| Hypersonic Transition Experiments in 3D Cone Flow with New Measurement Techniques |
Aug 2012 |
40 pages |
| Authors:
Dirk Heitmann; Rolf E Radespiel; TECHNICAL UNIV BRAUNSCHWEIG (GERMANY) INST OF FLUID MECHANICS
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 | This is the final report deals with laminar-turbulent transition measurements on an inclined cone at hypersonic Mach number. Within the flow field of an inclined cone three different boundary layer instabilities appear: first and second mode instability waves and crossflow vortices. Two different measurement techniques were applied: (i) IR-thermography was used for measuring stationary crossflow vortices. This instability was quantitatively measured. The position where these vortices evolve, their amplification and ... |
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| An Axisymmetric View of Concentric Eyewall Evolution in Hurricane Rita (2005) |
Aug 2012 |
21 pages |
| Authors:
Michael M Bell; Michael T Montgomery; Wen-Chau Lee; NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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| Multiplatform observations of Hurricane Rita (2005) were collected as part of the Hurricane Rainband and Intensity Change Experiment (RAINEX) field campaign during a concentric eyewall stage of the storm's life cycle that occurred during 21-22 September. Satellite, aircraft, dropwindsonde, and Doppler radar data are used here to examine the symmetric evolution of the hurricane as it underwent eyewall replacement. During the approximately 1-day observation period, developing convection associated with the ... |
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| Formation and Development of Diabatic Rossby Vortices in a 10-Year Climatology |
Jun 2012 |
145 pages |
| Authors:
Nengwei Shih; NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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| A diabatic Rossby vortex (DRV) is a short-scale, diabatically dominated, moist baroclinic disturbance that forms and grows in the absence of discernible upper tropospheric forcing. The overarching goal of this work is to expand on the limited amount of DRV research by examining the general characteristics of real-world DRVs that have been identified in an automated 10-year DRV climatology. The identified 314 DRVs form preferentially over warm ocean currents. All ... |
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| A First Look at the Structure of the Wave Pouch during the 2009 PREDICT-GRIP Dry Runs over the Atlantic |
Apr 2012 |
22 pages |
| Authors:
Zhuo Wang; Michael T Montgomery; Cody Fritz; ILLINOIS UNIV AT URBANA-CHAMPAIGN
|
| In support of the National Science Foundation Pre-Depression Investigation of Cloud-systems in the tropics (NSF PREDICT) and National Aeronautics and Space Administration Genesis and Rapid Intensification Processes (NASA GRIP) dry run exercises and National Oceanic and Atmospheric Administration Hurricane Intensity Forecast Experiment (NOAA IFEX) during the 2009 hurricane season a real-time wave-tracking algorithm and corresponding diagnostic analyses based on a recently proposed tropical cyclogenesis model were applied to tropical easterly ... |
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| On the Simulation of Free Flight Vortices in Ground Test Facilities |
29 Mar 2012 |
6 pages |
| Authors:
Hui Hu; Paul A Durbin; IOWA STATE UNIV AMES DEPT OF AEROSPACE ENGINEERING
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| The objectives of this project is to assess the effects of significant wind tunnel testing factors, such as test model blockage, vortex strength, inlet flow non-uniformities and inlet turbulence levels, on the near field behavior of strong wing-tip vortex structures through an integrated experimental, numerical and theoretical study. A primary motive is to assess the need for comprehensive corrections of wind tunnel testing data to simulate free flight conditions. The ... |
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| Effects of Stencil Width on Surface Ocean Geostrophic Velocity and Vorticity Estimation from Gridded Satellite Altimeter Data |
17 Mar 2012 |
19 pages |
| Authors:
Brian K Arbic; Robert B Scott; Dudley B Chelton; James G Richman; Jay F Shriver; NAVAL RESEARCH LAB STENNIS DETACHMENT STENNIS SPACE CENTER MS OCEANOGRAPHY DIV
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| Geostrophic velocity and vorticity are often estimated by finite difference differentiation of gridded sea surface height fields. Significant differences are obtained in the estimated velocity with the order of the difference operator of stencil width Speed-dependent biases of 10-20% are found for the traditional 3-point centered difference compared to wider, higher-order, stencils Additionally, wider stencils yield estimates of the anisotropy of velocity variance insensitive to the differences in grid ... |
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| Accurate Modeling of Stability and Control Properties for Fighter Aircraft from CFD |
Mar 2012 |
196 pages |
| Authors:
Jedediah H Butler; AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH GRADUATE SCHOOL OF ENGINEERING AND MANAGEMENT
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| Difficulties in obtaining accurate Stability and Control (S&C) data for nonlinear regions in the flight envelope early in the design phase often lead to costly fixes late in the acquisition process. Work examined herein addresses this problem by utilizing recent advances in Computational Fluid Dynamics (CFD) to create a high-fidelity database before any parts have to be physically produced. In combination with CFD, System Identification (SID) is used to characterize ... |
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| Potential Vorticity Streamers as Precursors to Tropical Cyclone Genesis in the Western Pacific |
Mar 2012 |
117 pages |
| Authors:
Edward J Rozak; NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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| The term tropical transition (TT) is used to describe the formation of a tropical cyclone from an extratropical precursor. The overarching goal of this thesis is to re-examine TT in the western North Pacific. This is accomplished via the synthesis of a subjective climatology of all tropical cyclones (TCs) from 2002-2008 and a case study analysis of ensemble prediction data for the particularly intriguing event of TS 16W in September ... |
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| Sound Generation in the Interaction of Two Isentropic Vortices |
02 Feb 2012 |
16 pages |
| Authors:
Shuhai Zhang; Hanxin Zhang; Chi-Wang Shu; BROWN UNIV PROVIDENCE RI DIV OF APPLIED MATHEMATICS
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| Through direct numerical simulation (DNS) for the sound generated by the interaction between two isentropic vortices, it is found that the interaction between two vortices with a large difference in their strengths or scales can generate continuous strong noise. The interaction between two isentropic vortices results in the formation of two vortex dipoles, with each vortex dipole containing two vortex cores. If there is a large difference in their initial ... |
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| Efficient FMM Accelerated Vortex Methods in Three Dimensions via the Lamb-Helmholtz Decomposition |
25 Jan 2012 |
20 pages |
| Authors:
Nail A Gumerov; Ramani Duraiswami; MARYLAND UNIV COLLEGE PARK INST FOR ADVANCED COMPUTER STUDIES
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| Vortex-element methods are often used to efficiently simulate incompressible flows using Lagrangian techniques. Use of the FMM (Fast Multipole Method) allows considerable speed up of both velocity evaluation and vorticity evolution terms in these methods. Both equations require field evaluation of constrained (divergence free) vector valued quantities (velocity, vorticity) and cross terms from these. These are usually evaluated by performing several FMM accelerated sums of scalar harmonic functions. We present ... |
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| Vortex-Induced Vibration: Universal Phenomena in Diverse VIV Systems |
28 Nov 2011 |
24 pages |
| Authors:
Charles H Williamson; CORNELL UNIV ITHACA NY DEPT OF MECHANICAL AND AEROSPACE ENGINEERING
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| The long-term goals of the research have been to investigate the important mechanisms involved in the interaction of current and waves with structures in the ocean. We have studied the ultra-high resolution controlled vibration of cylinders in a flow, and have been able to accurately predict free vibration response, as well as to understand free vibration phenomena, by employing energy portrait diagrams. We have constructed an accurate map of force ... |
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| High Temperature Superconducting State in Metallic Nanoclusters and Nano-Based Systems |
Oct 2011 |
12 pages |
| Authors:
Yury N Ovchinnikov; LANDAU INST FOR THEORETICAL PHYSICS MOSCOW (RUSSIA)
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| Main goal of project is the search of new materials with high temperature of the superconducting transition (order of room temperature). Main investigation objects are special nanoclusters with shell structure of the electron spectrum. The goal is investigation of the possibility of building of nets (two and three dimensional) from nanoclusters with high value of the superconducting transition temperature and possessing of possibility to transfer high value of transport current ... |
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| An Investigation of Rotational Influences on Tropical-Cyclone Size and Intensity |
Oct 2011 |
16 pages |
| Authors:
Roger K Smith; Christoph W Schmidt; Michael T Montgomery; NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF METEOROLOGY
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| We investigate the rotational constraint on the intensity and size of a tropical cyclones using a minimal, three-layer, axisymmetric tropical-cyclone model. In the first of two sets of experiments, the same initial baroclinic vortex is spun up in a quiescent environment with different levels of background rotation, characterized by the Coriolis parameter, f . It is found that the strongest vortices, as characterized by their final intensity, develop in environments ... |
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| Lidar for Lateral Mixing (LATMIX) |
30 Sep 2011 |
6 pages |
| Authors:
Brian M Concannon; NAVAL AIR SYSTEMS COMMAND PATUXENT RIVER MD
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| Our long-term goal is to better understand lateral mixing processes in the ocean on scales of 10 m to 10 km, i.e., the submesoscale. We aim to understand the underlying mechanisms and forcing, as well as the temporal, spatial, and scale variability of such mixing. The research will contribute to fundamental knowledge of ocean dynamics at these scales, and to efforts to properly parameterize sub-grid scale mixing and stirring in ... |
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| LIDAR Studies of Small-Scale Lateral Dispersion in the Ocean |
30 Sep 2011 |
8 pages |
| Authors:
James R Ledwell; Eugene A Terray; WOODS HOLE OCEANOGRAPHIC INSTITUTION MA DEPT OF APPLIED OCEAN PHYSICS AND ENGINEERING
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| Our long-term goal is to better understand lateral mixing processes in the ocean on scales of 10 m to 10 km (i.e., the submesoscale). We aim to understand the underlying mechanisms and forcing, as well as the temporal, spatial, and scale variability of such mixing. The research will contribute to fundamental knowledge of ocean dynamics at these scales, and to efforts to properly parameterize sub-grid scale mixing and stirring in ... |
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| LIDAR Studies of Small-Scale Lateral Dispersion in the Ocean |
30 Sep 2011 |
9 pages |
| Authors:
Miles A Sundermeyer; MASSACHUSETTS UNIV DARTMOUTH SCHOOL FOR MARINE SCIENCE AND TECHNOLOGY
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| Our long-term goal is to better understand lateral mixing processes in the ocean on scales of 10 m to 10 km (i.e., the submesoscale). We aim to understand the underlying mechanisms and forcing, as well as the temporal, spatial, and scale variability of such mixing. The research will contribute to fundamental knowledge of ocean dynamics at these scales, and to efforts to properly parameterize sub-grid scale mixing and stirring in ... |
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| Using NOGAPS Singular Vectors to Diagnose Large-scale Influences on Tropical Cyclogenesis |
30 Sep 2011 |
7 pages |
| Authors:
Sharanya J Majumdar; Melinda S Peng; Carolyn A Reynolds; James D Doyle; Chun-Chieh Wu; David S Nolan; MIAMI UNIV FL ROSENSTIEL SCHOOL OF MARINE AND ATMOSPHERIC SCIENCE
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| The overarching goal is to improve our understanding of synoptic-scale influences on tropical cyclone (TC) formation and motion in the western North Pacific Ocean, in the context of error growth in forecast models. Benefits to the Navy would include improved forecast skill of the structure and track of developing and recurving TCs. The first objective is to connect Singular Vector (SV) and ensemble perturbation growth to synopticscale dynamical influences on ... |
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| Origins of the Kuroshio and Mindanao Currents |
30 Sep 2011 |
3 pages |
| Authors:
Bo Qiu; HAWAII UNIV HONOLULU (MANOA CAMPUS) DEPT OF OCEANOGRAPHY
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| The long-term goal of this research is to quantify the processes leading to the bifurcation of the North Equatorial Current (NEC) into the northward flowing Kuroshio and the southward flowing Mindanao Current. The four objectives of this project are as follows: (1) to clarify the dynamic state of the NEC-Kuroshio-Mindanao Current system; (2) to quantify the temporal evolution of the upper ocean temperature and salinity (T/S) fields, the seasonal mixed ... |
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| Convection and Shear Flow in TC Development and Intensification |
30 Sep 2011 |
7 pages |
| Authors:
C P Chang; H C Kuo; C H Liu; NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF METEOROLOGY
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| LONG TERM GOALS: To study the dynamic processes of tropical cyclone (TC) development in the western North Pacific through field observational data and theoretical modeling. OBJECTIVES: The objectives are: (1) to study the convection and vorticity generations in the vortex environment that may lead to the development and intensification of TC; (2) to study the development and evolution of deep moist mesoscale convective system subject to strain effect due to ... |
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| Initialization, Prediction and Diagnosis of the Rapid Intensification of Tropical Cyclones using the Australian Community Climate and Earth System Simulator, ACCESS |
30 Sep 2011 |
13 pages |
| Authors:
Michael J Reeder; Noel E Davidson; Craig H Bishop; Jeffrey D Kepert; Peter Steinle; Kevin J Tory; Yimin Ma; NAVAL RESEARCH LAB MONTEREY CA
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| 1. Improved initialization and skilful prediction of Tropical Cyclone (TC) track, structure and intensity. 2. Improved prediction of Rapid Intensification (RI). 3. Improved understanding of the mechanisms of TC structure and intensity change, particularly Rapid Intensification. The plan is a 4-part, inter-connected program of: (a) basic research into initialization of realistic TC structures using the state-of-the-art 4-dimensional variational data assimilation system (4D-VAR) from ACCESS (Australian Community Climate and Earth System ... |
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| Analysis of Data from TCS-08 |
30 Sep 2011 |
8 pages |
| Authors:
David J Raymond; NEW MEXICO TECH SOCORRO
|
| The long-term goals of this project are to understand better the mechanisms operative in tropical cyclogenesis and to transfer this knowledge to large-scale models in order to improve forecasts of tropical storm formation. Since convection constitutes the biggest uncertainty in this process, our focus is to understand how convection affects and is affected by cyclone-scale flows. Our objective in this segment of the program was to extend our vorticity budget ... |
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| New Approaches to the Parameterization of Gravity-Wave and Flow-Blocking Drag due to Unresolved Mesoscale Orography Guided by Mesoscale Model Predictability Research |
30 Sep 2011 |
7 pages |
| Authors:
Stephen D Eckermann; NAVAL RESEARCH LAB WASHINGTON DC SPACE SCIENCE DIV
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| When surface flow impinges on orography with horizontal scales of 1-500 km, a variety of mesoscale dynamical responses can result, including gravity waves, upstream blocking, flow splitting and lee vortices. These dynamics produce important drag forces on the larger scale atmosphere. Because global numerical weather and climate prediction (NWCP) models under-resolve orography at these scales, all credible NWCP systems must include parameterizations of these missing orographic mesoscale drag (OMD) forces. ... |
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| Analysis and High-Resolution Modeling of Tropical Cyclogenesis during the TCS-08 and TPARC Field Campaign |
30 Sep 2011 |
8 pages |
| Authors:
Tim Li; Melinda S Peng; HAWAII UNIV HONOLULU (MANOA CAMPUS) SCHOOL OF OCEAN AND EARTH SCIENCE AND TECHNOLOGY
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| The accurate prediction of tropical cyclone (TC) genesis, structure, and intensity changes is critical to Navy missions and civilian activities in coastal areas. Significant gains have been made in TC track prediction over the past decades. However, genesis and intensity forecasts have shown very little progress during the same time period. A primary contributing factor to our lack of skill in the prediction of TC genesis and intensity is our ... |
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| Initialization of Tropical Cyclone Structure for Operational Application |
30 Sep 2011 |
5 pages |
| Authors:
Tim Li; Melinda S Peng; HAWAII UNIV HONOLULU (MANOA CAMPUS) SCHOOL OF OCEAN AND EARTH SCIENCE AND TECHNOLOGY
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| The long-term goal of this project is to improve the prediction of tropical cyclone (TC) genesis, structure, and intensity changes through improved representation of 3-dimensional TC structure in operational weather forecast models. The accurate prediction of TC genesis, structure, and intensity changes is critical to Navy missions and civilian activities in coastal areas. Significant gains have been made in TC track prediction over the past decades. However, genesis and intensity ... |
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| Predicting Tropical Cyclone Genesis |
30 Sep 2011 |
7 pages |
| Authors:
Melinda S Peng; James Hansen; Tim Li; NAVAL RESEARCH LAB MONTEREY CA
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| The long-term goal of this research is to provide probabilistic genesis forecast guidance to operational forecasters and develop a genesis index for operational dynamical model prediction of tropical cyclone (TC) genesis. Once regions of high TC genesis probability are identified, a movable, multi-nested version of COAMPS with resolution of roughly 3 km or less in the inner most grid will be used for predicting the genesis event. The objective of ... |
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| Lagrangian Coherent Structures in Tropical Cyclone Intensification |
21 Sep 2011 |
46 pages |
| Authors:
B Rutherford; G Dangelmayr; M T Montgomery; NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF METEOROLOGY
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| Recent work has suggested that tropical cyclones intensify via a pathway of rotating deep moist convection in the presence of enhanced fluxes of moisture from the ocean. The rotating deep convective structures possessing enhanced cyclonic vorticity within their cores have 5 been dubbed Vortical Hot Towers (VHTs). In general, the interaction between VHTs and the system-scale vortex, as well as the corresponding evolution of equivalent potential temperature theta(sub e) that ... |
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| Modeling the Impacts of Intraseasonal to Interannual Climate Variations on Tropical Cyclone Formations in the Western North Pacific |
Sep 2011 |
111 pages |
| Authors:
Stephanie A Johnson; NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF METEOROLOGY
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| We have analyzed the modulation of TC formations in the western North Pacific (WNP) during July-October by El Ni o (EN), La Ni a (LN), and the Madden Julian Oscillation (MJO). This analysis was conducted from the perspective of several large scale environmental factors (LSEFs) that strongly influence tropical cyclone (TC) formation: sea surface temperature (SST), low level relative vorticity, vertical wind shear, and upper level divergence. We examined the ... |
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| Can Wing Tip Vortices Be Accurately Simulated? |
JUL 2011 |
14 pages |
| Authors:
Ryan Termath; Jason Lechniak; Keerti Bhamidipati; AIR FORCE FLIGHT TEST CENTER EDWARDS AFB CA
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| Modeling and Simulation (M&S) computational fluid dynamics (CFD) techniques were used to better understand wing tip vortices about a wing section. The CFD results were compared to experimental wind tunnel data derived from the University of Iowa (Ref. 2). The experiment used Stereoscopic Particle Image Velocimetry (SPIV) to measure the flow field. The SPIV data from the experiment illustrates the vortex core development and behavior downstream of the trailing edge ... |
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| On the Evolution of Vortical Disturbances in Two-Fluid Boundary Layers |
JUL 2011 |
22 pages |
| Authors:
Tamer A. Zaki; IMPERIAL COLL LONDON (UNITED KINGDOM)
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| The low-frequency free-stream disturbances penetrate boundary layer despite the sheltering ability of the mean shear. These disturbances form streaks via the lift-up mechanism. The streaks subsequently become unstable and breakdown to turbulence. The stability of laminar boundary layers is examined in presence of a thin wall-film, of different viscosity. The influence of the film on the evolution of free-stream vortical modes and the generation of boundary layer streaks is solved ... |
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| Can Wing Tip Vortices Be Accurately Simulated? |
Jul 2011 |
|
| Authors:
Ryan Termath; Jason Lechniak; Keerti Bhamidipati; AIR FORCE FLIGHT TEST CENTER EDWARDS AFB CA
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| Modeling and Simulation (M&S) computational fluid dynamics (CFD) techniques were used to better understand wing tip vortices about a wing section. The CFD results were compared to experimental wind tunnel data derived from the University of Iowa (Ref. 2). The experiment used Stereoscopic Particle Image Velocimetry (SPIV) to measure the flow field. The SPIV data from the experiment illustrates the vortex core development and behavior downstream of the trailing edge ... |
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| Performance Analysis for Lateral-Line-Inspired Sensor Arrays |
JUN 2011 |
235 pages |
| Authors:
Vicente I. Fernandez; MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF MECHANICAL ENGINEERING
|
| The lateral line is a critical component of the fish sensory system, affecting aspects of behavior including maneuvering in complex fluid environments, schooling, and prey tracking. This sensory organ has no analog in ocean vehicles and could fill the gap for navigation left by sonar and vision systems in turbid cluttered environments. This thesis demonstrates and characterizes the ability of lateral-line-inspired pressure sensor arrays to perform two sensory tasks of ... |
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| Numerical Investigation of Serpentine Plasma Actuators for Separation Control at Low Reynolds Number |
Jun 2011 |
17 pages |
| Authors:
Mark Riherd; Subrata Roy; Miguel Visbal; FLORIDA UNIV GAINESVILLE DEPT OF MECHANICAL ENGINEERING
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| Dielectric Barrier Discharge (DBD) plasma actuators with serpentine shaped electrodes cause a change in the operational behavior of the flow control mechanism relative to the standard linear actuator due to the introduction of fully three dimensional vortices. A parametric study is performed on a partially separated transitional flow over an SD7003 airfoil. This study examines the change in behavior as a function of geometric parameters, in particular the geometric amplitude ... |
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| An Estimation of Turbulent Characteristics in the Low-Level Region of Intense Hurricanes Allen (1980) and Hugo (1989) |
May 2011 |
18 pages |
| Authors:
Jun A Zhang; Frank D Marks; Michael T Montgomery; Sylvie Lorsolo; NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF METEOROLOGY
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| This study analyzes the flight-level data collected by research aircraft that penetrated the eyewalls of category 5 Hurricane Hugo (1989) and category 4 Hurricane Allen (1980) between 1 km and the sea surface. Estimates of turbulent momentum flux, turbulent kinetic energy (TKE), and vertical eddy diffusivity are obtained before and during the eyewall penetrations. Spatial scales of turbulent eddies are determined through a spectral analysis. The turbulence parameters estimated for ... |
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| Unsteady Flow Structure on Low Aspect Ratio Wings |
06 Jan 2011 |
106 pages |
| Authors:
Donald Rockwell; LEHIGH UNIV BETHLEHEM PA DEPT OF MECHANICAL ENGINEERING AND MECHANICS
|
| The overall objective of this investigation was to determine the quantitative flow structure on low aspect ratio wings subjected to basic classes of maneuvers, in order to provide a basis for interpretation of induced forces. Techniques of particle image velocimetry were employed for critical planes of the flow field, and a technique of stereo particle image velocimetry was developed for water-based systems. Post-processing of the acquired images allowed determination of ... |
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| Separation Control with Nanosecond Pulse Driven Dielectric Barrier Discharge Plasma Actuators |
Jan 2011 |
43 pages |
| Authors:
Jesse Little; Keisuke Takashima; Munetake Nishihara; Igor Adamovich; Mo Samimy; ARIZONA UNIV TUCSON DEPT OF AEROSPACE AND MECHANICAL ENGINEERING
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| The efficacy of dielectric barrier discharge (DBD) plasmas driven by high voltage (approximately 15 kV) repetitive nanosecond pulses approximately 100 ns FWHM) for flow separation control is investigated experimentally on an airfoil leading edge up to Re=1x106 (62 m/s). Unlike AC-DBDs, the nanosecond pulse driven DBD plasma actuator transfers very little momentum to the neutral air, but generates compression waves similar to localized arc filament plasma actuators. A complex pattern ... |
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| Paradigms for Tropical-Cyclone Intensification |
Jan 2011 |
33 pages |
| Authors:
Michael T Montgomery; Roger K Smith; NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF METEOROLOGY
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| We review four paradigms of tropical-cyclone intensification that have emerged over the past five decades, discussing the relationship between them and highlighting their positive aspects and limitations. A major focus is on a new paradigm articulated in a series of recent papers by ourselves and colleagues. Unlike the three previous paradigms, all of which assumed axial symmetry, the new one recognizes the importance of rotating deep convection, which possesses local ... |
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| Dynamic Flight Maneuvering Using Virtual Control Surfaces Generated by Trapped Vorticity |
Dec 2010 |
75 pages |
| Authors:
Ari Glezer; Mark G Allen; Anthony J Calise; Anthony Leonard; James M McMichael; Robert D Moser; Arne J Pearlstein; GEORGIA INST OF TECH ATLANTA
|
| This MURI program addressed integrated closed-loop control of flow and dynamic maneuvering for small UAVs without moving control surfaces. Forces and moments were varied using synthetic jet actuators to effect vorticity generation/accumulation near lifting surfaces, with sensing provided by surface-mounted pressure and flow-direction sensors, and a reduced-order model (ROM) of vorticity dynamics coupled to and integrated with a vehicle dynamics model in an adaptive control architecture. |
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| Dynamics of Vorticity Defects in Stratified Shear |
19 Oct 2010 |
34 pages |
| Authors:
Anubhad Roy; WOODS HOLE OCEANOGRAPHIC INSTITUTION MA
|
| Stability of shear flows at high Reynolds number has been one of the cornerstones of hydrodynamic stability. A canonical problem which contains the basic features is that of a shear layer - two streams of different velocity owing past each other with different density. Helmholtz[18] and Kelvin[21] were probably the earliest to consider evolution of disturbances in a stratified vortex sheet. While attempting a more general case Rayleigh[27] approximated the ... |
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| A Multiscale Study of Tropical Cyclone Formation, Structure Change, and Predictability in the Western North Pacific Region and TCS08 Experiment Support |
30 SEP 2010 |
11 pages |
| Authors:
Michael T. Montgomery; Michael M. Bell; NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF METEOROLOGY
|
| The overarching objectives of this research project are to obtain an improved understanding of the formation, predictability and structure change of tropical cyclones in the Western Pacific region. These new insights will ultimately improve forecast guidance for U.S. Naval operations in this region. In recent work the P.I. and two of his collaborators have developed a new paradigm of tropical cyclogenesis that occurs within the critical layer of easterly waves ... |
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| Convection and Shear Flow in TC Development and Intensification |
30 SEP 2010 |
5 pages |
| Authors:
C. P. Chang; H. C. Kuo; C. H. Liu; NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF METEOROLOGY
|
| To study the dynamic processes of tropical cyclone (TC) development in the western North Pacific through field observational data and theoretical modeling. The objectives are: (1) to study the convection and vorticity generations in the vortex environment that may lead to the development and intensification of tropical cyclone; (2) to study the development and evolution of deep moist mesoscale convective system subject to strain effect due to the horizontal shear ... |
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| Simulating the Detachment of Leading Edge Vortices on Drosophila Melanogaster Using CFD |
13 Sep 2010 |
7 pages |
| Authors:
Alex Sabbatini; Gabriel Smith; Jeffrey S Pulskamp; Ronald G Polcawich; STANFORD UNIV CA DEPT OF MECHANICAL ENGINEERING
|
| Initial CFD simulations of quasi-steady hovering flight of the Drosophila sp. have studied the effects of delayed rotation of the wings at the end of each stroke and it s effect on the resulting unsteady aerodynamic forces found throughout the wing [8]. Further studies were carried out using the same CFD model as before to determine the lift and power requirements for Drosophila Virilis [7]. To verify the validity of ... |
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| Mesoscale Convective Vortices in Multiscale, Idealized Simulations: Dependence on Background State, Interdependency with Moist Baroclinic Cyclones, and Comparison with BAMEX Observations |
Apr 2010 |
23 pages |
| Authors:
Robert J Conzemius; Michael T Montgomery; NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF METEOROLOGY
|
| A set of multiscale, nested, idealized numerical simulations of mesoscale convective systems (MCSs) and mesoscale convective vortices (MCVs) was conducted. The purpose of these simulations was to investigate the dependence of MCV development and evolution on background conditions and to explore the relationship between MCVs and larger, moist baroclinic cyclones. In all experiments, no mesoscale convective system (MCS) developed until a larger-scale, moist baroclinic system with surface pressure amplitude of ... |
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| Developing a Control Strategy for Jets in Crossflow Using Direct Numerical Simulation |
29 MAR 2010 |
109 pages |
| Authors:
Krishnan Mahesh; MINNESOTA UNIV MINNEAPOLIS DEPT OF AEROSPACE ENGINEERING AND MECHANICS
|
| Direct numerical simulation is used to study the mixing of a passive scalar by a vortex ring issuing from a nozzle into stationary fluid. The "formation number" (Gharib et al 1998), is found to be 3.6. Simulations are performed for a range of stroke ratios encompassing the formation number, and the effect of stroke ratio on entrainment, and mixing is examined. When the stroke ratio is greater than the formation ... |
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| High-Fidelity Simulations of Moving and Flexible Airfoils at Low Reynolds Numbers (Postprint) |
Feb 2010 |
22 pages |
| Authors:
Miguel R Visbal; Raymond E Gordnier; Marshall C Galbraith; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH AIR VEHICLES DIR/ AERONAUTICAL SCIENCES DIV/COMPUTATIONAL SCIENCES BRANCH
|
| The present paper highlights results derived from the application of a high-fidelity simulation technique to the analysis of low-Reynolds-number transitional flows over moving and flexible canonical configurations motivated by small natural and man-made flyers. This effort addresses three separate fluid dynamic phenomena relevant to small fliers, including: laminar separation and transition over a stationary airfoil, transition effects on the dynamic stall vortex generated by a plunging airfoil, and the effect ... |
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| Advective Mixing in a Nondivergent Barotropic Hurricane Model |
20 Jan 2010 |
25 pages |
| Authors:
B Rutherford; G Dangelmayr; J Persing; W H Schubert; M T Montgomery; NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF METEOROLOGY
|
| This paper studies Lagrangian mixing in a two-dimensional barotropic model for hurricane-like vortices. Since such flows show high shearing in the radial direction particle separation across shear-lines is diagnosed through a Lagrangian field, referred to as R-field, that measures trajectory separation orthogonal to the Lagrangian velocity. The shear-lines are identified with the level-contours of another Lagrangian field, referred to as S-field, that measures the average shear-strength along a trajectory. Other ... |
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| Hurricane Boundary-Layer Theory |
Jan 2010 |
7 pages |
| Authors:
Roger K Smith; Michael T Montgomery; NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF METEOROLOGY
|
| In the light of the plethora of definitions for the hurricane boundary layer, we advocate a dynamical definition based on the distribution of agradient flow. We seek also to clarify the fundamental role of the boundary layer in the hurricane intensification process. In particular, we contrast the differences between unsteady boundary layers that are able to facilitate the spin-up of the vortex above and steady boundary layers that cannot. If ... |
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| Clarification on the Generation of Absolute and Potential Vorticity in Mesoscale Convective Vortices |
12 Oct 2009 |
16 pages |
| Authors:
R J Conzemius; M T Montgomery; NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF METEOROLOGY
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| In this paper, we clarify several outstanding issues concerning the predominant mechanism of vorticity generation in mesoscale convective vortices (MCVs) in weak to modest baroclinic environments with nonzero Coriolis parameter. We examine also the corresponding diabatic heating profiles of the convective and stratiform components of the MCS and their effects on the concentration and dilution of PV substance. |
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| Global Flow Instability and Control IV Held in Crete, Greece on September 28-October 2, 2009: A Synthesis of Presentations and Discussions |
Sep 2009 |
27 pages |
| Authors:
V Theofilis; NU-MODELING INC MADRID (SPAIN)
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| The Final Proceedings for Fourth Symposium on Global Flow Instability and Control, Hersonissos, Crete, Greece, on 28 September 2009 - 2 October 2009. The series of symposia was established in 2001, having as its primary objective the creation of a forum for presentation and discussion of current research and open issues in global flow instability and control. This has been particularly interesting in recent years in view of the increasing ... |
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| Nonlinear Aspects of Internal Waves in the Atmosphere |
20 Aug 2009 |
78 pages |
| Authors:
John P McHugh; NEW HAMPSHIRE UNIV DURHAM
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| Internal waves in the atmosphere are responsible for a significant percentage of atmospheric turbulence, particularly at the tropopause. This turbulence can interfere with Air Force operations, and is in need of improved prediction methods. The research has considered a sequence of idealized phenomena aimed at this ultimate goal. The results show that nonlinear effects enhance wave amplitude at the altitude where the buoyancy frequency changes suddenly. Vertically propagating wave packets ... |
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| Flow Visualization Studies over a UCAV 1303 Model |
Jun-2009 |
58 pages |
| Authors:
Weng H Chua; NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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| This study is a qualitative documentation of the main flow features over an Unmanned Combat Air Vehicle (UCAV) 1303 model by flow visualization techniques where it gives the first understanding of the UCAV maneuverability under steady and unsteady maneuver conditions. The relevant fluid flow physics is not available presently and, hence, this thesis concentrated on generating those critical details. Towards this goal, model studies were conducted on the United States ... |
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