VizieR Online Data Catalog: Veritas family members Yarkovsky drift rates (Carruba+, 2017)

NASA Astrophysics Data System (ADS)

Carruba, V.; Vokrouhlicky, D.; Nesvorny, D.

2017-05-01

Data about 274 identified Veritas members, their absolute magnitude, proper a, e, sin(i), g, and s, Lyapunov exponent (multiplied by a factor 10+6), and estimated mean Yarkovsky drift speed, in AU/Myr (no such value is available for (1086) Nata itself, that because of its relative large size has very limited Yarkovsky mobility). (1 data file).

Yarkovsky-Schach effect on space debris motion

NASA Astrophysics Data System (ADS)

Murawiecka, M.; Lemaitre, A.

2018-02-01

The Yarkovsky-Schach effect is a small perturbation affecting Earth satellites and space debris illuminated by the Sun. It was first applied to the orbit of LAGEOS satellites as an explanation of the residuals in orbital elements. In this work, we carry out several numerical integration tests taking into consideration various orbit and rotation parameters, in order to analyse this effect in a broader context. The semi-major axis variations remain small and depend on the spin axis attitude with respect to the Sun. We show that the force amplitude is maximised for orbits inclined with i ≈ 20-30°. We also observe the influence on other orbital elements, notably on the orbit inclination. However, these effects are clearly observed only on long timescales; in our simulations, we propagated the orbits for 200 y. The Yarkovsky-Schach effect is thus confirmed to have a minuscule magnitude. It should be taken into account in studies requiring high-precision orbit determination, or on expanded timescales.

Saturn's Rings, the Yarkovsky Effects, and the Ring of Fire

NASA Technical Reports Server (NTRS)

Rubincam, David Parry

2004-01-01

The dimensions of Saturn's A and B rings may be determined by the seasonal Yarkovsky effect and the Yarkovsky-Schach effect; the two effects confine the rings between approximately 1.68 and approximately 2.23 Saturn radii, in reasonable agreement with the observed values of 1.525 and 2.267. The C ring may be sparsely populated because its particles are transients on their way to Saturn; the infall may create a luminous Ring of Fire around Saturn's equator. The ring system may be young: in the past heat flow from Saturn's interior much above its present value would not permit rings to exist.

A mechanism of wave drag reduction in the thermal energy deposition experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Markhotok, A., E-mail: amarhotk@phys.washington.edu

2015-06-15

Many experimental studies report reduced wave drag when thermal energy is deposited in the supersonic flow upstream of a body. Though a large amount of research on this topic has been accumulated, the exact mechanism of the drag reduction is still unknown. This paper is to fill the gap in the understanding connecting multiple stages of the observed phenomena with a single mechanism. The proposed model provides an insight on the origin of the chain of subsequent transformations in the flow leading to the reduction in wave drag, such as typical deformations of the front, changes in the gas pressuremore » and density in front of the body, the odd shapes of the deflection signals, and the shock wave extinction in the plasma area. The results of numerical simulation based on the model are presented for three types of plasma parameter distribution. The spherical and cylindrical geometry has been used to match the data with the experimental observations. The results demonstrate full ability of the model to exactly explain all the features observed in the drag reduction experiments. Analytical expressions used in the model allow separating out a number of adjustment parameters that can be used to optimize thermal energy input and thus achieve fundamentally lower drag values than that of conventional approaches.« less

Analytic Theory for the Yarkovsky-O Effect on Obliquity

NASA Astrophysics Data System (ADS)

Nesvorný, David; Vokrouhlický, David

2008-07-01

The Yarkovsky-O'Keefe-Radzievski-Paddack (YORP) effect is a thermal radiation torque that causes small objects to speed up or slow down their rotation and modify their spin vector orientation. This effect has important implications for spin dynamics of diameter D lsim 50 km asteroids. In our previous work we developed an analytic theory for the component of the YORP torque that affects the spin rate. Here we extend these calculations to determine the effect of the YORP torque on obliquity. Our theory is limited to objects with near-spherical shapes. Two limiting cases are studied: (1) immediate emission of the thermal energy that occurs for surface thermal conductivity K = 0; (2) the effects of K ≠ 0 in the limit of small temporal variations of the surface temperature. We use the linearized heat transport equation to model (2). The results include explicit scaling of the YORP torque on obliquity with physical and dynamical parameters such as the thermal conductivity and spin rate. The dependence of torques on the obliquity is given as series of the Legendre polynomials. Comparisons show excellent agreement of the analytic results with the numerically calculated YORP torques for objects such as asteroids 1998 KY26 and (66391) 1999 KW4. We suggest that an important fraction of main belt asteroids may have specific obliquity values (generalized Slivan states) arising from the roots of the Legendre polynomials.

Dynamical Evolution of Asteroids and Meteoroids Using the Yarkovsky Effect

NASA Technical Reports Server (NTRS)

Bottke, William F., Jr.; Vokrouhlicky, David; Rubincam, David P.; Broz, Miroslav; Smith, David E. (Technical Monitor)

2001-01-01

The Yarkovsky effect is a thermal radiation force which causes objects to undergo semimajor axis drift and spin up/down as a function of their spin, orbit, and material properties. This mechanism can be used to (i) deliver asteroids (and meteoroids) with diameter D < 20 km from their parent bodies in the main belt to chaotic resonance zones capable of transporting this material to Earth-crossing orbits, (ii) disperse asteroid families, with drifting bodies jumping or becoming trapped in mean-motion and secular resonances within the main belt, and (iii) modify the rotation rates of asteroids a few km in diameter or smaller enough to explain the excessive number of very fast and very slow rotators among the small asteroids. Accordingly, we suggest that nongravitational forces, which produce small but meaningful effects on asteroid orbits and rotation rates over long timescales, should now be considered as important as collisions and gravitational perturbations to our overall understanding of asteroid evolution.

Thermal design of AOTV heatshields for a conical drag brake

NASA Technical Reports Server (NTRS)

Pitts, W. C.; Murbach, M. S.

1985-01-01

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

Magnon-drag thermopile.

PubMed

Costache, Marius V; Bridoux, German; Neumann, Ingmar; Valenzuela, Sergio O

2011-12-18

Thermoelectric effects in spintronics are gathering increasing attention as a means of managing heat in nanoscale structures and of controlling spin information by using heat flow. Thermal magnons (spin-wave quanta) are expected to play a major role; however, little is known about the underlying physical mechanisms involved. The reason is the lack of information about magnon interactions and of reliable methods to obtain it, in particular for electrical conductors because of the intricate influence of electrons. Here, we demonstrate a conceptually new device that enables us to gather information on magnon-electron scattering and magnon-drag effects. The device resembles a thermopile formed by a large number of pairs of ferromagnetic wires placed between a hot and a cold source and connected thermally in parallel and electrically in series. By controlling the relative orientation of the magnetization in pairs of wires, the magnon drag can be studied independently of the electron and phonon-drag thermoelectric effects. Measurements as a function of temperature reveal the effect on magnon drag following a variation of magnon and phonon populations. This information is crucial to understand the physics of electron-magnon interactions, magnon dynamics and thermal spin transport.

Dynamical spreading of small bodies in 1:1 resonance with planets by the diurnal Yarkovsky effect

NASA Astrophysics Data System (ADS)

Wang, Xuefeng; Hou, Xiyun

2017-10-01

A simple model is introduced to describe the inherent dynamics of Trojans in the presence of the diurnal Yarkovsky effect. For different spin statuses, the orbital elements of the Trojans (mainly semimajor axis, eccentricity and inclination) undergo different variations. The variation rate is generally very small, but the total variation of the semimajor axis or the orbit eccentricity over the age of the Solar system may be large enough to send small Trojans out of the regular region (or, vice versa, to capture small bodies in the regular region). In order to demonstrate the analytical analysis, we first carry out numerical simulations in a simple model, and then generalize these to two 'real' systems, namely the Sun-Jupiter system and the Sun-Earth system. In the Sun-Jupiter system, where the motion of Trojans is regular, the Yarkovsky effect gradually alters the libration width or the orbit eccentricity, forcing the Trojan to move from regular regionsto chaotic regions, where chaos may eventually cause it to escape. In the Sun-Earth system, where the motion of Trojans is generally chaotic, our limited numerical simulations indicate that the Yarkovsky effect is negligible for Trojans of 100 m in size, and even for larger ones. The Yarkovsky effect on small bodies captured in other 1:1 resonance orbits is also briefly discussed.

Orbital evolution and escape of Martian Trojans due to the Yarkovsky effect

NASA Astrophysics Data System (ADS)

Christou, Apostolos

2017-06-01

Recently it was shown that the Yarkovsky effect can lead to significant orbit change for Trojans of Mars [1,2] and that the orbital distribution of observed Trojans is consistent with a negative along-track acceleration of the same functional form as seasonal yarkovsky; this feature was used to constrain the age of the Eureka family of Mars Trojan asteroids [2]. In contrast, the Yarkovsky effect appears to have a negligible role in shaping observed families of Jupiter Trojans [3].To explore the evolution and end states of Trojans evolved by the Yarkosky effect, I have numerically integrated test particles under a model of the diurnal variant and for different values of the acceleration strength up to 10-2 AU/Myr for da/dt outside the resonance. I use as a starting point the orbits of the three largest Martian Trojans: 5261 Eureka, (101429) 1998 VF31 and (121514) 1999 UJ7.I find, as in [2], that the evolution of the inclination I and the libration amplitude L depends on the sign of the acceleration and is essentially deterministic. Considering the rate of change of the Tisserand constant [5,6] leads to a simple analytical expression that reproduces well the inclination evolution of the Trojans. The evolution of e is somewhat more stochastic, probably due to chaotic diffusion [4] and/or the influence of Mars’ eccentricity [2].Trojans escape upon reaching the boundaries of stability domains mapped out in [4], demarcated by resonances with principal secular modes and the Kozai resonance. The mechanism of escape is by increasing e and/or the libration amplitude to the point of allowing close encounters with Mars.During the presentation I will describe the ensemble evolution of Trojans under Yarkovsky, how it is related to the lifetime in the 1:1 resonance and discuss the implications for Trojan stability at Earth and Jupiter.[1] Christou, A.A., 2013, Icarus, 224, 144.[2] Ćuk, M., Christou, A.A., Hamilton, D.P., 2015, Icarus, 252, 339.[3] Milani, A., Knezević, Z

A New Approach on the Long Term Dynamics of NEO's Under Yarkovsky Effect.

NASA Astrophysics Data System (ADS)

Peláez, Jesús; Urrutxua, Hodei; Bombardelli, Claudio; Perez-Grande, Isabel

2011-12-01

A classical approach to the many-body problem is that of using special perturbation methods. Nowadays and due to the availability of high-speed computers is an essential tool in Space Dynamics which exhibits a great advantage: it is applicable to any orbit involving any number of bodies and all sorts of astrodynamical problems, especially when these problems fall into regions in which general perturbation theories are absent. One such case is, for example, that Near Earth Objects (NEO's) dynamics. In this field, the Group of Tether Dynamics of UPM (GDT) has developed a new regularisation scheme - called DROMO - which is characterised by only 8 ODE. This new regularisation scheme allows a new approach to the dynamics of NEO's in the long term, specially appropriated to consider the influence of the anisotropic thermal emission (Yarkovsky and YORP effects) on the dynamics. A new project, called NEODROMO, has been started in GDT that aims to provide a reliable tool for the long term dynamics of NEO's.

Yarkovsky effect and V-shapes: New method to compute family ages

NASA Astrophysics Data System (ADS)

Spoto, F.; Milani, A.; Cellino, A.; Knezevic, Z.; Novakovic, B.; Paolicchi, P.

2014-07-01

The computation of family ages is a high-priority goal. As a matter of principle, it can be achieved by using V-shape plots for the families old enough to have the Yarkovsky effect dominating the spread of the proper a and large enough for a statistically significant analysis of the shape. By performing an asteroid family classification with a very enlarged dataset, the results are not just ''more families'', but there are interesting qualitative changes. These are due to the large-number statistics, but also to the larger fraction of smaller objects contained in recently numbered asteroids. We are convinced that our method is effective in adding many smaller asteroids to the core families. As a result, we have a large number of families with very well defined V-shapes, thus with a good possibility of age estimation. We have developed our method to compute ages, which we believe is better than those used previously because it is more objective. Since there are no models for error in absolute magnitude H and for albedo, we have also developed a model of the error in the inverse of the diameter and then we have performed a weighted least-squares fit. We report at least 5/6 examples of dynamical families for which the computation of the V-shape is possible. These examples show the presence of different internal structure of the families, e.g., in the dynamical family of (4) Vesta, we have found two collisional families. The main problem in estimating the ages is the calibration. The difficulty in the Yarkovsky calibration, due to the need to extrapolate from near-Earth asteroids (NEAs) with measured da/dt to main-belt asteroids, is in most cases the main limitation to the accuracy of the age estimation. We obtain an age estimation by scaling the results for the NEA for which there is the best Yarkovsky effect determination, namely (101955) Bennu.

Averaged changes in the orbital elements of meteoroids due to Yarkovsky-Radzievskij force

NASA Astrophysics Data System (ADS)

Ryabova, Galina O.

2014-07-01

Yarkovsky-Radzievskij effect exceeds the Poynting-Robertson effect in the perturbing action on particles larger than 100 μm. We obtained formulae for averaged changes in a meteoroid's Keplerian orbital elements and used them to estimate dispersion in the Geminid meteoroid stream. It was found that dispersion in semi-major axis of the model shower increased nearly three times on condition that meteoroids rotation is fast, and the rotation axis is stable.

Cosmic Ray Exposure Ages of Stony Meteorites: Space Erosion or Yarkovsky?

NASA Technical Reports Server (NTRS)

Rubincam, David Parry

2014-01-01

Space erosion from dust impacts may set upper limits on the cosmic ray exposure (CRE) ages of stony meteorites. A meteoroid orbiting within the asteroid belt is bombarded by both cosmic rays and interplanetary dust particles. Galactic cosmic rays penetrate only the first few meters of the meteoroid; deeper regions are shielded. The dust particle impacts create tiny craters on the meteoroid's surface, wearing it away by space erosion (abrasion) at a particular rate. Hence a particular point inside a meteoroid accumulates cosmic ray products only until that point wears away, limiting CRE ages. The results would apply to other regolith-free surfaces in the solar system as well, so that abrasion may set upper CRE age limits which depend on the dusty environment. Calculations based on N. Divine's dust populations and on micrometeoroid cratering indicate that stony meteoroids in circular ecliptic orbits at 2 AU will record 21Ne CRE ages of approx.176 x 10(exp 6) years if dust masses are in the range 10(exp -21) - 10(exp -3) kg. This is in broad agreement with the maximum observed CRE ages of approx. 100 x 10(exp 6) years for stones. High erosion rates in the inner solar system may limit the CRE ages of Near-Earth Asteroids (NEAs) to approx. 120 x 10(exp 6) years. If abrasion should prove to be approx. 6 times quicker than found here, then space erosion may be responsible for many of the measured CRE ages of main belt stony meteorites. In that case the CRE ages may not measure the drift time to the resonances due to the Yarkovsky effects as in the standard scenario, and that for some reason Yarkovsky is ineffective.

Population control of Martian Trojans by the Yarkovsky & YORP effects

NASA Astrophysics Data System (ADS)

Christou, Apostolos; Borisov, Galin; Jacobson, Seth A.; Colas, Francois; dell'Oro, Aldo; Cellino, Alberto; Bagnulo, Stefano

2017-10-01

Mars is the only terrestrial planet supporting a stable population of Trojan asteroids. One, (5261) Eureka, has a family of smaller asteroids of similar composition (Borisov et al, 2017; Polishook et al, 2017) that likely separated from Eureka within the last 1 Gyr (Ćuk et al, 2015). Two other Trojans, (101429) 1998 VF31 and (121514) 1999 UJ7, of similar size and on similar orbits to Eureka, are not associated with families of asteroids, begging the question of what makes Eureka special.The Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect may have formed the Eureka family (Christou, 2013; Ćuk et al, 2015) by the spinning off of ``YORPlets’’, a mechanism also responsible for close orbital pairs of small Main Belt asteroids (Pravec et al, 2010). Eureka’s fast rotation rate (P=2.69 hr; Koehn et al, 2014), right at the so-called ``spin barrier’’ (Warner et al, 2009), apparently supports this.We obtained photometry of 101429 and 121514 to find out their rotation periods. We find an unusually long, ˜50 hr period for 121514; the asteroid may be in a ``tumbling’’ rotational state that inhibits YOPRlet production. On the other hand, the faster (P=7.7 hr) rotation we obtain for 101429 does not preclude it from having been spun up to the rotational fission limit during the most recent 10s of Myr.Instead, 101429’s location near a secular resonance (Scholl et al, 2005) may lead to rapid loss of any YORPlet asteroids. Indeed, test particles started at 101429’s orbit and evolving under the Yarkovsky effect escape within a few hundred Myr, several times faster than particles started near Eureka. We conclude that the stability enjoyed by asteroids in Eureka’s orbital vicinity, combined with the ability to readily populate that vicinity with new asteroids, are likely responsible for Eureka’s status as the only Martian Trojan with a family.

Progress towards a Drag-free SmallSat

NASA Astrophysics Data System (ADS)

Saraf, Shailendhar

The net force acting on a drag-free satellite is purely gravitational as all other forces, mainly atmospheric drag and solar radiation pressure, are canceled out. In order to achieve this, a free floating reference (test mass) inside the satellite is shielded against all forces but gravity and a system of thrusters is commanded by a control algorithm such that the relative displacement between the reference and the satellite stays constant. The main input to that control algorithm is the output of a sensor which measures the relative displacement between the satellite and the test mass. Internal disturbance forces such as electrostatic or magnetic forces cannot be canceled out his way and have to be minimized by a careful design of the satellite. A drag-free technology package is under development at Stanford since 2004. It includes an optical displacement sensor to measure the relative position of the test mass inside the satellite, a caging mechanism to lock the test mass during launch, a UV LED based charge management system to minimize the effect of electrostatic forces, a thermal enclosure, and the drag-free control algorithms. Possible applications of drag-free satellites in fundamental physics (Gravity Probe B, LISA), geodesy (GOCE), and navigation (TRIAD I). In this presentation we will highlight the progress of the technology development towards a drag-free mission. The planned mission on a SaudiSat bus will demonstrate drag-free technology on a small spacecraft at a fraction of the cost of previous drag-free missions. The target acceleration noise is 10-12 m/sec2. With multiple such satellites a GRACE-like mission with improved sensitivity and potentially improved spatial and temporal resolution can be achieved.

Yarkovsky-O'Keefe-Radzievskii-Paddack effect on tumbling objects

NASA Astrophysics Data System (ADS)

Breiter, S.; Rożek, A.; Vokrouhlický, D.

2011-11-01

A semi-analytical model of the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect on an asteroid spin in a non-principal axis rotation state is developed. The model describes the spin-state evolution in Deprit-Elipe variables, first-order averaged with respect to rotation and Keplerian orbital motion. Assuming zero conductivity, the YORP torque is represented by spherical harmonic series with vectorial coefficients, allowing us to use any degree and order of approximation. Within the quadrupole approximation of the illumination function we find the same first integrals involving rotational momentum, obliquity and dynamical inertia that were obtained by Cicaló & Scheeres. The integrals do not exist when higher degree terms of the illumination function are included, and then the asymptotic states known from Vokrouhlický et al. appear. This resolves an apparent contradiction between earlier results. Averaged equations of motion admit stable and unstable limit cycle solutions that were not previously detected. Non-averaged numerical integration by the Taylor series method for an exemplary shape of 3103 Eger is in good agreement with the semi-analytical theory.

Detection of Yarkovsky acceleration in the context of precovery observations and the future Gaia catalogue

NASA Astrophysics Data System (ADS)

Desmars, J.

2015-03-01

Context. The Yarkovsky effect is a weak non-gravitational force leading to a small variation of the semi-major axis of an asteroid. Using radar measurements and astrometric observations, it is possible to measure a drift in semi-major axis through orbit determination. Aims: This paper aims to detect a reliable drift in semi-major axis of near-Earth asteroids (NEAs) from ground-based observations and to investigate the impact of precovery observations and the future Gaia catalogue in the detection of a secular drift in semi-major axis. Methods: We have developed a precise dynamical model of an asteroid's motion taking the Yarkovsky acceleration into account and allowing the fitting of the drift in semi-major axis. Using statistical methods, we investigate the quality and the robustness of the detection. Results: By filtering spurious detections with an estimated maximum drift depending on the asteroid's size, we found 46 NEAs with a reliable drift in semi-major axis in good agreement with the previous studies. The measure of the drift leads to a better orbit determination and constrains some physical parameters of these objects. Our results are in good agreement with the 1 /D dependence of the drift and with the expected ratio of prograde and retrograde NEAs. We show that the uncertainty of the drift mainly depends on the length of orbital arc and in this way we highlight the importance of the precovery observations and data mining in the detection of consistent drift. Finally, we discuss the impact of Gaia catalogue in the determination of drift in semi-major axis.

Drag bit construction

DOEpatents

Hood, Michael

1986-01-01

A mounting movable with respect to an adjacent hard face has a projecting drag bit adapted to engage the hard face. The drag bit is disposed for movement relative to the mounting by encounter of the drag bit with the hard face. That relative movement regulates a valve in a water passageway, preferably extending through the drag bit, to play a stream of water in the area of contact of the drag bit and the hard face and to prevent such water play when the drag bit is out of contact with the hard face.

Quartz tuning-fork oscillations in He II and drag coefficient

NASA Astrophysics Data System (ADS)

Gritsenko, I. A.; Zadorozhko, A. A.; Neoneta, A. S.; Chagovets, V. K.; Sheshin, G. A.

2011-07-01

The temperature dependencies of drag coefficient for quartz tuning forks of various geometric dimensions, immersed in the He II, were determined experimentally in the temperature range 0.1-3 K. It is identified, that these dependencies are similar, but the values of drag coefficient are different for tuning forks with different geometric dimensions. It is shown, that the obtained specific drag coefficient depends only on the temperature and frequency of vibrations, when the value of drag coefficient is normalized to the surface area of moving tuning-fork prong. The temperature dependencies of normalized drag coefficient for the tuning forks of various dimensions, wire, and microsphere, oscillating in the Не II, are compared. It is shown, that in the ballistic regime of scattering of quasiparticles, these dependencies are identical and have a slope proportional to T4, which is determined by the density of thermal excitations. In the hydrodynamic regime at T > 0.5 K, the behavior of the temperature dependence of specific drag coefficient is affected by the size and frequency of vibrating body. The empirical relation, which allows to describe the behavior of specific drag coefficient for vibrating tuning forks, microsphere, and wire everywhere over the temperature region and at various frequencies, is proposed.

Drag coefficient Variability and Thermospheric models

NASA Astrophysics Data System (ADS)

Moe, Kenneth

Satellite drag coefficients depend upon a variety of factors: The shape of the satellite, its altitude, the eccentricity of its orbit, the temperature and mean molecular mass of the ambient atmosphere, and the time in the sunspot cycle. At altitudes where the mean free path of the atmospheric molecules is large compared to the dimensions of the satellite, the drag coefficients can be determined from the theory of free-molecule flow. The dependence on altitude is caused by the concentration of atomic oxygen which plays an important role by its ability to adsorb on the satellite surface and thereby affect the energy loss of molecules striking the surface. The eccentricity of the orbit determines the satellite velocity at perigee, and therefore the energy of the incident molecules relative to the energy of adsorption of atomic oxygen atoms on the surface. The temperature of the ambient atmosphere determines the extent to which the random thermal motion of the molecules influences the momentum transfer to the satellite. The time in the sunspot cycle affects the ambient temperature as well as the concentration of atomic oxygen at a particular altitude. Tables and graphs will be used to illustrate the variability of drag coefficients. Before there were any measurements of gas-surface interactions in orbit, Izakov and Cook independently made an excellent estimate that the drag coefficient of satellites of compact shape would be 2.2. That numerical value, independent of altitude, was used by Jacchia to construct his model from the early measurements of satellite drag. Consequently, there is an altitude dependent bias in the model. From the sparce orbital experiments that have been done, we know that the molecules which strike satellite surfaces rebound in a diffuse angular distribution with an energy loss given by the energy accommodation coefficient. As more evidence accumulates on the energy loss, more realistic drag coefficients are being calculated. These improved drag

Insights on the thermal impacts of wing colorization of migrating birds on their skin friction drag and the choice of their flight route.

PubMed

Hassanalian, M; Ayed, S Ben; Ali, M; Houde, P; Hocut, C; Abdelkefi, A

2018-02-01

The thermal effects of wing color in flight is investigated in four species of birds with respect to their flight routes, migration time, and geometric and behavioral characteristics. Considering the marine and atmospheric characteristics of these flight routes, a thermal analysis of the birds' wings is performed during their migration. The surrounding fluxes including the ocean flux and the solar irradiance are considered in an energy balance in order to determine the skin temperature of both sides of the wing. Applying the Blasius solution for heated boundary layers, it is shown that the color configuration of these migrating birds, namely black on the top side of the wings and white on the bottom side of the wings ("countershading"), results in a skin drag reduction, if compared to some other configurations, when both day and night are taken into consideration. This drag reduction can be considered as one of the effective factors for long endurance of these migrating birds. This research can provide the evolutionary perspective behind the colorization of these migrating birds. Copyright © 2018 Elsevier Ltd. All rights reserved.

Whose drag is it anyway? Drag kings and monarchy in the UK.

PubMed

Willox, Annabelle

2002-01-01

This chapter will show that the term "drag" in drag queen has a different meaning, history and value to the term "drag" in drag king. By exposing this basic, yet fundamental, difference this paper will expose the problems inherent in the assumption of parity between the two forms of drag. An exposition of how camp has been used to comprehend and theorise drag queens will facilitating an understanding of the parasitic interrelationship between camp and drag queen performances, while a critique of "Towards a Butch-Femme Aesthetic," by Sue Ellen Case, will point out the problematic assumptions made about camp when attributed to a cultural location different to the drag queen. By interrogating the historical, cultural and theoretical similarities and differences between drag kings, butches, drag queens and femmes this paper will expose the flawed assumption that camp can be attributed to all of the above without proviso, and hence expose why drag has a fundamentally different contextual meaning for kings and queens. This chapter will conclude by examining the work of both Judith Halberstam and Biddy Martin and the practical examples of drag king and queen performances provided at the UK drag contest held at The Fridge in Brixton, London on 23 June 1999.

Drag bit construction

DOEpatents

Hood, M.

1986-02-11

A mounting movable with respect to an adjacent hard face has a projecting drag bit adapted to engage the hard face. The drag bit is disposed for movement relative to the mounting by encounter of the drag bit with the hard face. That relative movement regulates a valve in a water passageway, preferably extending through the drag bit, to play a stream of water in the area of contact of the drag bit and the hard face and to prevent such water play when the drag bit is out of contact with the hard face. 4 figs.

Overview of external Nacelle drag and interference drag

NASA Technical Reports Server (NTRS)

Neal, R. D.

1975-01-01

A historical view of multi-jet engine installations is given that emphasizes integration of the powerplant and the airframe in aircraft design for improved reduction in external nacelle drag and interference drag characteristics.

Racializing white drag.

PubMed

Rhyne, Ragan

2004-01-01

While drag is primarily understood as a performance of gender, other performative categories such as race, class, and sexuality create drag meaning as well. Though other categories of identification are increasingly understood as essential elements of drag by performers of color, whiteness remains an unmarked category in the scholarship on drag performances by white queens. In this paper, I argue that drag by white queens must be understood as a performance of race as well as gender and that codes of gender excess are specifically constructed through the framework of these other axes of identity. This essay asks whether white performance by white queens necessarily reinscribes white supremacy through the performance of an unmarked white femininity, or might drag performance complicate (though not necessarily subvert) categories of race as well as gender? In this essay, I will suggest that camp drag performances, through the deployment of class as a crucial category of performative femininity, might indeed be a key site through which whiteness is denaturalized and its power challenged. Specifically, I will read on camp as a politicized mode of race, class and gender performance, focusing on the intersections of these categories of identity in the drag performance of Divine.

Drag reduction in nature

NASA Technical Reports Server (NTRS)

Bushnell, D. M.; Moore, K. J.

1991-01-01

Recent studies on the drag-reducing shapes, structures, and behaviors of swimming and flying animals are reviewed, with an emphasis on potential analogs in vehicle design. Consideration is given to form drag reduction (turbulent flow, vortex generation, mass transfer, and adaptations for body-intersection regions), skin-friction drag reduction (polymers, surfactants, and bubbles as surface 'additives'), reduction of the drag due to lift, drag-reduction studies on porpoises, and drag-reducing animal behavior (e.g., leaping out of the water by porpoises). The need for further research is stressed.

The effects of radiation drag on radial, relativistic hydromagnetic winds

NASA Technical Reports Server (NTRS)

Li, Zhi-Yun; Begelman, Mitchell C.; Chiueh, Tzihong

1992-01-01

The effects of drag on an idealized relativistic MHD wind of radial geometry are studied. The astrophysical motivation is to understand the effects of radiation drag on the dynamics of a jet or wind passing through the intense radiation field of an accreting compact object. From a critical point analysis, it is found that a slow magnetosonic point can appear in a dragged flow even in the absence of gravitational force, as a result of a balance between the drag force and the combination of thermal pressure and centrifugal forces. As in the undragged case, the Alfven point does not impose any constraints on the flow. Although it is formally possible for a dragged flow to possess more than one fast magnetosonic point, it is shown that this is unlikely in practice. In the limit of a 'cold', centrifugally driven flow, it is shown that the fast magnetosonic point moves to infinite radius, just as in the drag-free case. For a given mass flux, the total energy output carried to infinity, and the final partition between the kinetic energy and the Poynting flux, are the same for the dragged and the drag-free flows. The main effects of radiation drag are to increase the amount of energy and angular momentum extracted from the source and to redistribute the regions where acceleration occurs in the flow. This is accomplished through the storage and release of magnetic energy, as a result of additional winding and compression of the field caused by the action of the drag. For a relativistic wind, the dissipated energy can exceed the final kinetic energy of the flow and may be comparable to the total flow energy (which is dominated by Poynting flux). The energy lost to radiation drag will appear as a Doppler-boosted beam of scattered radiation, which could dominate the background radiation if the flow is well-collimated.

Determination of balloon drag

NASA Technical Reports Server (NTRS)

Conrad, George R.; Robbins, Edward J.

1991-01-01

The evolution of an empirical drag relationship that has stimulated rethinking regarding the physics of balloon drag phenomena is discussed. Combined parasitic drag from all sources in the balloon system are estimated to constitute less than 10 percent of the total system drag. It is shown that the difference between flight-determined drag coefficients and those based on the spherical assumption should be related to the square of the Froude number.

Flow drag and heat transfer characteristics of drag-reducing nanofluids with CuO nanoparticles

NASA Astrophysics Data System (ADS)

Wang, Ping-Yang; Wang, Xue-Jiao; Liu, Zhen-Hua

2017-02-01

A new kind of aqueous CuO nanofluid with drag-reducing performance was developed. The new working fluid was an aqueous CTAC (cetyltrimethyl ammonium chloride) solution with CuO nanoparticles added and has both special effects of drag-reducing and heat transfer enhancement. An experiment was carried out to investigate the forced convective flow and heat transfer characteristics of conventional drag reducing fluid (aqueous CTAC solution) and the new drag-reducing nanofluid in a test tube with an inner diameter of 25.6 mm. Results indicated that there were no obvious differences of the drag-reducing characteristics between conventional drag reducing fluid and new drag-reducing nanofluid. However, their heat transfer characteristics were obvious different. The heat transfer characteristics of the new drag-reducing nanofluid significantly depend on the liquid temperature, the nanoparticle concentration and the CTAC concentration. The heat transfer enhancement technology of nanofluid could be applied to solve the problem of heat transfer deterioration for conventional drag-reducing fluids.

Coulomb drag as a probe of the nature of compressible States in a magnetic field.

PubMed

Muraki, K; Lok, J G S; Kraus, S; Dietsche, W; von Klitzing, K; Schuh, D; Bichler, M; Wegscheider, W

2004-06-18

Magnetodrag reveals the nature of compressible states and the underlying interplay of disorder and interactions. At nu=3/2 clear T(4/3) dependence is observed, which signifies the metallic nature of the N=0 Landau level. In contrast, drag in higher Landau levels reveals an additional contribution, which anomalously grows with decreasing T before turning to zero following a thermal activation law. The anomalous drag is discussed in terms of electron-hole asymmetry arising from disorder and localization, and the crossover to normal drag at high fields as due to screening of disorder.

Aerodynamic Drag and Drag Reduction: Energy and Energy Savings (Invited)

NASA Technical Reports Server (NTRS)

Wood, Richard M.

2003-01-01

An assessment of the role of fluid dynamic resistance and/or aerodynamic drag and the relationship to energy use in the United States is presented. Existing data indicates that up to 25% of the total energy consumed in the United States is used to overcome aerodynamic drag, 27% of the total energy used in the United States is consumed by transportation systems, and 60% of the transportation energy or 16% of the total energy consumed in the United States is used to overcome aerodynamic drag in transportation systems. Drag reduction goals of 50% are proposed and discussed which if realized would produce a 7.85% total energy savings. This energy savings correlates to a yearly cost savings in the $30Billion dollar range.

Ab initio optimization of phonon drag effect for lower-temperature thermoelectric energy conversion.

PubMed

Zhou, Jiawei; Liao, Bolin; Qiu, Bo; Huberman, Samuel; Esfarjani, Keivan; Dresselhaus, Mildred S; Chen, Gang

2015-12-01

Although the thermoelectric figure of merit zT above 300 K has seen significant improvement recently, the progress at lower temperatures has been slow, mainly limited by the relatively low Seebeck coefficient and high thermal conductivity. Here we report, for the first time to our knowledge, success in first-principles computation of the phonon drag effect--a coupling phenomenon between electrons and nonequilibrium phonons--in heavily doped region and its optimization to enhance the Seebeck coefficient while reducing the phonon thermal conductivity by nanostructuring. Our simulation quantitatively identifies the major phonons contributing to the phonon drag, which are spectrally distinct from those carrying heat, and further reveals that although the phonon drag is reduced in heavily doped samples, a significant contribution to Seebeck coefficient still exists. An ideal phonon filter is proposed to enhance zT of silicon at room temperature by a factor of 20 to ∼ 0.25, and the enhancement can reach 70 times at 100 K. This work opens up a new venue toward better thermoelectrics by harnessing nonequilibrium phonons.

Sphere Drag and Heat Transfer

NASA Astrophysics Data System (ADS)

Duan, Zhipeng; He, Boshu; Duan, Yuanyuan

2015-07-01

Modelling fluid flows past a body is a general problem in science and engineering. Historical sphere drag and heat transfer data are critically examined. The appropriate drag coefficient is proposed to replace the inertia type definition proposed by Newton. It is found that the appropriate drag coefficient is a desirable dimensionless parameter to describe fluid flow physical behavior so that fluid flow problems can be solved in the simple and intuitive manner. The appropriate drag coefficient is presented graphically, and appears more general and reasonable to reflect the fluid flow physical behavior than the traditional century old drag coefficient diagram. Here we present drag and heat transfer experimental results which indicate that there exists a relationship in nature between the sphere drag and heat transfer. The role played by the heat flux has similar nature as the drag. The appropriate drag coefficient can be related to the Nusselt number. This finding opens new possibilities in predicting heat transfer characteristics by drag data. As heat transfer for flow over a body is inherently complex, the proposed simple means may provide an insight into the mechanism of heat transfer for flow past a body.

Sphere Drag and Heat Transfer.

PubMed

Duan, Zhipeng; He, Boshu; Duan, Yuanyuan

2015-07-20

Modelling fluid flows past a body is a general problem in science and engineering. Historical sphere drag and heat transfer data are critically examined. The appropriate drag coefficient is proposed to replace the inertia type definition proposed by Newton. It is found that the appropriate drag coefficient is a desirable dimensionless parameter to describe fluid flow physical behavior so that fluid flow problems can be solved in the simple and intuitive manner. The appropriate drag coefficient is presented graphically, and appears more general and reasonable to reflect the fluid flow physical behavior than the traditional century old drag coefficient diagram. Here we present drag and heat transfer experimental results which indicate that there exists a relationship in nature between the sphere drag and heat transfer. The role played by the heat flux has similar nature as the drag. The appropriate drag coefficient can be related to the Nusselt number. This finding opens new possibilities in predicting heat transfer characteristics by drag data. As heat transfer for flow over a body is inherently complex, the proposed simple means may provide an insight into the mechanism of heat transfer for flow past a body.

Thermal Tomography of Asteroid Surface Structure

NASA Astrophysics Data System (ADS)

Harris, Alan W.; Drube, Line

2016-12-01

Knowledge of the surface thermal inertia of an asteroid can provide insight into its surface structure: porous material has a lower thermal inertia than rock. We develop a means to estimate thermal inertia values of asteroids and use it to show that thermal inertia appears to increase with spin period in the case of main-belt asteroids (MBAs). Similar behavior is found on the basis of thermophysical modeling for near-Earth objects (NEOs). We interpret our results in terms of rapidly increasing material density and thermal conductivity with depth, and provide evidence that thermal inertia increases by factors of 10 (MBAs) to 20 (NEOs) within a depth of just 10 cm. Our results are consistent with a very general picture of rapidly changing material properties in the topmost regolith layers of asteroids and have important implications for calculations of the Yarkovsky effect, including its perturbation of the orbits of potentially hazardous objects and those of asteroid family members after the break-up event. Evidence of a rapid increase of thermal inertia with depth is also an important result for studies of the ejecta-enhanced momentum transfer of impacting vehicles (“kinetic impactors”) in planetary defense.

Drag-Free Control and Drag Force Recovery of Small Satellites

NASA Technical Reports Server (NTRS)

Nguyen, Anh N.; Conklin, John W.

2017-01-01

Drag-free satellites provide autonomous precision orbit determination, accurately map the static and time varying components of Earth's mass distribution, aid in our understanding of the fundamental force of gravity, and will ultimately open up a new window to our universe through the detection and observation of gravitational waves. At the heart of this technology is a gravitational reference sensor, which (a) contains and shields a free-floating proof mass from all non-gravitational forces, and (b) precisely measures the position of the test mass inside the sensor. Thus, both test mass and spacecraft follow a pure geodesic in spacetime. By tracking the position of a low Earth orbiting drag-free satellite we can directly determine the detailed shape of geodesics and through analysis, the higher order harmonics of the Earths geopotential. This paper explores two different drag-free control systems on small satellites. The first drag-free control system is a continuously compensated single thruster 3-unit CubeSat with a suspension-free spherical proof-mass. A feedback control system commands the thruster and Attitude and Determination Control System to fly the tender spacecraft with respect to the test mass. The spheres position is sensed with a LED-based differential optical shadow sensor, its electric charge controlled by photoemission using UV LEDs, and the spacecraft position is maintained with respect to the sphere using an ion electrospray propulsion system. This configuration is the most fuel-efficient drag-free system possible today. The second drag-free control system is an electro-statically suspended cubical proof-mass that is operated with a low duty cycle, limiting suspension force noise over brief, known time intervals on a small GRACE-II -like satellite. The readout is performed using a laser interferometer, which is immune to the dynamic range limitations of voltage references. This system eliminates the need for a thruster, enabling drag

YORP torques with 1D thermal model

NASA Astrophysics Data System (ADS)

Breiter, S.; Bartczak, P.; Czekaj, M.

2010-11-01

A numerical model of the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect for objects defined in terms of a triangular mesh is described. The algorithm requires that each surface triangle can be handled independently, which implies the use of a 1D thermal model. Insolation of each triangle is determined by an optimized ray-triangle intersection search. Surface temperature is modelled with a spectral approach; imposing a quasi-periodic solution we replace heat conduction equation by the Helmholtz equation. Non-linear boundary conditions are handled by an iterative, fast Fourier transform based solver. The results resolve the question of the YORP effect in rotation rate independence on conductivity within the non-linear 1D thermal model regardless of the accuracy issues and homogeneity assumptions. A seasonal YORP effect in attitude is revealed for objects moving on elliptic orbits when a non-linear thermal model is used.

Importance of Variable Density and Non-Boussinesq Effects on the Drag of Spherical Particles

NASA Astrophysics Data System (ADS)

Ganguli, Swetava; Lele, Sanjiva

2017-11-01

What are the forces that act on a particle as it moves in a fluid? How do they change in the presence of significant heat transfer from the particle, a variable density fluid or gravity? Last year, using particle-resolved simulations we quantified these effects on a single spherical particle and on particles in periodic lattices when O(10-3) 50%) in the absolute drag are observed as λ approaches unity. Oppenheimer, et al. (2016) [1] have proposed a theoretical formula for the drag of a heated sphere at extremely low Re. We show that when Re >O(10), inertial effects completely dominate the drag while when Re drag and our simulations agree well with [1]. In the middle, there is honest competition between inertial and viscous effects and the drag modification strongly depends on the thermally induced near-particle density variation causing a non-zero volumetric dilation rate. In the limit of λ approaching 0 (Stokes' limit), the drag modification can also be captured as a correction to Stokes' drag using a suitable scaling based on the dilation rate. Stanford University - Predictive Science Academic Alliance Program (PSSAP II).

Theory of concentration dependence in drag reduction by polymers and of the maximum drag reduction asymptote.

PubMed

Benzi, Roberto; Ching, Emily S C; Horesh, Nizan; Procaccia, Itamar

2004-02-20

A simple model of the effect of polymer concentration on the amount of drag reduction in turbulence is presented, simulated, and analyzed. The qualitative phase diagram of drag coefficient versus Reynolds number (Re) is recaptured in this model, including the theoretically elusive onset of drag reduction and the maximum drag reduction (MDR) asymptote. The Re-dependent drag and the MDR are analytically explained, and the dependence of the amount of drag on material parameters is rationalized.

Viscous drag reduction in boundary layers

NASA Technical Reports Server (NTRS)

Bushnell, Dennis M. (Editor); Hefner, Jerry N. (Editor)

1990-01-01

The present volume discusses the development status of stability theory for laminar flow control design, applied aspects of laminar-flow technology, transition delays using compliant walls, the application of CFD to skin friction drag-reduction, active-wave control of boundary-layer transitions, and such passive turbulent-drag reduction methods as outer-layer manipulators and complex-curvature concepts. Also treated are such active turbulent drag-reduction technique applications as those pertinent to MHD flow drag reduction, as well as drag reduction in liquid boundary layers by gas injection, drag reduction by means of polymers and surfactants, drag reduction by particle addition, viscous drag reduction via surface mass injection, and interactive wall-turbulence control.

Studies of Aerodynamic Drag.

DTIC Science & Technology

1982-12-01

31. Strouhal number vs Reynolds number - Effect of Wind tunnel Blockage. 150- P ecrit 100- 50k- o present d Qta o Mitry (1977) --Shair et ati (1963) 0...forces measured by the balance. 4.12 Final Tests A comprehensive set of drag measurements was taken with the new drag plates, the drag plates being

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

NASA Technical Reports Server (NTRS)

Slooff, J. W.

1986-01-01

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

Phonon Drag in Thin Films, Cases of Bi2Te3 and ZnTe

NASA Astrophysics Data System (ADS)

Chi, Hang; Uher, Ctirad

2014-03-01

At low temperatures, in (semi-)conductors subjected to a thermal gradient, charge carriers (electrons and holes) are swept (dragged) by out-of-equilibrium phonons due to strong electron-phonon interaction, giving rise to a large contribution to the Seebeck coefficient called the phonon-drag effect. Such phenomenon was surprisingly observed in our recent transport study of highly mismatched alloys as potential thermoelectric materials: a significant phonon-drag thermopower reaching 1.5-2.5 mV/K was recorded for the first time in nitrogen-doped ZnTe epitaxial layers on GaAs (100). In thin films of Bi2Te3, we demonstrate a spectacular influence of substrate phonons on charge carriers. We show that one can control and tune the position and magnitude of the phonon-drag peak over a wide range of temperatures by depositing thin films on substrates with vastly different Debye temperatures. Our experiments also provide a way to study the nature of the phonon spectrum in thin films, which is rarely probed but clearly important for a complete understanding of thin film properties and the interplay of the substrate and films. This work is supported by the Center for Solar and Thermal Energy Conversion, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0000957.

Computational flow predictions for hypersonic drag devices

NASA Technical Reports Server (NTRS)

Tokarcik, Susan; Venkatapathy, Ethiraj; Candler, Graham; Palmer, Grant

1991-01-01

The effectiveness of two types of hypersonic decelerators are computationally examined: mechanically deployable flares and inflatable ballutes. CFD is used to predict the flowfield around a solid rocket motor (SRM) with a deployed decelerator. The computations are performed with an ideal gas solver using an effective specific heat ratio of 1.15. The surface pressure coefficients, the drag, and the extent of the compression corner separation zone predicted by the ideal gas solver compare well with those predicted by the nonequilibrium solver. The ideal gas solver is computationally inexpensive and is shown to be well suited for preliminary design studies. The computed solutions are used to determine the size and shape of the decelerator that are required to achieve a drag coefficient of 5 in order to assure that the SRM will splash down in the Pacific Ocean. Heat transfer rates to the SRM and the decelerators are predicted to estimate the amount of thermal protection required.

Computational flow predictions for hypersonic drag devices

NASA Technical Reports Server (NTRS)

Tokarcik, Susan A.; Venkatapathy, Ethiraj

1993-01-01

The effectiveness of two types of hypersonic decelerators is examined: mechanically deployable flares and inflatable ballutes. Computational fluid dynamics (CFD) is used to predict the flowfield around a solid rocket motor (SRM) with a deployed decelerator. The computations are performed with an ideal gas solver using an effective specific heat ratio of 1.15. The results from the ideal gas solver are compared to computational results from a thermochemical nonequilibrium solver. The surface pressure coefficient, the drag, and the extend of the compression corner separation zone predicted by the ideal gas solver compare well with those predicted by the nonequilibrium solver. The ideal gas solver is computationally inexpensive and is shown to be well suited for preliminary design studies. The computed solutions are used to determine the size and shape of the decelerator that are required to achieve a drag coefficient of 5. Heat transfer rates to the SRM and the decelerators are predicted to estimate the amount of thermal protection required.

Experimental study of the effect of drag reducing agent on pressure drop and thermal efficiency of an air cooler

NASA Astrophysics Data System (ADS)

Peyghambarzadeh, S. M.; Hashemabadi, S. H.; Saffarian, H.; Shekari, F.

2016-01-01

Effect of polymeric drag reduction agents (DRAs) on pressure drop and heat transfer was studied. Aqueous solutions of carboxy methyl cellulose were used inside an air-finned heat exchanger. Despite the previous studies which indicated the importance of drag reduction just in turbulent flow, results of this study in laminar flow indicated that the addition of DRA increases drag reduction, and decreases the overall heat transfer coefficient.

THERMAL TOMOGRAPHY OF ASTEROID SURFACE STRUCTURE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harris, Alan W.; Drube, Line, E-mail: alan.harris@dlr.de

Knowledge of the surface thermal inertia of an asteroid can provide insight into its surface structure: porous material has a lower thermal inertia than rock. We develop a means to estimate thermal inertia values of asteroids and use it to show that thermal inertia appears to increase with spin period in the case of main-belt asteroids (MBAs). Similar behavior is found on the basis of thermophysical modeling for near-Earth objects (NEOs). We interpret our results in terms of rapidly increasing material density and thermal conductivity with depth, and provide evidence that thermal inertia increases by factors of 10 (MBAs) tomore » 20 (NEOs) within a depth of just 10 cm. Our results are consistent with a very general picture of rapidly changing material properties in the topmost regolith layers of asteroids and have important implications for calculations of the Yarkovsky effect, including its perturbation of the orbits of potentially hazardous objects and those of asteroid family members after the break-up event. Evidence of a rapid increase of thermal inertia with depth is also an important result for studies of the ejecta-enhanced momentum transfer of impacting vehicles (“kinetic impactors”) in planetary defense.« less

Catenaries in Drag

NASA Astrophysics Data System (ADS)

Chakrabarti, Brato; Hanna, James

2014-11-01

Dynamical equilibria of towed cables and sedimenting filaments have been the targets of much numerical work; here, we provide analytical expressions for the configurations of a translating and axially moving string subjected to a uniform body force and local, linear, anisotropic drag forces. Generically, these configurations comprise a five-parameter family of planar shapes determined by the ratio of tangential (axial) and normal drag coefficients, the angle between the translational velocity and the body force, the relative magnitudes of translational and axial drag forces with respect to the body force, and a scaling parameter. This five-parameter family of shapes is, in fact, a degenerate six-parameter family of equilibria in which inertial forces rescale the tension in the string without affecting its shape. Each configuration is represented by a first order dynamical system for the tangential angle of the body. Limiting cases include the dynamic catenaries with or without drag, and purely sedimenting or towed strings.

The Sensitivity of Large-Eddy Simulation to Local and Nonlocal Drag Coefficients at the Lower Boundary

NASA Technical Reports Server (NTRS)

Schowalter, D. G.; DeCroix, D. S.; Lin, Y. L.; Arya, S. P.; Kaplan, M. L.

1996-01-01

It was found that the homogeneity of the surface drag coefficient plays an important role in the large scale structure of turbulence in large-eddy simulation of the convective atmospheric boundary layer. Particularly when a ground surface temperature was specified, large horizontal anisotropies occurred when the drag coefficient depended upon local velocities and heat fluxes. This was due to the formation of streamwise roll structures in the boundary layer. In reality, these structures have been found to form when shear is approximately balanced by buoyancy. The present cases, however, were highly convective. The formation was caused by particularly low values of the drag coefficient at the entrance to thermal plume structures.

On the effects of thermal wake from the optical pulsating discharge on the body aerodynamic drag

NASA Astrophysics Data System (ADS)

Kiseleva, T. A.; Golyshev, A. A.; Yakovlev, V. I.; Orishich, A. M.

2018-03-01

The effect of an optical pulsed discharge created by CO2-laser with an average power of 1.8 kW on the aerodynamic drag of a model in a supersonic air flow is experimentally investigated. Experiments were carried out in a supersonic wind tunnel MAU-M (diameter of the nozzle outlet dc = 50 mm) on the modes M = 1,36, Re1 = 1.4-3.8*107 1/m. To ensure a stable optical breakdown, a jet of argon gas was introduced into the focusing region of the laser beam. As a result, a decrease in the aerodynamic drag force was obtained. It is shown, that the increasing of the laser pulses repetition frequency leads to the decreasing in the aerodynamic drag force. The maximum decrease was 15% at a maximum frequency f = 90 kHz.

Capital Drag: kinging in Washington, DC.

PubMed

Patterson, Jennifer Lyn

2002-01-01

Through individual interviews with three DC drag kings and detailed, first-person accounts of their performances, I examine the role the kings play within the lesbian community at Club Chaos in Dupont Circle. My interviews address how and why the kings started performing, how their drag characters relate to their everyday personalities and experiences as lesbian women, why performing in drag is important to them, why drag performances are important to the women who attend their shows, and how gay men and drag queens have responded to their performances. My descriptions of the kings' performances, the audience response, and the atmosphere they create at the club reflect my viewpoint as a lesbian audience participant who has much appreciation for drag queens and much curiosity about the burgeoning drag king scene. I conclude that drag kings provide a valuable service to lesbian communities by creating a safe, supportive environment in which lesbian performers and audience members can celebrate and explore their relationships to female masculinities and queer sexualities.

Forward orbital evolution of the Vesta Family with and without the Yarkovsky effect

NASA Astrophysics Data System (ADS)

Wlodarczyk, Ireneusz; Leliwa-Kopystynski, Jacek

2018-02-01

Vesta family members (VFMs), totally 17164, were selected by means of hierarchical clustering method (HCM) from the data base containing 393347 synthetic proper elements of numbered asteroids from the ASTDyS Catalogue (2015) updated in May 5, 2015. Keplerian elements from the Lowell Catalogue (2015) were used for studying orbital evolution of all 17164 VFMs in the time interval 1 Gy forward. Two cases were considered: evolution pass without the Yarkovsky effect (YN) and evolution pass with it (YY). It has been found that swarm of asteroids disperses about 28 times more efficient for the case YY than in the case YN. Efficiency of dispersion was studied versus semiaxis of asteroids relative to Vesta (smaller or larger than semiaxis of Vesta) as well as versus the sizes of asteroids. Weak relationships between size and efficiency of dispersion on YE have been found for the both cases YN and YY. The loss of number of the asteroids from VF weakly depends on their sizes. The total lost by number as well by mass is about 10% per 1 Gy.

Air Layer Drag Reduction

NASA Astrophysics Data System (ADS)

Ceccio, Steven; Elbing, Brian; Winkel, Eric; Dowling, David; Perlin, Marc

2008-11-01

A set of experiments have been conducted at the US Navy's Large Cavitation Channel to investigate skin-friction drag reduction with the injection of air into a high Reynolds number turbulent boundary layer. Testing was performed on a 12.9 m long flat-plate test model with the surface hydraulically smooth and fully rough at downstream-distance-based Reynolds numbers to 220 million and at speeds to 20 m/s. Local skin-friction, near-wall bulk void fraction, and near-wall bubble imaging were monitored along the length of the model. The instrument suite was used to access the requirements necessary to achieve air layer drag reduction (ALDR). Injection of air over a wide range of air fluxes showed that three drag reduction regimes exist when injecting air; (1) bubble drag reduction that has poor downstream persistence, (2) a transitional regime with a steep rise in drag reduction, and (3) ALDR regime where the drag reduction plateaus at 90% ± 10% over the entire model length with large void fractions in the near-wall region. These investigations revealed several requirements for ALDR including; sufficient volumetric air fluxes that increase approximately with the square of the free-stream speed, slightly higher air fluxes are needed when the surface tension is reduced, higher air fluxes are required for rough surfaces, and the formation of ALDR is sensitive to the inlet condition.

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.

Chiral drag force

DOE PAGES

Rajagopal, Krishna; Sadofyev, Andrey V.

2015-10-05

Here, we provide a holographic evaluation of novel contributions to the drag force acting on a heavy quark moving through strongly interacting plasma. The new contributions are chiral in the sense that they act in opposite directions in plasmas containing an excess of left- or right-handed quarks. The new contributions are proportional to the coefficient of the axial anomaly, and in this sense also are chiral. These new contributions to the drag force act either parallel to or antiparallel to an external magnetic field or to the vorticity of the fluid plasma. In all these respects, these contributions to themore » drag force felt by a heavy quark are analogous to the chiral magnetic effect (CME) on light quarks. However, the new contribution to the drag force is independent of the electric charge of the heavy quark and is the same for heavy quarks and antiquarks, meaning that these novel effects do not in fact contribute to the CME current. We show that although the chiral drag force can be non-vanishing for heavy quarks that are at rest in the local fluid rest frame, it does vanish for heavy quarks that are at rest in a suitably chosen frame. In this frame, the heavy quark at rest sees counterpropagating momentum and charge currents, both proportional to the axial anomaly coefficient, but feels no drag force. This provides strong concrete evidence for the absence of dissipation in chiral transport, something that has been predicted previously via consideration of symmetries. Along the way to our principal results, we provide a general calculation of the corrections to the drag force due to the presence of gradients in the flowing fluid in the presence of a nonzero chemical potential. We close with a consequence of our result that is at least in principle observable in heavy ion collisions, namely an anticorrelation between the direction of the CME current for light quarks in a given event and the direction of the kick given to the momentum of all the heavy

Bubble-induced skin-friction drag reduction and the abrupt transition to air-layer drag reduction

NASA Astrophysics Data System (ADS)

Elbing, Brian R.; Winkel, Eric S.; Lay, Keary A.; Ceccio, Steven L.; Dowling, David R.; Perlin, Marc

To investigate the phenomena of skin-friction drag reduction in a turbulent boundary layer (TBL) at large scales and high Reynolds numbers, a set of experiments has been conducted at the US Navy's William B. Morgan Large Cavitation Channel (LCC). Drag reduction was achieved by injecting gas (air) from a line source through the wall of a nearly zero-pressure-gradient TBL that formed on a flat-plate test model that was either hydraulically smooth or fully rough. Two distinct drag-reduction phenomena were investigated; bubble drag reduction (BDR) and air-layer drag reduction (ALDR).The streamwise distribution of skin-friction drag reduction was monitored with six skin-friction balances at downstream-distance-based Reynolds numbers to 220 million and at test speeds to 20.0msinitial zone1. These results indicated that there are three distinct regions associated with drag reduction with air injection: Region I, BDR; Region II, transition between BDR and ALDR; and Region III, ALDR. In addition, once ALDR was established: friction drag reduction in excess of 80% was observed over the entire smooth model for speeds to 15.3ms1 with the surface fully roughened (though approximately 50% greater volumetric air flux was required); and ALDR was sensitive to the inflow conditions. The sensitivity to the inflow conditions can be mitigated by employing a small faired step (10mm height in the experiment) that helps to create a fixed separation line.

A fundamental study of drag and an assessment of conventional drag-due-to-lift reduction devices

NASA Astrophysics Data System (ADS)

Yates, J. E.; Donald, C. D.

1986-09-01

The integral conservation laws of fluid mechanics are used to assess the drag efficiency of lifting wings, both CTOL and various out-of-plane configurations. The drag-due-to-lift is separated into two major components: (1) the induced drag-due-to-lift that depends on aspect ratio but is relatively independent of Reynolds number; (2) the form drag-due-to-lift that is independent of aspect ratio but dependent on the details of the wing section design, planform and Reynolds number. For each lifting configuration there is an optimal load distribution that yields the minimum value of drag-due-to-lift. For well designed high aspect ratio CTOL wings the two drag components are independent. With modern design technology CTOL wings can be (and usually are) designed with a drag-due-to-lift efficiency close to unity. Wing tip-devices (winglets, feathers, sails, etc.) can improve drag-due-to-lift efficiency by 10 to 15% if they are designed as an integral part of the wing. As add-on devices they can be detrimental. It is estimated that 25% improvements of wing drag-due-to-lift efficiency can be obtained with joined tip configurations and vertically separated lifting elements without considering additional benefits that might be realized by improved structural efficiency. It is strongly recommended that an integrated aerodynamic/structural approach be taken in the design of (or research on) future out-of-plane configurations.

A fundamental study of drag and an assessment of conventional drag-due-to-lift reduction devices

NASA Technical Reports Server (NTRS)

Yates, J. E.; Donald, C. D.

1986-01-01

The integral conservation laws of fluid mechanics are used to assess the drag efficiency of lifting wings, both CTOL and various out-of-plane configurations. The drag-due-to-lift is separated into two major components: (1) the induced drag-due-to-lift that depends on aspect ratio but is relatively independent of Reynolds number; (2) the form drag-due-to-lift that is independent of aspect ratio but dependent on the details of the wing section design, planform and Reynolds number. For each lifting configuration there is an optimal load distribution that yields the minimum value of drag-due-to-lift. For well designed high aspect ratio CTOL wings the two drag components are independent. With modern design technology CTOL wings can be (and usually are) designed with a drag-due-to-lift efficiency close to unity. Wing tip-devices (winglets, feathers, sails, etc.) can improve drag-due-to-lift efficiency by 10 to 15% if they are designed as an integral part of the wing. As add-on devices they can be detrimental. It is estimated that 25% improvements of wing drag-due-to-lift efficiency can be obtained with joined tip configurations and vertically separated lifting elements without considering additional benefits that might be realized by improved structural efficiency. It is strongly recommended that an integrated aerodynamic/structural approach be taken in the design of (or research on) future out-of-plane configurations.

Drag Coefficient Estimation in Orbit Determination

NASA Astrophysics Data System (ADS)

McLaughlin, Craig A.; Manee, Steve; Lichtenberg, Travis

2011-07-01

Drag modeling is the greatest uncertainty in the dynamics of low Earth satellite orbits where ballistic coefficient and density errors dominate drag errors. This paper examines fitted drag coefficients found as part of a precision orbit determination process for Stella, Starlette, and the GEOSAT Follow-On satellites from 2000 to 2005. The drag coefficients for the spherical Stella and Starlette satellites are assumed to be highly correlated with density model error. The results using MSIS-86, NRLMSISE-00, and NRLMSISE-00 with dynamic calibration of the atmosphere (DCA) density corrections are compared. The DCA corrections were formulated for altitudes of 200-600 km and are found to be inappropriate when applied at 800 km. The yearly mean fitted drag coefficients are calculated for each satellite for each year studied. The yearly mean drag coefficients are higher for Starlette than Stella, where Starlette is at a higher altitude. The yearly mean fitted drag coefficients for all three satellites decrease as solar activity decreases after solar maximum.

Induced drag of multiplanes

NASA Technical Reports Server (NTRS)

Prandtl, L

1924-01-01

The most important part of the resistance or drag of a wing system,the induced drag, can be calculated theoretically, when the distribution of lift on the individual wings is known. The calculation is based upon the assumption that the lift on the wings is distributed along the wing in proportion to the ordinates of a semi-ellipse. Formulas and numerical tables are given for calculating the drag. In this connection, the most favorable arrangements of biplanes and triplanes are discussed and the results are further elucidated by means of numerical examples.

The effect of sodium hydroxide on drag reduction using banana peel as a drag reduction agent

NASA Astrophysics Data System (ADS)

Kaur, H.; Jaafar, A.

2018-02-01

Drag reduction is observed as reduced frictional pressure losses under turbulent flow conditions. Drag reduction agent such as polymers can be introduced to increase the flowrate of water flowing and reduce the water accumulation in the system. Currently used polymers are synthetic polymers, which will harm our environment in excessive use of accumulation. A more environmentally-friendly drag reduction agent such as the polymer derived from natural sources or biopolymer, is then required for such purpose. As opposed to the synthetic polymers, the potential of biopolymers as drag reduction agents, especially those derived from a local plant source are not extensively explored. The drag reduction of a polymer produced from a local plant source within the turbulent regime was explored and assessed in this study using a rheometer, where a reduced a torque produced was perceived as a reduction of drag. This method proposed is less time consuming and is more practical which is producing carboxymethylcellulose from the banana peel. The cellulose powder was converted to carboxymethylcellulose (CMC) by etherification process. The carboxymethylation reaction during the synthesizing process was then optimized against the reaction temperature, reaction time and solubility. The biopolymers were then rheologically characterized, where the viscoelastic effects and the normal stresses produced by these biopolymers were utilized to further relate and explain the drag reduction phenomena. The research was structured to focus on producing the biopolymer and to assess the drag reduction ability of the biopolymer produced. The rheological behavior of the biopolymers was then analyzed based on the ability of reducing drag. The results are intended to expand the currently extremely limited experimental database. Based on the results, the biopolymer works as a good DRA.

Reducing cylinder drag by adding a plate

NASA Astrophysics Data System (ADS)

Frolov, Vladimir A.; Kozlova, Anna S.

2017-10-01

Reducing the drag of bodies is a central problem of modern aerohydrodynamics. The paper presents theoretical and experimental studies of a new method for reducing the drag of a circular cylinder. To reduce the drag we propose to install a flat plate along the flow in front of the cylinder. The theoretical investigation of the drag was carried out using FlowSimulation software. An experimental study of the body drag was performed in an open wind tunnel. The drag coefficient results of the cylinder depended on the different locations of the flat plate relative to the cylinder. The following geometric characteristics of the cylinder/plate are studied: the width of the gap between the cylinder and the plate and the meridional angle of the plate with respect to the cylinder. On the basis of Numerical and Physical Modeling, the values of the drag coefficient for the cylinder/plate are presented. The results included establishment the locations of the cylinder/plate which give the value of the drag coefficient for the combination of the two bodies. That total drag coefficient of the cylinder/plate can be less than the cylinder alone.

Turbulent drag reduction for external flows

NASA Technical Reports Server (NTRS)

Bushnell, D. M.

1985-01-01

A summary of turbulent drag reduction approaches applicable to external flows is given. Because relatively recent and exhaustive reviews exist for laminar flow control and polymer (hydrodynamic) drag reduction, the focus here is upon the emerging areas of nonplanar geometry and large-eddy alteration. Turbulent control techniques for air generally result in modest (but technologically significant) drag reductions (order of 20 percent or less), whereas hydrodynamic approaches can yield drag reductions the order of 70 percent. Suggestions are included for alternative concepts and optimization of existing approaches.

Drag reduction using metallic engineered surfaces with highly ordered hierarchical topographies: nanostructures on micro-riblets

NASA Astrophysics Data System (ADS)

Kim, Taekyung; Shin, Ryung; Jung, Myungki; Lee, Jinhyung; Park, Changsu; Kang, Shinill

2016-03-01

Durable drag-reduction surfaces have recently received much attention, due to energy-saving and power-consumption issues associated with harsh environment applications, such as those experienced by piping infrastructure, ships, aviation, underwater vehicles, and high-speed ground vehicles. In this study, a durable, metallic surface with highly ordered hierarchical structures was used to enhance drag-reduction properties, by combining two passive drag-reduction strategies: an air-layer effect induced by nanostructures and secondary vortex generation by micro-riblet structures. The nanostructures and micro-riblet structures were designed to increase slip length. The top-down fabrication method used to form the metallic hierarchical structures combined laser interference lithography, photolithography, thermal reflow, nanoimprinting, and pulse-reverse-current electrochemical deposition. The surfaces were formed from nickel, which has high hardness and corrosion resistance, making it suitable for use in harsh environments. The drag-reduction properties of various metal surfaces were investigated based on the surface structure: a bare surface, a nanostructured surface, a micro-riblet surface, and a hierarchically structured surface of nanostructures on micro-riblets.

Dragging a floating horizontal cylinder

NASA Astrophysics Data System (ADS)

Lee, Duck-Gyu; Kim, Ho-Young

2010-11-01

A cylinder immersed in a fluid stream experiences a drag, and it is well known that the drag coefficient is a function of the Reynolds number only. Here we study the force exerted on a long horizontal cylinder that is dragged perpendicular to its axis while floating on an air-water interface with a high Reynolds number. In addition to the flow-induced drag, the floating body is subjected to capillary forces along the contact line where the three phases of liquid/solid/gas meet. We first theoretically predict the meniscus profile around the horizontally moving cylinder assuming the potential flow, and show that the profile is in good agreement with that obtained experimentally. Then we compare our theoretical predictions and experimental measurement results for the drag coefficient of a floating horizontal cylinder that is given by a function of the Weber number and the Bond number. This study can help us to understand the horizontal motion of partially submerged objects at air-liquid interface, such as semi-aquatic insects and marine plants.

Turbulent drag reduction for external flows

NASA Technical Reports Server (NTRS)

Bushnell, D. M.

1983-01-01

Paper presents a review and summary of turbulent drag reduction approaches applicable to external flows. Because relatively recent and exhaustive reviews exist for laminar flow control and polymer (hydrodynamic) drag reduction, the paper focuses upon the emerging areas of nonplanar geometry and large eddy alteration. Turbulent control techniques for air generally result in modest (but technologically significant) drag reductions (order of 20 percent or less) whereas hydrodynamic approaches can yield drag reductions the order of 70 percent. Paper also includes suggestions for alternative concepts and optimization of existing approaches.

Drag reduction of a hairy disk

NASA Astrophysics Data System (ADS)

Niu, Jun; Hu, David L.

2011-10-01

We investigate experimentally the hydrodynamics of a hairy disk immersed in a two-dimensional flowing soap film. Drag force is measured as a function of hair length, density, and coating area. An optimum combination of these parameters yields a drag reduction of 17%, which confirms previous numerical predictions (15%). Flow visualization indicates the primary mechanism for drag reduction is the bending, adhesion, and reinforcement of hairs trailing the disk, which reduces wake width and traps "dead water." Thus, the use of hairy coatings can substantially reduce an object's drag while negligibly increasing its weight.

Engineering drag currents in Coulomb coupled quantum dots

NASA Astrophysics Data System (ADS)

Lim, Jong Soo; Sánchez, David; López, Rosa

2018-02-01

The Coulomb drag phenomenon in a Coulomb-coupled double quantum dot system is revisited with a simple model that highlights the importance of simultaneous tunneling of electrons. Previously, cotunneling effects on the drag current in mesoscopic setups have been reported both theoretically and experimentally. However, in both cases the sequential tunneling contribution to the drag current was always present unless the drag level position were too far away from resonance. Here, we consider the case of very large Coulomb interaction between the dots, whereby the drag current needs to be assisted by cotunneling events. As a consequence, a quantum coherent drag effect takes place. Further, we demonstrate that by properly engineering the tunneling probabilities using band tailoring it is possible to control the sign of the drag and drive currents, allowing them to flow in parallel or antiparallel directions. We also show that the drag current can be manipulated by varying the drag gate potential and is thus governed by electron- or hole-like transport.

On the Minimum Induced Drag of Wings

NASA Technical Reports Server (NTRS)

Bowers, Albion H.

2010-01-01

Of all the types of drag, induced drag is associated with the creation and generation of lift over wings. Induced drag is directly driven by the span load that the aircraft is flying at. The tools by which to calculate and predict induced drag we use were created by Ludwig Prandtl in 1903. Within a decade after Prandtl created a tool for calculating induced drag, Prandtl and his students had optimized the problem to solve the minimum induced drag for a wing of a given span, formalized and written about in 1920. This solution is quoted in textbooks extensively today. Prandtl did not stop with this first solution, and came to a dramatically different solution in 1932. Subsequent development of this 1932 solution solves several aeronautics design difficulties simultaneously, including maximum performance, minimum structure, minimum drag loss due to control input, and solution to adverse yaw without a vertical tail. This presentation lists that solution by Prandtl, and the refinements by Horten, Jones, Kline, Viswanathan, and Whitcomb

On the Minimum Induced Drag of Wings

NASA Technical Reports Server (NTRS)

Bowers, Albion H.

2011-01-01

Of all the types of drag, induced drag is associated with the creation and generation of lift over wings. Induced drag is directly driven by the span load that the aircraft is flying at. The tools by which to calculate and predict induced drag we use were created by Ludwig Prandtl in 1903. Within a decade after Prandtl created a tool for calculating induced drag, Prandtl and his students had optimized the problem to solve the minimum induced drag for a wing of a given span, formalized and written about in 1920. This solution is quoted in textbooks extensively today. Prandtl did not stop with this first solution, and came to a dramatically different solution in 1932. Subsequent development of this 1932 solution solves several aeronautics design difficulties simultaneously, including maximum performance, minimum structure, minimum drag loss due to control input, and solution to adverse yaw without a vertical tail. This presentation lists that solution by Prandtl, and the refinements by Horten, Jones, Kline, Viswanathan, and Whitcomb.

Vertical variations of coral reef drag forces

NASA Astrophysics Data System (ADS)

Asher, Shai; Niewerth, Stephan; Koll, Katinka; Shavit, Uri; LWI Collaboration; Technion Collaboration

2017-11-01

Corals rely on water flow for the supply of nutrients, particles and energy. Therefore, modeling of processes that take place inside the reef, such as respiration and photosynthesis, relies on models that describe the flow and concentration fields. Due to the high spatial heterogeneity of branched coral reefs, depth average models are usually applied. Such an average approach is insufficient when the flow spatial variation inside the reef is of interest. We report on measurements of vertical variations of drag force that are needed for developing 3D flow models. Coral skeletons were densely arranged along a laboratory flume. Two corals were CT-scanned and replaced with horizontally sliced 3D printed replicates. Drag profiles were measured by connecting the slices to costume drag sensors and velocity profiles were measured using a LDV. The measured drag of whole colonies was in excellent agreement with previous studies; however, these studies never showed how drag varies inside the reef. In addition, these distributions of drag force showed an excellent agreement with momentum balance calculations. Based on the results, we propose a new drag model that includes the dispersive stresses, and consequently displays reduced vertical variations of the drag coefficient.

A study of performance parameters on drag and heat flux reduction efficiency of combinational novel cavity and opposing jet concept in hypersonic flows

NASA Astrophysics Data System (ADS)

Sun, Xi-wan; Guo, Zhen-yun; Huang, Wei; Li, Shi-bin; Yan, Li

2017-02-01

The drag reduction and thermal protection system applied to hypersonic re-entry vehicles have attracted an increasing attention, and several novel concepts have been proposed by researchers. In the current study, the influences of performance parameters on drag and heat reduction efficiency of combinational novel cavity and opposing jet concept has been investigated numerically. The Reynolds-average Navier-Stokes (RANS) equations coupled with the SST k-ω turbulence model have been employed to calculate its surrounding flowfields, and the first-order spatially accurate upwind scheme appears to be more suitable for three-dimensional flowfields after grid independent analysis. Different cases of performance parameters, namely jet operating conditions, freestream angle of attack and physical dimensions, are simulated based on the verification of numerical method, and the effects on shock stand-off distance, drag force coefficient, surface pressure and heat flux distributions have been analyzed. This is the basic study for drag reduction and thermal protection by multi-objective optimization of the combinational novel cavity and opposing jet concept in hypersonic flows in the future.

Lift, Drag, and Pressure Distribution Effects Accompanying Drag-Reducing Polymer Injection on Two-Dimensional Hydrofoil

DTIC Science & Technology

1975-10-01

associated with drag- reducing polymers since Wu’s discovery of pump effects in 1969(16) Some of the research has involved tests on propellers finite span...AD-A022 433 LIFT, DRAG, AND PRESSURE DISTRIBUTION EFFECTS ACCOMPANYING DRAG- REDUCING POLYMER INJECTION ON TWO-DIMENSIONAL HYDROFOIL Daniel H. Fruman...et al Hydronautits, IncorponAted "Prepared f’or: Office of Naval Research October 197’ .!. S.IIE KA NTO CmaY - t 093103 A pprove!- for p~thic relpsa

Study of Automotive Aerodynamic Drag

DOT National Transportation Integrated Search

1975-09-01

Reductions of aerodynamic drag in the 20-25% range through the use of several established drag-reduction devices and minor design changes have been demonstrated on three large sales-volume 1974 and 1975 model American automobiles. Comparisons of test...

Drag reduction by a linear viscosity profile.

PubMed

De Angelis, Elisabetta; Casciola, Carlo M; L'vov, Victor S; Pomyalov, Anna; Procaccia, Itamar; Tiberkevich, Vasil

2004-11-01

Drag reduction by polymers in turbulent flows raises an apparent contradiction: the stretching of the polymers must increase the viscosity, so why is the drag reduced? A recent theory proposed that drag reduction, in agreement with experiments, is consistent with the effective viscosity growing linearly with the distance from the wall. With this self-consistent solution the reduction in the Reynolds stress overwhelms the increase in viscous drag. In this Rapid Communication we show, using direct numerical simulations, that a linear viscosity profile indeed reduces the drag in agreement with the theory and in close correspondence with direct simulations of the FENE-P model at the same flow conditions.

Reconfiguration parameters for drag of flexible cylindrical elements

NASA Astrophysics Data System (ADS)

John, Chapman; Wilson, Bruce; Gulliver, John

2015-11-01

This presentation compares parameters that characterize reconfiguration effects on flow resistance and drag. The drag forces occurring on flexible bluff bodies are different from the drag occurring on rigid bluff bodies due to reconfiguration. Drag force data, collected using a torque sensor in a flume, for simple cylindrical obstructions of the same shape and size but with different flexibility is used to fit drag parameters. The key parameter evaluated is a reference velocity factor u to account for drag reduction due to reconfiguration, similar to a Vogel exponent. Our equations preserves the traditional exponent of the drag relationship, but places a factor onto the drag coefficient for flexible elements, rather than a Vogel exponent arrangement applied to the flow velocity. Additionally we relate the reference velocity factor u to the modulus of elasticity of the material through the Cauchy Number. The use of a reference velocity factor u in place of a Vogel exponent appears viable to account for how the drag forces are altered by reconfiguration. The proposed formulation for drag reduction is more consistently estimated for the range of flexibilities in this study. Unfortunately, the mechanical properties of vegetation are not often readily available for reconfiguration relationships to the elastic modulus of vegetation to be of immediate practical use.

Transformance: reading the gospel in drag.

PubMed

McCune, Jeffrey Q

2004-01-01

Despite the large body of scholarship on drag and its performance of misogyny, mimicry, and masculinity, little attention has been paid to the role of musical genres in Black drag performance and its reception. This essay explores drag performances of gospel music and its relationship with the spectator at the Biology Bar, a Black gay drag site in Chicago. By examining the shift from the club "space" to the church "place," this research locates several possibilities for queer gospel performances. Through the introduction of a theory of transformance, this essay highlights the contradictions, complications, and complexities of the relationship between the Black church and the Black gay community.

Aerodynamic Drag Scoping Work.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Voskuilen, Tyler; Erickson, Lindsay Crowl; Knaus, Robert C.

This memo summarizes the aerodynamic drag scoping work done for Goodyear in early FY18. The work is to evaluate the feasibility of using Sierra/Low-Mach (Fuego) for drag predictions of rolling tires, particularly focused on the effects of tire features such as lettering, sidewall geometry, rim geometry, and interaction with the vehicle body. The work is broken into two parts. Part 1 consisted of investigation of a canonical validation problem (turbulent flow over a cylinder) using existing tools with different meshes and turbulence models. Part 2 involved calculating drag differences over plate geometries with simple features (ridges and grooves) defined bymore » Goodyear of approximately the size of interest for a tire. The results of part 1 show the level of noise to be expected in a drag calculation and highlight the sensitivity of absolute predictions to model parameters such as mesh size and turbulence model. There is 20-30% noise in the experimental measurements on the canonical cylinder problem, and a similar level of variation between different meshes and turbulence models. Part 2 shows that there is a notable difference in the predicted drag on the sample plate geometries, however, the computational cost of extending the LES model to a full tire would be significant. This cost could be reduced by implementation of more sophisticated wall and turbulence models (e.g. detached eddy simulations - DES) and by focusing the mesh refinement on feature subsets with the goal of comparing configurations rather than absolute predictivity for the whole tire.« less

Investigation of drag and heat reduction induced by a novel combinational lateral jet and spike concept in supersonic flows based on conjugate heat transfer approach

NASA Astrophysics Data System (ADS)

Zhu, Liang; Chen, Xiong; Li, Yingkun; Musa, Omer; Zhou, Changsheng

2018-01-01

When flying at supersonic or hypersonic speeds through the air, the drag and severe heating have a great impact on the vehicles, thus the drag reduction and thermal protection studies have attracted worldwide attention. In the current study, the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the shear stress transport (SST) k - ω turbulence model have been employed to investigate the flow behavior induced by a novel combinational lateral jet and spike concept in supersonic flows. A coupling conjugate heat transfer (CHT) approach has been applied to investigate the thermal protection, which takes the heat transfer of structure into consideration. After the code was validated by the available experimental results and the gird independency analysis was carried out, the influences of the spike length ratio, lateral jet pressure ratio and lateral jet location on the drag and heat reduction performance are analyzed comprehensively. The obtained results show that a remarkable reduction in the drag and heat flux is achieved when a lateral jet is added to the spike. This implies that the combinational lateral jet and spike concept in supersonic flows have a great benefit to the drag and heat reduction. Both the drag and heat reduction decrease with the increase of the lateral jet pressure ratio, and the heat flux is more sensitive to the lateral jet pressure ratio. The lateral jet should not be located in the bottom of the spike in order to realize better drag and heat reduction performance. The drag and heat flux could be reduced by about 45% by reasonable lateral jet location. The drag decreases with the increase of the spike length ratio whereas the heat flux is affected by the spike length ratio just in a certain range.

Cotunneling Drag Effect in Coulomb-Coupled Quantum Dots.

PubMed

Keller, A J; Lim, J S; Sánchez, David; López, Rosa; Amasha, S; Katine, J A; Shtrikman, Hadas; Goldhaber-Gordon, D

2016-08-05

In Coulomb drag, a current flowing in one conductor can induce a voltage across an adjacent conductor via the Coulomb interaction. The mechanisms yielding drag effects are not always understood, even though drag effects are sufficiently general to be seen in many low-dimensional systems. In this Letter, we observe Coulomb drag in a Coulomb-coupled double quantum dot and, through both experimental and theoretical arguments, identify cotunneling as essential to obtaining a correct qualitative understanding of the drag behavior.

When superfluids are a drag

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roberts, David C

2008-01-01

The article considers the dramatic phenomenon of seemingly frictionless flow of slow-moving superfluids. Specifically the question of whether an object in a superfluid flow experiences any drag force is addressed. A brief account is given of the history of this problem and it is argued that recent advances in ultracold atomic physics can shed much new light on this problem. The article presents the commonly held notion that sufficiently slow-moving superfluids can flow without drag and also discusses research suggesting that scattering quantum fluctuations might cause drag in a superfluid moving at any speed.

Polymer flexibility and turbulent drag reduction.

PubMed

Gillissen, J J J

2008-10-01

Polymer-induced drag reduction is the phenomenon by which the friction factor of a turbulent flow is reduced by the addition of small amounts of high-molecular-weight linear polymers, which conformation in solution at rest can vary between randomly coiled and rodlike. It is well known that drag reduction is positively correlated to viscous stresses, which are generated by extended polymers. Rodlike polymers always assume this favorable conformation, while randomly coiling chains need to be unraveled by fluid strain rate in order to become effective. The coiling and stretching of flexible polymers in turbulent flow produce an additional elastic component in the polymer stress. The effect of the elastic stresses on drag reduction is unclear. To study this issue, we compare direct numerical simulations of turbulent drag reduction in channel flow using constitutive equations describing solutions of rigid and flexible polymers. When compared at constant phi r2, both simulations predict the same amount of drag reduction. Here phi is the polymer volume fraction and r is the polymer aspect ratio, which for flexible polymers is based on average polymer extension at the channel wall. This demonstrates that polymer elasticity plays a marginal role in the mechanism for drag reduction.

Bioinspired surfaces for turbulent drag reduction

PubMed Central

Golovin, Kevin B.; Gose, James W.; Perlin, Marc; Ceccio, Steven L.; Tuteja, Anish

2016-01-01

In this review, we discuss how superhydrophobic surfaces (SHSs) can provide friction drag reduction in turbulent flow. Whereas biomimetic SHSs are known to reduce drag in laminar flow, turbulence adds many new challenges. We first provide an overview on designing SHSs, and how these surfaces can cause slip in the laminar regime. We then discuss recent studies evaluating drag on SHSs in turbulent flow, both computationally and experimentally. The effects of streamwise and spanwise slip for canonical, structured surfaces are well characterized by direct numerical simulations, and several experimental studies have validated these results. However, the complex and hierarchical textures of scalable SHSs that can be applied over large areas generate additional complications. Many studies on such surfaces have measured no drag reduction, or even a drag increase in turbulent flow. We discuss how surface wettability, roughness effects and some newly found scaling laws can help explain these varied results. Overall, we discuss how, to effectively reduce drag in turbulent flow, an SHS should have: preferentially streamwise-aligned features to enhance favourable slip, a capillary resistance of the order of megapascals, and a roughness no larger than 0.5, when non-dimensionalized by the viscous length scale. This article is part of the themed issue ‘Bioinspired hierarchically structured surfaces for green science’. PMID:27354731

Symmetry breaking for drag minimization

NASA Astrophysics Data System (ADS)

Roper, Marcus; Squires, Todd M.; Brenner, Michael P.

2005-11-01

For locomotion at high Reynolds numbers drag minimization favors fore-aft asymmetric slender shapes with blunt noses and sharp trailing edges. On the other hand, in an inertialess fluid the drag experienced by a body is independent of whether it travels forward or backward through the fluid, so there is no advantage to having a single preferred swimming direction. In fact numerically determined minimum drag shapes are known to exhibit almost no fore-aft asymmetry even at moderate Re. We show that asymmetry persists, albeit extremely weakly, down to vanishingly small Re, scaling asymptotically as Re^3. The need to minimize drag to maximize speed for a given propulsive capacity gives one possible mechanism for the increasing asymmetry in the body plans seen in nature, as organisms increase in size and swimming speed from bacteria like E-Coli up to pursuit predator fish such as tuna. If it is the dominant mechanism, then this signature scaling will be observed in the shapes of motile micro-organisms.

Biomimetic spiroid winglets for lift and drag control

NASA Astrophysics Data System (ADS)

Guerrero, Joel E.; Maestro, Dario; Bottaro, Alessandro

2012-01-01

In aeronautical engineering, drag reduction constitutes a challenge and there is room for improvement and innovative developments. The drag breakdown of a typical transport aircraft shows that the lift-induced drag can amount to as much as 40% of the total drag at cruise conditions and 80-90% of the total drag in take-off configuration. One way of reducing lift-induced drag is by using wingtip devices. By applying biomimetic abstraction of the principle behind a bird's wingtip feathers, we study spiroid wingtips, which look like an extended blended wingtip that bends upward by 360 degrees to form a large rigid ribbon. The numerical investigation of such a wingtip device is described and preliminary indications of its aerodynamic performance are provided.

Drag king magic: performing/becoming the other.

PubMed

Rosenfeld, Kathryn

2002-01-01

This chapter seeks to theorize drag king practice through the lenses of alterity, liminality, and performance theory, while attempting to complicate and reinvigorate discussions of identity raised by drag. I examine the ways in which drag king performance plumbs the concept of "the Other," and forces confrontation with a complex field of desire. Contemporary "queergirl" existence negotiates a range of desirable and desiring Others, from the polarities (i.e., butch-femme) unique to queer structures of desire, to the desire of those on the cultural margins for the power of those at the center, and vice versa. I employ anthropological theories of performance, mimesis, and liminality to establish a framework through which drag kings may be viewed as crucibles of this desire and agents of this power exchange. By performing maleness, drag kings expand and redraw the definitional boundaries of the male, interfere with the cultural power of mainstream maleness, and simultaneously transfer some of this power to themselves as queer women. At the same time, drag king existence forces a renegotiation of queergirl desire to encompass a range of masculinities. By performing/becoming the Other, drag kings engage in a practice of magic which transforms both margin and center.

Helicopter hub fairing and pylon interference drag

NASA Technical Reports Server (NTRS)

Graham, D. R.; Sung, D. Y.; Young, L. A.; Louie, A. W.; Stroub, R. H.

1989-01-01

A wind tunnel test was conducted to study the aerodynamics of helicopter hub and pylon fairings. The test was conducted in the 7-by 10 Foot Subsonic Wind Tunnel (Number 2) at Ames Research Center using a 1/5-scale XH-59A fuselage model. The primary focus of the test was on the rotor hub fairing and pylon mutual interference drag. Parametric studies of pylon and hub fairing geometry were also conducted. This report presents the major findings of the test as well as tabulated force and moment data, flow visualization photographs, and graphical presentations of the drag data. The test results indicate that substantial drag reduction can be attained through the use of a cambered hub fairing with circular arc upper surface and flat lower surface. Furthermore, a considerable portion of the overall drag reduction is attributed to the reduction in the hub-on-pylon interference drag. It is also observed that the lower surface curvature of the fairing has a strong influence on the hub fairing and on pylon interference drag. However, the drag reduction benefit that was obtained by using the cambered hub fairing with a flat lower surface was adversely affected by the clearance between the hub fairing and the pylon.

Drag coefficients for loose reactor parts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shi, L.; Doster, J.M.; Mayo, C.W.

1997-12-01

Loose-part monitoring systems are capable of providing estimates of loose-part mass and energy as well as impact location. Additional information regarding potentially damaging loose parts can be obtained by estimating loose-part velocity on the basis of free motion dynamics within the flow. To estimate the loose-part velocity, the drag coefficient of the part must be known. Traditionally, drag coefficients of three-dimensional bodies are measured in wind tunnels, by towing in free air or liquids, and with drop tests. These methods have disadvantages with respect to measuring drag coefficients for loose parts in that they require a fixed orientation, or themore » flow field is inconsistent with the turbulent flow conditions found in reactor systems. Though drag coefficients for some regularly shaped objects can be found in the literature, many shapes representative of typical loose parts have not been investigated. In this work, drag coefficients are measured for typical loose-part shapes, including bolts, nuts, pins, and hand tools within the flow conditions expected in reactor coolant systems.« less

Drag reduction in the turbulent Kolmogorov flow.

PubMed

Boffetta, Guido; Celani, Antonio; Mazzino, Andrea

2005-03-01

We investigate the phenomenon of drag reduction in a viscoelastic fluid model of dilute polymer solutions. By means of direct numerical simulations of the three-dimensional turbulent Kolmogorov flow we show that drag reduction takes place above a critical Reynolds number Re(c). An explicit expression for the dependence of Re(c) on polymer elasticity and diffusivity is derived. The values of the drag coefficient obtained for different fluid parameters collapse onto a universal curve when plotted as a function of the rescaled Reynolds number Re/ Re(c). The analysis of the momentum budget allows us to gain some insight on the physics of drag reduction, and suggests the existence of a Re-independent value of the drag cofficient--lower than the Newtonian one--for large Reynolds numbers.

14 CFR 25.937 - Turbopropeller-drag limiting systems.

Code of Federal Regulations, 2013 CFR

2013-01-01

...-drag limiting systems. Turbopropeller power airplane propeller-drag limiting systems must be designed... results in propeller drag in excess of that for which the airplane was designed under § 25.367. Failure of...

14 CFR 25.937 - Turbopropeller-drag limiting systems.

Code of Federal Regulations, 2012 CFR

2012-01-01

...-drag limiting systems. Turbopropeller power airplane propeller-drag limiting systems must be designed... results in propeller drag in excess of that for which the airplane was designed under § 25.367. Failure of...

14 CFR 25.937 - Turbopropeller-drag limiting systems.

Code of Federal Regulations, 2011 CFR

2011-01-01

...-drag limiting systems. Turbopropeller power airplane propeller-drag limiting systems must be designed... results in propeller drag in excess of that for which the airplane was designed under § 25.367. Failure of...

14 CFR 25.937 - Turbopropeller-drag limiting systems.

Code of Federal Regulations, 2010 CFR

2010-01-01

...-drag limiting systems. Turbopropeller power airplane propeller-drag limiting systems must be designed... results in propeller drag in excess of that for which the airplane was designed under § 25.367. Failure of...

14 CFR 25.937 - Turbopropeller-drag limiting systems.

Code of Federal Regulations, 2014 CFR

2014-01-01

...-drag limiting systems. Turbopropeller power airplane propeller-drag limiting systems must be designed... results in propeller drag in excess of that for which the airplane was designed under § 25.367. Failure of...

Bioinspired surfaces for turbulent drag reduction.

PubMed

Golovin, Kevin B; Gose, James W; Perlin, Marc; Ceccio, Steven L; Tuteja, Anish

2016-08-06

In this review, we discuss how superhydrophobic surfaces (SHSs) can provide friction drag reduction in turbulent flow. Whereas biomimetic SHSs are known to reduce drag in laminar flow, turbulence adds many new challenges. We first provide an overview on designing SHSs, and how these surfaces can cause slip in the laminar regime. We then discuss recent studies evaluating drag on SHSs in turbulent flow, both computationally and experimentally. The effects of streamwise and spanwise slip for canonical, structured surfaces are well characterized by direct numerical simulations, and several experimental studies have validated these results. However, the complex and hierarchical textures of scalable SHSs that can be applied over large areas generate additional complications. Many studies on such surfaces have measured no drag reduction, or even a drag increase in turbulent flow. We discuss how surface wettability, roughness effects and some newly found scaling laws can help explain these varied results. Overall, we discuss how, to effectively reduce drag in turbulent flow, an SHS should have: preferentially streamwise-aligned features to enhance favourable slip, a capillary resistance of the order of megapascals, and a roughness no larger than 0.5, when non-dimensionalized by the viscous length scale.This article is part of the themed issue 'Bioinspired hierarchically structured surfaces for green science'. © 2016 The Author(s).

The Characterization of Non-Gravitational Perturbations That Act on Near-Earth Asteroid Orbits

NASA Astrophysics Data System (ADS)

Margot, Jean-Luc; Greenberg, Adam H.; Verma, Ashok K.; Taylor, Patrick A.

2017-10-01

The Yarkovsky effect is a thermal process acting upon the orbits of small celestial bodies which can cause these orbits to slowly expand or contract with time. The effect is subtle -- typical drift rates lie near 1e-4 au/My for a ~1 km diameter object -- and is thus generally difficult to measure. However, objects with long observation intervals, as well as objects with radar detections, serve as excellent candidates for the observation of this effect.We analyzed both optical and radar astrometry for all numbered Near-Earth Asteroids (NEAs), as well as several un-numbered NEAs. In order to quantify the likelihood of Yarkovsky detections, we developed a metric based on the quality of Yarkovsky fits as compared to that of gravity-only fits. Based on the metric results, we report 167 objects with measured Yarkovsky drifts.Our Yarkovsky sample is the largest published set of such detections, and presents an opportunity to examine the physical properties of these NEAs and the Yarkovsky effect in a statistical manner. In particular, we confirm the Yarkovsky effect's theoretical size dependence of 1/D, where D is diameter. We also examine the efficiency with which this effect converts absorbed light into orbital drift. Using our set of 167 objects, we find typical efficiences of around 5%. This efficiency can be used to place bounds on spin and thermal properties. We report the ratio of positive to negative drift rates and interpret this ratio in terms of prograde/retrograde rotators and main belt escape mechanisms. The observed ratio has a probability of 1 in 9 million of occurring by chance, which confirms the presence of a non-gravitational influence. We examine how the presence of radar data affect the strength and precision of our detections. We find that, on average, the precision of radar+optical detections improves by a factor of approximately 1.6 for each additional apparition with ranging data compared to that of optical-only solutions.

A Natural History of the Drag Queen Phenomenon.

PubMed

Moncrieff, Michael; Lienard, Pierre

2017-01-01

The drag queen cultural phenomenon has been described at length. However, the depiction of outlandish and hyperbolic womanhood and taunting and formidable behavior at the core of drag queens' public persona has still to be fully accounted for. We argue that these aspects of the drag queen's public appearance could best be understood in a signaling framework. Publicly donning extravagant woman's costumes attracts harassment and brings financial, mating, and opportunity costs, generating the conditions for the transmission of honest signals. By successfully withstanding those odds, drag queen impersonators signal strategic qualities to members of the gay community. Data collected among gay and straight participants support a costly signaling reading of the drag queen cultural phenomenon. Participants generally agree that successful drag queens typically incur costs, while gaining specific social benefits.

Relaxation drag history of shock accelerated microparticles

DOE PAGES

Bordoloi, Ankur D.; Martinez, Adam A.; Prestridge, Katherine

2017-06-21

Experimental measurements of the displacements of shock accelerated microparticles from shortly after shock interaction to the particle relaxation time show time-dependent drag coefficients (more » $$C_{D}$$) that are much higher than those predicted by quasi-steady and unsteady drag models. Nylon particles with mean diameter of $$4~\\unicode[STIX]{x03BC}\\text{m}$$, accelerated by one-dimensional normal shocks (Mach number$$M_{s}=1.2$$, 1.3 and 1.4), have measured$$C_{D}$$values that follow a power-law behaviour. The drag is a function of the time-dependent Knudsen number,$$Kn^{\\ast }=M_{s}/Re_{p}$$, where the particle Reynolds number ($$Re_{p}$$) is calculated using the time-dependent slip velocity. Also, some portion of the drag can be attributed to quasi-steady forces, but the total drag cannot be predicted by current unsteady force models that are based on the Basset–Boussinesq–Oseen equation and pressure drag. The largest contribution to the total drag is the unsteady component ($$C_{D,us}$$) until the particle attains$$Kn^{\\ast }\\approx 0.5{-}1.0$$, then the unsteady contribution decays. The quasi-steady component ($$C_{D,qs}$$) increases almost linearly with$$Kn^{\\ast }$$, intersects the$$C_{D,us}$$at$$Kn^{\\ast }\\approx 2$$and becomes the primary contributor to the drag towards the end of the relaxation zone as$$Re_{p}\\rightarrow 0$$. Finally, there are currently no analytical models that are able to predict the nonlinear behaviour of the shock accelerated particles during the relaxation phase of the flow.« less

Relaxation drag history of shock accelerated microparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bordoloi, Ankur D.; Martinez, Adam A.; Prestridge, Katherine

Experimental measurements of the displacements of shock accelerated microparticles from shortly after shock interaction to the particle relaxation time show time-dependent drag coefficients (more » $$C_{D}$$) that are much higher than those predicted by quasi-steady and unsteady drag models. Nylon particles with mean diameter of $$4~\\unicode[STIX]{x03BC}\\text{m}$$, accelerated by one-dimensional normal shocks (Mach number$$M_{s}=1.2$$, 1.3 and 1.4), have measured$$C_{D}$$values that follow a power-law behaviour. The drag is a function of the time-dependent Knudsen number,$$Kn^{\\ast }=M_{s}/Re_{p}$$, where the particle Reynolds number ($$Re_{p}$$) is calculated using the time-dependent slip velocity. Also, some portion of the drag can be attributed to quasi-steady forces, but the total drag cannot be predicted by current unsteady force models that are based on the Basset–Boussinesq–Oseen equation and pressure drag. The largest contribution to the total drag is the unsteady component ($$C_{D,us}$$) until the particle attains$$Kn^{\\ast }\\approx 0.5{-}1.0$$, then the unsteady contribution decays. The quasi-steady component ($$C_{D,qs}$$) increases almost linearly with$$Kn^{\\ast }$$, intersects the$$C_{D,us}$$at$$Kn^{\\ast }\\approx 2$$and becomes the primary contributor to the drag towards the end of the relaxation zone as$$Re_{p}\\rightarrow 0$$. Finally, there are currently no analytical models that are able to predict the nonlinear behaviour of the shock accelerated particles during the relaxation phase of the flow.« less

Active aerodynamic drag reduction on morphable cylinders

NASA Astrophysics Data System (ADS)

Guttag, M.; Reis, P. M.

2017-12-01

We study a mechanism for active aerodynamic drag reduction on morphable grooved cylinders, whose topography can be modified pneumatically. Our design is inspired by the morphology of the Saguaro 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. Our analog experimental samples comprise a spoked rigid skeleton with axial cavities, covered by a stretched elastomeric film. Decreasing the inner pressure of the sample produces axial grooves, whose depth can be accurately varied, on demand. First, we characterize the relation between groove depth and pneumatic loading through a combination of precision mechanical experiments and finite element simulations. Second, wind tunnel tests are used to measure the aerodynamic drag coefficient (as a function of Reynolds number) of the grooved samples, with different levels of periodicity and groove depths. We focus specifically on the drag crisis and systematically measure the associated minimum drag coefficient and the critical Reynolds number at which it occurs. The results are in agreement with the classic literature of rough cylinders, albeit with an unprecedented level of precision and resolution in varying topography using a single sample. Finally, we leverage the morphable nature of our system to dynamically reduce drag for varying aerodynamic loading conditions. We demonstrate that actively controlling the groove depth yields a drag coefficient that decreases monotonically with Reynolds number and is significantly lower than the fixed sample counterparts. These findings open the possibility for the drag reduction of grooved cylinders to be operated over a wide range of flow conditions.

Correlated Coulomb Drag in Capacitively Coupled Quantum-Dot Structures.

PubMed

Kaasbjerg, Kristen; Jauho, Antti-Pekka

2016-05-13

We study theoretically Coulomb drag in capacitively coupled quantum dots (CQDs)-a bias-driven dot coupled to an unbiased dot where transport is due to Coulomb mediated energy transfer drag. To this end, we introduce a master-equation approach that accounts for higher-order tunneling (cotunneling) processes as well as energy-dependent lead couplings, and identify a mesoscopic Coulomb drag mechanism driven by nonlocal multielectron cotunneling processes. Our theory establishes the conditions for a nonzero drag as well as the direction of the drag current in terms of microscopic system parameters. Interestingly, the direction of the drag current is not determined by the drive current, but by an interplay between the energy-dependent lead couplings. Studying the drag mechanism in a graphene-based CQD heterostructure, we show that the predictions of our theory are consistent with recent experiments on Coulomb drag in CQD systems.

Analog VLSI system for active drag reduction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gupta, B.; Goodman, R.; Jiang, F.

1996-10-01

In today`s cost-conscious air transportation industry, fuel costs are a substantial economic concern. Drag reduction is an important way to reduce costs. Even a 5% reduction in drag translates into estimated savings of millions of dollars in fuel costs. Drawing inspiration from the structure of shark skin, the authors are building a system to reduce drag along a surface. Our analog VLSI system interfaces with microfabricated, constant-temperature shear stress sensors. It detects regions of high shear stress and outputs a control signal to activate a microactuator. We are in the process of verifying the actual drag reduction by controlling microactuatorsmore » in wind tunnel experiments. We are encouraged that an approach similar to one that biology employs provides a very useful contribution to the problem of drag reduction. 9 refs., 21 figs.« less

Drag reduction through self-texturing compliant bionic materials

PubMed Central

Liu, Eryong; Li, Longyang; Wang, Gang; Zeng, Zhixiang; Zhao, Wenjie; Xue, Qunji

2017-01-01

Compliant fish skin is effectively in reducing drag, thus the design and application of compliant bionic materials may be a good choice for drag reduction. Here we consider the drag reduction of compliant bionic materials. First, ZnO and PDMS mesh modified with n-octadecane were prepared, the drag reduction of self-texturing compliant n-octadecane were studied. The results show that the mesh modified by ZnO and PDMS possess excellent lipophilic and hydrophobic, thus n-octadecane at solid, semisolid and liquid state all have good adhesion with modified mesh. The states of n-octadecane changed with temperature, thus, the surface contact angle and adhesive force all varies obviously at different state. The contact angle decreases with temperature, the adhesive force shows a lower value at semisolid state. Furthermore, the drag testing results show that the compliant n-octadecane film is more effectively in drag reduction than superhydrophobic ZnO/PDMS film, indicating that the drag reduction mechanism of n-octadecane is significantly different with superhydrophobic film. Further research shows that the water flow leads to self-texturing of semisolid state n-octadecane, which is similar with compliant fish skin. Therefore, the compliant bionic materials of semisolid state n-octadecane with regular bulge plays a major role in the drag reduction. PMID:28053309

Drag reduction through self-texturing compliant bionic materials.

PubMed

Liu, Eryong; Li, Longyang; Wang, Gang; Zeng, Zhixiang; Zhao, Wenjie; Xue, Qunji

2017-01-05

Compliant fish skin is effectively in reducing drag, thus the design and application of compliant bionic materials may be a good choice for drag reduction. Here we consider the drag reduction of compliant bionic materials. First, ZnO and PDMS mesh modified with n-octadecane were prepared, the drag reduction of self-texturing compliant n-octadecane were studied. The results show that the mesh modified by ZnO and PDMS possess excellent lipophilic and hydrophobic, thus n-octadecane at solid, semisolid and liquid state all have good adhesion with modified mesh. The states of n-octadecane changed with temperature, thus, the surface contact angle and adhesive force all varies obviously at different state. The contact angle decreases with temperature, the adhesive force shows a lower value at semisolid state. Furthermore, the drag testing results show that the compliant n-octadecane film is more effectively in drag reduction than superhydrophobic ZnO/PDMS film, indicating that the drag reduction mechanism of n-octadecane is significantly different with superhydrophobic film. Further research shows that the water flow leads to self-texturing of semisolid state n-octadecane, which is similar with compliant fish skin. Therefore, the compliant bionic materials of semisolid state n-octadecane with regular bulge plays a major role in the drag reduction.

Drag reduction through self-texturing compliant bionic materials

NASA Astrophysics Data System (ADS)

Liu, Eryong; Li, Longyang; Wang, Gang; Zeng, Zhixiang; Zhao, Wenjie; Xue, Qunji

2017-01-01

Compliant fish skin is effectively in reducing drag, thus the design and application of compliant bionic materials may be a good choice for drag reduction. Here we consider the drag reduction of compliant bionic materials. First, ZnO and PDMS mesh modified with n-octadecane were prepared, the drag reduction of self-texturing compliant n-octadecane were studied. The results show that the mesh modified by ZnO and PDMS possess excellent lipophilic and hydrophobic, thus n-octadecane at solid, semisolid and liquid state all have good adhesion with modified mesh. The states of n-octadecane changed with temperature, thus, the surface contact angle and adhesive force all varies obviously at different state. The contact angle decreases with temperature, the adhesive force shows a lower value at semisolid state. Furthermore, the drag testing results show that the compliant n-octadecane film is more effectively in drag reduction than superhydrophobic ZnO/PDMS film, indicating that the drag reduction mechanism of n-octadecane is significantly different with superhydrophobic film. Further research shows that the water flow leads to self-texturing of semisolid state n-octadecane, which is similar with compliant fish skin. Therefore, the compliant bionic materials of semisolid state n-octadecane with regular bulge plays a major role in the drag reduction.

Interference drag in a simulated wing-fuselage juncture

NASA Technical Reports Server (NTRS)

Kubendran, L. R.; Mcmahon, H.; Hubbartt, J. E.

1984-01-01

The interference drag in a wing fuselage juncture as simulated by a flat plate and a body of constant thickness having a 1.5:1 elliptical leading edge is evaluated experimentally. The experimental measurements consist of mean velocity data taken with a hot wire at a streamwise location corresponding to 16 body widths downstream of the body leading edge. From these data, the interference drag is determined by calculating the total momentum deficit (momentum area) in the juncture and also in the two dimensional turbulent boundary layers on the flat plate and body at locations sufficiently far from the juncture flow effect. The interference drag caused by the juncture drag as measured at this particular streamwise station is -3% of the total drag due to the flat plate and body boundary layers in isolation. If the body is considered to be a wing having a chord and span equal to 16 body widths, the interference drag due to the juncture is only -1% of the frictional drag of one surface of such a wing.

Drag of ballistic electrons by an ion beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gurevich, V. L.; Muradov, M. I., E-mail: mag.muradov@mail.ioffe.ru

2015-12-15

Drag of electrons of a one-dimensional ballistic nanowire by a nearby one-dimensional beam of ions is considered. We assume that the ion beam is represented by an ensemble of heavy ions of the same velocity V. The ratio of the drag current to the primary current carried by the ion beam is calculated. The drag current turns out to be a nonmonotonic function of velocity V. It has a sharp maximum for V near v{sub nF}/2, where n is the number of the uppermost electron miniband (channel) taking part in conduction and v{sub nF} is the corresponding Fermi velocity. Thismore » means that the phenomenon of ion beam drag can be used for investigation of the electron spectra of ballistic nanostructures. We note that whereas observation of the Coulomb drag between two parallel quantum wires may in general be complicated by phenomena such as tunneling and phonon drag, the Coulomb drag of electrons of a one-dimensional ballistic nanowire by an ion beam is free of such spurious effects.« less

Analysis of Drag Reduction Methods and Mechanisms of Turbulent.

PubMed

Yunqing, Gu; Tao, Liu; Jiegang, Mu; Zhengzan, Shi; Peijian, Zhou

2017-01-01

Turbulent flow is a difficult issue in fluid dynamics, the rules of which have not been totally revealed up to now. Fluid in turbulent state will result in a greater frictional force, which must consume great energy. Therefore, it is not only an important influence in saving energy and improving energy utilization rate but also an extensive application prospect in many fields, such as ship domain and aerospace. Firstly, bionic drag reduction technology is reviewed and is a hot research issue now, the drag reduction mechanism of body surface structure is analyzed, such as sharks, earthworms, and dolphins. Besides, we make a thorough study of drag reduction characteristics and mechanisms of microgrooved surface and compliant wall. Then, the relevant drag reduction technologies and mechanisms are discussed, focusing on the microbubbles, the vibrant flexible wall, the coating, the polymer drag reduction additives, superhydrophobic surface, jet surface, traveling wave surface drag reduction, and the composite drag reduction methods. Finally, applications and advancements of the drag reduction technology in turbulence are prospected.

Analysis of Drag Reduction Methods and Mechanisms of Turbulent

PubMed Central

Tao, Liu; Jiegang, Mu; Zhengzan, Shi; Peijian, Zhou

2017-01-01

Turbulent flow is a difficult issue in fluid dynamics, the rules of which have not been totally revealed up to now. Fluid in turbulent state will result in a greater frictional force, which must consume great energy. Therefore, it is not only an important influence in saving energy and improving energy utilization rate but also an extensive application prospect in many fields, such as ship domain and aerospace. Firstly, bionic drag reduction technology is reviewed and is a hot research issue now, the drag reduction mechanism of body surface structure is analyzed, such as sharks, earthworms, and dolphins. Besides, we make a thorough study of drag reduction characteristics and mechanisms of microgrooved surface and compliant wall. Then, the relevant drag reduction technologies and mechanisms are discussed, focusing on the microbubbles, the vibrant flexible wall, the coating, the polymer drag reduction additives, superhydrophobic surface, jet surface, traveling wave surface drag reduction, and the composite drag reduction methods. Finally, applications and advancements of the drag reduction technology in turbulence are prospected. PMID:29104425

The ‘W’ Prawn-Trawl with Emphasised Drag-Force Transfer to Its Centre Line to Reduce Overall System Drag

PubMed Central

Balash, Cheslav; Sterling, David; Binns, Jonathan; Thomas, Giles; Bose, Neil

2015-01-01

For prawn trawling systems, drag reduction is a high priority as the trawling process is energy intensive. Large benefits have occurred through the use of multiple-net rigs and thin twine in the netting. An additional positive effect of these successful twine-area reduction strategies is the reduced amount of otter board area required to spread the trawl systems, which leads to further drag reduction. The present work investigated the potential of redirecting the drag-strain within a prawn trawl away from the wings and the otter boards to the centre line of the trawl, where top and bottom tongues have been installed, with an aim to minimise the loading/size of the otter boards required to spread the trawl. In the system containing the new ‘W’ trawl, the drag redirected to the centre-line tongues is transferred forward through a connected sled and towing wires to the trawler. To establish the extent of drag redirection to the centre-line tongues and the relative drag benefits of the new trawl system, conventional and ‘W’ trawls of 3.65 m headline length were tested firstly over a range of spread ratios in the flume tank, and subsequently at optimum spread ratio in the field. The developed ‘W’ trawl effectively directed 64% of netting-drag off the wings and onto the centre tongues, which resulted in drag savings in the field of ∼20% for the associated ‘W’ trawl/otter-board/sled system compared to the traditional trawl/otter-board arrangement in a single trawl or twin rig configuration. Furthermore, based on previously published data, the new trawl when used in a twin rig system is expected to provide approximately 12% drag reduction compared to quad rig. The twin ‘W’ trawl system also has benefits over quad rig in that a reduced number of cod-end/By-catch Reduction Device units need to be installed and attended each tow. PMID:25751251

14 CFR 23.937 - Turbopropeller-drag limiting systems.

Code of Federal Regulations, 2010 CFR

2010-01-01

... actuated after engine power loss, can move the propeller blades toward the feather position to reduce... General § 23.937 Turbopropeller-drag limiting systems. (a) Turbopropeller-powered airplane propeller-drag... normal or emergency operation results in propeller drag in excess of that for which the airplane was...

14 CFR 23.937 - Turbopropeller-drag limiting systems.

Code of Federal Regulations, 2012 CFR

2012-01-01

... actuated after engine power loss, can move the propeller blades toward the feather position to reduce... General § 23.937 Turbopropeller-drag limiting systems. (a) Turbopropeller-powered airplane propeller-drag... normal or emergency operation results in propeller drag in excess of that for which the airplane was...

14 CFR 23.937 - Turbopropeller-drag limiting systems.

Code of Federal Regulations, 2014 CFR

2014-01-01

... actuated after engine power loss, can move the propeller blades toward the feather position to reduce... General § 23.937 Turbopropeller-drag limiting systems. (a) Turbopropeller-powered airplane propeller-drag... normal or emergency operation results in propeller drag in excess of that for which the airplane was...

14 CFR 23.937 - Turbopropeller-drag limiting systems.

Code of Federal Regulations, 2013 CFR

2013-01-01

... actuated after engine power loss, can move the propeller blades toward the feather position to reduce... General § 23.937 Turbopropeller-drag limiting systems. (a) Turbopropeller-powered airplane propeller-drag... normal or emergency operation results in propeller drag in excess of that for which the airplane was...

14 CFR 23.937 - Turbopropeller-drag limiting systems.

Code of Federal Regulations, 2011 CFR

2011-01-01

... actuated after engine power loss, can move the propeller blades toward the feather position to reduce... General § 23.937 Turbopropeller-drag limiting systems. (a) Turbopropeller-powered airplane propeller-drag... normal or emergency operation results in propeller drag in excess of that for which the airplane was...

The maximum drag reduction asymptote

NASA Astrophysics Data System (ADS)

Choueiri, George H.; Hof, Bjorn

2015-11-01

Addition of long chain polymers is one of the most efficient ways to reduce the drag of turbulent flows. Already very low concentration of polymers can lead to a substantial drag and upon further increase of the concentration the drag reduces until it reaches an empirically found limit, the so called maximum drag reduction (MDR) asymptote, which is independent of the type of polymer used. We here carry out a detailed experimental study of the approach to this asymptote for pipe flow. Particular attention is paid to the recently observed state of elasto-inertial turbulence (EIT) which has been reported to occur in polymer solutions at sufficiently high shear. Our results show that upon the approach to MDR Newtonian turbulence becomes marginalized (hibernation) and eventually completely disappears and is replaced by EIT. In particular, spectra of high Reynolds number MDR flows are compared to flows at high shear rates in small diameter tubes where EIT is found at Re < 100. The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme (FP7/2007-2013) under REA grant agreement n° [291734].

ABM Drag_Pass Report Generator

NASA Technical Reports Server (NTRS)

Fisher, Forest; Gladden, Roy; Khanampornpan, Teerapat

2008-01-01

dragREPORT software was developed in parallel with abmREPORT, which is described in the preceding article. Both programs were built on the capabilities created during that process. This tool generates a drag_pass report that summarizes vital information from the MRO aerobreaking drag_pass build process to facilitate both sequence reviews and provide a high-level summarization of the sequence for mission management. The script extracts information from the ENV, SSF, FRF, SCMFmax, and OPTG files, presenting them in a single, easy-to-check report providing the majority of parameters needed for cross check and verification as part of the sequence review process. Prior to dragReport, all the needed information was spread across a number of different files, each in a different format. This software is a Perl script that extracts vital summarization information and build-process details from a number of source files into a single, concise report format used to aid the MPST sequence review process and to provide a high-level summarization of the sequence for mission management reference. This software could be adapted for future aerobraking missions to provide similar reports, review and summarization information.

Drag reduction in hydrocarbon-aluminum soap polymer systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zakin, J.L.; Lee, K.C.

1972-01-01

While the drag-reducing capability of solutions of aluminum soap in hydrocarbons in turbulent flow has been known for over 20 yr, investigations of the effects of concentration, soap type, and aging on drag reduction have only recently begun. The effects of aging, shear stress, and the presence of peptizers on drag reduction of hydrocarbon dispersions of aluminum soaps at relatively low concentrations were studied. These systems showed an apparent upper critical shear stress above which drag reduction was gradually lost. Degradation of the soap micelle structure occurred relatively rapidly above this point and recovery was slow. The effect of peptizersmore » is complex. In some situations, it enhanced and in others reduced the drag-reducing ability of the soap polymers. (13 refs.)« less

Active skin for turbulent drag reduction

NASA Astrophysics Data System (ADS)

Rediniotis, Othon K.; Lagoudas, Dimitris C.; Mani, Raghavendran; Karniadakis, George

2002-07-01

Drag reduction for aerial vehicles has a range of positive ramifications: reduced fuel consumption with the associated economic and environmental consequences, larger flight range and endurance and higher achievable flight speeds. This work capitalizes on recent advances in active turbulent drag reduction and active material based actuation to develop an active or 'smart' skin for turbulent drag reduction in realistic flight conditions. The skin operation principle is based on computational evidence that spanwise traveling waves of the right amplitude, wavelength and frequency can result in significant turbulent drag reduction. Such traveling waves can be induced in the smart skin via active-material actuation. The flow control technique pursued is 'micro' in the sense that only micro-scale wave amplitudes (order of 30mm) and energy inputs are sufficient to produce significant benefits. Two actuation principles have been proposed and analyzed. Different skin designs based on these two actuation principles have been discussed. The feasibility of these different actuation possibilities (such as Shape Memory Alloys and Piezoelectric material based actuators) and relative merits of different skin designs are discussed. The realization of a mechanically actuated prototype skin capable of generating a traveling wave, using a rapid prototyping machine, for the purpose of validating the proposed drag reduction technique is also presented.

Frictional Magneto-Coulomb Drag in Graphene Double-Layer Heterostructures.

PubMed

Liu, Xiaomeng; Wang, Lei; Fong, Kin Chung; Gao, Yuanda; Maher, Patrick; Watanabe, Kenji; Taniguchi, Takashi; Hone, James; Dean, Cory; Kim, Philip

2017-08-04

Coulomb interaction between two closely spaced parallel layers of conductors can generate the frictional drag effect by interlayer Coulomb scattering. Employing graphene double layers separated by few-layer hexagonal boron nitride, we investigate density tunable magneto- and Hall drag under strong magnetic fields. The observed large magnetodrag and Hall-drag signals can be related with Laudau level filling status of the drive and drag layers. We find that the sign and magnitude of the drag resistivity tensor can be quantitatively correlated to the variation of magnetoresistivity tensors in the drive and drag layers, confirming a theoretical formula for magnetodrag in the quantum Hall regime. The observed weak temperature dependence and ∼B^{2} dependence of the magnetodrag are qualitatively explained by Coulomb scattering phase-space argument.

Drag reduction by polymers in wall bounded turbulence.

PubMed

L'vov, Victor S; Pomyalov, Anna; Procaccia, Itamar; Tiberkevich, Vasil

2004-06-18

We elucidate the mechanism of drag reduction by polymers in turbulent wall-bounded flows: while momentum is produced at a fixed rate by the forcing, polymer stretching results in the suppression of momentum flux to the wall. On the basis of the equations of fluid mechanics we develop the phenomenology of the "maximum drag reduction asymptote" which is the maximum drag reduction attained by polymers. Based on Newtonian information only we demonstrate the existence of drag reduction, and with one experimental parameter we reach agreement with the experimental measurements.

Evaluation of Skin Friction Drag for Liner Applications in Aircraft

NASA Technical Reports Server (NTRS)

Gerhold, Carl H.; Brown, Martha C.; Jasinski, Christopher M.

2016-01-01

A parameter that is gaining significance in the evaluation of acoustic liner performance is the skin friction drag induced by air flow over the liner surface. Estimates vary widely regarding the amount of drag the liner induces relative to a smooth wall, from less than a 20% increase to nearly 100%, and parameters such as face sheet perforate hole diameter, percent open area, and sheet thickness are expected to figure prominently in the skin friction drag. Even a small increase in liner drag can impose an economic penalty, and current research is focused on developing 'low drag' liner concepts, with the goal being to approach the skin friction drag of a smooth wall. The issue of skin friction drag takes on greater significance as airframe designers investigate the feasibility of putting sound absorbing liners on the non-lifting surfaces of the wings and fuselage, for the purpose of reducing engine noise reflected and scattered toward observers on the ground. Researchers at the NASA Langley Research Center have embarked on investigations of liner skin friction drag with the aims of: developing a systematic drag measurement capability, establishing the drag of current liners, and developing liners that produce reduced drag without compromising acoustic performance. This paper discusses the experimental procedures that have been developed to calculate the drag coefficient based on the change in momentum thickness and the companion research program being carried out to measure the drag directly using a force balance. Liner samples that are evaluated include a solid wall with known roughness and conventional liners with perforated facesheets of varying hole diameter and percent open area.

Magnetically tunable 1D Coulomb drag: Theory

NASA Astrophysics Data System (ADS)

Tylan-Tyler, Anthony; Tang, Yuhe; Levy, Jeremy

In this work, we examine the Coulomb drag effect in 1D nanowires in close proximity, focusing on experimental parameters relevant to complex-oxide nanostructures. Previous work on this problem examined Coulomb drag through quantum point contacts, where effective capacitive coupling between the 2D leads of the system generates the drag voltage. In our case, the entire system is composed of 1D components and thus a more careful treatment of the Coulomb interactions is required. This more complex environment then leads to the ability to switch the drag voltage by an applied magnetic field without altering the current supplied to the drive system. We gratefully acknowledge financial support from ONR N00014-15-1-2847 and DOE DE-SC0014417.

Exceeding the Asymptotic Limit of Polymer Drag Reduction.

PubMed

Choueiri, George H; Lopez, Jose M; Hof, Björn

2018-03-23

The drag of turbulent flows can be drastically decreased by adding small amounts of high molecular weight polymers. While drag reduction initially increases with polymer concentration, it eventually saturates to what is known as the maximum drag reduction (MDR) asymptote; this asymptote is generally attributed to the dynamics being reduced to a marginal yet persistent state of subdued turbulent motion. Contrary to this accepted view, we show that, for an appropriate choice of parameters, polymers can reduce the drag beyond the suggested asymptotic limit, eliminating turbulence and giving way to laminar flow. At higher polymer concentrations, however, the laminar state becomes unstable, resulting in a fluctuating flow with the characteristic drag of the MDR asymptote. Our findings indicate that the asymptotic state is hence dynamically disconnected from ordinary turbulence.

Exceeding the Asymptotic Limit of Polymer Drag Reduction

NASA Astrophysics Data System (ADS)

Choueiri, George H.; Lopez, Jose M.; Hof, Björn

2018-03-01

The drag of turbulent flows can be drastically decreased by adding small amounts of high molecular weight polymers. While drag reduction initially increases with polymer concentration, it eventually saturates to what is known as the maximum drag reduction (MDR) asymptote; this asymptote is generally attributed to the dynamics being reduced to a marginal yet persistent state of subdued turbulent motion. Contrary to this accepted view, we show that, for an appropriate choice of parameters, polymers can reduce the drag beyond the suggested asymptotic limit, eliminating turbulence and giving way to laminar flow. At higher polymer concentrations, however, the laminar state becomes unstable, resulting in a fluctuating flow with the characteristic drag of the MDR asymptote. Our findings indicate that the asymptotic state is hence dynamically disconnected from ordinary turbulence.

Drag reduction by Acinetobacter calcoaceticus BD4.

PubMed

Sar, N; Rosenberg, E

1987-09-01

The encapsulated bacterium Acinetobacter calcoaceticus BD4 at a density of 3.6 X 10(9) cells per ml reduced the friction of turbulent water in a narrow pipe by 55%. This drag reduction was due to the tightly bound polysaccharide capsules (0.4 mg per ml) of culture. Capsule-deficient mutants of BD4 failed to reduce drag. The cell-bound polysaccharide demonstrated a threefold-higher drag-reducing activity than the polymer which was free in solution.

An Aerodynamic Assessment of Micro-Drag Generators (MDGs)

NASA Technical Reports Server (NTRS)

Bauer, Steven X. S.

1998-01-01

Commercial transports as well as fighter aircraft of the future are being designed with very low drag (friction and pressure). Concurrently, commuter airports are being built or envisioned to be built in the centers of metropolitan areas where shorter runways and/or reduced noise footprints on takeoff and landing are required. These requirements and the fact that drag is lower on new vehicles than on older aircraft have resulted in vehicles that require a large amount of braking force (from landing-gear brakes, spoilers, high-lift flaps, thrust reversers, etc.). Micro-drag generators (MDGs) were envisioned to create a uniformly distributed drag force along a vehicle by forcing the flow to separate on the aft-facing surface of a series of deployable devices, thus, generating drag. The devices are intended to work at any speed and for any type of vehicle (aircraft, ground vehicles, sea-faring vehicles). MDGs were applied to a general aviation wing and a representative fuselage shape and tested in two subsonic wind tunnels. The results showed increases in drag of 2 to 6 times that of a "clean" configuration.

Parasite-Drag Measurements of Five Helicopter Rotor Hubs

NASA Technical Reports Server (NTRS)

Churchill, Gary B.; Harrington, Robert D.

1959-01-01

An investigation has been conducted in the Langley full-scale tunnel to determine the parasite drag of five production-type helicopter rotor hubs. Some simple fairing arrangements were attempted in an effort to reduce the hub drag. The results indicate that, within the range of the tests, changes in angle of attack, hub rotational speed, and forward speed generally had only a small effect on the equivalent flat-plate area representing parasite drag. The drag coefficients of the basic hubs, based on projected hub frontal area, increased with hub area and varied from 0.5 to 0.76 for the hubs tested.

Thermal Model Correlation for Mars Reconnaissance Orbiter

NASA Technical Reports Server (NTRS)

Amundsen, Ruth M.; Dec, John A.; Gasbarre, Joseph F.

2007-01-01

The Mars Reconnaissance Orbiter (MRO) launched on August 12, 2005 and began aerobraking at Mars in March 2006. In order to save propellant, MRO used aerobraking to modify the initial orbit at Mars. The spacecraft passed through the atmosphere briefly on each orbit; during each pass the spacecraft was slowed by atmospheric drag, thus lowering the orbit apoapsis. The largest area on the spacecraft, most affected by aeroheating, was the solar arrays. A thermal analysis of the solar arrays was conducted at NASA Langley Research Center to simulate their performance throughout the entire roughly 6-month period of aerobraking. A companion paper describes the development of this thermal model. This model has been correlated against many sets of flight data. Several maneuvers were performed during the cruise to Mars, such as thruster calibrations, which involve large abrupt changes in the spacecraft orientation relative to the sun. The data obtained from these maneuvers allowed the model to be well-correlated with regard to thermal mass, conductive connections, and solar response well before arrival at the planet. Correlation against flight data for both in-cruise maneuvers and drag passes was performed. Adjustments made to the model included orientation during the drag pass, solar flux, Martian surface temperature, through-array resistance, aeroheating gradient due to angle of attack, and aeroheating accommodation coefficient. Methods of correlation included comparing the model to flight temperatures, slopes, temperature deltas between sensors, and solar and planet direction vectors. Correlation and model accuracy over 400 aeroheating drag passes were determined, with overall model accuracy better than 5 C.

Lesbian drag kings and the feminine embodiment of the masculine.

PubMed

Schacht, Steven P

2002-01-01

Part of an ongoing ethnography of an imperial sovereign court I am undertaking, this chapter explores the world of the lesbian drag king and the gendered performance she undertakes in this realm. Taking a relational, situational approach to understanding gender, the lesbian drag queen of the court is also examined in terms of how "her" image and actions give gendered meaning and confer import to the lesbian drag king. Note is also made of lesbian court members' often contradictory gendered relationships with the gay men in this setting: gay drag kings and gay drag kings. Although embodying a masculine persona in image and action has enabled some lesbian drag kings to successfully challenge the often sexist actions and reign of the gay men of the court, it has also resulted in some lesbian drag queens being subordinated in the process. Thus, as much as lesbian drag kings subvert existing gender hierarchies they also sometimes recreate them in the pursuit of situational power.

Invariant Type-B characteristics of drag-reducing microalgal biopolymer solutions

NASA Astrophysics Data System (ADS)

Gasljevic, K.; Hall, K.; Chapman, D.; Matthys, E. F.

2017-05-01

The drag-reducing properties of polysaccharides from marine microalgae were investigated. They were compared to two drag-reducing additives studied extensively in the past, synthetic poly(ethylene) oxide, one of the most effective drag-reducing additives; and Xanthan Gum, another biopolymer often considered a model polymer for chemical and rheological research. Compared to Xanthan Gum, the most effective polymers from our microalgae show a higher drag-reducing efficiency in terms of necessary concentration to achieve a given level of drag reduction. In addition, they show a striking Type-B drag reduction behavior, which may be a very useful quality in most drag reduction applications, thanks to the independence of the drag reduction level on flow conditions such as velocity, shear stress, and tube diameter. With these polymers from microalgae we did not see evidence of Type-A behavior over the wide range of conditions studied (including pipe diameters up to 52 mm). Importantly, this suggests that the Drag Reduction coefficient in pipe flow for ideal drag-reducing solutions such as the polysaccharides investigated here is invariant at a given additive concentration of flow or solution parameters like ionic strength and can be used as a solution property to predict its drag reduction effectiveness over a wide range of conditions. On the contrary, Xanthan Gum showed evidence of both Type-A behavior in large diameter pipes and Type-B behavior in smaller ones. The polymers from microalgae also showed high resistance to degradation. Considering that these microalgae are very effective producers of polysaccharides (both extracellular and intracellular), they appear to be very promising additives for drag reduction applications.

Wind-Tunnel Investigations of Blunt-Body Drag Reduction Using Forebody Surface Roughness

NASA Technical Reports Server (NTRS)

Whitmore, Stephen A.; Sprague, Stephanie; Naughton, Jonathan W.; Curry, Robert E. (Technical Monitor)

2001-01-01

This paper presents results of wind-tunnel tests that demonstrate a novel drag reduction technique for blunt-based vehicles. For these tests, the forebody roughness of a blunt-based model was modified using micomachined surface overlays. As forebody roughness increases, boundary layer at the model aft thickens and reduces the shearing effect of external flow on the separated flow behind the base region, resulting in reduced base drag. For vehicle configurations with large base drag, existing data predict that a small increment in forebody friction drag will result in a relatively large decrease in base drag. If the added increment in forebody skin drag is optimized with respect to base drag, reducing the total drag of the configuration is possible. The wind-tunnel tests results conclusively demonstrate the existence of a forebody dragbase drag optimal point. The data demonstrate that the base drag coefficient corresponding to the drag minimum lies between 0.225 and 0.275, referenced to the base area. Most importantly, the data show a drag reduction of approximately 15% when the drag optimum is reached. When this drag reduction is scaled to the X-33 base area, drag savings approaching 45,000 N (10,000 lbf) can be realized.

Experiment Evaluation of Skin Friction Drag by Surface Tailoring

NASA Astrophysics Data System (ADS)

Manigandan, S.; Gopal krishna, K.; Gagan Kumar, K.; Gunasekar, P.; Nithya, S.

2017-08-01

Reduction of drag is an important role of aerodynamic specialist in real time world. The performance of forward moving object improved when the drag is reduced. Skin friction drag caused when the fluid tending to shear along the surface of the body and it is dependent on energy expenditure. Initial research concluded that nearly 20 to 40% of total drag is skin friction drag, based on flight forward velocity. This means a lot of fuel burned. In this paper we investigate a methodology to reduce the skin friction drag by implementing different kinds of exterior treatments. The ideology inspired from the world fastest moving oceanic creature. Structures are fabricated based on the replica of scales of the oceanic creature. The outer skin of the aerofoil NACA0012 is modified like shark scales. Then it is tested using open type sub sonic wind tunnel. In addition to that, the leading edge thickness effect also studied. The turbulent flow phenomenon is validated at different velocities and compared with numerical results using STAR CCM+. From the plots and graphical results, it is found that the skin friction drag is generated less due to reduction of transverse shear stress present in turbulent flow and skin friction drag depends on boundary layer thickness and on the percentage of chord of flow separation. In addition to this, the result delivers that the ordinary polished surface produces more drag than the modified scales. The outlook of this technology is excrescence for different applications. This open section wind tunnel testing produces 10-15% reduction in drag and can be turn to high values when the experiment is conducted in closed section wind tunnel with real time atmospheric conditions, which can be done as a future work.

Prediction of drag at subsonic and transonic speeds using Euler methods

NASA Technical Reports Server (NTRS)

Nikfetrat, K.; Van Dam, C. P.; Vijgen, P. M. H. W.; Chang, I. C.

1992-01-01

A technique for the evaluation of aerodynamic drag from flowfield solutions based on the Euler equations is discussed. The technique is limited to steady attached flows around three-dimensional configurations in the absence of active systems such as surface blowing/suction and propulsion. It allows the decomposition of the total drag into induced drag and wave drag and, consequently, it provides more information on the drag sources than the conventional surface-pressure integration technique. The induced drag is obtained from the integration of the kinetic energy (per unit distance) of the trailing vortex system on a wake plane and the wave drag is obtained from the integration of the entropy production on a plane just downstream of the shocks. The drag-evaluation technique is applied to three-dimensional flowfield solutions for the ONERA M6 wing as well as an aspect-ratio-7 wing with an elliptic spanwise chord distribution and an NACA-0012 section shape. Comparisons between the drag obtained with the present technique and the drag based on the integration of surface pressures are presented for two Euler codes.

Measuring the Drag Force on a Falling Ball

ERIC Educational Resources Information Center

Cross, Rod; Lindsey, Crawford

2014-01-01

The effect of the aerodynamic drag force on an object in flight is well known and has been described in this and other journals many times. At speeds less than about 1 m/s, the drag force on a sphere is proportional to the speed and is given by Stokes' law. At higher speeds, the drag force is proportional to the velocity squared and is…

Superfluid drag in the two-component Bose-Hubbard model

NASA Astrophysics Data System (ADS)

Sellin, Karl; Babaev, Egor

2018-03-01

In multicomponent superfluids and superconductors, co- and counterflows of components have, in general, different properties. A. F. Andreev and E. P. Bashkin [Sov. Phys. JETP 42, 164 (1975)] discussed, in the context of He3/He4 superfluid mixtures, that interparticle interactions produce a dissipationless drag. The drag can be understood as a superflow of one component induced by phase gradients of the other component. Importantly, the drag can be both positive (entrainment) and negative (counterflow). The effect is known to have crucial importance for many properties of diverse physical systems ranging from the dynamics of neutron stars and rotational responses of Bose mixtures of ultracold atoms to magnetic responses of multicomponent superconductors. Although substantial literature exists that includes the drag interaction phenomenologically, only a few regimes are covered by quantitative studies of the microscopic origin of the drag and its dependence on microscopic parameters. Here we study the microscopic origin and strength of the drag interaction in a quantum system of two-component bosons on a lattice with short-range interaction. By performing quantum Monte Carlo simulations of a two-component Bose-Hubbard model we obtain dependencies of the drag strength on the boson-boson interactions and properties of the optical lattice. Of particular interest are the strongly correlated regimes where the ratio of coflow and counterflow superfluid stiffnesses can diverge, corresponding to the case of saturated drag.

Turbulent drag reduction and degradation of DNA.

PubMed

Choi, H J; Lim, S T; Lai, Pik-Yin; Chan, C K

2002-08-19

Turbulent drag reduction induced by lambda-DNA is studied. The double-stranded DNA is found to be a good drag reducer when compared with the other normal linear polymers. However, this drag reducing power disappears when the DNA denatures to form two single-strand molecules. Mechanical degradation of DNA is also different from that of the normal linear-chain polymers: DNA is always cut in half by the turbulence. Our results suggest that the mechanism for turbulent degradation of DNA is different from that of the normal flexible long-chain polymers.

Negative effects of commercial mussel dragging on eelgrass beds in Maine

USGS Publications Warehouse

Neckles, H.A.; Short, F.T.; Barker, S.; Kopp, B.S.

2005-01-01

A study by the US Geological Survey, the University of New Hampshire, and the Maine Department of Marine Resources showed that commercial mussel dragging poses a severe and long-lasting threat to eelgrass (Zostera marina). Dragging can damage large areas, with individual drag scars up to 79 acres in size found in Maine eelgrass beds. Dragging activity uproots eelgrass plants completely, removing leaves, rhizomes, and roots. Two independent methods were used to predict the rate of eelgrass recovery in heavily dragged areas. Under the best environmental conditions, complete revegetation of a dragged area would require an average of 11 years. Under conditions less favorable for eelgrass growth, such as reduced water quality, dragged areas could require more than 20 years to recover. Protection of eelgrass from commercial shellfish dragging will preserve important coastal habitat.

On the origin of the drag force on golf balls

NASA Astrophysics Data System (ADS)

Balaras, Elias; Beratlis, Nikolaos; Squires, Kyle

2017-11-01

It is well establised that dimples accelerate the drag-crisis on a sphere. The result of the early drag-crisis is a reduction of the drag coefficient by more than a factor of two when compared to a smooth sphere at the same Reynolds number. However, when the drag coefficients for smooth and dimpled spheres in the supercritical regime are compared, the latter is higher by a factor of two to three. To understand the origin of this behavior we conducted direct numerical simulations of the flow around a dimpled sphere, which is similar to commercially available golf balls, in the supercritical regime. By comparing the results to those for a smooth sphere it is found that dimples, although effective in accelerating the drag crisis, impose a local drag-penalty, which contributes significantly to the overall drag force. This finding challenges the broadly accepted view, that the dimples only indirectly affect the drag force on a golf ball by manipulating the structure of the turbulent boundary layer near the wall and consequently affect global separation. Within this view, typically the penalty on the drag force imposed by the dimples is assumed to be small and coming primarily from skin friction. The direct numerical simulations we will report reveal a very different picture.

Effect of Ice Formations on Section Drag of Swept NACA 63A-009 Airfoil with Partical-span Leading-edge Slat for Various Modes of Thermal Ice Protection

NASA Technical Reports Server (NTRS)

Von Glahn, Uwe H; Gray, Vernon H

1954-01-01

Studies were made to determine the effect of ice formations on the section drag of a 6.9-foot-chord 36 degree swept NACA 63A-009 airfoil with partial-span leading-edge slat. In general, the icing of a thin swept airfoil will result in greater aerodynamic penalties than for a thick unswept airfoil. Glaze-ice formations at the leading edge of the airfoil caused large increases in section drag even at liquid-water content of 0.39 gram per cubic meter. The use of an ice-free parting strip in the stagnation region caused a negligible change in drag compared with a completely unheated airfoil. Cyclic de-icing when properly applied caused the drag to decrease almost to the bare-airfoil drag value.

Radiation Pressure, Poynting-Robertson Drag, and Solar Wind Drag in the Restricted Three-Body Problem

NASA Technical Reports Server (NTRS)

Liou, Jer-Chyi; Zook, Herbert A.; Jackson, A. A.

1995-01-01

In this paper, we examine the effects of radiation pressure, Poynting-Robertson (PR) drag, and solar wind drag on dust grains trapped in mean motion resonances with the Sun and Jupiter in the restricted (negligible dust mass) three-body Problem. We especially examine the evolution of dust grains in the 1:1 resonance. As a first step, the Sun and Jupiter are idealized to both be in circular orbit about a common center of mass (circular restricted three-body problem). From the equation of motion of the dust particle in the rotating reference frame, the drag-induced time rate of change of its Jacobi "constant," C, is then derived and expressed in spherical coordinates. This new mathematical expression in spherical coordinates shows that C, in the 1:1 resonance, both oscillates and secularly increases with increasing time. The new expression gives rise to an easy understanding of how an orbit evolves when the radiation force and solar wind drag are included. All dust grain orbits are unstable in time when PR and solar wind drag are included in the Sun-Jupiter-dust system. Tadpole orbits evolve into horseshoe orbits; and these orbits continuously expand in size to lead to close encounters with Jupiter. Permanent trapping is impossible. Orbital evolutions of a dust grain trapped in the 1:1 resonance in the planar circular, an inclined case, an eccentric case, and the actual Sun-Jupiter case are numerically simulated and compared with each other and show grossly similar time behavior. Resonances other than 1:1 are also explored with the new expression. Stable exterior resonance trapping may be possible under certain conditions. One necessary condition for such a trap is derived. Trapping in interior resonances is shown to be always unstable.

Underwater drag-reducing effect of superhydrophobic submarine model.

PubMed

Zhang, Songsong; Ouyang, Xiao; Li, Jie; Gao, Shan; Han, Shihui; Liu, Lianhe; Wei, Hao

2015-01-01

To address the debates on whether superhydrophobic coatings can reduce fluid drag for underwater motions, we have achieved an underwater drag-reducing effect of large superhydrophobic submarine models with a feature size of 3.5 cm × 3.7 cm × 33.0 cm through sailing experiments of submarine models, modified with and without superhydrophobic surface under similar power supply and experimental conditions. The drag reduction rate reached as high as 15%. The fabrication of superhydrophobic coatings on a large area of submarine model surfaces was realized by immobilizing hydrophobic copper particles onto a precross-linked polydimethylsiloxane (PDMS) surface. The pre-cross-linking time was optimized at 20 min to obtain good superhydrophobicity for the underwater drag reduction effect by investigating the effect of pre-cross-linking on surface wettability and water adhesive property. We do believe that superhydrophobic coatings may provide a promising application in the field of drag-reducing of vehicle motions on or under the water surface.

A Conventional Liner Acoustic/Drag Interaction Benchmark Database

NASA Technical Reports Server (NTRS)

Howerton, Brian M.; Jones, Michael G.

2017-01-01

The aerodynamic drag of acoustic liners has become a significant topic in the design of such for aircraft noise applications. In order to evaluate the benefits of concepts designed to reduce liner drag, it is necessary to establish the baseline performance of liners employing the typical design features of conventional configurations. This paper details a set of experiments in the NASA Langley Grazing Flow Impedance Tube to quantify the relative drag of a number of perforate-over-honeycomb liner configurations at flow speeds of M=0.3 and 0.5. These conventional liners are investigated to determine their resistance factors using a static pressure drop approach. Comparison of the resistance factors gives a relative measurement of liner drag. For these same flow conditions, acoustic measurements are performed with tonal excitation from 400 to 3000 Hz at source sound pressure levels of 140 and 150 dB. Educed impedance and attenuation spectra are used to determine the interaction between acoustic performance and drag.

London 2012 Paralympic swimming: passive drag and the classification system.

PubMed

Oh, Yim-Taek; Burkett, Brendan; Osborough, Conor; Formosa, Danielle; Payton, Carl

2013-09-01

The key difference between the Olympic and Paralympic Games is the use of classification systems within Paralympic sports to provide a fair competition for athletes with a range of physical disabilities. In 2009, the International Paralympic Committee mandated the development of new, evidence-based classification systems. This study aims to assess objectively the swimming classification system by determining the relationship between passive drag and level of swimming-specific impairment, as defined by the current swimming class. Data were collected on participants at the London 2012 Paralympic Games. The passive drag force of 113 swimmers (classes 3-14) was measured using an electro-mechanical towing device and load cell. Swimmers were towed on the surface of a swimming pool at 1.5 m/s while holding their most streamlined position. Passive drag ranged from 24.9 to 82.8 N; the normalised drag (drag/mass) ranged from 0.45 to 1.86 N/kg. Significant negative associations were found between drag and the swimming class (τ = -0.41, p < 0.01) and normalised drag and the swimming class (τ = -0.60, p < 0.01). The mean difference in drag between adjacent classes was inconsistent, ranging from 0 N (6 vs 7) to 11.9 N (5 vs 6). Reciprocal Ponderal Index (a measure of slenderness) correlated moderately with normalised drag (r(P) = -0.40, p < 0.01). Although swimmers with the lowest swimming class experienced the highest passive drag and vice versa, the inconsistent difference in mean passive drag between adjacent classes indicates that the current classification system does not always differentiate clearly between swimming groups.

Drag reduction of nata de coco suspensions in circular pipe flow

NASA Astrophysics Data System (ADS)

Warashina, J.; Ogata, S.

2015-04-01

Reducing pipe friction by adding a drag-reducing agent has attracted interest as a means to reduce energy consumption. In addition to reducing drag, these agents are required to have a low environmental load and conserve natural resources. However, no drag-reducing agent currently satisfies both these conditions. We focused on nata de coco and found that the nata de coco fiber reduced drag by up to 25%. With respect to the mechanism of drag reduction by nata de coco fiber, the relationship between drag-reduction phenomena and the fiber form of nata de coco was investigated by visualization. We also found that the drag-reduction effect appeared to be due to the formation of networks of tangled fibers of nata de coco. However, drag reduction did not occur in the case in which fibers of nata de coco did not form networks.

Black String and Velocity Frame Dragging

NASA Astrophysics Data System (ADS)

Lee, Jungjai; Kim, Hyeong-Chan

We investigate velocity frame dragging with the boosted Schwarzschild black string solution and the boosted Kaluza-Klein bubble solution, in which a translational symmetry along the boosted z-coordinate is implemented. The velocity frame dragging effect can be nullified by the motion of an observer using the boost symmetry along the z-coordinate if it is not compact. However, in spacetime with the compact z-coordinate, we show that the effect cannot be removed since the compactification breaks the global Lorentz boost symmetry. As a result, the comoving velocity depends on r and the momentum parameter along the z-coordinate becomes an observer independent characteristic quantity of the black string and bubble solutions. The dragging induces a spherical ergo-region around the black string.

Experimental study of microbubble drag reduction on an axisymmetric body

NASA Astrophysics Data System (ADS)

Song, Wuchao; Wang, Cong; Wei, Yingjie; Zhang, Xiaoshi; Wang, Wei

2018-01-01

Microbubble drag reduction on the axisymmetric body is experimentally investigated in the turbulent water tunnel. Microbubbles are created by injecting compressed air through the porous medium with various average pore sizes. The morphology of microbubble flow and the size distribution of microbubble are observed by the high-speed visualization system. Drag measurements are obtained by the balance which is presented as the function of void ratio. The results show that when the air injection flow rate is high, uniformly dispersed microbubble flow is coalesced into an air layer with the larger increment rate of drag reduction ratio. The diameter distributions of microbubble under various conditions are submitted to normal distribution. Microbubble drag reduction can be divided into three distinguishable regions in which the drag reduction ratio experiences increase stage, rapid increase stage and stability stage, respectively, corresponding to the various morphologies of microbubble flow. Moreover, drag reduction ratio increases with the decreasing pore sizes of porous medium at the identical void ratio in the area of low speeds, while the effect of pore sizes on drag reduction is reduced gradually until it disappears with the increasing free stream speeds, which indicates that smaller microbubbles have better efficiency in drag reduction. This research results help to improve the understanding of microbubble drag reduction and provides helpful references for practical applications.

Concentrated energy addition for active drag reduction in hypersonic flow regime

NASA Astrophysics Data System (ADS)

Ashwin Ganesh, M.; John, Bibin

2018-01-01

Numerical optimization of hypersonic drag reduction technique based on concentrated energy addition is presented in this study. A reduction in wave drag is realized through concentrated energy addition in the hypersonic flowfield upstream of the blunt body. For the exhaustive optimization presented in this study, an in-house high precision inviscid flow solver has been developed. Studies focused on the identification of "optimum energy addition location" have revealed the existence of multiple minimum drag points. The wave drag coefficient is observed to drop from 0.85 to 0.45 when 50 Watts of energy is added to an energy bubble of 1 mm radius located at 74.7 mm upstream of the stagnation point. A direct proportionality has been identified between energy bubble size and wave drag coefficient. Dependence of drag coefficient on the upstream added energy magnitude is also revealed. Of the observed multiple minimum drag points, the energy deposition point (EDP) that offers minimum wave drag just after a sharp drop in drag is proposed as the most optimum energy addition location.

High accuracy satellite drag model (HASDM)

NASA Astrophysics Data System (ADS)

Storz, Mark F.; Bowman, Bruce R.; Branson, Major James I.; Casali, Stephen J.; Tobiska, W. Kent

The dominant error source in force models used to predict low-perigee satellite trajectories is atmospheric drag. Errors in operational thermospheric density models cause significant errors in predicted satellite positions, since these models do not account for dynamic changes in atmospheric drag for orbit predictions. The Air Force Space Battlelab's High Accuracy Satellite Drag Model (HASDM) estimates and predicts (out three days) a dynamically varying global density field. HASDM includes the Dynamic Calibration Atmosphere (DCA) algorithm that solves for the phases and amplitudes of the diurnal and semidiurnal variations of thermospheric density near real-time from the observed drag effects on a set of Low Earth Orbit (LEO) calibration satellites. The density correction is expressed as a function of latitude, local solar time and altitude. In HASDM, a time series prediction filter relates the extreme ultraviolet (EUV) energy index E10.7 and the geomagnetic storm index ap, to the DCA density correction parameters. The E10.7 index is generated by the SOLAR2000 model, the first full spectrum model of solar irradiance. The estimated and predicted density fields will be used operationally to significantly improve the accuracy of predicted trajectories for all low-perigee satellites.

Drag Reducing and Cavitation Resistant Coatings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pease, Leonard F.

2016-12-28

Client, Green Building Systems (GBS), presented PNNL a coating reported to reduce drag and prevent cavitation damage on marine vessels, turbines and pumps. The composition of the coating remains proprietary but has as constituents including silicon oxides, aliphatic carbon chains, and fluorine rich particles. The coating is spray applied to surfaces. Prior GBS testing and experiments suggest reduction of both drag and cavitation on industrial scale propellers, but the underlying mechanism for these effects remains unclear. Yet, the application is compelling because even modest reductions in drag to marine vessels and cavitation to propellers and turbines present a significant economicmore » and environmental opportunity. To discern among possible mechanisms, PNNL considered possible mechanisms with the client, executed multiple experiments, and completed one theoretical analysis (see appendix). The remainder of this report first considers image analysis to gain insight into drag reduction mechanisms and then exposes the coating to cavitation to explore its response to an intensely cavitating environment. Although further efforts may be warranted to confirm mechanisms, this report presents a first investigation into these coatings within the scope and resources of the technology assistance program (TAP).« less

Drag Reduction On Multiscale Superhydrophobic Surfaces

NASA Astrophysics Data System (ADS)

Jenner, Elliot; Barbier, Charlotte; D'Urso, Brian

2013-11-01

Fluid drag reduction is of great interest in a variety of fields, including hull engineering, microfluidics, and drug delivery. We fabricated samples with multi-scale superhydrophobic surfaces, which consist of hexagonally self-ordered microscopic spikes grown via anodization on macroscopic grooves cut in aluminum. The hydrodynamic drag properties were studied with a cone-and-plate rheometer, showing significant drag reduction near 15% in turbulent flow and near 30% in laminar flow. In addition to these experiments, numerical simulations were performed in order to estimate the slip length at high speeds. Furthermore, we will report on the progress of experiments with a new type of surface combining superhydrophobic surfaces like those discussed above with Slippery Liquid Infused Porous Surfaces (SLIPS), which utilize an oil layer to create a hydrophobic self-repairing surface. These ``Super-SLIPS'' may combine the best properties of both superhydrophobic surfaces and SLIPS, by combining a drag reducing air-layer and an oil layer which may improve durability and biofouling resistance. This research was supported by the ORNL Seed Money Program. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U.S. Dept. of Energy under contract DE-AC05-00OR22725.

Wind tunnel testing of low-drag airfoils

NASA Technical Reports Server (NTRS)

Harvey, W. Donald; Mcghee, R. J.; Harris, C. D.

1986-01-01

Results are presented for the measured performance recently obtained on several airfoil concepts designed to achieve low drag by maintaining extensive regions of laminar flow without compromising high-lift performance. The wind tunnel results extend from subsonic to transonic speeds and include boundary-layer control through shaping and suction. The research was conducted in the NASA Langley 8-Ft Transonic Pressure Tunnel (TPT) and Low Turbulence Pressure Tunnel (LTPT) which have been developed for testing such low-drag airfoils. Emphasis is placed on identifying some of the major factors influencing the anticipated performance of low-drag airfoils.

Drag reduction in channel flow using nonlinear control

NASA Technical Reports Server (NTRS)

Keefe, Laurence R.

1993-01-01

Two nonlinear control schemes have been applied to the problem of drag reduction in channel flow. Both schemes have been tested using numerical simulations at a mass flux Reynolds numbers of 4408, utilizing 2D nonlinear neutral modes for goal dynamics. The OGY-method, which requires feedback, reduces drag to 60-80 percent of the turbulent value at the same Reynolds number, and employs forcing only within a thin region near the wall. The H-method, or model-based control, fails to achieve any drag reduction when starting from a fully turbulent initial condition, but shows potential for suppressing or retarding laminar-to-turbulent transition by imposing instead a transition to a low drag, nonlinear traveling wave solution to the Navier-Stokes equation. The drag in this state corresponds to that achieved by the OGY-method. Model-based control requires no feedback, but in experiments to date has required the forcing be imposed within a thicker layer than the OGY-method. Control energy expenditures in both methods are small, representing less than 0.1 percent of the uncontrolled flow's energy.

Relativistic Gas Drag on Dust Grains and Implications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoang, Thiem, E-mail: thiemhoang@kasi.re.kr; Korea University of Science and Technology, Daejeon, 34113

We study the drag force on grains moving at relativistic velocities through interstellar gas and explore its application. First, we derive a new analytical formula of the drag force at high energies and find that it is significantly reduced compared to the classical model. Second, we apply the obtained drag force to calculate the terminal velocities of interstellar grains by strong radiation sources such as supernovae and active galactic nuclei (AGNs). We find that grains can be accelerated to relativistic velocities by very luminous AGNs. We then quantify the deceleration of relativistic spacecraft proposed by the Breakthrough Starshot initiative duemore » to gas drag on a relativistic lightsail. We find that the spacecraft’s decrease in speed is negligible because of the suppression of gas drag at relativistic velocities, suggesting that the lightsail may be open for communication during its journey to α Centauri without causing a considerable delay. Finally, we show that the damage to relativistic thin lightsails by interstellar dust is a minor effect.« less

Observing the variation of asteroid thermal inertia with heliocentric distance

NASA Astrophysics Data System (ADS)

Rozitis, B.; Green, S. F.; MacLennan, E.; Emery, J. P.

2018-06-01

Thermal inertia is a useful property to characterize a planetary surface, since it can be used as a qualitative measure of the regolith grain size. It is expected to vary with heliocentric distance because of its dependence on temperature. However, no previous investigation has conclusively observed a change in thermal inertia for any given planetary body. We have addressed this by using NEOWISE data and the Advanced Thermophysical Model to study the thermophysical properties of the near-Earth asteroids (1036) Ganymed, (1580) Betulia, and (276 049) 2002 CE26 as they moved around their highly eccentric orbits. We confirm that the thermal inertia values of Ganymed and 2002 CE26 do vary with heliocentric distance, although the degree of variation observed depends on the spectral emissivity assumed in the thermophysical modelling. We also confirm that the thermal inertia of Betulia did not change for three different observations obtained at the same heliocentric distance. Depending on the spectral emissivity, the variations for Ganymed and 2002 CE26 are potentially more extreme than that implied by theoretical models of heat transfer within asteroidal regoliths, which might be explained by asteroids having thermal properties that also vary with depth. Accounting for this variation reduces a previously observed trend of decreasing asteroid thermal inertia with increasing size, and suggests that the surfaces of small and large asteroids could be much more similar than previously thought. Furthermore, this variation can affect Yarkovsky orbital drift predictions by a few tens of per cent.

Discovery of Spin-Rate-Dependent Asteroid Thermal Inertia

NASA Astrophysics Data System (ADS)

Harris, Alan; Drube, Line

2016-10-01

Knowledge of the surface thermal inertia of an asteroid can provide insight into surface structure: porous material has a lower thermal inertia than rock. Using WISE/NEOWISE data and our new asteroid thermal-inertia estimator we show that the thermal inertia of main-belt asteroids (MBAs) appears to increase with spin period. Similar behavior is found in the case of thermophysically-modeled thermal inertia values of near-Earth objects (NEOs). We interpret our results in terms of rapidly increasing material density and thermal conductivity with depth, and provide evidence that thermal inertia increases by factors of 10 (MBAs) to 20 (NEOs) within a depth of just 10 cm. On the basis of a picture of depth-dependent thermal inertia our results suggest that, in general, thermal inertia values representative of solid rock are reached some tens of centimeters to meters below the surface in the case of MBAs (the median diameter in our dataset = 24 km). In the case of the much smaller (km-sized) NEOs a thinner porous surface layer is indicated, with large pieces of solid rock possibly existing just a meter or less below the surface. These conclusions are consistent with our understanding from in-situ measurements of the surfaces of the Moon, and a few asteroids, and suggest a very general picture of rapidly changing material properties in the topmost regolith layers of asteroids. Our results have important implications for calculations of the Yarkovsky effect, including its perturbation of the orbits of potentially hazardous objects and those of asteroid family members after the break-up event. Evidence of a rapid increase of thermal inertia with depth is also an important result for studies of the ejecta-enhanced momentum transfer of impacting vehicles ("kinetic impactors") in planetary defense.

Drag Corrections in High-Speed Wind Tunnels

NASA Technical Reports Server (NTRS)

Ludwieg, H.

1947-01-01

In the vicinity of a body in a wind tunnel the displacement effect of the wake, due to the finite dimensions of the stream, produces a pressure gradient which evokes a change of drag. In incompressible flow this change of drag is so small, in general, that one does not have to take it into account in wind-tunnel measurements; however, in compressible flow it beoomes considerably larger, so that a correction factor is necessary for measured values. Correction factors for a closed tunnel and an open jet with circular cross sections are calculated and compared with the drag - corrections already bown for high-speed tunnnels.

The OSIRIS-REx Thermal Emission Spectrometer (OTES)

NASA Astrophysics Data System (ADS)

Hamilton, Victoria; Christensen, Philip

2014-05-01

The OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) mission is a planetary science mission that will study and return a sample from the carbonaceous asteroid Bennu (1999 RQ36). It is the third mission selected under NASA's New Frontiers Program, and is scheduled to be launched in September of 2016 [1]. The spacecraft will carry a suite of instruments designed to map the physical and mineralogical/chemical properties of Bennu at extremely high spatial resolution (down to cm-scales) to both characterize the asteroid in detail (providing context for the returned sample and data for comparison to astronomical observations) and select a safe and scientifically compelling sample site. The OSIRIS-REx Thermal Emission Spectrometer (OTES) is an uncooled, FTIR point spectrometer that will map the thermal flux and spectral properties of the asteroid Bennu to characterize the Yarkovsky effect and map the surface mineralogy. OTES measures from ~5 - 50 µm with a signal to noise ratio (SNR) of >325 between 7.4 and 33.3 μm for a 325 K target. The design of the spectrometer is heritage from the Mars Global Surveyor TES and the Mars Exploration Rovers Mini-TES instruments. The heart of the instrument is a Michelson interferometer that collects one interferogram every two seconds (where each two-second data acquisition is called an ICK, for Incremental Counter Keeper). OTES's spectral resolution is 10 cm-1 and its field of view is 8 mrad, which is achieved with a 15.2-cm f/3.91 Ritchey-Chretien telescope. At Bennu, OTES will have an accuracy of better than 3% and a precision (noise equivalent spectral radiance, NESR) of ≤2.3x10-8 W cm-2 sr-1 /cm-1 between 300 and 1350 cm-1. These values are sufficient to quantify the thermal flux responsible for the Yarkovsky effect and detect signatures of key minerals having band depths ≥5%. OTES in-flight calibration will be achieved via a two-point calibration that uses space and an

Trimmed noncoplanar planforms with minimum vortex drag

NASA Technical Reports Server (NTRS)

Lamar, J. E.

1977-01-01

Vortex-lattice subsonic method determines mean camber surface for trimmed noncoplanar planforms with minimum vortex drag. Multiple surfaces can be designed together to yield trimmed configuration with minimum induced drag at some specified lift coefficient. Program is applicable to isolated wings, wing-canard configuration, tandem wing, and wing-winglet configuration.

Development of Drag Reducing Polymer of FDR-SPC

NASA Astrophysics Data System (ADS)

Lee, Inwon; Park, Hyun; Chun, Ho Hwan

2015-11-01

In this study, a novel FDR-SPC (Frictional Drag Reduction Self-Polishing Copolymer) is first synthesized in this study. The drag reducing functional radical such as PEGMA (Poly(ethylene) glycol methacrylate) has been utilized to participate in the synthesis process of the SPC. The release mechanism of drag reducing radical is accounted for the hydrolysis reaction between the FDR-SPC and seawater. The types of the baseline SPC monomers, the molecular weight and the mole fraction of PEGMA were varied in the synthesis process. The resulting SPCs were coated to the substrate plates for the subsequent hydrodynamic test for skin friction measurement. A significant reduction in Reynolds stress was observed in a range of specimen, with the maximum drag reduction being 15.9% relative to the smooth surface for PRD3-1.

Space Shuttle Orbiter Drag Chute Summary

NASA Technical Reports Server (NTRS)

Lowry, Charles H.

2013-01-01

This paper summarizes the development history and technical highlights of the Space Shuttle Orbiter Drag Chute Program. Data and references are given on the design, development, and testing of the system, plus several interesting operational issues and solutions. The last Shuttle flight was completed in 2011 and all the Orbiters have now become museum pieces. Before all the data from system development and the 86 Orbiter Drag Chute (ODC) operational landings is lost or forgotten, it may be useful to summarize it here and to identify data sources for future reference. Much has been written about various aspects of the program, and this summary has attempted to cite many such references to make available more detailed information. The ODC program was a high-visibility NASA program that afforded the opportunity to thoroughly engineer and test the chute system, far beyond so many of today s tight-budget programs. So the ODC program was extremely informative--it provided a wide scope of information including protective door jettison issues and solutions, wind tunnel data and analyses on chute stability and drag behind a huge and rather blunt forebody, component and system reuse, and chute cleaning methods. Technology and data created have aided several current and past parachute programs, and will continue to do so in the future. The original Orbiter preliminary design included a drag parachute-- it was deleted early to save weight. But after the 1987 Challenger accident and during the program redefinition phase that followed, Astronaut John Young presented a strong case for enhancing landing safety by adding nosegear steering, brake improvements, and reviving the drag chute.

Estimating the Instantaneous Drag-Wind Relationship for a Horizontally Homogeneous Canopy

NASA Astrophysics Data System (ADS)

Pan, Ying; Chamecki, Marcelo; Nepf, Heidi M.

2016-07-01

The mean drag-wind relationship is usually investigated assuming that field data are representative of spatially-averaged metrics of statistically stationary flow within and above a horizontally homogeneous canopy. Even if these conditions are satisfied, large-eddy simulation (LES) data suggest two major issues in the analysis of observational data. Firstly, the streamwise mean pressure gradient is usually neglected in the analysis of data from terrestrial canopies, which compromises the estimates of mean canopy drag and provides misleading information for the dependence of local mean drag coefficients on local velocity scales. Secondly, no standard approach has been proposed to investigate the instantaneous drag-wind relationship, a critical component of canopy representation in LES. Here, a practical approach is proposed to fit the streamwise mean pressure gradient using observed profiles of the mean vertical momentum flux within the canopy. Inclusion of the fitted mean pressure gradient enables reliable estimates of the mean drag-wind relationship. LES data show that a local mean drag coefficient that characterizes the relationship between mean canopy drag and the velocity scale associated with total kinetic energy can be used to identify the dependence of the local instantaneous drag coefficient on instantaneous velocity. Iterative approaches are proposed to fit specific models of velocity-dependent instantaneous drag coefficients that represent the effects of viscous drag and the reconfiguration of flexible canopy elements. LES data are used to verify the assumptions and algorithms employed by these new approaches. The relationship between mean canopy drag and mean velocity, which is needed in models based on the Reynolds-averaged Navier-Stokes equations, is parametrized to account for both the dependence on velocity and the contribution from velocity variances. Finally, velocity-dependent drag coefficients lead to significant variations of the calculated

An Experimental Investigation of Helicopter Rotor Hub Fairing Drag Characteristics

NASA Technical Reports Server (NTRS)

Sung, D. Y.; Lance, M. B.; Young, L. A.; Stroub, R. H.

1989-01-01

A study was done in the NASA 14- by 22-Foot Wind Tunnel at Langley Research Center on the parasite drag of different helicopter rotor hub fairings and pylons. Parametric studies of hub-fairing camber and diameter were conducted. The effect of hub fairing/pylon clearance on hub fairing/pylon mutual interference drag was examined in detail. Force and moment data are presented in tabular and graphical forms. The results indicate that hub fairings with a circular-arc upper surface and a flat lower surface yield maximum hub drag reduction; and clearance between the hub fairing and pylon induces high mutual-interference drag and diminishes the drag-reduction benefit obtained using a hub fairing with a flat lower surface. Test data show that symmetrical hub fairings with circular-arc surfaces generate 74 percent more interference drag than do cambered hub fairings with flat lower surfaces, at moderate negative angle of attack.

High accuracy satellite drag model (HASDM)

NASA Astrophysics Data System (ADS)

Storz, M.; Bowman, B.; Branson, J.

The dominant error source in the force models used to predict low perigee satellite trajectories is atmospheric drag. Errors in operational thermospheric density models cause significant errors in predicted satellite positions, since these models do not account for dynamic changes in atmospheric drag for orbit predictions. The Air Force Space Battlelab's High Accuracy Satellite Drag Model (HASDM) estimates and predicts (out three days) a dynamically varying high-resolution density field. HASDM includes the Dynamic Calibration Atmosphere (DCA) algorithm that solves for the phases and amplitudes of the diurnal, semidiurnal and terdiurnal variations of thermospheric density near real-time from the observed drag effects on a set of Low Earth Orbit (LEO) calibration satellites. The density correction is expressed as a function of latitude, local solar time and altitude. In HASDM, a time series prediction filter relates the extreme ultraviolet (EUV) energy index E10.7 and the geomagnetic storm index a p to the DCA density correction parameters. The E10.7 index is generated by the SOLAR2000 model, the first full spectrum model of solar irradiance. The estimated and predicted density fields will be used operationally to significantly improve the accuracy of predicted trajectories for all low perigee satellites.

Thermal Analysis Methods for Aerobraking Heating

NASA Technical Reports Server (NTRS)

Amundsen, Ruth M.; Gasbarre, Joseph F.; Dec, John A.

2005-01-01

As NASA begins exploration of other planets, a method of non-propulsively slowing vehicles at the planet, aerobraking, may become a valuable technique for managing vehicle design mass and propellant. An example of this is Mars Reconnaissance Orbiter (MRO), which will launch in late 2005 and reach Mars in March of 2006. In order to save propellant, MRO will use aerobraking to modify the initial orbit at Mars. The spacecraft will dip into the atmosphere briefly on each orbit, and during the drag pass, the atmospheric drag on the spacecraft will slow it, thus lowering the orbit apoapsis. The largest area on the spacecraft, and that most affected by the heat generated during the aerobraking process, is the solar arrays. A thermal analysis of the solar arrays was conducted at NASA Langley, to simulate their performance throughout the entire roughly 6-month period of aerobraking. Several interesting methods were used to make this analysis more rapid and robust. Two separate models were built for this analysis, one in Thermal Desktop for radiation and orbital heating analysis, and one in MSC.Patran for thermal analysis. The results from the radiation model were mapped in an automated fashion to the Patran thermal model that was used to analyze the thermal behavior during the drag pass. A high degree of automation in file manipulation as well as other methods for reducing run time were employed, since toward the end of the aerobraking period the orbit period is short, and in order to support flight operations the runs must be computed rapidly. All heating within the Patran Thermal model was combined in one section of logic, such that data mapped from the radiation model and aeroheating model, as well as skin temperature effects on the aeroheating and surface radiation, could be incorporated easily. This approach calculates the aeroheating at any given node, based on its position and temperature as well as the density and velocity at that trajectory point. Run times on

Drag reducing properties of microalgal exopolymers.

PubMed

Ramus, J; Kenney, B E; Shaughnessy, E J

1989-01-25

Dilute aqueous solutions of polymers released by marine phytoplankton (microalgae) were shown to effectively reduce drag in capillary pipe flow. Tests were performed in a capillary turbulent flow viscometer which extruded small samples under high pressures. In all, 22 species were screened, and the products of one chlorophyte and four rhodophyte species proved especially effective. The viscoelastic polymers produced by these species delayed the transition from laminar to turbulent flow to significantly higher Re. In general, polymeric regime segments come off the maximum drag reduction asymptote at characteristic retro-onset points, and come to lie approximately parallel to, but displaced upwards from the Prandtl-von Karman line. The delay to transition was shown to be dependent on additive polymer concentration, capillary diameter, and temperature. Ionic concentration, ionic composition, or pH had little effect on drag reducing properties.

Electron drag in ferromagnetic structures separated by an insulating interface

NASA Astrophysics Data System (ADS)

Kozub, V. I.; Muradov, M. I.; Galperin, Y. M.

2018-06-01

We consider electron drag in a system of two ferromagnetic layers separated by an insulating interface. The source of it is expected to be magnon-electron interactions. Namely, we assume that the external voltage is applied to the "active" layer stimulating electric current through this layer. In its turn, the scattering of the current-carrying electrons by magnons leads to a magnon drag current within this layer. The 3-magnons interactions between magnons in the two layers (being of non-local nature) lead to magnon drag within the "passive" layer which, correspondingly, produce electron drag current via processes of magnon-electron scattering. We estimate the drag current and compare it to the phonon-induced one.

Airflow in Gravity Sewers - Determination of Wastewater Drag Coefficient.

PubMed

Bentzen, Thomas Ruby; Østertoft, Kristian Kilsgaard; Vollertsen, Jes; Fuglsang, Emil Dietz; Nielsen, Asbjørn Haaning

2016-03-01

Several experiments have been conducted in order to improve the understanding of the wastewater drag and the wall frictional force acting on the headspace air in gravity sewers. The aim of the study is to improve the data basis for a numerical model of natural sewer ventilation. The results of the study shows that by integrating the top/side wall shear stresses the log-law models for the air velocity distribution along the unwetted perimeter resulted in a good agreement with the friction forces calculated by use of the Colebrook-White formula for hydraulic smooth pipes. Secondly, the water surface drags were found by log-law models of the velocity distribution in turbulent flows to fit velocity profiles measured from the water surface and by integrating the water surface drags along the wetted perimeter, mean water surface drags were found and a measure of the water surface drag coefficient was found.

Calculated Drag of an Aerial Refueling Assembly Through Airplane Performance Analysis

NASA Technical Reports Server (NTRS)

Vachon, Michael Jacob; Ray, Ronald J.

2004-01-01

The aerodynamic drag of an aerial refueling assembly was calculated during the Automated Aerial Refueling project at the NASA Dryden Flight Research Center. An F/A-18A airplane was specially instrumented to obtain accurate fuel flow measurements and to determine engine thrust. A standard Navy air refueling store with a retractable refueling hose and paradrogue was mounted to the centerline pylon of the F/A-18A airplane. As the paradrogue assembly was deployed and stowed, changes in the calculated thrust of the airplane occurred and were equated to changes in vehicle drag. These drag changes were attributable to the drag of the paradrogue assembly. The drag of the paradrogue assembly was determined to range from 200 to 450 lbf at airspeeds from 170 to 250 KIAS. Analysis of the drag data resulted in a single drag coefficient of 0.0056 for the paradrogue assembly that adequately matched the calculated drag for all flight conditions. The drag relief provided to the tanker airplane when a receiver airplane engaged the paradrogue is also documented from 35 to 270 lbf at the various flight conditions tested. The results support the development of accurate aerodynamic models to be used in refueling simulations and control laws for fully autonomous refueling.

A Computational and Experimental Study of Nonlinear Aspects of Induced Drag

NASA Technical Reports Server (NTRS)

Smith, Stephen C.

1996-01-01

Despite the 80-year history of classical wing theory, considerable research has recently been directed toward planform and wake effects on induced drag. Nonlinear interactions between the trailing wake and the wing offer the possibility of reducing drag. The nonlinear effect of compressibility on induced drag characteristics may also influence wing design. This thesis deals with the prediction of these nonlinear aspects of induced drag and ways to exploit them. A potential benefit of only a few percent of the drag represents a large fuel savings for the world's commercial transport fleet. Computational methods must be applied carefully to obtain accurate induced drag predictions. Trefftz-plane drag integration is far more reliable than surface pressure integration, but is very sensitive to the accuracy of the force-free wake model. The practical use of Trefftz plane drag integration was extended to transonic flow with the Tranair full-potential code. The induced drag characteristics of a typical transport wing were studied with Tranair, a full-potential method, and A502, a high-order linear panel method to investigate changes in lift distribution and span efficiency due to compressibility. Modeling the force-free wake is a nonlinear problem, even when the flow governing equation is linear. A novel method was developed for computing the force-free wake shape. This hybrid wake-relaxation scheme couples the well-behaved nature of the discrete vortex wake with viscous-core modeling and the high-accuracy velocity prediction of the high-order panel method. The hybrid scheme produced converged wake shapes that allowed accurate Trefftz-plane integration. An unusual split-tip wing concept was studied for exploiting nonlinear wake interaction to reduced induced drag. This design exhibits significant nonlinear interactions between the wing and wake that produced a 12% reduction in induced drag compared to an equivalent elliptical wing at a lift coefficient of 0.7. The

The thermal and physical characteristics of the Gao-Guenie (H5) meteorite

NASA Astrophysics Data System (ADS)

Beech, Martin; Coulson, Ian M.; Nie, Wenshuang; McCausland, Phil

2009-06-01

Measurements of the bulk density, grain density, porosity, and magnetic susceptibility of 19 Gao-Guenie H5 chondrite meteorite samples are presented. We find average values of bulk density < ρbulk>=3.46±0.07 g/cm 3, grain density < ρgrain>=3.53±0.08 g/cm 3, porosity < P(%)>=2.46±1.39, and bulk mass magnetic susceptibility =5.23±0.11. Measurements of the specific heat capacity for a 3.01-g Gao-Guenie sample, a 61.37-g Gao-Guenie sample, a 62.35-g Jilin H5 chondrite meteorite sample, and a 51.37-g Sikhote-Alin IIAB Iron meteorite sample are also presented. Temperature interpolation formula are further provided for the specific heat capacity, thermal conductivity, and thermal diffusivity of the 3.01-g Gao-Guenie sample in the temperature range 300< T (K)<800. We briefly review the possible effects of the newly deduced specific heat and thermal conductivity values on the ablation of meteoroids within the Earth's atmosphere, the modeling of asteroid interiors and the orbital evolution of meteoroids through the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect.

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

A Ground-Based Research Vehicle for Base Drag Studies at Subsonic Speeds

NASA Technical Reports Server (NTRS)

Diebler, Corey; Smith, Mark

2002-01-01

A ground research vehicle (GRV) has been developed to study the base drag on large-scale vehicles at subsonic speeds. Existing models suggest that base drag is dependent upon vehicle forebody drag, and for certain configurations, the total drag of a vehicle can be reduced by increasing its forebody drag. Although these models work well for small projectile shapes, studies have shown that they do not provide accurate predictions when applied to large-scale vehicles. Experiments are underway at the NASA Dryden Flight Research Center to collect data at Reynolds numbers to a maximum of 3 x 10(exp 7), and to formulate a new model for predicting the base drag of trucks, buses, motor homes, reentry vehicles, and other large-scale vehicles. Preliminary tests have shown errors as great as 70 percent compared to Hoerner's two-dimensional base drag prediction. This report describes the GRV and its capabilities, details the studies currently underway at NASA Dryden, and presents preliminary results of both the effort to formulate a new base drag model and the investigation into a method of reducing total drag by manipulating forebody drag.

Drag reduction using slippery liquid infused surfaces

NASA Astrophysics Data System (ADS)

Hultmark, Marcus; Stone, Howard; Smits, Alexander; Jacobi, Ian; Samaha, Mohamed; Wexler, Jason; Shang, Jessica; Rosenberg, Brian; Hellström, Leo; Fan, Yuyang

2013-11-01

A new method for passive drag reduction is introduced. A surface treatment inspired by the Nepenthes pitcher plant, previously developed by Wong et al. (2011), is utilized and its design parameters are studied for increased drag reduction and durability. Nano- and micro-structured surfaces infused with a lubricant allow for mobility within the lubricant itself when the surface is exposed to flow. The mobility causes slip at the fluid-fluid interface, which drastically reduces the viscous friction. These new surfaces are fundamentally different from the more conventional superhydrophobic surfaces previously used in drag reduction studies, which rely on a gas-liquid interface. The main advantage of the liquid infused surfaces over the conventional surfaces is that the lubricant adheres more strongly to the surface, decreasing the risk of failure when exposed to turbulence and other high-shear flows. We have shown that these surfaces can reduce viscous drag up to 20% in both Taylor-Couette flow and in a parallel plate rheometer. Supported under ONR Grants N00014-12-1-0875 and N00014-12-1-0962 (program manager Ki-Han Kim).

Measurements of drag and flow over biofilm

NASA Astrophysics Data System (ADS)

Hartenberger, Joel; Gose, James W.; Perlin, Marc; Ceccio, Steven L.

2017-11-01

Microbial `slime' biofilms detrimentally affect the performance of every day systems from medical devices to large ocean-going vessels. In flow applications, the presence of biofilm typically results in a drag increase and may alter the turbulence in the adjacent boundary layer. Recent studies emphasize the severity of the drag penalty associated with soft biofouling and suggest potential mechanisms underlying the increase; yet, fundamental questions remain-such as the role played by compliance and the contribution of form drag to the overall resistance experienced by a fouled system. Experiments conducted on live biofilm and 3D printed rigid replicas in the Skin-Friction Flow Facility at the University of Michigan seek to examine these factors. The hydrodynamic performance of the biofilms grown on test panels was evaluated through pressure drop measurements as well as conventional and microscale PIV. High-resolution, 3D rigid replicas of select cases were generated via additive manufacturing using surface profiles obtained from a laser scanning system. Drag and flow measurements will be presented along with details of the growth process and the surface profile characterization method.

Creating drag and lift curves from soccer trajectories

NASA Astrophysics Data System (ADS)

Goff, John Eric; Kelley, John; Hobson, Chad M.; Seo, Kazuya; Asai, Takeshi; Choppin, S. B.

2017-07-01

Trajectory analysis is an alternative to using wind tunnels to measure a soccer ball’s aerodynamic properties. It has advantages over wind tunnel testing such as being more representative of game play. However, previous work has not presented a method that produces complete, speed-dependent drag and lift coefficients. Four high-speed cameras in stereo-calibrated pairs were used to measure the spatial co-ordinates for 29 separate soccer trajectories. Those trajectories span a range of launch speeds from 9.3 to 29.9 m s-1. That range encompasses low-speed laminar flow of air over a soccer ball, through the drag crises where air flow is both laminar and turbulent, and up to high-speed turbulent air flow. Results from trajectory analysis were combined to give speed-dependent drag and lift coefficient curves for the entire range of speeds found in the 29 trajectories. The average root mean square error between the measured and modelled trajectory was 0.028 m horizontally and 0.034 m vertically. The drag and lift crises can be observed in the plots of drag and lift coefficients respectively.

Fuel Savings and Aerodynamic Drag Reduction from Rail Car Covers

NASA Technical Reports Server (NTRS)

Storms, Bruce; Salari, Kambiz; Babb, Alex

2008-01-01

The potential for energy savings by reducing the aerodynamic drag of rail cars is significant. A previous study of aerodynamic drag of coal cars suggests that a 25% reduction in drag of empty cars would correspond to a 5% fuel savings for a round trip [1]. Rail statistics for the United States [2] report that approximately 5.7 billion liters of diesel fuel were consumed for coal transportation in 2002, so a 5% fuel savings would total 284 million liters. This corresponds to 2% of Class I railroad fuel consumption nationwide. As part of a DOE-sponsored study, the aerodynamic drag of scale rail cars was measured in a wind tunnel. The goal of the study was to measure the drag reduction of various rail-car cover designs. The cover designs tested yielded an average drag reduction of 43% relative to empty cars corresponding to an estimated round-trip fuel savings of 9%.

The Effect of Surface Irregularities on Wing Drag. 3; Roughness

NASA Technical Reports Server (NTRS)

Hood, Manley J.

1938-01-01

Tests have been made in the N.A.C.A. 8-foot high-speed wind tunnel of the drag caused by roughness on the surface of an airfoil of N.A.C.A. 23012 section and 5-foot chord. The tests were made at speeds from 80 t o 500 miles per hour at lift coefficients from 0 to 0.30. For conditions corresponding to high-speed flight, the increase in the drag was 30 percent of the profile drag of the smooth airfoil for the roughness produced by spray painting and 63 percent for the roughness produced. by 0.0037-inch carborundum grains. About one-half the drag increase was caused by the roughness on the forward one-fourth of the airfoil. Sandpapering the painted surface with No. 400 sandpaper made it sufficiently smooth that the drag was no greater than when the surface was polished. In the lower part of the range investigated the drag due to roughness increased rapidly with Reynolds Number.

Drag Measurements of Porous Plate Acoustic Liners

NASA Technical Reports Server (NTRS)

Wolter, John D.

2005-01-01

This paper presents the results of direct drag measurements on a variety of porous plate acoustic liners. The existing literature describes numerous studies of drag on porous walls with injection or suction, but relatively few of drag on porous plates with neither injection nor suction. Furthermore, the porosity of the porous plate in existing studies is much lower than typically used in acoustic liners. In the present work, the acoustic liners consisted of a perforated face sheet covering a bulk acoustic absorber material. Factors that were varied in the experiment were hole diameter, hole pattern, face sheet thickness, bulk material type, and size of the gap (if any) between the face sheet and the absorber material.

Drag Coefficient and Foam in Hurricane Conditions.

NASA Astrophysics Data System (ADS)

Golbraikh, E.; Shtemler, Y.

2016-12-01

he present study is motivated by recent findings of saturation and even decrease in the drag coefficient (capping) in hurricane conditions, which is accompanied by the production of a foam layer on the ocean surface. As it is difficult to expect at present a comprehensive numerical modeling of the drag coefficient saturation that is followed by wave breaking and foam production, there is no complete confidence and understanding of the saturation phenomenon. Our semi-empirical model is proposed for the estimation of the foam impact on the variation of the effective drag coefficient, Cd , with the reference wind speed U10 in stormy and hurricane conditions. The proposed model treats the efficient air-sea aerodynamic roughness length as a sum of two weighted aerodynamic roughness lengths for the foam-free and foam-covered conditions. On the available optical and radiometric measurements of the fractional foam coverage,αf, combined with direct wind speed measurements in hurricane conditions, which provide the minimum of the effective drag coefficient, Cd for the sea covered with foam. The present model yields Cd10 versus U10 in fair agreement with that evaluated from both open-ocean and laboratory measurements of the vertical variation of mean wind speed in the range of U10 from low to hurricane speeds. The present approach opens opportunities for drag coefficient modeling in hurricane conditions and hurricane intensity estimation by the foam-coverage value using optical and radiometric measurements.

Effect of Boattail and Sidewall Curvature on Nozzle Drag Characteristics

NASA Technical Reports Server (NTRS)

Capone, Francis J.; Deere, Karen A.; Bangert, Linda S.; Pao, Paul S.

1999-01-01

The NASA-industry team has sponsored several studies in the last two years to address the installed nozzle boattail drag issues. Some early studies suggested that nozzle boattail drag could be as much as 25 to 40 percent of the subsonic cruise. As part of this study tests have been conducted at NASA-Langley to determine the uninstalled drag characteristics of a proposed nozzle. The overall objective was to determine the effects of nozzle external flap curvature and sidewall boattail variations. This test would also provide data for validating CFD predictions of nozzle boattail drag.

Gravitational mass attraction measurement for drag-free references

NASA Astrophysics Data System (ADS)

Swank, Aaron J.

Exciting new experiments in gravitational physics are among the proposed future space science missions around the world. Such future space science experiments include gravitational wave observatories, which require extraordinarily precise instruments for gravitational wave detection. In fact, future space-based gravitational wave observatories require the use of a drag free reference sensor, which is several orders of magnitude more precise than any drag free satellite launched to date. With the analysis methods and measurement techniques described in this work, there is one less challenge associated with achieving the high-precision drag-free satellite performance levels required by gravitational wave observatories. One disturbance critical to the drag-free performance is an acceleration from the mass attraction between the spacecraft and drag-free reference mass. A direct measurement of the gravitational mass attraction force is not easily performed. Historically for drag-free satellite design, the gravitational attraction properties were estimated by using idealized equations between a point mass and objects of regular geometric shape with homogeneous density. Stringent requirements are then placed on the density distribution and fabrication tolerances for the drag-free reference mass and satellite components in order to ensure that the allocated gravitational mass attraction disturbance budget is not exceeded due to the associated uncertainty in geometry and mass properties. Yet, the uncertainty associated with mass properties and geometry generate an unacceptable uncertainty in the mass attraction calculation, which make it difficult to meet the demanding drag-free performance requirements of future gravitational wave observatories. The density homogeneity and geometrical tolerances required to meet the overall drag-free performance can easily force the use of special materials or manufacturing processes, which are impractical or not feasible. The focus of

Enhanced viscous flow drag reduction using acoustic excitation

NASA Technical Reports Server (NTRS)

Nagel, Robert T.

1987-01-01

Proper acoustic excitation of a single large-eddy break-up device can increase the resulting drag reduction and, after approximately 40 to 50 delta downstream, provide net drag reduction. Precise optimization of the input time delay, amplitude and response threshold is difficult but possible to achieve. Drag reduction is improved with optimized conditions. The possibility of optimized processing strongly suggests a mechanism which involves interaction of the acoustic waves and large eddies at the trailing edge of the large eddy break-up device. Although the mechanism for spreading of this phenomenon is unknown, it is apparent that the drag reduction effect does tend to spread spanwise as the flow convects downstream. The phenomenon is not unique to a particular blade configuration or flow velocity, although all data have been obtained at relatively low Reynolds numbers. The general repeatibility of the results for small configuration changes serves as verification of the phenomenon.

Possibilities for drag reduction by boundary layer control

NASA Technical Reports Server (NTRS)

Naiman, I.

1946-01-01

The mechanics of laminar boundary layer transition are reviewed. Drag possibilities for boundary layer control are analyzed using assumed conditions of transition Reynolds number, inlet loss, number of slots, blower efficiency, and duct losses. Although the results of such analysis are highly favorable, those obtained by experimental investigations yield conflicting results, showing only small gains, and sometimes losses. Reduction of this data indicates that there is a lower limit to the quantity of air which must be removed at the slot in order to stabilize the laminar flow. The removal of insufficient air permits transition to occur while the removal of excessive amounts of air results in high power costs, with a net drag increases. With the estimated value of flow coefficient and duct losses equal to half the dynamic pressure, drag reductions of 50% may be obtained; with twice this flow coefficient, the drag saving is reduced to 25%.

Dragging of inertial frames.

PubMed

Ciufolini, Ignazio

2007-09-06

The origin of inertia has intrigued scientists and philosophers for centuries. Inertial frames of reference permeate our daily life. The inertial and centrifugal forces, such as the pull and push that we feel when our vehicle accelerates, brakes and turns, arise because of changes in velocity relative to uniformly moving inertial frames. A classical interpretation ascribed these forces to acceleration relative to some absolute frame independent of the cosmological matter, whereas an opposite view related them to acceleration relative to all the masses and 'fixed stars' in the Universe. An echo and partial realization of the latter idea can be found in Einstein's general theory of relativity, which predicts that a spinning mass will 'drag' inertial frames along with it. Here I review the recent measurements of frame dragging using satellites orbiting Earth.

Mars entry guidance based on an adaptive reference drag profile

NASA Astrophysics Data System (ADS)

Liang, Zixuan; Duan, Guangfei; Ren, Zhang

2017-08-01

The conventional Mars entry tracks a fixed reference drag profile (FRDP). To improve the landing precision, a novel guidance approach that utilizes an adaptive reference drag profile (ARDP) is presented. The entry flight is divided into two phases. For each phase, a family of drag profiles corresponding to various trajectory lengths is planned. Two update windows are investigated for the reference drag profile. At each window, the ARDP is selected online from the profile database according to the actual range-to-go. The tracking law for the selected drag profile is designed based on the feedback linearization. Guidance approaches using the ARDP and the FRDP are then tested and compared. Simulation results demonstrate that the proposed ARDP approach achieves much higher guidance precision than the conventional FRDP approach.

An entropy method for induced drag minimization

NASA Technical Reports Server (NTRS)

Greene, George C.

1989-01-01

A fundamentally new approach to the aircraft minimum induced drag problem is presented. The method, a 'viscous lifting line', is based on the minimum entropy production principle and does not require the planar wake assumption. An approximate, closed form solution is obtained for several wing configurations including a comparison of wing extension, winglets, and in-plane wing sweep, with and without a constraint on wing-root bending moment. Like the classical lifting-line theory, this theory predicts that induced drag is proportional to the square of the lift coefficient and inversely proportioinal to the wing aspect ratio. Unlike the classical theory, it predicts that induced drag is Reynolds number dependent and that the optimum spanwise circulation distribution is non-elliptic.

Low-drag events in transitional wall-bounded turbulence

NASA Astrophysics Data System (ADS)

Whalley, Richard D.; Park, Jae Sung; Kushwaha, Anubhav; Dennis, David J. C.; Graham, Michael D.; Poole, Robert J.

2017-03-01

Intermittency of low-drag pointwise wall shear stress measurements within Newtonian turbulent channel flow at transitional Reynolds numbers (friction Reynolds numbers 70 - 130) is characterized using experiments and simulations. Conditional mean velocity profiles during low-drag events closely approach that of a recently discovered nonlinear traveling wave solution; both profiles are near the so-called maximum drag reduction profile, a general feature of turbulent flow of liquids containing polymer additives (despite the fact that all results presented are for Newtonian fluids only). Similarities between temporal intermittency in small domains and spatiotemporal intermittency in large domains is thereby found.

Drag reduction obtained by modifying a standard truck

NASA Technical Reports Server (NTRS)

Sheridan, A. E.; Grier, S. J.

1978-01-01

A standard two-axle truck with a box-shaped cargo compartment was tested to determine whether significant reductions in aerodynamic drag could be obtained by modifying the front of the cargo compartment. The coastdown method was used to determine the total drag of the baseline vehicle, which had a square-cornered cargo box, and of several modified configurations. Test velocities ranged from 56.3 to 94.6 kilometers per hour (35 to 60 miles per hour). At 88.5 kilometers per hour (55 miles per hour), the aerodynamic drag reductions obtained with the modified configurations ranged from 8 to 30 percent.

Experimental and numerical investigation of low-drag intervals in turbulent boundary layer

NASA Astrophysics Data System (ADS)

Park, Jae Sung; Ryu, Sangjin; Lee, Jin

2017-11-01

It has been widely investigated that there is a substantial intermittency between high and low drag states in wall-bounded shear flows. Recent experimental and computational studies in a turbulent channel flow have identified low-drag time intervals based on wall shear stress measurements. These intervals are a weak turbulence state characterized by low-speed streaks and weak streamwise vortices. In this study, the spatiotemporal dynamics of low-drag intervals in a turbulent boundary layer is investigated using experiments and simulations. The low-drag intervals are monitored based on the wall shear stress measurement. We show that near the wall conditionally-sampled mean velocity profiles during low-drag intervals closely approach that of a low-drag nonlinear traveling wave solution as well as that of the so-called maximum drag reduction asymptote. This observation is consistent with the channel flow studies. Interestingly, the large spatial stretching of the streak is very evident in the wall-normal direction during low-drag intervals. Lastly, a possible connection between the mean velocity profile during the low-drag intervals and the Blasius profile will be discussed. This work was supported by startup funds from the University of Nebraska-Lincoln.

On the Effect of Rigid Swept Surface Waves on Turbulent Drag

NASA Technical Reports Server (NTRS)

Denison, M.; Wilkinson, S. P.; Balakumar, P.

2015-01-01

Passive turbulent drag reduction techniques are of interest as a cost effective means to improve air vehicle fuel consumption. In the past, rigid surface waves slanted at an angle from the streamwise direction were deemed ineffective to reduce skin friction drag due to the pressure drag that they generate. A recent analysis seeking similarities to the spanwise shear stress generated by spatial Stokes layers suggested that there may be a range of wavelength, amplitude, and orientation in which the wavy surface would reduce turbulent drag. The present work explores, by experiments and Direct Numerical Simulations (DNS), the effect of swept wavy surfaces on skin friction and pressure drag. Plates with shallow and deep wave patterns were rapid-prototyped and tested using a drag balance in the 7x11 inch Low-Speed Wind Tunnel at the NASA LaRC Research Center. The measured drag o set between the wavy plates and the reference at plate is found to be within the experimental repeatability limit. Oil vapor flow measurements indicate a mean spanwise flow over the deep waves. The turbulent flow in channels with at walls, swept wavy walls and spatial Stokes spanwise velocity forcing was simulated at a friction Reynolds number of two hundred. The time-averaged and dynamic turbulent flow characteristics of the three channel types are compared. The drag obtained for the channel with shallow waves is slightly larger than for the at channel, within the range of the experiments. In the case of the large waves, the simulation over predicts the drag. The shortcomings of the Stokes layer analogy model for the estimation of the spanwise shear stress and drag are discussed.

Turbulent structure in low-concentration drag-reducing channel flows

NASA Technical Reports Server (NTRS)

Luchik, T. S.; Tiederman, W. G.

1988-01-01

A two-component laser-Doppler velocimeter was used to obtain simultaneous measurements of the velocity components parallel and normal to the wall in two fully developed well-mixed low-concentration drag-reducing channel flows and one turbulent channel flow. For the drag-reducing flows, the average time between bursts was found to increase. Although the basic structure of the fundamental momentum transport event is shown to be the same in these drag-reducing flows, the lower-threshold Reynolds-stress-producing motions were found to be damped, while the higher-threshold motions were not. It is suggested that some strong turbulent motions are needed to maintain extended polymer molecules, which produce a solution with properties that can damp lower threshold turbulence and thereby reduce viscous drag.

RSRA vertical drag test report. [rotor systems research aircraft

NASA Technical Reports Server (NTRS)

Flemming, R. J.

1981-01-01

The Rotor Systems Research Aircraft (RSRA), because of its ability to measure rotor loads, was used to conduct an experiment to determine vertical drag, tail rotor blockage, and thrust augmentation as affected by ground clearance and flight velocity. The RSRA was flown in the helicopter configuration at speeds from 0 to 15 knots for wheel heights from 5 to 150 feet, and to 60 knots out of ground effect. The vertical drag trends in hover, predicted by theory and shown in model tests, were generally confirmed. The OGE hover vertical drag is 4.0 percent, 1.1 percent greater than predicted. The vertical drag decreases rapidly as wheel height is reduced, and is zero at a wheel height of 6 feet. The vertical drag also decreases with forward speed, approaching zero at sixty knots. The test data show the effect of wheel height and forward speed on thrust, gross weight capability, and power, and provide the relationships for power and collective pitch at constant gross weight required for the simulation of helicopter takeoffs and landings.

Plasma drag on a dust grain due to Coulomb collisions

NASA Technical Reports Server (NTRS)

Northrop, T. G.; Birmingham, T. J.

1990-01-01

Expressions are given for the drag due to Coulomb collisions on a charged dust grain moving through a plasma. The commonly used Chandrasekhar (1943) result does not include large scattering angles or plasma collective effects. An equation given by Morfill et al. (1980) which does include large scattering angles, is limited to one-dimensional plasma particle motion and can give at least an order of magnitude too much drag. This paper also makes use of an analogy between the drag problem and problems in electrostatics. This analogy permits generalization to any isotropic plasma of an observation made by Chandrasekhar for a Maxwellian, namely, that the drag is independent of the presence or absence of plasma particles moving faster than the grain. Finally, the contribution of plasma collective effects to the drag is studied with the inclusion of large scattering angles.

Absence of solute drag in solidification

NASA Astrophysics Data System (ADS)

Kittl, J. A.; Aziz, M. J.; Brunco, D. P.; Thompson, M. O.

1994-05-01

The interface response functions for alloy solidification were measured in the nondegenerate regime of partial solute trapping. We used a new technique to measure temperatures and velocities simultaneously during rapid solidification of Si-As alloys induced by pulsed laser melting. In addition, partition coefficients were determined using Rutherford backscattering. The results are in good agreement with predictions of the Continuous Growth Model without solute drag of M. J. Aziz and T. Kaplan [Acta Metall. 36, 1335 (1988)] and are inconsistent with all solute drag models.

Is drag luminosity effective in recurrent novae

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kato, Mariko; Hachisu, Izumi

1991-06-01

A study has been made of the efficiency of frictional processes in common envelope phase at outbursts of three recurrent novae T Pyx, U Sco, and RS Oph, by using steady-state wind models. The drag luminosity is found to depend strongly on the envelope mass. It may play an important role for a relatively massive envelope of about 0.0001 solar mass or more. For recurrent novae, however, acceleration due to the drag force is not important to eject the envelope mass because of its small envelope mass. Since the drag luminosity can be neglected at the extended phase of novamore » outburst, the light curves of these recurrent novae are determined only by the wind-driven mass loss as shown by Kato (1990). 23 refs.« less

Gliding flight: drag and torque of a hawk and a falcon with straight and turned heads, and a lower value for the parasite drag coefficient.

PubMed

Tucker, V A

2000-12-01

Raptors - falcons, hawks and eagles in this study - such as peregrine falcons (Falco peregrinus) that attack distant prey from high-speed dives face a paradox. Anatomical and behavioral measurements show that raptors of many species must turn their heads approximately 40 degrees to one side to see the prey straight ahead with maximum visual acuity, yet turning the head would presumably slow their diving speed by increasing aerodynamic drag. This paper investigates the aerodynamic drag part of this paradox by measuring the drag and torque on wingless model bodies of a peregrine falcon and a red-tailed hawk (Buteo jamaicensis) with straight and turned heads in a wind tunnel at a speed of 11.7 m s(-)(1). With a turned head, drag increased more than 50 %, and torque developed that tended to yaw the model towards the direction in which the head pointed. Mathematical models for the drag required to prevent yawing showed that the total drag could plausibly more than double with head-turning. Thus, the presumption about increased drag in the paradox is correct. The relationships between drag, head angle and torque developed here are prerequisites to the explanation of how a raptor could avoid the paradox by holding its head straight and flying along a spiral path that keeps its line of sight for maximum acuity pointed sideways at the prey. Although the spiral path to the prey is longer than the straight path, the raptor's higher speed can theoretically compensate for the difference in distances; and wild peregrines do indeed approach prey by flying along curved paths that resemble spirals. In addition to providing data that explain the paradox, this paper reports the lowest drag coefficients yet measured for raptor bodies (0.11 for the peregrine and 0.12 for the red-tailed hawk) when the body models with straight heads were set to pitch and yaw angles for minimum drag. These values are markedly lower than value of the parasite drag coefficient (C(D,par)) of 0.18 previously

"Let the drag race begin": the rewards of becoming a queen.

PubMed

Hopkins, Steven J

2004-01-01

Drawing upon my ethnographic experiences in a drag venue called The Park in Roanoke, Virginia, this article explores the experiences of female impersonators in terms of their early motivations for doing drag, how they create and maintain drag personas and identities, and the obstacles to becoming a queen. Departing from previous researchers that have framed female impersonation as a deviant, stigmatizing, and pathological activity, this research analyzes the significant benefits some drag queens garner by donning women's attire. An experiential understanding of drag reveals that the significant rewards from the activity--contextual power and status, self-affirmation and empowerment--are powerful motivating factors. Instead of being deviant and/or partaking in pathological behavior, female impersonators can be seen as operating on an incentive system where the benefits of doing drag positively enrich the quality of the performer's life in a context where successful queens are held in the highest regard.

Wave drag as the objective function in transonic fighter wing optimization

NASA Technical Reports Server (NTRS)

Phillips, P. S.

1984-01-01

The original computational method for determining wave drag in a three dimensional transonic analysis method was replaced by a wave drag formula based on the loss in momentum across an isentropic shock. This formula was used as the objective function in a numerical optimization procedure to reduce the wave drag of a fighter wing at transonic maneuver conditions. The optimization procedure minimized wave drag through modifications to the wing section contours defined by a wing profile shape function. A significant reduction in wave drag was achieved while maintaining a high lift coefficient. Comparisons of the pressure distributions for the initial and optimized wing geometries showed significant reductions in the leading-edge peaks and shock strength across the span.

Wing Tip Vortex Drag

NASA Technical Reports Server (NTRS)

Muirhead, V. U.

1975-01-01

Optimization of L/D through minimizing induced drag through a detailed flow study together with force, pressure and vorticity measurements is considered. Flow visualization with neutral helium bubbles provides an excellent means of observing the effects of configuration changes.

Drag force scaling for penetration into granular media.

PubMed

Katsuragi, Hiroaki; Durian, Douglas J

2013-05-01

Impact dynamics is measured for spherical and cylindrical projectiles of many different densities dropped onto a variety non-cohesive granular media. The results are analyzed in terms of the material-dependent scaling of the inertial and frictional drag contributions to the total stopping force. The inertial drag force scales similar to that in fluids, except that it depends on the internal friction coefficient. The frictional drag force scales as the square-root of the density of granular medium and projectile, and hence cannot be explained by the combination of granular hydrostatic pressure and Coulomb friction law. The combined results provide an explanation for the previously observed penetration depth scaling.

Sub-grid drag model for immersed vertical cylinders in fluidized beds

DOE PAGES

Verma, Vikrant; Li, Tingwen; Dietiker, Jean -Francois; ...

2017-01-03

Immersed vertical cylinders are often used as heat exchanger in gas-solid fluidized beds. Computational Fluid Dynamics (CFD) simulations are computationally expensive for large scale systems with bundles of cylinders. Therefore sub-grid models are required to facilitate simulations on a coarse grid, where internal cylinders are treated as a porous medium. The influence of cylinders on the gas-solid flow tends to enhance segregation and affect the gas-solid drag. A correction to gas-solid drag must be modeled using a suitable sub-grid constitutive relationship. In the past, Sarkar et al. have developed a sub-grid drag model for horizontal cylinder arrays based on 2Dmore » simulations. However, the effect of a vertical cylinder arrangement was not considered due to computational complexities. In this study, highly resolved 3D simulations with vertical cylinders were performed in small periodic domains. These simulations were filtered to construct a sub-grid drag model which can then be implemented in coarse-grid simulations. Gas-solid drag was filtered for different solids fractions and a significant reduction in drag was identified when compared with simulation without cylinders and simulation with horizontal cylinders. Slip velocities significantly increase when vertical cylinders are present. Lastly, vertical suspension drag due to vertical cylinders is insignificant however substantial horizontal suspension drag is observed which is consistent to the finding for horizontal cylinders.« less

Roles of size and kinematics in drag reduction for two tandem flexible foils

NASA Astrophysics Data System (ADS)

Chao, Li-Ming; Zhang, Dong; Pan, Guang

2017-11-01

The effect of size and kinematics difference between two tandem flexible foils on drag reduction have been numerically studied. Compared with single foil, it is found that the kinematics difference between two foils would not play a significant role in reducing drag, while the size difference between two foils significantly affects the drag reduction in this two foil system. For leading foil, it always enjoys drag reduction and the highest drag reduction can be observed at bigger size difference and gap distance between two foil as 22%. For trailing foil, it suffers drag increase when the gap distance between two foils is smaller, while it enjoys drag decrease when the size difference between two foils is bigger enough. The hydrodynamic interaction between such actively undulated foils also has been uncovered and used to explain the mechanisms of drag reduction.

Analysis and design of planar and non-planar wings for induced drag minimization

NASA Technical Reports Server (NTRS)

Straussfogel, Dennis M.; Maughmer, Mark D.

1991-01-01

Improvements in the aerodynamic efficiency of commercial transport aircraft will reduce fuel usage with subsequent reduced cost, both monetary and environmental. To this end, the current research is aimed at reducing the overall drag of these aircraft with specific emphasis on reducing the drag generated by the lifting surfaces. The ultimate goal of this program is to create a wing design methodology which optimizes the geometry of the wing for lowest total drag within the constraints of a particular design specification. The components of drag which must be considered include profile drag, and wave drag. Profile drag is dependent upon, among other things, the airfoil section and the total wetted area. Induced drag, which is manifested as energy left in the wake by the trailing vortex system is mostly a function of wing span, but also depends on other geometric wing parameters. Wave drag of the wing, important in the transonic flight regime, is largely affected by the airfoil section, wing sweep, and so forth. The optimization problem is that of assessing the various parameters which contribute to the different components of wing drag, and determining the wing geometry which generates the best overall performance for a given aircraft mission. The primary thrust of the research effort to date was in the study of induced drag. Results from the study are presented.

MP-Pic simulation of CFB riser with EMMS-based drag model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, F.; Song, F.; Benyahia, S.

2012-01-01

MP-PIC (multi-phase particle in cell) method combined with the EMMS (energy minimization multi- scale) drag force model was implemented with the open source program MFIX to simulate the gas–solid flows in CFB (circulatingfluidizedbed) risers. Calculated solid flux by the EMMS drag agrees well with the experimental value; while the traditional homogeneous drag over-predicts this value. EMMS drag force model can also predict the macro-and meso-scale structures. Quantitative comparison of the results by the EMMS drag force model and the experimental measurements show high accuracy of the model. The effects of the number of particles per parcel and wall conditions onmore » the simulation results have also been investigated in the paper. This work proved that MP-PIC combined with the EMMS drag model can successfully simulate the fluidized flows in CFB risers and it serves as a candidate to realize real-time simulation of industrial processes in the future.« less

Analytical solution for the normal emission portion of the averaged Yarkovsky-O'Keefe-Radzvieskii-Paddack coefficient for a single facet

NASA Astrophysics Data System (ADS)

Albuja, Antonella A.; Scheeres, Daniel J.

2015-02-01

The Yarkovsky-O'Keefe-Radzvieskii-Paddack (YORP) effect has been well studied for asteroids. This paper develops an analytic solution to find the normal emission YORP component for a single facet. The solution presented here does not account for self-shadowing or self-heating. The YORP coefficient for all facets can be summed together to find the total coefficient of the asteroid. The normal emission component of YORP has been shown to be the most important for asteroids and it directly affects the rate of change of the asteroid's spin period. The analytical solution found is a sole function of the facet's geometry and the obliquity of the asteroid. This solution is universal for any facet and its orientation. The behaviour of the coefficient is analysed with this analytical solution. The closed-form solution is used to find the total YORP coefficient for the asteroids Apollo and 1998 ML14 whose shape models are composed of different numbers of facets. The results are then compared to published results and those obtained through numerical quadrature for validation.

On the Minimum Induced Drag of Wings -or- Thinking Outside the Box

NASA Technical Reports Server (NTRS)

Bowers, Albion H.

2011-01-01

Of all the types of drag, induced drag is associated with the creation and generation of lift over wings. Induced drag is directly driven by the span load that the aircraft is flying at. The tools by which to calculate and predict induced drag we use were created by Ludwig Prandtl in 1903. Within a decade after Prandtl created a tool for calculating induced drag, Prandtl and his students had optimized the problem to solve the minimum induced drag for a wing of a given span, formalized and written about in 1920. This solution is quoted in textbooks extensively today. Prandtl did not stop with this first solution, and came to a dramatically different solution in 1932. Subsequent development of this 1932 solution solves several aeronautics design difficulties simultaneously, including maximum performance, minimum structure, minimum drag loss due to control input, and solution to adverse yaw without a vertical tail. This presentation lists that solution by Prandtl, and the refinements by Horten, Jones, Kline, Viswanathan, and Whitcomb.

Variability of bed drag on cohesive beds under wave action

USGS Publications Warehouse

Safak, Ilgar

2016-01-01

Drag force at the bed acting on water flow is a major control on water circulation and sediment transport. Bed drag has been thoroughly studied in sandy waters, but less so in muddy coastal waters. The variation of bed drag on a muddy shelf is investigated here using field observations of currents, waves, and sediment concentration collected during moderate wind and wave events. To estimate bottom shear stress and the bed drag coefficient, an indirect empirical method of logarithmic fitting to current velocity profiles (log-law), a bottom boundary layer model for combined wave-current flow, and a direct method that uses turbulent fluctuations of velocity are used. The overestimation by the log-law is significantly reduced by taking turbulence suppression due to sediment-induced stratification into account. The best agreement between the model and the direct estimates is obtained by using a hydraulic roughness of 10 -4">−4 m in the model. Direct estimate of bed drag on the muddy bed is found to have a decreasing trend with increasing current speed, and is estimated to be around 0.0025 in conditions where wave-induced flow is relatively weak. Bed drag shows an increase (up to fourfold) with increasing wave energy. These findings can be used to test the bed drag parameterizations in hydrodynamic and sediment transport models and the skills of these models in predicting flows in muddy environments.

The Effects of Some Surface Irregularities on Wing Drag

NASA Technical Reports Server (NTRS)

Drag, Manley

1939-01-01

The N.A.C.A. has conducted tests to provide more complete data than were previously available for estimating the effects of common surface irregularities on wing drag. The irregularities investigated included: brazier-head and countersunk rivets, spot welds, several types of sheet-metal joints, and surface roughness. Tests were also conducted to determine the over-all effect of manufacturing irregularities incidental to riveted aluminum alloy and to spot-welded stainless-steel construction. The tests were made in the 8-foot high speed wind tunnel at Reynolds Numbers up to 18,000,000. The results show that any of the surface irregularities investigated may increase wing drag enough to have important adverse effects on high-speed performance and economy. A method of estimating increases in wing drag caused by brazier-head rivets and lapped joints under conditions outside the range of the tests is suggested. Estimated drag increases due to rivets and lapped joints under conditions outside the range of the tests is suggested. Estimated drag increases due to rivets and lapped joints on a wing of 20-foot chord flying at 250 miles per hour are shown.

Constraining the Drag Coefficients of Meteors in Dark Flight

NASA Technical Reports Server (NTRS)

Carter, R. T.; Jandir, P. S.; Kress, M. E.

2011-01-01

Based on data in the aeronautics literature, we have derived functions for the drag coefficients of spheres and cubes as a function of Mach number. Experiments have shown that spheres and cubes exhibit an abrupt factor-of-two decrease in the drag coefficient as the object slows through the transonic regime. Irregularly shaped objects such as meteorites likely exhibit a similar trend. These functions are implemented in an otherwise simple projectile motion model, which is applicable to the non-ablative dark flight of meteors (speeds less than .+3 km/s). We demonstrate how these functions may be used as upper and lower limits on the drag coefficient of meteors whose shape is unknown. A Mach-dependent drag coefficient is potentially important in other planetary and astrophysical situations, for instance, in the core accretion scenario for giant planet formation.

Investigation of Drag Coefficient for Rigid Ballute-like Shapes

NASA Astrophysics Data System (ADS)

Carnasciali, Maria-Isabel; Mastromarino, Anthony

2014-11-01

One common method of decelerating an object during atmospheric entry, descent, and landing is the use of parachutes. Another deceleration technology is the ballute - a combination of balloon and parachute. A CFD study was conducted using commercially available software to investigate the flow-field and the coefficient of drag for various rigid ballute-like shapes at varying Reynolds numbers. The impact of size and placement of the burble-fence as well as number, size, and shape of inlets was considered. Recent experimental measurements conducted during NASA's Low-Density Supersonic Decelerator program revealed a much higher coefficient of drag (Cd) for ballutes than previously encountered. Using atmospheric drag to slow down and land reduces the need for heavy fuel and rocket engines and thus, high values of drag are desired. Funding for this work, in part, provided by the CT Space Grant Consortium.

Hydrodynamic Characteristics of Two Low-Drag Supercavitating Hydrofoils

NASA Technical Reports Server (NTRS)

McGehee, John R.; Johnson, Virgil E., Jr.

1959-01-01

An experimental investigation has been conducted in Langley tank no. 2 to determine the hydrodynamic characteristics of two low-drag supercavitating hydrofoils operating in a range of cavitation numbers from 0 to approximately 6. The hydrofoils had aspect ratios of 1 and 3, and the sections were derived by assuming five terms in the vorticity-distribution expansion of the equivalent airfoil. The aspect-ratio-1 hydrofoil was also tested at zero cavitation number with two sets of end plates having depths of 3/8 and 1/4 chords. Zero cavitation number was established by operating the hydrofoils near the water surface so that complete ventilation of the upper surfaces could be obtained. For those depths of submersion where complete ventilation was not obtained through vortex ventilation, two probes were used to introduce air to the upper surfaces of the hydrofoils and to induce complete ventilation. Data were obtained for a range of speeds from 20 to 80 fps, angles of attack from 2 to 20 deg, and ratios of depth of submersion to chord from 0 to 0.85. The experimental results obtained from the aspect-ratio-1 and aspect-ratio-3, five-term hydrofoils were compared with a three-dimensional zero-cavitation-number theory. The theoretical and experimental values of lift and center of pressure for the aspect-ratio-1 hydrofoil were in agreement, within engineering accuracy, for the range of lift coefficients investigated. The theoretical drag coefficients were lower, by a constant amount, than the experimental drag coefficients. The theoretical expressions derived for the lift, drag, and center of pressure of the aspect-ratio-3 hydrofoil were in agreement, within engineering accuracy, with the experimental values. The theoretical and experimental drag coefficients of the aspect-ratio-3 five-term hydrofoil were lower than the theoretical drag coefficients computed for a comparable Tulin-Burkart hydrofoil.

Aero-acoustics of Drag Generating Swirling Exhaust Flows

NASA Technical Reports Server (NTRS)

Shah, P. N.; Mobed, D.; Spakovszky, Z. S.; Brooks, T. F.; Humphreys, W. M. Jr.

2007-01-01

Aircraft on approach in high-drag and high-lift configuration create unsteady flow structures which inherently generate noise. For devices such as flaps, spoilers and the undercarriage there is a strong correlation between overall noise and drag such that, in the quest for quieter aircraft, one challenge is to generate drag at low noise levels. This paper presents a rigorous aero-acoustic assessment of a novel drag concept. The idea is that a swirling exhaust flow can yield a steady, and thus relatively quiet, streamwise vortex which is supported by a radial pressure gradient responsible for pressure drag. Flows with swirl are naturally limited by instabilities such as vortex breakdown. The paper presents a first aero-acoustic assessment of ram pressure driven swirling exhaust flows and their associated instabilities. The technical approach combines an in-depth aerodynamic analysis, plausibility arguments to qualitatively describe the nature of acoustic sources, and detailed, quantitative acoustic measurements using a medium aperture directional microphone array in combination with a previously established Deconvolution Approach for Mapping of Acoustic Sources (DAMAS). A model scale engine nacelle with stationary swirl vanes was designed and tested in the NASA Langley Quiet Flow Facility at a full-scale approach Mach number of 0.17. The analysis shows that the acoustic signature is comprised of quadrupole-type turbulent mixing noise of the swirling core flow and scattering noise from vane boundary layers and turbulent eddies of the burst vortex structure near sharp edges. The exposed edges are the nacelle and pylon trailing edge and the centerbody supporting the vanes. For the highest stable swirl angle setting a nacelle area based drag coefficient of 0.8 was achieved with a full-scale Overall Sound Pressure Level (OASPL) of about 40dBA at the ICAO approach certification point.

Ad/dressing the nation: drag and authenticity in post-apartheid South Africa.

PubMed

Spruill, Jennifer

2004-01-01

This paper examines a style of drag in South Africa that features "traditional African" clothing. In a region in which homosexuality is denigrated as a colonial, European import and "unAfrican," the meaning of "traditional drag" is deeply inflected by the question of cultural authenticity. This dragging practice fits within a distinctly post-colonial production of tradition and its self-conscious display--in the form of attire--of a decidedly "gay" one. Traditional drag also responds to ongoing politics within and between lesbian and gay communities about racial "representivity" and "transformation." The paper focuses on displays of traditional drag at Johannesburg's Gay and Lesbian Pride Parade but also explores the complex politics of publicity and address suggested by varying contexts in which traditional dress and drag are mobilized.

Lubricant-impregnated surfaces for drag reduction in viscous laminar flow

NASA Astrophysics Data System (ADS)

Solomon, Brian; Khalil, Karim; Varanasi, Kripa; MIT Team

2013-11-01

For the first time, we explore the potential of lubricant impregnated surfaces (LIS) in reducing drag. LIS, inspired by the surface of the Nepenthes pitcher plant, have been introduced as a novel way of functionalizing a surface. LIS are characterized by extremely low contact angle hysteresis and have been show to effectively repel various liquids including water, oils, ketchup and blood. Motivated by the slippery nature of such surfaces, we explore the potential of LIS to reduce drag in internal flows. We observe a reduction in drag for LIS surfaces in a viscous laminar drag flow and model the impact of relevant system parameters (lubricant viscosity, working fluid viscosity, solid fraction, depth of texture, etc.).

The economic impact of drag in general aviation

NASA Technical Reports Server (NTRS)

Neal, R. D.

1975-01-01

General aviation aircraft fuel consumption and operating costs are closely linked to drag reduction methods. Improvements in airplane drag are envisioned for new models; their effects will be in the 5 to 10% range. Major improvements in fuel consumption over existing turbofan airplanes will be the combined results of improved aerodynamics plus additional effects from advanced turbofan engine designs.

Superhydrophobic and polymer drag reduction in turbulent Taylor-Couette flow

NASA Astrophysics Data System (ADS)

Rajappan, Anoop; McKinley, Gareth H.

2017-11-01

We use a custom-built Taylor-Couette apparatus (radius ratio η = 0.75) to study frictional drag reduction by dilute polymer solutions and superhydrophobic (SH) surfaces in turbulent flows for 15000 < Re < 86000 . By monitoring the torque-speed scaling we show that the swirling flow becomes fully turbulent above Re = 15000 and we focus on measurements in this regime. By applying SH coatings on the inner cylinder, we can evaluate the drag reducing performance of the coating and calculate the effective slip length in turbulent flow using a suitably modified Prandtl-von Kármán analysis. We also investigate drag reduction by dilute polymer solutions, and show that natural biopolymers from plant mucilage can be an inexpensive and effective alternative to synthetic polymers in drag reduction applications, approaching the same maximum drag reduction asymptote. Finally we explore combinations of the two methods - one arising from wall slip and the other due to changes in turbulence dynamics in the bulk flow - and find that the two effects are not additive; interestingly, the effectiveness of polymer drag reduction is drastically reduced in the presence of an SH coating on the wall. This study was financially supported by the Office of Naval Research (ONR) through Contract No. 3002453814.

On hydrodynamics of drag and lift of the human arm.

PubMed

Gardano, Paola; Dabnichki, Peter

2006-01-01

The work presents results on drag and lift measurement conducted in a low speed wind tunnel on a replica of the entire human arm. The selected model positions were identical to those during purely rotational front crawl stroke in quasi-static conditions. A computational fluid dynamics model using Fluent showed close correspondence with the experimental results and confirmed the suitability of low speed wind tunnel for the drag and lift measurement in quasi-static conditions. The obtained profiles of the hydrodynamic forces were similar to the dynamic data presented in an earlier study suggesting that shape drag is a major contributing factor in propulsive force generation. The aim of this study was to underline the importance of the entire arm analysis, the elbow angle and a newly defined angle of attack representing the angle of shoulder rotation. It was found that both the maximum value of the drag force at 160 degrees elbow flexion angle and the momentum generated by it exceed the respective magnitudes for the fully extended arm. The latter is underlined by a prolonged plateau of near maximum drag that was obtained at shoulder angle range of 50-140 degrees suggesting that optimal arm configuration in terms of propulsive force generation requires elbow flexion. Furthermore it was found that drag trend is not consistent with the widely assumed and used sinus wave profile. A gap in the existing experimental research was filled as for the first time the entire arm lift and drag was measured across the entire stroke range.

Grid Quality and Resolution Issues from the Drag Prediction Workshop Series

NASA Technical Reports Server (NTRS)

Mavriplis, Dimitri J.; Vassberg, John C.; Tinoco, Edward N.; Mani, Mori; Brodersen, Olaf P.; Eisfeld, Bernhard; Wahls, Richard A.; Morrison, Joseph H.; Zickuhr, Tom; Levy, David;

Flight tests of external modifications used to reduce blunt base drag

NASA Technical Reports Server (NTRS)

Powers, Sheryll Goecke

1988-01-01

The effectiveness of a trailing disk (the trapped vortex concept) in reducing the blunt base drag of an 8-in diameter body of revolution was studied from measurements made both in flight and in full-scale wind-tunnel tests. The experiment demonstrated the significant base drag reduction capability of the trailing disk to Mach 0.93. The maximum base drag reduction obtained from a cavity tested on the flight body of revolution was not significant. The effectiveness of a splitter plate and a vented-wall cavity in reducing the base drag of a quasi-two-dimensional fuselage closure was studied from base pressure measurements made in flight. The fuselage closure was between the two engines of the F-111 airplane; therefore, the base pressures were in the presence of jet engine exhaust. For Mach numbers from 1.10 to 1.51, significant base drag reduction was provided by the vented-wall cavity configuration. The splitter plate was not considered effective in reducing base drag at any Mach number tested.

Skin friction drag reduction in turbulent flow using spanwise traveling surface waves

NASA Astrophysics Data System (ADS)

Musgrave, Patrick F.; Tarazaga, Pablo A.

2017-04-01

A major technological driver in current aircraft and other vehicles is the improvement of fuel efficiency. One way to increase the efficiency is to reduce the skin friction drag on these vehicles. This experimental study presents an active drag reduction technique which decreases the skin friction using spanwise traveling waves. A novel method is introduced for generating traveling waves which is low-profile, non-intrusive, and operates under various flow conditions. This wave generation method is discussed and the resulting traveling waves are presented. These waves are then tested in a low-speed wind tunnel to determine their drag reduction potential. To calculate the drag reduction, the momentum integral method is applied to turbulent boundary layer data collected using a pitot tube and traversing system. The skin friction coefficients are then calculated and the drag reduction determined. Preliminary results yielded a drag reduction of ≍ 5% for 244Hz traveling waves. Thus, this novel wave generation method possesses the potential to yield an easily implementable, non-invasive drag reduction technology.

Drag force in a D-instanton background

NASA Astrophysics Data System (ADS)

Zhang, Zi-qiang; Luo, Zhong-jie; Hou, De-fu

2018-06-01

We study the drag force and diffusion coefficient with respect to a moving heavy quark in a D-instanton background, which corresponds to the Yang-Mills theory in the deconfining, high-temperature phase. It is shown that the presence of the D-instanton density tends to increase the drag force and decrease the diffusion coefficient, reverse to the effects of the velocity and the temperature. Moreover, the inclusion of the D-instanton density makes the medium less viscous.

A comprehensive plan for helicopter drag reduction

NASA Technical Reports Server (NTRS)

Williams, R. M.; Montana, P. S.

1975-01-01

Current helicopters have parasite drag levels 6 to 10 times as great as fixed wing aircraft. The commensurate poor cruise efficiency results in a substantial degradation of potential mission capability. The paper traces the origins of helicopter drag and shows that the problem (primarily due to bluff body flow separation) can be solved by the adoption of a comprehensive research and development plan. This plan, known as the Fuselage Design Methodology, comprises both nonaerodynamic and aerodynamic aspects. The aerodynamics are discussed in detail and experimental and analytical programs are described which will lead to a solution of the bluff body problem. Some recent results of work conducted at the Naval Ship Research and Development Center (NSRDC) are presented to illustrate these programs. It is concluded that a 75-per cent reduction of helicopter drag is possible by the full implementation of the Fuselage Design Methodology.

Effect of Ice Formations on Section Drag of Swept NACA 63A-009 Airfoil with Partial-Span Leading-Edge Slat for Various Modes of Thermal Ice Protection

NASA Technical Reports Server (NTRS)

VonGlahn, Uwe H.; Gray, Vernon H.

1954-01-01

The effects of primary and runback ice formations on the section drag of a 36 deg swept NACA 63A-009 airfoil section with a partial-span leading-edge slat were studied over a range of angles of attack from 2 to 8 deg and airspeeds up to 260 miles per hour for icing conditions with liquid-water contents ranging from 0.39 to 1.23 grams per cubic meter and datum air temperatures from 10 to 25 F. The results with slat retracted showed that glaze-ice formations caused large and rapid increases in section drag coefficient and that the rate of change in section drag coefficient for the swept 63A-009 airfoil was about 2-1 times that for an unswept 651-212 airfoil. Removal of the primary ice formations by cyclic de-icing caused the drag to return almost to the bare-airfoil drag value. A comprehensive study of the slat icing and de-icing characteristics was prevented by limitations of the heating system and wake interference caused by the slat tracks and hot-gas supply duct to the slat. In general, the studies showed that icing on a thin swept airfoil will result in more detrimental aerodynamic characteristics than on a thick unswept airfoil.

The contact drag of towed demersal fishing gear components

NASA Astrophysics Data System (ADS)

O'Neill, F. G.; Summerbell, K.; Ivanović, A.

2018-01-01

The contact demersal towed fishing gears make with the seabed can lead to penetration of the substrate, lateral displacement of the sediment and a pressure field transmitted through the sediment. It will also contribute to the overall drag of the fishing gear. Consequently, there can be environmental effects such as habitat alteration and benthic mortality, and impacts to the fuel efficiency of the fishing operation which will affect emissions of nitrogen oxides, sulphur oxides and greenhouse gases such as CO2. Here we present the results of experimental trials that measure the contact drag of a range of elements that represent some of the components of towed demersal gears that are in contact with the seabed. We show that the contact drag of the gear components depends on their weight, geometry, the type of sediment on which they are towed and whether they are rolling or not. As expected, the contact drag of each gear component increases as its weight increases and the drag of fixed elements is greater than that of the rolling ones. The dependence on aspect ratio is more complex and the drag (per unit area) of narrow cylinders is less than that of wider ones when they roll on the finer sediment or are fixed (not permitted to roll) on the coarser sediment. When they roll on the coarse sediment there is no dependence on aspect ratio. Our results also suggest that fixed components may penetrate the seabed to a lesser depth when they are towed at higher speeds but when they roll there is no such relationship.

In-Flight Subsonic Lift and Drag Characteristics Unique to Blunt-Based Lifting Reentry Vehicles

NASA Technical Reports Server (NTRS)

Saltzman, Edwin J.; Wang, K. Charles; Iliff, Kenneth W.

2007-01-01

Lift and drag measurements have been analyzed for subsonic flight conditions for seven blunt-based reentry-type vehicles. Five of the vehicles are lifting bodies (M2-F1, M2-F2, HL-10, X-24A, and X-24B) and two are wing-body configurations (the X-15 and the Space Shuttle Enterprise). Base pressure measurements indicate that the base drag for full-scale vehicles is approximately three times greater than predicted by Hoerner's equation for three-dimensional bodies. Base drag and forebody drag combine to provide an optimal overall minimum drag (a drag "bucket") for a given configuration. The magnitude of this optimal drag, as well as the associated forebody drag, is dependent on the ratio of base area to vehicle wetted area. Counter-intuitively, the flight-determined optimal minimum drag does not occur at the point of minimum forebody drag, but at a higher forebody drag value. It was also found that the chosen definition for reference area for lift parameters should include the projection of planform area ahead of the wing trailing edge (i.e., forebody plus wing). Results are assembled collectively to provide a greater understanding of this class of vehicles than would occur by considering them individually.

Summary of the Fourth AIAA CFD Drag Prediction Workshop

NASA Technical Reports Server (NTRS)

Vassberg, John C.; Tinoco, Edward N.; Mani, Mori; Rider, Ben; Zickuhr, Tom; Levy, David W.; Brodersen, Olaf P.; Eisfeld, Bernhard; Crippa, Simone; Wahls, Richard A.;

The Influence of Heat Transfer on the Drag of Airfoils.

DTIC Science & Technology

1981-04-01

OF STANDARDS-1963-A LL b AFWAL-TR-81- 3030 THE INFLUENCE OF HEAT TRANSFER ON THE DRAG OF AIRFOILS DR. JOHN D. LEE The Aeronautical and Astronautical...if necReary mid identify by block number) Airfoils , Subsonic, Transonic, Supercritical, Laminar Flow, Transition, Drag Reduction, Heat Transfer...determine the effects of surface temperature on the drag of airfoils . Models of an aft- loaded profile and of a NACA 65A413 were tested with separate models

Phonon-drag magnetothermopower in Rashba spin-split two-dimensional electron systems.

PubMed

Biswas, Tutul; Ghosh, Tarun Kanti

2013-10-16

We study the phonon-drag contribution to the thermoelectric power in a quasi-two-dimensional electron system confined in GaAs/AlGaAs heterostructure in the presence of both Rashba spin-orbit interaction and perpendicular magnetic field at very low temperature. It is observed that the peaks in the phonon-drag thermopower split into two when the Rashba spin-orbit coupling constant is strong. This splitting is a direct consequence of the Rashba spin-orbit interaction. We show the dependence of phonon-drag thermopower on both magnetic field and temperature numerically. A power-law dependence of phonon-drag magnetothermopower on the temperature in the Bloch-Gruneisen regime is found. We also extract the exponent of the temperature dependence of phonon-drag thermopower for different parameters like electron density, magnetic field, and the spin-orbit coupling constant.

Statistical Analysis of the AIAA Drag Prediction Workshop CFD Solutions

NASA Technical Reports Server (NTRS)

Morrison, Joseph H.; Hemsch, Michael J.

2007-01-01

The first AIAA Drag Prediction Workshop (DPW), held in June 2001, evaluated the results from an extensive N-version test of a collection of Reynolds-Averaged Navier-Stokes CFD codes. The code-to-code scatter was more than an order of magnitude larger than desired for design and experimental validation of cruise conditions for a subsonic transport configuration. The second AIAA Drag Prediction Workshop, held in June 2003, emphasized the determination of installed pylon-nacelle drag increments and grid refinement studies. The code-to-code scatter was significantly reduced compared to the first DPW, but still larger than desired. However, grid refinement studies showed no significant improvement in code-to-code scatter with increasing grid refinement. The third AIAA Drag Prediction Workshop, held in June 2006, focused on the determination of installed side-of-body fairing drag increments and grid refinement studies for clean attached flow on wing alone configurations and for separated flow on the DLR-F6 subsonic transport model. This report compares the transonic cruise prediction results of the second and third workshops using statistical analysis.

Determination of the Pressure Drag of Airfoils by Integration of Surface Pressures

NASA Technical Reports Server (NTRS)

Phillips, William H.

1990-01-01

A study was conducted of the causes of pressure drag of subsonic airfoils. In a previous paper by the author, the pressure drag is obtained by calculating the total drag from the momentum defect in the boundary layer at the trailing edge and subtracting the friction drag obtained from integration of surface friction along the chord. Herein, the pressure drag is obtained by integrating the streamwise components of surface pressure around the airfoil. Studies were made to verify the accuracy of the integration procedure. The values of pressure drag were much smaller than those obtained by the previous method. This lack of agreement is attributed to the difficulty of calculating boundary layer conditions in the vicinity of the trailing edge and to the extreme sensitivity of the circulation and lift to the trailing edge conditions. The results of these studies are compared with those of previous investigations.

Intercooler cooling-air weight flow and pressure drop for minimum drag loss

NASA Technical Reports Server (NTRS)

Reuter, J George; Valerino, Michael F

1944-01-01

An analysis has been made of the drag losses in airplane flight of cross-flow plate and tubular intercoolers to determine the cooling-air weight flow and pressure drop that give a minimum drag loss for any given cooling effectiveness and, thus, a maximum power-plant net gain due to charge-air cooling. The drag losses considered in this analysis are those due to (1) the extra drag imposed on the airplane by the weight of the intercooler, its duct, and its supports and (2) the drag sustained by the cooling air in flowing through the intercooler and its duct. The investigation covers a range of conditions of altitude, airspeed, lift-drag ratio, supercharger-pressure ratio, and supercharger adiabatic efficiency. The optimum values of cooling air pressure drop and weight flow ratio are tabulated. Curves are presented to illustrate the results of the analysis.

14 CFR 25.697 - Lift and drag devices, controls.

Code of Federal Regulations, 2010 CFR

2010-01-01

... AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Design and Construction Control Systems § 25.697 Lift and drag devices, controls. (a) Each lift device control must be designed so that the pilots... drag device control must be designed and located to make inadvertent operation improbable. Lift and...

14 CFR 25.697 - Lift and drag devices, controls.

Code of Federal Regulations, 2012 CFR

2012-01-01

... AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Design and Construction Control Systems § 25.697 Lift and drag devices, controls. (a) Each lift device control must be designed so that the pilots... drag device control must be designed and located to make inadvertent operation improbable. Lift and...

14 CFR 25.697 - Lift and drag devices, controls.

Code of Federal Regulations, 2014 CFR

2014-01-01

... AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Design and Construction Control Systems § 25.697 Lift and drag devices, controls. (a) Each lift device control must be designed so that the pilots... drag device control must be designed and located to make inadvertent operation improbable. Lift and...

14 CFR 25.697 - Lift and drag devices, controls.

Code of Federal Regulations, 2011 CFR

2011-01-01

... AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Design and Construction Control Systems § 25.697 Lift and drag devices, controls. (a) Each lift device control must be designed so that the pilots... drag device control must be designed and located to make inadvertent operation improbable. Lift and...

Aerodynamic drag reduction tests on a box-shaped vehicle

NASA Technical Reports Server (NTRS)

Peterson, R. L.; Sandlin, D. R.

1981-01-01

The intent of the present experiment is to define a near optimum value of drag coefficient for a high volume type of vehicle through the use of a boattail, on a vehicle already having rounded front corners and an underbody seal, or fairing. The results of these tests will constitute a baseline for later follow-on studies to evaluate candidate methods of obtaining afterbody drag coefficients approaching the boattail values, but without resorting to such impractical afterbody extensions. The current modifications to the box-shaped vehicle consisted of a full and truncated boattail in conjunction with the faired and sealed underbody. Drag results from these configurations are compared with corresponding wind tunnel results of a 1/10 scale model. Test velocities ranged up to 96.6 km/h (60 mph) and the corresponding Reynolds numbers ranged up to 1.3 x 10 to the 7th power based on the vehicles length which includes the boattail. A simple coast-down technique was used to define drag.

Space Age Swimsuit Reduces Drag, Breaks Records

NASA Technical Reports Server (NTRS)

2008-01-01

A space shuttle and a competitive swimmer have a lot more in common than people might realize: Among other forces, both have to contend with the slowing influence of drag. NASA s Aeronautics Research Mission Directorate focuses primarily on improving flight efficiency and generally on fluid dynamics, especially the forces of pressure and viscous drag, which are the same for bodies moving through air as for bodies moving through water. Viscous drag is the force of friction that slows down a moving object through a substance, like air or water. NASA uses wind tunnels for fluid dynamics research, studying the forces of friction in gasses and liquids. Pressure forces, according to Langley Research Center s Stephen Wilkinson, dictate the optimal shape and performance of an airplane or other aero/hydro-dynamic body. In both high-speed flight and swimming, says Wilkinson, a thin boundary layer of reduced velocity fluid surrounds the moving body; this layer is about 2 centimeters thick for a swimmer.

Interference Effects and Drag of Struts on a Monoplane Wing

NASA Technical Reports Server (NTRS)

Ward, Kenneth E

1931-01-01

Tests were conducted in the Variable Density Wind Tunnel of the NACA to determine the importance of the interference effects and drag of struts on a monoplane. Inclined struts were placed upon a Gottingen 387 airfoil in the lower surface positions and in two upper surface positions. Tests were made at values of Reynolds Number comparable with those obtained in flight. It was found that the interference drag of struts may be as great as the drag of the struts alone.

Method for reducing the drag of blunt-based vehicles by adaptively increasing forebody roughness

NASA Technical Reports Server (NTRS)

Whitmore, Stephen A. (Inventor); Saltzman, Edwin J. (Inventor); Moes, Timothy R. (Inventor); Iliff, Kenneth W. (Inventor)

2005-01-01

A method for reducing drag upon a blunt-based vehicle by adaptively increasing forebody roughness to increase drag at the roughened area of the forebody, which results in a decrease in drag at the base of this vehicle, and in total vehicle drag.

EFFECTIVENESS OF NYLON DRAG STRAPS FOR BRAKING MONORAIL SLEDS.

DTIC Science & Technology

Velocity versus coast distance measurements on two monorail rocket sleds were conducted on the Holloman track to obtain numerical information on the...sleds and the drag straps. The straps as described are shown to increase the effective drag area of the monorail sleds used by approximately one square

Evaluation of a Drag-Free Control Concept for Missions in Low Earth Orbit

NASA Technical Reports Server (NTRS)

Fleck, Melissa E.; Starin, Scott R.

2003-01-01

Atmospheric drag causes the greatest uncertainty in the equations of motion for spacecraft in Low Earth Orbit (LEO). If atmospheric drag eflects can be continuously and autonomously counteracted through the use of a drag-fee control system, drag may essentially be eliminated from the equations of motion for the spacecraft. The main perturbations on the spacecraft will then be those due to the gravitational field, which are much more easily predicted Through dynamical analysis and numerical simulation, this paper presents some potential costs and benefits associated with the fuel used during continuous drag compensation. In light of this cost-benefit analysis, simulation results are used to validate the concept of drag-free control for LEO spacecraft missions having certain characteristics.

The interaction of drag queens and gay men in public and private spaces.

PubMed

Berkowitz, Dana; Belgrave, Linda; Halberstein, Robert A

2007-01-01

This study examines the issue of internal segregation within the gay community, focusing on the ways by which the drag queen subculture is distanced from larger mainstream gay society. Through the use of institutional ethnography, symbolic interactionism, and a naturalist approach to sociology, the researchers sought to understand the subjective experience of the drag queen, in particular how drag queens perceive their interactions with mainstream gay society. Data for this study were collected through a series of observations conducted in a variety of spatial contexts and interviews with 18 drag queens. Findings indicate that spatial distance between the drag queens and the mainstream gay men is dependent on both the social context and the level of professionalization of the drag queen. Although drag queens' perceptions of their status in the gay community are also dependent on the latter, discussions of relationship difficulties and the quest for a long-term romantic partner illustrate that discrimination within the gay community is both widespread and complex.

Effect of Jet-nozzle-expansion Ratio on Drag of Parabolic Afterbodies

NASA Technical Reports Server (NTRS)

Englert, Gerald W; Vargo, Donald J; Cubbison, Robert W

1954-01-01

The interaction of the flow from one convergent and two convergent-divergent nozzles on parabolic afterbodies was studied at free-stream Mach numbers of 2.0, 1.6, and 0.6 over a range of jet pressure ratio. The influence of the jet on boattail and base drag was very pronounced. Study of the total external afterbody drag values at supersonic speeds indicated that, over most of the high-pressure-ratio range, increasing the nozzle design expansion ratio increased the drag even though the boattail area was reduced. Increasing the pressure ratio tended to increase slightly the total-drag increment caused by angle-of-attack operation.

Drag Reduction by Riblets & Sharkskin Denticles: A Numerical Study

NASA Astrophysics Data System (ADS)

Boomsma, Aaron

Riblet films are a passive method of turbulent boundary layer control that can reduce viscous drag. They have been studied with great detail for over 30 years. Although common riblet applications include flows with Adverse Pressure Gradients (APG), nearly all research thus far has been performed in channel flows. Recent research has provided motivation to study riblets in more complicated turbulent flows with claims that riblet drag reduction can double in mild APG common to airfoils at moderate angles of attack. Therefore, in this study, we compare drag reduction by scalloped riblet films between riblets in a zero pressure gradient and those in a mild APG using high-resolution large eddy simulations. In order to gain a fundamental understanding of the relationship between drag reduction and pressure gradient, we simulated several different riblet sizes that encompassed a broad range of s + (riblet width in wall units), similarly to many experimental studies. We found that there was only a slight improvement in drag reduction for riblets in the mild APG. We also observed that peak values of streamwise turbulence intensity, turbulent kinetic energy, and streamwise vorticity scale with riblet width. Primary Reynolds shear stresses and turbulence kinetic energy production however scale with the ability of the riblet to reduce skin-friction. Another turbulent roughness of similar shape and size to riblets is sharkskin. The hydrodynamic function of sharkskin has been under investigation for the past 30 years. Current literature conflicts on whether sharkskin is able to reduce skin friction similarly to riblets. To contribute insights toward reconciling these conflicting views, Direct Numerical Simulations (DNS) are carried out to obtain detailed flow fields around realistic denticles. A sharp interface immersed boundary method is employed to simulate two arrangements of actual sharkskin denticles (from Isurus oxyrinchus) in a turbulent boundary layer at Retau ≈ 180

On the Decrease of the Oceanic Drag Coefficient in High Winds

NASA Astrophysics Data System (ADS)

Donelan, Mark A.

2018-02-01

The sheltering coefficient - prefixing Jeffreys' concept of the exponential wave growth rate at a gas-liquid interface - is shown to be Reynolds number dependent from laboratory measurements of waves and Reynolds stresses. There are two turbulent flow regimes: wind speed range of 2.5 to 30 m/s where the drag coefficients increase with wind speed, and wind speed range of 30 to 50 m/s where sheltering/drag coefficients decrease/saturate with wind speed. By comparing model calculations of drag coefficients - using a fixed sheltering coefficient - with ocean observations over a wind speed range of 1 to 50 m/s a similar Reynolds number dependence of the oceanic sheltering coefficient is revealed. In consequence the drag coefficient is a function of Reynolds number and wave age, and not just wind speed as frequently assumed. The resulting decreasing drag coefficient above 30 m/s is shown to be critical in explaining the rapid intensification so prominent in the climatology of Atlantic hurricanes. The Reynolds number dependence of the sheltering coefficient, when employed in coupled models, should lead to significant improvements in the prediction of intensification and decay of tropical cyclones. A calculation of curvature at the wave crest suggests that at wind speeds above 56.15 m/s all waves-breaking or not-induce steady flow separation leading to a minimum in the drag coefficient. This is further evidence of the veracity of the observations of the oceanic drag coefficient at high winds.

Hub and pylon fairing integration for helicopter drag reduction

NASA Technical Reports Server (NTRS)

Martin, D. M.; Mort, R. W.; Squires, P. K.; Young, L. A.

1991-01-01

The results of testing hub and pylon fairings mounted on a one-fifth scale helicopter with the goal of reducing parasite drag are presented. Lift, drag, and pitching moment, as well as side force and yawing moment, were measured. The primary objective of the test was to validate the drag reduction capability of integrated hub and pylon configurations in the aerodynamic environment produced by a rotating hub in forward flight. In addition to the baseline helicopter without fairings, three hub fairings and three pylon fairings were tested in various combinations. The three hub fairings tested reflect two different conceptual design approaches to implementing an integrated fairing configuration on an actual aircraft. The design philosophy is discussed in detail and comparisons are made between the wind tunnel models and potential full-scale prototypes. The data show that model drag can be reduced by as much as 20.8 percent by combining a small hub fairing with circular arc upper and flat lower surfaces and a nontapered 34-percent thick pylon fairing. Aerodynamic effects caused by the fairings, which may have a significant impact on static longitudinal and directional stability, were observed. The results support previous research which showed that the greatest reduction in model drag is achieved if the hub and pylon fairings are integrated with minimum gap between the two.

Innovative Flow Control Concepts for Drag Reduction

NASA Technical Reports Server (NTRS)

Lin, John C.; Whalen, Edward A.; Eppink, Jenna L.; Siochi, Emilie J.; Alexander, Michael G.; Andino, Marlyn Y.

2016-01-01

This paper highlights the technology development of two flow control concepts for aircraft drag reduction. The NASA Environmentally Responsible Aviation (ERA) project worked with Boeing to demonstrate these two concepts on a specially outfitted Boeing 757 ecoDemonstrator during the spring of 2015. The first flow control concept used Active Flow Control (AFC) to delay flow separation on a highly deflected rudder and increase the side force that it generates. This may enable a smaller vertical tail to provide the control authority needed in the event of an engine failure during takeoff and landing, while still operating in a conventional manner over the rest of the flight envelope. Thirty-one sweeping jet AFC actuators were installed and successfully flight-tested on the vertical tail of the 757 ecoDemonstrator. Pilot feedback, flow cone visualization, and analysis of the flight test data confirmed that the AFC is effective, as a smoother flight and enhanced rudder control authority were reported. The second flow control concept is the Insect Accretion Mitigation (IAM) innovation where surfaces were engineered to mitigate insect residue adhesion on a wing's leading edge. This is necessary because something as small as an insect residue on the leading edge of a laminar flow wing design can cause turbulent wedges that interrupt laminar flow, resulting in an increase in drag and fuel use. Several non-stick coatings were developed by NASA and applied to panels that were mounted on the leading edge of the wing of the 757 ecoDemonstrator. The performance of the coated surfaces was measured and validated by the reduction in the number of bug adhesions relative to uncoated control panels flown simultaneously. Both flow control concepts (i.e., sweeping jet actuators and non-stick coatings) for drag reduction were the culmination of several years of development, from wind tunnel tests to flight tests, and produced valuable data for the advancement of modern aircraft designs

Experimental Investigation of Convoluted Contouring for Aircraft Afterbody Drag Reduction

NASA Technical Reports Server (NTRS)

Deere, Karen A.; Hunter, Craig A.

1999-01-01

An experimental investigation was performed in the NASA Langley 16-Foot Transonic Tunnel to determine the aerodynamic effects of external convolutions, placed on the boattail of a nonaxisymmetric nozzle for drag reduction. Boattail angles of 15 and 22 were tested with convolutions placed at a forward location upstream of the boattail curvature, at a mid location along the curvature and at a full location that spanned the entire boattail flap. Each of the baseline nozzle afterbodies (no convolutions) had a parabolic, converging contour with a parabolically decreasing corner radius. Data were obtained at several Mach numbers from static conditions to 1.2 for a range of nozzle pressure ratios and angles of attack. An oil paint flow visualization technique was used to qualitatively assess the effect of the convolutions. Results indicate that afterbody drag reduction by convoluted contouring is convolution location, Mach number, boattail angle, and NPR dependent. The forward convolution location was the most effective contouring geometry for drag reduction on the 22 afterbody, but was only effective for M < 0.95. At M = 0.8, drag was reduced 20 and 36 percent at NPRs of 5.4 and 7, respectively, but drag was increased 10 percent for M = 0.95 at NPR = 7. Convoluted contouring along the 15 boattail angle afterbody was not effective at reducing drag because the flow was minimally separated from the baseline afterbody, unlike the massive separation along the 22 boattail angle baseline afterbody.

Drag reduction in plane Couette flow of dilute polymer solutions

NASA Astrophysics Data System (ADS)

Liu, Nansheng; Teng, Hao; Lu, Xiyun; Khomami, Bamin

2017-11-01

Drag reduction (DR) in the plane Couette flow (PCF) by the addition of flexible polymers has been studied by direct numerical simulation (DNS) in this work. Special interest has been directed to explore the similarity and difference in the DR features between the PCF and the plane Poiseuille flow (PPF), and to clarify the effects of large-scale structures (LSSs) on the near-wall turbulence. It has been demonstrated that in the near-wall region the drag-reduced PCF shares typical DR features similar to those reported for the drag-reduced PPF (White & Mungal 2008; Graham 2014), however in the core region intriguing differences are found between these two DR shear flows of polymeric solution. Specifically, in the core region of the drag-reduced PCF, the polymer chains are stretched substantial and absorb kinetic energy from the turbulent fluctuations. In commensurate, peak values of conformation tensor components Cyy and Czz occur in the core region. This finding is strikingly different from that of the drag-reduced PPF. For the drag-reduced PCF, the LSSs are found to have monotonically increasing effects on the near-wall flow as the Weissenberg number increases, and have their spanwise length scale unchanged. This work is supported by the NSFC Grants 11272306 and 11472268 and the NSF Grant CBET0755269. This research was also supported in part by allocation of advanced computational resources on DARTER by the National Institute for Computational Sciences (NICS).

Study on drag coefficient of rising bubble in still water

NASA Astrophysics Data System (ADS)

Shi, M. Y.; Qi, Mei; Yi, C. G.; Liu, D. Y.; Zhang, K. X.

2017-09-01

Research on the behavior of a rising bubble in still water is on the basis of Newton's theory of classical mechanics. Develop a calculation analysis and an experimental process of bubble rising behavior in order to search for an appropriate way of valuing drag coefficient, which is the key element toward this issue. Analyze the adaptability of the drag coefficient; compare the theoretical model to the real experimental model of rising bubble behavior. The result turns out that the change rate of radius could be ignored according to the analysis; the acceleration phase is transient; final velocity and the diameter of bubble do relate to the drag coefficient, but have no obvious relation with the depth of water. After series of inference analysis of the bubble behavior and experimental demonstration, a new drag coefficient and computing method is proposed.

Base Passive Porosity for Vehicle Drag Reduction

NASA Technical Reports Server (NTRS)

Bauer, Steven X. S. (Inventor); Wood, Richard M. (Inventor)

2003-01-01

A device for controlling drag on a ground vehicle. The device consists of a porous skin or skins mounted on the trailing surface and/or aft portions of the ground vehicle. The porous skin is separated from the vehicle surface by a distance of at least the thickness of the porous skin. Alternately, the trailing surface, sides, and/or top surfaces of the ground vehicle may be porous. The device minimizes the strength of the separation in the base and wake regions of the ground vehicle, thus reducing drag.

Outer-layer manipulators for turbulent drag reduction

NASA Technical Reports Server (NTRS)

Anders, J. B., Jr.

1990-01-01

The last ten years have yielded intriguing research results on aerodynamic boundary outer-layer manipulators as local skin friction reduction devices at low Reynolds numbers; net drag reduction device systems for entire aerodynamic configurations are nevertheless noted to remain elusive. Evidence has emerged for dramatic alterations of the structure of a turbulent boundary layer which persist for long distances downstream and reduce wall shear as a results of any one of several theoretically possible mechanisms. Reduced effectiveness at high Reynolds numbers may, however, limit the applicability of outer-layer manipulators to practical aircraft drag reduction.

Discovery of riblets in a bird beak (Rynchops) for low fluid drag

PubMed Central

2016-01-01

Riblet structures found on fast-swimming shark scales, such as those found on a mako shark, have been shown to reduce fluid drag. In previous experimental and modelling studies, riblets have been shown to provide drag reduction by lifting vortices formed in turbulent flow, decreasing overall shear stresses. Skimmer birds (Rynchops) are the only birds to catch fish in flight by flying just above the water surface with a submerged beak to fish for food. Because they need to quickly catch prey, reducing drag on their beak is advantageous. For the first time, riblet structures found on the beak of the skimmer bird have been studied experimentally and computationally for low fluid drag properties. In this study, skimmer replicas were studied for drag reduction through pressure drop in closed-channel, turbulent water flow. Pressure drop measurements are compared for black and yellow skimmer beaks in two configurations, and mako shark skin. In addition, two configurations of skimmer beak were modelled to compare drag properties and vortex structures. Results are discussed, and a conceptual model is presented to explain a possible drag reduction mechanism in skimmers. This article is part of the themed issue ‘Bioinspired hierarchically structured surfaces for green science’. PMID:27354734

Modification of near-wall coherent structures in polymer drag reduced flow: simulation

NASA Astrophysics Data System (ADS)

Dubief, Yves; White, Christopher; Shaqfeh, Eric; Moin, Parviz; Lele, Sanjiva

2002-11-01

Polymer drag reduced flows are investigated through direct numerical simulations of viscoelastic flows. The solver for the viscoelastic model (FENE-P) is based on higher-order finite difference schemes and a novel implicit time integration method. Its robustness allows the simulation of all drag reduction (DR) regimes from the onset to the maximum drag reduction (MDR). It also permits the use of realistic polymer length and concentration. The maximum polymer extension in our simulation matches that of a polystyrene molecule of 10^6 molecular weight. Two distinct regimes of polymer drag reduced flows are observed: at low drag reduction (LDR, DR< 40-50%), the near-wall structure is essentially similar to Newtonian wall turbulence whereas the high drag reduction regime (HDR, DR from 40-50% to MDR) shows significant differences in the organization of the coherent structures. The 3D information provided by numerical simulations allows the determination of the interaction of polymers and near-wall coherent structures. To isolate the contribution of polymers in the viscous sublayer, the buffer and the outer region of the flow, numerical experiments are performed where the polymer concentration is varied in the wall-normal direction. Finally a mechanism of polymer drag reduction derived from our results and PIV measurements is discussed.

Discovery of riblets in a bird beak (Rynchops) for low fluid drag.

PubMed

Martin, Samuel; Bhushan, Bharat

2016-08-06

Riblet structures found on fast-swimming shark scales, such as those found on a mako shark, have been shown to reduce fluid drag. In previous experimental and modelling studies, riblets have been shown to provide drag reduction by lifting vortices formed in turbulent flow, decreasing overall shear stresses. Skimmer birds (Rynchops) are the only birds to catch fish in flight by flying just above the water surface with a submerged beak to fish for food. Because they need to quickly catch prey, reducing drag on their beak is advantageous. For the first time, riblet structures found on the beak of the skimmer bird have been studied experimentally and computationally for low fluid drag properties. In this study, skimmer replicas were studied for drag reduction through pressure drop in closed-channel, turbulent water flow. Pressure drop measurements are compared for black and yellow skimmer beaks in two configurations, and mako shark skin. In addition, two configurations of skimmer beak were modelled to compare drag properties and vortex structures. Results are discussed, and a conceptual model is presented to explain a possible drag reduction mechanism in skimmers.This article is part of the themed issue 'Bioinspired hierarchically structured surfaces for green science'. © 2016 The Author(s).

Determination of the Drag Resistance Coefficients of Different Vehicles

ERIC Educational Resources Information Center

Fahsl, Christoph; Vogt, Patrik

2018-01-01

While it has been demonstrated how air resistance could be analyzed by using mobile devices, this paper demonstrates a method of how to determine the drag resistance coefficient "c" of a commercial automobile by using the acceleration sensor of a smartphone or tablet. In an academic context, the drag resistance is often mentioned, but…

Normal force and drag force in magnetorheological finishing

NASA Astrophysics Data System (ADS)

Miao, Chunlin; Shafrir, Shai N.; Lambropoulos, John C.; Jacobs, Stephen D.

2009-08-01

The material removal in magnetorheological finishing (MRF) is known to be controlled by shear stress, λ, which equals drag force, Fd, divided by spot area, As. However, it is unclear how the normal force, Fn, affects the material removal in MRF and how the measured ratio of drag force to normal force Fd/Fn, equivalent to coefficient of friction, is related to material removal. This work studies, for the first time for MRF, the normal force and the measured ratio Fd/Fn as a function of material mechanical properties. Experimental data were obtained by taking spots on a variety of materials including optical glasses and hard ceramics with a spot-taking machine (STM). Drag force and normal force were measured with a dual load cell. Drag force decreases linearly with increasing material hardness. In contrast, normal force increases with hardness for glasses, saturating at high hardness values for ceramics. Volumetric removal rate decreases with normal force across all materials. The measured ratio Fd/Fn shows a strong negative linear correlation with material hardness. Hard materials exhibit a low "coefficient of friction". The volumetric removal rate increases with the measured ratio Fd/Fn which is also correlated with shear stress, indicating that the measured ratio Fd/Fn is a useful measure of material removal in MRF.

Properties of the Mean Momentum Balance in Polymer Drag Reduced Channel Flow

NASA Astrophysics Data System (ADS)

White, Christopher; Dubief, Yves; Klewicki, Joseph

2014-11-01

The redistribution of mean momentum and the underlying mechanisms of the redistribution process in polymer drag reduced channel flow are investigated by employing a mean momentum equation based analysis. The work is motivated by recent studies that showed (contrary to long-held views) that polymers modify the von Karman coefficient, κ, at low drag reduction, and at some relatively high drag reduction eradicate the inertially dominated logarithmic region. Since κ is a manifestation of the underlying dynamical behaviors of wall-bounded flow, understanding how polymers modify κ is inherently important to understanding the dynamics of polymer drag reduced flow, and, consequently, the phenomenon of polymer drag reduction. The goal of the present study is to explore and quantify these effects within the framework of a mean momentum based analysis.

Thermospheric density and satellite drag modeling

NASA Astrophysics Data System (ADS)

Mehta, Piyush Mukesh

The United States depends heavily on its space infrastructure for a vast number of commercial and military applications. Space Situational Awareness (SSA) and Threat Assessment require maintaining accurate knowledge of the orbits of resident space objects (RSOs) and the associated uncertainties. Atmospheric drag is the largest source of uncertainty for low-perigee RSOs. The uncertainty stems from inaccurate modeling of neutral atmospheric mass density and inaccurate modeling of the interaction between the atmosphere and the RSO. In order to reduce the uncertainty in drag modeling, both atmospheric density and drag coefficient (CD) models need to be improved. Early atmospheric density models were developed from orbital drag data or observations of a few early compact satellites. To simplify calculations, densities derived from orbit data used a fixed CD value of 2.2 measured in a laboratory using clean surfaces. Measurements from pressure gauges obtained in the early 1990s have confirmed the adsorption of atomic oxygen on satellite surfaces. The varying levels of adsorbed oxygen along with the constantly changing atmospheric conditions cause large variations in CD with altitude and along the orbit of the satellite. Therefore, the use of a fixed CD in early development has resulted in large biases in atmospheric density models. A technique for generating corrections to empirical density models using precision orbit ephemerides (POE) as measurements in an optimal orbit determination process was recently developed. The process generates simultaneous corrections to the atmospheric density and ballistic coefficient (BC) by modeling the corrections as statistical exponentially decaying Gauss-Markov processes. The technique has been successfully implemented in generating density corrections using the CHAMP and GRACE satellites. This work examines the effectiveness, specifically the transfer of density models errors into BC estimates, of the technique using the CHAMP and

Hydrodynamic Drag Reduction

DTIC Science & Technology

2015-04-01

Computational Engineering unstructured RANS/LES/DES solver , Tenasi, was used to predict drag and simulate the free surface flow around the ACV over a...using a second-order accurate Roe approximate Riemann scheme, while viscous fluxes are evaluated using a second-order directional derivative approach...Predictions of rigid body ship motions for the SI75 container ship in incident waves and methodology for a one-way coupling of the Tenasi flow solver

A drag measurement technique for free piston shock tunnels

NASA Technical Reports Server (NTRS)

Sanderson, S. R.; Simmons, J. M.; Tuttle, S. L.

1991-01-01

A new technique is described for measuring drag with 100-microsecond rise time on a nonlifting model in a free piston shock tunnel. The technique involves interpretation of the stress waves propagating within the model and its support. A finite element representation and spectral methods are used to obtain a mean square optimal estimate of the time history of the aerodynamic loading. Thus, drag is measured instantaneously and the previous restriction caused by the mechanical time constant of balances is overcome. The effectiveness of the balance is demonstrated by measuring the drag on cones with 5 and 15 deg semi-vertex angles in nominally Mach 5.6 flow with stagnation enthalpies from 2.6 to 33 MJ/kg.

Drag, but not buoyancy, affects swim speed in captive Steller sea lions

PubMed Central

Suzuki, Ippei; Sato, Katsufumi; Fahlman, Andreas; Naito, Yasuhiko; Miyazaki, Nobuyuki; Trites, Andrew W.

2014-01-01

ABSTRACT Swimming at an optimal speed is critical for breath-hold divers seeking to maximize the time they can spend foraging underwater. Theoretical studies have predicted that the optimal swim speed for an animal while transiting to and from depth is independent of buoyancy, but is dependent on drag and metabolic rate. However, this prediction has never been experimentally tested. Our study assessed the effects of buoyancy and drag on the swim speed of three captive Steller sea lions (Eumetopias jubatus) that made 186 dives. Our study animals were trained to dive to feed at fixed depths (10–50 m) under artificially controlled buoyancy and drag conditions. Buoyancy and drag were manipulated using a pair of polyvinyl chloride (PVC) tubes attached to harnesses worn by the sea lions, and buoyancy conditions were designed to fall within the natural range of wild animals (∼12–26% subcutaneous fat). Drag conditions were changed with and without the PVC tubes, and swim speeds were recorded and compared during descent and ascent phases using an accelerometer attached to the harnesses. Generalized linear mixed-effect models with the animal as the random variable and five explanatory variables (body mass, buoyancy, dive depth, dive phase, and drag) showed that swim speed was best predicted by two variables, drag and dive phase (AIC = −139). Consistent with a previous theoretical prediction, the results of our study suggest that the optimal swim speed of Steller sea lions is a function of drag, and is independent of dive depth and buoyancy. PMID:24771620

Radiation forces on small particles in the solar system

NASA Technical Reports Server (NTRS)

Burns, J. A.; Lamy, P. L.; Soter, S.

1979-01-01

Solar radiation forces on small particles in the solar system are examined, and the resulting orbital evolution of interplanetary and circumplanetary dust is considered. An expression is derived for the effects of radiation pressure and Poynting-Robertson drag on small, spherical particles using the energy and momentum transformation laws of special relativity, and numerical examples are presented to illustrate that radiation pressure and Poynting-Robertson drag are only important for particles within a narrow size range. The orbital consequences of these radiation forces are considered both for heliocentric and planetocentric orbiting particles, and the coupling between particle sizes and dynamics is discussed. A qualitative derivation is presented for the differential Doppler effect, which is due to the differential Doppler shifting of radiation from approaching and receding solar hemispheres, and the Yarkovsky effect, which is important for rotating meter-to kilometer-sized particles, is briefly described.

Low lift-to-drag aero-assisted orbit transfer vehicles

NASA Technical Reports Server (NTRS)

Andrews, D. G.; Savage, R. T.

1984-01-01

The results of systems analysis conducted on low life drag ratio (L/D) aero-assisted orbit transfer vehicle (AOTV's) are presented. The objectives for this class of vehicle and formulate technology development plans and funding levels to bring the required technologies to readiness levels, as well as develop a credible decision data base encompassing the entire range of low L/D concepts for use in future NASA Aeroassist Orbit Transfer Vehicles studies. Each candidate low L/D concept, the aerobrake, the lifting brake, and the aeromaneuvering concept could be made to work with technologies achievable by the early 1990's. All concepts require flexible structure with flexible thermal protection system (TPS) to be successfully integrated into the shuttle orbiter for launch, all required improvements in guidance and control to fly the dispersed atmospheres at high altitude, and all concepts had potential to evolve from ground-based to space-based operations.

The computation of induced drag with nonplanar and deformed wakes

NASA Technical Reports Server (NTRS)

Kroo, Ilan; Smith, Stephen

1991-01-01

The classical calculation of inviscid drag, based on far field flow properties, is reexamined with particular attention to the nonlinear effects of wake roll-up. Based on a detailed look at nonlinear, inviscid flow theory, it is concluded that many of the classical, linear results are more general than might have been expected. Departures from the linear theory are identified and design implications are discussed. Results include the following: Wake deformation has little effect on the induced drag of a single element wing, but introduces first order corrections to the induced drag of a multi-element lifting system. Far field Trefftz-plane analysis may be used to estimate the induced drag of lifting systems, even when wake roll-up is considered, but numerical difficulties arise. The implications of several other approximations made in lifting line theory are evaluated by comparison with more refined analyses.

Variational and symplectic integrators for satellite relative orbit propagation including drag

NASA Astrophysics Data System (ADS)

Palacios, Leonel; Gurfil, Pini

2018-04-01

Orbit propagation algorithms for satellite relative motion relying on Runge-Kutta integrators are non-symplectic—a situation that leads to incorrect global behavior and degraded accuracy. Thus, attempts have been made to apply symplectic methods to integrate satellite relative motion. However, so far all these symplectic propagation schemes have not taken into account the effect of atmospheric drag. In this paper, drag-generalized symplectic and variational algorithms for satellite relative orbit propagation are developed in different reference frames, and numerical simulations with and without the effect of atmospheric drag are presented. It is also shown that high-order versions of the newly-developed variational and symplectic propagators are more accurate and are significantly faster than Runge-Kutta-based integrators, even in the presence of atmospheric drag.

Drag reduction in homogeneous turbulence by scale-dependent effective viscosity.

PubMed

Benzi, Roberto; Ching, Emily S C; Procaccia, Itamar

2004-08-01

We demonstrate, by using suitable shell models, that drag reduction in homogeneous turbulence is usefully discussed in terms of a scale-dependent effective viscosity. The essence of the phenomenon of drag reduction found in models that couple the velocity field to the polymers can be recaptured by an "equivalent" equation of motion for the velocity field alone, with a judiciously chosen scale-dependent effective viscosity that succinctly summarizes the important aspects of the interaction between the velocity and the polymer fields. Finally, we clarify the differences between drag reduction in homogeneous and in wall bounded flows.

Drag reductions obtained by modifying a box-shaped ground vehicle

NASA Technical Reports Server (NTRS)

Saltzman, E. J.; Meyer, R. R., Jr.; Lux, D. P.

1974-01-01

A box-shaped ground vehicle was used to simulate the aerodynamic drag of high volume transports, that is, delivery vans, trucks, or motor homes. The coast-down technique was used to define the drag of the original vehicle, having all square corners, and several modifications of the vehicle. Test velocities ranged up to 65 miles per hour, which provided maximum Reynolds numbers of 1 times 10 to the 7th power based on vehicle length. One combination of modifications produced a reduction in aerodynamic drag of 61 percent as compared with the original square-cornered vehicle.

Why fibers are better turbulent drag reducing agents than polymers

NASA Astrophysics Data System (ADS)

Boelens, Arnout; Muthukumar, Murugappan

2016-11-01

It is typically found in literature that fibers are not as effective as drag reducing agents as polymers. However, for low concentrations, when adding charged polymers to either distilled or salt water, it is found that polymers showing rod-like behavior are better drag reducing agents than polymers showing coil-like behavior. In this study, using hybrid Direct Numerical Simulation with Langevin dynamics, a comparison is performed between polymer and fiber stress tensors in turbulent flow. The stress tensors are found to be similar, suggesting a common drag reducing mechanism in the onset regime. Since fibers do not have an elastic backbone, this must be a viscous effect. Analysis of the viscosity tensor reveals that all terms are negligible, except the off-diagonal shear viscosity associated with rotation. Based on this analysis, we are able to explain why charged polymers showing rod-like behavior are better drag reducing agents than polymers showing coil-like behavior. Additionally, we identify the rotational orientation time as the unifying time scale setting a new time criterion for drag reduction by both flexible polymers and rigid fibers. This research was supported by NSF Grant No. DMR-1404940 and AFOSR Grant No. FA9550-14-1-0164.

Comparison of predicted and measured drag for a single-engine airplane

NASA Technical Reports Server (NTRS)

Ward, D. T.; Taylor, F. C.; Doo, J. T. P.

1985-01-01

Renewed interest in natural laminar flow (NLF) has rekindled designers' concerns that manufacturing deviations, (loss of surface contours or other surface imperfections) may destroy the effectiveness of NLF for an operational airplane. This paper reports on experimental research that compares predicted and measured boundary layer transition, total drag, and two-dimensional drag coefficients for three different wing surface conditions on an airplane typical of general aviation manufacturing technology. The three flight test phases included: (1) assessment of an unpainted airframe, (2) flight tests of the same airplane after painstakingly filling and sanding the wings to design contours, and (3) similar measurements after this airplane was painted. In each flight phase, transition locations were monitored using either sublimating chemicals or pigmented oil. As expected, total drag changes were difficult to measure. Two-dimensional drag coefficients were estimated using the Eppler-Somers code and measured with a wake rake in a method very similar to Jones' pitot traverse method. The net change in two-dimensional drag was approximately 20 counts between the unpainted airplane and the 'hand-smoothed' airplane for typical cruise flight conditions.

The Seebeck Coefficient and Phonon Drag in Silicon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mahan, Gerald; Lindsay, Lucas R.; Broido, David

2014-12-29

We present a theory of the phonon-drag Seebeck coe cient in nondegenerate semiconductors, and apply it to silicon for temperatures 30 < T < 300K. Our calculation uses only parameters from the literature, and previous calculations of the phonon lifetime. We nd excellent agreement with the measurements of Geballe and Hull [Phys.Rev. 98, 940 (1955)]. The phonon-drag term dominates at low temperature, and shows an important dependence on the dimensions of the experimental sample.

Improving the durability of a drag-reducing nanocoating by enhancing its mechanical stability.

PubMed

Cheng, Mengjiao; Zhang, Songsong; Dong, Hongyu; Han, Shihui; Wei, Hao; Shi, Feng

2015-02-25

The durability of superhydrophobic surface is a major problem to restrict industrial application of superhydrophobic materials from laboratory research, which can be attributed to a more general issue of mechanical stability for superhydrophobic coatings. Therefore, in order to handle this issue, we have fabricated a mechanically stable drag-reducing coating composed of elastic polydimethylsiloxane (PDMS) and hydrophobic copper particles on model ships, which can resist mechanical abrasion and has displayed a durable drag-reducing effect. In comparison with normal Au superhydrophobic coatings, the as-prepared PDMS/copper coatings showed durable drag reduction performance with a similar drag-reducing rate before (26%) and after (24%) mechanical abrasion. The mechanism for the enhanced mechanical stability and maintained drag reduction of the superhydrophobic surfaces was investigated through characterizations of surface morphology, surface wettability, and water adhesive force evaluation before and after abrasion. This is the first demonstration to realize the application of durable drag reduction by improving the mechanical stability of superhydrophobic coatings. We do believe that superhydrophobic surfaces with good resistance to mechanical abrasion or scratching may draw wide attention and gain significant applications with durable drag-reducing properties.

Balancing acts: drag queens, gender and faith.

PubMed

Sullivan-Blum, Constance R

2004-01-01

While engaged in research on the same-sex marriage debate in mainline denominations, I interviewed 23 LGBT Christians, four of whom were drag queens. While it is not possible to generalize from such a small sample, the drag queens in this study insist on maintaining their identity as Christians despite the hegemonic discourse that renders faith and LGBT identities mutually exclusive. They developed innovative approaches to reconciling their gender and sexual identities with their spirituality. Their innovations are potentially liberating not just for them personally, but for LGBT people generally because they challenge Christianity's rigid dichotomies of gender and sexuality.

Superconducting fluctuation current caused by gravitational drag

NASA Astrophysics Data System (ADS)

Tsuchida, Satoshi; Kuratsuji, Hiroshi

2017-12-01

We examine a possible effect of the Lense-Thirring field or gravitational drag by calculating the fluctuation current through a superconducting ring. The gravitational drag is induced by a rotating sphere, on top of which the superconducting ring is placed. The formulation is based on the Landau-Ginzburg free-energy functional of linear form. The resultant fluctuation current is shown to be greatly enhanced in the vicinity of the transition temperature, and the current also increases on increasing the winding number of the ring. These effects would provide a modest step towards magnification of tiny gravity.

Light-Drag Enhancement by a Highly Dispersive Rubidium Vapor.

PubMed

Safari, Akbar; De Leon, Israel; Mirhosseini, Mohammad; Magaña-Loaiza, Omar S; Boyd, Robert W

2016-01-08

The change in the speed of light as it propagates through a moving material has been a subject of study for almost two centuries. This phenomenon, known as the Fresnel light-drag effect, is quite small and usually requires a large interaction path length and/or a large velocity of the moving medium to be observed. Here, we show experimentally that the observed drag effect can be enhanced by over 2 orders of magnitude when the light beam propagates through a moving slow-light medium. Our results are in good agreement with the theoretical prediction, which indicates that, in the limit of large group indices, the strength of the light-drag effect is proportional to the group index of the moving medium.

Flexural phonon limited phonon drag thermopower in bilayer graphene

NASA Astrophysics Data System (ADS)

Ansari, Mohd Meenhaz; Ashraf, SSZ

2018-05-01

We investigate the phonon drag thermopower from flexural phonons as a function of electron temperature and carrier concentration in the Bloch-Gruneisen regime in non-strained bilayer graphene using Boltzmann transport equation approach. The flexural phonons are expected to be the major source of intrinsic scattering mechanism in unstrained bilayer graphene due to their large density. The flexural phonon modes dispersion relation is quadratic so these low energy flexural phonons abound at room temperature and as a result deform the bilayer graphene sheet in the out of plane direction and affects the transport properties. We also produce analytical result for phonon-drag thermopower from flexural phonons and find that phonon-drag thermopower depicts T2 dependence on temperature and n-1 on carrier concentration.

Full-Scale Wind-Tunnel Investigation of the Drag Characteristics of an HU2K Helicopter Fuselage

NASA Technical Reports Server (NTRS)

Scallion, William I.

1963-01-01

An investigation was conducted in the Langley full-scale tunnel to determine the drag characteristics of the HU2K helicopter fuselage. The effects of body shape, engine operation, appendages, and leakage on the model drag were determined. The results of the tests showed that the largest single contribution to the parasite drag was that of the rotor hub installation which produced about 80 percent of the drag of the sealed and faired production body. Fairings on the rotor hub and blade retentions, or a cleaned-up hub and retentions, appeared to be the most effective single modifications tested. The total drag of all protuberances and air leakage also contributed a major part of the drag - an 83-percent increase over the drag of the sealed and faired production body. An additional increment of drag was caused by the basic shape of the fuselage - 19 percent more than the drag obtained when the fuselage shape was extensively refaired. Another sizable increment of drag was caused by the engine oil-cooler exit which gave a drag of 8 percent of that of the sealed and faired production body.

Aerodynamic Efficiency Analysis on Modified Drag Generator of Tanker-Ship Using Symmetrical Airfoil

NASA Astrophysics Data System (ADS)

Moranova, Starida; Rahmat Hadiyatul A., S. T.; Indra Permana S., S. T.

2018-04-01

Time reduction of tanker ship spent in the sea should be applied for solving problems occured in oil and gas distribution, such as the unpunctuality of the distribution and oil spilling. The aerodynamic design for some parts that considered as drag generators is presumed to be one of the solution, utilizing our demand of the increasing speed. This paper suggests two examples of the more-aerodynamic design of a part in the tanker that is considered a drag generator, and reports the value of drag generated from the basic and the suggested aerodynamic designs. The new designs are made by adding the NACA airfoil to the cross section of the drag generator. The scenario is assumed with a 39 km/hour speed of tanker, neglecting the hydrodynamic effects occured in the tanker by cutting it at the waterline which separated the drag between air and water. The results of produced drag in each design are calculated by Computational Fluid Dynamic method.

Drag and heat flux reduction mechanism of blunted cone with aerodisks

NASA Astrophysics Data System (ADS)

Huang, Wei; Li, Lang-quan; Yan, Li; Zhang, Tian-tian

2017-09-01

The major challenge among a number of design requirements for hypersonic vehicles is the reduction of drag and aerodynamic heating. Of all these techniques of drag and heat flux reduction, application of forward facing aerospike conceived in 1950s is an effective and simpler technique to reduce the drag as well as the heat transfer rate for blunt nosed bodies at hypersonic Mach numbers. In this paper, the flow fields around a blunt cone with and without aerodisk flying at hypersonic Mach numbers are computed numerically, and the numerical simulations are conducted by specifying the freestream velocity, static pressure and static temperatures at the inlet of the computational domain with a three-dimensional, steady, Reynolds-averaged Navier-Stokes equation. An aerodisk is attached to the tip of the rod to reduce the drag and heat flux further. The influences of the length of rod and the diameter of aerodisk on the drag and heat flux reduction mechanism are analyzed comprehensively, and eight configurations are taken into consideration in the current study. The obtained results show that for all aerodisks, the reduction in drag of the blunt body is proportional to the extent of the recirculation dead air region. For long rods, the aerodisk is found not that beneficial in reducing the drag, and an aerodisk is more effective than an aerospike. The spike produces a region of recirculation separated flow that shields the blunt-nosed body from the incoming flow, and the recirculation region is formed around the root of the spike up to the reattachment point of the flow at the shoulder of the blunt body. The dynamic pressure in the recirculation area is highly reduced and thus leads to the decrease in drag and heat load on the surface of the blunt body. Because of the reattachment of the shear layer on the shoulder of the blunt body, the pressure near that point becomes large.

Normal Force and Drag Force in Magnetorheological Finishing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miao, C.; Shafrir, S.N.; Lambropoulos, J.C.

2010-01-13

The material removal in magnetorheological finishing (MRF) is known to be controlled by shear stress, tau, which equals drag force, Fd, divided by spot area, As. However, it is unclear how the normal force, Fn, affects the material removal in MRF and how the measured ratio of drag force to normal force Fd/Fn, equivalent to coefficient of friction, is related to material removal. This work studies, for the first time for MRF, the normal force and the measured ratio Fd/Fn as a function of material mechanical properties. Experimental data were obtained by taking spots on a variety of materials includingmore » optical glasses and hard ceramics with a spot-taking machine (STM). Drag force and normal force were measured with a dual load cell. Drag force decreases linearly with increasing material hardness. In contrast, normal force increases with hardness for glasses, saturating at high hardness values for ceramics. Volumetric removal rate decreases with normal force across all materials. The measured ratio Fd/Fn shows a strong negative linear correlation with material hardness. Hard materials exhibit a low “coefficient of friction”. The volumetric removal rate increases with the measured ratio Fd/Fn which is also correlated with shear stress, indicating that the measured ratio Fd/Fn is a useful measure of material removal in MRF.« less

Large Fizeau's light-dragging effect in a moving electromagnetically induced transparent medium.

PubMed

Kuan, Pei-Chen; Huang, Chang; Chan, Wei Sheng; Kosen, Sandoko; Lan, Shau-Yu

2016-10-03

As one of the most influential experiments on the development of modern macroscopic theory from Newtonian mechanics to Einstein's special theory of relativity, the phenomenon of light dragging in a moving medium has been discussed and observed extensively in different types of systems. To have a significant dragging effect, the long duration of light travelling in the medium is preferred. Here we demonstrate a light-dragging experiment in an electromagnetically induced transparent cold atomic ensemble and enhance the dragging effect by at least three orders of magnitude compared with the previous experiments. With a large enhancement of the dragging effect, we realize an atom-based velocimeter that has a sensitivity two orders of magnitude higher than the velocity width of the atomic medium used. Such a demonstration could pave the way for motional sensing using the collective state of atoms in a room temperature vapour cell or solid state material.

Reduction of turbulent skin-friction drag by oscillating discs

NASA Astrophysics Data System (ADS)

Wise, Daniel; Ricco, Pierre

2013-11-01

A new drag-reduction method, based on the active technique proposed by Ricco & Hahn (2013), i.e. steadily rotating flush-mounted discs, is studied by DNS. The effect of sinusoidally oscillating discs on the turbulent channel-flow drag is investigated at Reτ = 180 , based on the friction velocity of the stationary-wall case and the half channel height. A parametric investigation on the disc diameter, tip velocity and oscillation period yielded a maximum drag reduction of 18.5%. Regions of net power saved, calculated by considering the power spent to enforce the disc motion against the viscous resistance of the fluid, are found to reach up to 6.5% for low disc tip velocities. Significantly, the characteristic time-scale for the oscillating disc forcing is double that for the steadily rotating discs, representing a further step towards industrial implementation. The oscillating disc forcing, similar to the steadily rotating disc forcing, creates streamwise-elongated structures between the discs. These structures - largely unaffected by the periodic wall forcing and persisting throughout the entire period of the oscillation - are the main contributor to the additional Reynolds stresses term created by the disc forcing, and are important for the drag reduction mechanism.

Moffies, artists, and queens: race and the production of South African gay male drag.

PubMed

Swarr, Amanda Lock

2004-01-01

This article draws on seventeen months of ethnographic fieldwork in South Africa to explore the experiences of urban and township drag performers. I show that two distinct sex-gender-sexuality systems have emerged based in the sociopolitical history of South Africa, and I argue that urban drag produces race oppositionally and examine how township femininity creates raced forms of gender, sex, and sexuality. Contemporary South African drag foregrounds the performativity and constitution of race and gender. My analysis attempts to challenge definitions of "drag" and "audience," suggesting the necessity for an integrated reconceptualization of drag studies.

Optimizing Geometry Mediated Skin Friction Drag on Riblet-Textured Surfaces

NASA Astrophysics Data System (ADS)

Raayai, Shabnam; McKinley, Gareth

2016-11-01

Micro-scale riblets have been shown to modify the skin friction drag on patterned surfaces. Shark skin is widely known as a natural example of this passive drag reduction mechanism and artificial riblet tapes have been previously used in the America's Cups tournament resulting in a 1987 victory. Previous experiments with riblet surfaces in turbulent boundary layer flow have shown 4-8% reduction in the skin friction drag. Our computations with sinusoidal riblet surfaces in high Reynolds number laminar boundary layer flow and experiments with V-grooves in laminar Taylor-Couette flow also show that the reduction in skin friction can be substantial and depends on the spacing and height of the riblets. In the boundary layer setting, this frictional reduction is also a function of the length of the plate in the flow direction, while in the Taylor Couette setting it depends on the gap size. In the current work, we use scaling arguments and conformal mapping to establish a simplified theory for laminar flow over V-groove riblets and explore the self-similarity of the velocity contours near the patterned surface. We combine these arguments with theoretical and numerical calculations using Matlab and OpenFOAM to show that the drag reduction achievable in laminar flow over riblet surfaces depends on a rescaled form of the Reynolds number combined with the aspect ratio of the texture (defined in terms of the ratio of the height to spacing of the riblets). We then use these results to explain the underlying physical mechanisms driving frictional drag reduction and offer recommendations for designing low drag surfaces.

WAVDRAG- ZERO-LIFT WAVE DRAG OF COMPLEX AIRCRAFT CONFIGURATIONS

NASA Technical Reports Server (NTRS)

Craidon, C. B.

1994-01-01

WAVDRAG calculates the supersonic zero-lift wave drag of complex aircraft configurations. The numerical model of an aircraft is used throughout the design process from concept to manufacturing. WAVDRAG incorporates extended geometric input capabilities to permit use of a more accurate mathematical model. With WAVDRAG, the engineer can define aircraft components as fusiform or nonfusiform in terms of non-intersecting contours in any direction or more traditional parallel contours. In addition, laterally asymmetric configurations can be simulated. The calculations in WAVDRAG are based on Whitcomb's area-rule computation of equivalent-bodies, with modifications for supersonic speed. Instead of using a single equivalent-body, WAVDRAG calculates a series of equivalent-bodies, one for each roll angle. The total aircraft configuration wave drag is the integrated average of the equivalent-body wave drags through the full roll range of 360 degrees. WAVDRAG currently accepts up to 30 user-defined components containing a maximum of 50 contours as geometric input. Each contour contains a maximum of 50 points. The Mach number, angle-of-attack, and coordinates of angle-of-attack rotation are also input. The program warns of any fusiform-body line segments having a slope larger than the Mach angle. WAVDRAG calculates total drag and the wave-drag coefficient of the specified aircraft configuration. WAVDRAG is written in FORTRAN 77 for batch execution and has been implemented on a CDC CYBER 170 series computer with a central memory requirement of approximately 63K (octal) of 60 bit words. This program was developed in 1983.

Localized Density/Drag Prediction for Improved Onboard Orbit Propagation

DTIC Science & Technology

2009-09-01

Localized Density/Drag Prediction for Improved Onboard Orbit Propagation Nathan B. Stastny, Frank R. Chavez, Chin Lin, T. Alan Lovell , Robert A...Terrestrial Physics, Vol. 70, 774-793, 2008 3. Storz, M.F, Bowman, B.R., Branson, J.I., High Accuracy Satellite Drag Model (HASDM), AIAA/ AAS ...Geomagnetic Indices, AIAA/ AAS Astrodynamics Specialist Conference, Honolulu, HI, Aug. 2008 5. Bruinsma, S., Biancale, R., Total Densities Derived from

Using an Extended Dynamic Drag-and-Drop Assistive Program to Assist People with Multiple Disabilities and Minimal Motor Control to Improve Computer Drag-and-Drop Ability through a Mouse Wheel

ERIC Educational Resources Information Center

Shih, Ching-Hsiang

2012-01-01

Software technology is adopted by the current research to improve the Drag-and-Drop abilities of two people with multiple disabilities and minimal motor control. This goal was realized through a Dynamic Drag-and-Drop Assistive Program (DDnDAP) in which the complex dragging process is replaced by simply poking the mouse wheel and clicking. However,…

Flagging versus dragging as sampling methods for nymphal Ixodes scapularis (Acari: Ixodidae)

USGS Publications Warehouse

Rulison, Eric L.; Kuczaj, Isis; Pang, Genevieve; Hickling, Graham J.; Tsao, Jean I.; Ginsberg, Howard S.

2013-01-01

The nymphal stage of the blacklegged tick, Ixodes scapularis (Acari: Ixodidae), is responsible for most transmission of Borrelia burgdorferi, the etiologic agent of Lyme disease, to humans in North America. From 2010 to fall of 2012, we compared two commonly used techniques, flagging and dragging, as sampling methods for nymphal I. scapularis at three sites, each with multiple sampling arrays (grids), in the eastern and central United States. Flagging and dragging collected comparable numbers of nymphs, with no consistent differences between methods. Dragging collected more nymphs than flagging in some samples, but these differences were not consistent among sites or sampling years. The ratio of nymphs collected by flagging vs dragging was not significantly related to shrub density, so habitat type did not have a strong effect on the relative efficacy of these methods. Therefore, although dragging collected more ticks in a few cases, the numbers collected by each method were so variable that neither technique had a clear advantage for sampling nymphal I. scapularis.

Acoustic Liner Drag: Measurements on Novel Facesheet Perforate Geometries

NASA Technical Reports Server (NTRS)

Howerton, Brian M.; Jones, Michael G.

2016-01-01

Interest in characterization of the aerodynamic drag of acoustic liners has increased in the past several years. This paper details experiments in the NASA Langley Grazing Flow Impedance Tube to quantify the relative drag of several perforate-over-honeycomb liner configurations at flow speeds of centerline flow Mach number equals 0.3 and 0.5. Various perforate geometries and orientations are investigated to determine their resistance factors using a static pressure drop approach. Comparison of these resistance factors gives a relative measurement of liner drag. For these same flow conditions, acoustic measurements are performed with tonal excitation from 400 to 3000 hertz at source sound pressure levels of 140 and 150 decibels. Educed impedance and attenuation spectra are used to determine the impact of variations in perforate geometry on acoustic performance.

Minimization theory of induced drag subject to constraint conditions

NASA Technical Reports Server (NTRS)

Deyoung, J.

1979-01-01

Exact analytical solutions in terms of induced drag influence coefficients can be attained which define the spanwise loading with minimized induced drag, subject to specified constraint conditions, for any nonplanar wing shape or number of lift plus wing bending moment about a given wing span station. Example applications of the theory are made to a biplane, a wing in ground effect, a cruciform wing, a V-wing, a planar-wing winglet, and linked wingtips in formation flying. For minimal induced drag, the spanwise loading, relative to elliptic, is outboard for the biplane and is inboard for the wing in ground effect and for the planar-wing winglet. A spinoff of the triplane solution provides mathematically exact equations for downwash and sidewash about a planar vorticity sheet having an arbitrary loading distribution.

Turbulent Flow Enhancement by Polyelectrolyte Additives: Mechanistic Implications for Drag Reduction.

NASA Astrophysics Data System (ADS)

Wagger, David Leonard

1992-01-01

The drag reduction phenomenon was experimentally studied in two pipes, of diameters 1.46 and 1.02 cm, using seven polyelectrolytic HPAM additives, with molecular weights from 1 to 20 times 10^6 g/mole and degree of backbone hydrolysis from 8 to 60%, at concentrations from 1 to 1000 wppm, in saline solutions containing from 0.3 to 0.00001 N NaCl. Both laminar and turbulent flow behavior were greatly influenced by salinity-induced changes in the initial conformation of the HPAM additives. Initially collapsed, random-coiling conformations exhibited Newtonian laminar flow and Type-A turbulent drag reduction, while initially extended conformations exhibited shear-thinning in laminar flow and Type-B turbulent drag reduction. The gross-flow physics of Type-B drag reduction were delineated. A characteristic "ladder" structure prevailed, with polymeric regime segments that were roughly parallel to, but shifted upward from, the Prandtl-Karman line. In the polymeric regime, both Type-A fan and Type -B ladder structures were essentially independent of pipe diameter, and were scaled by the wall shear stress. The wall shear stress also scaled degradation during drag reduction. New onset and slope increment correlations were presented for Type-A drag reduction by HPAM additives. In Type-B drag reduction, flow enhancement was found proportional to additive concentration, and the intrinsic slip, Sigma = S^'/(c/M _{rm w}), varied roughly as the third power of backbone chain links N_ {rm bb}. New intrinsic slip and retro-onset correlations were presented for Type-B drag reduction by HPAM additives. Analysis of Type-B literature revealed a wide range of additive efficacies, with specific slips S^'/c from 0.0001 to 4. For the most effective additives, HPAM and asbestos fibers, the additive-pervaded volume fraction per unit flow enhancement, X_{rm v} /S^' ~ 3000, implied that these additives align during drag reduction. The slip ratio R_{rm sc}, which is the relative flow enhancement

The drag force on a subsonic projectile in a fluid complex plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ivlev, A. V.; Zhukhovitskii, D. I.

2012-09-15

The incompressible Navier-Stokes equation is employed to describe a subsonic particle flow induced in complex plasmas by a moving projectile. Drag forces acting on the projectile in different flow regimes are calculated. It is shown that, along with the regular neutral gas drag, there is an additional force exerted on the projectile due to dissipation in the surrounding particle fluid. This additional force provides significant contribution to the total drag.

Measuring the force of drag on air sheared sessile drops

NASA Astrophysics Data System (ADS)

Milne, Andrew J. B.; Fleck, Brian; Amirfazli, Alidad

2012-11-01

To blow a drop along or off of a surface (i.e. to shed the drop), the drag force on the drop (based on flow conditions, drop shape, and fluid properties) must overcome the adhesion force between the drop and the surface (based on surface tension, drop shape, and contact angle). While the shedding of sessile drops by shear flow has been studied [Milne, A. J. B. & Amirfazli, A. Langmuir 25, 14155 (2009).], no independent measurements of the drag or adhesion forces have been made. Likewise, analytic predictions are limited to hemispherical drops and low air velocities. We present, therefore, measurements of the drag force on sessile drops at air velocities up to the point of incipient motion. Measurements were made using a modified floating element shear sensor in a laminar low speed wind tunnel to record drag force over the surface with the drop absent, and over the combined system of the surface and drop partially immersed in the boundary layer. Surfaces of different wettabilities were used to study the effects of drop shape and contact angles, with drop volume ranged between approximately 10 and 100 microlitres. The drag force for incipient motion (which by definition equals the maximum of the adhesion force) is compared to simplified models for drop adhesion such as that of Furmidge

Simulating Electrophoresis with Discrete Charge and Drag

NASA Astrophysics Data System (ADS)

Mowitz, Aaron J.; Witten, Thomas A.

A charged asymmetric rigid cluster of colloidal particles in saline solution can respond in exotic ways to an electric field: it may spin or move transversely. These distinctive motions arise from the drag force of the neutralizing countercharge surrounding the cluster. Because of this drag, calculating the motion of arbitrary asymmetric objects with nonuniform charge is impractical by conventional methods. Here we present a new method of simulating electrophoresis, in which we replace the continuous object and the surrounding countercharge with discrete point-draggers, called Stokeslets. The balance of forces imposes a linear, self-consistent relation among the drag and Coulomb forces on the Stokeslets, which allows us to easily determine the object's motion via matrix inversion. By explicitly enforcing charge+countercharge neutrality, the simulation recovers the distinctive features of electrophoretic motion to few-percent accuracy using as few as 1000 Stokeslets. In particular, for uniformly charged objects, we observe the characteristic Smoluchowski independence of mobility on object size and shape. We then discuss electrophoretic motion of asymmetric objects, where our simulation method is particularly advantageous. This work is supported by a Grant from the US-Israel Binational Science Foundation.

Summary of Data from the First AIAA CFD Drag Prediction Workshop

NASA Technical Reports Server (NTRS)

Levy, David W.; Zickuhr, Tom; Vassberg, John; Agrawal, Shreekant; Wahls, Richard A.; Pirzadeh, Shahyar; Hemsch, Michael J.

2002-01-01

The results from the first AIAA CFD Drag Prediction Workshop are summarized. The workshop was designed specifically to assess the state-of-the-art of computational fluid dynamics methods for force and moment prediction. An impartial forum was provided to evaluate the effectiveness of existing computer codes and modeling techniques, and to identify areas needing additional research and development. The subject of the study was the DLR-F4 wing-body configuration, which is representative of transport aircraft designed for transonic flight. Specific test cases were required so that valid comparisons could be made. Optional test cases included constant-C(sub L) drag-rise predictions typically used in airplane design by industry. Results are compared to experimental data from three wind tunnel tests. A total of 18 international participants using 14 different codes submitted data to the workshop. No particular grid type or turbulence model was more accurate, when compared to each other, or to wind tunnel data. Most of the results overpredicted C(sub Lo) and C(sub Do), but induced drag (dC(sub D)/dC(sub L)(exp 2)) agreed fairly well. Drag rise at high Mach number was underpredicted, however, especially at high C(sub L). On average, the drag data were fairly accurate, but the scatter was greater than desired. The results show that well-validated Reynolds-Averaged Navier-Stokes CFD methods are sufficiently accurate to make design decisions based on predicted drag.

Light aircraft lift, drag, and moment prediction: A review and analysis

NASA Technical Reports Server (NTRS)

Smetana, F. O.; Summey, D. C.; Smith, N. S.; Carden, R. K.

1975-01-01

The historical development of analytical methods for predicting the lift, drag, and pitching moment of complete light aircraft configurations in cruising flight is reviewed. Theoretical methods, based in part on techniques described in the literature and in part on original work, are developed. These methods form the basis for understanding the computer programs given to: (1) compute the lift, drag, and moment of conventional airfoils, (2) extend these two-dimensional characteristics to three dimensions for moderate-to-high aspect ratio unswept wings, (3) plot complete configurations, (4) convert the fuselage geometric data to the correct input format, (5) compute the fuselage lift and drag, (6) compute the lift and moment of symmetrical airfoils to M = 1.0 by a simplified semi-empirical procedure, and (7) compute, in closed form, the pressure distribution over a prolate spheroid at alpha = 0. Comparisons of the predictions with experiment indicate excellent lift and drag agreement for conventional airfoils and wings. Limited comparisons of body-alone drag characteristics yield reasonable agreement. Also included are discussions for interference effects and techniques for summing the results above to obtain predictions for complete configurations.

On the relations between cratonic lithosphere thickness, plate motions, and basal drag

USGS Publications Warehouse

Artemieva, I.M.; Mooney, W.D.

2002-01-01

An overview of seismic, thermal, and petrological evidence on the structure of Precambrian lithosphere suggests that its local maximum thickness is highly variable (140-350 km), with a bimodal distribution for Archean cratons (200-220 km and 300-350 km). We discuss the origin of such large differences in lithospheric thickness, and propose that the lithospheric base can have large depth variations over short distances. The topography of Bryce Canyon (western USA) is proposed as an inverted analog of the base of the lithosphere. The horizontal and vertical dimensions of Archean cratons are strongly correlated: larger cratons have thicker lithosphere. Analysis of the bimodal distribution of lithospheric thickness in Archean cratons shows that the "critical" surface area for cratons to have thick (>300 km) keels is >6-8 ?? 106 km2 . Extrapolation of the linear trend between Archean lithospheric thickness and cratonic area to zero area yields a thickness of 180 km. This implies that the reworking of Archean crust should be accompanied by thinning and reworking of the entire lithospheric column to a thickness of 180 km in accord with thickness estimates for Proterozoic lithosphere. Likewise, extrapolation of the same trend to the size equal to the total area of all Archean cratons implies that the lithospheric thickness of a hypothesized early Archean supercontinent could have been 350-450 km decreasing to 280-400 km for Gondwanaland. We evaluate the basal drag model as a possible mechanism that may thin the cratonic lithosphere. Inverse correlations are found between lithospheric thickness and (a) fractional subduction length and (b) the effective ridge length. In agreement with theoretical predictions, lithospheric thickness of Archean keels is proportional to the square root of the ratio of the craton length (along the direction of plate motion) to the plate velocity. Large cratons with thick keels and low plate velocities are less eroded by basal drag than small

Shell model for drag reduction with polymer additives in homogeneous turbulence.

PubMed

Benzi, Roberto; De Angelis, Elisabetta; Govindarajan, Rama; Procaccia, Itamar

2003-07-01

Recent direct numerical simulations of the finite-extensibility nonlinear elastic dumbbell model with the Peterlin approximation of non-Newtonian hydrodynamics revealed that the phenomenon of drag reduction by polymer additives exists (albeit in reduced form) also in homogeneous turbulence. We use here a simple shell model for homogeneous viscoelastic flows, which recaptures the essential observations of the full simulations. The simplicity of the shell model allows us to offer a transparent explanation of the main observations. It is shown that the mechanism for drag reduction operates mainly on large scales. Understanding the mechanism allows us to predict how the amount of drag reduction depends on the various parameters in the model. The main conclusion is that drag reduction is not a universal phenomenon; it peaks in a window of parameters such as the Reynolds number and the relaxation rate of the polymer.

Simplified Models for the Drag Coefficient of a Pitched Baseball

ERIC Educational Resources Information Center

Kagan, David; Nathan, Alan M.

2014-01-01

The classic experiment to measure the drag coefficient involves dropping coffee filters. Wouldn't it be more fun to try something different? In fact, an experiment on the drag force is conducted nearly 4000 times a day during the baseball season and you have free access to this PITCHf/x data!

Influence of droplet spacing on drag coefficient in nonevaporating, monodisperse streams

NASA Astrophysics Data System (ADS)

Mulholland, J. A.; Srivastava, R. K.; Wendt, J. O. L.

1988-10-01

Trajectory measurements on single, monodisperse, nonevaporating droplet streams whose droplet size, velocity, and spacing were varied to yield initial Re numbers in the 90-290 range are presently used to ascertain the influence of droplet spacing on the drag coefficient of individual drops injected into a quiescent environment. A trajectory model containing the local drag coefficient was fitted to the experimental data by a nonlinear regression; over 40 additional trajectories were predicted with acceptable accuracy. This formulation will aid the computation of waste-droplet drag in flames for improved combustion-generated pollutant predictions.

Departure of microscopic friction from macroscopic drag in molecular fluid dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hanasaki, Itsuo; Fujiwara, Daiki; Kawano, Satoyuki, E-mail: kawano@me.es.osaka-u.ac.jp

2016-03-07

Friction coefficient of the Langevin equation and drag of spherical macroscopic objects in steady flow at low Reynolds numbers are usually regarded as equivalent. We show that the microscopic friction can be different from the macroscopic drag when the mass is taken into account for particles with comparable scale to the surrounding fluid molecules. We illustrate it numerically by molecular dynamics simulation of chloride ion in water. Friction variation by the atomistic mass effect beyond the Langevin regime can be of use in the drag reduction technology as well as the electro or thermophoresis.

Study of Aerodynamic Drag Reduction on a Full-Scale Tractor-Trailer

DOT National Transportation Integrated Search

1976-04-01

Aerodynamic drag tests were performed on a tractor-trailer combination using the coast-down method on a smooth, nearly level runway. The tests included an investigation of drag reduction obtained with add-on devices that are commercially available or...

The Effects of Surface Waviness and of Rib Stitching on Wing Drag

NASA Technical Reports Server (NTRS)

Hood, Manley J

1939-01-01

Surface waviness and rib stitching have been investigated as part of a series of tests to determine the effects on wing drag of common surface irregularities. The tests were made in the N.A.C.A. 8-foot high-speed wind tunnel at Reynolds Numbers up to 17,000,000. The results of the tests showed that the waviness common to airplane wings will cause no serious increase in drag unless the waviness exists on the forward part of the wing, where it may cause premature transition or premature compressibility effects. Waves 3 inches wide and 0.048 inch high, for example, increased the drag 1 percent when they covered the rear 67 percent of both surfaces and 10 percent when they covered the rear 92 percent. A single wave 3 inches wide and only 0.020 inch high at the 10.5-percent-chord point on the upper surface caused transition to occur on the wave and increased the drag 6 percent. Rib stitching increased the drag 7 percent when the rib spacing was 6 inches; the drag increment was proportional to the number of ribs for wider spacings. About one-third of the increase was due to premature transition at the forward ends of the stitching.

Atmospheric drag model calibrations for spacecraft lifetime prediction

NASA Technical Reports Server (NTRS)

Binebrink, A. L.; Radomski, M. S.; Samii, M. V.

1989-01-01

Although solar activity prediction uncertainty normally dominates decay prediction error budget for near-Earth spacecraft, the effect of drag force modeling errors for given levels of solar activity needs to be considered. Two atmospheric density models, the modified Harris-Priester model and the Jacchia-Roberts model, to reproduce the decay histories of the Solar Mesosphere Explorer (SME) and Solar Maximum Mission (SMM) spacecraft in the 490- to 540-kilometer altitude range were analyzed. Historical solar activity data were used in the input to the density computations. For each spacecraft and atmospheric model, a drag scaling adjustment factor was determined for a high-solar-activity year, such that the observed annual decay in the mean semimajor axis was reproduced by an averaged variation-of-parameters (VOP) orbit propagation. The SME (SMM) calibration was performed using calendar year 1983 (1982). The resulting calibration factors differ by 20 to 40 percent from the predictions of the prelaunch ballistic coefficients. The orbit propagations for each spacecraft were extended to the middle of 1988 using the calibrated drag models. For the Jaccia-Roberts density model, the observed decay in the mean semimajor axis of SME (SMM) over the 4.5-year (5.5-year) predictive period was reproduced to within 1.5 (4.4) percent. The corresponding figure for the Harris-Priester model was 8.6 (20.6) percent. Detailed results and conclusions regarding the importance of accurate drag force modeling for lifetime predictions are presented.

Transonic Drag Prediction Using an Unstructured Multigrid Solver

NASA Technical Reports Server (NTRS)

Mavriplis, D. J.; Levy, David W.

2001-01-01

This paper summarizes the results obtained with the NSU-3D unstructured multigrid solver for the AIAA Drag Prediction Workshop held in Anaheim, CA, June 2001. The test case for the workshop consists of a wing-body configuration at transonic flow conditions. Flow analyses for a complete test matrix of lift coefficient values and Mach numbers at a constant Reynolds number are performed, thus producing a set of drag polars and drag rise curves which are compared with experimental data. Results were obtained independently by both authors using an identical baseline grid and different refined grids. Most cases were run in parallel on commodity cluster-type machines while the largest cases were run on an SGI Origin machine using 128 processors. The objective of this paper is to study the accuracy of the subject unstructured grid solver for predicting drag in the transonic cruise regime, to assess the efficiency of the method in terms of convergence, cpu time, and memory, and to determine the effects of grid resolution on this predictive ability and its computational efficiency. A good predictive ability is demonstrated over a wide range of conditions, although accuracy was found to degrade for cases at higher Mach numbers and lift values where increasing amounts of flow separation occur. The ability to rapidly compute large numbers of cases at varying flow conditions using an unstructured solver on inexpensive clusters of commodity computers is also demonstrated.

PIV Measurements of Turbulent Pipe Flow with Drag-Reducing Megasupramolecules

NASA Astrophysics Data System (ADS)

Huynh, David; McMullen, Ryan; McKeon, Beverley; Lhota, Redmond; Wei, Ming-Hsin; Kornfield, Julia

2016-11-01

Toms (1948) was the first to observe that dissolving small amounts of high-molecular weight (HMW) polymers into a liquid can drastically reduce turbulent drag. Ever since, studying polymers in turbulence has been of great fundamental interest, as it can potentially provide insight into the self-sustaining mechanisms of wall turbulence. HMW polymers commonly employed for drag-reduction studies are plagued by chain scission due to the high shear rates accompanying turbulent flow at practical Reynolds numbers (Re); this shear degradation reduces the length of the polymer molecules, diminishing their effectiveness for drag-reduction. However, Wei et al. (2015) have recently developed "megasupramolecules" that perform comparably to traditional HMW polymers and circumvent the shear degradation problem by using end-associating polymers that can break and reassociate reversibly. Particle image velocimetry is used in specialized turbulent pipe flow experiments in the range Re 7.5x104-1.2x105 to investigate and compare the drag and turbulence characteristics of the (Newtonian) baseline, traditional HMW polymer solutions, and megrasupramolecules. The support of The Dow Corporation is gratefully acknowledged.

Numerical Simulations for Turbulent Drag Reduction Using Liquid Infused Surfaces

NASA Astrophysics Data System (ADS)

Arenas-Navarro, Isnardo

Numerical simulations of the turbulent flow over Super Hydrophobic and Liquid Infused Surfaces have been performed in this work. Three different textured surfaces have been considered: longitudinal square bars, transversal square bars and staggered cubes. The numerical code combines an immersed boundary method to mimic the substrate and a level set method to track the interface. Liquid Infused Surfaces reduce the drag by locking a lubricant within structured roughness to facilitate a slip velocity at the surface interface. The conceptual idea is similar to Super Hydrophobic Surfaces, which rely on a lubricant air layer, whereas liquid-infused surfaces use a preferentially wetting liquid lubricant to create a fluid-fluid interface. This slipping interface has been shown to be an effective method of passively reducing skin friction drag in turbulent flows. Details are given on the effect of the viscosity ratio between the two fluids and the dynamics of the interface on drag reduction. An attempt has been made to reconcile Super-Hydrophobic, Liquid Infused and rough wall under the same framework by correlating the drag to the wall normal velocity fluctuations.

Flexible conformable hydrophobized surfaces for turbulent flow drag reduction

NASA Astrophysics Data System (ADS)

Brennan, Joseph C.; Geraldi, Nicasio R.; Morris, Robert H.; Fairhurst, David J.; McHale, Glen; Newton, Michael I.

2015-05-01

In recent years extensive work has been focused onto using superhydrophobic surfaces for drag reduction applications. Superhydrophobic surfaces retain a gas layer, called a plastron, when submerged underwater in the Cassie-Baxter state with water in contact with the tops of surface roughness features. In this state the plastron allows slip to occur across the surface which results in a drag reduction. In this work we report flexible and relatively large area superhydrophobic surfaces produced using two different methods: Large roughness features were created by electrodeposition on copper meshes; Small roughness features were created by embedding carbon nanoparticles (soot) into Polydimethylsiloxane (PDMS). Both samples were made into cylinders with a diameter under 12 mm. To characterize the samples, scanning electron microscope (SEM) images and confocal microscope images were taken. The confocal microscope images were taken with each sample submerged in water to show the extent of the plastron. The hydrophobized electrodeposited copper mesh cylinders showed drag reductions of up to 32% when comparing the superhydrophobic state with a wetted out state. The soot covered cylinders achieved a 30% drag reduction when comparing the superhydrophobic state to a plain cylinder. These results were obtained for turbulent flows with Reynolds numbers 10,000 to 32,500.

Flexible conformable hydrophobized surfaces for turbulent flow drag reduction

PubMed Central

Brennan, Joseph C; Geraldi, Nicasio R; Morris, Robert H; Fairhurst, David J; McHale, Glen; Newton, Michael I

2015-01-01

In recent years extensive work has been focused onto using superhydrophobic surfaces for drag reduction applications. Superhydrophobic surfaces retain a gas layer, called a plastron, when submerged underwater in the Cassie-Baxter state with water in contact with the tops of surface roughness features. In this state the plastron allows slip to occur across the surface which results in a drag reduction. In this work we report flexible and relatively large area superhydrophobic surfaces produced using two different methods: Large roughness features were created by electrodeposition on copper meshes; Small roughness features were created by embedding carbon nanoparticles (soot) into Polydimethylsiloxane (PDMS). Both samples were made into cylinders with a diameter under 12 mm. To characterize the samples, scanning electron microscope (SEM) images and confocal microscope images were taken. The confocal microscope images were taken with each sample submerged in water to show the extent of the plastron. The hydrophobized electrodeposited copper mesh cylinders showed drag reductions of up to 32% when comparing the superhydrophobic state with a wetted out state. The soot covered cylinders achieved a 30% drag reduction when comparing the superhydrophobic state to a plain cylinder. These results were obtained for turbulent flows with Reynolds numbers 10,000 to 32,500. PMID:25975704

Evaluation of Aerodynamic Drag and Torque for External Tanks in Low Earth Orbit

PubMed Central

Stone, William C.; Witzgall, Christoph

2006-01-01

A numerical procedure is described in which the aerodynamic drag and torque in low Earth orbit are calculated for a prototype Space Shuttle external tank and its components, the “LO2” and “LH2” tanks, carrying liquid oxygen and hydrogen, respectively, for any given angle of attack. Calculations assume the hypersonic limit of free molecular flow theory. Each shell of revolution is assumed to be described by a series of parametric equations for their respective contours. It is discretized into circular cross sections perpendicular to the axis of revolution, which yield a series of ellipses when projected according to the given angle of attack. The drag profile, that is, the projection of the entire shell is approximated by the convex envelope of those ellipses. The area of the drag profile, that is, the drag area, and its center of area moment, that is, the drag center, are then calculated and permit determination of the drag vector and the eccentricity vector from the center of gravity of the shell to the drag center. The aerodynamic torque is obtained as the cross product of those vectors. The tanks are assumed to be either evacuated or pressurized with a uniform internal gas distribution: dynamic shifting of the tank center of mass due to residual propellant sloshing is not considered. PMID:27274926

Experimental trim drag values for conventional and supercritical wings. M.S. Thesis

NASA Technical Reports Server (NTRS)

Jacobs, P. F.

1981-01-01

Supercritical wings were studied to determine whether they incur higher trim drag values at cruise conditions than wide body technology wings. Relative trim drag increments were measured in an experimental wind tunnel investigation. The tests utilized high aspect ratio supercritical wing and a wide body wing in conjunction with five different horizontal tail configurations, mounted on a representative wide body fuselage. The three low tail configurations and two T tail configurations were chosen to measure the effects on horizontal tail size, location, and camber on the trim drag increments for the two wings. The increase in performance (lift to drag ratio) for supercritical wing over the wide body wing was 11 percent for both the optimum low tail and T tail configurations.

Real-Time Adaptive Least-Squares Drag Minimization for Performance Adaptive Aeroelastic Wing

NASA Technical Reports Server (NTRS)

Ferrier, Yvonne L.; Nguyen, Nhan T.; Ting, Eric

2016-01-01

This paper contains a simulation study of a real-time adaptive least-squares drag minimization algorithm for an aeroelastic model of a flexible wing aircraft. The aircraft model is based on the NASA Generic Transport Model (GTM). The wing structures incorporate a novel aerodynamic control surface known as the Variable Camber Continuous Trailing Edge Flap (VCCTEF). The drag minimization algorithm uses the Newton-Raphson method to find the optimal VCCTEF deflections for minimum drag in the context of an altitude-hold flight control mode at cruise conditions. The aerodynamic coefficient parameters used in this optimization method are identified in real-time using Recursive Least Squares (RLS). The results demonstrate the potential of the VCCTEF to improve aerodynamic efficiency for drag minimization for transport aircraft.

Translational viscous drags of an ellipsoid straddling an interface between two fluids.

PubMed

Boniello, Giuseppe; Stocco, Antonio; Gross, Michel; In, Martin; Blanc, Christophe; Nobili, Maurizio

2016-07-01

We study the dynamics of individual polystyrene ellipsoids of different aspect ratios trapped at the air-water interface. Using particle tracking and in situ vertical scanning interferometry techniques we are able to measure translational drags and the protrusion in air of the ellipsoids. We report that translational drags on the ellipsoid are unexpectedly enhanced: despite the fact that a noticeable part of the ellipsoid is in air, drags are found larger than the bulk one in water.

Drag reduction by herringbone riblet texture in direct numerical simulations of turbulent channel flow

NASA Astrophysics Data System (ADS)

Benschop, H. O. G.; Breugem, W.-P.

2017-08-01

A bird-feather-inspired herringbone riblet texture was investigated for turbulent drag reduction. The texture consists of blade riblets in a converging/diverging or herringbone pattern with spanwise wavelength Λf. The aim is to quantify the drag change for this texture as compared to a smooth wall and to study the underlying mechanisms. To that purpose, direct numerical simulations of turbulent flow in a channel with height Lz were performed. The Fukagata-Iwamoto-Kasagi identity for drag decomposition was extended to textured walls and was used to study the drag change mechanisms. For Λf/Lz ≳ O(10), the herringbone texture behaves similarly to a conventional parallel-riblet texture in yaw: the suppression of turbulent advective transport results in a slight drag reduction of 2%. For Λf/Lz ≲ O(1), the drag increases strongly with a maximum of 73%. This is attributed to enhanced mean and turbulent advection, which results from the strong secondary flow that forms over regions of riblet convergence/divergence. Hence, the employment of convergent/divergent riblets in the texture seems to be detrimental to turbulent drag reduction.

Large-scale control strategy for drag reduction in turbulent channel flows

NASA Astrophysics Data System (ADS)

Yao, Jie; Chen, Xi; Thomas, Flint; Hussain, Fazle

2017-06-01

In a recent article, Canton et al. [J. Canton et al., Phys. Rev. Fluids 1, 081501(R) (2016), 10.1103/PhysRevFluids.1.081501] reported significant drag reduction in turbulent channel flow by using large-scale, near-wall streamwise swirls following the control strategy of Schoppa and Hussain [W. Schoppa and F. Hussain, Phys. Fluids 10, 1049 (1998), 10.1063/1.869789] for low Reynolds numbers only, but found no drag reduction at high friction Reynolds numbers (Reτ=550 ). Here we show that the lack of drag reduction at high Re observed by Canton et al. is remedied by the proper choice of the large-scale control flow. In this study, we apply near-wall opposed wall-jet forcing to achieve drag reduction at the same (high) Reynolds number where Canton et al. found no drag reduction. The steady excitation is characterized by three control parameters, namely, the wall-jet-forcing amplitude A+, the spanwise spacing Λ+, and the wall jet height yc+ (+ indicates viscous scaling); the primary difference between Schoppa and Hussain's work (also that of Canton et al.) and this Rapid Communication is the emphasis on the explicit choice of yc+ here. We show as an example that with a choice of A+≈0.015 ,Λ+≈1200 , and yc+≈30 the flow control definitely suppresses the wall shear stress at a series of Reynolds numbers, namely, 19 %,14 % , and 12 % drag reductions at Reτ=180 , 395, and 550, respectively. Further study should explore optimization of these parameter values.

Shark-skin surfaces for fluid-drag reduction in turbulent flow: a review.

PubMed

Dean, Brian; Bhushan, Bharat

2010-10-28

The skin of fast-swimming sharks exhibits riblet structures aligned in the direction of flow that are known to reduce skin friction drag in the turbulent-flow regime. Structures have been fabricated for study and application that replicate and improve upon the natural shape of the shark-skin riblets, providing a maximum drag reduction of nearly 10 per cent. Mechanisms of fluid drag in turbulent flow and riblet-drag reduction theories from experiment and simulation are discussed. A review of riblet-performance studies is given, and optimal riblet geometries are defined. A survey of studies experimenting with riblet-topped shark-scale replicas is also given. A method for selecting optimal riblet dimensions based on fluid-flow characteristics is detailed, and current manufacturing techniques are outlined. Due to the presence of small amounts of mucus on the skin of a shark, it is expected that the localized application of hydrophobic materials will alter the flow field around the riblets in some way beneficial to the goals of increased drag reduction.

Statistical Analysis of CFD Solutions from the Third AIAA Drag Prediction Workshop

NASA Technical Reports Server (NTRS)

Morrison, Joseph H.; Hemsch, Michael J.

2007-01-01

The first AIAA Drag Prediction Workshop, held in June 2001, evaluated the results from an extensive N-version test of a collection of Reynolds-Averaged Navier-Stokes CFD codes. The code-to-code scatter was more than an order of magnitude larger than desired for design and experimental validation of cruise conditions for a subsonic transport configuration. The second AIAA Drag Prediction Workshop, held in June 2003, emphasized the determination of installed pylon-nacelle drag increments and grid refinement studies. The code-to-code scatter was significantly reduced compared to the first DPW, but still larger than desired. However, grid refinement studies showed no significant improvement in code-to-code scatter with increasing grid refinement. The third Drag Prediction Workshop focused on the determination of installed side-of-body fairing drag increments and grid refinement studies for clean attached flow on wing alone configurations and for separated flow on the DLR-F6 subsonic transport model. This work evaluated the effect of grid refinement on the code-to-code scatter for the clean attached flow test cases and the separated flow test cases.

On the secular decrease in the semimajor axis of Lageos orbit

NASA Technical Reports Server (NTRS)

Rubincam, D. P.

1980-01-01

The semimajor axis of the Lageos orbit is decreasing secularly at the rate of -1.1 mm/day due to an unknown force. Nine possible mechanisms are investigated. Five of the mechanisms, resonance with the Earth's gravitational field, gravitational radiation, the Poynting-Robertson effect, transfer of spin angular momentum to the orbital angular momentum, and drag from near Earth dust are ruled out because they are too small to require unacceptable assumptions to account for the observed rate. Three other mechanisms, the Yarkovsky effect, the Schach effect, and terrestrial radiation pressure could possibly give the proper order of magnitude for the decay rate, but the characteristic signatures of these perturbations do not agree with the observed secular decrease. Atmospheric drag from a combination of charged and neutral particles is the most likely cause for the orbital decay. This mechanism explains at least 71 percent of the observed rate of decrease of the semimajor axis.

Deplacement effect of the laminar boundary layer and the pressure drag

NASA Technical Reports Server (NTRS)

Gortler, H

1951-01-01

The displacement effect of the boundary layer on the outer frictionless flow is discussed for both steady and unsteady flows. The analysis is restricted to cases in which the potential flow pressure distribution remains valid for the boundary-layer calculation. Formulas are given for the dependence of the pressure drag, friction drag, and total drag of circular cylinders on the time from the start of motion for cases in which the velocity varies as a power of the time. Formulas for the locations and for the time for the appearance of the separation point are given for two dimensional bodies of arbitrary shape.

Drag reduction at a plane wall

NASA Technical Reports Server (NTRS)

Hill, D. C.

1993-01-01

The objective is to determine by analytical means how drag on a plane wall may be modified favorably using a minimal amount of flow information - preferably only information at the wall. What quantities should be measured? How should that information be assimilated in order to arrive at effective control? As a prototypical problem, incompressible, viscous flow, governed by the Navier-Stokes equations, past a plane wall at which the no-slip condition was modified was considered. The streamwise and spanwise velocity components are required to be zero, but the normal component is to be specified according to some control law. The challenge is to choose the wall-normal velocity component based on flow conditions at the wall so that the mean drag is as small as possible. There can be no net mass flux through the wall, and the total available control energy is constrained. A turbulent flow is highly unsteady and has detailed spatial structure. The mean drag on the wall is the integral over the wall of the local shear forces exerted by the fluid, which is then averaged in time; it is a 'macroscopic' property of the flow. It is not obvious how unsteady boundary control is to be applied in order to modify the mean flow most effectively, especially in view of the non- self-adjoint nature of the governing equations. An approximate analytical solution to the suboptimal scheme is pursued.

Computational Fluid Dynamics (CFD) Simulation of Drag Reduction by Riblets on Automobile

NASA Astrophysics Data System (ADS)

Ghazali, N. N. N.; Yau, Y. H.; Badarudin, A.; Lim, Y. C.

2010-05-01

One of the ongoing automotive technological developments is the reduction of aerodynamic drag because this has a direct impact on fuel reduction, which is a major topic due to the influence on many other requirements. Passive drag reduction techniques stand as the most portable and feasible way to be implemented in real applications. One of the passive techniques is the longitudinal microgrooves aligned in the flow direction, known as riblets. In this study, the simulation of turbulent flows over an automobile in a virtual wind tunnel has been conducted by computational fluid dynamics (CFD). Three important aspects of this study are: the drag reduction effect of riblets on smooth surface automobile, the position and geometry of the riblets on drag reduction. The simulation involves three stages: geometry modeling, meshing, solving and analysis. The simulation results show that the attachment of riblets on the rear roof surface reduces the drag coefficient by 2.74%. By adjusting the attachment position of the riblets film, reduction rates between the range 0.5%-9.51% are obtained, in which the position of the top middle roof optimizes the effect. Four riblet geometries are investigated, among them the semi-hexagon trapezoidally shaped riblets is considered the most effective. Reduction rate of drag is found ranging from -3.34% to 6.36%.

The Role of Rough Topography in Mediating Impacts of Bottom Drag in Eddying Ocean Circulation Models.

PubMed

Trossman, David S; Arbic, Brian K; Straub, David N; Richman, James G; Chassignet, Eric P; Wallcraft, Alan J; Xu, Xiaobiao

2017-08-01

Motivated by the substantial sensitivity of eddies in two-layer quasi-geostrophic (QG) turbulence models to the strength of bottom drag, this study explores the sensitivity of eddies in more realistic ocean general circulation model (OGCM) simulations to bottom drag strength. The OGCM results are interpreted using previous results from horizontally homogeneous, two-layer, flat-bottom, f-plane, doubly periodic QG turbulence simulations and new results from two-layer β -plane QG turbulence simulations run in a basin geometry with both flat and rough bottoms. Baroclinicity in all of the simulations varies greatly with drag strength, with weak drag corresponding to more barotropic flow and strong drag corresponding to more baroclinic flow. The sensitivity of the baroclinicity in the QG basin simulations to bottom drag is considerably reduced, however, when rough topography is used in lieu of a flat bottom. Rough topography reduces the sensitivity of the eddy kinetic energy amplitude and horizontal length scales in the QG basin simulations to bottom drag to an even greater degree. The OGCM simulation behavior is qualitatively similar to that in the QG rough bottom basin simulations in that baroclinicity is more sensitive to bottom drag strength than are eddy amplitudes or horizontal length scales. Rough topography therefore appears to mediate the sensitivity of eddies in models to the strength of bottom drag. The sensitivity of eddies to parameterized topographic internal lee wave drag, which has recently been introduced into some OGCMs, is also briefly discussed. Wave drag acts like a strong bottom drag in that it increases the baroclinicity of the flow, without strongly affecting eddy horizontal length scales.

No-Drag Frame for Anomalous Chiral Fluid

DOE PAGES

Stephanov, Mikhail A.; Yee, Ho-Ung

2016-03-24

For an anomalous fluid carrying dissipationless chiral magnetic and/or vortical currents we show that there is a frame in which a stationary obstacle experiences no drag, but energy and charge currents do not vanish, resembling superfluidity. Unlike ordinary superfluid flow, the anomalous chiral currents can transport entropy in this frame. Moreover, we show that the second law of thermodynamics completely determines the amounts of these anomalous nondissipative currents in the “no-drag frame” as polynomials in temperature and chemical potential with known anomaly coefficients. These general results are illustrated and confirmed by a calculation in the chiral kinetic theory and inmore » the quark-gluon plasma at high temperature.« less

An experimental determination of the drag coefficient of a Mens 8+ racing shell.

PubMed

Buckmann, James G; Harris, Samuel D

2014-01-01

This study centered around an experimental analysis of a Mens Lightweight Eight racing shell and, specifically, determining an approximation for the drag coefficient. A testing procedure was employed that used a Global Positioning System (GPS) unit in order to determine the acceleration and drag force on the shell, and through calculations yield a drag coefficient. The testing was run over several days in numerous conditions, and a 95% confidence interval was established to capture the results. The results obtained, over these varying trials, maintained a successful level of consistency. The significance of this study transcends the determination an approximation for the drag coefficient of the racing shell; it defined a successful means of quantifying performance of the shell itself. The testing procedures outlined in the study represent a uniform means of evaluating the factors that influence drag on the shell, and thus influence speed.

Coordination of multiple appendages in drag-based swimming.

PubMed

Alben, Silas; Spears, Kevin; Garth, Stephen; Murphy, David; Yen, Jeannette

2010-11-06

Krill are aquatic crustaceans that engage in long distance migrations, either vertically in the water column or horizontally for 10 km (over 200,000 body lengths) per day. Hence efficient locomotory performance is crucial for their survival. We study the swimming kinematics of krill using a combination of experiment and analysis. We quantify the propulsor kinematics for tethered and freely swimming krill in experiments, and find kinematics that are very nearly metachronal. We then formulate a drag coefficient model which compares metachronal, synchronous and intermediate motions for a freely swimming body with two legs. With fixed leg velocity amplitude, metachronal kinematics give the highest average body speed for both linear and quadratic drag laws. The same result holds for five legs with the quadratic drag law. When metachronal kinematics is perturbed towards synchronous kinematics, an analysis shows that the velocity increase on the power stroke is outweighed by the velocity decrease on the recovery stroke. With fixed time-averaged work done by the legs, metachronal kinematics again gives the highest average body speed, although the advantage over synchronous kinematics is reduced.

Differential Drag Demonstration: A Post-Mission Experiment with the EO-1 Spacecraft

NASA Technical Reports Server (NTRS)

Hull, Scott; Shelton, Amanda; Richardson, David

2017-01-01

Differential drag is a technique for altering the semi-major axis, velocity, and along-track position of a spacecraft in low Earth orbit. It involves varying the spacecrafts cross-sectional area relative to its velocity direction by temporarily changing attitude and solar array angles, thus varying the amount of atmospheric drag on the spacecraft. The technique has recently been proposed and used by at least three satellite systems for initial separation of constellation spacecraft after launch, stationkeeping during the mission, and potentially for conjunction avoidance. Similarly, differential drag has been proposed as a control strategy for rendezvous, removing the need for active propulsion. In theory, some operational missions that lack propulsion capability could use this approach for conjunction avoidance, though options are typically constrained for spacecraft that are already in orbit. Shortly before the spacecraft was decommissioned, an experiment was performed using NASAs EO-1 spacecraft in order to demonstrate differential drag on an operational spacecraft in orbit, and discover some of the effects differential drag might manifest. EO-1 was not designed to maintain off-nominal orientations for long periods, and as a result the team experienced unanticipated challenges during the experiment. This paper will discuss operations limitations identified before the experiment, as well as those discovered during the experiment. The effective displacement that resulted from increasing the drag area for 39 hours will be compared to predictions as well as the expected position if the spacecraft maintained nominal operations. A hypothetical scenario will also be examined, studying the relative risks of maintaining an operational spacecraft bus in order to maintain the near-maximum drag area orientation and hasten reentry.

Differential Drag Demonstration: A Post-Mission Experiment with the EO-1 Spacecraft

NASA Technical Reports Server (NTRS)

Hull, Scott; Shelton, Amanda; Richardson, David

2017-01-01

Differential drag is a technique for altering the semimajor axis, velocity, and along-track position of a spacecraft in low Earth orbit. It involves varying the spacecraft's cross-sectional area relative to its velocity direction by temporarily changing attitude and solar array angles, thus varying the amount of atmospheric drag on the spacecraft. The technique has recently been proposed and used by at least three satellite systems for initial separation of constellation spacecraft after launch, stationkeeping during the mission, and potentially for conjunction avoidance. Similarly, differential drag has been proposed as a control strategy for rendezvous, removing the need for active propulsion. In theory, some operational missions that lack propulsion capability could use this approach for conjunction avoidance, though options are typically constrained for spacecraft that are already in orbit. Shortly before the spacecraft was decommissioned, an experiment was performed using NASA's EO-1 spacecraft in order to demonstrate differential drag on an operational spacecraft in orbit, and discover some of the effects differential drag might manifest. EO-1 was not designed to maintain off-nominal orientations for long periods, and as a result the team experienced unanticipated challenges during the experiment. This paper will discuss operations limitations identified before the experiment, as well as those discovered during the experiment. The effective displacement that resulted from increasing the drag area for 39 hours will be compared to predictions as well as the expected position if the spacecraft maintained nominal operations. A hypothetical scenario will also be examined, studying the relative risks of maintaining an operational spacecraft bus in order to maintain the near-maximum drag area orientation and hasten reentry.

The myth and reality of Gray's paradox: implication of dolphin drag reduction for technology.

PubMed

Fish, Frank E

2006-06-01

The inconsistency for the calculated high drag on an actively swimming dolphin and underestimated muscle power available resulted in what has been termed Gray's paradox. Although Gray's paradox was flawed, it has been the inspiration for a variety of drag reduction mechanisms. This review examines the present state of knowledge of drag reduction specific to dolphins. Streamlining and special behaviors provide the greatest drag reduction for dolphins. Mechanisms to control flow by maintaining a completely laminar boundary layer over the body have not been demonstrated for dolphins.

Viscous flow drag reduction; Symposium, Dallas, Tex., November 7, 8, 1979, Technical Papers

NASA Technical Reports Server (NTRS)

Hough, G. R.

1980-01-01

The symposium focused on laminar boundary layers, boundary layer stability analysis of a natural laminar flow glove on the F-111 TACT aircraft, drag reduction of an oscillating flat plate with an interface film, electromagnetic precipitation and ducting of particles in turbulent boundary layers, large eddy breakup scheme for turbulent viscous drag reduction, blowing and suction, polymer additives, and compliant surfaces. Topics included influence of environment in laminar boundary layer control, generation rate of turbulent patches in the laminar boundary layer of a submersible, drag reduction of small amplitude rigid surface waves, and hydrodynamic drag and surface deformations generated by liquid flows over flexible surfaces.

Numerical Simulation of High Drag Reduction in a Turbulent Channel Flow with Polymer Additives

NASA Technical Reports Server (NTRS)

Dubief, Yves

2003-01-01

The addition of small amounts of long chain polymer molecules to wall-bounded flows can lead to dramatic drag reduction. Although this phenomenon has been known for about fifty years, the action of the polymers and its effect on turbulent structures are still unclear. Detailed experiments have characterized two distinct regimes (Warholic et al. 1999), which are referred to as low drag reduction (LDR) and high drag reduction (HDR). The first regime exhibits similar statistical trends as Newtonian flow: the log-law region of the mean velocity profile remains parallel to that of the Newtonian ow but its lower bound moves away from the wall and the upward shift of the log-region is a function of drag reduction, DR. Although streamwise fluctuations are increased and transverse ones are reduced, the shape of the rms velocity profiles is not qualitatively modified. At higher drag reductions, of the order of 40-50%, the ow enters the HDR regime for which the slope of the log-law is dramatically augmented and the Reynolds shear stress is small (Warholic et al. 1999; Ptasinski et al. 2001). The drag reduction is eventually bounded by a maximum drag reduction (MDR) (Virk & Mickley 1970) which is a function of the Reynolds number. While several experiments report mean velocity profiles very close to the empirical profile of Virk & Mickley (1970) for MDR conditions, the observations regarding the structure of turbulence can differ significantly. For instance, Warholic et al. (1999) measured a near-zero Reynolds shear stress, whereas a recent experiment (Ptasinski et al. 2001) shows evidence of non-negligible Reynolds stress in their MDR flow. To the knowledge of the authors, only the LDR regime has been documented in numerical simulations (Sureshkumar et al. 1997; Dimitropoulos et al. 1998; Min et al. 2001; Dubief & Lele 2001; Sibilla & Baron 2002). This paper discusses the simulation of polymer drag reduced channel ow at HDR using the FENE-P (Finite Elastic non

Acceleration Noise Considerations for Drag-free Satellite Geodesy Missions

NASA Astrophysics Data System (ADS)

Hong, S. H.; Conklin, J. W.

2016-12-01

The GRACE mission, which launched in 2002, opened a new era of satellite geodesy by providing monthly mass variation solutions with spatial resolution of less than 200 km. GRACE proved the usefulness of a low-low satellite-to-satellite tracking formation. Analysis of the GRACE data showed that the K-Band ranging system, which is used to measure the range between the two satellites, is the limiting factor for the precision of the solution. Consequently, the GRACE-FO mission, schedule for launch in 2017, will continue the work of GRACE, but will also test a new, higher precision laser ranging interferometer compared with the K-Band ranging system. Beyond GRACE-FO, drag-free systems are being considered for satellite geodesy missions. GOCE tested a drag-free attitude control system with a gravity gradiometer and showed improvements in the acceleration noise compensation compared to the electrostatic accelerometers used in GRACE. However, a full drag-free control system with a gravitational reference sensor has not yet been applied to satellite geodesy missions. More recently, this type of drag-free system was used in LISA Pathfinder, launched in 2016, with an acceleration noise performance two orders of magnitude better than that of GOCE. We explore the effects of drag-free performance in satellite geodesy missions similar to GRACE-FO by applying three different residual acceleration noises from actual space missions: GRACE, GOCE and LISA Pathfinder. Our solutions are limited to degree 60 spherical harmonic coefficients with biweekly time resolution. Our analysis shows that a drag-free system with acceleration noise performance comparable to GOCE and LISA-Pathfinder would greatly improve the accuracy of gravity solutions. In addition to these results, we also present the covariance shaping process used in the estimation. In the future, we plan to use actual acceleration noise data measured using the UF torsion pendulum. This apparatus is a ground facility at

COPE AND DRAG PATTERNS, EACH IS USED AT SEPARATE TIMES ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

COPE AND DRAG PATTERNS, EACH IS USED AT SEPARATE TIMES TO CREATE INDIVIDUAL MOLD. HALVES FOR AN EXHAUST MANIFOLD CASTING SIT IN FRONT OF MATCHPLATE PATTERNS WITH BOTH COPE AND DRAG SIDES AFFIXED TO A SINGLE PLATE, USED TO CREATE BOTH MOLD HALVES AT THE SAME TIME, IN THE BACKGROUND. - Southern Ductile Casting Company, Mold Making, 2217 Carolina Avenue, Bessemer, Jefferson County, AL

Analysis of Manning’s and Drag Coefficients for Flexible Submerged Vegetation

NASA Astrophysics Data System (ADS)

Yusof, Khamaruzaman Wan; Mujahid Muhammad, Muhammad; Mustafa, Muhammad Raza Ul; Azazi Zakaria, Nor; Gahani, Aminuddin Ab.

2017-06-01

Accurate determination of flow resistance is of great significance in modelling of open channels that will convey water efficiently. Although, resistance or drag induced by vegetation have been systematically studied for several decades, estimating of the resistance remain as a challenge. This is because most of previous studies use artificial vegetation to investigate flow - vegetation interactions. To overcome this, the present study evaluates the vegetation resistance in terms of Manning’s roughness coefficient and drag coefficient using a natural flexible vegetation (cow grass) under submerged condition. From the experimental result obtained, it was observed that the Manning’s and drag coefficients decreased with the increasing in average velocity. Also, graphical relationship between Manning’s coefficient, n and drag coefficient, CD has been developed with R2 = 0.9465, which indicate that there exist a strong correlation between n and CD, and one can use the proposed graphical model to predict the n - values corresponding to the CD - values.

Atmospheric form drag over Arctic sea ice derived from high-resolution IceBridge elevation data

NASA Astrophysics Data System (ADS)

Petty, A.; Tsamados, M.; Kurtz, N. T.

2016-02-01

Here we present a detailed analysis of atmospheric form drag over Arctic sea ice, using high resolution, three-dimensional surface elevation data from the NASA Operation IceBridge Airborne Topographic Mapper (ATM) laser altimeter. Surface features in the sea ice cover are detected using a novel feature-picking algorithm. We derive information regarding the height, spacing and orientation of unique surface features from 2009-2014 across both first-year and multiyear ice regimes. The topography results are used to explicitly calculate atmospheric form drag coefficients; utilizing existing form drag parameterizations. The atmospheric form drag coefficients show strong regional variability, mainly due to variability in ice type/age. The transition from a perennial to a seasonal ice cover therefore suggest a decrease in the atmospheric form drag coefficients over Arctic sea ice in recent decades. These results are also being used to calibrate a recent form drag parameterization scheme included in the sea ice model CICE, to improve the representation of form drag over Arctic sea ice in global climate models.

Design of a cusped field thruster for drag-free flight

NASA Astrophysics Data System (ADS)

Liu, H.; Chen, P. B.; Sun, Q. Q.; Hu, P.; Meng, Y. C.; Mao, W.; Yu, D. R.

2016-09-01

Drag-free flight has played a more and more important role in many space missions. The thrust control system is the key unit to achieve drag-free flight by providing a precise compensation for the disturbing force except gravity. The cusped field thruster has shown a significant potential to be capable of the function due to its long life, high efficiency, and simplicity. This paper demonstrates a cusped field thruster's feasibility in drag-free flight based on its instinctive characteristics and describes a detailed design of a cusped field thruster made by Harbin Institute of Technology (HIT). Furthermore, the performance test is conducted, which shows that the cusped field thruster can achieve a continuously variable thrust from 1 to 20 mN with a low noise and high resolution below 650 W, and the specific impulse can achieve 1800 s under a thrust of 18 mN and discharge voltage of 1000 V. The thruster's overall performance indicates that the cusped field thruster is quite capable of achieving drag-free flight. With the further optimization, the cusped field thruster will exhibit a more extensive application value.

Comparisons of AEROX computer program predictions of lift and induced drag with flight test data

NASA Technical Reports Server (NTRS)

Axelson, J.; Hill, G. C.

1981-01-01

The AEROX aerodynamic computer program which provides accurate predictions of induced drag and trim drag for the full angle of attack range and for Mach numbers from 0.4 to 3.0 is described. This capability is demonstrated comparing flight test data and AEROX predictions for 17 different tactical aircraft. Values of minimum (skin friction, pressure, and zero lift wave) drag coefficients and lift coefficient offset due to camber (when required) were input from the flight test data to produce total lift and drag curves. The comparisons of trimmed lift drag polars show excellent agreement between the AEROX predictions and the in flight measurements.

The interdependence of profile drag and lift with Joukowski type and related airfoils

NASA Technical Reports Server (NTRS)

Muttray, H

1935-01-01

On the basis of a systematic investigation of Gottingen wind-tunnel data on Joukowski type and related airfoils, it is shown in what manner the profile drag coefficient is dependent on the lift coefficient. The individual factors for the construction of the profile drag polars are given. They afford a more accurate calculation of the performance coefficients of airplane designs than otherwise attainable with the conventional assumption of constant drag coefficient.

On the diverse roles of fluid dynamic drag in animal swimming and flying

PubMed Central

2018-01-01

Questions of energy dissipation or friction appear immediately when addressing the problem of a body moving in a fluid. For the most simple problems, involving a constant steady propulsive force on the body, a straightforward relation can be established balancing this driving force with a skin friction or form drag, depending on the Reynolds number and body geometry. This elementary relation closes the full dynamical problem and sets, for instance, average cruising velocity or energy cost. In the case of finite-sized and time-deformable bodies though, such as flapping flyers or undulatory swimmers, the comprehension of driving/dissipation interactions is not straightforward. The intrinsic unsteadiness of the flapping and deforming animal bodies complicates the usual application of classical fluid dynamic forces balance. One of the complications is because the shape of the body is indeed changing in time, accelerating and decelerating perpetually, but also because the role of drag (more specifically the role of the local drag) has two different facets, contributing at the same time to global dissipation and to driving forces. This causes situations where a strong drag is not necessarily equivalent to inefficient systems. A lot of living systems are precisely using strong sources of drag to optimize their performance. In addition to revisiting classical results under the light of recent research on these questions, we discuss in this review the crucial role of drag from another point of view that concerns the fluid–structure interaction problem of animal locomotion. We consider, in particular, the dynamic subtleties brought by the quadratic drag that resists transverse motions of a flexible body or appendage performing complex kinematics, such as the phase dynamics of a flexible flapping wing, the propagative nature of the bending wave in undulatory swimmers, or the surprising relevance of drag-based resistive thrust in inertial swimmers. PMID:29445037

A Base Drag Reduction Experiment on the X-33 Linear Aerospike SR-71 Experiment (LASRE) Flight Program

NASA Technical Reports Server (NTRS)

Whitmore, Stephen A.; Moes, Timothy R.

1999-01-01

Drag reduction tests were conducted on the LASRE/X-33 flight experiment. The LASRE experiment is a flight test of a roughly 20% scale model of an X-33 forebody with a single aerospike engine at the rear. The experiment apparatus is mounted on top of an SR-71 aircraft. This paper suggests a method for reducing base drag by adding surface roughness along the forebody. Calculations show a potential for base drag reductions of 8-14%. Flight results corroborate the base drag reduction, with actual reductions of 15% in the high-subsonic flight regime. An unexpected result of this experiment is that drag benefits were shown to persist well into the supersonic flight regime. Flight results show no overall net drag reduction. Applied surface roughness causes forebody pressures to rise and offset base drag reductions. Apparently the grit displaced streamlines outward, causing forebody compression. Results of the LASRE drag experiments are inconclusive and more work is needed. Clearly, however, the forebody grit application works as a viable drag reduction tool.

Method for Reducing the Drag of Increasing Forebody Roughness Blunt-Based Vehicles by Adaptively Increasing Forebody Roughness

NASA Technical Reports Server (NTRS)

Whitmore, Stephen A. (Inventor); Saltzman, Edwin J. (Inventor); Moes, Timothy R. (Inventor); Iliff, Kenneth W. (Inventor)

2005-01-01

A method for reducing drag upon a blunt-based vehicle by adaptively increasing forebody roughness to increase drag at the roughened area of the forebody, which results in a decrease in drag at the base of this vehicle, and in total vehicle drag.

Chicks with dicks, men in dresses: what it means to be a drag queen.

PubMed

Taylor, Verta; Rupp, Leila J

2004-01-01

One of the burning questions about drag queens among both scholars and audiences is whether they are more gender-revolutionaries than gender-conservatives. Do they primarily destabilize gender and sexual categories by making visible the social basis of femininity and masculinity, heterosexuality and homosexuality? Or are they more apt to reinforce the dominant binary and hierarchical gender and sexual systems by appropriating gender displays and expressing sexual desires associated with traditional femininity and institutionalized heterosexuality? We address this question through a case study of drag queens at the 801 Cabaret in Key West, Florida. On the basis of life histories, observations of their performances, and focus groups with audience members, we examine the role of gender and sexuality in the process of becoming a drag queen and in the personal identities of drag queens. We find that transgenderism, same-sex sexuality, and theatrical performance are central to the personal identities of these drag queens, who use drag to forge personal and collective identities that are neither masculine nor feminine, but rather their own complex genders.

Drag coefficients for modeling flow through emergent vegetation in the Florida Everglades

USGS Publications Warehouse

Lee, J.K.; Roig, L.C.; Jenter, H.L.; Visser, H.M.

2004-01-01

Hydraulic data collected in a flume fitted with pans of sawgrass were analyzed to determine the vertically averaged drag coefficient as a function of vegetation characteristics. The drag coefficient is required for modeling flow through emergent vegetation at low Reynolds numbers in the Florida Everglades. Parameters of the vegetation, such as the stem population per unit bed area and the average stem/leaf width, were measured for five fixed vegetation layers. The vertically averaged vegetation parameters for each experiment were then computed by weighted average over the submerged portion of the vegetation. Only laminar flow through emergent vegetation was considered, because this is the dominant flow regime of the inland Everglades. A functional form for the vegetation drag coefficient was determined by linear regression of the logarithmic transforms of measured resistance force and Reynolds number. The coefficients of the drag coefficient function were then determined for the Everglades, using extensive flow and vegetation measurements taken in the field. The Everglades data show that the stem spacing and the Reynolds number are important parameters for the determination of vegetation drag coefficient. ?? 2004 Elsevier B.V. All rights reserved.

SATURATED TORQUE FORMULA FOR PLANETARY MIGRATION IN VISCOUS DISKS WITH THERMAL DIFFUSION: RECIPE FOR PROTOPLANET POPULATION SYNTHESIS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Masset, F. S.; Casoli, J., E-mail: masset@fis.unam.m, E-mail: jules.casoli@cea.f, E-mail: masset@fis.unam.m

2010-11-10

We provide torque formulae for low-mass planets undergoing type I migration in gaseous disks. These torque formulae put special emphasis on the horseshoe drag, which is prone to saturation: the asymptotic value reached by the horseshoe drag depends on a balance between coorbital dynamics (which tends to cancel out or saturate the torque) and diffusive processes (which tend to restore the unperturbed disk profiles, thereby desaturating the torque). We entertain the question of this asymptotic value and derive torque formulae that give the total torque as a function of the disk's viscosity and thermal diffusivity. The horseshoe drag features twomore » components: one that scales with the vortensity gradient and another that scales with the entropy gradient and constitutes the most promising candidate for halting inward type I migration. Our analysis, which is complemented by numerical simulations, recovers characteristics already noted by numericists, namely, that the viscous timescale across the horseshoe region must be shorter than the libration time in order to avoid saturation and that, provided this condition is satisfied, the entropy-related part of the horseshoe drag remains large if the thermal timescale is shorter than the libration time. Side results include a study of the Lindblad torque as a function of thermal diffusivity and a contribution to the corotation torque arising from vortensity viscously created at the contact discontinuities that appear at the horseshoe separatrices. For the convenience of the reader mostly interested in the torque formulae, Section 8 is self-contained.« less

Statistical Analysis of CFD Solutions from 2nd Drag Prediction Workshop

NASA Technical Reports Server (NTRS)

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

2004-01-01

In June 2001, the first AIAA Drag Prediction Workshop was held to evaluate results obtained from extensive N-Version testing of a series of RANS CFD codes. The geometry used for the computations was the DLR-F4 wing-body combination which resembles a medium-range subsonic transport. The cases reported include the design cruise point, drag polars at eight Mach numbers, and drag rise at three values of lift. Although comparisons of the code-to-code medians with available experimental data were similar to those obtained in previous studies, the code-to-code scatter was more than an order-of-magnitude larger than expected and far larger than desired for design and for experimental validation. The second Drag Prediction Workshop was held in June 2003 with emphasis on the determination of installed pylon-nacelle drag increments and on grid refinement studies. The geometry used was the DLR-F6 wing-body-pylon-nacelle combination for which the design cruise point and the cases run were similar to the first workshop except for additional runs on coarse and fine grids to complement the runs on medium grids. The code-to-code scatter was significantly reduced for the wing-body configuration compared to the first workshop, although still much larger than desired. However, the grid refinement studies showed no sign$cant improvement in code-to-code scatter with increasing grid refinement.

Drag reduction strategies

NASA Technical Reports Server (NTRS)

Hill, D. Christopher

1994-01-01

previously a description was given of an active control scheme using wall transpiration that leads to a 15% reduction in surface skin friction beneath a turbulent boundary layer, according to direct numerical simulation. In this research brief further details of that scheme and its variants are given together with some suggestions as to how sensor/actuator arrays could be configured to reduce surface drag. The research which is summarized here was performed during the first half of 1994. This research is motivated by the need to understand better how the dynamics of near-wall turbulent flow can be modified so that skin friction is reduced. The reduction of turbulent skin friction is highly desirable in many engineering applications. Experiments and direct numerical simulations have led to an increased understanding of the cycle of turbulence production and transport in the boundary layer and raised awareness of the possibility of disrupting the process with a subsequent reduction in turbulent skin friction. The implementation of active feedback control in a computational setting is a viable approach for the investigation of the modifications to the flow physics that can be achieved. Bewley et al. and Hill describe how ideas from optimal control theory are employed to give 'sub-optimal' drag reduction schemes. The objectives of the work reported here is to investigate in greater detail the assumptions implicit within such schemes and their limitations. It is also our objective to describe how an array of sensors and actuators could be arranged and interconnected to form a 'smart' surface which has low skin friction.

Nonuniform concentration - A mechanism for drag reduction.

NASA Technical Reports Server (NTRS)

Rivard, W. C.; Kulinski, E. S.

1972-01-01

A large reduction in drag coefficient has been observed in certain external flows of aqueous solutions with high molecular weight polymer additives. A change in the near wake configuration is phenomenologically responsible for the drag reduction, but the underlying mechanism is presently unknown. An analogy to known phenomena in particulate suspensions is drawn which suggests nonuniform concentration of the polymer additive as an explanation. An analysis of the boundary layer on a sphere with varying viscosity was made to investigate the effect. The results indicate early transition to turbulence for concentration variations whose length scale is small compared with the momentum boundary layer thickness. Stabilization and delayed transition are indicated for thicker concentration layers. Observations are suggested for the thin concentration layers.

Statistical Analysis of CFD Solutions from the Drag Prediction Workshop

NASA Technical Reports Server (NTRS)

Hemsch, Michael J.

2002-01-01

A simple, graphical framework is presented for robust statistical evaluation of results obtained from N-Version testing of a series of RANS CFD codes. The solutions were obtained by a variety of code developers and users for the June 2001 Drag Prediction Workshop sponsored by the AIAA Applied Aerodynamics Technical Committee. The aerodynamic configuration used for the computational tests is the DLR-F4 wing-body combination previously tested in several European wind tunnels and for which a previous N-Version test had been conducted. The statistical framework is used to evaluate code results for (1) a single cruise design point, (2) drag polars and (3) drag rise. The paper concludes with a discussion of the meaning of the results, especially with respect to predictability, Validation, and reporting of solutions.

Hydrodynamic flows of non-Fermi liquids: Magnetotransport and bilayer drag

NASA Astrophysics Data System (ADS)

Patel, Aavishkar A.; Davison, Richard A.; Levchenko, Alex

2017-11-01

We consider a hydrodynamic description of transport for generic two-dimensional electron systems that lack Galilean invariance and do not fall into the category of Fermi liquids. We study magnetoresistance and show that it is governed only by the electronic viscosity provided that the wavelength of the underlying disorder potential is large compared to the microscopic equilibration length. We also derive the Coulomb drag transresistance for double-layer non-Fermi-liquid systems in the hydrodynamic regime. As an example, we consider frictional drag between two quantum Hall states with half-filled lowest Landau levels, each described by a Fermi surface of composite fermions coupled to a U (1 ) gauge field. We contrast our results to prior calculations of drag of Chern-Simons composite particles and place our findings in the context of available experimental data.

Acoustic Liner Drag: A Parametric Study of Conventional Configurations

NASA Technical Reports Server (NTRS)

Howerton, Brian M.; Jones, Michael G.

2015-01-01

Interest in the characterization of the aerodynamic drag performance of acoustic liners has increased in the past several years. This paper details experiments in NASA Langley's Grazing Flow Impedance Tube to quantify the relative drag of several conventional perforate-over-honeycomb liner configurations. For a fixed porosity, facesheet hole diameter and cavity depth are varied to study the effect of each. These configurations are selected to span the range of conventional liner geometries used in commercial aircraft engines. Detailed static pressure and acoustic measurements are made for grazing flows up to M=0.5 at 140 dB SPL for tones between 400 and 2800 Hz. These measurements are used to calculate a resistance factor (?) for each configuration. Analysis shows a correlation between perforate hole size and the resistance factor but cavity depth seems to have little influence. Acoustic effects on liner drag are observed to be limited to the lower Mach numbers included in this investigation.

An investigation of the feasibility of active boundary layer thickening for aircraft drag reduction

NASA Technical Reports Server (NTRS)

Ash, R. L.; Koodalattupuram, C.

1986-01-01

The feasibility of using a forward mounted windmilling propeller to extract momentum from the flow around an axisymmetric body to reduce total drag has been studied. Numerical calculations indicate that a net drag reduction is possible when the energy extracted is returned to an aft mounted pusher propeller. However, net drag reduction requires very high device efficiencies. Results of an experimental program to study the coupling between a propeller wake and a turbulent boundary layer are also reported. The experiments showed that a complex coupling exists and simple modes for the flow field are not sufficiently accurate to predict total drag.

Effects of stern-foil submerged elevation on the lift and drag of a hydrofoil craft

NASA Astrophysics Data System (ADS)

Suastika, K.; Apriansyah

2018-03-01

Effects of the stern-foil submerged elevation on the lift and drag of a hydrofoil craft are studied by using computational fluid dynamics (CFD) and by considering three alternative stern-foil submerged elevations. The submerged elevation of the front foil is kept constant in all the alternatives. From among the alternatives, the deepest stern-foil placement results in the highest stern-foil lift with the highest foil’s lift-to-drag ratio. However, considering the lift-to-drag ratio of the whole foil-strut-hull system, the shallowest stern-foil placement results in the highest lift-to-drag ratio. The struts and the foil’s submerged elevation significantly affects the drag of the whole foil-strut-hull system.

Beyond the boundaries of the classroom: teaching about gender and sexuality at a drag show.

PubMed

Schacht, Steven P

2004-01-01

Like much of the general public, the vast majority of my students strongly hold dichotomous, essentialist outlooks about what the categories female and male/gay and straight are supposed to represent and be. One way that I have found to challenge these oppressive worldviews, and also to queer my classes in the process, is to take my course participants to drag shows and/or to use videotapes of drag queens and drag kings in my classes. As part of an ongoing ethnography of drag performers I am undertaking, I have taken over 300 students to drag shows over the past eight years. Female students have often found attending a drag show to be a fun experience free of the sexual harassment found in most bars, while male students often contextually experience being a social minority for the first time in their life. From both attending drag shows and/or watching recordings of them I show in class, students have reported gaining an experiential appreciation of the performed basis of gender, sexuality, and inequality. Or, stated slightly differently, students begin to understand how the stratification system metaphorically makes drag queens of us all. This, in turn, provides the basis of the foremost argument I make in all my classes: equality will not be realized until nondichotomous, truly new ways of relating to others are envisioned and acted upon.

Enhanced viscous flow drag reduction using acoustic excitation

NASA Technical Reports Server (NTRS)

Nagel, R. T.

1988-01-01

Large eddy break up devices (LEBUs) constitute a promising method of obtaining drag reduction in a turbulent boundary layer. Enhancement of the LEBU effectiveness by exciting its trailing edge with acoustic waves phase locked to the large scale structure influencing the momentum transfer to the wall is sought. An initial estimate of the required sound pressure level for an effective pulse was obtained by considering the magnitude of the pressure perturbations at the near wake of a thin plate in inviscid flow. Detailed skin friction measurments were obtained in the flow region downstream of a LEBU excited with acoustic waves. The data are compared with skin friction measurements of a simply manipulated flow, without acoustic excitation and with a plain flow configuration. The properties and the scales of motion in the flow regime downstream of the acoustically excited LEBU are studied. A parametric study based upon the characteristics of the acoustic input was pursued in addition to the careful mapping of the drag reduction phenomenon within the acoustically manipulated boundary layer. This study of boundary layer manipulation has lead to improved skin friction drag reduction and further understanding of the turbulent boundary layer.

Atmospheric Form Drag Coefficients Over Arctic Sea Ice Using Remotely Sensed Ice Topography Data, Spring 2009-2015

NASA Technical Reports Server (NTRS)

Petty, Alek A.; Tsamados, Michel C.; Kurtz, Nathan T.

2017-01-01

Sea ice topography significantly impacts turbulent energy/momentum exchange, e.g., atmospheric (wind) drag, over Arctic sea ice. Unfortunately, observational estimates of this contribution to atmospheric drag variability are spatially and temporally limited. Here we present new estimates of the neutral atmospheric form drag coefficient over Arctic sea ice in early spring, using high-resolution Airborne Topographic Mapper elevation data from NASA's Operation IceBridge mission. We utilize a new three-dimensional ice topography data set and combine this with an existing parameterization scheme linking surface feature height and spacing to form drag. To be consistent with previous studies investigating form drag, we compare these results with those produced using a new linear profiling topography data set. The form drag coefficient from surface feature variability shows lower values [less than 0.5-1 × 10(exp. -3)] in the Beaufort/Chukchi Seas, compared with higher values [greater than 0.5-1 ×10(exp. -3)] in the more deformed ice regimes of the Central Arctic (north of Greenland and the Canadian Archipelago), which increase with coastline proximity. The results show moderate interannual variability, including a strong increase in the form drag coefficient from 2013 to 2014/2015 north of the Canadian Archipelago. The form drag coefficient estimates are extrapolated across the Arctic with Advanced Scatterometer satellite radar backscatter data, further highlighting the regional/interannual drag coefficient variability. Finally, we combine the results with existing parameterizations of form drag from floe edges (a function of ice concentration) and skin drag to produce, to our knowledge, the first pan-Arctic estimates of the total neutral atmospheric drag coefficient (in early spring) from 2009 to 2015.

Aerodynamic drag crisis and its possible effect on the flight of baseballs

NASA Astrophysics Data System (ADS)

Frohlich, Cliff

1984-04-01

At Reynolds numbers above about 105 the aerodynamic drag force on a sphere drops sharply as the flow begins to become turbulent in the boundary layer. For baseballs, this ``drag crisis'' may occur at speeds which are typical for pitched or batted balls. The effects of the drag reduction on the behavior of both pitched and batted balls is significant, and may explain several features of the game of baseball which previously have been unexplained or attributed to other causes. In particular, the drag reduction may help to explain why pitched fastballs appear to rise, why pitched curve balls appear to drop sharply, and why home run production has increased since the introduction of the alleged ``lively ball.'' Calculations suggest that aerodynamic forces are as important a factor in fastpitch softball as in baseball, and that they are a critical factor in a number of other ball games.

Reducing drag of a commuter train, using engine exhaust momentum

NASA Astrophysics Data System (ADS)

Ha, Dong Keun

The objective of this thesis was to perform numerical investigations of two different methods of injecting fluid momentum into the air flow above a commuter train to reduce its drag. Based on previous aerodynamic modifications of heavy duty trucks in improving fuel efficiency, two structural modifications were designed and applied to a Metrolink Services commuter train in the Los Angeles (LA) County area to reduce its drag and subsequently improve fuel efficiency. The first modification was an L-shaped channel, added to the exhaust cooling fan above the locomotive roof to divert and align the exhaust gases in the axial direction. The second modification was adding an airfoil shaped lid over the L-shape channel, to minimize the drag of the perturbed structure, and thus reduce the overall drag. The computational fluid dynamic (CFD) software CCM+ from CD-Adapco with the ?-? turbulence model was used for the simulations. A single train set which consists of three vehicles: one locomotive, one trailer car and one cab car were used. All the vehicles were modeled based on the standard Metrolink fleet train size. The wind speed was at 90 miles per hour (mph), which is the maximum speed for the Orange County Metrolink line. Air was used as the exhaust gas in the simulation. The temperature of the exhausting air emitting out of the cooling fan on the roof was 150 F and the average fan speed was 120 mph. Results showed that with the addition of the lid, momentum injection results in reduced flow separation and pressure recovery behind the locomotive, which reduces the overall drag by at least 30%.

Spacecraft Re-Entry Impact Point Targeting Using Aerodynamic Drag

NASA Technical Reports Server (NTRS)

Omar, Sanny R.; Bevilacqua, Riccardo

2017-01-01

The ability to re-enter the atmosphere at a desired location is important for spacecraft containing components that may survive re-entry. While impact point targeting has traditionally been initiated through impulsive burns with chemical thrusters on large vehicles such as the Space Shuttle, and the Soyuz and Apollo capsules, many small spacecraft do not host thrusters and require an alternative means of impact point targeting to ensure that falling debris do not cause harm to persons or property. This paper discusses the use of solely aerodynamic drag force to perform this targeting. It is shown that by deploying and retracting a drag device to vary the ballistic coefficient of the spacecraft, any desired longitude and latitude on the ground can be targeted provided that the maneuvering begins early enough and the latitude is less than the inclination of the orbit. An analytical solution based on perturbations from a numerically propagated trajectory is developed to map the initial state and ballistic coefficient profile of a spacecraft to its impact point. This allows the ballistic coefficient profile necessary to reach a given target point to be rapidly calculated, making it feasible to generate the guidance for the decay trajectory onboard the spacecraft. The ability to target an impact point using aerodynamic drag will enhance the capabilities of small spacecraft and will enable larger space vehicles containing thrusters to save fuel by more effectively leveraging the available aerodynamic drag.

Summary of the Third AIAA CFD Drag Prediction Workshop

NASA Technical Reports Server (NTRS)

Vassberg, John C.; Tinoco, Edward N.; Mani, Mori; Brodersen, Olaf P.; Eisfeld, Bernhard; Wahls, Richard A.; Morrison, Joseph H.; Zickuhr, Tom; Laflin, Kelly R.; Mavriplis, DImitri J.

2007-01-01

The workshop focused on the prediction of both absolute and differential drag levels for wing-body and wing-al;one configurations of that are representative of transonic transport aircraft. The baseline DLR-F6 wing-body geometry, previously utilized in DPW-II, is also augmented with a side-body fairing to help reduce the complexity of the flow physics in the wing-body juncture region. In addition, two new wing-alone geometries have been developed for the DPW-II. Numerical calculations are performed using industry-relevant test cases that include lift-specific and fixed-alpha flight conditions, as well as full drag polars. Drag, lift, and pitching moment predictions from previous Reynolds-Averaged Navier-Stokes computational fluid Dynamics Methods are presented, focused on fully-turbulent flows. Solutions are performed on structured, unstructured, and hybrid grid systems. The structured grid sets include point-matched multi-block meshes and over-set grid systems. The unstructured and hybrid grid sets are comprised of tetrahedral, pyramid, and prismatic elements. Effort was made to provide a high-quality and parametrically consistent family of grids for each grid type about each configuration under study. The wing-body families are comprised of a coarse, medium, and fine grid, while the wing-alone families also include an extra-fine mesh. These mesh sequences are utilized to help determine how the provided flow solutions fair with respect to asymptotic grid convergence, and are used to estimate an absolute drag of each configuration.

Transonic Drag Prediction on a DLR-F6 Transport Configuration Using Unstructured Grid Solvers

NASA Technical Reports Server (NTRS)

Lee-Rausch, E. M.; Frink, N. T.; Mavriplis, D. J.; Rausch, R. D.; Milholen, W. E.

2004-01-01

A second international AIAA Drag Prediction Workshop (DPW-II) was organized and held in Orlando Florida on June 21-22, 2003. The primary purpose was to inves- tigate the code-to-code uncertainty. address the sensitivity of the drag prediction to grid size and quantify the uncertainty in predicting nacelle/pylon drag increments at a transonic cruise condition. This paper presents an in-depth analysis of the DPW-II computational results from three state-of-the-art unstructured grid Navier-Stokes flow solvers exercised on similar families of tetrahedral grids. The flow solvers are USM3D - a tetrahedral cell-centered upwind solver. FUN3D - a tetrahedral node-centered upwind solver, and NSU3D - a general element node-centered central-differenced solver. For the wingbody, the total drag predicted for a constant-lift transonic cruise condition showed a decrease in code-to-code variation with grid refinement as expected. For the same flight condition, the wing/body/nacelle/pylon total drag and the nacelle/pylon drag increment predicted showed an increase in code-to-code variation with grid refinement. Although the range in total drag for the wingbody fine grids was only 5 counts, a code-to-code comparison of surface pressures and surface restricted streamlines indicated that the three solvers were not all converging to the same flow solutions- different shock locations and separation patterns were evident. Similarly, the wing/body/nacelle/pylon solutions did not appear to be converging to the same flow solutions. Overall, grid refinement did not consistently improve the correlation with experimental data for either the wingbody or the wing/body/nacelle pylon configuration. Although the absolute values of total drag predicted by two of the solvers for the medium and fine grids did not compare well with the experiment, the incremental drag predictions were within plus or minus 3 counts of the experimental data. The correlation with experimental incremental drag was not

Determining the Drag Coefficient of Rotational Symmetric Objects Falling through Liquids

ERIC Educational Resources Information Center

Houari, Ahmed

2012-01-01

I will propose here a kinematic approach for measuring the drag coefficient of rotational symmetric objects falling through liquids. For this, I will show that one can obtain a measurement of the drag coefficient of a rotational symmetric object by numerically solving the equation of motion describing its fall through a known liquid contained in a…

Separability of drag and thrust in undulatory animals and machines

NASA Astrophysics Data System (ADS)

Bale, Rahul; Shirgaonkar, Anup A.; Neveln, Izaak D.; Bhalla, Amneet Pal Singh; Maciver, Malcolm A.; Patankar, Neelesh A.

2014-12-01

For nearly a century, researchers have tried to understand the swimming of aquatic animals in terms of a balance between the forward thrust from swimming movements and drag on the body. Prior approaches have failed to provide a separation of these two forces for undulatory swimmers such as lamprey and eels, where most parts of the body are simultaneously generating drag and thrust. We nonetheless show that this separation is possible, and delineate its fundamental basis in undulatory swimmers. Our approach unifies a vast diversity of undulatory aquatic animals (anguilliform, sub-carangiform, gymnotiform, bal-istiform, rajiform) and provides design principles for highly agile bioinspired underwater vehicles. This approach has practical utility within biology as well as engineering. It is a predictive tool for use in understanding the role of the mechanics of movement in the evolutionary emergence of morphological features relating to locomotion. For example, we demonstrate that the drag-thrust separation framework helps to predict the observed height of the ribbon fin of electric knifefish, a diverse group of neotropical fish which are an important model system in sensory neurobiology. We also show how drag-thrust separation leads to models that can predict the swimming velocity of an organism or a robotic vehicle.

Separability of drag and thrust in undulatory animals and machines

PubMed Central

Bale, Rahul; Shirgaonkar, Anup A.; Neveln, Izaak D.; Bhalla, Amneet Pal Singh; MacIver, Malcolm A.; Patankar, Neelesh A.

2014-01-01

For nearly a century, researchers have tried to understand the swimming of aquatic animals in terms of a balance between the forward thrust from swimming movements and drag on the body. Prior approaches have failed to provide a separation of these two forces for undulatory swimmers such as lamprey and eels, where most parts of the body are simultaneously generating drag and thrust. We nonetheless show that this separation is possible, and delineate its fundamental basis in undulatory swimmers. Our approach unifies a vast diversity of undulatory aquatic animals (anguilliform, sub-carangiform, gymnotiform, bal-istiform, rajiform) and provides design principles for highly agile bioinspired underwater vehicles. This approach has practical utility within biology as well as engineering. It is a predictive tool for use in understanding the role of the mechanics of movement in the evolutionary emergence of morphological features relating to locomotion. For example, we demonstrate that the drag-thrust separation framework helps to predict the observed height of the ribbon fin of electric knifefish, a diverse group of neotropical fish which are an important model system in sensory neurobiology. We also show how drag-thrust separation leads to models that can predict the swimming velocity of an organism or a robotic vehicle. PMID:25491270

Drag measurements of an axisymmetric nacelle mounted on a flat plate at supersonic speeds

NASA Technical Reports Server (NTRS)

Flamm, Jeffrey D.; Wilcox, Floyd J., Jr.

1995-01-01

An experimental investigation was conducted to determine the effect of diverter wedge half-angle and nacelle lip height on the drag characteristics of an assembly consisting of a nacelle fore cowl from a typical high-speed civil transport (HSCT) and a diverter mounted on a flat plate. Data were obtained for diverter wedge half-angles of 4.0 deg, 6.0 deg, and 8.0 deg and ratios of the nacelle lip height above a flat plate to the boundary-layer thickness (h(sub n)/delta) of approximately 0.87 to 2.45. Limited drag data were also obtained on a complete nacelle/diverter configuration that included fore and aft cowls. Although the nacelle/diverter drag data were not corrected for base pressures or internal flow drag, the data are useful for comparing the relative drag of the configuration tested. The tests were conducted in the Langley Unitary Plan Wind Tunnel at Mach numbers of 1.50, 1.80, 2.10, and 2.40 and Reynolds numbers ranging from 2.00 x 10(exp 6) to 5.00 x 10(exp 6) per foot. The results of this investigation showed that the nacelle/diverter drag essentially increased linearly with increasing h(sub n)/delta except near 1.0 where the data showed a nonlinear behavior. This nonlinear behavior was probably caused by the interaction of the shock waves from the nacelle/diverter configuration with the flat-plate boundary layer. At the lowest h(sub n)/delta tested, the diverter wedge half-angle had virtually no effect on the nacelle/diverter drag. However, as h(sub n)/delta increased, the nacelle/diverter drag increased as diverter wedge half-angle increased.

Drag reduction of turbulent pipe flows by circular-wall oscillation

NASA Astrophysics Data System (ADS)

Choi, Kwing-So; Graham, Mark

1998-01-01

An experimental study on turbulent pipe flows was conducted with a view to reduce their friction drag by oscillating a section of the pipe in a circumferential direction. The results indicated that the friction factor of the pipe is reduced by as much as 25% as a result of active manipulation of near-wall turbulence structure by circular-wall oscillation. An increase in the bulk velocity was clearly shown when the pipe was oscillated at a constant head, supporting the measured drag reduction in the present experiment. The percentage reduction in pipe friction was found to be better scaled with the nondimensional velocity of the oscillating wall than with its nondimensional period, confirming a suggestion that the drag reduction seem to be resulted from the realignment of longitudinal vortices into a circumferential direction by the wall oscillation.

Reduction of granular drag inspired by self-burrowing rotary seeds

NASA Astrophysics Data System (ADS)

Jung, Wonjong; Choi, Sung Mok; Kim, Wonjung; Kim, Ho-Young

2017-04-01

We present quantitative measurements and mat hematical analysis of the granular drag reduction by rotation, as motivated by the digging of Erodium and Pelargonium seeds. The seeds create a motion to dig into soil before germination using their moisture-responsive awns, which are originally helical shaped but reversibly deform to a linear configuration in a humid environment. We show that the rotation greatly lowers the resistance of soil against penetration because grain rearrangements near the intruder change the force chain network. We find a general correlation for the drag reduction by relative slip, leading to a mathematical model for the granular drag of a rotating intruder. In addition to shedding light on the mechanics of a rotating body in granular media, this work can guide us to design robots working in granular media with enhanced maneuverability.

Particular Solutions in Four body problem with solar wind drag

NASA Astrophysics Data System (ADS)

Kumari, Reena; Singh Kushvah, Badam

2012-07-01

To study the motion of a group of celestial objects/bodies interacting with each other under gravitational attraction. We formulated a four body problem with solar wind drag of one radiating body, rotating about their common center of mass with central configuration. We suppose that the governing forces of the motion of four body problems are mutual gravitational attractions of bodies and drag force of radiating body. Firstly, we derive the equations of motion using new co-ordinates for the four body problem. Again, we find the integrals of motions under different cases regarding to the mass of the bodies. Then we find the zero velocity surfaces and particular solutions. Finally, we examined the effect of solar wind drag on the motion of the four body problem. Keywords: Four Body Problem; Particular Solutions; Radiation Force; Zero Velocity Surfaces.

Aeroheating Thermal Model Correlation for Mars Global Surveyor (MGS) Solar Array

NASA Technical Reports Server (NTRS)

Amundsen, Ruth M.; Dec, John A.; George, Benjamin E.

2003-01-01

The Mars Global Surveyor (MGS) Spacecraft made use of aerobraking to gradually reduce its orbit period from a highly elliptical insertion orbit to its final science orbit. Aerobraking produces a high heat load on the solar arrays, which have a large surface area exposed to the airflow and relatively low mass. To accurately model the complex behavior during aerobraking, the thermal analysis needed to be tightly coupled to the spatially varying, time dependent aerodynamic heating. Also, the thermal model itself needed to accurately capture the behavior of the solar array and its response to changing heat load conditions. The correlation of the thermal model to flight data allowed a validation of the modeling process, as well as information on what processes dominate the thermal behavior. Correlation in this case primarily involved detailing the thermal sensor nodes, using as-built mass to modify material property estimates, refining solar cell assembly properties, and adding detail to radiation and heat flux boundary conditions. This paper describes the methods used to develop finite element thermal models of the MGS solar array and the correlation of the thermal model to flight data from the spacecraft drag passes. Correlation was made to data from four flight thermal sensors over three of the early drag passes. Good correlation of the model was achieved, with a maximum difference between the predicted model maximum and the observed flight maximum temperature of less than 5%. Lessons learned in the correlation of this model assisted in validating a similar model and method used for the Mars Odyssey solar array aeroheating analysis, which were used during onorbit operations.

Base drag prediction on missile configurations

NASA Technical Reports Server (NTRS)

Moore, F. G.; Hymer, T.; Wilcox, F.

1993-01-01

New wind tunnel data have been taken, and a new empirical model has been developed for predicting base drag on missile configurations. The new wind tunnel data were taken at NASA-Langley in the Unitary Wind Tunnel at Mach numbers from 2.0 to 4.5, angles of attack to 16 deg, fin control deflections up to 20 deg, fin thickness/chord of 0.05 to 0.15, and fin locations from 'flush with the base' to two chord-lengths upstream of the base. The empirical model uses these data along with previous wind tunnel data, estimating base drag as a function of all these variables as well as boat-tail and power-on/power-off effects. The new model yields improved accuracy, compared to wind tunnel data. The new model also is more robust due to inclusion of additional variables. On the other hand, additional wind tunnel data are needed to validate or modify the current empirical model in areas where data are not available.

System technology analysis of aeroassisted orbital transfer vehicles - Moderate lift/drag

NASA Technical Reports Server (NTRS)

Florence, D. E.; Fischer, G.

1983-01-01

The utilization of procedures involving aerodynamic braking and/or aerodynamic maneuvering on return from higher altitude orbits to low-earth orbit makes it possible to realize significant performance benefits. The present study is concerned with a number of mission scenarios for Aeroassisted Orbital Transfer Vehicles (AOTV) and the impact of potential technology advances in the performance enhancement of the class of AOTV's having a hypersonic lift to drag ratio (L/D) of 0.75 to 1.5. It is found that the synergistic combination of a hypersonic L/D of 1.2, an advanced cryopropelled engine, and an LH2 drop tank (1-1/2 stage) leads to a single 65,000 pound shuttle, two-man geosynchronous mission with 2100 pounds of useful paylod. Additional payload enhancement is possible with AOTV dry weight reductions due to technology advances in the areas of vehicle structures and thermal protection systems and other subsystems.

The Effect of Surface Irregularities on Wing Drag. II - Lap Joints. 2; Lap Joints

NASA Technical Reports Server (NTRS)

Hood, Manley J.

1938-01-01

Tests have been made in the NACA 8-foot high-speed wind tunnel of the drag caused by four types of lap joint. The tests were made on an airfoil of NACA 23012 section and 5-foot chord and covered in a range of speeds from 80 to 500 miles per hour and lift coefficients from 0 to 0.30. The increases in profile drag caused by representative arrangements of laps varied from 4 to 9%. When there were protruding rivet heads on the surface, the addition of laps increased the drag only slightly. Laps on the forward part of a wing increased the drag considerably more than those farther back.

State dragging using the quantum Zeno effect

NASA Astrophysics Data System (ADS)

Hacohen-Gourgy, Shay; Martin, Leigh; GarcíA-Pintos, Luis Pedro; Dressel, Justin; Siddiqi, Irfan

The quantum Zeno effect is the suppression of Hamiltonian evolution by continuous measurement. It arises as a consequence of the quantum back-action pushing the state towards an eigenstate of the measurement operator. Rotating the operator at a rate much slower than the measurement rate will effectively drag the state with it. We use our recently developed scheme, which enables dynamic control of the measurement operator, to demonstrate this dragging effect on a superconducting transmon qubit. Since the system is continuously measured, the deterministic trajectory can be monitored, and quantum jumps can be detected in real-time. Furthermore, we perform this with two observables that are set to be either commuting or non-commuting, demonstrating new quantum dynamics. This work was supported by the Army Research Office and the Air Force Research Laboratory.

Drag and lift forces in granular media

NASA Astrophysics Data System (ADS)

Guillard, F.; Forterre, Y.; Pouliquen, O.

2013-09-01

Forces exerted on obstacles moving in granular media are studied. The experiment consists in a horizontal cylinder rotating around the vertical axis in a granular medium. Both drag forces and lift forces experienced by the cylinder are measured. The first striking result is obtained during the first half rotation, before the cylinder crosses its wake. Despite the symmetry of the object, a strong lift force is measured, about 20 times the buoyancy. The scaling of this force is studied experimentally. The second remarkable observation is made after several rotations. The drag force dramatically drops and becomes independent of depth, showing that it no longer scales with the hydrostatic pressure. The rotation of the cylinder induces a structure in the packing, which screens the weight of the grains above

Kevlar/PMR-15 reduced drag DC-9 reverser stang fairing

NASA Technical Reports Server (NTRS)

Kawai, R. T.

1982-01-01

A reduced drag fairing for the afterbody enclosing the thrust reverser actuators on the DC-9 has been developed with Kevlar-49/PMR-15 advanced composite material. The improved fairing reduces airplane drag 1% compared to the production baseline. Use of composites reduces weight 40% compared to an equivalent metal fairing. The Kevlar-49/PMR-15 advanced composite is an organic matrix material system that can be used at temperatures up to 500 F.

Low temperature thermoelectric properties of hot pressed composite samples of CrSb2: evidence for possible phonon-drag effect.

NASA Astrophysics Data System (ADS)

Pokharel, Mani; Koirala, Machhindra; Ren, Zhifeng; Opeil, Cyril

We present on the thermoelectric transport properties of CrSb2 samples prepared by hot-press densification in the temperature range of 2 - 350 K. At around 10 K, the thermal conductivity of CrSb2 decreases dramatically by three orders of magnitude compared to the single crystal counterpart. Analysis shows that the reduced thermal conductivity results from increased scattering of the phonons off the grain-boundaries within the samples. A strong interrelationship between the thermal conductivity and the Seebeck coefficient is observed; indicating a significant presence of phonon-drag effect in this system. With ZT = 0.018 at 310 K for the sample hot pressed at 600 oC, an increase in ZT by 80 % over the previously reported values for polycrystalline samples is achieved. We gratefully acknowledge funding for this work by the Department of Defense, United States Air Force Office of Scientific Researchs MURI program under contract FA9550-10-1-0533.

Aeronomy coexperiments on drag-free satellites with proportional thrusters: GP-B and STEP

NASA Astrophysics Data System (ADS)

Jafry, Yusuf R.

1992-01-01

GP-B and STEP are two proposed experiments in basic physics which will utilize drag-free spacecraft in 600 km polar orbits around the earth. By monitoring the activity of the drag-free compensators, it will be possible to obtain in situ drag measurements from which variations in atmospheric density and winds can be observed with unprecedented resolution. With the inclusion of neutral mass spectrometers, it will be possible to distinguish the effects of the various species; thus significantly enhancing the aeronomic contribution of the drag data. The drag information will be contained in both the motion of the spacecraft about the drag-free proof-mass, and the thruster activity. A new smoother has been developed to deconvolve the net forces from the proof-mass sensor measurements. The smoother is an adaptation of an existing algorithm, which has been tailored to cater for completely unknown inputs. After the deconvolution process, the thrust force must be subtracted from the net force to yield the estimate of the drag. Hence, the accuracy of the drag measurements will ultimately depend on the accuracy of the thruster calibration. Perhaps the largest source of uncertainty will be associated with impingement of the thruster plumes on the spacecraft surfaces. It is thus desirable to model these effects. Owing to the low thrust levels, the flow through the GP-B nozzles will be highly rarefied, rendering the conventional continuum model invalid. An experimental procedure was thus devised to characterize the plume structure. A mass spectrometer, modified from a helium leak detector, was used to measure the mass flux distribution. The observed plume shapes were found to be essentially unchanged with mass flow. The experimental results were compared with Boyd's DSMC solutions pertaining to the nozzle geometries and flow conditions used in the experiments. For the assumption of diffuse interaction with the nozzle walls, the numerical results were found to be in excellent

Quantifying drag on wellbore casings in moving salt sheets

NASA Astrophysics Data System (ADS)

Weijermars, R.; Jackson, M. P. A.; Dooley, T. P.

2014-08-01

Frontier hydrocarbon development projects in the deepwater slopes of the Gulf of Mexico Basin, Santos Basin and Lower Congo Basin all require wells to cross ductile layers of autochthonous or allochthonous salt moving at peak rates of 100 mm yr-1. The Couette-Poiseuille number is introduced here to help pinpoint the depth of shear stress reversal in such salt layers. For any well-planned through salt, the probable range of creep forces of moving salt needs to be taken into account when designing safety margins and load-factor tolerance of the well casing. Drag forces increase with wellbore diameter, but more significantly with effective viscosity and speed of the creeping salt layer. The potential drag forces on cased wellbores in moving salt sheets are estimated analytically using a range of salt viscosities (1015-1019 Pa s) and creep rates (0-10 mm yr-1). Drag on perfectly rigid casing of infinite strength may reach up to 13 Giga Newton per meter wellbore length in salt having a viscosity of 1019 Pa s. Well designers may delay stress accumulations due to salt drag when flexible casing accommodates some of the early displacement and strain. However, all creeping salt could displace, fracture and disconnect well casing, eventually. The shear strength of typical heavy duty well casing (about 1000 MPa) can be reached due to drag by moving salt. Internal flow of salt will then fracture the casing near salt entry and exit points, but the structural damage is likely to remain unnoticed early in the well-life when the horizontal shift of the wellbore is still negligibly small (at less than 1 cm yr-1). Disruption of casing and production flow lines within the anticipated service lifetime of a well remains a significant risk factor within distinct zones of low-viscosity salt which may reach ultrafast creep rates of 100 mm yr-1.

Drop tower with no aerodynamic drag

NASA Technical Reports Server (NTRS)

Kendall, J. M., Jr.

1981-01-01

Cooling air accelerated to match velocity of falling object eliminates drag. 3 meter drop tower with suction fan and specific geometry causes air to accelerate downward at 1 g. Although cooling of molten material released from top is slow because surrounding air moves with it, drop remains nearly spherical.

Measurements of long-range enhanced collisional velocity drag through plasma wave damping

NASA Astrophysics Data System (ADS)

Affolter, M.; Anderegg, F.; Dubin, D. H. E.; Driscoll, C. F.

2018-05-01

We present damping measurements of axial plasma waves in magnetized, multispecies ion plasmas. At high temperatures T ≳ 10-2 eV, collisionless Landau damping dominates, whereas, at lower temperatures T ≲ 10-2 eV, the damping arises from interspecies collisional drag, which is dependent on the plasma composition and scales roughly as T-3 /2 . This drag damping is proportional to the rate of parallel collisional slowing, and is found to exceed classical predictions of collisional drag damping by as much as an order of magnitude, but agrees with a new collision theory that includes long-range collisions. Centrifugal mass separation and collisional locking of the species occur at ultra-low temperatures T ≲ 10-3 eV, which reduce the drag damping from the T-3 /2 collisional scaling. These mechanisms are investigated by measuring the damping of higher frequency axial modes, and by measuring the damping in plasmas with a non-equilibrium species profile.

On the Minimum Induced Drag of Wings

NASA Technical Reports Server (NTRS)

Bowers, Albion H.

2007-01-01

This viewgraph presentation reviews the minimum induced drag of wings. The topics include: 1) The History of Spanload Development of the optimum spanload Winglets and their implications; 2) Horten Sailplanes; and 3) Flight Mechanics & Adverse yaw.

Drag and sprint performance of wheelchair basketball players.

PubMed

Coutts, K D

1994-01-01

The purpose of this study was to measure the wheelchair drag and maximal sprint performance abilities of wheelchair basketball players and to make comparisons between male and female players. A group of nine male and eight female wheelchair basketball players attending a national training camp consented to serve as subjects. Each subject completed six coast-down trials at speeds from a walking pace (1 to 1.5 m/s) to maximal for determining wheelchair drag and then performed four maximal sprint trials from a stationary start over the length (35 m) of the gymnasium floor. A portable computer that recorded the time to the nearest 0.001 second of each half revolution of a rear wheel was attached to the wheelchair of each subject. The drag force during the coast-down trials and the power output during the sprint trials were determined from the recorded data. Differences between the genders in a number of subject and trial variables were evaluated by t-tests using the 0.05 level of significance. There were no significant differences between the means of the male and female groups in age (27 vs. 28 yrs), wheelchair mass (12.0 vs. 11.61 kg), or regression predicted drag forces at speeds of 2 m/s (5.3 vs. 5.5 N) and 5 m/s (16.7 vs. 13.5 N). The male subjects were significantly heavier (78.3 vs. 59.1 kg) and had a higher tire pressure (123 vs. 94 psi). In the sprint trial results, the males exhibited a significantly higher maximal speed (4.75 vs. 4.08 m/s), higher peak acceleration (1.32 vs. 1.03 m/s/s), and a higher peak power output (530 vs. 264 w).

An active attitude control system for a drag sail satellite

NASA Astrophysics Data System (ADS)

Steyn, Willem Herman; Jordaan, Hendrik Willem

2016-11-01

The paper describes the development and simulation results of a full ADCS subsystem for the deOrbitSail drag sail mission. The deOrbitSail satellite was developed as part of an European FP7 collaboration research project. The satellite was launched and commissioning started on 10th July 2015. Various new actuators and sensors designed for this mission will be presented. The deOrbitSail satellite is a 3U CubeSat to deploy a 4 by 4 m drag sail from an initial 650 km circular polar low earth orbit. With an active attitude control system it will be shown that by maximising the drag force, the expected de-orbiting period from the initial altitude will be less than 50 days. A future application of this technology will be the use of small drag sails as low-cost devices to de-orbit LEO satellites, when they have reached their end of life, without having to use expensive propulsion systems. Simulation and Hardware-in-Loop experiments proved the feasibility of the proposed attitude control system. A magnetic-only control approach using a Y-Thomson spin, is used to detumble the 3U Cubesat with stowed sail and subsequently to 3-axis stabilise the satellite to be ready for the final deployment phase. Minituarised torquer rods, a nano-sized momentum wheel, attitude sensor hardware (magnetometer, sun, earth) developed for this phase will be presented. The final phase will be to deploy and 3-axis stabilise the drag sail normal to the satellite's velocity vector, using a combined Y-momentum wheel and magnetic controller. The design and performance improvements when using a 2-axis translation stage to adjust the sail centre-of-pressure to satellite centre-of-mass offset, will also be discussed, although for launch risk reasons this stage was not included in the final flight configuration. To accurately determine the drag sail's attitude during the sunlit part of the orbit, an accurate wide field of view dual sensor to measure both the sun and nadir vector direction was developed for

The Drag Penalty of Lateral Asymmetries in Formation Flight

NASA Astrophysics Data System (ADS)

Weihs, Daniel; Gabbay, Karen

2006-11-01

It has long been known that formation flight of birds and aircraft results in a significant energy saving due to reduction in induced drag. However measured gains have consistently been lower, usually explained by viscous effects neglected by the potential flow model for lift and induced drag. We show that the inherent asymmetry of the flow-field in the general case results in rolling and yawing moments, which need to be corrected by control surface reflection. This deflection results in an increase in drag, which partially cancels the gains mentioned above. Using classical lifting line theory and elliptical lift distributions on two or more wings flying in formation we show that the penalty incurred by these corrections can reduce the expected gains by up to 25%. We also show that the gains for an individual in formation flight grow with the number of members of the formation, up to about 7 members, the added gains becoming negligible beyond that number. The present results are relevant for large aspect-ratio, fixed wing aircraft, and gliding bird flocks.

Automated design of minimum drag light aircraft fuselages and nacelles

NASA Technical Reports Server (NTRS)

Smetana, F. O.; Fox, S. R.; Karlin, B. E.

1982-01-01

The constrained minimization algorithm of Vanderplaats is applied to the problem of designing minimum drag faired bodies such as fuselages and nacelles. Body drag is computed by a variation of the Hess-Smith code. This variation includes a boundary layer computation. The encased payload provides arbitrary geometric constraints, specified a priori by the designer, below which the fairing cannot shrink. The optimization may include engine cooling air flows entering and exhausting through specific port locations on the body.

Buoyancy increase and drag-reduction through a simple superhydrophobic coating.

PubMed

Hwang, Gi Byoung; Patir, Adnan; Page, Kristopher; Lu, Yao; Allan, Elaine; Parkin, Ivan P

2017-06-08

A superhydrophobic paint was fabricated using 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES), TiO 2 nanoparticles and ethanol. The paint has potential for aquatic application of a superhydrophobic coating as it induces increased buoyancy and drag reduction. Buoyance testing showed that the reduction of surface energy by superhydrophobic coating made it feasible that glass, a high density material, was supported by the surface tension of water. In a miniature boat sailing test, it was shown that the low energy surface treatment decreased the adhesion of water molecules to the surface of the boat resulting in a reduction of the drag force. Additionally, a robust superhydrophobic surface was fabricated through layer-by-layer coating using adhesive double side tape and the paint, and after a 100 cm abrasion test with sand paper, the surface still retained its water repellency, enhanced buoyancy and drag reduction.

Mass center estimation of a drag-free satellite

NASA Technical Reports Server (NTRS)

Sanz Fernandez De Cordova, S.; Debra, D. B.

1975-01-01

The mass center location of a spinning drag-free satellite can be estimated because there is control required to accelerate the mass center along the axis of spin as long as there is some nutation in the spinning motion. Linear and nonlinear models are compared and observability discussed. Online estimation fails when nutation is damped so an offline mechanization is proposed. A new sensor has been designed to permit greater relative motion than was possible on the drag-free satellite flown in 1972 (JH-1). Experimental laboratory results using a spinning vehicle with the new sensor mounted 30 cm from a spherical air bearing support are presented which confirm earlier simulation results.

Bioinspired superhydrophobic, self-cleaning and low drag surfaces

NASA Astrophysics Data System (ADS)

Bhushan, Bharat

2013-09-01

Nature has evolved objects with desired functionality using commonly found materials. Nature capitalizes on hierarchical structures to achieve functionality. The understanding of the functions provided by objects and processes found in nature can guide us to produce nanomaterials, nanodevices, and processes with desirable functionality. This article provides an overview of four topics: (1) Lotus Effect used to develop superhydrophobic and self-cleaning/antifouling surfaces with low adhesion, (2) Shark Skin Effect to develop surfaces with low fluid drag and anti-fouling characteristics, and (3-4) Rice Leaf and Butterfly Wing Effect to develop superhydrophobic and self-cleaning surfaces with low drag. Rice Leaf and Butterfly Wings combine the Shark Skin and Lotus Effects.

Development of FDR-AF (Frictional Drag Reduction Anti-Fouling) Marine Coating

NASA Astrophysics Data System (ADS)

Lee, Inwon; Park, Hyun; Chun, Ho Hwan; GCRC-SOP Team

2013-11-01

In this study, a novel skin-friction reducing marine paint has been developed by mixing fine powder of PEO(PolyEthyleneOxide) with SPC (Self-Polishing Copolymer) AF (Anti-Fouling) paint. The PEO is well known as one of drag reducing agent to exhibit Toms effect, the attenuation of turbulent flows by long chain polymer molecules in the near wall region. The frictional drag reduction has been implemented by injecting such polymer solutions to liquid flows. However, the injection holes have been a significant obstacle to marine application. The present PEO-containing marine paint is proposed as an alternative to realize Toms effect without any hole on the ship surface. The erosion mechanism of SPC paint resin and the subsequent dissolution of PEO enable the controlled release of PEO solution from the coating. Various tests such as towing tank drag measurement of flat plate and turbulence measurement in circulating water tunnel demonstrated over 10% frictional drag reduction compared with conventional AF paint. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) through GCRC-SOP(No. 2011-0030013).

Fluid Dynamics of Small, Rugged Vacuum Pumps of Viscous-Drag Type

NASA Technical Reports Server (NTRS)

Russell, John M.

2002-01-01

The need to identify spikes in the concentration of hazardous gases during countdowns to space shuttle launches has led Kennedy Space Center to acquire considerable expertise in the design, construction, and operation of special-purpose gas analyzers of mass-spectrometer type. If such devices could be miniaturized so as to fit in a small airborne package or backpack them their potential applications would include integrated vehicle health monitoring in later-generation space shuttles and in hazardous material detection in airports, to name two examples. The bulkiest components of such devices are vacuum pumps, particularly those that function in the low vacuum range. Now some pumps that operate in the high vacuum range (e.g. molecular-drag and turbomolecular pumps) are already small and rugged. The present work aims to determine whether, on physical grounds, one may or may not adopt the molecular-drag principle to the low-vacuum range (in which case viscous-drag principle is the appropriate term). The deliverable of the present effort is the derivation and justification of some key formulas and calculation methods for the preliminary design of a single-spool, spiral-channel viscous-drag pump.

Wigs, laughter, and subversion: Charles Busch and strategies of drag performance.

PubMed

Niles, Richard

2004-01-01

This paper examines the strategies of drag performer/ playwright Charles Busch. His performance aesthetic is explored and shown to be subversive even though its initial impulse is to entertain. Basing my arguments on the work of Judith Butler, Elin Diamond, and others, I argue that drag queens like Busch can not only entertain but also make audiences question and criticize through drag's power to create a Brechtian alienation effect and historicize the subject. After showing how he can be viewed as a drag queen, I give a brief biography and discuss such contested terms as "camp" and "gay sensibility." I then focus on Busch's staged reading of Ibsen's Hedda Gahler andA Doll's House, both done in one afternoon at Theatre for The New City (6 May 2000). By examining the performance of Busch and his fellow actors, I demonstrate how a contemporary relevancy is achieved by having the roles played by a female impersonator whose acting choices are filtered through a gay sensibility. The ongoing dialectic between spectator and performer creates a historicized moment in performance that underscores the gender dynamics in unexpected and stimulating ways.

Analysis and design of planar and non-planar wings for induced drag minimization

NASA Technical Reports Server (NTRS)

Mortara, Karl W.; Straussfogel, Dennis M.; Maughmer, Mark D.

1992-01-01

The goal of the work reported herein is to develop and validate computational tools to be used for the design of planar and non-planar wing geometries for minimum induced drag. Because of the iterative nature of the design problem, it is important that, in addition to being sufficiently accurate for the problem at hand, these tools need to be reasonably fast and computationally efficient. Toward this end, a method of predicting induced drag in the presence of a free wake has been coupled with a panel method. The induced drag prediction technique is based on the application of the Kutta-Joukowski law at the trailing edge. Until now, the use of this method has not been fully explored and pressure integration and Trefftz-plane calculations favored. As is shown in this report, however, the Kutta-Joukowski method is able to give better results for a given amount of effort than the more commonly used techniques, particularly when relaxed wakes and non-planar wing geometries are considered. Using these methods, it is demonstrated that a reduction in induced drag can be achieved through non-planar wing geometries. It remains to determine what overall drag reductions are possible when the induced drag reduction is traded-off against increased wetted area. With the design methodology that is described herein, such trade studies can be performed in which the non-linear effects of the free wake are taken into account.

Airfoil Drag Reduction using Controlled Trapped Vorticity Concentrations

NASA Astrophysics Data System (ADS)

Desalvo, Michael; Glezer, Ari

2017-11-01

The aerodynamic performance of a lifting surface at low angles of attack (when the base flow is fully attached) is improved through fluidic modification of its ``apparent'' shape by superposition of near-surface trapped vorticity concentrations. In the present wind tunnel investigations, a controlled trapped vorticity concentration is formed on the pressure surface of an airfoil (NACA 4415) using a hybrid actuator comprising a passive obstruction of scale O(0.01c) and an integral synthetic jet actuator. The jet actuation frequency [Stact O(10)] is selected to be at least an order of magnitude higher than the characteristic unstable frequency of the airfoil wake, thereby decoupling the actuation from the global instabilities of the base flow. Regulation of vorticity accumulation in the vicinity of the actuator by the jet effects changes in the local pressure, leading in turn to changes in the airfoil's drag and lift. Trapped vorticity can lead to a significant reduction in drag and reduced lift (owing to the sense of the vorticity), e.g. at α =4° and Re = 6.7 .105 the drag and lift reductions are 14% and 2%, respectively. PIV measurements show the spatial variation in the distribution of vorticity concentrations and yield estimates of the corresponding changes in circulation.

Aerodynamic drag reduction by vertical splitter plates

NASA Astrophysics Data System (ADS)

Gilliéron, Patrick; Kourta, Azeddine

2010-01-01

The capacity of vertical splitter plates placed at the front or the rear of a simplified car geometry to reduce drag, with and without skew angle, is investigated for Reynolds numbers between 1.0 × 106 and 1.6 × 106. The geometry used is a simplified geometry to represent estate-type vehicles, for the rear section, and MPV-type vehicle. Drag reductions of nearly 28% were obtained for a zero skew angle with splitter plates placed at the front of models of MPV or utility vehicles. The results demonstrate the advantage of adapting the position and orientation of the splitter plates in the presence of a lateral wind. All these results confirm the advantage of this type of solution, and suggest that this expertise should be used in the automotive field to reduce consumption and improve dynamic stability of road vehicles.

RotCFD Analysis of the AH-56 Cheyenne Hub Drag

NASA Technical Reports Server (NTRS)

Solis, Eduardo; Bass, Tal A.; Keith, Matthew D.; Oppenheim, Rebecca T.; Runyon, Bryan T.; Veras-Alba, Belen

2016-01-01

In 2016, the U.S. Army Aviation Development Directorate (ADD) conducted tests in the U.S. Army 7- by 10- Foot Wind Tunnel at NASA Ames Research Center of a nonrotating 2/5th-scale AH-56 rotor hub. The objective of the tests was to determine how removing the mechanical control gyro affected the drag. Data for the lift, drag, and pitching moment were recorded for the 4-bladed rotor hub in various hardware configurations, azimuth angles, and angles of attack. Numerical simulations of a selection of the configurations and orientations were then performed, and the results were compared with the test data. To generate the simulation results, the hardware configurations were modeled using Creo and Rhinoceros 5, three-dimensional surface modeling computer-aided design (CAD) programs. The CAD model was imported into Rotorcraft Computational Fluid Dynamics (RotCFD), a computational fluid dynamics (CFD) tool used for analyzing rotor flow fields. RotCFD simulation results were compared with the experimental results of three hardware configurations at two azimuth angles, two angles of attack, and with and without wind tunnel walls. The results help validate RotCFD as a tool for analyzing low-drag rotor hub designs for advanced high-speed rotorcraft concepts. Future work will involve simulating additional hub geometries to reduce drag or tailor to other desired performance levels.

Heat Models of Asteroids and the YORP Effect

NASA Astrophysics Data System (ADS)

Golubov, O.

The Yarkovsky-O'Keefe-Radzievski-Paddack (YORP) effect is a torque of light pressure recoil forces acting on an asteroid. We show how this torque can be expressed as an integral of a universal function over the surface of an asteroid, and discuss generalizations of this expression for the case of non-Lambert's scattering laws, non-convex shapes of asteroids, and non-zero heat conductivity. Then we discuss tangential YORP (TYORP), which appears due to uneven heat conductivity in stones lying on the surface of an asteroid. TYORP manifests itself as a drag, which pulls the surface in the tangential direction. Finally, we discuss relation and interplay between the normal YORP and the tangential YORP.

Spacecraft drag-free technology development: On-board estimation and control synthesis

NASA Technical Reports Server (NTRS)

Key, R. W.; Mettler, E.; Milman, M. H.; Schaechter, D. B.

1982-01-01

Estimation and control methods for a Drag-Free spacecraft are discussed. The functional and analytical synthesis of on-board estimators and controllers for an integrated attitude and translation control system is represented. The framework for detail definition and design of the baseline drag-free system is created. The techniques for solution of self-gravity and electrostatic charging problems are applicable generally, as is the control system development.

Calculated Drag of an Aerial Refueling Assembly Through Airplane Performance Analysis

NASA Technical Reports Server (NTRS)

Vachon, Jake; Ray, Ronald; Calianno, Carl

2004-01-01

This viewgraph document reviews NASA Dryden's work on Aerial refueling, with specific interest in calculating the drag of the refueling system. The aerodynamic drag of an aerial refueling assembly was calculated during the Automated Aerial Refueling project at the NASA Dryden Flight Research Center. An F/A-18A airplane was specially instrumented to obtain accurate fuel flow measurements and to determine engine thrust

Comparison of NTF Experimental Data with CFD Predictions from the Third AIAA CFD Drag Prediction Workshop

NASA Technical Reports Server (NTRS)

Vassberg, John C.; Tinoco, Edward N.; Mani, Mori; Levy, David; Zickuhr, Tom; Mavriplis, Dimitri J.; Wahls, Richard A.; Morrison, Joseph H.; Brodersen, Olaf P.; Eisfeld, Bernhard;

Getting the temperature right: Understanding thermal emission from airless bodies

NASA Astrophysics Data System (ADS)

Bandfield, J.; Greenhagen, B. T.; Hayne, P. O.; Williams, J. P.; Paige, D. A.

2016-12-01

Thermal infrared measurements are crucial for understanding a wide variety of processes present on airless bodies throughout the solar system. Although these data can be complex, they also contain an enormous amount of useful information. By building a framework for understanding thermal infrared datasets, significant advances are possible in the understanding of regolith development, detection of H2O and OH-, characterizing the nature and magnitude of Yarkovsky and YORP effects, and determination of the properties of newly identified asteroids via telescopic measurements. Airless bodies can have both extremely rough and insulating surfaces. For example, these two properties allow for sunlit and shaded or buried lunar materials separated by just a few centimeters to vary by 200K. In this sense, there is no "correct" temperature interpretable from orbital, or even in-situ, measurements. The surface contains a wide mixture of temperatures in the field of view, and rougher surfaces greatly enhance this anisothermality. We have used the Lunar Reconnaissance Orbiter Diviner Radiometer to characterize these effects by developing new targeting and analysis methods, including extended off-nadir observations and combined surface roughness and thermal modeling (Fig. 1). These measurements and models have shown up to 100K brightness temperature differences from measurements that differ only in the viewing angle of the observation. In addition, the thermal emission near 3 μm can be highly dependent on the surface roughness, resulting in more extensive and prominent lunar 3 μm H2O and OH-absorptions than indicated in data corrected by isothermal models. The datasets serve as a foundation for the derivation and understanding of surface spectral and thermophysical properties. Roughness and anisothermality effects are likely to dominate infrared measurements from many spacecraft, including LRO, Dawn, BepiColombo, OSIRIS-REx, Hayabusa-2, and Europa Clipper.

Re-Entry Point Targeting for LEO Spacecraft using Aerodynamic Drag

NASA Technical Reports Server (NTRS)

Omar, Sanny; Bevilacqua, Riccardo; Fineberg, Laurence; Treptow, Justin; Johnson, Yusef; Clark, Scott

2016-01-01

Most Low Earth Orbit (LEO) spacecraft do not have thrusters and re-enter atmosphere in random locations at uncertain times. Objects pose a risk to persons, property, or other satellites. Has become a larger concern with the recent increase in small satellites. Working on a NASA funded project to design a retractable drag device to expedite de-orbit and target a re-entry location through modulation of the drag area. Will be discussing the re-entry point targeting algorithm here.

Progress in Frictional Drag Reduction Summer 1971 to Summer 1972

DTIC Science & Technology

1973-01-01

directed at achieving •nprovey sea wnd Air ii .- wa for•ted in March 1967 by merging the David Taylor Madei Basin at CizIeniAir, ’ýplr/t]La with ihe...means. Greskovich and Shrier (50) show that polymers also provide drag reduction in two-phase systems such as gas-liquid systems. Medical applications...May 1971). 50. Greskovich, E. J. and A. J. Shrier , "Drag Reduction in Two- Phase Flows," Industrial and Engineering Chemistry (Fundamentals), Vol. 10

Optimal control of lift/drag ratios on a rotating cylinder

NASA Technical Reports Server (NTRS)

Ou, Yuh-Roung; Burns, John A.

1992-01-01

We present the numerical solution to a problem of maximizing the lift to drag ratio by rotating a circular cylinder in a two-dimensional viscous incompressible flow. This problem is viewed as a test case for the newly developing theoretical and computational methods for control of fluid dynamic systems. We show that the time averaged lift to drag ratio for a fixed finite-time interval achieves its maximum value at an optimal rotation rate that depends on the time interval.

Utilising flags to reduce drag around a short finite circular cylinder

NASA Astrophysics Data System (ADS)

Javadi, Kh.; Kiani, F.; Tahaye Abadi, M.

2018-03-01

This paper utilises flags to decrease the drag around a short finite circular cylinder. Wall-adapted large eddy simulation and two-way fluid-structure interaction methods were applied to resolve unsteady turbulent flow structure. The far-field Reynolds number of the current configuration based on the cylinder diameter was chosen to be 20,000. In addition, the length-to-diameter ratio of the cylinder was assumed to be L/D = 2 whereas the flexible flag had a width-to-diameter ratio of W/D = 1.5. The results were compared with the regular short finite circular cylinder and the rigid flagged cylinder in our previous work. The results indicate that utilising flags inside the near-wake region of the cylinder reduces the pressure drag. The physical mechanism of this drag reduction is presented.

Nonequilibrium Tuning of the Thermal Casimir Effect.

PubMed

Dean, David S; Lu, Bing-Sui; Maggs, A C; Podgornik, Rudolf

2016-06-17

In net-neutral systems correlations between charge fluctuations generate strong attractive thermal Casimir forces and engineering these forces to optimize nanodevice performance is an important challenge. We show how the normal and lateral thermal Casimir forces between two plates containing Brownian charges can be modulated by decorrelating the system through the application of an electric field, which generates a nonequilibrium steady state with a constant current in one or both plates, reducing the ensuing fluctuation-generated normal force while at the same time generating a lateral drag force. This hypothesis is confirmed by detailed numerical simulations as well as an analytical approach based on stochastic density functional theory.

Inlet Aerodynamics and Ram Drag of Laser-Propelled Lightcraft Vehicles

NASA Astrophysics Data System (ADS)

Langener, Tobias; Myrabo, Leik; Rusak, Zvi

2010-05-01

Numerical simulations are used to study the aerodynamic inlet properties of three axisymmetric configurations of laser-propelled Lightcraft vehicles operating at subsonic, transonic and supersonic speeds up to Mach 5. The 60 cm vehicles were sized for launching 0.1-1.0 kg nanosatellites with combined-cycle airbreathing/rocket engines, transitioning between propulsion modes at roughly Mach 5-6. Results provide the pressure, temperature, density, and velocity flowfields around and through the three representative vehicle/engine configurations, as well as giving the resulting ram drag and total drag coefficients—all as a function of flight Mach number. Simulations with rotating boundaries were also carried out, since for stability reasons, Lightcraft are normally spun up before lift-off. Given the three alternatives, it is demonstrated that the optimal geometry for minimum drag is the configuration with a parabola nose; hence, these inlet flow conditions are being applied in subsequent "direct connect" 2D laser propulsion experiments in a small transonic flow facility.

Evaluation of WRF Simulations With Different Selections of Subgrid Orographic Drag Over the Tibetan Plateau

NASA Astrophysics Data System (ADS)

Zhou, X.; Beljaars, A.; Wang, Y.; Huang, B.; Lin, C.; Chen, Y.; Wu, H.

2017-09-01

Weather Research and Forecasting (WRF) simulations with different selections of subgrid orographic drag over the Tibetan Plateau have been evaluated with observation and ERA-Interim reanalysis. Results show that the subgrid orographic drag schemes, especially the turbulent orographic form drag (TOFD) scheme, efficiently reduce the 10 m wind speed bias and RMS error with respect to station measurements. With the combination of gravity wave, flow blocking and TOFD schemes, wind speed is simulated more realistically than with the individual schemes only. Improvements are also seen in the 2 m air temperature and surface pressure. The gravity wave drag, flow blocking drag, and TOFD schemes combined have the smallest station mean bias (-2.05°C in 2 m air temperature and 1.27 hPa in surface pressure) and RMS error (3.59°C in 2 m air temperature and 2.37 hPa in surface pressure). Meanwhile, the TOFD scheme contributes more to the improvements than the gravity wave drag and flow blocking schemes. The improvements are more pronounced at low levels of the atmosphere than at high levels due to the stronger drag enhancement on the low-level flow. The reduced near-surface cold bias and high-pressure bias over the Tibetan Plateau are the result of changes in the low-level wind components associated with the geostrophic balance. The enhanced drag directly leads to weakened westerlies but also enhances the a-geostrophic flow in this case reducing (enhancing) the northerlies (southerlies), which bring more warm air across the Himalaya Mountain ranges from South Asia (bring less cold air from the north) to the interior Tibetan Plateau.

Verification of drag-reduction capabilities of stiff compliant coatings in air flow at moderate speeds

NASA Astrophysics Data System (ADS)

Boiko, Andrey V.; Kulik, Victor M.; Chun, Ho-Hwan; Lee, Inwon

2011-12-01

Skin frictional drag reduction efficiency of "stiff" compliant coating was investigated in a wind tunnel experiment. Flat plate compliant coating inserts were installed in a wind tunnel and the measurements of skin frictional drag and velocity field were carried out. The compliant coatings with varying viscoelastic properties had been prepared using different composition. In order to optimize the coating thickness, the most important design parameter, the dynamic viscoelastic properties had been determined experimentally. The aging of the materials (variation of their properties) during half a year was documented as well. A design procedure proposed by Kulik et al. (2008) was applied to get an optimal value for the coating thickness. Along with the drag measurement using the strain balance, velocity and pressure were measured for different coatings. The compliant coatings with the thickness h = 7mm achieved 4~5% drag reduction within a velocity range 30~40 m/s. The drag reduction mechanism of the attenuation of turbulence velocity fluctuations due to the compliant coating was demonstrated. It is envisioned that larger drag reduction effect is obtainable at higher flow velocities for high speed trains and subsonic aircrafts.

Drag-n-fly: a Proposal in Response to a Low Reynolds Number Station Keeping Mission

NASA Technical Reports Server (NTRS)

Foohey, Mark; Niehaus, John; Neumann, Jenny; Deviny, Pat; Zurovchak, Jerry; Brenner, Joey; Gendron, Peter

1990-01-01

The Drag-n-Fly is a remotely piloted, low Reynolds number vehicle. It was designed to maintain level controlled flight and fly a closed course at flight speeds corresponding to Reynolds numbers of less than 2 x 10(exp 5) and as close to 1 x 10(exp 5) as possible. The success of the mission will be associated with achieving the lowest mean chord Reynolds number possible and maximizing loiter time on the course. The flight plan for the Drag-n-Fly calls for the vehicle to ascent to a cruise altitude of 25 ft. The airfoil selected for the Drag-n-Fly is a Spica chosen for its high lift coefficient at low Reynolds number. The propulsion system for the Drag-n-Fly consists of a 10 inch diameter propeller mounted on the front of the vehicle. Structural support for the Drag-n-Fly comes from four box beams running the length of the fuselage. The tail and horizontal stabilizers are located far aft of the lifting surface in order to assure proper static stability. The present design for the Drag-n-Fly will meet the criteria for the present mission.

In-situ measurement of electroosmotic drag coefficient in Nafion membrane for the PEMFC.

PubMed

Peng, Zhe; Morin, Arnaud; Huguet, Patrice; Schott, Pascal; Pauchet, Joël

2011-11-10

A new method based on hydrogen pump has been developed to measure the electroosmotic drag coefficient in representative PEMFC operating conditions. It allows eliminating the back-flow of water which leads to some errors in the calculation of this coefficient with previously reported electrochemical methods. Measurements have been performed on 50 μm thick Nafion membranes both extruded and recast. Contrary to what has been described in most of previous published works, the electroosmotic drag coefficient decreases as the membrane water content increases. The same trend is observed for temperatures between 25 and 80 °C. For the same membrane water content, the electroosmotic drag coefficient increases with temperature. In the same condition, there is no difference in drag coefficient for extruded Nafion N112 and recast Nafion NRE212. These results are discussed on the basis of the two commonly accepted proton transport mechanisms, namely, Grotthus and vehicular.

Drag crisis moderation by thin air layers sustained on superhydrophobic spheres falling in water.

PubMed

Jetly, Aditya; Vakarelski, Ivan U; Thoroddsen, Sigurdur T

2018-02-28

We investigate the effect of thin air layers naturally sustained on superhydrophobic surfaces on the terminal velocity and drag force of metallic spheres free falling in water. The surface of 20 mm to 60 mm steel or tungsten-carbide spheres is rendered superhydrophobic by a simple coating process that uses a commercially available hydrophobic agent. By comparing the free fall of unmodified spheres and superhydrophobic spheres in a 2.5 meter tall water tank, it is demonstrated that even a very thin air layer (∼1-2 μm) that covers the freshly dipped superhydrophobic sphere can reduce the drag force on the spheres by up to 80%, at Reynolds numbers from 10 5 to 3 × 10 5 , owing to an early drag crisis transition. This study complements prior investigations on the drag reduction efficiency of model gas layers sustained on heated metal spheres falling in liquid by the Leidenfrost effect. The drag reduction effects are expected to have significant implications for the development of sustainable air-layer-based energy saving technologies.

Drag Measurements over Embedded Cavities in a Low Reynolds Number Couette Flow

NASA Astrophysics Data System (ADS)

Gilmer, Caleb; Lang, Amy; Jones, Robert

2010-11-01

Recent research has revealed that thin-walled, embedded cavities in low Reynolds number flow have the potential to reduce the net viscous drag force acting on the surface. This reduction is due to the formation of embedded vortices allowing the outer flow to pass over the surface via a roller bearing effect. It is also hypothesized that the scales found on butterfly wings may act in a similar manner to cause a net increase in flying efficiency. In this experimental study, rectangular embedded cavities were designed as a means of successfully reducing the net drag across surfaces in a low Reynolds number flow. A Couette flow was generated via a rotating conveyor belt immersed in a tank of high viscosity mineral oil above which the plates with embedded cavities were placed. Drag induced on the plate models was measured using a force gauge and compared directly to measurements acquired over a flat plate. Various cavity aspect ratios and gap heights were tested in order to determine the conditions under which the greatest drag reductions occurred.

A preliminary investigation of the drag and ventilation characteristics of livestock haulers

NASA Technical Reports Server (NTRS)

Hoffman, J. A.; Sandin, D. R.

1983-01-01

A wind tunnel evaluation of the drag and ventilation characteristics of a conventional (unmodified) and five modified subscale model livestock haulers at 0 deg yaw angle has been made. The unmodified livestock hauler has a relatively high drag coefficient, and a low velocity recirculation region exists in the forward portion of the hauler. The use of a streamlined forebody and enclosed gap reduced the drag coefficient of one model by 42% and improved the rate at which contaminants can be flushed from the cargo compartment by a factor of 2.5. From the limited data obtained, any increase in the fraction of open area of the trailer sides was found to improve the trailer ventilation. The use of a ram air inlet can improve the ventilation within the hauler and remove the low velocity recirculation region at the expense of a modest increase in the truck's drag coefficient. A mathematical model for vehicles with ram air or NACA submerged inlets was developed and appears to adequately predict the ventilation characteristics of livestock haulers.

Effects of Winglets on the Drag of a Low-Aspect-Ratio Configuration

NASA Technical Reports Server (NTRS)

Smith, Leigh Ann; Campbell, Richard L.

1996-01-01

A wind-tunnel investigation has been performed to determine the effect of winglets on the induced drag of a low-aspect-ratio wing configuration at Mach numbers between 0.30 and 0.85 and a nominal angle-of-attack range from -2 deg to 20 deg. Results of the tests at the cruise lift coefficient showed significant increases in lift-drag ratio for the winglet configuration relative to a wing-alone configuration designed for the same lift coefficient and Mach number. Further, even larger increases in lift-drag ratio were observed at lift coefficients above the design value at all Mach numbers tested. The addition of these winglets had a negligible effect on the static lateral-directional stability characteristics of the configuration. No tests were made to determine the effect of these winglets at supersonic Mach numbers, where increases in drag caused by winglets might be more significant. Computational analyses were also performed for the two configurations studied. Linear and small-disturbance formulations were used. The codes were found to give reasonable performance estimates sufficient for predicting changes of this magnitude.

Drag Reduction Through Distributed Electric Propulsion

NASA Technical Reports Server (NTRS)

Stoll, Alex M.; Bevirt, JoeBen; Moore, Mark D.; Fredericks, William J.; Borer, Nicholas K.

2014-01-01

One promising application of recent advances in electric aircraft propulsion technologies is a blown wing realized through the placement of a number of electric motors driving individual tractor propellers spaced along each wing. This configuration increases the maximum lift coefficient by providing substantially increased dynamic pressure across the wing at low speeds. This allows for a wing sized near the ideal area for maximum range at cruise conditions, imparting the cruise drag and ride quality benefits of this smaller wing size without decreasing takeoff and landing performance. A reference four-seat general aviation aircraft was chosen as an exemplary application case. Idealized momentum theory relations were derived to investigate tradeoffs in various design variables. Navier-Stokes aeropropulsive simulations were performed with various wing and propeller configurations at takeoff and landing conditions to provide insight into the effect of different wing and propeller designs on the realizable effective maximum lift coefficient. Similar analyses were performed at the cruise condition to ensure that drag targets are attainable. Results indicate that this configuration shows great promise to drastically improve the efficiency of small aircraft.

Controlling turbulent drag across electrolytes using electric fields.

PubMed

Ostilla-Mónico, Rodolfo; Lee, Alpha A

2017-07-01

Reversible in operando control of friction is an unsolved challenge that is crucial to industrial tribology. Recent studies show that at low sliding velocities, this control can be achieved by applying an electric field across electrolyte lubricants. However, the phenomenology at high sliding velocities is yet unknown. In this paper, we investigate the hydrodynamic friction across electrolytes under shear beyond the transition to turbulence. We develop a novel, highly parallelised numerical method for solving the coupled Navier-Stokes Poisson-Nernst-Planck equation. Our results show that turbulent drag cannot be controlled across dilute electrolytes using static electric fields alone. The limitations of the Poisson-Nernst-Planck formalism hint at ways in which turbulent drag could be controlled using electric fields.

Disturbance of eelgrass Zostera marina by commercial mussel Mytilus edulis harvesting in Maine: Dragging impacts and habitat recovery

USGS Publications Warehouse

Neckles, Hilary A.; Short, Frederick T.; Barker, Seth; Kopp, Blaine S.

2005-01-01

We studied the effects of commercial harvest of blue mussels Mytilus edulis on eelgrass Zostera marina L. in Maquoit Bay, Maine, USA, at a hierarchy of scales. We used aerial photography, underwater video, and eelgrass population- and shoot-based measurements to quantify dragging impacts within 4 sites that had been disturbed at different times over an approximate 7 yr interval, and to project eelgrass meadow recovery rates. Dragging had disturbed 10% of the eelgrass cover in Maquoit Bay, with dragged sites ranging from 3.4 to 31.8 ha in size. Dragging removed above- and belowground plant material from the majority of the bottom in the disturbed sites. One year following dragging, eelgrass shoot density, shoot height and total biomass of disturbed sites averaged respectively 2 to 3%, 46 to 61% and <1% that of the reference sites. Substantial differences in eelgrass biomass persisted between disturbed and reference sites up to 7 yr after dragging. Dragging did not affect physical characteristics of the sediment. The pattern and rate of eelgrass bed recovery depended strongly on initial dragging intensity; areas of relatively light dragging with many remnant eelgrass patches (i.e. patches that were missed by the mussel dredge) showed considerable revegetation in 1 yr. However, by developing recovery trajectories from measurements at sites disturbed in different years, we projected that it would require a mean of 10.6 yr for recovery of eelgrass shoot density within the areas of intense dragging characterizing most of the disturbed sites. A spatial simulation model based on measured rates of lateral patch-expansion (mean 12.5 cm yr-1) and new-patch recruitment (mean 0.19 patches m-2 yr-1) yielded a mean bed recovery time of 9 to 11 yr following dragging, depending on initial degree of plant removal. Model simulations suggested that with favorable environmental conditions, eelgrass beds might recover from dragging disturbance in 6 yr; conversely, recovery under

Disturbance of eelgrass Zostera marina by commercial mussel Mytilus edulis harvesting in Maine: Dragging impacts and habitat recovery

USGS Publications Warehouse

Neckles, H.A.; Short, F.T.; Barker, S.; Kopp, B.S.

2005-01-01

We studied the effects of commercial harvest of blue mussels Mytilus edulis on eelgrass Zostera marina L. in Maquoit Bay, Maine, USA, at a hierarchy of scales. We used aerial photography, underwater video, and eelgrass population- and shoot-based measurements to quantify dragging impacts within 4 sites that had been disturbed at different times over an approximate 7 yr interval, and to project eelgrass meadow recovery rates. Dragging had disturbed 10% of the eelgrass cover in Maquoit Bay, with dragged sites ranging from 3.4 to 31.8 ha in size. Dragging removed above- and belowground plant material from the majority of the bottom in the disturbed sites. One year following dragging, eelgrass shoot density, shoot height and total biomass of disturbed sites averaged respectively 2 to 3 %, 46 to 61 % and <1 % that of the reference sites. Substantial differences in eelgrass biomass persisted between disturbed and reference sites up to 7 yr after dragging. Dragging did not affect physical characteristics of the sediment. The pattern and rate of eelgrass bed recovery depended strongly on initial dragging intensity; areas of relatively light dragging with many remnant eelgrass patches (i.e. patches that were missed by the mussel dredge) showed considerable revegetation in 1 yr. However, by developing recovery trajectories from measurements at sites disturbed in different years, we projected that it would require a mean of 10.6 yr for recovery of eelgrass shoot density within the areas of intense dragging characterizing most of the disturbed sites. A spatial simulation model based on measured rates of lateral patch-expansion (mean 12.5 cm yr-1) and new-patch recruitment (mean 0.19 patches m-2 yr-1) yielded a mean bed recovery time of 9 to 11 yr following dragging, depending on initial degree of plant removal. Model simulations suggested that with favorable environmental conditions, eelgrass beds might recover from dragging disturbance in 6 yr; conversely, recovery under

Preliminary flight-determined subsonic lift and drag characteristics of the X-29A forward-swept-wing airplane

NASA Technical Reports Server (NTRS)

Hicks, John W.; Huckabine, Thomas

1989-01-01

The X-29A subsonic lift and drag characteristics determined, met, or exceeded predictions, particularly with respect to the drag polar shapes. Induced drag levels were as great as 20 percent less than wind tunnel estimates, particularly at coefficients of lift above 0.8. Drag polar shape comparisons with other modern fighter aircraft showed the X-29A to have a better overall aircraft aerodynamic Oswald efficiency factor for the same aspect ratio. Two significant problems arose in the data reduction and analysis process. These included uncertainties in angle of attack upwash calibration and effects of maneuver dynamics on drag levels. The latter problem resulted from significantly improper control surface automatic camber control scheduling. Supersonic drag polar results were not obtained during this phase because of a lack of engine instrumentation to measure afterburner fuel flow.

Effect of salt on turbulent drag reduction of xanthan gum.

PubMed

Hong, Cheng Hai; Choi, Hyoung Jin; Zhang, Ke; Renou, Frederic; Grisel, Michel

2015-05-05

The turbulent flow of an aqueous KCl solution driven by a rotating disc in a closed chamber showed significant drag reduction (DR) when a small amount of xanthan gum (XG) was added. The effects of the experimental parameters (XG and KCl concentrations, and time) on the drag reduction efficiency were examined. While the DR efficiency of XG decreased with increasing salt (KCl) concentration, the time-dependent DR efficiency was found to be fitted well using Brostow model equation. Copyright © 2014 Elsevier Ltd. All rights reserved.

Longitudinal afterbody grooves and shoulder radiusing for low-speed bluff body drag reduction

NASA Technical Reports Server (NTRS)

Howard, F. G.; Quass, B. F.; Weinstein, L. M.; Bushnell, D. M.

1981-01-01

A new low-speed drag reduction approach is proposed which employs longitudinal surface V-shaped grooves cutting through the afterbody shoulder region. The test Reynolds number range was from 20,000 to 200,000 based on undisturbed free-stream flow and a body diameter of 6.08 cm. The V-grooves are shown to be most effective in reducing drag when the afterbody shoulder radius is zero. Reductions in drag of up to 33% have been measured for this condition. For large shoulder radius, the grooves are only effective at the lower Reynolds numbers of the test.

Stream-wise distribution of skin-friction drag reduction on a flat plate with bubble injection

NASA Astrophysics Data System (ADS)

Qin, Shijie; Chu, Ning; Yao, Yan; Liu, Jingting; Huang, Bin; Wu, Dazhuan

2017-03-01

To investigate the stream-wise distribution of skin-friction drag reduction on a flat plate with bubble injection, both experiments and simulations of bubble drag reduction (BDR) have been conducted in this paper. Drag reductions at various flow speeds and air injection rates have been tested in cavitation tunnel experiments. Visualization of bubble flow pattern is implemented synchronously. The computational fluid dynamics (CFD) method, in the framework of Eulerian-Eulerian two fluid modeling, coupled with population balance model (PBM) is used to simulate the bubbly flow along the flat plate. A wide range of bubble sizes considering bubble breakup and coalescence is modeled based on experimental bubble distribution images. Drag and lift forces are fully modeled based on applicable closure models. Both predicted drag reductions and bubble distributions are in reasonable concordance with experimental results. Stream-wise distribution of BDR is revealed based on CFD-PBM numerical results. In particular, four distinct regions with different BDR characteristics are first identified and discussed in this study. Thresholds between regions are extracted and discussed. And it is highly necessary to fully understand the stream-wise distribution of BDR in order to establish a universal scaling law. Moreover, mechanism of stream-wise distribution of BDR is analysed based on the near-wall flow parameters. The local drag reduction is a direct result of near-wall max void fraction. And the near-wall velocity gradient modified by the presence of bubbles is considered as another important factor for bubble drag reduction.

Magnetic Viscous Drag for Friction Labs

ERIC Educational Resources Information Center

Gaffney, Chris; Catching, Adam

2016-01-01

The typical friction lab performed in introductory mechanics courses is usually not the favorite of either the student or the instructor. The measurements are not all that easy to make, and reproducibility is usually a troublesome issue. This paper describes the augmentation of such a friction lab with a study of the viscous drag on a magnet…

Drag effects and vortex states in binary superfluids in optical lattices

NASA Astrophysics Data System (ADS)

Meyerovich, Alexander; Kuklov, Anatoly

2005-03-01

Drag effects in two-condensate superfluids (A and B) in optical lattices are explored in strongly interacting limit. Mutual drag changes circulation quanta of vortices depending on the component concentration and interaction. This is a lattice analog of ^3He-HeII mixtures, in which the drag, proportional to the difference between bare and effective masses of quasiparticles, causes pressure-driven transitions in vortex charges [1]. The vortex binding in the hard-core boson limit relies, in contrast to the soft-core case studied in Monte Carlo simulations [2], on the vacancy-assisted tunneling. The model lattice for study of such effects is introduced. The variational and Monte Carlo calculations for the system, in which the tunneling for component A depends on the concentration of B, show the possibility of formation of the quasi-molecular condensate ABm in addition to the condensates of A and B. A strong drag, leading to the composite vortices with multiple quanta, also becomes possible. The work is supported by NSF grants DMR-0077266 and ITR-405460001 and PSC-CUNY- 665560035. 1. A. E. Meyerovich, Phys. Rev. A 68, 05162 (2003); Sov. Phys.-JETP 60, 41 (1984) 2. A. Kuklov, N. Prokof'ev, and B. Svistunov, Phys. Rev. Lett. 92, 030403 (2004)

The Effects of Propulsive Jetting on Drag of a Streamlined body

NASA Astrophysics Data System (ADS)

Krieg, Michael; Mohseni, Kamran

2017-11-01

Recently an abundance of bioinspired underwater vehicles have emerged to leverage eons of evolution. Our group has developed a propulsion technique inspired by jellyfish and squid. Propulsive jets are generated by ingesting and expelling water from a flexible internal cavity. We have demonstrated thruster capabilities for maneuvering on AUV platforms, where the internal thruster geometry minimized forward drag; however, such a setup cannot characterize propulsive efficiency. Therefore, we created a new streamlined vehicle platform that produces unsteady jets for forward propulsion rather than maneuvering. The streamlined jetting body is placed in a water tunnel and held stationary while jetting frequency and background flow velocity are varied. For each frequency/velocity pair the flow field is measured around the surface and in the wake using PIV. Using the zero jetting frequency as a baseline for each background velocity, the passive body drag is related to the velocity distribution. For cases with active jetting the drag and jetting forces are estimated from the velocity field and compared to the passive case. For this streamlined body, the entrainment of surrounding flow into the propulsive jet can reduce drag forces in addition to the momentum transfer of the jet itself. Office of Naval Research.

Four and eight faceted domes effects on drag force and image in missile application

NASA Astrophysics Data System (ADS)

Sakarya, Doǧan Uǧur

2017-10-01

Drag force effect is an important aspect of range performance in missile applications. Depending on domes geometry, this effect can be decreased. Hemispherical domes have great image uniformity but more drag force has an effect on it. Four and eight faceted domes decrease drag force. However, environment reflections cause a noise in a system. Also depending on the faceted domes shape, sun and other sources in the environment are deformed in the face of them and these deformed objects result in a false target in an image. In this study; hemispherical, four faceted and eight faceted domes are compared with respect to drag force. Furthermore, images are captured by using these manufactured domes. To compare domes effects on images, scenarios are generated and automatic target acquisition algorithm is used.

Guidance Scheme for Modulation of Drag Devices to Enable Return from Low Earth Orbit

NASA Technical Reports Server (NTRS)

Dutta, Soumyo; Bowes, Angela L.; Cianciolo, Alicia D.; Glass, Christopher E.; Powell, Richard W.

2017-01-01

Passive drag devices provide opportunities to return payloads from low Earth orbits quickly without using onboard propulsive systems to de-orbit the spacecraft. However, one potential disadvantage of such systems has been the lack of landing accuracy. Drag modulation or changing the shape of the drag device during flight offer a way to control the de-orbit trajectory and target a specific landing location. This paper discusses a candidate passive drag based system, called Exo-brake, as well as efforts to model the dynamics of the vehicle as it de-orbits and guidance schemes used to control the trajectory. Such systems can enable quick return of payloads from low Earth orbit assets like the International Space Station without the use of large re-entry cargo capsules or propulsive systems.

Dynamical evolution of differentiated asteroid families

NASA Astrophysics Data System (ADS)

Martins-Filho, W. S.; Carvano, J.; Mothe-Diniz, T.; Roig, F.

2014-10-01

The project aims to study the dynamical evolution of a family of asteroids formed from a fully differentiated parent body, considering family members with different physical properties consistent with what is expected from the break up of a body formed by a metallic nucleus surrounded by a rocky mantle. Initially, we study the effects of variations in density, bond albedo, and thermal inertia in the semi-major axis drift caused by the Yarkovsky effect. The Yarkovsky effect is a non-conservative force caused by the thermal re-radiation of the solar radiation by an irregular body. In Solar System bodies, it is known to cause changes in the orbital motions (Peterson, 1976), eventually bringing asteroids into transport routes to near-Earth space, such as some mean motion resonances. We expressed the equations of variation of the semi-major axis directly in terms of physical properties (such as the mean motion, frequency of rotation, conductivity, thermal parameter, specific heat, obliquity and bond albedo). This development was based on the original formalism for the Yarkovsky effect (i.e., Bottke et al., 2006 and references therein). The derivation of above equations allowed us to closely study the variation of the semi-major axis individually for each physical parameter, clearly showing that the changes in semi-major axis for silicate bodies is twice or three times greater than for metal bodies. The next step was to calculate the orbital elements of a synthetic family after the break-up. That was accomplished assuming that the catastrophic disruption energy is given by the formalism described by Stewart and Leinhardt (2009) and assuming an isotropic distribution of velocities for the fragments of the nucleus and the mantle. Finally, the orbital evolution of the fragments is implemented using a simpletic integrator, and the result compared with the distribution of real asteroid families.

Determination of the drag resistance coefficients of different vehicles

NASA Astrophysics Data System (ADS)

Fahsl, Christoph; Vogt, Patrik

2018-05-01

While it has been demonstrated how air resistance could be analyzed by using mobile devices, this paper demonstrates a method of how to determine the drag resistance coefficient c of a commercial automobile by using the acceleration sensor of a smartphone or tablet. In an academic context, the drag resistance is often mentioned, but little attention is paid to quantitative measurements. This experiment was driven by the fact that this physical value is most certainly neglected because of its difficult measurability. In addition to that, this experiment gives insights on how the aerodynamic factor of an automobile affects the energy dissipation and thus how much power is required by automobile transportation.

Control of the electromagnetic drag using fluctuating light fields

NASA Astrophysics Data System (ADS)

Pastor, Víctor J. López; Marqués, Manuel I.

2018-05-01

An expression for the electromagnetic drag force experienced by an electric dipole in a light field consisting of a monochromatic plane wave with polarization and phase randomly fluctuating is obtained. The expression explicitly considers the transformations of the field and frequency due to the Doppler shift and the change of the polarizability response of the electric dipole. The conditions to be fulfilled by the polarizability of the dipole in order to obtain a positive, a null, and a negative drag coefficient are analytically determined and checked against numerical simulations for the dynamics of a silver nanoparticle. The theoretically predicted diffusive, superdiffusive, and exponentially accelerated dynamical regimes are numerically confirmed.

Fluid drag reduction and efficient self-cleaning with rice leaf and butterfly wing bioinspired surfaces

NASA Astrophysics Data System (ADS)

Bixler, Gregory D.; Bhushan, Bharat

2013-08-01

Researchers are continually inspired by living nature to solve complex challenges. For example, unique surface characteristics of rice leaves and butterfly wings combine the shark skin (anisotropic flow leading to low drag) and lotus leaf (superhydrophobic and self-cleaning) effects, producing the so-called rice and butterfly wing effect. In this paper, we present an overview of rice leaf and butterfly wing fluid drag and self-cleaning studies. In addition, we examine two other promising aquatic surfaces in nature known for such properties, including fish scales and shark skin. Morphology, drag, self-cleaning, contact angle, and contact angle hysteresis data are presented to understand the role of wettability, viscosity, and velocity. Liquid repellent coatings are utilized to recreate or combine various effects. Discussion is provided along with conceptual models describing the role of surface structures related to low drag, self-cleaning, and antifouling properties. Modeling provides design guidance when developing novel low drag and self-cleaning surfaces for applications in the medical, marine, and industrial fields.

Laminar flow drag reduction on soft porous media.

PubMed

Mirbod, Parisa; Wu, Zhenxing; Ahmadi, Goodarz

2017-12-08

While researches have focused on drag reduction of various coated surfaces such as superhydrophobic structures and polymer brushes, the insights tso understand the fundamental physics of the laminar skin friction coefficient and the related drag reduction due to the formation of finite velocity at porous surfaces is still relatively unknown. Herein, we quantitatively investigated the flow over a porous medium by developing a framework to model flow of a Newtonian fluid in a channel where the lower surface was replaced by various porous media. We showed that the flow drag reduction induced by the presence of the porous media depends on the values of the permeability parameter α = L/(MK) 1/2 and the height ratio δ = H/L, where L is the half thickness of the free flow region, H is the thickness and K is the permeability of the fiber layer, and M is the ratio of the fluid effective dynamic viscosity μ e in porous media to its dynamic viscosity μ. We also examined the velocity and shear stress profiles for flow over the permeable layer for the limiting cases of α → 0 and α → ∞. The model predictions were compared with the experimental data for specific porous media and good agreement was found.

A method for the reduction of aerodynamic drag of road vehicles

NASA Technical Reports Server (NTRS)

Pamadi, Bandu N.; Taylor, Larry W.; Leary, Terrance O.

1990-01-01

A method is proposed for the reduction of the aerodynamic drag of bluff bodies, particularly for application to road transport vehicles. This technique consists of installation of panels on the forward surface of the vehicle facing the airstream. With the help of road tests, it was demonstrated that the attachment of proposed panels can reduce aerodynamic drag of road vehicles and result in significant fuel cost savings and conservation of energy resources.

High Speed Civil Transport (HSCT) Isolated Nacelle Transonic Boattail Drag Study and Results Using Computational Fluid Dynamics (CFD)

NASA Technical Reports Server (NTRS)

Midea, Anthony C.; Austin, Thomas; Pao, S. Paul; DeBonis, James R.; Mani, Mori

2005-01-01

Nozzle boattail drag is significant for the High Speed Civil Transport (HSCT) and can be as high as 25 percent of the overall propulsion system thrust at transonic conditions. Thus, nozzle boattail drag has the potential to create a thrust drag pinch and can reduce HSCT aircraft aerodynamic efficiencies at transonic operating conditions. In order to accurately predict HSCT performance, it is imperative that nozzle boattail drag be accurately predicted. Previous methods to predict HSCT nozzle boattail drag were suspect in the transonic regime. In addition, previous prediction methods were unable to account for complex nozzle geometry and were not flexible enough for engine cycle trade studies. A computational fluid dynamics (CFD) effort was conducted by NASA and McDonnell Douglas to evaluate the magnitude and characteristics of HSCT nozzle boattail drag at transonic conditions. A team of engineers used various CFD codes and provided consistent, accurate boattail drag coefficient predictions for a family of HSCT nozzle configurations. The CFD results were incorporated into a nozzle drag database that encompassed the entire HSCT flight regime and provided the basis for an accurate and flexible prediction methodology.

High Speed Civil Transport (HSCT) Isolated Nacelle Transonic Boattail Drag Study and Results Using Computational Fluid Dynamics (CFD)

NASA Technical Reports Server (NTRS)

Midea, Anthony C.; Austin, Thomas; Pao, S. Paul; DeBonis, James R.; Mani, Mori

1999-01-01

Nozzle boattail drag is significant for the High Speed Civil Transport (HSCT) and can be as high as 25% of the overall propulsion system thrust at transonic conditions. Thus, nozzle boattail drag has the potential to create a thrust-drag pinch and can reduce HSCT aircraft aerodynamic efficiencies at transonic operating conditions. In order to accurately predict HSCT performance, it is imperative that nozzle boattail drag be accurately predicted. Previous methods to predict HSCT nozzle boattail drag were suspect in the transonic regime. In addition, previous prediction methods were unable to account for complex nozzle geometry and were not flexible enough for engine cycle trade studies. A computational fluid dynamics (CFD) effort was conducted by NASA and McDonnell Douglas to evaluate the magnitude and characteristics of HSCT nozzle boattail drag at transonic conditions. A team of engineers used various CFD codes and provided consistent, accurate boattail drag coefficient predictions for a family of HSCT nozzle configurations. The CFD results were incorporated into a nozzle drag database that encompassed the entire HSCT flight regime and provided the basis for an accurate and flexible prediction methodology.

Influence of thermal stratification and slip conditions on stagnation point flow towards variable thicked Riga plate

NASA Astrophysics Data System (ADS)

Anjum, A.; Mir, N. A.; Farooq, M.; Khan, M. Ijaz; Hayat, T.

2018-06-01

This article addresses thermally stratified stagnation point flow of viscous fluid induced by a non-linear variable thicked Riga plate. Velocity and thermal slip effects are incorporated to disclose the flow analysis. Solar thermal radiation phenomenon is implemented to address the characteristics of heat transfer. Variations of different physical parameters on the horizontal velocity and temperature distributions are described through graphs. Graphical interpretations of skin friction coefficient (drag force at the surface) and Nusselt number (rate of heat transfer) are also addressed. Modified Hartman number and thermal stratification parameter result in reduction of temperature distribution.

Optimization of flexible wing structures subject to strength and induced drag constraints

NASA Technical Reports Server (NTRS)

Haftka, R. T.

1977-01-01

An optimization procedure for designing wing structures subject to stress, strain, and drag constraints is presented. The optimization method utilizes an extended penalty function formulation for converting the constrained problem into a series of unconstrained ones. Newton's method is used to solve the unconstrained problems. An iterative analysis procedure is used to obtain the displacements of the wing structure including the effects of load redistribution due to the flexibility of the structure. The induced drag is calculated from the lift distribution. Approximate expressions for the constraints used during major portions of the optimization process enhance the efficiency of the procedure. A typical fighter wing is used to demonstrate the procedure. Aluminum and composite material designs are obtained. The tradeoff between weight savings and drag reduction is investigated.

Mechanics of load-drag-unload contact cleaning of gecko-inspired fibrillar adhesives.

PubMed

Abusomwan, Uyiosa A; Sitti, Metin

2014-10-14

Contact self-cleaning of gecko-inspired synthetic adhesives with mushroom-shaped tips has been demonstrated recently using load-drag-unload cleaning procedures similar to that of the natural animal. However, the underlying mechanics of contact cleaning has yet to be fully understood. In this work, we present a detailed experiment of contact self-cleaning that shows that rolling is the dominant mechanism of cleaning for spherical microparticle contaminants, during the load-drag-unload procedure. We also study the effect of dragging rate and normal load on the particle rolling friction. A model of spherical particle rolling on an elastomer fibrillar adhesive interface is developed and agrees well with the experimental results. This study takes us closer to determining design parameters for achieving self-cleaning fibrillar adhesives.

Maximum drag reduction asymptotes and the cross-over to the Newtonian plug

NASA Astrophysics Data System (ADS)

Benzi, R.; de Angelis, E.; L'Vov, V. S.; Procaccia, I.; Tiberkevich, V.

2006-03-01

We employ the full FENE-P model of the hydrodynamics of a dilute polymer solution to derive a theoretical approach to drag reduction in wall-bounded turbulence. We recapture the results of a recent simplified theory which derived the universal maximum drag reduction (MDR) asymptote, and complement that theory with a discussion of the cross-over from the MDR to the Newtonian plug when the drag reduction saturates. The FENE-P model gives rise to a rather complex theory due to the interaction of the velocity field with the polymeric conformation tensor, making analytic estimates quite taxing. To overcome this we develop the theory in a computer-assisted manner, checking at each point the analytic estimates by direct numerical simulations (DNS) of viscoelastic turbulence in a channel.

Drag reduction using wrinkled surfaces in high Reynolds number laminar boundary layer flows

NASA Astrophysics Data System (ADS)

Raayai-Ardakani, Shabnam; McKinley, Gareth H.

2017-09-01

Inspired by the design of the ribbed structure of shark skin, passive drag reduction methods using stream-wise riblet surfaces have previously been developed and tested over a wide range of flow conditions. Such textures aligned in the flow direction have been shown to be able to reduce skin friction drag by 4%-8%. Here, we explore the effects of periodic sinusoidal riblet surfaces aligned in the flow direction (also known as a "wrinkled" texture) on the evolution of a laminar boundary layer flow. Using numerical analysis with the open source Computational Fluid Dynamics solver OpenFOAM, boundary layer flow over sinusoidal wrinkled plates with a range of wavelength to plate length ratios ( λ / L ), aspect ratios ( 2 A / λ ), and inlet velocities are examined. It is shown that in the laminar boundary layer regime, the riblets are able to retard the viscous flow inside the grooves creating a cushion of stagnant fluid that the high-speed fluid above can partially slide over, thus reducing the shear stress inside the grooves and the total integrated viscous drag force on the plate. Additionally, we explore how the boundary layer thickness, local average shear stress distribution, and total drag force on the wrinkled plate vary with the aspect ratio of the riblets as well as the length of the plate. We show that riblets with an aspect ratio of close to unity lead to the highest reduction in the total drag, and that because of the interplay between the local stress distribution on the plate and stream-wise evolution of the boundary layer the plate has to exceed a critical length to give a net decrease in the total drag force.

The Effect of Nose Shape on the Drag of Bodies of Revolution at Zero Angle of Attack

NASA Technical Reports Server (NTRS)

Seiff, Alvin; Sandahl, Carl A.

1951-01-01

The subject of this paper is the drag of the nose section of bodies of revolution at zero angle of attack. The magnitude of the nose drag in relation to the total drag is very distinctly a function of the body design and the Mach number. It can range from a very small fraction of the total drag of the order of 10 percent to a very large fraction as high as 80 percent. The natural objective of nose design is to minimize the drag, but this objective is not always the primary one. Sometimes other factors overshadow the desire for minimum drag. The most conspicuous example of this is the proposal of guidance engineers that large-diameter spheres and other very blunt shapes be used at the nose tip. This paper will attempt to discuss both phases of the problem, noses for minimum drag and noses with very blunt tips. The state of the theory will also be reviewed and recent theoretical developments described, since the theory still remains a very valuable tool for assaying the effects of compromises in design and departure from shapes for which experimental data are available.

ON THE HORSESHOE DRAG OF A LOW-MASS PLANET. I. MIGRATION IN ISOTHERMAL DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casoli, J.; Masset, F. S., E-mail: jules.casoli@cea.f, E-mail: frederic.masset@cea.f, E-mail: jules.casoli@cea.f

2009-09-20

We investigate the unsaturated horseshoe drag exerted on a low-mass planet by an isothermal gaseous disk. In the globally isothermal case, we use a formalism, based on the use of a Bernoulli invariant, that takes into account pressure effects, and that extends the torque estimate to a region wider than the horseshoe region. We find a result that is strictly identical to the standard horseshoe drag. This shows that the horseshoe drag accounts for the torque of the whole corotation region, and not only of the horseshoe region, thereby deserving to be called corotation torque. We find that evanescent wavesmore » launched downstream of the horseshoe U-turns by the perturbations of vortensity exert a feedback on the upstream region, that render the horseshoe region asymmetric. This asymmetry scales with the vortensity gradient and with the disk's aspect ratio. It does not depend on the planetary mass, and it does not have any impact on the horseshoe drag. Since the horseshoe drag has a steep dependence on the width of the horseshoe region, we provide an adequate definition of the width that needs to be used in horseshoe drag estimates. We then consider the case of locally isothermal disks, in which the temperature is constant in time but depends on the distance to the star. The horseshoe drag appears to be different from the case of a globally isothermal disk. The difference, which is due to the driving of vortensity in the vicinity of the planet, is intimately linked to the topology of the flow. We provide a descriptive interpretation of these effects, as well as a crude estimate of the dependency of the excess on the temperature gradient.« less

Bis-urea-based supramolecular polymer: the first self-assembled drag reducer for hydrocarbon solvents.

PubMed

Sabadini, Edvaldo; Francisco, Kelly R; Bouteiller, Laurent

2010-02-02

The hydrodynamic drag reduction phenomenon, also termed the Toms effect, is an unusual case involving macromolecules in solution in which the resistance to flow is reduced comparatively to that of the pure solvent. Although the effect is relatively well characterized, it is still unclear from the molecular viewpoint. The presence of some amount of a polymer with high molecular weight can produce large levels of drag reduction in turbulent flow as a result of the interactions of the long structures with the small vortices developed during the flow. For this reason, the effect is very attractive in the pumping process because a significant amount of energy can be saved. In aqueous systems, giant micelles can be spontaneously formed, driven by the hydrophobic effect, and are effective drag reducers. Giant micelles are interesting in promoting drag reduction because the noncovalent and reversible aggregation of the surfactant molecules avoids mechanical degradation, which typically occurs with classical polymers, due to irreversible scission of the backbone. In this letter, we present the first hydrodynamic drag reducer for hydrocarbons based on a self-assembled polymer formed from the reversible aggregation of bis-urea monomers. This system forms two competitive polymeric structures--the tube (T) and the filament (F) forms--which are in equilibrium with each other. Our rheology results in octane and toluene are fully consistent with calorimetry data and show that only the longest form, T, is able to promote the drag reduction effect.

Form drag in rivers due to small-scale natural topographic features: 1. Regular sequences

USGS Publications Warehouse

Kean, J.W.; Smith, J.D.

2006-01-01

Small-scale topographic features are commonly found on the boundaries of natural rivers, streams, and floodplains. A simple method for determining the form drag on these features is presented, and the results of this model are compared to laboratory measurements. The roughness elements are modeled as Gaussian-shaped features defined in terms of three parameters: a protrusion height, H; a streamwise length scale, ??; and a spacing between crests, ??. This shape is shown to be a good approximation to a wide variety of natural topographic bank features. The form drag on an individual roughness element embedded in a series of identical elements is determined using the drag coefficient of the individual element and a reference velocity that includes the effects of roughness elements further upstream. In addition to calculating the drag on each element, the model determines the spatially averaged total stress, skin friction stress, and roughness height of the boundary. The effects of bank roughness on patterns of velocity and boundary shear stress are determined by combining the form drag model with a channel flow model. The combined model shows that drag on small-scale topographic features substantially alters the near-bank flow field. These methods can be used to improve predictions of flow resistance in rivers and to form the basis for fully predictive (no empirically adjusted parameters) channel flow models. They also provide a foundation for calculating the near-bank boundary shear stress fields necessary for determining rates of sediment transport and lateral erosion.

The Total-Pressure Recovery and Drag Characteristics of Several Auxiliary Inlets at Transonic Speeds

NASA Technical Reports Server (NTRS)

Dennard, John S.

1959-01-01

Several flush and scoop-type auxiliary inlets have been tested for a range of Mach numbers from 0.55 to 1.3 to determine their transonic total-pressure recovery and drag characteristics. The inlet dimensions were comparable with the thickness of the boundary layer in which they were tested. Results indicate that flush inlets should be inclined at very shallow angles with respect to the surface for optimum total-pressure recovery and drag characteristics. Deep, narrow inlets have lower drag than wide shallow ones at Mach numbers greater than 0.9 but at lower Mach numbers the wider inlets proved superior. Inlets with a shallow approach ramp, 7 deg, and diverging ramp walls which incorporated boundary-layer bypass had lower drag than any other inlet tested for Mach numbers up to 1.2 and had the highest pressure recovery of all of the flush inlets. The scoop inlets, which operated in a higher velocity flow than the flush inlets, had higher drag coefficients. Several of these auxiliary inlets projected multiple, periodic shock waves into the stream when they were operated at low mass-flow ratios.

Sub-grid drag models for horizontal cylinder arrays immersed in gas-particle multiphase flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sarkar, Avik; Sun, Xin; Sundaresan, Sankaran

2013-09-08

Immersed cylindrical tube arrays often are used as heat exchangers in gas-particle fluidized beds. In multiphase computational fluid dynamics (CFD) simulations of large fluidized beds, explicit resolution of small cylinders is computationally infeasible. Instead, the cylinder array may be viewed as an effective porous medium in coarse-grid simulations. The cylinders' influence on the suspension as a whole, manifested as an effective drag force, and on the relative motion between gas and particles, manifested as a correction to the gas-particle drag, must be modeled via suitable sub-grid constitutive relationships. In this work, highly resolved unit-cell simulations of flow around an arraymore » of horizontal cylinders, arranged in a staggered configuration, are filtered to construct sub-grid, or `filtered', drag models, which can be implemented in coarse-grid simulations. The force on the suspension exerted by the cylinders is comprised of, as expected, a buoyancy contribution, and a kinetic component analogous to fluid drag on a single cylinder. Furthermore, the introduction of tubes also is found to enhance segregation at the scale of the cylinder size, which, in turn, leads to a reduction in the filtered gas-particle drag.« less

Effects of Increasing Drag on Conjunction Assessment

NASA Technical Reports Server (NTRS)

Frigm, Ryan Clayton; McKinley, David P.

2010-01-01

Conjunction Assessment Risk Analysis relies heavily on the computation of the Probability of Collision (Pc) and the understanding of the sensitivity of this calculation to the position errors as defined by the covariance. In Low Earth Orbit (LEO), covariance is predominantly driven by perturbations due to atmospheric drag. This paper describes the effects of increasing atmospheric drag through Solar Cycle 24 on Pc calculations. The process of determining these effects is found through analyzing solar flux predictions on Energy Dissipation Rate (EDR), historical relationship between EDR and covariance, and the sensitivity of Pc to covariance. It is discovered that while all LEO satellites will be affected by the increase in solar activity, the relative effect is more significant in the LEO regime around 700 kilometers in altitude compared to 400 kilometers. Furthermore, it is shown that higher Pc values can be expected at larger close approach miss distances. Understanding these counter-intuitive results is important to setting Owner/Operator expectations concerning conjunctions as solar maximum approaches.