<p>BOND, RYAN BOMAR. A Conservative Interblock Communication Algorithmfor Dynamically Discontinuous Multiblock Interface Grids.(Under the direction of Dr. D. Scott McRae.)<p> An algorithm is presented for the conservative communication between gridblocks where point connectivity is not maintained across across theinterface. The algorithm is specifically designed for dynamicdiscontinuities, e.g. those that arise when dynamic r-refinementadaptation is performed on two adjacent blocks without the constraint ofboundary point connectivity. r-Refinement adaptation involves moving thepoints in the computational mesh to better resolve features in thesolution field. Discontinuously connected multiblock boundaries arenecessary for problems where adjacent blocks have significantly differentadaptation requirements or problems where one block is to be adapted whilean adjacent block is left stationary. In programs where adaptation isbeing performed in parallel, discontinuously connected multiblockboundaries allow the adaptation to continue on different processorswithout the need for communication and subsequent agreement of where theboundary points should be located.<p>The communication between two adjacent blocks must be conservative toallow the simulation of compressible flow problems. Simply interpolatingthe boundary data to transfer information from one block to the otherviolates conservation, so other means of transferring the information mustbe employed. A technique for generating ghost cells and setting theirdependent variable values is presented. The method is conservative,accurate, robust, and computationally efficient.<p>Tests of the algorithm on both statically and dynamically discontinuousgrids are presented, and the computational efficiency of the algorithm isdiscussed. The algorithm was tested using the diffusion equation, linearwave equation, and the set of Euler equations. Since the algorithm isapplicable to any CFD problem where conservative communication isnecessary between discontinuous blocks, it can be used when adaptationcriteria are different between adjacent blocks, when an adapted block isadjacent to an unadapted block, or when enhanced parallelism can beachieved by relaxing boundary point connectivity.<p><P>

<p>Price, Jennifer Lou. Unsteady Measurements and Computations on an Oscillating Airfoil with Gurney Flaps. (Under the direction of Dr. Ndaona Chokani)The effect of a Gurney flap on an unsteady airfoil flow is experimentally and computationally examined. In the experiment, the details of the unsteady boundary layer events on the forward portion of the airfoil are measured. In the computation, the features of the global unsteady flow are documented and correlated with the experimental observations.The experiments were conducted in the North Carolina State University subsonic wind tunnel on an oscillating airfoil at pitch rates of 65.45 degrees/sec and 130.9 degrees/sec. The airfoil has a NACA0012 cross-section and is equipped with a 1.5% or 2.5% chord Gurney flap. The airfoil is tested at Reynolds numbers of 96,000, 169,000 and 192,000 for attached and light dynamic stall conditions. An array of surface-mounted hot-film sensors on the forward 25% chord of the airfoil is used to measure the unsteady laminar boundary layer separation, transition-to-turbulence, and turbulent reattachment. In parallel with the experiments incompressible Navier-Stokes computations are conducted for the light dynamic stall conditions on the airfoil with a 2.5%c Gurney flap at a Reynolds number of 169,000.The experimental measurements show that the effect of the Gurney flap is to move the separation, transition and reattachment forward on the airfoil. This effect is more marked during the airfoil's pitch-down than during pitch-up. The computational results verify these observations, and also show that the shedding of the dynamic stall vortex is delayed. Thus the adverse effects of dynamic stall are mitigated by the Gurney flap.<P>

Commercial expansion beyond Earth orbit demands efficient, low cost and regular access to space that is not given by current launch systems. An alternative to rocketry has been proposed in the use of tethers as a method of in-space propulsion. One possible implementation of tether propulsion involves the use of a long, vertically oriented tether orbiting the Earth. A suborbital launch vehicle will deliver a payload to the tether’s lower tip, which will then be carried up its length by an elevator car to the upper tip, where the payload is released on a transfer orbit. The orbiting space elevator represents a reusable second stage of a launch system designed to place payloads in high Earth orbit or trans-lunar trajectories. This study investigates several dynamics problems encountered in an Earth orbiting tether propulsion system. In addition to calculating the structural requirements for the tether to safely bear the payload mass, several analytical estimation methods of the tether’s orbital response to loading have been developed and compared to previous studies. A detailed mathematical simulation of the tether’s orbital stability has been created, accounting for natural perturbations to the tether’s orbit. With the dynamic simulation of the elevator’s orbit, predictions of the total tether mass required to handle a payload with out degrading its orbit have been quantified. The performance required by the suborbital launch vehicle’s operation has also been examined. Minimum propellant trajectories to the elevator’s lower tip are found using a Hamiltonian based trajectory optimization routine. The launch vehicle maneuvering requirements needed for rendezvous with the orbiting elevator have also been explored. The margins of performance needed for a launch vehicle to deliver a payload to the elevator lower tip have been calculated to be roughly equivalent to a single stage to orbit mission profile. The usefulness of the tether within the context of a trans-lunar transportation system has also been investigated. It has been shown that elevator-based transit to the Moon offers significant savings in Δv over a traditional rocket-based transportation scheme.

This research is an analytical investigation of wave interactions in a simulated liquid rocket engine with uniform injection imposed at the faceplate. Of significant interest are the secondary nonlinear flows, particularly acoustic streaming, induced by transverse wave impingement over the engine injector surface. The corresponding cylindrical chamber has a small length-to-diameter ratio with respect to solid and hybrid rockets. Given their low chamber aspect ratios, liquid thrust engines are known to experience severe tangential and radial oscillation modes more often than longitudinal ones. Experimental evidence demonstrates the production of large peak-to-trough amplitude flow oscillations along with the development of a strong central vortex structure in many unstable liquid engines. These phenomena are accompanied by elevated heat transfer to the injector faceplates, strong roll torques and chamber over pressurization. In order to model this behavior, tangential and radial waves are superimposed onto a basic mean-flow model that consists of a steady, uniform axial velocity throughout the chamber. Considerable effort is given to correctly satisfy the no-slip condition at the chamber’s injector face. The viscous boundary layer used to satisfy the no-slip condition is the location at which acoustic streaming develops. Sidewall boundary layers that develop at the lateral wall are not considered, being inconsequential to the flow in the vicinity of the headwall. Using perturbation tools, both potential and viscous flow equations are linearized in the pressure wave amplitude and solved to the second order. The effects of the headwall Mach number are leveraged as well. While the potential flow analysis does not predict any acoustic streaming effects, the viscous solution carried out to the second-order approximation gives rise to steady secondary flow patterns near the headwall. These axisymmetric, steady contributions to the tangential and radial traveling waves are induced by the convective flow motion through interactions with inertial and viscous forces. Suppressing either the convective terms or viscosity at the headwall can lead to spurious solutions that are free from streaming. In the present research, streaming is initiated at the headwall, within the boundary layer, and extends throughout the chamber. The study suggests that nonlinear streaming effects of tangential and radial waves inside a cylinder with headwall injection act to alter the outer solution. As a result of streaming, the radial wave velocities are intensified in one half of the domain and reduced in the opposite half at any instant of time. Similarly, the tangential wave velocities are either enhanced or weakened in two opposing sectors that are at a 90 degree angle to the radial velocity counterparts. The second-order viscous solution that is obtained clearly displays both an oscillating and a steady flow component. It is found that the steady contribution due to streaming can potentially promote the development of large amplitude steepened wave forms. The delineation of this mechanism is crucial for the advancement of analytical tools employed in the prediction of combustion instability. In the present study, streaming is examined in the context of traveling transverse waves. Extending the analysis to standing wave motion is carried out and reported in a straightforward fashion.

This paper is an investigation into the laminar separation bubble that frequently plagues airborne vehicles operating in the low Reynolds number regime – experimentally found to be typically present in flows with Reynolds numbers below 106 (Lissaman 1983). The specific application driving the present investigation is the fixed wing performance of unmanned micro air vehicles (MAVs), defined by their maximum chord length of 6 inches and current cruising speeds of 10-20 meters per second (Mueller 2001). A basic generic model was chosen for this investigation: a circular arc (section of 16 inch diameter PVC pipe) with sharp leading and trailing edges having a chord length of 9.3 inches and height of 1.5 inches. This airfoil model was tested in the UTSI water tunnel at Reynolds numbers of 27,000 and 45,000. The goal of this study was to gain some insight into the boundary layer behaviour through the use of dye injection for flow visualization and hot film anemometry for quantitative velocity measurements. Small diameter cylinders were then statically placed upstream of the model to determine their interaction with the laminar separation bubble and its effects on the boundary layer downstream over the airfoil model. The length and height of the laminar separation bubble was found to be impacted with a small cylindrical wire placed upstream at all Reynolds numbers and angles of attack with the exception of an 18 degree angle of attack at the higher Reynolds number. However, these changes did not result in a substantial or distinguishable improvement in the downstream separation point. The laminar separation bubble was found to be nearly or completely eliminated when a thermocouple wire was placed upstream of the leading edge. Although the elimination of the bubble would result in only a minor decrease in drag and increase in lift, there would be a possible improvement in the stability of the leading edge stall and possible reduction or elimination in the hysteresis associated with stall.

The United States Marine Corps contracted Bell Helicopter Textron Inc. (BHTI) to develop and field new versions of the aging UH-1N and AH-1W helicopters. As part of the development effort of the H-1 Upgrades, BHTI was tasked with development of a folding rotor system and the associated equipment necessary to support main rotor folding operations. The blade fold equipment (BFE) was constrained throughout the development process by a list of conflicting requirements. The requirements for commonality, versatility, simplicity, light weight, rapid application, and durability, while each was generally reasonable, could not be satisfied with one set of equipment. The resulting BFE was ineffective for everyday use. The purpose of this thesis was to evaluate the design requirements of the BFE, specifically the blade fold racks. An investigation of the source of requirements was conducted, followed by interviews with system experts and end users. Additional data were gathered during the program-sponsored test events from January through May 2005. In order to develop a suitable and effective set of BFE, the H-1 Upgrades program should reduce the set of design requirements on the new blade fold racks, specifically: 1. Modify the H-1 Upgrades aircraft to incorporate an automatic folding rotor system or a blade indexing motor. 2. Redesign the blade fold racks for a reduced set of configurations and load conditions. 3. Consider a simple, one piece, clamping blade fold rack.

The P-3C is a U.S. Navy aircraft designed for the Maritime Patrol and Reconnaissance mission. Although capable in a number of mission areas, the aircraft’s Anti-Submarine Warfare capabilities have received much attention lately due to improvements in diesel submarine technology. The acoustic systems on the P-3C needed a better way to more rapidly incorporate new technology while working within a constrained budget environment. The purpose of this study is to show how the P-3C Acoustic System can be transformed by shifting from the slow, expensive traditional Military Specification (MILSPEC) development process to the successful Acoustic Rapid Commercial-Off-The-Shelf (COTS) Insertion (ARCI) process developed for the submarine community. This paper, authored by the Deputy Program Manager for P-3C Acoustic Systems, describes the requirements of the airborne ASW mission and provide the history and architecture of the current acoustic system. It then shows how the constraints of the Department of Defense Acquisition policies present challenges to the incorporation of the latest COTS components, and outline the advantages and disadvantages of using these components. Using the submarine ARCI Program framework, this paper shows that an Air ARCI program can be made to work with the P-3C acoustic system through the use of Abbreviated Acquisition Programs and periodic technological refreshes to the system. These periodic updates using less expensive COTS components will be combined with an open architecture to ease the incorporation of new software and hardware from across all platforms. This will allow the system to remain up to date while significantly reducing development costs, weight, power, volume, and cooling requirements. There are risks inherent in using COTS components that must be managed through the use of comprehensive system-level testing, adherence to schedule and a stabilized funding stream. There must also be a plan in place to manage component End of Life issues and the effects of vendor-initiated hardware revisions. Finally, given the heavy operational use of the aircraft around the world, the use of test assets and Fleet aircraft installations must be balanced with operational needs to provide the best combination of technological currency, cost, configuration management, and supportability and spares reduction.

Subsonic cavity flow tests of an L/D = 3.5 cavity, with three different diameter rods in crossflow, 1/8", 3/16", and 1/4", were conducted using the High Speed Wind Tunnel in the University of Tennessee Space Institute’s Gas Dynamic Laboratory. The average Mach number flow over the duration of the four phase testing sequence was 0.52, with a unit Reynolds number of 13.8 x 106. With the use of a dynamic pressure transducer and a laser PIV system, Spectral and Flow Visualization data was collected with aim of investigating the effect of the rods in crossflow on cavity flow. However, for reasons beyond the control of this investigation, a converging-diverging supersonic nozzle was used in place of a subsonic nozzle. As a result, the separated, or near separated, flow on the diverging side of the nozzle created a region of low kinetic energy flow approximately 5 mm above the floor of the tunnel test section. Despite the presence of this undesirable feature, the Baseline cavity, without a rod in crossflow, was found to resonate at 1413 Hz and produced an average peak amplitude tone of 148.7 dB SPL. The effect of placing different diameter rods in the crossflow was to reduce the amount, and intensity, of shear layer interactions, by helping to loft the flow over the trailing edge of the cavity. The best results were achieved with a 1/4" diameter rod, which, on average, provided 15.1 dB SPL of acoustic suppression. It was concluded that the suppression observed in this particular experiment was the result of blockage and lofting effects, which helped the shear layer to span the length of the cavity and reduce the intensity of the shear layer interactions at the trailing edge.

Digitization of physical parameters for the display and recording by computers is the essential aspect of any airborne data acquisition system. The objective of this thesis was to develop a data acquisition system for General Aviation research and certification flight testing based on a low-cost Commercial Off-The- Shelf (COTS) hardware, in particular, a common glass cockpit system for experimental aircraft. A kneeboard computer was used to monitor data communications between the various devices of the Grand Rapids Technology (GRT) Electronic Flight Information System (EFIS). The monitored data was then displayed for use in-flight, and recorded aboard the aircraft for post-flight data reduction. The developed system and software was tested in simulation on virtual and actual hardware, on an Extra 300 in ground testing, and in flight. An in flight air-data calibration and several common stability and control certification test points were flown to evaluate and demonstrate the usefulness of the system. Special consideration was paid to work flow prior to, during, and after the flight with the overall goal of reducing the time required for data reduction. The output of this research work includes software for decoding data files logged on one common low-cost EFIS, software for monitoring, displaying, and recording EFIS data on a kneeboard computer in-flight, and tools for managing and viewing data files after the flight. From this research work, it is concluded that commercially available EFIS systems do in fact provide a core data set which is useful in flight research and flight test certification programs. The 15 Hz sampling rate of the GRT system was more than sufficient for all the test points evaluated as a part of this research. The cost of the tested hardware was less than $10,000 at current pricing (2009). The resultant system is compact, adds little weight to a test aircraft, has few interfaces to aircraft systems, and allows for future growth and the incorporation of new sensor types and interfaces. The addition of a flight test air-data boom with angle of attack and sideslip vanes and control position and force sensors would create a very complete data acquisition package without the expense of purpose designed hardware.

A performance analysis for skip and glide is being studied to investigate the potential usage of waverider technology for interplanetary explorations. While the skip and glide equations themselves were first explored by Eggers, this thesis will implement his equations, but then add waverider technology, to determine the possibility of using trajectory assist to navigate around four planets (Earth, Mars, Jupiter and Venus). All trajectory calculations will be based on the waverider lift-to-drag ratios for various planets to determine the maximum range distance. For this research, skip and glide trajectory will be handled separately to determine which is best suited in covering the most distance for a given planet. Ballistic trajectory will only be mentioned in reference to the derivation of the skip trajectory equation, but will not be covered by itself in this research. Hence, it is possible to study a total of 98 cases of skip trajectories, 12 cases of glide trajectories and any additional cases for the four planets. Even though the skip and glide equations bear no planetary effect, all results listed in this research are based on Earth with a waverider lift-to-drag (L/D) ratio of 8.61. For a skip trajectory, the maximum number of skips is set to be 3. A high velocity ratio of 1.0 results in a low incidence angle of 0.1° with the highest range parameter of 3.52 after 3 skips. A low velocity ratio of 0.2, on the other hand, would result in a high incidence of angle of 39.5° with the least range parameter coverage of 0.05. lying the same velocity ratio and lift-to-drag to both skip and glide trajectory calculations result in a big percent difference. For example, a L/D = 8.61 and a velocity ratio (Vf) of 1.0 will have a skip range parameter of 3.52 (22,451.09 km) after 3 skips. The glide range parameter, on the other hand, comes out to be 20.60 (131,389.89 km). The percent increase turns out to be around 485.23%. Based on these numbers, it is clear that using a glide trajectory by itself would gain the most range distance for Earth.