Twenty-five years of aerodynamic research with IR imaging: A survey

Infrared imaging used in aerodynamic research evolved during the last 25 years into a rewarding experimental technique for investigation of body-flow viscous interactions, such as heat flux determination and boundary layer transition. The technique of infrared imaging matched well its capability to produce useful results, with the expansion of testing conditions in the entire spectrum of wind tunnels, from hypersonic high-enthalpy facilities to cryogenic transonic wind tunnels. With unique achievements credited to its past, the current trend suggests a change in attitude towards this technique: from the perception as an exotic, project-oriented tool, to the status of a routine experimental procedure

Low Speed Flowfield Characterization by Infrared Measurements of Surface Temperatures

An experimental program was aimed at identifying areas in low speed aerodynamic research where infrared imaging systems can make significant contributions. Implementing a new technique, a long electrically heated wire was placed across a laminar jet. By measuring the temperature distribution along the wire with the IR imaging camera, the flow behavior was identified. Furthermore, using Nusselt number correlations, the velocity distribution could be deduced. The same approach was used to survey wakes behind cylinders in a wind-tunnel. This method is suited to investigate flows with position dependent velocities, e.g., boundary layers, confined flows, jets, wakes and shear layers. It was found that the IR imaging camera cannot accurately track high gradient temperature fields. A correction procedure was devised to account for this limitation. Other wind-tunnel experiments included tracking the development of the laminar boundary layer over a warmed flat plate by measuring the chordwise temperature distribution. This technique was applied also to the flow downstream from a rearward facing step. Finally, the IR imaging system was used to study boundary layer behavior over an airfoil at angles of attack from zero up to separation. The results were confirmed with tufts observable both visually and with the IR imaging camera

Battery Centric Serial Hybrid Aircraft Performance and Design Space

The design space and flight envelope of a battery centric serial hybrid aircraft has been analytically derived. The formulation assumes cruising flight only and all energy available is used. The flight envelope can be generated for any conventional propeller driven serial hybrid aircraft. The advantageous combination of an electric motor and controllable-pitch electric propeller was also explored. The results are used to be able to control efficiency and noise at constant thrust and therefore constant airspeed. Manufacturer provided electric motor and propeller data is used for efficiency purposes. Since the electric motor is virtually silent compared to the propeller, published noise evaluation methods are used to estimate the noise footprint of the propeller. Serial hybrid aircraft are appealing for their expansion of the flight envelope compared to fully electric aircraft and for their potential to operate where gasoline engines alone cannot. A serial hybrid configuration also allows for a controlled efficiency output and noise footprint to be able to either reduce emissions and cost or mitigate noise over noise sensitive areas. While a fully electric aircraft can achieve the efficiency and noise solutions, the serial hybrid solution offers considerably better range and endurance, making it viable for longer haul flights at higher airspeeds

Haunted Stories, Haunted Selves: Ghosts in Latin American Jewish Literature

This study approaches haunting in Latin American Jewish Literature from the 1990s through the 2010s as it appears in works by and featuring the descendants of Jewish immigrants. In these decades, this trope is frequently invoked as both a literary metaphor and a critical lens. It arises from and activates a number of themes common in trauma studies and in postmodernism, such as loss, the transmission of memory, our relationships to the past, the rupturing of traditional realities and questions of what can be known and represented. It is particularly prevalent amongst those who pen and protagonize the works examined due both to their historical and identitary positions. They are the children and grandchildren of Jewish immigrants to Latin America, inheritors of traumatic memory, and, as Jews and as thinkers in the era of postmodernism, people with particular relationships to time, history and identity. This study separates haunting by modes of encounter, looking at its figuration into ghosts, its power in haunted places and its embodiment in ghostly objects. By parsing this trope from numerous perspectives, this study examines how the motifs conjured in and by the ghostly link to the construction of identities, how these are inscribed within a larger context of group and nation, and how haunting creates ground for new modes of encountering and relating realities

From primal sketches to the recovery of intensity and reflectance representations

A local change in intensity (edge) is a characteristic that is preserved when an image is filtered through a bandpass filter. Primal sketch representations of images, using the bandpass-filtered data, have become a common process since Marr proposed his model for early human vision. Here, researchers move beyond the primal sketch extraction to the recovery of intensity and reflectance representations using only the bandpass-filtered data. Assessing the response of an ideal step edge to the Laplacian of Gaussian (NAb/A squared G) filter, they found that the resulting filtered data preserves the original change of intensity that created the edge in addition to the edge location. Using the filtered data, they can construct the primal sketches and recover the original (relative) intensity levels between the boundaries. It was found that the result of filtering an ideal step edge with the Intensity-Dependent Spatial Summation (IDS) filter preserves the actual intensity on both sides of the edge, in addition to the edge location. The IDS filter also preserves the reflectance ratio at the edge location. Therefore, one can recover the intensity levels between the edge boundaries as well as the (relative) reflectance representation. The recovery of the reflectance representation is of special interest as it erases shadowing degradations and other dependencies on temporal illumination. This method offers a new approach to low-level vision processing as well as to high data-compression coding. High compression can be gained by transmitting only the information associated with the edge location (edge primitives) that is necessary for the recover

Do Parents Matter? Effects of Lender Affiliation Through the Mortgage Boom and Bust

It is widely acknowledged that the 2007 mortgage crisis was preceded by a broad deterioration in underwriting diligence. This paper shows that this deterioration varied by the industry affiliation of mortgage lenders. Loans issued by homebuilders and stand-alone lenders were significantly less likely to default than loans issued by depository banks and affiliates of major financial institutions. I argue that homebuilders and stand-alone lenders had the least financial capacity to hold mortgages, and their resulting need to sell loans quickly on the secondary market forced them to issue safer loans. Tests of other explanations, including differences in information and incentives to avoid foreclosure externalities, receive little support. This study highlights a novel means by which firm boundaries influence firm adaptation to changing market conditions by defining the boundaries of the internal capital markets and hence the relative constraints of constituent units

A concept for transition mapping on a 10 deg-cone in the National Transonic Facility using flow-pressure variation

A conceptual study was performed to define a technique for mapping the boundary-layer transition on a 10 deg-Cone in the National Transonic Facility (NTF) as a means of determining this cryogenic-tunnel suitability for laminar flow testing. A major challenge was to devise a test matrix using a fixed surface pitot probe, varying the flow pressure to pr oduce the actual Reynolds numbers for boundary-layer transition. This constraint resulted from a lack of a suitable and reliable electrical motor to drive the probe along the cone's surface under cryogenic flow conditions. The initial phase of this research was performed by the author in collaboration with the late Dr. William B. Igoe from the Aerodynamics Division at NASA Langley Research Center. His comments made during the drafting of this document were invaluable and a source of inspiration

Stereo-Video Data Reduction of Wake Vortices and Trailing Aircrafts

This report presents stereo image theory and the corresponding image processing software developed to analyze stereo imaging data acquired for the wake-vortex hazard flight experiment conducted at NASA Langley Research Center. In this experiment, a leading Lockheed C-130 was equipped with wing-tip smokers to visualize its wing vortices, while a trailing Boeing 737 flew into the wake vortices of the leading airplane. A Rockwell OV-10A airplane, fitted with video cameras under its wings, flew at 400 to 1000 feet above and parallel to the wakes, and photographed the wake interception process for the purpose of determining the three-dimensional location of the trailing aircraft relative to the wake. The report establishes the image-processing tools developed to analyze the video flight-test data, identifies sources of potential inaccuracies, and assesses the quality of the resultant set of stereo data reduction