Search

Space contributes to the security and economic stability of the United States. However, numerous studies, articles, and surveys state export control is hurting the space industrial base. The nation's ability [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2010.07.009 Byline: D.J. Scheeres (a), C.M. Hartzell (a), P. Sanchez (a), M. Swift (b) Keywords: Asteroids; Asteroids, Surfaces; Asteroid Eros; Asteroid Itokawa Abstract: The scaling of physical forces to the extremely low ambient gravitational acceleration regimes found on the surfaces of small asteroids is performed. Resulting from this, it is found that van der Waals cohesive forces between regolith grains on asteroid surfaces should be a dominant force and compete with particle weights and be greater, in general, than electrostatic and solar radiation pressure forces. Based on this scaling, we interpret previous experiments performed on cohesive powders in the terrestrial environment as being relevant for the understanding of processes on asteroid surfaces. The implications of these terrestrial experiments for interpreting observations of asteroid surfaces and macro-porosity are considered, and yield interpretations that differ from previously assumed processes for these environments. Based on this understanding, we propose a new model for the end state of small, rapidly rotating asteroids which allows them to be comprised of relatively fine regolith grains held together by van der Waals cohesive forces. Author Affiliation: (a) Department of Aerospace Engineering Sciences, The University of Colorado, Boulder, CO 80309-0429, USA (b) School of Physics and Astronomy, The University of Nottingham University Park, Nottingham NG7 2RD, United Kingdom Article History: Received 29 January 2010; Revised 7 July 2010; Accepted 8 July 2010

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2010.07.006 Byline: Anders Nottrott, Jan Kleissl Keywords: California; Satellite; Solar resource assessment; SUNY model; Validation Abstract: Satellite derived global horizontal solar irradiance (GHI) from the SUNY modeled dataset in the National Solar Radiation Database (NSRDB) was compared to measurements from 27 weather stations in California during the years 1998-2005. The statistics of spatial and temporal differences between the two datasets were analyzed and related to meteorological phenomena. Overall mean bias errors (MBE) of the NSRDB-SUNY indicated a GHI overprediction of 5%, which is smaller than the sensor accuracy of ground stations. However, at coastal sites, year-round systematic positive MBEs in the NSRDB-SUNY data up to 18% were observed and monthly MBEs increased up to 54% in the summer months during the morning. These differences were explained by a tendency for the NSRDB-SUNY model to overestimate GHI under cloudy conditions at the coast during summer mornings. A persistent positive evening MBE which was independent of site location and cloudiness occurred at all stations and was explained by an error in the time-shifting method applied in the NSRDB-SUNY. A correction method was derived for these two errors to improve the accuracy of the NSRDB-SUNY data in California. Author Affiliation: Mechanical and Aerospace Engineering, University of California, San Diego, United States Article History: Received 16 October 2009; Revised 2 July 2010; Accepted 6 July 2010 Article Note: (miscellaneous) Communicated by: Associate Editor Frank Vignola

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.paerosci.2010.03.001 Byline: H. Xia (a), P.G. Tucker (a), W.N. Dawes (b) Abstract: In the past two decades, the level set concept has been extensively explored. The superiority of the differential level set to other more ad hoc methods as a formal framework for directly/indirectly solving 'front-propagation' natured problems is now fully established. Nowadays, in many areas of aerospace related computational fluid dynamics, applications of level set methods can be found. This paper gives a brief review of these applications and how level sets can be useful in tackling challenging computational aerospace problems. The use of level sets in premixed turbulent combustion, aero-acoustics, geometry definition/morphing, meshing and turbulence modeling is explored in detail and other applications discussed. Author Affiliation: (a) Whittle Lab, Department of Engineering, University of Cambridge, 1 JJ Thomson Avenue, Cambridge CB3 0DY, UK (b) CFD Lab, Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, UK

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.paerosci.2010.01.001 Byline: W. Shyy (a), H. Aono (a), S.K. Chimakurthi (a), P. Trizila (a), C.-K. Kang (a), C.E.S. Cesnik (a), H. Liu (b) Abbreviations: AoA, angle of attack; LEV, leading edge vortex; MAV, micro air vehicle; MTV, molecular tagging velocimetry Abstract: Micro air vehicles (MAVs) have the potential to revolutionize our sensing and information gathering capabilities in areas such as environmental monitoring and homeland security. Flapping wings with suitable wing kinematics, wing shapes, and flexible structures can enhance lift as well as thrust by exploiting large-scale vortical flow structures under various conditions. However, the scaling invariance of both fluid dynamics and structural dynamics as the size changes is fundamentally difficult. The focus of this review is to assess the recent progress in flapping wing aerodynamics and aeroelasticity. It is realized that a variation of the Reynolds number (wing sizing, flapping frequency, etc.) leads to a change in the leading edge vortex (LEV) and spanwise flow structures, which impacts the aerodynamic force generation. While in classical stationary wing theory, the tip vortices (TiVs) are seen as wasted energy, in flapping flight, they can interact with the LEV to enhance lift without increasing the power requirements. Surrogate modeling techniques can assess the aerodynamic outcomes between two- and three-dimensional wing. The combined effect of the TiVs, the LEV, and jet can improve the aerodynamics of a flapping wing. Regarding aeroelasticity, chordwise flexibility in the forward flight can substantially adjust the projected area normal to the flight trajectory via shape deformation, hence redistributing thrust and lift. Spanwise flexibility in the forward flight creates shape deformation from the wing root to the wing tip resulting in varied phase shift and effective angle of attack distribution along the wing span. Numerous open issues in flapping wing aerodynamics are highlighted. Author Affiliation: (a) Department of Aerospace Engineering, University of Michigan, FXB 1320 Beal Avenue, Ann Arbor, MI 48109, USA (b) Graduate School of Engineering, Chiba University, 1-33 Yayoi-cho, Chiba, Chiba 263-8522, Japan

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2010.05.016 Byline: Jay McMahon (a), Daniel Scheeres (b) Keywords: Asteroids, Dynamics; Celestial mechanics; Solar radiation; Satellites of asteroids; Near-Earth objects Abstract: A previous theory by the authors for detailed modeling of the binary YORP effect is reviewed and expanded to accommodate doubly-synchronous binary systems, as well as a method for non-dimensionalizing the coefficients for application to binary systems where a shape model to compute its own coefficients is not available. The theory is also expanded to account for the effects of primary J.sub.2 and the Sun's 3rd body perturbation on the secular orbit evolution. The newly expanded theory is applied to the binary near-Earth Asteroid 1999 KW4, for which a detailed shape model is available. The result of simulation of the secular evolutionary equations shows that the KW4 orbit will be double in size in approximately 22,000 years, and will reach the Hill radius in approximately 54,000 years. The simulation also shows that the eccentricity will alternate growing and shrinking in magnitude, depending on the location of the solar node in the body-fixed frame. Therefore the eccentricity is not fixed to evolve in the opposite sign as the semi-major axis unless the circulation of the node (with a period of 500 years) is averaged out as well. The current orbit expansion rate for KW4 of 7cm per year is shown to be detectable with observations of the mean anomaly which grows quadratically in time with an expanding orbit. Finally, the KW4 results are scaled for application to a number of other binary systems for which detailed shape models are not available. This application shows that the orbits considered can expand to their Hill radius in the range of 10.sup.4-10.sup.6 years. This implies rapid formation of binary systems is necessary to support the large percentage of binaries observed in the NEA population. Author Affiliation: (a) Aerospace Engineering Sciences, 431 UCB, University of Colorado, Boulder, CO 80309-0431, United States (b) Aerospace Engineering Sciences, 429 UCB, University of Colorado, Boulder, CO 80309-0429, United States Article History: Received 18 March 2010; Revised 24 May 2010; Accepted 25 May 2010

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2010.01.035 Byline: Marina Brozovic (a), Lance A.M. Benner (a), Christopher Magri (b), Steven J. Ostro (a), Daniel J. Scheeres (c), Jon D. Giorgini (a), Michael C. Nolan (d), Jean-Luc Margot (e), Raymond F. Jurgens (a), Randy Rose (a) Keywords: Radar observations; Asteroids Abstract: Arecibo (2380MHz, 12.6cm) and Goldstone (8560MHz, 3.5cm) delay-Doppler radar images obtained in July and August of 2000 reveal that 4486 Mithra is an irregular, significantly bifurcated object, with a central valley [approximately equal to]380m deep and a long axis potentially exceeding 2km. With its bimodal appearance, Mithra is a strong candidate for a contact binary asteroid. Sequences of Goldstone images spanning up to 3h per day show very little rotation and establish that Mithra is an unusually slow rotator. We used Goldstone and Arecibo data to estimate Mithra's 3D shape and spin state. We obtain prograde (I' =337[degrees], [beta] =19[degrees]) and retrograde (I' =154[degrees], [beta] =-19[degrees]) models that give comparable fits, have very similar shapes roughly resembling an hourglass, and have a rotation period of 67.5[+ or -]6.0h. The dimensions of these two models are very similar; for the prograde solution the maximum dimensions are X =2.35[+ or -]0.15km, Y =1.65[+ or -]0.10km, Z =1.44[+ or -]0.10km. Dynamical analysis of our models suggests that in the past, Mithra most likely went through a period of even slower rotation with its obliquity close to 90[degrees]. The spin rate is predicted to be increasing due to thermal torque (YORP), while the obliquity, which is currently +68[degrees] and +106[degrees] for the prograde and retrograde models, respectively, is predicted to move away from 90[degrees]. Author Affiliation: (a) Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109-8099, USA (b) University of Maine at Farmington, Preble Hall, Farmington, ME 04938, USA (c) Aerospace Engineering Sciences, University of Colorado, Boulder, CO 80309-0429, USA (d) Arecibo Observatory, National Astronomy and Ionosphere Center, Arecibo, PR 00613, USA (e) Department of Earth and Space Sciences, University of California, Los Angeles, CA 90095-1567, USA Article History: Received 14 September 2009; Revised 3 January 2010; Accepted 31 January 2010

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2010.01.012 Byline: Andrew C. Walker (a), Sergey L. Gratiy (c), David B. Goldstein (a), Chris H. Moore (a), Philip L. Varghese (a), Laurence M. Trafton (b), Deborah A. Levin (c), Benedicte Stewart (a) Keywords: Io; Atmospheres, Dynamics; Atmospheres, Structure; Jupiter, Satellites; Satellites, Atmospheres Abstract: Io's sublimation-driven atmosphere is modeled using the direct simulation Monte Carlo (DSMC) method. These rarefied gas dynamics simulations improve upon earlier models by using a three-dimensional domain encompassing the entire planet computed in parallel. The effects of plasma heating, planetary rotation, inhomogeneous surface frost, molecular residence time of SO.sub.2 on the exposed (non-volatile) rocky surface, and surface temperature distribution are investigated. Circumplanetary flow is predicted to develop from the warm dayside toward the cooler nightside. Io's rotation leads to a highly asymmetric frost surface temperature distribution (due to the frost's high thermal inertia) which results in circumplanetary flow that is not axi-symmetric about the subsolar point. The non-equilibrium thermal structure of the atmosphere, specifically vibrational and rotational temperatures, is also examined. Plasma heating is found to significantly inflate the atmosphere on both the dayside and nightside. The plasma energy flux causes high temperatures at high altitudes but plasma energy depletion through the dense gas column above the warmest frost permits gas temperatures cooler than the surface at low altitudes. A frost map (Doute, S., Schmitt, B., Lopes-Gautier, R., Carlson, R., Soderblom, L., Shirley, J., and the Galileo NIMS Team [2001]. Icarus 149, 107-132) is used to control the sublimated flux of SO.sub.2 which can result in inhomogeneous column densities that vary by nearly a factor of four for the same surface temperature. A short residence time for SO.sub.2 molecules on the 'rock' component is found to smooth lateral atmospheric inhomogeneities caused by variations in the surface frost distribution, creating an atmosphere that looks nearly identical to one with uniform frost coverage. A longer residence time is found to agree better with mid-infrared observations (Spencer, J.R., Lellouch, E., Richter, M.J., Lopez-Valverde, M.A., Jessup, K.L, Greathouse, T.K., Flaud, J. [2005]. Icarus 176, 283-304) and reproduce the observed anti-jovian/sub-jovian column density asymmetry. The computed peak dayside column density for Io assuming a surface frost temperature of 115K agrees with those suggested by Lyman-[alpha] observations (Feaga, L.M., McGrath, M., Feldman, P.D. [2009]. Icarus 201, 570-584). On the other hand, the peak dayside column density at 120K is a factor of five larger and is higher than the upper range of observations (Jessup, K.L., Spencer, J.R., Ballester, G.E., Howell, R.R., Roesler, F., Vigel, M., Yelle, R. [2004]. Icarus 169, 197-215;). Author Affiliation: (a) Department of Aerospace Engineering, University of Texas, Austin, TX 78712, United States (b) Department of Astronomy, University of Texas, Austin, TX 78712, United States (c) Department of Aerospace Engineering, Pennsylvania State University, University Park, PA 16802, United States Article History: Received 2 July 2009; Revised 12 January 2010; Accepted 13 January 2010

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.08.027 Byline: Sergey L. Gratiy (a), Deborah A. Levin (a), Andrew C. Walker (b) Keywords: Radiative transfer; Io Abstract: Validation of global numerical models of planetary atmospheres requires simulating images and spectra from the IR to UV spectral regions in order to compare them with remote observations. This paper describes Rassvet, a 3-D spherical-shell backward Monte Carlo radiative transfer model developed for such simulations. It utilizes a new methodology for calculating atmospheric brightness in scattered sunlight by introducing the concept of an 'effective emission source'. This allows for the accumulation of the scattered contribution along the entire path of a ray and the calculation of the atmospheric radiation when both scattered sunlight and thermal emission contribute to the remote measurement - which was not possible in previous models. A 'polychromatic' algorithm is extended for applications with the backward Monte Carlo method and implemented in the model. It allows for the calculation of radiative intensity for several wavelengths simultaneously, resulting in improved efficiency. The capabilities of the model are demonstrated by simulating remote measurements from the atmosphere of Io. Author Affiliation: (a) Department of Aerospace Engineering, Pennsylvania State University, University Park, PA 16802, USA (b) Department of Aerospace Engineering, University of Texas at Austin, Austin, TX 78712, USA Article History: Received 9 March 2009; Revised 14 August 2009; Accepted 31 August 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.paerosci.2009.10.001 Byline: Ayse Gul Gungor, Suresh Menon Abstract: A new hybrid approach to model high Reynolds number wall-bounded turbulent flows is developed based on coupling a two-level simulation (TLS) approach (Kemenov and Menon, 2006 , 2007 in the inner region with conventional large eddy simulation (LES) away from the wall. This new approach is significantly different from previous near-wall approaches for LES. In this hybrid TLS-LES approach, a very fine small-scale (SS) mesh is embedded inside the coarse LES mesh. The SS equations capture fine-scale temporal and spatial variations in all three Cartesian directions for all three velocity components near the wall. The TLS-LES equations are derived using a new scale separation operator that allows a smooth transition between the two regions, with the equations in the transition region obtained by blending the TLS large-scale and LES equations. New terms in the hybrid region are identified. The TLS-LES approach is used to study the near-wall features in canonical turbulent channel flows for a range of Reynolds number using relatively coarse large-scale (LS) grids. Results show that the TLS-LES approach is able to capture the effect of both the LS and SS features in the wall region consistently for the range of simulated Reynolds number. Author Affiliation: School of Aerospace Engineering, Georgia Institute of Technology, 270 Ferst Drive, Atlanta, GA 30332-0150, USA

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.paerosci.2009.08.002 Byline: T.K. Barlas, G.A.M. van Kuik Abstract: This article presents a review of the state of the art and present status of active aeroelastic rotor control research for wind turbines. Using advanced control concepts to reduce loads on the rotor can offer great reduction to the total cost of wind turbines. With the increasing size of wind turbine blades, the need for more sophisticated load control techniques has induced the interest for locally distributed aerodynamic control systems with build-in intelligence on the blades. Such concepts are often named in popular terms 'smart structures' or 'smart rotor control'. The review covers the full span of the subject, starting from the need for more advanced control systems emerging from the operating conditions of modern wind turbines and current load reduction control capabilities. An overview of available knowledge and up-to date progress in application of active aerodynamic control is provided, starting from concepts, methods and achieved results in aerospace and helicopter research. Moreover, a thorough analysis on different concepts for smart rotor control applications for wind turbines is performed, evaluating available options for aerodynamic control surfaces, actuators (including smart materials), sensors and control techniques. Next, feasibility studies for wind turbine applications, preliminary performance evaluation and novel computational and experimental research approaches are reviewed. The potential of load reduction using smart rotor control concepts is shown and key issues are discussed. Finally, existing knowledge and future requirements on modeling issues of smart wind turbine rotors are discussed. This study provides an overview of smart rotor control for wind turbines, discusses feasibility of future implementation, quantifies key parameters and shows the challenges associated with such an approach. Author Affiliation: Delft University Wind Energy Research Institute (DUWIND), Wind Energy Group, Faculty of Aerospace Engineering, Kluyverweg 1, 2629 HS Delft, The Netherlands

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2009.08.002 Byline: Murat Tekelioglu (a), Byard D. Wood (b) Keywords: Hybrid lighting; Optical fibers; Light transmission; Solar lighting Abstract: Light transfer (10m) has been shown in recent experiments that used large-core optical fibers. Theoretical models are not extensive, however, and a further correlation between the theory and experiments has not been given. In this paper, straight and bent fiber subsystem models are introduced with skew and meridional rays to predict the light transmission of POFs (plastic optical fibers). Such fibers have been realized, for example, in HSL (hybrid solar lighting) systems. The purpose of this paper is to combine the straight and bent fiber subsystems to estimate the light transmission of HSL systems. It is shown that meridional rays, for which the optical-loss parameters were estimated, better represent the experimental results compared to skew rays ([+ or -]5.3% vs [+ or -]24.7% of %-difference). Model predictions were compared with the results of a commercial software. Sensitivity analysis on the subsystems indicated the most-to-least significant parameters in light transmission. Author Affiliation: (a) Mechanical Engineering Department, University of Nevada, Reno, NV 89557, USA (b) Mechanical and Aerospace Engineering Department, Utah State University, Logan, UT 84322, USA Article History: Received 29 October 2008; Revised 16 July 2009; Accepted 6 August 2009 Article Note: (miscellaneous) Communicated by: Associate Editor J.-L. Scartezzini

A highly efficient local-piston theory is presented for the prediction of inviscid unsteady pressure loads at supersonic and hypersonic speeds. A steady mean flow solution is first obtained by an Euler method. The classical piston theory is modified to apply locally at each point on the airfoil surface on top of the local mean flow to obtain the unsteady pressure perturbations caused by the deviation of the airfoil surface from its mean location without the need of performing unsteady Euler computations. Results of two- and three-dimensional unsteady air loads and flutter predictions are compared with those obtained by the classical piston theory and an unsteady Euler method to assess the accuracy and validity range in airfoil thickness, flight Mach number, and angle of attack and with the presence of blunt leading edges. The local-piston theory is found to offer superior accuracy and much wider validity range compared with the classical piston theory, with the cost of only a fraction of the computational time needed by an unsteady Euler method. DOI: 10.2514/1.37750

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.robot.2009.06.004 Byline: Cong Bang Pham (a), Song Huat Yeo (b), Guilin Yang (c), I-Ming Chen (b) Abstract: For Cable-Driven Parallel Manipulators (CDPMs), employing redundant driving cables is necessary to obtain the full manipulation of the moving platform because of the unilateral driving property of the cables. Unlike rigid-link manipulators, the workspace of CDPMs is always determined and characterized by positive tension status of driving cables. In addition, it has been realized that the Tension Factor (TF) reflecting the relative tension distribution among the driving cables is an appropriate measure to evaluate the quality of tension restraint for CDPMs. However, since redundant cables are employed to drive the moving platform, the TF values are not unique for a particular moving platform pose. Therefore, how to determine the workspace and obtain the optimal TF value so as to generate a workspace with optimized performance become the major subjects of this paper. It is shown that the workspace can be generally formed from tension conditions verified by a recursive dimension-reduction approach and that the optimal TF value at every pose can be efficiently determined through a linear optimization approach, although it is essentially a nonlinear optimization problem. Computational examples are provided to demonstrate the effectiveness of the proposed algorithms. Author Affiliation: (a) School of Mechanical Engineering, Ho-Chi-Minh University of Technology, Viet Nam (b) School of Mechanical & Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore (c) Mechatronics Group, Singapore Institute of Manufacturing Technology, 71 Nanyang Drive, Singapore 638075, Singapore Article History: Received 14 December 2006; Revised 16 June 2009; Accepted 17 June 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2008.12.009 Byline: Todd P. Otanicar (a), Patrick E. Phelan (a), Jay S. Golden (b)(c) Keywords: Optical properties; Fluids; Solar thermal energy Abstract: A method for experimentally determining the extinction index of four liquids (water, ethylene glycol, propylene glycol, and Therminol VP-1) commonly used in solar thermal energy applications was developed. In addition to the extinction index, we report the refractive indices available within the literature for these four fluids. The final value reported is the solar-weighted absorption coefficient for the fluids demonstrating each fluid's baseline capacity for absorbing solar energy. Water is shown to be the best absorber of solar energy of the four fluids, but it is still a weak absorber, only absorbing 13% of the energy. These values represent the baseline potential for a fluid to be utilized in a direct absorption solar thermal collector. Author Affiliation: (a) Department of Mechanical and Aerospace Engineering, National Center of Excellence on SMART Innovations, Arizona State University, P.O. Box 876106, Tempe, AZ 85287-6106, USA (b) Department of Civil and Environmental Engineering, National Center of Excellence on SMART Innovations, Arizona State University, P.O. Box 876106, Tempe, AZ 85287-6106, USA (c) School of Sustainability, National Center of Excellence on SMART Innovations, Arizona State University, P.O. Box 876106, Tempe, AZ 85287-6106, USA Article History: Received 2 June 2008; Revised 25 November 2008; Accepted 21 December 2008 Article Note: (miscellaneous) Communicated by: Associate Editor Darren Bagnall

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.01.006 Byline: C.H. Moore, D.B. Goldstein, P.L. Varghese, L.M. Trafton, B. Stewart Keywords: Io; Atmospheres; evolution; Atmospheres; dynamics; Eclipses; Satellites; atmospheres Abstract: A one-dimensional Direct Simulation Monte Carlo (DSMC) model is used to examine the effects of a non-condensable species on Io's sulfur dioxide sublimation atmosphere during eclipse and just after egress. Since the vapor pressure of SO.sub.2 is extremely sensitive to temperature, the frost-supported dayside sublimation atmosphere had generally been expected to collapse during eclipse as the surface temperature dropped. For a pure SO.sub.2 atmosphere, however, it was found that during the first 10 min of eclipse, essentially no change in the atmospheric properties occurs at altitudes above [approximately equal to]100km due to the finite ballistic/acoustic time. Hence immediately after ingress the auroral emission morphology above 100 km should resemble that of the immediate pre-eclipse state. Furthermore, the collapse dynamics are found to be greatly altered by the presence of even a small amount of a non-condensable species which forms a diffusion layer near the surface that prevents rapid collapse. It is found that after 10 min essentially no collapse has occurred at altitudes above [approximately equal to]20km when a nominal mole fraction of non-condensable gas is present. Collapse near the surface occurs relatively quickly until a static diffusion layer many mean free paths thick of the non-condensable gas builds up which then retards further collapse of the SO.sub.2 atmosphere. For example, for an initial surface temperature of 110 K and 35% non-condensable mole-fraction, the ratio of the SO.sub.2 column density to the initial column density was found to be 0.73 after 10 min, 0.50 after 30 min, and 0.18 at the end of eclipse. However, real gas species (SO, O.sub.2) may not be perfectly non-condensable at Io's surface temperatures. If the gas species was even weakly condensable (non-zero sticking/reaction coefficient) then the effect of the diffusion layer on the dynamics was dramatically reduced. In fact, if the sticking coefficient of the non-condensable exceeds [approximately equal to]0.25, the collapse dynamics are effectively the same as if there were no non-condensable present. This sensitivity results because the loss of non-condensable to the surface reduces the effective diffusion layer size, and the formation of an effective diffusion layer requires that the layer be stationary; this does not occur if the surface is a sink. Upon egress, vertical stratification of the condensable and non-condensable species occurs, with the non-condensable species being lifted (or pushed) to higher altitudes by the sublimating SO.sub.2 after the sublimating atmosphere becomes collisional. Stratification should affect the morphology and intensity of auroral glows shortly after egress. Author Affiliation: Department of Aerospace Engineering and Engineering Mechanics, The University of Texas at Austin, 1 University Station, C0600, Austin, TX 78712, USA Article History: Received 15 September 2008; Revised 5 January 2009; Accepted 8 January 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.12.029 Byline: Marina Brozovic (a), Steven J. Ostro (a), Lance A.M. Benner (a), Jon D. Giorgini (a), Raymond F. Jurgens (a), Randy Rose (a), Michael C. Nolan (b), Alice A. Hine (b), Christopher Magri (c), Daniel J. Scheeres (d), Jean-Luc Margot (e) Keywords: Radar observations; Asteroids Abstract: Near-Earth Asteroid 4660 Nereus has been identified as a potential spacecraft target since its 1982 discovery because of the low delta-V required for a spacecraft rendezvous. However, surprisingly little is known about its physical characteristics. Here we report Arecibo (S-band, 2380-MHz, 13-cm) and Goldstone (X-band, 8560-MHz, 3.5-cm) radar observations of Nereus during its 2002 close approach. Analysis of an extensive dataset of delay-Doppler images and continuous wave (CW) spectra yields a model that resembles an ellipsoid with principal axis dimensions X=510[+ or -]20m, Y=330[+ or -]20m and Z= 241.sub.-10.sup.+80m. The pole direction is approximately located at ecliptic pole longitude and latitude of I'=+25[degrees], [beta]=+80[degrees] with the uncertainty radius of 10[degrees]. Our modeling yields a refined rotation period of 15.16[+ or -]0.04h. Nereus has a circular polarization (SC/OC) ratio of 0.74[+ or -]0.08, which implies substantial near-surface centimeter-to-decimeter scale roughness. Dynamical analysis of our model suggests that YORP alteration of the rotation period may become evident within a few years. Nereus has two stable synchronous orbits where natural material may remain in orbit, while most asteroids observed to date do not have such stable synchronous orbits. We also find that spacecraft orbits about Nereus are feasible. Author Affiliation: (a) Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109-8099, USA (b) Arecibo Observatory, National Astronomy and Ionosphere Center, Box 995, Arecibo, PR 00613, USA (c) University of Maine at Farmington, Preble Hall, 173 High St., Farmington, ME 04938, USA (d) Aerospace Engineering Sciences, University of Colorado, Boulder, CO 80309-0429, USA (e) Department of Astronomy, Cornell University, 304 Space Sciences Bldg., Ithaca, NY 14853, USA Article History: Received 11 June 2008; Revised 1 December 2008; Accepted 2 December 2008

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.12.021 Byline: Eugene G. Fahnestock (a), Daniel J. Scheeres (b) Keywords: Asteroids; Asteroids; dynamics; Satellites of asteroids; Asteroids; surfaces; Regoliths Abstract: We examine the hypothesis that within close binary asteroid systems with super-synchronously rotating, roughly spheroidal primary (Alpha) and synchronous elongated secondary (Beta), continued YORP angular acceleration of the primary causes it to spin at rates where loose material near its equator is lofted from the surface. Subsequent interaction of the material with the binary components causes that material to lose angular momentum and re-impact Alpha. In this process angular momentum is transferred to the orbit, causing the orbit to expand. We confirm this hypothesis through precise dynamic and approximate statistical simulation. For this we use the well-characterized 1999 KW4 system model, as KW4 typifies the class of binaries of interest. Our results visibly demonstrate the transfer of angular momentum and the hypothesized orbit evolution mechanism. In particular, we observe regulation of Alpha spin rate at the rate for which material lofting begins on the same side of Alpha as Beta, but not yet on the opposite side. We observe nearly constant Alpha angular momentum while the orbit angular momentum grows steadily. The linear fit to that growth is consistent with the YORP torque angular acceleration applied. Lofting occurs in fast transient episodes separated by long periods of slow spin-up under that acceleration. The average amount of material aloft and rate of mass lofting are interesting metrics for the system's lofting activity level contained in our results, but are not physically descriptive at any particular instant, given episodic lofting. We translate the orbit angular momentum growth to average semi-major axis change rate with a simple formula, whose integration also leads to time scales for the system evolution several times faster than standard tidal evolution (such as present orbit size doubling time of 2.5[+ or -]0.7 Myr for KW4). The observationally-supported end state of the system's evolution is likely separation into two asteroids on closely-related heliocentric orbits. Possible shedding of sufficiently more material from the still YORP-torqued primary may form a new secondary and repeat the overall system evolution. Author Affiliation: (a) Department of Aerospace Engineering, University of Michigan, 2008 FXB Building, 1320 Beal Avenue, Ann Arbor, MI 48109, United States (b) Department of Aerospace Engineering Sciences/Colorado Center for Astrodynamics Research, University of Colorado, Engineering Center, ECOT 611, 429 UCB, Boulder, CO 80309, United States Article History: Received 9 April 2008; Revised 13 December 2008; Accepted 15 December 2008

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.09.012 Byline: Alan W. Harris (a), Eugene G. Fahnestock (b), Petr Pravec (c) Keywords: Asteroids; Asteroids; dynamics; Asteroids; rotation; Rotational dynamics; Tides; solid body Abstract: We examine the shape of a 'rubble pile' asteroid as it slowly gains angular momentum by YORP torque, to the point where 'landsliding' occurs. We find that it evolves to a 'top' shape with constant angle of repose from the equator up to mid-latitude, closely resembling the shapes of several nearly critically spinning asteroids imaged by radar, most notably (66391) 1999 KW4 [Ostro, S.J., Margot, J.-L., Benner, L.A.M., Giorgini, J.D., Scheeres, D.J., Fahnestock, E.G., Broschart, S.B., Bellerose, J., Nolan, M.C., Magri, C., Pravec, P., Scheirich, P., Rose, R., Jurgens, R.F., De Jong, E.M., Suzuki, S., 2006. Science 314, 1276-1280]. Similar calculations for non-spinning extremely prolate or oblate 'rubble piles' show that even loose rubble can sustain shapes far from fluid equilibrium, thus inferences based on fluid equilibrium are generally useless for inferring bulk properties such as density of small bodies. We also investigate the tidal effects of a binary system with a 'top shape' primary spinning at near the critical limit for stability. We find that very close to the stability limit, the tide from the secondary can actually levitate loose debris from the surface and re-deposit it, in a process we call 'tidal saltation.' In the process, angular momentum is transferred from the primary spin to the satellite orbit, thus maintaining the equilibrium of near-critical spin as YORP continues to add angular momentum to the system. We note that this process is in fact dynamically related to the process of 'shepherding' of narrow rings by neighboring satellites. Author Affiliation: (a) Space Science Institute, 4800 Orange Knoll Avenue, La CaA[+ or -]ada, CA 91011, USA (b) Department of Aerospace Engineering, University of Michigan, 2008 FXB Building, 1320 Beal Avenue, Ann Arbor, MI 48109, USA (c) Astronomical Institute, Academy of Sciences of the Czech Republic, FriAova 1, CZ-25165 OndAejov, Czech Republic Article History: Received 29 April 2008; Revised 8 September 2008; Accepted 11 September 2008 Article Note: (dedication) We dedicate this paper to our friend and colleague Steven J. Ostro. Ostro has pioneered the field of radar astronomy, particularly in exploring near-Earth asteroids and the methods of inversion of both radar and optical data to obtain shape models of irregular bodies. Without such tools we would not have detailed 'images' of asteroids and binary systems that provide the essential input for the modeling in Sections 2 and 4 of this paper. Anyone who has co-authored a paper with Steve is aware, sometimes painfully so, of his insistence on rigorous analysis, and that it is at least as important to explore and define what one cannot say from the data, as it is to present what one can say. It is in this spirit that we present Section 3 of this paper.

In the highly technological aerospace world, paper is still widely used to document space system integration and test (I&T) operations. E-Logbook (electronic logbook) is a new technology designed to replace current documentation processes of space system I&T operations, such as connector mate and demate, flight hardware and flight software component installation, material mixes or electronic ground support equipment (EGSE) validation. It also includes new documentation concepts, such as the shift log, which improves project awareness and optimizes the shift hand-over process, and the configuration log, which instantly reports on the global I&T state of the space system and greatly enhances information gathering prior to major test events or project reviews. The design of E-Logbook focuses not only on a reliable and efficient relational database, but also on an ergonomic human-computer interactive (HCI) system of graphical user interfaces (GUI) that can help reduce human error and improve I&T discipline and management oversight. E-Logbook has been used for the I&T of the large area telescope (LAT) of the gamma-ray large area space telescope (GLAST) scientific satellite at the Stanford Linear Accelerator Center (SLAC). After 19 months of operation, more than 41,000 records have been created for the different documentation components or I&T Logs, with no data having been corrupted or critically lost. 94% of the operators and 100% of the management exposed to E-Logbook prefer it to paper logbooks and recommend its use in the aerospace industry.

Direct numerical simulation of transition flow over a blunt cone with a freestream Mach number of 6, Reynolds number of 10,000 based on the nose radius, and a 1-deg angle of attack is performed by using a seventh-order weighted essentially nonoscillatory scheme for the convection terms of the Navier-Stokes equations, together with an eighth-order central finite difference scheme for the viscous terms. The wall blow-and-suction perturbations, including random perturbation and multifrequency perturbation, are used to trigger the transition. The maximum amplitude of the wall-normal velocity disturbance is set to 1% of the freestream velocity. The obtained transition locations on the cone surface agree well with each other for both cases. Transition onset is located at about 500 times the nose radius in the leeward section and 750 times the nose radius in the windward section. The frequency spectrum of velocity and pressure fluctuations at different streamwise locations are analyzed and compared with the linear stability theory. The second-mode disturbance wave is deemed to be the dominating disturbance because the growth rate of the second mode is much higher than the first mode. The reason why transition in the leeward section occurs earlier than that in the windward section is analyzed. It is not because of higher local growth rate of disturbance waves in the leeward section, but because the growth start location of the dominating second-mode wave in the leeward section is much earlier than that in the windward section. DOI: 10.2514/1.37305

The fluorescence ratio technique for processing planar laser-induced fluorescence data was generalized for quantitative imaging of the injectant mole fraction and extended to quantify the density distributions in a nonreacting supersonic mixing flowfield. The original fluorescence ratio approach was first developed by Hartfield et al. (Hartfield, R. J., Jr., Abbitt, J. D., III, and McDaniel, J. C., 'Injectant Mole Fraction Imaging in Compressible Mixing Flow Using Planar Laser-Induced Iodine Fluorescence,' Optics Letters, Vol. 1, No. 16, Aug. 1989, pp. 850-852.) for tests in a special closed-loop wind tunnel to eliminate the effects of thermodynamic property variations on planar laser-induced fluorescence signals in compressible flowfields. This approach provided us a quantitative means of planar mole-fraction measurement; however, it implicitly assumed that the tracer molecules were seeded at the same fraction in both the main and the secondary flows. In the present study, we generalized the Hartfield et al. method by considering differences in the tracer-seeding rates for obtaining planar images of mole fraction and density. Experimental validation of the new method was carried out in a mixing flowfield formed by sonic transverse injection into a Mach 1.9 supersonic airstream. The injectant mole-fraction distribution obtained from planar laser- induced fluorescence data processed by our new approach showed better agreement with the gas-sampling data than one based on the Hartfield et al. method. The density distribution was verified by comparison with the theoretical density ratio across the oblique shock wave. DOI: 10.2514/1.37783

Three-dimensional laminar wall jets of a Newtonian fluid and two shear-thinning non-Newtonian fluids were numerically investigated. The complete nonlinear incompressible Navier-Stokes equation was solved using a colocated finite volume based in-house computational fluid dynamics code. For each fluid, the computation was performed at three Reynolds numbers. The results showed that the streamwise velocity profiles for the Newtonian fluid became self-similar but the more shear-thinning fluid never achieved a self-similar condition. Significant differences were observed among the profiles for the various fluids in the inner region. Although the transverse and spanwise components of the velocity decreased substantially with increasing Reynolds number, the values fur the non-Newtonian fluids were generally an order of magnitude larger than the corresponding values for the Newtonian fluid. Depending on the specific fluid and Reynolds number, the apparent viscosities were up to 4 orders of magnitude higher than the dynamic viscosity of water. Consequently, the spread of the jet in both the transverse and spanwise directions, decay of the maximum streamwise velocity, and the skin friction coefficient depend strongly on both Reynolds number and nature of the fluid. The results also show that the jet half-width in the transverse direction is significantly higher than in the spanwise direction. DOI: 10.2514/1.37081

Proper orthogonal decomposition was employed to turbulent flows over an open cavity to investigate the spatial characteristics of coherent structures responsible for self-sustained oscillations. The distributions of pressure fluctuations were analyzed by using snapshot-based proper orthogonal decomposition. When self-sustained oscillations took place for [Re.sub.D] = 12,000 in the cavity geometry of L/D = 2, three pairs of alternative patterns were shown in the first and second modes of pressure fluctuations. By examining both temporal evolutions and spanwise distributions of the first two modes, quasi-two-dimensional vortical formations were shown to be responsible for the self-sustained oscillations. In turbulent cavity flows of [Re.sub.D] = 3000, however, the periodic oscillations were not observed, due to the irregular shedding of three-dimensional vortical structures. For the application of proper orthogonal decomposition analysis to experimental data, the decomposition was employed to the spatial distributions of v-v correlations on the lip line of cavity geometry. DOI: 10.2514/1.36860

Broadband shock cell noise is an important component of aircraft interior noise during cruise. At cruise, the secondary jet of most modern day jet engines is supersonic. As a result, a shock cell structure develops in the jet plume. The interaction of large turbulence structures of the jet flow and the periodic components of the shock cells results in the emission of highly directional broadband shock cell noise. The primary objective of this investigation is to develop a computational method to calculate the shock cell structures of dual-stream jets issued from separate flow nozzles. Computation of the Fourier modes of such shock cell structures is also considered. Based on the dominant wave numbers computed by the method developed, the frequencies at the peaks of broadband shock cell noise spectra at various radiation directions are calculated. Good agreements are found with experimental measurements over a wide range of primary and secondary jet Mach numbers. The good agreements provide a validation of the accuracy of the computation method. DOI: 10.2514/1.37045

This paper introduces a new technique for robust aeroelastic analysis that extends standard linear flutter analysis to take deterministic uncertainty and variation into account. The basic principle of the proposed [mu]-p method is to exploit structured-singular-value (or [mu]) analysis to investigate if the system uncertainties can make the flutter determinant zero for a given flutter eigenvalue p. This makes it possible to compute regions of feasible eigenvalues in the complex plane as well as extreme eigenvalues that can he used to predict damping bounds and perform robust flutter analysis. The capability to predict damping bounds at subcritical flight conditions is a very attractive feature of the new method, as flight testing is rarely taken to the flutter point. The [mu]-p formulation also opens up new possibilities to bound the magnitude of the system uncertainties based on frequency and/or damping estimates from flight testing. In the final part of the paper, the [mu]-p framework is successfully applied to perform robust aeroelastic analysis of a low-speed wind-tunnel model. DOI: 10.2514/1.35859

Existing aeroelastic analyses for finite wings have been mostly limited to cases with a steady freestream. In reality, however, the inflowing freestream can often be unsteady and pulsating. Therefore, this paper presents unsteady aerodynamic and aeroelastic analyses for a finite wing under a pulsating freestream. A new three-dimensional unsteady vortex lattice model under a pulsating freestream has been developed in discrete-time domain to examine unsteady aerodynamic forces acting on a vibrating wing. The structural behavior of the wing has been analyzed using a three-dimensional plate model. An aeroelastic model is then constructed by coupling the unsteady aerodynamic model with the structural model. Since the freestream velocity is assumed to be time-varying, the flutter onset of a wing under pulsating freestream is predicted by Floquet analysis. Numerical results of an untwisted and untapered wing show that the new time domain method can predict the aeroelastic stability as well as time history of the isolated wing under a pulsating freestream. DOI: 10.2514/1.33731

A one-dimensional control volume formulation is developed for the determination of jet mixing noise reduction due to water injection. The analysis starts from the conservation of mass, momentum, and energy for the control volume and introduces the concept of effective jet parameters I jet temperature, jet velocity, and jet Mach number). It is shown that the water-to-jet mass flow rate ratio is an important parameter characterizing the jet noise reduction on account of gas-to-droplet momentum and heat transfer. Two independent dimensionless invariant groups are postulated and provide the necessary relations for the droplet size and droplet Reynolds number. Results are presented illustrating the effect of mass flow rate ratio on the jet mixing noise reduction for a range of jet Mach numbers and jet Reynolds numbers. Predictions from the model show satisfactory comparison with available test data on perfectly expanded hot supersonic jets. The results suggest that significant noise reductions can be achieved at increased flow rate ratios. DOI: 10.2514/1.33599

We present the results of a series of measurements in which an array of capacitive V-dot probes are used to determine the surface potential in a single dielectric barrier discharge plasma operated as an aerodynamic plasma actuator. From these measurements, we determine the longitudinal electric field in the plasma. The results show that the surface immediately (within the first alternating current cycle of the plasma discharge) acquires a net positive surface charge, so that the electric field in the plasma is asymmetric, the magnitude of the maximum field being more than 50% larger in the negative than the positive polarity. The measurements also show that there is a region several millimeters downstream from the exposed electrode edge over which the electric field maintains a constant positive (downstream) polarity over the course of the discharge cycle. DOI: 10.2514/1.33973

The joined wing is a new concept of the airplane wing. The forewing and the aft wing are joined together in the joined wing. The joined wing can lead to increased aerodynamic performances and reduction of the structural weight. The structural behavior of the joined wing has a high geometric nonlinearity according to the external loads. Therefore, the nonlinear behavior should be considered in the optimization of the joined wing. It is well known that conventional nonlinear response optimization is extremely expensive; thus, the conventional method is almost impossible to use for large-scale structures such as the joined wing. In this research, geometric nonlinear response optimization of a joined wing is carried out by using equivalent loads. The used structure is a joined wing that is currently being developed in the U.S. Air Force Research Laboratory. Equivalent loads are the load sets that generate the same response field in linear analysis as that from nonlinear analysis. In the equivalent loads method, the external loads are transformed to the equivalent loads for linear static analysis, and linear response optimization is carried out based on the equivalent loads. The design is updated by the results of linear response optimization. Nonlinear analysis is carried out again and the process proceeds in a cyclic manner until the convergence criteria are satisfied. It was verified that the equivalent loads method is equivalent to a gradient-based method; therefore, the solution is the same as that of exact nonlinear response optimization. The fully stressed design method is also used for nonlinear response optimization of a joined wing. The results from the fully stressed design and the equivalent loads method are compared. DOI: 10.2514/1.33428

A theoretical model for the penetration of a liquid jet in subsonic gaseous crossflow is developed. The model allows for the deformation of the jet cross section from circular to elliptic shapes along its path. A force balance analysis on an elliptical liquid element is performed. Aerodynamic, viscous, and surface tension forces are considered counting for the nonlinear terms at large deformations. The effect of mass shedding is also included in the model. This effect changes the jet trajectory and deformation at higher Weber numbers. In addition, the drag coefficients of elliptical cylindrical elements with different aspect ratios are calculated numerically for a range of Reynolds numbers. It is observed that the drag coefficient of the cylindrical element changes considerably with Reynolds number and the jet deformation. The change in the drag force considerably affects the jet deflection in the gas stream. Results show that the liquid-to-gas momentum ratio is not the only governing parameter in predicting the jet trajectory. Gas Weber number, rate of mass shedding from the jet, jet cross-sectional deformation, variation in the drag coefficient, and variation in the liquid and gas properties all affect the jet penetration. DOI: 10.2514/1.28254

A computational fluid dynamics analysis of acoustic modes and instabilities in an experimental longitudinal test chamber is presented. The experimental configuration is a uni-element recessed injector post combined with a variable-length combustion chamber. The computations employ the nonlinear Euler equations with mass and heat addition in the injector and combustion chamber and response functions to represent combustion dynamics. Analytical solutions and experimental comparisons are used to verily and validate the computational model. The results demonstrate the importance of including the lull Euler equations for predicting the frequencies and mode shapes in the injector-combustor configuration as well as for representing nonlinear phenomena such as wave steepening and the excitation of higher harmonics. The present approach therefore promises to be a useful platform for testing and calibrating combustion response functions for combustion instability models. DOI: 10.2514/1.28125

Many engineering applications are characterized by implicit response functions that are expensive to evaluate and sometimes nonlinear in their behavior, making reliability analysis difficult. This paper develops an efficient reliability analysis method that accurately characterizes the limit state throughout the random variable space. The method begins with a Gaussian process model built from a very small number of samples, and then adaptively chooses where to generate subsequent samples to ensure that the model is accurate in the vicinity of the limit state. The resulting Gaussian process model is then sampled using multimodal adaptive importance sampling to calculate the probability of exceeding (or failing to exceed) the response level of interest. By locating multiple points on or near the limit state, more complex and nonlinear limit states can be modeled, leading to more accurate probability integration. By concentrating the samples in the area where accuracy is important (i.e., in the vicinity of the limit state), only a small number of true function evaluations are required to build a quality surrogate model. The resulting method is both accurate for any arbitrarily shaped limit state and computationally efficient even for expensive response functions. This new method is applied to a collection of example problems including one that analyzes the reliability of a microelectromechanical system device that current available methods have difficulty solving either accurately or efficiently.

The primary goal of this research is to develop a framework for dealing with multi-objective, multidisciplinary optimization problems with a large number of variables. The proposed method is expected to provide a relatively uniformly spaced, widely distributed Pareto front. To achieve this end, a novel integration of the adaptive weighted sum method within a concurrent subspace optimization framework is presented. In the bilevel framework of concurrent subspace optimization, the adaptive weighted sum is used to make tradeoffs among multiple, conflicting objectives. To obtain better distributed solutions, two modifications are made. First, an additional equality constraint in suboptimization for each expected solution is relaxed because it causes slow convergence within the bilevel optimization framework. The probability of entrapment in local minima can also be reduced. Second, the mesh of the Pareto front patches is modified due to the low efficiency of the original scheme. The proposed method is demonstrated with three multidisciplinary design optimization problems: 1) a numerical multidisciplinary design optimization test problem with a convex Pareto front, available within the NASA multidisciplinary design optimization Test Suite; 2) a test problem with a nonconvex Pareto front, which is not easily solved; and 3) a conceptual design of a subsonic passenger aircraft, which consists of two objectives, four design variables, five coupling behavior variables, seven constraints in aerodynamics, and weight discipline. The primary results show that the proposed method is promising with regard to obtaining a uniformly spaced, widely distributed, and smooth Pareto front and is applicable in the design of large-scale, complex engineering systems such as aircraft.

An adiabatic homogeneous model to account for multiperforated liners in combustion chamber flow simulations is described. It is based on a suction and an injection model to reproduce the average effect of effusion cooling on both sides of the plate. The coupled suction/injection model has been specifically designed to be used in industrial full- scale computations of gas turbine combustion chambers, where effusion cooling is commonly used for controlling the temperature of the liners. Notably, it can be used with a coarse grid, the real perforated plate being replaced by a homogeneous boundary condition where the model is applied. The new modeled boundary condition conserves the inviscid part of the wall fluxes, which are shown to be the main contribution, as evidenced by the analysis of former wall-resolved simulations. Conserving the wall fluxes allows reproduction of the global structure of the flow and leads to reasonable comparisons with experimental data. Hence, the proposed new model provides a practical way to account for multiperforated plates with inclined perforations without resolving the flow in the perforations.

The testing of aeroelastically and aerothermoelastically scaled wind-tunnel models in hypersonic flow is not feasible; thus, computational aeroelasticity and aerothermoelasticity are essential to the development of hypersonic vehicles. Several fundamental issues in this area are examined by performing a systematic computational study of the hypersonic aeroelastic and aerothermoelastic behavior of a three-dimensional configuration. Specifically, the flutter boundary of a low-aspect-ratio wing, representative of a fin or control surface on a hypersonic vehicle, is studied over a range of altitudes using third-order piston theory and Euler and Navier--Stokes aerodynamics. The sensitivity of the computational-fluid-dynamics-based aeroelastic analysis to grid resolution and parameters governing temporal accuracy are considered. In general, good agreement at moderate-to-high altitudes was observed for the three aerodynamic models. However, the wing flutters at unrealistic Mach numbers in the absence of aerodynamic heating. Therefore, because aerodynamic heating is an inherent feature of hypersonic flight and the aeroelastic behavior of a vehicle is sensitive to structural variations caused by heating, an aerothermoelastic methodology is developed that incorporates the heat transfer between the fluid and structure based on computational-fluid-dynamics-generated aerodynamic heating. The aerothermoelastic solution procedure is then applied to the low-aspect-ratio wing operating on a representative hypersonic trajectory. In the latter study, the sensitivity of the flutter margin to perturbations in trajectory angle of attack and Mach number is considered. Significant reductions in the flutter boundary of the heated wing are observed. The wing is also found to be susceptible to thermal buckling.

Reduction of jet noise continues to be an important research topic. Exhaust-nozzle chevrons have been shown to reduce jet noise, but parametric effects, including immersion amount and azimuthal distribution, are not well understood. Additionally, thrust loss due to static chevrons at cruise suggests a significant benefit from deployable chevrons. The focus of this study is the development of an adaptive-chevron concept for the primary purpose of parametric studies for jet noise reduction in the laboratory and secondarily for development of technology that can be leveraged for full-scale systems. The adaptive-chevron concept employed in this work consists of a laminated composite structure with embedded shape memory alloy actuators. The actuators are embedded on one side of the middle surface such that joule heating of the actuators causes them to attempt recovery of prestrain, thereby generating a moment and deflecting the structure. A brief description of the chevron design is given followed by details of the fabrication approach. Results from bench-top tests are presented and correlated with numerical predictions from a model for such structures that was previously implemented in MSC.Nastran and ABAQUS. Excellent performance and agreement with predictions is demonstrated. Results from tests in a representative flow environment are also presented. Excellent performance is again achieved for both open- and closed-loop tests, the latter demonstrating control of deflection to a specified immersion into the flow. The actuation authority and immersion performance is shown to be relatively insensitive to nozzle pressure ratio. Very repeatable immersion control with modest power requirements is demonstrated.

Direct reduction of aero-optical aberrations incurred by a laser propagated through a refractive turbulent flow has been achieved by introducing plasma into the flow at various pulsing frequencies. The plasma is generated by a dielectric barrier discharge device which operates at elevated pressure to force flow near the separation point of a single-stream shear layer that is generated in a variable pressure wind-tunnel testing facility with Re ~ 6 x [10.sup.6] and [M.sub.[infinity]] ~ 0.9. The levels of aero-optical aberrations present in the laser are determined by directly profiling the propagated laser using a high-resolution Shack--Hartmann wave front sensor with ~ 1000 microlenses. Reductions in the ensemble-averaged optical path difference root mean square of up to 27% were achieved. Whole-field shadowgraphs were recorded for various forcing frequencies and indicate that the observed aero-optical effects are the result of modifications in the level of organization of the large structures. Because the dominant contributions to the aberrations in unforced flows are caused by large-scale organized structures, our findings indicate that the mechanism by which the significant reduction is observed in the forced experiments is due to large-scale suppression of the turbulent structures directly effected by the pulsed plasma actuator. Conversely, increases in the aero-optical aberrations, which have also been observed at certain plasma pulsing frequencies, are the result of large-scale regularization of the structures within the turbulent shear layer. The presence of these large-scale suppression and regularization mechanisms is confirmed by the shadowgraphs at forced cases compared with the unforced case.

Active flow control using fluidic actuators, via arrays of synthetic jet actuators, was used to provide control power for the Stingray unmanned aerial vehicle in the longitudinal (pitch) and lateral (roll) directions at low angles of attack. Using this technique, the pitch and roll moments were altered such that the effect is similar to that of a deflection of conventional control effectors. The control effectiveness of the synthetic jets on the aerodynamic performance of the Stingray unmanned aerial vehicle was investigated experimentally in a wind tunnel. Global flow measurements were conducted, where the moments and forces on the vehicle were measured using a six-component sting balance. The effect of the actuation was also examined on the surface static pressure at two spanwise locations. In addition, a particle image velocimetry technique was used to quantify the flowfield over the model, both the global flowfield as well as the localized interaction domain near the synthetic jet orifice. The synthetic jets were able to alter the local streamlines and displace the boundary layer through the formation of a small quasi-steady interaction region on the suction surface of the Stingray unmanned aerial vehicle's wing. Phase-locked particle image velocimetry data were acquired to provide insight into the growth, propagation, and decay of the synthetic jets impulse and their interaction with the crossflow. Furthermore, the changes induced on the moments and forces can be proportionally controlled by either changing the momentum coefficient or by driving the synthetic jets with a pulse modulation waveform. This can lead the way for future development of closed-loop control models.

Dual particle image velocimetry (dual PIV) measurements have been performed to investigate the space-time correlations in two subsonic isothermal round jets at Mach numbers of 0.6 and 0.9. The correlation scales are analyzed along the centerline and in the shear-layer center over the first 11 jet diameters from the nozzle exit. To provide robust results over a wide range of flow conditions, these correlation scales are given in terms of their appropriate quantities, namely, the mean or rms velocity in reference to velocity and the momentum thickness or the half-velocity diameter in reference to length in the shear layer and on the jet axis, respectively. From these results, a discussion on the modeling of turbulence in jets is addressed. The self-similarity of some space correlation functions in the shear layer and on the jet axis is shown. Furthermore, far enough downstream in the shear layer, some of the ratios between the space and time scales are relatively close to the values expected in homogeneous and isotropic turbulence. It is also found that the ratio between the integral length and the time scales in the fixed frame is of the order of the local mean flow velocity. In the convected frame, the appropriate scaling factor is the rms velocity.

The ablation process of the Stardust thermal protection material is designed to reduce aerodynamic heating during reentry for extreme conditions. The coupling of ablation species with the flowfield is investigated in this work using the direct simulation Monte Carlo method for transitional to near-continuum flows. To model surface thermal and chemical ablation processes, a variable surface temperature wall is obtained assuming a radiative heat flux balanced by convective heat flux. It is found that chemical ablation due to the reaction between thermal protection system carbon materials and gaseous oxygen and nitrogen atoms is dominant compared with thermal ablation. As the altitude decreases, the forebody surface temperature increases, the ablation process becomes more intensive, and the influence of ionization reactions on the flowfield becomes more important due to denser freestream conditions.

The flowfield of the NLF-0414 airfoil with a prescribed ice shape is characterized with numerical solutions to the Navier--Stokes equations. Three flow solvers are used: ZEN, a code developed at CIRA, FLUENT, a commercially available code, and CFL3D, a NASA developed solver. For each code two turbulence models are selected: the Spalart--Allmaras and the shear stress transport [kappa]--[omega] model. An effort is devoted to ascertain the degree of uncertainty among the numerical codes and turbulence models. Integrated forces and pressure coefficient distributions are compared among the analytic solutions and with available experimental data. The conditions include a range of incidence angles covering pre- and poststall for a freestream Mach number and a Reynolds number of 0.21 and 4.6 x [10.sup.6], respectively. Generally, steady-state solutions are obtained; however, unsteady solutions are acquired for the highest angles of attack.

This paper presents an experimental investigation on the control of airfoil aerodynamics at poststall angle of attack using a surface perturbation technique. Piezoceramic actuators were deployed to create a local surface perturbation on a NACA0012 airfoil, along with an open-loop control system, to manipulate flow around the airfoil. Two different control signals were examined, i.e., square and sine waves. Whereas the lift and drag forces were measured using a load cell, the flow was documented using a particle image velocimetry, laser Doppler anemometer and a single hot wire. The surface perturbation significantly improved the airfoil aerodynamics fur 12 [less than or equal to] [alpha] [less than or equal to] < 20 deg. The control effect with the square-wave excitation was found to be much more effective than that with the sine wave. The control was most effective at [alpha] = 14 deg: the mean lift coefficient, lift-to-drag ratio, and figure of merit (i.e., the ratio of the power to aerodynamic efficiencies) were enhanced by 35, 64, and 44%, respectively, whereas the mean drag coefficient dropped by 23%. Furthermore, the airfoil stall was postponed by 3 deg. The physics behind the observations were discussed in detail.