Experimental Investigation of Supercooled Water Droplet Breakup near the Leading Edge of an Airfoil

This paper presents the results of an experimental study on supercooled droplet deformation and breakup near the leading edge of an airfoil. The results are compared to prior room-temperature droplet deformation results to explore the effects of droplet supercooling. The experiments were conducted in the Adverse Environment Rotor Test Stand at The Pennsylvania State University. An airfoil model placed at the end of the rotor blades mounted onto the hub in the Adverse Environment Rotor Test Stand chamber was moved at speeds ranging between 50 and 80 ms. The temperature of the chamber was 20C. A monotonic droplet generator was used to produce droplets that fell perpendicular to the airfoil path. High-speed imaging was employed to observe the interaction between the droplets and the airfoil. Cases with equal slip and initial velocity were selected for the two environmental conditions. The airfoil velocity was 60 ms, and the slip velocity for both sets of data was 40 ms. The deformation of the weakly supercooled and warm droplets did not present different trends. The similar behavior for both conditions indicates that water supercooling has no effect on particle deformation for the range of supercooling of the droplets tested and the selected impact velocity

Establishing a Ballistic Test Methodology for Documenting the Containment Capability of Small Gas Turbine Engine Compressors

A test methodology currently employed for large engines was extended to quantify the ballistic containment capability of a small turboshaft engine compressor case. The approach involved impacting the inside of a compressor case with a compressor blade. A gas gun propelled the blade into the case at energy levels representative of failed compressor blades. The test target was a full compressor case. The aft flange was rigidly attached to a test stand and the forward flange was attached to a main frame to provide accurate boundary conditions. A window machined in the case allowed the projectile to pass through and impact the case wall from the inside with the orientation, direction and speed that would occur in a blade-out event. High-peed, digital-video cameras provided accurate velocity and orientation data. Calibrated cameras and digital image correlation software generated full field displacement and strain information at the back side of the impact point

Fragment Size Distribution for Ice Particle Impacts on a Glass Plate

This work presents the results of an experimental study of ice particle impacts on a flat glass plate. The experiment was conducted at the Ballistics Impact Laboratory of NASA Glenn Research Center. The main objective of the experiment was to gain understanding about the modifications needed to the experimental configuration for a future parametric study at a larger range of values for particle diameters and other parameters. This was achieved by studying the effect of the velocity of an impacting ice particle on the post-impact fragment size and distribution for a reduced range of impacting particle diameters. Pre-impact particle diameter and velocity data were captured with a high-speed side camera. Post-impact fragment data were captured in a single frame with a 29-megapixel camera located above and normal to the target. Repeat runs were conducted for ice particles with diameters ranging from 1.7 to 2.9 millimeters, impacting at velocities between 39 and 98 meters per second. The fragment areas were measured, and the corresponding equivalent diameters and histogram distributions were calculated. Analysis of the data showed that the average equivalent diameter for the fragments in a run was an order of magnitude smaller than the diameter of the impacting ice particle. The histograms for equivalent diameter distribution were nonnormal with long tails, with most of the fragments having equivalent diameters concentrated toward the minimum value of the fragment size that could be resolved. Factors affecting the accuracy of the data during the digital imaging analysis were identified. Needed modifications to the setup to handle small size ice particles and other testing conditions were also identified

Improvements in High Speed, High Resolution Dynamic Digital Image Correlation for Experimental Evaluation of Composite Drive System Components

Composite materials have the potential to reduce the weight of rotating drive system components. However, these components are more complex to design and evaluate than static structural components in part because of limited ability to acquire deformation and failure initiation data during dynamic tests. Digital image correlation (DIC) methods have been developed to provide precise measurements of deformation and failure initiation for material test coupons and for structures under quasi-static loading. Attempts to use the same methods for rotating components (presented at the AHS International 68th Annual Forum in 2012) are limited by high speed camera resolution, image blur, and heating of the structure by high intensity lighting. Several improvements have been made to the system resulting in higher spatial resolution, decreased image noise, and elimination of heating effects. These improvements include the use of a high intensity synchronous microsecond pulsed LED lighting system, different lenses, and changes in camera configuration. With these improvements, deformation measurements can be made during rotating component tests with resolution comparable to that which can be achieved in static test

High Speed Thermal Imaging on Ballistic Impact of Triaxially Braided Composites

Ballistic impact experiments were performed on triaxially braided polymer matrix composites to study the heat generated in the material due to projectile velocity and penetration damage. Quantifying the heat generation phenomenon is crucial for attaining a better understanding of composite behavior and failure under impact loading. The knowledge gained can also be used to improve physics-based models which can numerically simulate impact of composites. Triaxially braided (0/+60/-60) composite panels were manufactured with T700S standard modulus carbon fiber and two epoxy resins. The PR520 (toughened) and 3502 (untoughened) resin systems were used to make different panels to study the effects of resin properties on temperature rise. Ballistic impact tests were conducted on these composite panels using a gas gun, and different projectile velocities were applied to study the effect on the temperature results. Temperature contours were obtained from the rear surface of the panel during the test through a high speed, infrared (IR) thermal imaging system. The contours show that high temperatures were locally generated and more pronounced along the axial tows for the T700S/PR520 composite specimens; whereas, tests performed on T700S/3502 composite panels using similar impact velocities demonstrated a widespread area of lower temperature rises. Nondestructive, ultrasonic C-scan analyses were performed to observe and verify the failure patterns in the impacted panels. Overall, the impact experimentation showed temperatures exceeding 525 K (485degF) in both composites which is well above the respective glass transition temperatures for the polymer constituents. This expresses the need for further high strain rate testing and measurement of the temperature and deformation fields to fully understand the complex behavior and failure of the material in order to improve the confidence in designing aerospace components with these materials

Mechanism of Supercooled Water Droplet Breakup near the Leading Edge of an Airfoil

This work presents the results of an experimental study on supercooled droplet deformation and breakup near the leading edge of an airfoil. The results are compared to prior room temperature droplet deformation results to explore the effects of droplet supercooling. The experiments were conducted in the Adverse Environment Rotor Test Stand (AERTS) at The Pennsylvania State University. An airfoil model placed at the end of the rotor blades mounted onto the hub in the AERTS chamber was moved at speeds ranging between 50 and 80 m/sec. The temperature of the chamber was set at -20C. A monotonic droplet generator was used to produce droplets that fell from above, perpendicular to the path of the airfoil. The supercooled state of the droplets was determined by measurement of the temperature of the drops at various locations below the droplet generator exit. A temperature prediction code was also used to estimate the temperature of the droplets based on vertical velocity and the distance traveled by droplets from the droplet generator to the airfoil stagnation line. High speed imaging was employed to observe the interaction between the droplets and the airfoil. The high speed imaging provided droplet deformation information as the droplet approached the airfoil near the stagnation line. A tracking software program was used to measure the horizontal and vertical displacement of the droplet against time. It was demonstrated that to compare the effects of water supercooling on droplet deformation, the ratio of the slip velocity and the initial droplet velocity must be equal. A case with equal slip velocity to initial velocity ratios was selected for room temperature and supercooled droplet conditions. The airfoil velocity was 60 m/s and the slip velocity for both sets of data was 40 m/s. In these cases, the deformation of the weakly supercooled and warm droplets did not present different trends. The similar behavior for both environmental conditions indicates that water supercooling has no effect on particle deformation for the limited range of the weak supercooling of the droplets tested and the selected impact velocity. The assumption of a constant surface tension value was further supported by the equal trend of the Bond number obtained for supercooled and room temperature droplets

Electric Motor Noise from Small Quadcopters

The increased interest in electric motors for propulsion systems has driven interest in quantifying the contribution of electric motor noise to the overall sound levels and possible human annoyance of the propulsion system. This work presents acoustic measurements of electric motors used for small quadcopters to quantify the sound produced by a number of outrunning motors with different types of controllers. Results are presented for loaded and unloaded motors as installed and uninstalled configurations. Motor resonance frequencies were measured and computed. Current probe measurements showed that the supply current from the controllers contained significant harmonic content for the conventional and sinewave controllers. Acoustic results showed motor noise is typically radiated at frequencies near the mode 2 vibration frequency at roughly 5000 Hz. Electric motor noise was evident in the spectra produced by many of the motor-controller combinations for motors loaded with propellers with levels often greater than those for the motor alone due to increase in the stator magnetic flux density with increased current. An installed configuration produced increases in acoustic radiation over that of the uninstalled motor in a frequency range near the mode 1 vibration frequency near 1200 Hz. A companion paper (Part I - Acoustic Measurements), focuses on source identification using a phased array and directivity characteristics for a baseline configuration

Impact Testing of Aluminum 2024 and Titanium 6Al-4V for Material Model Development

One of the difficulties with developing and verifying accurate impact models is that parameters such as high strain rate material properties, failure modes, static properties, and impact test measurements are often obtained from a variety of different sources using different materials, with little control over consistency among the different sources. In addition there is often a lack of quantitative measurements in impact tests to which the models can be compared. To alleviate some of these problems, a project is underway to develop a consistent set of material property, impact test data and failure analysis for a variety of aircraft materials that can be used to develop improved impact failure and deformation models. This project is jointly funded by the NASA Glenn Research Center and the FAA William J. Hughes Technical Center. Unique features of this set of data are that all material property data and impact test data are obtained using identical material, the test methods and procedures are extensively documented and all of the raw data is available. Four parallel efforts are currently underway: Measurement of material deformation and failure response over a wide range of strain rates and temperatures and failure analysis of material property specimens and impact test articles conducted by The Ohio State University; development of improved numerical modeling techniques for deformation and failure conducted by The George Washington University; impact testing of flat panels and substructures conducted by NASA Glenn Research Center. This report describes impact testing which has been done on aluminum (Al) 2024 and titanium (Ti) 6Al-4vanadium (V) sheet and plate samples of different thicknesses and with different types of projectiles, one a regular cylinder and one with a more complex geometry incorporating features representative of a jet engine fan blade. Data from this testing will be used in validating material models developed under this program. The material tests and the material models developed in this program will be published in separate reports

Photogrammetry Measurements During a Tanking Test on the Space Shuttle External Tank, ET-137

On November 5, 2010, a significant foam liberation threat was observed as the Space Shuttle STS-133 launch effort was scrubbed because of a hydrogen leak at the ground umbilical carrier plate. Further investigation revealed the presence of multiple cracks at the tops of stringers in the intertank region of the Space Shuttle External Tank. As part of an instrumented tanking test conducted on December 17, 2010, a three dimensional digital image correlation photogrammetry system was used to measure radial deflections and overall deformations of a section of the intertank region. This paper will describe the experimental challenges that were overcome in order to implement the photogrammetry measurements for the tanking test in support of STS-133. The technique consisted of configuring and installing two pairs of custom stereo camera bars containing calibrated cameras on the 215-ft level of the fixed service structure of Launch Pad 39-A. The cameras were remotely operated from the Launch Control Center 3.5 miles away during the 8 hour duration test, which began before sunrise and lasted through sunset. The complete deformation time history was successfully computed from the acquired images and would prove to play a crucial role in the computer modeling validation efforts supporting the successful completion of the root cause analysis of the cracked stringer problem by the Space Shuttle Program. The resulting data generated included full field fringe plots, data extraction time history analysis, section line spatial analyses and differential stringer peak ]valley motion. Some of the sample results are included with discussion. The resulting data showed that new stringer crack formation did not occur for the panel examined, and that large amounts of displacement in the external tank occurred because of the loads derived from its filling. The measurements acquired were also used to validate computer modeling efforts completed by NASA Marshall Space Flight Center (MSFC)

Experimental Techniques for Evaluating the Effects of Aging on Impact and High Strain Rate Properties of Triaxial Braided Composite Materials

An experimental program is underway to measure the impact and high strain rate properties of triaxial braided composite materials and to quantify any degradation in properties as a result of thermal and hygroscopic aging typically encountered during service. Impact tests are being conducted on flat panels using a projectile designed to induce high rate deformation similar to that experienced in a jet engine fan case during a fan blade-out event. The tests are being conducted on as-fabricated panels and panels subjected to various numbers of aging cycles. High strain rate properties are being measured using a unique Hopkinson bar apparatus that has a larger diameter than conventional Hopkinson bars. This larger diameter is needed to measure representative material properties because of the large unit cell size of the materials examined in this work. In this paper the experimental techniques used for impact and high strain rate testing are described and some preliminary results are presented for both as-fabricated and aged composites