NASA Glenn Research Center Research Articles

First Preliminary Results From U.S. Round-Robin Tests

The first preliminary results are reported from the U.S. Round-Robin Test on Plasma Expansion Speed. The tests were performed at the NASA Glenn Research Center on two coupons (six strings) of International Space Station (ISS) solar cell arrays, with a separate small array to obtain arcs (because it is so difficult to get ISS arrays to arc). ISS arrays were used because they have no exposed interconnects to act as bare current collectors and confuse the experimental results. The preconstructed ISS strings were laid out approximately parallel to the plasma expansion velocity to allow for the best test of the simple plasma expansion front current waveform model. Several Langmuir probes were arranged above and to the sides of the sample to allow for measurement of the plasma propagation speed. In the initial set of tests, primary arcs and the consequent current waveforms were measured in a Low Earth Orbit-type plasma. In a second set of tests, two electron guns with diffusers were used to provide an approximately uniform Geosynchronous Earth Orbit-type environment, and primary arcs and current waveforms were obtained. The objective of this and other round-robin tests is to characterize primary arc waveforms in terms of speed and degree of discharge of arc plasmas produced by primary arcs, and their dependences on environment, capacitance per unit area, arc voltage, temperature, and so on. The final goal is to allow engineering estimates of arc current peaks and half-widths to allow confident design and construction of space solar arrays, and to allow mitigation techniques to be evaluated. This is the first in an extended series of tests to be performed at six different U.S. facilities, and with participation from ten different U.S. organizations.

Experimental Investigation of Flow Condensation in Microgravity

Future manned space missions are expected to greatly increase the space vehicle's size, weight, and heat dissipation requirements. An effective means to reducing both size and weight is to replace single-phase thermal management systems with two-phase counterparts that capitalize upon both latent and sensible heat of the coolant rather than sensible heat alone. This shift is expected to yield orders of magnitude enhancements in flow boiling and condensation heat transfer coefficients. A major challenge to this shift is a lack of reliable tools for accurate prediction of two-phase pressure drop and heat transfer coefficient in reduced gravity. Developing such tools will require a sophisticated experimental facility to enable investigators to perform both flow boiling and condensation experiments in microgravity in pursuit of reliable databases. This study will discuss the development of the Flow Boiling and Condensation Experiment (FBCE) for the International Space Station (ISS), which was initiated in 2012 in collaboration between Purdue University and NASA Glenn Research Center. This facility was recently tested in parabolic flight to acquire condensation data for FC-72 in microgravity, aided by high-speed video analysis of interfacial structure of the condensation film. The condensation is achieved by rejecting heat to a counter flow of water, and experiments were performed at different mass velocities of FC-72 and water and different FC-72 inlet qualities. It is shown that the film flow varies from smooth-laminar to wavy-laminar and ultimately turbulent with increasing FC-72 mass velocity. The heat transfer coefficient is highest near the inlet of the condensation tube, where the film is thinnest, and decreases monotonically along the tube, except for high FC-72 mass velocities, where the heat transfer coefficient is enhanced downstream. This enhancement is attributed to both turbulence and increased interfacial waviness. One-ge correlations are shown to predict the average condensation heat transfer coefficient with varying degrees of success, and a recent correlation is identified for its superior predictive capability, evidenced by a mean absolute error of 21.7%.

Techniques for monitoring damage in ceramic matrix composites

This article offers a review of various nondestructive evaluation and structural health monitoring techniques that have been successfully utilized for assessing the damage state of woven ceramic matrix composites consisting of silicon carbide fibers and silicon carbide matrices. The techniques include acousto-ultrasonics, modal acoustic emissions, electrical resistance, impedance-based structural health monitoring, pulsed thermography, as well as thermoelastic stress analysis. The damage, in the form of distributed matrix cracks and delaminations, was introduced using multiple tactics. These included load/unload/reload uniaxial tensile tests, creep tests, and ballistic impact. Although other nondestructive evaluation techniques have been applied to this material system, the select nondestructive evaluation tools described here are limited to approaches that are of current research interest within programs at the NASA Glenn Research Center.

Unstructured large eddy simulations of heated supersonic twin jets

Unstructured large eddy simulations are performed with the compressible flow solver ”Charles” developed at Cascade Technologies, for heated supersonic over-expanded jets issued from a twin nozzle. The study focuses on the modeling of the internal flow and its effects on the flow-field in the jet plume and ultimately on the radiated noise. In this work, near-wall adaptive mesh refinement, synthetic inflow turbulence and wall modeling are used inside the nozzle. In addition to the converging-diverging nozzle geometry, the computational domain includes the Y-duct, S-ducts, and angle adapter upstream of the nozzles, to realistically reproduce the elements of the experimental configuration where the internal flow conditions and wall modeling can be expected to affect the external flow-field and sound-field predictions. Comparisons between the numerical predictions and experimental PIV and far-field noise measurements from NASA Glenn Research Center will be presented and discussed.

Simulation of secondary and separated flow in a diffusing S-duct using four different turbulence models

The focus of this article is on the numerical simulation of compressible flow in a diffusing S-duct inlet; this flow is characterized by secondary flow as well as regions of boundary layer separation. The S-duct geometry produces streamline curvature and an adverse pressure gradient resulting in these flow characteristics. The geometry used in this investigation is based on a NASA Glenn Research Center experimental diffusing S-duct that was studied in the early 1990s. The computational fluid dynamics flow solver ANSYS - FLUENT is employed in the investigation of compressible flow through the S-duct. A second-order accurate, steady, density-based solver is employed in a finite-volume framework. The three-dimensional Reynolds-Averaged Navier-Stokes equations are solved on a structured mesh with a number of turbulence models, namely the Spalart–Allmaras (SA), k-ɛ, k-ω SST, and Transition SST models, and the results are compared with the experimental data. The computed results capture the flow field and pressure recovery with acceptable accuracy when compared with the experimental data. The turbulence model giving the best results is identified.

Laboratory and modeling studies on the effects of water and soot emissions and ambient conditions on the properties of contrail ice particles in the jet regime

Abstract. Contrails and contrail-induced cirrus clouds are identified as the most uncertain components in determining aviation impacts on global climate change. Parameters affecting contrail ice particle formation immediately after the engine exit plane (< 5 s in plume age) may be critical to ice particle properties used in large-scale models predicting contrail radiative forcing. Despite this, detailed understanding of these parametric effects is still limited. In this paper, we present results from recent laboratory and modeling studies conducted to investigate the effects of water and soot emissions and ambient conditions on near-field formation of contrail ice particles and ice particle properties. The Particle Aerosol Laboratory (PAL) at the NASA Glenn Research Center and the Aerodyne microphysical parcel model for contrail ice particle formation were employed. Our studies show that exhaust water concentration has a significant impact on contrail ice particle formation and properties. When soot particles were introduced, ice particle formation was observed only when exhaust water concentration was above a critical level. When no soot or sulfuric acid was introduced, no ice particle formation was observed, suggesting that ice particle formation from homogeneous nucleation followed by homogeneous freezing of liquid water was unfavorable. Soot particles were found to compete for water vapor condensation, and higher soot concentrations emitted into the chamber resulted in smaller ice particles being formed. Chamber conditions corresponding to higher cruising altitudes were found to favor ice particle formation. The microphysical model captures trends of particle extinction measurements well, but discrepancies between the model and the optical particle counter measurements exist as the model predicts narrower ice particle size distributions and ice particle sizes nearly a factor of two larger than measured. These discrepancies are likely due to particle loss and scatter during the experimental sampling process and the lack of treatment of turbulent mixing in the model. Our combined experimental and modeling work demonstrates that formation of contrail ice particles can be reproduced in the NASA PAL facility, and the parametric understanding of the ice particle properties from the model and experiments can potentially be used in large-scale models to provide better estimates of the impact of aviation contrails on climate change.

Finite element modeling of ballistic impact on multi-layer Kevlar 49 fabrics

This paper presents a material model suitable for simulating the behavior of dry fabrics subjected to ballistic impact. The developed material model is implemented in a commercial explicit finite element (FE) software LS-DYNA through a user defined material subroutine (UMAT). The constitutive model is developed using data from uniaxial quasi-static and high strain rate tension tests, picture frame tests and friction tests. Different finite element modeling schemes using shell finite elements are used to study efficiency and accuracy issues. First, single FE layer (SL) and multiple FE layers (ML) were used to simulate the ballistic tests conducted at NASA Glenn Research Center (NASA-GRC). Second, in the multiple layer configuration, a new modeling approach called Spiral Modeling Scheme (SMS) was tried and compared to the existing Concentric Modeling Scheme (CMS). Regression analyses were used to fill missing experimental data – the shear properties of the fabric, damping coefficient and the parameters used in Cowper-Symonds (CS) model which account for strain rate effect on material properties, in order to achieve close match between FE simulations and experimental data. The difference in absorbed energy by the fabric after impact, displacement of fabric near point of impact, and extent of damage were used as metrics for evaluating the material model. In addition, the ballistic limits of the multi-layer fabrics for various configurations were also determined.

High-Speed Turbofan Noise Reduction Using Foam-Metal Liner Over-the-Rotor

A Williams International FJ44-3A turbofan engine was used to demonstrate the high-speed fan noise reduction potential of a foam-metal liner installed in close proximity to the fan rotor. The engine was tested in the NASA Glenn Research Center’s Aeroacoustic Propulsion Laboratory. Two foam-metal liner designs were tested and compared to the hardwall baseline. Traditional single degree-of-freedom liner designs were also evaluated to provide a comparison to the state-of-the art design. This report presents the test setup and documents the test conditions. Far-field acoustic levels and limited engine performance results are also presented. The results show that the foam-metal liner achieved up to 5 dB of attenuation in the forward-quadrant radiated-acoustic power levels, which is equivalent to the traditional single degree-of-freedom liner design. Modest changes in engine performance were noted.

Fluid–Structure Interaction Simulations of a Tension-Cone Inflatable Aerodynamic Decelerator

A series of fluid–structure interaction simulations of an aerodynamic tension-cone supersonic decelerator prototype intended for large mass payload deployment in planetary explorations are discussed. The fluid–structure interaction computations combine large deformation analysis of thin shells with large-eddy simulation of compressible turbulent flows using a loosely coupled approach to enable quantification of the dynamics of the vehicle. The simulation results are compared with experiments carried out at the NASA Glenn Research Center. Reasonably good agreement between the simulations and the experiment is observed throughout a deflation cycle. The simulations help to illuminate the details of the dynamic progressive buckling of the tension-cone decelerator that ultimately results in the collapse of the structure as the inflation pressure is decreased. Furthermore, the tension-cone decelerator exhibits a transient oscillatory behavior under impulsive loading that ultimately dies out. The frequency of these oscillations was determined to be related to the acoustic time scale in the compressed subsonic region between the bow shock and the structure. As shown, when the natural frequency of the structure and the frequency of the compressed subsonic region approximately match, the decelerator exhibits relatively large nonaxisymetric oscillations. The observed response appears to be a fluid–structure interaction resonance resulting from an acoustic chamber (pistonlike) mode exciting the structure.

Simulations and Measurements of the Vibroacoustic Effects of Replacing Rolling Element Bearings With Journal Bearings in a Simple Gearbox

The effects of replacing rolling element bearings with journal bearings on the noise and vibration of a simple gearbox are computationally and experimentally evaluated. A modified component mode synthesis (CMS) approach is used, where the component modes of the shafting and gearbox housing are modeled using finite element analysis (FEA). Instead of using component modes with free boundary conditions, which is typical of CMS, the shafting and gearbox are coupled using nominal impedances computed for the different bearing types, improving convergence of the solution. Methods for computing the actual bearing impedances, including the high damping coefficients in journal bearings, are summarized. The sound radiated by the gearbox is computed using a boundary element (BE) model. The modeling results are validated against measurements made at the NASA Glenn Research Center. Both simulations and measurements reveal that the journal bearings, although highly damped, do not necessarily lead to strong reductions in gearbox vibration and noise.

Aircraft Turbine Engine Control Research at NASA Glenn Research Center

This paper provides an overview of the aircraft turbine engine control research at NASA Glenn Research Center (GRC). A brief introduction to the engine control problem is first provided with a description of the state-of-the-art control law structure. A historical aspect of engine control development since the 1940s is then provided with a special emphasis on the contributions of GRC. With the increased emphasis on aircraft safety, enhanced performance, and affordability, as well as the need to reduce the environmental impact of aircraft, there are many new challenges being faced by the designers of aircraft propulsion systems. The Controls and Dynamics Branch (CDB) at the GRC is leading and participating in various projects to develop advanced propulsion controls and diagnostics technologies that will help meet the challenging goals of NASA Aeronautics Research Mission programs. The rest of the paper provides an overview of the various CDB technology development activities in aircraft engine control and diagnostics, both current and some accomplished in the recent past. The motivation for each of the research efforts, the research approach, technical challenges, and the key progress to date are summarized.

Modification and Tests of Particle Probe Tips to Mitigate Effects of Ice Shattering

Abstract Ice particle shattering may significantly contaminate measurements taken by airborne particle probes in ice clouds. Environment Canada and the NASA Glenn Research Center (GRC) undertook efforts to modify and test probe tips in order to mitigate the effect of shattering on measurements. This work presents an overview of the results obtained during the design work on the particle probe arm tips. Even though this work was focused on the modifications of three of the probes—Particle Measuring Systems Inc. (PMS) Forward Scattering Spectrometer Probe and optical array probe, and Droplet Measurement Technologies (DMT) Cloud Imaging Probe—the outcomes of this work bear a general character and are applicable to other similar instruments. The results of the airflow analysis around the probe’s housing and the simulations of particle bouncing from the probe tips are discussed here. The originally designed and modified tips were tested in a high-speed wind tunnel in ice and liquid sprays. The ice particle bouncing processes as well as patterns of water shedding over the surface of the probes arms were studied with the help of a high-speed video camera. It was found that at aircraft speed, after bouncing from a solid surface, ice particles may travel several centimeters across the airflow and bounce forward up to 1 cm. For the first time it has been directly documented with high-speed video recording that the sample volumes of particle probes with the originally designed tips are contaminated by shattered and bounced particles. A set of recommendations on the existing modification and the design of future particle probe housings is presented.

Aircraft Icing Research at NASA Glenn Research Center

The National Aeronautics and Space Administration Glenn Research Center (GRC; and its predecessor organizations) has been and continues to be a focal point for research in the field of aircraft icing. This paper provides a historical perspective on the contributions that GRC research has made to the field, as well as a synopsis of the current research being conducted at the center. The GRC’s icing research has been comprehensive, covering the characterization of the icing environment, investigations into the physics of ice accretion on aircraft surfaces, studies of the impact of icing on aircraft aerodynamics and engine performance, icing instrumentation development, and simulation of ice growth on aircraft using wind tunnels and computational methods. This research has led to improved safety for flight in icing conditions through contributions to the development of icing regulations; a greater understanding of the effects of ice accretion; and the development of experimental and computational methods to aid in the design of aircraft and aircraft subsystems (including ice protection systems) that can operate safely in an icing environment.

History of Electrochemical and Energy Storage Technology Development at NASA Glenn Research Center

The National Aeronautics and Space Administration Glenn Research Center (GRC) has a rich heritage of developing electrochemical technologies and energy storage systems for aerospace. Primary and rechargeable batteries, fuel cells, flywheels, and regenerative fuel cells are among the GRC’s portfolio of energy storage devices and primary power systems. These technologies have been developed for missions and applications such as low Earth orbit and geosynchronous Earth orbit satellites, space shuttle, astronaut spacesuit, International Space Station, landers and rovers, and lunar and planetary habitats. The desire for lower mass, lower volume, higher efficiency, and more reliable power systems has most often been the driving force behind the development of these technologies. Often, as with fuel cells for the early Gemini and Apollo missions, development of the technology has been mission enabling. Although many of these technologies were initially developed for applications in space, the existence of such capabilities or development successes at GRC has led to their adoption for terrestrial uses or further research and development for terrestrial applications, including electric vehicles, unmanned aerial and underwater vehicles, and all-electric aircraft. This paper discusses the history of and the current research and development at the GRC in electrochemical and energy storage technologies. The future outlook for each of these technologies is also addressed.

Turbine Rotor Disk Health Monitoring Assessment Based on Sensor Technology and Spin Tests Data

The paper focuses on presenting data obtained from spin test experiments of a turbine engine like rotor disk and assessing their correlation to the development of a structural health monitoring and fault detection system. The data were obtained under various operating conditions such as the rotor disk being artificially induced with and without a notch and rotated at a rotational speed of up to 10,000 rpm under balanced and imbalanced state. The data collected included blade tip clearance, blade tip timing measurements, and shaft displacements. Two different sensor technologies were employed in the testing: microwave and capacitive sensors, respectively. The experimental tests were conducted at the NASA Glenn Research Center's Rotordynamics Laboratory using a high precision spin system. Disk flaw observations and related assessments from the collected data for both sensors are reported and discussed.

A Novel Signal Processing Technique for Separating Tonal and Broadband Noise Components from Counter-Rotating Open-Rotor Acoustic Data

Renewed interest in counter-rotating open-rotor technology for aircraft propulsion application has prompted the development of advanced diagnostic tools to enable improved design and improved acoustical performance of open rotors. In particular, the determination of tonal and broadband components of open-rotor noise spectra is essential for properly assessing the noise control parameters and for validating noise prediction codes. Techniques that have been successfully used for processing acoustic data from single rotors (fans, propellers, etc.) do not work well for counter-rotating open-rotor systems in that the tonal and broadband noise components cannot be separated from raw acoustic data properly, particularly when the two rotors are driven independently without synchronization. The need for a new signal processing tool for counter-rotating open rotors was thus envisioned and is presented in this work. The new technique has been verified to perform well against simulated data as well as real acoustic data available from scale-model open-rotor tests at NASA-Glenn Research Center. Based on the results, the applicability and limitations of the technique are discussed in the paper.

Active Piezoelectric Vibration Control of Subscale Composite Fan Blades

As part of the Fundamental Aeronautics program, researchers at NASA Glenn Research Center (GRC) are investigating new technologies supporting the development of lighter, quieter, and more efficient fans for turbomachinery applications. High performance fan blades designed to achieve such goals will be subjected to higher levels of aerodynamic excitations which could lead to more serious and complex vibration problems. Piezoelectric materials have been proposed as a means of decreasing engine blade vibration either through a passive damping scheme, or as part of an active vibration control system. For polymer matrix fiber composite blades, the piezoelectric elements could be embedded within the blade material, protecting the brittle piezoceramic material from the airflow and from debris. To investigate this idea, spin testing was performed on two General Electric Aviation (GE) subscale composite fan blades in the NASA GRC Dynamic Spin Rig Facility. The first bending mode (1B) was targeted for vibration control. Because these subscale blades are very thin, the piezoelectric material was surface-mounted on the blades. Three thin piezoelectric patches were applied to each blade—two actuator patches and one small sensor patch. These flexible macro-fiber-composite patches were placed in a location of high resonant strain for the 1B mode. The blades were tested up to 5000 rpm, with patches used as sensors, as excitation for the blade, and as part of open- and closed-loop vibration control. Results show that with a single actuator patch, active vibration control causes the damping ratio to increase from a baseline of 0.3% critical damping to about 1.0% damping at 0 rpm. As the rotor speed approaches 5000 rpm, the actively controlled blade damping ratio decreases to about 0.5% damping. This occurs primarily because of centrifugal blade stiffening, and can be observed by the decrease in the generalized electromechanical coupling with rotor speed.

Large Eddy Simulations of Film-Cooling Flows With a Micro-Ramp Vortex Generator

Large eddy simulations were performed to study the effect of a micro-ramp on an inclined turbulent jet interacting with a cross-flow in a film-cooling configuration. The micro-ramp vortex generator is placed downstream of the film-cooling jet. Changes in vortex structure and film-cooling effectiveness are evaluated. Coherent turbulent structures characteristic of a jet in a cross-flow are analyzed and the genesis of the counter-rotating vortex pair in the jet is discussed. Results are reported for two film-cooling configurations, where the primary difference is the way the jet inflow boundary conditions are prescribed. In the first configuration, the jet conditions are prescribed using a precursor simulation and in the second the jet is modeled using a plenum/pipe configuration. The latter configuration was designed based on previous wind tunnel experiments at NASA Glenn Research Center, and the present results are meant to supplement those experiments. It is found that the micro-ramp improves film-cooling effectiveness by generating near-wall counter-rotating vortices which help entrain coolant from the jet and transport it to the surface. The pair of vortices generated by the micro-ramp are of opposite sense to the vortex pair embedded in the jet.

NASA Glenn’s Contributions to Aircraft Engine Noise Research

This report reviews all engine noise research conducted at the NASA Glenn Research Center over the past 70 years. This report includes a historical perspective of the Center and the facilities used to conduct the research. Major noise research programs are highlighted to show their impact on industry and on the development of aircraft noise reduction technology. Noise reduction trends are discussed, and future aircraft concepts are presented. Since the 1960s, research results show that the average perceived noise level has been reduced by about 20 decibels (dB). Studies also show that, depending on the size of the airport, the aircraft fleet mix, and the actual growth in air travel, another 15 to 17 dB reduction will be required to achieve NASA's long-term goal of providing technologies to limit objectionable noise to the boundaries of an average airport.

Bioscience and Medical Technology: From the Earth to Space and Back

AbstractThroughout the 70-year history of NASA Glenn Research Center (GRC), technology development efforts that promoted advancement in aeronautics technologies, aerospace sciences, materials for hostile environments, and microgravity physics have also enabled the maturation of technologies that have affected medical practice on Earth, in the air, and in space. GRC’s unique skill mix, required for aeronautics research and space exploration, ultimately also advanced the development of a wide array of capabilities applicable to biomedical engineering. This paper presents a historical review of notable biomedical endeavors at GRC that have addressed common and uncommon medical conditions afflicting both astronauts and non-astronauts. It also highlights the unique physiological stressors associated with residing in space. The physiological changes associated with these stimuli present evolving challenges for researchers to devise new and innovative medical interventions and technologies.