Showing papers in "Journal of Spacecraft and Rockets in 2005"

Navier-Stokes Solutions with Finite Rate Ablation for Planetary Mission Earth Reentries

Abstract: A formulation of finite rate ablation surface boundary conditions, including oxidation, nitridation, and sublimation of carbonaceous material with pyrolysis gas injection, based on surface species mass conservation, has been developed. These surface boundary conditions are discretized and integrated with a Navier-Stokes solver. This numerical procedure can predict aerothermal heating, chemical species concentration, and carbonaceous material ablation rates over the heat-shield surface of reentry space vehicles. Two finite rate gas-surface interaction models, based on the work of Park and of Zhluktov and Abe, are considered. Three test cases are studied. The stream conditions of these test cases are typical for Earth reentry from a planetary mission with both oxygen and nitrogen fully or partially dissociated inside the shock layer. Predictions from both gas-surface interaction models are compared with those obtained by using chemical equilibrium ablation tables. Stagnation point convective heat fluxes predicted by using Park's finite rate model are usually below those obtained from chemical equilibrium tables and Zhluktov and Abe's model. Recession predictions from Zhluktov and Abe's model are usually lower than those obtained from Park's model and from chemical equilibrium tables. The effect of species mass diffusion on the predicted ablation rate is also examined.

Cost-Benefit Analysis of the Aerocapture Mission Set

Abstract: Calculations have been performed to qualify the cost and delivered mass advantages of aerocapture at all destinations in the solar system with significant atmospheres.

Navier-Stokes Computations for a Spinning Projectile from Subsonic to Supersonic Speeds

Abstract: A computational study has been undertaken to predict the static-aerodynamic, Magnus-moment, and roll-damping coefficients of a standard spinning projectile using a single, modern, unstructured Navier-Stokes flow solver. Numerical results without engraving and semi-empirical results have been obtained for a wide range of Mach numbers to include subsonic, transonic, and supersonic flight regimes. Effects of 0-, 2-, and 5-deg angles of attack have been investigated. Flowfield characteristics of each flight regime are briefly explored. A comparison of coefficients calculated from the computational fluid dynamics results are made to both experimental range data as well as semi-empirical aeroprediction code results with some success. Good predictive capabilities are found for the static aerodynamic coefficients throughout all of the flight regimes. Discrepancies arise between the computational results and the experimental results for the Magnus moment and roll-damping coefficients due in part to the lack of engraving on the computational model.

Time-Accurate Numerical Prediction of Free-Flight Aerodynamics of a Finned Projectile

Abstract: This article describes a new multidisciplinary computational study undertaken to compute the flight trajectories and simultaneously predict the unsteady free-flight aerodynamics of a finned projectile configuration. Actual flight trajectories are computed using an advanced coupled computational fluid dynamics/rigid body dynamics technique in a body-fixed coordinate system. An advanced time-accurate Navier–Stokes computational technique has been used in computational fluid dynamics to compute the unsteady aerodynamics associated with the free flight of the finned projectile at supersonic speeds. Computed positions and orientations of the projectile have been compared with actual data measured from free-flight tests and are found to be generally in good agreement with the data. Predicted aerodynamics forces and moments also compare well with the forces and moments used in the 6 degree of freedom fits of the results of the same tests. Unsteady numerical results obtained from the coupled method show the flowfield, the aerodynamic coefficients, and the flight paths of the projectile.

Effective Modeling and Nonlinear Shell Analysis of Thin Membranes Exhibiting Structural Wrinkling

Abstract: Thin solar sail membranes of very large span are being envisioned for near-term space missions. One major design issue that is inherent to these very flexible structures is the formation of wrinkling patterns. Structural wrinkles may deteriorate a solar sail's performance and, in certain cases, structural integrity. A geometrically nonlinear, updated Lagrangian shell formulation is employed using the ABAQUS finite element code to simulate the formation of wrinkled deformations in thin-film membranes. The restrictive assumptions of true membranes as defined by tension field theory are not invoked. Two effective modeling strategies are introduced to facilitate convergent solutions of wrinkled equilibrium states. They include 1) the application of small, pseudorandom, out-of-plane geometric imperfections that ensure initiation of the requisite membrane-to-bending coupling in a geometrically nonlinear analysis and 2) the truncation of corner regions, where concentrated loads are prescribed, to improve load transfer, mesh quality, and kinematics and to reduce severe concentration of membrane stresses. The corner truncation necessitates replacing the concentrated force with a statically equivalent distributed traction. Several numerical studies are carried out, and the results are compared with recent experimental data. Good agreement is observed between the numerical simulations and experimental data.

Generalized Model for Solar Sails

Abstract: E define a new methodology for the analytic description of the force and moment generated by a solar sail of arbitrary shape and surface optical properties. We find that the total force and moment generated by the sail can be completely defined by the computation of a number of constants of the sail, which are only functions of the sail geometry and independent of the incident light. Given these constants, some standard sail properties, and the incident light pressure and direction, the total force and moment acting on the sail can be computed using simple formulas. Specifically, we can characterize the force generated by a solar sail of arbitrary sail geometry under general illumination conditions with 18 numbers. To characterize the moment requires an additional 36 numbers. The advantages of this description are that these constants can be computed off-line and are defined for arbitrarily shaped sails, meaning that only one formalism must be coded to deal with all types of sails. There are a number of limits to this approach. First, this model tacitly assumes that the sail will not change shape as its attitude varies, thus their utility might be somewhat limited or constrained to relatively small angular motions. This limitation will be addressed in the future. Second, it assumes that there is no self-shadowing, that is, that every element of the sail surface will “see” an incident ray. This is a reasonable assumption given the likely mode in which a solar sail will be operated.

Design and testing of a control moment gyroscope cluster for small satellites

Abstract: Experimental results on the performance of a control moment gyroscope cluster are presented. The goal is to design and evaluate a control moment gyroscope cluster for three-axis control for agile small satellites. The experimental data are compared with simulation (theoretical) results and both are used to verify the principles, advantages, and performance specifications of a control moment gyroscope cluster for a small satellite, in a practical way. Control moment gyroscope systems are considered in the literature to be more efficient devices, from an electrical power point of view, than current actuators such as reaction/momentum wheels. Experimental measurements are presented and then compared to two reaction wheels of different size. Control moment gyroscopes are shown to have a potential performance advantage over reaction/momentum wheels for spacecraft with agile requirements.

Application of Accelerometer Data to Mars Odyssey Aerobraking and Atmospheric Modeling

Abstract: Aerobraking was an enabling technology for the Mars Odyssey mission, even though it involved risk due primarily to the variability of the Mars upper atmosphere. To reduce the risk, numerous analyses, based on various data types, were performed during operations. The use of one such data type, measurements from spacecrafts accelerometers, for determining atmospheric density during Odyssey aerobraking operations is reported. Accelerometer data were analyzed in near real time to provide estimates of density at periapsis, maximum density, density scale height, latitudinal gradient, longitudinal wave variations, and location of the polar vortex. Summaries of the aerobraking phase of the mission, the accelerometer data analysis methods and operational procedures, applications to determining thermospheric properties, and several remaining issues on interpretation of the data are discussed. Although acceleration was measured along three orthogonal axes, only data from the component along the axis nominally into the flow were used during operations. For a 1-s count time, the rms noise level, derived from the acceleration, varied from 0.07 to 0.5 mm/s 2 , permitting density recovery to between 0.15 and 1.1 kg/km 3 , or about 2% of the mean density at periapsis during aerobraking. Preflight estimates of natural variability based on Mars Global Surveyor accelerometer measurements proved reliable in the midlatitudes but overestimated the variability inside the polar vortex.

Aerodynamic Predictions, Comparisons, and Validations Using Missile DATCOM (97) and Aeroprediction 98 (AP98)

Abstract: The U.S. Air Force Missile DATCOM (97 version) and the Naval Surface Warfare Center Dahlgren Division Aeroprediction 98 (AP98) are two widely used aerodynamic prediction codes. These codes predict aerodynamic forces, moments, and stability derivatives as a function of angle of attack and Mach number for a wide range of axisymmetric and nonaxisymmetric missile configurations. This study evaluates the accuracy of each code compared to experimental wind-tunnel data for a variety of missile configurations and flight conditions. The missile configurations in this study include axisymmetric body alone, body wing tail, and body tail. The aerodynamic forces under investigation were normal force, pitching moment, axial force, and center-of-pressure location. For the configurations detailed in this paper, these case studies show normal force prediction for both codes to have minimal error. Both AP98 and Missile DATCOM were effective in predicting pitching-moment coefficients, though at times limiting factors were necessary. Finally, both AP98 and DATCOM predict reasonable axial-force coefficients for most cases, though AP98 proved more accurate for the body-wing-tail and body-tail configurations evaluated in this study.

Control of Hypersonic Turbulent Skin Friction by Boundary-Layer Combustion of Hydrogen

Abstract: Shvab-Zeldovich coupling of flow variables has been used to extend Van Driest's theory of turbulent boundary-layer skin friction to include injection and combustion of hydrogen in the boundary layer. The resulting theory is used to make predictions of skin friction and heat transfer that are found to be consistent with experimental and numerical results. Using the theory to extrapolate to larger downstream distances at the same experimental conditions, it is found that the reduction in skin-friction drag with hydrogen mixing and combustion is three times that with mixing alone. In application to flow on a flat plate at mainstream velocities of 2, 4, and 6 knits, and Reynolds numbers from 3 X 10(6) to 1 x 10(8), injection and combustion of hydrogen yielded values of skin-friction drag that were less than one-half of the no-injection skin-friction drag, together with a net reduction in heat transfer when the combustion heat release in air was less than the stagnation enthalpy. The mass efficiency of hydrogen injection, as measured by effective specific impulse values, was approximately 2000 s.

Number of Arcs Estimated on Solar Array of a Geostationary Satellite

Abstract: Plasma parameters of geosynchronous orbit measured by Los Alamos National Laboratory satellites are analyzed statistically. For each set of plasma parameters, charging analysis is carried out, taking a geostationary satellite representing a typical telecommunication satellite as an example. The number of expected trigger arcs on a solar array is calculated based on the charging duration with severe inverted potential gradient conditions expected in orbit. Using the number of trigger arcs, an appropriate duration of electrostatic discharge ground test is proposed to test the insulation strength against sustained arc phenomena.

Pulsed Plasma Thruster System for Microsatellites

Abstract: The design and qualification of a pulsed plasma thruster (PPT) system for microsatellites is presented. Developed for the University of Washington's Dawgstar satellite, the micro-PPT provides formation keeping, orbit maintenance, and attitude control functions for satellites in the 10-100-kg range. Thrust is created when solid Teflon® propellant is ionized by a pulsed, high-current electrical arc and accelerated by a combination of electromagnetic and gas dynamic forces. The system presented provides thrust levels from 60 to 275 μN with specific impulses up to 266 s. A centralized power-processing unit utilizing high voltage switching enables a reduction in system mass when compared to previous designs. The total mass for the system presented is 4.20 kg, which enables control of three axes of rotation and two axes of translation. Approximately 1.7 million pulses were successfully accumulated on the flight qualification unit, representing a total system impulse of approximately 1000 N s. Mission design, mechanical and electrical design, and detailed results from ground testing are discussed.

2001 Mars Odyssey Aerobraking

Abstract: The Mars Odyssey spacecraft was inserted into a highly elliptical capture orbit about Mars on October 24, 2001. This paper details the strategy, implementation, and results of the aerobraking phase of the mission.

Debonding Failure of Sandwich-Composite Cryogenic Fuel Tank with Internal Core Pressure

Abstract: A summary of the failure analyses and testing that were conducted to determine the cause of the X-33 liquidhydrogen tank failure is presented. Ply-level stress analyses were conducted to explain the formation of microcracks in the plies of the inner and outer facesheet laminates of the honeycomb sandwich walls of the tank under known thermal and mechanical loads. The microcracks allowed the ingression of liquid- and gaseous-hydrogen and gaseous-nitrogen purge gas that produced higher than expected sandwich core pressures in the tank. Single cantilever beam tests were used to determine the toughness of the interface between the facesheets and honeycomb core. Fracture mechanics analyses were developed to determine strain-energy release rates for known foreign object debris shapes and sizes and known and statistically possible core internal pressures. The fracture mechanics analyses were validated by comparing with results of blowoff tests that were fabricated from undamaged tank sandwich material. Strain-energy release rates from the validated analyses were then compared with known and statistically possible values of toughness determined from the single cantilever beam tests. These analyses and tests were then used to substantiate a scenario for failure of the X-33 liquid-hydrogen tank that includes microcracking of the inner facesheets and ensuing ingression of hydrogen and nitrogen, a low bondline strength and toughness, and the presence of foreign object debris. Nomenclature ¯ A −1 jk =i nverse of the laminate stiffness matrix transformed to the local coordinates a, b = dimensions of debond Eii = elastic modulus in the ith principal material

Geometric Analysis of Free-Return Trajectories Following a Gravity-Assisted Flyby

Abstract: The purpose of this study is to systematically identify all feasible trajectories following a gravity-assisted flyby that immediately return to the flyby body with no intermediate maneuvers. Every class of possible transfer angles is considered including even-nπ, odd-nπ, and generic return orbits. Lambert's problem is solved for a desired time-of-flight range allowing the possibility for multiple spacecraft and celestial body revolutions. The solutions are expressed geometrically, and the resulting velocity diagram is a mission-planning tool with potential applications that include cycler trajectories and planetary moon tours. The generalized free-return solutions can be used to construct loitering orbits about one celestial body or transfers between multiple bodies. Several previously documented cycler trajectories are improved using the discussed solutions.

Oxidation Behavior of Siliconcarbide-Based Materials by Using New Probe Techniques

Abstract: Hysteresis of passive to active and active to passive transition of SiC oxidation behavior has been investigated theoretically, numerically, and experimentally. Theoretical and experimental investigations show a strong interaction between transition and catalysis. Dependence on plasma composition is shown.Arecently developed reaction model has been implemented in the advanced nonequilibrium Navier–Stokes code URANUS. Results are presented for the highly dissociated flow around the MIRKA capsule. In this case, radiation adiabatic surface temperatures have been found to be 120Khigher for active oxidation conditions as compared to passive oxidation conditions. To investigate transition behavior in detail, various new probe measurement techniques have been developed. Important additional observations have been made in chemical nonequilibrium.Within plasma wind-tunnel testing, a sudden temperature increase of up to 400 K was found with the transition from passive to active oxidation. Theoretical and numerical predictions show good qualitative and quantitative agreement with experimental results.

Self-Pressurization of Large Spherical Cryogenic Tanks in Space

Abstract: The pressurization of large cryogenic storage tanks under microgravity conditions is investigated by coupling a lumped thermodynamic model of the vapor region with a complete solution of the flow and temperature fields in the liquid. Numerical results indicate that in microgravity both buoyancy and natural convection are still important and play a significant role in phase distribution and tank pressurization. A spherical vapor region initially placed at the center of the tank deforms and moves to one side of the tank before any significant pressure rise. Long-term results obtained with the vapor region near the tank wall show that, even in microgravity, natural convection leads to thermal stratification in the liquid and significantly alters the initial pressure rise. The final rate of pressure rise agrees with a lumped thermodynamic model of the entire system, but the final pressure levels depart from thermodynamic predictions because of initial transients. The history of the maximum liquid superheat and subcooling is also determined for each configuration.

Near-Optimal Solar-Sail Orbit-Raising from Low Earth Orbit

Abstract: Introduction S OLAR-SAIL technology has attracted the interest of the scientific community as an advanced propulsion means capable of promoting the reduction of mission costs, the increase of payload mass fraction, and the feasibility of missions that are not practically accessible via conventional propulsion because of their large V requirements. Optimal solar-sail trajectories have long been investigated because of their importance for practical mission analysis purposes.1 Although globally optimal trajectories are especially well suited for interplanetary missions, there are many instances where different engineering constraints limit the possibility of using optimal steering laws. Accordingly, simpler maneuver strategies are required. This happens in most planet-centered problems, including orbitraising and Earth-escape trajectories. In these cases suboptimal (or locally optimal) control laws that maximize the instantaneous rate of change of a particular orbital element or another scalar function of the orbital elements are often employed. This approach not only provides simple answers to the designer, but also gives steering laws that, in many cases, are close to minimum-time solutions. For these reasons, locally optimal control laws for ideal sails have been studied in various forms with different perturbation models. In most papers available in the literature,2−7 the simplifying assumption of neglecting the aerodynamic drag is made. Although the aerodynamic drag has been sometimes taken into account in the mission analysis,8,9 no systematic study concerning its effects on the solar-sail trajectories is currently available. Air drag is known to be negligible above 1000 km, even if its effects are strongly influenced by the solar activity. Nevertheless, air drag can become important as long as particular maneuvers, such as orbit raising from low Earth orbit, are concerned. Accordingly, in this Note we analyze the effects of air drag on sail trajectories in a systematic way, deriving a locally optimal steering law that takes a suitable aerodynamic model into account. To this end, the sail is treated as a flat plate, and a hyperthermal flow model is assumed. The corresponding trajectories are near-minimum-time solutions for low characteristic accelerations. The steering law is shown to depend on the ratio between the local dynamic pressure and the solar radiation

Thermal buckling of metal foam sandwich panels for convective thermal protection systems

Abstract: Sandwich panels with metal foam cores are studied with application to actively cooled thermal protection systems. To evaluate these panels under thermal loading, a novel experimental technique and load frame, which provide a prominent improvement in the simultaneous preservation of thermal and mechanical boundary conditions during thermomechanical structural testing, are introduced and validated. With this technique, the response of metal foam sandwich panels (MFSPs) to thermally induced in-plane equibiaxial loading is investigated, and the elastoplastic pre- and postbuckling response of MFSPs is measured and analyzed. The in-plane response of the panels is quantified with strain-gauge measurements, and the out-of-plane response across the surface of the panel is captured via shadow moire interferometry. These measurements provide direct visualization and quantification of the initial buckled mode shapes, as well as the evolution of the elastoplastic postbuckled mode shapes from initial buckling into the postbuckling regime. This experimental investigation is the first of its kind, complementing the largely theoretical and numerical body of information on the thermomechanical response of sandwich panels.

Modeling of Mechanical Ablation in Thermal Protection Systems

Abstract: An integrated thermomechanical modeling of response of low-temperature ablative thermal protection system under thermal loading encountered by reentry vehicles is presented. Of the three thermal protection mechanisms, thermal, chemical, and mechanical ablations, only the latter is assumed to influence the recession in the presence of aerodynamic surface shear for materials with low shear strength at higher temperatures. A model for the mechanical ablation (erosion) is presented that is based on the matching point scheme. The degenerated doubly curved shell element is employed in the modeling. This enables consideration of the general type of aerodynamic loads, distributed and varying with surface and time coordinates, which differs from the earlier studies reported in the open literature. The finite element method uses polynomial approximation to represent the nonlinear through-thickness temperature profile and explicit-through-thickness integration in the computation of element matrices. This brings in computational efficiency without loss of numerical accuracy, particularly in the context of multilayered construction. No attempt is made to compute the incident heat flux and other aerodynamic loads. Numerical examples are presented for specified loads to bring out the influences of material properties and heating rates on surface recession and are based mostly on assumed material properties.

Degradation of High-Voltage Solar Array Due to Arcing in Plasma Environment

Abstract: A degradation test for a solar array coupon against electrostatic discharge was performed under a simulated lowEarth-orbit environment as part of research project to develop the next-generation 400-V high-voltage solar array technology. All tests were performed in a vacuum chamber with a plasma source. An inductance‐capacitance‐ resistance circuit was used to simulate the arc current that would flow by collecting electric charge stored on cover glasses. Arcs were repeated until the solar array coupon showed degradation of electrical output. The locations, current waveform, and voltage waveforms of all the arcs during the tests were recorded. The electrical output of the coupon was measured without opening the vacuum chamber. The arc that damaged a solar cell was identified; the cell was damaged by only one arc, which occurred at the edge of the cell.

Air-Launching Earth to Orbit: Effects of Launch Conditions and Vehicle Aerodynamics

Abstract: Introduction T HE purpose of this study is to determine the benefits of airlaunching expendable or reusable launch vehicles (LV) by using quantitative methods. Air-launch vehicles consist of at least two stages, a carrier aircraft and a rocket-powered LV. The carrier aircraft can be either subsonic or supersonic capable and can even include balloons. Air launch is one of the leading concepts that can meet today’s launch requirements of both responsive and low cost. Previous work in this area has identified nonquantitative benefits and drawbacks of air-launch methods.1 In this Note, many different air-launch scenarios associated with different release, launch conditions, and vehicle aerodynamics are modeled and simulated using trajectory optimizations. The trajectory optimization is conducted using POST, a numerical integration program based on the three-degree-of-freedom equations of motion of a flight vehicle.2 More than 160 simulations were conducted in which launch altitude, speed, and flight-path angle were varied, and the effect of adding a wing was also modeled.

High-temperature thermodynamic properties of Mars-atmosphere components

Abstract: Methods of calculation of high-temperature thermodynamic properties for some selected Mars-atmosphere components in the temperature range from 200 to 50,000 K and results are discussed and compared with previous works. Aspects such as quasi-bound rotational states, cutoff criteria, and autoionizing states are considered.

Hypersonic Experimental Facility for Magnetoaerodynamic Interactions

Abstract: A hypersonic, weakly ionized gas experimental facility has been exclusively designed for basic research in magnetoaerodynamic& The weakly ionized air is generated by a combination of direct-current discharge, radio frequency radiation, or a combination of both in a blowdown, open-jet, Mach 5 channel. A collection of plasma diagnostic tools including optical spectroscopy, microwave devices, and Langmuir probes have also been successfully developed. The plasma field is determined to have an electron temperature around 10,000 K and the electron number density up to 2 × 10 1 2 /cm 3 . The magnetic field can be provided by a steady-state solenoid that can generate a maximum magnetic flux density up to 3 T or arrays of permanent magnets. Under this laboratory testing environment, the maximum Stuart number per unit length is around 1.5 per meter. As an example of the utility of the facility, a successful hypersonic magnetoaerodynamics experiment demonstrating the potential of a plasma actuator is described. In this experiment, the effect of an electromagnetic perturbation by a glow discharge near the leading edge is further amplified by viscous-inviscid interaction, creating a significant pressure rise over the plate surface. The induced surface pressure exhibits potential as a virtual flap for flow control.

Optimal Design of Two-Stage-To-Orbit Space Planes with Airbreathing Engines

Abstract: Many candidate concepts of reusable space transportation vehicles have been proposed around the world. Our aim in this study is to apply an optimization method for conceptual designs of two-stage-to-orbit (TSTO) space planes with airbreathing engines on the first-stage boosters and to obtain necessary vehicle sizes and their optimal flight trajectories. First, we integrate analysis methods into the optimization problem, the solution of which yield the minimized total dry mass of the first-stage booster and the second-stage orbiter. This information allows us to determine the optimal vehicle configuration and flight trajectory for a highly feasible TSTO space plane. The optimal solutions show that TSTO space planes with boosters powered by rocket engines added to the airbreathing engines are lighter in total dry mass than vehicles with boosters propelled by only airbreathing engines. However, it is necessary to lighten and miniaturize vehicle components to achieve greater feasibility. In addition, the trajectory optimizations enable the booster to glide back to a launch site using little propellant, despite the long downrange path from the staging point of the ascent trajectory. This study confirms that the analysis and optimization method proposed are effective.

Dynamic Wrinkle Reduction Strategies for Cable Suspended Membrane Structures

Abstract: The present study addresses vibration mitigation of membrane structures the boundaries of which are surrounded by weblike perimeter cables. This proposed membrane design realizes significant structural mass reduction when compared to the conventional catenary design. A key dynamic characteristic of the proposed structure is that support perturbations propagated into the outer perimeter cables have a minor effect on the vibration frequencies of the membrane. This property has been exploited in the development of vibration mitigation strategies using active control. This is corroborated by carrying out nonlinear transient analysis, which accounts for the effect of wrinkles in the membrane. The results confirm that disturbances emanating from the support structures can be isolated by the outer perimeter cables while maintaining the interior membrane in a wrinkle-free taut condition. A simple active control law has been developed and applied to only the outer perimeter cables. Numerical simulations show that the combination of the web-cable girded membranes and the proposed vibration mitigation strategy can provide sufficient damping for both in-plane and out-of-plane vibrations.

Streamwise Vortex Instability and Transition on the Hyper-2000 Scramjet Forebody

Abstract: Despite the closely coupled multidisciplinary design of hypersonic airbreathing vehicles, the boundary layer transition mechanisms that are important on the forebody ahead of the scramjet inlet are not well understood. The present paper investigates transition induced by the growth of streamwise vortices on a scramjet forebody geometry similar to the Hyper- X. Characteristics of the separation zone near the first compression corner are visualized with oil-flow experiments. These experiments also reveal the presence of regularly spaced streamwise vortices on the compression ramp even in the absence of controlled disturbance generators. The growth and decay of these vortices are inferred from the heat-transfer rates measured using temperature-sensitive-paints. The streamwise vortices are enhanced in a controlled and repeatable manner by wrapping tapes around the leading edge. The vortices grow significantly on the second compression ramp and then decay, suggesting transition onset. The disturbance growth seems to show a systematic trend with unit Reynolds number, although this trend was not consistently seen for all cases. For some of the cases, the disturbances showed the largest growth when the roughness spacing was close to the vortex spacing seen in the oil-flow images.

Construction of a Unified Continuum/Kinetic Solver for Aerodynamic Problems

Abstract: We describe our progress toward the development of a unified flow solver (UFS) that can automatically separate nonequilibrium and near-equilibrium domains and switch between continuum and kinetic solvers to combine the efficiency of continuum models with the accuracy of kinetic models. Direct numerical solution of the Boltzmann transport equation is used in kinetic regions, whereas kinetic schemes of gas dynamics are used elsewhere. The efficiency and numerical stability of the UFS is attained by using similar computational techniques for the kinetic and continuum solvers and by employing intelligent domain decomposition algorithms. Different criteria for identifying kinetic and continuum areas and two different mechanisms of coupling Boltzmann and Euler solvers are explored. Solutions of test problems with small Knudsen number are presented to illustrate the capabilities of the UFS for different conditions. It is shown that the UFS can automatically introduce and remove kinetic patches to maximize the accuracy and efficiency of simulations. To our knowledge, this is the first attempt to use direct Boltzmann and continuum flow solvers for developing a hybrid code with solution adaptive domain decomposition.

Airframe-propulsion integration methodology for waverider-derived hypersonic cruise aircraft design concepts

Abstract: This paper describes the methodology employed for a practical preliminary level integration of a conicallyderived hypersonic waverider airframe with its propulsion system. A Mach 9 baseline vehicle is generated using an inverse design approach and the streamline tracing method. Turboramjets are used to accelerate the vehicle from takeo to a transition speed of Mach 5 where Scramjets takeover and accelerate the vehicle to hypersonic cruise speed of Mach 9 at an altitude of 30km as described herein. The integration of the propulsion units and their inlets, with the airframe, are explored and demonstrated by approximately matching the thrust from the low-speed units to that from the high-speed ones. The propulsion / airframe integration forms part of the work towards developing a full practical design methodology for hypersonic cruise aircraft concepts.

Toolkit for updating interplanetary proton-cumulated fluence models

Abstract: The evaluation of mission-integrated solar proton fluences in interplanetary space currently depends on statistical modeling based on energetic proton measurements recorded over a few solar cycles. Most models rely on a description of events fluence and occurrence based on a compound Poisson process for which the parameters are derived from a fit of empirical distributions of the measurements. The output is then the cumulative probability as a function of the level of fluence not to be exceeded. However, the effects of assumptions and uncertainties on the model output are in general overlooked. In this paper such effects are investigated for the well-known JPL-91 model. The use of simultaneously measured observations from different spacecraft have shown that model outputs differ mainly because of three effects: difference in calibration between the data sets, discrepancy in event selection of significant amplitudes caused by data gaps or artifacts, and separation of events into multiple events by one spacecraft but treated as one large event in the other. A complete list of solar proton event fluences from January 1974 to May 2002 is produced based on measurements from the IMP-8, GOES-7, and GOES-8 spacecraft, because calibrations between these data sets were found to be in good agreement and they cover almost three solar cycles. Artifacts caused by, for example, data errors, have been extracted after careful inspection of the list, and comparison with other available fluence data has been made to account for missed events in the data sets. The list is published to facilitate further review and future updates. An approach to generate future updates of a solar energetic particle cumulated fluence model is proposed. Related tools and data are provided.