Brian Argrow

BULK VISCOSITY: PAST TO PRESENT

A review of the concept of a bulk viscosity coefficient β is presented, involving a discussion of theoretical approaches and a summary of existing experimental data. Two independent viscosity coefficients μ and A are obtained in the viscous stress tensor as a result of the isotropic Newtonian assumption. Hence, all solutions of the Navier-Stokes equations must make an assumption regarding the functional form of A. With β=λ+2/3μ by definition, the assumption is often arbitrarily made that the two viscosity coefficients are not independent, with β =0. This assumption has been shown to be valid only for dilute monatomic gases and is equivalent to stating that dilatational flowfield effects are not significant. Theoretical approaches for quantifying β are classified according to whether the subject fluid is dilute or dense. Experimental methods used to estimate bulk viscosity are described. Existing experimental data are summarized for each fluid classification, and issues related to using these data for dilatational flows in local thermodynamic equilibrium are addressed

Application of Bethe-Zel'dovich-Thompson Fluids in Organic Rankine Cycle Engines

Thenovel concept ofimproving organicRankinecycleengines (ORCEs)by exploiting the unusual e uid dynamic behaviorofaspecialclassofworkinge uidsknownasBethe ‐Zel’dovich‐Thompson(BZT)e uidsisexplored.ORCEs are currently manufactured and used for numerous remote terrestrial applications requiring reliable, unattended power.OneofthemajorlossmechanismsinORCEsisshockwavesgenerated intheturbinestage.Operatingunder theproperthermodynamicconditions, a BZT working e uid can potentially weaken oreliminate shock waves. This would reduce losses due to both the wave drag from shocks as well as losses from boundary-layer separation due to shock ree ections on the turbine blades. Two-dimensional e owe elds through realistic symmetric impulse turbinecascades arecompared using a e ux-limited, e nite differencenumerical schemeto assess differences in e ow efe ciencies. Resultsshowsignie cantimprovementsin turbineefe cienciesforBZTworkinge uidsoverconventional ORCE working e uids.

SONIC BOOM MINIMIZATION REVISITED

We revisit the classical Jones-Seebass-GeorgeDarden theory of sonic boom minimization, noting that minimum achievable sonic boom is related to the aircrafts weight divided by the three-halves power of its length. We then summarize studies of sonic boom acceptability and the effects of vibrational relaxation on very weak shock waves, This leads us to conclude that a small, appropriately designed, supersonic business jets sonic boom may be nearly inaudible outdoors and hardly discernible indoors.

The tempest unmanned aircraft system for in situ observations of tornadic supercells: Design and VORTEX2 flight results

This paper reports results from field deployments of the Tempest Unmanned Aircraft System, the first of its kind of unmanned aircraft system designed to perform in situ sampling of supercell thunderstorms, including those that produce tornadoes. A description of the critical system components, consisting of the unmanned aircraft, ground support vehicles, communications network, and custom software, is given. The unique concept of operations and regulatory issues for this type of highly nomadic and dynamic system are summarized, including airspace regulatory decisions from the Federal Aviation Administration to accommodate unmanned aircraft system operations for the study of supercell thunderstorms. A review of the system performance and concept of operations effectiveness during flights conducted for the spring 2010 campaign of the VORTEX2 project is provided. These flights resulted in the first-ever sampling of the rear flank gust front and airmass associated with the rear flank downdraft of a supercell thunderstorm by an unmanned aircraft system. A summary of the lessons learned, future work, and next steps is provided.

Theory for producing a single-phase rarefaction shock wave in a shock tube

Although predicted early in the 20th century, a single-phase vapour rarefaction shock wave has yet to be demonstrated experimentally. Results from a previous shock tube experiment appear to indicate a rarefaction shock wave. These results are discussed and their interpretation challenged. In preparation for a new shock tube experiment, a global theory is developed, utilizing a van der Waals fluid, for demonstrating a single-phase vapour rarefaction shock wave in the incident flow of the shock tube. The flow consists of four uniform regions separated by three constant-speed discontinuities: a rarefaction shock, a compression shock, and a contact surface. Entropy jumps and upstream supersonic Mach number conditions are verified for both shock waves. The conceptual van der Waals model is applied to the fluid perfluoro-tripentylamine (FC-70, C 15 F 33 N) analytically, and verified with computational simulations. The analysis predicts a small region of initial states that may be used to unequivocally demonstrate the existence of a single-phase vapour rarefaction shock wave

Computational analysis of dense gas shock tube flow

Nonclassical phenomena associated with the classical dynamics of real gases in a conventional shock tube are studied. A TVD predictor-corrector (TVD-MacCormack) scheme with reflective endwall boundary conditions is used for the one-dimensional Euler equations to simulate the evolution of the wave field of a van der Waals gas. Depending upon the initial conditions of the gas, wave fields are produced that contain nonclassical phenomena such as expansion shocks, composite waves, splitting shocks, etc. In addition, the interactions of waves reflected from the endwalls produce both classical and nonclassical phenomena. Wave field evolution is depicted using plots of the flow variables at specific times and withx-t diagrams.

The Collaborative Colorado–Nebraska Unmanned Aircraft System Experiment

The Collaborative Colorado–Nebraska Unmanned Aircraft System Experiment (CoCoNUE) was executed on 1 March and 30 September 2009. The principal objective of this project was to examine the feasibility of using a small unmanned aircraft operating semi-autonomously with an onboard autopilot to observe atmospheric phenomena within the terrestrial boundary layer covered by the United States National Airspace System. The application of an unmanned aircraft system (UAS; the aircraft along with the communications and logistics infrastructure required for operation) is beset by a number of engineering and regulatory challenges. This article discusses the strategies implemented to meet these challenges. Airmass boundaries served as the target of the flights conducted. These atmospheric phenomena have the fortuitous combination of an across-boundary scale that yields a coherent signal in the in situ meteorological data that can be collected by a UAS and an along-boundary scale that can be easily tracked via the exis...

Radio Source Localization by a Cooperating UAV Team

This paper describes the development of a networked UAV communication, command, and control (NetUAVC3) architecture. The NetUAVC 3 project is divided into three stages. Stage 1 focused on developing algorithms for tying network intelligence and mission-level tasking information into automatic flight controls. Stage 2 will conclude with a demonstration of leashing UAVs to mobile nodes, and Stage 3 will conclude with a demonstration of radio source localization by a cooperating UAV team. This presentation will describe the NetUAVC 3 architecture currently under development. The Stage 1 system will be presented, including the onboard flight management architecture and monitoring and command & control software that exploits the existing AUGNet mesh network. The radio localization problem, in which one or more UAVs react cooperatively to localize the location of a radio emitter, will also be introduced. Source localization is cast as a distributed estimation problem. Aircraft mobility is exploited to improve the observability, in terms of the Fisher Information Matrix, of this estimation problem. Aircraft motion is coordinated through iterative consensus by individual receding horizon controllers on each vehicle.

Assessment of thermodynamic models for dense gas dynamics

The accuracy of thermodynamic models in the computation of nonclassical gasdynamic phenomena is discussed, to investigate their suitability in connection with the design of experimental apparatuses aimed at the observation of nonclassical wavefields. The Soave–Redlich–Kwong and the Peng–Robinson are preliminarily suggested as alternative thermodynamic models to the Martin–Hou usually considered in nonclassical gasdynamics of fluorinated substances. The validity of these models is assessed by comparisons to reference experimental data for fluorinated R13, R125, C318, FC-72, FC-75, and SF6 and to the Martin–Hou model itself. The three models are found to exhibit a comparable accuracy for reduced volumes ranging from 1.4 to 2.5 and near the critical isotherm, i.e., in the thermodynamic region where heavier fluorinated substances such as PP10 are expected to exhibit nonclassical gasdynamic phenomena. The Soave–Redlich–Kwong and the Peng–Robinson models are then used to supplement previous numerical results fo...

Shape optimization methodology for reducing the sonic boom initial pressure rise

A shape optimization methodology for reducing the initial shock pressure rise on the ground of a supersonic aircraft is presented. This methodology combines elements from the linearized aerodynamic theory, such as the Whitham F function, with elements from the nonlinear aerodynamic theory, such as the prediction of lift distribution by an Euler or a Navier-Stokes flow solver. It is applied to the optimization of two different airplane concepts developed by Reno Aeronautical and Lockheed Martin, respectively, for the Defense Advanced Research Projects Agencys Quiet Supersonic Platform program. For Reno Aeronauticals laminar-flow supersonic aircraft, the initial shock pressure rise on the ground is reduced by a factor close to 2, from 1.224 psf (58.605 N/m 2 ) at a freestream Mach number of 1.5 to 0.671 psf (32.127 N/m 2 ), while maintaining constant lift For Lockheed Martins point of departure aircraft, a tenfold reduction of the initial shock pressure rise on the ground is demonstrated, from 1.623 psf (77.71 N/m 2 ) at a freestream Mach number of 1.5 to 0.152 psf (7.278 N/m 2 ), also while maintaining constant lift.