Showing papers by "ASRC Aerospace Corporation published in 2011"

Fundamental Ice Crystal Accretion Physics Studies

Abstract: Due to numerous engine power-loss events associated with high-altitude convective weather, ice accretion within an engine due to ice-crystal ingestion is being investigated. The National Aeronautics and Space Administration (NASA) and the National Research Council (NRC) of Canada are starting to examine the physical mechanisms of ice accretion on surfaces exposed to ice-crystal and mixed-phase conditions. In November 2010, two weeks of testing occurred at the NRC Research Altitude Facility utilizing a single wedge-type airfoil designed to facilitate fundamental studies while retaining critical features of a compressor stator blade or guide vane. The airfoil was placed in the NRC cascade wind tunnel for both aerodynamic and icing tests. Aerodynamic testing showed excellent agreement compared with CFD data on the icing pressure surface and allowed calculation of heat transfer coefficients at various airfoil locations. Icing tests were performed at Mach numbers of 0.2 to 0.3, total pressures from 93 to 45 kPa, and total temperatures from 5 to 15 C. Ice and liquid water contents ranged up to 20 and 3 grams per cubic meter, respectively. The ice appeared well adhered to the surface in the lowest pressure tests (45 kPa) and, in a particular case, showed continuous leading-edge ice growth to a thickness greater than 15 millimeters in 3 minutes. Such widespread deposits were not observed in the highest pressure tests, where the accretions were limited to a small area around the leading edge. The suction surface was typically ice-free in the tests at high pressure, but not at low pressure. The icing behavior at high and low pressure appeared to be correlated with the wet-bulb temperature, which was estimated to be above 0 C in tests at 93 kPa and below 0 C in tests at lower pressure, the latter enhanced by more evaporative cooling of water. The authors believe that the large ice accretions observed in the low pressure tests would undoubtedly cause the aerodynamic performance of a compressor component such as a stator blade to degrade significantly, and could damage downstream components if shed.

On the Effective Thermal Conductivity of Porous Packed Beds with Uniform Spherical Particles

Abstract: Point contact models for the effective thermal conductivity of porous media with uniform spherical inclusions have been briefly reviewed. The model of Zehner and Schlunder (1970) has been further validated with recent experimental data over a broad range of conductivity ratio from 8 to 1200 and over a range of solids fraction up to about 0.8. The comparisons further confirm the validity of Zehner-Schlunder model, known to be applicable for conductivity ratios less than about 2000, above which area contact between the particles becomes significant. This validation of the Zehner-Schlunder model has implications for its use in the prediction of the effective thermal conductivity of water frost (with conductivity ratio around 100) which arises in many important areas of technology.

Extensible Rectangular Nozzle Model System

Abstract: The design process for the Extensible Rectangular Nozzle (ERN) Model System is summarized. The ERN task is currently funded under the Supersonic project in NASA's Fundamental Aeronautics Program. The task supports the generation of innovative conceptual aerodynamic designs of aircraft exhaust nozzles. Reduced acoustic emissions with improved nozzle performance has been the task goal. New acoustic test rig hardware has been designed for operation at the NASA Glenn Research Center's Aero-Acoustic Propulsion Laboratory (AAPL). Testing of the new rig hardware will provide the experimental data to validate computational predictions of acoustics and performance. The design process has progressed from concept selection through to fabrication-ready three- dimensional (3D) computer solid models. Flow transition ducts have been designed to transition from round piping to a rectangular cross-section. Rectangular convergent baseline nozzle concepts with aspect ratio (AR) of 2, 4 and 8 have been designed for mounting to the flow transition ducts. Initial parametric variations on the baseline nozzles have been modeled and analyzed. Parametric nozzle concepts have included bevel, sidewall-cutback, chevron and combinations of these technologies. The structured Wind-US Reynolds- averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) code has been used throughout the design process as the main flow analysis tool. Aerodynamic design trade studies have been performed of the transition within the nozzle flow-path from a round to a rectangular cross-section in order to minimize flow non-uniformities. The definition of the nozzle external surface has been coupled to both the results from the preliminary mechanical design and supporting internal and external nozzle CFD. Finite-element based structural analyses provide the key mechanical predictions for the hardware components and assembly stack-ups, with hand calculations to help estimate factors of safety. The internal and external flow-lines for the concepts have been screened for aerodynamic performance and expected noise generation at the takeoff condition for nozzle pressure ratios (NPR) ranging from near sonic to a maximum NPR of 3.5. Jet plume predictions at NPR of 1.86 and 2.5 takeoff conditions are presented for a number of the concepts. Updates based on the CFD predictions have been implemented within the 3D computer solid models and mechanically verified throughout the design process. The detachable rectangular nozzle designs for each AR, along with the AR-specific round-to-rectangular transition ducts to which the nozzles attach, represent the key outputs of this design phase. Future acoustic spectral analyses will use the RANS CFD solutions as input during calculations of jet noise. The predictions can then be validated with the experimental test data obtained using the rig hardware. Together with the acoustic predictions, this work will help build up a database of acoustic and aerodynamic predictions to be used in systems-level trade studies of second- generation ("N+2") supersonic commercial transport vehicles.

Implementation of an Integrated On-Board Aircraft Engine Diagnostic Architecture

Abstract: An on-board diagnostic architecture for aircraft turbofan engine performance trending, parameter estimation, and gas-path fault detection and isolation has been developed and evaluated in a simulation environment. The architecture incorporates two independent models: a realtime self-tuning performance model providing parameter estimates and a performance baseline model for diagnostic purposes reflecting long-term engine degradation trends. This architecture was evaluated using flight profiles generated from a nonlinear model with realistic fleet engine health degradation distributions and sensor noise. The architecture was found to produce acceptable estimates of engine health and unmeasured parameters, and the integrated diagnostic algorithms were able to perform correct fault isolation in approximately 70 percent of the tested cases

Surface oxidation study of single wall carbon nanotubes

Abstract: Functionalization of single wall carbon nanotubes (SWCNTs) is desirable to enhance their ability to be incorporated into polymers and enhance their bonding with the matrix. One approach to carbon nanotube functionalization is by oxidation via a strong oxidizing agent or refluxing in strong acids. However, this approach can damage the nanotubes, leading to the introduction of defects and/or shorter nanotubes. Such damage can adversely affect the mechanical, thermal, and electrical properties. A more benign approach to nanotube functionalization has been developed involving photo-oxidation. Chemical analysis by XPS revealed that the oxygen content of the photo-oxidized SWCNTs was 11.3?at.% compared to 6.7?at.% for SWCNTs oxidized by acid treatment. The photo-oxidized SWCNTs produced by this method can be used directly in various polymer matrices or can be further modified by additional chemical reactions.

Commercial Modular Aero-Propulsion System Simulation 40k

Abstract: The Commercial Modular Aero-Propulsion System Simulation 40k (CMAPSS40k) software package is a nonlinear dynamic simulation of a 40,000-pound (approximately equals 178-kN) thrust class commercial turbofan engine, written in the MATLAB/Simulink environment. The model has been tuned to capture the behavior of flight test data, and is capable of running at any point in the flight envelope [up to 40,000 ft (approximately equals 12,200 m) and Mach 0.8]. In addition to the open-loop engine, the simulation includes a controller whose architecture is representative of that found in industry. C-MAPSS40k fills the need for an easy-to-use, realistic, transient simulation of a medium-size commercial turbofan engine with a representative controller. It is a detailed component level model (CLM) written in the industry-standard graphical MATLAB/Simulink environment to allow for easy modification and portability. At the time of this reporting, no other such model exists in the public domain.

Application of an Optimal Tuner Selection Approach for On-Board Self-Tuning Engine Models

Abstract: An enhanced design methodology for minimizing the error in on-line Kalman filter-based aircraft engine performance estimation applications is presented in this paper. It specifically addresses the underdetermined estimation problem, in which there are more unknown parameters than available sensor measurements. This work builds upon an existing technique for systematically selecting a model tuning parameter vector of appropriate dimension to enable estimation by a Kalman filter, while minimizing the estimation error in the parameters of interest. While the existing technique was optimized for open-loop engine operation at a fixed design point, in this paper an alternative formulation is presented that enables the technique to be optimized for an engine operating under closed-loop control throughout the flight envelope. The theoretical Kalman filter mean squared estimation error at a steady-state closed-loop operating point is derived, and the tuner selection approach applied to minimize this error is discussed. A technique for constructing a globally optimal tuning parameter vector, which enables full-envelope application of the technology, is also presented, along with design steps for adjusting the dynamic response of the Kalman filter state estimates. Results from the application of the technique to linear and nonlinear aircraft engine simulations are presented and compared to the conventional approach of tuner selection. The new methodology is shown to yield a significant improvement in on-line Kalman filter estimation accuracy.Copyright © 2011 by ASME

Engine Icing Modeling and Simulation (Part I): Ice Crystal Accretion on Compression System Components and Modeling its Effects on Engine Performance

Abstract: During the past two decades the occurrence of ice accretionwithin commercial high bypass aircraft turbine engines undercertain operating conditions has been reported. Numerousengine anomalies have taken place at high altitudes that wereattributed to ice crystal ingestion such as degraded engineperformance, engine roll back, compressor surge and stall,and even flameout of the combustor. As ice crystals areingested into the engine and low pressure compressionsystem, the air temperature increases and a portion of the icemelts allowing the ice-water mixture to stick to the metalsurfaces of the engine core. The focus of this paper is onestimating the effects of ice accretion on the low pressurecompressor, and quantifying its effects on the engine systemthroughout a notional flight trajectory. In this paper it wasnecessary to initially assume a temperature range in whichengine icing would occur. This provided a mechanism tolocate potential component icing sites and allow thecomputational tools to add blockages due to ice accretion in aparametric fashion. Ultimately the location and level ofblockage due to icing would be provided by an ice accretioncode. To proceed, an engine system modeling code and amean line compressor flow analysis code were utilized tocalculate the flow conditions in the fan-core and low pressurecompressor and to identify potential locations within thecompressor where ice may accrete. Note that there is abaseline value of aerodynamic blockage due to low velocityair near the compressor inner and outer walls and bladesurfaces (boundary layer blockage). There is also a blockagedue to the blade metal thickness. In this study, the “additionalblockage” refers to blockage due to the accretion of ice on themetal surfaces. Once the potential locations of ice accretionare identified, the levels of additional blockage due toaccretion were parametrically varied to estimate the effectson the low pressure compressor blade row performanceoperating within the engine system environment. This studyincludes detailed analysis of compressor and engineperformance during cruise and descent operating conditionsat several altitudes within the notional flight trajectory. Thepurpose of this effort is to develop the codes to provide apredictive capability to forecast the onset of engine icingevents, such that they could help in the avoidance of theseevents.It has been reported that ice crystal accretion in gas turbineengines is dependent on the amount of mixed phaseconditions (liquid and solid) that exist. In addition, theproblem of ice accretion is highly multi-disciplinary, since itinvolves heat transfer from the air to the compressor metalsurfaces. The first phase of this study focuses on addressingthe thermodynamic cycle through the engine system code andthe mean line flow analysis through the compressor through aflight trajectory. The second phase of this study focuses on

Analysis of Screen Channel LAD Bubble Point Tests in Liquid Oxygen at Elevated Temperature

Abstract: The purpose of this paper is to examine the key parameters that affect the bubble point pressure for screen channel Liquid Acquisition Devices in cryogenic liquid oxygen at elevated pressures and temperatures. An in depth analysis of the effect of varying temperature, pressure, and pressurization gas on bubble point is presented. Testing of a 200 x 1400 and 325 x 2300 Dutch Twill screen sample was conducted in the Cryogenics Components Lab 7 facility at the NASA Glenn Research Center in Cleveland, Ohio. Test conditions ranged from 92 to 130K and 0.138 - 1.79 MPa. Bubble point is shown to be a strong function of temperature with a secondary dependence on pressure. The pressure dependence is believed to be a function of the amount of evaporation and condensation occurring at the screen. Good agreement exists between data and theory for normally saturated liquid but the model generally under predicts the bubble point in subcooled liquid. Better correlation with the data is obtained by using the liquid temperature at the screen to determine surface tension of the fluid, as opposed to the bulk liquid temperature.

Aerodynamic Effects of Simulated Ice Accretion on a Generic Transport Model

Abstract: An experimental research effort was begun to develop a database of airplane aerodynamic characteristics with simulated ice accretion over a large range of incidence and sideslip angles. Wind-tunnel testing was performed at the NASA Langley 12-ft Low-Speed Wind Tunnel using a 3.5 percent scale model of the NASA Langley Generic Transport Model. Aerodynamic data were acquired from a six-component force and moment balance in static-model sweeps from alpha = -5deg to 85deg and beta = -45 deg to 45 deg at a Reynolds number of 0.24 x10(exp 6) and Mach number of 0.06. The 3.5 percent scale GTM was tested in both the clean configuration and with full-span artificial ice shapes attached to the leading edges of the wing, horizontal and vertical tail. Aerodynamic results for the clean airplane configuration compared favorably with similar experiments carried out on a 5.5 percent scale GTM. The addition of the large, glaze-horn type ice shapes did result in an increase in airplane drag coefficient but had little effect on the lift and pitching moment. The lateral-directional characteristics showed mixed results with a small effect of the ice shapes observed in some cases. The flow visualization images revealed the presence and evolution of a spanwise-running vortex on the wing that was the dominant feature of the flowfield for both clean and iced configurations. The lack of ice-induced performance and flowfield effects observed in this effort was likely due to Reynolds number effects for the clean configuration. Estimates of full-scale baseline performance were included in this analysis to illustrate the potential icing effects.

A Sensitivity Study of Commercial Aircraft Engine Response for Emergency Situations

Abstract: This paper contains the details of a sensitivity study in which the variation in a commercial aircraft engine's outputs is observed for perturbations in its operating condition inputs or control parameters. This study seeks to determine the extent to which various controller limits can be modified to improve engine performance, while capturing the increased risk that results from the changes. In an emergency, the engine may be required to produce additional thrust, respond faster, or both, to improve the survivability of the aircraft. The objective of this paper is to propose changes to the engine controller and determine the costs and benefits of the additional capabilities produced by the engine. This study indicates that the aircraft engine is capable of producing additional thrust, but at the cost of an increased risk of an engine failure due to higher turbine temperatures and rotor speeds. The engine can also respond more quickly to transient commands, but this action reduces the remaining stall margin to possibly dangerous levels. To improve transient response in landing scenarios, a control mode known as High Speed Idle is proposed that increases the responsiveness of the engine and conserves stall margin

Evaluation of Icing Scaling on Swept NACA 0012 Airfoil Models

Abstract: Icing scaling tests in the NASA Glenn Icing Research Tunnel (IRT) were performed on swept wing models using existing recommended scaling methods that were originally developed for straight wing. Some needed modifications on the stagnation-point local collection efficiency (i.e., beta(sub 0) calculation and the corresponding convective heat transfer coefficient for swept NACA 0012 airfoil models have been studied and reported in 2009, and the correlations will be used in the current study. The reference tests used a 91.4-cm chord, 152.4-cm span, adjustable sweep airfoil model of NACA 0012 profile at velocities of 100 and 150 knot and MVD of 44 and 93 mm. Scale-to-reference model size ratio was 1:2.4. All tests were conducted at 0deg angle of attack (AoA) and 45deg sweep angle. Ice shape comparison results were presented for stagnation-point freezing fractions in the range of 0.4 to 1.0. Preliminary results showed that good scaling was achieved for the conditions test by using the modified scaling methods developed for swept wing icing.

Implementation of Enhanced Propulsion Control Modes for Emergency Flight Operation

Abstract: Aircraft engines can be effective actuators to help pilots avert or recover from emergency situations. Emergency control modes are being developed to enhance the engines performance to increase the probability of recovery under these circumstances. This paper discusses a proposed implementation of an architecture that requests emergency propulsion control modes, allowing the engines to deliver additional performance in emergency situations while still ensuring a specified safety level. In order to determine the appropriate level of engine performance enhancement, information regarding the current emergency scenario (including severity) and current engine health must be known. This enables the engine to operate beyond its nominal range while minimizing overall risk to the aircraft. In this architecture, the flight controller is responsible for determining the severity of the event and the level of engine risk that is acceptable, while the engine controller is responsible for delivering the desired performance within the specified risk range. A control mode selector specifies an appropriate situation-specific enhanced mode, which the engine controller then implements. The enhanced control modes described in this paper provide additional engine thrust or response capabilities through the modification of gains, limits, and the control algorithm, but increase the risk of engine failure. The modifications made to the engine controller to enable the use of the enhanced control modes are described, as are the interaction between the various subsystems and importantly, the interaction between the flight controller/pilot and the propulsion control system. Simulation results demonstrate how the system responds to requests for enhanced operation and the corresponding increase in performance.

Effect of Graphene Addition on Shape Memory Behavior of Epoxy Resins

Abstract: Shape memory polymers (SMPs) and composites are a special class of smart materials known for their ability to change size and shape upon exposure to an external stimulus (e.g. light, heat, pH, or magnetic field). These materials are commonly used for biomedical applications; however, recent attempts have been made towards developing SMPs and composites for use in aircraft and space applications. Implementing SMPs and composites to create a shape change effect in some aircraft structures could potentially reduce drag, decrease fuel consumption, and improve engine performance. This paper discusses the development of suitable materials to use in morphing aircraft structures. Thermally responsive epoxy SMPs and nanocomposites were developed and the shape memory behavior and thermo-mechanical properties were studied. Overall, preliminary results from dynamic mechanical analysis (DMA) showed that thermally actuated shape memory epoxies and nanocomposites possessed Tgs near approximately 168 C. When graphene nanofiller was added, the storage modulus and crosslinking density decreased. On the other hand, the addition of graphene enhanced the recovery behavior of the shape memory nanocomposites. It was assumed that the addition of graphene improved shape memory recovery by reducing the crosslinking density and increasing the elasticity of the nanocomposites.

Measurement of Volatile Particulate Matter Emissions From Aircraft Engines Using a Simulated Plume Aging System

Abstract: Aircraft exhaust contains nonvolatile (soot) particulate matter (PM), trace gas pollutants, and volatile PM precursor material. Nonvolatile soot particles are predominantly present at the engine exit plane, but volatile PM precursors form new particles or add mass to the existing ones as the exhaust is diluted and cooled. Accurately characterizing the volatile PM mass, number, and size distribution is challenging due to this evolving nature and the impact of local ambient conditions on the gas-to-particle conversion processes. To accurately and consistently measure the aircraft PM emissions, a dilution and aging sampling system that can condense volatile precursors to particle phase to simulate atmospheric evolution of aircraft engine exhaust has been developed. In this paper, field demonstration of its operation is described. The dilution/aging probe system was tested using both a combustor rig and on-wing CFM56-7 engines. During the combustor rig testing at NASA Glenn Research Center, the dilution/aging probe supported formation of both nucleation/growth mode particles and soot coatings. The results showed that by increasing residence time, the nucleation particles become larger in size, increase in total mass, and decrease in number. During the on-wing CFM56-7 engine testing at Chicago Midway Airport, the dilution/aging probe was able to form soot coatings as well as nucleation mode particles, unlike conventional 1-m probe engine measurements. The number concentration of nucleation particles depended on sample fraction and relative humidity of the dilution air. The performance of the instrument is analyzed and explained using computational microphysics simulations.Copyright © 2011 by ASME

Engine Icing Modeling and Simulation (Part 2): Performance Simulation of Engine Rollback Phenomena

Abstract: Ice buildup in the compressor section of a commercial aircraft gas turbine engine can cause a number of engine failures. One of these failure modes is known as engine rollback: an uncommanded decrease in thrust accompanied by a decrease in fan speed and an increase in turbine temperature. This paper describes the development of a model which simulates the system level impact of engine icing using the Commercial Modular Aero-Propulsion System Simulation 40k (C-MAPSS40k). When an ice blockage is added to C-MAPSS40k, the control system responds in a manner similar to that of an actual engine, and, in cases with severe blockage, an engine rollback is observed. Using this capability to simulate engine rollback, a proof-of-concept detection scheme is developed and tested using only typical engine sensors. This paper concludes that the engine control system s limit protection is the proximate cause of iced engine rollback and that the controller can detect the buildup of ice particles in the compressor section. This work serves as a feasibility study for continued research into the detection and mitigation of engine rollback using the propulsion control system.

An Emergency Engine Response Requirement Analysis Tool for Lateral-Directional Dynamic Aircraft Stability

Abstract: In an effort to use the propulsion system to augment or replace a damaged flight control system in emergency situations, engine response requirements must be developed to set goals for engine transient operation. The propulsion system dynamics are much slower than the response obtained from conventional flight controls, and depending on placement may be much less effective. In this paper, an analysis method to determine engine response requirements for lateral-directional stability is developed for the case where the vertical stabilizer has sustained damage. The output of the tool is then validated against the nonlinear Generic Transport Model (GTM) with second order engine models. Results from the application of the analysis tool to various types of aircraft, including the GTM, are presented for various flight conditions and levels of vertical stabilizer damage.

Mach 0.3 Burner Rig Facility at the NASA Glenn Materials Research Laboratory

Abstract: This Technical Memorandum presents the current capabilities of the state-of-the-art Mach 0.3 Burner Rig Facility. It is used for materials research including oxidation, corrosion, erosion and impact. Consisting of seven computer controlled jet-fueled combustors in individual test cells, these relatively small rigs burn just 2 to 3 gal of jet fuel per hour. The rigs are used as an efficient means of subjecting potential aircraft engine/airframe advanced materials to the high temperatures, high velocities and thermal cycling closely approximating actual operating environments. Materials of various geometries and compositions can be evaluated at temperatures from 700 to 2400 F. Tests are conducted not only on bare superalloys and ceramics, but also to study the behavior and durability of protective coatings applied to those materials.

The Effect of Faster Engine Response on the Lateral Directional Control of a Damaged Aircraft

Abstract: The integration of flight control and propulsion control has been a much discussed topic, especially for emergencies where the engines may be able to help stabilize and safely land a damaged aircraft. Previous research has shown that for the engines to be effective as flight control actuators, the response time to throttle commands must be improved. Other work has developed control modes that accept a higher risk of engine failure in exchange for improved engine response during an emergency. In this effort, a nonlinear engine model (the Commercial Modular Aero-Propulsion System Simulation 40k) has been integrated with a nonlinear airframe model (the Generic Transport Model) in order to evaluate the use of enhanced-response engines as alternative yaw rate control effectors. Tests of disturbance rejection and command tracking were used to determine the impact of the engines on the aircraft’s dynamical behavior. Three engine control enhancements that improve the response time of the engine were implemented and tested in the integrated simulation. The enhancements were shown to increase the engine’s effectiveness as a yaw rate control effector when used in an automatic feedback loop. The improvement is highly dependent upon flight condition; the airframe behavior is markedly improved at low altitude, low speed conditions, and relatively unchanged at high altitude, high speed.

Assessment of Some Atomization Models Used in Spray Calculations

Abstract: The paper presents the results from a validation study undertaken as a part of the NASA s fundamental aeronautics initiative on high altitude emissions in order to assess the accuracy of several atomization models used in both non-superheat and superheat spray calculations. As a part of this investigation we have undertaken the validation based on four different cases to investigate the spray characteristics of (1) a flashing jet generated by the sudden release of pressurized R134A from cylindrical nozzle, (2) a liquid jet atomizing in a subsonic cross flow, (3) a Parker-Hannifin pressure swirl atomizer, and (4) a single-element Lean Direct Injector (LDI) combustor experiment. These cases were chosen because of their importance in some aerospace applications. The validation is based on some 3D and axisymmetric calculations involving both reacting and non-reacting sprays. In general, the predicted results provide reasonable agreement for both mean droplet sizes (D32) and average droplet velocities but mostly underestimate the droplets sizes in the inner radial region of a cylindrical jet.

Microencapsulation of Self Healing Agents for Corrosion Control Coatings

Abstract: Corrosion, the environmentally induced degradation of materials, is a very costly problem that has a major impact on the global economy. Results from a 2-year breakthrough study released in 2002 by the U.S. Federal Highway Administration (FHWA) showed that the total annual estimated direct cost associated with metallic corrosion in nearly every U.S. industry sector was a staggering $276 billion, approximately 3.1% of the nation's Gross Domestic Product (GOP). Corrosion protective coatings are widely used to protect metallic structures from the detrimental effects of corrosion but their effectiveness can be seriously compromised by mechanical damage, such as a scratch, that exposes the metallic substrate. The incorporation of a self healing mechanism into a corrosion control coating would have the potential to significantly increase its effectiveness and useful lifetime. This paper describes work performed to incorporate a number of microcapsule-based self healing systems into corrosion control coatings. The work includes the preparation and evaluation of self-healing systems based on curable epoxy, acrylate, and siloxane resins, as well as, microencapsulated systems based on passive, solvent born, healing agent delivery. The synthesis and optimization of microcapsule-based self healing systems for thin coating (less than 100 micron) will be presented.

Design for On-Sun Evaluation of Evaporator Receivers

Abstract: A heat pipe designed for operation as a solar power receiver should be optimized to accept the solar energy flux and transfer this heat into a reactor. Optical properties of the surface, thermal conductance of the receiver wall, contact resistance of the heat pipe wick, and other heat pipe wick properties ultimately define the maximum amount of power that can be extracted from the concentrated sunlight impinging on the evaporator surface. Modeling of solar power receivers utilizing optical and physical properties provides guidance to their design. On-sun testing is another important means of gathering information on performance. A test rig is being designed and built to conduct on-sun testing. The test rig is incorporating a composite strip mirror concentrator developed as part of a Small Business Innovative Research effort and delivered to NASA Glenn Research Center. In the strip concentrator numerous, lightweight composite parabolic strips of simple curvature were combined to form an array 1.5 m x 1.5 m in size. The line focus of each strip is superimposed in a central area simulating a point of focus. A test stand is currently being developed to hold the parabolic strip concentrator, track the sun, and turn the beam downward towards the ground. The hardware is intended to be sufficiently versatile to accommodate on-sun testing of several receiver concepts, including those incorporating heat pipe evaporators. Characterization devices are also being developed to evaluate the effectiveness of the solar concentrator, including a receiver designed to conduct calorimetry. This paper describes the design and the characterization devices of the on-sun test rig, and the prospect of coupling the concentrated sunlight to a heat pipe solar power receiver developed as part of another Small Business Innovative Research effort.

Synthesis of Elongated Microcapsules

Abstract: One of the factors that influence the effectiveness of self-healing in functional materials is the amount of liquid healing agents that can be delivered to the damaged area. The use of hollow tubes or fibers and the more sophisticated micro-vascular networks has been proposed as a way to increase the amount of healing agents that can be released when damage is inflicted. Although these systems might be effective in some specific applications, they are not practical for coatings applications. One possible practical way to increase the healing efficiency is to use microcapsules with high-aspect-ratios, or elongated microcapsules. It is understood that elongated microcapsules will be more efficient because they can release more healing agent than a spherical microcapsule when a crack is initiated in the coating. Although the potential advantage of using elongated microcapsules for self healing applications is clear, it is very difficult to make elongated microcapsules from an emulsion system because spherical microcapsules are normally formed due to the interfacial tension between the dispersed phase and the continuous phase. This paper describes the two methods that have been developed by the authors to synthesize elongated microcapsules. The first method involves the use of an emulsion with intermediate stability and the second involves the application of mechanical shear conditions to the emulsion.

Fiber Bragg Based Optical Sensors for Extreme Temperatures

Abstract: In this paper techniques used to manufacture thermally stable fiber Bragg gratings capable to operate at extreme temperatures for long durations of time are analyzed. Results on packaging and long durability tests performed on sensor units comprised of chemical composition grating or CCG-type fiber Bragg gratings are also reported. The tests included exposure of the packaged sensors to 1000 °C thermal environments for up to 1000 hours and thermal cycling at rates up to 400 °C/min.

An Aerodynamic and Acoustic Assessment of Convergent- Divergent Nozzles with Chevrons

Abstract: Flow analyses at takeoff conditions have been performed for a typical military nozzle with chevrons. A baseline nozzle and ten chevron configurations of varying flow penetration, length, and width have been screened for aerodynamic performance and acoustic signature. These studies have been undertaken to further the process of generating databases with medium-level fidelity tools. These tools have been selected to provide meaningful physical insight regarding geometrically varied parameters in reasonable engineering turnaround times. Databases based on the concept variations can then be incorporated into lower fidelity systems-level design tools. This capability will more readily provide the designer access to the information stored within the databases during future commercial supersonic aircraft system trade studies. Three-dimensional Computational Fluid Dynamics (CFD) simulations have been performed with the Wind-US Reynolds-Averaged Navier-Stokes structured code. These simulations have provided the necessary input for the JeNo jet noise prediction code. The aerodynamic and acoustic code predictions have been analyzed. Identifiable trends between the chevron designs have been captured for mixing noise and performance relative to the baseline model. Increased chevron penetration has resulted in more aggressive mixing and reduced peak noise. Increased chevron penetration has also resulted in a loss in thrust and increased high-frequency acoustic noise. Grid-resolution studies followed by JeNo evaluation of the jet mixing noise has helped reduce turnaround time while allowing the qualitative trends to be captured. Finer grid simulations will be needed for more resolved shock cell prediction within the nozzle plume for subsequent broadband shock noise studies. Future comparison of experimental data, with and without fan bypass flow, will further quantify the accuracy of the trends.

Timescale Correlation between Marine Atmospheric Exposure and Accelerated Corrosion Testing - Part 2

Abstract: Evaluation of metal-based structures has long relied on atmospheric exposure test sites to determine corrosion resistance in marine environments. Traditional accelerated corrosion testing relies on mimicking the exposure conditions, often incorporating salt spray and ultraviolet (UV) radiation, and exposing the metal to continuous or cyclic conditions of the corrosive environment. Their success for correlation to atmospheric exposure is often a concern when determining the timescale to which the accelerated tests can be related. Accelerated laboratory testing, which often focuses on the electrochemical reactions that occur during corrosion conditions, has yet to be universally accepted as a useful tool in predicting the long term service life of a metal despite its ability to rapidly induce corrosion. Although visual and mass loss methods of evaluating corrosion are the standard and their use is imperative, a method that correlates timescales from atmospheric exposure to accelerated testing would be very valuable. This work uses surface chemistry to interpret the chemical changes occurring on low carbon steel during atmospheric and accelerated corrosion conditions with the objective of finding a correlation between its accelerated and long-term corrosion performance. The current results of correlating data from marine atmospheric exposure conditions at the Kennedy Space Center beachside corrosion test site, alternating seawater spray, and immersion in typical electrochemical laboratory conditions, will be presented. Key words: atmospheric exposure, accelerated corrosion testing, alternating seawater spray, marine, correlation, seawater, carbon steel, long-term corrosion performance prediction, X-ray photoelectron spectroscopy.

Structural Design of Ares V Interstage Composite Structure

Abstract: Preliminary and detailed design studies were performed to mature composite structural design concepts for the Ares V Interstage structure as a part of NASA s Advanced Composite Technologies Project. Aluminum honeycomb sandwich and hat-stiffened composite panel structural concepts were considered. The structural design and analysis studies were performed using HyperSizer design sizing software and MSC Nastran finite element analysis software. System-level design trade studies were carried out to predict weight and margins of safety for composite honeycomb-core sandwich and composite hat-stiffened skin design concepts. Details of both preliminary and detailed design studies are presented in the paper. For the range of loads and geometry considered in this work, the hat-stiffened designs were found to be approximately 11-16 percent lighter than the sandwich designs. A down-select process was used to choose the most favorable structural concept based on a set of figures of merit, and the honeycomb sandwich design was selected as the best concept based on advantages in manufacturing cost.

Liquid Methane Conditioning Capabilities Developed at the NASA Glenn Research Center's Small Multi- Purpose Research Facility (SMiRF) for Accelerated Lunar Surface Storage Thermal Testing

Abstract: Glenn Research Center s Creek Road Cryogenic Complex, Small Multi-Purpose Research Facility (SMiRF) recently completed validation / checkout testing of a new liquid methane delivery system and liquid methane (LCH4) conditioning system. Facility checkout validation was conducted in preparation for a series of passive thermal control technology tests planned at SMiRF in FY10 using a flight-like propellant tank at simulated thermal environments from 140 to 350K. These tests will validate models and provide high quality data to support consideration of LCH4/LO2 propellant combination option for a lunar or planetary ascent stage.An infrastructure has been put in place which will support testing of large amounts of liquid methane at SMiRF. Extensive modifications were made to the test facility s existing liquid hydrogen system for compatibility with liquid methane. Also, a new liquid methane fluid conditioning system will enable liquid methane to be quickly densified (sub-cooled below normal boiling point) and to be quickly reheated to saturation conditions between 92 and 140 K. Fluid temperatures can be quickly adjusted to compress the overall test duration. A detailed trade study was conducted to determine an appropriate technique to liquid conditioning with regard to the SMiRF facility s existing infrastructure. In addition, a completely new roadable dewar has been procured for transportation and temporary storage of liquid methane. A new spherical, flight-representative tank has also been fabricated for integration into the vacuum chamber at SMiRF. The addition of this system to SMiRF marks the first time a large-scale liquid methane propellant test capability has been realized at Glenn.This work supports the Cryogenic Fluid Management Project being conducted under the auspices of the Exploration Technology Development Program, providing focused cryogenic fluid management technology efforts to support NASA s future robotic or human exploration missions.

Validating PIV Measurements in Supersonic Jets Using Shadowgraph Optical Imaging

Abstract: Particle Image Velocimetry (PIV) is a planar fluid velocity measurement technique, wellestablished worldwide in research and in industry to acquire two or three component planar velocity data in a wide variety of fluid flows. Specifically in this work, 2D PIV was applied to characterize the supersonic flow field of a screech-reducing jet nozzle design on the Nozzle Acoustic Test Rig (NATR) in the Aero-Acoustic Propulsion Lab (AAPL) at NASA Glenn Research Center (GRC). The PIV data were acquired in the stream-wise configuration allowing for mapping the jet plume flow field at numerous locations downstream. Based on a growing experience level and understanding of jet flows, more confidence is being given to Computational Fluid Dynamic (CFD) prediction codes. Typically, PIV as well as other diagnostic measurement tools are used to validate the CFD predictions. Recently, a large difference between the PIV measurements and the CFD predictions of a supersonic jet flow was observed, leading to concerns about accuracy and overall quality of the PIV measurement campaign. In order to alleviate these apprehensions, the shadowgraph optical imaging method was applied to the same flows to provide supplementary supersonic flow field data. Shadowgraph images are completely independent of PIV measurements which provide a robust qualitative PIV validation solution in supersonic flows.