) the vertical profile of leaf density, (3) canopy height, and (4) canopy gap fraction.more » We found roughness parameters to be highly variable, but uncovered positive relationships between displacement height and maximum canopy height, aerodynamic canopy height and maximum canopy height and leaf area index, and eddy-penetration depth and gap fraction. We also found negative relationships between aerodynamic canopy height and gap fraction, as well as between eddy-penetration depth and maximum canopy height and leaf area index. We generalized our model results into a virtual "biometric" parameterization that relates roughness length and displacement height to canopy height, leaf area index, and gap fraction. Using a decade of wind and canopy-structure observations in a site in Michigan, we tested the effectiveness of our model-driven biometric parameterization approach in predicting the friction velocity over heterogeneous and disturbed canopies. We compared the accuracy of these predictions with the friction-velocity predictions obtained from the common simple approximation related to canopy height, the values calculated with large-eddy simulations of the explicit canopy structure as measured by airborne and ground-based lidar, two other parameterization approaches that utilize varying canopy-structure inputs, and the annual and decadal means of the surface roughness parameters at

  17. Detecting surface roughness effects on the atmospheric boundary layer via AIRSAR data: A field experiment in Death Valley, California

    NASA Technical Reports Server (NTRS)

    Blumberg, Dan G.; Greeley, Ronald

    1992-01-01

    The part of the troposphere influenced by the surface of the earth is termed the atmospheric boundary layer. Flow within this layer is influenced by the roughness of the surface; rougher surfaces induce more turbulence than smoother surfaces and, hence, higher atmospheric transfer rates across the surface. Roughness elements also shield erodible particles, thus decreasing the transport of windblown particles. Therefore, the aerodynamic roughness length (z(sub 0)) is an important parameter in aeolian and atmospheric boundary layer processes as it describes the aerodynamic properties of the underlying surface. z(sub 0) is assumed to be independent of wind velocity or height, and dependent only on the surface topography. It is determined using in situ measurements of the wind speed distribution as a function of height. For dry, unvegetated soils the intensity of the radar backscatter (sigma(sup 0)) is affected primarily by surface roughness at a scale comparable with the radar wavelength. Thus, both wind and radar respond to surface roughness variations on a scale of a few meters or less. Greeley showed the existence of a correlation between z(sub 0) and sigma(sup 0). This correlation was based on measurements over lava flows, alluvial fans, and playas in the southwest deserts of the United States. It is shown that the two parameters behave similarly also when there are small changes over a relatively homogeneous surface.

  18. Rough surface improves stability of air- sounding balloons

    NASA Technical Reports Server (NTRS)

    Scoggins, J. R.

    1965-01-01

    Aerodynamic stability of balloons used for measuring the intensity and direction of atmospheric winds at various elevations is improved by incorporating a rough surface on the balloons. The rough-surfaced balloon is useful for collecting wind profiles and other meteorological data.

  19. Impact of surface roughness and soil texture on mineral dust emission fluxes modeling

    NASA Astrophysics Data System (ADS)

    Menut, Laurent; PéRez, Carlos; Haustein, Karsten; Bessagnet, Bertrand; Prigent, Catherine; Alfaro, StéPhane

    2013-06-01

    Dust production models (DPM) used to estimate vertical fluxes of mineral dust aerosols over arid regions need accurate data on soil and surface properties. The Laboratoire Inter-Universitaire des Systemes Atmospheriques (LISA) data set was developed for Northern Africa, the Middle East, and East Asia. This regional data set was built through dedicated field campaigns and include, among others, the aerodynamic roughness length, the smooth roughness length of the erodible fraction of the surface, and the dry (undisturbed) soil size distribution. Recently, satellite-derived roughness length and high-resolution soil texture data sets at the global scale have emerged and provide the opportunity for the use of advanced schemes in global models. This paper analyzes the behavior of the ERS satellite-derived global roughness length and the State Soil Geographic data base-Food and Agriculture Organization of the United Nations (STATSGO-FAO) soil texture data set (based on wet techniques) using an advanced DPM in comparison to the LISA data set over Northern Africa and the Middle East. We explore the sensitivity of the drag partition scheme (a critical component of the DPM) and of the dust vertical fluxes (intensity and spatial patterns) to the roughness length and soil texture data sets. We also compare the use of the drag partition scheme to a widely used preferential source approach in global models. Idealized experiments with prescribed wind speeds show that the ERS and STATSGO-FAO data sets provide realistic spatial patterns of dust emission and friction velocity thresholds in the region. Finally, we evaluate a dust transport model for the period of March to July 2011 with observed aerosol optical depths from Aerosol Robotic Network sites. Results show that ERS and STATSGO-FAO provide realistic simulations in the region.

  20. Impact of Surface Roughness and Soil Texture on Mineral Dust Emission Fluxes Modeling

    NASA Technical Reports Server (NTRS)

    Menut, Laurent; Perez, Carlos; Haustein, Karsten; Bessagnet, Bertrand; Prigent, Catherine; Alfaro, Stephane

    2013-01-01

    Dust production models (DPM) used to estimate vertical fluxes of mineral dust aerosols over arid regions need accurate data on soil and surface properties. The Laboratoire Inter-Universitaire des Systemes Atmospheriques (LISA) data set was developed for Northern Africa, the Middle East, and East Asia. This regional data set was built through dedicated field campaigns and include, among others, the aerodynamic roughness length, the smooth roughness length of the erodible fraction of the surface, and the dry (undisturbed) soil size distribution. Recently, satellite-derived roughness length and high-resolution soil texture data sets at the global scale have emerged and provide the opportunity for the use of advanced schemes in global models. This paper analyzes the behavior of the ERS satellite-derived global roughness length and the State Soil Geographic data base-Food and Agriculture Organization of the United Nations (STATSGO-FAO) soil texture data set (based on wet techniques) using an advanced DPM in comparison to the LISA data set over Northern Africa and the Middle East. We explore the sensitivity of the drag partition scheme (a critical component of the DPM) and of the dust vertical fluxes (intensity and spatial patterns) to the roughness length and soil texture data sets. We also compare the use of the drag partition scheme to a widely used preferential source approach in global models. Idealized experiments with prescribed wind speeds show that the ERS and STATSGO-FAO data sets provide realistic spatial patterns of dust emission and friction velocity thresholds in the region. Finally, we evaluate a dust transport model for the period of March to July 2011 with observed aerosol optical depths from Aerosol Robotic Network sites. Results show that ERS and STATSGO-FAO provide realistic simulations in the region.

  1. Wind-Speed Profile and Roughness Sublayer Depth Modelling in Urban Boundary Layers

    NASA Astrophysics Data System (ADS)

    Pelliccioni, Armando; Monti, Paolo; Leuzzi, Giovanni

    2016-08-01

    We propose a new formulation for the wind-speed profile in the urban boundary layer, which can be viewed as a generalisation of the commonly used logarithmic law. The model is based on the assumption that the role played by the classical aerodynamic roughness length and the displacement height in the logarithmic law is taken by a sole variable, the local length scale, which follows a pattern of exponential decrease with height. Starting from wind-speed profiles collected at Villa Pamphili park, Rome, Italy, an empirical fit is used to determine the model parameters. The results show that the local length scale depends also on the friction velocity and that, with appropriate normalization, it reduces to a family of curves that spreads according to the planar area fraction. Another novel aspect is the estimation of the roughness sublayer depth, which can be expressed as a function of the friction velocity and morphometric quantities such as the building height and the planar area fraction. It is also found that the rate of growth with height of the Prandtl mixing length linked to the new formulation is, just above the canopy, lower than the canonical value 0.41, and approaches the latter value well above the roughness sublayer. The model performance is tested by comparison with laboratory and field data reported in the literature.

  2. Some aerodynamic considerations related to wind tunnel model surface definition

    NASA Technical Reports Server (NTRS)

    Gloss, B. B.

    1980-01-01

    The aerodynamic considerations related to model surface definition are examined with particular emphasis in areas of fabrication tolerances, model surface finish, and orifice induced pressure errors. The effect of model surface roughness texture on skin friction is also discussed. It is shown that at a given Reynolds number, any roughness will produce no skin friction penalty.

  3. The boundary layer over turbine blade models with realistic rough surfaces

    NASA Astrophysics Data System (ADS)

    McIlroy, Hugh M., Jr.

    The impact of turbine blade surface roughness on aerodynamic performance and heat loads is well known. Over time, as the turbine blades are exposed to heat loads, the external surfaces of the blades become rough. Also, for film-cooled blades, surface degradation can have a significant impact on film-cooling effectiveness. Many studies have been conducted on the effects of surface degradation/roughness on engine performance but most investigations have modeled the rough surfaces with uniform or two-dimensional roughness patterns. The objective of the present investigation is to conduct measurements that will reveal the influence of realistic surface roughness on the near-wall behavior of the boundary layer. Measurements have been conducted at the Matched-Index-of-Refraction (MIR) Facility at the Idaho National Engineering and Environmental Laboratory with a laser Doppler velocimeter. A flat plate model of a turbine blade has been developed that produces a transitional boundary layer, elevated freestream turbulence and an accelerating freestream in order to simulate conditions on the suction side of a high-pressure turbine blade. Boundary layer measurements have been completed over a smooth plate model and over a model with a strip of realistic rough surface. The realistic rough surface was developed by scaling actual turbine blade surface data that was provided by U.S. Air Force Research Laboratory. The results indicate that bypass transition occurred very early in the flow over the model and that the boundary layer remained unstable throughout the entire length of the test plate; the boundary layer thickness and momentum thickness Reynolds numbers increased over the rough patch; and the shape factor increased over the rough patch but then decreased downstream of the patch relative to the smooth plate case; in the rough patch case the flow experienced two transition reversals with laminar-like behavior achieved by the end of the test plate; streamwise turbulence

  4. Classical Aerodynamic Theory

    NASA Technical Reports Server (NTRS)

    Jones, R. T. (Compiler)

    1979-01-01

    A collection of papers on modern theoretical aerodynamics is presented. Included are theories of incompressible potential flow and research on the aerodynamic forces on wing and wing sections of aircraft and on airship hulls.

  5. Electrokinetic transport in microchannels with random roughness

    SciTech Connect

    Wang, Moran; Kang, Qinjun

    2008-01-01

    We present a numerical framework to model the electrokinetic transport in microchannels with random roughness. The three-dimensional microstructure of the rough channel is generated by a random generation-growth method with three statistical parameters to control the number density, the total volume fraction, and the anisotropy characteristics of roughness elements. The governing equations for the electrokinetic transport are solved by a high-efficiency lattice Poisson?Boltzmann method in complex geometries. The effects from the geometric characteristics of roughness on the electrokinetic transport in microchannels are therefore modeled and analyzed. For a given total roughness volume fraction, a higher number density leads to a lower fluctuation because of the random factors. The electroosmotic flow rate increases with the roughness number density nearly logarithmically for a given volume fraction of roughness but decreases with the volume fraction for a given roughness number density. When both the volume fraction and the number density of roughness are given, the electroosmotic flow rate is enhanced by the increase of the characteristic length along the external electric field direction but is reduced by that in the direction across the channel. For a given microstructure of the rough microchannel, the electroosmotic flow rate decreases with the Debye length. It is found that the shape resistance of roughness is responsible for the flow rate reduction in the rough channel compared to the smooth channel even for very thin double layers, and hence plays an important role in microchannel electroosmotic flows.

  6. NASA aerodynamics program

    NASA Technical Reports Server (NTRS)

    Williams, Louis J.; Hessenius, Kristin A.; Corsiglia, Victor R.; Hicks, Gary; Richardson, Pamela F.; Unger, George; Neumann, Benjamin; Moss, Jim

    1992-01-01

    The annual accomplishments is reviewed for the Aerodynamics Division during FY 1991. The program includes both fundamental and applied research directed at the full spectrum of aerospace vehicles, from rotorcraft to planetary entry probes. A comprehensive review is presented of the following aerodynamics elements: computational methods and applications; CFD validation; transition and turbulence physics; numerical aerodynamic simulation; test techniques and instrumentation; configuration aerodynamics; aeroacoustics; aerothermodynamics; hypersonics; subsonics; fighter/attack aircraft and rotorcraft.

  7. NASA aerodynamics program

    NASA Technical Reports Server (NTRS)

    Holmes, Bruce J.; Schairer, Edward; Hicks, Gary; Wander, Stephen; Blankson, Isiaiah; Rose, Raymond; Olson, Lawrence; Unger, George

    1990-01-01

    Presented here is a comprehensive review of the following aerodynamics elements: computational methods and applications, computational fluid dynamics (CFD) validation, transition and turbulence physics, numerical aerodynamic simulation, drag reduction, test techniques and instrumentation, configuration aerodynamics, aeroacoustics, aerothermodynamics, hypersonics, subsonic transport/commuter aviation, fighter/attack aircraft and rotorcraft.

  8. Does surface roughness amplify wetting?

    SciTech Connect

    Malijevský, Alexandr

    2014-11-14

    Any solid surface is intrinsically rough on the microscopic scale. In this paper, we study the effect of this roughness on the wetting properties of hydrophilic substrates. Macroscopic arguments, such as those leading to the well-known Wenzel's law, predict that surface roughness should amplify the wetting properties of such adsorbents. We use a fundamental measure density functional theory to demonstrate the opposite effect from roughness for microscopically corrugated surfaces, i.e., wetting is hindered. Based on three independent analyses we show that microscopic surface corrugation increases the wetting temperature or even makes the surface hydrophobic. Since for macroscopically corrugated surfaces the solid texture does indeed amplify wetting there must exist a crossover between two length-scale regimes that are distinguished by opposite response on surface roughening. This demonstrates how deceptive can be efforts to extend the thermodynamical laws beyond their macroscopic territory.

  9. Bifurcations in unsteady aerodynamics

    NASA Technical Reports Server (NTRS)

    Tobak, M.; Unal, A.

    1986-01-01

    Nonlinear algebraic functional expansions are used to create a form for the unsteady aerodynamic response that is consistent with solutions of the time dependent Navier-Stokes equations. An enumeration of means of invalidating Frechet differentiability of the aerodynamic response, one of which is aerodynamic bifurcation, is proposed as a way of classifying steady and unsteady aerodynamic phenomena that are important in flight dynamics applications. Accomodating bifurcation phenomena involving time dependent equilibrium states within a mathematical model of the aerodynamic response raises an issue of memory effects that becomes more important with each successive bifurcation.

  10. A climatology of formation conditions for aerodynamic contrails

    NASA Astrophysics Data System (ADS)

    Gierens, K.; Dilger, F.

    2013-06-01

    Aerodynamic contrails are defined in this paper as line shaped ice clouds caused by aerodynamically triggered cooling over the wings of an aircraft in cruise which become visible immediately at the trailing edge of the wing or close to it. Effects at low altitudes like condensation to liquid droplets and their potential heterogeneous freezing are excluded from our definition. We study atmospheric conditions that allow formation of aerodynamic contrails. These conditions are stated and then applied to atmospheric data, first to a special case where an aerodynamic contrail was actually observed and then to a full year of global reanalysis data. We show where, when (seasonal variation), and how frequently (probability) aerodynamic contrails can form, and how this relates to actual patterns of air traffic. We study the formation of persistent aerodynamic contrails as well. Finally we check whether aerodynamic and exhaust contrails can coexist in the atmosphere. We show that visible aerodynamic contrails are possible only in an altitude range between roughly 540 and 250 hPa, and that the ambient temperature is the most important parameter, not the relative humidity. Finally we give an argument for our believe that currently aerodynamic contrails have a much smaller climate effect than exhaust contrails, which may however change in future with more air traffic in the tropics.

  11. Fundamental Aspects of the Aerodynamics of Turbojet Engine Combustors

    NASA Technical Reports Server (NTRS)

    Barrere, M.

    1978-01-01

    Aerodynamic considerations in the design of high performance combustors for turbojet engines are discussed. Aerodynamic problems concerning the preparation of the fuel-air mixture, the recirculation zone where primary combustion occurs, the secondary combustion zone, and the dilution zone were examined. An aerodynamic analysis of the entire primary chamber ensemble was carried out to determine the pressure drop between entry and exit. The aerodynamics of afterburn chambers are discussed. A model which can be used to investigate the evolution of temperature, pressure, and rate and efficiency of combustion the length of the chamber was developed.

  12. Aerodynamic Simulation of Ice Accretion on Airfoils

    NASA Technical Reports Server (NTRS)

    Broeren, Andy P.; Addy, Harold E., Jr.; Bragg, Michael B.; Busch, Greg T.; Montreuil, Emmanuel

    2011-01-01

    This report describes recent improvements in aerodynamic scaling and simulation of ice accretion on airfoils. Ice accretions were classified into four types on the basis of aerodynamic effects: roughness, horn, streamwise, and spanwise ridge. The NASA Icing Research Tunnel (IRT) was used to generate ice accretions within these four types using both subscale and full-scale models. Large-scale, pressurized windtunnel testing was performed using a 72-in.- (1.83-m-) chord, NACA 23012 airfoil model with high-fidelity, three-dimensional castings of the IRT ice accretions. Performance data were recorded over Reynolds numbers from 4.5 x 10(exp 6) to 15.9 x 10(exp 6) and Mach numbers from 0.10 to 0.28. Lower fidelity ice-accretion simulation methods were developed and tested on an 18-in.- (0.46-m-) chord NACA 23012 airfoil model in a small-scale wind tunnel at a lower Reynolds number. The aerodynamic accuracy of the lower fidelity, subscale ice simulations was validated against the full-scale results for a factor of 4 reduction in model scale and a factor of 8 reduction in Reynolds number. This research has defined the level of geometric fidelity required for artificial ice shapes to yield aerodynamic performance results to within a known level of uncertainty and has culminated in a proposed methodology for subscale iced-airfoil aerodynamic simulation.

  13. Determining Surface Roughness in Urban Areas Using Lidar Data

    NASA Technical Reports Server (NTRS)

    Holland, Donald

    2009-01-01

    An automated procedure has been developed to derive relevant factors, which can increase the ability to produce objective, repeatable methods for determining aerodynamic surface roughness. Aerodynamic surface roughness is used for many applications, like atmospheric dispersive models and wind-damage models. For this technique, existing lidar data was used that was originally collected for terrain analysis, and demonstrated that surface roughness values can be automatically derived, and then subsequently utilized in disaster-management and homeland security models. The developed lidar-processing algorithm effectively distinguishes buildings from trees and characterizes their size, density, orientation, and spacing (see figure); all of these variables are parameters that are required to calculate the estimated surface roughness for a specified area. By using this algorithm, aerodynamic surface roughness values in urban areas can then be extracted automatically. The user can also adjust the algorithm for local conditions and lidar characteristics, like summer/winter vegetation and dense/sparse lidar point spacing. Additionally, the user can also survey variations in surface roughness that occurs due to wind direction; for example, during a hurricane, when wind direction can change dramatically, this variable can be extremely significant. In its current state, the algorithm calculates an estimated surface roughness for a square kilometer area; techniques using the lidar data to calculate the surface roughness for a point, whereby only roughness elements that are upstream from the point of interest are used and the wind direction is a vital concern, are being investigated. This technological advancement will improve the reliability and accuracy of models that use and incorporate surface roughness.

  14. Unsteady transonic aerodynamics

    SciTech Connect

    Nixon, D.

    1989-01-01

    Various papers on unsteady transonic aerodynamics are presented. The topics addressed include: physical phenomena associated with unsteady transonic flows, basic equations for unsteady transonic flow, practical problems concerning aircraft, basic numerical methods, computational methods for unsteady transonic flows, application of transonic flow analysis to helicopter rotor problems, unsteady aerodynamics for turbomachinery aeroelastic applications, alternative methods for modeling unsteady transonic flows.

  15. Uncertainty in Computational Aerodynamics

    NASA Technical Reports Server (NTRS)

    Luckring, J. M.; Hemsch, M. J.; Morrison, J. H.

    2003-01-01

    An approach is presented to treat computational aerodynamics as a process, subject to the fundamental quality assurance principles of process control and process improvement. We consider several aspects affecting uncertainty for the computational aerodynamic process and present a set of stages to determine the level of management required to meet risk assumptions desired by the customer of the predictions.

  16. A climatology of formation conditions for aerodynamic contrails

    NASA Astrophysics Data System (ADS)

    Gierens, K.; Dilger, F.

    2013-11-01

    Aircraft at cruise levels can cause two kinds of contrails, the well known exhaust contrails and the less well-known aerodynamic contrails. While the possible climate impact of exhaust contrails has been studied for many years, research on aerodynamic contrails began only a few years ago and nothing is known about a possible contribution of these ice clouds to climate impact. In order to make progress in this respect, we first need a climatology of their formation conditions and this is given in the present paper. Aerodynamic contrails are defined here as line shaped ice clouds caused by aerodynamically triggered cooling over the wings of an aircraft in cruise which become visible immediately at the trailing edge of the wing or close to it. Effects at low altitudes like condensation to liquid droplets and their potential heterogeneous freezing are excluded from our definition. We study atmospheric conditions that allow formation of aerodynamic contrails. These conditions are stated and then applied to atmospheric data: first to a special case where an aerodynamic contrail was actually observed and then to a full year of global reanalysis data. We show where, when (seasonal variation), and how frequently (probability) aerodynamic contrails can form, and how this relates to actual patterns of air traffic. We study the formation of persistent aerodynamic contrails as well. Furthermore, we check whether aerodynamic and exhaust contrails can coexist in the atmosphere. We show that visible aerodynamic contrails are possible only in an altitude range between roughly 540 and 250 hPa, and that the ambient temperature is the most important parameter, not the relative humidity. Finally, we argue that currently aerodynamic contrails have a much smaller climate effect than exhaust contrails, which may however change in future with more air traffic in the tropics.

  17. Aerodynamic characteristics of airfoils with ice accretions

    NASA Technical Reports Server (NTRS)

    Bragg, M. B.; Gregorek, G. M.

    1982-01-01

    Results of a wind tunnel test to evaluate the performance of an airfoil with simulated rime ice are presented with theoretical comparisons. A NACA 65A413 airfoil was tested in the OSU 6 x 22 inch Transonic Airfoil Wind Tunnel at a Reynolds number near three million and Mach numbers from 0.20 to 0.80. The model was tested in four configurations to determine the aero-dynamic effects of the roughness and shape of a rime ice accretion. The simulated rime ice shape was obtained analytically using a time-stepping dry ice accretion computer code. Lift, drag, moment coefficients, and pressure distributions for the clean and simulated rime ice cases are reported. The measured degradation in airfoil performance is compared to an analytical method which uses existing airfoil analysis computer codes with empirical corrections for the surface roughness. A discussion of the empirical surface roughness correction and uses of other airfoil computer methods is included.

  18. Airfoil Ice-Accretion Aerodynamics Simulation

    NASA Technical Reports Server (NTRS)

    Bragg, Michael B.; Broeren, Andy P.; Addy, Harold E.; Potapczuk, Mark G.; Guffond, Didier; Montreuil, E.

    2007-01-01

    NASA Glenn Research Center, ONERA, and the University of Illinois are conducting a major research program whose goal is to improve our understanding of the aerodynamic scaling of ice accretions on airfoils. The program when it is completed will result in validated scaled simulation methods that produce the essential aerodynamic features of the full-scale iced-airfoil. This research will provide some of the first, high-fidelity, full-scale, iced-airfoil aerodynamic data. An initial study classified ice accretions based on their aerodynamics into four types: roughness, streamwise ice, horn ice, and spanwise-ridge ice. Subscale testing using a NACA 23012 airfoil was performed in the NASA IRT and University of Illinois wind tunnel to better understand the aerodynamics of these ice types and to test various levels of ice simulation fidelity. These studies are briefly reviewed here and have been presented in more detail in other papers. Based on these results, full-scale testing at the ONERA F1 tunnel using cast ice shapes obtained from molds taken in the IRT will provide full-scale iced airfoil data from full-scale ice accretions. Using these data as a baseline, the final step is to validate the simulation methods in scale in the Illinois wind tunnel. Computational ice accretion methods including LEWICE and ONICE have been used to guide the experiments and are briefly described and results shown. When full-scale and simulation aerodynamic results are available, these data will be used to further develop computational tools. Thus the purpose of the paper is to present an overview of the program and key results to date.

  19. Laws of Flow in Rough Pipes

    NASA Technical Reports Server (NTRS)

    Nikuradse, J

    1950-01-01

    An experimental investigation is made of the turbulent flow of water in pipes with various degrees of relative roughness. The pipes range in size from 25 to 100 millimeters in diameter and from 1800 to 7050 millimeters in length. Flow velocities permitted Reynolds numbers from about 10 (sup. 4) to 10 (sup. 6). The laws of resistance and velocity distributions were obtained as a function of relative roughness and Reynolds number. Mixing length, as described by Prandtl's mixing-length formula, is discussed in relation to the experimental results.

  20. Physics of badminton shuttlecocks. Part 1 : aerodynamics

    NASA Astrophysics Data System (ADS)

    Cohen, Caroline; Darbois Texier, Baptiste; Quéré, David; Clanet, Christophe

    2011-11-01

    We study experimentally shuttlecocks dynamics. In this part we show that shuttlecock trajectory is highly different from classical parabola. When one takes into account the aerodynamic drag, the flight of the shuttlecock quickly curves downwards and almost reaches a vertical asymptote. We solve the equation of motion with gravity and drag at high Reynolds number and find an analytical expression of the reach. At high velocity, this reach does not depend on velocity anymore. Even if you develop your muscles you will not manage to launch the shuttlecock very far because of the ``aerodynamic wall.'' As a consequence you can predict the length of the field. We then discuss the extend of the aerodynamic wall to other projectiles like sports balls and its importance.

  1. Advanced turboprop installation aerodynamics

    NASA Technical Reports Server (NTRS)

    Smith, R. C.

    1981-01-01

    The expected aerodynamic effects of a propfan installed on a thick supercritical wing are summarized qualitatively. Nacelle/wing and jet interactions, slipstream incremental velocity, nonuniform inflow, and swirl loss recovery are discussed.

  2. Aerodynamic Lifting Force.

    ERIC Educational Resources Information Center

    Weltner, Klaus

    1990-01-01

    Describes some experiments showing both qualitatively and quantitatively that aerodynamic lift is a reaction force. Demonstrates reaction forces caused by the acceleration of an airstream and the deflection of an airstream. Provides pictures of demonstration apparatus and mathematical expressions. (YP)

  3. On the calibration of Mars Orbiter Laser Altimeter surface roughness estimates using high-resolution DTMs

    NASA Astrophysics Data System (ADS)

    Poole, W.; Muller, J.-P.; Gupta, S.

    2012-04-01

    Planetary surface roughness is critical in the selection of suitable landing sites for robotic lander or roving missions. It has also been used in the identification of terrain, for better calibration of radar returns and improved understanding of aerodynamic roughness [1]. One of the secondary science goals of the Mars Orbiter Laser Altimeter (MOLA) was the study of surface roughness at 100 m, using the backscatter pulse width of the laser pulse, which has a footprint of 168 m in diameter [2]. The pulse width values in the final release (version L) of the MOLA Precision Experiment Data Record (PEDR) have been corrected for across track slopes and the removal of 'bad points', and footprint diameter was revised to 75 m, with a 35 m response length in [3]. We look here at comparing surface roughness values derived from the MOLA pulse-width data with surface roughness estimates derived at various scales from high-resolution digital terrain models (DTMs) to determine if these theoretically derived surface roughness lengths are physically meaningful. The final four potential landing sites for Mars Science Laboratory were used in this study, as they have extensive HiRISE (1m) and HRSC (50m) DTM coverage [4]. Pulse width data from both the MOLA PEDR (version L) and the data used in [3] was collected and compared for each of the sites against surface roughness estimates at various scales from HiRISE, and HRSC, DTMs using the RMS height. This assumed a circular footprint for each MOLA footprint and that the horizontal geolocation of the PEDR MOLA footprints was sufficiently accurate to only extract those DTM points which lay inside the footprints. Results from the MOLA PEDR data were extremely poor, and show no correlation with surface roughness measurements from DTMs. Results using the corrected data in [3] were mixed. Eberswalde and Holden Craters both show significantly improved correlations for a variety of surface roughness scales. The best correlations were found to

  4. Effective field model of roughness in magnetic nano-structures

    SciTech Connect

    Lepadatu, Serban

    2015-12-28

    An effective field model is introduced here within the micromagnetics formulation, to study roughness in magnetic structures, by considering sub-exchange length roughness levels as a perturbation on a smooth structure. This allows the roughness contribution to be separated, which is found to give rise to an effective configurational anisotropy for both edge and surface roughness, and accurately model its effects with fine control over the roughness depth without the explicit need to refine the computational cell size to accommodate the roughness profile. The model is validated by comparisons with directly roughened structures for a series of magnetization switching and domain wall velocity simulations and found to be in excellent agreement for roughness levels up to the exchange length. The model is further applied to vortex domain wall velocity simulations with surface roughness, which is shown to significantly modify domain wall movement and result in dynamic pinning and stochastic creep effects.

  5. Aerodynamics of Heavy Vehicles

    NASA Astrophysics Data System (ADS)

    Choi, Haecheon; Lee, Jungil; Park, Hyungmin

    2014-01-01

    We present an overview of the aerodynamics of heavy vehicles, such as tractor-trailers, high-speed trains, and buses. We introduce three-dimensional flow structures around simplified model vehicles and heavy vehicles and discuss the flow-control devices used for drag reduction. Finally, we suggest important unsteady flow structures to investigate for the enhancement of aerodynamic performance and future directions for experimental and numerical approaches.

  6. Aerodynamic Shutoff Valve

    NASA Technical Reports Server (NTRS)

    Horstman, Raymond H.

    1992-01-01

    Aerodynamic flow achieved by adding fixed fairings to butterfly valve. When valve fully open, fairings align with butterfly and reduce wake. Butterfly free to turn, so valve can be closed, while fairings remain fixed. Design reduces turbulence in flow of air in internal suction system. Valve aids in development of improved porous-surface boundary-layer control system to reduce aerodynamic drag. Applications primarily aerospace. System adapted to boundary-layer control on high-speed land vehicles.

  7. Scattering of Rarefied Gas Atoms from Rough Surface Simulated with Fractals

    NASA Astrophysics Data System (ADS)

    Aksenova, Olga A.

    2003-05-01

    The fractal approach to the model of surface roughness in the problem of gas-surface interaction is developed on the base of the generalization of two-dimensional model of roughness proposed by Blackmore and Zhou. The relation between the parameters of the model and the values influencing the aerodynamic coefficients is investigated. Computed results are compared with the values obtained using statistical model of roughness — the isotropic Gaussian random field.

  8. Interaction of turbulent length scales with wind turbine blades

    NASA Astrophysics Data System (ADS)

    Torres-Nieves, Sheilla N.

    Understanding the effects of free-stream turbulence (FST) and surface roughness on the flow around wind turbine blades is imperative in the quest for higher wind turbine efficiency, specially under stall conditions. While many investigations have focused on the aerodynamic loads on wind turbine airfoils, there are no studies that examine the effects of free-stream turbulence and surface roughness on the velocity field around a wind turbine airfoil. Hence, the aim of this investigation is to study the influence of high levels of FST on the flow around smooth and rough surfaces with pressure gradients. Moreover, of great importance in this study is the examination of how the length scales of turbulence and surface roughness interact in the flow over wind turbine airfoils to affect flow separation. Particle Image Velocimetry measurements were performed to analyze the overall flow around a S809 wind turbine blade. Results indicate that when the flow is fully attached, free-stream turbulence significantly decreases aerodynamic efficiency by 82%, yielding to higher loads and fatigue on the blades. On the contrary, when the flow is separated, the effect is reversed and aerodynamic performance is slightly improved (i.e., by 5%) by the presence of the free-stream turbulence. Analysis of the mean flow over the suction surface shows that, under stall conditions, free-stream turbulence delays separation, and surface roughness advances separation. Interestingly, the highly non-linear interaction between free-stream turbulence and surface roughness results in the further advancement of separation. Of particular interest is the study of the region closer to the wall (i.e., the boundary layer), where the flow interacts with both the surface of the blade and the free-stream. Turbulent boundary layer experiments subject to an external favorable pressure gradient (FPG) were performed to study the influence of FST, surface roughness and external pressure gradient (present around the

  9. Aerodynamic Surface Stress Intermittency and Conditionally Averaged Turbulence Statistics

    NASA Astrophysics Data System (ADS)

    Anderson, W.

    2015-12-01

    Aeolian erosion of dry, flat, semi-arid landscapes is induced (and sustained) by kinetic energy fluxes in the aloft atmospheric surface layer. During saltation -- the mechanism responsible for surface fluxes of dust and sediment -- briefly suspended sediment grains undergo a ballistic trajectory before impacting and `splashing' smaller-diameter (dust) particles vertically. Conceptual models typically indicate that sediment flux, q (via saltation or drift), scales with imposed aerodynamic (basal) stress raised to some exponent, n, where n > 1. Since basal stress (in fully rough, inertia-dominated flows) scales with the incoming velocity squared, u^2, it follows that q ~ u^2n (where u is some relevant component of the above flow field, u(x,t)). Thus, even small (turbulent) deviations of u from its time-averaged value may play an enormously important role in aeolian activity on flat, dry landscapes. The importance of this argument is further augmented given that turbulence in the atmospheric surface layer exhibits maximum Reynolds stresses in the fluid immediately above the landscape. In order to illustrate the importance of surface stress intermittency, we have used conditional averaging predicated on aerodynamic surface stress during large-eddy simulation of atmospheric boundary layer flow over a flat landscape with momentum roughness length appropriate for the Llano Estacado in west Texas (a flat agricultural region that is notorious for dust transport). By using data from a field campaign to measure diurnal variability of aeolian activity and prevailing winds on the Llano Estacado, we have retrieved the threshold friction velocity (which can be used to compute threshold surface stress under the geostrophic balance with the Monin-Obukhov similarity theory). This averaging procedure provides an ensemble-mean visualization of flow structures responsible for erosion `events'. Preliminary evidence indicates that surface stress peaks are associated with the passage of

  10. Powered-Lift Aerodynamics and Acoustics. [conferences

    NASA Technical Reports Server (NTRS)

    1976-01-01

    Powered lift technology is reviewed. Topics covered include: (1) high lift aerodynamics; (2) high speed and cruise aerodynamics; (3) acoustics; (4) propulsion aerodynamics and acoustics; (5) aerodynamic and acoustic loads; and (6) full-scale and flight research.

  11. Applied computational aerodynamics

    SciTech Connect

    Henne, P.A.

    1990-01-01

    The present volume discusses the original development of the panel method, the mapping solutions and singularity distributions of linear potential schemes, the capabilities of full-potential, Euler, and Navier-Stokes schemes, the use of the grid-generation methodology in applied aerodynamics, subsonic airfoil design, inverse airfoil design for transonic applications, the divergent trailing-edge airfoil innovation in CFD, Euler and potential computational results for selected aerodynamic configurations, and the application of CFD to wing high-lift systems. Also discussed are high-lift wing modifications for an advanced-capability EA-6B aircraft, Navier-Stokes methods for internal and integrated propulsion system flow predictions, the use of zonal techniques for analysis of rotor-stator interaction, CFD applications to complex configurations, CFD applications in component aerodynamic design of the V-22, Navier-Stokes computations of a complete F-16, CFD at supersonic/hypersonic speeds, and future CFD developments.

  12. Nonlinear aerodynamic wing design

    NASA Technical Reports Server (NTRS)

    Bonner, Ellwood

    1985-01-01

    The applicability of new nonlinear theoretical techniques is demonstrated for supersonic wing design. The new technology was utilized to define outboard panels for an existing advanced tactical fighter model. Mach 1.6 maneuver point design and multi-operating point compromise surfaces were developed and tested. High aerodynamic efficiency was achieved at the design conditions. A corollary result was that only modest supersonic penalties were incurred to meet multiple aerodynamic requirements. The nonlinear potential analysis of a practical configuration arrangement correlated well with experimental data.

  13. Computational aerodynamics and design

    NASA Technical Reports Server (NTRS)

    Ballhaus, W. F., Jr.

    1982-01-01

    The role of computational aerodynamics in design is reviewed with attention given to the design process; the proper role of computations; the importance of calibration, interpretation, and verification; the usefulness of a given computational capability; and the marketing of new codes. Examples of computational aerodynamics in design are given with particular emphasis on the Highly Maneuverable Aircraft Technology. Finally, future prospects are noted, with consideration given to the role of advanced computers, advances in numerical solution techniques, turbulence models, complex geometries, and computational design procedures. Previously announced in STAR as N82-33348

  14. Aerodynamics of Race Cars

    NASA Astrophysics Data System (ADS)

    Katz, Joseph

    2006-01-01

    Race car performance depends on elements such as the engine, tires, suspension, road, aerodynamics, and of course the driver. In recent years, however, vehicle aerodynamics gained increased attention, mainly due to the utilization of the negative lift (downforce) principle, yielding several important performance improvements. This review briefly explains the significance of the aerodynamic downforce and how it improves race car performance. After this short introduction various methods to generate downforce such as inverted wings, diffusers, and vortex generators are discussed. Due to the complex geometry of these vehicles, the aerodynamic interaction between the various body components is significant, resulting in vortex flows and lifting surface shapes unlike traditional airplane wings. Typical design tools such as wind tunnel testing, computational fluid dynamics, and track testing, and their relevance to race car development, are discussed as well. In spite of the tremendous progress of these design tools (due to better instrumentation, communication, and computational power), the fluid dynamic phenomenon is still highly nonlinear, and predicting the effect of a particular modification is not always trouble free. Several examples covering a wide range of vehicle shapes (e.g., from stock cars to open-wheel race cars) are presented to demonstrate this nonlinear nature of the flow field.

  15. Roughness and function

    NASA Astrophysics Data System (ADS)

    Thomas, T. R.

    2014-01-01

    A function map is used to locate applications of roughness in separation-velocity space. The importance of roughness in contact mechanics is demonstrated and versions of the plasticity index are introduced and compared. Case studies of roughness and function are presented from tribology and the life sciences. Tribological examples are taken from the automotive industry and include the manufacture of vehicle bodies, and drive train tribology, particularly cylinder liner, cam and gearbox friction and wear. From the life sciences, problems of prosthetic fixation and tribology are shown to depend on roughness. The interaction of haptics and surface finish is described and illustrated. A number of other areas of application are listed. Finally the likely future importance of structured surfaces is discussed.

  16. Surface Roughness, Optical Shadowing, and Radar Backscatter

    NASA Astrophysics Data System (ADS)

    Shepard, M. K.; Campbell, B. A.

    1996-03-01

    The topography of natural surfaces at scales of a few meters or less is commonly referred to as roughness. These variations in height and slope, their magnitude, and the changes in structure as a function of scale length are of fundamental importance to interpretation of geologic emplacement regimes and subsequent modification. For most planetary studies and many terrestrial situations, no in situ observations of the ground are available, and remote sensing data are used to infer the nature of the terrain. For optical, infrared, and microwave measurements, surface roughness and its scale-dependence have a large impact on the brightness, polarization, angular scattering properties, and wavelength-dependence of reflected energy. The link between surface roughness and specific remote sensing properties for many types of observations, however, remains elusive. We focus here on the nature of roughness and its scale-dependence for terrestrial rocky surfaces, and the effect of such changes on optical shadowing and radar backscatter.

  17. Effect of roughness on water flow through a single rough fracture

    NASA Astrophysics Data System (ADS)

    Chen, Z.; Zhou, Z.; WANG, J.; Guo, Q.; Dou, Z.

    2015-12-01

    A single fracture (SF) usually has rough surfaces with points of contact. Though relative roughness was considered in quantifying flow through a single rough fracture (SRF) previously, additional factors such as the distribution of rough elements and bending degree of streamlines are rarely considered before. Semi-empirical friction factor (f) and discharge per unit width (q) equations are first deduced based on the consideration of relative roughness, roughness elements distribution and streamline reattachment length in this study. A horizontal SRF model is set up and a series of experiments and simulations are performed. Main conclusions are drawn: recirculation of streamlines occurred in the rough element and its intensity increases with the entering angle of the streamlines into the element and Reynolds number (Re); streamlines are discontinuously distributed when asperity height is large, leading to departure from Darcy's law (non-linear flow); the non-linearity of flow increases with the asperity height and Re; the relative roughness for not affecting water flow through a SRF should be much less than 0.033, a benchmark value commonly used previously for neglecting the roughness effect; the revised f and q equations under laminar flow through a SRF are shown to be better than previously proposed equations.

  18. Wetting on rough self-affine surfaces

    NASA Astrophysics Data System (ADS)

    Palasantzas, George

    1995-05-01

    In this paper, we present a general investigation of the effective potential for complete wetting on self-affine rough surfaces. The roughness effect is investigated by means of the height-height correlation model in Fourier space ~(1+aξ2q2)-1-H. The parameters H and ξ are, respectively, the roughness exponent and the substrate in-plane correlation length. It is observed that the effect of H on the free interface profile is significant for ξlength), and becomes negligible for wetting-layer thickness larger than a characteristic thickness τ~ξu for long-range substrate forces. Finally, the large Y (Y>>ξ) regime is characterized by a power-law scaling ~Y-2.

  19. Aerodynamics and thermal physics of helicopter ice accretion

    NASA Astrophysics Data System (ADS)

    Han, Yiqiang

    Ice accretion on aircraft introduces significant loss in airfoil performance. Reduced lift-to- drag ratio reduces the vehicle capability to maintain altitude and also limits its maneuverability. Current ice accretion performance degradation modeling approaches are calibrated only to a limited envelope of liquid water content, impact velocity, temperature, and water droplet size; consequently inaccurate aerodynamic performance degradations are estimated. The reduced ice accretion prediction capabilities in the glaze ice regime are primarily due to a lack of knowledge of surface roughness induced by ice accretion. A comprehensive understanding of the ice roughness effects on airfoil heat transfer, ice accretion shapes, and ultimately aerodynamics performance is critical for the design of ice protection systems. Surface roughness effects on both heat transfer and aerodynamic performance degradation on airfoils have been experimentally evaluated. Novel techniques, such as ice molding and casting methods and transient heat transfer measurement using non-intrusive thermal imaging methods, were developed at the Adverse Environment Rotor Test Stand (AERTS) facility at Penn State. A novel heat transfer scaling method specifically for turbulent flow regime was also conceived. A heat transfer scaling parameter, labeled as Coefficient of Stanton and Reynolds Number (CSR = Stx/Rex --0.2), has been validated against reference data found in the literature for rough flat plates with Reynolds number (Re) up to 1x107, for rough cylinders with Re ranging from 3x104 to 4x106, and for turbine blades with Re from 7.5x105 to 7x106. This is the first time that the effect of Reynolds number is shown to be successfully eliminated on heat transfer magnitudes measured on rough surfaces. Analytical models for ice roughness distribution, heat transfer prediction, and aerodynamics performance degradation due to ice accretion have also been developed. The ice roughness prediction model was

  20. Evaluation of the surface roughness effect on suspended particle deposition near unpaved roads

    SciTech Connect

    Zhu, Dongzi; Gillies, J. A.; Etyemezian, V.; Nikolich, G.; Shaw, William J.

    2015-11-11

    The downwind transport and deposition of suspended dust raised by a vehicle driving on unpaved roads was studied for four differently vegetated surfaces in the USA states of Kansas and Washington, and one barren surface in Nevada. A 10 m high tower adjacent to the source (z10 m downwind) and an array of multi-channel optical particle counters at three positions downwind of the source measured the flux of particles and the particle size distribution in the advecting dust plumes in the horizontal and vertical directions. Aerodynamic parameters such as friction velocity (u*) and surface roughness length (z0) were calculated from wind speed measurements made on the tower. Particle number concentration, PM10 mass exhibited an exponential decay along the direction of transport. Coarse particles accounted for z95% of the PM10 mass, at least to a downwind distance of 200 m from the source. PM10 removed by deposition was found to increase with increasing particle size and increasing surface roughness under similar moderate wind speed conditions. The surface of dense, long grass (1.2 m high and complete surface cover) had the greatest reduction of PM10 among the five surfaces tested due to deposition induced by turbulence effects created by the rougher surface and by enhanced particle impaction/ interception effects to the grass blades.

  1. HYSHOT-2 Aerodynamics

    NASA Astrophysics Data System (ADS)

    Cain, T.; Owen, R.; Walton, C.

    2005-02-01

    The scramjet flight test Hyshot-2, flew on the 30 July 2002. The programme, led by the University of Queensland, had the primary objective of obtaining supersonic combustion data in flight for comparison with measurements made in shock tunnels. QinetiQ was one of the sponsors, and also provided aerodynamic data and trajectory predictions for the ballistic re-entry of the spinning sounding rocket. The unconventional missile geometry created by the nose-mounted asymmetric-scramjet in conjunction with the high angle of attack during re-entry makes the problem interesting. This paper presents the wind tunnel measurements and aerodynamic calculations used as input for the trajectory prediction. Indirect comparison is made with data obtained in the Hyshot-2 flight using a 6 degree-of-freedom trajectory simulation.

  2. Rarefied-flow aerodynamics

    NASA Technical Reports Server (NTRS)

    Potter, J. Leith

    1992-01-01

    Means for relatively simple and quick procedures are examined for estimating aerodynamic coefficients of lifting reentry vehicles. The methods developed allow aerospace designers not only to evaluate the aerodynamics of specific shapes but also to optimize shapes under given constraints. The analysis was also studied of the effect of thermomolecular flow on pressures measured by an orifice near the nose of a Space Shuttle Orbiter at altitudes above 75 km. It was shown that pressures corrected for thermomolecular flow effect are in good agreement with values predicted by independent theoretical methods. An incidental product was the insight gained about the free molecular thermal accommodation coefficient applicable under 'real' conditions of high speed flow in the Earth's atmosphere. The results are presented as abstracts of referenced papers. One reference paper is presented in its entirety.

  3. Advanced Aerodynamic Control Effectors

    NASA Technical Reports Server (NTRS)

    Wood, Richard M.; Bauer, Steven X. S.

    1999-01-01

    A 1990 research program that focused on the development of advanced aerodynamic control effectors (AACE) for military aircraft has been reviewed and summarized. Data are presented for advanced planform, flow control, and surface contouring technologies. The data show significant increases in lift, reductions in drag, and increased control power, compared to typical aerodynamic designs. The results presented also highlighted the importance of planform selection in the design of a control effector suite. Planform data showed that dramatic increases in lift (greater than 25%) can be achieved with multiple wings and a sawtooth forebody. Passive porosity and micro drag generator control effector data showed control power levels exceeding that available from typical effectors (moving surfaces). Application of an advanced planform to a tailless concept showed benefits of similar magnitude as those observed in the generic studies.

  4. Aerodynamic noise sources

    NASA Astrophysics Data System (ADS)

    Munin, A. G.; Kuznetsov, V. M.; Leontev, E. A.

    A general theory is developed for aerodynamic sound generation and its propagation in an inhomogeneous medium. Results of theoretical and experimental studies of the acoustic characteristics of jets are discussed, and a solution is presented to the problem concerning the noise from a section, free rotor, and a rotor located inside a channel. Sound propagation in a channel with flow and selection of soundproofing liners for the channel walls are also discussed.

  5. Freight Wing Trailer Aerodynamics

    SciTech Connect

    Graham, Sean; Bigatel, Patrick

    2004-10-17

    Freight Wing Incorporated utilized the opportunity presented by this DOE category one Inventions and Innovations grant to successfully research, develop, test, patent, market, and sell innovative fuel and emissions saving aerodynamic attachments for the trucking industry. A great deal of past scientific research has demonstrated that streamlining box shaped semi-trailers can significantly reduce a truck's fuel consumption. However, significant design challenges have prevented past concepts from meeting industry needs. Market research early in this project revealed the demands of truck fleet operators regarding aerodynamic attachments. Products must not only save fuel, but cannot interfere with the operation of the truck, require significant maintenance, add significant weight, and must be extremely durable. Furthermore, SAE/TMC J1321 tests performed by a respected independent laboratory are necessary for large fleets to even consider purchase. Freight Wing used this information to create a system of three practical aerodynamic attachments for the front, rear and undercarriage of standard semi trailers. SAE/TMC J1321 Type II tests preformed by the Transportation Research Center (TRC) demonstrated a 7% improvement to fuel economy with all three products. If Freight Wing is successful in its continued efforts to gain market penetration, the energy and environmental savings would be considerable. Each truck outfitted saves approximately 1,100 gallons of fuel every 100,000 miles, which prevents over 12 tons of CO2 from entering the atmosphere. If all applicable trailers used the technology, the country could save approximately 1.8 billion gallons of diesel fuel, 18 million tons of emissions and 3.6 billion dollars annually.

  6. TAD- THEORETICAL AERODYNAMICS PROGRAM

    NASA Technical Reports Server (NTRS)

    Barrowman, J.

    1994-01-01

    This theoretical aerodynamics program, TAD, was developed to predict the aerodynamic characteristics of vehicles with sounding rocket configurations. These slender, axisymmetric finned vehicle configurations have a wide range of aeronautical applications from rockets to high speed armament. Over a given range of Mach numbers, TAD will compute the normal force coefficient derivative, the center-of-pressure, the roll forcing moment coefficient derivative, the roll damping moment coefficient derivative, and the pitch damping moment coefficient derivative of a sounding rocket configured vehicle. The vehicle may consist of a sharp pointed nose of cone or tangent ogive shape, up to nine other body divisions of conical shoulder, conical boattail, or circular cylinder shape, and fins of trapezoid planform shape with constant cross section and either three or four fins per fin set. The characteristics computed by TAD have been shown to be accurate to within ten percent of experimental data in the supersonic region. The TAD program calculates the characteristics of separate portions of the vehicle, calculates the interference between separate portions of the vehicle, and then combines the results to form a total vehicle solution. Also, TAD can be used to calculate the characteristics of the body or fins separately as an aid in the design process. Input to the TAD program consists of simple descriptions of the body and fin geometries and the Mach range of interest. Output includes the aerodynamic characteristics of the total vehicle, or user-selected portions, at specified points over the mach range. The TAD program is written in FORTRAN IV for batch execution and has been implemented on an IBM 360 computer with a central memory requirement of approximately 123K of 8 bit bytes. The TAD program was originally developed in 1967 and last updated in 1972.

  7. Aerodynamics of High-Speed Trains

    NASA Astrophysics Data System (ADS)

    Schetz, Joseph A.

    This review highlights the differences between the aerodynamics of high-speed trains and other types of transportation vehicles. The emphasis is on modern, high-speed trains, including magnetic levitation (Maglev) trains. Some of the key differences are derived from the fact that trains operate near the ground or a track, have much greater length-to-diameter ratios than other vehicles, pass close to each other and to trackside structures, are more subject to crosswinds, and operate in tunnels with entry and exit events. The coverage includes experimental techniques and results and analytical and numerical methods, concentrating on the most recent information available.

  8. Random rough surface photofabrication

    NASA Astrophysics Data System (ADS)

    Brissonneau, Vincent; Escoubas, Ludovic; Flory, François; Berginc, Gérard

    2011-10-01

    Random rough surfaces are of primary interest for their optical properties: reducing reflection at the interface or obtaining specific scattering diagram for example. Thus controlling surface statistics during the fabrication process paves the way to original and specific behaviors of reflected optical waves. We detail an experimental method allowing the fabrication of random rough surfaces showing tuned statistical properties. A two-step photoresist exposure process was developed. In order to initiate photoresist polymerization, an energy threshold needs to be reached by light exposure. This energy is brought by a uniform exposure equipment comprising UV-LEDs. This pre-exposure is studied by varying parameters such as optical power and exposure time. The second step consists in an exposure based on the Gray method.1 The speckle pattern of an enlarged scattered laser beam is used to insolate the photoresist. A specific photofabrication bench using an argon ion laser was implemented. Parameters such as exposure time and distances between optical components are discussed. Then, we describe how we modify the speckle-based exposure bench to include a spatial light modulator (SLM). The SLM used is a micromirror matrix known as Digital Micromirror Device (DMD) which allows spatial modulation by displaying binary images. Thus, the spatial beam shape can be tuned and so the speckle pattern on the photoresist is modified. As the photoresist photofabricated surface is correlated to the speckle pattern used to insolate, the roughness parameters can be adjusted.

  9. Changes of the spruce forest stand aerodynamic properties during ten growing seasons

    NASA Astrophysics Data System (ADS)

    Hurtalova, T.; Matejka, F.; Janous, D.; Czerny, R.

    2009-04-01

    Objective of this study was to quantify the influence of a young spruce forest stand on airflow and its aerodynamic characteristics during ten growing seasons. With this aim the wind speed profiles measured in and above investigated spruce stand during growing seasons, from May to October, 1998-2007 were analysed. Experimental site is situated on a mild slope with SW orientation in the locality Bílý Kříž (49o30'17'' N, 18o32'28'' E, 898-908 m a.s.l.), which is in the highest part of the Moravian-Silesian Beskydy Mts, Czech Republic. The experimental site consisting of two plots Fd and Fs with different tree density is created by the monoculture of young Norway spruce stand (Picea abies L., Karst) with age of 17 years in 1998. Each of these plots has the area of 2500 m2, density of 2600 trees/ha in Fd plot and 2400 trees/ha in Fs plot in 1998, and gradually 1652 trees/ha (Fd) and 1428 trees/ha (Fs) in 2007. The aerodynamic characteristics can be described by the roughness length (z0) and the zero plane displacement (d). The presented study aims to analyse the changes in d and z0 values for a young spruce forest stand during ten consecutive growing seasons, and to relate the aerodynamic properties of an air layer affected by this stand to its growth parameters. It is known, that the local terrain and structure of forest stand influenced the direction and power of the airflow, as well as the structure of vertical wind speed profiles. From the wind speed profile analysis it follows, that the investigated spruce stand was in an aerodynamic unsteady state and then d and z0 values vary also with the wind speed. During investigated seasons the mean seasonal z0 values ranged between 0.48 m and 1.32 m in Fd and the corresponding values in Fs plot varied between 0.41 m and 1.36 m. The mean seasonal d values varied between 0.60h and 0.76h in Fd, and 61h and 0.76h in Fs, h is mean stand height.

  10. Mask roughness induced LER: a rule of thumb -- paper

    SciTech Connect

    McClinton, Brittany; Naulleau, Patrick

    2010-03-12

    Much work has already been done on how both the resist and line-edge roughness (LER) on the mask affect the final printed LER. What is poorly understood, however, is the extent to which system-level effects such as mask surface roughness, illumination conditions, and defocus couple to speckle at the image plane, and currently factor into LER limits. Here, we propose a 'rule-of-thumb' simplified solution that provides a fast and powerful method to obtain mask roughness induced LER. We present modeling data on an older generation mask with a roughness of 230 pm as well as the ultimate target roughness of 50 pm. Moreover, we consider feature sizes of 50 nm and 22 nm, and show that as a function of correlation length, the LER peaks at the condition that the correlation length is approximately equal to the resolution of the imaging optic.

  11. Aerodynamic challenges of ALT

    NASA Technical Reports Server (NTRS)

    Hooks, I.; Homan, D.; Romere, P. O.

    1985-01-01

    The approach and landing test (ALT) of the Space Shuttle Orbiter presented a number of unique challenges in the area of aerodynamics. The purpose of the ALT program was both to confirm the use of the Boeing 747 as a transport vehicle for ferrying the Orbiter across the country and to demonstrate the flight characteristics of the Orbiter in its approach and landing phase. Concerns for structural fatigue and performance dictated a tailcone be attached to the Orbiter for ferry and for the initial landing tests. The Orbiter with a tailcone attached presented additional challenges to the normal aft sting concept of wind tunnel testing. The landing tests required that the Orbiter be separated from the 747 at approximately 20,000 feet using aerodynamic forces to fly the vehicles apart. The concept required a complex test program to determine the relative effects of the two vehicles on each other. Also of concern, and tested, was the vortex wake created by the 747 and the means for the Orbiter to avoid it following separation.

  12. The Aerodynamic Plane Table

    NASA Technical Reports Server (NTRS)

    Zahm, A F

    1924-01-01

    This report gives the description and the use of a specially designed aerodynamic plane table. For the accurate and expeditious geometrical measurement of models in an aerodynamic laboratory, and for miscellaneous truing operations, there is frequent need for a specially equipped plan table. For example, one may have to measure truly to 0.001 inch the offsets of an airfoil at many parts of its surface. Or the offsets of a strut, airship hull, or other carefully formed figure may require exact calipering. Again, a complete airplane model may have to be adjusted for correct incidence at all parts of its surfaces or verified in those parts for conformance to specifications. Such work, if but occasional, may be done on a planing or milling machine; but if frequent, justifies the provision of a special table. For this reason it was found desirable in 1918 to make the table described in this report and to equip it with such gauges and measures as the work should require.

  13. Aerodynamic design using numerical optimization

    NASA Technical Reports Server (NTRS)

    Murman, E. M.; Chapman, G. T.

    1983-01-01

    The procedure of using numerical optimization methods coupled with computational fluid dynamic (CFD) codes for the development of an aerodynamic design is examined. Several approaches that replace wind tunnel tests, develop pressure distributions and derive designs, or fulfill preset design criteria are presented. The method of Aerodynamic Design by Numerical Optimization (ADNO) is described and illustrated with examples.

  14. Aerodynamic coefficients and transformation tables

    NASA Technical Reports Server (NTRS)

    Ames, Joseph S

    1918-01-01

    The problem of the transformation of numerical values expressed in one system of units into another set or system of units frequently arises in connection with aerodynamic problems. Report contains aerodynamic coefficients and conversion tables needed to facilitate such transformation. (author)

  15. Aerodynamics of a Party Balloon

    ERIC Educational Resources Information Center

    Cross, Rod

    2007-01-01

    It is well-known that a party balloon can be made to fly erratically across a room, but it can also be used for quantitative measurements of other aspects of aerodynamics. Since a balloon is light and has a large surface area, even relatively weak aerodynamic forces can be readily demonstrated or measured in the classroom. Accurate measurements…

  16. On Wings: Aerodynamics of Eagles.

    ERIC Educational Resources Information Center

    Millson, David

    2000-01-01

    The Aerodynamics Wing Curriculum is a high school program that combines basic physics, aerodynamics, pre-engineering, 3D visualization, computer-assisted drafting, computer-assisted manufacturing, production, reengineering, and success in a 15-hour, 3-week classroom module. (JOW)

  17. Prediction of Frictional Drag over Rough Walls using Surface Statistics

    NASA Astrophysics Data System (ADS)

    Flack, Karen; Schultz, Michael

    2014-11-01

    Although the frictional drag of rough-wall-bounded flows has been studied extensively, several practical questions remain largely unresolved. First, the relationship between the shape of the roughness function in transitionally-rough regime and the surface topography which gives rise to it are not well understood. Second, it is not completely clear which textural parameters best describe a rough surface in a hydraulic sense. Furthermore, the range of roughness wavelengths that influence the skin-friction is not well established. The focus of the present work is to attempt to address these questions with a systematic study of the skin-friction of fifteen rough surfaces that were generated by grit blasting. The hydrodynamic tests were carried out over a large Reynolds number range. Five surfaces were prepared by grit blasting with a single scale blast media. These underwent hydrodynamic testing and were subsequently blasted with secondary and tertiary scale media in order to investigate the role that the incorporation of additional roughness length scales plays in determining the shape of the roughness function and the resulting hydraulic length scale. The presentation will focus on the appropriate statistical scales for prediction of the roughness function. Spatial filtering prior to the calculation of surface statistics will also be discussed. Work supported by the Office of Naval Research.

  18. Identifying Changes in Snowpack Surface Roughness Characteristics

    NASA Astrophysics Data System (ADS)

    Fassnacht, S. R.; Corrao, M. V.; Deems, J. S.; Stednick, J. D.

    2006-12-01

    The flow of air over a surface is influenced by its roughness. The surface of a snowpack is smooth relative to the underlying ground surface. The relative roughness of the snowpack surface changes directionally, spatially, and temporally, due to deposition, erosion, and melt. To examine these changes in snowpack surface roughness at the microtopographic scale for a Northern Colorado site, the surface was photographed using a darker-coloured roughness board that was inserted into the snowpack so that a black (board) versus white (snow) contrast existed along the entire length of the board. The board was 1-m long and was inserted 11 times at 10-cm intervals to create a 1-m by 1-m mesh. The orientation of the boards was rotated 90 degrees to provide finer resolution data in perpendicular directions. For the 1-m boards, the pixel resolution was approximately 0.4 mm. To measure the snow grain scale, a crystal card was photographed and yielded a pixel resolution of approximately 0.1 mm. Incorporating image processing issues such as image contrast and brightness, the digital images were translated into individual lines. These lines were used to compute semi- variograms in log-log space, from which the magnitude of semi-variance, the fractal dimensions, and the scale break were computed. The semi-variogram characteristics were used to illustrate directional, spatial, and temporal changes in snowpack surface roughness.

  19. Unsteady aerodynamics of blade rows

    NASA Technical Reports Server (NTRS)

    Verdon, Joseph M.

    1989-01-01

    The requirements placed on an unsteady aerodynamic theory intended for turbomachinery aeroelastic or aeroacoustic applications are discussed along with a brief description of the various theoretical models that are available to address these requirements. The major emphasis is placed on the description of a linearized inviscid theory which fully accounts for the affects of a nonuniform mean or steady flow on unsteady aerodynamic response. Although this linearization was developed primarily for blade flutter prediction, more general equations are presented which account for unsteady excitations due to incident external aerodynamic disturbances as well as those due to prescribed blade motions. The motivation for this linearized unsteady aerodynamic theory is focused on, its physical and mathematical formulation is outlined and examples are presented to illustrate the status of numerical solution procedures and several effects of mean flow nonuniformity on unsteady aerodynamic response.

  20. Equilibrium CO bond lengths

    NASA Astrophysics Data System (ADS)

    Demaison, Jean; Császár, Attila G.

    2012-09-01

    Based on a sample of 38 molecules, 47 accurate equilibrium CO bond lengths have been collected and analyzed. These ultimate experimental (reEX), semiexperimental (reSE), and Born-Oppenheimer (reBO) equilibrium structures are compared to reBO estimates from two lower-level techniques of electronic structure theory, MP2(FC)/cc-pVQZ and B3LYP/6-311+G(3df,2pd). A linear relationship is found between the best equilibrium bond lengths and their MP2 or B3LYP estimates. These (and similar) linear relationships permit to estimate the CO bond length with an accuracy of 0.002 Å within the full range of 1.10-1.43 Å, corresponding to single, double, and triple CO bonds, for a large number of molecules. The variation of the CO bond length is qualitatively explained using the Atoms in Molecules method. In particular, a nice correlation is found between the CO bond length and the bond critical point density and it appears that the CO bond is at the same time covalent and ionic. Conditions which permit the computation of an accurate ab initio Born-Oppenheimer equilibrium structure are discussed. In particular, the core-core and core-valence correlation is investigated and it is shown to roughly increase with the bond length.

  1. The role of free stream turbulence and blade surface conditions on the aerodynamic performance of wind turbine blades

    NASA Astrophysics Data System (ADS)

    Maldonado, Victor Hugo

    Wind turbines operate within the atmospheric boundary layer (ABL) which gives rise to turbulence among other flow phenomena. There are several factors that contribute to turbulent flow: The operation of wind turbines in two layers of the atmosphere, the surface layer and the mixed layer. These layers often have unstable wind conditions due to the daily heating and cooling of the atmosphere which creates turbulent thermals. In addition, wind turbines often operate in the wake of upstream turbines such as in wind farms; where turbulence generated by the rotor can be compounded if the turbines are not sited properly. Although turbulent flow conditions are known to affect performance, i.e. power output and lifespan of the turbine, the flow mechanisms by which atmospheric turbulence and other external conditions (such as blade debris contamination) adversely impact wind turbines are not known in enough detail to address these issues. The main objectives of the current investigation are thus two-fold: (i) to understand the interaction of the turbulent integral length scales and surface roughness on the blade and its effect on aerodynamic performance, and (ii) to develop and apply flow control (both passive and active) techniques to alleviate some of the adverse fluid dynamics phenomena caused by the atmosphere (i.e. blade contamination) and restore some of the aerodynamic performance loss. In order to satisfy the objectives of the investigation, a 2-D blade model based on the S809 airfoil for horizontal axis wind turbine (HAWT) applications was manufactured and tested at the Johns Hopkins University Corrsin Stanley Wind Tunnel facility. Additional levels of free stream turbulence with an intensity of 6.14% and integral length scale of about 0.321 m was introduced into the flow via an active grid. The free stream velocity was 10 m/s resulting in a Reynolds number based on blade chord of Rec ≃ 2.08x105. Debris contamination on the blade was modeled as surface roughness

  2. Theory of adhesion: Role of surface roughness

    NASA Astrophysics Data System (ADS)

    Persson, B. N. J.; Scaraggi, M.

    2014-09-01

    We discuss how surface roughness influences the adhesion between elastic solids. We introduce a Tabor number which depends on the length scale or magnification, and which gives information about the nature of the adhesion at different length scales. We consider two limiting cases relevant for (a) elastically hard solids with weak (or long ranged) adhesive interaction (DMT-limit) and (b) elastically soft solids with strong (or short ranged) adhesive interaction (JKR-limit). For the former cases we study the nature of the adhesion using different adhesive force laws (F ˜ u-n, n = 1.5-4, where u is the wall-wall separation). In general, adhesion may switch from DMT-like at short length scales to JKR-like at large (macroscopic) length scale. We compare the theory predictions to results of exact numerical simulations and find good agreement between theory and simulation results.

  3. Rough and Tumble Play 101

    ERIC Educational Resources Information Center

    Carlson, Frances

    2009-01-01

    Many people fear that play-fighting or rough and tumble play is the same as real fighting. There is also a fear that this rough play will become real fighting if allowed to continue. Most of all, parents and teachers fear that during the course of rough and tumble play a child may be hurt. To provide for and allow children to play rough without…

  4. Aerodynamics of Small Vehicles

    NASA Astrophysics Data System (ADS)

    Mueller, Thomas J.

    In this review we describe the aerodynamic problems that must be addressed in order to design a successful small aerial vehicle. The effects of Reynolds number and aspect ratio (AR) on the design and performance of fixed-wing vehicles are described. The boundary-layer behavior on airfoils is especially important in the design of vehicles in this flight regime. The results of a number of experimental boundary-layer studies, including the influence of laminar separation bubbles, are discussed. Several examples of small unmanned aerial vehicles (UAVs) in this regime are described. Also, a brief survey of analytical models for oscillating and flapping-wing propulsion is presented. These range from the earliest examples where quasi-steady, attached flow is assumed, to those that account for the unsteady shed vortex wake as well as flow separation and aeroelastic behavior of a flapping wing. Experiments that complemented the analysis and led to the design of a successful ornithopter are also described.

  5. Reciprocity relations in aerodynamics

    NASA Technical Reports Server (NTRS)

    Heaslet, Max A; Spreiter, John R

    1953-01-01

    Reverse flow theorems in aerodynamics are shown to be based on the same general concepts involved in many reciprocity theorems in the physical sciences. Reciprocal theorems for both steady and unsteady motion are found as a logical consequence of this approach. No restrictions on wing plan form or flight Mach number are made beyond those required in linearized compressible-flow analysis. A number of examples are listed, including general integral theorems for lifting, rolling, and pitching wings and for wings in nonuniform downwash fields. Correspondence is also established between the buildup of circulation with time of a wing starting impulsively from rest and the buildup of lift of the same wing moving in the reverse direction into a sharp-edged gust.

  6. Vortex flow aerodynamics

    NASA Technical Reports Server (NTRS)

    Smith, J. H. B.; Campbell, J. F.; Young, A. D. (Editor)

    1992-01-01

    The principal emphasis of the meeting was to be on the understanding and prediction of separation-induced vortex flows and their effects on vehicle performance, stability, control, and structural design loads. This report shows that a substantial amount of the papers covering this area were received from a wide range of countries, together with an attendance that was even more diverse. In itself, this testifies to the current interest in the subject and to the appropriateness of the Panel's choice of topic and approach. An attempt is made to summarize each paper delivered, and to relate the contributions made in the papers and in the discussions to some of the important aspects of vortex flow aerodynamics. This reveals significant progress and important clarifications, but also brings out remaining weaknesses in predictive capability and gaps in understanding. Where possible, conclusions are drawn and areas of continuing concern are identified.

  7. Pavement roughness and skid properties

    NASA Astrophysics Data System (ADS)

    Road roughness and roadway safety as it relates to both surface and air transportation are discussed. The role of road roughness in vehicle ride, the measurement of roughness, the evaluation of riding confort, and the effect of grooving pavements are discussed. The effects of differential pavement friction on the response of cars in skidding maneuvers is discussed.

  8. Determination of Joint Roughness Coefficients Using Roughness Parameters

    NASA Astrophysics Data System (ADS)

    Jang, Hyun-Sic; Kang, Seong-Seung; Jang, Bo-An

    2014-11-01

    This study used precisely digitized standard roughness profiles to determine roughness parameters such as statistical and 2D discontinuity roughness, and fractal dimensions. Our methods were based on the relationship between the joint roughness coefficient (JRC) values and roughness parameters calculated using power law equations. Statistical and 2D roughness parameters, and fractal dimensions correlated well with JRC values, and had correlation coefficients of over 0.96. However, all of these relationships have a 4th profile (JRC 6-8) that deviates by more than ±5 % from the JRC values given in the standard roughness profiles. This indicates that this profile is statistically different than the others. We suggest that fractal dimensions should be measured within the entire range of the divider, instead of merely measuring values within a suitable range. Normalized intercept values also correlated with the JRC values, similarly to the fractal dimension values discussed above. The root mean square first derivative values, roughness profile indexes, 2D roughness parameter, and fractal dimension values decreased as the sampling interval increased. However, the structure function values increased very rapidly with increasing sampling intervals. This indicates that the roughness parameters are not independent of the sampling interval, and that the different relationships between the JRC values and these roughness parameters are dependent on the sampling interval.

  9. Aerodynamic properties of agricultural and natural surfaces in northwestern Tarim Basin

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Friction velocity (u*) and aerodynamic roughness (z0) are important parameters that influence soil erosion, but no attempts have been made to quantify these parameters as affected by different land use types in the northwestern Tarim Basin. Wind velocity profiles were measured and used to determine ...

  10. Aerodynamic Classification of Swept-Wing Ice Accretion

    NASA Technical Reports Server (NTRS)

    Broeren, Andy; Diebold, Jeff; Bragg, Mike

    2013-01-01

    The continued design, certification and safe operation of swept-wing airplanes in icing conditions rely on the advancement of computational and experimental simulation methods for higher fidelity results over an increasing range of aircraft configurations and performance, and icing conditions. The current state-of-the-art in icing aerodynamics is mainly built upon a comprehensive understanding of two-dimensional geometries that does not currently exist for fundamentally three-dimensional geometries such as swept wings. The purpose of this report is to describe what is known of iced-swept-wing aerodynamics and to identify the type of research that is required to improve the current understanding. Following the method used in a previous review of iced-airfoil aerodynamics, this report proposes a classification of swept-wing ice accretion into four groups based upon unique flowfield attributes. These four groups are: ice roughness, horn ice, streamwise ice, and spanwise-ridge ice. For all of the proposed ice-shape classifications, relatively little is known about the three-dimensional flowfield and even less about the effect of Reynolds number and Mach number on these flowfields. The classifications and supporting data presented in this report can serve as a starting point as new research explores swept-wing aerodynamics with ice shapes. As further results are available, it is expected that these classifications will need to be updated and revised.

  11. Turbulent boundary layer flow over broad-banded roughness

    NASA Astrophysics Data System (ADS)

    Pawlak, Geno; Aghsaee, Payam; Mazrouei, Saeed; Leonardi, Stefano; Rajagopalan, Krishnakumar; Kobayashi, Marcelo

    2014-11-01

    The response of the boundary layer to a regular roughness is often parameterized in terms of the length scales defining the roughness. Difficulty arises in the case of broad-banded and highly irregular roughness distributions such as over coral reefs or urban canopies where the length scale that determines the response of the boundary layer is not clear. Here we use a spectral description for roughness to create idealized two-dimensional irregular roughness profiles, using square waves as a basis function. Laboratory experiments along with Direct Numerical Simulations (DNS) are used to examine the hydrodynamic response to the broad-banded roughness and flow characteristics are related to geometric characteristics of the boundary. The simulations and experiments show that the nature of the flow over two-dimensional irregular walls can be determined as a function of the hydrodynamic origin, which, in turn, can be determined as a function of a mean cavity shape. Results are interpreted in terms of the spectral characteristics of the roughness. The contribution of the various spectral components to the total drag is analyzed for each case. The roughness spectrum influences the flow through the shape of the cavities on the wall and can provide some guidance in predicting the nature of the flow.

  12. Computational aerodynamics and artificial intelligence

    NASA Technical Reports Server (NTRS)

    Kutler, P.; Mehta, U. B.

    1984-01-01

    Some aspects of artificial intelligence are considered and questions are speculated on, including how knowledge-based systems can accelerate the process of acquiring new knowledge in aerodynamics, how computational fluid dynamics may use 'expert' systems and how expert systems may speed the design and development process. The anatomy of an idealized expert system called AERODYNAMICIST is discussed. Resource requirements are examined for using artificial intelligence in computational fluid dynamics and aerodynamics. Considering two of the essentials of computational aerodynamics - reasoniing and calculating - it is believed that a substantial part of the reasoning can be achieved with artificial intelligence, with computers being used as reasoning machines to set the stage for calculating. Expert systems will probably be new assets of institutions involved in aeronautics for various tasks of computational aerodynamics.

  13. Computational aerodynamics and artificial intelligence

    NASA Technical Reports Server (NTRS)

    Mehta, U. B.; Kutler, P.

    1984-01-01

    The general principles of artificial intelligence are reviewed and speculations are made concerning how knowledge based systems can accelerate the process of acquiring new knowledge in aerodynamics, how computational fluid dynamics may use expert systems, and how expert systems may speed the design and development process. In addition, the anatomy of an idealized expert system called AERODYNAMICIST is discussed. Resource requirements for using artificial intelligence in computational fluid dynamics and aerodynamics are examined. Three main conclusions are presented. First, there are two related aspects of computational aerodynamics: reasoning and calculating. Second, a substantial portion of reasoning can be achieved with artificial intelligence. It offers the opportunity of using computers as reasoning machines to set the stage for efficient calculating. Third, expert systems are likely to be new assets of institutions involved in aeronautics for various tasks of computational aerodynamics.

  14. Turbine Aerodynamics Design Tool Development

    NASA Technical Reports Server (NTRS)

    Huber, Frank W.; Turner, James E. (Technical Monitor)

    2001-01-01

    This paper presents the Marshal Space Flight Center Fluids Workshop on Turbine Aerodynamic design tool development. The topics include: (1) Meanline Design/Off-design Analysis; and (2) Airfoil Contour Generation and Analysis. This paper is in viewgraph form.

  15. Surface roughness scattering in multisubband accumulation layers

    NASA Astrophysics Data System (ADS)

    Fu, Han; Reich, K. V.; Shklovskii, B. I.

    2016-06-01

    Accumulation layers with very large concentrations of electrons where many subbands are filled became recently available due to ionic liquid and other new methods of gating. The low-temperature mobility in such layers is limited by the surface roughness scattering. However, theories of roughness scattering so far dealt only with the small-density single subband two-dimensional electron gas (2DEG). Here we develop a theory of roughness-scattering limited mobility for the multisubband large concentration case. We show that with growing 2D electron concentration n the surface dimensionless conductivity σ /(2 e2/h ) first decreases as ∝n-6 /5 and then saturates as ˜(d aB/Δ2)≫1 , where d and Δ are the characteristic length and height of the surface roughness and aB is the effective Bohr radius. This means that in spite of the shrinkage of the 2DEG thickness and the related increase of the scattering rate the 2DEG remains a good metal.

  16. Optical roughness measurements on specially designed roughness standards

    NASA Astrophysics Data System (ADS)

    Danzl, R.; Helmli, F.; Rubert, P.; Prantl, M.

    2008-09-01

    The measurement of surface texture is one of the most common and important ways to judge the quality of a technical surface. In order to verify whether a metrology device is able to measure certain types of roughness accurately, various roughness standards with calibrated roughness values are available. While almost all roughness standards produced so far have been designed for tactile systems we demonstrate how the optical metrology device InfiniteFocus can be applied to special roughness standards that have been artificially roughened. Experiments are performed on standards with periodic structure and the results of the optical system are compared to the calibrated values obtained by tactile systems with different tip radius. Additionally the profile-based measurements are compared to area-based measurements conform to a recently developed ISO standard draft. Finally roughness measurements on real surfaces are presented.

  17. ROUGHNESS ANALYSIS OF VARIOUSLY POLISHED NIOBIUM SURFACES

    SciTech Connect

    Ribeill, G.; Reece, C.

    2008-01-01

    Niobium superconducting radio frequency (SRF) cavities have gained widespread use in accelerator systems. It has been shown that surface roughness is a determining factor in the cavities’ effi ciency and maximum accelerating potential achievable through this technology. Irregularities in the surface can lead to spot heating, undesirable local electrical fi eld enhancement and electron multipacting. Surface quality is typically ensured through the use of acid etching in a Buffered Chemical Polish (BCP) bath and electropolishing (EP). In this study, the effects of these techniques on surface morphology have been investigated in depth. The surface of niobium samples polished using different combinations of these techniques has been characterized through atomic force microscopy (AFM) and stylus profi lometry across a range of length scales. The surface morphology was analyzed using spectral techniques to determine roughness and characteristic dimensions. Experimentation has shown that this method is a valuable tool that provides quantitative information about surface roughness at different length scales. It has demonstrated that light BCP pretreatment and lower electrolyte temperature favors a smoother electropolish. These results will allow for the design of a superior polishing process for niobium SRF cavities and therefore increased accelerator operating effi ciency and power.

  18. Aerodynamics of badminton shuttlecocks

    NASA Astrophysics Data System (ADS)

    Verma, Aekaansh; Desai, Ajinkya; Mittal, Sanjay

    2013-08-01

    A computational study is carried out to understand the aerodynamics of shuttlecocks used in the sport of badminton. The speed of the shuttlecock considered is in the range of 25-50 m/s. The relative contribution of various parts of the shuttlecock to the overall drag is studied. It is found that the feathers, and the net in the case of a synthetic shuttlecock, contribute the maximum. The gaps, in the lower section of the skirt, play a major role in entraining the surrounding fluid and causing a difference between the pressure inside and outside the skirt. This pressure difference leads to drag. This is confirmed via computations for a shuttlecock with no gaps. The synthetic shuttle experiences more drag than the feather model. Unlike the synthetic model, the feather shuttlecock is associated with a swirling flow towards the end of the skirt. The effect of the twist angle of the feathers on the drag as well as the flow has also been studied.

  19. Aerodynamics of bird flight

    NASA Astrophysics Data System (ADS)

    Dvořák, Rudolf

    2016-03-01

    Unlike airplanes birds must have either flapping or oscillating wings (the hummingbird). Only such wings can produce both lift and thrust - two sine qua non attributes of flying.The bird wings have several possibilities how to obtain the same functions as airplane wings. All are realized by the system of flight feathers. Birds have also the capabilities of adjusting the shape of the wing according to what the immediate flight situation demands, as well as of responding almost immediately to conditions the flow environment dictates, such as wind gusts, object avoidance, target tracking, etc. In bird aerodynamics also the tail plays an important role. To fly, wings impart downward momentum to the surrounding air and obtain lift by reaction. How this is achieved under various flight situations (cruise flight, hovering, landing, etc.), and what the role is of the wing-generated vortices in producing lift and thrust is discussed.The issue of studying bird flight experimentally from in vivo or in vitro experiments is also briefly discussed.

  20. Aerodynamics of Laminar Flames

    NASA Astrophysics Data System (ADS)

    Law, Chung K.

    2000-11-01

    The presentation will review recent advances in the understanding of the structure, dynamics, and geometry of stretched, nonequidiffusive, laminar premixed flames, as exemplified by the unsteady propagation of wrinkled flames in nonuniform flow fields. It is first shown that by considering the effects of aerodynamic stretch on the flame structure, and by allowing for mixture nonequidiffusion, the flame responses, especially the flame propagation speed, can be quantitatively as well as qualitatively modified from the idealized planar limit. Subsequently, by treating the flame as a level surface propagating with the stretch-affected flame speed, problems of increasing complexity are presented to illustrate various features of flame propagation. The illustration first treats the flame as a structureless surface propagating into a constant-density combustible with a constant velocity * the laminar flame speed, and demonstrates the phenomena of cusp formation and volumetric burning rate augmentation through flame wrinkling. By using the stretch-affected flame speed, we then describe the phenomena of cusp broadening as well as tip opening of the Bunsen flame. Finally, by allowing for the density jump across the flame surface, a unified dispersion relation is derived for the intrinsic hydrodynamic, body-force, and nonequidiffusive modes of flame

  1. Introduction. Computational aerodynamics.

    PubMed

    Tucker, Paul G

    2007-10-15

    The wide range of uses of computational fluid dynamics (CFD) for aircraft design is discussed along with its role in dealing with the environmental impact of flight. Enabling technologies, such as grid generation and turbulence models, are also considered along with flow/turbulence control. The large eddy simulation, Reynolds-averaged Navier-Stokes and hybrid turbulence modelling approaches are contrasted. The CFD prediction of numerous jet configurations occurring in aerospace are discussed along with aeroelasticity for aeroengine and external aerodynamics, design optimization, unsteady flow modelling and aeroengine internal and external flows. It is concluded that there is a lack of detailed measurements (for both canonical and complex geometry flows) to provide validation and even, in some cases, basic understanding of flow physics. Not surprisingly, turbulence modelling is still the weak link along with, as ever, a pressing need for improved (in terms of robustness, speed and accuracy) solver technology, grid generation and geometry handling. Hence, CFD, as a truly predictive and creative design tool, seems a long way off. Meanwhile, extreme practitioner expertise is still required and the triad of computation, measurement and analytic solution must be judiciously used.

  2. Parametric Study of Urban-Like Topographic Statistical Moments Relevant to a Priori Modelling of Bulk Aerodynamic Parameters

    NASA Astrophysics Data System (ADS)

    Zhu, Xiaowei; Iungo, G. Valerio; Leonardi, Stefano; Anderson, William

    2016-08-01

    For a horizontally homogeneous, neutrally stratified atmospheric boundary layer (ABL), aerodynamic roughness length, z_0 , is the effective elevation at which the streamwise component of mean velocity is zero. A priori prediction of z_0 based on topographic attributes remains an open line of inquiry in planetary boundary-layer research. Urban topographies - the topic of this study - exhibit spatial heterogeneities associated with variability of building height, width, and proximity with adjacent buildings; such variability renders a priori, prognostic z_0 models appealing. Here, large-eddy simulation (LES) has been used in an extensive parametric study to characterize the ABL response (and z_0 ) to a range of synthetic, urban-like topographies wherein statistical moments of the topography have been systematically varied. Using LES results, we determined the hierarchical influence of topographic moments relevant to setting z_0 . We demonstrate that standard deviation and skewness are important, while kurtosis is negligible. This finding is reconciled with a model recently proposed by Flack and Schultz (J Fluids Eng 132:041203-1-041203-10, 2010), who demonstrate that z_0 can be modelled with standard deviation and skewness, and two empirical coefficients (one for each moment). We find that the empirical coefficient related to skewness is not constant, but exhibits a dependence on standard deviation over certain ranges. For idealized, quasi-uniform cubic topographies and for complex, fully random urban-like topographies, we demonstrate strong performance of the generalized Flack and Schultz model against contemporary roughness correlations.

  3. Roughness characteristics of natural channels

    USGS Publications Warehouse

    Barnes, Harry Hawthorne

    1967-01-01

    Color photographs and descriptive data are presented for 50 stream channels for which roughness coefficients have been determined. All hydraulic computations involving flow in open channels require an evaluation of the roughness characteristics of the channel. In the absence of a satisfactory quantitative procedure this evaluation remains chiefly an art. The ability to evaluate roughness coefficients must be developed through experience. One means of gaining this experience is by examining and becoming acquainted with the appearance of some typical channels whose roughness coefficients are known. The photographs and data contained in this report represent a wide range of channel conditions. Familiarity with the appearance, geometry, and roughness characteristics of these channels will improve the engineer's ability to select roughness coefficients for other channels .

  4. Surface roughness measurements

    NASA Technical Reports Server (NTRS)

    Howard, Thomas G.

    1994-01-01

    The Optics Division is currently in the research phase of producing grazing-incidence mirrors to be used in x-ray detector applications. The traditional method of construction involves labor-intensive glass grinding. This also culminates in a relatively heavy mirror. For lower resolution applications, the mirrors may be of a replicated design which involves milling a mandrel as a negative of the final shape and electroplating the cylindrical mirror onto it. The mirror is then separated from the mandrel by cooling. The mandrel will shrink more than the 'shell' (mirror) allowing it to be pulled from the mandrel. Ulmer (2) describes this technique and its variations in more detail. To date, several mirrors have been tested at MSFC by the Optical Fabrication Branch by focusing x-ray energy onto a detector with limited success. Little is known about the surface roughness of the actual mirror. Hence, the attempt to gather data on these surfaces. The test involves profiling the surface of a sample, replicating the surface as described above, and then profiling the replicated surface.

  5. A rough earth scattering model for multipath prediction

    NASA Technical Reports Server (NTRS)

    Page, L. J.; Chestnut, P. C.

    1970-01-01

    The most important phenomena to be considered in a model of radio wave communication between earth satellites are scattering from the surface of the earth. A model is derived and implemented on a computer to predict the field received after reflection from a rough, spherical earth. The scattering integrals are computed numerically; the domain of integration is the appropriate region on the surface of the earth. Calculations have been performed at VHF frequencies and for terrain which could be described as marshy land. Rough surface scattering calculations must be performed over a spherical earth when satellites are involved. There is a definite dependence on the values of the roughness, and the correlation length.

  6. Roughness Measurement of Dental Materials

    NASA Astrophysics Data System (ADS)

    Shulev, Assen; Roussev, Ilia; Karpuzov, Simeon; Stoilov, Georgi; Ignatova, Detelina; See, Constantin von; Mitov, Gergo

    2016-06-01

    This paper presents a roughness measurement of zirconia ceramics, widely used for dental applications. Surface roughness variations caused by the most commonly used dental instruments for intraoral grinding and polishing are estimated. The applied technique is simple and utilizes the speckle properties of the scattered laser light. It could be easily implemented even in dental clinic environment. The main criteria for roughness estimation is the average speckle size, which varies with the roughness of zirconia. The algorithm used for the speckle size estimation is based on the normalized autocorrelation approach.

  7. Application of 3D printing technology in aerodynamic study

    NASA Astrophysics Data System (ADS)

    Olasek, K.; Wiklak, P.

    2014-08-01

    3D printing, as an additive process, offers much more than traditional machining techniques in terms of achievable complexity of a model shape. That fact was a motivation to adapt discussed technology as a method for creating objects purposed for aerodynamic testing. The following paper provides an overview of various 3D printing techniques. Four models of a standard NACA0018 aerofoil were manufactured in different materials and methods: MultiJet Modelling (MJM), Selective Laser Sintering (SLS) and Fused Deposition Modeling (FDM). Various parameters of the models have been included in the analysis: surface roughness, strength, details quality, surface imperfections and irregularities as well as thermal properties.

  8. Measurement technology for micro-scale aerodynamics

    NASA Astrophysics Data System (ADS)

    Martin, Michael James

    As micro-technology improves, it may become possible to build flying vehicles at length scales of millimeters, or even microns. Successful design of vehicles at such sizes requires understanding of the fluid mechanics of flight at the micron scale. While biological flight has been studied at these scales, many questions remain to be answered for flight at these scales. Previous work has not determined the limiting scales of continuum aerodynamics for low-speed flight. This study begins with the development of a new scaling law based on boundary layer theory. The laminar boundary layer equations were solved non-dimensionally for slip flow conditions. These results show that a measurable decrease in skin friction, as well as changes in heat transfer, and flow stability, may occur as the boundary layer Knudsen number approaches 0.01. These flow conditions correspond to airfoil chords of up to 100 microns, pressures of 0.1 to 1.0 atmospheres, and velocities from 30 to 100 m/s. Based on this scaling law, specialized wind-tunnel test facilities were designed to operate at scales not previously studied. The novel wind-tunnel allows for independent control of Reynolds and Knudsen numbers on static airfoils. A draw-through, low turbulence, low-pressure wind tunnel with a 1 cm cross section was built and tested. The flow through these facilities is characterized, and recommendations are made for future wind-tunnel development. To allow testing at these scales, micro-scale airfoils, with chords of 100 microns, thicknesses of 5 microns, and a span of 1 cm were fabricated using MEMS fabrication technology. Fabrication of free-standing micro-structures with meso-scale spans and micro-scale cross sections required the development of specialized fabrication processes. These airfoils were integrated with piezoresistive force sensors, allowing measurement of aerodynamic forces. The airfoil structures were successfully released within the tunnel. The actual aerodynamic load on the

  9. Configuration Aerodynamics: Past - Present - Future

    NASA Technical Reports Server (NTRS)

    Wood, Richard M.; Agrawal, Shreekant; Bencze, Daniel P.; Kulfan, Robert M.; Wilson, Douglas L.

    1999-01-01

    The Configuration Aerodynamics (CA) element of the High Speed Research (HSR) program is managed by a joint NASA and Industry team, referred to as the Technology Integration Development (ITD) team. This team is responsible for the development of a broad range of technologies for improved aerodynamic performance and stability and control characteristics at subsonic to supersonic flight conditions. These objectives are pursued through the aggressive use of advanced experimental test techniques and state of the art computational methods. As the HSR program matures and transitions into the next phase the objectives of the Configuration Aerodynamics ITD are being refined to address the drag reduction needs and stability and control requirements of High Speed Civil Transport (HSCT) aircraft. In addition, the experimental and computational tools are being refined and improved to meet these challenges. The presentation will review the work performed within the Configuration Aerodynamics element in 1994 and 1995 and then discuss the plans for the 1996-1998 time period. The final portion of the presentation will review several observations of the HSR program and the design activity within Configuration Aerodynamics.

  10. Aerodynamic drag on intermodal railcars

    NASA Astrophysics Data System (ADS)

    Kinghorn, Philip; Maynes, Daniel

    2014-11-01

    The aerodynamic drag associated with transport of commodities by rail is becoming increasingly important as the cost of diesel fuel increases. This study aims to increase the efficiency of intermodal cargo trains by reducing the aerodynamic drag on the load carrying cars. For intermodal railcars a significant amount of aerodynamic drag is a result of the large distance between loads that often occurs and the resulting pressure drag resulting from the separated flow. In the present study aerodynamic drag data have been obtained through wind tunnel testing on 1/29 scale models to understand the savings that may be realized by judicious modification to the size of the intermodal containers. The experiments were performed in the BYU low speed wind tunnel and the test track utilizes two leading locomotives followed by a set of five articulated well cars with double stacked containers. The drag on a representative mid-train car is measured using an isolated load cell balance and the wind tunnel speed is varied from 20 to 100 mph. We characterize the effect that the gap distance between the containers and the container size has on the aerodynamic drag of this representative rail car and investigate methods to reduce the gap distance.

  11. Influence of Nanoscale Surface Roughness on Colloidal Force Measurements.

    PubMed

    Zou, Yi; Jayasuriya, Sunil; Manke, Charles W; Mao, Guangzhao

    2015-09-29

    Forces between colloidal particles determine the performances of many industrial processes and products. Colloidal force measurements conducted between a colloidal particle AFM probe and particles immobilized on a flat substrate are valuable in selecting appropriate surfactants for colloidal stabilization. One of the features of inorganic fillers and extenders is the prevalence of rough surfaces-even the polymer latex particles, often used as model colloidal systems including the current study, have rough surfaces albeit at a much smaller scale. Surface roughness is frequently cited as the reason for disparity between experimental observations and theoretical treatment but seldom verified by direct evidence. This work reports the effect of nanoscale surface roughness on colloidal force measurements carried out in the presence of surfactants. We applied a heating method to reduce the mean surface roughness of commercial latex particles from 30 to 1 nm. We conducted force measurements using the two types of particles at various salt and surfactant concentrations. The surfactants used were pentaethylene glycol monododecyl ether, Pluronic F108, and a styrene/acrylic copolymer, Joncryl 60. In the absence of the surfactant, nanometer surface roughness affects colloidal forces only in high salt conditions when the Debye length becomes smaller than the surface roughness. The adhesion is stronger between colloids with higher surface roughness and requires a higher surfactant concentration to be eliminated. The effect of surface roughness on colloidal forces was also investigated as a function of the adsorbed surfactant layer structure characterized by AFM indentation and dynamic light scattering. We found that when the layer thickness exceeds the surface roughness, the colloidal adhesion is less influenced by surfactant concentration variation. This study demonstrates that surface roughness at the nanoscale can influence colloidal forces significantly and should be taken

  12. Methods of reducing vehicle aerodynamic drag

    SciTech Connect

    Sirenko V.; Rohatgi U.

    2012-07-08

    A small scale model (length 1710 mm) of General Motor SUV was built and tested in the wind tunnel for expected wind conditions and road clearance. Two passive devices, rear screen which is plate behind the car and rear fairing where the end of the car is aerodynamically extended, were incorporated in the model and tested in the wind tunnel for different wind conditions. The conclusion is that rear screen could reduce drag up to 6.5% and rear fairing can reduce the drag by 26%. There were additional tests for front edging and rear vortex generators. The results for drag reduction were mixed. It should be noted that there are aesthetic and practical considerations that may allow only partial implementation of these or any drag reduction options.

  13. New technology in turbine aerodynamics.

    NASA Technical Reports Server (NTRS)

    Glassman, A. J.; Moffitt, T. P.

    1972-01-01

    Cursory review of some recent work that has been done in turbine aerodynamic research. Topics discussed include the aerodynamic effect of turbine coolant, high work-factor (ratio of stage work to square of blade speed) turbines, and computer methods for turbine design and performance prediction. Experimental cooled-turbine aerodynamics programs using two-dimensional cascades, full annular cascades, and cold rotating turbine stage tests are discussed with some typical results presented. Analytically predicted results for cooled blade performance are compared to experimental results. The problems and some of the current programs associated with the use of very high work factors for fan-drive turbines of high-bypass-ratio engines are discussed. Computer programs have been developed for turbine design-point performance, off-design performance, supersonic blade profile design, and the calculation of channel velocities for subsonic and transonic flowfields. The use of these programs for the design and analysis of axial and radial turbines is discussed.

  14. Recent advances in computational aerodynamics

    NASA Astrophysics Data System (ADS)

    Agarwal, Ramesh K.; Desse, Jerry E.

    1991-04-01

    The current state of the art in computational aerodynamics is described. Recent advances in the discretization of surface geometry, grid generation, and flow simulation algorithms have led to flowfield predictions for increasingly complex and realistic configurations. As a result, computational aerodynamics is emerging as a crucial enabling technology for the development and design of flight vehicles. Examples illustrating the current capability for the prediction of aircraft, launch vehicle and helicopter flowfields are presented. Unfortunately, accurate modeling of turbulence remains a major difficulty in the analysis of viscosity-dominated flows. In the future inverse design methods, multidisciplinary design optimization methods, artificial intelligence technology and massively parallel computer technology will be incorporated into computational aerodynamics, opening up greater opportunities for improved product design at substantially reduced costs.

  15. Aerodynamics Research Revolutionizes Truck Design

    NASA Technical Reports Server (NTRS)

    2008-01-01

    During the 1970s and 1980s, researchers at Dryden Flight Research Center conducted numerous tests to refine the shape of trucks to reduce aerodynamic drag and improved efficiency. During the 1980s and 1990s, a team based at Langley Research Center explored controlling drag and the flow of air around a moving body. Aeroserve Technologies Ltd., of Ottawa, Canada, with its subsidiary, Airtab LLC, in Loveland, Colorado, applied the research from Dryden and Langley to the development of the Airtab vortex generator. Airtabs create two counter-rotating vortices to reduce wind resistance and aerodynamic drag of trucks, trailers, recreational vehicles, and many other vehicles.

  16. Rotor/body aerodynamic interactions

    NASA Technical Reports Server (NTRS)

    Betzina, M. D.; Smith, C. A.; Shinoda, P.

    1983-01-01

    A wind tunnel investigation was conducted in which independent, steady state aerodynamic forces and moments were measured on a 2.24 m diam. two bladed helicopter rotor and on several different bodies. The mutual interaction effects for variations in velocity, thrust, tip-path-plane angle of attack, body angle of attack, rotor/body position, and body geometry were determined. The results show that the body longitudinal aerodynamic characteristics are significantly affected by the presence of a rotor and hub, and that the hub interference may be a major part of such interaction. The effects of the body on the rotor performance are presented.

  17. Rotor/body aerodynamic interactions

    NASA Technical Reports Server (NTRS)

    Betzina, M. D.; Smith, C. A.; Shinoda, P.

    1985-01-01

    A wind tunnel investigation was conducted in which independent, steady state aerodynamic forces and moments were measured on a 2.24 m diam. two bladed helicopter rotor and on several different bodies. The mutual interaction effects for variations in velocity, thrust, tip-path-plane angle of attack, body angle of attack, rotor/body position, and body geometry were determined. The results show that the body longitudinal aerodynamic characteristics are significantly affected by the presence of a rotor and hub, and that the hub interference may be a major part of such interaction. The effects of the body on the rotor performance are presented.

  18. Adsorption of Polymers on Rough Surfaces

    NASA Astrophysics Data System (ADS)

    Venkatakrishnan, Abishek; Kuppa, Vikram

    2014-03-01

    Most of the surfaces encountered in nature display irregularity and self-similarity at certain length scales. Such real surfaces can be mimicked via fractal surfaces using an algorithm that produces random surfaces. The problem of polymer chains adsorbed on smooth surfaces has been well understood whereas adsorption on rough surfaces still remains unclear due to the complexity involved in equilibration and sampling of molecules in such systems. The enthalpic interactions between the monomers and the entropic penalty arising due to adsorption on rough surfaces are significantly different from smooth surfaces. In this study, we investigate the adsorption of freely rotating polymer chains on fractal surfaces by Monte-Carlo molecular simulations. Random fractal surfaces are generated using the diamond-square algorithm for different values of the Hurst parameter. Properties like monomer-surface interaction, density profiles, chain orientation profiles and distribution of adsorbed chain fractions are investigated. We also demonstrate the significant effect of fractal dimension on adsorption of polymers on rough surfaces.

  19. Langley Symposium on Aerodynamics, volume 1

    NASA Technical Reports Server (NTRS)

    Stack, Sharon H. (Compiler)

    1986-01-01

    The purpose of this work was to present current work and results of the Langley Aeronautics Directorate covering the areas of computational fluid dynamics, viscous flows, airfoil aerodynamics, propulsion integration, test techniques, and low-speed, high-speed, and transonic aerodynamics. The following sessions are included in this volume: theoretical aerodynamics, test techniques, fluid physics, and viscous drag reduction.

  20. Unsteady aerodynamics modeling for flight dynamics application

    NASA Astrophysics Data System (ADS)

    Wang, Qing; He, Kai-Feng; Qian, Wei-Qi; Zhang, Tian-Jiao; Cheng, Yan-Qing; Wu, Kai-Yuan

    2012-02-01

    In view of engineering application, it is practicable to decompose the aerodynamics into three components: the static aerodynamics, the aerodynamic increment due to steady rotations, and the aerodynamic increment due to unsteady separated and vortical flow. The first and the second components can be presented in conventional forms, while the third is described using a one-order differential equation and a radial-basis-function (RBF) network. For an aircraft configuration, the mathematical models of 6-component aerodynamic coefficients are set up from the wind tunnel test data of pitch, yaw, roll, and coupled yawroll large-amplitude oscillations. The flight dynamics of an aircraft is studied by the bifurcation analysis technique in the case of quasi-steady aerodynamics and unsteady aerodynamics, respectively. The results show that: (1) unsteady aerodynamics has no effect upon the existence of trim points, but affects their stability; (2) unsteady aerodynamics has great effects upon the existence, stability, and amplitudes of periodic solutions; and (3) unsteady aerodynamics changes the stable regions of trim points obviously. Furthermore, the dynamic responses of the aircraft to elevator deflections are inspected. It is shown that the unsteady aerodynamics is beneficial to dynamic stability for the present aircraft. Finally, the effects of unsteady aerodynamics on the post-stall maneuverability are analyzed by numerical simulation.

  1. Clouds Versus Carbon: Predicting Vegetation Roughness by Maximizing Productivity

    NASA Technical Reports Server (NTRS)

    Olsen, Lola M.

    2004-01-01

    Surface roughness is one of the dominant vegetation properties that affects land surface exchange of energy, water, carbon, and momentum with the overlying atmosphere. We hypothesize that the canopy structure of terrestrial vegetation adapts optimally to climate by maximizing productivity, leading to an optimum surface roughness. An optimum should exist because increasing values of surface roughness cause increased surface exchange, leading to increased supply of carbon dioxide for photosynthesis. At the same time, increased roughness enhances evapotranspiration and cloud cover, thereby reducing the supply of photosynthetically active radiation. We demonstrate the optimum through sensitivity simulations using a coupled dynamic vegetation-climate model for present day conditions, in which we vary the value of surface roughness for vegetated surfaces. We find that the maximum in productivity occurs at a roughness length of 2 meters, a value commonly used to describe the roughness of today's forested surfaces. The sensitivity simulations also illustrate the strong climatic impacts of vegetation roughness on the energy and water balances over land: with increasing vegetation roughness, solar radiation is reduced by up to 20 W/sq m in the global land mean, causing shifts in the energy partitioning and leading to general cooling of the surface by 1.5 K. We conclude that the roughness of vegetated surfaces can be understood as a reflection of optimum adaptation, and it is associated with substantial changes in the surface energy and water balances over land. The role of the cloud feedback in shaping the optimum underlines the importance of an integrated perspective that views vegetation and its adaptive nature as an integrated component of the Earth system.

  2. Aerodynamic penalties of heavy rain on a landing aircraft

    NASA Technical Reports Server (NTRS)

    Haines, P. A.; Luers, J. K.

    1982-01-01

    The aerodynamic penalties of very heavy rain on landing aircraft were investigated. Based on severity and frequency of occurrence, the rainfall rates of 100 mm/hr, 500 mm/hr, and 2000 mm/hr were designated, respectively, as heavy, severe, and incredible. The overall and local collection efficiencies of an aircraft encountering these rains were calculated. The analysis was based on raindrop trajectories in potential flow about an aircraft. All raindrops impinging on the aircraft are assumed to take on its speed. The momentum loss from the rain impact was later used in a landing simulation program. The local collection efficiency was used in estimating the aerodynamic roughness of an aircraft in heavy rain. The drag increase from this roughness was calculated. A number of landing simulations under a fixed stick assumption were done. Serious landing shortfalls were found for either momentum or drag penalties and especially large shortfalls for the combination of both. The latter shortfalls are comparable to those found for severe wind shear conditions.

  3. Adjustment of roughness sublayer in turbulent flows over two-dimensional idealised roughness elements

    NASA Astrophysics Data System (ADS)

    HO, Yat-Kiu; LIU, Chun-Ho

    2015-04-01

    The atmospheric boundary layer (ABL) immediately above the urban canopy is the roughness sublayer (RSL). In this layer, flows and turbulence are strongly affected by the roughness elements beneath, e.g. building obstacles. The wind flows over urban areas could be represented by conventional logarithmic law of the wall (log-law) in the neutrally stratified ABL. However, in the RSL region, the vertical wind profile deviates from that predicted from log-law and the effect could be extended from ground level up to several canopy heights. As a result, the Monin-Obukhov similarity theory (MOST) fails and an additional length scale is required to describe the flows. The key aim of this study is to introduce a simple wind profile model which accounts for the effect of the RSL in neutral stratification using wind tunnel experiments. Profile measurements of wind speeds and turbulence quantities over various two-dimensional (2D) idealised roughness elements are carried out in an open-circuit wind tunnel with test section of size 560 mm (width) × 560 mm (height) × 6 m (length). The separation between the roughness elements is varied systematically so that ten different types of surface forms are adopted. The velocity measurements are obtained by hot-wire anemometry using X-probe design (for UW- measurements) with a constant temperature anemometer. For each configuration, eight vertical profiles are collected over the canopy, including solid boundaries and cavities of the roughness elements. Firstly, we compute the measurement results using conventional MOST to determine different roughness parameters. Afterwards, we derive the RSL height from the Reynolds stress profiles. Since the profiles taken from different locations of the canopy are eventually converged with increasing height, we use this 'congregated height' to define the RSL height. Next, we introduce an alternative function, i.e. power-law function, instead of MOST, to describe the velocity profile in attempt to

  4. New technology in turbine aerodynamics

    NASA Technical Reports Server (NTRS)

    Glassman, A. J.; Moffitt, T. P.

    1972-01-01

    A cursory review is presented of some of the recent work that has been done in turbine aerodynamic research at NASA-Lewis Research Center. Topics discussed include the aerodynamic effect of turbine coolant, high work-factor (ratio of stage work to square of blade speed) turbines, and computer methods for turbine design and performance prediction. An extensive bibliography is included. Experimental cooled-turbine aerodynamics programs using two-dimensional cascades, full annular cascades, and cold rotating turbine stage tests are discussed with some typical results presented. Analytically predicted results for cooled blade performance are compared to experimental results. The problems and some of the current programs associated with the use of very high work factors for fan-drive turbines of high-bypass-ratio engines are discussed. Turbines currently being investigated make use of advanced blading concepts designed to maintain high efficiency under conditions of high aerodynamic loading. Computer programs have been developed for turbine design-point performance, off-design performance, supersonic blade profile design, and the calculation of channel velocities for subsonic and transonic flow fields. The use of these programs for the design and analysis of axial and radial turbines is discussed.

  5. Sensitivity analysis in computational aerodynamics

    NASA Technical Reports Server (NTRS)

    Bristow, D. R.

    1984-01-01

    Information on sensitivity analysis in computational aerodynamics is given in outline, graphical, and chart form. The prediction accuracy if the MCAERO program, a perturbation analysis method, is discussed. A procedure for calculating perturbation matrix, baseline wing paneling for perturbation analysis test cases and applications of an inviscid sensitivity matrix are among the topics covered.

  6. Aerodynamic laboratory at Cuatro Vientos

    NASA Technical Reports Server (NTRS)

    JUBERA

    1922-01-01

    This report presents a listing of the many experiments in aerodynamics taking place at Cuatro Vientos. Some of the studies include: testing spheres, in order to determine coefficients; mechanical and chemical tests of materials; and various tests of propeller strength and flexibility.

  7. Shuttle reentry aerodynamic heating test

    NASA Technical Reports Server (NTRS)

    Pond, J. E.; Mccormick, P. O.; Smith, S. D.

    1971-01-01

    The research for determining the space shuttle aerothermal environment is reported. Brief summaries of the low Reynolds number windward side heating test, and the base and leeward heating and high Reynolds number heating test are included. Also discussed are streamline divergence and the resulting effect on aerodynamic heating, and a thermal analyzer program that is used in the Thermal Environment Optimization Program.

  8. Dynamic Soaring: Aerodynamics for Albatrosses

    ERIC Educational Resources Information Center

    Denny, Mark

    2009-01-01

    Albatrosses have evolved to soar and glide efficiently. By maximizing their lift-to-drag ratio "L/D", albatrosses can gain energy from the wind and can travel long distances with little effort. We simplify the difficult aerodynamic equations of motion by assuming that albatrosses maintain a constant "L/D". Analytic solutions to the simplified…

  9. POEMS in Newton's Aerodynamic Frustum

    ERIC Educational Resources Information Center

    Sampedro, Jaime Cruz; Tetlalmatzi-Montiel, Margarita

    2010-01-01

    The golden mean is often naively seen as a sign of optimal beauty but rarely does it arise as the solution of a true optimization problem. In this article we present such a problem, demonstrating a close relationship between the golden mean and a special case of Newton's aerodynamical problem for the frustum of a cone. Then, we exhibit a parallel…

  10. Rotary wing aerodynamically generated noise

    NASA Technical Reports Server (NTRS)

    Schmitz, F. J.; Morse, H. A.

    1982-01-01

    The history and methodology of aerodynamic noise reduction in rotary wing aircraft are presented. Thickness noise during hover tests and blade vortex interaction noise are determined and predicted through the use of a variety of computer codes. The use of test facilities and scale models for data acquisition are discussed.

  11. Aerodynamic design via control theory

    NASA Technical Reports Server (NTRS)

    Jameson, Antony

    1988-01-01

    The question of how to modify aerodynamic design in order to improve performance is addressed. Representative examples are given to demonstrate the computational feasibility of using control theory for such a purpose. An introduction and historical survey of the subject is included.

  12. Radar-aeolian roughness project

    NASA Technical Reports Server (NTRS)

    Greeley, Ronald; Dobrovolskis, A.; Gaddis, L.; Iversen, J. D.; Lancaster, N.; Leach, Rodman N.; Rasnussen, K.; Saunders, S.; Vanzyl, J.; Wall, S.

    1991-01-01

    The objective is to establish an empirical relationship between measurements of radar, aeolian, and surface roughness on a variety of natural surfaces and to understand the underlying physical causes. This relationship will form the basis for developing a predictive equation to derive aeolian roughness from radar backscatter. Results are given from investigations carried out in 1989 on the principal elements of the project, with separate sections on field studies, radar data analysis, laboratory simulations, and development of theory for planetary applications.

  13. Surface roughness scattering of electrons in bulk mosfets

    SciTech Connect

    Zuverink, Amanda Renee

    2015-11-01

    Surface-roughness scattering of electrons at the Si-SiO2 interface is a very important consideration when analyzing Si metal-oxide-semiconductor field-effect transistors (MOSFETs). Scattering reduces the mobility of the electrons and degrades the device performance. 250-nm and 50-nm bulk MOSFETs were simulated with varying device parameters and mesh sizes in order to compare the effects of surface-roughness scattering in multiple devices. The simulation framework includes the ensemble Monte Carlo method used to solve the Boltzmann transport equation coupled with a successive over-relaxation method used to solve the two-dimensional Poisson's equation. Four methods for simulating the surface-roughness scattering of electrons were implemented on both devices and compared: the constant specularity parameter, the momentum-dependent specularity parameter, and the real-space-roughness method with both uniform and varying electric fields. The specularity parameter is the probability of an electron scattering speculariy from a rough surface. It can be chosen as a constant, characterizing partially diffuse scattering of all electrons from the surface the same way, or it can be momentum dependent, where the size of rms roughness and the normal component of the electron wave number determine the probability of electron-momentum randomization. The real-space rough surface method uses the rms roughness height and correlation length of an actual MOSFET to simulate a rough interface. Due to their charge, electrons scatter from the electric field and not directly from the surface. If the electric field is kept uniform, the electrons do not perceive the roughness and scatter as if from a at surface. However, if the field is allowed to vary, the electrons scatter from the varying electric field as they would in a MOSFET. These methods were implemented for both the 50-nm and 250-nm MOSFETs, and using the rms roughness heights and correlation lengths for real devices. The

  14. Roughness of Hawaiian volcanic terrains

    NASA Astrophysics Data System (ADS)

    Morris, Aisha R.; Anderson, F. Scott; Mouginis-Mark, Peter J.; Haldemann, Albert F. C.; Brooks, Benjamin A.; Foster, James

    2008-12-01

    We performed analyses of topographic variation (surface roughness) using a new 2-D mapping method which shows that understanding the relationship between data resolution, Hurst exponent, y intercept, RMS deviation, and cell size is important for assessing surface processes. We use this new method to assess flows at six field sites in Kilauea caldera, Hawaii, using three data sets at different resolutions, TOPSAR (10 m/pixel), airborne lidar (1 m/pixel), and tripod-mounted lidar (0.02-0.03 m/pixel). The flows studied include ponded pahoehoe flows, compound pahoehoe flows, and jumbled, slabby pahoehoe. The 2-D quantification of surface roughness for the Kilauea lava flows indicates that features formed during emplacement and modification of the flows exhibit statistically distinct roughness signatures. The 2-D method provides a tool for unit mapping based on surface roughness. Key findings indicate that the new 2-D method provides more robust results than 1-D methods for surface roughness because of larger 2-D sample sizes and the removal of 1-D directional bias leading to a reduction in error. Furthermore, data set resolution relative to the scale of the features under study is important to consider when designing a 2-D surface roughness study. Future applications to topographic data sets from Mars will provide information on flow emplacement conditions and spatial and temporal evolution of volcanic provinces on Mars.

  15. Aerodynamic Classification of Swept-Wing Ice Accretion

    NASA Technical Reports Server (NTRS)

    Diebold, Jeff M.; Broeren, Andy P.; Bragg, Michael B.

    2013-01-01

    The continued design, certification and safe operation of swept-wing airplanes in icing conditions rely on the advancement of computational and experimental simulation methods for higher fidelity results over an increasing range of aircraft configurations and performance, and icing conditions. The current state-of-the-art in icing aerodynamics is mainly built upon a comprehensive understanding of two-dimensional geometries that does not currently exist for fundamentally three-dimensional geometries such as swept wings. The purpose of this report is to describe what is known of iced-swept-wing aerodynamics and to identify the type of research that is required to improve the current understanding. Following the method used in a previous review of iced-airfoil aerodynamics, this report proposes a classification of swept-wing ice accretion into four groups based upon unique flowfield attributes. These four groups are: ice roughness, horn ice, streamwise ice and spanwise-ridge ice. In the case of horn ice it is shown that a further subclassification of nominally 3D or highly 3D horn ice may be necessary. For all of the proposed ice-shape classifications, relatively little is known about the three-dimensional flowfield and even less about the effect of Reynolds number and Mach number on these flowfields. The classifications and supporting data presented in this report can serve as a starting point as new research explores swept-wing aerodynamics with ice shapes. As further results are available, it is expected that these classifications will need to be updated and revised.

  16. Aerodynamic Classification of Swept-Wing Ice Accretion

    NASA Technical Reports Server (NTRS)

    Diebold, Jeff M.; Broeren, Andy P.; Bragg, Michael B.

    2013-01-01

    The continued design, certification and safe operation of swept-wing airplanes in icing conditions rely on the advancement of computational and experimental simulation methods for higher fidelity results over an increasing range of aircraft configurations and performance, and icing conditions. The current stateof- the-art in icing aerodynamics is mainly built upon a comprehensive understanding of two-dimensional geometries that does not currently exist for fundamentally three-dimensional geometries such as swept wings. The purpose of this report is to describe what is known of iced-swept-wing aerodynamics and to identify the type of research that is required to improve the current understanding. Following the method used in a previous review of iced-airfoil aerodynamics, this report proposes a classification of swept-wing ice accretion into four groups based upon unique flowfield attributes. These four groups are: ice roughness, horn ice, streamwise ice and spanwise-ridge ice. In the case of horn ice it is shown that a further subclassification of "nominally 3D" or "highly 3D" horn ice may be necessary. For all of the proposed ice-shape classifications, relatively little is known about the three-dimensional flowfield and even less about the effect of Reynolds number and Mach number on these flowfields. The classifications and supporting data presented in this report can serve as a starting point as new research explores swept-wing aerodynamics with ice shapes. As further results are available, it is expected that these classifications will need to be updated and revised.

  17. Aerodynamics of a linear oscillating cascade

    NASA Technical Reports Server (NTRS)

    Buffum, Daniel H.; Fleeter, Sanford

    1990-01-01

    The steady and unsteady aerodynamics of a linear oscillating cascade are investigated using experimental and computational methods. Experiments are performed to quantify the torsion mode oscillating cascade aerodynamics of the NASA Lewis Transonic Oscillating Cascade for subsonic inlet flowfields using two methods: simultaneous oscillation of all the cascaded airfoils at various values of interblade phase angle, and the unsteady aerodynamic influence coefficient technique. Analysis of these data and correlation with classical linearized unsteady aerodynamic analysis predictions indicate that the wind tunnel walls enclosing the cascade have, in some cases, a detrimental effect on the cascade unsteady aerodynamics. An Euler code for oscillating cascade aerodynamics is modified to incorporate improved upstream and downstream boundary conditions and also the unsteady aerodynamic influence coefficient technique. The new boundary conditions are shown to improve the unsteady aerodynamic influence coefficient technique. The new boundary conditions are shown to improve the unsteady aerodynamic predictions of the code, and the computational unsteady aerodynamic influence coefficient technique is shown to be a viable alternative for calculation of oscillating cascade aerodynamics.

  18. The effect of sidewall roughness on line edge roughness in top-down scanning electron microscopy images

    NASA Astrophysics Data System (ADS)

    Verduin, T.; Lokhorst, S. R.; Kruit, P.; Hagen, C. W.

    2015-03-01

    We have investigated in a numerical study the determination of sidewall roughness (SWR) from top down scanning electron microscopy (SEM) images. In a typical metrology application, top-down SEM images are acquired in a (critical-dimension) SEM and the roughness is analyzed. However, the true size, shape and roughness characteristics of resist features are not fully investigated in the analysis of top-down SEM images. In reality, rough resist features are complex three-dimensional structures and the characterization naturally extends to the analysis of SWR. In this study we randomly generate images of rough lines and spaces, where the lines are made of PMMA on a silicon substrate. The lines that we study have a length of 2 µm, a width of 32nm and a height of 32 nm. The SWR is modeled by using the power spectral density (PSD) function of Palasantzas, which characterizes roughness by the standard deviation σ, correlation length ξ and roughness exponent α . The actual roughness is generated by application of the method of Thorsos in two dimensions. The images are constructed by using a home-built program for simulating electron-specimen interactions. The program that we have developed is optimized for complex arbitrary geometries and large number of incident low energy primary electrons by using multi-core CPUs and GPUs. The program uses the dielectric function model for inelastic scattering events and has an implementation specifically for low energy electrons. A satisfactory comparison is made between the secondary electron yields from the home-built program and another program found in literature. In order to reduce the risk of shrinkage, we use a beam energy of 300 eV and a spot size of 3 nm. Each pixel is exposed with 20 electrons on average (≍ 276 µC/cm2), following the Poisson distribution to account for illumination shot noise. We have assumed that the detection of electrons is perfect and does not introduce additional noise. We measure line edge

  19. Wetting and Roughness: Pattern Formation in a Rough Fracture

    NASA Astrophysics Data System (ADS)

    Pahlavan, A. A.; Cueto-Felgueroso, L.; McKinley, G. H.; Juanes, R.

    2015-12-01

    Wetting phenomena are inherently multiscale; owing to the complex nature of porous and fractured media, immiscible flows in this setting continue to challenge our microscopic and macroscopic descriptions. To gain some insight into the interplay between wettability and roughness of the medium, here we study experimentally the immiscible displacement of one fluid by another in a Hele-Shaw cell (two glass plates separated by a thin gap) with rough surfaces. We use a radial Hele-Shaw cell and saturate it with highly viscous silicone oil; we then inject a less viscous liquid at the center of the cell. Displacement of a more viscous liquid by a less viscous one leads to a hydrodynamic instability, known as viscous fingering. Wettability of the medium, however, has a profound influence on the displacement patterns and can lead to a complete suppression of the viscous fingering instability. Roughness, on the other hand, amplifies the wettability of the medium, making a wetting surface even more wetting and a non-wetting surface even more non-wetting. Roughness can also lead to contact-line pinning and intermittent avalanche-like behavior in the flow. We study the interplay between roughness and wettability of the medium by isolating each effect. We then propose a phase diagram that classifies the different displacement patterns, elucidating the underlying physics at play across scales.

  20. Aerodynamic properties of turbulent combustion fields

    NASA Technical Reports Server (NTRS)

    Hsiao, C. C.; Oppenheim, A. K.

    1985-01-01

    Flow fields involving turbulent flames in premixed gases under a variety of conditions are modeled by the use of a numerical technique based on the random vortex method to solve the Navier-Stokes equations and a flame propagation algorithm to trace the motion of the front and implement the Huygens principle, both due to Chorin. A successive over-relaxation hybrid method is applied to solve the Euler equation for flows in an arbitrarily shaped domain. The method of images, conformal transformation, and the integral-equation technique are also used to treat flows in special cases, according to their particular requirements. Salient features of turbulent flame propagation in premixed gases are interpreted by relating them to the aerodynamic properties of the flow field. Included among them is the well-known cellular structure of flames stabilized by bluff bodies, as well as the formation of the characteristic tulip shape of flames propagating in ducts. In its rudimentary form, the mechanism of propagation of a turbulent flame is shown to consist of: (1) rotary motion of eddies at the flame front, (2) self-advancement of the front at an appropriate normal burning speed, and (3) dynamic effects of expansion due to exothermicity of the combustion reaction. An idealized model is used to illustrate these fundamental mechanisms and to investigate basic aerodynamic features of flames in premixed gases. The case of a confined flame stabilized behind a rearward-facing step is given particular care and attention. Solutions are shown to be in satisfactory agreement with experimental results, especially with respect to global properties such as the average velocity profiles and reattachment length.

  1. Roughness effects in uncompensated antiferromagnets

    SciTech Connect

    Charilaou, M.; Hellman, F.

    2015-02-28

    Monte Carlo simulations show that roughness in uncompensated antiferromagnets decreases not just the surface magnetization but also the net magnetization and particularly strongly affects the temperature dependence. In films with step-type roughness, each step creates a new compensation front that decreases the global net magnetization. The saturation magnetization decreases non-monotonically with increasing roughness and does not scale with the surface area. Roughness in the form of surface vacancies changes the temperature-dependence of the magnetization; when only one surface has vacancies, the saturation magnetization will decrease linearly with surface occupancy, whereas when both surfaces have vacancies, the magnetization is negative and exhibits a compensation point at finite temperature, which can be tuned by controlling the occupancy. Roughness also affects the spin-texture of the surfaces due to long-range dipolar interactions and generates non-collinear spin configurations that could be used in devices to produce locally modified exchange bias. These results explain the strongly reduced magnetization found in magnetometry experiments and furthers our understanding of the temperature-dependence of exchange bias.

  2. Computer Simulation of Aircraft Aerodynamics

    NASA Technical Reports Server (NTRS)

    Inouye, Mamoru

    1989-01-01

    The role of Ames Research Center in conducting basic aerodynamics research through computer simulations is described. The computer facilities, including supercomputers and peripheral equipment that represent the state of the art, are described. The methodology of computational fluid dynamics is explained briefly. Fundamental studies of turbulence and transition are being pursued to understand these phenomena and to develop models that can be used in the solution of the Reynolds-averaged Navier-Stokes equations. Four applications of computer simulations for aerodynamics problems are described: subsonic flow around a fuselage at high angle of attack, subsonic flow through a turbine stator-rotor stage, transonic flow around a flexible swept wing, and transonic flow around a wing-body configuration that includes an inlet and a tail.

  3. Control of helicopter rotorblade aerodynamics

    NASA Technical Reports Server (NTRS)

    Fabunmi, James A.

    1991-01-01

    The results of a feasibility study of a method for controlling the aerodynamics of helicopter rotorblades using stacks of piezoelectric ceramic plates are presented. A resonant mechanism is proposed for the amplification of the displacements produced by the stack. This motion is then converted into linear displacement for the actuation of the servoflap of the blades. A design which emulates the actuation of the servoflap on the Kaman SH-2F is used to demonstrate the fact that such a system can be designed to produce the necessary forces and velocities needed to control the aerodynamics of the rotorblades of such a helicopter. Estimates of the electrical power requirements are also presented. A Small Business Innovation Research (SBIR) Phase 2 Program is suggested, whereby a bench-top prototype of the device can be built and tested. A collaborative effort between AEDAR Corporation and Kaman Aerospace Corporation is anticipated for future effort on this project.

  4. Viking entry aerodynamics and heating

    NASA Technical Reports Server (NTRS)

    Polutchko, R. J.

    1974-01-01

    The characteristics of the Mars entry including the mission sequence of events and associated spacecraft weights are described along with the Viking spacecraft. Test data are presented for the aerodynamic characteristics of the entry vehicle showing trimmed alpha, drag coefficient, and trimmed lift to drag ratio versus Mach number; the damping characteristics of the entry configuration; the angle of attack time history of Viking entries; stagnation heating and pressure time histories; and the aeroshell heating distribution as obtained in tests run in a shock tunnel for various gases. Flight tests which demonstrate the aerodynamic separation of the full-scale aeroshell and the flying qualities of the entry configuration in an uncontrolled mode are documented. Design values selected for the heat protection system based on the test data and analysis performed are presented.

  5. Aerodynamic investigation by infrared imaging

    NASA Technical Reports Server (NTRS)

    Roberts, A. Sidney, Jr.; Mcree, Griffith J.; Gartenberg, Ehud

    1988-01-01

    Infrared imaging systems can be used to measure temperatures of actively heated bodies immersed in an airstream. This monitoring of the convective heat transfer process, provides also information about the interaction between the body and the flow. The concept appeals to Nusselt/Reynolds numbers relations in order to produce data of interest from surface temperatures. Two test cases are presented and reference is made to analytical results: the mapping of a laminar jet and the temperature distribution along a constant power heated flat plate in laminar boundary layer regime. Although this research is currently focused on low speed aerodynamics, the extension to high speed aerodynamics, where the body undergoes frictional heating is of interest in this context, too.

  6. Aerodynamic instability: A case history

    NASA Technical Reports Server (NTRS)

    Eisenmann, R. C.

    1985-01-01

    The identification, diagnosis, and final correction of complex machinery malfunctions typically require the correlation of many parameters such as mechanical construction, process influence, maintenance history, and vibration response characteristics. The progression is reviewed of field testing, diagnosis, and final correction of a specific machinery instability problem. The case history presented addresses a unique low frequency instability problem on a high pressure barrel compressor. The malfunction was eventually diagnosed as a fluidic mechanism that manifested as an aerodynamic disturbance to the rotor assembly.

  7. Aerodynamic Design Using Neural Networks

    NASA Technical Reports Server (NTRS)

    Rai, Man Mohan; Madavan, Nateri K.

    2003-01-01

    The design of aerodynamic components of aircraft, such as wings or engines, involves a process of obtaining the most optimal component shape that can deliver the desired level of component performance, subject to various constraints, e.g., total weight or cost, that the component must satisfy. Aerodynamic design can thus be formulated as an optimization problem that involves the minimization of an objective function subject to constraints. A new aerodynamic design optimization procedure based on neural networks and response surface methodology (RSM) incorporates the advantages of both traditional RSM and neural networks. The procedure uses a strategy, denoted parameter-based partitioning of the design space, to construct a sequence of response surfaces based on both neural networks and polynomial fits to traverse the design space in search of the optimal solution. Some desirable characteristics of the new design optimization procedure include the ability to handle a variety of design objectives, easily impose constraints, and incorporate design guidelines and rules of thumb. It provides an infrastructure for variable fidelity analysis and reduces the cost of computation by using less-expensive, lower fidelity simulations in the early stages of the design evolution. The initial or starting design can be far from optimal. The procedure is easy and economical to use in large-dimensional design space and can be used to perform design tradeoff studies rapidly. Designs involving multiple disciplines can also be optimized. Some practical applications of the design procedure that have demonstrated some of its capabilities include the inverse design of an optimal turbine airfoil starting from a generic shape and the redesign of transonic turbines to improve their unsteady aerodynamic characteristics.

  8. Unsteady aerodynamics of insect flight.

    PubMed

    Ellington, C P

    1995-01-01

    Over the past decade, the importance of unsteady aerodynamic mechanisms for flapping insect flight has become widely recognised. Even at the fastest flight speeds, the old quasi-steady aerodynamic interpretation seems inadequate to explain the extra lift produced by the wings. Recent experiments on rigid model wings have confirmed the effectiveness of several postulated high-lift mechanisms. Delayed stall can produce extra lift for several chords of travel during the translational phases of the wingbeat. Lift can also be enhanced by circulation created during pronation and supination by rotational mechanisms: the fling/peel, the near fling/peel and isolated rotation. These studies have revealed large leading-edge vortices which contribute to the circulation around the wing, augmenting the lift. The mechanisms show distinctive patterns of vortex shedding from leading and trailing edges. The results of flow visualization experiments on tethered insects are reviewed in an attempt to identify the high-lift mechanisms actually employed. The fling/peel mechanism is clearly used by some insects. The near fling/peel is the wing motion most commonly observed, but evidence for the production of high lift remains indirect. For many insects, lift on the upstroke probably results from delayed stall instead of the flex mechanism of isolated rotation. The large leading-edge vortices from experiments on rigid model wings are greatly reduced or missing around the real insect wings, often making the identification of aerodynamic mechanisms inconclusive. A substantial spanwise flow component has been detected over the aerodynamic upper wing surface, which should transport leading-edge vorticity towards the wingtip before it has much time to roll up. This spanwise transport, arising from centrifugal acceleration, is probably a general phenomenon for flapping insect flight. It should reduce and stabilise any leading-edge vortices that are present, which is essential for preventing

  9. Applied aerodynamics: Challenges and expectations

    NASA Technical Reports Server (NTRS)

    Peterson, Victor L.; Smith, Charles A.

    1993-01-01

    Aerospace is the leading positive contributor to this country's balance of trade, derived largely from the sale of U.S. commercial aircraft around the world. This powerfully favorable economic situation is being threatened in two ways: (1) the U.S. portion of the commercial transport market is decreasing, even though the worldwide market is projected to increase substantially; and (2) expenditures are decreasing for military aircraft, which often serve as proving grounds for advanced aircraft technology. To retain a major share of the world market for commercial aircraft and continue to provide military aircraft with unsurpassed performance, the U.S. aerospace industry faces many technological challenges. The field of applied aerodynamics is necessarily a major contributor to efforts aimed at meeting these technological challenges. A number of emerging research results that will provide new opportunities for applied aerodynamicists are discussed. Some of these have great potential for maintaining the high value of contributions from applied aerodynamics in the relatively near future. Over time, however, the value of these contributions will diminish greatly unless substantial investments continue to be made in basic and applied research efforts. The focus: to increase understanding of fluid dynamic phenomena, identify new aerodynamic concepts, and provide validated advanced technology for future aircraft.

  10. X-34 Vehicle Aerodynamic Characteristics

    NASA Technical Reports Server (NTRS)

    Brauckmann, Gregory J.

    1998-01-01

    The X-34, being designed and built by the Orbital Sciences Corporation, is an unmanned sub-orbital vehicle designed to be used as a flying test bed to demonstrate key vehicle and operational technologies applicable to future reusable launch vehicles. The X-34 will be air-launched from an L-1011 carrier aircraft at approximately Mach 0.7 and 38,000 feet altitude, where an onboard engine will accelerate the vehicle to speeds above Mach 7 and altitudes to 250,000 feet. An unpowered entry will follow, including an autonomous landing. The X-34 will demonstrate the ability to fly through inclement weather, land horizontally at a designated site, and have a rapid turn-around capability. A series of wind tunnel tests on scaled models was conducted in four facilities at the NASA Langley Research Center to determine the aerodynamic characteristics of the X-34. Analysis of these test results revealed that longitudinal trim could be achieved throughout the design trajectory. The maximum elevon deflection required to trim was only half of that available, leaving a margin for gust alleviation and aerodynamic coefficient uncertainty. Directional control can be achieved aerodynamically except at combined high Mach numbers and high angles of attack, where reaction control jets must be used. The X-34 landing speed, between 184 and 206 knots, is within the capabilities of the gear and tires, and the vehicle has sufficient rudder authority to control the required 30-knot crosswind.

  11. Roughness Perception in Virtual Textures.

    PubMed

    Unger, B; Hollis, R; Klatzky, R

    2011-01-01

    Haptic devices allow the production of virtual textured surfaces for psychophysical experiments. Some studies have shown inconsistencies between virtual and real textures with respect to their psychophysical functions for roughness, leading to speculation that virtual textures differ in some way from real ones. We have determined the psychophysical function for roughness using textures rendered with a high-fidelity magnetic levitation haptic device. A constraint surface algorithm was used to simulate the motion of a spherical probe over trapezoidal gratings and randomly dithered cones. The shape of the psychophysical functions for roughness is consistent between subjects but varies with changes in texture and probe geometry. For dithered cones, inverted "U"-shaped functions were found nearly identical, in maxima and curvature, to those in the literature for real textures with similar geometry. PMID:26963163

  12. Recent Studies of Runway Roughness

    NASA Technical Reports Server (NTRS)

    Morris, Garland; Hall, Albert W.

    1965-01-01

    Recent studies of NASA research related to aircraft operating problems on rough runways are presented. Some of these investigations were conducted cooperatively with the airport operators, with the Federal Aviation Agency, and with the U.S. Air Force. The studies show that criteria based on power spectral levels of runway-profile data are not sufficient to define acceptable levels of runway roughness from the piloting viewpoint. Because of the large variation in response characteristics between various types of aircraft, a runway may be acceptable for some aircraft and unacceptable for others. A criterion for roughness, therefore, should be expressed in terms of aircraft response - preferably, cockpit acceleration. A criterion suggested is that the maximum vertical acceleration in the cockpit should not exceed +/- 0.4 g for sections of the runway where precise aircraft control is required.

  13. A numerical and experimental study of the effects of dynamic roughness on laminar leading edge separation

    NASA Astrophysics Data System (ADS)

    Gall, Peter D.

    The aircraft industry, as a whole, has been deeply concerned with improving the aerodynamic efficiency of current and future flight vehicles, particularly in the commercial and military markets. However, of particular interest to the field of aerodynamics is the elusive concept of a workable flow control mechanism. Effective flow control is a concept which if properly applied can increase aerodynamic efficiency. Various concepts and ideas to obtain successful flow control have been studied in an attempt to reap these rewards. Some examples include boundary layer blowing (steady and periodic), suction, and compliant walls for laminar flow control. The overall goal of flow control is to increase performance by increasing lift, reducing drag, and delaying or eliminating leading edge separation. The specific objectives of flow control are to (1) delay or eliminate flow separation, (2) delay boundary layer transition, and (3) and reduce skin friction drag. The purpose of this research is to investigate dynamic roughness as a novel method of flow control technology for external boundary layer flows. As opposed to standard surface roughness, dynamic roughness incorporates small time dependent perturbations to the surface of the airfoil. These surface perturbations are actual humps and/or ridges on the surface of the airfoil that are on the scale of the laminar boundary, and oscillate with an unsteady motion. Research has shown that this can provide a means to modify the instantaneous and mean velocity profile near the wall and favorably control the existing state of the boundary layer. Several flow control parameters were studied including dynamic roughness frequency, amplitude, and geometry. The results of this study have shown, both numerically and experimentally, that dynamic roughness can provide an effective means for eliminating both a short and long laminar separation bubble and possibly prove a viable alternative in effective flow control, hence reaping some of

  14. Aerodynamics of a finite wing with simulated ice

    NASA Technical Reports Server (NTRS)

    Bragg, M. B.; Khodadoust, A.; Kerho, M.

    1992-01-01

    The effect of a simulated glaze ice accretion on the aerodynamic performance of a three-dimensional wing is studied experimentally. Results are reviewed from earlier two-dimensional tests which show the character of the large leading-edge separation bubbles caused by the simulated ice accretion. The 2-D bubbles are found to closely resemble well known airfoil laminar separation bubbles. For the 3-D experiments a semispan wing of effective aspect ratio five was mounted from the sidewall of the UIUC subsonic wind tunnel. The model uses a NACA 0012 airfoil section on a rectangular planform with interchangeable tip and root sections to allow for 0- and 30-degree sweep. A three-component sidewall balance was used to measure lift, drag and pitching moment on the clean and iced model. Fluorescent oil flow visualization has been performed on the iced model and reveals extensive spanwise and vortical flow in the separation bubble aft of the upper surface horn. Sidewall interaction and spanwise nonuniformity are also seen on the unswept model. Comparisons to the computed flow fields are shown. Results are also shown for roughness effects on the straight wing. Sand grain roughness on the ice shape is seen to have a different effect than isolated 3-D roughness elements.

  15. Characterization of Pressure Sensitive Paint Intrusiveness Effects on Aerodynamic Data

    NASA Technical Reports Server (NTRS)

    Amer, Tahani R.; Liu, Tianshu; Oglesby, Donald M.

    2001-01-01

    One effect of using pressure sensitive paint (PSP) is the potential intrusiveness to the aerodynamic characteristics of the model. The paint thickness and roughness may affect the pressure distribution. and therefore, the forces and moments on the wind tunnel model. A study of these potential intrusive effects was carried out at NASA Langley Research Center where a series of wind tunnel tests were conducted using the Modem Design of Experiments (MDOE) test approach. The PSP effects on the integrated forces were measured on two different models at different test conditions in both the Low Turbulence Pressure Tunnel (LTPT) and the Unitary Plan Wind Tunnel (UPWT) at Langley. The paint effect was found to be very small over a range of Reynolds numbers, Mach numbers and angles of attack. This is due to the very low surface roughness of the painted surface. The surface roughness, after applying the NASA Langley developed PSP, was lower than that of the clean wing. However, the PSP coating had a localized effects on the pressure taps, which leads to an appreciable decrease in the pressure tap reading.

  16. Characteristics of Pressure Sensitive Paint Intrusiveness Effects on Aerodynamic Data

    NASA Technical Reports Server (NTRS)

    Amer, Tahani R.; Liu, Tianshu; Oglesby, Donald M.

    2001-01-01

    One effect of using pressure sensitive paint (PSP) is the potential intrusiveness to the aerodynamic characteristics of the model. The paint thickness and roughness may affect the pressure distribution, and therefore, the forces and moments on the wind tunnel model. A study of these potential intrusive effects was carried out at NASA Langley Research Center where a series of wind tunnel tests were conducted using the Modem Design of Experiments (MDOE) test approach. The PSP effects on the integrated forces were measured on two different models at different test conditions in both the Low Turbulence Pressure Tunnel (LTPT) and the Unitary Plan Wind Tunnel (UPWT) at Langley. The paint effect was found to be very small over a range of Reynolds numbers, Mach numbers and angles of attack. This is due to the very low surface roughness of the painted surface. The surface roughness, after applying the NASA Langley developed PSP, was lower than that of the clean wing. However, the PSP coating had a localized effects on the pressure taps, which leads to an appreciable decrease in the pressure tap reading.

  17. Topographical length scales of hierarchical superhydrophobic surfaces

    NASA Astrophysics Data System (ADS)

    Dhillon, P. K.; Brown, P. S.; Bain, C. D.; Badyal, J. P. S.; Sarkar, S.

    2014-10-01

    The morphology of hydrophobic CF4 plasma fluorinated polybutadiene surfaces has been characterised using atomic force microscopy (AFM). Judicious choice of the plasma power and exposure duration leads to formation of three different surface morphologies (Micro, Nano, and Micro + Nano). Scaling theory analysis shows that for all three surface topographies, there is an initial increase in roughness with length scale followed by a levelling-off to a saturation level. At length scales around 500 nm, it is found that the roughness is very similar for all three types of surfaces, and the saturation roughness value for the Micro + Nano morphology is found to be intermediate between those for the Micro and Nano surfaces. Fast Fourier Transform (FFT) analysis has shown that the Micro + Nano topography comprises a hierarchical superposition of Micro and Nano morphologies. Furthermore, the Micro + Nano surfaces display the highest local roughness (roughness exponent α = 0.42 for length scales shorter than ∼500 nm), which helps to explain their superhydrophobic behaviour (large water contact angle (>170°) and low hysteresis (<1°)).

  18. Aerodynamic Characterization of a Thin, High-Performance Airfoil for Use in Ground Fluids Testing

    NASA Technical Reports Server (NTRS)

    Broeren, Andy P.; Lee, Sam; Clark, Catherine

    2013-01-01

    The FAA has worked with Transport Canada and others to develop allowance times for aircraft operating in ice-pellet precipitation. Wind-tunnel testing has been carried out to better understand the flowoff characteristics and resulting aerodynamic effects of anti-icing fluids contaminated with ice pellets using a thin, high-performance wing section at the National Research Council of Canada Propulsion and Icing Wind Tunnel. The objective of this paper is to characterize the aerodynamic behavior of this wing section in order to better understand the adverse aerodynamic effects of anti-icing fluids and ice-pellet contamination. Aerodynamic performance data, boundary-layer surveys and flow visualization were conducted at a Reynolds number of approximately 6.0 x 10(exp 6) and a Mach number of 0.12. The clean, baseline model exhibited leading-edge stall characteristics including a leading-edge laminar separation bubble and minimal or no separation on the trailing edge of the main element or flap. These results were consistent with expected 2-D aerodynamics and showed no anomalies that could adversely affect the evaluation of anti-icing fluids and ice-pellet contamination on the wing. Tests conducted with roughness and leading-edge flow disturbances helped to explain the aerodynamic impact of the anti-icing fluids and contamination. The stalling characteristics of the wing section with fluid and contamination appear to be driven at least partially by the effects of a secondary wave of fluid that forms near the leading edge as the wing is rotated in the simulated takeoff profile. These results have provided a much more complete understanding of the adverse aerodynamic effects of anti-icing fluids and ice-pellet contamination on this wing section. This is important since these results are used, in part, to develop the ice-pellet allowance times that are applicable to many different airplanes.

  19. Aerodynamic Characterization of a Thin, High-Performance Airfoil for Use in Ground Fluids Testing

    NASA Technical Reports Server (NTRS)

    Broeren, Andy P.; Lee, Sam; Clark, Catherine

    2013-01-01

    The FAA has worked with Transport Canada and others to develop allowance times for aircraft operating in ice-pellet precipitation. Wind-tunnel testing has been carried out to better understand the flowoff characteristics and resulting aerodynamic effects of anti-icing fluids contaminated with ice pellets using a thin, high-performance wing section at the National Research Council of Canada Propulsion and Icing Wind Tunnel. The objective of this paper is to characterize the aerodynamic behavior of this wing section in order to better understand the adverse aerodynamic effects of anti-icing fluids and ice-pellet contamination. Aerodynamic performance data, boundary-layer surveys and flow visualization were conducted at a Reynolds number of approximately 6.0×10(exp 6) and a Mach number of 0.12. The clean, baseline model exhibited leading-edge stall characteristics including a leading-edge laminar separation bubble and minimal or no separation on the trailing edge of the main element or flap. These results were consistent with expected 2-D aerodynamics and showed no anomalies that could adversely affect the evaluation of anti-icing fluids and ice-pellet contamination on the wing. Tests conducted with roughness and leading-edge flow disturbances helped to explain the aerodynamic impact of the anti-icing fluids and contamination. The stalling characteristics of the wing section with fluid and contamination appear to be driven at least partially by the effects of a secondary wave of fluid that forms near the leading edge as the wing is rotated in the simulated takeoff profile. These results have provided a much more complete understanding of the adverse aerodynamic effects of anti-icing fluids and ice-pellet contamination on this wing section. This is important since these results are used, in part, to develop the ice-pellet allowance times that are applicable to many different airplanes.

  20. Various remote sensing approaches to understanding roughness in the marginal ice zone

    NASA Astrophysics Data System (ADS)

    Gupta, Mukesh

    Multi-platform based measurement approaches to understanding complex marginal ice zone (MIZ) are suggested in this paper. Physical roughness measurements using ship- and helicopter-based laser systems combined with ship-based active microwave backscattering (C-band polarimetric coherences) and dual-polarized passive microwave emission (polarization ratio, PR and spectral gradient ratios, GR at 37 and 89 GHz) are presented to study diverse sea ice types found in the MIZ. Autocorrelation functions are investigated for different sea ice roughness types. Small-scale roughness classes were discriminated using data from a ship-based laser profiler. The polarimetric coherence parameter ρHHVH , is not found to exhibit any observable sensitivity to the surface roughness for all incidence angles. Rubble-ridges, pancake ice, snow-covered frost flowers, and dense frost flowers exhibit separable signatures using GR-H and GR-V at >70° incidence angles. This paper diagnosed changes in sea ice roughness on a spatial scale of ∼0.1-4000 m and on a temporal scale of ∼1-240 days (ice freeze-up to summer melt). The coupling of MIZ wave roughness and aerodynamic roughness in conjunction with microwave emission and backscattering are future avenues of research. Additionally, the integration of various datasets into thermodynamic evolution model of sea ice will open pathways to successful development of inversion models of MIZ behavior.

  1. Plant Communities of Rough Rock.

    ERIC Educational Resources Information Center

    Jacobs, Linda

    A unit of study on plants grown in the Navajo community of Rough Rock, Arizona, is presented in sketches providing the common Navajo name for the plant, a literal English translation, the English name of the plant, and the Latin name. A brief description of each plant includes where the plant grows, how the Navajos use the plant, and the color and…

  2. Community School at Rough Rock.

    ERIC Educational Resources Information Center

    Erickson, Donald A.; Schwartz, Henrietta

    The objective of the evaluation of Rough Rock Demonstration School (RRDS) on the Navajo Reservation was to examine, in terms of its own stated objectives, the school's organizational and social system as a whole. Chapters in the 1969 evaluation report are "What We Did and Why,""The Schools That Were Compared,""Community Relationships,""The…

  3. 31 CFR 592.310 - Rough diamond.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 31 Money and Finance:Treasury 3 2014-07-01 2014-07-01 false Rough diamond. 592.310 Section 592.310... ASSETS CONTROL, DEPARTMENT OF THE TREASURY ROUGH DIAMONDS CONTROL REGULATIONS General Definitions § 592.310 Rough diamond. The term rough diamond means any diamond that is unworked or simply sawn,...

  4. 31 CFR 592.310 - Rough diamond.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 31 Money and Finance:Treasury 3 2013-07-01 2013-07-01 false Rough diamond. 592.310 Section 592.310... ASSETS CONTROL, DEPARTMENT OF THE TREASURY ROUGH DIAMONDS CONTROL REGULATIONS General Definitions § 592.310 Rough diamond. The term rough diamond means any diamond that is unworked or simply sawn,...

  5. 31 CFR 592.310 - Rough diamond.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 31 Money and Finance: Treasury 3 2010-07-01 2010-07-01 false Rough diamond. 592.310 Section 592... FOREIGN ASSETS CONTROL, DEPARTMENT OF THE TREASURY ROUGH DIAMONDS CONTROL REGULATIONS General Definitions § 592.310 Rough diamond. The term rough diamond means any diamond that is unworked or simply...

  6. 31 CFR 592.310 - Rough diamond.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 31 Money and Finance:Treasury 3 2012-07-01 2012-07-01 false Rough diamond. 592.310 Section 592.310... ASSETS CONTROL, DEPARTMENT OF THE TREASURY ROUGH DIAMONDS CONTROL REGULATIONS General Definitions § 592.310 Rough diamond. The term rough diamond means any diamond that is unworked or simply sawn,...

  7. 31 CFR 592.310 - Rough diamond.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 31 Money and Finance:Treasury 3 2011-07-01 2011-07-01 false Rough diamond. 592.310 Section 592.310... ASSETS CONTROL, DEPARTMENT OF THE TREASURY ROUGH DIAMONDS CONTROL REGULATIONS General Definitions § 592.310 Rough diamond. The term rough diamond means any diamond that is unworked or simply sawn,...

  8. Application of Rough Sets to Information Retrieval.

    ERIC Educational Resources Information Center

    Miyamoto, Sadaaki

    1998-01-01

    Develops a method of rough retrieval, an application of the rough set theory to information retrieval. The aim is to: (1) show that rough sets are naturally applied to information retrieval in which categorized information structure is used; and (2) show that a fuzzy retrieval scheme is induced from the rough retrieval. (AEF)

  9. Aerodynamic lift effect on satellite orbits

    NASA Technical Reports Server (NTRS)

    Karr, G. R.; Cleland, J. G.; Devries, L. L.

    1975-01-01

    Numerical quadrature is employed to obtain orbit perturbation results from the general perturbation equations. Both aerodynamic lift and drag forces are included in the analysis of the satellite orbit. An exponential atmosphere with and without atmospheric rotation is used. A comparison is made of the perturbations which are caused by atmospheric rotation with those caused by satellite aerodynamic effects. Results indicate that aerodynamic lift effects on the semi-major axis and orbit inclination can be of the same order as the effects of atmosphere rotation depending upon the orientation of the lift vector. The results reveal the importance of including aerodynamic lift effects in orbit perturbation analysis.

  10. HIAD-2 (Hypersonic Inflatable Aerodynamic Decelerator)

    NASA Video Gallery

    The Hypersonic Inflatable Aerodynamic Decelerator (HIAD) project is a disruptive technology that will accommodate the atmospheric entry of heavy payloads to planetary bodies such as Mars. HIAD over...

  11. Surface Roughness Characterization of Niobium Subjected to Incremental BCP and EP Processing Steps

    SciTech Connect

    Hui Tian; Guihem Ribeill; Charles Reece; Michael Kelley

    2008-02-12

    The surface of niobium samples polished under incremental Buffered Chemical Polish (BCP) and Electro-Polishing (EP) have been characterized through Atomic Force Microscopy (AFM) and stylus profilometry across a range of length of scales. The results were analyzed using Power Density Spectral (PSD) technique to determine roughness and characteristic dimensions. This study has shown that the PSD method is a valuable tool that provides quantitative information about surface roughness at different length scales.

  12. Progress in computational unsteady aerodynamics

    NASA Technical Reports Server (NTRS)

    Obayashi, Shigeru

    1993-01-01

    After vigorous development for over twenty years, Computational Fluid Dynamics (CFD) in the field of aerospace engineering has arrived at a turning point toward maturity. This paper discusses issues related to algorithm development for the Euler/Navier Stokes equations, code validation and recent applications of CFD for unsteady aerodynamics. Algorithm development is a fundamental element for a good CFD program. Code validation tries to bridge the reliability gap between CFD and experiment. Many of the recent applications also take a multidisciplinary approach, which is a future trend for CFD applications. As computers become more affordable, CFD is expected to be a better scientific and engineering tool.

  13. The basic aerodynamics of floatation

    SciTech Connect

    Davies, M.J.; Wood, D.H.

    1983-09-01

    The original derivation of the basic theory governing the aerodynamics of both hovercraft and modern floatation ovens, requires the validity of some extremely crude assumptions. However, the basic theory is surprisingly accurate. It is shown that this accuracy occurs because the final expression of the basic theory can be derived by approximating the full Navier-Stokes equations in a manner that clearly shows the limitations of the theory. These limitations are used in discussing the relatively small discrepancies between the theory and experiment, which may not be significant for practical purposes.

  14. Aerodynamics. [numerical simulation using supercomputers

    NASA Technical Reports Server (NTRS)

    Graves, Randolph A., Jr.

    1988-01-01

    A projection is made of likely improvements in the economics of commercial aircraft operation due to developments in aerodynamics in the next half-century. Notable among these improvements are active laminar flow control techniques' application to third-generation SSTs, in order to achieve an L/D value of about 20; this is comparable to current subsonic transports, and has the further consequence of reducing cabin noise. Wave-cancellation systems may also be used to eliminate sonic boom overpressures, and rapid-combustion systems may be able to eliminate all pollutants from jet exhausts other than CO2.

  15. Aerodynamics. [Numerical simulation using supercomputers

    SciTech Connect

    Graves, R.A. Jr.

    1988-01-01

    A projection is made of likely improvements in the economics of commercial aircraft operation due to developments in aerodynamics in the next half-century. Notable among these improvements are active laminar flow control techniques' application to third-generation SSTs, in order to achieve an L/D value of about 20; this is comparable to current subsonic transports, and has the further consequence of reducing cabin noise. Wave-cancellation systems may also be used to eliminate sonic boom overpressures, and rapid-combustion systems may be able to eliminate all pollutants from jet exhausts other than CO/sub 2/.

  16. Ghost imaging for a reflected object with a rough surface

    SciTech Connect

    Wang Chunfang; Zhang Dawei; Chen Bin; Bai Yanfeng

    2010-12-15

    Ghost imaging for the reflected object with rough surface is investigated. The surface height variance {sigma}{sub h}{sup 2} and the correlation length l{sub c} have been introduced to characterize the rough surface. Based on a simple scattering model, we derive the analytical expressions which are used to describe the effects of {sigma}{sub h}{sup 2} and l{sub c} on ghost imaging. The results show that both {sigma}{sub h}{sup 2} and l{sub c} have no influence on the image resolution, while the convergence of the correlation decreases as {sigma}{sub h}{sup 2} increases. Additionally, the bucket detector used in the test arm can dramatically improve the visibility of ghost images. The results are backed up by numerical simulations, in which a Monte Carlo approach to generate a rough surface has been used.

  17. Effects of Leading Edge Defect on the Aerodynamic and Flow Characteristics of an S809 Airfoil

    PubMed Central

    Wang, Yan; Zheng, Xiaojing; Hu, Ruifeng; Wang, Ping

    2016-01-01

    Background Unexpected performance degradation occurs in wind turbine blades due to leading edge defect when suffering from continuous impacts with rain drops, hails, insects, or solid particles during its operation life. To assess this issue, this paper numerically investigates the steady and dynamic stall characteristics of an S809 airfoil with various leading edge defects. More leading edge defect sizes and much closer to practical parameters are investigated in the paper. Methodology Numerical computation is conducted using the SST k-ω turbulence model, and the method has been validated by comparison with existed published data. In order to ensure the calculation convergence, the residuals for the continuity equation are set to be less than 10−7 and 10−6 in steady state and dynamic stall cases. The simulations are conducted with the software ANSYS Fluent 13.0. Results It is found that the characteristics of aerodynamic coefficients and flow fields are sensitive to leading edge defect both in steady and dynamic conditions. For airfoils with the defect thickness of 6%tc, leading edge defect has a relative small influence on the aerodynamics of S809 airfoil. For other investigated defect thicknesses, leading edge defect has much greater influence on the flow field structures, pressure coefficients and aerodynamic characteristics of airfoil at relative small defect lengths. For example, the lift coefficients decrease and drag coefficients increase sharply after the appearance of leading edge defect. However, the aerodynamic characteristics could reach a constant value when the defect length is large enough. The flow field, pressure coefficient distribution and aerodynamic coefficients do not change a lot when the defect lengths reach to 0.5%c,1%c, 2%c and 3%c with defect thicknesses of 6%tc, 12%tc,18%tc and 25%tc, respectively. In addition, the results also show that the critical defect length/thickness ratio is 0.5, beyond which the aerodynamic characteristics

  18. Influence of surface roughness on the polarimetric characteristics of a wire-grid grating polarizer.

    PubMed

    Ryu, Hojeong; Joon Yoon, Soon; Kim, Donghyun

    2008-10-20

    The influence of surface roughness on the polarimetric performance of a wire-grid polarizer (WGP) is numerically investigated using rigorous coupled-wave analysis over 100 random surface realizations. Surface roughness is modeled with a Gaussian surface, represented by two independent parameters: surface height deviation and correlation length of a profile. The results show that WGP performance can suffer from significant degradation as well as increased deviation with surface roughness, although the extent varies with specific parameters. The influence of roughness was also examined with respect to grating period as a WGP parameter and incident light properties, such as wavelength and angle.

  19. Addressing scale dependence in roughness and morphometric statistics derived from point cloud data.

    NASA Astrophysics Data System (ADS)

    Buscombe, D.; Wheaton, J. M.; Hensleigh, J.; Grams, P. E.; Welcker, C. W.; Anderson, K.; Kaplinski, M. A.

    2015-12-01

    The heights of natural surfaces can be measured with such spatial density that almost the entire spectrum of physical roughness scales can be characterized, down to the morphological form and grain scales. With an ability to measure 'microtopography' comes a demand for analytical/computational tools for spatially explicit statistical characterization of surface roughness. Detrended standard deviation of surface heights is a popular means to create continuous maps of roughness from point cloud data, using moving windows and reporting window-centered statistics of variations from a trend surface. If 'roughness' is the statistical variation in the distribution of relief of a surface, then 'texture' is the frequency of change and spatial arrangement of roughness. The variance in surface height as a function of frequency obeys a power law. In consequence, roughness is dependent on the window size through which it is examined, which has a number of potential disadvantages: 1) the choice of window size becomes crucial, and obstructs comparisons between data; 2) if windows are large relative to multiple roughness scales, it is harder to discriminate between those scales; 3) if roughness is not scaled by the texture length scale, information on the spacing and clustering of roughness `elements' can be lost; and 4) such practice is not amenable to models describing the scattering of light and sound from rough natural surfaces. We discuss the relationship between roughness and texture. Some useful parameters which scale vertical roughness to characteristic horizontal length scales are suggested, with examples of bathymetric point clouds obtained using multibeam from two contrasting riverbeds, namely those of the Colorado River in Grand Canyon, and the Snake River in Hells Canyon. Such work, aside from automated texture characterization and texture segmentation, roughness and grain size calculation, might also be useful for feature detection and classification from point

  20. Rough Clustering for Cancer Datasets

    NASA Astrophysics Data System (ADS)

    Herawan, Tutut

    Cancer is becoming a leading cause of death among people in the whole world. It is confirmed that the early detection and accurate diagnosis of this disease can ensure a long survival of the patients. Expert systems and machine learning techniques are gaining popularity in this field because of the effective classification and high diagnostic capability. This paper presents the application of rough set theory for clustering two cancer datasets. These datasets are taken from UCI ML repository. The method is based on MDA technique proposed by [11]. To select a clustering attribute, the maximal degree of the rough attributes dependencies in categorical-valued information systems is used. Further, we use a divide-and-conquer method to partition/cluster the objects. The results show that MDA technique can be used to cluster to the data. Further, we present clusters visualization using two dimensional plot. The plot results provide user friendly navigation to understand the cluster obtained.

  1. Dynamic Stall in Pitching Airfoils: Aerodynamic Damping and Compressibility Effects

    NASA Astrophysics Data System (ADS)

    Corke, Thomas C.; Thomas, Flint O.

    2015-01-01

    Dynamic stall is an incredibly rich fluid dynamics problem that manifests itself on an airfoil during rapid, transient motion in which the angle of incidence surpasses the static stall limit. It is an important element of many manmade and natural flyers, including helicopters and supermaneuverable aircraft, and low-Reynolds number flapping-wing birds and insects. The fluid dynamic attributes that accompany dynamic stall include an eruption of vorticity that organizes into a well-defined dynamic stall vortex and massive excursions in aerodynamic loads that can couple with the airfoil structural dynamics. The dynamic stall process is highly sensitive to surface roughness that can influence turbulent transition and to local compressibility effects that occur at free-stream Mach numbers that are otherwise incompressible. Under some conditions, dynamic stall can result in negative aerodynamic damping that leads to limit-cycle growth of structural vibrations and rapid mechanical failure. The mechanisms leading to negative damping have been a principal interest of recent experiments and analysis. Computational fluid dynamic simulations and low-order models have not been good predictors so far. Large-eddy simulation could be a viable approach although it remains computationally intensive. The topic is technologically important owing to the desire to develop next-generation rotorcraft that employ adaptive rotor dynamic stall control.

  2. Aerodynamic surface stress intermittency and conditionally averaged turbulence statistics

    NASA Astrophysics Data System (ADS)

    Anderson, William; Lanigan, David

    2015-11-01

    Aeolian erosion is induced by aerodynamic stress imposed by atmospheric winds. Erosion models prescribe that sediment flux, Q, scales with aerodynamic stress raised to exponent, n, where n > 1 . Since stress (in fully rough, inertia-dominated flows) scales with incoming velocity squared, u2, it follows that q ~u2n (where u is some relevant component of the flow). Thus, even small (turbulent) deviations of u from its time-mean may be important for aeolian activity. This rationale is augmented given that surface layer turbulence exhibits maximum Reynolds stresses in the fluid immediately above the landscape. To illustrate the importance of stress intermittency, we have used conditional averaging predicated on stress during large-eddy simulation of atmospheric boundary layer flow over an arid, bare landscape. Conditional averaging provides an ensemble-mean visualization of flow structures responsible for erosion `events'. Preliminary evidence indicates that surface stress peaks are associated with the passage of inclined, high-momentum regions flanked by adjacent low-momentum regions. We characterize geometric attributes of such structures and explore streamwise and vertical vorticity distribution within the conditionally averaged flow field. This work was supported by the National Sci. Foundation, Phys. and Dynamic Meteorology Program (PM: Drs. N. Anderson, C. Lu, and E. Bensman) under Grant # 1500224. Computational resources were provided by the Texas Adv. Comp. Center at the Univ. of Texas.

  3. Sensing roughness and polish direction

    NASA Astrophysics Data System (ADS)

    Jakobsen, M. L.; Olesen, A. S.; Larsen, H. E.; Stubager, J.; Hanson, S. G.; Pedersen, T. F.; Pedersen, H. C.

    2016-04-01

    As a part of the work carried out on a project supported by the Danish council for technology and innovation, we have investigated the option of smoothing standard CNC machined surfaces. In the process of constructing optical prototypes, involving custom-designed optics, the development cost and time consumption can become relatively large numbers in a research budget. Machining the optical surfaces directly is expensive and time consuming. Alternatively, a more standardized and cheaper machining method can be used, but then the object needs to be manually polished. During the polishing process the operator needs information about the RMS-value of the surface roughness and the current direction of the scratches introduces by the polishing process. The RMS-value indicates to the operator how far he is from the final finish, and the scratch orientation is often specified by the customer in order to avoid complications during the casting process. In this work we present a method for measuring the RMS-values of the surface roughness while simultaneously determining the polishing direction. We are mainly interested in the RMS-values in the range from 0 - 100 nm, which corresponds to the finish categories of A1, A2 and A3. Based on simple intensity measurements we estimates the RMS-value of the surface roughness, and by using a sectioned annual photo-detector to collect the scattered light we can determine the direction of polishing and distinguish light scattered from random structures and light scattered from scratches.

  4. Rough-to-smooth transition of an equilibrium neutral constant stress layer. [atmospheric flow over rough terrain

    NASA Technical Reports Server (NTRS)

    Logan, E., Jr.; Fichtl, G. H.

    1975-01-01

    A model is proposed for low-level atmospheric flows over terrains of changing roughness length, such as those found at the windward end of landing strips adjoining rough terrain. The proposed model is used to develop a prediction technique for calculating transition wind and shear-stress profiles in the region following surface roughness discontinuity. The model for the transition region comprises two layers: a logarithmic layer and a buffer layer. The flow is assumed to be steady, two-dimensional, and incompressible, with neutral hydrostatic stability. A diagram is presented for a typical wind profile in the transition region, obtained from the logarithmic and velocity defect profiles using shear stress calculated by relevant equations.

  5. Dynamic stall and aerodynamic damping

    SciTech Connect

    Rasmussen, F.; Petersen, J.T.; Madsen, H.A.

    1999-08-01

    A dynamic stall model is used to analyze and reproduce open air blade section measurements as well as wind tunnel measurements. The dynamic stall model takes variations in both angle of attack and flow velocity into account. The paper gives a brief description of the dynamic stall model and presents results from analyses of dynamic stall measurements for a variety of experiments with different airfoils in wind tunnel and on operating rotors. The wind tunnel experiments comprises pitching as well as plunging motion of the airfoils. The dynamic stall model is applied for derivation of aerodynamic damping characteristics for cyclic motion of the airfoils in flapwise and edgewise direction combined with pitching. The investigation reveals that the airfoil dynamic stall characteristics depend on the airfoil shape, and the type of motion (pitch, plunge). The aerodynamic damping characteristics, and thus the sensitivity to stall induced vibrations, depend highly on the relative motion of the airfoil in flapwise and edgewise direction, and on a possibly coupled pitch variation, which is determined by the structural characteristics of the blade.

  6. Orion Crew Module Aerodynamic Testing

    NASA Technical Reports Server (NTRS)

    Murphy, Kelly J.; Bibb, Karen L.; Brauckmann, Gregory J.; Rhode, Matthew N.; Owens, Bruce; Chan, David T.; Walker, Eric L.; Bell, James H.; Wilson, Thomas M.

    2011-01-01

    The Apollo-derived Orion Crew Exploration Vehicle (CEV), part of NASA s now-cancelled Constellation Program, has become the reference design for the new Multi-Purpose Crew Vehicle (MPCV). The MPCV will serve as the exploration vehicle for all near-term human space missions. A strategic wind-tunnel test program has been executed at numerous facilities throughout the country to support several phases of aerodynamic database development for the Orion spacecraft. This paper presents a summary of the experimental static aerodynamic data collected to-date for the Orion Crew Module (CM) capsule. The test program described herein involved personnel and resources from NASA Langley Research Center, NASA Ames Research Center, NASA Johnson Space Flight Center, Arnold Engineering and Development Center, Lockheed Martin Space Sciences, and Orbital Sciences. Data has been compiled from eight different wind tunnel tests in the CEV Aerosciences Program. Comparisons are made as appropriate to highlight effects of angle of attack, Mach number, Reynolds number, and model support system effects.

  7. X-33 Hypersonic Aerodynamic Characteristics

    NASA Technical Reports Server (NTRS)

    Murphy, Kelly J.; Nowak, Robert J.; Thompson, Richard A.; Hollis, Brian R.; Prabhu, Ramadas K.

    1999-01-01

    Lockheed Martin Skunk Works, under a cooperative agreement with NASA, will design, build, and fly the X-33, a half-scale prototype of a rocket-based, single-stage-to-orbit (SSTO), reusable launch vehicle (RLV). A 0.007-scale model of the X-33 604BOO02G configuration was tested in four hypersonic facilities at the NASA Langley Research Center to examine vehicle stability and control characteristics and to populate the aerodynamic flight database for the hypersonic regime. The vehicle was found to be longitudinally controllable with less than half of the total body flap deflection capability across the angle of attack range at both Mach 6 and Mach 10. Al these Mach numbers, the vehicle also was shown to be longitudinally stable or neutrally stable for typical (greater than 20 degrees) hypersonic flight attitudes. This configuration was directionally unstable and the use of reaction control jets (RCS) will be necessary to control the vehicle at high angles of attack in the hypersonic flight regime. Mach number and real gas effects on longitudinal aerodynamics were shown to be small relative to X-33 control authority.

  8. X-33 Hypersonic Aerodynamic Characteristics

    NASA Technical Reports Server (NTRS)

    Murphy, Kelly J.; Nowak, Robert J.; Thompson, Richard A.; Hollis, Brian R.; Prabhu, Ramadas K.

    1999-01-01

    Lockheed Martin Skunk Works, under a cooperative agreement with NASA, will build and fly the X-33, a half-scale prototype of a rocket-based, single-stage-to-orbit (SSTO), reusable launch vehicle (RLV). A 0.007-scale model of the X-33 604B0002G configuration was tested in four hypersonic facilities at the NASA Langley Research Center to examine vehicle stability and control characteristics and to populate an aerodynamic flight database in the hypersonic regime, The vehicle was found to be longitudinally controllable with less than half of the total body flap deflection capability across the angle of attack range at both Mach 6 and Mach 10. At these Mach numbers, the vehicle also was shown to be longitudinally stable or neutrally stable for typical (greater than 20 degrees) hypersonic flight attitudes. This configuration was directionally unstable and the use of reaction control jets (RCS) will be necessary to control the vehicle at high angles of attack in the hypersonic flight regime. Mach number and real gas effects on longitudinal aerodynamics were shown to be small relative to X-33 control authority.

  9. X-33 Hypersonic Aerodynamic Characteristics

    NASA Technical Reports Server (NTRS)

    Murphy, Kelly J.; Nowak, Robert J.; Thompson, Richard A.; Hollis, Brian R.; Prabhu, Ramadas K.

    1999-01-01

    Lockheed Martin Skunk Works, under a cooperative agreement with NASA, will build and fly the X-33, a half-scale prototype of a rocket-based, single-stage-to-orbit (SSTO), reusable launch vehicle (RLV). A 0.007-scale model of the X-33 604B0002G configuration was tested in four hypersonic facilities at the NASA Langley Research Center to examine vehicle stability and control characteristics and to populate an aerodynamic flight database i n the hypersonic regime. The vehicle was found to be longitudinally controllable with less than half of the total body flap deflection capability across the angle of attack range at both Mach 6 and Mach 10. At these Mach numbers, the vehicle also was shown to be longitudinally stable or neutrally stable for typical (greater than 20 degrees) hypersonic flight attitudes. This configuration was directionally unstable and the use of reaction control jets (RCS) will be necessary to control the vehicle at high angles of attack in the hypersonic flight regime. Mach number and real gas effects on longitudinal aerodynamics were shown to be small relative to X-33 control authority.

  10. X-33 Hypersonic Aerodynamic Characteristics

    NASA Technical Reports Server (NTRS)

    Murphy, Kelly J.; Nowak, Robert J.; Thompson, Richard A.; Hollis, Brian R.; Prabhu, Ramadas K.

    1999-01-01

    Lockheed Martin Skunk Works, under a cooperative agreement with NASA, will build and fly the X-33, a half-scale prototype of a rocket-based, single-stage-to-orbit (SSTO), reusable launch vehicle (RLV). A 0.007-scale model of the X-33 604B0002G configuration was tested in four hypersonic facilities at the NASA Langley Research Center to examine vehicle stability and control characteristics and to populate an aerodynamic flight database in the hypersonic regime. The vehicle was found to be longitudinally controllable with less than half of the total body flap deflection capability across the angle of attack range at both Mach 6 and Mach 10. At these Mach numbers, the vehicle also was shown to be longitudinally stable or neutrally stable for typical (greater than 20 degrees) hypersonic flight attitudes. This configuration was directionally unstable and the use of reaction control jets (RCS) will be necessary to control the vehicle at high angles of attack in the hypersonic flight regime. Mach number and real gas effects on longitudinal aerodynamics were shown to be small relative to X-33 control authority.

  11. Aerodynamics of the hovering hummingbird.

    PubMed

    Warrick, Douglas R; Tobalske, Bret W; Powers, Donald R

    2005-06-23

    Despite profound musculoskeletal differences, hummingbirds (Trochilidae) are widely thought to employ aerodynamic mechanisms similar to those used by insects. The kinematic symmetry of the hummingbird upstroke and downstroke has led to the assumption that these halves of the wingbeat cycle contribute equally to weight support during hovering, as exhibited by insects of similar size. This assumption has been applied, either explicitly or implicitly, in widely used aerodynamic models and in a variety of empirical tests. Here we provide measurements of the wake of hovering rufous hummingbirds (Selasphorus rufus) obtained with digital particle image velocimetry that show force asymmetry: hummingbirds produce 75% of their weight support during the downstroke and only 25% during the upstroke. Some of this asymmetry is probably due to inversion of their cambered wings during upstroke. The wake of hummingbird wings also reveals evidence of leading-edge vortices created during the downstroke, indicating that they may operate at Reynolds numbers sufficiently low to exploit a key mechanism typical of insect hovering. Hummingbird hovering approaches that of insects, yet remains distinct because of effects resulting from an inherently dissimilar-avian-body plan.

  12. Aerodynamic design on high-speed trains

    NASA Astrophysics Data System (ADS)

    Ding, San-San; Li, Qiang; Tian, Ai-Qin; Du, Jian; Liu, Jia-Li

    2016-04-01

    Compared with the traditional train, the operational speed of the high-speed train has largely improved, and the dynamic environment of the train has changed from one of mechanical domination to one of aerodynamic domination. The aerodynamic problem has become the key technological challenge of high-speed trains and significantly affects the economy, environment, safety, and comfort. In this paper, the relationships among the aerodynamic design principle, aerodynamic performance indexes, and design variables are first studied, and the research methods of train aerodynamics are proposed, including numerical simulation, a reduced-scale test, and a full-scale test. Technological schemes of train aerodynamics involve the optimization design of the streamlined head and the smooth design of the body surface. Optimization design of the streamlined head includes conception design, project design, numerical simulation, and a reduced-scale test. Smooth design of the body surface is mainly used for the key parts, such as electric-current collecting system, wheel truck compartment, and windshield. The aerodynamic design method established in this paper has been successfully applied to various high-speed trains (CRH380A, CRH380AM, CRH6, CRH2G, and the Standard electric multiple unit (EMU)) that have met expected design objectives. The research results can provide an effective guideline for the aerodynamic design of high-speed trains.

  13. A new technique for aerodynamic noise calculation

    NASA Technical Reports Server (NTRS)

    Hardin, J. C.; Pope, D. S.

    1992-01-01

    A novel method for the numerical analysis of aerodynamic noise generation is presented. The method involves first solving for the time-dependent incompressible flow for the given geometry. This fully nonlinear method that is tailored to extract the relevant acoustic fluctuations seems to be an efficient approach to the numerical analysis of aerodynamic noise generation.

  14. Aerodynamic seal assemblies for turbo-machinery

    SciTech Connect

    Bidkar, Rahul Anil; Wolfe, Christopher; Fang, Biao

    2015-09-29

    The present application provides an aerodynamic seal assembly for use with a turbo-machine. The aerodynamic seal assembly may include a number of springs, a shoe connected to the springs, and a secondary seal positioned about the springs and the shoe.

  15. Distributed Aerodynamic Sensing and Processing Toolbox

    NASA Technical Reports Server (NTRS)

    Brenner, Martin; Jutte, Christine; Mangalam, Arun

    2011-01-01

    A Distributed Aerodynamic Sensing and Processing (DASP) toolbox was designed and fabricated for flight test applications with an Aerostructures Test Wing (ATW) mounted under the fuselage of an F-15B on the Flight Test Fixture (FTF). DASP monitors and processes the aerodynamics with the structural dynamics using nonintrusive, surface-mounted, hot-film sensing. This aerodynamic measurement tool benefits programs devoted to static/dynamic load alleviation, body freedom flutter suppression, buffet control, improvement of aerodynamic efficiency through cruise control, supersonic wave drag reduction through shock control, etc. This DASP toolbox measures local and global unsteady aerodynamic load distribution with distributed sensing. It determines correlation between aerodynamic observables (aero forces) and structural dynamics, and allows control authority increase through aeroelastic shaping and active flow control. It offers improvements in flutter suppression and, in particular, body freedom flutter suppression, as well as aerodynamic performance of wings for increased range/endurance of manned/ unmanned flight vehicles. Other improvements include inlet performance with closed-loop active flow control, and development and validation of advanced analytical and computational tools for unsteady aerodynamics.

  16. Aerodynamics of Sounding-Rocket Geometries

    NASA Technical Reports Server (NTRS)

    Barrowman, J.

    1982-01-01

    Theoretical aerodynamics program TAD predicts aerodynamic characteristics of vehicles with sounding-rocket configurations. These slender, Axisymmetric finned vehicles have a wide range of aeronautical applications from rockets to high-speed armament. TAD calculates characteristics of separate portions of vehicle, calculates interference between portions, and combines results to form total vehicle solution.

  17. Future Computer Requirements for Computational Aerodynamics

    NASA Technical Reports Server (NTRS)

    1978-01-01

    Recent advances in computational aerodynamics are discussed as well as motivations for and potential benefits of a National Aerodynamic Simulation Facility having the capability to solve fluid dynamic equations at speeds two to three orders of magnitude faster than presently possible with general computers. Two contracted efforts to define processor architectures for such a facility are summarized.

  18. The aerodynamics of small Reynolds numbers

    NASA Technical Reports Server (NTRS)

    Schmitz, F. W.

    1980-01-01

    Aerodynamic characteristics of wing model gliders and bird wings in particular are discussed. Wind tunnel measurements and aerodynamics of small Reynolds numbers are enumerated. Airfoil behavior in the critical transition from laminar to turbulent boundary layer, which is more important to bird wing models than to large airplanes, was observed. Experimental results are provided, and an artificial bird wing is described.

  19. Spin relaxation in graphene nanoribbons in the presence of substrate surface roughness

    NASA Astrophysics Data System (ADS)

    Chaghazardi, Zahra; Touski, Shoeib Babaee; Pourfath, Mahdi; Faez, Rahim

    2016-08-01

    In this work, spin transport in corrugated armchair graphene nanoribbons (AGNRs) is studied. We survey combined effects of spin-orbit interaction and surface roughness, employing the non-equilibrium Green's function formalism and multi-orbitals tight-binding model. Rough substrate surfaces have been statistically generated and the hopping parameters are modulated based on the bending and distance of corrugated carbon atoms. The effects of surface roughness parameters, such as roughness amplitude and correlation length, on spin transport in AGNRs are studied. The increase of surface roughness amplitude results in the coupling of σ and π bands in neighboring atoms, leading to larger spin flipping rate and therefore reduction of the spin-polarization, whereas a longer correlation length makes AGNR surface smoother and increases spin-polarization. Moreover, spin diffusion length of carriers is extracted and its dependency on the roughness parameters is investigated. In agreement with experimental data, the spin diffusion length for various substrate ranges between 2 and 340 μm. Our results indicate the importance of surface roughness on spin-transport in graphene.

  20. Simulation Study of the Flow Boundary Condition for Rough Surfaces

    NASA Astrophysics Data System (ADS)

    He, Gang; Robbins, Mark O.

    2001-03-01

    In order to solve a flow problem with the continuum Navier-Stokes equation, a boundary condition must be assumed. In most cases, a no-slip condition is used, i.e. the velocity of the fluid is set equal to that of a bounding solid at their interface. Deviations from this condition can be quantified by a slip length S that represents the additional width of fluid that would be needed to accomodate any velocity difference at the interface. Previous simulations with atomically flat surfaces show that S can be very large in certain limits. (P. A. Thompson and M. O. Robbins, Phys. Rev. A, 41), 6830(1990). ( J.-L. Barrat and L. Bocquet, Phys. Rev. Lett., 82), 4671(1999). A dramatic divergence with S as shear rate increases has also been seen.( P. A. Thompson and S. M. Troian, Nature, 389), 360(1997) We have extended these simulations to surfaces with random roughness, steps, and angled facets typical of twin boundaries. In all cases, S decreases rapidly as the roughness increases. When peak-to-peak roughness is only two atomic diameters, values of S have dropped from more than 20 diameters to only one or two. In addition, the non-linear regime where S diverges with shear rate is supressed by surface roughness. These results suggest that the experimental behavior of atomically flat surfaces such as mica may be very different than that of more typical rough surfaces.

  1. Controlling Surface Roughness to Enhance Mass Flow Rates in Nanochannels

    NASA Astrophysics Data System (ADS)

    Zimon, Malgorzata; Emerson, David; Reese, Jason

    2012-11-01

    A very active field of research in fluid mechanics and material science is predicting the behavior of Newtonian fluids flowing over porous media with different wettabilities. Opposite effects have been observed: some state that wall roughness always suppresses fluid-slip, whereas others show that for some cases roughness may reduce the surface friction. In this work, MD simulations were carried out to further investigate physical mechanisms for liquid slip, and factors affecting it. A rough wall was formed by either periodically spaced rectangular protrusions or was represented by a cosine wave. The MD simulations were conducted to study Poiseuille and Couette flow of liquid argon in a nanochannel with hydrophilic kryptonian walls. The effect of wall roughness and interface wettability on the streaming velocity, and the slip-length at the walls, is observed to be significant. Our results show a dependency of mass flow rate on the type of flow and topography of the channel walls. For a fixed magnitude of the driving force, an increase in the mass flow rate, compared to the smooth surface, was observed for the wavy roughness, whereas the opposite effect was observed for Couette flow where a higher slip was obtained for rectangular gaps. The study is funded in the UK by the Engineering and Physical Sciences Research Council.

  2. Mechanisms resulting in accreted ice roughness

    NASA Technical Reports Server (NTRS)

    Bilanin, Alan J.; Chua, Kiat

    1992-01-01

    Icing tests conducted on rotating cylinders in the BF Goodrich's Icing Research Facility indicate that a regular, deterministic, icing roughness pattern is typical. The roughness pattern is similar to kernels of corn on a cob for cylinders of diameter typical of a cob. An analysis is undertaken to determine the mechanisms which result in this roughness to ascertain surface scale and amplitude of roughness. Since roughness and the resulting augmentation of the convected heat transfer coefficient has been determined to most strongly control the accreted ice in ice prediction codes, the ability to predict a priori, location, amplitude and surface scale of roughness would greatly augment the capabilities of current ice accretion models.

  3. Aerodynamic effects of flexibility in flapping wings.

    PubMed

    Zhao, Liang; Huang, Qingfeng; Deng, Xinyan; Sane, Sanjay P

    2010-03-01

    Recent work on the aerodynamics of flapping flight reveals fundamental differences in the mechanisms of aerodynamic force generation between fixed and flapping wings. When fixed wings translate at high angles of attack, they periodically generate and shed leading and trailing edge vortices as reflected in their fluctuating aerodynamic force traces and associated flow visualization. In contrast, wings flapping at high angles of attack generate stable leading edge vorticity, which persists throughout the duration of the stroke and enhances mean aerodynamic forces. Here, we show that aerodynamic forces can be controlled by altering the trailing edge flexibility of a flapping wing. We used a dynamically scaled mechanical model of flapping flight (Re approximately 2000) to measure the aerodynamic forces on flapping wings of variable flexural stiffness (EI). For low to medium angles of attack, as flexibility of the wing increases, its ability to generate aerodynamic forces decreases monotonically but its lift-to-drag ratios remain approximately constant. The instantaneous force traces reveal no major differences in the underlying modes of force generation for flexible and rigid wings, but the magnitude of force, the angle of net force vector and centre of pressure all vary systematically with wing flexibility. Even a rudimentary framework of wing veins is sufficient to restore the ability of flexible wings to generate forces at near-rigid values. Thus, the magnitude of force generation can be controlled by modulating the trailing edge flexibility and thereby controlling the magnitude of the leading edge vorticity. To characterize this, we have generated a detailed database of aerodynamic forces as a function of several variables including material properties, kinematics, aerodynamic forces and centre of pressure, which can also be used to help validate computational models of aeroelastic flapping wings. These experiments will also be useful for wing design for small

  4. Aerodynamic effects of flexibility in flapping wings

    PubMed Central

    Zhao, Liang; Huang, Qingfeng; Deng, Xinyan; Sane, Sanjay P.

    2010-01-01

    Recent work on the aerodynamics of flapping flight reveals fundamental differences in the mechanisms of aerodynamic force generation between fixed and flapping wings. When fixed wings translate at high angles of attack, they periodically generate and shed leading and trailing edge vortices as reflected in their fluctuating aerodynamic force traces and associated flow visualization. In contrast, wings flapping at high angles of attack generate stable leading edge vorticity, which persists throughout the duration of the stroke and enhances mean aerodynamic forces. Here, we show that aerodynamic forces can be controlled by altering the trailing edge flexibility of a flapping wing. We used a dynamically scaled mechanical model of flapping flight (Re ≈ 2000) to measure the aerodynamic forces on flapping wings of variable flexural stiffness (EI). For low to medium angles of attack, as flexibility of the wing increases, its ability to generate aerodynamic forces decreases monotonically but its lift-to-drag ratios remain approximately constant. The instantaneous force traces reveal no major differences in the underlying modes of force generation for flexible and rigid wings, but the magnitude of force, the angle of net force vector and centre of pressure all vary systematically with wing flexibility. Even a rudimentary framework of wing veins is sufficient to restore the ability of flexible wings to generate forces at near-rigid values. Thus, the magnitude of force generation can be controlled by modulating the trailing edge flexibility and thereby controlling the magnitude of the leading edge vorticity. To characterize this, we have generated a detailed database of aerodynamic forces as a function of several variables including material properties, kinematics, aerodynamic forces and centre of pressure, which can also be used to help validate computational models of aeroelastic flapping wings. These experiments will also be useful for wing design for small robotic

  5. Light reflection from finite conductors with a Gaussian random roughness using Kirchhoff and geometric optics approximations

    NASA Astrophysics Data System (ADS)

    Sassi, Imed; Khemiri, Mehdi; Oumezzine, Mohamed

    2016-09-01

    A comparison between exact solutions and two approximate models, Kirchhoff approximation (KA) and geometric optics approximation (GOA), for reflection from random Gaussian rough conductive metallic surfaces for three regimes of correlation length in both cases of polarization TM and TE has been reported. The phenomenon of excitation of surface plasmons (SPs) has been shown only at TM polarization for KA. The domains of validity of both approximate models have been quantified. It is shown that accuracy and efficiency of any approximate method depended of various parameters: surface roughness, polarization, SPs effects, wavelength, and surface materials. KA is efficient for weakly rough surfaces with correlation length greater than wavelength, but when rms height increases GOA is more suitable than KA. Excitation of SPs is observed only at TM-polarized light, only for weakly rough surfaces with correlation length less than wavelength using KA and not GOA.

  6. Investigation of the effect of roughness of duct surfaces of a supersonic high-pressure stage of an axial compressor on its characteristics

    NASA Astrophysics Data System (ADS)

    Inozemtsev, A. A.; Plotnikov, A. I.

    2015-03-01

    Results of calculations and experimental investigations of characteristics of a supersonic high-pressure wide-chord stage of an axial compressor are presented. The influence of surface roughness on the characteristics of this stage are analyzed. A method of identification of aerodynamic flow parameters in the compressor duct is described.

  7. The basic aerodynamics of floatation

    NASA Astrophysics Data System (ADS)

    Davies, M. J.; Wood, D. H.

    1983-09-01

    It is pointed out that the basic aerodynamics of modern floatation ovens, in which the continuous, freshly painted metal strip is floated, dried, and cured, is the two-dimensional analog of that of hovercraft. The basic theory for the static lift considered in connection with the study of hovercraft has had spectacular success in describing the experimental results. This appears surprising in view of the crudity of the theory. The present investigation represents an attempt to explore the reasons for this success. An outline of the basic theory is presented and an approach is shown for deriving the resulting expressions for the lift from the full Navier-Stokes equations in a manner that clearly indicates the limitations on the validity of the expressions. Attention is given to the generally good agreement between the theory and the axisymmetric (about the centerline) results reported by Jaumotte and Kiedrzynski (1965).

  8. On Cup Anemometer Rotor Aerodynamics

    PubMed Central

    Pindado, Santiago; Pérez, Javier; Avila-Sanchez, Sergio

    2012-01-01

    The influence of anemometer rotor shape parameters, such as the cups' front area or their center rotation radius on the anemometer's performance was analyzed. This analysis was based on calibrations performed on two different anemometers (one based on magnet system output signal, and the other one based on an opto-electronic system output signal), tested with 21 different rotors. The results were compared to the ones resulting from classical analytical models. The results clearly showed a linear dependency of both calibration constants, the slope and the offset, on the cups' center rotation radius, the influence of the front area of the cups also being observed. The analytical model of Kondo et al. was proved to be accurate if it is based on precise data related to the aerodynamic behavior of a rotor's cup. PMID:22778638

  9. Aerodynamic research on tipvane windturbines

    NASA Astrophysics Data System (ADS)

    Vanbussel, G. J. W.; Vanholten, T.; Vankuik, G. A. M.

    1982-09-01

    Tipvanes are small auxiliary wings mounted at the tips of windturbine blades in such a way that a diffuser effect is generated, resulting in a mass flow augmentation through the turbine disc. For predicting aerodynamic loads on the tipvane wind turbine, the acceleration potential is used and an expansion method is applied. In its simplest form, this method can essentially be classified as a lifting line approach, however, with a proper choice of the basis load distributions of the lifting line, the numerical integration of the pressurefield becomes one dimensional. the integration of the other variable can be performed analytically. The complete analytical expression for the pressure field consists of two series of basic pressure fields. One series is related to the basic load distributions over the turbineblade, and the other series to the basic load distribution over the tipvane.

  10. System for determining aerodynamic imbalance

    NASA Technical Reports Server (NTRS)

    Churchill, Gary B. (Inventor); Cheung, Benny K. (Inventor)

    1994-01-01

    A system is provided for determining tracking error in a propeller or rotor driven aircraft by determining differences in the aerodynamic loading on the propeller or rotor blades of the aircraft. The system includes a microphone disposed relative to the blades during the rotation thereof so as to receive separate pressure pulses produced by each of the blades during the passage thereof by the microphone. A low pass filter filters the output signal produced by the microphone, the low pass filter having an upper cut-off frequency set below the frequency at which the blades pass by the microphone. A sensor produces an output signal after each complete revolution of the blades, and a recording display device displays the outputs of the low pass filter and sensor so as to enable evaluation of the relative magnitudes of the pressure pulses produced by passage of the blades by the microphone during each complete revolution of the blades.

  11. Rarefaction Effects in Hypersonic Aerodynamics

    NASA Astrophysics Data System (ADS)

    Riabov, Vladimir V.

    2011-05-01

    The Direct Simulation Monte-Carlo (DSMC) technique is used for numerical analysis of rarefied-gas hypersonic flows near a blunt plate, wedge, two side-by-side plates, disk, torus, and rotating cylinder. The role of various similarity parameters (Knudsen and Mach numbers, geometrical and temperature factors, specific heat ratios, and others) in aerodynamics of the probes is studied. Important kinetic effects that are specific for the transition flow regime have been found: non-monotonic lift and drag of plates, strong repulsive force between side-by-side plates and cylinders, dependence of drag on torus radii ratio, and the reverse Magnus effect on the lift of a rotating cylinder. The numerical results are in a good agreement with experimental data, which were obtained in a vacuum chamber at low and moderate Knudsen numbers from 0.01 to 10.

  12. Aerodynamic characteristics of aerofoils I

    NASA Technical Reports Server (NTRS)

    1921-01-01

    The object of this report is to bring together the investigations of the various aerodynamic laboratories in this country and Europe upon the subject of aerofoils suitable for use as lifting or control surfaces on aircraft. The data have been so arranged as to be of most use to designing engineers and for the purposes of general reference. The absolute system of coefficients has been used, since it is thought by the National Advisory Committee for Aeronautics that this system is the one most suited for international use, and yet is one for which a desired transformation can be easily made. For this purpose a set of transformation constants is included in this report.

  13. Unsteady Aerodynamics of Insect Flight

    NASA Astrophysics Data System (ADS)

    Wang, Z. Jane

    2000-03-01

    The myth `bumble-bees can not fly according to conventional aerodynamics' simply reflects our poor understanding of unsteady viscous fluid dynamics. In particular, we lack a theory of vorticity shedding due to dynamic boundaries at the intermediate Reynolds numbers relevant to insect flight, typically between 10^2 and 10^4, where both viscous and inertial effects are important. In our study, we compute unsteady viscous flows, governed by the Navier-Stokes equation, about a two dimensional flapping wing which mimics the motion of an insect wing. I will present two main results: the existence of a prefered frequency in forward flight and its physical origin, and 2) the vortex dynamics and forces in hovering dragonfly flight.

  14. On cup anemometer rotor aerodynamics.

    PubMed

    Pindado, Santiago; Pérez, Javier; Avila-Sanchez, Sergio

    2012-01-01

    The influence of anemometer rotor shape parameters, such as the cups' front area or their center rotation radius on the anemometer's performance was analyzed. This analysis was based on calibrations performed on two different anemometers (one based on magnet system output signal, and the other one based on an opto-electronic system output signal), tested with 21 different rotors. The results were compared to the ones resulting from classical analytical models. The results clearly showed a linear dependency of both calibration constants, the slope and the offset, on the cups' center rotation radius, the influence of the front area of the cups also being observed. The analytical model of Kondo et al. was proved to be accurate if it is based on precise data related to the aerodynamic behavior of a rotor's cup.

  15. Aerodynamic seals for rotary machine

    DOEpatents

    Bidkar, Rahul Anil; Cirri, Massimiliano; Thatte, Azam Mihir; Williams, John Robert

    2016-02-09

    An aerodynamic seal assembly for a rotary machine includes multiple sealing device segments disposed circumferentially intermediate to a stationary housing and a rotor. Each of the segments includes a shoe plate with a forward-shoe section and an aft-shoe section having multiple labyrinth teeth therebetween facing the rotor. The sealing device segment also includes multiple flexures connected to the shoe plate and to a top interface element, wherein the multiple flexures are configured to allow the high pressure fluid to occupy a forward cavity and the low pressure fluid to occupy an aft cavity. Further, the sealing device segments include a secondary seal attached to the top interface element at one first end and positioned about the flexures and the shoe plate at one second end.

  16. Aerodynamic Noise Generated by Shinkansen Cars

    NASA Astrophysics Data System (ADS)

    KITAGAWA, T.; NAGAKURA, K.

    2000-03-01

    The noise value (A -weighted sound pressure level, SLOW) generated by Shinkansen trains, now running at 220-300 km/h, should be less than 75 dB(A) at the trackside. Shinkansen noise, such as rolling noise, concrete support structure noise, and aerodynamic noise are generated by various parts of Shinkansen trains. Among these aerodynamic noise is important because it is the major contribution to the noise generated by the coaches running at high speed. In order to reduce the aerodynamic noise, a number of improvements to coaches have been made. As a result, the aerodynamic noise has been reduced, but it still remains significant. In addition, some aerodynamic noise generated from the lower parts of cars remains. In order to investigate the contributions of these noises, a method of analyzing Shinkansen noise has been developed and applied to the measured data of Shinkansen noise at speeds between 120 and 315 km/h. As a result, the following conclusions have been drawn: (1) Aerodynamic noise generated from the upper parts of cars was reduced considerably by smoothing car surfaces. (2) Aerodynamic noise generated from the lower parts of cars has a major influence upon the wayside noise.

  17. Aerodynamic fairing/brake for high-speed trains

    SciTech Connect

    Ende, R.E.

    1993-06-29

    A dual aerodynamic function assembly for high speed MAGLEV trains having adjacent in-line cars is described comprising: a series of flaps pivotally mounted by means of a hinge to a circumferential segment of a car end, each flap displaceable to a first position covering a gap existing between the car end and a confronting end of an adjacent car thereby serving as a fairing; a second position at an oblique angle to the path of travel thereby creating drag on the train resulting in braking; and means for actuating the flaps to one or the other position; wherein the flaps have rectangular shapes along those lengths of the circumferential segment which are linear; and further wherein the flaps have contoured edges along those lengths of the circumferential segment which are curved so as to create a close edgewise fit to create a more continuous drag braking surface.

  18. Experimental aerodynamic characteristics of missiles with square cross sections

    NASA Astrophysics Data System (ADS)

    Zollars, G. J.; Yechout, R. T.; Daniel, D. C.; Lijewski, L. E.

    1983-05-01

    A series of quantitative and qualitative tests were conducted to expand the aerodynamic data base of square cross-section missiles. Quantitative tests included measuring forces and moments acting on square missiles, and measuring flowfield pressures on the leeward side of square missiles at various configurations and orientations in a subsonic wind tunnel. Force and moment data is presented showing the effects of variation in body corner radius, nose and fin shapes, pitch angle, and roll angle. Flowfield pressure and crossflow velocity data are presented for missiles of various pitch angles, roll angles, body corner radii, and fineness ratios (length to width ratio). In addition, flowfield data is shown along the axial length of a square missile. Qualitative tests included photographic tuft grids in the flowfield and photographing oil shear stress patterns on the surface of various missiles. These qualitative photographs are presented for various missile configurations and orientations.

  19. Intelligent Information Retrieval Using Rough Set Approximations.

    ERIC Educational Resources Information Center

    Srinivasan, Padmini

    1989-01-01

    Describes rough sets theory and discusses the advantages it offers for information retrieval, including the implicit inclusion of Boolean logic, term weighting, ranked retrieval output, and relevance feedback. Rough set formalism is compared to Boolean, vector, and fuzzy models of information retrieval and a small scale evaluation of rough sets is…

  20. An experimental study of separation control on ultra-highly-loaded low pressure turbine blade by surface roughness

    NASA Astrophysics Data System (ADS)

    Sun, Shuang; Lei, Zhijun; Lu, Xingen; Zhao, Shengfeng; Zhu, Junqiang

    2015-06-01

    An experimental study is conducted to improve an aft-loaded ultra-high-lift low pressure turbine (LPT) blade at low Reynolds number (Re) in steady state. The objective is to investigate the effect of blade roughness on the performance of LPT blade. The roughness is used as a passive flow control method which is to reduce total pressure loss and expand LPT operating margin. The experiment is performed on a low-speed cascade facility. 3 roughness heights and 3 deposit positions are investigated in the experiment which forms a large test matrix. A three-hole probe is used to detect flow aerodynamic performance and a hotwire probe is used to detect the characteristic of suction boundary layer. Regional roughness can suppress separation loss and bring fairly low turbulent dissipation loss. Detailed surveys near the blade surface shows that the loss reduction is due to the disappearance of separation bubble from the early transition onset.

  1. Extensive wetting due to roughness

    SciTech Connect

    Yost, F.G.; Michael, J.R.; Eisenmann, E.T. . Center for Solder Science and Technology)

    1995-01-01

    Typically, a small mass of eutectic Sn-Pb solder wets a copper surface and flows radially outward to form a hemispherical shape with a contact angle of approx. 15--20 deg. When a similar mass of solder wets and thick electroless copper coated substrate, rapid radial flow commences and surprising new effects occur. Thick coats of electroless copper have a nodular surface structure and spreading on it does not subside until all solder is consumed. When the nodular structure is wetted by solder a coastline'' with many nearby islands'' are defined. Photos of regions at the wetting front were taken in the backscatter imaging mode of an SEM. These images show that solder wets the valleys between the surface nodules forming a delicate, lacy arrangement. The geometry of this coastal'' solder structure is described as fractal-like having a dimension D = 1.38 making it similar to drying fronts and cloud configurations. The importance of surface roughness in wetting phenomena is discussed in the light of an extensive history on the subject. It is shown that for spontaneous flow, assisted by roughness, the surface geometry must consist of local angles that are larger than the equilibrium contact angle. Kinetics of the wetting process are demonstrated by image analysis of wetted area taken from videotaped experiments. These experimental kinetics are shown to be similar in form to flow in open channel capillaries.

  2. Calibration of surface roughness standards

    NASA Astrophysics Data System (ADS)

    Thalmann, R.; Nicolet, A.; Meli, F.; Picotto, G. B.; Matus, M.; Carcedo, L.; Hemming, B.; Ganioglu, O.; De Chiffre, L.; Saraiva, F.; Bergstrand, S.; Zelenika, S.; Tonmueanwai, A.; Tsai, C.-L.; Shihua, W.; Kruger, O.; de Souza, M. M.; Salgado, J. A.; Ramotowski, Z.

    2016-01-01

    The key comparison EURAMET.L-K8.2013 on roughness was carried out in the framework of a EURAMET project starting in 2013 and ending in 2015. It involved the participation of 17 National Metrology Institutes from Europe, Asia, South America and Africa representing four regional metrology organisations. Five surface texture standards of different type were circulated and on each of the standards several roughness parameters according to the standard ISO 4287 had to be determined. 32 out of 395 individual results were not consistent with the reference value. After some corrective actions the number of inconsistent results could be reduced to 20, which correspond to about 5% of the total and can statistically be expected. In addition to the material standards, two softgauges were circulated, which allow to test the software of the instruments used in the comparison. The comparison results help to support the calibraton and measurement capabilities (CMCs) of the laboratories involved in the CIPM MRA. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

  3. Plume Dispersion over Idealized Urban-liked Roughness with Height Variation: an LES Approach

    NASA Astrophysics Data System (ADS)

    Wong, Colman Ching Chi; Liu, Chun-Ho

    2013-04-01

    Human activities (e.g. vehicular emission) are the primary pollutant sources affecting the health and living quality of stakeholders in modern compact cities. Gaussian plume dispersion model is commonly used for pollutant distribution estimate that works well over rural areas with flat terrain. However, its major parameters, dispersion coefficients, exclude the effect of surface roughness that unavoidably prone to error handling the pollutant transport in the urban boundary layer (UBL) over building roughness. Our recent large-eddy simulation (LES) has shown that urban surfaces affect significantly the pollutant dispersion over idealized, identical two-dimensional (2D) street canyons of uniform height. As an extension to our on-going effort, this study is conceived to investigate how rough urban surfaces, which are constructed by 2D street canyons of non-uniform height, modify the UBL pollutant dispersion . A series of LESs with idealized roughness elements of non-uniform heights were performed in neutral stratification. Building models with two different heights were placed alternatively in the computational domain to construct 2D street canyons in cross flows. The plume dispersion from a ground-level passive pollutant source over more realistic urban areas was then examined. Along with the existing building-height-to-street-width (aspect) ratio (AR), a new parameter, building-height variability (BHV), is used to measure the building height unevenness. Four ARs (1, 0.5, 0.25 and 0.125) and three BHVs (20%, 40% and 60%) were considered in this study. Preliminary results show that BHV greatly increases the aerodynamic roughness of the hypothetical urban surfaces for narrow street canyons. Analogous to our previous findings, the air exchange rate (ACH) of street canyons increases with increasing friction factor, implying that street-level ventilation could be improved by increasing building roughness via BHV. In addition, the parameters used in dispersion coefficient

  4. The effect of adding roughness and thickness to a transonic axial compressor rotor

    NASA Technical Reports Server (NTRS)

    Suder, Kenneth L.; Chima, Rodrick V.; Strazisar, Anthony J.; Roberts, William B.

    1995-01-01

    The performance deterioration of a high speed axial compressor rotor due to surface roughness and airfoil thickness variations is reported. A 0.025 mm (0.001 in.) thick rough coating with a surface finish of 2.54-3.18 RMS microns (100-125 RMS microinches) is applied to the pressure and suction surface of the rotor blades. Coating both surfaces increases the leading edge thickness by 10% at the hub and 20% at the tip. Application of this coating results in a loss in efficiency of 6 points and a 9% reduction in the pressure ratio across the rotor at an operating condition near the design point. To separate the effect of thickness and roughness, a smooth coating of equal thickness is also applied to the blade. The smooth coating surface finish is 0.254-0.508 RMS microns (10-20 RMS microinches), compared to the bare metal blade surface finish of 0.508 RMS microns (20 RMS microinches). The smooth coating results in approximately half of the performance deterioration found from the rough coating. Both coatings are then applied to different portions of the blade surface to determine which portions of the airfoil are most sensitive to thickness/roughness variations. Aerodynamic performance measurements are presented for a number of coating configurations at 60%, 80%, and 100% of design speed. The results indicate that thickness/roughness over the first 10% of blade chord accounts for virtually all of the observed performance degradation for the smooth coating, compared to about 70% of the observed performance degradation for the rough coating. The performance deterioration is investigated in more detail at design speed using laser anemometer measurements as well as predictions generated by a quasi-3D Navier-Stokes flow solver which includes a surface roughness model. Measurements and analysis are performed on the baseline blade and the full-coverage smooth and rough coatings. The results indicate that coating the blade causes a thickening of the blade boundary layers. The

  5. Aerodynamics in the classroom and at the ball park

    NASA Astrophysics Data System (ADS)

    Cross, Rod

    2012-04-01

    Experiments suitable for classroom projects or demonstrations are described concerning the aerodynamics of polystyrene balls. A light ball with sufficient backspin can curve vertically upward through the air, defying gravity and providing a dramatic visual demonstration of the Magnus effect. A ball projected with backspin can also curve downward with a vertical acceleration greater than that due to gravity if the Magnus force is negative. These effects were investigated by filming the flight of balls projected in an approximately horizontal direction so that the lift and drag forces could be easily measured. The balls were also fitted with artificial raised seams and projected with backspin toward a vertical target in order to measure the sideways deflection over a known horizontal distance. It was found that (a) a ball with a seam on one side can deflect either left or right depending on its launch speed and (b) a ball with a baseball seam can also deflect sideways even when there is no sideways component of the drag or lift forces acting on the ball. Depending on the orientations of the seam and the spin axis, a sideways force on a baseball can arise either if there is rough patch on one side of the ball or if there is a smooth patch. A scuff ball with a rough patch on one side is illegal in baseball. The effect of a smooth patch is a surprising new observation.

  6. Experimental study of aerodynamic damping in arrays of vibrating cantilevers

    NASA Astrophysics Data System (ADS)

    Kimber, M.; Lonergan, R.; Garimella, S. V.

    2009-11-01

    Cantilever structures vibrating in a fluid are encountered in numerous engineering applications. The aerodynamic loading from a fluid can have a large effect on both the resonance frequency and damping, and has been the subject of numerous studies. The aerodynamic loading on a single beam is altered when multiple beams are configured in an array. In such situations, neighboring beams interact through the fluid and their dynamic behavior is modified. In this work, aerodynamic interactions between neighboring cantilever beams operating near their first resonance mode and vibrating at amplitudes comparable to their widths are experimentally explored. The degree to which two beams become coupled through the fluid is found to be sensitive to vibration amplitude and proximity of neighboring components in the array. The cantilever beams considered are slender piezoelectric fans (approximately 6 cm in length), and are caused to vibrate in-phase and out-of-phase at frequencies near their fundamental resonance values. Aerodynamic damping is expressed in terms of the quality factor for two different array configurations and estimated for both in-phase and out-of-phase conditions. The two array configurations considered are for neighboring fans placed face-to-face and edge-to-edge. It is found that the damping is greatly influenced by proximity of neighboring fans and phase difference. For the face-to-face configuration, a reduction in damping is observed for in-phase vibration, while it is greatly increased for out-of-phase vibration; the opposite effect is seen for the edge-to-edge configuration. The resonance frequencies also show a dependence on the phase difference, but these changes are small compared to those observed for damping. Correlations are developed based on the experimental data which can be used to predict the aerodynamic damping in arrays of vibrating cantilevers. The distance at which the beams no longer interact is quantified for both array configurations

  7. Transpiration Control Of Aerodynamics Via Porous Surfaces

    NASA Technical Reports Server (NTRS)

    Banks, Daniel W.; Wood, Richard M.; Bauer, Steven X. S.

    1993-01-01

    Quasi-active porous surface used to control pressure loading on aerodynamic surface of aircraft or other vehicle, according to proposal. In transpiration control, one makes small additions of pressure and/or mass to cavity beneath surface of porous skin on aerodynamic surface, thereby affecting rate of transpiration through porous surface. Porous skin located on forebody or any other suitable aerodynamic surface, with cavity just below surface. Device based on concept extremely lightweight, mechanically simple, occupies little volume in vehicle, and extremely adaptable.

  8. Performance aerodynamics of aeroassisted orbital transfer vehicles

    NASA Technical Reports Server (NTRS)

    Wilhite, A. W.; Arrington, J. P.; Mccandless, R. S.

    1984-01-01

    A method for predicting the performance aerodynamics of aeroassisted orbital transfer vehicles was developed based on techniques that were used in the aerodynamic databook of the Space Shuttle orbiter and theories from the Hypersonic Arbitrary Body Program. The method spans the entire flight profile of the aeroassisted orbital transfer vehicles from the extreme high altitude non-continuum regime to the highly viscous continuum regime. Results from this method are compared with flight data from the Shuttle orbiter, Apollo Capsule, and the Viking Aeroshell. Finally, performance aerodynamics are estimated for three aeroassisted orbital transfer vehicles that range from low to high lift-to-drag ratio configurations.

  9. 14 CFR 25.445 - Auxiliary aerodynamic surfaces.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Auxiliary aerodynamic surfaces. 25.445... § 25.445 Auxiliary aerodynamic surfaces. (a) When significant, the aerodynamic influence between auxiliary aerodynamic surfaces, such as outboard fins and winglets, and their supporting...

  10. 14 CFR 25.445 - Auxiliary aerodynamic surfaces.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Auxiliary aerodynamic surfaces. 25.445... § 25.445 Auxiliary aerodynamic surfaces. (a) When significant, the aerodynamic influence between auxiliary aerodynamic surfaces, such as outboard fins and winglets, and their supporting...

  11. 14 CFR 25.445 - Auxiliary aerodynamic surfaces.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Auxiliary aerodynamic surfaces. 25.445... § 25.445 Auxiliary aerodynamic surfaces. (a) When significant, the aerodynamic influence between auxiliary aerodynamic surfaces, such as outboard fins and winglets, and their supporting...

  12. 14 CFR 25.445 - Auxiliary aerodynamic surfaces.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Auxiliary aerodynamic surfaces. 25.445... § 25.445 Auxiliary aerodynamic surfaces. (a) When significant, the aerodynamic influence between auxiliary aerodynamic surfaces, such as outboard fins and winglets, and their supporting...

  13. 1997 NASA High-Speed Research Program Aerodynamic Performance Workshop. Volume 1; Configuration Aerodynamics

    NASA Technical Reports Server (NTRS)

    Baize, Daniel G. (Editor)

    1999-01-01

    The High-Speed Research Program and NASA Langley Research Center sponsored the NASA High-Speed Research Program Aerodynamic Performance Workshop on February 25-28, 1997. The workshop was designed to bring together NASA and industry High-Speed Civil Transport (HSCT) Aerodynamic Performance technology development participants in areas of Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High-Lift, Flight Controls, Supersonic Laminar Flow Control, and Sonic Boom Prediction. The workshop objectives were to (1) report the progress and status of HSCT aerodynamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientist and engineers working HSCT aerodynamics. In particular, single- and multi-point optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT Motion Simulator results were presented along with executive summaries for all the Aerodynamic Performance technology areas.

  14. Lewis icing research tunnel test of the aerodynamic effects of aircraft ground deicing/anti-icing fluids

    NASA Technical Reports Server (NTRS)

    Runyan, L. James; Zierten, Thomas A.; Hill, Eugene G.; Addy, Harold E., Jr.

    1992-01-01

    A wind tunnel investigation of the effect of aircraft ground deicing/anti-icing fluids on the aerodynamic characteristics of a Boeing 737-200ADV airplane was conducted. The test was carried out in the NASA Lewis Icing Research Tunnel. Fluids tested include a Newtonian deicing fluid, three non-Newtonian anti-icing fluids commercially available during or before 1988, and eight new experimental non-Newtonian fluids developed by four fluid manufacturers. The results show that fluids remain on the wind after liftoff and cause a measurable lift loss and drag increase. These effects are dependent on the high-lift configuration and on the temperature. For a configuration with a high-lift leading-edge device, the fluid effect is largest at the maximum lift condition. The fluid aerodynamic effects are related to the magnitude of the fluid surface roughness, particularly in the first 30 percent chord. The experimental fluids show a significant reduction in aerodynamic effects.

  15. Using the HARV simulation aerodynamic model to determine forebody strake aerodynamic coefficients from flight data

    NASA Technical Reports Server (NTRS)

    Messina, Michael D.

    1995-01-01

    The method described in this report is intended to present an overview of a process developed to extract the forebody aerodynamic increments from flight tests. The process to determine the aerodynamic increments (rolling pitching, and yawing moments, Cl, Cm, Cn, respectively) for the forebody strake controllers added to the F/A - 18 High Alpha Research Vehicle (HARV) aircraft was developed to validate the forebody strake aerodynamic model used in simulation.

  16. Large eddy simulations of surface roughness parameter sensitivity to canopy-structure characteristics

    DOE PAGES

    Maurer, K. D.; Bohrer, G.; Ivanov, V. Y.

    2014-11-27

    Surface roughness parameters are at the core of every model representation of the coupling and interactions between land-surface and atmosphere, and are used in every model of surface fluxes. However, most models assume these parameters to be a fixed property of plant functional type and do not vary them in response to spatial or temporal changes to canopy structure. In part, this is due to the difficulty of reducing the complexity of canopy structure and its spatiotemporal dynamic and heterogeneity to less than a handful of parameters describing its effects of atmosphere–surface interactions. In this study we use large-eddy simulationsmore » to explore, in silico, the effects of canopy structure characteristics on surface roughness parameters. We performed a virtual experiment to test the sensitivity of resolved surface roughness to four axes of canopy structure: (1) leaf area index, (2) the vertical profile of leaf density, (3) canopy height, and (4) canopy gap fraction. We found roughness parameters to be highly variable, but were able to find positive relationships between displacement height and maximum canopy height, aerodynamic canopy height and maximum canopy height and leaf area index, and eddy-penetration depth and gap fraction. We also found negative relationships between aerodynamic canopy height and gap fraction, and between eddy-penetration depth and maximum canopy height and leaf area index. Using a decade of wind and canopy structure observations in a site in Michigan, we tested the effectiveness of our model-resolved parameters in predicting the frictional velocity over heterogeneous and disturbed canopies. We compared it with three other semi-empirical models and with a decade of meteorological observations. We found that parameterizations with fixed representations of roughness performed relatively well. Nonetheless, some empirical approaches that incorporate seasonal and inter-annual changes to the canopy structure performed even better than

  17. The roles of aerodynamic and inertial forces on maneuverability in flapping flight

    NASA Astrophysics Data System (ADS)

    Vejdani, Hamid; Boerma, David; Swartz, Sharon; Breuer, Kenneth

    2015-11-01

    We investigate the relative contributions of aerodynamic and the whole-body dynamics in generating extreme maneuvers. We developed a 3D dynamical model of a body (trunk) and two rectangular wings using a Lagrangian formulation. The trunk has 6 degrees of freedom and each wing has 4 degrees of actuation (flapping, sweeping, wing pronation/supination and wing extension/flexion) and can be massless (like insect wings) or relatively massive (like bats). To estimate aerodynamic forces, we use a blade element method; drag and lift are calculated using a quasi-steady model. We validated our model using several benchmark tests, including gliding and hovering motion. To understand the roles of aerodynamic and inertial forces, we start the investigation by constraining the wing motion to flapping and wing length extension/flexion motion. This decouples the trunk degrees of freedom and affects only roll motion. For bats' dynamics (massive wings), the model is much more maneuverable than the insect dynamics case, and the effect of inertial forces dominates the behavior of the system. The role of the aerodynamic forces increases when the wings have sweeping and flapping motion, which affects the pitching motion of the body. We also analyzed the effect of all wing motions together on the behavior of the model in the presence and in the absence of aerodynamic forces.

  18. 1999 NASA High-Speed Research Program Aerodynamic Performance Workshop. Volume 1; Configuration Aerodynamics

    NASA Technical Reports Server (NTRS)

    Hahne, David E. (Editor)

    1999-01-01

    NASA's High-Speed Research Program sponsored the 1999 Aerodynamic Performance Technical Review on February 8-12, 1999 in Anaheim, California. The review was designed to bring together NASA and industry High-Speed Civil Transport (HSCT) Aerodynamic Performance technology development participants in the areas of Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High Lift, and Flight Controls. The review objectives were to: (1) report the progress and status of HSCT aerodynamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientists and engineers working on HSCT aerodynamics. In particular, single and midpoint optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT simulation results were presented, along with executive summaries for all the Aerodynamic Performance technology areas. The HSR Aerodynamic Performance Technical Review was held simultaneously with the annual review of the following airframe technology areas: Materials and Structures, Environmental Impact, Flight Deck, and Technology Integration. Thus, a fourth objective of the Review was to promote synergy between the Aerodynamic Performance technology area and the other technology areas of the HSR Program. This Volume 1/Part 1 publication covers configuration aerodynamics.

  19. Aerodynamic Characterization of a Modern Launch Vehicle

    NASA Technical Reports Server (NTRS)

    Hall, Robert M.; Holland, Scott D.; Blevins, John A.

    2011-01-01

    A modern launch vehicle is by necessity an extremely integrated design. The accurate characterization of its aerodynamic characteristics is essential to determine design loads, to design flight control laws, and to establish performance. The NASA Ares Aerodynamics Panel has been responsible for technical planning, execution, and vetting of the aerodynamic characterization of the Ares I vehicle. An aerodynamics team supporting the Panel consists of wind tunnel engineers, computational engineers, database engineers, and other analysts that address topics such as uncertainty quantification. The team resides at three NASA centers: Langley Research Center, Marshall Space Flight Center, and Ames Research Center. The Panel has developed strategies to synergistically combine both the wind tunnel efforts and the computational efforts with the goal of validating the computations. Selected examples highlight key flow physics and, where possible, the fidelity of the comparisons between wind tunnel results and the computations. Lessons learned summarize what has been gleaned during the project and can be useful for other vehicle development projects.

  20. Aerodynamic Performance of Hand Launch Glider

    NASA Astrophysics Data System (ADS)

    Koike, Masaru; Ishii, Mitsuru

    In recent years Micro Air Vehicles (MAV) for disaster aerial video are developed vigorously. In order to improve aerodynamic performance of MAV wing performance in low Reynolds numbers (Re) need to be improved, but research on the theme are very rare. In category of Hand Launch Glider, a kind of model aircraft, glide performance are competed, as a result high performance airfoils in Re is around 20,000 are developed. Therefore for MAV's aerodynamic performance improvement airfoils of Hand Launch Gliders should be referred and aerodynamic characteristics of the airfoils desired to be studied. So in this research, aerodynamic characteristics of the gliders are measured in wind tunnel. And also consistency between wind tunnel test and glide test in calm air is examined to confirm reliability of wind tunnel test. Comparison of different airfoils and flow visualization are also performed.

  1. Hypervelocity Free-Flight Aerodynamic Facility (HFFAF)

    NASA Video Gallery

    The HFFAF is the only aeroballistic range the nation currently capable of testing in gases other than air and at sub-atmospheric pressures. It is used primarily to study the aerodynamics, Aerotherm...

  2. Aerodynamic Forces on a Vibrating Unstaggered Cascade

    NASA Technical Reports Server (NTRS)

    Soehngen, H.

    1957-01-01

    The unsteady aerodynamic forces, [based on two-dimensional incompressible flow considerations], are determined for an unstaggered cascade, the blades of which are vibrating in phase in an approach flow parallel to the blades.

  3. Aerodynamic Analyses Requiring Advanced Computers, Part 1

    NASA Technical Reports Server (NTRS)

    1975-01-01

    Papers are presented which deal with results of theoretical research on aerodynamic flow problems requiring the use of advanced computers. Topics discussed include: viscous flows, boundary layer equations, turbulence modeling and Navier-Stokes equations, and internal flows.

  4. Aerodynamic Analyses Requiring Advanced Computers, part 2

    NASA Technical Reports Server (NTRS)

    1975-01-01

    Papers given at the conference present the results of theoretical research on aerodynamic flow problems requiring the use of advanced computers. Topics discussed include two-dimensional configurations, three-dimensional configurations, transonic aircraft, and the space shuttle.

  5. Uniaxial aerodynamic attitude control of artificial satellites

    NASA Technical Reports Server (NTRS)

    Sazonov, V. V.

    1983-01-01

    Within the context of a simple mechanical model the paper examines the movement of a satellite with respect to the center of masses under conditions of uniaxial aerodynamic attitude control. The equations of motion of the satellite take account of the gravitational and restorative aerodynamic moments. It is presumed that the aerodynamic moment is much larger than the gravitational, and the motion equations contain a large parameter. A two-parameter integrated surface of these equations is constructed in the form of formal series in terms of negative powers of the large parameter, describing the oscillations and rotations of the satellite about its lengthwise axis, approximately oriented along the orbital tangent. It is proposed to treat such movements as nominal undisturbed motions of the satellite under conditions of aerodynamic attitude control. A numerical investigation is made for the above integrated surface.

  6. Switchable and Tunable Aerodynamic Drag on Cylinders

    NASA Astrophysics Data System (ADS)

    Guttag, Mark; Lopéz Jiménez, Francisco; Upadhyaya, Priyank; Kumar, Shanmugam; Reis, Pedro

    We report results on the performance of Smart Morphable Surfaces (Smporhs) that can be mounted onto cylindrical structures to actively reduce their aerodynamic drag. Our system comprises of an elastomeric thin shell with a series of carefully designed subsurface cavities that, once depressurized, lead to a dramatic deformation of the surface topography, on demand. Our design is inspired by the morphology of the giant cactus (Carnegiea gigantea) which possesses an array of axial grooves, thought to help reduce aerodynamic drag, thereby enhancing the structural robustness of the plant under wind loading. We perform systematic wind tunnel tests on cylinders covered with our Smorphs and characterize their aerodynamic performance. The switchable and tunable nature of our system offers substantial advantages for aerodynamic performance when compared to static topographies, due to their operation over a wider range of flow conditions.

  7. Switchable and Tunable Aerodynamic Drag on Cylinders

    NASA Astrophysics Data System (ADS)

    Guttag, Mark; Lopez Jimenez, Francisco; Reis, Pedro

    2015-11-01

    We report results on the performance of Smart Morphable Surfaces (Smporhs) that can be mounted onto cylindrical structures to actively reduce their aerodynamic drag. Our system comprises of an elastomeric thin shell with a series of carefully designed subsurface cavities that, once depressurized, lead to a dramatic deformation of the surface topography, on demand. Our design is inspired by the morphology of the giant cactus (Carnegiea gigantea) which possesses an array of axial grooves, which are thought to help reduce aerodynamic drag, thereby enhancing the structural robustness of the plant under wind loading. We perform systematic wind tunnel tests on cylinders covered with our Smorphs and characterize their aerodynamic performance. The switchable and tunable nature of our system offers substantial advantages for aerodynamic performance when compared to static topographies, due to their operation over a wider range of flow conditions.

  8. Aerodynamic and Aeroelastic Insights using Eigenanalysis

    NASA Technical Reports Server (NTRS)

    Heeg, Jennifer; Dowell, Earl H.

    1999-01-01

    This paper presents novel analytical results for eigenvalues and eigenvectors produced using discrete time aerodynamic and aeroelastic models. An unsteady, incompressible vortex lattice aerodynamic model is formulated in discrete time; the importance of several modeling parameters is examined. A detailed study is made of the behavior of the aerodynamic eigenvalues both in discrete and continuous time. The aerodynamic model is then incorporated into aeroelastic equations of motion. Eigenanalyses of the coupled equations produce stability results and modal characteristics which are valid for critical and non-critical velocities. Insight into the modeling and physics associated with aeroelastic system behavior is gained by examining both the eigenvalues and the eigenvectors. Potential pitfalls in discrete time model construction and analysis are examined.

  9. HSR Aerodynamic Performance Status and Challenges

    NASA Technical Reports Server (NTRS)

    Gilbert, William P.; Antani, Tony; Ball, Doug; Calloway, Robert L.; Snyder, Phil

    1999-01-01

    This paper describes HSR (High Speed Research) Aerodynamic Performance Status and Challenges. The topics include: 1) Aero impact on HSR; 2) Goals and Targets; 3) Progress and Status; and 4) Remaining Challenges. This paper is presented in viewgraph form.

  10. A Reduced-Complexity Investigation of Blunt Leading-Edge Separation Motivated by UCAV Aerodynamics

    NASA Technical Reports Server (NTRS)

    Luckring, James M.; Boelens, Okko J.

    2015-01-01

    A reduced complexity investigation for blunt-leading-edge vortical separation has been undertaken. The overall approach is to design the fundamental work in such a way so that it relates to the aerodynamics of a more complex Uninhabited Combat Air Vehicle (UCAV) concept known as SACCON. Some of the challenges associated with both the vehicle-class aerodynamics and the fundamental vortical flows are reviewed, and principles from a hierarchical complexity approach are used to relate flow fundamentals to system-level interests. The work is part of roughly 6-year research program on blunt-leading-edge separation pertinent to UCAVs, and was conducted under the NATO Science and Technology Organization, Applied Vehicle Technology panel.

  11. Roughness of Weddell Sea Ice and Estimates of the Air-Ice Drag Coefficient

    NASA Astrophysics Data System (ADS)

    Andreas, Edgar L.; Lange, Manfred A.; Ackley, Stephen F.; Wadhams, Peter

    1993-07-01

    The roughness of a sheet of sea ice encodes its deformational history and determines its aerodynamic coupling with the overlying air and underlying water. Here we report snow surface, ice surface, and ice underside roughness computed from 47 surface elevation profiles collected during a transect of the Weddell Sea. The roughness for each surface, parameterized as the standard deviation of the surface elevation, segregates according to whether or not a floe has been deformed: deformed ice has greater roughness than undeformed ice. Regardless of deformational history, the underside roughness is almost always greater than the snow surface and ice surface roughnesses, which are nearly equal. Roughness spectra for all three surfaces and for both deformed and undeformed ice roll off roughly as k-1 when the wavenumber k is between 0.1 and 3 rad m-1. The snow surface and underside spectra roll off somewhat faster than k-1, and the ice surface spectra roll off somewhat slower than k-1. Both top and underside Arctic ice roughness spectra, on the other hand, have been reported to roll off faster than k-2. We speculate that the excess spectral intensity at high wavenumbers in the Antarctic ice surface spectra results from the small-scale roughness that the ice sheet had on consolidation. This excess high-wavenumber spectral intensity persists in the ice surface spectra of second-year ice. Evidently, once formed, the ice surface remains unchanged on the microscale until the entire ice sheet melts. With a remote measurement of roughness, we should be able to decide whether an ice floe is deformed or undeformed. Our spectral analysis hints that remote sensing may also be able to differentiate between first-year and second-year ice. From the snow surface spectra, we compute a roughness scale ξ that parameterizes the air-ice momentum coupling and lets us estimate the neutral stability drag coefficient referenced to a height of 10 m, CDN10. Typical CDN10 values are 1.1-1.4 × 10

  12. Means for controlling aerodynamically induced twist

    NASA Technical Reports Server (NTRS)

    Elber, W. (Inventor)

    1982-01-01

    A control mechanism which provides active compensation for aerodynamically induced twist deformation of high aspect ratio wings consists of a torque tube, internal to each wing and rigidly attached near the tip of each wing, which is moved by an actuator located in the aircraft fuselage. As changes in the aerodynamic loads on the wings occur the torque tube is rotated to compensate for the induced wing twist.

  13. The oscillating wing with aerodynamically balanced elevator

    NASA Technical Reports Server (NTRS)

    Kussner, H G; Schwartz, I

    1941-01-01

    The two-dimensional problem of the oscillating wing with aerodynamically balanced elevator is treated in the manner that the wing is replaced by a plate with bends and stages and the airfoil section by a mean line consisting of one or more straights. The computed formulas and tables permit, on these premises, the prediction of the pressure distribution and of the aerodynamic reactions of oscillating elevators and tabs with any position of elevator hinge in respect to elevator leading edge.

  14. Transition Experiments on Blunt Bodies with Distributed Roughness in Hypersonic Free Flight in Carbon Dioxide

    NASA Technical Reports Server (NTRS)

    Wilder, Michael C.; Reda, Daniel C.; Prabhu, Dinesh K.

    2015-01-01

    Blunt-body geometries were flown through carbon dioxide in the NASA Ames Hypervelocity Free Flight Aerodynamic Facility to investigate the influence of distributed surface roughness on transition to turbulence in CO2-dominated atmospheres, such as those of Mars and Venus. Tests were also performed in air for direct comparison with archival results. Models of hemispherical and spherically-blunted large-angle conical geometries were flown at speeds between 2.8 km/s and 5.1 km/s and freestream pressures between 50 Torr and 228 Torr. Transition fronts were determined from global surface heat flux distributions measured using thermal imaging techniques. Distributed surface roughness was produced by grit-blasting the model surfaces. Real-gas Navier-Stokes solutions were used to calculate non-dimensional correlating parameters at the measured transition onset locations. Transition-onset locations correlated well with a constant roughness Reynolds number based on the mean roughness element height. The critical roughness Reynolds number for transition onset determined for flight in CO2 was 223 +/- 25%. This mean value is lower than the critical value of 250 +/- 20% previously-established from tests conducted in air, but within the bounds of the expected measurement uncertainty.

  15. Roughness Based Crossflow Transition Control for a Swept Airfoil Design Relevant to Subsonic Transports

    NASA Technical Reports Server (NTRS)

    Li, Fei; Choudhari, Meelan M.; Carpenter, Mark H.; Malik, Mujeeb R.; Eppink, Jenna; Chang, Chau-Lyan; Streett, Craig L.

    2010-01-01

    A high fidelity transition prediction methodology has been applied to a swept airfoil design at a Mach number of 0.75 and chord Reynolds number of approximately 17 million, with the dual goal of an assessment of the design for the implementation and testing of roughness based crossflow transition control and continued maturation of such methodology in the context of realistic aerodynamic configurations. Roughness based transition control involves controlled seeding of suitable, subdominant crossflow modes in order to weaken the growth of naturally occurring, linearly more unstable instability modes via a nonlinear modification of the mean boundary layer profiles. Therefore, a synthesis of receptivity, linear and nonlinear growth of crossflow disturbances, and high-frequency secondary instabilities becomes desirable to model this form of control. Because experimental data is currently unavailable for passive crossflow transition control for such high Reynolds number configurations, a holistic computational approach is used to assess the feasibility of roughness based control methodology. Potential challenges inherent to this control application as well as associated difficulties in modeling this form of control in a computational setting are highlighted. At high Reynolds numbers, a broad spectrum of stationary crossflow disturbances amplify and, while it may be possible to control a specific target mode using Discrete Roughness Elements (DREs), nonlinear interaction between the control and target modes may yield strong amplification of the difference mode that could have an adverse impact on the transition delay using spanwise periodic roughness elements.

  16. Fourier functional analysis for unsteady aerodynamic modeling

    NASA Technical Reports Server (NTRS)

    Lan, C. Edward; Chin, Suei

    1991-01-01

    A method based on Fourier analysis is developed to analyze the force and moment data obtained in large amplitude forced oscillation tests at high angles of attack. The aerodynamic models for normal force, lift, drag, and pitching moment coefficients are built up from a set of aerodynamic responses to harmonic motions at different frequencies. Based on the aerodynamic models of harmonic data, the indicial responses are formed. The final expressions for the models involve time integrals of the indicial type advocated by Tobak and Schiff. Results from linear two- and three-dimensional unsteady aerodynamic theories as well as test data for a 70-degree delta wing are used to verify the models. It is shown that the present modeling method is accurate in producing the aerodynamic responses to harmonic motions and the ramp type motions. The model also produces correct trend for a 70-degree delta wing in harmonic motion with different mean angles-of-attack. However, the current model cannot be used to extrapolate data to higher angles-of-attack than that of the harmonic motions which form the aerodynamic model. For linear ramp motions, a special method is used to calculate the corresponding frequency and phase angle at a given time. The calculated results from modeling show a higher lift peak for linear ramp motion than for harmonic ramp motion. The current model also shows reasonably good results for the lift responses at different angles of attack.

  17. NDT and E for the surface roughness of marble

    NASA Astrophysics Data System (ADS)

    Avdelidis, Nicolas P.; Moropoulou, Antonia; Delegou, Ekaterini T.; Almond, Darryl P.

    2004-04-01

    Two non-contact NDT and E (non-destructive testing and evaluation) techniques were employed in the inspection of quarry Pentelic marble samples; surface profilometry and infrared thermography. The samples were processed with different roughness treatments (i.e. 60, 80, 100, 220, 400 and 600 mesh) and were evaluated in the laboratory. Furthermore, different surface cleaning treatments were applied to a Pentelic marble surface in situ and then representative samples were collected and evaluated in the laboratory by the means of these two non-destructive techniques. Quantitative analysis of all samples was performed. In particular, the surface roughness parameter Rq at a specific length scale and 3-D micro-topography plots were attained by the use of the laser profilometry scanning approach, whilst temperature - time plots displaying the intensity of pixels as a function of time on the obtained thermal images were also obtained with the intention of distinguishing the influence of the applied roughness treatments. Results indicate that these two non-destructive techniques can be used for the assessment of surface roughness.

  18. The Aerodynamic Properties of Spruce Twig Elements.

    NASA Astrophysics Data System (ADS)

    Grant, Richard Harrison

    1982-03-01

    The drag force and eddy shedding of three-pronged spruce twigs has been measured in a low speed wind tunnel for velocities ranging from 15 to 450 cm/s. The force on the twig at a given flow velocity is affected by the needle density of the twig and the twig orientation and flexibility. Based on the eddy shedding of the twig in 380 cm/s flow, the twig diameter is identified as the important length scale. Using the Strouhal relationship, the effective diameter of the twig is calculated to be approximately equal to the measured needle-tip to needle-tip twig diameter of a single-prong. Based on the twig diameter parallel to the flow, the experimental Re ranged from 200 to 12,000. The twig drag coefficient values suggest three flow regimes over the range of Re studied. These regimes are defined by the trend of the drag coefficient with increasing Re. The onset of the flow regimes is a function of the twig incidence with the regimes shifting up the Re scale with decreasing twig incidence angle. The twig drag response is compared and likened to that of a circular cylinder. In low Re flow the twig acts as a porous circular cylinder with the twig response primarily due to skin friction. In high Re flow the twig acts as a roughened solid circular cylinder with the twig response primarily due to form drag. The difference in the effective diameter and the measured diameter is defined to be the surface roughness. Based on the twig roughness, the critical Reynolds number for spruce twigs is calculated to be about 16,000 with a critical flow velocity of 10 m/s. Using the twig diameter length scale, the drag coefficients for spruce twigs and trees are compared providing a continuum of drag response for Reynolds 200 to 40,000. Based on the circular cylinder model of flow through and around and drag on the spruce twig, whole tree drag measurements can be explained.

  19. Aerodynamics and combustion of axial swirlers

    NASA Astrophysics Data System (ADS)

    Fu, Yongqiang

    A multipoint lean direct injection (LDI) concept was introduced recently in non-premixed combustion to obtain both low NOx emissions and good combustion stability. In this concept, a key feature is the injection of finely atomized fuel into the high-swirling airflow at the combustor dome that provides a homogenous, lean fuel-air mixture. In order to achieve the fine atomization and mixing of the fuel and air quickly and uniformly, a good swirler design should be studied. The focus of this dissertation is to investigate the aerodynamics and combustion of the swirling flow field in a multipoint Lean Direct Injector combustor. A helical axial-vaned swirler with a short internal convergent-divergent venturi was used. Swirlers with various vane angles and fuel nozzle insertion lengths have been designed. Three non-dimensional parameter effects on non-reacting, swirling flow field were studied: swirler number, confinement ratio and Reynolds number. Spray and combustion characteristics on the single swirler were studied to understand the mechanism of fuel-air mixing in this special configuration. Multi-swirler interactions were studied by measuring the confined flow field of a multipoint swirler array with different configurations. Two different swirler arrangements were investigated experimentally, which include a co-swirling array and a counter-swirling array. In order to increase the range of stability of multipoint LDI combustors, an improved design were also conducted. The results show that the degree of swirl and the level of confinement have a clear impact on the mean and turbulent flow fields. The swirling flow fields may also change significantly with the addition of a variety of simulated fuel nozzle insertion lengths. The swirler with short insertion has the stronger swirling flow as compared with the long insertion swirler. Reynolds numbers, with range of current study, will not alter mean and turbulent properties of generated flows. The reaction of the spray

  20. Aerodynamics of intermittent bounds in flying birds

    NASA Astrophysics Data System (ADS)

    Tobalske, Bret W.; Hearn, Jason W. D.; Warrick, Douglas R.

    Flap-bounding is a common flight style in small birds in which flapping phases alternate with flexed-wing bounds. Body lift is predicted to be essential to making this flight style an aerodynamically attractive flight strategy. To elucidate the contributions of the body and tail to lift and drag during the flexed-wing bound phase, we used particle image velocimetry (PIV) and measured properties of the wake of zebra finch (Taeniopygia guttata, N = 5), flying at 6-10 m s- 1 in a variable speed wind tunnel as well as flow around taxidermically prepared specimens (N = 4) mounted on a sting instrumented with force transducers. For the specimens, we varied air velocity from 2 to 12 m s- 1 and body angle from -15∘ to 50∘. The wake of bounding birds and mounted specimens consisted of a pair of counterrotating vortices shed into the wake from the tail, with induced downwash in the sagittal plane and upwash in parasagittal planes lateral to the bird. This wake structure was present even when the tail was entirely removed. We observed good agreement between force measures derived from PIV and force transducers over the range of body angles typically used by zebra finch during forward flight. Body lift:drag (L:D) ratios averaged 1.4 in live birds and varied between 1 and 1.5 in specimens at body angles from 10∘ to 30∘. Peak (L:D) ratio was the same in live birds and specimens (1.5) and was exhibited in specimens at body angles of 15∘ or 20∘, consistent with the lower end of body angles utilized during bounds. Increasing flight velocity in live birds caused a decrease in CL and CD from maximum values of 1.19 and 0.95 during flight at 6 m s- 1 to minimum values of 0.70 and 0.54 during flight at 10 m s- 1. Consistent with delta-wing theory as applied to birds with a graduated-tail shape, trimming the tail to 0 and 50% of normal length reduced L:D ratios and extending tail length to 150% of normal increased L:D ratio. As downward induced velocity is present in the

  1. Aerodynamics of intermittent bounds in flying birds

    NASA Astrophysics Data System (ADS)

    Tobalske, Bret W.; Hearn, Jason W. D.; Warrick, Douglas R.

    2009-05-01

    Flap-bounding is a common flight style in small birds in which flapping phases alternate with flexed-wing bounds. Body lift is predicted to be essential to making this flight style an aerodynamically attractive flight strategy. To elucidate the contributions of the body and tail to lift and drag during the flexed-wing bound phase, we used particle image velocimetry (PIV) and measured properties of the wake of zebra finch ( Taeniopygia guttata, N = 5), flying at 6-10 m s-1 in a variable speed wind tunnel as well as flow around taxidermically prepared specimens ( N = 4) mounted on a sting instrumented with force transducers. For the specimens, we varied air velocity from 2 to 12 m s-1 and body angle from -15° to 50°. The wake of bounding birds and mounted specimens consisted of a pair of counter-rotating vortices shed into the wake from the tail, with induced downwash in the sagittal plane and upwash in parasagittal planes lateral to the bird. This wake structure was present even when the tail was entirely removed. We observed good agreement between force measures derived from PIV and force transducers over the range of body angles typically used by zebra finch during forward flight. Body lift:drag ( L: D) ratios averaged 1.4 in live birds and varied between 1 and 1.5 in specimens at body angles from 10° to 30°. Peak ( L: D) ratio was the same in live birds and specimens (1.5) and was exhibited in specimens at body angles of 15° or 20°, consistent with the lower end of body angles utilized during bounds. Increasing flight velocity in live birds caused a decrease in C L and C D from maximum values of 1.19 and 0.95 during flight at 6 m s-1 to minimum values of 0.70 and 0.54 during flight at 10 m s-1. Consistent with delta-wing theory as applied to birds with a graduated-tail shape, trimming the tail to 0 and 50% of normal length reduced L: D ratios and extending tail length to 150% of normal increased L: D ratio. As downward induced velocity is present in the

  2. The aerodynamics of supersonic parachutes

    SciTech Connect

    Peterson, C.W.

    1987-06-01

    A discussion of the aerodynamics and performance of parachutes flying at supersonic speeds is the focus of this paper. Typical performance requirements for supersonic parachute systems are presented, followed by a review of the literature on supersonic parachute configurations and their drag characteristics. Data from a recent supersonic wind tunnel test series is summarized. The value and limitations of supersonic wind tunnel data on hemisflo and 20-degree conical ribbon parachutes behind several forebody shapes and diameters are discussed. Test techniques were derived which avoided many of the opportunities to obtain erroneous supersonic parachute drag data in wind tunnels. Preliminary correlations of supersonic parachute drag with Mach number, forebody shape and diameter, canopy porosity, inflated canopy diameter and stability are presented. Supersonic parachute design considerations are discussed and applied to a M = 2 parachute system designed and tested at Sandia. It is shown that the performance of parachutes in supersonic flows is a strong function of parachute design parameters and their interactions with the payload wake.

  3. Aerodynamics of Unsteady Sailing Kinetics

    NASA Astrophysics Data System (ADS)

    Keil, Colin; Schutt, Riley; Borshoff, Jennifer; Alley, Philip; de Zegher, Maximilien; Williamson, Chk

    2015-11-01

    In small sailboats, the bodyweight of the sailor is proportionately large enough to induce significant unsteady motion of the boat and sail. Sailors use a variety of kinetic techniques to create sail dynamics which can provide an increment in thrust, thereby increasing the boatspeed. In this study, we experimentally investigate the unsteady aerodynamics associated with two techniques, ``upwind leech flicking'' and ``downwind S-turns''. We explore the dynamics of an Olympic class Laser sailboat equipped with a GPS, IMU, wind sensor, and camera array, sailed expertly by a member of the US Olympic team. The velocity heading of a sailing boat is oriented at an apparent wind angle to the flow. In contrast to classic flapping propulsion, the heaving of the sail section is not perpendicular to the sail's motion through the air. This leads to heave with components parallel and perpendicular to the incident flow. The characteristic motion is recreated in a towing tank where the vortex structures generated by a representative 2-D sail section are observed using Particle Image Velocimetry and the measurement of thrust and lift forces. Amongst other results, we show that the increase in driving force, generated due to heave, is larger for greater apparent wind angles.

  4. Parachute Aerodynamics From Video Data

    NASA Technical Reports Server (NTRS)

    Schoenenberger, Mark; Queen, Eric M.; Cruz, Juan R.

    2005-01-01

    A new data analysis technique for the identification of static and dynamic aerodynamic stability coefficients from wind tunnel test video data is presented. This new technique was applied to video data obtained during a parachute wind tunnel test program conducted in support of the Mars Exploration Rover Mission. Total angle-of-attack data obtained from video images were used to determine the static pitching moment curve of the parachute. During the original wind tunnel test program the static pitching moment curve had been determined by forcing the parachute to a specific total angle-of -attack and measuring the forces generated. It is shown with the new technique that this parachute, when free to rotate, trims at an angle-of-attack two degrees lower than was measured during the forced-angle tests. An attempt was also made to extract pitch damping information from the video data. Results suggest that the parachute is dynamically unstable at the static trim point and tends to become dynamically stable away from the trim point. These trends are in agreement with limit-cycle-like behavior observed in the video. However, the chaotic motion of the parachute produced results with large uncertainty bands.

  5. Aerodynamic characteristics of French consonants

    NASA Astrophysics Data System (ADS)

    Demolin, Didier; Hassid, Sergio; Soquet, Alain

    2001-05-01

    This paper reports some aerodynamic measurements made on French consonants with a group of ten speakers. Speakers were recorded while saying nonsense words in phrases such as papa, dis papa encore. The nonsense words in the study combined each of the French consonants with three vowels /i, a, u/ to from two syllables words with the first syllable being the same as the second. In addition to the audio signal, recordings were made of the oral airflow, the pressure of the air in the pharynx above the vocal folds and the pressure of the air in the trachea just below the vocal folds. The pharyngeal pressure was recorded via a catheter (i.d. 5 mm) passed through the nose so that its open end could be seen in the pharynx below the uvula. The subglottal pressure was recorded via a tracheal puncture between the first and the second rings of the trachea or between the cricoid cartilage and the first tracheal ring. Results compare subglottal presssure, pharyngeal pressure, and airflow values. Comparisons are made between values obtained with male and female subjects and various types of consonants (voiced versus voiceless at the same place of articulation, stops, fricatives, and nasals).

  6. Skylon Aerodynamics and SABRE Plumes

    NASA Technical Reports Server (NTRS)

    Mehta, Unmeel; Afosmis, Michael; Bowles, Jeffrey; Pandya, Shishir

    2015-01-01

    An independent partial assessment is provided of the technical viability of the Skylon aerospace plane concept, developed by Reaction Engines Limited (REL). The objectives are to verify REL's engineering estimates of airframe aerodynamics during powered flight and to assess the impact of Synergetic Air-Breathing Rocket Engine (SABRE) plumes on the aft fuselage. Pressure lift and drag coefficients derived from simulations conducted with Euler equations for unpowered flight compare very well with those REL computed with engineering methods. The REL coefficients for powered flight are increasingly less acceptable as the freestream Mach number is increased beyond 8.5, because the engineering estimates did not account for the increasing favorable (in terms of drag and lift coefficients) effect of underexpanded rocket engine plumes on the aft fuselage. At Mach numbers greater than 8.5, the thermal environment around the aft fuselage is a known unknown-a potential design and/or performance risk issue. The adverse effects of shock waves on the aft fuselage and plumeinduced flow separation are other potential risks. The development of an operational reusable launcher from the Skylon concept necessitates the judicious use of a combination of engineering methods, advanced methods based on required physics or analytical fidelity, test data, and independent assessments.

  7. Coupling of WRF meteorological model to WAM spectral wave model through sea surface roughness at the Balearic Sea: impact on wind and wave forecasts

    NASA Astrophysics Data System (ADS)

    Tolosana-Delgado, R.; Soret, A.; Jorba, O.; Baldasano, J. M.; Sánchez-Arcilla, A.

    2012-04-01

    Meteorological models, like WRF, usually describe the earth surface characteristics by tables that are function of land-use. The roughness length (z0) is an example of such approach. However, over sea z0 is modeled by the Charnock (1955) relation, linking the surface friction velocity u*2 with the roughness length z0 of turbulent air flow, z0 = α-u2* g The Charnock coefficient α may be considered a measure of roughness. For the sea surface, WRF considers a constant roughness α = 0.0185. However, there is evidence that sea surface roughness should depend on wave energy (Donelan, 1982). Spectral wave models like WAM, model the evolution and propagation of wave energy as a function of wind, and include a richer sea surface roughness description. Coupling WRF and WAM is thus a common way to improve the sea surface roughness description of WRF. WAM is a third generation wave model, solving the equation of advection of wave energy subject to input/output terms of: wind growth, energy dissipation and resonant non-linear wave-wave interactions. Third generation models work on the spectral domain. WAM considers the Charnock coefficient α a complex yet known function of the total wind input term, which depends on the wind velocity and on the Charnock coefficient again. This is solved iteratively (Janssen et al., 1990). Coupling of meteorological and wave models through a common Charnock coefficient is operationally done in medium-range met forecasting systems (e.g., at ECMWF) though the impact of coupling for smaller domains is not yet clearly assessed (Warner et al, 2010). It is unclear to which extent the additional effort of coupling improves the local wind and wave fields, in comparison to the effects of other factors, like e.g. a better bathymetry and relief resolution, or a better circulation information which might have its influence on local-scale meteorological processes (local wind jets, local convection, daily marine wind regimes, etc.). This work, within the

  8. Roughness of undoped graphene and its short-range induced gauge field

    NASA Astrophysics Data System (ADS)

    Abedpour, N.; Neek-Amal, M.; Asgari, Reza; Shahbazi, F.; Nafari, N.; Tabar, M. Reza Rahimi

    2007-11-01

    We present both numerical and analytical studies of graphene roughness with a crystal structure including 500×500 atoms. The roughness can effectively result in a random gauge field and has important consequences for its electronic structure. Our results show that its height fluctuations in small scales have a scaling behavior with a temperature dependent roughness exponent in the interval of 0.6<χ<0.7 . The correlation function of height fluctuations depends on temperature with a characteristic length scale of ≈90Å (at room temperature). We show that the correlation function of the induced gauge field has a short-range nature with a correlation length of about ≃2-3Å . We also treat the problem analytically by using the Martin-Siggia-Rose method. The renormalization group flows did not yield any delocalized-localized transition arising from the graphene roughness. Our results are in good agreement with recent experimental observations.

  9. Unsteady Aerodynamic Force Sensing from Measured Strain

    NASA Technical Reports Server (NTRS)

    Pak, Chan-Gi

    2016-01-01

    A simple approach for computing unsteady aerodynamic forces from simulated measured strain data is proposed in this study. First, the deflection and slope of the structure are computed from the unsteady strain using the two-step approach. Velocities and accelerations of the structure are computed using the autoregressive moving average model, on-line parameter estimator, low-pass filter, and a least-squares curve fitting method together with analytical derivatives with respect to time. Finally, aerodynamic forces over the wing are computed using modal aerodynamic influence coefficient matrices, a rational function approximation, and a time-marching algorithm. A cantilevered rectangular wing built and tested at the NASA Langley Research Center (Hampton, Virginia, USA) in 1959 is used to validate the simple approach. Unsteady aerodynamic forces as well as wing deflections, velocities, accelerations, and strains are computed using the CFL3D computational fluid dynamics (CFD) code and an MSC/NASTRAN code (MSC Software Corporation, Newport Beach, California, USA), and these CFL3D-based results are assumed as measured quantities. Based on the measured strains, wing deflections, velocities, accelerations, and aerodynamic forces are computed using the proposed approach. These computed deflections, velocities, accelerations, and unsteady aerodynamic forces are compared with the CFL3D/NASTRAN-based results. In general, computed aerodynamic forces based on the lifting surface theory in subsonic speeds are in good agreement with the target aerodynamic forces generated using CFL3D code with the Euler equation. Excellent aeroelastic responses are obtained even with unsteady strain data under the signal to noise ratio of -9.8dB. The deflections, velocities, and accelerations at each sensor location are independent of structural and aerodynamic models. Therefore, the distributed strain data together with the current proposed approaches can be used as distributed deflection

  10. Prediction of reduced thermal conductivity in nano-engineered rough semiconductor nanowires

    NASA Astrophysics Data System (ADS)

    Martin, Pierre N.; Aksamija, Zlatan; Pop, Eric; Ravaioli, Umberto

    2009-11-01

    We explore phonon decay processes necessary to the design of efficient rough semiconductor nanowire (NW) thermoelectric devices. A novel approach to surface roughness-limited thermal conductivity of Si, Ge, and GaAs NW with diameter D < 500 nm is presented. In particular, a frequency-dependent phonon scattering rate is computed from perturbation theory and related to a description of the surface through the root-mean-square roughness height Δ and autocovariance length L. Using a full phonon dispersion relation, the thermal conductivity varies quadratically with diameter and roughness as (D/Δ)2. Computed results are in agreement with experimental data, and predict remarkably low thermal conductivity below 1 W/m/K in rough-etched 56 nm Ge and GaAs NW at room temperature.

  11. The Long Range Persistence of Wakes Behind a Row of Roughness Elements

    NASA Technical Reports Server (NTRS)

    Goldstein, M. E.; Sescu, Adrian; Duck, Peter W.; Choudhari, Meelan

    2010-01-01

    We consider a periodic array of relatively small roughness elements whose spanwise separation is of the order of the local boundary-layer thickness and construct a local asymptotic high-Reynolds-number solution that is valid in the vicinity of the roughness. The resulting flow decays on the very short streamwise length scale of the roughness, but the solution eventually becomes invalid at large downstream distances and a new solution has to be constructed in the downstream region. This latter result shows that the roughness-generated wakes can persist over very long streamwise distances, which are much longer than the distance between the roughness elements and the leading edge. Detailed numerical results are given for the far wake structure.

  12. Modeling Powered Aerodynamics for the Orion Launch Abort Vehicle Aerodynamic Database

    NASA Technical Reports Server (NTRS)

    Chan, David T.; Walker, Eric L.; Robinson, Philip E.; Wilson, Thomas M.

    2011-01-01

    Modeling the aerodynamics of the Orion Launch Abort Vehicle (LAV) has presented many technical challenges to the developers of the Orion aerodynamic database. During a launch abort event, the aerodynamic environment around the LAV is very complex as multiple solid rocket plumes interact with each other and the vehicle. It is further complicated by vehicle separation events such as between the LAV and the launch vehicle stack or between the launch abort tower and the crew module. The aerodynamic database for the LAV was developed mainly from wind tunnel tests involving powered jet simulations of the rocket exhaust plumes, supported by computational fluid dynamic simulations. However, limitations in both methods have made it difficult to properly capture the aerodynamics of the LAV in experimental and numerical simulations. These limitations have also influenced decisions regarding the modeling and structure of the aerodynamic database for the LAV and led to compromises and creative solutions. Two database modeling approaches are presented in this paper (incremental aerodynamics and total aerodynamics), with examples showing strengths and weaknesses of each approach. In addition, the unique problems presented to the database developers by the large data space required for modeling a launch abort event illustrate the complexities of working with multi-dimensional data.

  13. 1999 NASA High-Speed Research Program Aerodynamic Performance Workshop. Volume 1; Configuration Aerodynamics

    NASA Technical Reports Server (NTRS)

    Hahne, David E. (Editor)

    1999-01-01

    NASA's High-Speed Research Program sponsored the 1999 Aerodynamic Performance Technical Review on February 8-12, 1999 in Anaheim, California. The review was designed to bring together NASA and industry High-Speed Civil Transport (HSCT) Aerodynamic Performance technology development participants in the areas of Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High Lift, and Flight Controls. The review objectives were to (1) report the progress and status of HSCT aerodynamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientists and engineers working on HSCT aerodynamics. In particular, single and midpoint optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT simulation results were presented, along with executive summaries for all the Aerodynamic Performance technology areas. The HSR Aerodynamic Performance Technical Review was held simultaneously with the annual review of the following airframe technology areas: Materials and Structures, Environmental Impact, Flight Deck, and Technology Integration. Thus, a fourth objective of the Review was to promote synergy between the Aerodynamic Performance technology area and the other technology areas of the HSR Program. This Volume 1/Part 2 publication covers the design optimization and testing sessions.

  14. 1998 NASA High-Speed Research Program Aerodynamic Performance Workshop. Volume 1; Configuration Aerodynamics

    NASA Technical Reports Server (NTRS)

    McMillin, S. Naomi (Editor)

    1999-01-01

    NASA's High-Speed Research Program sponsored the 1998 Aerodynamic Performance Technical Review on February 9-13, in Los Angeles, California. The review was designed to bring together NASA and industry HighSpeed Civil Transport (HSCT) Aerodynamic Performance technology development participants in areas of. Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High-Lift, and Flight Controls. The review objectives were to: (1) report the progress and status of HSCT aerodynamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientists and engineers working HSCT aerodynamics. In particular, single and multi-point optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT simulation results were presented along with executive summaries for all the Aerodynamic Performance technology areas. The HSR Aerodynamic Performance Technical Review was held simultaneously with the annual review of the following airframe technology areas: Materials and Structures, Environmental Impact, Flight Deck, and Technology Integration. Thus, a fourth objective of the Review was to promote synergy between the Aerodynamic Performance technology area and the other technology areas of the HSR Program.

  15. 1998 NASA High-Speed Research Program Aerodynamic Performance Workshop. Volume 1; Configuration Aerodynamics

    NASA Technical Reports Server (NTRS)

    McMillin, S. Naomi (Editor)

    1999-01-01

    NASA's High-Speed Research Program sponsored the 1998 Aerodynamic Performance Technical Review on February 9-13, in Los Angeles, California. The review was designed to bring together NASA and industry High-Speed Civil Transport (HSCT) Aerodynamic Performance technology development participants in areas of Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High-Lift, and Flight Controls. The review objectives were to (1) report the progress and status of HSCT aerodynamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientists and engineers working HSCT aerodynamics. In particular, single and multi-point optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT simulation results were presented along with executive summaries for all the Aerodynamic Performance technology areas. The HSR Aerodynamic Performance Technical Review was held simultaneously with the annual review of the following airframe technology areas: Materials and Structures, Environmental Impact, Flight Deck, and Technology Integration. Thus, a fourth objective of the Review was to promote synergy between the Aerodynamic Performance technology area and the other technology areas of the HSR Program.

  16. Transient platoon aerodynamics and bluff body flows

    NASA Astrophysics Data System (ADS)

    Tsuei, Lun

    There are two components of this experimental work: transient vehicle platoon aerodynamics and bluff-body flows. The transient aerodynamic effects in a four-vehicle platoon during passing maneuvers and in-line oscillations are investigated. A vehicle model is moved longitudinally parallel to a four-car platoon to simulate passing maneuvers. The drag and side forces experienced by each platoon member are measured using strain gauge balances. The resulting data are presented as dimensionless coefficients. It is shown that each car in the platoon experiences a repulsive side force when the passing vehicle is in the neighborhood of its rear half. The side force reverses its direction and becomes an attractive force when the passing vehicle moves to the neighborhood of its front half. The drag force experienced by each platoon member is increased when the passing vehicle is in its proximity. The effects of the lateral spacing and relative velocity between the platoon and the passing vehicle, as well as the shape of the passing vehicle, are also investigated. Similar trends are observed in simulations of both a vehicle passing a platoon and a platoon overtaking a vehicle. During the in-line oscillation experiments, one of the four platoon members is forced to undergo longitudinal periodic motions. The drag force experienced by each platoon member is determined simultaneously during the oscillations. The effects of the location of the oscillating vehicle, the shape of the vehicles and the displacement and velocity amplitudes of the oscillation are examined. The results from the transient conditions are compared to those from the steady tests in the same setup. In the case of a four-car platoon, the drag variations experienced by the vehicles adjacent to the oscillating vehicle are discussed using a cavity model. It is found that when the oscillating car moves forward and approaches its upstream neighbor, itself and its downstream neighbor experiences an increased drag

  17. Influence of surface roughness on gecko adhesion.

    PubMed

    Huber, Gerrit; Gorb, Stanislav N; Hosoda, Naoe; Spolenak, Ralph; Arzt, Eduard

    2007-07-01

    In this study we show the influence of surface roughness on gecko adhesion on both the nano- and macroscales. We present experimental data for the force necessary to pull off single spatulae from hard rough substrates and also detail observations on living geckos clinging to various surfaces. Both experiments consistently show that the effective adhesion shows a minimum for a root mean square roughness ranging from 100 to 300nm.

  18. Aerodynamic Parameter Identification of a Venus Lander

    NASA Astrophysics Data System (ADS)

    Sykes, Robert A.

    An analysis was conducted to identify the parameters of an aerodynamic model for a Venus lander based on experimental free-flight data. The experimental free-flight data were collected in the NASA Langley 20-ft Vertical Spin Tunnel with a 25-percent Froude-scaled model. The experimental data were classified based on the wind tunnel run type: runs where the lander model was unperturbed over the course of the run, and runs were the model was perturbed (principally in pitch, yaw, and roll) by the wind tunnel operator. The perturbations allow for data to be obtained at higher wind angles and rotation rates than those available from the unperturbed data. The model properties and equations of motion were used to determine experimental values for the aerodynamic coefficients. An aerodynamic model was selected using a priori knowledge of axisymmetric blunt entry vehicles. The least squares method was used to estimate the aerodynamic parameters. Three sets of results were obtained from the following data sets: perturbed, unperturbed, and the combination of both. The combined data set was selected for the final set of aerodynamic parameters based on the quality of the results. The identified aerodynamic parameters are consistent with that of the static wind tunnel data. Reconstructions, of experimental data not used in the parameter identification analyses, achieved similar residuals as those with data used to identify the parameters. Simulations of the experimental data, using the identified parameters, indicate that the aerodynamic model used is incapable of replicating the limit cycle oscillations with stochastic peak amplitudes observed during the test.

  19. 1997 NASA High-Speed Research Program Aerodynamic Performance Workshop. Volume 1; Configuration Aerodynamics

    NASA Technical Reports Server (NTRS)

    Baize, Daniel G. (Editor)

    1999-01-01

    The High-Speed Research Program and NASA Langley Research Center sponsored the NASA High-Speed Research Program Aerodynamic Performance Workshop on February 25-28, 1997. The workshop was designed to bring together NASA and industry High-Speed Civil Transport (HSCT) Aerodynamic Performance technology development participants in area of Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High-Lift, Flight Controls, Supersonic Laminar Flow Control, and Sonic Boom Prediction. The workshop objectives were to (1) report the progress and status of HSCT aerodyamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientist and engineers working HSCT aerodynamics. In particular, single- and multi-point optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT Motion Simulator results were presented along with executive summaries for all the Aerodynamic Performance technology areas.

  20. The relationship between radar scattering and surface roughness of lunar volcanic features

    NASA Astrophysics Data System (ADS)

    Jawin, Erica R.; Kiefer, Walter S.; Fassett, Caleb I.; Bussey, D. Benjamin J.; Cahill, Joshua T. S.; Dyar, M. Darby; Lawrence, Samuel J.; Spudis, Paul D.

    2014-11-01

    Lunar roughness measurements derived from the Lunar Orbiter Laser Altimeter are compared to 12.6 cm wavelength radar data collected by the Miniature Radio Frequency instrument and 70 cm wavelength radar data collected by the Arecibo Observatory. These data are compared to assess how surface and subsurface roughness are correlated and affected by parameters including age and composition at length scales between 0.1 and 100 m. A range of features are analyzed including volcanic domes (Marius Hills, Rümker Hills, Gruithuisen, and Mairan Domes); mare (Imbrium, Serenitatis, and Oceanus Procellarum); pyroclastic dark mantle deposits (Sinus Aestuum, Sulpicius Gallus, and Mare Vaporum); and two young craters (Copernicus and Tycho). Statistically significant positive correlations exist between topographic roughness and both P- and S-band circular polarization ratios. The strongest correlation is observed at the longest length scales. Correlations weaken as length scales become less similar, potentially due to distinct processes controlling surface modification. Roughness is not significantly correlated with local slope. Although the Marius Hills are compositionally distinct from the Gruithuisen and Mairan domes, they are indistinguishable in roughness characteristics. Conversely, the Rümker Hills, mare, and dark mantle deposits are smoother at the length scales examined, possibly due to fine-grained mantling of regolith or pyroclastic deposits. The floor and ejecta of Tycho are the roughest surfaces measured in this study, while the floor and ejecta of Copernicus overlap the roughness distribution of the volcanic features. This study shows that many factors control the evolution of roughness over time on various length scales.

  1. Rough set models of Physarum machines

    NASA Astrophysics Data System (ADS)

    Pancerz, Krzysztof; Schumann, Andrew

    2015-04-01

    In this paper, we consider transition system models of behaviour of Physarum machines in terms of rough set theory. A Physarum machine, a biological computing device implemented in the plasmodium of Physarum polycephalum (true slime mould), is a natural transition system. In the behaviour of Physarum machines, one can notice some ambiguity in Physarum motions that influences exact anticipation of states of machines in time. To model this ambiguity, we propose to use rough set models created over transition systems. Rough sets are an appropriate tool to deal with rough (ambiguous, imprecise) concepts in the universe of discourse.

  2. Simplified Approach to Predicting Rough Surface Transition

    NASA Technical Reports Server (NTRS)

    Boyle, Robert J.; Stripf, Matthias

    2009-01-01

    Turbine vane heat transfer predictions are given for smooth and rough vanes where the experimental data show transition moving forward on the vane as the surface roughness physical height increases. Consiste nt with smooth vane heat transfer, the transition moves forward for a fixed roughness height as the Reynolds number increases. Comparison s are presented with published experimental data. Some of the data ar e for a regular roughness geometry with a range of roughness heights, Reynolds numbers, and inlet turbulence intensities. The approach ta ken in this analysis is to treat the roughness in a statistical sense , consistent with what would be obtained from blades measured after e xposure to actual engine environments. An approach is given to determ ine the equivalent sand grain roughness from the statistics of the re gular geometry. This approach is guided by the experimental data. A roughness transition criterion is developed, and comparisons are made with experimental data over the entire range of experimental test co nditions. Additional comparisons are made with experimental heat tran sfer data, where the roughness geometries are both regular as well a s statistical. Using the developed analysis, heat transfer calculatio ns are presented for the second stage vane of a high pressure turbine at hypothetical engine conditions.

  3. Influence of inflow angle on flexible flap aerodynamic performance

    NASA Astrophysics Data System (ADS)

    Y Zhao, H.; Ye, Z.; Li, Z. M.; Li, C.

    2013-12-01

    Large scale wind turbines have larger blade lengths and weights, which creates new challenges for blade design. This paper selects NREL S809 airfoil, and uses the parameterized technology to realize the flexible trailing edge deformation, researches the dynamic aerodynamic characteristics in the process of continuous flexible deformation, analyses the influence of inflow angle on flexible flap aerodynamic performance, in order to further realize the flexible wind turbine blade design and provides some references for the active control scheme. The results show that compared with the original airfoil, proper trailing edge deformation can improve the lift coefficient, reduce the drag coefficient, and thereby more efficiently realize flow field active control. With inflow angle increases, dynamic lift-drag coefficient hysteresis loop shape deviation occurs, even turns into different shapes. Appropriate swing angle can improve the flap lift coefficient, but may cause early separation of flow. To improve the overall performance of wind turbine blades, different angular control should be used at different cross sections, in order to achieve the best performance.

  4. Aerodynamics of saccate pollen and its implications for wind pollination.

    PubMed

    Schwendemann, Andrew B; Wang, George; Mertz, Meredith L; McWilliams, Ryan T; Thatcher, Scott L; Osborn, Jeffrey M

    2007-08-01

    Pollen grains of many wind-pollinated plants contain 1-3 air-filled bladders, or sacci. Sacci are thought to help orient the pollen grain in the pollination droplet. Sacci also increase surface area of the pollen grain, yet add minimal mass, thereby increasing dispersal distance; however, this aerodynamic hypothesis has not been tested in a published study. Using scanning electron and transmission electron microscopy, mathematical modeling, and the saccate pollen of three extant conifers with structurally different pollen grains (Pinus, Falcatifolium, Dacrydium), we developed a computational model to investigate pollen flight. The model calculates terminal settling velocity based on structural characters of the pollen grain, including lengths, widths, and depths of the main body and sacci; angle of saccus rotation; and thicknesses of the saccus wall, endoreticulations, intine, and exine. The settling speeds predicted by the model were empirically validated by stroboscopic photography. This study is the first to quantitatively demonstrate the adaptive significance of sacci for the aerodynamics of wind pollination. Modeling pollen both with and without sacci indicated that sacci can reduce pollen settling speeds, thereby increasing dispersal distance, with the exception of pollen grains having robust endoreticulations and those with thick saccus walls. Furthermore, because the mathematical model is based on structural characters and error propagation methods show that the model yields valid results when sample sizes are small, the flight dynamics of fossil pollen can be investigated. Several fossils were studied, including bisaccate (Pinus, Pteruchus, Caytonanthus), monosaccate (Gothania), and nonsaccate (Monoletes) pollen types.

  5. Influence of compound bedforms on hydraulic roughness in a tidal environment

    NASA Astrophysics Data System (ADS)

    Lefebvre, Alice; Ernstsen, Verner B.; Winter, Christian

    2011-12-01

    The effect exerted by the seabed morphology on the flow is commonly expressed by the hydraulic roughness, a fundamental parameter in the understanding and simulation of hydro- and sediment dynamics in coastal areas. This study quantifies the hydraulic roughness of large compound bedforms throughout a tidal cycle and investigates its relationship to averaged bedform dimensions. Consecutive measurements with an acoustic Doppler current profiler and a multibeam echosounder were carried out in the Jade tidal channel (North Sea, Germany) along large compound bedforms comprising ebb-oriented primary bedforms with superimposed smaller secondary bedforms. Spatially averaged velocity profiles produced log-linear relationships which were used to calculate roughness lengths. During the flood phase, the velocity profiles were best described by a single log-linear fit related to the roughness created by the secondary bedforms. During the ebb phase, the velocity profiles were segmented, showing the existence of at least two boundary layers: a lower one scaling with the superimposed secondary bedforms and an upper one scaling with the ebb-oriented primary bedforms. The drag induced by the primary bedform during the ebb phase is suggested to be related to flow expansion, separation, and recirculation on the downstream side of the bedform. Three existing formulas were tested to predict roughness lengths from the local bedform dimensions. All three predicted the right order of magnitude for the average roughness length but failed to predict its variation over the tidal cycle.

  6. Investigation of the influence of a step change in surface roughness on turbulent heat transfer

    NASA Technical Reports Server (NTRS)

    Taylor, Robert P.; Coleman, Hugh W.; Taylor, J. Keith; Hosni, M. H.

    1991-01-01

    The use is studied of smooth heat flux gages on the otherwise very rough SSME fuel pump turbine blades. To gain insights into behavior of such installations, fluid mechanics and heat transfer data were collected and are reported for a turbulent boundary layer over a surface with a step change from a rough surface to a smooth surface. The first 0.9 m length of the flat plate test surface was roughened with 1.27 mm hemispheres in a staggered, uniform array spaced 2 base diameters apart. The remaining 1.5 m length was smooth. The effect of the alignment of the smooth surface with respect to the rough surface was also studied by conducting experiments with the smooth surface aligned with the bases or alternatively with the crests of the roughness elements. Stanton number distributions, skin friction distributions, and boundary layer profiles of temperature and velocity are reported and are compared to previous data for both all rough and all smooth wall cases. The experiments show that the step change from rough to smooth has a dramatic effect on the convective heat transfer. It is concluded that use of smooth heat flux gages on otherwise rough surfaces could cause large errors.

  7. Comparative study of line roughness metrics of chemically amplified and inorganic resists for EUV

    NASA Astrophysics Data System (ADS)

    Fallica, Roberto; Buitrago, Elizabeth; Ekinci, Yasin

    2016-03-01

    We present a comprehensive study of the roughness metrics of different resists. Dense line/space (L/S) images of polymethyl methacrylate (PMMA), hydrogen silsesquioxane (HSQ), different chemically amplified resists (CARs), and metal oxide based resists have been patterned by extreme ultraviolet interference lithography (EUV-IL). The three line width roughness metrics: r.m.s. value σLWR, correlation length ξ and roughness exponent α, were measured by metrological analysis of top down SEM images and compared for the different resists imaged here. It was found, that all metrics are required to fully describe the roughness of each resist. Our measurements indicate that few of the state-of-the- art resists tested here can meet the International Technology Roadmap for Semiconductors (ITRS) requirements for σLWR. The correlation length ξ has been found to be considerably higher in polymer-based materials in comparison to non-polymers. The roughness exponent α, interpreted using the concept of fractal geometry, is mainly affected by acid diffusion in CARs where it produces line edges with a higher complexity than in non-CAR resists. These results indicate that different resists platforms show very different LWR resist metrics and roughness is not only manifested in the σLWR but in all parameters. Therefore, all roughness metrics should be taken into account in the performance comparison of the resist, since they can have a substantial impact on the device performance.

  8. Aerodynamic heating in hypersonic flows

    NASA Technical Reports Server (NTRS)

    Reddy, C. Subba

    1993-01-01

    Aerodynamic heating in hypersonic space vehicles is an important factor to be considered in their design. Therefore the designers of such vehicles need reliable heat transfer data in this respect for a successful design. Such data is usually produced by testing the models of hypersonic surfaces in wind tunnels. Most of the hypersonic test facilities at present are conventional blow-down tunnels whose run times are of the order of several seconds. The surface temperatures on such models are obtained using standard techniques such as thin-film resistance gages, thin-skin transient calorimeter gages and coaxial thermocouple or video acquisition systems such as phosphor thermography and infrared thermography. The data are usually reduced assuming that the model behaves like a semi-infinite solid (SIS) with constant properties and that heat transfer is by one-dimensional conduction only. This simplifying assumption may be valid in cases where models are thick, run-times short, and thermal diffusivities small. In many instances, however, when these conditions are not met, the assumption may lead to significant errors in the heat transfer results. The purpose of the present paper is to investigate this aspect. Specifically, the objectives are as follows: (1) to determine the limiting conditions under which a model can be considered a semi-infinite body; (2) to estimate the extent of errors involved in the reduction of the data if the models violate the assumption; and (3) to come up with correlation factors which when multiplied by the results obtained under the SIS assumption will provide the results under the actual conditions.

  9. The aerodynamics of insect flight.

    PubMed

    Sane, Sanjay P

    2003-12-01

    The flight of insects has fascinated physicists and biologists for more than a century. Yet, until recently, researchers were unable to rigorously quantify the complex wing motions of flapping insects or measure the forces and flows around their wings. However, recent developments in high-speed videography and tools for computational and mechanical modeling have allowed researchers to make rapid progress in advancing our understanding of insect flight. These mechanical and computational fluid dynamic models, combined with modern flow visualization techniques, have revealed that the fluid dynamic phenomena underlying flapping flight are different from those of non-flapping, 2-D wings on which most previous models were based. In particular, even at high angles of attack, a prominent leading edge vortex remains stably attached on the insect wing and does not shed into an unsteady wake, as would be expected from non-flapping 2-D wings. Its presence greatly enhances the forces generated by the wing, thus enabling insects to hover or maneuver. In addition, flight forces are further enhanced by other mechanisms acting during changes in angle of attack, especially at stroke reversal, the mutual interaction of the two wings at dorsal stroke reversal or wing-wake interactions following stroke reversal. This progress has enabled the development of simple analytical and empirical models that allow us to calculate the instantaneous forces on flapping insect wings more accurately than was previously possible. It also promises to foster new and exciting multi-disciplinary collaborations between physicists who seek to explain the phenomenology, biologists who seek to understand its relevance to insect physiology and evolution, and engineers who are inspired to build micro-robotic insects using these principles. This review covers the basic physical principles underlying flapping flight in insects, results of recent experiments concerning the aerodynamics of insect flight, as well

  10. Smoothening in thin-film deposition on rough substrates.

    PubMed

    de Assis, T A; Reis, F D A Aarão

    2015-11-01

    The evolution of the surface roughness W of a thin film deposited on a rough substrate is studied with a model of temperature-activated adatom diffusion, irreversible lateral aggregation, and no step energy barrier, in which the main parameter is the ratio R of diffusion and deposition rates. At sufficiently low temperatures (R≲10), the average number of adatom steps after adsorption is very small, thus W monotonically increases with time t due to an approximately uncorrelated deposition at short times. If the temperature is not very low (R∼10(3) or larger), smoothening occurs at short times and the Villain-Lai-Das Sarma (VLDS) growth equation governs the long time roughening, which is attained after a crossover time t(c) that increases with the correlation length ξ(i) of the substrate. Scaling arguments predict the dependence of t(c) on temperature and on the substrate production time and the scaling relation for the difference between the roughness of films deposited on rough and flat substrates, in good agreement with numerical results. The effect of temperature is not a direct extension of previous results on flat substrates because the short wavelength fluctuations delay the formation of terraces. For this reason, the effective energy obtained from the dependence of t(c) on R is 40% of the energy of activated adatom diffusion. A scaling law for the initial smoothening is proposed as W/W(i)=Ψ(t/t(c1)), with a crossover time t(c1)≡R(-θ)ξ(i)(z), where W(i) is the substrate roughness, θ≈0.4, and z is the VLDS dynamical exponent. It provides good data collapse if W is not very small and is suggested to be tested experimentally. PMID:26651710

  11. Missile Aerodynamics for Ascent and Re-entry

    NASA Technical Reports Server (NTRS)

    Watts, Gaines L.; McCarter, James W.

    2012-01-01

    Aerodynamic force and moment equations are developed for 6-DOF missile simulations of both the ascent phase of flight and a tumbling re-entry. The missile coordinate frame (M frame) and a frame parallel to the M frame were used for formulating the aerodynamic equations. The missile configuration chosen as an example is a cylinder with fixed fins and a nose cone. The equations include both the static aerodynamic coefficients and the aerodynamic damping derivatives. The inclusion of aerodynamic damping is essential for simulating a tumbling re-entry. Appended information provides insight into aerodynamic damping.

  12. Bat flight: aerodynamics, kinematics and flight morphology.

    PubMed

    Hedenström, Anders; Johansson, L Christoffer

    2015-03-01

    Bats evolved the ability of powered flight more than 50 million years ago. The modern bat is an efficient flyer and recent research on bat flight has revealed many intriguing facts. By using particle image velocimetry to visualize wake vortices, both the magnitude and time-history of aerodynamic forces can be estimated. At most speeds the downstroke generates both lift and thrust, whereas the function of the upstroke changes with forward flight speed. At hovering and slow speed bats use a leading edge vortex to enhance the lift beyond that allowed by steady aerodynamics and an inverted wing during the upstroke to further aid weight support. The bat wing and its skeleton exhibit many features and control mechanisms that are presumed to improve flight performance. Whereas bats appear aerodynamically less efficient than birds when it comes to cruising flight, they have the edge over birds when it comes to manoeuvring. There is a direct relationship between kinematics and the aerodynamic performance, but there is still a lack of knowledge about how (and if) the bat controls the movements and shape (planform and camber) of the wing. Considering the relatively few bat species whose aerodynamic tracks have been characterized, there is scope for new discoveries and a need to study species representing more extreme positions in the bat morphospace. PMID:25740899

  13. Aerodynamics of high-speed railway train

    NASA Astrophysics Data System (ADS)

    Raghunathan, Raghu S.; Kim, H.-D.; Setoguchi, T.

    2002-10-01

    Railway train aerodynamic problems are closely associated with the flows occurring around train. Much effort to speed up the train system has to date been paid on the improvement of electric motor power rather than understanding the flow around the train. This has led to larger energy losses and performance deterioration of the train system, since the flows around train are more disturbed due to turbulence of the increased speed of the train, and consequently the flow energies are converted to aerodynamic drag, noise and vibrations. With the speed-up of train, many engineering problems which have been neglected at low train speeds, are being raised with regard to aerodynamic noise and vibrations, impulse forces occurring as two trains intersect each other, impulse wave at the exit of tunnel, ear discomfort of passengers inside train, etc. These are of major limitation factors to the speed-up of train system. The present review addresses the state of the art on the aerodynamic and aeroacoustic problems of high-speed railway train and highlights proper control strategies to alleviate undesirable aerodynamic problems of high-speed railway train system.

  14. Bat flight: aerodynamics, kinematics and flight morphology.

    PubMed

    Hedenström, Anders; Johansson, L Christoffer

    2015-03-01

    Bats evolved the ability of powered flight more than 50 million years ago. The modern bat is an efficient flyer and recent research on bat flight has revealed many intriguing facts. By using particle image velocimetry to visualize wake vortices, both the magnitude and time-history of aerodynamic forces can be estimated. At most speeds the downstroke generates both lift and thrust, whereas the function of the upstroke changes with forward flight speed. At hovering and slow speed bats use a leading edge vortex to enhance the lift beyond that allowed by steady aerodynamics and an inverted wing during the upstroke to further aid weight support. The bat wing and its skeleton exhibit many features and control mechanisms that are presumed to improve flight performance. Whereas bats appear aerodynamically less efficient than birds when it comes to cruising flight, they have the edge over birds when it comes to manoeuvring. There is a direct relationship between kinematics and the aerodynamic performance, but there is still a lack of knowledge about how (and if) the bat controls the movements and shape (planform and camber) of the wing. Considering the relatively few bat species whose aerodynamic tracks have been characterized, there is scope for new discoveries and a need to study species representing more extreme positions in the bat morphospace.

  15. An integrated aerodynamic/propulsion study for generic aero-space planes based on waverider concepts

    NASA Technical Reports Server (NTRS)

    Rasmussen, M. L.; Emanuel, George

    1989-01-01

    The design of a unified aero-space plane based on waverider technology is analyzed. The overall aerodynamic design and performance of an aero-space plane are discussed in terms of the forebody, scramjet, and afterbody. Other subjects considered in the study are combustion/nozzle optimization, the idealized tip-to-tail waverider model, and the two-dimensional minimum length nozzle. Charts and graphs are provided to show the results of the preliminary investigations.

  16. Flap noise and aerodynamic results for model QCSEE over-the-wing configurations

    NASA Technical Reports Server (NTRS)

    Olsen, W.; Burns, R.; Groesbeck, D. E.

    1977-01-01

    Noise spectra in three dimensions and aerodynamic data were measured for a model of the NASA quiet clean short-haul experimental engine (QCSEE) over-the-wing configuration. The effects of flap length, nozzle exhaust velocity, and nozzle geometry were determined using a single nozzle and wing-flap segment. The scaled-up model data is representative of full scale flap noise with the QCSEE engine.

  17. Diffuse scattered field of elastic waves from randomly rough surfaces using an analytical Kirchhoff theory

    NASA Astrophysics Data System (ADS)

    Shi, F.; Lowe, M. J. S.; Xi, X.; Craster, R. V.

    2016-07-01

    We develop an elastodynamic theory to predict the diffuse scattered field of elastic waves by randomly rough surfaces, for the first time, with the aid of the Kirchhoff approximation (KA). Analytical expressions are derived incorporating surface statistics, to represent the expectation of the angular distribution of the diffuse intensity for different modes. The analytical solutions are successfully verified with numerical Monte Carlo simulations, and also validated by comparison with experiments. We then apply the theory to quantitatively investigate the effects of the roughness and the shear-to-compressional wave speed ratio on the mode conversion and the scattering intensity, from low to high roughness within the valid region of KA. Both the direct and the mode converted intensities are significantly affected by the roughness, which leads to distinct scattering patterns for different wave modes. The mode conversion effect is very strong around the specular angle and it is found to increase as the surface appears to be more rough. In addition, the 3D roughness induced coupling between the out-of-plane shear horizontal (SH) mode and the in-plane modes is studied. The intensity of the SH mode is shown to be very sensitive to the out-of-plane correlation length, being influenced more by this than by the RMS value of the roughness. However, it is found that the depolarization pattern for the diffuse field is independent of the actual value of the roughness.

  18. Subsonic aerodynamic characteristics of a space shuttle orbiter

    NASA Technical Reports Server (NTRS)

    Ellison, J. C.

    1973-01-01

    A space shuttle orbiter has been studied in a low turbulence pressure tunnel at a Mach number of 0.25 and Reynolds numbers from 4.17 x 1 million to 29. 17 x 1 million, based model length. The angle of attack range was about -4 to 24 deg at angles of sideslip of 0 and 5 deg. Static longitudinal and lateral directional aerodynamic characteristics were obtained for elevon deflections from 0 to -20 deg. The model was longitudinally stable at all test conditions; however, depending on Reynolds number and eleven deflection angle, the model was directionally unstable for angles of attack between 9 and 17 deg. The model had a maximum trimmed lift drag ratio of about 6.25 which occured at an angle of attack of about 9 deg with an elevon deflection of -10 deg.

  19. Specular Reflection from Rough Surfaces Revisited

    ERIC Educational Resources Information Center

    Yasuda, Kensei; Kim, Alvin; Cho, Hayley; Timofejev, Timofej; Walecki, Wojciech J.; Klep, James; Edelson, Amy S.; Walecki, Abigail S.; Walecki, Eve S.; Walecki, Peter S.

    2016-01-01

    In his beautiful paper, Hasan Fakhruddin reported observations of mirror-like reflections in the rough surface of a ground glass plate. Similar effects have been recently employed for metrology of the roughness of optical diffusers used in modern light emitting device illumination systems. We report the observations of specular reflection in…

  20. Computational Methods for Rough Classification and Discovery.

    ERIC Educational Resources Information Center

    Bell, D. A.; Guan, J. W.

    1998-01-01

    Rough set theory is a new mathematical tool to deal with vagueness and uncertainty. Computational methods are presented for using rough sets to identify classes in datasets, finding dependencies in relations, and discovering rules which are hidden in databases. The methods are illustrated with a running example from a database of car test results.…

  1. Roughness configuration matters for aeolian sediment flux

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The parameterisation of surface roughness effects on aeolian sediment transport is a key source of uncertainty in wind erosion models. Roughness effects are typically represented by bulk drag-partitioning schemes that scale the threshold friction velocity (u*t) for soil entrainment by the ratio of s...

  2. Wetting properties of molecularly rough surfaces

    SciTech Connect

    Svoboda, Martin; Lísal, Martin; Malijevský, Alexandr

    2015-09-14

    We employ molecular dynamics simulations to study the wettability of nanoscale rough surfaces in systems governed by Lennard-Jones (LJ) interactions. We consider both smooth and molecularly rough planar surfaces. Solid substrates are modeled as a static collection of LJ particles arranged in a face-centered cubic lattice with the (100) surface exposed to the LJ fluid. Molecularly rough solid surfaces are prepared by removing several strips of LJ atoms from the external layers of the substrate, i.e., forming parallel nanogrooves on the surface. We vary the solid-fluid interactions to investigate strongly and weakly wettable surfaces. We determine the wetting properties by measuring the equilibrium droplet profiles that are in turn used to evaluate the contact angles. Macroscopic arguments, such as those leading to Wenzel’s law, suggest that surface roughness always amplifies the wetting properties of a lyophilic surface. However, our results indicate the opposite effect from roughness for microscopically corrugated surfaces, i.e., surface roughness deteriorates the substrate wettability. Adding the roughness to a strongly wettable surface shrinks the surface area wet with the liquid, and it either increases or only marginally affects the contact angle, depending on the degree of liquid adsorption into the nanogrooves. For a weakly wettable surface, the roughness changes the surface character from lyophilic to lyophobic due to a weakening of the solid-fluid interactions by the presence of the nanogrooves and the weaker adsorption of the liquid into the nanogrooves.

  3. Identification of aerodynamic models for maneuvering aircraft

    NASA Technical Reports Server (NTRS)

    Lan, C. Edward; Hu, C. C.

    1992-01-01

    A Fourier analysis method was developed to analyze harmonic forced-oscillation data at high angles of attack as functions of the angle of attack and its time rate of change. The resulting aerodynamic responses at different frequencies are used to build up the aerodynamic models involving time integrals of the indicial type. An efficient numerical method was also developed to evaluate these time integrals for arbitrary motions based on a concept of equivalent harmonic motion. The method was verified by first using results from two-dimensional and three-dimensional linear theories. The developed models for C sub L, C sub D, and C sub M based on high-alpha data for a 70 deg delta wing in harmonic motions showed accurate results in reproducing hysteresis. The aerodynamic models are further verified by comparing with test data using ramp-type motions.

  4. Aerodynamics of magnetic levitation (MAGLEV) trains

    NASA Technical Reports Server (NTRS)

    Schetz, Joseph A.; Marchman, James F., III

    1996-01-01

    High-speed (500 kph) trains using magnetic forces for levitation, propulsion and control offer many advantages for the nation and a good opportunity for the aerospace community to apply 'high tech' methods to the domestic sector. One area of many that will need advanced research is the aerodynamics of such MAGLEV (Magnetic Levitation) vehicles. There are important issues with regard to wind tunnel testing and the application of CFD to these devices. This talk will deal with the aerodynamic design of MAGLEV vehicles with emphasis on wind tunnel testing. The moving track facility designed and constructed in the 6 ft. Stability Wind Tunnel at Virginia Tech will be described. Test results for a variety of MAGLEV vehicle configurations will be presented. The last topic to be discussed is a Multi-disciplinary Design approach that is being applied to MAGLEV vehicle configuration design including aerodynamics, structures, manufacturability and life-cycle cost.

  5. History of the numerical aerodynamic simulation program

    NASA Technical Reports Server (NTRS)

    Peterson, Victor L.; Ballhaus, William F., Jr.

    1987-01-01

    The Numerical Aerodynamic Simulation (NAS) program has reached a milestone with the completion of the initial operating configuration of the NAS Processing System Network. This achievement is the first major milestone in the continuing effort to provide a state-of-the-art supercomputer facility for the national aerospace community and to serve as a pathfinder for the development and use of future supercomputer systems. The underlying factors that motivated the initiation of the program are first identified and then discussed. These include the emergence and evolution of computational aerodynamics as a powerful new capability in aerodynamics research and development, the computer power required for advances in the discipline, the complementary nature of computation and wind tunnel testing, and the need for the government to play a pathfinding role in the development and use of large-scale scientific computing systems. Finally, the history of the NAS program is traced from its inception in 1975 to the present time.

  6. Summary analysis of the Gemini entry aerodynamics

    NASA Technical Reports Server (NTRS)

    Whitnah, A. M.; Howes, D. B.

    1972-01-01

    The aerodynamic data that were derived in 1967 from the analysis of flight-generated data for the Gemini entry module are presented. These data represent the aerodynamic characteristics exhibited by the vehicle during the entry portion of Gemini 2, 3, 5, 8, 10, 11, and 12 missions. For the Gemini, 5, 8, 10, 11, and 12 missions, the flight-generated lift-to-drag ratios and corresponding angles of attack are compared with the wind tunnel data. These comparisons show that the flight generated lift-to-drag ratios are consistently lower than were anticipated from the tunnel data. Numerous data uncertainties are cited that provide an insight into the problems that are related to an analysis of flight data developed from instrumentation systems, the primary functions of which are other than the evaluation of flight aerodynamic performance.

  7. Nonlinear aerodynamic modeling using multivariate orthogonal functions

    NASA Technical Reports Server (NTRS)

    Morelli, Eugene A.

    1993-01-01

    A technique was developed for global modeling of nonlinear aerodynamic coefficients using multivariate orthogonal functions based on the data. Each orthogonal function retained in the model was decomposed into an expansion of ordinary polynomials in the independent variables, so that the final model could be interpreted as selectively retained terms from a multivariable power series expansion. A predicted squared-error metric was used to determine the orthogonal functions to be retained in the model; analytical derivatives were easily computed. The approach was demonstrated on the Z-body axis aerodynamic force coefficient (Cz) wind tunnel data for an F-18 research vehicle which came from a tabular wind tunnel and covered the entire subsonic flight envelope. For a realistic case, the analytical model predicted experimental values of Cz very well. The modeling technique is shown to be capable of generating a compact, global analytical representation of nonlinear aerodynamics. The polynomial model has good predictive capability, global validity, and analytical differentiability.

  8. Miniature Trailing Edge Effector for Aerodynamic Control

    NASA Technical Reports Server (NTRS)

    Lee, Hak-Tae (Inventor); Bieniawski, Stefan R. (Inventor); Kroo, Ilan M. (Inventor)

    2008-01-01

    Improved miniature trailing edge effectors for aerodynamic control are provided. Three types of devices having aerodynamic housings integrated to the trailing edge of an aerodynamic shape are presented, which vary in details of how the control surface can move. A bucket type device has a control surface which is the back part of a C-shaped member having two arms connected by the back section. The C-shaped section is attached to a housing at the ends of the arms, and is rotatable about an axis parallel to the wing trailing edge to provide up, down and neutral states. A flip-up type device has a control surface which rotates about an axis parallel to the wing trailing edge to provide up, down, neutral and brake states. A rotating type device has a control surface which rotates about an axis parallel to the chord line to provide up, down and neutral states.

  9. Photogrammetry of a Hypersonic Inflatable Aerodynamic Decelerator

    NASA Technical Reports Server (NTRS)

    Kushner, Laura Kathryn; Littell, Justin D.; Cassell, Alan M.

    2013-01-01

    In 2012, two large-scale models of a Hypersonic Inflatable Aerodynamic decelerator were tested in the National Full-Scale Aerodynamic Complex at NASA Ames Research Center. One of the objectives of this test was to measure model deflections under aerodynamic loading that approximated expected flight conditions. The measurements were acquired using stereo photogrammetry. Four pairs of stereo cameras were mounted inside the NFAC test section, each imaging a particular section of the HIAD. The views were then stitched together post-test to create a surface deformation profile. The data from the photogram- metry system will largely be used for comparisons to and refinement of Fluid Structure Interaction models. This paper describes how a commercial photogrammetry system was adapted to make the measurements and presents some preliminary results.

  10. Aerodynamic tests of Darrieus wind turbine blades

    SciTech Connect

    Migliore, P.G.; Walters, R.E.; Wolfe, W.P.

    1983-03-01

    An indoor facility for the aerodynamic testing of Darrieus turbine blades was developed. Lift, drag, and moment coefficients were measured for two blades whose angle of attack and chord-to-radius ratio were varied. The first blade used an NACA 0015 airfoil section; the second used a 15% elliptical cross section with a modified circular arc trailing edge. Blade aerodynamic coefficients were corrected to section coefficients for comparison to published rectilinear flow data. Although the airfoil sections were symmetrical, moment coefficients were not zero and the lift and drag curves were asymmetrical about zero lift coefficient and angle of attack. These features verified the predicted virtual camber and incidence phenomena. Boundary-layer centrifugal effects were manifested by discontinuous lift curves and large differences in the angle of zero lift between th NACA 0015 and elliptical airfoils. It was concluded that rectilinear flow aerodynamic data are not applicable to Darrieus turbine blades, even for small chord-to-radius ratios.

  11. High-lift aerodynamics: Prospects and plans

    NASA Technical Reports Server (NTRS)

    Olson, Lawrence E.

    1992-01-01

    The emergence of high-lift aerodynamics is reviewed as one of the key technologies to the development of future subsonic transport aircraft. Airport congestion, community noise, economic competitiveness, and safety - the drivers that make high-lift an important technology - are discussed. Attention is given to the potentially synergistic integration of high-lift aerodynamics with two other advanced technologies: ultra-high bypass ratio turbofan engines and hybrid laminar flow control. A brief review of the ongoing high-lift research program at Ames Research Center is presented. Suggestions for future research directions are made with particular emphasis on the development and validation of computational codes and design methods. It is concluded that the technology of high-lift aerodynamics analysis and design should move boldly into the realm of high Reynolds number, three-dimensional flows.

  12. Aerodynamic optimization studies on advanced architecture computers

    NASA Technical Reports Server (NTRS)

    Chawla, Kalpana

    1995-01-01

    The approach to carrying out multi-discipline aerospace design studies in the future, especially in massively parallel computing environments, comprises of choosing (1) suitable solvers to compute solutions to equations characterizing a discipline, and (2) efficient optimization methods. In addition, for aerodynamic optimization problems, (3) smart methodologies must be selected to modify the surface shape. In this research effort, a 'direct' optimization method is implemented on the Cray C-90 to improve aerodynamic design. It is coupled with an existing implicit Navier-Stokes solver, OVERFLOW, to compute flow solutions. The optimization method is chosen such that it can accomodate multi-discipline optimization in future computations. In the work , however, only single discipline aerodynamic optimization will be included.

  13. Aerodynamic analysis of a tumbling American football

    NASA Astrophysics Data System (ADS)

    Hare, Daniel Edmundson

    In this study, the aerodynamic effects on an American football are characterized, especially in a tumbling, or end-over-end, motion as seen in a typical kickoff or field goal attempt. The objective of this study is to establish aerodynamic coefficients for the dynamic motion of a tumbling American football. A subsonic wind tunnel was used to recreate a range of air velocities that, when coupled with rotation rates and differing laces orientations, would provide a test bed for aerodynamic drag, side, and lift coefficient analysis. Test results quantify effect of back-spin and top-spin on lift force. Results show that the presence of laces imposes a side force in the opposite direction of the laces orientation. A secondary system was installed to visualize air flow around the tumbling ball and record high-speed video of wake patterns, as a qualitative check of measured force directions.

  14. Wind turbine aerodynamics research needs assessment

    NASA Astrophysics Data System (ADS)

    Stoddard, F. S.; Porter, B. K.

    1986-01-01

    A prioritized list is developed for wind turbine aerodynamic research needs and opportunities which could be used by the Department of Energy program management team in detailing the DOE Five-Year Wind Turbine Research Plan. The focus of the Assessment was the basic science of aerodynamics as applied to wind turbines, including all relevant phenomena, such as turbulence, dynamic stall, three-dimensional effects, viscosity, wake geometry, and others which influence aerodynamic understanding and design. The study was restricted to wind turbines that provide electrical energy compatible with the utility grid, and included both horizontal axis wind turbines (HAWT) and vertical axis wind turbines (VAWT). Also, no economic constraints were imposed on the design concepts or recommendations since the focus of the investigation was purely scientific.

  15. Specular Reflection from Rough Surfaces Revisited

    NASA Astrophysics Data System (ADS)

    Yasuda, Kensei; Kim, Alvin; Cho, Hayley; Timofejev, Timofej; Walecki, Wojciech J.; Klep, James; Edelson, Amy S.; Walecki, Abigail S.; Walecki, Eve S.; Walecki, Peter S.

    2016-10-01

    In his beautiful paper, Hasan Fakhruddin reported observations of mirror-like reflections in the rough surface of a ground glass plate. Similar effects have been recently employed for metrology of the roughness of optical diffusers used in modern light emitting device illumination systems. We report the observations of specular reflection in nontransparent rough surfaces at oblique angles, where roughness was treated as a variable. We present a simple trigonometry-based model explaining the observed phenomenon, which we experimentally validated using aluminum surfaces that have controlled roughness. The reported demonstration requires no special equipment, other than cellphone cameras, dielectric or metal plate, and sandpaper, and serves as an introduction to wave optics. This activity can be used to get further insight into everyday applications of wave optics for students already familiar with wave optics fundamentals.

  16. Modeling surface roughness scattering in metallic nanowires

    SciTech Connect

    Moors, Kristof; Sorée, Bart; Magnus, Wim

    2015-09-28

    Ando's model provides a rigorous quantum-mechanical framework for electron-surface roughness scattering, based on the detailed roughness structure. We apply this method to metallic nanowires and improve the model introducing surface roughness distribution functions on a finite domain with analytical expressions for the average surface roughness matrix elements. This approach is valid for any roughness size and extends beyond the commonly used Prange-Nee approximation. The resistivity scaling is obtained from the self-consistent relaxation time solution of the Boltzmann transport equation and is compared to Prange-Nee's approach and other known methods. The results show that a substantial drop in resistivity can be obtained for certain diameters by achieving a large momentum gap between Fermi level states with positive and negative momentum in the transport direction.

  17. Slip due to surface roughness for a Newtonian liquid in a viscous microscale disk pump

    NASA Astrophysics Data System (ADS)

    Ligrani, Phil; Blanchard, Danny; Gale, Bruce

    2010-05-01

    In the present study, hydrophobic roughness is used to induce near-wall slip in a single rotating-disk micropump operating with Newtonian water. The amount of induced slip is altered by employing different sizes of surface roughness on the rotating disk. The magnitudes of slip length and slip velocities increase as the average size of the surface roughness becomes larger. In the present study, increased slip magnitudes from roughness are then associated with reduced pressure rise through the pump and lower radial-line-averaged shear stress magnitudes (determined within slip planes). Such shear stress and pressure rise variations are similar to those which would be present if the slip is induced by the intermolecular interactions which are associated with near-wall microscale effects. The present slip-roughness effects are quantified experimentally over rotational speeds from 50 to 1200 rpm, pressure increases from 0 to 312 kPa, net flow rates of 0-100 μl/min, and fluid chamber heights from 6.85 to 29.2 μm. Verification is provided by comparisons with analytic results determined from the rotating Couette flow forms of the Navier-Stokes equations, with different disk rotational speeds, disk roughness levels, and fluid chamber heights. These data show that slip length magnitudes show significant dependence on radial-line-averaged shear stress for average disk roughness heights of 404 and 770 nm. These slip length data additionally show a high degree of organization when normalized using by either the average roughness height or the fluid chamber height. For the latter case, such behavior provides evidence that the flow over a significant portion of the passage height is affected by the roughness, and near-wall slip velocities, especially when the average roughness height amounts to 11% of the h =6.86 μm passage height of the channel. Such scaling of the disk slip length bdisk with fluid chamber height h is consistent with d-type roughness scaling in macroscale

  18. Effects of Ice Accretion on Aircraft Aerodynamics

    NASA Technical Reports Server (NTRS)

    Bragg, Michael B.

    1998-01-01

    The primary objective of this research was to support the development of a new ice accretion model by improving our physical understanding of the ice accretion process through experimental measurements. The focus was on the effect of the initial ice roughness (smooth/rough boundary) on the accretion process. This includes understanding the boundary-layer development over the roughness and especially its effect on the heat transfer which is fundamental to the ice accretion process. The research focused on acquiring the experimental data needed to formulate a new ice accretion physical model. Research was conducted to analyze boundary-layer data taken on a NACA 0012 airfoil with roughness to simulate the smooth/rough boundary. The effect of isolated roughness on boundary-layer transition was studied experimentally to determine if the classical critical roughness Reynolds number criteria could be applied to transition in the airfoil leading-edge area. The effect of simulated smooth/rough boundary roughness on convective heat transfer was studied to complete the study. During the course of this research the effect of free-stream wind tunnel turbulence on the boundary layer was measured. Since this quantity was not well known, research to accurately measure the wind tunnel turbulence in an icing cloud was undertaken. Preliminary results were attained and the final data were acquired, reduced and presented under a subsequent grant.

  19. Air flow testing on aerodynamic truck

    NASA Technical Reports Server (NTRS)

    1975-01-01

    After leasing a cab-over tractor-trailer from a Southern California firm, Dryden researchers added sheet metal modifications like those shown here. They rounded the front corners and edges, and placed a smooth fairing on the cab's roofs and sides extending back to the trailer. During the investigation of truck aerodynamics, the techniques honed in flight research proved highly applicable. By closing the gap between the cab and the trailer, for example, researchers discovered a significant reduction in aerodynamic drag, one resulting in 20 to 25 percent less fuel consumption than the standard design. Many truck manufacturers subsequently incorporated similar modifications on their products.

  20. Unstructured mesh algorithms for aerodynamic calculations

    NASA Technical Reports Server (NTRS)

    Mavriplis, D. J.

    1992-01-01

    The use of unstructured mesh techniques for solving complex aerodynamic flows is discussed. The principle advantages of unstructured mesh strategies, as they relate to complex geometries, adaptive meshing capabilities, and parallel processing are emphasized. The various aspects required for the efficient and accurate solution of aerodynamic flows are addressed. These include mesh generation, mesh adaptivity, solution algorithms, convergence acceleration, and turbulence modeling. Computations of viscous turbulent two-dimensional flows and inviscid three-dimensional flows about complex configurations are demonstrated. Remaining obstacles and directions for future research are also outlined.

  1. Method of reducing drag in aerodynamic systems

    NASA Technical Reports Server (NTRS)

    Hrach, Frank J. (Inventor)

    1993-01-01

    In the present method, boundary layer thickening is combined with laminar flow control to reduce drag. An aerodynamic body is accelerated enabling a ram turbine on the body to receive air at velocity V sub 0. The discharge air is directed over an aft portion of the aerodynamic body producing boundary layer thickening. The ram turbine also drives a compressor by applying torque to a shaft connected between the ram turbine and the compressor. The compressor sucks in lower boundary layer air through inlets in the shell of the aircraft producing laminar flow control and reducing drag. The discharge from the compressor is expanded in a nozzle to produce thrust.

  2. Aerodynamics of Shuttle Orbiter at high altitudes

    NASA Technical Reports Server (NTRS)

    Rault, Didier F. G.

    1993-01-01

    The high-altitude/high-Knudsen number aerodynamics of the Shuttle Orbiter are computed from Low-Earth Orbit down to 100 km using three-dimensional direct simulation Monte Carlo and free molecule codes. Results are compared with Blanchard's latest Shuttle aerodynamic model, which is based on in-flight accelerometer measurements, and bridging formula models. Good comparison is observed, except for the normal force and pitching moment coefficients. The present results were obtained for a generic Shuttle geometry configuration corresponding to a zero deflection for all control surfaces.

  3. Rarefied Transitional Bridging of Blunt Body Aerodynamics

    NASA Technical Reports Server (NTRS)

    Wilmoth, R. G.; Blanchard, R. C.; Moss, J. N.

    1998-01-01

    The bridging procedures discussed provide an accurate engineering method for predicting rarefied transitional aerodynamics of spherically-blunted cone entry vehicles. The single-point procedure offers a way to improve the bridging procedures while minimizing the computational effort. However, the accuracy of these procedures ultimately depends on accurate knowledge of the aerodynamics in the free-molecular and continuum limits. The excellent agreement shown for DSMC predictions and bridging relations with the Viking flight data in transitional regime enhance the coincidence in these procedures.

  4. Unsteady Aerodynamics - Subsonic Compressible Inviscid Case

    NASA Technical Reports Server (NTRS)

    Balakrishnan, A. V.

    1999-01-01

    This paper presents a new analytical treatment of Unsteady Aerodynamics - the linear theory covering the subsonic compressible (inviscid) case - drawing on some recent work in Operator Theory and Functional Analysis. The specific new results are: (a) An existence and uniqueness proof for the Laplace transform version of the Possio integral equation as well as a new closed form solution approximation thereof. (b) A new representation for the time-domain solution of the subsonic compressible aerodynamic equations emphasizing in particular the role of the initial conditions.

  5. Direct use of linear time-domain aerodynamics in aeroservoelastic analysis: Aerodynamic model

    NASA Technical Reports Server (NTRS)

    Woods, J. A.; Gilbert, Michael G.

    1990-01-01

    The work presented here is the first part of a continuing effort to expand existing capabilities in aeroelasticity by developing the methodology which is necessary to utilize unsteady time-domain aerodynamics directly in aeroservoelastic design and analysis. The ultimate objective is to define a fully integrated state-space model of an aeroelastic vehicle's aerodynamics, structure and controls which may be used to efficiently determine the vehicle's aeroservoelastic stability. Here, the current status of developing a state-space model for linear or near-linear time-domain indicial aerodynamic forces is presented.

  6. Measuring Thermodynamic Length

    SciTech Connect

    Crooks, Gavin E

    2007-09-07

    Thermodynamic length is a metric distance between equilibrium thermodynamic states. Among other interesting properties, this metric asymptotically bounds the dissipation induced by a finite time transformation of a thermodynamic system. It is also connected to the Jensen-Shannon divergence, Fisher information, and Rao's entropy differential metric. Therefore, thermodynamic length is of central interestin understanding matter out of equilibrium. In this Letter, we will consider how to denethermodynamic length for a small system described by equilibrium statistical mechanics and how to measure thermodynamic length within a computer simulation. Surprisingly, Bennett's classic acceptance ratio method for measuring free energy differences also measures thermodynamic length.

  7. Nonlinear problems in flight dynamics involving aerodynamic bifurcations

    NASA Technical Reports Server (NTRS)

    Tobak, M.; Chapman, G. T.

    1985-01-01

    Aerodynamic bifurcation is defined as the replacement of an unstable equilibrium flow by a new stable equilibrium flow at a critical value of a parameter. A mathematical model of the aerodynamic contribution to the aircraft's equations of motion is amended to accommodate aerodynamic bifurcations. Important bifurcations such as, the onset of large-scale vortex-shedding are defined. The amended mathematical model is capable of incorporating various forms of aerodynamic responses, including those associated with dynamic stall of airfoils.

  8. Predicting bed form roughness: the influence of lee side angle

    NASA Astrophysics Data System (ADS)

    Lefebvre, Alice; Winter, Christian

    2016-04-01

    Flow transverse bedforms (ripples and dunes) are ubiquitous in rivers and coastal seas. Local hydrodynamics and transport conditions depend on the size and geometry of these bedforms, as they constitute roughness elements at the bed. Bedform influence on flow energy must be considered for the understanding of flow dynamics, and in the development and application of numerical models. Common estimations or predictors of form roughness (friction factors) are based mostly on data of steep bedforms (with angle-of-repose lee slopes), and described by highly simplified bedform dimensions (heights and lengths). However, natural bedforms often are not steep, and differ in form and hydraulic effect relative to idealised bedforms. Based on systematic numerical model experiments, this study shows how the hydraulic effect of bedforms depends on the flow structure behind bedforms, which is determined by the bedform lee side angle, aspect ratio and relative height. Simulations reveal that flow separation behind bedform crests and, thus, a hydraulic effect is induced at lee side angles steeper than 11 to 18° depending on relative height, and that a fully developed flow separation zone exists only over bedforms with a lee side angle steeper than 24°. Furthermore, the hydraulic effect of bedforms with varying lee side angle is evaluated and a reduction function to common friction factors is proposed. A function is also developed for the Nikuradse roughness (k s), and a new equation is proposed which directly relates k s to bedform relative height, aspect ratio and lee side angle.

  9. Measurement and prediction of rough wall effects on friction factor - Uniform roughness results

    NASA Astrophysics Data System (ADS)

    Scaggs, W. F.; Taylor, Robert P.; Coleman, Hugh W.

    The results of an experimental investigation of the effects of surface roughness on turbulent pipe flow friction factors are presented and compared with predictions from a previously published discrete element roughness model. Friction factor data were acquired over a pipe Reynolds number range from 10,000 to 600,000 for nine different uniformly rough surfaces. These surfaces covered a range of roughness element sizes, spacings and shapes. Predictions from the discrete element roughness model were in very good agreement with the data.

  10. Index for aerodynamic data from the Bumblebee program

    NASA Technical Reports Server (NTRS)

    Cronvich, L. L.; Barnes, G. A.

    1978-01-01

    The Bumblebee program, was designed to provide a supersonic guided missile. The aerodynamics program included a fundamental research effort in supersonic aerodynamics as well as a design task in developing both test vehicles and prototypes of tactical missiles. An index of aerodynamic missile data developed in this program is presented.

  11. 14 CFR 25.445 - Auxiliary aerodynamic surfaces.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Auxiliary aerodynamic surfaces. 25.445... AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Structure Control Surface and System Loads § 25.445 Auxiliary aerodynamic surfaces. (a) When significant, the aerodynamic influence...

  12. On the roughness measurement on knee prostheses.

    PubMed

    Jaber, Sami Abdel; Ruggiero, Alessandro; Battaglia, Santina; Affatato, Saverio

    2015-01-01

    The majority of total knee replacements currently implanted present an articulation composed of two metal parts, femoral and tibial components, between which there is a polyethylene insert serving as a bearing surface. The finishing surface of the metal components is a very important factor in minimizing the polyethylene wear rate and, later, the gradual production of metal and plastic debris. Considering the role of surface roughness on volumetric wear rates, the purpose of this study is to develop a protocol for the roughness characterization of total knee prosthesis (TKP) metal components, taking into consideration a limited number of points on each surface. Six mobile TKP of different sizes (three size 2 and three size 6) were tested on a knee joint simulator to compare the wear behavior of each group. After 2 million cycles the weight loss by the polyethylene inserts was measured with gravimetric method and the surface roughness of the metallic components was assessed in terms of average surface roughness, Ra, skewness, Rsk, and total roughness, Rt. Roughness measurement involved 29 points on each femoral condyle and 26 points on each metal tibial plate. The data collected has shown an increased roughness upon wear testing for both the investigated TKP sizes. No statistical differences were observed between the two groups for both the parameters Ra, Rsk, and Rt. The surface of all metallic components became more negatively skewed, indicating diminishing peaks. The various parameters were correlated to the volumetric loss using a linear regression analysis. PMID:25588764

  13. Heat transfer to rough turbine blading

    NASA Astrophysics Data System (ADS)

    Tarada, Fathi Hasan Ali

    1987-12-01

    The project arose from an industrial interest in the quantification of the effects of external surface roughness on the temperatures, both local and means, of internally cooled gas turbine blades, with a view to estimating the possible changes in operating life. Such roughness may occur due to the process involved in the production of the blades or during operation in hostile environments. A dual theoretical and experimental approach was employed to better understand and predict the complex mechanisms influencing the boundary-layer heat transfer on turbine blade surfaces. In order to quantify typical blade roughness levels, a blade roughness survey was undertaken as a pre-cursor to the experimental investigations. The experimental component consisted of heat transfer measurements to one rotor blade and two nozzle guide vanes, with different levels and types of external surface roughness, and with and without significant free-stream turbulence intensity, using two heat transfer measurement techniques. The (dominant) theoretical component comprised the derivation of a low Reynolds number k-epsilon turbulence model, supplemented by an algebraic stress model, for rough curved boundary layer flow, and the development of topographical models of stochastic surface roughness. Computer programs were written to implement the theoretical models developed, and extensive validation tests were conducted with reference to published data sets.

  14. Turbulent flow in smooth and rough pipes.

    PubMed

    Allen, J J; Shockling, M A; Kunkel, G J; Smits, A J

    2007-03-15

    Recent experiments at Princeton University have revealed aspects of smooth pipe flow behaviour that suggest a more complex scaling than previously noted. In particular, the pressure gradient results yield a new friction factor relationship for smooth pipes, and the velocity profiles indicate the presence of a power-law region near the wall and, for Reynolds numbers greater than about 400x103 (R+>9x103), a logarithmic region further out. New experiments on a rough pipe with a honed surface finish with krms/D=19.4x10-6, over a Reynolds number range of 57x103-21x106, show that in the transitionally rough regime this surface follows an inflectional friction factor relationship rather than the monotonic relationship given in the Moody diagram. Outer-layer scaling of the mean velocity data and streamwise turbulence intensities for the rough pipe show excellent collapse and provide strong support for Townsend's outer-layer similarity hypothesis for rough-walled flows. The streamwise rough-wall spectra also agree well with the corresponding smooth-wall data. The pipe exhibited smooth behaviour for ks+ < or =3.5, which supports the suggestion that the original smooth pipe was indeed hydraulically smooth for ReD< or =24x106. The relationship between the velocity shift, DeltaU/utau, and the roughness Reynolds number, ks+, has been used to generalize the form of the transition from smooth to fully rough flow for an arbitrary relative roughness krms/D. These predictions apply for honed pipes when the separation of pipe diameter to roughness height is large, and they differ significantly from the traditional Moody curves.

  15. Understanding EUV mask blank surface roughness induced LWR and associated roughness requirement

    SciTech Connect

    Yan, Pei-Yang; Zhang, Guojing; Gullickson, Eric M.; Goldberg, Kenneth A.; Benk, Markus P.

    2015-03-01

    Extreme ultraviolet lithography (EUVL) mask multi-layer (ML) blank surface roughness specification historically comes from blank defect inspection tool requirement. Later, new concerns on ML surface roughness induced wafer pattern line width roughness (LWR) arise. In this paper, we have studied wafer level pattern LWR as a function of EUVL mask surface roughness via High-NA Actinic Reticle Review Tool. We found that the blank surface roughness induced LWR at current blank roughness level is in the order of 0.5nm 3σ for NA=0.42 at the best focus. At defocus of ±40nm, the corresponding LWR will be 0.2nm higher. Further reducing EUVL mask blank surface roughness will increase the blank cost with limited benefit in improving the pattern LWR, provided that the intrinsic resist LWR is in the order of 1nm and above.

  16. Tandem Differential Mobility Analyzer/Aerodynamic Particle Sizer (APS) Handbook

    SciTech Connect

    Collins, D

    2010-06-18

    The tandem differential mobility analyzer (TDMA) is a single instrument that cycles through a series of complementary measurements of the physical properties of size-resolved submicron particles. In 2008, the TDMA was augmented through the addition of an aerodynamic particle sizer (APS), which extends the upper limit of the measured size distribution into the supermicron range. These two instruments are operated in parallel, but because they are controlled by a common computer and because the size distributions measured by the two are integrated in the produced datastreams, they are described together here. Throughout the day, the TDMA sequentially measures submicron aerosol size distributions and size-resolved hygroscopic growth distributions. More specifically, the instrument is operated as a scanning DMA to measure size distributions and as a TDMA to measure size-resolved hygroscopicity. A typical measurement sequence requires roughly 45 minutes. Each morning additional measurements are made of the relative humidity (RH) dependent hygroscopicity and temperature-dependent volatility of size-resolved particles. When the outside temperature and RH are within acceptable ranges, the hydration state of size-resolved particles is also characterized. The measured aerosol distributions complement the array of aerosol instruments in the Aerosol Observing System (AOS) and provide additional details of the light-scattering and cloud-nucleating characteristics of the aerosol.

  17. Quantifying the Effect of Pressure Sensitive Paint On Aerodynamic Data

    NASA Technical Reports Server (NTRS)

    Amer, T. R.; Obara, C. J.; Liu, T.

    2003-01-01

    A thin pressure sensitive paint (PSP) coating can slightly modify the overall shape of a wind-tunnel model and produce surface roughness or smoothness that does not exist on the unpainted model. These undesirable changes in model geometry may alter flow over the model, and affect the pressure distribution and aerodynamic forces and moments on the model. This study quantifies the effects of PSP on three models in low-speed, transonic and supersonic flow regimes. At a 95% confidence level, the PSP effects on the integrated forces are insignificant for a slender arrow-wing-fuselage model and delta wing model with two different paints at Mach 0.2, 1.8, and 2.16 relative to the total balance accuracy limit. The data displayed a repeatability of 2.5 drag counts, while the balance accuracy limit was about 5.5 drag counts. At transonic speeds, the paint has a localized effect at high angles of attack and has a resolvable effect on the normal force, which is significant relative to the balance accuracy limit. For low speeds, the PSP coating has a localized effect on the pressure tap measurements, which leads to an appreciable decrease in the pressure tap reading. Moreover, the force and moment measurements had a poor precision, which precluded the ability to measure the PSP effect for this particular test.

  18. Experimental aerodynamic study of a car-type bluff body

    NASA Astrophysics Data System (ADS)

    Conan, Boris; Anthoine, Jérôme; Planquart, Philippe

    2011-05-01

    The Ahmed body is used as a reference model for fundamental studies of car-type bluff body aerodynamics, in particular focused on the influence of the rear slant angle on the drag coefficient. The objectives of the present work are to obtain reliable drag coefficient comparable to the literature and to explain, based on the nature of the flow, its variation when changing the rear slant angle from 10° to 40°. The drag coefficients measured in both an open and a closed test sections differ by less than 0.5% which proves the reliability and reproducibility of the results. The sensitivity of the drag coefficient to some parameters such as the model roughness or the oncoming boundary layer and the lack of precise information on these parameters in the literature could explain the difference observed with the Ahmed drag coefficient data. The various types of measurement techniques used in the study underline their complementarity. The combination of particle image velocimetry and oil visualization provides a deeper understanding of the flow behaviour around the Ahmed body and a physical interpretation of the drag coefficient evolution.

  19. Numerical Schemes for Rough Parabolic Equations

    SciTech Connect

    Deya, Aurelien

    2012-04-15

    This paper is devoted to the study of numerical approximation schemes for a class of parabolic equations on (0,1) perturbed by a non-linear rough signal. It is the continuation of Deya (Electron. J. Probab. 16:1489-1518, 2011) and Deya et al. (Probab. Theory Relat. Fields, to appear), where the existence and uniqueness of a solution has been established. The approach combines rough paths methods with standard considerations on discretizing stochastic PDEs. The results apply to a geometric 2-rough path, which covers the case of the multidimensional fractional Brownian motion with Hurst index H>1/3.

  20. An aerodynamic load criterion for airships

    NASA Technical Reports Server (NTRS)

    Woodward, D. E.

    1975-01-01

    A simple aerodynamic bending moment envelope is derived for conventionally shaped airships. This criterion is intended to be used, much like the Naval Architect's standard wave, for preliminary estimates of longitudinal strength requirements. It should be useful in tradeoff studies between speed, fineness ratio, block coefficient, structure weight, and other such general parameters of airship design.

  1. Efficient Global Aerodynamic Modeling from Flight Data

    NASA Technical Reports Server (NTRS)

    Morelli, Eugene A.

    2012-01-01

    A method for identifying global aerodynamic models from flight data in an efficient manner is explained and demonstrated. A novel experiment design technique was used to obtain dynamic flight data over a range of flight conditions with a single flight maneuver. Multivariate polynomials and polynomial splines were used with orthogonalization techniques and statistical modeling metrics to synthesize global nonlinear aerodynamic models directly and completely from flight data alone. Simulation data and flight data from a subscale twin-engine jet transport aircraft were used to demonstrate the techniques. Results showed that global multivariate nonlinear aerodynamic dependencies could be accurately identified using flight data from a single maneuver. Flight-derived global aerodynamic model structures, model parameter estimates, and associated uncertainties were provided for all six nondimensional force and moment coefficients for the test aircraft. These models were combined with a propulsion model identified from engine ground test data to produce a high-fidelity nonlinear flight simulation very efficiently. Prediction testing using a multi-axis maneuver showed that the identified global model accurately predicted aircraft responses.

  2. Aerodynamic Design of Axial Flow Compressors

    NASA Technical Reports Server (NTRS)

    Bullock, R. O. (Editor); Johnsen, I. A.

    1965-01-01

    An overview of 'Aerodynamic systems design of axial flow compressors' is presented. Numerous chapters cover topics such as compressor design, ptotential and viscous flow in two dimensional cascades, compressor stall and blade vibration, and compressor flow theory. Theoretical aspects of flow are also covered.

  3. Aerodynamic drag in cycling: methods of assessment.

    PubMed

    Debraux, Pierre; Grappe, Frederic; Manolova, Aneliya V; Bertucci, William

    2011-09-01

    When cycling on level ground at a speed greater than 14 m/s, aerodynamic drag is the most important resistive force. About 90% of the total mechanical power output is necessary to overcome it. Aerodynamic drag is mainly affected by the effective frontal area which is the product of the projected frontal area and the coefficient of drag. The effective frontal area represents the position of the cyclist on the bicycle and the aerodynamics of the cyclist-bicycle system in this position. In order to optimise performance, estimation of these parameters is necessary. The aim of this study is to describe and comment on the methods used during the last 30 years for the evaluation of the effective frontal area and the projected frontal area in cycling, in both laboratory and actual conditions. Most of the field methods are not expensive and can be realised with few materials, providing valid results in comparison with the reference method in aerodynamics, the wind tunnel. Finally, knowledge of these parameters can be useful in practice or to create theoretical models of cycling performance.

  4. Recent Experiments at the Gottingen Aerodynamic Institute

    NASA Technical Reports Server (NTRS)

    Ackeret, J

    1925-01-01

    This report presents the results of various experiments carried out at the Gottingen Aerodynamic Institute. These include: experiments with Joukowski wing profiles; experiments on an airplane model with a built-in motor and functioning propeller; and the rotating cylinder (Magnus Effect).

  5. A Generic Nonlinear Aerodynamic Model for Aircraft

    NASA Technical Reports Server (NTRS)

    Grauer, Jared A.; Morelli, Eugene A.

    2014-01-01

    A generic model of the aerodynamic coefficients was developed using wind tunnel databases for eight different aircraft and multivariate orthogonal functions. For each database and each coefficient, models were determined using polynomials expanded about the state and control variables, and an othgonalization procedure. A predicted squared-error criterion was used to automatically select the model terms. Modeling terms picked in at least half of the analyses, which totalled 45 terms, were retained to form the generic nonlinear aerodynamic (GNA) model. Least squares was then used to estimate the model parameters and associated uncertainty that best fit the GNA model to each database. Nonlinear flight simulations were used to demonstrate that the GNA model produces accurate trim solutions, local behavior (modal frequencies and damping ratios), and global dynamic behavior (91% accurate state histories and 80% accurate aerodynamic coefficient histories) under large-amplitude excitation. This compact aerodynamics model can be used to decrease on-board memory storage requirements, quickly change conceptual aircraft models, provide smooth analytical functions for control and optimization applications, and facilitate real-time parametric system identification.

  6. Identification of aerodynamic models for maneuvering aircraft

    NASA Technical Reports Server (NTRS)

    Chin, Suei; Lan, C. Edward

    1990-01-01

    Due to the requirement of increased performance and maneuverability, the flight envelope of a modern fighter is frequently extended to the high angle-of-attack regime. Vehicles maneuvering in this regime are subjected to nonlinear aerodynamic loads. The nonlinearities are due mainly to three-dimensional separated flow and concentrated vortex flow that occur at large angles of attack. Accurate prediction of these nonlinear airloads is of great importance in the analysis of a vehicle's flight motion and in the design of its flight control system. A satisfactory evaluation of the performance envelope of the aircraft may require a large number of coupled computations, one for each change in initial conditions. To avoid the disadvantage of solving the coupled flow-field equations and aircraft's motion equations, an alternate approach is to use a mathematical modeling to describe the steady and unsteady aerodynamics for the aircraft equations of motion. Aerodynamic forces and moments acting on a rapidly maneuvering aircraft are, in general, nonlinear functions of motion variables, their time rate of change, and the history of maneuvering. A numerical method was developed to analyze the nonlinear and time-dependent aerodynamic response to establish the generalized indicial function in terms of motion variables and their time rates of change.

  7. User's guide to program FLEXSTAB. [aerodynamics

    NASA Technical Reports Server (NTRS)

    Cavin, R. K., III; Colunga, D.

    1975-01-01

    A manual is presented for correctly submitting program runs in aerodynamics on the UNIVAC 1108 computer system. All major program modules are included. Control cards are documented for the user's convenience, and card parameters are included in order to provide some idea as to reasonable time estimates for the program modules.

  8. Nozzle Aerodynamic Stability During a Throat Shift

    NASA Technical Reports Server (NTRS)

    Kawecki, Edwin J.; Ribeiro, Gregg L.

    2005-01-01

    An experimental investigation was conducted on the internal aerodynamic stability of a family of two-dimensional (2-D) High Speed Civil Transport (HSCT) nozzle concepts. These nozzles function during takeoff as mixer-ejectors to meet acoustic requirements, and then convert to conventional high-performance convergent-divergent (CD) nozzles at cruise. The transition between takeoff mode and cruise mode results in the aerodynamic throat and the minimum cross-sectional area that controls the engine backpressure shifting location within the nozzle. The stability and steadiness of the nozzle aerodynamics during this so called throat shift process can directly affect the engine aerodynamic stability, and the mechanical design of the nozzle. The objective of the study was to determine if pressure spikes or other perturbations occurred during the throat shift process and, if so, identify the caused mechanisms for the perturbations. The two nozzle concepts modeled in the test program were the fixed chute (FC) and downstream mixer (DSM). These 2-D nozzles differ principally in that the FC has a large over-area between the forward throat and aft throat locations, while the DSM has an over-area of only about 10 percent. The conclusions were that engine mass flow and backpressure can be held constant simultaneously during nozzle throat shifts on this class of nozzles, and mode shifts can be accomplished at a constant mass flow and engine backpressure without upstream pressure perturbations.

  9. Aerodynamic analysis of an isolated vehicle wheel

    NASA Astrophysics Data System (ADS)

    Leśniewicz, P.; Kulak, M.; Karczewski, M.

    2014-08-01

    Increasing fuel prices force the manufacturers to look into all aspects of car aerodynamics including wheels, tyres and rims in order to minimize their drag. By diminishing the aerodynamic drag of vehicle the fuel consumption will decrease, while driving safety and comfort will improve. In order to properly illustrate the impact of a rotating wheel aerodynamics on the car body, precise analysis of an isolated wheel should be performed beforehand. In order to represent wheel rotation in contact with the ground, presented CFD simulations included Moving Wall boundary as well as Multiple Reference Frame should be performed. Sliding mesh approach is favoured but too costly at the moment. Global and local flow quantities obtained during simulations were compared to an experiment in order to assess the validity of the numerical model. Results of investigation illustrates dependency between type of simulation and coefficients (drag and lift). MRF approach proved to be a better solution giving result closer to experiment. Investigation of the model with contact area between the wheel and the ground helps to illustrate the impact of rotating wheel aerodynamics on the car body.

  10. Rarefield-Flow Shuttle Aerodynamics Flight Model

    NASA Technical Reports Server (NTRS)

    Blanchard, Robert C.; Larman, Kevin T.; Moats, Christina D.

    1994-01-01

    A model of the Shuttle Orbiter rarefied-flow aerodynamic force coefficients has been derived from the ratio of flight acceleration measurements. The in-situ, low-frequency (less than 1Hz), low-level (approximately 1 x 10(exp -6) g) acceleration measurements are made during atmospheric re-entry. The experiment equipment designed and used for this task is the High Resolution Accelerometer Package (HiRAP), one of the sensor packages in the Orbiter Experiments Program. To date, 12 HiRAP re-entry mission data sets spanning a period of about 10 years have been processed. The HiRAP-derived aerodynamics model is described in detail. The model includes normal and axial hypersonic continuum coefficient equations as function of angle of attack, body-flap deflection, and elevon deflection. Normal and axial free molecule flow coefficient equations as a function of angle of attack are also presented, along with flight-derived rarefied-flow transition bridging formulae. Comparisons are made between the aerodynamics model, data from the latest Orbiter Operational Aerodynamic Design Data Book, applicable computer simulations, and wind-tunnel data.

  11. Aerodynamics of high frequency flapping wings

    NASA Astrophysics Data System (ADS)

    Hu, Zheng; Roll, Jesse; Cheng, Bo; Deng, Xinyan

    2010-11-01

    We investigated the aerodynamic performance of high frequency flapping wings using a 2.5 gram robotic insect mechanism developed in our lab. The mechanism flaps up to 65Hz with a pair of man-made wing mounted with 10cm wingtip-to-wingtip span. The mean aerodynamic lift force was measured by a lever platform, and the flow velocity and vorticity were measured using a stereo DPIV system in the frontal, parasagittal, and horizontal planes. Both near field (leading edge vortex) and far field flow (induced flow) were measured with instantaneous and phase-averaged results. Systematic experiments were performed on the man-made wings, cicada and hawk moth wings due to their similar size, frequency and Reynolds number. For insect wings, we used both dry and freshly-cut wings. The aerodynamic force increase with flapping frequency and the man-made wing generates more than 4 grams of lift at 35Hz with 3 volt input. Here we present the experimental results and the major differences in their aerodynamic performances.

  12. Aerodynamic beam generator for large particles

    DOEpatents

    Brockmann, John E.; Torczynski, John R.; Dykhuizen, Ronald C.; Neiser, Richard A.; Smith, Mark F.

    2002-01-01

    A new type of aerodynamic particle beam generator is disclosed. This generator produces a tightly focused beam of large material particles at velocities ranging from a few feet per second to supersonic speeds, depending on the exact configuration and operating conditions. Such generators are of particular interest for use in additive fabrication techniques.

  13. Rough-Wall Channel Analysis Using Suboptimal Control Theory

    NASA Technical Reports Server (NTRS)

    Flores, O.; Jimenez, J.; Tenpleton, J.

    2003-01-01

    The original aim of this work was to shed some light on the physics of turbulence over rough walls using large-eddy simulations and the suboptimal-control wall boundary conditions introduced by Nicoud et al. It was hoped that, if that algorithm was used to fit the mean velocity profile of the simulations to that of a rough-walled channel, instead of to a smooth one, the wall stresses introduced by the control algorithm would give some indication of what aspects of rough walls are most responsible for the modification of the flow in real turbulence. It was similarly expected that the structure of the resulting velocity fluctuations would share some of the characteristics of rough-walled flows, thus again suggesting what is intrinsic and what is accidental in the effect of geometric wall roughness. A secondary goal was to study the effect of 'unphysical' boundary conditions on the outside flow by observing how a relatively major change of the target velocity profile, and therefore presumably of the applied wall stresses, modifies properties such as the dominant length scales of the velocity fluctuations away from the wall. As will be seen below, this secondary goal grew more important during the course of the study, which was carried out during a short summer visit of the first two authors to the CTR. It became clear that there are open questions about the way in which the control algorithm models the boundary conditions, even for smooth walls, and that these questions make the physical interpretation of the results difficult. Considerable more work in that area seems to be needed before even relatively advanced large-eddy simulations, such as these, can be used to draw conclusions about the physics of wall-bounded turbulent flows. The numerical method is the same as in Nicoud et al. The modifications introduced in the original code are briefly described in section 2, but the original paper should be consulted for a full description of the algorithm. The results are

  14. Effect of inclusion density on ductile fracture toughness and roughness

    NASA Astrophysics Data System (ADS)

    Srivastava, A.; Ponson, L.; Osovski, S.; Bouchaud, E.; Tvergaard, V.; Needleman, A.

    2014-02-01

    Three dimensional calculations of ductile fracture under mode I plane strain, small scale yielding conditions are carried out using an elastic-viscoplastic constitutive relation for a progressively cavitating solid with two populations of void nucleating second phase particles. Larger inclusions that result in void nucleation at an early stage are modeled discretely while smaller particles that require large strains to nucleate voids are homogeneously distributed. Full field solutions are obtained for eight volume fractions, ranging from 1% to 19%, of randomly distributed larger inclusions. For each volume fraction calculations are carried out for seven random distributions of inclusion centers. Crack growth resistance curves and fracture surface roughness statistics are calculated using standard procedures. The crack growth resistance is characterized in terms of both JIC and the tearing modulus TR. For all volume fractions considered, the computed fracture surfaces are self-affine over a size range of nearly two orders of magnitude with a microstructure independent roughness exponent of 0.53 with a standard error of 0.0023. The cut-off length of the scale invariant regime is found to depend on the inclusion volume fraction. Consideration of the full statistics of the fracture surface roughness revealed other parameters that vary with inclusion volume fraction. For smaller values of the discretely modeled inclusion volume fraction (≤7%), there is a linear correlation between several measures of fracture surface roughness and both JIC and TR. In this regime crack growth is dominated by a void-by-void process. For greater values of the discretely modeled inclusion volume fraction, crack growth mainly involves multiple void interactions and no such correlation is found.

  15. In vivo recording of aerodynamic force with an aerodynamic force platform: from drones to birds.

    PubMed

    Lentink, David; Haselsteiner, Andreas F; Ingersoll, Rivers

    2015-03-01

    Flapping wings enable flying animals and biomimetic robots to generate elevated aerodynamic forces. Measurements that demonstrate this capability are based on experiments with tethered robots and animals, and indirect force calculations based on measured kinematics or airflow during free flight. Remarkably, there exists no method to measure these forces directly during free flight. Such in vivo recordings in freely behaving animals are essential to better understand the precise aerodynamic function of their flapping wings, in particular during the downstroke versus upstroke. Here, we demonstrate a new aerodynamic force platform (AFP) for non-intrusive aerodynamic force measurement in freely flying animals and robots. The platform encloses the animal or object that generates fluid force with a physical control surface, which mechanically integrates the net aerodynamic force that is transferred to the earth. Using a straightforward analytical solution of the Navier-Stokes equation, we verified that the method is accurate. We subsequently validated the method with a quadcopter that is suspended in the AFP and generates unsteady thrust profiles. These independent measurements confirm that the AFP is indeed accurate. We demonstrate the effectiveness of the AFP by studying aerodynamic weight support of a freely flying bird in vivo. These measurements confirm earlier findings based on kinematics and flow measurements, which suggest that the avian downstroke, not the upstroke, is primarily responsible for body weight support during take-off and landing.

  16. In vivo recording of aerodynamic force with an aerodynamic force platform: from drones to birds

    PubMed Central

    Lentink, David; Haselsteiner, Andreas F.; Ingersoll, Rivers

    2015-01-01

    Flapping wings enable flying animals and biomimetic robots to generate elevated aerodynamic forces. Measurements that demonstrate this capability are based on experiments with tethered robots and animals, and indirect force calculations based on measured kinematics or airflow during free flight. Remarkably, there exists no method to measure these forces directly during free flight. Such in vivo recordings in freely behaving animals are essential to better understand the precise aerodynamic function of their flapping wings, in particular during the downstroke versus upstroke. Here, we demonstrate a new aerodynamic force platform (AFP) for non-intrusive aerodynamic force measurement in freely flying animals and robots. The platform encloses the animal or object that generates fluid force with a physical control surface, which mechanically integrates the net aerodynamic force that is transferred to the earth. Using a straightforward analytical solution of the Navier–Stokes equation, we verified that the method is accurate. We subsequently validated the method with a quadcopter that is suspended in the AFP and generates unsteady thrust profiles. These independent measurements confirm that the AFP is indeed accurate. We demonstrate the effectiveness of the AFP by studying aerodynamic weight support of a freely flying bird in vivo. These measurements confirm earlier findings based on kinematics and flow measurements, which suggest that the avian downstroke, not the upstroke, is primarily responsible for body weight support during take-off and landing. PMID:25589565

  17. In vivo recording of aerodynamic force with an aerodynamic force platform: from drones to birds.

    PubMed

    Lentink, David; Haselsteiner, Andreas F; Ingersoll, Rivers

    2015-03-01

    Flapping wings enable flying animals and biomimetic robots to generate elevated aerodynamic forces. Measurements that demonstrate this capability are based on experiments with tethered robots and animals, and indirect force calculations based on measured kinematics or airflow during free flight. Remarkably, there exists no method to measure these forces directly during free flight. Such in vivo recordings in freely behaving animals are essential to better understand the precise aerodynamic function of their flapping wings, in particular during the downstroke versus upstroke. Here, we demonstrate a new aerodynamic force platform (AFP) for non-intrusive aerodynamic force measurement in freely flying animals and robots. The platform encloses the animal or object that generates fluid force with a physical control surface, which mechanically integrates the net aerodynamic force that is transferred to the earth. Using a straightforward analytical solution of the Navier-Stokes equation, we verified that the method is accurate. We subsequently validated the method with a quadcopter that is suspended in the AFP and generates unsteady thrust profiles. These independent measurements confirm that the AFP is indeed accurate. We demonstrate the effectiveness of the AFP by studying aerodynamic weight support of a freely flying bird in vivo. These measurements confirm earlier findings based on kinematics and flow measurements, which suggest that the avian downstroke, not the upstroke, is primarily responsible for body weight support during take-off and landing. PMID:25589565

  18. Aerodynamic shape optimization using control theory

    NASA Technical Reports Server (NTRS)

    Reuther, James

    1996-01-01

    Aerodynamic shape design has long persisted as a difficult scientific challenge due its highly nonlinear flow physics and daunting geometric complexity. However, with the emergence of Computational Fluid Dynamics (CFD) it has become possible to make accurate predictions of flows which are not dominated by viscous effects. It is thus worthwhile to explore the extension of CFD methods for flow analysis to the treatment of aerodynamic shape design. Two new aerodynamic shape design methods are developed which combine existing CFD technology, optimal control theory, and numerical optimization techniques. Flow analysis methods for the potential flow equation and the Euler equations form the basis of the two respective design methods. In each case, optimal control theory is used to derive the adjoint differential equations, the solution of which provides the necessary gradient information to a numerical optimization method much more efficiently then by conventional finite differencing. Each technique uses a quasi-Newton numerical optimization algorithm to drive an aerodynamic objective function toward a minimum. An analytic grid perturbation method is developed to modify body fitted meshes to accommodate shape changes during the design process. Both Hicks-Henne perturbation functions and B-spline control points are explored as suitable design variables. The new methods prove to be computationally efficient and robust, and can be used for practical airfoil design including geometric and aerodynamic constraints. Objective functions are chosen to allow both inverse design to a target pressure distribution and wave drag minimization. Several design cases are presented for each method illustrating its practicality and efficiency. These include non-lifting and lifting airfoils operating at both subsonic and transonic conditions.

  19. Surface roughness effects on bidirectional reflectance

    NASA Technical Reports Server (NTRS)

    Smith, T. F.; Hering, R. G.

    1972-01-01

    An experimental study of surface roughness effects on bidirectional reflectance of metallic surfaces is presented. A facility capable of irradiating a sample from normal to grazing incidence and recording plane of incidence bidirectional reflectance measurements was developed. Samples consisting of glass, aluminum alloy, and stainless steel materials were selected for examination. Samples were roughened using standard grinding techniques and coated with a radiatively opaque layer of pure aluminum. Mechanical surface roughness parameters, rms heights and rms slopes, evaluated from digitized surface profile measurements are less than 1.0 micrometers and 0.28, respectively. Rough surface specular, bidirectional, and directional reflectance measurements for selected values of polar angle of incidence and wavelength of incident energy within the spectral range of 1 to 14 micrometers are reported. The Beckmann bidirectional reflectance model is compared with reflectance measurements to establish its usefulness in describing the magnitude and spatial distribution of energy reflected from rough surfaces.

  20. Surface roughness effects on bidirectional reflectance.

    NASA Technical Reports Server (NTRS)

    Smith, T. F.; Hering, R. G.

    1973-01-01

    An experimental study of surface roughness effects on bidirectional reflectance of metallic surfaces is presented. Samples consisting of glass, aluminum alloy, and stainless steel materials were roughened using standard grinding techniques and coated with a radiatively opaque layer of pure aluminum. Surface roughness parameters, rms height and rms slope, were evaluated from digitized surface profile measurements and are less than 1.0 micron, and 0.28, respectively. Rough-surface specular, bidirectional, and directional reflectance measurements for selected values of polar angle and wavelength of incident energy within the range from 10 to 80 deg and from 1 to 14 microns, respectively, are reported. The influence of surface roughness is discussed in terms of rms height and rms slope.

  1. Effect of Surface Roughness on Hydrodynamic Bearings

    NASA Technical Reports Server (NTRS)

    Majumdar, B. C.; Hamrock, B. J.

    1981-01-01

    A theoretical analysis on the performance of hydrodynamic oil bearings is made considering surface roughness effect. The hydrodynamic as well as asperity contact load is found. The contact pressure was calculated with the assumption that the surface height distribution was Gaussian. The average Reynolds equation of partially lubricated surface was used to calculate hydrodynamic load. An analytical expression for average gap was found and was introduced to modify the average Reynolds equation. The resulting boundary value problem was then solved numerically by finite difference methods using the method of successive over relaxation. The pressure distribution and hydrodynamic load capacity of plane slider and journal bearings were calculated for various design data. The effects of attitude and roughness of surface on the bearing performance were shown. The results are compared with similar available solution of rough surface bearings. It is shown that: (1) the contribution of contact load is not significant; and (2) the hydrodynamic and contact load increase with surface roughness.

  2. Simplified models for mask roughness induced LER

    SciTech Connect

    McClinton, Brittany; Naulleau, Patrick

    2011-02-21

    The ITRS requires < 1.2nm line-edge roughness (LER) for the 22nm half-pitch node. Currently, we can consistently achieve only about 3nm LER. Further progress requires understanding the principle causes of LER. Much work has already been done on how both the resist and LER on the mask effect the final printed LER. What is poorly understood, however, is the extent to which system-level effects such as mask surface roughness, illumination conditions, and defocus couple to speckle at the image plane, and factor into LER limits. Presently, mask-roughness induced LER is studied via full 2D aerial image modeling and subsequent analysis of the resulting image. This method is time consuming and cumbersome. It is, therefore, the goal of this research to develop a useful 'rule-of-thumb' analytic model for mask roughness induced LER to expedite learning and understanding.

  3. Impact of phonon-surface roughness scattering on thermal conductivity of thin si nanowires.

    PubMed

    Martin, Pierre; Aksamija, Zlatan; Pop, Eric; Ravaioli, Umberto

    2009-03-27

    We present a novel approach for computing the surface roughness-limited thermal conductivity of silicon nanowires with diameter D<100 nm. A frequency-dependent phonon scattering rate is computed from perturbation theory and related to a description of the surface through the root-mean-square roughness height Delta and autocovariance length L. Using a full phonon dispersion relation, we find a quadratic dependence of thermal conductivity on diameter and roughness as (D/Delta)(2). Computed results show excellent agreement with experimental data for a wide diameter and temperature range (25-350 K), and successfully predict the extraordinarily low thermal conductivity of 2 W m(-1) K-1 at room temperature in rough-etched 50 nm silicon nanowires. PMID:19392295

  4. Phonon thermal conductivity in silicon nanowires: The effects of surface roughness at low temperatures

    NASA Astrophysics Data System (ADS)

    Hyun Oh, Jung; Shin, Mincheol; Jang, Moon-Gyu

    2012-02-01

    Using a Green's function method based on an elastic wave equation, the effects of surface roughness and the nanowire-contact interface scattering on phonon thermal conductivity are studied at low temperatures. It is found that the interface geometry between a nanowire and its contacts affects the transmission function at small energies related to the gapless modes and it gives rise to deviated results from the universal conductance. It is also shown that the surface roughness is crucial in the suppression of phonon thermal conductivity with reducing the nanowire size by averaging the transmission function over the rough-surface configurations. Furthermore, the phonon mean free path is proportional to the ratio of the correlation length and roughness heights quadratically as well as the cross-section area of the nanowire.

  5. Massively Parallel Computation of Soil Surface Roughness Parameters on A Fermi GPU

    NASA Astrophysics Data System (ADS)

    Li, Xiaojie; Song, Changhe

    2016-06-01

    Surface roughness is description of the surface micro topography of randomness or irregular. The standard deviation of surface height and the surface correlation length describe the statistical variation for the random component of a surface height relative to a reference surface. When the number of data points is large, calculation of surface roughness parameters is time-consuming. With the advent of Graphics Processing Unit (GPU) architectures, inherently parallel problem can be effectively solved using GPUs. In this paper we propose a GPU-based massively parallel computing method for 2D bare soil surface roughness estimation. This method was applied to the data collected by the surface roughness tester based on the laser triangulation principle during the field experiment in April 2012. The total number of data points was 52,040. It took 47 seconds on a Fermi GTX 590 GPU whereas its serial CPU version took 5422 seconds, leading to a significant 115x speedup.

  6. Dynamic modeling and simulation of rough cylindrical micro/nanoparticle manipulation with atomic force microscopy.

    PubMed

    Korayem, Moharam H; Badkoobeh Hezaveh, Hedieh; Taheri, Moein

    2014-12-01

    In this paper, the process of pushing rough cylindrical micro/nanoparticles on a surface with an atomic force microscope (AFM) probe is investigated. For this purpose, the mechanics of contact involving adhesion are studied first. Then, a method is presented for estimating the real area of contact between a rough cylindrical particle (whose surface roughness is described by the Rumpf and Rabinovich models) and a smooth surface. A dynamic model is then obtained for the pushing of rough cylindrical particles on a surface with an AFM probe. Afterwards, the process is simulated for different particle sizes and various roughness dimensions. Finally, by reducing the length of the cylindrical particle, the simulation condition is brought closer to the manipulation condition of a smooth spherical particle on a rough substrate, and the simulation results of the two cases are compared. Based on the simulation results, the critical force and time of manipulation diminish for rough particles relative to smooth ones. Reduction in the aspect ratio at a constant cross-section radius and the radius of asperities (height of asperities based on the Rabinovich model) results in an increase in critical force and time of manipulation.

  7. Permeability of self-affine rough fractures

    PubMed

    Drazer; Koplik

    2000-12-01

    The permeability of two-dimensional fractures with self-affine fractal roughness is studied via analytic arguments and numerical simulations. The limit where the roughness amplitude is small compared with average fracture aperture is analyzed by a perturbation method, while in the opposite case of narrow aperture, we use heuristic arguments based on lubrication theory. Numerical simulations, using the lattice Boltzmann method, are used to examine the complete range of aperture sizes, and confirm the analytic arguments. PMID:11138092

  8. How supercontinents and superoceans affect seafloor roughness.

    PubMed

    Whittaker, Joanne M; Müller, R Dietmar; Roest, Walter R; Wessel, Paul; Smith, Walter H F

    2008-12-18

    Seafloor roughness varies considerably across the world's ocean basins and is fundamental to controlling the circulation and mixing of heat in the ocean and dissipating eddy kinetic energy. Models derived from analyses of active mid-ocean ridges suggest that ocean floor roughness depends on seafloor spreading rates, with rougher basement forming below a half-spreading rate threshold of 30-35 mm yr(-1) (refs 4, 5), as well as on the local interaction of mid-ocean ridges with mantle plumes or cold-spots. Here we present a global analysis of marine gravity-derived roughness, sediment thickness, seafloor isochrons and palaeo-spreading rates of Cretaceous to Cenozoic ridge flanks. Our analysis reveals that, after eliminating effects related to spreading rate and sediment thickness, residual roughness anomalies of 5-20 mGal remain over large swaths of ocean floor. We found that the roughness as a function of palaeo-spreading directions and isochron orientations indicates that most of the observed excess roughness is not related to spreading obliquity, as this effect is restricted to relatively rare occurrences of very high obliquity angles (>45 degrees ). Cretaceous Atlantic ocean floor, formed over mantle previously overlain by the Pangaea supercontinent, displays anomalously low roughness away from mantle plumes and is independent of spreading rates. We attribute this observation to a sub-Pangaean supercontinental mantle temperature anomaly leading to slightly thicker than normal Late Jurassic and Cretaceous Atlantic crust, reduced brittle fracturing and smoother basement relief. In contrast, ocean crust formed above Pacific superswells, probably reflecting metasomatized lithosphere underlain by mantle at only slightly elevated temperatures, is not associated with basement roughness anomalies. These results highlight a fundamental difference in the nature of large-scale mantle upwellings below supercontinents and superoceans, and their impact on oceanic crustal

  9. How supercontinents and superoceans affect seafloor roughness.

    PubMed

    Whittaker, Joanne M; Müller, R Dietmar; Roest, Walter R; Wessel, Paul; Smith, Walter H F

    2008-12-18

    Seafloor roughness varies considerably across the world's ocean basins and is fundamental to controlling the circulation and mixing of heat in the ocean and dissipating eddy kinetic energy. Models derived from analyses of active mid-ocean ridges suggest that ocean floor roughness depends on seafloor spreading rates, with rougher basement forming below a half-spreading rate threshold of 30-35 mm yr(-1) (refs 4, 5), as well as on the local interaction of mid-ocean ridges with mantle plumes or cold-spots. Here we present a global analysis of marine gravity-derived roughness, sediment thickness, seafloor isochrons and palaeo-spreading rates of Cretaceous to Cenozoic ridge flanks. Our analysis reveals that, after eliminating effects related to spreading rate and sediment thickness, residual roughness anomalies of 5-20 mGal remain over large swaths of ocean floor. We found that the roughness as a function of palaeo-spreading directions and isochron orientations indicates that most of the observed excess roughness is not related to spreading obliquity, as this effect is restricted to relatively rare occurrences of very high obliquity angles (>45 degrees ). Cretaceous Atlantic ocean floor, formed over mantle previously overlain by the Pangaea supercontinent, displays anomalously low roughness away from mantle plumes and is independent of spreading rates. We attribute this observation to a sub-Pangaean supercontinental mantle temperature anomaly leading to slightly thicker than normal Late Jurassic and Cretaceous Atlantic crust, reduced brittle fracturing and smoother basement relief. In contrast, ocean crust formed above Pacific superswells, probably reflecting metasomatized lithosphere underlain by mantle at only slightly elevated temperatures, is not associated with basement roughness anomalies. These results highlight a fundamental difference in the nature of large-scale mantle upwellings below supercontinents and superoceans, and their impact on oceanic crustal

  10. Reflection of X-rays from a rough surface at extremely small grazing angles.

    PubMed

    Wen, Mingwu; Kozhevnikov, Igor V; Wang, Zhanshan

    2015-09-21

    Peculiarities of X-ray diffraction from a rough surface at an extremely small grazing angle of an incident beam are theoretically studied. The interrelation of four diffraction channels (coherent reflectance, coherent transmittance, diffuse scattering in vacuum, and scattering into the matter depth) is analyzed for different limiting cases (large and small correlation length of roughness and large and extremely small grazing angle of incident radiation). Both the Debye-Waller and the Nevot-Croce factors are demonstrated to describe improperly the features of X-ray diffraction at extremely small grazing angles. More appropriate simple analytic expressions for the specular reflectivity and total integrated scattering in vacuum are obtained instead. Transformation of one limiting diffraction regime into another one with variation in the correlation length of roughness is discussed.

  11. Cells preferentially grow on rough substrates.

    PubMed

    Gentile, Francesco; Tirinato, Luca; Battista, Edmondo; Causa, Filippo; Liberale, Carlo; di Fabrizio, Enzo M; Decuzzi, Paolo

    2010-10-01

    Substrate nanotopography affects cell adhesion and proliferation and is fundamental to the rational design of bio-adhesives, to tissue engineering and to the development of assays for in-vitro screening. Cell behavior on rough substrates is still elusive, and the results presented in the open literature remain controversial. Here, the proliferation of cells on electrochemically etched silicon substrates with different roughness and nearly similar surface energy was studied over three days with confocal and atomic force microscopy. The surface profile of the substrates is a self-affine fractal with a roughness R(a) growing with the etching time from approximately 2 to 100 nm and a fractal dimension D ranging between about 2 (nominally flat surface) and 2.6. For four cell types, the number of adhering cells and their proliferation rates exhibited a maximum on moderately rough (R(a) approximately 10-45 nm) nearly Brownian (D approximately 2.5) substrates. The observed cell behavior was satisfactorily interpreted within the theory of adhesion to randomly rough solids. These findings demonstrated the importance of nanogeometry in cell stable adhesion and growth, suggesting that moderately rough substrates with large fractal dimension could selectively boost cell proliferation. PMID:20637503

  12. Rough surface reconstruction for ultrasonic NDE simulation

    SciTech Connect

    Choi, Wonjae; Shi, Fan; Lowe, Michael J. S.; Skelton, Elizabeth A.; Craster, Richard V.

    2014-02-18

    The reflection of ultrasound from rough surfaces is an important topic for the NDE of safety-critical components, such as pressure-containing components in power stations. The specular reflection from a rough surface of a defect is normally lower than it would be from a flat surface, so it is typical to apply a safety factor in order that justification cases for inspection planning are conservative. The study of the statistics of the rough surfaces that might be expected in candidate defects according to materials and loading, and the reflections from them, can be useful to develop arguments for realistic safety factors. This paper presents a study of real rough crack surfaces that are representative of the potential defects in pressure-containing power plant. Two-dimensional (area) values of the height of the roughness have been measured and their statistics analysed. Then a means to reconstruct model cases with similar statistics, so as to enable the creation of multiple realistic realizations of the surfaces, has been investigated, using random field theory. Rough surfaces are reconstructed, based on a real surface, and results for these two-dimensional descriptions of the original surface have been compared with those from the conventional model based on a one-dimensional correlation coefficient function. In addition, ultrasonic reflections from them are simulated using a finite element method.

  13. Aerodynamic Simulation of the MARINTEK Braceless Semisubmersible Wave Tank Tests

    NASA Astrophysics Data System (ADS)

    Stewart, Gordon; Muskulus, Michael

    2016-09-01

    Model scale experiments of floating offshore wind turbines are important for both platform design for the industry as well as numerical model validation for the research community. An important consideration in the wave tank testing of offshore wind turbines are scaling effects, especially the tension between accurate scaling of both hydrodynamic and aerodynamic forces. The recent MARINTEK braceless semisubmersible wave tank experiment utilizes a novel aerodynamic force actuator to decouple the scaling of the aerodynamic forces. This actuator consists of an array of motors that pull on cables to provide aerodynamic forces that are calculated by a blade-element momentum code in real time as the experiment is conducted. This type of system has the advantage of supplying realistically scaled aerodynamic forces that include dynamic forces from platform motion, but does not provide the insights into the accuracy of the aerodynamic models that an actual model-scale rotor could provide. The modeling of this system presents an interesting challenge, as there are two ways to simulate the aerodynamics; either by using the turbulent wind fields as inputs to the aerodynamic model of the design code, or by surpassing the aerodynamic model and using the forces applied to the experimental turbine as direct inputs to the simulation. This paper investigates the best practices of modeling this type of novel aerodynamic actuator using a modified wind turbine simulation tool, and demonstrates that bypassing the dynamic aerodynamics solver of design codes can lead to erroneous results.

  14. Structural and Critical Behaviors of Ag Rough Films Deposited on Liquid Substrates

    NASA Astrophysics Data System (ADS)

    Ye, Gao-xiang; Feng, Chun-mu; Zhang, Qi-rui; Ge, Hong-liang; Zhang, Xuan-jia

    1996-10-01

    A new Ag rough film system, deposited on silicone oil surfaces by rf-magnetron sputtering method, has been fabricated. The chrysanthemum-like surface morphology at micron length scale is observed. It is proposed that the anomalous critical behavior mainly results from the relative shift between the Ag atom clusters and the substrate. The discussion of the deposition mechanism is also presented.

  15. Interactions Between Surface Roughness and Orography in the Generation of Lake-Effect Precipitation

    NASA Astrophysics Data System (ADS)

    Lofgren, B. M.

    2005-12-01

    The lake effect produces large amounts of precipitation in certain regions bordering on large lakes, generally during the fall to early winter seasons. Among the affected regions are areas bordering the Laurentian Great Lakes of North America, with the primary lake-effect precipitation zones lying near the eastern edge of the lakes. Lake-effect precipitation is due to shallow convection, usually at the mesobeta scale. Factors that are prerequisite to lake-effect precipitation are: 1. plentiful evaporation of water from the lake, 2. an unstable boundary layer created by cold air overlying warmer water, and 3. uplift sufficient to trigger moist convection, via either low-level convergence due to boundary-layer friction or orographic uplift. Some aspects of the relative influence of these uplift mechanisms are examined in this paper. The direct effect of reducing the roughness length of land surfaces near the lakes might be expected to be a reduction in the uplift by frictional low-level convergence. However, in a comparison between RAMS-model simulations with higher and lower values of surface roughness length over land, the result was the opposite -- lower surface roughness length increased upward velocity and precipitation near the lee side of the lakes. The apparent mechanism is that the lower surface roughness length permits an overall higher wind speed in the boundary layer, resulting in greater orographic uplift as the wind reaches shore.

  16. Freight Wing Trailer Aerodynamics Final Technical Report

    SciTech Connect

    Sean Graham

    2007-10-31

    Freight Wing Incorporated utilized the opportunity presented by a DOE category two Inventions and Innovations grant to commercialize and improve upon aerodynamic technology for semi-tuck trailers, capable of decreasing heavy vehicle fuel consumption, related environmental damage, and U.S. consumption of foreign oil. Major project goals included the demonstration of aerodynamic trailer technology in trucking fleet operations, and the development and testing of second generation products. A great deal of past scientific research has demonstrated that streamlining box shaped semi-trailers can significantly reduce a truck’s fuel consumption. However, significant design challenges have prevented past concepts from meeting industry needs. Freight Wing utilized a 2003 category one Inventions and Innovations grant to develop practical solutions to trailer aerodynamics. Fairings developed for the front, rear, and bottom of standard semi-trailers together demonstrated a 7% improvement to fuel economy in scientific tests conducted by the Transportation Research Center (TRC). Operational tests with major trucking fleets proved the functionality of the products, which were subsequently brought to market. This category two grant enabled Freight Wing to further develop, test and commercialize its products, resulting in greatly increased understanding and acceptance of aerodynamic trailer technology. Commercialization was stimulated by offering trucking fleets 50% cost sharing on trial implementations of Freight Wing products for testing and evaluation purposes. Over 230 fairings were implemented through the program with 35 trucking fleets including industry leaders such as Wal-Mart, Frito Lay and Whole Foods. The feedback from these testing partnerships was quite positive with product performance exceeding fleet expectations in many cases. Fleet feedback also was also valuable from a product development standpoint and assisted the design of several second generation products

  17. Neandertal clavicle length

    PubMed Central

    Trinkaus, Erik; Holliday, Trenton W.; Auerbach, Benjamin M.

    2014-01-01

    The Late Pleistocene archaic humans from western Eurasia (the Neandertals) have been described for a century as exhibiting absolutely and relatively long clavicles. This aspect of their body proportions has been used to distinguish them from modern humans, invoked to account for other aspects of their anatomy and genetics, used in assessments of their phylogenetic polarities, and used as evidence for Late Pleistocene population relationships. However, it has been unclear whether the usual scaling of Neandertal clavicular lengths to their associated humeral lengths reflects long clavicles, short humeri, or both. Neandertal clavicle lengths, along with those of early modern humans and latitudinally diverse recent humans, were compared with both humeral lengths and estimated body masses (based on femoral head diameters). The Neandertal do have long clavicles relative their humeri, even though they fall within the ranges of variation of early and recent humans. However, when scaled to body masses, their humeral lengths are relatively short, and their clavicular lengths are indistinguishable from those of Late Pleistocene and recent modern humans. The few sufficiently complete Early Pleistocene Homo clavicles seem to have relative lengths also well within recent human variation. Therefore, appropriately scaled clavicular length seems to have varied little through the genus Homo, and it should not be used to account for other aspects of Neandertal biology or their phylogenetic status. PMID:24616525

  18. Aerodynamic Design Criteria for Class 8 Heavy Vehicles Trailer Base Devices to Attain Optimum Performance

    SciTech Connect

    Salari, K; Ortega, J

    2010-12-13

    Lawrence Livermore National Laboratory (LLNL) as part of its Department of Energy (DOE), Energy Efficiency and Renewable Energy (EERE), and Vehicle Technologies Program (VTP) effort has investigated class 8 tractor-trailer aerodynamics for many years. This effort has identified many drag producing flow structures around the heavy vehicles and also has designed and tested many new active and passive drag reduction techniques and concepts for significant on the road fuel economy improvements. As part of this effort a database of experimental, computational, and conceptual design for aerodynamic drag reduction devices has been established. The objective of this report is to provide design guidance for trailer base devices to improve their aerodynamic performance. These devices are commonly referred to as boattails, base flaps, tail devices, and etc. The information provided here is based on past research and our most recent full-scale experimental investigations in collaboration with Navistar Inc. Additional supporting data from LLNL/Navistar wind tunnel, track test, and on the road test will be published soon. The trailer base devices can be identified by 4 flat panels that are attached to the rear edges of the trailer base to form a closed cavity. These devices have been engineered in many different forms such as, inflatable and non-inflatable, 3 and 4-sided, closed and open cavity, and etc. The following is an in-depth discussion with some recommendations, based on existing data and current research activities, of changes that could be made to these devices to improve their aerodynamic performance. There are 6 primary factors that could influence the aerodynamic performance of trailer base devices: (1) Deflection angle; (2) Boattail length; (3) Sealing of edges and corners; (4) 3 versus 4-sided, Position of the 4th plate; (5) Boattail vertical extension, Skirt - boattail transition; and (6) Closed versus open cavity.

  19. The influence of carrier roughness on adhesion, content uniformity and the in vitro deposition of terbutaline sulphate from dry powder inhalers.

    PubMed

    Flament, Marie-Pierre; Leterme, Pierre; Gayot, Anne

    2004-05-01

    The aim of this study was to establish a correlation between carrier characteristics and the dispersibility of drug from the blend. The influence of the roughness of a commonly used carrier material, lactose monohydrate, on the adhesion, dose uniformity, and aerodynamic properties of a model drug, terbutaline sulphate was investigated. Evaluation of adhesion was carried out with a mechanical sieve and an Alpine air-jet sieve. For the characterisation of lactose roughness, we used image analysis software. Aerodynamic evaluation of fine particle dose and emitted dose was obtained using a twin stage impinger. The study with the mechanical sieve demonstrated that at least 60% of drug adheres to lactose. The Alpine air-jet sieve assays showed there was a correlation between drug separation from a carrier by sieving and that obtained from longer in vitro deposition studies. Adhesion, blend homogeneity and stability are related to the surface roughness of the lactose used as carrier. There is a linear relationship between the parameters "fine particle fraction" and "roughness". A compromise between homogeneity and drug liberation must be found: a certain roughness is necessary to allow for drug adhesion and blend homogeneity, but if too high it will prevent drug liberation after inhalation.

  20. The influence of carrier roughness on adhesion, content uniformity and the in vitro deposition of terbutaline sulphate from dry powder inhalers.

    PubMed

    Flament, Marie-Pierre; Leterme, Pierre; Gayot, Anne

    2004-05-01

    The aim of this study was to establish a correlation between carrier characteristics and the dispersibility of drug from the blend. The influence of the roughness of a commonly used carrier material, lactose monohydrate, on the adhesion, dose uniformity, and aerodynamic properties of a model drug, terbutaline sulphate was investigated. Evaluation of adhesion was carried out with a mechanical sieve and an Alpine air-jet sieve. For the characterisation of lactose roughness, we used image analysis software. Aerodynamic evaluation of fine particle dose and emitted dose was obtained using a twin stage impinger. The study with the mechanical sieve demonstrated that at least 60% of drug adheres to lactose. The Alpine air-jet sieve assays showed there was a correlation between drug separation from a carrier by sieving and that obtained from longer in vitro deposition studies. Adhesion, blend homogeneity and stability are related to the surface roughness of the lactose used as carrier. There is a linear relationship between the parameters "fine particle fraction" and "roughness". A compromise between homogeneity and drug liberation must be found: a certain roughness is necessary to allow for drug adhesion and blend homogeneity, but if too high it will prevent drug liberation after inhalation. PMID:15081150

  1. Aerodynamic Simulation of Runback Ice Accretion

    NASA Technical Reports Server (NTRS)

    Broeren, Andy P.; Whalen, Edward A.; Busch, Greg T.; Bragg, Michael B.

    2010-01-01

    This report presents the results of recent investigations into the aerodynamics of simulated runback ice accretion on airfoils. Aerodynamic tests were performed on a full-scale model using a high-fidelity, ice-casting simulation at near-flight Reynolds (Re) number. The ice-casting simulation was attached to the leading edge of a 72-in. (1828.8-mm ) chord NACA 23012 airfoil model. Aerodynamic performance tests were conducted at the ONERA F1 pressurized wind tunnel over a Reynolds number range of 4.7?10(exp 6) to 16.0?10(exp 6) and a Mach (M) number ran ge of 0.10 to 0.28. For Re = 16.0?10(exp 6) and M = 0.20, the simulated runback ice accretion on the airfoil decreased the maximum lift coe fficient from 1.82 to 1.51 and decreased the stalling angle of attack from 18.1deg to 15.0deg. The pitching-moment slope was also increased and the drag coefficient was increased by more than a factor of two. In general, the performance effects were insensitive to Reynolds numb er and Mach number changes over the range tested. Follow-on, subscale aerodynamic tests were conducted on a quarter-scale NACA 23012 model (18-in. (457.2-mm) chord) at Re = 1.8?10(exp 6) and M = 0.18, using low-fidelity, geometrically scaled simulations of the full-scale castin g. It was found that simple, two-dimensional simulations of the upper- and lower-surface runback ridges provided the best representation of the full-scale, high Reynolds number iced-airfoil aerodynamics, whereas higher-fidelity simulations resulted in larger performance degrada tions. The experimental results were used to define a new subclassification of spanwise ridge ice that distinguishes between short and tall ridges. This subclassification is based upon the flow field and resulting aerodynamic characteristics, regardless of the physical size of the ridge and the ice-accretion mechanism.

  2. Surface Roughness of the Moon Derived from Multi-frequency Radar Data

    NASA Astrophysics Data System (ADS)

    Fa, W.

    2011-12-01

    globally using the regolith composition and the relation among the dielectric constant, bulk density, and regolith composition. The statistical properties of lunar surface roughness are described by the root mean square (RMS) height and correlation length, which represent the vertical and horizontal scale of the roughness. The correlation length and its scale dependence are studied using the topography data from laser altimeter observations from recent lunar missions. As these two parameters are known, surface roughness (RMS slope) can be estimated by minimizing the difference between the observed and modeled radar echo strength. Surface roughness of several regions over Oceanus Procellarum and southeastern highlands on lunar nearside are studied, and preliminary results show that maira is smoother than highlands at 70 cm scale, whereas the situation turns opposite at 12 and 4 cm scale. Surface roughness of young craters is in general higher than that of maria and highlands, indicating large rock population produced during impacting process.

  3. Using Large-Scale Roughness Elements to Control Sand and Dust Flux at the Keeler Dunes, Keeler, CA

    NASA Astrophysics Data System (ADS)

    Gillies, John; McCarley-Holder, Grace

    2014-05-01

    Controlling dust emission from areas that subsequently degrade air quality and threaten human and animal health and reduce the quality of life for people residing in proximity to such sources is necessary, but also challenging. Recent research has indicated that arrays of large roughness elements (height >0.3 m) can be used effectively to modulate sand transport and the associated dust emissions. Prediction of the rate of sand flux reduction as a function of downwind distance upon entering an array of roughness elements, and the equilibrium flux reduction in the interior of the array is possible using the known geometric properties of the roughness elements, their number, and published relationships. Air quality in the town of Keeler, CA (36 deg 29' 17.92" N, 117 deg 52' 24.62" W) is degraded by levels of particulate matter <10 µm aerodynamic diameter (PM10) during periods of elevated wind speeds due to sand transport and dust emissions in the nearby Keeler Dunes. A demonstration project was designed to evaluate the effectiveness of an array of roughness elements composed of solid elements and managed vegetation to meet sand and dust flux reduction criteria. This project has two major goals: 1) to demonstrate that solid roughness elements placed on areas of the Keeler Dunes immediately arrest sand movement to specified levels (target of 85% reduction), and 2) to assess whether native plant species, planted in the sheltered area of the solid roughness elements can effectively thrive and subsequently replace the solid roughness to achieve the desired sand flux reduction control efficiency. This poster describes the results related mostly to objective one, as considerable time has to pass before sufficient data will be obtained to evaluate the success of the planted and managed vegetation to achieve a control level provided by the solid element roughness array.

  4. Aerodynamic characteristics of a distinct wing-body configuration at Mach 6: Experiment, theory, and the hypersonic isolation principle

    NASA Technical Reports Server (NTRS)

    Penland, J. A.; Pittman, J. L.

    1985-01-01

    An experimental investigation has been conducted to determine the effect of wing leading edge sweep and wing translation on the aerodynamic characteristics of a wing body configuration at a free stream Mach number of about 6 and Reynolds number (based on body length) of 17.9 x 10 to the 6th power. Seven wings with leading edge sweep angles from -20 deg to 60 deg were tested on a common body over an angle of attack range from -12 deg to 10 deg. All wings had a common span, aspect ratio, taper ratio, planform area, and thickness ratio. Wings were translated longitudinally on the body to make tests possible with the total and exposed mean aerodynamic chords located at a fixed body station. Aerodynamic forces were found to be independent of wing sweep and translation, and pitching moments were constant when the exposed wing mean aerodynamic chord was located at a fixed body station. Thus, the Hypersonic Isolation Principle was verified. Theory applied with tangent wedge pressures on the wing and tangent cone pressures on the body provided excellent predictions of aerodynamic force coefficients but poor estimates of moment coefficients.

  5. Employing terrestrial photogrammetry to determine surface roughness on a debris covered glacier

    NASA Astrophysics Data System (ADS)

    Steiner, J. F.; Miles, E. S.; Brun, F.; Detert, M.

    2015-12-01

    Aerodynamic surface roughness is an essential parameter in energy balance studies on glaciers. While actual measurements on bare ice glaciers are rare, a number of literature values exist for different types of ice and snow covers. There are only very few constant values suggested in the literature for debris covered glaciers and actual measurements are even scarcer. This is a significant shortcoming as the debris surface is often very heterogeneous, which results in variable turbulent fluxes. These fluxes, which use surface roughness as an input parameter, are also employed to derive debris thickness from surface temperature. The increased use of aerial and terrestrial photogrammetry on glaciers provides an opportunity to better account for this present shortcoming. On a number of locations of Lirung Glacier in the Nepalese Himalayas we produced high resolution DEMs from terrestrial photogrammetry, from 1 x 1 m plots to a wider basin spanning more than 100 m. These images were then downsampled to different resolutions, ranging from one millimeter to a few centimeters. Employing different equations from the literature we determine surface roughness at different scales. This way we can discuss (1) the variability of results between different commonly used approaches, (2) the variability of surface roughness in space and (3) the impact of image resolution. From a tower with wind and temperature sensors at different heights we additionally infer surface roughness locally. We can then compare these values as well as see the effect of different wind speeds on the derivation of the value. Employing a software originally developed to determine grain size distributions in river beds from optical imagery, we additionally determine rock shapes and size as well as provide an estimate for the grain size distribution of the debris cover. This could provide an initial step to a better estimation of the porous space of the debris cover, which is essential to determine energy flux

  6. The work budget of rough faults

    NASA Astrophysics Data System (ADS)

    Newman, Patrick J.; Ashley Griffith, W.

    2014-12-01

    Faults in nature have measurable roughness at many scales and are not planar as generally idealized. We utilize the boundary element method to model the geomechanical response of synthetic rough faults in an isotropic, linear elastic continuum to external tectonic loading in terms of the work budget. Faults are generated with known fractal roughness parameters, including the root mean square slope (β), a measure of roughness amplitude, and the Hurst exponent (H), a measure of geometric self-similarity. Energy within the fault models is partitioned into external work (Wext), internal elastic strain energy (Wint), gravitational work (Wgrav), frictional work (Wfric), and seismic energy (Wseis). Results confirm that Wext, or work done on the external model boundaries, is smallest for a perfectly planar fault, and steadily increases with increasing β. This pattern is also observed in Wint, the energy expended in deforming the host rock. The opposite is true for gravitational work, or work done against gravity in uplifting host rock, as well as with frictional work, or energy dissipated with frictional slip on the fault, and Wseis, or seismic energy released during slip events. Effects of variation in H are not as large as for β, but Wgrav, Wfric, and Wseis increase with increasing H, with Wint and Wext decreasing across the same range. Remarkably, however, for a narrow range of roughness amplitudes which are commonly observed along natural faults, the total work of the system remains approximately constant, while slightly larger than the total work of a planar fault. Faults evolve toward the most mechanically efficient configuration; therefore we argue that this range of roughness amplitudes may represent an energy barrier, preventing faults from removing asperities and evolving to smooth, planar discontinuities. A similar conclusion is drawn from simulations at relatively shallow depths, with results showing that shallower faults have larger energy barriers, and can

  7. Simulation of vortex-dominated aerodynamic flows by a point-vortex method

    SciTech Connect

    Jia, Z.

    1988-01-01

    A numerical study was made to simulate vortex-dominated aerodynamic flows by the point-vortex method. Attention was divided into three different aspects: a nascent vortex-shedding algorithm, numerical demonstration of the point-vortex method, and the calculation of some example of aerodynamic interesting flows, which include two major categories: unsteady flow about a flat plate at a fixed angle of attack with and without a leading edge flap, and the transient, vortical cross flow produced by a slender delta wing. Evolution of the vortex traces, streamlines, surface pressure, and forces are studied. Flow features based on data obtained by different point-vortex shedding rates and different integration time steps and schemes are found to be consistent with each other on length and time scales comparable to as well as considerably smaller than those of the global flow.

  8. Transition aerodynamics for close-coupled wing-canard configuration. [V/STOL operations

    NASA Technical Reports Server (NTRS)

    Paulson, J. W., Jr.; Thomas, J. L.; Winston, M. M.

    1979-01-01

    A series of wind-tunnel tests have been conducted in the Langley V/STOL tunnel to investigate the low-speed longitudinal aerodynamics of two powered close-coupled wing-canard fighter configurations. A brief review is provided of the high angle-of-attack data for the two wing-canard configurations tested showing the benefits and problem areas of powered lift. A takeoff and landing analysis is presented which defines the area in which a fighter-type aircraft must operate in order to achieve 305-m field lengths. The wing-canard configuration data are analyzed in detail showing the problems of obtaining high lift, high drag, and trimmed moments. Assuming that power will be used to trim the aircraft, data are presented comparing the transition aerodynamics of the wing-canard configuration using a nose jet with several V/STOL configurations.

  9. Transonic and supersonic ground effect aerodynamics

    NASA Astrophysics Data System (ADS)

    Doig, G.

    2014-08-01

    A review of recent and historical work in the field of transonic and supersonic ground effect aerodynamics has been conducted, focussing on applied research on wings and aircraft, present and future ground transportation, projectiles, rocket sleds and other related bodies which travel in close ground proximity in the compressible regime. Methods for ground testing are described and evaluated, noting that wind tunnel testing is best performed with a symmetry model in the absence of a moving ground; sled or rail testing is ultimately preferable, though considerably more expensive. Findings are reported on shock-related ground influence on aerodynamic forces and moments in and accelerating through the transonic regime - where force reversals and the early onset of local supersonic flow is prevalent - as well as more predictable behaviours in fully supersonic to hypersonic ground effect flows.

  10. Integrated structural-aerodynamic design optimization

    NASA Technical Reports Server (NTRS)

    Haftka, R. T.; Kao, P. J.; Grossman, B.; Polen, D.; Sobieszczanski-Sobieski, J.

    1988-01-01

    This paper focuses on the processes of simultaneous aerodynamic and structural wing design as a prototype for design integration, with emphasis on the major difficulty associated with multidisciplinary design optimization processes, their enormous computational costs. Methods are presented for reducing this computational burden through the development of efficient methods for cross-sensitivity calculations and the implementation of approximate optimization procedures. Utilizing a modular sensitivity analysis approach, it is shown that the sensitivities can be computed without the expensive calculation of the derivatives of the aerodynamic influence coefficient matrix, and the derivatives of the structural flexibility matrix. The same process is used to efficiently evaluate the sensitivities of the wing divergence constraint, which should be particularly useful, not only in problems of complete integrated aircraft design, but also in aeroelastic tailoring applications.

  11. High speed civil transport aerodynamic optimization

    NASA Technical Reports Server (NTRS)

    Ryan, James S.

    1994-01-01

    This is a report of work in support of the Computational Aerosciences (CAS) element of the Federal HPCC program. Specifically, CFD and aerodynamic optimization are being performed on parallel computers. The long-range goal of this work is to facilitate teraflops-rate multidisciplinary optimization of aerospace vehicles. This year's work is targeted for application to the High Speed Civil Transport (HSCT), one of four CAS grand challenges identified in the HPCC FY 1995 Blue Book. This vehicle is to be a passenger aircraft, with the promise of cutting overseas flight time by more than half. To meet fuel economy, operational costs, environmental impact, noise production, and range requirements, improved design tools are required, and these tools must eventually integrate optimization, external aerodynamics, propulsion, structures, heat transfer, controls, and perhaps other disciplines. The fundamental goal of this project is to contribute to improved design tools for U.S. industry, and thus to the nation's economic competitiveness.

  12. CFD research, parallel computation and aerodynamic optimization

    NASA Technical Reports Server (NTRS)

    Ryan, James S.

    1995-01-01

    Over five years of research in Computational Fluid Dynamics and its applications are covered in this report. Using CFD as an established tool, aerodynamic optimization on parallel architectures is explored. The objective of this work is to provide better tools to vehicle designers. Submarine design requires accurate force and moment calculations in flow with thick boundary layers and large separated vortices. Low noise production is critical, so flow into the propulsor region must be predicted accurately. The High Speed Civil Transport (HSCT) has been the subject of recent work. This vehicle is to be a passenger vehicle with the capability of cutting overseas flight times by more than half. A successful design must surpass the performance of comparable planes. Fuel economy, other operational costs, environmental impact, and range must all be improved substantially. For all these reasons, improved design tools are required, and these tools must eventually integrate optimization, external aerodynamics, propulsion, structures, heat transfer and other disciplines.

  13. Aerodynamic interference between two Darrieus wind turbines

    SciTech Connect

    Schatzle, P.R.; Klimas, P.C.; Spahr, H.R.

    1981-04-01

    The effect of aerodynamic interference on the performance of two curved bladed Darrieus-type vertical axis wind turbines has been calculated using a vortex/lifting line aerodynamic model. The turbines have a tower-to-tower separation distance of 1.5 turbine diameters, with the line of turbine centers varying with respect to the ambient wind direction. The effects of freestream turbulence were neglected. For the cases examined, the calculations showed that the downwind turbine power decrement (1) was significant only when the line of turbine centers was coincident with the ambient wind direction, (2) increased with increasing tipspeed ratio, and (3) is due more to induced flow angularities downstream than to speed deficits near the downstream turbine.

  14. Wind turbine trailing edge aerodynamic brakes

    SciTech Connect

    Migliore, P G; Miller, L S; Quandt, G A

    1995-04-01

    Five trailing-edge devices were investigated to determine their potential as wind-turbine aerodynamic brakes, and for power modulation and load alleviation. Several promising configurations were identified. A new device, called the spoiler-flap, appears to be the best alternative. It is a simple device that is effective at all angles of attack. It is not structurally intrusive, and it has the potential for small actuating loads. It is shown that simultaneous achievement of a low lift/drag ratio and high drag is the determinant of device effectiveness, and that these attributes must persist up to an angle of attack of 45{degree}. It is also argued that aerodynamic brakes must be designed for a wind speed of at least 45 m/s (100 mph).

  15. Unsteady aerodynamic modeling for arbitrary motions

    NASA Technical Reports Server (NTRS)

    Edwards, J. W.; Ashley, H.; Breakwell, J. V.

    1977-01-01

    A study is presented on the unsteady aerodynamic loads due to arbitrary motions of a thin wing and their adaptation for the calculation of response and true stability of aeroelastic modes. In an Appendix, the use of Laplace transform techniques and the generalized Theodorsen function for two-dimensional incompressible flow is reviewed. New applications of the same approach are shown also to yield airloads valid for quite general small motions. Numerical results are given for the two-dimensional supersonic case. Previously proposed approximate methods, starting from simple harmonic unsteady theory, are evaluated by comparison with exact results obtained by the present approach. The Laplace inversion integral is employed to separate the loads into 'rational' and 'nonrational' parts, of which only the former are involved in aeroelastic stability of the wing. Among other suggestions for further work, it is explained how existing aerodynamic computer programs may be adapted in a fairly straightforward fashion to deal with arbitrary transients.

  16. Atmospheric determination for Shuttle aerodynamic studies

    NASA Technical Reports Server (NTRS)

    Price, J. M.

    1983-01-01

    Evaluation of the aerodynamic performance of the Shuttle during atmospheric reentry requires a determination of the free-stream atmospheric properties along the entry path. This determination must be of the best possible accuracy in order to fully utilize the Shuttle as an aerodynamic flight research vehicle. To accomplish this, two Shuttle Orbiter experiments, the Shuttle Upper Atmosphere Mass Spectrometer (SUMS) and the Shuttle Entry Air Data System (SEADS), are being developed to provide onboard measurements. SUMS will measure freestream parameters in the high altitude (above 90 km), high Mach number (M above 20) regions where conventional static pressure measurements are not available. SEADS will provide research quality data below about 90 km. Since these two experiments were not installed for the Shuttle developmental flights, an alternate method was needed to determine the freestream atmospheric properties along the entry trajectory. The method which was developed is described with a discussion of the results from the first five Shuttle flights.

  17. Rarefaction effects on Galileo probe aerodynamics

    NASA Technical Reports Server (NTRS)

    Moss, James N.; LeBeau, Gerald J.; Blanchard, Robert C.; Price, Joseph M.

    1996-01-01

    Solutions of aerodynamic characteristics are presented for the Galileo Probe entering Jupiter's hydrogen-helium atmosphere at a nominal relative velocity of 47.4 km/s. Focus is on predicting the aerodynamic drag coefficient during the transitional flow regime using the direct simulation Monte Carlo (DSMC) method. Accuracy of the probe's drag coefficient directly impacts the inferred atmospheric properties that are being extracted from the deceleration measurements made by onboard accelerometers as part of the Atmospheric Structure Experiment. The range of rarefaction considered in the present study extends from the free molecular limit to continuum conditions. Comparisons made with previous calculations and experimental measurements show the present results for drag to merge well with Navier-Stokes and experimental results for the least rarefied conditions considered.

  18. Device for reducing vehicle aerodynamic resistance

    DOEpatents

    Graham, Sean C.

    2006-08-22

    A device for reducing vehicle aerodynamic resistance for vehicles having a generally rectangular body disposed above rear wheels, comprising a plurality of load bearing struts attached to the bottom of the rectangular body adjacent its sides, a plurality of opposing flat sheets attached to the load bearing struts, and angled flaps attached to the lower edge of the opposing sheets defining an obtuse angle with the opposing flat sheets extending inwardly with respect to the sides of the rectangular body to a predetermined height above the ground, which, stiffen the opposing flat sheets, bend to resist damage when struck by the ground, and guide airflow around the rear wheels of the vehicle to reduce its aerodynamic resistance when moving.

  19. Device for reducing vehicle aerodynamic resistance

    DOEpatents

    Graham, Sean C.

    2006-03-07

    A device for reducing vehicle aerodynamic resistance for vehicles having a generally rectangular flat front face comprising a plurality of load bearing struts of a predetermined size attached to the flat front face adjacent the sides and top thereof, a pair of pliable opposing flat sheets having an outside edge portion attached to the flat front face adjacent the sides thereof and an upper edge with a predetermined curve; the opposing flat sheets being bent and attached to the struts to form effective curved airfoil shapes, and a top pliable flat sheet disposed adjacent the top of the flat front face and having predetermined curved side edges, which, when the top sheet is bent and attached to the struts to form an effective curved airfoil shape, mate with the curved upper edges of the opposing sheets to complete the aerodynamic device.

  20. Nash equilibrium and multi criterion aerodynamic optimization

    NASA Astrophysics Data System (ADS)

    Tang, Zhili; Zhang, Lianhe

    2016-06-01

    Game theory and its particular Nash Equilibrium (NE) are gaining importance in solving Multi Criterion Optimization (MCO) in engineering problems over the past decade. The solution of a MCO problem can be viewed as a NE under the concept of competitive games. This paper surveyed/proposed four efficient algorithms for calculating a NE of a MCO problem. Existence and equivalence of the solution are analyzed and proved in the paper based on fixed point theorem. Specific virtual symmetric Nash game is also presented to set up an optimization strategy for single objective optimization problems. Two numerical examples are presented to verify proposed algorithms. One is mathematical functions' optimization to illustrate detailed numerical procedures of algorithms, the other is aerodynamic drag reduction of civil transport wing fuselage configuration by using virtual game. The successful application validates efficiency of algorithms in solving complex aerodynamic optimization problem.

  1. Mimicking the humpback whale: An aerodynamic perspective

    NASA Astrophysics Data System (ADS)

    Aftab, S. M. A.; Razak, N. A.; Mohd Rafie, A. S.; Ahmad, K. A.

    2016-07-01

    This comprehensive review aims to provide a critical overview of the work on tubercles in the past decade. The humpback whale is of interest to aerodynamic/hydrodynamic researchers, as it performs manoeuvres that baffle the imagination. Researchers have attributed these capabilities to the presence of lumps, known as tubercles, on the leading edge of the flipper. Tubercles generate a unique flow control mechanism, offering the humpback exceptional manoeuverability. Experimental and numerical studies have shown that the flow pattern over the tubercle wing is quite different from conventional wings. Research on the Tubercle Leading Edge (TLE) concept has helped to clarify aerodynamic issues such as flow separation, tonal noise and dynamic stall. TLE shows increased lift by delaying and restricting spanwise separation. A summary of studies on different airfoils and reported improvement in performance is outlined. The major contributions and limitations of previous work are also reported.

  2. Aerodynamic Shape Optimization Using Hybridized Differential Evolution

    NASA Technical Reports Server (NTRS)

    Madavan, Nateri K.

    2003-01-01

    An aerodynamic shape optimization method that uses an evolutionary algorithm known at Differential Evolution (DE) in conjunction with various hybridization strategies is described. DE is a simple and robust evolutionary strategy that has been proven effective in determining the global optimum for several difficult optimization problems. Various hybridization strategies for DE are explored, including the use of neural networks as well as traditional local search methods. A Navier-Stokes solver is used to evaluate the various intermediate designs and provide inputs to the hybrid DE optimizer. The method is implemented on distributed parallel computers so that new designs can be obtained within reasonable turnaround times. Results are presented for the inverse design of a turbine airfoil from a modern jet engine. (The final paper will include at least one other aerodynamic design application). The capability of the method to search large design spaces and obtain the optimal airfoils in an automatic fashion is demonstrated.

  3. Vortical sources of aerodynamic force and moment

    NASA Technical Reports Server (NTRS)

    Wu, J. Z.; Wu, J. M.

    1989-01-01

    It is shown that the aerodynamic force and moment can be expressed in terms of vorticity distribution (and entropy variation for compressible flow) on near wake plane, or in terms of boundary vorticity flux on the body surface. Thus the vortical sources of lift and drag are clearly identified, which is the real physical basis of optimal aerodynamic design. Moreover, these sources are highly compact, hence allowing one to concentrate on key local regions of the configuration, which have dominating effect to the lift and drag. A detail knowledge of the vortical low requires measuring or calculating the vorticity and dilatation field, which is however still a challenging task. Nevertheless, this type of formulation has some unique advantages; and how to set up a well-posed problem, in particular how to establish vorticity-dilatation boundary conditions, is addressed.

  4. Aerodynamic control with passively pitching wings

    NASA Astrophysics Data System (ADS)

    Gravish, Nick; Wood, Robert

    Flapping wings may pitch passively under aerodynamic and inertial loads. Such passive pitching is observed in flapping wing insect and robot flight. The effect of passive wing pitch on the control dynamics of flapping wing flight are unexplored. Here we demonstrate in simulation and experiment the critical role wing pitching plays in yaw control of a flapping wing robot. We study yaw torque generation by a flapping wing allowed to passively rotate in the pitch axis through a rotational spring. Yaw torque is generated through alternating fast and slow upstroke and and downstroke. Yaw torque sensitively depends on both the rotational spring force law and spring stiffness, and at a critical spring stiffness a bifurcation in the yaw torque control relationship occurs. Simulation and experiment reveal the dynamics of this bifurcation and demonstrate that anomalous yaw torque from passively pitching wings is the result of aerodynamic and inertial coupling between the pitching and stroke-plane dynamics.

  5. An Interactive Educational Tool for Compressible Aerodynamics

    NASA Technical Reports Server (NTRS)

    Benson, Thomas J.

    1994-01-01

    A workstation-based interactive educational tool was developed to aid in the teaching of undergraduate compressible aerodynamics. The tool solves for the supersonic flow past a wedge using the equations found in NACA 1135. The student varies the geometry or flow conditions through a graphical user interface and the new conditions are calculated immediately. Various graphical formats present the variation of flow results to the student. One such format leads the student to the generation of some of the graphs found in NACA-1135. The tool includes interactive questions and answers to aid in both the use of the tool and to develop an understanding of some of the complexities of compressible aerodynamics. A series of help screens make the simulator easy to learn and use. This paper will detail the numerical methods used in the tool and describe how it can be used and modified.

  6. Hypersonic viscous flow over large roughness elements

    NASA Astrophysics Data System (ADS)

    Chang, Chau-Lyan; Choudhari, Meelan M.

    2011-06-01

    Viscous flow over discrete or distributed surface roughness has great implications for hypersonic flight due to aerothermodynamic considerations related to laminar-turbulent transition. Current prediction capability is greatly hampered by the limited knowledge base for such flows. To help fill that gap, numerical computations are used to investigate the intricate flow physics involved. An unstructured mesh, compressible Navier-Stokes code based on the space-time conservation element, solution element (CESE) method is used to perform time-accurate Navier-Stokes calculations for two roughness shapes investigated in wind tunnel experiments at NASA Langley Research Center. It was found through 2D parametric study that at subcritical Reynolds numbers, spontaneous absolute instability accompanying by sustained vortex shedding downstream of the roughness is likely to take place at subsonic free-stream conditions. On the other hand, convective instability may be the dominant mechanism for supersonic boundary layers. Three-dimensional calculations for both a rectangular and a cylindrical roughness element at post-shock Mach numbers of 4.1 and 6.5 also confirm that no self-sustained vortex generation from the top face of the roughness is observed, despite the presence of flow unsteadiness for the smaller post-shock Mach number case.

  7. Hypersonic Viscous Flow Over Large Roughness Elements

    NASA Technical Reports Server (NTRS)

    Chang, Chau-Lyan; Choudhari, Meelan M.

    2009-01-01

    Viscous flow over discrete or distributed surface roughness has great implications for hypersonic flight due to aerothermodynamic considerations related to laminar-turbulent transition. Current prediction capability is greatly hampered by the limited knowledge base for such flows. To help fill that gap, numerical computations are used to investigate the intricate flow physics involved. An unstructured mesh, compressible Navier-Stokes code based on the space-time conservation element, solution element (CESE) method is used to perform time-accurate Navier-Stokes calculations for two roughness shapes investigated in wind tunnel experiments at NASA Langley Research Center. It was found through 2D parametric study that at subcritical Reynolds numbers, spontaneous absolute instability accompanying by sustained vortex shedding downstream of the roughness is likely to take place at subsonic free-stream conditions. On the other hand, convective instability may be the dominant mechanism for supersonic boundary layers. Three-dimensional calculations for both a rectangular and a cylindrical roughness element at post-shock Mach numbers of 4.1 and 6.5 also confirm that no self-sustained vortex generation from the top face of the roughness is observed, despite the presence of flow unsteadiness for the smaller post-shock Mach number case.

  8. New aspects of subsonic aerodynamic noise theory

    NASA Technical Reports Server (NTRS)

    Goldstein, M. E.; Howes, W. L.

    1973-01-01

    A theory of aerodynamic noise is presented which differs from Lighthill's theory primarily in the way in which convection of the noise sources is treated. The sound directivity pattern obtained from the present theory agrees better with jet-noise directivity data than does that obtained from Lighthill's theory. The results imply that the shear-noise contribution to jet noise is smaller than previously expected.

  9. Aerodynamic design lowers truck fuel consumption

    NASA Technical Reports Server (NTRS)

    Steers, L.

    1978-01-01

    Energy-saving concepts in truck design are emerging from developing new shapes with improved aerodynamic flow properties that can reduce air-drag coefficient of conventional tractor-trailers without requiring severe design changes or compromising load-carrying capability. Improvements are expected to decrease somewhat with increased wind velocities and would be affected by factors such as terrain, driving techniques, and mechanical condition.

  10. Aerodynamic considerations in open shelters. Final report

    SciTech Connect

    Hickman, R.G.

    1984-11-01

    Aerodynamic factors are addressed bearing on the suitability of open structures as blast shelters. Blast closures and attenuator designs are discussed. The research on shelter filling is reviewed; this includes both experimental and theoretical work on scale models and full-scale structures of large dimensions. Shock-dominated and pressure-gradient-dominated shelter-filling mechanisms are described and their potential effects on people are discussed.

  11. Device for reducing vehicle aerodynamic resistance

    DOEpatents

    Graham, Sean C.

    2005-02-15

    A device for a vehicle with a pair of swinging rear doors, which converts flat sheets of pliable material hinged to the sides of the vehicle adjacent the rear thereof into effective curved airfoils that reduce the aerodynamic resistance of the vehicle, when the doors are closed by hand, utilizing a plurality of stiffeners disposed generally parallel to the doors and affixed to the sheets and a plurality of collapsible tension bearings struts attached to each stiffener and the adjacent door.

  12. The aerodynamics of hovering flight in Drosophila.

    PubMed

    Fry, Steven N; Sayaman, Rosalyn; Dickinson, Michael H

    2005-06-01

    Using 3D infrared high-speed video, we captured the continuous wing and body kinematics of free-flying fruit flies, Drosophila melanogaster, during hovering and slow forward flight. We then 'replayed' the wing kinematics on a dynamically scaled robotic model to measure the aerodynamic forces produced by the wings. Hovering animals generate a U-shaped wing trajectory, in which large drag forces during a downward plunge at the start of each stroke create peak vertical forces. Quasi-steady mechanisms could account for nearly all of the mean measured force required to hover, although temporal discrepancies between instantaneous measured forces and model predictions indicate that unsteady mechanisms also play a significant role. We analyzed the requirements for hovering from an analysis of the time history of forces and moments in all six degrees of freedom. The wing kinematics necessary to generate sufficient lift are highly constrained by the requirement to balance thrust and pitch torque over the stroke cycle. We also compare the wing motion and aerodynamic forces of free and tethered flies. Tethering causes a strong distortion of the stroke pattern that results in a reduction of translational forces and a prominent nose-down pitch moment. The stereotyped distortion under tethered conditions is most likely due to a disruption of sensory feedback. Finally, we calculated flight power based directly on the measurements of wing motion and aerodynamic forces, which yielded a higher estimate of muscle power during free hovering flight than prior estimates based on time-averaged parameters. This discrepancy is mostly due to a two- to threefold underestimate of the mean profile drag coefficient in prior studies. We also compared our values with the predictions of the same time-averaged models using more accurate kinematic and aerodynamic input parameters based on our high-speed videography measurements. In this case, the time-averaged models tended to overestimate flight

  13. HSCT high lift system aerodynamic requirements

    NASA Technical Reports Server (NTRS)

    Paulson, John A.

    1992-01-01

    The viewgraphs and discussion of high lift system aerodynamic requirements are provided. Low speed aerodynamics has been identified as critical to the successful development of a High Speed Civil Transport (HSCT). The airplane must takeoff and land at a sufficient number of existing or projected airports to be economically viable. At the same time, community noise must be acceptable. Improvements in cruise drag, engine fuel consumption, and structural weight tend to decrease the wing size and thrust required of engines. Decreasing wing size increases the requirements for effective and efficient low speed characteristics. Current design concepts have already been compromised away from better cruise wings for low speed performance. Flap systems have been added to achieve better lift-to-drag ratios for climb and approach and for lower pitch attitudes for liftoff and touchdown. Research to achieve improvements in low speed aerodynamics needs to be focused on areas most likely to have the largest effect on the wing and engine sizing process. It would be desirable to provide enough lift to avoid sizing the airplane for field performance and to still meet the noise requirements. The airworthiness standards developed in 1971 will be the basis for performance requirements for an airplane that will not be critical to the airplane wing and engine size. The lift and drag levels that were required to meet the performance requirements of tentative airworthiness standards established in 1971 and that were important to community noise are identified. Research to improve the low speed aerodynamic characteristics of the HSCT needs to be focused in the areas of performance deficiency and where noise can be reduced. Otherwise, the wing planform, engine cycle, or other parameters for a superior cruising airplane would have to be changed.

  14. The Effect of Volumetric Porosity on Roughness Element Drag

    NASA Astrophysics Data System (ADS)

    Gillies, John; Nickling, William; Nikolich, George; Etyemezian, Vicken

    2016-04-01

    Much attention has been given to understanding how the porosity of two dimensional structures affects the drag force exerted by boundary-layer flow on these flow obstructions. Porous structures such as wind breaks and fences are typically used to control the sedimentation of sand and snow particles or create micro-habitats in their lee. Vegetation in drylands also exerts control on sediment transport by wind due to aerodynamic effects and interaction with particles in transport. Recent research has also demonstrated that large spatial arrays of solid three dimensional roughness elements can be used to reduce sand transport to specified targets for control of wind erosion through the effect of drag partitioning and interaction of the moving sand with the large (>0.3 m high) roughness elements, but porous elements may improve the effectiveness of this approach. A thorough understanding of the role porosity plays in affecting the drag force on three-dimensional forms is lacking. To provide basic understanding of the relationship between the porosity of roughness elements and the force of drag exerted on them by fluid flow, we undertook a wind tunnel study that systematically altered the porosity of roughness elements of defined geometry (cubes, rectangular cylinders, and round cylinders) and measured the associated change in the drag force on the elements under similar Reynolds number conditions. The elements tested were of four basic forms: 1) same sized cubes with tubes of known diameter milled through them creating three volumetric porosity values and increasing connectivity between the tubes, 2) cubes and rectangular cylinders constructed of brass screen that nested within each other, and 3) round cylinders constructed of brass screen that nested within each other. The two-dimensional porosity, defined as the ratio of total surface area of the empty space to the solid surface area of the side of the element presented to the fluid flow was conserved at 0.519 for

  15. Future Challenges and Opportunities in Aerodynamics

    NASA Technical Reports Server (NTRS)

    Kumar, Ajay; Hefner, Jerry N.

    2000-01-01

    Investments in aeronautics research and technology have declined substantially over the last decade, in part due to the perception that technologies required in aircraft design are fairly mature and readily available. This perception is being driven by the fact that aircraft configurations, particularly the transport aircraft, have evolved only incrementally, over last several decades. If however, one considers that the growth in air travel is expected to triple in the next 20 years, it becomes quickly obvious that the evolutionary development of technologies is not going to meet the increased demands for safety, environmental compatibility, capacity, and economic viability. Instead, breakthrough technologies will he required both in traditional disciplines of aerodynamics, propulsion, structures, materials, controls, and avionics as well as in the multidisciplinary integration of these technologies into the design of future aerospace vehicles concepts. The paper discusses challenges and opportunities in the field of aerodynamics over the next decade. Future technology advancements in aerodynamics will hinge on our ability, to understand, model, and control complex, three-dimensional, unsteady viscous flow across the speed range. This understanding is critical for developing innovative flow and noise control technologies and advanced design tools that will revolutionize future aerospace vehicle systems and concepts. Specifically, the paper focuses on advanced vehicle concepts, flow and noise control technologies, and advanced design and analysis tools.

  16. The Aerodynamics of a Flying Sports Disc

    NASA Astrophysics Data System (ADS)

    Potts, Jonathan R.; Crowther, William J.

    2001-11-01

    The flying sports disc is a spin-stabilised axi-symmetric wing of quite remarkable design. A typical disc has an approximate elliptical cross-section and hollowed out under-side cavity, such as the Frisbee(TM) disc. An experimental study of flying disc aerodynamics, including both spinning and non-spinning tests, has been carried out in the wind tunnel. Load measurements, pressure data and flow visualisation techniques have enabled an explanation of the flow physics and provided data for free-flight simulations. A computer simulation that predicts free-flight trajectories from a given set of initial conditions was used to investigate the dynamics of a flying disc. This includes a six-degree of freedom mathematical model of disc flight mechanics, with aerodynamic coefficients derived from experimental data. A flying sports disc generates lift through forward velocity just like a conventional wing. The lift contributed by spin is insignificant and does not provide nearly enough down force to support hover. Without spin, the disc tumbles ground-ward under the influence of an unstable aerodynamic pitching moment. From a backhand throw however, spin is naturally given to the disc. The unchanged pitching moment now results in roll, due to gyroscopic precession, stabilising the disc in free-flight.

  17. Flapping wing aerodynamics: from insects to vertebrates.

    PubMed

    Chin, Diana D; Lentink, David

    2016-04-01

    More than a million insects and approximately 11,000 vertebrates utilize flapping wings to fly. However, flapping flight has only been studied in a few of these species, so many challenges remain in understanding this form of locomotion. Five key aerodynamic mechanisms have been identified for insect flight. Among these is the leading edge vortex, which is a convergent solution to avoid stall for insects, bats and birds. The roles of the other mechanisms - added mass, clap and fling, rotational circulation and wing-wake interactions - have not yet been thoroughly studied in the context of vertebrate flight. Further challenges to understanding bat and bird flight are posed by the complex, dynamic wing morphologies of these species and the more turbulent airflow generated by their wings compared with that observed during insect flight. Nevertheless, three dimensionless numbers that combine key flow, morphological and kinematic parameters - the Reynolds number, Rossby number and advance ratio - govern flapping wing aerodynamics for both insects and vertebrates. These numbers can thus be used to organize an integrative framework for studying and comparing animal flapping flight. Here, we provide a roadmap for developing such a framework, highlighting the aerodynamic mechanisms that remain to be quantified and compared across species. Ultimately, incorporating complex flight maneuvers, environmental effects and developmental stages into this framework will also be essential to advancing our understanding of the biomechanics, movement ecology and evolution of animal flight. PMID:27030773

  18. Improving the aerodynamics of top fuel dragsters

    SciTech Connect

    Winn, R.C.; Kohlman, D.L.; Kenner, M.T.

    1998-07-01

    The standard drag race is a straight ahead quarter mile race from a standing stop. As engine technology has improved, the speeds attained at the end of the quarter mile have increased. As the speed has increased, the importance of aerodynamic effects on the dragster has also increased. Lift and drag are the two primary aerodynamic effects. Lift is produced vertically downward to increase the normal force on the rear wheels, thereby increasing the ability to transmit energy from the engine through the wheels to the racetrack. Drag is an unwanted aerodynamic effect. Drag is produced by viscous interaction between the dragster and the air, by separation causing profile drag, and as a result of the lift being produced. This paper addresses the mechanisms of lift and drag production by a high speed dragster and proposes some design changes that can decrease the drag while maintaining the necessary negative lift. Preliminary wind tunnel tests on dragster models confirm that reductions in drag can be achieved. The effects of these changes on the elapsed time and final speed are estimated using a computer simulation of a quarter mile drag race. The simulation predicts a decrease in elapsed time of almost 0.1 seconds and an increase in top speed of approximately 10 miles per hour.

  19. Aerodynamic Design Opportunities for Future Supersonic Aircraft

    NASA Technical Reports Server (NTRS)

    Wood, Richard M.; Bauer, Steven X. S.; Flamm, Jeffrey D.

    2002-01-01

    A discussion of a diverse set of aerodynamic opportunities to improve the aerodynamic performance of future supersonic aircraft has been presented and discussed. These ideas are offered to the community in a hope that future supersonic vehicle development activities will not be hindered by past efforts. A number of nonlinear flow based drag reduction technologies are presented and discussed. The subject technologies are related to the areas of interference flows, vehicle concepts, vortex flows, wing design, advanced control effectors, and planform design. The authors also discussed the importance of improving the aerodynamic design environment to allow creativity and knowledge greater influence. A review of all of the data presented show that pressure drag reductions on the order of 50 to 60 counts are achievable, compared to a conventional supersonic cruise vehicle, with the application of several of the discussed technologies. These drag reductions would correlate to a 30 to 40% increase in cruise L/D (lift-to-drag ratio) for a commercial supersonic transport.

  20. Aerodynamics for the Mars Phoenix Entry Capsule

    NASA Technical Reports Server (NTRS)

    Edquist, Karl T.; Desai, Prasun N.; Schoenenberger, Mark

    2008-01-01

    Pre-flight aerodynamics data for the Mars Phoenix entry capsule are presented. The aerodynamic coefficients were generated as a function of total angle-of-attack and either Knudsen number, velocity, or Mach number, depending on the flight regime. The database was constructed using continuum flowfield computations and data from the Mars Exploration Rover and Viking programs. Hypersonic and supersonic static coefficients were derived from Navier-Stokes solutions on a pre-flight design trajectory. High-altitude data (free-molecular and transitional regimes) and dynamic pitch damping characteristics were taken from Mars Exploration Rover analysis and testing. Transonic static coefficients from Viking wind tunnel tests were used for capsule aerodynamics under the parachute. Static instabilities were predicted at two points along the reference trajectory and were verified by reconstructed flight data. During the hypersonic instability, the capsule was predicted to trim at angles as high as 2.5 deg with an on-axis center-of-gravity. Trim angles were predicted for off-nominal pitching moment (4.2 deg peak) and a 5 mm off-axis center-ofgravity (4.8 deg peak). Finally, hypersonic static coefficient sensitivities to atmospheric density were predicted to be within uncertainty bounds.

  1. Asymmetric Uncertainty Expression for High Gradient Aerodynamics

    NASA Technical Reports Server (NTRS)

    Pinier, Jeremy T

    2012-01-01

    When the physics of the flow around an aircraft changes very abruptly either in time or space (e.g., flow separation/reattachment, boundary layer transition, unsteadiness, shocks, etc), the measurements that are performed in a simulated environment like a wind tunnel test or a computational simulation will most likely incorrectly predict the exact location of where (or when) the change in physics happens. There are many reasons for this, includ- ing the error introduced by simulating a real system at a smaller scale and at non-ideal conditions, or the error due to turbulence models in a computational simulation. The un- certainty analysis principles that have been developed and are being implemented today do not fully account for uncertainty in the knowledge of the location of abrupt physics changes or sharp gradients, leading to a potentially underestimated uncertainty in those areas. To address this problem, a new asymmetric aerodynamic uncertainty expression containing an extra term to account for a phase-uncertainty, the magnitude of which is emphasized in the high-gradient aerodynamic regions is proposed in this paper. Additionally, based on previous work, a method for dispersing aerodynamic data within asymmetric uncer- tainty bounds in a more realistic way has been developed for use within Monte Carlo-type analyses.

  2. Flapping wing aerodynamics: from insects to vertebrates.

    PubMed

    Chin, Diana D; Lentink, David

    2016-04-01

    More than a million insects and approximately 11,000 vertebrates utilize flapping wings to fly. However, flapping flight has only been studied in a few of these species, so many challenges remain in understanding this form of locomotion. Five key aerodynamic mechanisms have been identified for insect flight. Among these is the leading edge vortex, which is a convergent solution to avoid stall for insects, bats and birds. The roles of the other mechanisms - added mass, clap and fling, rotational circulation and wing-wake interactions - have not yet been thoroughly studied in the context of vertebrate flight. Further challenges to understanding bat and bird flight are posed by the complex, dynamic wing morphologies of these species and the more turbulent airflow generated by their wings compared with that observed during insect flight. Nevertheless, three dimensionless numbers that combine key flow, morphological and kinematic parameters - the Reynolds number, Rossby number and advance ratio - govern flapping wing aerodynamics for both insects and vertebrates. These numbers can thus be used to organize an integrative framework for studying and comparing animal flapping flight. Here, we provide a roadmap for developing such a framework, highlighting the aerodynamic mechanisms that remain to be quantified and compared across species. Ultimately, incorporating complex flight maneuvers, environmental effects and developmental stages into this framework will also be essential to advancing our understanding of the biomechanics, movement ecology and evolution of animal flight.

  3. Survey of lift-fan aerodynamic technology

    NASA Technical Reports Server (NTRS)

    Hickey, David H.; Kirk, Jerry V.

    1993-01-01

    Representatives of NASA Ames Research Center asked that a summary of technology appropriate for lift-fan powered short takeoff/vertical landing (STOVL) aircraft be prepared so that new programs could more easily benefit from past research efforts. This paper represents one of six prepared for that purpose. The authors have conducted or supervised the conduct of research on lift-fan powered STOVL designs and some of their important components for decades. This paper will first address aerodynamic modeling requirements for experimental programs to assure realistic, trustworthy results. It will next summarize the results or efforts to develop satisfactory specialized STOVL components such as inlets and flow deflectors. It will also discuss problems with operation near the ground, aerodynamics while under lift-fan power, and aerodynamic prediction techniques. Finally, results of studies to reduce lift-fan noise will be presented. The paper will emphasize results from large scale experiments, where available, for reasons that will be brought out in the discussion. Some work with lift-engine powered STOVL aircraft is also applicable to lift-fan technology and will be presented herein. Small-scale data will be used where necessary to fill gaps.

  4. Myofilament length dependent activation

    SciTech Connect

    de Tombe, Pieter P.; Mateja, Ryan D.; Tachampa, Kittipong; Mou, Younss Ait; Farman, Gerrie P.; Irving, Thomas C.

    2010-05-25

    The Frank-Starling law of the heart describes the interrelationship between end-diastolic volume and cardiac ejection volume, a regulatory system that operates on a beat-to-beat basis. The main cellular mechanism that underlies this phenomenon is an increase in the responsiveness of cardiac myofilaments to activating Ca{sup 2+} ions at a longer sarcomere length, commonly referred to as myofilament length-dependent activation. This review focuses on what molecular mechanisms may underlie myofilament length dependency. Specifically, the roles of inter-filament spacing, thick and thin filament based regulation, as well as sarcomeric regulatory proteins are discussed. Although the 'Frank-Starling law of the heart' constitutes a fundamental cardiac property that has been appreciated for well over a century, it is still not known in muscle how the contractile apparatus transduces the information concerning sarcomere length to modulate ventricular pressure development.

  5. Length Paradox in Relativity

    ERIC Educational Resources Information Center

    Martins, Roberto de A.

    1978-01-01

    Describes a thought experiment using a general analysis approach with Lorentz transformations to show that the apparent self-contradictions of special relativity concerning the length-paradox are really non-existant. (GA)

  6. The minimal channel: a fast and direct method for characterising roughness

    NASA Astrophysics Data System (ADS)

    MacDonald, Michael; Chung, Daniel; Hutchins, Nicholas; Chan, Leon; Ooi, Andrew; García-Mayoral, Ricardo

    2016-04-01

    Roughness only alters the near-wall region of turbulent flow and leaves the outer-layer unaffected, making it a prime candidate for the minimal-span channel framework which only captures the near-wall flow. Recently, Chung et al. (J. Fluid Mech., vol. 773, 2015, pp. 418-431) showed that the minimal-span channel can accurately characterise the hydraulic behaviour of roughness. Following on from this, we aim to further optimise the minimal-span channel framework by primarily noting that the outer layer it produces is inherently incorrect, and as such modifications to this region can be made to improve performance. Firstly, a half-height channel with slip wall is shown to reproduce the near-wall behaviour seen in a standard channel, but with half the number of grid points. Next, a forcing model is introduced into the outer layer of a half-height channel. This reduces the high streamwise velocity associated with the minimal channel and allows for a larger computational time step. The streamwise length of the channel is also investigated independent of the previous improvements, and suggests the minimum length should be at least 3 times the spanwise width and also 1000 viscous-units long, whichever is longer. Finally, an investigation is conducted to see if varying the roughness Reynolds number with time is a feasible method for obtaining the full hydraulic behaviour of a rough surface, instead of running multiple simulations at fixed roughness Reynolds numbers.

  7. Discrete Roughness Transition for Hypersonic Flight Vehicles

    NASA Technical Reports Server (NTRS)

    Berry, Scott A.; Horvath, Thomas J.

    2007-01-01

    The importance of discrete roughness and the correlations developed to predict the onset of boundary layer transition on hypersonic flight vehicles are discussed. The paper is organized by hypersonic vehicle applications characterized in a general sense by the boundary layer: slender with hypersonic conditions at the edge of the boundary layer, moderately blunt with supersonic, and blunt with subsonic. This paper is intended to be a review of recent discrete roughness transition work completed at NASA Langley Research Center in support of agency flight test programs. First, a review is provided of discrete roughness wind tunnel data and the resulting correlations that were developed. Then, results obtained from flight vehicles, in particular the recently flown Hyper-X and Shuttle missions, are discussed and compared to the ground-based correlations.

  8. Editorial: Redefining Length

    SciTech Connect

    Sprouse, Gene D.

    2011-07-15

    Technological changes have moved publishing to electronic-first publication where the print version has been relegated to simply another display mode. Distribution in HTML and EPUB formats, for example, changes the reading environment and reduces the need for strict pagination. Therefore, in an effort to streamline the calculation of length, the APS journals will no longer use the printed page as the determining factor for length. Instead the journals will now use word counts (or word equivalents for tables, figures, and equations) to establish length; for details please see http://publish.aps.org/authors/length-guide. The title, byline, abstract, acknowledgment, and references will not be included in these counts allowing authors the freedom to appropriately credit coworkers, funding sources, and the previous literature, bringing all relevant references to the attention of readers. This new method for determining length will be easier for authors to calculate in advance, and lead to fewer length-associated revisions in proof, yet still retain the quality of concise communication that is a virtue of short papers.

  9. Post-Flight Aerodynamic and Aerothermal Model Validation of a Supersonic Inflatable Aerodynamic Decelerator

    NASA Technical Reports Server (NTRS)

    Tang, Chun; Muppidi, Suman; Bose, Deepak; Van Norman, John W.; Tanimoto, Rebekah; Clark, Ian

    2015-01-01

    NASA's Low Density Supersonic Decelerator Program is developing new technologies that will enable the landing of heavier payloads in low density environments, such as Mars. A recent flight experiment conducted high above the Hawaiian Islands has demonstrated the performance of several decelerator technologies. In particular, the deployment of the Robotic class Supersonic Inflatable Aerodynamic Decelerator (SIAD-R) was highly successful, and valuable data were collected during the test flight. This paper outlines the Computational Fluid Dynamics (CFD) analysis used to estimate the aerodynamic and aerothermal characteristics of the SIAD-R. Pre-flight and post-flight predictions are compared with the flight data, and a very good agreement in aerodynamic force and moment coefficients is observed between the CFD solutions and the reconstructed flight data.

  10. Evaluation of Dry, Rough Vacuum Pumps

    NASA Technical Reports Server (NTRS)

    Hunter, Brian

    2006-01-01

    This document provides information on the testing and evaluation of thirteen dry rough vacuum pumps of various designs and from various manufacturers. Several types of rough vacuum pumps were evaluated, including scroll, roots, and diaphragm pumps. Tests included long term testing, speed curve generation, voltage variance, vibrations emissions and susceptibility, electromagnetic interference emissions and susceptibility, static leak rate, exhaust restriction, response/recovery time tests, and a contamination analysis for scroll pumps. Parameters were found for operation with helium, which often is not provided from the manufacturer

  11. Surface roughness evolution of nanocomposite thin films

    SciTech Connect

    Turkin, A. A.; Pei, Y. T.; Shaha, K. P.; Chen, C. Q.; Vainshtein, D. I.; Hosson, J. Th. M. de

    2009-01-01

    An analysis of dynamic roughening and smoothening mechanisms of thin films grown with pulsed-dc magnetron sputtering is presented. The roughness evolution has been described by a linear stochastic equation, which contains the second- and fourth-order gradient terms. Dynamic smoothening of the growing interface is explained by ballistic effects resulting from impingements of ions to the growing thin film. These ballistic effects are sensitive to the flux and energy of impinging ions. The predictions of the model are compared with experimental data, and it is concluded that the thin film roughness can be further controlled by adjusting waveform, frequency, and width of dc pulses.

  12. Surface roughness effects in elastohydrodynamic contacts

    NASA Technical Reports Server (NTRS)

    Tripp, J. H.; Hamrock, B. J.

    1985-01-01

    Surface roughness effects in full-film EHL contacts were studied. A flow factor modification to the Reynolds equation was applied to piezoviscous-elastic line contacts. Results for ensemble-averaged film shape, pressure distribution, and other mechanical quantities were obtained. Asperities elongated in the flow direction by a factor exceeding two decreased both film shape and pressure extrema at constant load; isotropic or transverse asperities increased these extrema. The largest effects are displayed by traction, which increased by over 5% for isotropic or transverse asperities and by slightly less for longitudinal roughness.

  13. Venus surface roughness and Magellan stereo data

    NASA Technical Reports Server (NTRS)

    Maurice, Kelly E.; Leberl, Franz W.; Norikane, L.; Hensley, Scott

    1994-01-01

    Presented are results of some studies to develop tools useful for the analysis of Venus surface shape and its roughness. Actual work was focused on Maxwell Montes. The analyses employ data acquired by means of NASA's Magellan satellite. The work is primarily concerned with deriving measurements of the Venusian surface using Magellan stereo SAR. Roughness was considered by means of a theoretical analyses based on digital elevation models (DEM's), on single Magellan radar images combined with radiometer data, and on the use of multiple overlapping Magellan radar images from cycles 1, 2, and 3, again combined with collateral radiometer data.

  14. Fused silica fine grinding with low roughness

    NASA Astrophysics Data System (ADS)

    Dai, Lei; Gu, Yongqiang; Wu, Di

    2014-08-01

    Lithography-optics is one of the most complex optical systems. The fine grinding process is the most important step before polishing. Roughness and sub-surface damage (SSD) are essential outputs of fine grinding. We demonstrate the method that use fix abrasive cup tool with CNC grinding machine to complete the fine grinding process, even instead of lapping process. And experiment sample roughness can reach 23.40nm rms and Ra 18.554nm. The SSD estimate is about 2 μm which is also smaller than commercial lapping process. The fine grinding output can satisfy the lithography optic fabrication demands and efficiently reduce the polishing time.

  15. Roughness Perception of Haptically Displayed Fractal Surfaces

    NASA Technical Reports Server (NTRS)

    Costa, Michael A.; Cutkosky, Mark R.; Lau, Sonie (Technical Monitor)

    2000-01-01

    Surface profiles were generated by a fractal algorithm and haptically rendered on a force feedback joystick, Subjects were asked to use the joystick to explore pairs of surfaces and report to the experimenter which of the surfaces they felt was rougher. Surfaces were characterized by their root mean square (RMS) amplitude and their fractal dimension. The most important factor affecting the perceived roughness of the fractal surfaces was the RMS amplitude of the surface. When comparing surfaces of fractal dimension 1.2-1.35 it was found that the fractal dimension was negatively correlated with perceived roughness.

  16. Tritium Pumps for ITER Roughing System

    SciTech Connect

    Antipenkov, Alexander; Day, Christian; Mack, August; Wagner, Robert; Laesser, Rainer

    2005-07-15

    The ITER roughing system provides for both the initial pump-down of the vessel itself and the regular pump-out of the batch-regenerating cryopumps. This system must have a large pumping speed and cope with the radioactive gas tritium at the same time. The present paper shall highlight the results of the ITER roughing train optimization, discuss the modification of a Roots pump for tritium, and present the results of a ferrofluidic seal test and the first tests of a tailor-made tritium-proof Roots pump with inactive gases.

  17. Mask roughness induced LER control and mitigation: aberrations sensitivity study and alternate illumination scheme

    SciTech Connect

    McClinton, Brittany M.; Naulleau, Patrick P.

    2011-03-11

    Here we conduct a mask-roughness-induced line-edge-roughness (LER) aberrations sensitivity study both as a random distribution amongst the first 16 Fringe Zernikes (for overall aberration levels of 0.25, 0.50, and 0.75nm rms) as well as an individual aberrations sensitivity matrix over the first 37 Fringe Zernikes. Full 2D aerial image modeling for an imaging system with NA = 0.32 was done for both the 22-nm and 16-nm half-pitch nodes on a rough mask with a replicated surface roughness (RSR) of 100 pm and a correlation length of 32 nm at the nominal extreme-ultraviolet lithography (EUVL) wavelength of 13.5nm. As the ideal RSR value for commercialization of EUVL is 50 pm and under, and furthermore as has been shown elsewhere, a correlation length of 32 nm of roughness on the mask sits on the peak LER value for an NA = 0.32 imaging optic, these mask roughness values and consequently the aberration sensitivity study presented here, represent a worst-case scenario. The illumination conditions were chosen based on the possible candidates for the 22-nm and 16-nm half-pitch nodes, respectively. In the 22-nm case, a disk illumination setting of {sigma} = 0.50 was used, and for the 16-nm case, crosspole illumination with {sigma} = 0.10 at an optimum offset of dx = 0 and dy = .67 in sigma space. In examining how to mitigate mask roughness induced LER, we considered an alternate illumination scheme whereby a traditional dipole's angular spectrum is extended in the direction parallel to the line-and-space mask absorber pattern to represent a 'strip'. While this illumination surprisingly provides minimal improvement to the LER as compared to several alternate illumination schemes, the overall imaging quality in terms of image-log-slope (ILS) and contrast is improved.

  18. Numerical and experimental investigations on unsteady aerodynamics of flapping wings

    NASA Astrophysics Data System (ADS)

    Yu, Meilin

    The development of a dynamic unstructured grid high-order accurate spectral difference (SD) method for the three dimensional compressible Navier-Stokes (N-S) equations and its applications in flapping-wing aerodynamics are carried out in this work. Grid deformation is achieved via an algebraic blending strategy to save computational cost. The Geometric Conservation Law (GCL) is imposed to ensure that grid deformation will not contaminate the flow physics. A low Mach number preconditioning procedure is conducted in the developed solver to handle the bio-inspired flow. The capability of the low Mach number preconditioned SD solver is demonstrated by a series of two dimensional (2D) and three dimensional (3D) simulations of the unsteady vortex dominated flow. Several topics in the flapping wing aerodynamics are numerically and experimentally investigated in this work. These topics cover some of the cutting-edge issues in flapping wing aerodynamics, including the wake structure analysis, airfoil thickness and kinematics effects on the aerodynamic performances, vortex structure analysis around 3D flapping wings and the kinematics optimization. Wake structures behind a sinusoidally pitching NACA0012 airfoil are studied with both experimental and numerical approaches. The experiments are carried out with Particle Image Velocimetry (PIV) and two types of wake transition processes, namely the transition from a drag-indicative wake to a thrust-indicative wake and that from the symmetric wake to the asymmetric wake are distinguished. The numerical results from the developed SD solver agree well with the experimental results. It is numerically found that the deflective direction of the asymmetric wake is determined by the initial conditions, e.g. initial phase angle. As most insects use thin wings (i. e., wing thickness is only a few percent of the chord length) in flapping flight, the effects of airfoil thickness on thrust generation are numerically investigated by simulating

  19. Nanoscale Roughness and Morphology Affect the IsoElectric Point of Titania Surfaces

    PubMed Central

    Borghi, Francesca; Vyas, Varun; Podestà, Alessandro; Milani, Paolo

    2013-01-01

    We report on the systematic investigation of the role of surface nanoscale roughness and morphology on the charging behaviour of nanostructured titania (TiO2) surfaces in aqueous solutions. IsoElectric Points (IEPs) of surfaces have been characterized by direct measurement of the electrostatic double layer interactions between titania surfaces and the micrometer-sized spherical silica probe of an atomic force microscope in NaCl aqueous electrolyte. The use of a colloidal probe provides well-defined interaction geometry and allows effectively probing the overall effect of nanoscale morphology. By using supersonic cluster beam deposition to fabricate nanostructured titania films, we achieved a quantitative control over the surface morphological parameters. We performed a systematical exploration of the electrical double layer properties in different interaction regimes characterized by different ratios of characteristic nanometric lengths of the system: the surface rms roughness Rq, the correlation length ξ and the Debye length λD. We observed a remarkable reduction by several pH units of IEP on rough nanostructured surfaces, with respect to flat crystalline rutile TiO2. In order to explain the observed behavior of IEP, we consider the roughness-induced self-overlap of the electrical double layers as a potential source of deviation from the trend expected for flat surfaces. PMID:23874708

  20. The effect of inhomogeneous roughness on radar backscattering from slightly deformed sea ice

    SciTech Connect

    Dierking, W.; Carlstroem, A.; Ulander, L.M.H.

    1997-01-01

    This paper focuses on the spatially varying backscattering signature of an area of refrozen brash ice observed by a ship based scatterometer. The measurements were carried out as part of the Baltic Experiment for ERS-1 in 1994. The scatterometer was operated at 5.4 GHz at different incidence angles and polarizations. By analyzing the scatterometer data over azimuth scans, it was found that the backscattering variabilities are not only due to fading but also contain a textural component. Surface height profiles were measured using a laser. The observed ice surface roughness was nonstationary over the measurement area. The ice surface can be approximated by adjacent patches of stationary roughness with patch dimensions of about 4.5 m. From the roughness spectra of different stationary patches, two roughness classes can be distinguished. The implications of estimating the roughness parameters from relatively short profile lengths is discussed and the effect on theoretical predictions of the backscattering coefficient is investigated. The texture variance is evaluated theoretically on the basis of the simulated backscattering coefficients of the two observed roughness classes and is found to compare with the scatterometer data.