FUNDAMENTAL STUDY AND DEVELOPMENT OF TUNED ACTIVE FLOW CONTROL ACTUATORS

A novel, multi-level, flow-control actuator was developed using piezoceramic materials. Several actuators were fabricated in various shapes and sizes to produce a variety of effects for flow control applications. The actuators were studied in a quiescent-air bench test to understand the vibrations produced by various actuator shapes. The actuator flow-control effect was studied experimentally with flat-plate and cavity configurations, and was studied numerically using moving boundary conditions and dynamic meshing. The disturbances produced by the actuator couple with the cavity flow field producing increased cavity tones, increased vorticity, and sustainment of large-scale vorticity downstream of the cavity. The combined actuation result, from perturbations upstream of the cavity to increased vorticity downstream of the cavity, is the novel multi-level actuator developed and studied in this research. The largest actuator was experimentally tested in boundary layers with free-stream Mach numbers from 0.1 to 0.5 and Reynolds numbers, based on momentum thickness, from approximately 800 to 3600. Actuator effects were measured using high-frequency-response pressure instrumentation in the floor downstream of the actuator. The actuator produced disturbances with amplitudes at least 30 dB above the noise floor and frequencies nine-times the actuator driving frequency. The disturbances created by the actuator coupled with the boundary layer flow and were observable up to 62 kHz. A time-dependent effect from changing actuation frequency was observed on the stability of the flow. A compact, multi-actuator pack was designed to study multi-level flow control using experimental tests of a two-dimensional cavity flow at Mach numbers of 0.1, 0.2, and 0.3. Actuator operation did not produce amplified cavity oscillations at all Rossiter tones in the experiments. However, significant flow coupling occurred when the actuator driving frequency matched a Rossiter tone and a fundamental cavity acoustic tone. The cavity amplifications were stronger when the distance between the actuator and the cavity leading edge was increased. The numerical simulations showed that the actuator produced cavity flow amplifications at the first Rossiter tone about 8 dB higher amplitude than without actuation

Rapid development of tornado-like vortices by simulated supercells

February 15, 2002.Also issued as author's dissertation (Ph.D.) -- Colorado State University, 2002.Includes bibliographical references.The Regional Atmospheric Modeling System (RAMS) is used to examine the evolution of low-level vorticity beneath a modeled supercell thunderstorm. The simulations are per­ formed using seven-species bulk microphysics in a horizontally-homogeneous domain, and are initialized through the use of a warm bubble. A mesocyclonic circulation becomes apparent a kilometer above the ground after 45 minutes of simulation time, and vertical vorticity of similar magnitude develops along the gust front near the surface by 55 minutes. A proximately five minutes later a transition occurs; the maximum vorticity beneath cloud base becomes vertically co-located, and translates with nearly constant grid-relative velocity. The vorticity increases by a factor of five during the five minutes following the co-location of the vorticity. An intense pressure deficit develops within the region of closed streamlines. It is shown that the concentration of vorticity is not dynamically forced by vertical pressure gradients or buoyancy, but occurs in a quasi-horizontal framework. The process is similar to models of non-supercell tomadogenesis in the literature that invoke the non-linear pooling of vorticity by barotropic processes, but with modification due to the presence of large-scale plane convergence. Specifically, the plane convergence allows the vorticity to concentrate at much faster time scales and without need of the coalescence of several discrete vorticity centers. The relevance to observed tomadic vortices and the implications for future modeling work are discussed.Sponsored by the National Science Foundation under grant ATM9900929

Proceedings, MSVSCC 2014

Proceedings of the 8th Annual Modeling, Simulation & Visualization Student Capstone Conference held on April 17, 2014 at VMASC in Suffolk, Virginia

Deep Model for Improved Operator Function State Assessment

A deep learning framework is presented for engagement assessment using EEG signals. Deep learning is a recently developed machine learning technique and has been applied to many applications. In this paper, we proposed a deep learning strategy for operator function state (OFS) assessment. Fifteen pilots participated in a flight simulation from Seattle to Chicago. During the four-hour simulation, EEG signals were recorded for each pilot. We labeled 20- minute data as engaged and disengaged to fine-tune the deep network and utilized the remaining vast amount of unlabeled data to initialize the network. The trained deep network was then used to assess if a pilot was engaged during the four-hour simulation

Terrestrial Environment (Climatic) Criteria Guidelines for Use in Aerospace Vehicle Development, 1993 Revision

Guidelines on terrestrial environment data specifically applicable in the development of design requirements/specifications for NASA aerospace vehicles and associated equipment development are provided. The primary geographic areas encompassed are the John F. Kennedy Space Center, FL; Vandenberg AFB, CA; Edwards AFB, CA; Michoud Assembly Facility, New Orleans, LA; John C. Stennis Space Center, MS; Lyndon B. Johnson Space Center, Houston, TX; and the White Sands Missile Range, NM. In addition, a section was included to provide information on the general distribution of natural environmental extremes in the conterminous United States that may be needed to specify design criteria in the transportation of space vehicle subsystems and components. A summary of climatic extremes for worldwide operational needs is also included. Although not considered as a specific vehicle design criterion, a section on atmospheric attenuation was added since sensors on certain Earth orbital experiment missions are influenced by the Earth's atmosphere. The latest available information on probable climatic extremes is presented and supersedes information presented in TM X-64589, TM X-64757, TM X-78118, and TM-82473. Information is included on atmospheric chemistry, seismic criteria, and on a mathematical model to predict atmospheric dispersion of aerospace engine exhaust cloud rise and growth. There is also a section on atmospheric cloud phenomena. The information is recommended for use in the development of aerospace vehicle and associated equipment design and operational criteria, unless otherwise stated in contract work specifications. The environmental data are primarily limited to information below 90 km

Holography and Optical Filtering

Holography and optical filtering techniques for structural analysis, material tests, and astronomical observation - conferenc

Acoustic Waves

The concept of acoustic wave is a pervasive one, which emerges in any type of medium, from solids to plasmas, at length and time scales ranging from sub-micrometric layers in microdevices to seismic waves in the Sun's interior. This book presents several aspects of the active research ongoing in this field. Theoretical efforts are leading to a deeper understanding of phenomena, also in complicated environments like the solar surface boundary. Acoustic waves are a flexible probe to investigate the properties of very different systems, from thin inorganic layers to ripening cheese to biological systems. Acoustic waves are also a tool to manipulate matter, from the delicate evaporation of biomolecules to be analysed, to the phase transitions induced by intense shock waves. And a whole class of widespread microdevices, including filters and sensors, is based on the behaviour of acoustic waves propagating in thin layers. The search for better performances is driving to new materials for these devices, and to more refined tools for their analysis

Index to NASA Tech Briefs, 1975

This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs