New Concepts in Film Cooling for Turbine Blades
In one of NASA Glenn's innovations, a shaped recess can be formed on a surface associated with fluid flow. Often V-shaped, this shaped recess can be configured to create or induce fluid effects, temperature effects, or shedding effects. For example, the shaped recess can be paired (upstream or downstream) with a cooling channel. The configuration of the shaped recess can mitigate the lift-off or separation of the cooling jets that are produced by the cooling channels, thus keeping the cooling jets trained on turbine blades and enhancing the effectiveness of the film-cooling process. The second innovation produced to improve film cooling addresses problems that occur when high-blowing ratios, such as those that occur during transient operation, threaten to diminish cooling effectiveness by creating jet detachment. To keep the cooling jet attached to the turbine blade, and also to spread the jet in the spanwise direction, NASA Glenn inventors have successfully used cooling holes that reduce loss by blowing in the upstream direction. In addition, fences may be used upstream of the holes to bend the cooling flow back toward the downstream direction to further reduce mixing losses. These two innovations represent a significant leap forward in making film cooling for turbine blades, and therefore the operation of turbine engines, more efficient.
Turbofan Engine Acoustic Liner Design and Analysis Tools
The technologies address the reduction of fan noise in aircraft engines through two avenues: The first invention is a statistical approach to liner design when detailed fan source noise information is not available. This invention uses a statistical representation of the fan source with a duct acoustic propagation and radiation code to determine the optimum impedance spectra for acoustic liners embedded in the walls of the engine nacelle. This optimization may be based on predicted in-duct or far-field acoustic levels. Acoustic liner models are then used to identify geometric liner parameters needed to produce impedance spectra that most closely match these optimum spectra, and therefore provide maximum fan noise reduction. The simulated statistical fan source model accounts for the variation of the fans sound spectrum as the flight conditions change and provides the added benefit of generating confidence intervals for the predicted liner performance. Increased weighting may be applied to specific frequencies and/or operating conditions within the liner design. Thus, the entire broadband frequency spectrum may be targeted simultaneously. This can offer a major advantage over current liner design approaches that focus on narrow-band attenuation spectra (i.e., target individual fan tones) and are generally not broadband in character. The other invention is a graphical tool that allows real-time design and analysis of acoustic liners to achieve optimized broadband acoustic liners. Thus, it takes advantage of recently improved manufacturing techniques to allow implementation of liners in unconventional locations. One example is liners mounted in the body of fan exit guide vanes to reduce engine fan noise. Referred to as ILIAD, the software uses a point-and-click interface to graphically create acoustic chambers within a 2-D representation of the liner design space while predicting the resulting acoustic parameters. Variable-depth chambers are accommodated to maximize the number and length of chambers that can be put in the available space. At the same time, the software computes all of the modeling predictions of the acoustic characteristics to maintain performance levels. Designers will see the acoustic effects of geometry changes instantly. Although the prediction capability is relatively well-known, the ability to perform this calculation in an interactive design environment is new. ILIAD enables the exploration of numerous liner design possibilities quickly and efficiently.
Biologically Inspired Wing Flow Control
Applied to a typical aluminum airfoil on a fixed wing aircraft, the technology involves adding a flexible strip which can adjust itself to the air flow to obtain drag reduction. Alternatively, sensors and actuators can be used for feedback control to make adjustments to the strip to optimize drag reduction. Depending on specific applications, the strip could be of an aluminum plate, polymer membrane, composite sheet or smart material plate. The effects of SETE on the wing aerodynamics are mainly due to modifications of the airfoil camber and of the flow structure at the trailing edge. The resulting improvement in aerodynamic efficiency leads to greater fuel efficiency and vibration control. For small aircraft like unmanned aerial vehicles (UAVs), the device can prevent flow separation, which can lead to stalling. The cover photo shows the asymmetry of the flow field induced by SETE where wake is turned downward, indicating a deflected momentum stream tube and generation of additional lift. The wake structure is not appreciably altered indicating that the parasite drag is not significantly affected. Figure 2 is a CFD simulation at 6 degree deflection.
Scintillating Quantum Dots for Imaging X-rays (SQDIX) for Aircraft Inspection
The SQDIX system is an enabling technology that will have game-changing impacts across many fields including DoE, DoD, NASA, medical imaging fields, aircraft inspection and many other fields. StQDs are sensitive to x-ray radiation and emit visible photons that are tunable in wavelength. Development of this technology will greatly impact NASAs ability to use X-Rays as an inspection method. This directly addresses the Aviation Safety challenge in the 2010 National Aeronautics R&D Plan to monitor and assess the health of aircraft more efficiently and effectively as well as all NASA spaceflights beyond earths magnetic field.
Nested Focusing Optics for Compact Neutron Sources
Conventional neutron beam experiments demand high fluxes that can only be obtained at research facilities equipped with a reactor source and neutron optics. However, access to these facilities is limited. The NASA technology uses grazing incidence reflective optics to produce focused beams of neutrons (Figure 1) from compact commercially available sources, resulting in higher flux concentrations. Neutrons are doubly reflected off of a parabolic and hyperbolic mirror at a sufficiently small angle, creating neutron beams that are convergent, divergent, or parallel. Neutron flux can be increased by concentrically nesting mirrors with the same focal length and curvature, resulting in a convergence of multiple neutron beams at a single focal point. The improved flux from the compact source may be used for non-destructive testing, imaging, and materials analysis. The grazing incidence neutron optic mirrors are fabricated using an electroformed nickel replication technique developed by NASA and the Harvard-Smithsonian Center for Astrophysics (Figure 2). A machined aluminum mandrel is super-polished to a surface roughness of 3-4 angstroms root mean square and plated with layers of highly reflective nickel-cobalt alloy. Residual stresses that can cause mirror warping are eliminated by periodically reversing the anode and cathode polarity of the electroplating system, resulting in a deformation-free surface. The fabrication process has been used to produce 0.5 meter and 1.0 meter lenses.
materials and coatings
Hydrophobic Epoxy Coating for Insect Adhesion Mitigation
This technology is a copolymeric epoxy coating that is loaded with a fluorinated aliphatic chemical species and nano- to microscale particle fillers. The coating was developed as a hydrophobic and non-wetting coating for aerodynamic surfaces to prevent accumulation of insect strike remains that can lead to natural laminar flow disruption and aerodynamic inefficiencies. The coating achieves hydrophobicity in two ways. First, the fluorinated aliphatic chemical species are hydrophobic surface modification additives that preferentially migrate to the polymer surface that is exposed to air. Secondly, the incorporation of particle fillers produces a micro-textured surface that displays excellent resistance to wetting. Combined, these two factors increase hydrophobicity and can also be used to readily generate superhydrophobic surfaces.
materials and coatings
Chemical and Topographical Surface Modifications for Insect Adhesion Mitigation
The technology is a method of mitigating insect residue adhesion to various surfaces upon insect impact. The process involves topographical modification of the surface using laser ablation patterning followed by chemical modification or particulate inclusion in a polymeric matrix. Laser ablation patterning is performed by a commercially available laser system and the chemical spray deposition is composed of nanometer sized silica particles with a hydrophobic solution (e.g. heptadecafluoro-1,1,2,2-tetrahydrodecyltriethoxysilane) in an aqueous ethanol solution. Both topographic and chemical modification of the substrate is necessary to achieve the desired performance.
materials and coatings
Engineered Matrix Self-Healing Composites
When a ceramic matrix cracks, the crack often occurs at the interface between the fibers and the matrix. Glenn scientists have invented a method to fabricate engineered matrix composites (EMCs) using slurry casting and melt infiltration techniques. These EMCs are designed to match the coefficient of thermal expansion (CTE) of the SiC fiber. With this technique, the matrix is better able to withstand loading conditions at high temperatures, and any cracks that develop are prevented from spreading or deepening. This important feature, called "crack tip blunting", should allow the matrix to carry some load before transferring to the reinforcing SiC fibers, thereby increasing the durability of the composite. The other unique feature of this matrix is its ability to convert ingressed oxygen, which can lead to damaging oxidation of the fibers, to low-viscosity oxides. These oxides spread through capillary action and fill any fine cracks they encounter, thereby "self-healing" and protecting the fibers. The innovators at Glenn also modified the melt infiltration process so less free silicon remains after the process. Typically, the presence of free silicon limits the use of these composites to conditions under 2400°F, but composites made with this engineered matrix are designed to be used at or above 2700°F, further extending the possible properties and applications of this new design. This is an early-stage technology requiring additional development. Glenn welcomes co-development opportunities.
materials and coatings
Silicon Carbide (SiC) Fiber-Reinforced SiC Matrix Composites
Aimed at structural applications up to 2700°F, NASA's patented technologies start with two types of high-strength SiC fibers that significantly enhance the thermo-structural performance of the commercially available boron-doped and sintered small-diameter “Sylramic” SiC fiber. These enhancement processes can be done on single fibers, multi-fiber tows, or component-shaped architectural preforms without any loss in fiber strength. The processes not only enhance every fiber in the preforms and relieve their weaving stresses, but also allow the preforms to be made into more shapes. Environmental resistance is also enhanced during processing by the production of a protective in-situ grown boron-nitride (iBN) coating on the fibers. Thus the two types of converted fibers are called “Sylramic-iBN” and “Super Sylramic-iBN”. For high CMC toughness, two separate chemical vapor infiltration (CVI) steps are used, one to apply a boron nitride coating on the fibers of the preform and the other to form the SiC-based matrix. The preforms are then heat treated not only to densify and shrink the CVI BN coating away from the SiC matrix (outside debonding), but also to increase its creep resistance, temperature capability, and thermal conductivity. One crucial advantage in this suite of technologies lies in its unprecedented customizability. The SiC/SiC CMC can be tailored to specific conditions by down-selecting the optimum fiber, fiber coating, fiber architecture, and matrix materials and processes. In any formulation, though, the NASA-processed SiC fibers display high tensile strength and the best creep-rupture resistance of any commercial SiC fiber, with strength retention to over 2700°F.
mechanical and fluid systems
Lightweight, High-Strength Hybrid Gear
The use of composites in a rotorcraft drive system, with their low density and high strength, can improve power to weight ratio. NASA Glenn inventors have succeeded in reducing the weight of large-scale gears for rotorcraft and other applications, which are conventionally machined from forgings, by using composite material as the web of the gear between the gear teeth and a metallic hub. The hybrid gear has a metallic shaft and outer gear rim, with composite layup between the shaft interface and the gear tooth rim. The Hybrid Gear was built and tested at NASA Glenn and found to be 20% lighter than all-steel gears. In an endurance test consisting of over 300x10<sup>6</sup> gear revolutions at 10,000 RPM and 250 PSI torque load, the hybrid gear operated without problem and showed no fatigue in post-test inspection. Through the use of various composite materials and ply layups, this hybrid gear fabrication method can accommodate complex shapes. Hybrid gear designs can also be tailored to optimize mechanical and acoustic performance, while reducing noise and critical vibration modes.