Keywords: Aerodynamics, CFD, Fluid Dynamics
Abstract: Thermal modeling of current and future electronics requires consideration of a broad range of spatial and temporal scales spanning six orders of magnitude. This talk describes hierarchical modeling of sub-continuum heat transfer with Boltzmann transport equation, lattice Boltzmann and atomistic molecular dynamics approaches. It also outlines the challenges to model nanoscale thermal transport and to integrate solutions across multiple length scales ranging from nanometers to macro scales. For illustration purposes, relevant thermal behavior in thin films, self-heating in silicon-on-insulator transistors and transient electrostatic discharges are considered.

Keywords: Performance, Design Optimization
Abstract: This presentation focuses on some of the issues that will inspire future aircraft concepts and the technologies that may enable more efficient flight over the next 20-30 years. With fuel costs starting to dominate direct operating costs and with increasing concern over aviation's impact on the global environment, the need for more-than-incremental improvements in aircraft efficiency is clear.

Although gains in turbofan engine performance have led the historical trend in fuel efficiency, current engines achieve an overall efficiency of about 40%, and continued improvement becomes increasingly difficult. Airframe drag is the reason that energy is required for air transport, and future research must focus on drag reduction to achieve large changes in aviation energy consumption.

Several unconventional configuration concepts hold promise for future air transportation. These include designs well-suited to extensive natural laminar flow, wings that employ high authority load control, and aircraft that exploit formation flight. The importance of improved modeling and multidisciplinary optimization is even greater for these designs to avoid comparing a refined conventional concept with an immature new idea. Examples of design studies with higher fidelity modeling illustrate the challenges and possibilities of future aircraft concepts.

Keywords: Aerospace Sructures Design and Manufacturing
Abstract: Today, we are experiencing a growing need to extend the reach of VTOL aviation into highly obstructed airspace such as urban environments. In response to this emerging need, Urban Aeronautics is developing the “AirMule” a new, VTOL internal-rotor Unmanned Air Vehicle, which has in excess of 500 Kg load carrying capability, 100-120 Knot cruise speed, precise maneuvering, and is designed for safe operation in harsh weather conditions with FAA-level safety. Currently, our work on AirMule is focused on military use, specifically Cargo Supply and Casualty Evacuation (CasEvac). Urban Aeronautics as recently received interest by Civil and Para-Military operators for operating the AirMule in a variety of roles that extend beyond the missions envisioned for the military. These include nuclear disaster response, utility maintenance and repair, various off-shore drilling platform related tasks, inspection and maintenance of concrete structures and bridges and firefighting. These potential missions and technical provisions to facilitate them will be described and discussed in the presentation.

Keywords: Aerospace Sructures Design and Manufacturing
Abstract: The degree of maturation of UAS technology makes them attractive for civil operation, especially where human work is dangerous or monotonic. Usages can vary between photography with micro UAS to cargo shipment by huge UAS. Implementation of UAS technology can even improve the safety of the manned aviation. The present talk will focus on identifying the technology gaps still needed to fill and analyse the possibilities of civil certification in the framework of existing civil aviation laws and procedures. The main technological gap is the development of Sense (See, Detect) and Avoid systems, to provide the same capability as the man in the cockpit. The most appropriate certification method, for the stage of special usage, and before full integration in the civil airspace is Type Certification in the Restricted Category followed by granting Airworthiness Certificates in the Restricted Category. This enables the requirement of operational limitations and mitigation methods suitable to the specific application.

Keywords: Aerodynamics, CFD, Fluid Dynamics
Abstract: Wall bounded and free turbulent shear flows have been observed to contain organized coherent structures such as hairpin vortices, counter-rotating vortex pairs (CVP’s) and streaks (regions of high and low velocity). In order to be able to follow the temporal evolution of such coherent structures we have developed an analytical based method which is capable of following the evolution of a localized disturbance in flows with constant homogenous shear, in which the base velocity varies at most linearly with space. In this paper we briefly present the method and some preliminary results characterizing the development of localized Gaussian vortices, having various initial amplitudes and orientations, embedded in different types of base flows.

Keywords: Aerodynamics, CFD, Fluid Dynamics, Numerical Methods, Modeling Simulation
Abstract: It is a well known fact that hypersonic wind tunnels can not reproduce turbulent boundary layer on smooth model surface. This is a generic problem which has a negative impact on prediction of stability characteristic on any high velocity project development. To overcome the problem it is necessary to artificially induce the boundary layer to a turbulent state by means of surface roughness on the nose of the model at special positions. Such capability had been developed starting in the 1960s in the USA during the cold war. Moreover, since the 1980s up to very recently, huge experimental database has been built for civilian projects like the space shuttle. These activities has generated hundreds of costly wind tunnel experiments and resulted with various empirical transition criteria. Computational Fluid Dynamics (CFD) must play a major role in the development of hypersonic vehicles because ground test facilities, including the IAI Hypersonic Wind tunnel (HYWT), are not able to fully simulate flight conditions. The Navier-Stokes parallel multigrid code NES (Navier-Stokes Euler System), has evolved to a standard design and research tool at IAI to address flow regimes ranging from subsonic to hypersonic velocities. To enable CFD to be a practical technology in order to develop numerically a trip database, one has developed innovative technologies which consist of fast tools that generate automatically a grid around a model having hundreds of trips, and efficient interface program to extract boundary layer edge properties. In addition, High Performance Computing (HPC) cluster with InfiniBand switch combined with Intel Nehalem i7 fast processors and efficient Intel compiler has been allocated to allow short massive parallel computation turnaround. A parametric study on a five degree half angle cone with different bluntness ratios has been conducted. This investigation has been carried out at the operation conditions existing at the IAI HYWT. Based on existing transition criteria, charts of the effective perturbation height were produced taking into account the Reynolds and Mach numbers, as well as the bluntness ratio variations. Preliminary computational work had been carried out on the tripping effectiveness as to alter the drag and the pitching moment coefficients of various configurations; then followed by the examination of existing transition criteria on the mentioned cone. Finally, methods for production of trip implants were surveyed within the scope to conduct experiments in the IAI HYWT.

Keywords: Aerodynamics, CFD, Fluid Dynamics
Abstract: Flow fields characterized by chord-based Reynolds numbers of 5000 to 15000 over a stationary model of a hummingbird wing (Calypte anna) are analyzed below. Utilizing two experimental techniques, constant-temperature anemometry and particle image velocimetry, the high fidelity results depict a laminar-to-turbulent transition process that develops over the wing. At zero angle of attack the velocity undulations are mostly governed by convective instability mechanisms. At higher angle of attack, this mechanism does not fully explain the wide undulation spectrum that was measured experimentally. The results confirm that transitional flow mechanisms evolve from a Reynolds number which is as low as 5000. At a more characteristic Reynolds number of 15000, the flow spectrum matches that of fully turbulent flow, which encourages bubble reattachment. In view of these conclusions, this study could serve as the first step toward better understanding of the flow mechanisms over steady revolving and periodically flapping wings at these Reynolds numbers.

Keywords: Aerodynamics, CFD, Fluid Dynamics
Abstract: Propulsion systems, which use hot gases produced by combustion of fuel and oxidizer to generate thrust by expanding these gases through a nozzle, create a typical hot plume, which radiates over a wide spectrum. The most distinct radiation band is located in the IR range and can be readily measured by various methods. Prediction of the radiometric radiation signature of the hot plume is a complex problem. This procedure involves prediction of the chemical process of the combustion and the composition of the products generated. The temperature and composition of the plume depends on the operating conditions of the engine, the interaction of the hot plume with the surrounding atmosphere and the relative velocity of to the surrounding atmosphere. Each molecule, which compose the motor plume, radiate in the IR band when heated at different wave lengths. The strength of the radiated energy depends on the exact composition and temperature of each molecule in the plume. In this work we compare measurements from a Boeing 777 engine at flight to predictions of the IR signature. The prediction of the IR signature is based on a detailed simulation of the flow field and IR radiation calculation, which uses the flow field as input. The aim of the investigation was the measurement of the radiometric radiation signature of the jet plume and the comparison to CFD flow field and radiation calculations which were performed by IMI.

Keywords: Aerodynamics, CFD, Fluid Dynamics, Numerical Methods, Modeling Simulation, Propulsion
Abstract: Plumes from hydrocarbon-fueled rockets usually contain some amount of soot. Soot radiates a continuous, near-blackbody spectrum, and, as such, even a minor amount of soot plays a critical role in the characteristics of the infrared radiation emission.. The contribution of soot to the plume radiation depends on several factors including; the amount of soot, particle physical characteristics, concentration, and temperature distribution in the flow field. The temperature and trajectories of solid particles can differ from those of the plume due to the particle’s mechanical and thermal inertia. Exhaust plume simulations were performed using the CFD FLUENT code for solving two-phase Navier-Stokes equations, coupled with chemical reactions and soot particle combustion. Exhaust plumes with soot mass loading of 2% were simulated for three altitudes of 2km, 8km and 16km. Radial distributions of the cloud particle density were obtained for different distances along the flow. The particle concentration increased at the plume periphery, as a result of the particle deceleration at the boundary layer inside the nozzle. The particle temperature is higher than the gaseous temperature of the plume. The temperature difference between the soot particle and the plume along corresponding trajectories is about 5% – 10%. The infrared radiation from the plumes with carbon soot was calculated. Its intensity was found to be dependent on particle distribution in the plume.

Keywords: Aerodynamics, CFD, Fluid Dynamics
Abstract: The objective of this investigation is an analysis of the influence of air (gas) bubbles addition into a flow of water (liquid) and its influence on key parameters of the flow. In particular, an analogy is sought between the influence of air addition to a water flow and that of heat addition to an air (gas) only flow (so-called Rayleigh Line). It is assumed that in both cases the major effect on the flow results from the change of density. The motivation for this study stems from a comprehensive investigation on basic phenomena related to air-augmented waterjet propulsion. The air augmented waterjet concept is similar to the aeronautical jet engine. However, unlike a jet engine where the source of additional energy is a combustion process, the marine propulsor receives its additional energy from air bubbles converting their expansion work ∫pdV into kinetic energy of the exhaust jet, hence increasing the jet thrust. Elaboration on the air augmented water jet propulsion and the related thermodynamic cycle is summarized by Gany and by Gany and Gofer for different operating modes (ramjet and boost phase modes). In practice, the effectiveness and efficiency of the two-phase jet work cycle are influenced by the air injection scheme and stagnation pressure losses resulting from the air addition to the flow.

Keywords: Structural Dynamics, Aeroelasticity
Abstract: Dowell's simplification, which represents the pressure field in terms of a series of mode functions of a rigid cavity, and a constrained Ritz series method based in satisfaction of Hamilton's principle, are alternative methods for deriving relatively low order models of the response of a cavity surrounded by an elastic structure. The primary steps entailed in each method are summarized herein. The modal analysis of such models offer interesting features not typically encountered in structural dynamics. For Dowell's simplification, asymmetry of the equations requires evaluation of adjoint eigenfunctions, and the Ritz series formulation requires consideration of the effect of rank deficiency of the inertia matrix associated with the inclusion of algebraic equations of constraint. These issues are addressed, and the analysis procedures are employed to evaluate the modal properties of a prototypical one-dimensional waveguide. A comparison of the results to those obtained from an analysis of the field equations leads to some observations regarding the accuracy of both formulations.

Keywords: Structural Dynamics, Aeroelasticity
Abstract: The effectiveness of two sliding microflap configurations, with a height of 1:5% of blade chord, were examined for simultaneous vibration and noise reduction under heavy BVI conditions in descending flight at mu = 0:15. The first was a dual microflap configuration, and the second one was a five microflap configuration. The performance of the micro flaps were also compared to a dual plain flap configuration. A new saturation control algorithm was developed for limiting the micro flap or flap deflections such that best utilization of on blade controllers implemented through multiple control surfaces is achieved. The conclusions demonstrate the effectiveness and control authority of the microflap for simultaneous BVI noise and vibration control in rotorcraft and establish the microflap as a viable active device for on-blade rotor control.

Keywords: Structural Dynamics, Aeroelasticity
Abstract: Increased-Order Modeling (IOM) is a practical and efficient approach to the modeling of dynamic systems that are mostly linear, but their behavior may be significantly affected by separable nonlinearities. The approach is based on the augmentation of a main linear block with nonlinear feedback loops that represent the important system nonlinearities. A new IOM-based framework for nonlinear aeroservoelastic simulations is discussed. The framework was designed to serve two purposes, efficient dynamic-loads calculations for industrial applications, and investigation of the effects of structural, aerodynamic and control-system nonlinearities on aircraft stability and response characteristics. The solution sequence starts with the calculation of frequency response functions of the linear system with the nonlinear elements disconnected. Time-domain responses of the linear block to specific gust, maneuver or direct-force excitations, and to control input impulses, are then calculated using Fast-Fourier-Transform (FFT/IFFT) techniques. The response is then corrected by incremental nonlinear effects in a process that combines time domain solutions of the nonlinear elements and convolution integrals for the linear parts with impulse response functions. Three nonlinear aeroelastic studies are posed and solved in a unified and systematic manner within the IOM framework. The cases are industrial dynamic design loads with nonlinear control, limit-cycle oscillations (LCO) of plate-type fins with nonlinear plate elements, and dynamic gust loads with nonlinear aerodynamics.

Keywords: Parameter Estimation, Fault Detection and Isolation, Guidance Navigation
Abstract: A new approach is proposed to solve the alignment problem of two rigidly attached axis frames by measuring and processing the relative orientation change of each one of the frames due to a common angular motion, given by rotation quaternions. This problem can usually be formulated in terms of angular rate vector observation, and solved as a general Wahba problem. Nevertheless, in certain cases it is advantageous to use directly angular position information, e.g., to avoid a numerical differentiation procedure, to process smoother measurements, or to circumvent too severe restrictions on the required angular motion. The derived result is shown to have exactly the form of the famous Davenport's q-method devised for solving the Wahba problem, with the orientation change quaternion vector parts playing the role of vector observations.

Keywords: Parameter Estimation, Fault Detection and Isolation, Space Systems, Astrodynamics, Guidance Navigation
Abstract: A recently introduced algorithm for hybrid estimation in jump Markov systems was developed via the approach of conditionally-linear (CL) filtering. The hybrid filter KCL combines a single Kalman filter for state estimation with a single CL filter for mode estimation. The KCL filter was designed with the state and mode filters interacting in an interlaced manner. The present work is concerned with the development of novel hybrid estimators for jump Markov systems. A first algorithm is developed via a reformulation of the hybrid system model as a bilinear system with respect to the state and the mode, to which standard linear filtering techniques were applied. The method is straightforward and shows satisfactory results on a simple numerical example. Good performances however require control dependent terms that enhance observabiltity. Furthermore, two novel algorithms are presented as an extension of the KCL filter. The contribution of this work consists in augmenting the estimators' design models, thereby contributing to more accurate statistical computations. The state filter block is designed with the state vector augmented by a mode estimation error. In the other block, the mode filter is designed with the mode vector augmented by a partial state estimation error. Extensive simulations are performed to illustrate the advantages and drawbacks of the method and to compare it with existing hybrid filters. The extended KCL filtering approach is applied to a problem of attitude estimation using line-of-sight observations and gyro measurements, which faulty modes are modeled via randomly appearing biases. Monte-Carlo simulations show that the proposed approach succeeds in estimating the attitude while tracking the modes conditional probabilities.

Keywords: Parameter Estimation, Fault Detection and Isolation, Numerical Methods, Modeling Simulation, Aerospace Systems and Systems Engineering
Abstract: This paper presents the preliminary results of a time-domain parameter identification effort with flight data collected at West Virginia University (WVU) using a Small Unmanned Aerial Vehicle (UAV) – the WVU “Phastball”. Traditional doublet maneuvers on the longitudinal and lateral channels were performed by a Remote Control (R/C) pilot. From the flight data, a linear state space model was first derived using the Matlab® System Identification toolbox and then optimized using System IDentification Programs for AirCraft (SIDPAC) software package. The optimized linear state space model was then used to generate the aerodynamic coefficients, which were in turn optimized using a non-linear optimization technique and their accuracy validated within a Simulink simulator. The aircraft model thus identified will be used in the design, implementation and flight test validation of fault tolerant flight control schemes on the WVU Phastball.

Keywords: Numerical Methods, Modeling Simulation
Abstract: Thin layers with material properties which differ significantly from those of their adjacent media appear in a variety of applications, as in the form of fiber coatings in composite materials or protecting surface layers in the case of external coating. Fully modeling these layers by standard Finite Element (FE) analysis is often associated with difficult meshing and high computational cost. As an alternative, asymptotic procedures are considered. They model these thin domains as interfaces of no thickness on which appropriate boundary conditions are devised. A previous IACAS paper was devoted to introducing the first-order asymptotic interface noel proposed by Bovik in 1994 and later generalized by Benveniste in 2006 and showing how it can be incorporated in a FE formulation, to yield an accurate and efficient computational scheme for problems involving circular thin layers. This paper is an extension of that first idea, to general shape layers, and layers in the form of external coating. We here consider linear scalar elliptic problems in two dimensions, prototyped by steady-state heat conduction.

Keywords: Materials, Solid Mechanics
Abstract: The onset of plastic yielding in a system of a sphere with a hard coating layer loaded by a rigid flat is studied using finite element analysis. The effect of coating thickness and material properties of both coating and substrate on the critical normal load, critical contact area and critical interference at the onset of plasticity is investigated. Three different locations where plastic yielding first occurs are found. A dimensionless coating parameter is defined, which allows optimization in terms of highest critical load. A possible weakening effect caused by using an ultra thin coating layer is revealed.

Keywords: Structural Dynamics, Aeroelasticity, Materials, Solid Mechanics
Abstract: There are many cases of structural designs where structural elements are in contact with one another, with no elastic connection between these elements. In such cases the structural elements can be separated during loading, and then collide, especially when the external excitation is dynamic. In many cases, collisions can be avoided if a certain preload is presented between such elements. While collisions exist, dynamic stresses can be generated in the elastic systems. On the other hand, the prevention of collisions by a preload may cause a high static stress which is presented in the structure during its whole service history. The understanding of the phenomenon is vital to the structural designer, and the best way to understand the combined structural behavior is to use simplified models so that the designer is able to check the influence of structural parameters on the structural behavior. In most cases, structural designers use a finite element code to solve the structural behavior of their designs. Codes like NASTRAN, ANSYS and other include "contact elements" which allow inclusion of contact and collisions time histories of displacements, accelerations and stresses. Nevertheless these codes include some limitations that the designer should be aware of, when colliding structural elements are included in his analysis. In this presentation, a simple contact-collision system is solved analytically, and some interesting results of the phenomenon are demonstrated. Then a simplified two degrees of freedom equivalent system is solved using the ANSYS finite element program. A third solution (with two sub-cases) of a 2-D finite element model with many degrees of freedom is also presented pointing to some interesting phenomenon based on the propagation of stress waves in re

Keywords: Combustion, Materials, Solid Mechanics
Abstract: This work presents an energetic material based on nano-porous silicon fuel impregnated with an oxidizer. The nano-porous silicon layers were prepared by anodization of silicon in a hydrofluoric acid solution and characterized to study the influence of the electric current density on the nano-porous structure properties. The oxidizer impregnation process was studied thoroughly in order to achieve optimized pore filling by the oxidizer. Feasibility proof for an energetic reaction of nano-porous silicon impregnated with an oxidizer was demonstrated by thermal analysis using differential scanning calorimetry.

Keywords: Combustion, Propulsion
Abstract: A non-asymptotic based mathematical analysis of premixed spray propagation is presented. The analysis makes use of a distributed approximation of the Arrhenius exponential term in the reaction rate expression. A double spray is considered for the first in which both liquid oxygen and liquid fuel feature as sprays of droplets in the unburned pre-mixture. Such a situation arises in rocket engines in which two initially separate spray streams mix in a turbulent shear flow so that locally one dimensionally propagating double spray premixed flames are created. The analysis leads to an analytical expression for the laminar burning velocity dependent on the spray-related parameters for the fuel and oxidant, and gas-related parameters. Typical thermal and velocity maps in parametric space are presented.

Keywords: Combustion, Performance, Design Optimization
Abstract: In this paper a number of tests performed using composite solid propellants containing ammonium perchlorate (APC) are presented. The main goal of these experiments is to correlate rheological factors present during casting to the solid propellant burn rate distribution across the web. Tests performed at our facilities and also at other facilities around the world reveal that the casting method can have an effect on the shape of the pressure history curve as well as the global burn rate. We have also noticed that the burn rate measured in different orientations (relative to a central bore) can vary. In this paper we present these observations and provide a hypothesis, backed by experimental results, that a major factor in these phenomena is the shape of the APC crystals and their ability to orient themselves along flow lines during propellant casting.

Keywords: Aerodynamics, CFD, Fluid Dynamics
Abstract: Flapping flight is a subject of interest for more than two decades. During this time it has been found that a stable leading edge vortex is responsible for the high lift coefficient that flapping and revolving wings can produce. However, many of these studies were limited to Reynolds numbers of few hundred, which characterize insects. Recently, the interest on designing and realizing miniature hovering vehicles requires expanding our understanding of the basic flow mechanism which govern such wing maneuvers at higher Reynolds numbers. In this study the flow field over an accelerating rotating wing model is analyzed in various Reynolds numbers using particle image velocimetry. The study depicts the characteristic size and time scales of the leading edge vortex up to Reynolds number 2000. It is shown that LEV circulation capacity increases with Reynolds number; nevertheless, in order to obtain higher LEV circulation (which is related directly to the wing’s lift) the wing acceleration profile should be prescribed accordingly.

Keywords: Aerodynamics, CFD, Fluid Dynamics, Propulsion
Abstract: Aeronautical technology has evolved substantially from the first human-made airplane, back in 1903. Yet, flying animals (e.g., birds), which represent one of nature's finest locomotion methods, still feature superiority on any current technology, in respect to flight efficiency. Today, engineers mimic nature in order to take advantage of such unconventional propulsion and lift generation methods, used by flying animals, to enhance performances or supplant traditional methods (fixed wings aircraft). One of the remaining puzzles is the role of unsteady motion in the flow due to the wing flapping and its contribution to the forces acting on the animal during the flapping flight. The wake of a freely flying European Starling was investigated as a case study of unsteady wing aerodynamics. Measurements of the near-wake downstream of the bird have been taken in a hypobaric wind tunnel specially designed for avian research. The experiments were performed using long duration high-speed PIV system, which enables a continuous acquisition of images for 20 minutes using two cameras. High-speed videos recorded the wing and body motion simultaneously with the PIV. The wake region has been characterized through the calculation of velocity and vorticity fields. Mean velocity profiles provide evidence of three different flight modes. Drag and lift have been estimated by means of mean velocity deficit and circulation at the wake region. Time evolution of the velocity field depicts the unsteady motion in the flow due to the presence of the flapping wings. Consequently, the wake topography has been reconstructed emphasizing flow features as function of time. Correlations between the wing kinematics and the flow field characteristics are presented. It is shown that the unsteady aerodynamics plays a major role in the formation of drag and lift during flapping flight.

Keywords: Aerodynamics, CFD, Fluid Dynamics, Structural Dynamics, Aeroelasticity
Abstract: The optical measurements, their processing, and their evaluation discussed in this paper, are part of a comprehensive parametric experimental research of the aerodynamic behavior of a two-dimensional Sail-Wing profile. This part of the research accomplished and even surpassed the original requirements, and significantly contributed to analysis and understanding of the observed phenomena. Main results include: sail geometry for the full range of required pitch angles, cloth types and sail slacks; Verification of the existence of three regions with distinct behavior modes; Identification of distinct regional separation for each type of sail; Frequency of the standing wave at the high-angle region for each type of sail. The regions are: (a) Un-taut sail with random changes at small pitch angles; (b) Taut sail without discernable vibrations at mid-range angles; (c) Taut sail with observable vibrations around an average profile at high pitch angles.

Keywords: Aeroacoustics
Abstract: We study the motion and sound of a thin elastic plate actuated at its leading edge by small-amplitude periodic pitching and heaving, and subject to uniform low-Mach flow. When the frequency of actuation coincides with an eigenfrequency Omega_{mathrm{res}} of the unforced plate, a resonance motion is excited and the plate oscillates at the corresponding eigenmode. The dynamical description is used to formulate the acoustic problem, where the sources of sound include the plate velocity and fluid vorticity. Acoustic radiation of a dipole type is calculated and discussed in the limit where the plate is acoustically compact. It is found that plate elasticity has opposite effects on sound radiation, depending on the forcing frequency: at frequencies close to Omega_{mathrm{res}}, the near-resonance motion results in the generation of high sound levels; however, at frequencies far from Omega_{mathrm{res}}, plate elasticity reduces the amplitude of plate deflection (compared to that of a rigid plate), leading to noise reduction. The results identify the trailing edge noise as the main source of sound, dominating the sound generated by direct plate motion. The analysis is suggested as a preliminary tool for examining the acoustic signature of flapping flight, common in insects and flapping micro-air-vehicles.

Keywords: Performance, Design Optimization
Abstract: The use of propulsive lift provides STOL performance that significantly reduces field-length capabilities and lowers approach speeds for improved safety. ESTOL aircraft could use runways at much smaller airports than the conventional aircrafts, allowing expansion of commercial flights to many more locations .Enabling commercial flights to take off and land in ever-shorter distances is an ongoing goal for aircraft designers, and several approaches are under development.

Keywords: Performance, Design Optimization, Aerospace Sructures Design and Manufacturing, Aerospace Systems and Systems Engineering
Abstract: As part of conceptual design effort for a civil air-vehicle many sizing decisions should be taken. These decisions should be taken despite existence of chicken-or-the-egg dilemmas, i.e. deciding the aircraft configuration sizing parameters without knowing its appearance and performance, and deciding its appearance and performance without knowing its sizing parameters. The paper gives a review of a multi-disciplinary framework, which uses modeFrontier® environment. This framework consists of several software modules which were integrated into a single synergic tool. In the current scope this design tool is used to decide the aircraft wing loading while taking into account various performance constraints. The importance of the multidisciplinary analysis tool is demonstrated and its ability to handle large number of cross-influences is discussed. The existence of several disciplines integrated into a single multidisciplinary tool may introduce some difficulties, mainly if engineering intuition is involved.

Keywords: Performance, Design Optimization
Abstract: In December 2003, the world celebrated a century of powered flight. Leaps in technological progress through the years have led aviation from small, fragile wooden biplanes that barely took off the ground, to modern carbon fiber, transonic jet airliners. New advanced subsystems and structural materials, design concepts, manufacturing and assembly methodologies – all allow further improvement in aircraft efficiency and reduction in costs. It's hard to foresee future trends of aviation, but careful analysis of the sum of the trends in each aspect of civil aircraft development, can allow a glimpse into the future of commercial aviation.

Keywords: Performance, Design Optimization, Propulsion, Aerospace Sructures Design and Manufacturing
Abstract: The paper presents a prop-rotor design method for an electric propulsion system. Prop-rotor design problem involves a compromise between two different flight conditions: hover and cruise. This drives the designer to use a multidisciplinary design optimization framework. In the current case the design framework is based on ESTECO modeFrontier® design environment. The process formulation refers to a multi-goal design problem with several design constraints. Two basic models are discussed in detail: the prop-rotor aerodynamic model and the electric power system model. A test case of prop-rotor design is presented for an example airvehicle, with electric propulsion system, weights 100kgf. The results are presented in a comprehensive Pareto front format which enables the designer to choose the appropriate compromise out of the entire design space. The results emphasize the importance of a well-tailored prop-rotor for a given air-vehicle and the advantage of using an optimization tools for a multidisciplinary design problem.

Keywords: Structural Dynamics, Aeroelasticity, Aerodynamics, CFD, Fluid Dynamics, Numerical Methods, Modeling Simulation
Abstract: A problem of a cable exposed to environmental influences such as gravity and aerodynamics is relevant in various fields of engineering. Though, an analytical treatment of the cable's dynamic response is a challenging task. In the current work, a mathematical representation of cable dynamics is achieved through discretization into finite segments. The proposed model allows one to examine complex configurations such as non-uniform geometry and nonconservative medium. A validation based on comparison to known solutions is performed. A preliminary stability analysis of the externally forced cable is presented. Possible stabilizing methods of oscillatory responses are suggested.

Keywords: Structural Dynamics, Aeroelasticity
Abstract: The generation of state models to simulate aeroelastic forces over time has already led to many developments. The methods most commonly used are Roger’s or “Minimum State” methods. The obtaining of models with several variables (Mach number, incidence, lift, etc.) and of parameterized models is developed. These models are applied to the calibration of aeroelastic forces to obtain: - Given flutter stagnation pressure curves as a function of the Mach number. - Given frequency response functions (FRF).

Keywords: Parameter Estimation, Fault Detection and Isolation, Guidance Navigation, Aerospace Systems and Systems Engineering
Abstract: A variety of aerospace applications such as orbital rendezvous, powered descent to the surface of a celestial object, aircraft landing, and missile intercept require some form of a desired collision. Other aerospace applications such as orbital satellite inspection, formation flying, and air traffic control require collision avoidance. A key element of each of all these applications is position/velocity state estimation. Since a collision can often times be detected with a simple inexpensive accelerometer, this paper considers the addition of an accelerometer-based collision measurement to the state estimation process and provides evidence that the information associated with a negative collision measurement, i.e. a collision has not occurred, can provide useful state information and reduce state uncertainties.

Keywords: Parameter Estimation, Fault Detection and Isolation, Control
Abstract: We consider the problem of tracking the state of a hybrid system capable of performing a bounded number of mode transitions in the presence of spurious, or cluttered measurements. The system is assumed to follow, at each time, one of a predefined dynamical models. Two types of uncertainties make the problem challenging. The first is the data uncertainty that follows from the fact that the true measurement of the state is indistinguishable from the clutter measurements that do not carry useful information. The second problem is the intrinsic model uncertainty. Both reasons prevent the computation of the optimal estimator. On the other hand, the mode transitions are not Markov thus ruling out the direct use of standard approaches for state estimation in cluttered environment. We derive an efficient estimation scheme for systems in cluttered environments capable of performing a bounded number of mode transitions. At the heart of this scheme is a transformation of the non-Markov model set to an equivalent Markovian one and a subsequent utilization of standard approaches matched to the new mode set. The algorithm's performance is evaluated via a simulation study, and shown to outperform the standard popular approaches in a typical example.

Keywords: Parameter Estimation, Fault Detection and Isolation, Control
Abstract: The modeling and optimization of the operation of autonomous weapon systems and ISR systems which employ an ATR module for target classification calls for a theory of state estimation for discrete systems. In this paper a theory of state estimation for discrete system is developed. Sensor fusion is addressed and a recursive, Kalman filter - like state estimation algorithm, for the case where the measurements, taken by an imperfect sensor, are discrete, is presented.

Keywords: Guidance Navigation, Space Systems, Astrodynamics, Control
Abstract: This work deals with the solution to the coupled optimization problem of multiple-satellite orbital transfer. The studied problem involves a coupled formulation of the terminal conditions of the satellites. The solution was achieved using functional optimization techniques by a combined algorithm. The combined algorithm is based on the First Order Gradient and Neighboring Extremals algorithms. In the scope of this work, a generic multiple-satellite orbital transfer optimization tool was developed. This work includes examples for satellites with electrical propulsion systems and comparison to previously published results.

Keywords: Control, Space Systems, Astrodynamics, Guidance Navigation
Abstract: This work presents an extension of the state dependent Riccati equation method (SDRE), a powerful technique for optimal estimation and control of nonlinear systems. Following the standard SDRE approach, nonlinear model equations are recast as pseudolinear equations with a state-dependent coefficient matrix. Exploiting the non-uniqueness of this parametrization, this work formulates a nonlinear optimization problem with respect to the weights of linear combination of primary state-dependent coefficient matrices. The measure of performance is the classical infinite-horizon integral cost quadratic with respect to the state and the control. The controller assumes an SDRE-like structure, but where the gains becomes nonlinear functions of the decision variables. The proposed solution implements two types of gradient-based iterative methods (steepest descent and Newton steps) where the gradient of the integral cost is numerically evaluated. In order to allow for on-line implementation, a simpler suboptimal algorithm is devised where the controller switches among a finite set of possible SDRE controllers, which are implemented in parallel. The application of the optimized SDRE method to attitude stabilization for rigid body dynamics with full information and actuation is developed and illustrated via numerical simulations. Further, the application to attitude and attitude rates estimation is described and implemented on a numerical example. Extensive Monte-Carlo simulations show satisfying performances of both the stabilization and the estimation applications.

Keywords: Guidance Navigation, Control
Abstract: A class of linear multi-input multi-output optimal guidance in the sense of L2 and H-∞ is presented and solved in a closed form. The cost includes quadratic terminal part on the state and a quadratic integral on the control. In particular, the matrix Riccati differential equation is solved in a closed form. This enables one to recover and extend previous results. Moreover, any future application can be solved directly as a special case, as demonstrated in the paper.

Keywords: Propulsion, Combustion
Abstract: Composite propellants typically contain up to 20% aluminum powder for the enhancement of energetic performance. During combustion aluminized solid propellants tend to experience the undesirable phenomena of agglomeration – merging of small aluminum particles to large agglomerates, which may not fully burn inside the motor. The current research examines new innovative methods to decrease agglomeration phenomena, mainly by decreasing the aluminum ignition time. One of these methods is coating the aluminum particles in a thin nickel layer. Using an in-house nickel coating process, studies had shown a dramatic decrease in ignition time and temperature for nickel-coated aluminum particles, compared to regular, as-received aluminum. Another method used in order to decrease agglomeration was the inclusion of porous aluminum particles. In a previous work, a substantial decrease in ignition temperature was reported for porous aluminum with respect to regular aluminum powder, as well as shortening in particle ignition time. Combustion of aluminized solid propellant was conducted in various pressures (up to 50atm), and photographed with a high speed video camera. A laser particle analyzer was also used to measure the size of the ejected combustion products. Close observations of the burning strands revealed that the use of nickel-coated or porous aluminum leads to a decreased diameter of ejected aluminum agglomerates. It could be seen that large agglomerates were ejected from the propellant containing regular aluminum, and smaller particles, at higher flux, were ejected from the propellant containing porous or nickel-coated aluminum. A definite reduction in median agglomerate diameter was demonstrated throughout the pressure range for both nickel-coated and porous aluminum. Experiments have shown that on average, the diameter of agglomerates resulting from nickel-coated aluminum is roughly 70% of the diameter of agglomerates resulting from regular aluminum. For porous aluminum, the reduction of average agglomerate diameter is even greater, reaching approximately 40%. The work presents a theoretical model predicting the nature and extent of the agglomeration phenomena, including calculated average agglomerate diameter. Essentially, the model compares the ignition time of aluminum particles with the time taking them to fully accumulate in the mobile layer situated between the bulk solid propellant and the flame above it. Calculations show that ignition time shortens when nickel-coated or porous aluminum is used. It can be seen that the agglomeration number (defined as the ratio between ignition time and accumulation time) is significantly decreased with reduced ignition temperature, leading to a decreased level of agglomeration. A calculation for the agglomerate diameter is introduced, taking into account the characteristic distance of the mobile layer. Predictions of the model were conducted for propellants with different compositions and in various pressu

Keywords: Propulsion, Combustion
Abstract: The German Aerospace Center, DLR operates on its test site for rocket engines in Lampoldshausen a large number of test facilities of various size. Subject of the engine tests is research, development and qualification of propulsion systems for the European space activities. These test activities shall be extended by a test program for education purpose. Undergraduate students of rocket science will have the opportunity to set up their own test rig and test a specimen of their own design. The infrastructure of the DLR test site will enable testing at a power level which is normally not possible in the environment of university research. Beside the students research target a main purpose of student-test-campaigns is to introduce the students to the procedures and principles which are applied on professional rocket test facilities. As a forerunner the first undergraduate student developed and conducted a one-week-test-campaign with a small hybrid thruster in November 2011. The results and experience of this first student work is presented here.

Keywords: Combustion, Propulsion
Abstract: Although the main concern when dealing with fuel-sprays in combustion chambers is spray evaporation, since the fuel drops vaporize and combustion takes place between the fuel vapors and the gaseous oxidizer, close to the injector, droplet coalescence is an additional factor which may also play an important role in this process. For example, Tambour has shown in a theoretical study, which favorably compares with experimental data, that at the center of a spray jet produced by a twin-fluid atomizer, droplet coalescence is a dominant effect whereas close to the edges of the spray jet, evaporation is dominant. In addition, in liquid rocket engines, in configurations where liquid oxidizer jets impinge on liquid fuel jets, or in opposed spray jets, coalescence again plays an important role. It is clear that droplet coalescence in a spray is a discrete phenomenon. Thus, the most fundamental differential equations that describe the evolution in discrete drop size distributions are discrete coupled equations known as the Smulochowski Equations. Although Smulochowski's equations are discrete, the solutions for these equations are continuous, and hence, yield results with anomalies which stem from mixing discrete equations with continuous solutions. The purpose of the present study is to suggest new techniques to correct the solutions in order to overcome these anomalies. We begin with Smulochowski's solution which is limited to an initial mono-size drop distribution and then after a short time interval we switch into the Tambour-Seinfeld solution which is capable of handling any arbitrary initial multi-size droplet distribution. We continue employing the Tambour-Seinfeld solution by "stopping" our computational procedure at short time intervals and restarting a "new" problem at each time interval which has a new initial multi-size droplet distribution. However, each time that we start a "new" problem, we "get rid" of the droplet fractions which are in fact non-physical but we manage to conserve the total mass in the system by compensating for these fractions. In Chapter 1, we present analytical spray coalescence basics and the Tambour-Seinfeld analytical solutions. Then in Chapter 2, we present the calculations which lead to fractions of droplets in the drop size evolution and to the "missing mass" effects in the system as a whole. A brief description of the new techniques is presented, with corrections so the solutions so that droplets will remain integers and no mass will be missing in the system in the solutions for the time evolution of drop sizes.

Keywords: Propulsion, Combustion
Abstract: Radial profiles of temperature and soot volume fraction of a laminar diffusion flame of Jet A-1 fuel and air were measured. The experimental setup consisted of two main parts – the burner and the measurement system. Co-annular burner, with the fuel flowing from the central tube and the air from the external one was used. In order to facilitate the vaporization, the fuel was diluted with nitrogen. The fuel delivery tube was kept at temperatures above the vaporization point. The co-flow air was also heated in order to prevent condensation of the fuel. The air annulus was inserted with metal foam in order to create a uniform velocity profile at the exit. A honeycomb was placed 20-30 cm above the flame to make sure the flame remained laminar.

The measurements were done by a non-intrusive, optical system. The radiation that is emitted by the flame was passed to a spectrometer using an optical setup. A charged couple device (CCD) camera was used to record the emission intensity of the spectrum. By measuring the local spectral emission property field, it was possible to obtain the temperature of the flame. Rayleigh expressions for emission and scattering were used. Measuring the emission intensity at multiple wavelengths allowed to estimate the temperature without the need to estimate the absorption coefficient of the particles. Knowledge of the temperature field allowed to obtain the soot volume fraction by a simple calculation.