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Sample records for wake vortex model

  1. Review of Idealized Aircraft Wake Vortex Models

    NASA Technical Reports Server (NTRS)

    Ahmad, Nashat N.; Proctor, Fred H.; Duparcmeur, Fanny M. Limon; Jacob, Don

    2014-01-01

    Properties of three aircraft wake vortex models, Lamb-Oseen, Burnham-Hallock, and Proctor are reviewed. These idealized models are often used to initialize the aircraft wake vortex pair in large eddy simulations and in wake encounter hazard models, as well as to define matched filters for processing lidar observations of aircraft wake vortices. Basic parameters for each vortex model, such as peak tangential velocity and circulation strength as a function of vortex core radius size, are examined. The models are also compared using different vortex characterizations, such as the vorticity magnitude. Results of Euler and large eddy simulations are presented. The application of vortex models in the postprocessing of lidar observations is discussed.

  2. Multi-Model Ensemble Wake Vortex Prediction

    NASA Technical Reports Server (NTRS)

    Koerner, Stephan; Holzaepfel, Frank; Ahmad, Nash'at N.

    2015-01-01

    Several multi-model ensemble methods are investigated for predicting wake vortex transport and decay. This study is a joint effort between National Aeronautics and Space Administration and Deutsches Zentrum fuer Luft- und Raumfahrt to develop a multi-model ensemble capability using their wake models. An overview of different multi-model ensemble methods and their feasibility for wake applications is presented. The methods include Reliability Ensemble Averaging, Bayesian Model Averaging, and Monte Carlo Simulations. The methodologies are evaluated using data from wake vortex field experiments.

  3. Wake Vortex Inverse Model User's Guide

    NASA Technical Reports Server (NTRS)

    Lai, David; Delisi, Donald

    2008-01-01

    NorthWest Research Associates (NWRA) has developed an inverse model for inverting landing aircraft vortex data. The data used for the inversion are the time evolution of the lateral transport position and vertical position of both the port and starboard vortices. The inverse model performs iterative forward model runs using various estimates of vortex parameters, vertical crosswind profiles, and vortex circulation as a function of wake age. Forward model predictions of lateral transport and altitude are then compared with the observed data. Differences between the data and model predictions guide the choice of vortex parameter values, crosswind profile and circulation evolution in the next iteration. Iterations are performed until a user-defined criterion is satisfied. Currently, the inverse model is set to stop when the improvement in the rms deviation between the data and model predictions is less than 1 percent for two consecutive iterations. The forward model used in this inverse model is a modified version of the Shear-APA model. A detailed description of this forward model, the inverse model, and its validation are presented in a different report (Lai, Mellman, Robins, and Delisi, 2007). This document is a User's Guide for the Wake Vortex Inverse Model. Section 2 presents an overview of the inverse model program. Execution of the inverse model is described in Section 3. When executing the inverse model, a user is requested to provide the name of an input file which contains the inverse model parameters, the various datasets, and directories needed for the inversion. A detailed description of the list of parameters in the inversion input file is presented in Section 4. A user has an option to save the inversion results of each lidar track in a mat-file (a condensed data file in Matlab format). These saved mat-files can be used for post-inversion analysis. A description of the contents of the saved files is given in Section 5. An example of an inversion input

  4. Updated Results for the Wake Vortex Inverse Model

    NASA Technical Reports Server (NTRS)

    Robins, Robert E.; Lai, David Y.; Delisi, Donald P.; Mellman, George R.

    2008-01-01

    NorthWest Research Associates (NWRA) has developed an Inverse Model for inverting aircraft wake vortex data. The objective of the inverse modeling is to obtain estimates of the vortex circulation decay and crosswind vertical profiles, using time history measurements of the lateral and vertical position of aircraft vortices. The Inverse Model performs iterative forward model runs using estimates of vortex parameters, vertical crosswind profiles, and vortex circulation as a function of wake age. Iterations are performed until a user-defined criterion is satisfied. Outputs from an Inverse Model run are the best estimates of the time history of the vortex circulation derived from the observed data, the vertical crosswind profile, and several vortex parameters. The forward model, named SHRAPA, used in this inverse modeling is a modified version of the Shear-APA model, and it is described in Section 2 of this document. Details of the Inverse Model are presented in Section 3. The Inverse Model was applied to lidar-observed vortex data at three airports: FAA acquired data from San Francisco International Airport (SFO) and Denver International Airport (DEN), and NASA acquired data from Memphis International Airport (MEM). The results are compared with observed data. This Inverse Model validation is documented in Section 4. A summary is given in Section 5. A user's guide for the inverse wake vortex model is presented in a separate NorthWest Research Associates technical report (Lai and Delisi, 2007a).

  5. Evaluation of Fast-Time Wake Vortex Models using Wake Encounter Flight Test Data

    NASA Technical Reports Server (NTRS)

    Ahmad, Nashat N.; VanValkenburg, Randal L.; Bowles, Roland L.; Limon Duparcmeur, Fanny M.; Gloudesman, Thijs; van Lochem, Sander; Ras, Eelco

    2014-01-01

    This paper describes a methodology for the integration and evaluation of fast-time wake models with flight data. The National Aeronautics and Space Administration conducted detailed flight tests in 1995 and 1997 under the Aircraft Vortex Spacing System Program to characterize wake vortex decay and wake encounter dynamics. In this study, data collected during Flight 705 were used to evaluate NASA's fast-time wake transport and decay models. Deterministic and Monte-Carlo simulations were conducted to define wake hazard bounds behind the wake generator. The methodology described in this paper can be used for further validation of fast-time wake models using en-route flight data, and for determining wake turbulence constraints in the design of air traffic management concepts.

  6. NASA wake vortex research

    NASA Technical Reports Server (NTRS)

    Stough, H. P., III; Greene, George C.; Stewart, Eric C.; Stuever, Robert A.; Jordan, Frank L., Jr.; Rivers, Robert A.; Vicroy, Dan D.

    1993-01-01

    NASA is conducting research that will enable safe improvements in the capacity of the nation's air transportation system. The wake-vortex hazard is a factor in establishing the minimum safe spacing between aircraft during landing and takeoff operations and, thus, impacts airport capacity. The ability to accurately model the wake hazard and determine safe separation distances for a wide range of aircraft and operational scenarios may provide the basis for significant increases in airport capacity. Current and planned NASA research is described which is focused on increasing airport capacity by safely reducing wake-hazard-imposed aircraft separations through advances in a number of technologies including vortex motion and decay prediction, vortex encounter modeling, wake-vortex hazard characterization, and in situ flow sensing.

  7. Development of a rotor wake-vortex model, volume 1

    NASA Technical Reports Server (NTRS)

    Majjigi, R. K.; Gliebe, P. R.

    1984-01-01

    Certain empirical rotor wake and turbulence relationships were developed using existing low speed rotor wave data. A tip vortex model was developed by replacing the annulus wall with a row of image vortices. An axisymmetric turbulence spectrum model, developed in the context of rotor inflow turbulence, was adapted to predicting the turbulence spectrum of the stator gust upwash.

  8. A Coupled Probabilistic Wake Vortex and Aircraft Response Prediction Model

    NASA Technical Reports Server (NTRS)

    Gloudemans, Thijs; Van Lochem, Sander; Ras, Eelco; Malissa, Joel; Ahmad, Nashat N.; Lewis, Timothy A.

    2016-01-01

    Wake vortex spacing standards along with weather and runway occupancy time, restrict terminal area throughput and impose major constraints on the overall capacity and efficiency of the National Airspace System (NAS). For more than two decades, the National Aeronautics and Space Administration (NASA) has been conducting research on characterizing wake vortex behavior in order to develop fast-time wake transport and decay prediction models. It is expected that the models can be used in the systems level design of advanced air traffic management (ATM) concepts that safely increase the capacity of the NAS. It is also envisioned that at a later stage of maturity, these models could potentially be used operationally, in groundbased spacing and scheduling systems as well as on the flight deck.

  9. Unsteady Free-Wake Vortex Particle Model for HAWT

    NASA Astrophysics Data System (ADS)

    Bogateanu, R.; Frunzulicǎ, F.; Cardos, V.

    2010-09-01

    In the design of horizontal axis wind turbines (HAWT) one problem is to determine the aeroelastic behaviour of the rotor blades for the various wind inflow conditions. A step in this process is to predict with accuracy the aerodynamic loads on the blades. The Vortex Lattice Method (VLM) provides a transparent investigation concerning the role of various physical parameters which influence the aerodynamic problem. In this paper we present a method for the calculation of the non-uniform induced downwash of a HAWT rotor using the vortex ring model for the lifting surface coupled with an unsteady free-wake vortex particle model. Comparative studies between results obtained with different models of wake for a generic HAWT are presented.

  10. Wake Vortex Minimization

    NASA Technical Reports Server (NTRS)

    1977-01-01

    A status report is presented on research directed at reducing the vortex disturbances of aircraft wakes. The objective of such a reduction is to minimize the hazard to smaller aircraft that might encounter these wakes. Inviscid modeling was used to study trailing vortices and viscous effects were investigated. Laser velocimeters were utilized in the measurement of aircraft wakes. Flight and wind tunnel tests were performed on scale and full model scale aircraft of various design. Parameters investigated included the effect of wing span, wing flaps, spoilers, splines and engine thrust on vortex attenuation. Results indicate that vortives may be alleviated through aerodynamic means.

  11. Evaluation of a Wake Vortex Upset Model Based on Simultaneous Measurements of Wake Velocities and Probe-Aircraft Accelerations

    NASA Technical Reports Server (NTRS)

    Short, B. J.; Jacobsen, R. A.

    1979-01-01

    Simultaneous measurements were made of the upset responses experienced and the wake velocities encountered by an instrumented Learjet probe aircraft behind a Boeing 747 vortex-generating aircraft. The vortex-induced angular accelerations experienced could be predicted within 30% by a mathematical upset response model when the characteristics of the wake were well represented by the vortex model. The vortex model used in the present study adequately represented the wake flow field when the vortices dissipated symmetrically and only one vortex pair existed in the wake.

  12. Modeling of Wake-vortex Aircraft Encounters. Appendix B

    NASA Technical Reports Server (NTRS)

    Smith, Sonya T.

    1999-01-01

    There are more people passing through the world's airports today than at any other time in history. With this increase in civil transport, airports are becoming capacity limited. In order to increase capacity and thus meet the demands of the flying public, the number of runways and number of flights per runway must be increased. In response to the demand, the National Aeronautics and Space Administration (NASA), in conjunction with the Federal Aviation Administration (FAA), airport operators, and the airline industry are taking steps to increase airport capacity without jeopardizing safety. Increasing the production per runway increases the likelihood that an aircraft will encounter the trailing wake-vortex of another aircraft. The hazard of a wake-vortex encounter is that heavy load aircraft can produce high intensity wake turbulence, through the development of its wing-tip vortices. A smaller aircraft following in the wake of the heavy load aircraft will experience redistribution of its aerodynamic load. This creates a safety hazard for the smaller aircraft. Understanding this load redistribution is of great importance, particularly during landing and take-off. In this research wake-vortex effects on an encountering 10% scale model of the B737-100 aircraft are modeled using both strip theory and vortex-lattice modeling methods. The models are then compared to wind tunnel data that was taken in the 30ft x 60ft wind tunnel at NASA Langley Research Center (LaRC). Comparisons are made to determine if the models will have acceptable accuracy when parts of the geometry are removed, such as the horizontal stabilizer and the vertical tail. A sensitivity analysis was also performed to observe how accurately the models could match the experimental data if there was a 10% error in the circulation strength. It was determined that both models show accurate results when the wing, horizontal stabilizer, and vertical tail were a part of the geometry. When the horizontal

  13. Nonlinear modelling of vortex shedding control in cylinder wakes

    NASA Astrophysics Data System (ADS)

    Roussopoulos, Kimon; Monkewitz, Peter A.

    Kármán vortex shedding behind a cylinder placed at right angles to a uniform flow is known to be a limit cycle oscillation that results from the saturation of a global instability of the wake flow. In this paper we study the feedback control of Kármán vortex shedding for Reynolds numbers (based on cylinder diameter) close to the critical value of Re c ≈ 47 using “single input - single output” (SISO) proportional control. A model is presented that combines the linear streamwise global mode amplitude equation and the nonlinear spanwise Ginzburg-Landau equation and correctly models the three-dimensional effects observed in the controlled wake of finite length cyclinders. In particular it is demonstrated that for long cylinders vortex shedding can only be suppressed at the spanwise location of the sensor even though the actuation occurs uniformly over the entire span. At a fixed streamwise position the spanwise variation of the shedding angle is thereby given by the “hole solution” of Nozaki and Bekki, J. Phys. Soc. Jpn. 53 (1984) 1581.

  14. Coupling of a free wake vortex ring near-wake model with the Jensen and Larsen far-wake deficit models

    NASA Astrophysics Data System (ADS)

    van Heemst, J. W.; Baldacchino, D.; Mehta, D.; van Bussel, G. J. W.

    2015-06-01

    This paper presents a simple physical model to improve the currently used far-wake deficit models in the wind industry. The main improvement is deemed on the determination of the wake deficit in the near-wake. A Vortex Ring Model (VRM) is used to calculate the induced velocities in the near-wake, which are then coupled to the Jensen far-wake model and the Larsen far-wake model based on the concept of Eddy Viscosity (EV). The inviscid near-wake VRM is based on the shedding of discrete tip vortex rings released from a uniformly loaded actuator disc. The model is validated against wind tunnel measurements from experiments with a two- bladed turbine and a circular metal mesh with a uniform porosity to represent an actuator disc. The VRM shows a good agreement with the experimental data with respect to the wake deficit evolution. The VRM is coupled with two well-known engineering type far-wake models: the Jensen and Larsen wake deficit models. The results of the coupling of the VRM and the more elaborated Larsen far-wake model are compared against a 3D Large Eddy Simulation (LES) CFD model. This comparison shows the effect of different near-wake models on the development of centreline velocities in the far-wake. The centreline velocity deficit predicted by the VRM-Larsen model more closely matches LES calculations in comparison with the reference Larsen model.

  15. Documentation for Three Wake Vortex Model Data Sets from Simulation of Flight 587 Wake Vortex Encounter Accident Case

    NASA Technical Reports Server (NTRS)

    Switzer, George F.

    2008-01-01

    This document contains a general description for data sets of a wake vortex system in a turbulent environment. The turbulence and thermal stratification of the environment are representative of the conditions on November 12, 2001 near John F. Kennedy International Airport. The simulation assumes no ambient winds. The full three dimensional simulation of the wake vortex system from a Boeing 747 predicts vortex circulation levels at 80% of their initial value at the time of the proposed vortex encounter. The linked vortex oval orientation showed no twisting, and the oval elevations at the widest point were about 20 meters higher than where the vortex pair joined. Fred Proctor of NASA?s Langley Research Center presented the results from this work at the NTSB public hearing that started 29 October 2002. This document contains a description of each data set including: variables, coordinate system, data format, and sample plots. Also included are instructions on how to read the data.

  16. Free Wake Techniques for Rotor Aerodynamic Analylis. Volume 2: Vortex Sheet Models

    NASA Technical Reports Server (NTRS)

    Tanuwidjaja, A.

    1982-01-01

    Results of computations are presented using vortex sheets to model the wake and test the sensitivity of the solutions to various assumptions used in the development of the models. The complete codings are included.

  17. Evaluation of Fast-Time Wake Vortex Prediction Models

    NASA Technical Reports Server (NTRS)

    Proctor, Fred H.; Hamilton, David W.

    2009-01-01

    Current fast-time wake models are reviewed and three basic types are defined. Predictions from several of the fast-time models are compared. Previous statistical evaluations of the APA-Sarpkaya and D2P fast-time models are discussed. Root Mean Square errors between fast-time model predictions and Lidar wake measurements are examined for a 24 hr period at Denver International Airport. Shortcomings in current methodology for evaluating wake errors are also discussed.

  18. A mathematical model of 2P and 2C vortex wakes

    NASA Astrophysics Data System (ADS)

    Stremler, Mark A.; Salmanzadeh, Alireza; Basu, Saikat; Williamson, Charles H. K.

    2011-07-01

    We present a mathematical model of the vortex wake modes that appear behind neighboring and/or oscillating, flapping, and swimming bodies in which there are four vortices generated in an anti-symmetric pattern during each shedding cycle. The two-dimensional potential flow model consists of four point vortices with strengths ±Γ in a spatially periodic domain. The relative vortex positions are restricted by a discrete symmetry that is motivated by the spatial symmetry observed in experimental wakes. The strength restriction and the imposed symmetry result in the model system being an integrable Hamiltonian dynamical system. We find that the point vortex motion can be one of four distinct types based on the values of linear impulse and Hamiltonian. Two of these types correspond to 2P wakes and consist of two oppositely signed, counter-rotating vortex pairs. One of these types corresponds to 2C wakes and consists of two like-signed, co-rotating vortex pairs. The fourth type is an exchanging mode in which the two vortices near the wake centerline translate faster than the outer two vortices. Scaled comparisons of the model with both a 2P and a 2C experimental wake show good representation of the experimentally observed vortex dynamics and lead to estimates of the experimental vortex strengths.

  19. The NASA-Langley Wake Vortex Modelling Effort in Support of an Operational Aircraft Spacing System

    NASA Technical Reports Server (NTRS)

    Proctor, Fred H.

    1998-01-01

    Two numerical modelling efforts, one using a large eddy simulation model and the other a numerical weather prediction model, are underway in support of NASA's Terminal Area Productivity program. The large-eddy simulation model (LES) has a meteorological framework and permits the interaction of wake vortices with environments characterized by crosswind shear, stratification, humidity, and atmospheric turbulence. Results from the numerical simulations are being used to assist in the development of algorithms for an operational wake-vortex aircraft spacing system. A mesoscale weather forecast model is being adapted for providing operational forecast of winds, temperature, and turbulence parameters to be used in the terminal area. This paper describes the goals and modelling approach, as well as achievements obtained to date. Simulation results will be presented from the LES model for both two and three dimensions. The 2-D model is found to be generally valid for studying wake vortex transport, while the 3-D approach is necessary for realistic treatment of decay via interaction of wake vortices and atmospheric boundary layer turbulence. Meteorology is shown to have an important affect on vortex transport and decay. Presented are results showing that wake vortex transport is unaffected by uniform fog or rain, but wake vortex transport can be strongly affected by nonlinear vertical change in the ambient crosswind. Both simulation and observations show that atmospheric vortices decay from the outside with minimal expansion of the core. Vortex decay and the onset three-dimensional instabilities are found to be enhanced by the presence of ambient turbulence.

  20. Development of a rotor wake/vortex model. Volume 2: User's manual for computer program

    NASA Technical Reports Server (NTRS)

    Majjigi, R. K.; Gliebe, P. R.

    1984-01-01

    The principal objective was to establish a verified rotor wake/vortex model for specific application to fan and compressor rotor-stator interaction and resulting noise generation. A description and flow chart of the Rotor Wake/Vortex Model computer program, a listing of the program, definitions of the input/output parameters, a sample input/output case, and input files for Rotor 55, the JT15D rotor, and Rotor 67, Stage 1 are provided.

  1. Wind turbine wake stability investigations using a vortex ring modelling approach

    NASA Astrophysics Data System (ADS)

    Baldacchino, Daniel; van Bussel, Gerard J. W.

    2014-12-01

    In the present study, a simple inviscid vortex ring (VR) modelling approach is used to represent the developing rotor wake. This allows a straightforward investigation and comparison of the impact of uniform, yawed and sheared flow conditions on the development of the rotor wake, with the additional possibility of including ground effect. The effect of instabilities on the development of the wake is manually introduced in the form of perturbations of strength, ring position and size. The phenomenon of vortex filament interaction or leapfrogging, could play a role in the observation of unsteady phenomena and is therefore also addressed. Such a study is hence performed in light of recent conflicting views on the causes of wake meandering: is the observed dynamic wake behaviour a result of large scale turbulent forcing or do more subtle and intrinsic wake instabilities play a role? This study concludes that the presence of the ground and external perturbations, most notably changes in the wake pitch and the rotor thrust coefficient, can significantly affect the steady development of the wake. The mutual vortex pairing instability, whilst displaying interesting periodic behaviour, does not correlate with periodic wake behaviour reported by Medici et al. [1]. However, in the absence of unsteady inflow, it is shown that the wake of a Horizontal Axis Wind Turbine (HAWT) is certainly prone to displaying unstable, dynamic behaviour caused by these additional factors.

  2. Helicopter blade-vortex interaction locations: Scale-model acoustics and free-wake analysis results

    NASA Technical Reports Server (NTRS)

    Hoad, Danny R.

    1987-01-01

    The results of a model rotor acoustic test in the Langley 4by 7-Meter Tunnel are used to evaluate a free-wake analytical technique. An acoustic triangulation technique is used to locate the position in the rotor disk where the blade-vortex interaction noise originates. These locations, along with results of the rotor free-wake analysis, are used to define the geometry of the blade-vortex interaction noise phenomena as well as to determine if the free-wake analysis is a capable diagnostic tool. Data from tests of two teetering rotor systems are used in these analyses.

  3. Passive Wake Vortex Control

    SciTech Connect

    Ortega, J M

    2001-10-18

    The collapse of the Soviet Union and ending of the Cold War brought about many significant changes in military submarine operations. The enemies that the US Navy faces today and in the future will not likely be superpowers armed with nuclear submarines, but rather smaller, rogue nations employing cheaper diesel/electric submarines with advanced air-independent propulsion systems. Unlike Cold War submarine operations, which occurred in deep-water environments, future submarine conflicts are anticipated to occur in shallow, littoral regions that are complex and noisy. Consequently, non-acoustic signatures will become increasingly important and the submarine stealth technology designed for deep-water operations may not be effective in these environments. One such non-acoustic signature is the surface detection of a submarine's trailing vortex wake. If a submarine runs in a slightly buoyant condition, its diving planes must be inclined at a negative angle of attack to generate sufficient downforce, which keeps the submarine from rising to the surface. As a result, the diving planes produce a pair of counter-rotating trailing vortices that propagate to the water surface. In previous deep-water operations, this was not an issue since the submarines could dive deep enough so that the vortex pair became incoherent before it reached the water surface. However, in shallow, littoral environments, submarines do not have the option of diving deep and, hence, the vortex pair can rise to the surface and leave a distinct signature that might be detectable by synthetic aperture radar. Such detection would jeopardize not only the mission of the submarine, but also the lives of military personnel on board. There has been another attempt to solve this problem and reduce the intensity of trailing vortices in the wakes of military submarines. The research of Quackenbush et al. over the past few years has been directed towards an idea called ''vortex leveraging.'' This active concept

  4. Nested contour-dynamic models for axisymmetric vortex rings and vortex wakes

    NASA Astrophysics Data System (ADS)

    O'Farrell, Clara; Dabiri, John O.

    2013-11-01

    Jetting swimmers, such as squid and jellyfish, propel themselves by forming vortex rings. It is known that vortex rings cannot grow indefinitely, but rather ``pinch off'' once they reach their physical limit, and that a decrease in efficiency of fluid transport is associated with pinch-off. Previously, the Norbury family of vortices has been used as a model for axisymmetric vortex rings, and the response of this family to shape perturbations has been characterized. We improve upon the Norbury models, using nested patches of vorticity to construct a family of models for vortex rings generated by a piston-cylinder apparatus at different stroke ratios. The perturbation response of this family is considered by the introduction of a small region of vorticity at the rear of the vortex, which mimics the addition of circulation to a growing vortex ring by a feeding shear layer. Model vortex rings are found to either accept the additional circulation or shed it into a tail, depending on the perturbation size. A change in the behavior of the model vortex rings is identified at a stroke ratio of three. We hypothesize that this change in response is analogous to pinch-off, and that pinch-off might be understood and predicted based on the perturbation responses of model vortex rings.

  5. Models of Wake-Vortex Spreading Mechanisms and Their Estimated Uncertainties

    NASA Technical Reports Server (NTRS)

    Rossow, Vernon J.; Hardy, Gordon H.; Meyn, Larry A.

    2006-01-01

    One of the primary constraints on the capacity of the nation's air transportation system is the landing capacity at its busiest airports. Many airports with nearly-simultaneous operations on closely-spaced parallel runways (i.e., as close as 750 ft (246m)) suffer a severe decrease in runway acceptance rate when weather conditions do not allow full utilization. The objective of a research program at NASA Ames Research Center is to develop the technologies needed for traffic management in the airport environment so that operations now allowed on closely-spaced parallel runways under Visual Meteorological Conditions can also be carried out under Instrument Meteorological Conditions. As part of this overall research objective, the study reported here has developed improved models for the various aerodynamic mechanisms that spread and transport wake vortices. The purpose of the study is to continue the development of relationships that increase the accuracy of estimates for the along-trail separation distances available before the vortex wake of a leading aircraft intrudes into the airspace of a following aircraft. Details of the models used and their uncertainties are presented in the appendices to the paper. Suggestions are made as to the theoretical and experimental research needed to increase the accuracy of and confidence level in the models presented and instrumentation required or more precise estimates of the motion and spread of vortex wakes. The improved wake models indicate that, if the following aircraft is upwind of the leading aircraft, the vortex wakes of the leading aircraft will not intrude into the airspace of the following aircraft for about 7s (based on pessimistic assumptions) for most atmospheric conditions. The wake-spreading models also indicate that longer time intervals before wake intrusion are available when atmospheric turbulence levels are mild or moderate. However, if the estimates for those time intervals are to be reliable, further study

  6. Vortex interactions and decay in aircraft wakes

    NASA Technical Reports Server (NTRS)

    Bilanin, A. J.; Teske, M. E.; Dupdonaldson, C.; Williamson, G. G.

    1977-01-01

    The dynamic interaction of aircraft wake vortices was investigated using both inviscid and viscous models. For the viscous model, a computer code was developed using a second-order closure model of turbulent transport. The phenomenon of vortex merging which results in the rapid aging of a vortex wake was examined in detail. It was shown that the redistribution of vorticity during merging results from both convective and diffusive mechanisms.

  7. Numerical Modeling Studies of Wake Vortex Transport and Evolution Within the Planetary Boundary Layer

    NASA Technical Reports Server (NTRS)

    Lin, Yuh-Lang; Arya, S. Pal; Kaplan, Michael L.; Han, Jongil

    2000-01-01

    The fundamental objective of this research is study behavior of aircraft wake vortices within atmospheric boundary layer (ABL) in support of developing the system, Aircraft VOrtex Spacing System (AVOSS), under NASA's Terminal Area Productivity (TAR) program that will control aircraft spacing within the narrow approach corridors of airports. The purpose of the AVOSS system is to increase airport capacity by providing a safe reduction in separation of aircraft compared to the now-existing flight rules. In our first funding period (7 January 19994 - 6 April 1997), we have accomplished extensive model development and validation of ABL simulations. Using the validated model, in our second funding period (7 April 1997 - 6 April 2000) we have investigated the effects of ambient atmospheric turbulence on vortex decay and descent, Crow instability, and wake vortex interaction with the ground. Recognizing the crucial influence of ABL turbulence on wake vortex behavior, we have also developed a software generating vertical profiles of turbulent kinetic energy (TKE) or energy dissipation rate (EDR), which are, in turn, used as input data in the AVOSS prediction algorithms.

  8. NASA Wake Vortex Research for Aircraft Spacing

    NASA Technical Reports Server (NTRS)

    Perry, R. Brad; Hinton, David A.; Stuever, Robert A.

    1996-01-01

    The National Aeronautics and Space Administration (NASA) is addressing airport capacity enhancements during instrument meteorological conditions through the Terminal Area Productivity (TAP) program. Within TAP, the Reduced Spacing Operations (RSO) subelement at the NASA Langley Research Center is developing an Aircraft Vortex Spacing System (AVOSS). AVOSS will integrate the output of several inter-related areas to produce weather dependent, dynamic wake vortex spacing criteria. These areas include current and predicted weather conditions, models of wake vortex transport and decay in these weather conditions, real-time feedback of wake vortex behavior from sensors, and operationally acceptable aircraft/wake interaction criteria. In today's ATC system, the AVOSS could inform ATC controllers when a fixed reduced separation becomes safe to apply to large and heavy aircraft categories. With appropriate integration into the Center/TRACON Automation System (CTAS), AVOSS dynamic spacing could be tailored to actual generator/follower aircraft pairs rather than a few broad aircraft categories.

  9. Numerical modeling studies of wake vortex transport and evolution within the planetary boundary layer

    NASA Technical Reports Server (NTRS)

    Lin, Yuh-Lang; Arya, S. Pal; Kaplan, Michael L.

    1994-01-01

    The proposed research involves four tasks. The first of these is to simulate accurately the turbulent processes in the atmospheric boundary layer. TASS was originally developed to study meso-gamma scale phenomena, such as tornadic storms, microbursts and windshear effects in terminal areas. Simulation of wake vortex evolution, however, will rely on appropriate representation of the physical processes in the surface layer and mixed layer. This involves two parts. First, a specified heat flux boundary condition must be implemented at the surface. Using this boundary condition, simulation results will be compared to experimental data and to other model results for validation. At this point, any necessary changes to the model will be implemented. Next, a surface energy budget parameterization will be added to the model. This will enable calculation of the surface fluxes by accounting for the radiative heat transfer to and from the ground and heat loss to the soil rather than simple specification of the fluxes. The second task involves running TASS with prescribed wake vortices in the initial condition. The vortex models will be supplied by NASA Langley Research Center. Sensitivity tests will be performed on different meteorological environments in the atmospheric boundary layer, which include stable, neutral, and unstable stratifications, calm and severe wind conditions, and dry and wet conditions. Vortex strength may be varied as well. Relevant non-dimensional parameters will include the following: Richardson number or Froude number, Bowen ratio, and height to length scale ratios. The model output will be analyzed and visualized to better understand the transport, decay, and growth rates of the wake vortices. The third task involves running simulations using observed data. MIT Lincoln Labs is currently planning field experiments at the Memphis airport to measure both meteorological conditions and wake vortex characteristics. Once this data becomes available, it can be

  10. Recent NASA Wake-Vortex Flight Tests, Flow-Physics Database and Wake-Development Analysis

    NASA Technical Reports Server (NTRS)

    Vicroy, Dan D.; Vijgen, Paul M.; Reimer, Heidi M.; Gallegos, Joey L.; Spalart, Philippe R.

    1998-01-01

    A series of flight tests over the ocean of a four engine turboprop airplane in the cruise configuration have provided a data set for improved understanding of wake vortex physics and atmospheric interaction. An integrated database has been compiled for wake characterization and validation of wake-vortex computational models. This paper describes the wake-vortex flight tests, the data processing, the database development and access, and results obtained from preliminary wake-characterization analysis using the data sets.

  11. Comparisons of Crosswind Velocity Profile Estimates Used in Fast-Time Wake Vortex Prediction Models

    NASA Technical Reports Server (NTRS)

    Pruis, Mathew J.; Delisi, Donald P.; Ahmad, Nashat N.

    2011-01-01

    Five methods for estimating crosswind profiles used in fast-time wake vortex prediction models are compared in this study. Previous investigations have shown that temporal and spatial variations in the crosswind vertical profile have a large impact on the transport and time evolution of the trailing vortex pair. The most important crosswind parameters are the magnitude of the crosswind and the gradient in the crosswind shear. It is known that pulsed and continuous wave lidar measurements can provide good estimates of the wind profile in the vicinity of airports. In this study comparisons are made between estimates of the crosswind profiles from a priori information on the trajectory of the vortex pair as well as crosswind profiles derived from different sensors and a regional numerical weather prediction model.

  12. Vortex Wake Geometry of a Model Tilt Rotor in Forward Flight

    NASA Technical Reports Server (NTRS)

    Wadcock, Alan J.; Yamauchi, Gloria K.; Rutkowski, Michael (Technical Monitor)

    2001-01-01

    A full-span 0.25-scale V-22 tiltrotor was tested in the NASA Ames 40-by 80-Foot Wind Tunnel in November 2000. The main objective of the test was to acquire a comprehensive database to validate tiltrotor analyses. Figure 1 shows the model installed in the Ames 40- by 80-Foot Wind Tunnel. Rotor and vehicle performance measurements were taken in addition to wing pressures, acoustics, and flow visualization. A dual acoustic traverse system was installed to measure blade-vortex interaction (BVI) noise levels and directivity. Test conditions included hover and forward flight in helicopter mode. Angle-of-attack and thrust sweeps for three tunnel speeds were acquired before model problems caused the premature conclusion of the test. The test will resume in the Ames 80- by 120-Foot Wind Tunnel in late 2001. This paper will focus on the wake geometry measurements that were acquired during the test. The wake geometry measurements were a small subset of a larger matrix of planned measurements designed to study the development and structure of the dual vortex system generated during BVI conditions. The present paper will provide wake geometry data for four test conditions. In addition, the data will be compared with previously acquired wake measurements from an isolated tiltrotor

  13. Three-Phased Wake Vortex Decay

    NASA Technical Reports Server (NTRS)

    Proctor, Fred H.; Ahmad, Nashat N.; Switzer, George S.; LimonDuparcmeur, Fanny M.

    2010-01-01

    A detailed parametric study is conducted that examines vortex decay within turbulent and stratified atmospheres. The study uses a large eddy simulation model to simulate the out-of-ground effect behavior of wake vortices due to their interaction with atmospheric turbulence and thermal stratification. This paper presents results from a parametric investigation and suggests improvements for existing fast-time wake prediction models. This paper also describes a three-phased decay for wake vortices. The third phase is characterized by a relatively slow rate of circulation decay, and is associated with the ringvortex stage that occurs following vortex linking. The three-phased decay is most prevalent for wakes imbedded within environments having low-turbulence and near-neutral stratification.

  14. ASRS Reports on Wake Vortex Encounters

    NASA Technical Reports Server (NTRS)

    Connell, Linda J.; Taube, Elisa Ann; Drew, Charles Robert; Barclay, Tommy Earl

    2010-01-01

    ASRS is conducting a structured callback research project of wake vortex incidents reported to the ASRS at all US airports, as well as wake encounters in the enroute environment. This study has three objectives: (1) Utilize the established ASRS supplemental data collection methodology and provide ongoing analysis of wake vortex encounter reports; (2) Document event dynamics and contributing factors underlying wake vortex encounter events; and (3) Support ongoing FAA efforts to address pre-emptive wake vortex risk reduction by utilizing ASRS reporting contributions.

  15. Wake Vortex Advisory System (WakeVAS) Concept of Operations

    NASA Technical Reports Server (NTRS)

    Rutishauser, David; Lohr, Gary; Hamilton, David; Powers, Robert; McKissick, Burnell; Adams, Catherine; Norris, Edward

    2003-01-01

    NASA Langley Research Center has a long history of aircraft wake vortex research, with the most recent accomplishment of demonstrating the Aircraft VOrtex Spacing System (AVOSS) at Dallas/Forth Worth International Airport in July 2000. The AVOSS was a concept for an integration of technologies applied to providing dynamic wake-safe reduced spacing for single runway arrivals, as compared to current separation standards applied during instrument approaches. AVOSS included state-of-the-art weather sensors, wake sensors, and a wake behavior prediction algorithm. Using real-time data AVOSS averaged a 6% potential throughput increase over current standards. This report describes a Concept of Operations for applying the technologies demonstrated in the AVOSS to a variety of terminal operations to mitigate wake vortex capacity constraints. A discussion of the technological issues and open research questions that must be addressed to design a Wake Vortex Advisory System (WakeVAS) is included.

  16. Interfacing comprehensive rotorcraft analysis with advanced aeromechanics and vortex wake models

    NASA Astrophysics Data System (ADS)

    Liu, Haiying

    -2, and the CSD program, DYMORE, is also established. The ability to accurately capture the wake structure around a helicopter rotor is crucial for rotorcraft performance analysis. In the third part of this thesis, a new representation of the wake vortex structure based on Non-Uniform Rational B-Spline (NURBS) curves and surfaces is proposed to develop an efficient model for prescribed and free wakes. NURBS curves and surfaces are able to represent complex shapes with remarkably little data. The proposed formulation has the potential to reduce the computational cost associated with the use of Helmholtz's law and the Biot-Savart law when calculating the induced flow field around the rotor. An efficient free-wake analysis will considerably decrease the computational cost of comprehensive rotorcraft analysis, making the approach more attractive to routine use in industrial settings.

  17. Wake Vortex Research in the USA (WakeNet-USA)

    NASA Technical Reports Server (NTRS)

    Lang, Steve; Bryant, Wayne

    2006-01-01

    This viewgraph presentation reviews the cooperative work that FAA and NASA are engaged in to safely increase the capacity of the National Airspace System by studying the wake vortex operations. Wake vortex avoidance is a limiting factor in defining separation standards in the airport terminal area and could become a reducing separation standards in en route airspace.

  18. NOWVIV - Nowcasting wake vortex impact variables

    NASA Astrophysics Data System (ADS)

    Tafferner, A.; Birke, L.; Frech, M.

    2003-04-01

    A central task of the ongoing DLR project "Wirbelschleppe" (Wake Vortex) is to forecast meteorological quantities which influence the behaviour of wake vortices of landing aircraft. In the first place these are wind, temperature and turbulence, resp. the vertical shear thereof, which impact the lateral drift and turbulent decay of wake vortices. For this purpose the nowcasting system NOWVIV has been developed at DLR. It combines operational forecasts of the Lokal Modell (LM; Doms and Schaettler 1999) of the German weather service DWD with a high-resolution forecasting system. For the latter, the NOAA/FSL version of the mesoscale model MM5 (Grell et al. 2000) has been adapted to particular sites. Orography, land use, and soil type have been generated from available data sources for a 80 km square domain centered on a particular airport with a horizontal resolution of 2.1 km. As a good representation of the boundary layer is of particular importance for predicting wake vortex impact variables, the vertical spacing of model layers has been selected rather small throughout the lower model atmosphere, starting with 20 m at the ground and increasing to about 60 m at 2 km height. NOWVIV delivers vertical profiles of vortex impact variables, which are used by the wake prediction model ``P2P'' developed at DLR (Holzaepfel 2002) to predict wake vortex behaviour. During the two field campaigns ``WakeOP'' and ``WakeTOUL'' in April/May 2001 and May/June 2002 which aimed at measuring (by lidar) and predicting wake vortex behaviour of landing aircraft, NOWVIV has been run in an operational mode for the airports of Oberpfaffenhofen (Germany) and Tarbes (France). A statistical evaluation of the NOWVIV forecasting performance during these campaigns achieved satisfactory results as compared to local measurements of wind and temperature from radio acoustic sounding instruments (Frech et al. 2002). However, there are uncertainties in the daily variation of the boundary layer. Also, the

  19. Dynamics of the vortex wakes of flying and swimming vertebrates.

    PubMed

    Rayner, J M

    1995-01-01

    The vortex wakes of flying and swimming animals provide evidence of the history of aero- and hydrodynamic force generation during the locomotor cycle. Vortex-induced momentum flux in the wake is the reaction of forces the animal imposes on its environment, which must be in equilibrium with inertial and external forces. In flying birds and bats, the flapping wings generate lift both to provide thrust and to support the weight. Distinct wingbeat and wake movement patterns can be identified as gaits. In flow visualization experiments, only two wake patterns have been identified: a vortex ring gait with inactive upstroke, and a continuous vortex gait with active upstroke. These gaits may be modelled theoretically by free vortex and lifting line theory to predict mechanical energy consumption, aerodynamic forces and muscle activity. Longer-winged birds undergo a distinct gait change with speed, but shorter-winged species use the vortex ring gait at all speeds. In swimming fish, the situation is more complex: the wake vortices form a reversed von Kármán vortex street, but little is known about the mechanism of generation of the wake, or about how it varies with speed and acceleration or with body form and swimming mode. An unresolved complicating factor is the interaction between the drag wake of the flapping fish body and the thrusting wake from the tail. PMID:8571221

  20. Wake Vortex Algorithm Scoring Results

    NASA Technical Reports Server (NTRS)

    Robins, R. E.; Delisi, D. P.; Hinton, David (Technical Monitor)

    2002-01-01

    This report compares the performance of two models of trailing vortex evolution for which interaction with the ground is not a significant factor. One model uses eddy dissipation rate (EDR) and the other uses the kinetic energy of turbulence fluctuations (TKE) to represent the effect of turbulence. In other respects, the models are nearly identical. The models are evaluated by comparing their predictions of circulation decay, vertical descent, and lateral transport to observations for over four hundred cases from Memphis and Dallas/Fort Worth International Airports. These observations were obtained during deployments in support of NASA's Aircraft Vortex Spacing System (AVOSS). The results of the comparisons show that the EDR model usually performs slightly better than the TKE model.

  1. Analysis of vortex wake encounter upsets

    NASA Technical Reports Server (NTRS)

    Johnson, W. A.; Teper, G. L.

    1974-01-01

    The problem of an airplane being upset by encountering the vortex wake of a large transport on takeoff or landing is currently receiving considerable attention. This report describes the technique and results of a study to assess the effectiveness of automatic control systems in alleviating vortex wake upsets. A six-degree-of-freedom nonlinear digital simulation was used for this purpose. The analysis included establishing the disturbance input due to penetrating a vortex wake from an arbitrary position and angle. Simulations were computed for both a general aviation airplane and a commercial jet transport. Dynamic responses were obtained for the penetrating aircraft with no augmentation, and with various command augmentation systems, as well as with human pilot control. The results of this preliminary study indicate that attitude command augmentation systems can provide significant alleviation of vortex wake upsets; and can do it better than a human pilot.

  2. An unsteady vortex lattice method model of a horizontal axis wind turbine operating in an upstream rotor wake

    NASA Astrophysics Data System (ADS)

    Hankin, D.; Graham, J. M. R.

    2014-12-01

    An unsteady formulation of the vortex lattice method, VLM, is presented that uses a force- free representation of the wake behind a horizontal axis wind turbine, HAWT, to calculate the aerodynamic loading on a turbine operating in the wake of an upstream rotor. A Cartesian velocity grid is superimposed over the computational domain to facilitate the representation of the atmospheric turbulence surrounding the turbine and wind shear. The wake of an upstream rotor is modelled using two methods: a mean velocity deficit with superimposed turbulence, based on experimental observations, and a purely numeric periodic boundary condition. Both methods are treated as frozen and propagated with the velocity grid. Measurements of the mean thrust and blade root bending moment on a three bladed horizontal axis rotor modelling a 5 MW HAWT at 1:250 scale were carried out in a wind tunnel. Comparisons are made between operation in uniform flow and in the wake of a similarly loaded rotor approximately 6.5 diameters upstream. The measurements were used to validate the output from the VLM simulations, assuming a completely rigid rotor. The trends in the simulation thrust predictions are found to compare well with the uniform flow case, except at low tip speed ratios where there are losses due to stall which are yet to be included in the model. The simple wake model predicts the mean deficit, whilst the periodic boundary condition captures more of the frequency content of the loading in an upstream wake. However, all the thrust loads are over-predicted. The simulation results severely overestimate the bending moment, which needs addressing. However, the reduction in bending due to the simple wake model is found to reflect the experimental data reasonably well.

  3. Feasibility of wake vortex monitoring systems for air terminals

    NASA Technical Reports Server (NTRS)

    Wilson, D. J.; Shrider, K. R.; Lawrence, T. R.

    1972-01-01

    Wake vortex monitoring systems, especially those using laser Doppler sensors, were investigated. The initial phases of the effort involved talking with potential users (air traffic controllers, pilots, etc.) of a wake vortex monitoring system to determine system requirements from the user's viewpoint. These discussions involved the volumes of airspace to be monitored for vortices, and potential methods of using the monitored vortex data once the data are available. A subsequent task led to determining a suitable mathematical model of the vortex phenomena and developing a mathematical model of the laser Doppler sensor for monitoring the vortex flow field. The mathematical models were used in combination to help evaluate the capability of laser Doppler instrumentation in monitoring vortex flow fields both in the near vicinity of the sensor (within 1 kilometer and at long ranges(10 kilometers).

  4. Vortex Wakes of Subsonic Transport Aircraft

    NASA Technical Reports Server (NTRS)

    Rossow, Vernon J.; Nixon, David (Technical Monitor)

    1999-01-01

    A historical overview will be presented of the research conducted on the structure and modification of the vortices generated by the lifting surfaces of subsonic transport aircraft. The seminar will describe the three areas of vortex research; namely, the magnitude of the hazard posed, efforts to reduce the hazard to an acceptable level, and efforts to develop a systematic means for avoiding vortex wakes. It is first pointed out that the characteristics of lift-generated vortices are related to the aerodynamic shapes that produce them and that various arrangements of surfaces can be used to produce different vortex structures. The largest portion of the research conducted to date has been directed at finding ways to reduce the hazard potential of lift-generated vortices shed by subsonic transport aircraft in the vicinity of airports during landing and takeoff operations. It is stressed that lift-generated vortex wakes are so complex that progress towards a solution requires application of a combined theoretical and experimental research program because either alone often leads to incorrect conclusions. It is concluded that a satisfactory aerodynamic solution to the wake-vortex problem at airports has not yet been found but a reduction in the impact of the wake-vortex hazard on airport capacity may become available in the foreseeable future through wake-vortex avoidance concepts currently under study. The material to be presented in this overview is drawn from articles published in aerospace journals that are available publicly.

  5. Measurements and modeling of flow structure in the wake of a low profile wishbone vortex generator

    NASA Technical Reports Server (NTRS)

    Wendt, B. J.; Hingst, W. R.

    1994-01-01

    The results of an experimental examination of the vortex structures shed from a low profile 'wishbone' generator are presented. The vortex generator height relative to the turbulent boundary layer was varied by testing two differently sized models. Measurements of the mean three-dimensional velocity field were conducted in cross-stream planes downstream of the vortex generators. In all cases, a counter-rotating vortex pair was observed. Individual vortices were characterized by three descriptors derived from the velocity data; circulation, peak vorticity, and cross-stream location of peak vorticity. Measurements in the cross plane at two axial locations behind the smaller wishbone characterize the downstream development of the vortex pairs. A single region of stream wise velocity deficit is shared by both vortex cores. This is in contrast to conventional generators, where each core coincides with a region of velocity deficit. The measured cross-stream velocities for each case are compared to an Oseen model with matching descriptors. The best comparison occurs with the data from the larger wishbone.

  6. Wake-Vortex Hazards During Cruise

    NASA Technical Reports Server (NTRS)

    Rossow, Vernon J.; James, Kevin D.; Nixon, David (Technical Monitor)

    1998-01-01

    Even though the hazard posed by lift-generated wakes of subsonic transport aircraft has been studied extensively for approach and departure at airports, only a small amount of effort has gone into the potential hazard at cruise altitude. This paper reports on a studio of the wake-vortex hazard during cruise because encounters may become more prevalent when free-flight becomes available and each aircraft, is free to choose its own route between destinations. In order to address the problem, the various fluid-dynamic stages that vortex wakes usually go through as they age will be described along with estimates of the potential hazard that each stage poses. It appears that a rolling-moment hazard can be just as severe at cruise as for approach at airports, but it only persists for several minutes. However, the hazard posed by the downwash in the wake due to the lift on the generator aircraft persists for tens of minutes in a long narrow region behind the generating aircraft. The hazard consists of severe vertical loads when an encountering aircraft crosses the wake. A technique for avoiding vortex wakes at cruise altitude will be described. To date the hazard posed by lift-generated vortex wakes and their persistence at cruise altitudes has been identified and subdivided into several tasks. Analyses of the loads to be encounter and are underway and should be completed shortly. A review of published literature on the subject has been nearly completed (see text) and photographs of vortex wakes at cruise altitudes have been taken and the various stages of decay have been identified. It remains to study and sort the photographs for those that best illustrate the various stages of decay after they are shed by subsonic transport aircraft at cruise altitudes. The present status of the analysis and the paper are described.

  7. Civil aircraft vortex wake. TsAGI's research activities

    NASA Astrophysics Data System (ADS)

    Chernyshev, S. L.; Gaifullin, A. M.; Sviridenko, Yu. N.

    2014-11-01

    This paper provides a review of research conducted in TsAGI (Central AeroHydrodynamic Institute) concerning a vortex wake behind an airliner. The research into this area of theoretical and practical importance have been done both in Russia and in other countries, for which these studies became a vital necessity at the end of the 20th century. The paper describes the main methods and ratios on which software systems used to calculate the evolution of a vortex wake in a turbulent atmosphere are based. Verification of calculation results proved their acceptable consistency with the known experimental data. The mechanism of circulation loss in a vortex wake which is based on the analytical solution for the problem of two vortices diffusing in a viscous fluid is also described. The paper also describes the model of behavior of an aircraft which has deliberately or unintentionally entered a vortex wake behind another aircraft. Approximated results of calculations performed according to this model by means of artificial neural networks enabled the researchers to model the dynamics of an aircraft in a vortex wake on flight simulators on-line.

  8. Simulation of wake vortex radiometric detection via jet exhaust proxy

    NASA Astrophysics Data System (ADS)

    Daniels, Taumi S.

    2015-06-01

    This paper describes an analysis of the potential of an airborne hyperspectral imaging IR instrument to infer wake vortices via turbine jet exhaust as a proxy. The goal was to determine the requirements for an imaging spectrometer or radiometer to effectively detect the exhaust plume, and by inference, the location of the wake vortices. The effort examines the gas spectroscopy of the various major constituents of turbine jet exhaust and their contributions to the modeled detectable radiance. Initially, a theoretical analysis of wake vortex proxy detection by thermal radiation was realized in a series of simulations. The first stage used the SLAB plume model to simulate turbine jet exhaust plume characteristics, including exhaust gas transport dynamics and concentrations. The second stage used these plume characteristics as input to the Line By Line Radiative Transfer Model (LBLRTM) to simulate responses from both an imaging IR hyperspectral spectrometer or radiometer. These numerical simulations generated thermal imagery that was compared with previously reported wake vortex temperature data. This research is a continuation of an effort to specify the requirements for an imaging IR spectrometer or radiometer to make wake vortex measurements. Results of the two-stage simulation will be reported, including instrument specifications for wake vortex thermal detection. These results will be compared with previously reported results for IR imaging spectrometer performance.

  9. Simulation of Wake Vortex Radiometric Detection via Jet Exhaust Proxy

    NASA Technical Reports Server (NTRS)

    Daniels, Taumi S.

    2015-01-01

    This paper describes an analysis of the potential of an airborne hyperspectral imaging IR instrument to infer wake vortices via turbine jet exhaust as a proxy. The goal was to determine the requirements for an imaging spectrometer or radiometer to effectively detect the exhaust plume, and by inference, the location of the wake vortices. The effort examines the gas spectroscopy of the various major constituents of turbine jet exhaust and their contributions to the modeled detectable radiance. Initially, a theoretical analysis of wake vortex proxy detection by thermal radiation was realized in a series of simulations. The first stage used the SLAB plume model to simulate turbine jet exhaust plume characteristics, including exhaust gas transport dynamics and concentrations. The second stage used these plume characteristics as input to the Line By Line Radiative Transfer Model (LBLRTM) to simulate responses from both an imaging IR hyperspectral spectrometer or radiometer. These numerical simulations generated thermal imagery that was compared with previously reported wake vortex temperature data. This research is a continuation of an effort to specify the requirements for an imaging IR spectrometer or radiometer to make wake vortex measurements. Results of the two-stage simulation will be reported, including instrument specifications for wake vortex thermal detection. These results will be compared with previously reported results for IR imaging spectrometer performance.

  10. An Operational Wake Vortex Sensor Using Pulsed Coherent Lidar

    NASA Technical Reports Server (NTRS)

    Barker, Ben C., Jr.; Koch, Grady J.; Nguyen, D. Chi

    1998-01-01

    NASA and FAA initiated a program in 1994 to develop methods of setting spacings for landing aircraft by incorporating information on the real-time behavior of aircraft wake vortices. The current wake separation standards were developed in the 1970's when there was relatively light airport traffic and a logical break point by which to categorize aircraft. Today's continuum of aircraft sizes and increased airport packing densities have created a need for re-evaluation of wake separation standards. The goals of this effort are to ensure that separation standards are adequate for safety and to reduce aircraft spacing for higher airport capacity. Of particular interest are the different requirements for landing under visual flight conditions and instrument flight conditions. Over the years, greater spacings have been established for instrument flight than are allowed for visual flight conditions. Preliminary studies indicate that the airline industry would save considerable money and incur fewer passenger delays if a dynamic spacing system could reduce separations at major hubs during inclement weather to the levels routinely achieved under visual flight conditions. The sensor described herein may become part of this dynamic spacing system known as the "Aircraft VOrtex Spacing System" (AVOSS) that will interface with a future air traffic control system. AVOSS will use vortex behavioral models and short-term weather prediction models in order to predict vortex behavior sufficiently into the future to allow dynamic separation standards to be generated. The wake vortex sensor will periodically provide data to validate AVOSS predictions. Feasibility of measuring wake vortices using a lidar was first demonstrated using a continuous wave (CW) system from NASA Marshall Space Flight Sensor and tested at the Volpe National Transportation Systems Center's wake vortex test site at JFK International Airport. Other applications of CW lidar for wake vortex measurement have been made

  11. Vortex wake alleviation studies with a variable twist wing

    NASA Technical Reports Server (NTRS)

    Holbrook, G. T.; Dunham, D. M.; Greene, G. C.

    1985-01-01

    Vortex wake alleviation studies were conducted in a wind tunnel and a water towing tank using a multisegmented wing model which provided controlled and measured variations in span load. Fourteen model configurations are tested at a Reynolds number of one million and a lift coefficient of 0.6 in the Langley 4- by 7-Meter Tunnel and the Hydronautics Ship Model Basin water tank at Hydronautics, Inc., Laurel, Md. Detailed measurements of span load and wake velocities at one semispan downstream correlate well with each other, with inviscid predictions of span load and wake roll up, and with peak trailing-wing rolling moments measured in the far wake. Average trailing-wing rolling moments are found to be an unreliable indicator of vortex wake intensity because vortex meander does not scale between test facilities and free-air conditions. A tapered-span-load configuration, which exhibits little or no drag penalty, is shown to offer significant downstream wake alleviation to a small trailing wing. The greater downstream wake alleviation achieved with the addition of spoilers to a flapped-wing configuration is shown to result directly from the high incremental drag and turbulence associated with the spoilers and not from the span load alteration they cause.

  12. Analog Processing Assembly for the Wake Vortex Lidar Experiment

    NASA Technical Reports Server (NTRS)

    Stowe, Edwood G.

    1995-01-01

    The Federal Aviation Administration (FAA) and NASA have initiated a joint study in the development of reliable means of tracking, detecting, measuring, and predicting trailing wake-vortices of commercial aircraft. Being sought is an accurate model of the wake-vortex hazard, sufficient to increase airport capacity by reducing minimum safe spacings between planes. Several means of measurement are being evaluated for application to wake-vortex detection and tracking, including Doppler RADAR (Radio Detection and Ranging) systems, 2-micron Doppler LIDAR (Light Detection And Ranging) systems, and SODAR (Sound Detection And Ranging) systems. Of specific interest there is the lidar system, which has demonstrated numerous valuable capabilities as a vortex sensor Aerosols entrained in the vortex flow make the wake velocity signature visible to the lidar, (the observable lidar signal is essentially a measurement of the line-of-sight velocity of the aerosols). Measurement of the occurrence of a wake vortex requires effective reception and monitoring of the beat signal which results from the frequency-offset between the transmitted pulse and the backscattered radiation. This paper discusses the mounting, analysis, troubleshooting, and possible use of an analog processing assembly designed for such an application.

  13. Tip Vortex and Wake Characteristics of a Counterrotating Open Rotor

    NASA Technical Reports Server (NTRS)

    VanZante, Dale E.; Wernet, Mark P.

    2012-01-01

    One of the primary noise sources for Open Rotor systems is the interaction of the forward rotor tip vortex and blade wake with the aft rotor. NASA has collaborated with General Electric on the testing of a new generation of low noise, counterrotating Open Rotor systems. Three-dimensional particle image velocimetry measurements were acquired in the intra-rotor gap of the Historical Baseline blade set. The velocity measurements are of sufficient resolution to characterize the tip vortex size and trajectory as well as the rotor wake decay and turbulence character. The tip clearance vortex trajectory is compared to results from previously developed models. Forward rotor wake velocity profiles are shown. Results are presented in a form as to assist numerical modeling of Open Rotor system aerodynamics and acoustics.

  14. Analysis of rotor wake aerodynamics during maneuvering flight using a free-vortex wake methodology

    NASA Astrophysics Data System (ADS)

    Ananthan, Shreyas

    The problem of helicopter rotor wake aerodynamics during maneuvering flight conditions was analyzed using a time-accurate, free-vortex wake methodology. The free-vortex method consists of a Lagrangian representation of the rotor flow field using vortex elements, where the evolution of the flow field is simulated by tracking the free motion of these vortex elements and calculating their induced velocity field. Traditionally, free-vortex methods are inviscid, incompressible models, but in the present approach the viscous effects are incorporated using a viscous splitting method where the viscous and inviscid terms are modeled as successive sub-processes. The rotor aerodynamics and rigid blade flapping dynamics are closely coupled with the wake model and solved for in a consistent manner using the same numerical scheme. Validations of the methodology with experimental data were performed to study the wake response to perturbations in collective and cyclic pitch inputs. The numerical simulations captured all the essential wake dynamics observed in flow visualization. The predictions of the transient inflow and airloads response were found to be in excellent agreement with the available experimental measurements. It was observed that the rotor wake was extremely sensitive to perturbations in collective and cyclic blade pitch inputs. The characteristic wake response was found to be the bundling of the wake vorticity into a vortex ring structure. The evolution, convection and subsequent breakdown of this bundled ring of tip-vortices was found to be highly nonlinear, and occurs with a temporal lag. The nonlinear induced velocity field associated with unsteady wake evolution can cause considerable fluctuations in the rotor airloads time-history if the bundled tip-vortex structure comes into close proximity to the rotor blades. Furthermore, the interaction of these tip-vortices with the blades results in steep gradients in the rotor airloads across the rotor disk, thereby

  15. A Probabilistic Wake Vortex Lateral Transport Model Using Data from SFO and DEN

    NASA Technical Reports Server (NTRS)

    Mellman, George R.; Delisi, Donald P.

    2008-01-01

    In a previous report, we considered the behavior of the lateral position of vortices as a function of time after vortex formation for Out of Ground Effects (OGE) data for aircraft landing at San Francisco International Airport (SFO). We quantified the spread in lateral position as a function of time and examined how predictable lateral position is under a variety of assumptions. The combination of spread and predictability allowed us to derive probability distribution functions (PDFs) for lateral position given observed crosswind (CW) velocities. In this study, we examine the portability of these PDFs with respect to other landing sites. To this end, we consider OGE data obtained by the Federal Aviation Administration for landings at Denver International Airport (DEN) between 04/05/2006 and 06/03/2006. We consider vortices from both B733 (Boeing 737 models 200-500) and B757 (Boeing 757) aircraft. The data set contains 635 B733 landings and 506 B757 landings. The glide slope altitude for these measurements was 280 m, determined by the average initial vortex observation adjusted for a 3-second delay in the initial observation. The comparable SFO altitude was 158 m. We note that the principal mechanism for lateral transport in the OGE regime is advection by the ambient wind. This implies that a simple crosswind correction may be effective in explaining much of the variation in the lateral transport data. In this study, we again consider the use of ASOS data and average Lidar crosswind data over the vortex altitude range to predict vortex location as a function of time.

  16. A new methodology for free wake analysis using curved vortex elements

    NASA Technical Reports Server (NTRS)

    Bliss, Donald B.; Teske, Milton E.; Quackenbush, Todd R.

    1987-01-01

    A method using curved vortex elements was developed for helicopter rotor free wake calculations. The Basic Curve Vortex Element (BCVE) is derived from the approximate Biot-Savart integration for a parabolic arc filament. When used in conjunction with a scheme to fit the elements along a vortex filament contour, this method has a significant advantage in overall accuracy and efficiency when compared to the traditional straight-line element approach. A theoretical and numerical analysis shows that free wake flows involving close interactions between filaments should utilize curved vortex elements in order to guarantee a consistent level of accuracy. The curved element method was implemented into a forward flight free wake analysis, featuring an adaptive far wake model that utilizes free wake information to extend the vortex filaments beyond the free wake regions. The curved vortex element free wake, coupled with this far wake model, exhibited rapid convergence, even in regions where the free wake and far wake turns are interlaced. Sample calculations are presented for tip vortex motion at various advance ratios for single and multiple blade rotors. Cross-flow plots reveal that the overall downstream wake flow resembles a trailing vortex pair. A preliminary assessment shows that the rotor downwash field is insensitive to element size, even for relatively large curved elements.

  17. Wake Vortex Transport in Proximity to the Ground

    NASA Technical Reports Server (NTRS)

    Hamilton, David W.; Proctor, Fred H.

    2000-01-01

    A sensitivity study for aircraft wake vortex transport has been conducted using a validated large eddy simulation (LES) model. The study assumes neutrally stratified and nonturbulent environments and includes the consequences of the ground. The numerical results show that the nondimensional lateral transport is primarily influenced by the magnitude of the ambient crosswind and is insensitive to aircraft type. In most of the simulations, the ground effect extends the lateral position of the downwind vortex about one initial vortex spacing (b(sub o)) in the downstream direction. Further extension by as much as one b(sub o) occurs when the downwind vortex remains 'in ground effect' (IGE) for relatively long periods of time. Results also show that a layer-averaged ambient wind velocity can be used to bound the time for lateral transport of wake vortices to insure safe operations on a parallel runway.

  18. Meteorology and Wake Vortex Influence on American Airlines FL-587 Accident

    NASA Technical Reports Server (NTRS)

    Proctor, Fred H.; Hamilton, David W.; Rutishauser, David K.; Switzer, George F.

    2004-01-01

    The atmospheric environment surrounding the crash of American Airlines Flight 587 is investigated. Examined are evidence for any unusual atmospheric conditions and the potential for encounters with aircraft wake vortices. Computer simulations are carried out with two different vortex prediction models and a Large Eddy Simulation model. Wind models are proposed for studying aircraft and pilot response to the wake vortex encounter.

  19. Vortex dynamics in the wake of a mechanical fish

    NASA Astrophysics Data System (ADS)

    Brücker, Christoph; Bleckmann, Horst

    This study focuses on the three-dimensional flow around a mechanical fish model, which reproduces the typical undulatory body and fin motion of a carangiform swimmer. The mechanical model consists of a flexible skeleton embedded in a soft transparent silicone body, which is connected with two cams to a flapping and bending hinge generating a traveling wave motion with increasing amplitude from anterior to posterior, extending to a combined heaving and pitching motion at the fin. The model is submerged in a water tank and towed at the characteristic swimming speed for the neutral swimming mode at U/V = 1. The method of Scanning Particle Image Velocimetry was used to analyze the three-dimensional time-dependent flow field in the axial and saggital planes. The results confirm the earlier observations that the wake develops into a chain of vortex rings which travel sidewards perpendicular to the swimming direction. However, instead of one single vortex shed at each tail beat half-cycle we observed a pair of two vortex rings being shed. Each pair consists of a larger main vortex ring corresponding to the tail beat start-stop vortex, while the second vortex ring is due to the body bending motion. The existence of the second vortex reflects the role of the body in undulatory swimming. A simplified model of the fish body comparing it to a plate with a hinged flap demonstrates the link between the sequence of kinematics and vortex shedding.

  20. Vortex dynamics in the wake of a mechanical fish

    NASA Astrophysics Data System (ADS)

    Brücker, Christoph; Bleckmann, Horst

    2007-11-01

    This study focuses on the three-dimensional flow around a mechanical fish model, which reproduces the typical undulatory body and fin motion of a carangiform swimmer. The mechanical model consists of a flexible skeleton embedded in a soft transparent silicone body, which is connected with two cams to a flapping and bending hinge generating a traveling wave motion with increasing amplitude from anterior to posterior, extending to a combined heaving and pitching motion at the fin. The model is submerged in a water tank and towed at the characteristic swimming speed for the neutral swimming mode at U/V = 1. The method of Scanning Particle Image Velocimetry was used to analyze the three-dimensional time-dependent flow field in the axial and saggital planes. The results confirm the earlier observations that the wake develops into a chain of vortex rings which travel sidewards perpendicular to the swimming direction. However, instead of one single vortex shed at each tail beat half-cycle we observed a pair of two vortex rings being shed. Each pair consists of a larger main vortex ring corresponding to the tail beat start stop vortex, while the second vortex ring is due to the body bending motion. The existence of the second vortex reflects the role of the body in undulatory swimming. A simplified model of the fish body comparing it to a plate with a hinged flap demonstrates the link between the sequence of kinematics and vortex shedding.

  1. Vortex Core Size in the Rotor Near-Wake

    NASA Technical Reports Server (NTRS)

    Young, Larry A.

    2003-01-01

    Using a kinetic energy conservation approach, a number of simple analytic expressions are derived for estimating the core size of tip vortices in the near-wake of rotors in hover and axial-flow flight. The influence of thrust, induced power losses, advance ratio, and vortex structure on rotor vortex core size is assessed. Experimental data from the literature is compared to the analytical results derived in this paper. In general, three conclusions can be drawn from the work in this paper. First, the greater the rotor thrust, t h e larger the vortex core size in the rotor near-wake. Second, the more efficient a rotor is with respect to induced power losses, the smaller the resulting vortex core size. Third, and lastly, vortex core size initially decreases for low axial-flow advance ratios, but for large advance ratios core size asymptotically increases to a nominal upper limit. Insights gained from this work should enable improved modeling of rotary-wing aerodynamics, as well as provide a framework for improved experimental investigations of rotor a n d advanced propeller wakes.

  2. Transitions in the vortex wake behind the plunging profile

    NASA Astrophysics Data System (ADS)

    Kozłowski, Tomasz; Kudela, Henryk

    2014-12-01

    In this study we investigate numerically the vortex wake formation behind the profile performing simple harmonic motion known in the literature as plunging. This research was inspired by the flapping motion which is appropriate for birds, insects and fishes. We assume the two dimensional model of flow. Depending on the parameters such as plunging amplitude, frequency and the Reynolds number, we demonstrate many different types of vortex street behind the profile. It is well known that the type of vortex wake determines the hydrodynamic forces acting on the profile. Dependences of the plunging amplitude, the Strouhal number and various topology vortices are established by constructing the phase transition diagram. The areas in the diagram related to the drag, thrust, and lift force generation are captured. We notice also the areas where the vorticity field is disordered. The disordered vorticity field does not allow maintenance of the periodic forces on the profile. An increase in the Reynolds number leads to the transition of the vortex wake behind the profile. The transition is caused by the phenomenon of boundary layer eruption. Further increase of the Reynolds number causes the vortex street related to the generation of the lift force to vanish.

  3. Mathematical models for exotic wakes

    NASA Astrophysics Data System (ADS)

    Basu, Saikat; Stremler, Mark

    2014-11-01

    Vortex wakes are a common occurrence in the environment around us; the most famous example being the von Kármán vortex street with two vortices being shed by the bluff body in each cycle. However, frequently there can be many other more exotic wake configurations with different vortex arrangements, based on the flow parameters and the bluff body dimensions and/or its oscillation characteristics. Some examples include wakes with periodic shedding of three vortices (`P+S' mode) and four vortices (symmetric `2P' mode, staggered `2P' mode, `2C' mode). We present mathematical models for such wakes assuming two-dimensional potential flows with embedded point vortices. The spatial alignment of the vortices is inspired by the experimentally observed wakes. The idealized system follows a Hamiltonian formalism. Model-based analysis reveals a rich dynamics pertaining to the relative vortex motion in the mid-wake region. Downstream evolution of the vortices, as predicted from the model results, also show good correspondence with wake-shedding experiments performed on flowing soap films.

  4. Proceedings of the NASA First Wake Vortex Dynamic Spacing Workshop

    NASA Technical Reports Server (NTRS)

    Creduer, Leonard (Editor); Perry, R. Brad (Editor)

    1997-01-01

    A Government and Industry workshop on wake vortex dynamic spacing systems was conducted on May 13-15, 1997, at the NASA Langley Research Center. The purpose of the workshop was to disclose the status of ongoing NASA wake vortex R&D to the international community and to seek feedback on the direction of future work to assure an optimized research approach. Workshop sessions examined wake vortex characterization and physics, wake sensor technologies, aircraft/wake encounters, terminal area weather characterization and prediction, and wake vortex systems integration and implementation. A final workshop session surveyed the Government and Industry perspectives on the NASA research underway and related international wake vortex activities. This document contains the proceedings of the workshop including the presenters' slides, the discussion following each presentation, the wrap-up panel discussion, and the attendees' evaluation feedback.

  5. Flow visualization of vortex interactions in multiple vortex wakes behind aircraft

    NASA Technical Reports Server (NTRS)

    Ciffone, D. L.; Lonzo, C., Jr.

    1975-01-01

    A flow visualization technique was developed which allows the nature of lift-generated wakes behind aircraft models to be investigated. The technique was applied to models being towed underwater in a ship model basin. Seven different configurations of a small-scale model of a 747 transport aircraft were used to allow observation of typical vortex interactions and merging in multiple vortex wakes. It was established that the motion of the wake vortices is often sensitive to small changes in either wing span loading or model attitude. Landing gear deployement was found to cause a far-field reformation of vorticity behind a model configuration which dissipated concentrated vorticity in the near-field wake. Alleviation of wake vorticity is achievable by configuring the wing span loading to cause the wake vortices to move in paths that result in their interactions and merging. The vortices shed from the horizontal stabilizer always moved down rapidly into the wake and merged with the other vortices, primarily the inboard flap vortices.

  6. Implementation and validation of a wake model for vortex-surface interactions in low speed forward flight

    NASA Technical Reports Server (NTRS)

    Komerath, Narayanan M.; Schreiber, Olivier A.

    1987-01-01

    The wake model was implemented using a VAX 750 and a Microvax II workstation. Online graphics capability using a DISSPLA graphics package. The rotor model used by Beddoes was significantly extended to include azimuthal variations due to forward flight and a simplified scheme for locating critical points where vortex elements are placed. A test case was obtained for validation of the predictions of induced velocity. Comparison of the results indicates that the code requires some more features before satisfactory predictions can be made over the whole rotor disk. Specifically, shed vorticity due to the azimuthal variation of blade loading must be incorporated into the model. Interactions between vortices shed from the four blades of the model rotor must be included. The Scully code for calculating the velocity field is being modified in parallel with these efforts to enable comparison with experimental data. To date, some comparisons with flow visualization data obtained at Georgia Tech were performed and show good agreement for the isolated rotor case. Comparison of time-resolved velocity data obtained at Georgia Tech also shows good agreement. Modifications are being implemented to enable generation of time-averaged results for comparison with NASA data.

  7. Wake evolution and trailing vortex instabilities

    NASA Astrophysics Data System (ADS)

    Odemark, Ylva; Fransson, Jens H. M.

    2011-11-01

    The production losses and inhomogeneous loads of wind power turbines placed in the wake of another turbine is a well-known problem when building new wind power farms, and a subject of intensive research. The present work aims at developing an increased understanding of the behaviour of turbine wakes, with special regard to wake evolution and the stability of the trailing vortices. Single point velocity measurements with hot-wire anemometry were performed in the wake of a small-scale model turbine. The model was placed in the middle of the wind tunnel test section, outside the boundary layers from the wind tunnel walls. In order to study the stability of the wake and the trailing vortices, a disturbance was introduced at the end of the nacelle. This was accomplished through two orifices perpendicular to the main flow, which were connected to a high-pressure tank and two fast-switching valves. Both varicose and sinusoidal modes of different frequencies could be triggered. By also triggering the measurements on the blade passage, the meandering of the wake and the disturbance frequency, phase averaged results could be computed. The results for different frequencies as well as studies of wake evolution will be presented.

  8. Wake Vortex Field Measurement Program at Memphis, Tennessee: Data Guide

    NASA Technical Reports Server (NTRS)

    Campbell, S. D.; Dasey, T. J.; Freehart, R. E.; Heinrichs, R. M.; Mathews, M. P.; Perras, G. H.; Rowe, G. S.

    1997-01-01

    Eliminating or reducing current restrictions in the air traffic control system due to wake vortex considerations would yield increased capacity, decreased delays, and cost savings. Current wake vortex separation standards are widely viewed as very conservative under most conditions. However, scientific uncertainty about wake vortex behavior under different atmospheric conditions remains a barrier to development of an adaptive vortex spacing system. The objective of the wake vortex field measurement efforts during December, 1994 and August, 1995 at Memphis, TN were to record wake vortex behavior for varying atmospheric conditions and types of aircraft. This effort is part of a larger effort by the NASA Langley Research Center to develop an Aircraft Vortex Spacing System (AVOSS) as an element of the Terminal Area Productivity (TAP) program. The TAP program is being performed in concert with the FAA Terminal Air Traffic Control Automation (TATCA) program and ATC Automation. Wake vortex behavior was observed using a mobile continuous-wave (CW) coherent laser Doppler radar (lidar) developed at Lincoln Laboratory. This lidar features a number of improvements over previous systems, including the first-ever demonstration of an automatic wake vortex detection and tracking algorithm.

  9. Evaluation of the discrete vortex wake cross flow model using vector computers. Part 1: Theory and application

    NASA Technical Reports Server (NTRS)

    1979-01-01

    The current program had the objective to modify a discrete vortex wake method to efficiently compute the aerodynamic forces and moments on high fineness ratio bodies (f approximately 10.0). The approach is to increase computational efficiency by structuring the program to take advantage of new computer vector software and by developing new algorithms when vector software can not efficiently be used. An efficient program was written and substantial savings achieved. Several test cases were run for fineness ratios up to f = 16.0 and angles of attack up to 50 degrees.

  10. Analysis of the Radar Reflectivity of Aircraft Vortex Wakes

    NASA Technical Reports Server (NTRS)

    Shariff, Karim; Wray, Alan; Yan, Jerry (Technical Monitor)

    2000-01-01

    Radar has been proposed as a way to track wake vortices to reduce aircraft spacing and tests have revealed radar echoes from aircraft wakes in clear air. The results are always interpreted qualitatively using Tatarski's theory of weak scattering by isotropic atmospheric turbulence. The goal of the present work was to predict the value of the radar cross-section (RCS) using simpler models. This is accomplished in two steps. First, the refractive index is obtained. Since the structure of the aircraft wakes is different from atmospheric turbulence, three simple mechanisms specific to vortex wakes are considered: (1) Radial density gradient in a two-dimensional vortex, (2) three-dimensional fluctuations in the vortex cores, and (3) Adiabatic transport of the atmospheric fluid in a two-dimensional oval surrounding the pair of vortices. The index of refraction is obtained more precisely for the two-dimensional mechanisms than for the three-dimensional ones. In the second step, knowing the index of refraction, a scattering analysis is performed. Tatarski's weak scattering approximation is kept but the usual assumptions of a far-field and a uniform incident wave are dropped. Neither assumption is generally valid for a wake that is coherent across the radar beam. For analytical insight, a simpler approximation that invokes, in addition to weak scattering, the far-field and wide cylindrical beam assumptions, is also developed and compared with the more general analysis. The predicted RCS values for the oval surround the vortices (mechanism C) agree with the experiments of Bilson conducted over a wide range of frequencies. However, the predictions have a cut-off away from normal incidence which is not present in the measurements. Estimates suggest that this is due to turbulence in the baroclinic vorticity generated at the boundary of the oval. The reflectivity of a vortex itself (mechanism A) is comparable to that of the oval (mechanism C) but cuts-off at frequencies lower

  11. Prediction and Control of Vortex Dominated and Vortex-wake Flows

    NASA Technical Reports Server (NTRS)

    Kandil, Osama

    1996-01-01

    This report describes the activities and accomplishments under this research grant, including a list of publications and dissertations, produced in the field of prediction and control of vortex dominated and vortex wake flows.

  12. Wake Vortex Detection: Phased Microphone vs. Linear Infrasonic Array

    NASA Technical Reports Server (NTRS)

    Shams, Qamar A.; Zuckerwar, Allan J.; Sullivan, Nicholas T.; Knight, Howard K.

    2014-01-01

    Sensor technologies can make a significant impact on the detection of aircraft-generated vortices in an air space of interest, typically in the approach or departure corridor. Current state-of-the art sensor technologies do not provide three-dimensional measurements needed for an operational system or even for wake vortex modeling to advance the understanding of vortex behavior. Most wake vortex sensor systems used today have been developed only for research applications and lack the reliability needed for continuous operation. The main challenges for the development of an operational sensor system are reliability, all-weather operation, and spatial coverage. Such a sensor has been sought for a period of last forty years. Acoustic sensors were first proposed and tested by National Oceanic and Atmospheric Administration (NOAA) early in 1970s for tracking wake vortices but these acoustic sensors suffered from high levels of ambient noise. Over a period of the last fifteen years, there has been renewed interest in studying noise generated by aircraft wake vortices, both numerically and experimentally. The German Aerospace Center (DLR) was the first to propose the application of a phased microphone array for the investigation of the noise sources of wake vortices. The concept was first demonstrated at Berlins Airport Schoenefeld in 2000. A second test was conducted in Tarbes, France, in 2002, where phased microphone arrays were applied to study the wake vortex noise of an Airbus 340. Similarly, microphone phased arrays and other opto-acoustic microphones were evaluated in a field test at the Denver International Airport in 2003. For the Tarbes and Denver tests, the wake trajectories of phased microphone arrays and lidar were compared as these were installed side by side. Due to a built-in pressure equalization vent these microphones were not suitable for capturing acoustic noise below 20 Hz. Our group at NASA Langley Research Center developed and installed an

  13. Two Dimensional Wake Vortex Simulations in the Atmosphere: Preliminary Sensitivity Studies

    NASA Technical Reports Server (NTRS)

    Proctor, F. H.; Hinton, D. A.; Han, J.; Schowalter, D. G.; Lin, Y.-L.

    1998-01-01

    A numerical large-eddy simulation model is currently being used to quantify aircraft wake vortex behavior with meteorological observables. The model, having a meteorological framework, permits the interaction of wake vortices with environments characterized by crosswind shear, stratification, and humidity. The addition of grid-scale turbulence as an initial condition appeared to have little consequence. Results show that conventional nondimensionalizations work very well for vortex pairs embedded in stably stratified flows. However, this result is based on simple environments with constant Brunt-Vaisala frequency. Results presented here also show that crosswind profiles exert important and complex interactions on the trajectories of wake vortices. Nonlinear crosswind profiles tended to arrest the descent of wake vortex pairs. The member of the vortex pair with vorticity of same sign as the vertical change in the ambient along-track vorticity may be deflected upwards.

  14. Wake Vortex Tracking Using a 35 GHz Pulsed Doppler Radar

    NASA Technical Reports Server (NTRS)

    Neece, Robert T.; Britt, Charles L.; White, Joseph H.; Mudukutore, Ashok; Nguyen, Chi; Hooper, Bill

    2005-01-01

    , two numerical models were utilized in system simulations. The results of this study improve our understanding of the method of detection, resolution requirements for range and azimuth, pulse compression, and performance prediction. Simulations applying pulse compression techniques show that detection is good in heavy fog to greater than 2000 m. Both compressed and uncompressed short pulses show the vortex structure. To explore operational challenges, siting and scanning strategies were also analyzed. Simulation results indicate that excellent wake vortex detection, tracking and classification is possible in drizzle (+15 dBZ) and heavy fog (- 13 dBZ) using short pulse techniques (<99ns) at ranges on the order of 900 m, with a modest power of 500 W output. At 1600 m, detection can be expected at reflectivities as low as -13 dBZ (heavy fog). The radar system, as designed and built, has the potential to support field studies of a wake vortex spacing system in low-visibility conditions ranging from heavy fog to rain, when sited within 2000m of the flight path.

  15. Coherent Pulsed Lidar Sensing of Wake Vortex Position and Strength, Winds and Turbulence in the Terminal Area

    NASA Technical Reports Server (NTRS)

    Brockman, Philip; Barker, Ben C., Jr.; Koch, Grady J.; Nguyen, Dung Phu Chi; Britt, Charles L., Jr.; Petros, Mulugeta

    1999-01-01

    NASA Langley Research Center (LaRC) has field tested a 2.0 gm, 100 Hertz, pulsed coherent lidar to detect and characterize wake vortices and to measure atmospheric winds and turbulence. The quantification of aircraft wake-vortex hazards is being addressed by the Wake Vortex Lidar (WVL) Project as part of Aircraft Vortex Spacing System (AVOSS), which is under the Reduced Spacing Operations Element of the Terminal Area Productivity (TAP) Program. These hazards currently set the minimum, fixed separation distance between two aircraft and affect the number of takeoff and landing operations on a single runway under Instrument Meteorological Conditions (IMC). The AVOSS concept seeks to safely reduce aircraft separation distances, when weather conditions permit, to increase the operational capacity of major airports. The current NASA wake-vortex research efforts focus on developing and validating wake vortex encounter models, wake decay and advection models, and wake sensing technologies. These technologies will be incorporated into an automated AVOSS that can properly select safe separation distances for different weather conditions, based on the aircraft pair and predicted/measured vortex behavior. The sensor subsystem efforts focus on developing and validating wake sensing technologies. The lidar system has been field-tested to provide real-time wake vortex trajectory and strength data to AVOSS for wake prediction verification. Wake vortices, atmospheric winds, and turbulence products have been generated from processing the lidar data collected during deployments to Norfolk (ORF), John F. Kennedy (JFK), and Dallas/Fort Worth (DFW) International Airports.

  16. Simulation of Rotary-Wing Near-Wake Vortex Structures Using Navier-Stokes CFD Methods

    NASA Technical Reports Server (NTRS)

    Kenwright, David; Strawn, Roger; Ahmad, Jasim; Duque, Earl; Warmbrodt, William (Technical Monitor)

    1997-01-01

    This paper will use high-resolution Navier-Stokes computational fluid dynamics (CFD) simulations to model the near-wake vortex roll-up behind rotor blades. The locations and strengths of the trailing vortices will be determined from newly-developed visualization and analysis software tools applied to the CFD solutions. Computational results for rotor nearwake vortices will be used to study the near-wake vortex roll up for highly-twisted tiltrotor blades. These rotor blades typically have combinations of positive and negative spanwise loading and complex vortex wake interactions. Results of the computational studies will be compared to vortex-lattice wake models that are frequently used in rotorcraft comprehensive codes. Information from these comparisons will be used to improve the rotor wake models in the Tilt-Rotor Acoustic Code (TRAC) portion of NASA's Short Haul Civil Transport program (SHCT). Accurate modeling of the rotor wake is an important part of this program and crucial to the successful design of future civil tiltrotor aircraft. The rotor wake system plays an important role in blade-vortex interaction noise, a major problem for all rotorcraft including tiltrotors.

  17. An Improved Wake Vortex Tracking Algorithm for Multiple Aircraft

    NASA Technical Reports Server (NTRS)

    Switzer, George F.; Proctor, Fred H.; Ahmad, Nashat N.; LimonDuparcmeur, Fanny M.

    2010-01-01

    The accurate tracking of vortex evolution from Large Eddy Simulation (LES) data is a complex and computationally intensive problem. The vortex tracking requires the analysis of very large three-dimensional and time-varying datasets. The complexity of the problem is further compounded by the fact that these vortices are embedded in a background turbulence field, and they may interact with the ground surface. Another level of complication can arise, if vortices from multiple aircrafts are simulated. This paper presents a new technique for post-processing LES data to obtain wake vortex tracks and wake intensities. The new approach isolates vortices by defining "regions of interest" (ROI) around each vortex and has the ability to identify vortex pairs from multiple aircraft. The paper describes the new methodology for tracking wake vortices and presents application of the technique for single and multiple aircraft.

  18. Wake Vortex Advisory System (WakeVAS) Evaluation of Impacts on the National Airspace System

    NASA Technical Reports Server (NTRS)

    Smith, Jeremy C.; Dollyhigh, Samuel M.

    2005-01-01

    This report is one of a series that describes an ongoing effort in high-fidelity modeling/simulation, evaluation and analysis of the benefits and performance metrics of the Wake Vortex Advisory System (WakeVAS) Concept of Operations being developed as part of the Virtual Airspace Modeling and Simulation (VAMS) project. A previous study, determined the overall increases in runway arrival rates that could be achieved at 12 selected airports due to WakeVAS reduced aircraft spacing under Instrument Meteorological Conditions. This study builds on the previous work to evaluate the NAS wide impacts of equipping various numbers of airports with WakeVAS. A queuing network model of the National Airspace System, built by the Logistics Management Institute, Mclean, VA, for NASA (LMINET) was used to estimate the reduction in delay that could be achieved by using WakeVAS under non-visual meteorological conditions for the projected air traffic demand in 2010. The results from LMINET were used to estimate the total annual delay reduction that could be achieved and from this, an estimate of the air carrier variable operating cost saving was made.

  19. Numerical Simulation of the Aircraft Wake Vortex Flowfield

    NASA Technical Reports Server (NTRS)

    Ahmad, Nashat N.; Proctor, Fred H.; Perry, R. Brad

    2013-01-01

    The near wake vortex flowfield from a NACA0012 half-wing was simulated using a fully unstructured Navier-Stokes flow solver in three dimensions at a chord Reynolds number of 4.6 million and a Mach number of approximately 0.15. Several simulations were performed to examine the effect of boundary conditions, mesh resolution and turbulence scheme on the formation of wingtip vortex and its downstream propagation. The standard Spalart-Allmaras turbulence model was compared with the Dacles-Mariani and Spalart-Shur corrections for rotation and curvature effects. The simulation results were evaluated using the data from experiment performed at NASA Ames' 32in x 48in low speed wind tunnel.

  20. Wake Vortex Transport and Decay in Ground Effect: Vortex Linking with the Ground

    NASA Technical Reports Server (NTRS)

    Proctor, Fred H.; Hamilton, David W.; Han, Jongil

    2000-01-01

    Numerical simulations are carried out with a three-dimensional Large-Eddy Simulation (LES) model to explore the sensitivity of vortex decay and transport in ground effect (IGE). The vortex decay rates are found to be strongly enhanced following maximum descent into ground effect. The nondimensional decay rate is found to be insensitive to the initial values of circulation, height, and vortex separation. The information gained from these simulations is used to construct a simple decay relationship. This relationship compares well with observed data from an IGE case study. Similarly, a relationship for lateral drift due to ground effect is constructed from the LES data. In the second part of this paper, vortex linking with the ground is investigated. Our numerical simulations of wake vortices for IGE show that a vortex may link with its image beneath the ground, if the intensity of the ambient turbulence is moderate to high. This linking with the ground (which is observed in real cases)gives the appearance of a vortex tube that bends to become vertically oriented and which terminates at the ground. From the simulations conducted, the linking time for vortices in the free atmosphere; i.e., a function of ambient turbulence intensity.

  1. Relationship between Aeolian tone and Wake Vortex from Inclined Flat Blade

    NASA Astrophysics Data System (ADS)

    Yoshitake, Sho; Hayashi, Hidechito; Sasaki, Souichi; Fukano, Tohru

    The three dimensional structure of the wake vortex was investigated in relating to the aeolian tone from the inclined blade. It was pointed out that the aeolian tone is largest not at zero, but at ten degree of the inclined angle. The correlation length of the wake vortex in span becomes large at small inclined angles. The large scale structures of the wake vortex are generated in zero and ten degree of inclined angle. The shape of the structure is influenced with the span-wise velocity in the dead air region. There are small scale spots of the pressure fluctuation at the trailing edge. The spots are interacted each other and make a large cluster of the pressure fluctuation. It is proposed that the scale of it is decided by the timing of the wake vortex formation. And the shape of the wake vortex structure is closely related with the scale of it. The correlation length of the wake vortex is calculated from the shape of the structure. The estimation of aeolian tone by using the length with Fukano's model is well coincided to experiments.

  2. A three dimensional unsteady iterative panel method with vortex particle wakes and boundary layer model for bio-inspired multi-body wings

    NASA Astrophysics Data System (ADS)

    Dhruv, Akash; Blower, Christopher; Wickenheiser, Adam M.

    2015-03-01

    The ability of UAVs to operate in complex and hostile environments makes them useful in military and civil operations concerning surveillance and reconnaissance. However, limitations in size of UAVs and communication delays prohibit their operation close to the ground and in cluttered environments, which increase risks associated with turbulence and wind gusts that cause trajectory deviations and potential loss of the vehicle. In the last decade, scientists and engineers have turned towards bio-inspiration to solve these issues by developing innovative flow control methods that offer better stability, controllability, and maneuverability. This paper presents an aerodynamic load solver for bio-inspired wings that consist of an array of feather-like flaps installed across the upper and lower surfaces in both the chord- and span-wise directions, mimicking the feathers of an avian wing. Each flap has the ability to rotate into both the wing body and the inbound airflow, generating complex flap configurations unobtainable by traditional wings that offer improved aerodynamic stability against gusting flows and turbulence. The solver discussed is an unsteady three-dimensional iterative doublet panel method with vortex particle wakes. This panel method models the wake-body interactions between multiple flaps effectively without the need to define specific wake geometries, thereby eliminating the need to manually model the wake for each configuration. To incorporate viscous flow characteristics, an iterative boundary layer theory is employed, modeling laminar, transitional and turbulent regions over the wing's surfaces, in addition to flow separation and reattachment locations. This technique enables the boundary layer to influence the wake strength and geometry both within the wing and aft of the trailing edge. The results obtained from this solver are validated using experimental data from a low-speed suction wind tunnel operating at Reynolds Number 300,000. This method

  3. Wake-vortex structure from lift and torque induced on a following wing

    NASA Technical Reports Server (NTRS)

    Rossow, Vernon J.

    1993-01-01

    A procedure based on vortex lattice theory to interpret the lift and torque measured on a following model in a wind tunnel is developed to retrieve the velocity distribution in the vortex wake that caused the induced forces. It is concluded that the retrieval procedure has a potential for reliably determining the structure of vortex wakes that trail from the wings of subsonic transport aircraft. Tests using idealized theoretical models show that the procedure is highly reliable and accurate. However, certain difficulties are found in the retrieval procedure when applied to actual data measured with following wings of various sizes in a wind tunnel.

  4. Application of Wind Tunnel Free-Flight Technique for Wake Vortex Encounters

    NASA Technical Reports Server (NTRS)

    Brandon, Jay M.; Jordan, Frank L., Jr.; Stuever, Robert A.; Buttrill, Catherine W.

    1997-01-01

    A wind tunnel investigation was conducted in the Langley 30- by 60-Foot Tunnel to assess the free-flight test technique as a tool in research on wake vortex encounters. A typical 17.5-percent scale business-class jet airplane model was flown behind a stationary wing mounted in the forward portion of the wind tunnel test section. The span ratio (model span-generating wingspan) was 0.75. The wing angle of attack could be adjusted to produce a vortex of desired strength. The test airplane model was successfully flown in the vortex and through the vortex for a range of vortex strengths. Data obtained included the model airplane body axis accelerations, angular rates, attitudes, and control positions as a function of vortex strength and relative position. Pilot comments and video records were also recorded during the vortex encounters.

  5. Turbulence Climatology at Dallas/Ft.Worth (DFW) Airport: Implications for a Departure Wake Vortex Spacing System

    NASA Technical Reports Server (NTRS)

    Perras, G. H.; Dasey, T. J.

    2000-01-01

    Potential adaptive wake vortex spacing systems may need to rely on wake vortex decay rather than wake vortex transport in reducing wake separations. A wake vortex takeoff-spacing system in particular will need to rely on wake decay. Ambient turbulence is the primary influence on wake decay away from the ground. This study evaluated 18 months of ambient turbulence measurements at Dallas/Ft. Worth (DFW) Airport. The measurements show minor variation in the turbulence levels at various times of the year or times of the day for time periods when a departure system could be used. Arrival system operation was also examined, and a slightly lower overall turbulence level was found as compared to departure system benefit periods. The Sarpkaya model, a validated model of wake vortex behavior, was applied to various turbulence levels and compared to the DFW turbulence statistics. The results show that wake vortices from heavy aircraft on takeoff should dissipate within one minute for the majority of the time and will rarely last two minutes. These results will need to be verified by wake vortex measurements on departure.

  6. Developments and Validations of Fully Coupled CFD and Practical Vortex Transport Method for High-Fidelity Wake Modeling in Fixed and Rotary Wing Applications

    NASA Technical Reports Server (NTRS)

    Anusonti-Inthra, Phuriwat

    2010-01-01

    A novel Computational Fluid Dynamics (CFD) coupling framework using a conventional Reynolds-Averaged Navier-Stokes (BANS) solver to resolve the near-body flow field and a Particle-based Vorticity Transport Method (PVTM) to predict the evolution of the far field wake is developed, refined, and evaluated for fixed and rotary wing cases. For the rotary wing case, the RANS/PVTM modules are loosely coupled to a Computational Structural Dynamics (CSD) module that provides blade motion and vehicle trim information. The PVTM module is refined by the addition of vortex diffusion, stretching, and reorientation models as well as an efficient memory model. Results from the coupled framework are compared with several experimental data sets (a fixed-wing wind tunnel test and a rotary-wing hover test).

  7. Rotor Wake Vortex Definition Using 3C-PIV Measurements: Corrected for Vortex Orientation

    NASA Technical Reports Server (NTRS)

    Burley, Casey L.; Brooks, Thomas F.; vanderWall, Berend; Richard, Hughues Richard; Raffel, Markus; Beaumier, Philippe; Delrieux, Yves; Lim, Joon W.; Yu, Yung H.; Tung, Chee

    2003-01-01

    Three-component (3-C) particle image velocimetry (PIV) measurements, within the wake across a rotor disk plane, are used to determine wake vortex definitions important for BVI (Blade Vortex Interaction) and broadband noise prediction. This study is part of the HART II test program conducted using a 40 percent scale BO-105 helicopter main rotor in the German-Dutch Wind Tunnel (DNW). In this paper, measurements are presented of the wake vortex field over the advancing side of the rotor operating at a typical descent landing condition. The orientations of the vortex (tube) axes are found to have non-zero tilt angles with respect to the chosen PIV measurement cut planes, often on the order of 45 degrees. Methods for determining the orientation of the vortex axis and reorienting the measured PIV velocity maps (by rotation/projection) are presented. One method utilizes the vortex core axial velocity component, the other utilizes the swirl velocity components. Key vortex parameters such as vortex core size, strength, and core velocity distribution characteristics are determined from the reoriented PIV velocity maps. The results are compared with those determined from velocity maps that are not corrected for orientation. Knowledge of magnitudes and directions of the vortex axial and swirl velocity components as a function of streamwise location provide a basis for insight into the vortex evolution.

  8. Effects of spoilers and gear on B-747 wake vortex velocities

    NASA Technical Reports Server (NTRS)

    Luebs, A. B.; Bradfute, J. G.; Ciffone, D. L.

    1976-01-01

    Vortex velocities were measured in the wakes of four configurations of a 0.61-m span model of a B-747 aircraft. The wakes were generated by towing the model underwater in a ship model basin. Tangential and axial velocity profiles were obtained with a scanning laser velocimeter as the wakes aged to 35 span lengths behind the model. A 45 deg deflection of two outboard flight spoilers with the model in the landing configuration resulted in a 36 percent reduction in wake maximum tangential velocity, altered velocity profiles, and erratic vortex trajectories. Deployment of the landing gear with the inboard flaps in the landing position and outboard flaps retracted had little effect on the flap vortices to 35 spans, but caused the wing tip vortices to have: (1) more diffuse velocity profiles; (2) a 27 percent reduction in maximum tangential velocity; and (3) a more rapid merger with the flap vortices.

  9. Feasibility of an onboard wake vortex avoidance system

    NASA Technical Reports Server (NTRS)

    Bilanin, Alan J.; Teske, Milton E.; Curtiss, Howard C., Jr.

    1987-01-01

    It was determined that an onboard vortex wake detection system using existing, proven instrumentation is technically feasible. This system might be incorporated into existing onboard systems such as a wind shear detection system, and might provide the pilot with the location of a vortex wake, as well as an evasive maneuver so that the landing separations may be reduced. It is suggested that this system might be introduced into our nation's commuter aircraft fleet and major air carrier fleet and permit a reduction of current landing separation standards, thereby reducing takeoff and departure delays.

  10. NWRA AVOSS Wake Vortex Prediction Algorithm. 3.1.1

    NASA Technical Reports Server (NTRS)

    Robins, R. E.; Delisi, D. P.; Hinton, David (Technical Monitor)

    2002-01-01

    This report provides a detailed description of the wake vortex prediction algorithm used in the Demonstration Version of NASA's Aircraft Vortex Spacing System (AVOSS). The report includes all equations used in the algorithm, an explanation of how to run the algorithm, and a discussion of how the source code for the algorithm is organized. Several appendices contain important supplementary information, including suggestions for enhancing the algorithm and results from test cases.

  11. Large Eddy Simulation of Aircraft Wake Vortices in a Homogeneous Atmospheric Turbulence: Vortex Decay and Descent

    NASA Technical Reports Server (NTRS)

    Han, Jongil; Lin, Yuh-Lang; Arya, S. Pal; Proctor, Fred H.

    1999-01-01

    The effects of ambient turbulence on decay and descent of aircraft wake vortices are studied using a validated, three-dimensional: large-eddy simulation model. Numerical simulations are performed in order to isolate the effect of ambient turbulence on the wake vortex decay rate within a neutrally-stratified atmosphere. Simulations are conducted for a range of turbulence intensities, by injecting wake vortex pairs into an approximately homogeneous and isotropic turbulence field. The decay rate of the vortex circulation increases clearly with increasing ambient turbulence level, which is consistent with field observations. Based on the results from the numerical simulations, simple decay models are proposed as functions of dimensionless ambient turbulence intensity (eta) and dimensionless time (T) for the circulation averaged over a range of radial distances. With good agreement with the numerical results, a Gaussian type of vortex decay model is proposed for weak turbulence: while an exponential type of Tortex decay model can be applied for strong turbulence. A relationship for the vortex descent based on above vortex decay model is also proposed. Although the proposed models are based on simulations assuming neutral stratification, the model predictions are compared to Lidar vortex measurements observed during stable, neutral, and unstable atmospheric conditions. In the neutral and unstable atmosphere, the model predictions appear to be in reasonable agreement with the observational data, while in the stably-stratified atmosphere, they largely underestimate the observed circulation decay with consistent overestimation of the observed vortex descent. The underestimation of vortex decay during stably-stratified conditions suggests that stratification has an important influence on vortex decay when ambient levels of turbulence are weak.

  12. Assessment of a wake vortex flight test program

    NASA Technical Reports Server (NTRS)

    Spangler, S. B.; Dillenius, M. F. E.; Schwind, R. G.; Nielsen, J. N.

    1974-01-01

    A proposed flight test program to measure the characteristics of wake vortices behind a T-33 aircraft was investigated. A number of facets of the flight tests were examined to define the parameters to be measured, the anticipated vortex characteristics, the mutual interference between the probe aircraft and the wake, the response of certain instruments to be used in obtaining measurements, the effect of condensation on the wake vortices, and methods of data reduction. Recommendations made as a result of the investigation are presented.

  13. Simulating Wake Vortex Detection with the Sensivu Doppler Wind Lidar Simulator

    NASA Technical Reports Server (NTRS)

    Ramsey, Dan; Nguyen, Chi

    2014-01-01

    In support of NASA's Atmospheric Environment Safety Technologies NRA research topic on Wake Vortex Hazard Investigation, Aerospace Innovations (AI) investigated a set of techniques for detecting wake vortex hazards from arbitrary viewing angles, including axial perspectives. This technical report describes an approach to this problem and presents results from its implementation in a virtual lidar simulator developed at AI. Threedimensional data volumes from NASA's Terminal Area Simulation System (TASS) containing strong turbulent vortices were used as the atmospheric domain for these studies, in addition to an analytical vortex model in 3-D space. By incorporating a third-party radiative transfer code (BACKSCAT 4), user-defined aerosol layers can be incorporated into atmospheric models, simulating attenuation and backscatter in different environmental conditions and altitudes. A hazard detection algorithm is described that uses a twocomponent spectral model to identify vortex signatures observable from arbitrary angles.

  14. Measurements of Aircraft Wake Vortex Separation at High Arrival Rates and a Proposed New Wake Vortex Separation Philosophy

    NASA Technical Reports Server (NTRS)

    Rutishauser, David; Donohue, George L.; Haynie, Rudolph C.

    2003-01-01

    This paper presents data and a proposed new aircraft wake vortex separation standard that argues for a fundamental re-thinking of international practice. The current static standard, under certain atmospheric conditions, presents an unnecessary restriction on system capacity. A new approach, that decreases aircraft separation when atmospheric conditions dictate, is proposed based upon the availability of new instrumentation and a better understanding of wake physics.

  15. Development and testing of laser Doppler system components for wake vortex monitoring. Volume 1: Scanner development, laboratory and field testing and system modeling

    NASA Technical Reports Server (NTRS)

    Wilson, D. J.; Krause, M. C.; Coffey, E. W.; Huang, C. C.; Edwards, B. B.; Shrider, K. R.; Jetton, J. L.; Morrison, L. K.

    1974-01-01

    A servo-controlled range/elevation scanner for the laser Doppler velocimeter (LDV) was developed and tested in the field to assess its performance in detecting and monitoring aircraft trailing vortices in an airport environment. The elevation scanner provides a capability to manually point the LDV telescope at operator chosen angles from 3.2 deg. to 89.6 deg within 0.2 deg, or to automatically scan the units between operator chosen limits at operator chosen rates of 0.1 Hz to 0.5 Hz. The range scanner provides a capability to manually adjust the focal point of the system from a range of 32 meters to a range of 896 meters under operator control, or to scan between operator chosen limits and at rates from 0.1 Hz to 6.9 Hz. The scanner controls are designed to allow simulataneous range and elevation scanning so as to provide finger scan patterns, arc scan patterns, and vertical line scan patterns. The development and testing of the unit is discussed, along with a fluid dynamic model of the wake vortex developed in a laser Doppler vortex sensor simulation program.

  16. Numerical Study of Wake Vortex Behavior in Turbulent Domains with Ambient Stratification

    NASA Technical Reports Server (NTRS)

    Switzer, George F.; Proctor, Fred H.

    2000-01-01

    A three-dimensional large eddy simulation model is used to investigate the sensitivity of ambient stratification with turbulence on the behavior of aircraft wake vortices. Modeled ambient turbulence levels range from very weak to moderate, and stratification levels range from strongly stable to unstable. The results of profound significance from this study are: 1) very little sensitivity between vortex linking time and the level of stratification, 2) the mean vortex separation remained nearly constant regardless of stratification and turbulence (at least prior to linking), 3) the wake vortices did not rise regardless of the level of stratification, and 4) for very strong stratification, the vortex stopped descending and quickly dissipated even before vortex linking could occur. These results are supported by experimental data and are contrary to conclusions from other numerical studies that assume laminar flow and/or relatively-low Reynolds numbers.

  17. Aircraft Wake Vortex Measurements at Denver International Airport

    NASA Technical Reports Server (NTRS)

    Dougherty, Robert P.; Wang, Frank Y.; Booth, Earl R.; Watts, Michael E.; Fenichel, Neil; D'Errico, Robert E.

    2004-01-01

    Airport capacity is constrained, in part, by spacing requirements associated with the wake vortex hazard. NASA's Wake Vortex Avoidance Project has a goal to establish the feasibility of reducing this spacing while maintaining safety. Passive acoustic phased array sensors, if shown to have operational potential, may aid in this effort by detecting and tracking the vortices. During August/September 2003, NASA and the USDOT sponsored a wake acoustics test at the Denver International Airport. The central instrument of the test was a large microphone phased array. This paper describes the test in general terms and gives an overview of the array hardware. It outlines one of the analysis techniques that is being applied to the data and gives sample results. The technique is able to clearly resolve the wake vortices of landing aircraft and measure their separation, height, and sinking rate. These observations permit an indirect estimate of the vortex circulation. The array also provides visualization of the vortex evolution, including the Crow instability.

  18. A Candidate Wake Vortex Strength Definition for Application to the NASA Aircraft Vortex Spacing System (AVOSS)

    NASA Technical Reports Server (NTRS)

    Hinton, David A.; Tatnall, Chris R.

    1997-01-01

    A significant effort is underway at NASA Langley to develop a system to provide dynamical aircraft wake vortex spacing criteria to Air Traffic Control (ATC). The system under development, the Aircraft Vortex Spacing System (AVOSS), combines the inputs of multiple subsystems to provide separation matrices with sufficient stability for use by ATC and sufficient monitoring to ensure safety. The subsystems include a meteorological subsystem, a wake behavior prediction subsystem, a wake sensor subsystem, and system integration and ATC interfaces. The proposed AVOSS is capable of using two factors, singly or in combination, for reducing in-trail spacing. These factors are wake vortex motion out of a predefined approach corridor and wake decay below a strength that is acceptable for encounter. Although basic research into the wake phenomena has historically used wake total circulation as a strength parameter, there is a requirement for a more specific strength definition that may be applied across multiple disciplines and teams to produce a real-time, automated system. This paper presents some of the limitations of previous applications of circulation to aircraft wake observations and describes the results of a preliminary effort to bound a spacing system strength definition.

  19. Experimental investigation of the asymmetric body vortex wake

    NASA Technical Reports Server (NTRS)

    Oberkampf, W. L.; Shivananda, T. P.; Owen, F. K.

    1980-01-01

    An experimental investigation of the asymmetric body vortex wake of a circular cylinder in high subsonic flow is presented. Laser velocimeter, force and moment, and surface hot wire measurements were obtained for a freestream Mach number of 0.6 and Reynolds number (based on body diameter) of 0.62 x 10 to the 6th. Two component laser velocimeter measurements were made at three body cross-flow planes, x/d = 4, 8, and 12, and angles of attack of 25, 35, and 45 deg. Laser vapor screen photographs were also obtained at these body stations and angles of attack. Surface hot wire measurements were used to determine if any vortex switching occurred at various angles of attack of the body. The laser velocimeter measurements are related to the vapor screen photographs and side force measurements. These results show that more than one asymmetric body vortex wake configuration can exist for the same angle of attack and body roll angle.

  20. Trailing Vortex Measurements in the Wake of a Hovering Rotor Blade with Various Tip Shapes

    NASA Technical Reports Server (NTRS)

    Martin, Preston B.; Leishman, J. Gordon

    2003-01-01

    This work examined the wake aerodynamics of a single helicopter rotor blade with several tip shapes operating on a hover test stand. Velocity field measurements were conducted using three-component laser Doppler velocimetry (LDV). The objective of these measurements was to document the vortex velocity profiles and then extract the core properties, such as the core radius, peak swirl velocity, and axial velocity. The measured test cases covered a wide range of wake-ages and several tip shapes, including rectangular, tapered, swept, and a subwing tip. One of the primary differences shown by the change in tip shape was the wake geometry. The effect of blade taper reduced the initial peak swirl velocity by a significant fraction. It appears that this is accomplished by decreasing the vortex strength for a given blade loading. The subwing measurements showed that the interaction and merging of the subwing and primary vortices created a less coherent vortical structure. A source of vortex core instability is shown to be the ratio of the peak swirl velocity to the axial velocity deficit. The results show that if there is a turbulence producing region of the vortex structure, it will be outside of the core boundary. The LDV measurements were supported by laser light-sheet flow visualization. The results provide several benchmark test cases for future validation of theoretical vortex models, numerical free-wake models, and computational fluid dynamics results.

  1. Near wake vortex dynamics of a hovering hawkmoth

    NASA Astrophysics Data System (ADS)

    Aono, Hikaru; Shyy, Wei; Liu, Hao

    2009-02-01

    Numerical investigation of vortex dynamics in near wake of a hovering hawkmoth and hovering aerodynamics is conducted to support the development of a biology-inspired dynamic flight simulator for flapping wing-based micro air vehicles. Realistic wing-body morphologies and kinematics are adopted in the numerical simulations. The computed results show 3D mechanisms of vortical flow structures in hawkmoth-like hovering. A horseshoe-shaped primary vortex is observed to wrap around each wing during the early down- and upstroke; the horseshoe-shaped vortex subsequently grows into a doughnut-shaped vortex ring with an intense jet-flow present in its core, forming a downwash. The doughnut-shaped vortex rings of the wing pair eventually break up into two circular vortex rings as they propagate downstream in the wake. The aerodynamic yawing and rolling torques are canceled out due to the symmetric wing kinematics even though the aerodynamic pitching torque shows significant variation with time. On the other hand, the time-varying the aerodynamics pitching torque could make the body a longitudinal oscillation over one flapping cycle.

  2. Viscous effects on a vortex wake in ground effect

    NASA Technical Reports Server (NTRS)

    Zheng, Z.; Ash, Robert L.

    1992-01-01

    Wake vortex trajectories and strengths are altered radically by interactions with the ground plane. Prediction of vortex strength and location is especially important in the vicinity of airports. Simple potential flow methods have been found to yield reasonable estimates of vortex descent rates in an otherwise quiescent ambient background, but those techniques cannot be adjusted for more realistic ambient conditions and they fail to provide satisfactory estimates of ground-coupled behavior. The authors have been involved in a systematic study concerned with including viscous effects in a wake-vortex system which is near the ground plane. The study has employed numerical solutions to the Navier-Stokes equations, as well as perturbation techniques to study ground coupling with a descending vortex pair. Results of a two-dimensional, unsteady numerical-theoretical study are presented in this paper. A time-based perturbation procedure has been developed which permits the use of analytical solutions to an inner and outer flow domain for the initial flow field. Predictions have been compared with previously reported laminar experimental results. In addition, the influence of stratification and turbulence on vortex behavior near the ground plane has been studied.

  3. A Parametric Study of Accelerations of an Airplane Due to a Wake Vortex System

    NASA Technical Reports Server (NTRS)

    Stewart, Eric C.

    1999-01-01

    A study was conducted using strip theory to systematically investigate the effects of progressively more complete descriptions of the interaction of an airplane with a wake vortex system. The emphasis was in roll-dominant, parallel, vortex encounters. That is, the simulated airplane's longitudinal axis was nearly parallel to the rotation axis of the vortex system for most of the results presented. The study began with a drag-less rectangular wing in the flow field of a single vortex and progressed to a complete airplane with aerodynamic surfaces possessing taper, sweep, dihedral, and stalling and immersed in the flow field of a vortex pair in ground effect. The effects of the pitch, roll, and yaw attitudes of the airplane on the calculated accelerations were also investigated. The airplane had the nominal characteristics of a Boeing 757, and the vortex flow field had the nominal characteristics of the wake of a Boeing 767. The Bumham-Hallock model of a vortex flow field was used throughout the study. The data are presented mainly in terms of contours of equal acceleration in a two-dimensional area centered on the vortex pair and having dimensions of 300 feet by 300 feet.

  4. Use of Individual Flight Corridors to Avoid Vortex Wakes

    NASA Technical Reports Server (NTRS)

    Rossow, Vernon J.

    2001-01-01

    Vortex wakes of aircraft pose a hazard to following aircraft until the energetic parts of their flow fields have decayed to a harmless level. It is suggested here that in-trail spacings between aircraft can be significantly and safely reduced by designing an individual, vortex-free flight corridor for each aircraft. Because each aircraft will then have its own flight corridor, which is free of vortex wakes while in use by the assigned aircraft, the time intervals between aircraft operations can be safely reduced to the order of seconds. The productivity of airports can then be substantially increased. How large the offset distances between operational corridors need to be to have them vortex free, and how airports need to be changed to accommodate an individual flight-corridor process for landing and takeoff operations, are explored. Estimates are then made of the productivity of an individual flight-corridor system as a function of the in-trail time interval between operations for various values of wake decay time, runway width, and the velocity of a sidewind. The results confirm the need for short time intervals between aircraft operations if smaller offset distances and increased productivity are to be achieved.

  5. On the Development of Turbulent Wakes from Vortex Streets

    NASA Technical Reports Server (NTRS)

    Roshko, Anatol

    1953-01-01

    Wake development behind circular cylinders at Reynolds numbers from 40 to 10,000 was investigated in a low-speed wind tunnel. Standard hotwire techniques were used to study the velocity fluctuations. The Reynolds number range of periodic vortex shedding is divided into two distinct subranges. At R = 40 to 150, called the stable range, regular vortex streets are formed and no turbulent motion is developed. The range R = 150 to 300 is a transition range to a regime called the irregular range, in which turbulent velocity fluctuations accompany the periodic formation of vortices. The turbulence is initiated by laminar-turbulent transition in the free layers which spring from the separation points on the cylinder. This transition first occurs in the range R = 150 to 300. Spectrum and statistical measurements were made to study the velocity fluctuations. In the stable range the vortices decay by viscous diffusion. In the irregular range the diffusion is turbulent and the wake becomes fully turbulent in 40 to 50 diameters downstream. It was found that in the stable range the vortex street has a periodic spanwise structure. The dependence of shedding frequency on velocity was successfully used to measure flow velocity. Measurements in the wake of a ring showed that an annular vortex street is developed.

  6. Numerical Study of a Long-Lived, Isolated Wake Vortex in Ground Effect

    NASA Technical Reports Server (NTRS)

    Proctor, Fred H.

    2014-01-01

    This paper examines a case observed during the 1990 Idaho Falls Test program, in which a wake vortex having an unusually long lifetime was observed while in ground effect. A numerical simulation is performed with a Large Eddy Simulation model to understand the response of the environment in affecting this event. In the simulation, it was found that one of the vortices decayed quickly, with the remaining vortex persisting beyond the time-bound of typical vortex lifetimes. This unusual behavior was found to be related to the first and second vertical derivatives of the ambient crosswind.

  7. Aircraft wake-vortex minimization by use of flaps

    NASA Technical Reports Server (NTRS)

    Corsiglia, V. R.; Dunham, R. E., Jr.

    1977-01-01

    A survey was made of research on the alleviation of the trailing vortex hazard by altering span loading with flaps on the generator airplane. Flap configurations of the generator that shed multiple vortices were found to have wakes that dispersed by vortex merging and sinusoidal instability. Reductions of approximately 50 percent in both the wake rolling moment imposed on a following aircraft and the aircraft separation requirement were achieved in the ground based and flight test experiments by deflecting the trailing edge flaps more inboard than outboard. Significantly, this configuration did not increase the drag or vibration on the generating aircraft compared to the conventional landing configuration. Ground based results of rolling moment measurement and flow visualization are shown, using a water tow facility, an air tow facility, and a wind tunnel. Flight test results are also shown, using a full scale B-747 airplane. General agreement was found among the results of the various ground based facilities and the flight tests.

  8. Characterizing the Hazard of a Wake Vortex Encounter

    NASA Technical Reports Server (NTRS)

    Vicroy, Dan D.; Brandon, Jay; Greene, George; Rivers, Robert; Shah, Gautam; Stewart, Eric; Stuever, Robert

    1998-01-01

    The National Aeronautics and Space Administration (NASA) is conducting research with the goal of enabling safe improvements in the capacity of the nation's air transportation system. The wake vortex upset hazard is an important factor in establishing the minimum safe spacing between aircraft during landing and take-off operations, thus impacting airport capacity. Static and free-flight wind tunnel tests and flight tests have provided an extensive data set for improved understanding of vortex encounter dynamics and simulation. Piloted and batch simulation studies are also ongoing to establish a first-order hazard metric and determine the limits of an operationally acceptable wake induced upset. This paper outlines NASA's research in these areas.

  9. Evaluation of the discrete vortex wake cross flow model using vector computers. Part 2: User's manual for DIVORCE

    NASA Technical Reports Server (NTRS)

    Deffenbaugh, F. D.; Vitz, J. F.

    1979-01-01

    The users manual for the Discrete Vortex Cross flow Evaluator (DIVORCE) computer program is presented. DIVORCE was developed in FORTRAN 4 for the DCD 6600 and CDC 7600 machines. Optimal calls to a NASA vector subroutine package are provided for use with the CDC 7600.

  10. Vortex age as a wake turbulence scaling parameter

    NASA Technical Reports Server (NTRS)

    Marshall, J. R.; Marchman, J. F., III

    1973-01-01

    Research which was conducted to determine the significance of vortex age as a scaling parameter in wake turbulence development and dissipation is reported. Tests were conducted at three angles of attack, three free stream speeds, and seven downstream positions from 2 to 30 chordlengths using an NACA 0012 wing and a five hole yawhead pitot probe. The end surface of the wing tip was flat. Speeds were selected to give a predetermined range of vortex ages. The complete velocity structure of the vortex was measured at each station and speed. The resulting plots of maximum tangential velocity and vortex core diameter versus downstream distance and vortex age indicate that vortex age is not a self sufficient scaling parameter. In addition to the expected effect of lift coefficient there is also a definite free stream speed influence at high wing angles of attack. The exact cause and nature of this effect is not fully understood, but it does not appear to be explainable in terms of Mach number or Reynolds number; however, the influence of tip edge shape on spanwise flow separation appears to be an important factor.

  11. Rotor Vortex Wake in Close Proximity of Walls in Hover

    NASA Astrophysics Data System (ADS)

    Konus, Mehmet Fatih; Savas, Omer

    2014-11-01

    Expanding flight envelopes of rotorcraft raise concerns about their behavior in very close proximity of walls or corners where the separation between the wall and the rotor disk can almost vanish. A series of experiments are conducted in a water tank to study the hover behavior of the wake of a 25-cm diameter three-bladed rotor at 8 rev/s. Particle image velocimetry, strain gage force balance measurements and flow visualization are employed. The vortex wake, which is axisymmetric on the average in an unbounded surrounding, is distorted increasingly with decreasing separation from a wall or corner. The vortex wake bends toward the wall and into the corner. The individual helical filaments off the rotor tips are distorted and closely follow the wall. Intermittent reversed vortical flow regions appear upstream of the rotor disk in the proximity of the wall. The mean streamlines indicate that the wake is bent toward the wall or into the corner. The component of the thrust vector along the axis of the rotor decreases. These observation suggest that the thrust vector progressively deviates from the geometric axis of the rotor.

  12. Historical Overview of Research on Lift-Generated Vortex Wakes

    NASA Technical Reports Server (NTRS)

    Rossow, Vernon J.

    2001-01-01

    A historical overview is presented of research conducted on the structure and modification of the vortices generated by the lifting surfaces of subsonic transport aircraft. Although primarily presented from an experimental point of view, the use of relatively compact theoretical formulations and concepts are used to indicate the progress made. It is pointed out that the first objective of the research is to reduce the magnitude of the hazard potential posed by the wakes of aircraft by modifying the aerodynamics of the wake-generating aircraft. A secondary objective is to develop the technology that will make it possible to safely avoid vortex wakes in the airport environment for increased capacity. If either or both objectives are achieved, the hazard posed by vortex wakes should have a greatly reduced impact on the operational capacity of airports for landings and takeoffs. Since a satisfactory solution to either of these two goals have not yet been achieved, the last part of the presentation will be devoted to a discussion of some requirements that have been placed on any prospective solution to either goal, if is to be acceptable. The material to be used in the presentation is published in the open literature.

  13. Measurement of Vortex Strength and Core Diameter in the Wake of a Hovering Rotor

    NASA Technical Reports Server (NTRS)

    Wadcock, Alan J.

    1997-01-01

    Detailed hot wire measurements have been acquired in the tip vortex of a three-bladed model tilt rotor in hover. Testing was conducted at a rotor tip speed of 752 ft/sec, a Reynolds number (based on blade tip chord) of 1.77 x 10(exp 6), for thrust coefficients up to 0.0160. A figure shows the hot wire mounted above the inverted rotor at the Outside Aerodynamic Rotor Facility (OARF) at NASA Ames Research Center. Strobed shadowgraph flow visualization was used to define the vortex trajectory as an aid in hot wire positioning. Considerable variations in tip vortex structure with time were observed, even from the same blade, under essentially uniform test conditions. The only velocity signatures analyzed were those corresponding to passage of the probe directly through the center of the vortex. These time histories were ensemble averaged after compensating for jitter in the vortex arrival time at the probe, thereby retaining the core structure with minimal smearing. An example of a mean velocity signature, after ensemble averaging, is shown. The mean velocity signature was analyzed under the assumption of constant (unknown) translation speed of the vortex filament past the fixed probe. The translation speed of the vortex is deduced and the vortex strength and core diameter inferred. The results were highly unexpected. The indicated vortex strength is seen to decrease rapidly after first blade passage. In addition, the core radius is seen to decrease with increasing wake age, not increase as might be expected from simple diffusion.

  14. Circular cylinder wakes and vortex-induced vibrations

    NASA Astrophysics Data System (ADS)

    Bearman, P. W.

    2011-07-01

    This paper presents a selective review of recent research on vortex-induced vibrations of isolated circular cylinders and the flow and vibration of circular cylinders in a tandem arrangement; a common thread being that the topics raised are of particular interest to the author. The influence of Reynolds number on the response of isolated cylinders is presented and recent developments using forced vibration are discussed. The response of a cylinder free to respond in the in-line and transverse directions is contrasted with that of a cylinder responding in only one direction. The interference between two circular cylinders is discussed and prominence given to the case of cylinders in a tandem arrangement. The origin of the time-mean lift force on the downstream cylinder is considered together with the cause of the large amplitude transverse vibration experienced by the cylinder above vortex resonance. This wake-induced vibration is shown to be a form of vortex-induced vibration.

  15. A self-consistent model for the saturation dynamics of the vortex shedding around the mean flow in the unstable cylinder wake

    NASA Astrophysics Data System (ADS)

    Mantič-Lugo, Vladislav; Arratia, Cristóbal; Gallaire, François

    2015-07-01

    The supercritical instability leading to the Bénard-von Karman vortex street in a cylinder wake is a well known example of supercritical Hopf bifurcation: the steady solution becomes linearly unstable and saturates into a periodic limit cycle. Nonetheless, a simplified physical formulation accurately predicting the transition dynamics of the saturation process is lacking. Building upon our previous work, we present here a simple self-consistent model that provides a clear description of the saturation mechanism in a quasi-steady manner by means of coupling the instantaneous mean flow with its most unstable eigenmode and its instantaneous amplitude through the Reynolds stress. The system is coupled for different oscillation amplitudes, providing an instantaneous mean flow as function of an equivalent time. A transient physical picture is described, wherein a harmonic perturbation grows and changes in amplitude, frequency, and structure due to the modification of the mean flow by the Reynolds stress forcing, saturating when the flow is marginally stable. Comparisons with direct numerical simulations show an accurate prediction of the instantaneous amplitude, frequency, and growth rate, as well as the saturated mean flow, the oscillation amplitude, frequency, and the resulting mean Reynolds stresses.

  16. Influence of structural flexibility on the wake vortex pattern of airfoils undergoing harmonic pitch oscillation

    NASA Astrophysics Data System (ADS)

    Monnier, B.; Naguib, A. M.; Koochesfahani, M. M.

    2015-04-01

    Reported herein is an investigation of the influence of the structural flexibility of sinusoidally pitching airfoils on the pattern of vorticity shed into the wake. For rigid airfoils, it is well known that, depending on the oscillation frequency and amplitude, this pattern takes the form of the classical or reverse von Kármán vortex street. The pattern may be characterized by the vortex circulation ( Γ o ), vortex-to-vortex streamwise and cross-stream spacing ( a and b, respectively), and vortex core radius ( R). In the present work, these four parameters are obtained from particle image velocimetry measurements in the wake of airfoils consisting of a rigid "head" and flexible "tail" at chord Reynolds number of 2010 for different tail flexibilities. The results show that flexible airfoils exhibit the switch from classical to reverse von Kármán vortex street (i.e., change in the sign of b) at a reduced frequency of oscillation lower than their rigid counterpart. At a given oscillation frequency, the Strouhal number at which this switch occurs is smallest for a given airfoil structural flexibility; which becomes stiffer with increasing frequency. Using Strouhal number based on the actual trailing edge oscillation amplitude, reasonable scaling is found of the dependence of not only b but also Γ o , a and R on the motion and structure parameters for all airfoils investigated. These results are complemented with analyses using a vortex array model, which together with the identified scaling of the wake vortex parameters, provide basis for the computation of the net thrust acting on the airfoil.

  17. Validation of Vortex-Lattice Method for loads on wings in lift-generated wakes

    NASA Technical Reports Server (NTRS)

    Rossow, J.

    1994-01-01

    A study is described that evaluates the accuracy of vortex-lattice methods when they are used to compute the loads induced on aircraft as they encounter lift-generated wakes. The evaluation is accomplished by use of measurements made in the 80- by 120-foot wind tunnel of the lift, rolling-moment, and downwash in the wake of three configurations of a model of a subsonic transport aircraft. The downwash measurements are used as input for a vortex-lattice code in order to compute the lift and rolling moment induced on wings that have a span of 0.186, 0.510, or 1.022 times the span of the wake-generating model. Comparison of the computed results with the measured lift and rolling moment distributions are used to determine the accuracy of the vortex-lattice code. It was found that the vortex-lattice method is very reliable as long as the span of the encountering of following wing is less than about 0.2 of the generator span. As the span of the following wing increases above 0.2, the vortex-lattice method continues to correctly predict the trends and nature of the induced loads, but it overpredicts the magnitude of the loads by increasing amounts. The increase in deviation of the computed from the measured loads with size of the following wing is attributed to the increase in distortion of the structure of the vortex wake as it approaches and passes the larger following wings.

  18. Flight test investigation of the vortex wake characteristics behind a Boeing 727 during two-segment and normal ILS approaches

    NASA Technical Reports Server (NTRS)

    Garodz, L. J.

    1975-01-01

    A series of flight tests were performed to evaluate the vortex wake characteristics of a Boeing 727 (B727-200) aircraft during conventional and two-segment ILS approaches. Flights of the B727, equipped with smoke generators for vortex marking, were flown wherein its vortex wake was intentionally encountered by a Lear Jet model 23 (LR-23) or a Piper Twin Comanche (Pa-30); and its vortex location during landing approach was measured using a system of photo-theodolites. The tests showed that at a given separation distance there were no differences in the upsets resulting from deliberate vortex encounters during the two types of approaches. Timed mappings of the position of the landing configuration vortices showed that they tended to descend approximately 91 meters (300 feet) below the flight path of the B727. The flaps of the B727 have a dominant effect on the character of the trailed wake vortex. The clean wing produces a strong, concentrated vortex. As the flaps are lowered, the vortex system becomes more diffuse. Pilot opinion and roll acceleration data indicate that 4.5 nautical miles would be a minimum separation distance at which roll control could be maintained during parallel encounters of the B727's landing configuration wake by small aircraft.

  19. Large-Eddy Simulations and Lidar Measurements of Vortex-Pair Breakup in Aircraft Wakes

    NASA Technical Reports Server (NTRS)

    Lewellen, D. C.; Lewellen, W. S.; Poole, L. R.; DeCoursey, R. J.; Hansen, G. M.; Hostetler, C. A.; Kent, G. S.

    1998-01-01

    Results of large-eddy simulations of an aircraft wake are compared with results from ground-based lidar measurements made at NASA Langley Research Center during the Subsonic Assessment Near-Field Interaction Flight Experiment field tests. Brief reviews of the design of the field test for obtaining the evolution of wake dispersion behind a Boeing 737 and of the model developed for simulating such wakes are given. Both the measurements and the simulations concentrate on the period from a few seconds to a few minutes after the wake is generated, during which the essentially two-dimensional vortex pair is broken up into a variety of three-dimensional eddies. The model and experiment show similar distinctive breakup eddies induced by the mutual interactions of the vortices, after perturbation by the atmospheric motions.

  20. Prediction of the hub vortex instability within wind turbine wakes and effects of the incoming wind and turbine aerodynamic characteristics

    NASA Astrophysics Data System (ADS)

    Iungo, Giacomo Valerio; Viola, Francesco; Camarri, Simone; Porté-Agel, Fernando; Gallaire, Francois

    2014-11-01

    Instability of the hub vortex, which is a vorticity structure present in wind turbine near-wake and mainly oriented along the streamwise direction, is predicted from wake velocity measurements. In this work, stability analysis is performed on wind tunnel velocity measurements acquired in the wake produced from a wind turbine model immersed in a uniform flow. Turbulence effects on wake dynamics are taken into account by modeling the Reynolds stresses through eddy-viscosity models, which are calibrated on the wind tunnel data. This formulation leads to the identification of one dominant mode associated with the hub vortex instability, which is characterized by a counter-winding single-helix mode. Moreover, this analysis also predicts accurately the frequency of the hub vortex instability observed experimentally. The hub vortex instability is also investigated by considering incoming wind fields with different turbulence characteristics, different turbine aerodynamic designs and operational regimes, which affect the morphology of the wake vorticity structures and their dynamics. The ultimate goal of this work consists in providing useful information for predicting wind turbine wake dynamics and their effects on downstream wake recovery, thus to maximize wind power harvesting.

  1. Wind shear and vortex wake research in UK, 1982

    NASA Technical Reports Server (NTRS)

    Woodfield, A. A.

    1983-01-01

    A wind shear and vortex wake and their impact on aircraft were investigated. The systems and advice to help pilots, and rational scientific methods to assist in advising certification authorities and those interested in improving flight safety were developed. Wind Shear and Vortex Wakes are related, they are both invisible enemies of aircraft in the form of large disturbances in the atmosphere, both cause major accidents. Problems of building wakes at airports are is considered. Research on wind shear was initiated by the American FAA following the Boston, New York and Denver accidents to civil airliners. This resulted in: useful advice to pilots about wind shear; better attempts by the meteorologists at forecasting wind shear conditions; and useful ideas for wind shear measurement and warning systems. Three major research tasks are outstanding: (1) Worldwide measurements to give reliable estimates of probability and details of the forms of large wind shears; (2) Developments of real time wind shear measuring systems for ground or airborne use; and (3) Establishing relationships between measured wind shear and the potential hazard to an aircraft, or class of aircraft.

  2. Validation of Vortex-Lattice Method for Loads on Wings in Lift-Generated Wakes

    NASA Technical Reports Server (NTRS)

    Rossow, Vernon J.

    1995-01-01

    A study is described that evaluates the accuracy of vortex-lattice methods when they are used to compute the loads induced on aircraft as they encounter lift-generated wakes. The evaluation is accomplished by the use of measurements made in the 80 by 120 ft Wind Tunnel of the lift, rolling moment, and downwash in the wake of three configurations of a model of a subsonic transport aircraft. The downwash measurements are used as input for a vortex-lattice code in order to compute the lift and rolling moment induced on wings that have a span of 0.186, 0.510, or 1.022 times the span of the wake-generating model. Comparison of the computed results with the measured lift and rolling-moment distributions the vortex-lattice method is very reliable as long as the span of the encountering or following wing is less than about 0.2 of the generator span. As the span of the following wing increases above 0.2, the vortex-lattice method continues to correctly predict the trends and nature of the induced loads, but it overpredicts the magnitude of the loads by increasing amounts.

  3. A preliminary study of a wake vortex encounter hazard boundary for a B737-100 airplane

    NASA Technical Reports Server (NTRS)

    Reimer, Heidi M.; Vicroy, Dan D.

    1996-01-01

    A preliminary batch simulation study was conducted to define the wake decay required for a Boeing 737-100 airplane to safely encounter a Boeing 727 wake and land. The baseline six-degree-of-freedom B737 simulation was modified to include a wake model and the strip-theory calculation of the vortex-induced forces and moments. The guidance and control inputs for the airplane were provided by an autoland system. The wake strength and encounter altitude were varied to establish a safe encounter boundary. The wake was positioned such that the desired flight path traversed the core of the port Vortex. Various safe landing criteria were evaluated for defining a safe encounter boundary. A sensitivity study was also conducted to assess the effects of encounter model inaccuracies.

  4. Aircraft Wake Vortex Measurement with Coherent Doppler Lidar

    NASA Astrophysics Data System (ADS)

    Wu, Songhua; Liu, Bingyi; Liu, Jintao

    2016-06-01

    Aircraft vortices are generated by the lift-producing surfaces of the aircraft. The variability of near-surface conditions can change the drop rate and cause the cell of the wake vortex to twist and contort unpredictably. The pulsed Coherent Doppler Lidar Detection and Ranging is an indispensable access to real aircraft vortices behavior which transmitting a laser beam and detecting the radiation backscattered by atmospheric aerosol particles. Experiments for Coherent Doppler Lidar measurement of aircraft wake vortices has been successfully carried out at the Beijing Capital International Airport (BCIA). In this paper, the authors discuss the Lidar system, the observation modes carried out in the measurements at BCIA and the characteristics of vortices.

  5. On the Development of Turbulent Wakes from Vortex Streets

    NASA Technical Reports Server (NTRS)

    Roshko, Anatol

    1954-01-01

    Wake development behind circular cylinders at Reynolds numbers from 40 to 10,000 was investigated in a low-speed wind tunnel. Standard hot-wire techniques were used to study the velocity fluctuations. The Reynolds number range of periodic vortex shedding is divided into two distinct subranges. At r=40 to 150, called the stable range, regular vortex streets are formed and no turbulent velocity fluctuations accompany the periodic formation of vortices. The range r=150 to 300 is a transition range to a regime called the irregular range, in which turbulent velocity fluctuations accompany the periodic formation of vortices. The turbulence is initiated by laminar-turbulent transition in the free layers which spring from the separation points on the cylinder. The transition first occurs in the range r=150 to 300. Spectrum and statistical measurements were made to study the velocity fluctuations.

  6. Generation of vortex rings by nonstationary laser wake field

    SciTech Connect

    Tsintsadze, N.L.; Murtaza, G.; Shah, H.A.

    2006-01-15

    A new concept of generating quasistatic magnetic fields, vortex rings, and electron jets in an isotropic homogeneous plasma is presented. The propagation of plasma waves, generated by a relativistically intense short pulse laser, is investigated by using the kinetic model and a novel nonpotential, time-dependent ponderomotive force is derived by obtaining a hydrodynamic equation of motion. This force can in turn generate quasistatic magnetic fields, vortex rings, and electron jets. It is also shown that the vortex rings can become a means for accelerating electrons, which are initially in equilibrium. The conservation of canonical momentum circulation and the frozen-in condition for the vorticity is discussed. The excitation of the vortex waves by the modulation of the amplitude of the plasma waves is considered. These vortex waves, which generate a lower hybrid mode propagating across the generated magnetic field, are also investigated.

  7. Spectral Characteristics of Wake Vortex Sound During Roll-Up

    NASA Technical Reports Server (NTRS)

    Booth, Earl R., Jr. (Technical Monitor); Zhang, Yan; Wang, Frank Y.; Hardin, Jay C.

    2003-01-01

    This report presents an analysis of the sound spectra generated by a trailing aircraft vortex during its rolling-up process. The study demonstrates that a rolling-up vortex could produce low frequency (less than 100 Hz) sound with very high intensity (60 dB above threshold of human hearing) at a distance of 200 ft from the vortex core. The spectrum then drops o rapidly thereafter. A rigorous analytical approach has been adopted in this report to derive the spectrum of vortex sound. First, the sound pressure was solved from an alternative treatment of the Lighthill s acoustic analogy approach [1]. After the application of Green s function for free space, a tensor analysis was applied to permit the removal of the source term singularity of the wave equation in the far field. Consequently, the sound pressure is expressed in terms of the retarded time that indicates the time history and spacial distribution of the sound source. The Fourier transformation is then applied to the sound pressure to compute its spectrum. As a result, the Fourier transformation greatly simplifies the expression of the vortex sound pressure involving the retarded time, so that the numerical computation is applicable with ease for axisymmetric line vortices during the rolling-up process. The vortex model assumes that the vortex circulation is proportional to the time and the core radius is a constant. In addition, the velocity profile is assumed to be self-similar along the aircraft flight path, so that a benchmark vortex velocity profile can be devised to obtain a closed form solution, which is then used to validate the numerical calculations for other more realistic vortex profiles for which no closed form solutions are available. The study suggests that acoustic sensors operating at low frequency band could be profitably deployed for detecting the vortex sound during the rolling-up process.

  8. Vortex dislocations in wake-type flow induced by spanwise disturbances

    NASA Astrophysics Data System (ADS)

    Ling, Guo Can; Zhao, Hong Liang

    2009-07-01

    Vortex dislocations in wake-type flow induced by three types of spanwise disturbances superimposed on an upstream velocity profile are investigated by direct numerical simulations. Three distinct modes of vortex dislocations and flow transitions have been found. A local spanwise exponential decay disturbance leads to the appearance of a twisted chainlike mode of vortex dislocation. A stepped spanwise disturbance causes a streamwise periodic spotlike mode of vortex dislocation. A spanwise sinusoidal wavy disturbance with a moderate waviness causes a strong unsteadiness of wake behavior. This unsteadiness starts with a systematic periodic mode of vortex dislocation in the spanwise direction followed by the spanwise vortex shedding suppressed completely with increased time and the near wake becoming a steady shear flow. Characteristics of these modes of vortex dislocation and complex vortex linkages over the dislocation, as well as the corresponding dynamic processes related to the appearance of dislocations, are described by examining the variations of vortex lines and vorticity distribution. The nature of the vortex dislocation is demonstrated by the substantial vorticity modification of the spanwise vortex from the original spanwise direction to streamwise and vertical directions, accompanied by the appearance of noticeable vortex branching and complex vortex linking, all of which are produced at the locations with the biggest phase difference or with a frequency discontinuity between shedding cells. The effect of vortex dislocation on flow transition, either to an unsteady irregular vortex flow or suppression of the Kármán vortex shedding making the wake flow steady state, is analyzed. Distinct similarities are found in the mechanism and main flow phenomena between the present numerical results obtained in wake-type flows and the experimental-numerical results of cylinder wakes reported in previous studies.

  9. NASA AVOSS Fast-Time Wake Prediction Models: User's Guide

    NASA Technical Reports Server (NTRS)

    Ahmad, Nash'at N.; VanValkenburg, Randal L.; Pruis, Matthew

    2014-01-01

    The National Aeronautics and Space Administration (NASA) is developing and testing fast-time wake transport and decay models to safely enhance the capacity of the National Airspace System (NAS). The fast-time wake models are empirical algorithms used for real-time predictions of wake transport and decay based on aircraft parameters and ambient weather conditions. The aircraft dependent parameters include the initial vortex descent velocity and the vortex pair separation distance. The atmospheric initial conditions include vertical profiles of temperature or potential temperature, eddy dissipation rate, and crosswind. The current distribution includes the latest versions of the APA (3.4) and the TDP (2.1) models. This User's Guide provides detailed information on the model inputs, file formats, and the model output. An example of a model run and a brief description of the Memphis 1995 Wake Vortex Dataset is also provided.

  10. Development of a Wake Vortex Spacing System for Airport Capacity Enhancement and Delay Reduction

    NASA Technical Reports Server (NTRS)

    Hinton, David A.; OConnor, Cornelius J.

    2000-01-01

    The Terminal Area Productivity project has developed the technologies required (weather measurement, wake prediction, and wake measurement) to determine the aircraft spacing needed to prevent wake vortex encounters in various weather conditions. The system performs weather measurements, predicts bounds on wake vortex behavior in those conditions, derives safe wake spacing criteria, and validates the wake predictions with wake vortex measurements. System performance to date indicates that the potential runway arrival rate increase with Aircraft VOrtex Spacing System (AVOSS), considering common path effects and ATC delivery variance, is 5% to 12% depending on the ratio of large and heavy aircraft. The concept demonstration system, using early generation algorithms and minimal optimization, is performing the wake predictions with adequate robustness such that only 4 hard exceedances have been observed in 1235 wake validation cases. This performance demonstrates the feasibility of predicting wake behavior bounds with multiple uncertainties present, including the unknown aircraft weight and speed, weather persistence between the wake prediction and the observations, and the location of the weather sensors several kilometers from the approach location. A concept for the use of the AVOSS system for parallel runway operations has been suggested, and an initial study at the JFK International Airport suggests that a simplified AVOSS system can be successfully operated using only a single lidar as both the weather sensor and the wake validation instrument. Such a selfcontained AVOSS would be suitable for wake separation close to the airport, as is required for parallel approach concepts such as SOIA.

  11. Far-Field Turbulent Vortex-Wake/Exhaust Plume Interaction for Subsonic and HSCT Airplanes

    NASA Technical Reports Server (NTRS)

    Kandil, Osama A.; Adam, Ihab; Wong, Tin-Chee

    1996-01-01

    Computational study of the far-field turbulent vortex-wake/exhaust plume interaction for subsonic and high speed civil transport (HSCT) airplanes is carried out. The Reynolds-averaged Navier-Stokes (NS) equations are solved using the implicit, upwind, Roe-flux-differencing, finite-volume scheme. The two-equation shear stress transport model of Menter is implemented with the NS solver for turbulent-flow calculation. For the far-field study, the computations of vortex-wake interaction with the exhaust plume of a single engine of a Boeing 727 wing in a holding condition and two engines of an HSCT in a cruise condition are carried out using overlapping zonal method for several miles downstream. These results are obtained using the computer code FTNS3D. The results of the subsonic flow of this code are compared with those of a parabolized NS solver known as the UNIWAKE code.

  12. Vortex Particle-Mesh methods for large scale LES of aircraft wakes

    NASA Astrophysics Data System (ADS)

    Chatelain, Philippe; Duponcheel, Matthieu; Marichal, Yves; Winckelmans, Grégoire

    2015-11-01

    Vortex methods solve the NS equations in vorticity-velocity formulation. The present Particle-Mesh variant exploits the advantages of a hybrid approach: advection is handled by the particles while the mesh allows the evaluation of the differential operators and the use of fast Poisson solvers (here a Fourier-based solver which allows for unbounded directions and inlet/outlet boundaries). A lifting line approach models the vorticity sources in the flow; its immersed treatment efficiently captures the development of vorticity from thin sheets into 3-D field. Large scale simulations of aircraft wakes (including ``encounter'' cases where a following aircraft flies into the wake) are presented, which also demonstrate the performance of the methodology: the adequate treatment of particle distortion, the high-order discretization, and the multiscale subgrid models allow to capture wake dynamics with minimal spurious dispersion and diffusion.

  13. Pulsed coherent fiber lidar transceiver for aircraft in-flight turbulence and wake-vortex hazard detection

    NASA Astrophysics Data System (ADS)

    Akbulut, M.; Hwang, J.; Kimpel, F.; Gupta, S.; Verdun, H.

    2011-06-01

    We report on the development of a fiber-optic pulsed coherent lidar transceiver for wind-velocity and aircraft wake-vortex hazard detection. The all-fiber 1.5μm transmitter provides up to 560 μJ energy at 25 kHz with 800 ns pulse width (pump limited). Performance simulations indicate wake-vortex hazard signature detection up to ~2.5km range with a receiver sensitivity of ~2 fW (SNR=6), suited for an aircraft landing scenario. Furthermore, the transceiver is implemented using high-speed FPGA based control and digital-signal-processing, enabling its use as a flexible pulse-format multi-function in-flight lidar sensor. We present the latest laboratory results and preliminary testing of this pulsed coherent lidar transceiver, along with the lidar performance simulation of wake-vortex eddy models.

  14. An Investigation of Candidate Sensor-Observable Wake Vortex Strength Parameters for the NASA Aircraft Vortex Spacing System (AVOSS)

    NASA Technical Reports Server (NTRS)

    Tatnall, Chistopher R.

    1998-01-01

    The counter-rotating pair of wake vortices shed by flying aircraft can pose a threat to ensuing aircraft, particularly on landing approach. To allow adequate time for the vortices to disperse/decay, landing aircraft are required to maintain certain fixed separation distances. The Aircraft Vortex Spacing System (AVOSS), under development at NASA, is designed to prescribe safe aircraft landing approach separation distances appropriate to the ambient weather conditions. A key component of the AVOSS is a ground sensor, to ensure, safety by making wake observations to verify predicted behavior. This task requires knowledge of a flowfield strength metric which gauges the severity of disturbance an encountering aircraft could potentially experience. Several proposed strength metric concepts are defined and evaluated for various combinations of metric parameters and sensor line-of-sight elevation angles. Representative populations of generating and following aircraft types are selected, and their associated wake flowfields are modeled using various wake geometry definitions. Strength metric candidates are then rated and compared based on the correspondence of their computed values to associated aircraft response values, using basic statistical analyses.

  15. Three Dimensional Vortex Wake Structure of Flapping Wings in Hovering Flight

    NASA Astrophysics Data System (ADS)

    Cheng, Bo; Liu, Yun; Deng, Xinyan; Bio-Robotics Lab Team

    2013-11-01

    Flapping wings create complex vortex structures in the wake, as the vortices of one wing stroke shed periodically and travel downwards with the induced flow. However, the detailed three-dimensional vorticity distribution and evolution in the far wake are scarcely understood experimentally. In this study, the three-dimensional vortex wake structure in both the near and far field of a dynamically-scaled flapping wing was investigated experimentally, using volumetric three component velocimetry. Summarily, the overall result of the wing action is to create a coherent vortex structure consisting of a tip vortex (TV), trailing-edge shear layer (TESL) and leading-edge vortex (LEV). The shed TESL rolls up into a root vortex (RV); together with the TV in the wake, they contracts radially but stretch tangentially in the wake. Concurrently, the downwash is distributed in an arc-shaped region enclosed by the stretched tangential vorticity of TVs and RVs. Overall, a closed vortex ring structure is not observed in the current study, because there is no well-established starting and stopping vortex structures that smoothly connect to TV and RV. Finally, evaluation of the vorticity transport equation shows that both TV and RV, while convected downwards, undergo vortex stretching, a three-dimensional phenomenon in rotating flows. It also confirms that the vorticity evolution is dominated by convection with secondary tilting/stretch effects, while the magnitude of vorticity dissipation is negligible.

  16. Vortex Identification in the Wake of a Wind Turbine Array

    NASA Astrophysics Data System (ADS)

    Aseyev, Aleksandr; Cal, Raul

    2014-11-01

    A 4 × 3 wind turbine array boundary layer is analyzed through Particle Image Velocimetry data gathered directly forward and aft of the first and last row turbines at the centerline in a wind tunnel. Vortex identification techniques are able to capture vortical structures. Q-criterion, Δ -criterion, and λ - 2 criterion are evaluated and compared for this flow. Q-criterion and λ - 2 criterion provided a clear indication of regions where vortical activity exists while the Δ -criterion is not able to capture these regions. Galilean decomposition, Reynolds decomposition, vorticity, and swirling strength were used to further understand the location and behavior of the vortices. The various criterion displayed the high magnitude vortices, resulting from the blade tips and located immediately in areas of high shear. Using Galilean and Reynolds decomposition, swirling motions are shown hugging vortex regions in agreement with the identification criterion. The percentages used in the Galilean decomposition were 20 and 50 percent of a convective velocity of 7 m/s. As the vortices convect downstream, these vortices weaken in magnitude to approximately 25 percent of those present in the near wake.

  17. Volumetric imaging of shark tail hydrodynamics reveals a three-dimensional dual-ring vortex wake structure

    PubMed Central

    Flammang, Brooke E.; Lauder, George V.; Troolin, Daniel R.; Strand, Tyson

    2011-01-01

    Understanding how moving organisms generate locomotor forces is fundamental to the analysis of aerodynamic and hydrodynamic flow patterns that are generated during body and appendage oscillation. In the past, this has been accomplished using two-dimensional planar techniques that require reconstruction of three-dimensional flow patterns. We have applied a new, fully three-dimensional, volumetric imaging technique that allows instantaneous capture of wake flow patterns, to a classic problem in functional vertebrate biology: the function of the asymmetrical (heterocercal) tail of swimming sharks to capture the vorticity field within the volume swept by the tail. These data were used to test a previous three-dimensional reconstruction of the shark vortex wake estimated from two-dimensional flow analyses, and show that the volumetric approach reveals a different vortex wake not previously reconstructed from two-dimensional slices. The hydrodynamic wake consists of one set of dual-linked vortex rings produced per half tail beat. In addition, we use a simple passive shark-tail model under robotic control to show that the three-dimensional wake flows of the robotic tail differ from the active tail motion of a live shark, suggesting that active control of kinematics and tail stiffness plays a substantial role in the production of wake vortical patterns. PMID:21543357

  18. Successive stages and the role of natural vortex dislocations in three-dimensional wake transition

    NASA Astrophysics Data System (ADS)

    Braza, M.; Faghani, D.; Persillon, H.

    2001-07-01

    The time-history of the development of the three-dimensional transition features in a nominally two-dimensional flow configuration is established for Reynolds number 220 in a cylinder wake. The identification of the successive stages that evolve very fast during experiments is possible by means of direct numerical simulation. The physical processes related to the creation of streamwise and vertical vorticity components and their impact on the spanwise waviness of the main von Kármán vortex filaments are analysed by means of the Craik Leibovich shearing instability mechanism and a comparative discussion is given with respect to the elliptic stability theory. This study proves the existence of a further stage in the three-dimensional transition, which substantially modifies the regular spanwise undulation. This is a systematic and repetitive development of natural vortex dislocations in the near wake. The definition of this kind of structure is provided, as well as its properties related to a drastic reduction of the fundamental frequency and to the selection of a lower path in the Strouhal Reynolds number relation. The induced amplitude modulation of the flow properties along the span is also evaluated. Quantification of these properties is carried out by using wavelet analysis and autoregressive modelling of the time series. The reasons for the development of natural vortex dislocations are analysed and related to specific modulations of the spanwise structure of the longitudinal velocity upstream separation. From this part of the study an optimum shape for the spanwise distribution of this component can be specified, able to trigger the vortex dislocations in wake flows and therefore useful to apply in the context of stability theory analyses and in further DNS studies.

  19. Dynamic Wind Loads and Vortex Structures in the Wake of a Wind Turbine

    NASA Astrophysics Data System (ADS)

    Hu, Hui; Yang, Zifeng; Sarkar, Partha

    2010-11-01

    We report an experimental study to characterize the dynamic wind loads and evolution of wake vortex flow structures downstream of a horizontal axis wind turbine (HAWT). The experiments were conducted in a wind tunnel with a wind turbine model placed in a boundary layer flow developed over rough and smooth surfaces in order to study the effects of roughness and the resulting velocity and turbulence fields on the wake characteristics and fatigue loads acting on the wind turbine. In addition to measuring dynamic wind loads (both aerodynamic forces and moments) acting on the wind turbine model using a six-component load cell, a high-resolution Particle Image Velocimetry (PIV) system was used to make phase-locked flow field measurements to quantify the time-evolution of the wake vortex and turbulence flow structures shedding from wind turbine blades. The detailed flow field measurements were correlated with the wind load measurements to elucidate the underlying physics associated with turbine power generation and fatigue loads acting on wind turbines.

  20. Vortex Formation in the Wake of Dark Matter Propulsion

    NASA Astrophysics Data System (ADS)

    Robertson, G. A.; Pinheiro, M. J.

    Future spaceflight will require a new theory of propulsion; specifically one that does not require mass ejection. A new theory is proposed that uses the general view that closed currents pervade the entire universe and, in particular, there is a cosmic mechanism to expel matter to large astronomical distances involving vortex currents as seen with blazars and blackholes. At the terrestrial level, force producing vortices have been related to the motion of wings (e.g., birds, duck paddles, fish's tail). In this paper, vortex structures are shown to exist in the streamlines aft of a spaceship moving at high velocity in the vacuum. This is accomplished using the density excitation method per a modified Chameleon Cosmology model. This vortex structure is then shown to have similarities to spacetime models as Warp-Drive and wormholes, giving rise to the natural extension of Hawking and Unruh radiation, which provides the propulsive method for space travel where virtual electron-positron pairs, absorbed by the gravitational expansion forward of the spaceship emerge from an annular vortex field aft of the spaceship as real particles, in-like to propellant mass ejection in conventional rocket theory.

  1. An experimental investigation of bending wave instability modes in a generic four-vortex wake

    SciTech Connect

    Babie, Brian M.; Nelson, Robert C.

    2010-07-15

    An experimental study of a planar wake consisting of four vortices that simulate the trailing vortex wakes generated by transport airplanes in either takeoff or landing configurations is presented. The objective of this study was to examine naturally occurring wake instabilities. Specifically, the focus of the study was centered on bending wave instabilities of which the Crow instability represents a particular case. A unique method of generating a four-vortex wake was developed for this study. The four-vortex wake generating device permitted direct variation of the spacing between vortices as well as control over the vortex circulation strength. Two quantitative flow visualization experiments were instrumental in identifying wake configurations that were conducive to the rapid growth of bending wave modes and in the identification of the long-wavelength mode. Detailed experiments were also conducted to examine the flow structure in the near-field or roll-up region using a four sensor, hot-wire probe that could measure all three velocity components in the wake simultaneously. The results of both the flow visualization and hot-wire experiments indicate that the long-wavelength mode and the first short-wavelength mode likely dominate the far-field wake physics and may potentially be utilized in a wake control strategy.

  2. A comparison of airborne wake vortex detection measurements with values predicted from potential theory

    NASA Technical Reports Server (NTRS)

    Stewart, Eric C.

    1991-01-01

    An analysis of flight measurements made near a wake vortex was conducted to explore the feasibility of providing a pilot with useful wake avoidance information. The measurements were made with relatively low cost flow and motion sensors on a light airplane flying near the wake vortex of a turboprop airplane weighing approximately 90000 lbs. Algorithms were developed which removed the response of the airplane to control inputs from the total airplane response and produced parameters which were due solely to the flow field of the vortex. These parameters were compared with values predicted by potential theory. The results indicated that the presence of the vortex could be detected by a combination of parameters derived from the simple sensors. However, the location and strength of the vortex cannot be determined without additional and more accurate sensors.

  3. Effect of wake structure on blade-vortex interaction phenomena: Acoustic prediction and validation

    NASA Technical Reports Server (NTRS)

    Gallman, Judith M.; Tung, Chee; Schultz, Klaus J.; Splettstoesser, Wolf; Buchholz, Heino

    1995-01-01

    During the Higher Harmonic Control Aeroacoustic Rotor Test, extensive measurements of the rotor aerodynamics, the far-field acoustics, the wake geometry, and the blade motion for powered, descent, flight conditions were made. These measurements have been used to validate and improve the prediction of blade-vortex interaction (BVI) noise. The improvements made to the BVI modeling after the evaluation of the test data are discussed. The effects of these improvements on the acoustic-pressure predictions are shown. These improvements include restructuring the wake, modifying the core size, incorporating the measured blade motion into the calculations, and attempting to improve the dynamic blade response. A comparison of four different implementations of the Ffowcs Williams and Hawkings equation is presented. A common set of aerodynamic input has been used for this comparison.

  4. Three-dimensional vortex wake structure of flapping wings in hovering flight

    PubMed Central

    Cheng, Bo; Roll, Jesse; Liu, Yun; Troolin, Daniel R.; Deng, Xinyan

    2014-01-01

    Flapping wings continuously create and send vortices into their wake, while imparting downward momentum into the surrounding fluid. However, experimental studies concerning the details of the three-dimensional vorticity distribution and evolution in the far wake are limited. In this study, the three-dimensional vortex wake structure in both the near and far field of a dynamically scaled flapping wing was investigated experimentally, using volumetric three-component velocimetry. A single wing, with shape and kinematics similar to those of a fruitfly, was examined. The overall result of the wing action is to create an integrated vortex structure consisting of a tip vortex (TV), trailing-edge shear layer (TESL) and leading-edge vortex. The TESL rolls up into a root vortex (RV) as it is shed from the wing, and together with the TV, contracts radially and stretches tangentially in the downstream wake. The downwash is distributed in an arc-shaped region enclosed by the stretched tangential vorticity of the TVs and the RVs. A closed vortex ring structure is not observed in the current study owing to the lack of well-established starting and stopping vortex structures that smoothly connect the TV and RV. An evaluation of the vorticity transport equation shows that both the TV and the RV undergo vortex stretching while convecting downwards: a three-dimensional phenomenon in rotating flows. It also confirms that convection and secondary tilting and stretching effects dominate the evolution of vorticity. PMID:24335561

  5. Three-dimensional vortex wake structure of flapping wings in hovering flight.

    PubMed

    Cheng, Bo; Roll, Jesse; Liu, Yun; Troolin, Daniel R; Deng, Xinyan

    2014-02-01

    Flapping wings continuously create and send vortices into their wake, while imparting downward momentum into the surrounding fluid. However, experimental studies concerning the details of the three-dimensional vorticity distribution and evolution in the far wake are limited. In this study, the three-dimensional vortex wake structure in both the near and far field of a dynamically scaled flapping wing was investigated experimentally, using volumetric three-component velocimetry. A single wing, with shape and kinematics similar to those of a fruitfly, was examined. The overall result of the wing action is to create an integrated vortex structure consisting of a tip vortex (TV), trailing-edge shear layer (TESL) and leading-edge vortex. The TESL rolls up into a root vortex (RV) as it is shed from the wing, and together with the TV, contracts radially and stretches tangentially in the downstream wake. The downwash is distributed in an arc-shaped region enclosed by the stretched tangential vorticity of the TVs and the RVs. A closed vortex ring structure is not observed in the current study owing to the lack of well-established starting and stopping vortex structures that smoothly connect the TV and RV. An evaluation of the vorticity transport equation shows that both the TV and the RV undergo vortex stretching while convecting downwards: a three-dimensional phenomenon in rotating flows. It also confirms that convection and secondary tilting and stretching effects dominate the evolution of vorticity. PMID:24335561

  6. Thrust Production and Wake Structure of an Actuated Lamprey Model

    NASA Astrophysics Data System (ADS)

    Buchholz, James; Smits, Alexander

    2004-11-01

    Thrust generation is studied for a flexible lamprey model which is actuated periodically to produce a streamwise traveling wave. Shape memory alloy actuators are used to achieve this deformation. The flow field is investigated using DPIV and flow visualization for a range of Strouhal numbers based on peak-to-peak amplitude of the trailing edge. The vortex kinematics in the spanwise and streamwise planes are examined, and a three-dimensional unsteady vortex model of the wake will be discussed.

  7. Separation of Lift-Generated Vortex Wakes Into Two Diverging Parts

    NASA Technical Reports Server (NTRS)

    Rossow, Vernon J.; Brown, Anthony P.

    2010-01-01

    As part of an ongoing study of the spreading rate of lift-generated vortex wakes, the present investigation considers possible reasons as to why segments of lift-generated wakes sometimes depart from the main part of the wake to move rapidly in either an upward or downward direction. It is assumed that deficiencies or enhancements of the lift carry over across the fuselage-shrouded wing are the driving mechanism for departures of wake-segments. The computations presented first indicate that upwardly departing wake segments that were observed and photographed could have been produced by a deficiency in lift carryover across the fuselage-shrouded part of the wing. Computations made of idealized vortex wakes indicate that upward departure of a wake segment requires a centerline reduction in the span loading of 70% or more, whether the engines are at idle or robust thrust. Similarly, it was found that downward departure of wake segments is produced when the lift over the center part of the wing is enhanced. However, it was also found that downward departures do not occur without the presence of robust engine-exhaust streams (i.e., engines must NOT be at idle). In those cases, downward departures of a wake segment occurs when the centerline value of the loading is enhanced by any amount between about 10% to 100%. Observations of condensation trails indicate that downward departure of wake segments is rare. Upward departures of wake segments appears to be more common but still rare. A study to determine the part of the aircraft that causes wake departures has not been carried out. However, even though departures of wake segments rarely occur, some aircraft do regularly shed these wake structures. If aircraft safety is to be assured to a high degree of reliability, and a solution for eliminating them is not implemented, existing guidelines for the avoidance of vortex wakes [1,3] may need to be broadened to include possible increases in wake sizes caused by vertical

  8. Unsteady vortex lattice techniques applied to wake formation and performance of the statically thrusting propeller

    NASA Technical Reports Server (NTRS)

    Hall, G. F.

    1975-01-01

    The application is considered of vortex lattice techniques to the problem of describing the aerodynamics and performance of statically thrusting propellers. A numerical lifting surface theory to predict the aerodynamic forces and power is performed. The chordwise and spanwise loading is modelled by bound vortices fixed to a twisted flat plate surface. In order to eliminate any apriori assumptions regarding the wake shape, it is assumed the propeller starts from rest. The wake is generated in time and allowed to deform under its own self-induced velocity field as the motion of the propeller progresses. The bound circulation distribution is then determined with time by applying the flow tangency boundary condition at certain selected control points on the blades. The aerodynamics of the infinite wing and finite wing are also considered. The details of wake formation and roll-up are investigated, particularly the localized induction effect. It is concluded that proper wake roll-up and roll-up rates can be established by considering the details of motion at the instant of start.

  9. Vortex and wake-induced vibrations of a tandem arrangement of two flexible circular cylinders with near wake interference

    NASA Astrophysics Data System (ADS)

    Huera-Huarte, F. J.; Bearman, P. W.

    2011-02-01

    Results showing the dynamic response of a tandem arrangement of two vertical high aspect ratio (length over diameter) and low mass ratio (mass over mass of displaced fluid) flexible cylinders vibrating at low mode number are presented in this paper. Two circular cylinder models were aligned with the flow, so the downstream or trailing cylinder was immersed in the wake of the leading one. Centre-to-centre distances from 2 to 4 diameters were studied. The models were very similar in design, with external diameters of 16 mm and a total length of 1.5 m. Reynolds numbers up to 12 000 were achieved with reduced velocities, based on the fundamental natural frequency of the downstream cylinder in still water, up to 16. The trailing model had a mass ratio of 1.8 with a combined mass-damping parameter of 0.049, whilst the corresponding figures for the leading cylinder were 1.45 and 0.043, respectively. The dynamic response of the trailing model has been analysed by studying cross-flow and in-line amplitudes, dominant frequencies and modal amplitudes. The dynamic response of the leading one is analysed by means of its cross-flow amplitudes and dominant frequencies and it is also related to the motion of the trailing cylinder by studying the synchronisation between their instantaneous cross-flow motions. Planar digital particle image velocimetry (DPIV) was used to visualise the wake. Different response regimes have been identified based on the type of oscillations exhibited by the cylinders: vortex-induced (VIV), wake-induced (WIV) or combinations of both.

  10. The timing of vortex shedding in a cylinder wake imposed by periodic inflow perturbations

    NASA Astrophysics Data System (ADS)

    Konstantinidis, E.; Balabani, S.; Yianneskis, M.

    2005-10-01

    The interaction of vortex shedding from a circular cylinder with an inflow which has low-amplitude periodic velocity oscillations (perturbations) superimposed upon it, was investigated experimentally by means of particle image velocimetry. The experiments were made at three perturbation frequencies across the lock-on range in which the vortex shedding frequency is synchronized with the subharmonic of the imposed frequency. The basic wake pattern in this range is antisymmetric vortex shedding, i.e. the familiar 2S mode. The timing of vortex shedding is defined with respect to the cross-flow oscillation of the wake which is found to play a critical role. Quantitative analysis of the phase-referenced patterns of vorticity distribution in the wake shows that a vortex is actually shed from the cylinder when the cross-flow oscillation of the wake is strongest, marked by a sudden drop in the computed vortex strength. At the middle of the lock-on range, shedding occurs near the minimum inflow velocity in the cycle or, equivalently, during the forward stroke of a cylinder oscillating in-line with the flow. It is argued that the imposed timing of vortex shedding relative to the cylinder motion induces a negative excitation from the fluid, which might explain why the in-line response of a freely vibrating cylinder exhibits two positive excitation regions separated by the lock-on region found in forced oscillations.

  11. Control of wake and vortex shedding behind a porous circular obstacle by exerting an external magnetic field

    NASA Astrophysics Data System (ADS)

    Bovand, M.; Rashidi, S.; Dehghan, M.; Esfahani, J. A.; Valipour, M. S.

    2015-07-01

    In this article the finite volume method (FVM) is carried out to simulate the flow around and through a two-dimensional porous cylinder. An external magnetic field is used to control the wake behind the bluff body and also to suppress the vortex shedding phenomena. The Darcy-Brinkman-Forchheimer model has been used for modeling the flow in the porous medium. Effects of Stuart (N), Reynolds (Re) and Darcy (Da) numbers on the flow behavior have been investigated. The results show that the critical Stuart number for suppress vortex shedding decreases with increasing the Darcy numbers. Also, the Stuart number for disappearance the re-circulating wake increases with increased Reynolds number for both porous and solid cylinders.

  12. Evaluation of Fast-Time Wake Models Using Denver 2006 Field Experiment Data

    NASA Technical Reports Server (NTRS)

    Ahmad, Nash’at N.; Pruis, Matthew J.

    2015-01-01

    The National Aeronautics and Space Administration conducted a series of wake vortex field experiments at Denver in 2003, 2005, and 2006. This paper describes the lidar wake vortex measurements and associated meteorological data collected during the 2006 deployment, and includes results of recent reprocessing of the lidar data using a new wake vortex algorithm and estimates of the atmospheric turbulence using a new algorithm to estimate eddy dissipation rate from the lidar data. The configuration and set-up of the 2006 field experiment allowed out-of-ground effect vortices to be tracked in lateral transport further than any previous campaign and thereby provides an opportunity to study long-lived wake vortices in moderate to low crosswinds. An evaluation of NASA's fast-time wake vortex transport and decay models using the dataset shows similar performance as previous studies using other field data.

  13. Wake Geometry Measurements and Analytical Calculations on a Small-Scale Rotor Model

    NASA Technical Reports Server (NTRS)

    Ghee, Terence A.; Berry, John D.; Zori, Laith A. J.; Elliott, Joe W.

    1996-01-01

    An experimental investigation was conducted in the Langley 14- by 22-Foot Subsonic Tunnel to quantify the rotor wake behind a scale model helicopter rotor in forward level flight at one thrust level. The rotor system in this test consisted of a four-bladed fully articulated hub with blades of rectangular planform and an NACA 0012 airfoil section. A laser light sheet, seeded with propylene glycol smoke, was used to visualize the vortex geometry in the flow in planes parallel and perpendicular to the free-stream flow. Quantitative measurements of wake geometric proper- ties, such as vortex location, vertical skew angle, and vortex particle void radius, were obtained as well as convective velocities for blade tip vortices. Comparisons were made between experimental data and four computational method predictions of experimental tip vortex locations, vortex vertical skew angles, and wake geometries. The results of these comparisons highlight difficulties of accurate wake geometry predictions.

  14. Rotor Wake Vortex Definition: Initial Evaluation of 3-C PIV Results of the Hart-II Study

    NASA Technical Reports Server (NTRS)

    Burley, Casey L.; Brooks, Thomas F.; vanderWall, Berend; Richard, Hughes; Raffel, Markus; Beaumier, Philippe; Delrieux, Yves; Lim, Joon W.; Yu, Yung H.; Tung, Chee

    2002-01-01

    An initial evaluation is made of extensive three-component (3C) particle image velocimetry (PIV) measurements within the wake across a rotor disk plane. The model is a 40 percent scale BO-105 helicopter main rotor in forward flight simulation. This study is part of the HART II test program conducted in the German-Dutch Wind Tunnel (DNW). Included are wake vortex field measurements over the advancing and retreating sides of the rotor operating at a typical descent landing condition important for impulsive blade-vortex interaction (BVI) noise. Also included are advancing side results for rotor angle variations from climb to steep descent. Using detailed PIV vector maps of the vortex fields, methods of extracting key vortex parameters are examined and a new method was developed and evaluated. An objective processing method, involving a center-of-vorticity criterion and a vorticity 'disk' integration, was used to determine vortex core size, strength, core velocity distribution characteristics, and unsteadiness. These parameters are mapped over the rotor disk and offer unique physical insight for these parameters of importance for rotor noise and vibration prediction.

  15. An approximate model of vortex decay in the atmosphere

    NASA Technical Reports Server (NTRS)

    Greene, G. C.

    1985-01-01

    An approximate analysis of atmospheric effects on wake vortex motion and decay is presented. The effects of density stratification, turbulence, and Reynolds number are combined in a single model so that the relative importance of different parameters can be determined. Predicted wake motion is shown to be in good agreement with limited data from both ground facility and flight test measurements taken under low turbulence conditions. Wake decay was found to depend strongly on both density stratification and turbulence. For typical levels of turbulence, wake decay was found to result from the 'Crow instability' except under strongly stratified conditions.

  16. Periodic vortex shedding in the supersonic wake of a planar plate

    NASA Technical Reports Server (NTRS)

    Xing, W. F.; Marenbach, G.

    1985-01-01

    Vortex sheets in the wake have been mainly studied in incompressible flows and in the transonic region. Heinemann et al. (1976) have shown that for the subsonic region the Strouhal number is nearly independent of the Mach number. Motallebi and Norbury (1981) have observed an increase in the Strouhal number in transonic supersonic flow at Mach numbers up to 1.25. The present investigation is concerned with an extension of the studies of vortex shedding to higher supersonic Mach numbers, taking into account questions regarding the possibility of a generation of stable von Karman vortex paths in the considered Mach number range. It is found that the vortex sheet observed in a supersonic wake behind a rough plate is only stable and reproducible in cases involving a certain surface roughness and certain aspects of trailing edge geometry.

  17. Progress Towards the Investigation of Technical Issues Relevant to the Design of an Aircraft Wake Vortex Advisory System (WakeVAS)

    NASA Technical Reports Server (NTRS)

    Rutishauser, David K.

    2003-01-01

    Wake vortex separations applied to aircraft during instrument operations have been shown to potentially introduce inefficiencies in air traffic operations during certain weather conditions conducive to short duration wake hazards between pairs of landing aircraft. NASA Langley Research Center (LaRC) demonstrated an integration of technologies that provided real-time observations and predictions of aircraft wake behavior, from which reduced wake spacing from the current criteria was derived. In order to take this proof of concept to an operational prototype system, NASA has been working in cooperation with the FAA and other government and industry members to design operational concepts for a Wake Vortex Advisory System (WakeVAS). In addition to concept development, open research issues are being addressed and activities to quantify system requirements and specifications are currently underway. This paper describes the technological issues relevant to WakeVAS development and current NASA efforts to address these issues.

  18. Dynamics of the Turbulent Wake of Rigid and Flexible Cylinders Subject to Vortex-Induced Vibrations

    NASA Astrophysics Data System (ADS)

    Evangelinos, Constantinos; Karniadakis, George Em.

    1998-11-01

    We present DNS simulation results for flow past a flexible cylinder subject to vortex-induced vibrations at a Reynolds number of 1000. The structure is modeled using the wave equation (simplified cable) or the beam equation. The structural parameters are chosen to obtain lock-in excitation for the fundamental mode of vibration. The transition to a traveling wave solution from the standing wave initial conditions is studied, along with the phase relationship in time between structural displacement and hydrodynamic force variations. The differences and similarities between a cable and a beam are investigated further by looking at the energy variations of the excited structural modes in time. Time history point statistics for the near wake are examined, and spectra and correlation lengths are compared with each other, with those for a stationary cylinder, and with those of a rigid vibrating cylinder.

  19. Characterizing the wake vortex signature for an active line of sight remote sensor. M.S. Thesis Technical Report No. 19

    NASA Technical Reports Server (NTRS)

    Heil, Robert Milton

    1994-01-01

    A recurring phenomenon, described as a wake vortex, develops as an aircraft approaches the runway to land. As the aircraft moves along the runway, each of the wing tips generates a spiraling and expanding cone of air. During the lifetime of this turbulent event, conditions exist over the runway which can be hazardous to following aircraft, particularly when a small aircraft is following a large aircraft. Left to themselves, these twin vortex patterns will converge toward each other near the center of the runway, harmlessly dissipating through interaction with each other or by contact with the ground. Unfortunately, the time necessary to disperse the vortex is often not predictable, and at busy airports can severely impact terminal area productivity. Rudimentary methods of avoidance are in place. Generally, time delays between landing aircraft are based on what is required to protect a small aircraft. Existing ambient wind conditions can complicate the situation. Reliable detection and tracking of a wake vortex hazard is a major technical problem which can significantly impact runway productivity. Landing minimums could be determined on the basis of the actual hazard rather than imposed on the basis of a worst case scenario. This work focuses on using a windfield description of a wake vortex to generate line-of-sight Doppler velocity truth data appropriate to an arbitrarily located active sensor such as a high resolution radar or lidar. The goal is to isolate a range Doppler signature of the vortex phenomenon that can be used to improve detection. Results are presented based on use of a simplified model of a wake vortex pattern. However, it is important to note that the method of analysis can easily be applied to any vortex model used to generate a windfield snapshot. Results involving several scan strategies are shown for a point sensor with a range resolution of 1 to 4 meters. Vortex signatures presented appear to offer potential for detection and tracking.

  20. Aircraft wake vortex velocity measurements using a scanning CO2 laser Doppler velocimeter

    NASA Technical Reports Server (NTRS)

    Dimarzio, C. A.; Sonnenschein, C. M.; Jeffreys, H. B.

    1975-01-01

    A CO2 laser Doppler velocimeter was employed in the study of pairs of counterrotating vortices trailing aircraft in an airport air space. A laser positioned on an extended runway centerline scans a vertical plane perpendicular to the centerline. Vortex location, measurement of vortex transport, and measurement of the properties of aircraft wake vortex flow fields are achieved via spectral analysis of the data. Highest amplitude in the spectrum, the associated maximum velocity, the highest velocity above the amplitude threshold, and the total number of frequency (velocity) cells above thresholds are studied as parameters in analysis of the vortex-associated flow field. The profile of the radial variation of tangential velocity is studied, and two special problems are examined: location of the vortex center and error introduced by crosswind.

  1. Transient Vortex Structures in the Near Wake of a Wing during Pitch Up/Down Maneuvers

    NASA Astrophysics Data System (ADS)

    Graff, Emilio; Grivel, Morgane; Williams, David

    2012-11-01

    The vorticity distribution in the wake of a thin airfoil reflects the lift and bound circulation history of the wing. During a pitch-up maneuver from 0 degrees to some higher angle of attack (assuming attached flow), a ``starting vortex'' is formed in the wake whose circulation is opposite in strength to the bound circulation in the wing. However, a finite time is required for the starting vortex to fully develop, and if the wing pitches down to a smaller angle of attack before the first starting vortex has reached full strength then an imbalance in the wake circulation occurs. The delay time between the up/down pitch motions and the maximum angle of attack determine which additional vortices must be formed to satisfy Kelvin's theorem. In addition to the irrotational flow vortices that form, vorticity associated with the viscous boundary layers also accumulates into discrete vortices that accompany each ``starting vortex.'' The complicated distributions of vortices and their evolution in the wake are examined with detailed PIV, smoke-visualization, and numerical simulations at Re = 240 to 70,000. The support for David Williams by AFOSR Grant FA9550-09-1-0189 is gratefully acknowledged.

  2. Aircraft Wake Vortex Parametrization Based on 1.5-μm Coherent Doppler Lidar Data

    NASA Astrophysics Data System (ADS)

    Banakh, V. A.; Smalikho, I. N.

    2016-06-01

    A strategy of measurement by a 1.5-μm pulsed coherent Doppler lidar "Stream Line" has been developed, and a method for estimation of aircraft wake vortices from the lidar data has been proposed. The principal possibility of obtaining the information about the vortex situation over an airport airfield with the Stream Line lidar has been demonstrated.

  3. Tomographic particle image velocimetry of desert locust wakes: instantaneous volumes combine to reveal hidden vortex elements and rapid wake deformation

    PubMed Central

    Bomphrey, Richard J.; Henningsson, Per; Michaelis, Dirk; Hollis, David

    2012-01-01

    Aerodynamic structures generated by animals in flight are unstable and complex. Recent progress in quantitative flow visualization has advanced our understanding of animal aerodynamics, but measurements have hitherto been limited to flow velocities at a plane through the wake. We applied an emergent, high-speed, volumetric fluid imaging technique (tomographic particle image velocimetry) to examine segments of the wake of desert locusts, capturing fully three-dimensional instantaneous flow fields. We used those flow fields to characterize the aerodynamic footprint in unprecedented detail and revealed previously unseen wake elements that would have gone undetected by two-dimensional or stereo-imaging technology. Vortex iso-surface topographies show the spatio-temporal signature of aerodynamic force generation manifest in the wake of locusts, and expose the extent to which animal wakes can deform, potentially leading to unreliable calculations of lift and thrust when using conventional diagnostic methods. We discuss implications for experimental design and analysis as volumetric flow imaging becomes more widespread. PMID:22977102

  4. Airloads, wakes, and aeroelasticity

    NASA Technical Reports Server (NTRS)

    Johnson, Wayne

    1990-01-01

    Fundamental considerations regarding the theory of modeling of rotary wing airloads, wakes, and aeroelasticity are presented. The topics covered are: airloads and wakes, including lifting-line theory, wake models and nonuniform inflow, free wake geometry, and blade-vortex interaction; aerodynamic and wake models for aeroelasticity, including two-dimensional unsteady aerodynamics and dynamic inflow; and airloads and structural dynamics, including comprehensive airload prediction programs. Results of calculations and correlations are presented.

  5. Method of radial velocities for the estimation of aircraft wake vortex parameters from data measured by coherent Doppler lidar.

    PubMed

    Smalikho, I N; Banakh, V A; Holzäpfel, F; Rahm, S

    2015-09-21

    The method of radial velocities (RV) is applied to estimate aircraft wake vortex parameters from measurements conducted with pulsed coherent Doppler lidar (PCDL). Operations of the Stream Line lidar and the 2-µm PCDL are simulated numerically to analyze the accuracy of the estimated wake vortex parameters with the RV method. The RV method is also used to estimate wake vortex trajectories and circulation from lidar measurements at Tomsk and Munich airports. The method of velocity envelopes and the RV method are compared employing data gathered with the 2-µm PCDL. The domain of applicability of the RV method is determined. PMID:26406749

  6. Turbulent vortex streets and the entrainment mechanism of the turbulent wake

    NASA Technical Reports Server (NTRS)

    Papailiou, D. D.; Lykoudis, P. S.

    1974-01-01

    The results of an experimental investigation of a turbulent vortex street in the range from 1000 to 20,000 are presented. The vortex street was created by the motion of a circular cylinder in a motionless fluid (mercury). Photographs obtained showed that the turbulent street, created by the vortex shedding behind the cylinder, persisted at longer downstream distances and higher Reynolds numbers than previously reported in the literature. A theory was developed to account for the experimental measurements pertaining to the change of the geometrical characteristics, (the distance between the two rows of vortices and the longitudinal distance between two consecutive vortices on the same row), of the street in the downstream direction. The implications of the structure of the vortex street on the entrainment mechanism of the turbulent wake are discussed.

  7. Analysis of wake vortex flight test data behind a T-33 aircraft

    NASA Technical Reports Server (NTRS)

    Kuhn, G. D.; Jacobsen, R. A.

    1975-01-01

    Measurements of the vortex system behind a T-33 aircraft were obtained by a Learjet equipped with a boom carrying a three-wire, hot-wire anemometry probe and other instrumentation. Analysis of the measurements using a computerized geometric method indicated the vortices had a core radius of approximately 0.11 meter with a maximum velocity of 25 meters per second. The hot-wire anemometer was found to be a practical and sensitive instrument for determining in-flight vortex velocities. No longitudinal instabilities, buoyant effects or vortex breakdowns were evident in the data which included vortex wake cross sections from 0.24 to 5.22 kilometers behind the T-33.

  8. Parallel direct numerical simulation of wake vortex detection using monostatic and bistatic radio acoustic sounding systems

    NASA Astrophysics Data System (ADS)

    Boluriaan Esfahaani, Said

    A parallel two-dimensional code is developed in this thesis to numerically simulate wake vortex detection using a Radio Acoustic Sounding System (RASS). The Maxwell equations for media with non-uniform permittivity and the linearized Euler equations for media with non-uniform mean flow are the main framework for the simulations. The code is written in Fortran 90 with the Message Passing Interface (MPI) for parallel implementation. The main difficulty encountered with a time accurate simulation of a RASS is the number of samples required to resolve the Doppler shift in the scattered electromagnetic signal. Even for a 1D simulation with a typical scatterer size, the CPU time required to run the code is far beyond currently available computer resources. Two solutions that overcome this problem are described. In the first the actual electromagnetic wave propagation speed is replaced with a much lower value. This allows an explicit, time accurate numerical scheme to be used. In the second the governing differential equations are recast in order to remove the carrier frequency and solve only for the frequency shift using an implicit scheme with large time steps. The numerical stability characteristics of the resulting discretized equation with complex coefficients are examined. A number of cases for both the monostatic and bistatic configurations are considered. First, a uniform mean flow is considered and the RASS simulation is performed for two different types of incident acoustic field, namely a short single frequency acoustic pulse and a continuous broadband acoustic source. Both the explicit and implicit schemes are examined and the mean flow velocity is determined from the spectrum of the backscattered electromagnetic signal with very good accuracy. Second, the Taylor and Oseen vortex models are considered and their velocity field along the incident electromagnetic beam is retrieved. The Abel transform is then applied to the velocity profiles determined by both

  9. Mesoscale Simulation Data for Initializing Fast-Time Wake Transport and Decay Models

    NASA Technical Reports Server (NTRS)

    Ahmad, Nashat N.; Proctor, Fred H.; Vanvalkenburg, Randal L.; Pruis, Mathew J.; LimonDuparcmeur, Fanny M.

    2012-01-01

    The fast-time wake transport and decay models require vertical profiles of crosswinds, potential temperature and the eddy dissipation rate as initial conditions. These inputs are normally obtained from various field sensors. In case of data-denied scenarios or operational use, these initial conditions can be provided by mesoscale model simulations. In this study, the vertical profiles of potential temperature from a mesoscale model were used as initial conditions for the fast-time wake models. The mesoscale model simulations were compared against available observations and the wake model predictions were compared with the Lidar measurements from three wake vortex field experiments.

  10. Prediction and control of vortex-dominated and vortex-wake flows

    NASA Technical Reports Server (NTRS)

    Kandil, Osama

    1993-01-01

    This progress report documents the accomplishments achieved in the period from December 1, 1992 until November 30, 1993. These accomplishments include publications, national and international presentations, NASA presentations, and the research group supported under this grant. Topics covered by documents incorporated into this progress report include: active control of asymmetric conical flow using spinning and rotary oscillation; supersonic vortex breakdown over a delta wing in transonic flow; shock-vortex interaction over a 65-degree delta wing in transonic flow; three dimensional supersonic vortex breakdown; numerical simulation and physical aspects of supersonic vortex breakdown; and prediction of asymmetric vortical flows around slender bodies using Navier-Stokes equations.

  11. Estimation of aircraft wake vortex parameters from data measured by a Stream Line lidar

    NASA Astrophysics Data System (ADS)

    Smalikho, I. N.; Banakh, V. A.

    2015-11-01

    A method for estimation of aircraft wake vortex parameters (coordinates of axis and circulation of vortices) from raw data measured by a pulsed coherent Doppler lidar "Stream Line" has been offered. By numerical simulation we found optimal measurement parameters, with which it is possible to obtain information about the wake vortices, despite the low level of echo signal inherent to this lidar. The method was tested in an experiment at the airfield of Tomsk airport. The results of the experimental data processing are consistent with theoretical calculations for the type of aircrafts involved in this experiment.

  12. Analytical model of rotor wake aerodynamics in ground effect

    NASA Technical Reports Server (NTRS)

    Saberi, H. A.

    1983-01-01

    The model and the computer program developed provides the velocity, location, and circulation of the tip vortices of a two-blade helicopter in and out of the ground effect. Comparison of the theoretical results with some experimental measurements for the location of the wake indicate that there is excellent accuracy in the vicinity of the rotor and fair amount of accuracy far from it. Having the location of the wake at all times enables us to compute the history of the velocity and the location of any point in the flow. The main goal of out study, induced velocity at the rotor, can also be calculated in addition to stream lines and streak lines. Since the wake location close to the rotor is known more accurately than at other places, the calculated induced velocity over the disc should be a good estimate of the real induced velocity, with the exception of the blade location, because each blade was replaced only by a vortex line. Because no experimental measurements of the wake close to the ground were available to us, quantitative evaluation of the theoretical wake was not possible. But qualitatively we have been able to show excellent agreement. Comparison of flow visualization with out results has indicated the location of the ground vortex is estimated excellently. Also the flow field in hover is well represented.

  13. N-S Simulations of Crow-Type Instabilities in Vortex Wake

    NASA Technical Reports Server (NTRS)

    Zheng, Z. C.; Baek, K.

    1999-01-01

    Three-dimensional Navier-Stokes simulations of the Crow instability of wake vortices are conducted using large-eddy simulations without background turbulence. Sinusoidal displacement has been specified as the initial perturbation for the vortex system. The results have shown that the minimum Crow instability wavelength is about one vortex spacing shorter than predicted by Crow's linear stability theory. The planar- standing-wave-angle value and the amplitude indifference behavior agree with Crow's analysis. Simulations with periodicity in the axial direction have indicated minor influence of axial flow on the Crow instability.

  14. Computation of rotor aerodynamic loads with a constant vorticity contour free wake model

    NASA Technical Reports Server (NTRS)

    Quackenbush, Todd R.; Wachspress, Daniel A.; Boschitsch, Alexander H.

    1991-01-01

    An analytical method is presented which facilitates the study of isolated rotors with an improved approach to wake simulation. Vortex filaments are simulated along contours of constant sheet strength for the sheet of vorticity resulting from each rotor blade. Curved vortex elements comprise the filaments which can be distorted by the local velocity field. Called the Constant Vorticity Contour wake model, the approach permits the simulation of the blades' wakes corresponding to the full span of the rotor blade. The discretization of the wake of the rotor blade produces spacing and structure that are consistent with the spatial and temporal variations in the loading. A vortex-lattice aerodynamic model of the blade is also included which introduces a finite-element structural model of the blade and consideration of the force and moment trim analysis. Results of the present version of the simulation, called RotorCRAFT, are found to correlate well with H-34 flight-test data.

  15. Flow visualization of the wake of a transport aircraft model with lateral-control oscillations

    NASA Technical Reports Server (NTRS)

    Jordan, F. L., Jr.

    1983-01-01

    An exploratory flow visualization study conducted in the Langley Vortex Research Facility to investigate the effectiveness of lateral control surface oscillations as a potential method for wake vortex attenuation on a 0.03 scale model of a wide body jet transport aircraft is described. Effects of both asymmetric surface oscillation (control surfaces move as with normal lateral control inputs) and symmetric surface oscillation (control surfaces move in phase) are presented. The asymmetric case simulated a flight maneuver which was previously investigated on the transport aircraft during NASA/FAA flight tests and which resulted in substantial wake vortex attenuation. Effects on the model wake vortex systems were observed by propelling the model through a two dimensional smoke screen perpendicular to the model flight path. Results are presented as photographic time histories of the wake characteristics recorded with high speed still cameras. Effects of oscillation on the wake roll up are described in some detail, and the amount of vortex attenuation observed is discussed in comparative terms. Findings were consistent with flight test results in that only a small amount of rotation was observed in the wake for the asymmetric case. A possible aerodynamic mechanism contributing to this attenuation is suggested.

  16. Aircraft Wake Vortex Spacing System (AVOSS) Performance Update and Validation Study

    NASA Technical Reports Server (NTRS)

    Rutishauser, David K.; OConnor, Cornelius J.

    2001-01-01

    An analysis has been performed on data generated from the two most recent field deployments of the Aircraft Wake VOrtex Spacing System (AVOSS). The AVOSS provides reduced aircraft spacing criteria for wake vortex avoidance as compared to the FAA spacing applied under Instrument Flight Rules (IFR). Several field deployments culminating in a system demonstration at Dallas Fort Worth (DFW) International Airport in the summer of 2000 were successful in showing a sound operational concept and the system's potential to provide a significant benefit to airport operations. For DFW, a predicted average throughput increase of 6% was observed. This increase implies 6 or 7 more aircraft on the ground in a one-hour period for DFW operations. Several studies of performance correlations to system configuration options, design options, and system inputs are also reported. The studies focus on the validation performance of the system.

  17. A multi-element vortex lattice method for calculating the geometry and effects of a helicopter rotor wake in forward flight

    NASA Technical Reports Server (NTRS)

    Berry, John D.

    1988-01-01

    A method is described for the analysis of the unsteady, incompressible potential flow associated with a helicopter rotor and it's wake in forward flight. This method is particularly useful in low advance ratio flight due to the major contribution, in the near field, of the deformed wake. The rotor geometry is prescribed and the unsteady wake geometry is computed from the local flow perturbation velocities. The wake is modeled as a full vortex lattice. The rotor geometry is arbitrary and several rotor blades can be represented. The unsteady airloads on the rotor blades are computed in the presence of the deformed rotor wake by a time-stepping technique. Solution for the load distribution on the blade surfaces is found by prescribing boundary conditions in a reference system which rotates with the blade tips. Transformation tensors are used to describe the contribution of the wake in the inertial system to the rotor in the rotating reference system. The effects of blade cyclic pitch variation are computed using a rotation tensor. The deformation of the wake is computed in the inertial frame. The wake is started impulsively from rest, allowing a natural convection of the wake with time.

  18. Wake Sensor Evaluation Program and Results of JFK-1 Wake Vortex Sensor Intercomparisons

    NASA Technical Reports Server (NTRS)

    Barker, Ben C., Jr.; Burnham, David C.; Rudis, Robert P.

    1997-01-01

    The overall approach should be to: (1) Seek simplest, sufficiently robust, integrated ground based sensor systems (wakes and weather) for AVOSS; (2) Expand all sensor performance cross-comparisons and data mergings in on-going field deployments; and (3) Achieve maximal cost effectiveness through hardware/info sharing. An effective team is in place to accomplish the above tasks.

  19. Numerical Modeling Studies of Wake Vortices: Real Case Simulations

    NASA Technical Reports Server (NTRS)

    Shen, Shao-Hua; Ding, Feng; Han, Jongil; Lin, Yuh-Lang; Arya, S. Pal; Proctor, Fred H.

    1999-01-01

    A three-dimensional large-eddy simulation model, TASS, is used to simulate the behavior of aircraft wake vortices in a real atmosphere. The purpose for this study is to validate the use of TASS for simulating the decay and transport of wake vortices. Three simulations are performed and the results are compared with the observed data from the 1994-1995 Memphis field experiments. The selected cases have an atmospheric environment of weak turbulence and stable stratification. The model simulations are initialized with appropriate meteorological conditions and a post roll-up vortex system. The behavior of wake vortices as they descend within the atmospheric boundary layer and interact with the ground is discussed.

  20. Experiments on the vortex wake of a swimming knifefish

    NASA Astrophysics Data System (ADS)

    Taylor, Zachary J.; Liberzon, Alexander; Gurka, Roi; Holzman, Roi; Reesbeck, Thomas; Diez, F. Javier

    2013-08-01

    The knifefish species propels itself by generating a reverse Kármán street using an anal fin, and the propulsion of this species is known to be highly efficient (Blake in Can J Zool 61:1432-1441, 1983). Previous studies have suggested that there is an optimal swimming range for fish based on the amplitude and frequency of the reverse Kármán street. In the current study, experiments have been performed to measure the ratio between the amplitude and wavelength of vortices in the wake of a knifefish. It is suggested that the wave efficiency can be estimated by optimizing the thrust created by the reverse Kármán street for a given spacing ratio, and present observations have an average value of 0.89. The relationship established between spacing ratio and wave efficiency, in addition to the measured parameters, will be invaluable for bio-inspired designs based on the knifefish.

  1. Exploration of the vortex wake behind of wind turbine rotor

    NASA Astrophysics Data System (ADS)

    Massouh, F.; Dobrev, I.

    2007-07-01

    The present paper describes a wind tunnel study of flow downstream a small horizontal axis wind turbine (HAWT). The experimental investigations were carried out with the use of particle image velocimetry (PIV). To obtain the flow field in the rotating frame of reference, the phase-locked technique was applied. Explorations were carried out in azimuth planes with different angles. The 3D velocity field was reconstituted by processing the images resulting from the explored azimuth planes. In addition to PIV investigations, hot-wire measurements were also carried out immediately behind the wind turbine rotor at different radial and axial distances. The obtained results are very useful to analyze wind turbine wake and to constitute a reference for CFD computation.

  2. An Evaluation of the Measurement Requirements for an In-Situ Wake Vortex Detection System

    NASA Technical Reports Server (NTRS)

    Fuhrmann, Henri D.; Stewart, Eric C.

    1996-01-01

    Results of a numerical simulation are presented to determine the feasibility of estimating the location and strength of a wake vortex from imperfect in-situ measurements. These estimates could be used to provide information to a pilot on how to avoid a hazardous wake vortex encounter. An iterative algorithm based on the method of secants was used to solve the four simultaneous equations describing the two-dimensional flow field around a pair of parallel counter-rotating vortices of equal and constant strength. The flow field information used by the algorithm could be derived from measurements from flow angle sensors mounted on the wing-tip of the detecting aircraft and an inertial navigation system. The study determined the propagated errors in the estimated location and strength of the vortex which resulted from random errors added to theoretically perfect measurements. The results are summarized in a series of charts and a table which make it possible to estimate these propagated errors for many practical situations. The situations include several generator-detector airplane combinations, different distances between the vortex and the detector airplane, as well as different levels of total measurement error.

  3. Prediction of the vortex wake for noncircular missiles in supersonic flow

    NASA Technical Reports Server (NTRS)

    Mendenhall, M. R.; Perkins, S. C., Jr.

    1984-01-01

    Engineering prediction methods with the capability to calculate induced effects of lee-side separation vorticity associated with circular and noncircular missiles at high angles of attack in supersonic flow are compared. Methods of interest include a discrete vortex cloud technique, concentrated vortex models, and solutions of Euler's equations with specified separation. Comparison of measured and predicted surface pressure distributions and flow field surveys are presented for bodies with circular and elliptic cross sections. Two flow models for computing lee-side vortex-induced effects on control fins in the vicinity of the vortex field are examined, and suggestions regarding the appropriate flow model for specific situations are included.

  4. Visualization on fish's wake

    NASA Astrophysics Data System (ADS)

    Li, Xuemin; Lu, Xiyun; Yin, Xiezhen

    2002-05-01

    In this paper an experiment on wake of Goldfish swimming unrestricted was conducted in a water tunnel. Method of color liquid was used to visualize the wake. Results show that there is reverse Karman vortex street in symmetrical plane of the wake and the Strouhal frequency of the fish is in the range 0.25-0.35. A 3D vortex ring chain model was presented.

  5. Wake transition and vortex street interaction in flows generated by traveling localized Lorentz forces in a shallow electrolyte layer

    NASA Astrophysics Data System (ADS)

    Roman, Joel; Cuevas, Sergio

    2014-11-01

    We present an experimental and numerical study of the vortex street produced by a traveling localized Lorentz force, namely a magnetic obstacle, in a thin layer of electrolyte. The Lorentz force is generated by the interaction a localized magnetic field created by a small permanent magnet which travels with a uniform velocity underneath a rectangular container and a uniform D.C. current applied transversally to the motion of the magnet. We find that by increasing the Reynolds number (based on the velocity of the magnet) the wake generated by the magnetic obstacle presents a transition from the Bénard-von Kármán (BvK) wake to the reversed BvK wake. In addition, we analyze the flow past a pair magnetic obstacles side-by-side in a thin layer of electrolyte by varying the separation between the magnets and the intensity of the applied current. The attention is focused in the interference of the wakes created by the magnetic obstacles. Numerical simulations based on a quasi-two dimensional numerical model present a satisfactory agreement with experimental results. Work supported by CONACYT, Mexico under Project 131399. J. Roman acknowledges a grant from CONACYT.

  6. Coupled wake boundary layer model of windfarms

    NASA Astrophysics Data System (ADS)

    Stevens, Richard; Gayme, Dennice; Meneveau, Charles

    2014-11-01

    We present a coupled wake boundary layer (CWBL) model that describes the distribution of the power output in a windfarm. The model couples the traditional, industry-standard wake expansion/superposition approach with a top-down model for the overall windfarm boundary layer structure. Wake models capture the effect of turbine positioning, while the top-down approach represents the interaction between the windturbine wakes and the atmospheric boundary layer. Each portion of the CWBL model requires specification of a parameter that is unknown a-priori. The wake model requires the wake expansion rate, whereas the top-down model requires the effective spanwise turbine spacing within which the model's momentum balance is relevant. The wake expansion rate is obtained by matching the mean velocity at the turbine from both approaches, while the effective spanwise turbine spacing is determined from the wake model. Coupling of the constitutive components of the CWBL model is achieved by iterating these parameters until convergence is reached. We show that the CWBL model predictions compare more favorably with large eddy simulation results than those made with either the wake or top-down model in isolation and that the model can be applied successfully to the Horns Rev and Nysted windfarms. The `Fellowships for Young Energy Scientists' (YES!) of the Foundation for Fundamental Research on Matter supported by NWO, and NSF Grant #1243482.

  7. Initialization and Simulation of Three-Dimensional Aircraft Wake Vortices

    NASA Technical Reports Server (NTRS)

    Ash, Robert L.; Zheng, Z. C.

    1997-01-01

    This paper studies the effects of axial velocity profiles on vortex decay, in order to properly initialize and simulate three-dimensional wake vortex flow. Analytical relationships are obtained based on a single vortex model and computational simulations are performed for a rather practical vortex wake, which show that the single vortex analytical relations can still be applicable at certain streamwise sections of three-dimensional wake vortices.

  8. Wake modes of a cylinder undergoing free streamwise vortex-induced vibrations

    NASA Astrophysics Data System (ADS)

    Cagney, N.; Balabani, S.

    2013-04-01

    Simultaneous measurements of the response of a circular cylinder experiencing vortex-induced vibrations (VIVs) in the streamwise direction and the resulting wake field were performed for a range of reduced velocities using time-resolved Particle-Image Velocimetry in the Reynolds number range 450-3700. The dominant vortex shedding mode was identified using phase-averaged vorticity fields. The cylinder response amplitude was characterised by two response branches, separated by a low amplitude region at resonance, as has been previously reported in the literature. During the first response branch the wake exhibited not only the symmetric S-I mode, but also the alternate A-II mode at slightly higher reduced velocities. For both modes, the vortices were observed to be shed at the cylinder response frequency, but rearranged downstream into a more stable structure in which the velocity fluctuations were no longer synchronised to the cylinder motion. A special case of the A-II mode, referred to as the SA mode, was found to dominate in the second response branch and the low amplitude region, while the far wake and the cylinder motion were synchronised (lock-in). A change in the timing of the vortex shedding with respect to the cylinder motion was observed between the low amplitude region and the second response branch. This is likely to correspond to a change in the fluid forcing and levels of excitation, and may explain the variation in the cylinder amplitude observed in this region. Lock-in and the second response branch were found to coincide with a contraction of the wake and an increase in strength of the shed vortices. This work reveals the inherent differences between the extensively studied case of transverse-only VIV and the streamwise-only case, which is crucial if the wealth of information available on transverse VIV is to be extended to the more practical two degree-of-freedom case.

  9. Runway Wake Vortex, Crosswind, and Visibility Detection with a Scintillometer at Schiphol Airport

    NASA Astrophysics Data System (ADS)

    van Dinther, D.; Hartogensis, O. K.; Holtslag, A. A. M.

    2015-12-01

    We evaluate the performance and investigate the capability of a scintillometer to detect wake vortices, crosswind and visibility near an airport runway. An experiment is carried out at Schiphol airport (Amsterdam, The Netherlands), where an optical scintillometer is positioned alongside a runway. An algorithm is developed to detect wake vortices, and also the strength of the wake vortex, from the variance in the scintillation signal. The algorithm shows promising results in detecting wake vortices and their strengths during the night. During the day, the scintillometer signal is dominated by environmental turbulence and wake vortices are no longer detectable. The crosswind measured by the scintillometer is compared with wind-speed and wind-direction data at the airport. Our results show that, after applying an outlier filter, the scintillometer is able to measure the crosswind over the short time period of 3 s required for aviation applications. The outlier filter does not compromise the capability of the scintillometer to obtain the maximum 3 s crosswind over a 10-min time frame correctly. Finally, a transmission method is used to obtain the visibility from the scintillometer signal, which is then compared with that obtained from a visibility sensor. The scintillometer is able to identify periods of low visibility correctly, although it shows a high amount of scatter around the exact visibility value.

  10. Flight Test Analysis of the Forces and Moments Imparted on a B737-100 Airplane During Wake Vortex Encounters

    NASA Technical Reports Server (NTRS)

    Roberts, Chistopher L.

    2001-01-01

    Aircraft travel has become a major form of transportation. Several of our major airports are operating near their capacity limit, increasing congestion and delays for travelers. As a result, the National Aeronautics and Space Administration (NASA) has been working in conjunction with the Federal Aviation Administration (FAA), airline operators, and the airline industry to increase airport capacity without sacrificing public safety. One solution to the problem is to increase the number of airports and build new. runways; yet, this solution is becoming increasingly difficult due to limited space. A better solution is to increase the production per runway. This solution increases the possibility that one aircraft will encounter the trailing wake of another aircraft. Hazardous wake vortex encounters occur when an aircraft encounters the wake produced by a heavier aircraft. This heavy-load aircraft produces high-intensity wake turbulence that redistributes the aerodynamic loads of trailing smaller aircraft. This situation is particularly hazardous for smaller aircraft during takeoffs and landings. In order to gain a better understanding of the wake-vortex/aircraft encounter phenomena, NASA Langley Research Center conducted a series of flight tests from 1995 through 1997. These tests were designed to gather data for the development a wake encounter and wake-measurement data set with the accompanying atmospheric state information. This data set is being compiled into a database that can be used by wake vortex researchers to compare with experimental and computational results. The purpose of this research is to derive and implement a procedure for calculating the wake-vortex/aircraft interaction portion of that database by using the data recorded during those flight tests. There were three objectives to this research. Initially, the wake-induced forces and moments from each flight were analyzed based on varying flap deflection angles. The flap setting alternated between 15

  11. Vortex Wake Turbulence: Flight Tests Conducted During 1970

    NASA Technical Reports Server (NTRS)

    1971-01-01

    A flight test program designed to obtain data on the characteristics of wing-tip vortices generated by large jet aircraft was initiated on 12 February 1970. The objective was to update the interim air traffic separation standards issued on 21 January 1970 restricting the airspace behind the B-747 and C-5A aircraft 60 deg either side and 2,000 feet below to a distance of 10 miles. The program involved flight tests at three different locations, which were conducted simultaneously. (1) At the Edwards Air Force Base test range, a NASA CV-990 and F-104 probed the vortices of a C-5A. This supplemented previous flight tests in U-3A and F-104 behind a B-52 and C-5A. (2) At Seattle, the Boeing Company probed the vortices of a B-747 and a B-707-300 with a B-737 and F-86. In addition, approach, landing, takeoff, and crossing runway tests were conducted with a B-737 trailing a B-747. Immediately following the Edwards tests, the NASA CV-990 proceeded to Seattle and engaged in probing flights behind the same B-747 and B-707-300. (3) At Idaho Falls, Idaho, FAA personnel, utilizing the Atomic Energy Commission and Environmental Science Services Administration facilities and a 200 ft, instrumented tower, conducted 114 flights past the tower. The aircraft were positioned to permit their vortices to descend into the air flow sensors and smoke generated from various levels on the tower. This permitted obtaining measurements and photography of the vortex core diameters, tangential velocities and related characteristics. Immediately following this test phase, analysis of the interrelated data was completed by the project managers representing NASA, Boeing and FAA and a Compilation of Work Papers was issued on 30 April 1970. These data were the basis of a revised General Notice issued on 26 February 1970 which, in essence, modified the restricted airspace to five miles behind heavy jets in the 300,000 lb. gross takeoff weight category.

  12. A Sensitivity Study of the Aircraft Vortex Spacing System (AVOSS) Wake Predictor Algorithm to the Resolution of Input Meteorological Profiles

    NASA Technical Reports Server (NTRS)

    Rutishauser, David K.; Butler, Patrick; Riggins, Jamie

    2004-01-01

    The AVOSS project demonstrated the feasibility of applying aircraft wake vortex sensing and prediction technologies to safe aircraft spacing for single runway arrivals. On average, AVOSS provided spacing recommendations that were less than the current FAA prescribed spacing rules, resulting in a potential airport efficiency gain. Subsequent efforts have included quantifying the operational specifications for future Wake Vortex Advisory Systems (WakeVAS). In support of these efforts, each of the candidate subsystems for a WakeVAS must be specified. The specifications represent a consensus between the high-level requirements and the capabilities of the candidate technologies. This report documents the beginnings of an effort to quantify the capabilities of the AVOSS Prediction Algorithm (APA). Specifically, the APA horizontal position and circulation strength output sensitivity to the resolution of its wind and turbulence inputs is examined. The results of this analysis have implications for the requirements of the meteorological sensing and prediction systems comprising a WakeVAS implementation.

  13. Vortex pairing in the wake of an oscillating bubble rising in a thin-gap cell

    NASA Astrophysics Data System (ADS)

    Ern, Patricia; Filella, Audrey; Roig, Véronique

    2015-11-01

    We investigate experimentally the oscillatory motion and wake of a bubble rising in a counter flow in a thin gap cell (3 mm) by shadowgraphy and PIV. The equivalent diameter d of the bubble in the plane of the cell is used to define the Archimedes number Ar =√{/gd3 } ν (ν is the kinematic viscosity and g the gravitational acceleration). The counter flow is characterized by the Reynolds number Recf based on the mean liquid velocity and the gap thickness. For 500 <= Ar <= 5500 and 0 <=Recf <= 200 , the mean vertical velocity of the bubble relative to the counter flow, Vbr, corresponds to the mean rising velocity in liquid at rest; and the frequency and the amplitude of the oscillatory motion superpose for all Recf when normalized with Vbr and the timescale d /Vbr . For a given size of the bubble (d 9 . 5 mm and Ar 2800) corresponding to a Reynolds number based on Vbr and d of about 1900, we then investigate in detail the wake associated to the bubble in several counter flows. As Recf increases, the number of vortices released increases. Furthermore, the wake of the bubble undergoes vortex pairing for 0 <=Recf <= 110), whereas no vortex pairing is observed for Recf >= 140 .

  14. The Transition from Thick to Thin Plate Wake Physics: Whither Vortex Shedding?

    NASA Technical Reports Server (NTRS)

    Rai, Man Mohan

    2016-01-01

    The near and very near wake of a flat plate with a circular trailing edge is investigated with data from direct numerical simulations. Computations were performed for six different combinations of the Reynolds numbers based on plate thickness (D) and boundary layer momentum thickness upstream of the trailing edge (theta). Unlike the case of the cylinder, these Reynolds numbers are independent parameters for the flat plate. The separating boundary layers are turbulent in all the cases investigated. One objective of the study is to understand the changes in the wake vortex shedding process as the plate thickness is reduced (increasing theta/D). The value of D varies by a factor of 16 and that of theta by approximately 5 in the computations. Vortex shedding is vigorous in the low theta/D cases with a substantial decrease in shedding intensity in the large theta/D cases. Other shedding characteristics are also significantly altered with increasing theta/D. A visualization of the shedding process in the different cases is provided and discussed. The basic shedding mechanism is explored in depth. The effect of changing theta/D on the time-averaged, near-wake velocity statistics is also discussed. A functional relationship between the shedding frequency and the Reynolds numbers mentioned above is obtained.

  15. Vortex- and wake-induced vibrations of a tandem arrangement of two flexible circular cylinders with far wake interference

    NASA Astrophysics Data System (ADS)

    Huera-Huarte, F. J.; Gharib, M.

    2011-07-01

    The dynamic response of two flexible cylinders in tandem arrangement partially immersed in a uniform flow is analysed. The centre-to-centre separations, larger than 4 and up to 8 diameters, were chosen to fall in the regime in which two separate wakes exist behind each one of the models. For the cases presented here, it has been confirmed that the main excitation mechanism is wake-induced vibration (WIV). The rear cylinder shows large amplitudes of response, at reduced velocities over the expected ones at lock-in when a cylinder is undergoing VIV being isolated. This type of response has been also observed by other researchers in experiments with flexibly mounted cylinders in the wake of stationary ones, we also provide data here, for cases with the front cylinder being stationary.

  16. An all-fiber, modular, compact wind lidar for wind sensing and wake vortex applications

    NASA Astrophysics Data System (ADS)

    Prasad, Narasimha S.; Sibell, Russel; Vetorino, Steven; Higgins, Richard; Tracy, Allen

    2015-05-01

    This paper discusses an innovative, compact and eyesafe coherent lidar system developed for wind and wake vortex sensing applications. With an innovative all-fiber and modular transceiver architecture, the wind lidar system has reduced size, weight and power requirements, and provides enhanced performance along with operational elegance. This all-fiber architecture is developed around fiber seed laser coupled to uniquely configured fiber amplifier modules. The innovative features of this lidar system, besides its all fiber architecture, include pulsewidth agility and user programmable 3D hemispherical scanner unit. Operating at a wavelength of 1.5457 microns and with a PRF of up to 20 KHz, the lidar transmitter system is designed as a Class 1 system with dimensions of 30"(W) x 46"(L) x 60"(H). With an operational range exceeding 10 km, the wind lidar is configured to measure wind velocities of greater than 120 m/s with an accuracy of +/- 0.2 m/s and allow range resolution of less than 15 m. The dynamical configuration capability of transmitted pulsewidths from 50 ns to 400 ns allows high resolution wake vortex measurements. The scanner uses innovative liquid metal slip ring and is built using 3D printer technology with light weight nylon. As such, it provides continuous 360 degree azimuth and 180 degree elevation scan angles with an incremental motion of 0.001 degree. The lidar system is air cooled and requires 110 V for its operation. This compact and modular lidar system is anticipated to provide mobility, reliability, and ease of field deployment for wind and wake vortex measurements. Currently, this wind lidar is undergoing validation tests under various atmospheric conditions. Preliminary results of these field measurements of wind characteristics that were recently carried out in Colorado are discussed.

  17. An All-Fiber, Modular, Compact Wind Lidar for Wind Sensing and Wake Vortex Applications

    NASA Technical Reports Server (NTRS)

    Prasad, Narasimha S.; Sibell, Russ; Vetorino, Steve; Higgins, Richard; Tracy, Allen

    2015-01-01

    This paper discusses an innovative, compact and eyesafe coherent lidar system developed for wind and wake vortex sensing applications. With an innovative all-fiber and modular transceiver architecture, the wind lidar system has reduced size, weight and power requirements, and provides enhanced performance along with operational elegance. This all-fiber architecture is developed around fiber seed laser coupled to uniquely configured fiber amplifier modules. The innovative features of this lidar system, besides its all fiber architecture, include pulsewidth agility and user programmable 3D hemispherical scanner unit. Operating at a wavelength of 1.5457 microns and with a PRF of up to 20 KHz, the lidar transmitter system is designed as a Class 1 system with dimensions of 30"(W) x 46"(L) x 60"(H). With an operational range exceeding 10 km, the wind lidar is configured to measure wind velocities of greater than 120 m/s with an accuracy of +/- 0.2 m/s and allow range resolution of less than 15 m. The dynamical configuration capability of transmitted pulsewidths from 50 ns to 400 ns allows high resolution wake vortex measurements. The scanner uses innovative liquid metal slip ring and is built using 3D printer technology with light weight nylon. As such, it provides continuous 360 degree azimuth and 180 degree elevation scan angles with an incremental motion of 0.001 degree. The lidar system is air cooled and requires 110 V for its operation. This compact and modular lidar system is anticipated to provide mobility, reliability, and ease of field deployment for wind and wake vortex measurements. Currently, this wind lidar is undergoing validation tests under various atmospheric conditions. Preliminary results of these field measurements of wind characteristics that were recently carried out in Colorado are discussed.

  18. Flutter clearance flight tests of an OV-10A airplane modified for wake vortex flight experiments

    NASA Technical Reports Server (NTRS)

    Doggett, Robert V., Jr.; Rivera, Jose A., Jr.; Stewart, Eric C.

    1995-01-01

    The envelope expansion, flight flutter tests of a modified OV-10A aircraft are described. For the wake vortex research program, the airplane was modified to incorporate three forward-extending instrumentation booms, one extending forward from each wing tip and one from the right side of the fuselage. The booms were instrumented with sensors to measure the velocity and direction of local air flow. The flutter test results show that the modified OV-10A aircraft is free from flutter at speeds up to 330 KEAS at 5000 feet altitude.

  19. Numerical Studies of Three-dimensional Breakdown in Trailing Vortex Wakes

    NASA Technical Reports Server (NTRS)

    Evans, P. F.; Hackett, J. E.

    1976-01-01

    Finite element, three dimensional relaxation methods are used to calculate the development of vortex wakes behind aircraft for a considerable downstream distance. The inclusion of a self-induction term in the solution, dependent upon local curvature and vortex core radius, permits calculation of finite lifetimes for systems for which infinite life would be predicted two dimensionally. The associated computer program is described together with single-pair, twin-pair, and multiple-pair studies carried out using it. It is found, in single-pair studies, that there is a lower limit to the wavelengths at which the Crow-type of instability can occur. Below this limit, self-induction effects cause the plane of the disturbance waves to rotate counter to the vortex direction. Self induction in two dimensionally generated twin spiral waves causes an increase in axial length which becomes more marked with decreasing initial wavelength. The time taken for vortex convergence toward the center plane is correspondingly increased. The limited parametric twin-pair study performed suggests that time-to-converge increases with increasing flap span. Limited studies of Boeing 747 configurations show correct qualitative response to removal of the outer flap and to gear deployment, as compared with wind tunnel and flight test experience.

  20. Secondary vortex street in the wake of two tandem circular cylinders at low Reynolds number

    NASA Astrophysics Data System (ADS)

    Wang, Si-Ying; Tian, Fang-Bao; Jia, Lai-Bing; Lu, Xi-Yun; Yin, Xie-Zhen

    2010-03-01

    The experiments on two tandem circular cylinders were conducted in a horizontal soap film tunnel for the Reynolds number Re=60 , 80, and 100 and the nondimensional center-to-center spacing Γ ranging in 1˜12 . The flow patterns were recorded by a high-speed camera and the vortex shedding frequency was obtained by a spatiotemporal evolution method. The secondary vortex formation (SVF) mode characterized by the formation of a secondary vortex street in the wake of the downstream cylinder was found at large Γ . Moreover, some typical modes predicted by previous investigations, including the single bluff-body, shear layer reattachment, and synchronization of vortex shedding modes, were also revisited in our experiments. Further, numerical simulations were carried out using a space-time finite-element method and the results confirmed the existence of the SVF mode. The mechanism of SVF mode was analyzed in terms of the numerical results. The dependence of the Strouhal number Sr on Γ was given and the flow characteristics relevant to the critical spacing values and the hysteretic mode transitions were investigated.

  1. Information Requirements for Supervisory Air Traffic Controllers in Support of a Wake Vortex Departure System

    NASA Technical Reports Server (NTRS)

    Lohr, Gary W.; Williams, Daniel M.; Trujillo, Anna C.

    2008-01-01

    Closely Space Parallel Runway (CSPR) configurations are capacity limited for departures due to the requirement to apply wake vortex separation standards from traffic departing on the adjacent parallel runway. To mitigate the effects of this constraint, a concept focusing on wind dependent departure operations has been developed, known as the Wake Turbulence Mitigation for Departures (WTMD). This concept takes advantage of the fact that crosswinds of sufficient velocity blow wakes generated by aircraft departing from the downwind runway away from the upwind runway. Consequently, under certain conditions, wake separations on the upwind runway would not be required based on wakes generated by aircraft on the downwind runway, as is currently the case. It follows that information requirements, and sources for this information, would need to be determined for airport traffic control tower (ATCT) supervisory personnel who would be charged with decisions regarding use of the procedure. To determine the information requirements, data were collected from ATCT supervisors and controller-in-charge qualified individuals at Lambert-St. Louis International Airport (STL) and George Bush Houston Intercontinental Airport (IAH). STL and IAH were chosen as data collection sites based on the implementation of a WTMD prototype system, operating in shadow mode, at these locations. The 17 total subjects (STL: 5, IAH: 12) represented a broad-base of air traffic experience. Results indicated that the following information was required to support the conduct of WTMD operations: current and forecast weather information, current and forecast traffic demand and traffic flow restrictions, and WTMD System status information and alerting. Subjects further indicated that the requisite information is currently available in the tower cab with the exception of the WTMD status and alerting. Subjects were given a demonstration of a display supporting the prototype systems and unanimously stated that the

  2. Experimental and theoretical analysis of vortex breakdown in the wake of the 25∘ Ahmed body

    NASA Astrophysics Data System (ADS)

    Jermann, Cyril; Meliga, Philippe; Pujals, Gregory; Gallaire, Francois; Serre, Eric

    2014-11-01

    We study experimentally and theoretically the wake of the 25circ; Ahmed body, considered a suitable test-case to reproduce the two counter-rotating longitudinal vortices widely encountered in automotive aerodynamics. The three-dimensional experimental mean flow is reconstructed at high Reynolds number (Re = 2 . 8 ×106) from a series of cross-flow time-averaged planes acquired with a moving automated Stereo-PIV system. We observe a sharp decay of the axial velocity and vorticity in the near-wake, 0 . 5 times the projected length of the slanted surface downstream the square back, where the streamwise vortices is subjected to a strong adverse pressure gradient and the turbulent kinetic energy exhibits a peak in the vortex core. A stability analysis of the experimental velocity shows that the flow undergoes vortex breakdown roughly at the same position, through a transition from supercritical (x < 0 . 5) to subcritical (x > 0 . 5) conditions and the accumulation of upstream propagating axisymmetric waves.

  3. Coulombic contribution and fat center vortex model

    SciTech Connect

    Rafibakhsh, Shahnoosh; Deldar, Sedigheh

    2007-02-27

    The fat (thick) center vortex model is one of the phenomenological models which is fairly successful to interpret the linear potential between static sources. However, the Coulombic part of the potential has not been investigated by the model yet. In an attempt to get the Coulombic contribution and to remove the concavity of the potentials, we are studying different vortex profiles and vortex sizes.

  4. Experimental investigation of the wake behind a model of wind turbine in a water flume

    NASA Astrophysics Data System (ADS)

    Okulov, V. L.; Naumov, I. N.; Kabardin, I.; Mikkelsen, R.; Sørensen, J. N.

    2014-12-01

    The flow behind the model of wind turbine rotor is investigated experimentally in a water flume using Particle Image Velocimetry. The study carried out involves rotors of three bladed wind turbine designed using Glauert's optimization. The transitional regime, generally characterized as in between the regime governed by stable organized vortical structures and the turbulent wake, develops from disturbances of the tip and root vorticies through vortex paring and further complex behaviour towards the fully turbulent wake. Our PIV measurements pay special attention to the onset of the instabilities. The near wake characteristics (development of expansion, tip vortex position, deficit velocity and rotation in the wake) have been measured for different tip speed ratio to compare with main assumptions and conclusions of various rotor theories.

  5. An experimental investigation of vortex stability, tip shapes, compressibility, and noise for hovering model rotors

    NASA Technical Reports Server (NTRS)

    Tangler, J. L.; Wohlfeld, R. M.; Miley, S. J.

    1973-01-01

    Schlieren methods of flow visualization and hot-wire anemometry for velocity measurements were used to investigate the wakes generated by hovering model propellers and rotors. The research program was directed toward investigating (1) the stability of the tip vortex, (2) the effects produced by various tip shapes on performance and tip vortex characteristics, and (3) the shock formation and noise characteristics associated with various tip shapes. A free-wake analysis was also conducted for comparison with the vortex stability experimental results. Schlieren photographs showing wake asymmetry, interaction, and instability are presented along with a discussion of the effects produced by the number of blades, collective pitch, and tip speed. Two hot-wire anemometer techniques, used to measure the maximum circumferential velocity in the tip vortex, are discussed.

  6. Vortex wake, downwash distribution, aerodynamic performance and wingbeat kinematics in slow-flying pied flycatchers

    PubMed Central

    Muijres, Florian T.; Bowlin, Melissa S.; Johansson, L. Christoffer; Hedenström, Anders

    2012-01-01

    Many small passerines regularly fly slowly when catching prey, flying in cluttered environments or landing on a perch or nest. While flying slowly, passerines generate most of the flight forces during the downstroke, and have a ‘feathered upstroke’ during which they make their wing inactive by retracting it close to the body and by spreading the primary wing feathers. How this flight mode relates aerodynamically to the cruising flight and so-called ‘normal hovering’ as used in hummingbirds is not yet known. Here, we present time-resolved fluid dynamics data in combination with wingbeat kinematics data for three pied flycatchers flying across a range of speeds from near hovering to their calculated minimum power speed. Flycatchers are adapted to low speed flight, which they habitually use when catching insects on the wing. From the wake dynamics data, we constructed average wingbeat wakes and determined the time-resolved flight forces, the time-resolved downwash distributions and the resulting lift-to-drag ratios, span efficiencies and flap efficiencies. During the downstroke, slow-flying flycatchers generate a single-vortex loop wake, which is much more similar to that generated by birds at cruising flight speeds than it is to the double loop vortex wake in hovering hummingbirds. This wake structure results in a relatively high downwash behind the body, which can be explained by the relatively active tail in flycatchers. As a result of this, slow-flying flycatchers have a span efficiency which is similar to that of the birds in cruising flight and which can be assumed to be higher than in hovering hummingbirds. During the upstroke, the wings of slowly flying flycatchers generated no significant forces, but the body–tail configuration added 23 per cent to weight support. This is strikingly similar to the 25 per cent weight support generated by the wing upstroke in hovering hummingbirds. Thus, for slow-flying passerines, the upstroke cannot be regarded as

  7. Atmospheric Boundary Layer Sensors for Application in a Wake Vortex Advisory System

    NASA Technical Reports Server (NTRS)

    Zak, J. Allen; Rutishauser, David (Technical Monitor)

    2003-01-01

    Remote sensing of the atmospheric boundary layer has advanced in recent years with the development of commercial off-the-shelf (COTS) radar, sodar, and lidar wind profiling technology. Radio acoustic sounding systems for vertical temperature profiles of high temporal scales (when compared to routine balloon soundings- (radiosondes) have also become increasingly available as COTS capabilities. Aircraft observations during landing and departures are another source of available boundary layer data. This report provides an updated assessment of available sensors, their performance specifications and rough order of magnitude costs for a potential future aircraft Wake Vortex Avoidance System (WakeVAS). Future capabilities are also discussed. Vertical profiles of wind, temperature, and turbulence are anticipated to be needed at airports in any dynamic wake avoidance system. Temporal and spatial resolution are dependent on the selection of approach and departure corridors to be protected. Recommendations are made for potential configurations of near-term sensor technologies and for testing some of the sensor systems in order to validate performance in field environments with adequate groundtruth.

  8. Recent developments in rotor wake modeling for helicopter noise prediction

    NASA Technical Reports Server (NTRS)

    Poling, D.; Dadone, L.; Althoff, S.

    1991-01-01

    A preliminary test/theory correlation evaluation is conducted for wake measurement test results obtained by LDV for a B360 helicopter rotor, at conditions critical to the understanding of wake-rollup and blade-vortex interaction phenomena. The LDV data were complemented by acoustic, blade pressure, rotor performance, and blade/control load measurements.

  9. Overview of the preparation and use of an OV-10 aircraft for wake vortex hazards flight experiments

    NASA Technical Reports Server (NTRS)

    Stuever, Robert A.; Stewart, Eric C.; Rivers, Robert A.

    1995-01-01

    An overview is presented of the development, use, and current flight-test status of a highly instrumented North American Rockwell OV-10A Bronco as a wake-vortex-hazards research aircraft. A description of the operational requirements and measurements criteria, the resulting instrumentation systems and aircraft modifications, system-calibration and research flights completed to date, and current flight status are included. These experiments are being conducted by the National Aeronautics and Space Administration as part of an effort to provide the technology to safely improve the capacity of the nation's air transportation system and specifically to provide key data in understanding and predicting wake vortex decay, transport characteristics, and the dynamics of encountering wake turbulence. The OV-10A performs several roles including meteorological measurements platform, wake-decay quantifier, and trajectory-quantifier for wake encounters. Extensive research instrumentation systems include multiple airdata sensors, video cameras with cockpit displays, aircraft state and control-position measurements, inertial aircraft-position measurements, meteorological measurements, and an on-board personal computer for real-time processing and cockpit display of research data. To date, several of the preliminary system check flights and two meteorological-measurements deployments have been completed. Several wake encounter and wake-decay-measurements flights are planned for the fall of 1995.

  10. Flight Test Analysis of the Forces and Moments Imparted on a B737-100 Aircraft During Wake Vortex Encounters

    NASA Technical Reports Server (NTRS)

    Roberts, Christopher L.; Smith, Sonya T.; Vicroy, Dan D.

    2000-01-01

    Several of our major airports are operating at or near their capacity limit, increasing congestion and delays for travelers. As a result, the National Aeronautics and Space Administration (NASA) has been working in conjunction with the Federal Aviation Administration (FAA), airline operators, and the airline industry to increase airport capacity and safety. As more and more airplanes are placed into the terminal area the probability of encountering wake turbulence is increased. The NASA Langley Research Center conducted a series of flight tests from 1995 through 1997 to develop a wake encounter and wake-measurement data set with the accompanying atmospheric state information. The purpose of this research is to use the data from those flights to compute the wake-induced forced and moments exerted on the aircraft The calculated forces and moments will then be compiled into a database that can be used by wake vortex researchers to compare with experimental and computational results.

  11. Anomalous vortex shedding and wake profiles in quasi-two-dimensional flows

    NASA Astrophysics Data System (ADS)

    Fontana, Paul W.; Dams, Dominic A.

    2014-11-01

    Vortex shedding by circular cylinders in a vertical soap film channel exhibits anomalously low shedding frequencies compared with observations in conventional systems. Furthermore, the Strouhal number (St = fD /U∞ , where f is the shedding frequency, D the cylinder diameter, and U∞ the upstream flow speed) is not uniquely determined by the Reynolds number (Re = DU∞ / ν , where ν is the kinematic viscosity). We have previously argued that Ekman friction is a likely cause [Bull. Amer. Phys. Soc. 57(17), R10.7]. Other possibilities include gravity, which in this system acts as a forcing mechanism not typically present during vortex shedding measurements, surface tension effects, or variable-viscosity effects due to variations in film thickness. Theory to predict the shedding frequency is lacking and so it is unclear if or how each of these mechanisms should affect it, but understanding the anomaly may elucidate the shedding process. We present two-dimensional profiles of velocity, viscosity, and surface friction measured in the wake of the cylinder under several sets of flow parameters and discuss their implications for the various candidates. The results do not support variable viscosity as a cause.

  12. TURBULENT DIFFUSION BEHIND VEHICLES: EXPERI-MENTALLY DETERMINED INFLUENCE OF VORTEX PAIR IN VEHICLE WAKE

    EPA Science Inventory

    The wake of a moving vehicle was simulated using a wind tunnel with a moving floor. he vehicle models, both scale and block-shaped, were held in a fixed position while the floor moved at the upstream air speed. his simulates an automobile traveling on a straight highway in still ...

  13. Measurements of fish's wake by PIV

    NASA Astrophysics Data System (ADS)

    Li, Xuemin; Wu, Yanfeng; Lu, Xiyun; Yin, Xiezhen

    2003-04-01

    In this paper an experiment on measurements of the wake of Goldfish carassius auratus swimming unrestricted was conducted in a water tunnel. Color liquid was used to visualize the wake of the fish and PIV was used to measure velocity field of the wake. Results show that there is reverse Karman vortex street in symmetrical plane of the fish's wake and the Strouhal frequency of the fish is about 0.35 udner the different experimental conditions. The distribution of velocity and vorticity in the wake of Goldfish was measured by PIV and formation of reverse Karman vortex street in the wake was studied in a model experiment.

  14. Simulations of the flow past a cylinder using an unsteady double wake model

    NASA Astrophysics Data System (ADS)

    Ramos-García, N.; Sarlak, H.; Andersen, S. J.; Sørensen, J. N.

    2016-06-01

    In the present work, the in-house UnSteady Double Wake Model (USDWM) is used to simulate flows past a cylinder at subcritical, supercritical, and transcritical Reynolds numbers. The flow model is a two-dimensional panel method which uses the unsteady double wake technique to model flow separation and its dynamics. In the present work the separation location is obtained from experimental data and fixed in time. The highly unsteady flow field behind the cylinder is analyzed in detail, comparing the vortex shedding charactericts under the different flow conditions.

  15. Turbulent diffusion behind vehicles: Experimentally determined influence of vortex pair in vehicle wake

    SciTech Connect

    Thompson, R.S.; Eskridge, R.E.

    1987-01-01

    The wake of a moving vehicle was stimulated using a wind tunnel with a moving floor. The vehicle models, both scale and block-shaped, were held in a fixed position while the floor moved at the upstream air speed. This simulates an automobile traveling on a straight highway in still ambient air. Vertical and lateral profiles of mean and fluctuating velocities and mean tracer concentration were obtained. Profiles were taken at distances of 15-60 model heights downstream. Two exhaust source positions were used: at the center of the rear of the vehicle and on the side just behind the rear wheel. It was found that the scale vehicles induce a pair of vortices in the wake that modify the velocity and concentration patterns in a minor way from that of the block car.

  16. On vortex evolution in the wake of axisymmetric and non-axisymmetric low-aspect-ratio accelerating plates

    NASA Astrophysics Data System (ADS)

    Fernando, John N.; Rival, David E.

    2016-01-01

    Impulsively started, low-aspect-ratio elliptical and rectangular flat plates were investigated to determine the role of geometric asymmetries on vortex evolution. Dye visualizations, force measurements, and particle image velocimetry were used throughout to characterize the variation between shapes. For all the shapes studied, aspect ratio was observed to have the largest influence on force production and vortex evolution. Non-uniform curvature and edge discontinuities characteristic of ellipses (with aspect ratios other than one) and rectangles, respectively, play a secondary role. Furthermore, it was shown that stably attached vortex rings form behind the circular and square flat plates, which reduce the instantaneous drag force of each plate until the vortex rings break down. In contrast, all flat plates with aspect ratios other than one are subjected to fast-modulating elliptical vortex rings in the wake. These vortex rings increase the drag force of each plate until pinch-off occurs. Finally, pinch-off was identified with the streamwise pressure-gradient field and compared with formation numbers calculated using the circulation-based methodology, yielding good agreement for all plates with aspect ratios greater than one.

  17. Flight test investigation of the vortex wake characteristics behind a Boeing 727 during two-segment and normal ILS approaches (A joint NASA/FAA report)

    NASA Technical Reports Server (NTRS)

    Barber, M. R.; Kurkowski, R. L.; Garodz, L. J.; Robinson, G. H.; Smith, H. J.; Jacobsen, R. A.; Stinnett, G. W., Jr.; Mcmurtry, T. C.; Tymczyszyn, J. J.; Devereaux, R. L.

    1975-01-01

    Flight tests were performed to evaluate the vortex wake characteristics of a Boeing 727 aircraft during conventional and two-segment instrument landing approaches. Smoke generators were used for vortex marking. The vortex was intentionally intercepted by a Lear Jet and a Piper Comanche aircraft. The vortex location during landing approach was measured using a system of phototheodolites. The tests showed that at a given separation distance there are no readily apparent differences in the upsets resulting from deliberate vortex encounters during the two types of approaches. The effect of the aircraft configuration on the extent and severity of the vortices is discussed.

  18. Computation of high resolution unsteady airloads using a constant vorticity contour free wake model

    NASA Technical Reports Server (NTRS)

    Quackenbush, T. R.; Lam, C.-M. G.; Bliss, D. B.

    1992-01-01

    Recent work in the study of helicopter aerodynamic loading for acoustics applications has involved research on the development of an exceptionally efficient simulation of the velocity field induced by the rotor's vortex wake. This paper summarizes the work to date on the development of this analysis, which builds on the refined constant vorticity contour (CVC) free wake model recently developed for application to the study of vibratory loading. The particular focus of this paper is on demonstrations of a reconstruction approach that efficiently computes both the flow fields and airloads induced by CVC wakes on lifting rotor blades. Results of recent calculations on both main rotor and tail rotors are presented. These calculations show that by employing flow field reconstruction it is possible to apply the CVC wake analysis with temporal and spatial resolution suitable for acoustics applications while reducing the computation time required by one to two orders of magnitude relative to the direct calculations used in traditional methods.

  19. Vortex dynamics and associated fluid forcing in the near wake of a light and heavy tethered sphere in uniform flow

    NASA Astrophysics Data System (ADS)

    Krakovich, A.; Eshbal, L.; van Hout, R.

    2013-11-01

    Time-resolved particle image velocimetry measurements of vortex-induced vibrations of a negatively ("heavy") and positively ("light") buoyant tethered sphere in uniform flow, and its wake characteristics were performed in a closed-loop water channel. Experiments for both spheres were performed at similar bulk velocities, ranging between 0.048 < U < 0.32 m/s, corresponding to reduced velocities, 2.2 < U * < 13.5. Initially stationary, with increasing U, the amplitude response displayed periodic oscillations beyond the Hopf bifurcation as a result of "lock-in" between vortex shedding and the natural structural frequency. However, while the heavy sphere's amplitude decreased beyond U * = 7.0, the light sphere's amplitude continuously increased. In the periodic oscillation region, flow field characteristics in the wakes of both spheres (at comparable U * ) were similar, characterized by alternately shed hairpin vortices having a horizontal symmetry plane. Primary vortex trajectories in the frame of reference of the sphere collapsed for different U * (but not for different m * ) when scaled by f 2,s/ U, where f 2,s is the sphere's transverse oscillation frequency. This allows determination of vortex positions based on sphere dynamics and bulk flow conditions only. Associated vortex convection velocities as a function of downstream position from the sphere also nearly collapsed when normalized by U. In addition, fluid forcing and energy transfer from fluid to sphere were estimated based on an analogy between aircraft trailing vortices and hairpin vortices. Maximum forcing occurred at vortex pinch-off. For the highest comparable U * , despite different amplitudes, total transferred energy during one oscillation period was similar for both spheres. Changes in sphere dynamics must therefore be related to differences in inertia.

  20. Calculation of asymmetric vortex separation on cones and tangent ogives based on a discrete vortex model

    NASA Technical Reports Server (NTRS)

    Chin, Suei; Lan, C. Edward; Gainer, Thomas G.

    1989-01-01

    The boundary value problem for vortex separation at zero sideslip on cones and tangent ogives is set up by means of a discrete vortex model. The nonlinear algebraic equations for the boundary value problem admit multiple, physically feasible solutions, including the symmetric and asymmetric vortex solutions. Multiple solutions are proposed as an alternative explanation of the existence of asymmetric vortex separation at zero sideslip.

  1. PIV and LDA measurements of the wake behind a wind turbine model

    NASA Astrophysics Data System (ADS)

    Naumov, I. V.; Mikkelsen, R. F.; Okulov, V. L.; Sørensen, J. N.

    2014-06-01

    In the present work we review the results of a series of measurements of the flow behind a model scale of a horizontal axis wind turbine rotor carried out at the water flume at Technical University of Denmark (DTU). The rotor is three-bladed and designed using Glauert theory for tip speed ratio λ =5 with a constant design lift coefficient along the span, CLdesign= 0.8. The measurements include dye visualization, Particle Image Velocimetry and Laser Doppler Anemometry. The wake instability has been studied in the range λ =3 - 9 at different cross-sections from the very near wake up to 10 rotor diameters downstream from the rotor. The initial flume flow was subject to a very low turbulence level with a uniform velocity profile, limiting the influence of external disturbances on the development of the inherent vortex instability. Using PIV measurements and visualizations, special attention was paid to detect and categorize different types of wake instabilities and the development of the flow in the near and the far wake. In parallel to PIV, LDA measurements provided data for various rotor regimes, revealing the existence of three main regular frequencies governing the development of different processes and instabilities in the rotor wake. In the far wake a constant frequency corresponding to the Strouhal number was found for the long-scale instabilities. This Strouhal number is in good agreement with the well-known constant that usually characterizes the oscillation in wakes behind bluff bodies. From associated visualizations and reconstructions of the flow field, it was found that the dynamics of the far wake is associated with the precession (rotation) of a helical vortex core. The data indicate that Strouhal number of this precession is independent of the rotor angular speed.

  2. Simulating Virtual Terminal Area Weather Data Bases for Use in the Wake Vortex Avoidance System (Wake VAS) Prediction Algorithm

    NASA Technical Reports Server (NTRS)

    Kaplan, Michael L.; Lin, Yuh-Lang

    2004-01-01

    During the research project, sounding datasets were generated for the region surrounding 9 major airports, including Dallas, TX, Boston, MA, New York, NY, Chicago, IL, St. Louis, MO, Atlanta, GA, Miami, FL, San Francico, CA, and Los Angeles, CA. The numerical simulation of winter and summer environments during which no instrument flight rule impact was occurring at these 9 terminals was performed using the most contemporary version of the Terminal Area PBL Prediction System (TAPPS) model nested from 36 km to 6 km to 1 km horizontal resolution and very detailed vertical resolution in the planetary boundary layer. The soundings from the 1 km model were archived at 30 minute time intervals for a 24 hour period and the vertical dependent variables as well as derived quantities, i.e., 3-dimensional wind components, temperatures, pressures, mixing ratios, turbulence kinetic energy and eddy dissipation rates were then interpolated to 5 m vertical resolution up to 1000 m elevation above ground level. After partial validation against field experiment datasets for Dallas as well as larger scale and much coarser resolution observations at the other 8 airports, these sounding datasets were sent to NASA for use in the Virtual Air Space and Modeling program. The application of these datasets being to determine representative airport weather environments to diagnose the response of simulated wake vortices to realistic atmospheric environments. These virtual datasets are based on large scale observed atmospheric initial conditions that are dynamically interpolated in space and time. The 1 km nested-grid simulated datasets providing a very coarse and highly smoothed representation of airport environment meteorological conditions. Details concerning the airport surface forcing are virtually absent from these simulated datasets although the observed background atmospheric processes have been compared to the simulated fields and the fields were found to accurately replicate the flows

  3. Comparison of the lifting-line free vortex wake method and the blade-element-momentum theory regarding the simulated loads of multi-MW wind turbines

    NASA Astrophysics Data System (ADS)

    Hauptmann, S.; Bülk, M.; Schön, L.; Erbslöh, S.; Boorsma, K.; Grasso, F.; Kühn, M.; Cheng, P. W.

    2014-12-01

    Design load simulations for wind turbines are traditionally based on the blade- element-momentum theory (BEM). The BEM approach is derived from a simplified representation of the rotor aerodynamics and several semi-empirical correction models. A more sophisticated approach to account for the complex flow phenomena on wind turbine rotors can be found in the lifting-line free vortex wake method. This approach is based on a more physics based representation, especially for global flow effects. This theory relies on empirical correction models only for the local flow effects, which are associated with the boundary layer of the rotor blades. In this paper the lifting-line free vortex wake method is compared to a state- of-the-art BEM formulation with regard to aerodynamic and aeroelastic load simulations of the 5MW UpWind reference wind turbine. Different aerodynamic load situations as well as standardised design load cases that are sensitive to the aeroelastic modelling are evaluated in detail. This benchmark makes use of the AeroModule developed by ECN, which has been coupled to the multibody simulation code SIMPACK.

  4. Laboratory measurements of vortex- and wake-induced vibrations of a tandem arrangement of two flexible risers

    NASA Astrophysics Data System (ADS)

    Liu, Huai-zeng; Wang, Fei; Jiang, Guo-sheng; Guo, Hai-yan; Li, Xiao-min

    2016-03-01

    The dynamic response of two flexible model risers in tandem arrangement immersed in a stepped current was analyzed. The risers, with an external diameter of 20 mm and a total length of 6200 mm, had an aspect ratio of 310. They were hinged to the support structure at the center-to-center distances away 3-12 times the external diameter. The top 1200 mm was exposed to a uniform current at a speed which was up to 0.9 m/s (the Reynolds number was 18000) and the rest in still water. The dynamic responses, which were obtained through the Fiber Bragg Grating strain gauges mounted on the surface, were analyzed by studying the cross-flow amplitudes and modal weights. The cross-flow vibration were observed up to the third mode, and the modal transformation from the second mode to the third mode was clearly observed. The experiment confirmed that the typical vortex-induced vibration (VIV) had occurred on the up-stream riser. But for the down-stream riser, the main excitation mechanism was wake-induced vibration (WIV). The modal transformation of WIV was more complex than that of VIV, which might be helpful for other researchers to study the interference effect.

  5. On Use of Global Positioning Technology for Solution of Wake Vortex Problem

    NASA Technical Reports Server (NTRS)

    Rossow, Vernon J.; Olson, Lawerence E. (Technical Monitor)

    1997-01-01

    Improved precision of the flight paths used by aircraft to approach and depart airports is becoming available when the Global Positioning System (GPS) is implemented at airports. An overview will be given of published information on how GPS precision guidance at airports can be used to avoid encounters with the lift-generated vortices shed by preceding aircraft during landing. It is pointed out that GPS provides two needed services to bring about improved avoidance capability. Firstly, GPS pseudolites are being built and installed at airports so that, when coupled with autopilot systems currently available on subsonic transport aircraft, the aircraft can make precision approaches for zero visibility landings. The same equipment can also be used for precision approaches for wake-vortex avoidance. Secondly, regular monitoring of atmospheric motions along the approach corridor can be obtained by use of GPS equipment on board aircraft that are in the flight corridors. That is, wind velocity is determined by use of GPS equipment to measure the ground speed of the aircraft and then combined with onboard instrumentation to measure the airspeed of the aircraft. The difference between the two measurements yields the wind velocity. When the measured wind velocities are transmitted to an airport ground station they are used to monitor whether air motions adverse for safety in the flight corridor are present. If any parts of the corridor are unsafe, the spacing of the aircraft, or the location of the flight corridor being used, is modified. It is estimated that the spacings between any combination of aircraft can then be safely reduced to a uniform 3 n. mi. Information to be presented is contained in an article published in the AIAA Journal of Aircraft, May-June 1996.

  6. Vortex-Body Interactions: A Critical Assessment. Coupled Gap-Wake Instabilities/Turbulence: A Source of Noise

    NASA Technical Reports Server (NTRS)

    Rockwell, Donald

    1999-01-01

    This program has involved, first of all, a critical state-of-the-art assessment of vortex-body interactions. Then, efforts were focused on experimental investigation on coupled-wake instabilities and turbulence occurring in a two-cylinder system. An extensive review was undertaken on the effect of incident vortices on various types of bodies. These incident vortices have a length scale of the same order of magnitude as the scale of the body. The body can take on various forms, including, for example, a circular cylinder, a blade or a wing. The classes of vortex-body interaction that were critically assessed include: (1) Periodic distortion of the incident (primary) vortex and shedding of secondary vorticity from the surface of the body. (2) Modulated vortex distortion and shedding at a leading-edge or surface due to incidence of a complex system of vortices. (3) Vortex distortion and shedding in presence of body oscillation. (4) Three-dimensional vortex interaction and shedding. For all of these classes of vortex-body interaction, quantitative topologies of the vorticity distributions and streamline patterns were found to be central to a unified description of mechanisms of vortex distortion and shedding. In most cases, it was possible to define relationships between vortex interactions and unsteady loading at the body surface. This phase of the program was an experimental investigation of a two-cylinder system, which simulated a central aspect of a four-wheel bogie on a large-scale commercial aircraft. The overall aim of this experimental research program was to determine the crucial elements of the unsteadiness in the gap and near-wake regions as a function of time using cinema-based techniques. During the research program, various image evaluation techniques were employed. They involved assessment of instantaneous velocity fields, streamline topology and patterns of vorticity. Experiments were performed in a large-scale water channel using a high

  7. The structure of the wake generated by a submarine model in yaw

    NASA Astrophysics Data System (ADS)

    Ashok, A.; Van Buren, T.; Smits, A. J.

    2015-06-01

    The turbulent wake of a submarine model in yaw was investigated using stereoscopic particle image velocimetry at The model (DARPA SUBOFF idealized submarine geometry) is mounted in a low-speed wind tunnel using a support that mimics the sail, and it is yawed so that the body moves in the plane normal to the support. The measurements reveal the formation of a pair of streamwise vortices that are asymmetric in strength. The weaker vortex quickly diffuses, and in the absence of further diffusion, the stronger vortex maintains its strength even at the furthest downstream location. It is suggested that the flow fields obtained here using a semi-infinite sail as a support will be similar to those obtained using a finite length sail since its tip vortex would not interact significantly with the body vortices present in the wake, at least for a considerable distance downstream of the stern Hence, a submarine in yaw is expected to generate wakes which are inherently more persistent than one in pitch, and the strong asymmetries in yaw are expected to produce a net rolling moment on the body.

  8. A Scanning laser-velocimeter technique for measuring two-dimensional wake-vortex velocity distributions. [Langley Vortex Research Facility

    NASA Technical Reports Server (NTRS)

    Gartrell, L. R.; Rhodes, D. B.

    1980-01-01

    A rapid scanning two dimensional laser velocimeter (LV) has been used to measure simultaneously the vortex vertical and axial velocity distributions in the Langley Vortex Research Facility. This system utilized a two dimensional Bragg cell for removing flow direction ambiguity by translating the optical frequency for each velocity component, which was separated by band-pass filters. A rotational scan mechanism provided an incremental rapid scan to compensate for the large displacement of the vortex with time. The data were processed with a digital counter and an on-line minicomputer. Vaporized kerosene (0.5 micron to 5 micron particle sizes) was used for flow visualization and LV scattering centers. The overall measured mean-velocity uncertainity is less than 2 percent. These measurements were obtained from ensemble averaging of individual realizations.

  9. Near wakes of advanced turbopropellers

    NASA Technical Reports Server (NTRS)

    Hanson, D. B.; Patrick, W. P.

    1989-01-01

    The flow in the wake of a model single rotation Prop-Fan rotor operating in a wind tunnel was traversed with a hot-wire anemometer system designed to determine the 3 periodic velocity components. Special data acquisition and data reduction methods were required to deal with the high data frequency, narrow wakes, and large fluctuating air angles in the tip vortex region. The model tip helical Mach number was 1.17, simulating the cruise condition. Although the flow field is complex, flow features such as viscous velocity defects, vortex sheets, tip vortices, and propagating acoustic pulses are clearly identified with the aid of a simple analytical wake theory.

  10. Application of a panel method to wake-vortex/wing interaction and comparison with experimental data

    NASA Technical Reports Server (NTRS)

    Smith, Brian E.; Ross, James C.

    1987-01-01

    The ability of the Vortex Separation AEROdynamics (VSAERO) program to calculate aerodynamic loads on wings due to interaction with free vortices was studied. The loads were calculated for various positions of a downstream following wing relative to an upstream vortex-generating wing. Calculated vortex-induced span loads, rolling-moment coefficients, and lift coefficients on the following wing were compared with experimental results of McMillan et al. and El-Ramly et al. Comparisons of calculated and experimental vortex tangential velocities were also made.

  11. Vortex-induced vibrations of two cylinders in tandem arrangement in the proximity–wake interference region

    PubMed Central

    BORAZJANI, IMAN; SOTIROPOULOS, FOTIS

    2009-01-01

    We investigate numerically vortex-induced vibrations (VIV) of two identical two-dimensional elastically mounted cylinders in tandem in the proximity–wake interference regime at Reynolds number Re = 200 for systems having both one (transverse vibrations) and two (transverse and in-line) degrees of freedom (1-DOF and 2-DOF, respectively). For the 1-DOF system the computed results are in good qualitative agreement with available experiments at higher Reynolds numbers. Similar to these experiments our simulations reveal: (1) larger amplitudes of motion and a wider lock-in region for the tandem arrangement when compared with an isolated cylinder; (2) that at low reduced velocities the vibration amplitude of the front cylinder exceeds that of the rear cylinder; and (3) that above a threshold reduced velocity, large-amplitude VIV are excited for the rear cylinder with amplitudes significantly larger than those of the front cylinder. By analysing the simulated flow patterns we identify the VIV excitation mechanisms that lead to such complex responses and elucidate the near-wake vorticity dynamics and vortex-shedding modes excited in each case. We show that at low reduced velocities vortex shedding provides the initial excitation mechanism, which gives rise to a vertical separation between the two cylinders. When this vertical separation exceeds one cylinder diameter, however, a significant portion of the incoming flow is able to pass through the gap between the two cylinders and the gap-flow mechanism starts to dominate the VIV dynamics. The gap flow is able to periodically force either the top or the bottom shear layer of the front cylinder into the gap region, setting off a series of very complex vortex-to-vortex and vortex-to-cylinder interactions, which induces pressure gradients that result in a large oscillatory force in phase with the vortex shedding and lead to the experimentally observed larger vibration amplitudes. When the vortex shedding is the dominant

  12. Studies of aircraft wake chemistry and dispersion

    NASA Technical Reports Server (NTRS)

    Poppoff, I. G.; Farlow, N. H.; Anderson, L. B.

    1974-01-01

    Use of aerospace technology to study aircraft wakes is reviewed. It is shown how aerospace vehicles can be used to provide data for increased understanding of the atmosphere and of aircraft exhaust trails where knowledge is inadequate to evaluate fully the potential impact of the engine emissions. Models of aircraft near-field exhaust wakes are characterized by jet, vortex, and dispersion regimes. Wake growth in the jet regime is self-determined and rapid, whereas further spreading is inhibited in the vortex regime because of circulating vortex motion. Wake diffusion in the dispersion regime is initially influenced by aircraft induced turbulence but is dominated later by small-scale atmospheric turbulence. Computed fluid mechanical results show the importance of effects such as wake buoyancy, wind shear, turbulence, and traffic corridor exhaust buildup on dispersion of the wake. In the jet regime the exhaust characteristics and thermochemistry serve to illustrate initial chemical changes involving potential pollutant species.

  13. An experimental study of the unsteady vortex structures in the wake of a root-fixed flapping wing

    NASA Astrophysics Data System (ADS)

    Hu, Hui; Clemons, Lucas; Igarashi, Hirofumi

    2011-08-01

    An experimental study was conducted to characterize the evolution of the unsteady vortex structures in the wake of a root-fixed flapping wing with the wing size, stroke amplitude, and flapping frequency within the range of insect characteristics for the development of novel insect-sized nano-air-vehicles (NAVs). The experiments were conducted in a low-speed wing tunnel with a miniaturized piezoelectric wing (i.e., chord length, C = 12.7 mm) flapping at a frequency of 60 Hz (i.e., f = 60 Hz). The non-dimensional parameters of the flapping wing are chord Reynolds number of Re = 1,200, reduced frequency of k = 3.5, and non-dimensional flapping amplitude at wingtip h = A/C = 1.35. The corresponding Strouhal number (Str) is 0.33 , which is well within the optimal range of 0.2 < Str < 0.4 used by flying insects and birds and swimming fishes for locomotion. A digital particle image velocimetry (PIV) system was used to achieve phased-locked and time-averaged flow field measurements to quantify the transient behavior of the wake vortices in relation to the positions of the flapping wing during the upstroke and down stroke flapping cycles. The characteristics of the wake vortex structures in the chordwise cross planes at different wingspan locations were compared quantitatively to elucidate underlying physics for a better understanding of the unsteady aerodynamics of flapping flight and to explore/optimize design paradigms for the development of novel insect-sized, flapping-wing-based NAVs.

  14. Two dimensional thick center vortex model

    NASA Astrophysics Data System (ADS)

    Rafibakhsh, Shahnoosh; Ahmadi, Alireza

    2016-01-01

    The potential between static color source is calculated in the SU (3) gauge group by introducing a two dimensional vortex flux. To generalize the model, the length of the Wilson loop is equal to R oriented along the x axis, and the vortex flux is considered as a function of x and y. The comparison between the generalized model and the original one shows that the intermediate linear regime is increased significantly and better agreement with Casimir scaling is achieved. Furthermore, the model is applied to calculate the potential between baryons.

  15. Vertical Axis Wind Turbine flows using a Vortex Particle-Mesh method: from near to very far wakes

    NASA Astrophysics Data System (ADS)

    Backaert, Stephane; Chatelain, Philippe; Winckelmans, Gregoire; Kern, Stefan; Maeder, Thierry; von Terzi, Dominic; van Rees, Wim; Koumoutsakos, Petros

    2012-11-01

    A Vortex Particle-Mesh (VPM) method with immersed lifting lines has been developed and validated. The vorticity-velocity formulation of the NS equations is treated in a hybrid way: particles handle advection while the mesh is used to evaluate the differential operators and for the fast Poisson solvers (here a Fourier-based solver which simultaneously allows for unbounded directions and inlet/outlet boundaries). Both discretizations communicate through high order interpolation. The immersed lifting lines handle the creation of vorticity from the blade elements and its early development. LES of Vertical Axis Wind Turbine (VAWT) flows are performed, with a relatively fine resolution (128 and 160 grid points per blade) and for computational domains extending up to 6 D and 14 D downstream of the rotor. The wake complex development is captured in details, from the blades to the near wake coherent vortices, to the transitional ones, to the fully developed turbulent far wake. Mean flow statistics in planes (horizontal, vertical and cross) are also presented. A case with a realistic turbulent wind inflow is also considered. The physics are more complex than for HAWT flows. Computational resources provided by a PRACE award.

  16. Implementation and validation of a wake model for low-speed forward flight

    NASA Technical Reports Server (NTRS)

    Komerath, Narayanan M.; Schreiber, Olivier A.

    1987-01-01

    The computer implementation and calculations of the induced velocities produced by a wake model consisting of a trailing vortex system defined from a prescribed time averaged downwash distribution are detailed. Induced velocities are computed by approximating each spiral turn by a pair of large straight vortex segments positioned at critical points relative to where the induced velocity is required. A remainder term for the rest of the spiral is added. This approach results in decreased computation time compared to classical models where each spiral turn is broken down in small straight vortex segments. The model includes features such a harmonic variation of circulation, downwash outside of the blade and/or outside the tip path plane, blade bound vorticity induced velocity with harmonic variation of circulation and time averaging. The influence of various options and parameters on the results are investigated and results are compared to experimental field measurements with which, a resonable agreement is obtained. The capabilities of the model as well as its extension possibilities are studied. The performance of the model in predicting the recently-acquired NASA Langley Inflow data base for a four-bladed rotor is compared to that of the Scully Free Wake code, a well-established program which requires much greater computational resources. It is found that the two codes predict the experimental data with essentially the same accuracy, and show the same trends.

  17. Vortex safety in aviation

    NASA Astrophysics Data System (ADS)

    Turchak, L. I.

    2012-10-01

    The objective is the general review of impact of aircraft wake vortices on the follower aircraft encountering the wake. Currently, the presence of wake vortices past aircraft limits the airspace capacity and flight safety level for aircraft of different purposes. However, wake vortex nature and evolution have not been studied in full measure. A mathematical model simulating the process of near wake generation past bodies of different shapes, as well as the wake evolution after rolling-up into wake vortices (far wake) is developed. The processes are suggested to be modeled by means of the Method of Discrete Vortices. Far wake evolution is determined by its complex interaction with the atmosphere and ground boundary layer. The main factors that are supposed to take into account are: wind and ambient turbulence 3Ddistributions, temperature stratification of the atmosphere, wind shear, as well as some others which effects will be manifested as considerable during the investigation. The ground boundary layer effects on wake vortex evolution are substantial at low flight altitudes and are determined through the boundary layer separation.

  18. Flight test to determine feasibility of a proposed airborne wake vortex detection concept

    NASA Technical Reports Server (NTRS)

    Branstetter, James R.; Hastings, E. C., Jr.; Patterson, James C., Jr.

    1991-01-01

    This investigation was conducted to determine the radial extent at which aircraft mounted flow vanes or roll rate gyros can sense the circulatory flow field that exists around the lift induced vortex system generated by an aircraft in flight. The probe aircraft was equipped with wingtip sensors for measuring angle of attack and angle of sideslip, and with a fuselage mounted gyroscope for measuring roll rate. Analysis of flight test data indicated that the vortex was detectable at a lateral distance of about 105 feet (best results) using unsophisticated equipment. Measurements were made from the centerline of the probe aircraft to the center of the nearest vortex with the probe aircraft flying between one half and one and one half miles behind the vortex generating aircraft.

  19. Time-resolved vortex wake of a common swift flying over a range of flight speeds

    PubMed Central

    Henningsson, P.; Muijres, F. T.; Hedenström, A.

    2011-01-01

    The wake of a freely flying common swift (Apus apus L.) is examined in a wind tunnel at three different flight speeds, 5.7, 7.7 and 9.9 m s−1. The wake of the bird is visualized using high-speed stereo digital particle image velocimetry (DPIV). Wake images are recorded in the transverse plane, perpendicular to the airflow. The wake of a swift has been studied previously using DPIV and recording wake images in the longitudinal plane, parallel to the airflow. The high-speed DPIV system allows for time-resolved wake sampling and the result shows features that were not discovered in the previous study, but there was approximately a 40 per cent vertical force deficit. As the earlier study also revealed, a pair of wingtip vortices are trailing behind the wingtips, but in addition, a pair of tail vortices and a pair of ‘wing root vortices’ are found that appear to originate from the wing/body junction. The existence of wing root vortices suggests that the two wings are not acting as a single wing, but are to some extent aerodynamically detached from each other. It is proposed that this is due to the body disrupting the lift distribution over the wing by generating less lift than the wings. PMID:21131333

  20. Improving Vortex Models via Optimal Control Theory

    NASA Astrophysics Data System (ADS)

    Hemati, Maziar; Eldredge, Jeff; Speyer, Jason

    2012-11-01

    Flapping wing kinematics, common in biological flight, can allow for agile flight maneuvers. On the other hand, we currently lack sufficiently accurate low-order models that enable such agility in man-made micro air vehicles. Low-order point vortex models have had reasonable success in predicting the qualitative behavior of the aerodynamic forces resulting from such maneuvers. However, these models tend to over-predict the force response when compared to experiments and high-fidelity simulations, in part because they neglect small excursions of separation from the wing's edges. In the present study, we formulate a constrained minimization problem which allows us to relax the usual edge regularity conditions in favor of empirical determination of vortex strengths. The optimal vortex strengths are determined by minimizing the error with respect to empirical force data, while the vortex positions are constrained to evolve according to the impulse matching model developed in previous work. We consider a flat plate undergoing various canonical maneuvers. The optimized model leads to force predictions remarkably close to the empirical data. Additionally, we compare the optimized and original models in an effort to distill appropriate edge conditions for unsteady maneuvers.

  1. Engineering models for merging wakes in wind farm optimization applications

    NASA Astrophysics Data System (ADS)

    Machefaux, E.; Larsen, G. C.; Murcia Leon, J. P.

    2015-06-01

    The present paper deals with validation of 4 different engineering wake superposition approaches against detailed CFD simulations and covering different turbine interspacing, ambient turbulence intensities and mean wind speeds. The first engineering model is a simple linear superposition of wake deficits as applied in e.g. Fuga. The second approach is the square root of sums of squares approach, which is applied in the widely used PARK program. The third approach, which is presently used with the Dynamic Wake Meandering (DWM) model, assumes that the wake affected downstream flow field to be determined by a superposition of the ambient flow field and the dominating wake among contributions from all upstream turbines at any spatial position and at any time. The last approach developed by G.C. Larsen is a newly developed model based on a parabolic type of approach, which combines wake deficits successively. The study indicates that wake interaction depends strongly on the relative wake deficit magnitude, i.e. the deficit magnitude normalized with respect to the ambient mean wind speed, and that the dominant wake assumption within the DWM framework is the most accurate.

  2. Vortex Generator Model Developed for Turbomachinery

    NASA Technical Reports Server (NTRS)

    Chima, Rodrick V.

    2002-01-01

    A computational model was developed at the NASA Glenn Research Center to investigate possible uses of vortex generators (VG's) for improving the performance of turbomachinery. A vortex generator is a small, winglike device that generates vortices at its tip. The vortices mix high-speed core flow with low-speed boundary layer flow and, thus, can be used to delay flow separation. VG's also turn the flow near the walls and, thus, can be used to control flow incidence into a turbomachinery blade row or to control secondary flows.

  3. Development and application of a method for predicting rotor free wake positions and resulting rotor blade air loads. Volume 1: Model and results

    NASA Technical Reports Server (NTRS)

    Sadler, S. G.

    1971-01-01

    Rotor wake geometries are predicted by a process similar to the startup of a rotor in a free stream. An array of discrete trailing and shed vortices is generated with vortex strengths corresponding to stepwise radial and azimuthal blade circulations. The array of shed and trailing vortices is limited to an arbitrary number of azimuthal steps behind each blade. The remainder of the wake model of each blade is an arbitrary number of trailing vortices. Vortex element end points were allowed to be transported by the resultant velocity of the free stream and vortex-induced velocities. Wake geometry, wake flow, and wake-induced velocity influence coefficients are generated by this program for use in the blade loads portion of the calculations. Blade loads computations include the effects of nonuniform inflow due to a free wake, nonlinear airfoil characteristics, and response of flexible blades to the applied loads. Computed wake flows and blade loads are compared with experimentally measured data. Predicted blade loads, response and shears and moments are obtained for a model rotor system having two independent rotors. The effects of advance ratio, vertical separation of rotors, different blade radius ratios, and different azimuthal spacing of the blades of one rotor with respect to the other are investigated.

  4. The Development of a Plan for the Assessment, Improvement and Deployment of a Radar Acoustic Sounding System (RASS) for Wake Vortex Detection

    NASA Technical Reports Server (NTRS)

    Morris, Philip J.; McLaughlin, Dennis K.; Gabrielson, Thomas B.; Boluriaan, Said

    2004-01-01

    This report describes the activities completed under a grant from the NASA Langley Research Center to develop a plan for the assessment, improvement, and deployment of a Radar Acoustic Sounding System (RASS) for the detection of wake vortices. A brief review is provided of existing alternative instruments for wake vortex detection. This is followed by a review of previous implementations and assessment of a RASS. As a result of this review, it is concluded that the basic features of a RASS have several advantages over other commonly used wake vortex detection and measurement systems. Most important of these features are the good fidelity of the measurements and the potential for all weather operation. To realize the full potential of this remote sensing instrument, a plan for the development of a RASS designed specifically for wake vortex detection and measurement has been prepared. To keep costs to a minimum, this program would start with the development an inexpensive laboratory-scale version of a RASS system. The new instrument would be developed in several stages, each allowing for a critical assessment of the instrument s potential and limitations. The instrument, in its initial stages of development, would be tested in a controlled laboratory environment. A jet vortex simulator, a prototype version of which has already been fabricated, would be interrogated by the RASS system. The details of the laboratory vortex would be measured using a Particle Image Velocimetry (PIV) system. In the early development stages, the scattered radar signal would be digitized and the signal post-processed to determine how extensively and accurately the RASS could measure properties of the wake vortex. If the initial tests prove to be successful, a real-time, digital signal processing system would be developed as a component of the RASS system. At each stage of the instrument development and testing, the implications of the scaling required for a full-scale instrument would be

  5. Computation of potential flows with embedded vortex rings and applications to helicopter rotor wakes

    NASA Technical Reports Server (NTRS)

    Roberts, T. W.

    1983-01-01

    A finite difference scheme for solving the motion of a number of vortex rings is developed. The method is an adaptation of the 'cloud-in-cell' technique to axisymmetric flows, and is thus a combined Eulerian-Lagrangian technique. A straightforward adaptation of the cloud-in-cell scheme to an axisymmetric flow field is shown to introduce a grid dependent self-induced velocity to each vortex ring. To correct this behavior the potential is considered to consist of two parts, a local and a global field. An improved difference formula is derived, allowing the accurate calculation of the potential at points near vortex locations. The local potential is then subtracted before calculating the velocity, leaving only the influences of the remaining vortices. The correct self-induced velocity is then explicitly added to the vortex velocity. Calculations of the motion of one and two vortex rings are performed, demonstrating the ability of the new method to eliminate the grid dependence of the self-induced velocity. The application of the method to the calculation of helicopter rotor flows in hover is attempted.

  6. Study of the far wake vortex field generated by a rectangular airfoil in a water tank

    NASA Technical Reports Server (NTRS)

    Lezius, D. K.

    1973-01-01

    Underwater towing experiments were carried out with a rectangular airfoil of aspect ratio 5.3 at 4 and 8 deg angles of attack and at chord-based Reynolds numbers between 2 x 100,000 and 7.5 x 100,000. Quantitative measurements by means of the hydrogen bubble technique indicated lower peak swirl velocities in the range of 100 to 1000 lenghts downstream than have been measured in wind tunnel of flight tests. The maximum circumferential velocity decayed whereas the turbulent eddy viscosity increased. This behavior and other known rates of vortex decay are explained in terms of an analytical solution for the vortex problem with time varying eddy viscosity. It is shown that this case corresponds to nonequilibrium turbulent vortex flow.

  7. Comparison of Engineering Wake Models with CFD Simulations

    NASA Astrophysics Data System (ADS)

    Andersen, S. J.; Sørensen, J. N.; Ivanell, S.; Mikkelsen, R. F.

    2014-06-01

    The engineering wake models by Jensen [1] and Frandsen et al. [2] are assessed for different scenarios simulated using Large Eddy Simulation and the Actuator Line method implemented in the Navier-Stokes equations. The scenarios include the far wake behind a single wind turbine, a long row of turbines in an atmospheric boundary layer, idealised cases of an infinitely long row of wind turbines and infinite wind farms with three different spacings. Both models include a wake expansion factor, which is calibrated to fit the simulated wake velocities. The analysis highlights physical deficiencies in the ability of the models to universally predict the wake velocities, as the expansion factor can be fitted for a given case, but with not apparent transition between the cases.

  8. The effect of single-horn glaze ice on the vortex structures in the wake of a horizontal axis wind turbine

    NASA Astrophysics Data System (ADS)

    Jin, Zhe-Yan; Dong, Qiao-Tian; Yang, Zhi-Gang

    2015-02-01

    The present study experimentally investigated the effect of a simulated single-horn glaze ice accreted on rotor blades on the vortex structures in the wake of a horizontal axis wind turbine by using the stereoscopic particle image velocimetry (Stereo-PIV) technique. During the experiments, four horizontal axis wind turbine models were tested, and both "free-run" and "phase-locked" Stereo-PIV measurements were carried out. Based on the "free-run" measurements, it was found that because of the simulated single-horn glaze ice, the shape, vorticity, and trajectory of tip vortices were changed significantly, and less kinetic energy of the airflow could be harvested by the wind turbine. In addition, the "phase-locked" results indicated that the presence of simulated single-horn glaze ice resulted in a dramatic reduction of the vorticity peak of the tip vortices. Moreover, as the length of the glaze ice increased, both root and tip vortex gaps were found to increase accordingly.

  9. The role of atmospheric shear, turbulence and a ground plane on the dissipation of aircraft vortex wakes

    NASA Technical Reports Server (NTRS)

    Bilanin, A. J.; Teske, M. E.; Hirsh, J. E.

    1978-01-01

    Enhanced dispersion of two-dimensional trailed vortex pairs within simplified neutral atmospheric backgrounds is studied numerically for three conditions: when the pair is imbedded in a constant turbulent bath (constant dissipation); when the pair is subjected to a mean cross-wind shear; and when the pair is near the ground. Turbulent transport is modeled using second-order closure turbulent transport theory. The turbulent background fields are constructed using a superequilibrium approximation. The computed results allow several general conclusions to be drawn with regard to the reduction in circulation of the vortex pair and the rolling moment induced on a following aircraft: (1) the rate of decay of a vortex pair increases with increasing background dissipation rate; (2) cross-wind shear disperses the vortex whose vorticity is opposite to the background; and (3) the proximity of a ground plane reduces the hazard of the pair by scrubbing. The phenomenon of vortex bounce is explained in terms of secondary vorticity produced at the ground plane. Qualitative comparisons are made with available experimental data, and inferences of these results upon the persistence of aircraft trailing vortices are discussed.

  10. Velocity and rolling-moment measurements in the wake of a swept-wing model in the 40 by 80 foot wind tunnel

    NASA Technical Reports Server (NTRS)

    Rossow, V. J.; Corsiglia, V. R.; Schwind, R. G.; Frick, J. K. D.; Lemmer, O. J.

    1975-01-01

    Measurements were made in the wake of a swept wing model to study the structure of lift generated vortex wakes shed by conventional span loadings and by several span loadings designed to reduce wake velocities. Variations in the span loading on the swept wing generator were obtained by deflecting seven flap segments on each side by amounts determined by vortex lattice theory to approximate the desired span loadings. The resulting wakes were probed with a three component, hot wire probe to measure velocity, and with a wing to measure the rolling moment that would be induced on a following aircraft. The experimental techniques are described herein, and the measured velocity and rolling moments are presented, along with some comparisons with the applicable theories.

  11. A mathematical model of the sleep/wake cycle.

    PubMed

    Rempe, Michael J; Best, Janet; Terman, David

    2010-05-01

    We present a biologically-based mathematical model that accounts for several features of the human sleep/wake cycle. These features include the timing of sleep and wakefulness under normal and sleep-deprived conditions, ultradian rhythms, more frequent switching between sleep and wakefulness due to the loss of orexin and the circadian dependence of several sleep measures. The model demonstrates how these features depend on interactions between a circadian pacemaker and a sleep homeostat and provides a biological basis for the two-process model for sleep regulation. The model is based on previous "flip-flop" conceptual models for sleep/wake and REM/NREM and we explore whether the neuronal components in these flip-flop models, with the inclusion of a sleep-homeostatic process and the circadian pacemaker, are sufficient to account for the features of the sleep/wake cycle listed above. The model is minimal in the sense that, besides the sleep homeostat and constant cortical drives, the model includes only those nuclei described in the flip-flop models. Each of the cell groups is modeled by at most two differential equations for the evolution of the total population activity, and the synaptic connections are consistent with those described in the flip-flop models. A detailed analysis of the model leads to an understanding of the mathematical mechanisms, as well as insights into the biological mechanisms, underlying sleep/wake dynamics. PMID:19557415

  12. A vortex entrainment model applied to slender delta wings

    NASA Technical Reports Server (NTRS)

    Coe, P. L., Jr.

    1974-01-01

    A mathematical model of the vortex flow over a slender sharp-edged delta wing is proposed, and is shown to provide good agreement with the experiment. Although the technique requires experimental data in the form of the vortex core locations, it does account for the previously ignored mass entrainment of the vortex core.

  13. Energetic Turbulence Structures in the Wake of Model Wind Turbines

    NASA Astrophysics Data System (ADS)

    Sheng, Jian; Mehdi, Faraz; Chamorro, Leonardo P.

    2013-11-01

    Wind turbine wakes contain complex and energetic flow structures. Characterizing the near-wake field is critical to assess flow-structure interactions and evaluate asymmetric loadings that trigger premature structural failure. Although the turbulence flow structure in the far-wake region is important in the wind farm design, an integrated characterization of the entire wake flow would provide clearer mechanistic view on other phenomena such wake meandering and unsteady interactions with the blades of downwind turbines. High-speed Particle Image Velocimetry (PIV) is carried out over a model wind turbine in a neutrally stratified boundary layer flow. The measurements are made at consecutive locations ranging from three rotor diameters upstream to twelve rotor diameters downstream of the unit. Vortical structures within the wake including tip, root and hub vortices are identified and followed as they advect downstream. The evolution of these dominant near-wake flow structures are quantified and provide us a better understanding of interactions between turbine wake and boundary layer. The spatial distribution of the mean and fluctuating velocity, as well as energy spectrum and turbulent kinetic budget are also discussed.

  14. A Lagrangian approach to vortex identification in swimming and flying animal wakes.

    NASA Astrophysics Data System (ADS)

    Peng, Jifeng; Dabiri, John

    2006-11-01

    The fluid wakes of swimming and flying animals are generally time-dependent. The Eulerian velocity field, which can be measured by existing DPIV measurement techniques, does not directly indicate the flow geometry in this type of unsteady flows. In this study, a Lagrangian approach is developed to determine the Lagrangian Coherent Structures, which are physical boundaries separating flow regions with distinct dynamics, including vortices. The determination of morphology and kinematics of vortices is necessary in estimating time-dependent locomotive forces (Dabiri, J. Exp. Bio., 2006). It also provides information in studying fluid transport in animal swimming and flying. The application of the method is demonstrated by studying the wake of a bluegill sunfish pectoral fin and that of a free-swimming jellyfish.

  15. Ribbon Surface Pressure and Wake Velocity Data for the Experimental Validation of a Vortex-Based Parachute Inflation Code

    SciTech Connect

    MCBRIDE,DONALD DEAN; CLARK JR,EDWARD LEE; HENFLING,JOHN F.

    2001-06-01

    An experiment to measure surface pressure data on a series of three stainless steel simulated parachute ribbons was conducted. During the first phase of the test, unsteady pressure measurements were made on the windward and leeward sides of the ribbons to determine the statistical properties of the surface pressures. Particle Image Velocimetry (PIV) measurements were simultaneously made to establish the velocity field in the wake of the ribbons and its correlation with the pressure measurements. In the second phase of the test, steady-state pressure measurements were made to establish the pressure distributions. In the third phase, the stainless steel ribbons were replaced with nylon ribbons and PIV measurements were made in the wake. A detailed error analysis indicates that the accuracy of the pressure measurements was very good. However, an anomaly in the flow field caused the wake behind the stainless steel ribbons to establish itself in a stable manner on one side of the model. This same stability was not present for the nylon ribbon model although an average of the wake velocity data indicated an apparent 2{degree} upwash in the wind tunnel flow field. Since flow angularity upstream of the model was not measured, the use of the data for code validation is not recommended without a second experiment to establish that upstream boundary condition.

  16. Intercomparison among plasma wake models for plasmaspheric and ionospheric conditions

    NASA Technical Reports Server (NTRS)

    Samir, U.; Comfort, R. H.; Wright, K. H., Jr.; Stone, N. H.

    1987-01-01

    The angular distributions of ions in the wake of a body moving through a space plasma computed from three different models are compared in order to investigate wake current depletion ratios under conditions simulating the topside ionosphere and plasmasphere. Results demonstrate the importance of taking into account the thermal flux at low Mach numbers and the angular acceptance of ion detectors in making theory-experiment comparisons. For all models considered, gradients in the angular variations of the fluxes are shown to be steeper near the wake-ambient interface than closer to the maximum rarefaction region.

  17. Propeller tip vortex interactions

    NASA Technical Reports Server (NTRS)

    Johnston, Robert T.; Sullivan, John P.

    1990-01-01

    Propeller wakes interacting with aircraft aerodynamic surfaces are a source of noise and vibration. For this reason, flow visualization work on the motion of the helical tip vortex over a wing and through the second stage of a counterrotation propeller (CRP) has been pursued. Initially, work was done on the motion of a propeller helix as it passes over the center of a 9.0 aspect ratio wing. The propeller tip vortex experiences significant spanwise displacements when passing across a lifting wing. A stationary propeller blade or stator was installed behind the rotating propeller to model the blade vortex interaction in a CRP. The resulting vortex interaction was found to depend on the relative vortex strengths and vortex sign.

  18. Airloads and Wake Geometry Calculations for an Isolated Tiltrotor Model in a Wind Tunnel

    NASA Technical Reports Server (NTRS)

    Johnson, Wayne

    2001-01-01

    Comparisons of measured and calculated aerodynamic behavior of a tiltrotor model are presented. The test of the Tilt Rotor Aeroacoustic Model (TRAM) with a single, 0.25-scale V-22 rotor in the German-Dutch Wind Tunnel (DNW) provides an extensive set of aeroacoustic, performance, and structural loads data. The calculations were performed using the rotorcraft comprehensive analysis CAMRAD II. Presented are comparisons of measured and calculated performance for hover and helicopter mode operation, and airloads for helicopter mode. Calculated induced power, profile power, and wake geometry provide additional information about the aerodynamic behavior. An aerodynamic and wake model and calculation procedure that reflects the unique geometry and phenomena of tiltrotors has been developed. There are major differences between this model and the corresponding aerodynamic and wake model that has been established for helicopter rotors. In general, good correlation between measured and calculated performance and airloads behavior has been shown. Two aspects of the analysis that clearly need improvement are the stall delay model and the trailed vortex formation model.

  19. Helicopter rotor wake geometry and its influence in forward flight. Volume 1: Generalized wake geometry and wake effect on rotor airloads and performance

    NASA Technical Reports Server (NTRS)

    Egolf, T. A.; Landgrebe, A. J.

    1983-01-01

    An analytic investigation to generalize wake geometry of a helicopter rotor in steady level forward flight and to demonstrate the influence of wake deformation in the prediction of rotor airloads and performance is described. Volume 1 presents a first level generalized wake model based on theoretically predicted tip vortex geometries for a selected representative blade design. The tip vortex distortions are generalized in equation form as displacements from the classical undistorted tip vortex geometry in terms of vortex age, blade azimuth, rotor advance ratio, thrust coefficient, and number of blades. These equations were programmed to provide distorted wake coordinates at very low cost for use in rotor airflow and airloads prediction analyses. The sensitivity of predicted rotor airloads, performance, and blade bending moments to the modeling of the tip vortex distortion are demonstrated for low to moderately high advance ratios for a representative rotor and the H-34 rotor. Comparisons with H-34 rotor test data demonstrate the effects of the classical, predicted distorted, and the newly developed generalized wake models on airloads and blade bending moments. Use of distorted wake models results in the occurrence of numerous blade-vortex interactions on the forward and lateral sides of the rotor disk. The significance of these interactions is related to the number and degree of proximity to the blades of the tip vortices. The correlation obtained with the distorted wake models (generalized and predicted) is encouraging.

  20. Vortex Density Models for Superconductivity and Superfluidity

    NASA Astrophysics Data System (ADS)

    Baldo, S.; Jerrard, R. L.; Orlandi, G.; Soner, H. M.

    2013-02-01

    We study some functionals that describe the density of vortex lines in superconductors subject to an applied magnetic field, and in Bose-Einstein condensates subject to rotational forcing, in quite general domains in 3 dimensions. These functionals are derived from more basic models via Gamma-convergence, here and in the companion paper (Baldo et al. in Arch Rat Mech Anal 205(3):699-752, 2012). In our main results, we use these functionals to obtain leading order descriptions of the first critical applied magnetic field (for superconductors) and forcing (for Bose-Einstein), above which ground states exhibit nontrivial vorticity, as well as a characterization of the vortex density in terms of a non local vector-valued generalization of the classical obstacle problem.

  1. Knuckleball and Flying Disk: Boundary Layer Transitions, Separations and Vortex Wakes in Sports Aerodynamics

    NASA Astrophysics Data System (ADS)

    Higuchi, Hiroshi; Kiura, Toshiro; Goto, Yuichiro; Hiramoto, Riho

    2001-11-01

    In spite of their popularity, flow structures over common baseball and flying disks have not been studied in detail. A slowly rotating baseball is subject to erratic flight paths, and is known as a knuckleball. In the present experiment, the characteristic of force acting on a baseball was obtained and the velocity vector field near the surface of the ball and the wake were measured with the DPIV technique. The seam triggered the boundary layer transition or caused the boundary layer separation itself. The laminar/turbulent boundary layer separations were identified with specific ball orientations. Corresponding three-dimensional wake pattern and the side force result in unpredictable trajectories. In the second part of the talk, flow physics regarding a spin-stabilized flying disk is addressed. The roll-up of trailing vortices was visualized in detail and their vorticity field was measured with the DPIV. The vortical flow over the disk produced flow reattachment at a very high angle of attack. The boundary layer at low angles of attack was affected by the surface motion with asymmetric boundary layer transitions as evidenced by the flow visualization and the hot wire survey. The flow separation and attachment on the underside cavity were also affected by the rotation.

  2. Improvement of a near wake model for trailing vorticity

    NASA Astrophysics Data System (ADS)

    Pirrung, G. R.; Hansen, M. H.; Madsen, H. A.

    2014-12-01

    A near wake model, originally proposed by Beddoes, is further developed. The purpose of the model is to account for the radially dependent time constants of the fast aerodynamic response and to provide a tip loss correction. It is based on lifting line theory and models the downwash due to roughly the first 90 degrees of rotation. This restriction of the model to the near wake allows for using a computationally efficient indicial function algorithm. The aim of this study is to improve the accuracy of the downwash close to the root and tip of the blade and to decrease the sensitivity of the model to temporal discretization, both regarding numerical stability and quality of the results. The modified near wake model is coupled to an aerodynamics model, which consists of a blade element momentum model with dynamic inflow for the far wake and a 2D shed vorticity model that simulates the unsteady buildup of both lift and circulation in the attached flow region. The near wake model is validated against the test case of a finite wing with constant elliptical bound circulation. An unsteady simulation of the NREL 5 MW rotor shows the functionality of the coupled model.

  3. Flight Data Reduction of Wake Velocity Measurements Using an Instrumented OV-10 Airplane

    NASA Technical Reports Server (NTRS)

    Vicroy, Dan D.; Stuever, Robert A.; Stewart, Eric C.; Rivers, Robert A.

    1999-01-01

    A series of flight tests to measure the wake of a Lockheed C- 130 airplane and the accompanying atmospheric state have been conducted. A specially instrumented North American Rockwell OV-10 airplane was used to measure the wake and atmospheric conditions. An integrated database has been compiled for wake characterization and validation of wake vortex computational models. This paper describes the wake- measurement flight-data reduction process.

  4. The dynamics of vortex streets in channels

    NASA Astrophysics Data System (ADS)

    Wang, Xiaolin; Alben, Silas

    2015-07-01

    We develop a model to numerically study the dynamics of vortex streets in channel flows. Previous work has studied the vortex wakes of specific vortex generators. Here, we study a wide range of vortex wakes including regular and reverse von Kármán streets with various strengths, geometries, and Reynolds numbers (Re) by applying a smoothed von Kármán street as an inflow condition. We find that the spatial structure of the inflow vortex street is maintained for the reverse von Kármán street and altered for the regular street. For regular streets, we identify a transition to asymmetric dynamics which happens when Re increases, or vortices are stronger, or vortex streets are compressed horizontally or extended vertically. We also determine the effects of these parameters on vortex street inversion.

  5. Typhoon effect on Kuroshio and Green Island wake: a modelling study

    NASA Astrophysics Data System (ADS)

    Hsu, T.-W.; Chou, M.-H.; Hou, T.-H.; Liang, S.-J.

    2015-12-01

    Green Island located in the typhoon active eastern Taiwan coastal water is the potential Kuroshio power plant site. In this study, a high resolution (250-2250 m) shallow-water equations (SWEs) model is used to investigate the effect of typhoon on the hydrodynamics of Kuroshio and Green Island wake. Two wind induced flows, typhoon Soulik and Holland's wind field model, are studied. Simulation results of the typhoon Soulik indicate that salient characteristics of Kuroshio and downstream island wake seems less affected by the typhoon Soulik because typhoon Soulik is 250 km away Green Island and the wind speed near Green Island is small. Moreover, Kuroshio currents increase when flow is in the same direction as the counterclockwise rotation of typhoon, and vice versa. This finding is in favorable agreements with the TOROS observed data. The SWEs model, forced by the Kuroshio and Holland's wind field model, successfully reproduces the downstream recirculation and meandering vortex street. Numerical results unveil that the slow moving typhoon has a more significant impact on the Kuroshio and downstream Green Island wake than the fast moving typhoon does. Due to the counterclockwise rotation of typhoon, Kuroshio currents increase (decrease) in the right (left) of the moving typhoon's track. This rightward bias phenomenon is evident, especially when typhoon moves in the same direction as the Kuroshio mainstream.

  6. The effect of asymmetric vortex wake characteristics on a slender delta wing undergoing wing rock motion

    NASA Technical Reports Server (NTRS)

    Arena, A. S., Jr.; Nelson, R. C.

    1989-01-01

    An experimental investigation into the fluid mechanisms responsible for wing rock on a slender delta wing with 80 deg leading edge sweep has been conducted. Time history and flow visualization data are presented for a wide angle-of-attack range. The use of an air bearing spindle has allowed the motion of the wing to be free from bearing friction or mechanical hysteresis. A bistable static condition has been found in vortex breakdown at an angle of attack of 40 deg which causes an overshoot of the steady state rocking amplitude. Flow visualization experiments also reveal a difference in static and dynamic breakdown locations on the wing. A hysteresis loop in dynamic breakdown location similar to that seen on pitching delta wings was observed as the wing was undergoing the limit cycle oscillation.

  7. Comparing offshore wind farm wake observed from satellite SAR and wake model results

    NASA Astrophysics Data System (ADS)

    Bay Hasager, Charlotte

    2014-05-01

    are modeled by various types of wake models. In the EERA DTOC project the model suite consists of engineering models (Ainslie, DWM, GLC, PARK, WASP/NOJ), simplified CFD models (FUGA, FarmFlow), full CFD models (CRES-flowNS, RANS), mesoscale model (SKIRON, WRF) and coupled meso-scale and microscale models. The comparison analysis between the satellite wind wake and model results will be presented and discussed. It is first time a comprehensive analysis is performed on this subject. The topic gains increasing importance because there is a growing need to precisely model also mid- and far-field wind farms wakes for development and planning of offshore wind farm clusters.

  8. Model-based control of vortex shedding at low Reynolds numbers

    NASA Astrophysics Data System (ADS)

    Illingworth, Simon J.

    2016-03-01

    Model-based feedback control of vortex shedding at low Reynolds numbers is considered. The feedback signal is provided by velocity measurements in the wake, and actuation is achieved using blowing and suction on the cylinder's surface. Using two-dimensional direct numerical simulations and reduced-order modelling techniques, linear models of the wake are formed at Reynolds numbers between 45 and 110. These models are used to design feedback controllers using H_∞ loop-shaping. Complete suppression of shedding is demonstrated up to Re = 110—both for a single-sensor arrangement and for a three-sensor arrangement. The robustness of the feedback controllers is also investigated by applying them over a range of off-design Reynolds numbers, and good robustness properties are seen. It is also observed that it becomes increasingly difficult to achieve acceptable control performance—measured in a suitable way—as Reynolds number increases.

  9. On the acoustic signature of tandem airfoils: The sound of an elastic airfoil in the wake of a vortex generator

    NASA Astrophysics Data System (ADS)

    Manela, A.

    2016-07-01

    The acoustic signature of an acoustically compact tandem airfoil setup in uniform high-Reynolds number flow is investigated. The upstream airfoil is considered rigid and is actuated at its leading edge with small-amplitude harmonic pitching motion. The downstream airfoil is taken passive and elastic, with its motion forced by the vortex-street excitation of the upstream airfoil. The non-linear near-field description is obtained via potential thin-airfoil theory. It is then applied as a source term into the Powell-Howe acoustic analogy to yield the far-field dipole radiation of the system. To assess the effect of downstream-airfoil elasticity, results are compared with counterpart calculations for a non-elastic setup, where the downstream airfoil is rigid and stationary. Depending on the separation distance between airfoils, airfoil-motion and airfoil-wake dynamics shift between in-phase (synchronized) and counter-phase behaviors. Consequently, downstream airfoil elasticity may act to amplify or suppress sound through the direct contribution of elastic-airfoil motion to the total signal. Resonance-type motion of the elastic airfoil is found when the upstream airfoil is actuated at the least stable eigenfrequency of the downstream structure. This, again, results in system sound amplification or suppression, depending on the separation distance between airfoils. With increasing actuation frequency, the acoustic signal becomes dominated by the direct contribution of the upstream airfoil motion, whereas the relative contribution of the elastic airfoil to the total signature turns negligible.

  10. Wind-tunnel measurements in the wakes of structures

    NASA Technical Reports Server (NTRS)

    Woo, H. G. C.; Peterka, J. A.; Cermak, J. E.

    1977-01-01

    Detailed measurements of longitudinal mean velocity, turbulence intensity, space correlations, and spectra made in the wake of two rectangular scaled models in simulated atmospheric boundary-layer winds are presented. The model buildings were 1:50 scale models of two trailers. Results of a flow visualization study of the wake geometry are analyzed with some singular point theorems. Two hypothetical flow patterns of the detailed wake geometry are proposed. Some preliminary studies of the vortex wake, effects of the model size, model aspect ratios, and boundary layer characteristics on the decay rate and extent of the wake are also presented and discussed.

  11. A comprehensive comparison of turbulence models in the far wake

    NASA Technical Reports Server (NTRS)

    Cimbala, John M.

    1993-01-01

    In the present study, the far wake was examined numerically using an implicit, upwind, finite-volume, compressible Navier-Stokes code. The numerical grid started at 500 equivalent circular cylinder diameters in the wave, and extended to 4000 equivalent diameters. By concentrating only on the far wake, the numerical difficulties and fine mesh requirements near the wake-generating body were eliminated. At the time of this writing, results for the K-epsilon and K-omega turbulence models at low Mach number have been completed and show excellent agreement with previous incompressible results and far-wake similarity solutions. The code is presently being used to compare the performance of various other turbulence models, including Reynolds stress models and the new anisotropic two-equation turbulence models being developed at NASA Langley. By increasing our physical understanding of the deficiencies and limits of these models, it is hoped that improvements to the universality of the models can be made. Future plans include examination of two-dimensional momentumless wakes as well.

  12. Perturbation response of model vortex rings and dipoles

    NASA Astrophysics Data System (ADS)

    O'Farrell, Clara; Dabiri, John O.

    2012-11-01

    Jetting swimmers, such as squid or jellyfish, propel themselves by forming axisymmetric vortex rings. It is known that vortex rings cannot grow indefinitely, but rather ``pinch off'' once they reach their physical limit, and that a decrease in efficiency of fluid transport is associated with pinch-off. In contrast, two-dimensional vortex dipoles have been found to grow well beyond the physical limit observed in axisymmetric vortex rings. Previously, the Norbury and Pierrehumbert families of vortices have been used as models for axisymmetric vortex rings and two-dimensional dipoles respectively, and the response of these two families to shape perturbations has been characterized. In this study, we improve upon the Norbury and Pierrehumbert models, using nested contours to obtain more realistic models for experimentally-generated vortex rings and dipoles. The resulting vortices are subjected to shape perturbations akin to those previously introduced to members of the Norbury and Pierrehumbert families, and their response is characterized.

  13. A study of the rotor wake of a small-scale rotor model in forward flight using laser light sheet flow visualization with comparisons to analytical models

    NASA Technical Reports Server (NTRS)

    Ghee, Terence A.; Elliott, Joe W.

    1992-01-01

    An experimental investigation was conducted in the 14 by 22 ft subsonic tunnel at NASA Langley Research Center to quantify the rotor wake behind a scale model helicopter rotor in forward flight (mu = 0.15 and 0.23) at one thrust level (C sub T = 0.0064). The rotor system used in the present test consisted of a four-bladed, fully articulated hub and utilized blades of rectangular planform with a NACA-0012 airfoil section. A laser light sheet, seeded with propylene glycol smoke, was used to visualize the flow in planes parallel and perpendicular to the freestream flow. Quantitative measurements of vortex location, vertical skew angle, and vortex particle void radius were obtained for vortices in the flow; convective velocities were obtained for blade tip vortices. Comparisons were made between the experimental results and the wake geometry generated by computational predictions. The results of these comparisons show that the interaction between wake vortex structures is an important consideration for correctly predicting the wake geometry.

  14. Discrete-vortex model for the symmetric-vortex flow on cones

    NASA Technical Reports Server (NTRS)

    Gainer, Thomas G.

    1990-01-01

    A relatively simple but accurate potential flow model was developed for studying the symmetric vortex flow on cones. The model is a modified version of the model first developed by Bryson, in which discrete vortices and straight-line feeding sheets were used to represent the flow field. It differs, however, in the zero-force condition used to position the vortices and determine their circulation strengths. The Bryson model imposed the condition that the net force on the feeding sheets and discrete vortices must be zero. The proposed model satisfies this zero-force condition by having the vortices move as free vortices, at a velocity equal to at the local crossflow velocity at their centers. When the free-vortex assumption is made, a solution is obtained in the form of two nonlinear algebraic equations that relate the vortex center coordinates and vortex strengths to the cone angle and angle of attack. The vortex center locations calculated using the model are in good agreement with experimental values. The cone normal forces as well as center locations are in good agreement with the vortex cloud method of calculating symmetric flow fields.

  15. Review of Wind Turbine Wake Models and Future Directions (Presentation)

    SciTech Connect

    Churchfield, M. J.

    2013-08-01

    This presentation gives a brief overview to wind turbine wake modeling, ranging from models used in the 1980s up to the present. The presentation shows the strengths and weaknesses of various models and discusses the needs of the wind energy industry and research sectors. Both power production and loads analysis are discussed.

  16. Source Term Model for an Array of Vortex Generator Vanes

    NASA Technical Reports Server (NTRS)

    Buning, P. G. (Technical Monitor); Waithe, Kenrick A.

    2003-01-01

    A source term model was developed for numerical simulations of an array of vortex generators. The source term models the side force created by a vortex generator being modeled. The model is obtained by introducing a side force to the momentum and energy equations that can adjust its strength automatically based on a local flow. The model was tested and calibrated by comparing data from numerical simulations and experiments of a single low-profile vortex generator vane, which is only a fraction of the boundary layer thickness, over a flat plate. The source term model allowed a grid reduction of about seventy percent when compared with the numerical simulations performed on a fully gridded vortex generator without adversely affecting the development and capture of the vortex created. The source term model was able to predict the shape and size of the stream wise vorticity and velocity contours very well when compared with both numerical simulations and experimental data.

  17. Comparison of experimental and analytical predictions of rotor blade-vortex interactions using model scale acoustic data

    NASA Technical Reports Server (NTRS)

    Martin, R. M.; Elliott, J. W.; Hoad, D. R.

    1984-01-01

    Helicopter blade-vortex interaction (BVI) noise is studied using a model scale rotor acoustic data base and an analytical rotor wake prediction method. The variation of BVI acoustic levels with vehicle flight conditions (forward speed and disk attitude) is presented. Calculations of probable BVI locations on the rotor disk are made for a range of operating conditions using the measured acoustic signals and an acoustic ray tracing technique. Analytical predictions of possible BVI locations on the rotor disk are made using a generalized distorted wake analysis program. Comparisons of the interaction locations are made with the results of both the analytic approach and the acoustic ray tracing technique.

  18. Effects of incoming wind condition and wind turbine aerodynamics on the hub vortex instability

    NASA Astrophysics Data System (ADS)

    Ashton, R.; Viola, F.; Gallaire, F.; Iungo, G. V.

    2015-06-01

    Dynamics and instabilities occurring in the near-wake of wind turbines have a crucial role for the wake downstream evolution, and for the onset of far-wake instabilities. Furthermore, wake dynamics significantly affect the intra-wind farm wake flow, wake interactions and potential power losses. Therefore, the physical understanding and predictability of wind turbine wake instabilities become a nodal point for prediction of wind power harvesting and optimization of wind farm layout. This study is focused on the prediction of the hub vortex instability encountered within wind turbine wakes under different operational conditions of the wind turbine. Linear stability analysis of the wake flow is performed by means of a novel approach that enables to take effects of turbulence on wake instabilities into account. Stability analysis is performed by using as base flow the time-averaged wake velocity field at a specific downstream location. The latter is modeled through Carton-McWilliams velocity profiles by mimicking the presence of the hub vortex and helicoidal tip vortices, and matching the wind turbine thrust coefficient predicted through the actuator disc model. The results show that hub vortex instability is promoted by increasing the turbine thrust coefficient. Indeed, a larger aerodynamic load produces an enhanced wake velocity deficit and axial shear, which are considered the main sources for the wake instability. Nonetheless, wake swirl also promotes hub vortex instability, and it can also affect the azimuthal wavenumber of the most unstable mode.

  19. Full-potential modeling of blade-vortex interactions

    NASA Technical Reports Server (NTRS)

    Jones, H. E.; Caradonna, F. X.

    1986-01-01

    A comparison is made of four different models for predicting the unsteady loading induced by a vortex passing close to an airfoil. (1) The first model approximates the vortex effect as a change in the airfoil angle of attack. (2) The second model is related to the first but, instead of imposing only a constant velocity on the airfoil, the distributed effect of the vortex is computed and used. This is analogous to a lifting surface method. (3) The third model is to specify a branch cut discontinuity in the potential field. The vortex is modeled as a jump in potential across the branch cut, the edge of which represents the center of the vortex. (4) The fourth method models the vortex expressing the potential as the sum of a known potential due to the vortex and an unknown perturbation due to the airfoil. The purpose of the current study is to investigate the four vortex models described above and to determine their relative merits and suitability for use in large three-dimensional codes.

  20. High resolution numerical modeling of mesoscale island wakes and sensitivity to static topographic relief data

    NASA Astrophysics Data System (ADS)

    Nunalee, C. G.; Horváth, Á.; Basu, S.

    2015-03-01

    Recent decades have witnessed a drastic increase in the fidelity of numerical weather prediction (NWP) modeling. Currently, both research-grade and operational NWP models regularly perform simulations with horizontal grid spacings as fine as 1 km. This migration towards higher resolution potentially improves NWP model solutions by increasing the resolvability of mesoscale processes and reducing dependency on empirical physics parameterizations. However, at the same time, the accuracy of high-resolution simulations, particularly in the atmospheric boundary layer (ABL), are also sensitive to orographic forcing which can have significant variability on the same spatial scale as, or smaller than, NWP model grids. Despite this sensitivity, many high resolution atmospheric simulations do not consider uncertainty with respect to selection of static terrain height dataset. In this paper, we use the Weather Research and Forecasting (WRF) model to simulate realistic cases of lower tropospheric flow over and downstream of mountainous islands using both the default global 30 s United States Geographic Survey terrain height dataset (GTOPO30) and the 3 s Shuttle Radar Topography Mission (SRTM) terrain height dataset. Our results demonstrate cases where the differences between GTOPO30-based and SRTM-based model terrain height are significant enough to produce entirely different orographic wake mechanics, such as vortex shedding vs. no vortex shedding. These results are also compared to MODIS visible satellite imagery and highlight the importance of considering uncertain static boundary conditions when running high-resolution mesoscale models.

  1. Theoretical modelling of wakes from retractable flapping wings in forward flight.

    PubMed

    Parslew, Ben; Crowther, William J

    2013-01-01

    A free-wake method is used to simulate the wake from retractable, jointed wings. The method serves to complement existing experimental studies that visualise flying animal wakes. Simulated wakes are shown to be numerically convergent for a case study of the Rock Pigeon in minimum power cruising flight. The free-wake model is robust in simulating wakes for a range of wing geometries and dynamics without requiring changes to the numerical method. The method is found to be useful for providing low order predictions of wake geometries. However, it is not well suited to reconstructing 3d flowfields as solutions are sensitive to the numerical mesh node locations. PMID:23882442

  2. A Neuron-Based Model of Sleep-Wake Cycles

    NASA Astrophysics Data System (ADS)

    Postnova, Svetlana; Peters, Achim; Braun, Hans

    2008-03-01

    In recent years it was discovered that a neuropeptide orexin/hypocretin plays a main role in sleep processes. This peptide is produced by the neurons in the lateral hypothalamus, which project to almost all brain areas. We present a computational model of sleep-wake cycles, which is based on the Hodgkin-Huxley type neurons and considers reciprocal glutaminergic projections between the lateral hypothalamus and the prefrontal cortex. Orexin is released as a neuromodulator and is required to keep the neurons firing, which corresponds to the wake state. When orexin is depleted the neurons are getting silent as observed in the sleep state. They can be reactivated by the circadian signal from the suprachiasmatic nucleus and/or external stimuli (alarm clock). Orexin projections to the thalamocortical neurons also can account for their transition from tonic firing activity during wakefulness to synchronized burst discharges during sleep.

  3. Modeling Vortex Generators in a Navier-Stokes Code

    NASA Technical Reports Server (NTRS)

    Dudek, Julianne C.

    2011-01-01

    A source-term model that simulates the effects of vortex generators was implemented into the Wind-US Navier-Stokes code. The source term added to the Navier-Stokes equations simulates the lift force that would result from a vane-type vortex generator in the flowfield. The implementation is user-friendly, requiring the user to specify only three quantities for each desired vortex generator: the range of grid points over which the force is to be applied and the planform area and angle of incidence of the physical vane. The model behavior was evaluated for subsonic flow in a rectangular duct with a single vane vortex generator, subsonic flow in an S-duct with 22 corotating vortex generators, and supersonic flow in a rectangular duct with a counter-rotating vortex-generator pair. The model was also used to successfully simulate microramps in supersonic flow by treating each microramp as a pair of vanes with opposite angles of incidence. The validation results indicate that the source-term vortex-generator model provides a useful tool for screening vortex-generator configurations and gives comparable results to solutions computed using gridded vanes.

  4. Finite difference modeling of rotor flows including wake effects

    NASA Technical Reports Server (NTRS)

    Caradonna, F. X.; Desopper, A.; Tung, C.

    1982-01-01

    Rotary wing finite difference methods are investigated. The main concern is the specification of boundary conditions to properly account for the effect of the wake on the blade. Examples are given of an approach where wake effects are introduced by specifying an equivalent angle of attack. An alternate approach is also given where discrete vortices are introduced into the finite difference grid. The resulting computations of hovering and high advance ratio cases compare well with experiment. Some consideration is also given to the modeling of low to moderate advance ratio flows.

  5. Wake model for helicopter rotors in high speed flight

    NASA Technical Reports Server (NTRS)

    Johnson, Wayne R.

    1988-01-01

    Two alternative approaches are developed to calculate blade-vortex interaction airloads on helicopter rotors: second order lifting-line theory, and a lifting surface theory correction. The common approach of using a larger vortex core radius to account for lifting-surface effects is quantified. The second order lifting-line theory also improves the modeling of yawed flow and swept tips. Calculated results are compared with wind tunnel measurements of lateral flapping, and with flight test measurements of blade section lift on SA349/2 and H-34 helicopter rotors. The tip vortex core radius required for good correlation with the flight test data is about 20 percent chord, which is within the range of measured viscous core sizes for helicopter rotors.

  6. Modeling Vortex Generators in the Wind-US Code

    NASA Technical Reports Server (NTRS)

    Dudek, Julianne C.

    2010-01-01

    A source term model which simulates the effects of vortex generators was implemented into the Wind-US Navier Stokes code. The source term added to the Navier-Stokes equations simulates the lift force which would result from a vane-type vortex generator in the flowfield. The implementation is user-friendly, requiring the user to specify only three quantities for each desired vortex generator: the range of grid points over which the force is to be applied and the planform area and angle of incidence of the physical vane. The model behavior was evaluated for subsonic flow in a rectangular duct with a single vane vortex generator, supersonic flow in a rectangular duct with a counterrotating vortex generator pair, and subsonic flow in an S-duct with 22 co-rotating vortex generators. The validation results indicate that the source term vortex generator model provides a useful tool for screening vortex generator configurations and gives comparable results to solutions computed using a gridded vane.

  7. The modelling of symmetric airfoil vortex generators

    NASA Technical Reports Server (NTRS)

    Reichert, B. A.; Wendt, B. J.

    1996-01-01

    An experimental study is conducted to determine the dependence of vortex generator geometry and impinging flow conditions on shed vortex circulation and crossplane peak vorticity for one type of vortex generator. The vortex generator is a symmetric airfoil having a NACA 0012 cross-sectional profile. The geometry and flow parameters varied include angle-of-attack alfa, chordlength c, span h, and Mach number M. The vortex generators are mounted either in isolation or in a symmetric counter-rotating array configuration on the inside surface of a straight pipe. The turbulent boundary layer thickness to pipe radius ratio is delta/R = 0. 17. Circulation and peak vorticity data are derived from crossplane velocity measurements conducted at or about 1 chord downstream of the vortex generator trailing edge. Shed vortex circulation is observed to be proportional to M, alfa, and h/delta. With these parameters held constant, circulation is observed to fall off in monotonic fashion with increasing airfoil aspect ratio AR. Shed vortex peak vorticity is also observed to be proportional to M, alfa, and h/delta. Unlike circulation, however, peak vorticity is observed to increase with increasing aspect ratio, reaching a peak value at AR approx. 2.0 before falling off.

  8. Analytical modeling of turbine wakes in yawed conditions

    NASA Astrophysics Data System (ADS)

    Bastankhah, Majid; Porté-Agel, Fernando

    2016-04-01

    Increasing wind energy production has become a unanimous plan for virtually all the developed countries. In addition to constructing new wind farms, this goal can be achieved by making wind farms more efficient. Control strategies in wind farms, such as manipulating the yaw angle of the turbines, have the potential to make wind farms more efficient. Costly numerical simulations or measurements cannot be, however, employed to assess the viability of this strategy in the numerous different scenarios happening in real wind farms. In this study, we aim to develop an inexpensive and simple analytical model that is able for the first time to predict the whole wake of a yawed turbine with an acceptable accuracy. The proposed analytical model is built upon the simplified version of the Reynolds-averaged Navier-Stokes equations. Apart from the ability of the model to predict wake flows in yawed conditions, it can provide a better understanding of turbine wakes in this complex situation. For example, it can give valuable insights on how the wake deflection varies by changing turbine and incoming flow characteristics, such as the thrust coefficient of the turbine or the ambient turbulence.

  9. CFD modeling and analysis of rotor wake in hover interacting with a ground plane

    NASA Astrophysics Data System (ADS)

    Kalra, Tarandeep Singh

    The action of the rotor wake on loose sediment on the ground is primarily responsible for inducing the rotorcraft brownout phenomenon. Therefore, any simulation of brownout must be capable of accurately predicting the velocity field induced by the rotor when it is operating in ground effect. This work attempts to use a compressible, structured, overset Reynolds-Averaged Navier-Stokes (RANS) based solver to simulate hovering rotors in ground effect (IGE) to demonstrate the capability of the code to provide accurate tip vortex flow field predictions, and provide a good understanding of the ground-wake interactions. The computations are performed for a micro-scale rotor (0.086m radius, aspect ratio of 4.387 operating at a tip Mach number of 0.08 and Reynolds number of 32,500) and a sub-scale rotor (0.408m radius, aspect ratio of 9.132 operating at a tip Mach number of 0.24 and Reynolds number of 250,000) in order to compare to experimental measurements. The micro-scale rotor has a rectangular tip shape and is simulated three rotor heights: 1.5R, 1.0R and 0.5R above ground (R = Rotor radius). The sub-scale rotor is simulated at one particular rotor height (i.e. 1R) but with four different tip shapes: rectangular, swept, BERP-like and slotted tip. Various mesh placement strategies are devised to efficiently capture the path of the tip vortices for both regimes. The micro-scale rotor simulations are performed using the Spalart Allmaras (S-A) turbulence model. The examination of the IGE tip vortex flow field suggests high degree of instabilities close to the ground. In addition, the induced velocities arising from the proximity of the rotor tip vortices causes flow separation at the ground. The sub-scale rotor simulations show a smeared out flow field even at early wake ages due to excessive turbulence levels. The distance function in the S-A turbulence model is modified using the Delayed Detached Eddy Simulation (DDES) approach and a correction to length scaling is

  10. A free wake method for performance prediction of VAWT

    NASA Astrophysics Data System (ADS)

    Ilin, S.; Dumitrescu, H.; Cardos, V.; Dumitrache, A.

    2012-09-01

    Based on the lifting line theory and a free vortex wake model, a method including dynamic stall effects is presented for predicting the performance of a three-dimensional vertical-axis wind turbine (VAWT). A vortex model is used in which the wake is composed of trailing streamwise and shedding spanwise vortices, whose strengths are equal to the change in the bound vortex strength as dictated by Helmholtz and Kelvin's theorems. Performance parameters are calculated by application of the Biot-Savart law along with the Kutta-Joukowski theorem and a semi-empirical dynamic stall model. Predictions are shown to compare favorably with existing experimental data.

  11. Field measurements in the wake of a model wind turbine

    NASA Astrophysics Data System (ADS)

    Pol, Suhas; Taylor, Amelia; Bilbao, Argenis; Doostalab, Ali; Novoa, Santiago; Westergaard, Carsten; Hussain, Fazle; Sheng, Jian; Ren, Beibei; Giesselmann, Michael; Glauser, Mark; Castillo, Luciano

    2014-06-01

    As a first step to study the dynamics of a wind farm' we experimentally explored the flow field behind a single wind turbine of diameter 1.17 m at a hub height of 6.25 m. A 10 m tower upstream of the wind farm characterizes the atmospheric conditions and its influence on the wake evolution. A vertical rake of sonic anemometers is clustered around the hub height on a second tower' 6D downstream of the turbine. We present preliminary observations from a 1- hour block of data recorded in near-neutral atmospheric conditions. The ratio of the standard deviation of power to the inflow velocity is greater than three' revealing adverse effects of inflow turbulence on the power and load fluctuations. Furthermore' the wake defect and Reynolds stress and its gradient are pronounced at 6D. The flux of energy due to Reynolds stresses is similar to that reported in wind tunnel studies. The swirl and mixing produces a constant temperature wake which results in a density jump across the wake interface. Further field measurements will explore the dynamics of a model wind farm' including the effects of atmospheric variability.

  12. Confining bond rearrangement in the random center vortex model

    NASA Astrophysics Data System (ADS)

    Altarawneh, Derar; Höllwieser, Roman; Engelhardt, Michael

    2016-03-01

    We present static meson-meson and baryon-antibaryon potentials in Z (2 ) and Z (3 ) random center vortex models for the infrared sector of Yang-Mills theory, i.e., hypercubic lattice models of random vortex world surfaces. In particular, we calculate multiple Polyakov loop correlators corresponding to static meson-meson or baryon-antibaryon configurations in a center vortex background and observe that their expectation values follow the minimal area law, displaying bond rearrangement behavior, a characteristic expected for the confining dynamics of the strong interaction. The static meson-meson and baryon-antibaryon potentials are compared with theoretical predictions and lattice QCD simulations.

  13. A Hydrodynamic Model of Lateral Line of Fish for Vortex Sensing

    NASA Astrophysics Data System (ADS)

    Ren, Zheng; Mohseni, Kamran

    2010-11-01

    In this study, potential flow theory is adopted to model flow field around a fish-like body in the presence of a Karman vortex street moving along one side of the body. The external flow field is modeled in two dimensions while a fish-like body is obtained by Joukowski Transformation. Pressure distribution on the body surface is computed according to the model. The lateral line trunk canal (LLTC) of a fish is modeled as a slight tube along its body with pores uniformly distributed along the surface of the tube. With the external flow known, the flow inside LLTC driven by the pressure gradient between a pair of consecutive pores has been solved analytically. Furthermore, parametric studies are performed in order to determine the effect of various flow parameters on the pressure distribution on body surface and flow distribution inside the LLTC. The results indicate that the signature of the vortex street can be found by measuring the flow velocity distribution inside the LLTC, which serves as a possible elucidation on how a fish sense the vortex street from the flow filed inside its LLTC. Hence, it is reasonable to suggest that the LLTC of a fish is able to detect the signature of the wake vortices shed by a nearby object or fish.

  14. System Identification of a Vortex Lattice Aerodynamic Model

    NASA Technical Reports Server (NTRS)

    Juang, Jer-Nan; Kholodar, Denis; Dowell, Earl H.

    2001-01-01

    The state-space presentation of an aerodynamic vortex model is considered from a classical and system identification perspective. Using an aerodynamic vortex model as a numerical simulator of a wing tunnel experiment, both full state and limited state data or measurements are considered. Two possible approaches for system identification are presented and modal controllability and observability are also considered. The theory then is applied to the system identification of a flow over an aerodynamic delta wing and typical results are presented.

  15. Stably stratified building wakes

    SciTech Connect

    Kothari, K.M.; Peterka, J.A.; Meroney, R.N.

    1980-01-01

    The velocity and temperature wake behind an isolated building placed in a stably stratified turbulent boundary layer has been investigated utilizing wind tunnel tests and mathematical analysis. The mean velocity and mean temperature decrease but turbulence intensity and temperature fluctuation intensity increase as a result of the momentum wake. However, the vortex wake increases mean velocity and mean temperature, and decreases turbulence intensity and temperature fluctuation intensity along the centerline of the wake.

  16. Time-resolved particle image velocimetry measurements of vortex and shear layer dynamics in the near wake of a tethered sphere

    NASA Astrophysics Data System (ADS)

    van Hout, R.; Katz, A.; Greenblatt, D.

    2013-07-01

    The coupling between shear layer, near wake dynamics, and structural oscillations downstream of a tethered spherical pendulum undergoing vortex induced vibrations (VIV) has been experimentally investigated using time-resolved particle image velocimetry in a wind tunnel. One quarter of the sphere was imaged in the field of view (spatial resolution 0.043D) that extended to 1.17D from the sphere's center (D is the sphere diameter). Reynolds numbers based on D, ranged between 493 ≤ Re ≤ 2218 and reduced velocities between 3.18 ≤ U* ≤ 14.1, covering a non-oscillating sphere, periodic oscillations, and the onset of non-stationary sphere oscillations. After the first Hopf bifurcation, the sphere exhibited large amplitude periodic oscillations and the near-wake vortices periodically interacted with the sphere and flapping shear layer. At U* = 5.97, a "secondary" counterclockwise rotating vortex seemed to facilitate shear layer pinch-off. In agreement with the onset of shear layer instabilities for a stationary sphere, only at Re = 2218 power spectra of velocity fluctuations inside the shear layer indicated a weak, broad frequency peak centered at 15 Hz similar as those measured for stationary cylinders and spheres. This peak was consistent with the results of linear instability theory indicating that despite the inherent three-dimensionality of the shear layer, its instability characteristics (at least for the Re investigated here) can be considered to be quasi-two-dimensional. Small-scale, near-wake structures were observed in the instantaneous swirling strength maps at all U* and it is conjectured here that their interaction with the sphere and separating shear layer is the feedback mechanism through which VIV occurs and is sustained.

  17. Cylinder wakes in flowing soap films.

    PubMed

    Vorobieff, P; Ecke, R E

    1999-09-01

    We present an experimental characterization of cylinder wakes in flowing soap films. From instantaneous velocity and thickness fields, we find the vortex-shedding frequency, mean-flow velocity, and mean-film thickness. Using the empirical relationship between the Reynolds and Strouhal numbers obtained for cylinder wakes in three dimensions, we estimate the effective soap-film viscosity and its dependence on film thickness. We also compare the decay of vorticity with that in a simple Rankine vortex model with a dissipative term to account for air drag. PMID:11970100

  18. Cylinder wakes in flowing soap films

    SciTech Connect

    Vorobieff, P.; Ecke, R.E. ); Vorobieff, P. )

    1999-09-01

    We present an experimental characterization of cylinder wakes in flowing soap films. From instantaneous velocity and thickness fields, we find the vortex-shedding frequency, mean-flow velocity, and mean-film thickness. Using the empirical relationship between the Reynolds and Strouhal numbers obtained for cylinder wakes in three dimensions, we estimate the effective soap-film viscosity and its dependence on film thickness. We also compare the decay of vorticity with that in a simple Rankine vortex model with a dissipative term to account for air drag. [copyright] [ital 1999] [ital The American Physical Society

  19. A Critical Review of the Transport and Decay of Wake Vortices in Ground Effect

    NASA Technical Reports Server (NTRS)

    Sarpkaya, T.

    2004-01-01

    This slide presentation reviews the transport and decay of wake vortices in ground effect and cites a need for a physics-based parametric model. The encounter of a vortex with a solid body is always a complex event involving turbulence enhancement, unsteadiness, and very large gradients of velocity and pressure. Wake counter in ground effect is the most dangerous of them all. The interaction of diverging, area-varying, and decaying aircraft wake vortices with the ground is very complex because both the vortices and the flow field generated by them are altered to accommodate the presence of the ground (where there is very little room to maneuver) and the background turbulent flow. Previous research regarding vortex models, wake vortex decay mechanisms, time evolution within in ground effect of a wake vortex pair, laminar flow in ground effect, and the interaction of the existing boundary layer with a convected vortex are reviewed. Additionally, numerical simulations, 3-dimensional large-eddy simulations, a probabilistic 2-phase wake vortex decay and transport model and a vortex element method are discussed. The devising of physics-based, parametric models for the prediction of (operational) real-time response, mindful of the highly three-dimensional and unsteady structure of vortices, boundary layers, atmospheric thermodynamics, and weather convective phenomena is required. In creating a model, LES and field data will be the most powerful tools.

  20. A Hybrid Vortex Sheet / Point Vortex Model for Unsteady Separated Flows

    NASA Astrophysics Data System (ADS)

    Darakananda, Darwin; Eldredge, Jeff D.; Colonius, Tim; Williams, David R.

    2015-11-01

    The control of separated flow over an airfoil is essential for obtaining lift enhancement, drag reduction, and the overall ability to perform high agility maneuvers. In order to develop reliable flight control systems capable of realizing agile maneuvers, we need a low-order aerodynamics model that can accurately predict the force response of an airfoil to arbitrary disturbances and/or actuation. In the present work, we integrate vortex sheets and variable strength point vortices into a method that is able to capture the formation of coherent vortex structures while remaining computationally tractable for control purposes. The role of the vortex sheet is limited to tracking the dynamics of the shear layer immediately behind the airfoil. When parts of the sheet develop into large scale structures, those sections are replaced by variable strength point vortices. We prevent the vortex sheets from growing indefinitely by truncating the tips of the sheets and transfering their circulation into nearby point vortices whenever the length of sheet exceeds a threshold. We demonstrate the model on a variety of canonical problems, including pitch-up and impulse translation of an airfoil at various angles of attack. Support by the U.S. Air Force Office of Scientific Research (FA9550-14-1-0328) with program manager Dr. Douglas Smith is gratefully acknowledged.

  1. Volumetric LiDAR scanning of a wind turbine wake and comparison with a 3D analytical wake model

    NASA Astrophysics Data System (ADS)

    Carbajo Fuertes, Fernando; Porté-Agel, Fernando

    2016-04-01

    A correct estimation of the future power production is of capital importance whenever the feasibility of a future wind farm is being studied. This power estimation relies mostly on three aspects: (1) a reliable measurement of the wind resource in the area, (2) a well-established power curve of the future wind turbines and, (3) an accurate characterization of the wake effects; the latter being arguably the most challenging one due to the complexity of the phenomenon and the lack of extensive full-scale data sets that could be used to validate analytical or numerical models. The current project addresses the problem of obtaining a volumetric description of a full-scale wake of a 2MW wind turbine in terms of velocity deficit and turbulence intensity using three scanning wind LiDARs and two sonic anemometers. The characterization of the upstream flow conditions is done by one scanning LiDAR and two sonic anemometers, which have been used to calculate incoming vertical profiles of horizontal wind speed, wind direction and an approximation to turbulence intensity, as well as the thermal stability of the atmospheric boundary layer. The characterization of the wake is done by two scanning LiDARs working simultaneously and pointing downstream from the base of the wind turbine. The direct LiDAR measurements in terms of radial wind speed can be corrected using the upstream conditions in order to provide good estimations of the horizontal wind speed at any point downstream of the wind turbine. All this data combined allow for the volumetric reconstruction of the wake in terms of velocity deficit as well as turbulence intensity. Finally, the predictions of a 3D analytical model [1] are compared to the 3D LiDAR measurements of the wind turbine. The model is derived by applying the laws of conservation of mass and momentum and assuming a Gaussian distribution for the velocity deficit in the wake. This model has already been validated using high resolution wind-tunnel measurements

  2. Center vortex model for Sp(2) Yang-Mills theory

    SciTech Connect

    Engelhardt, M.; Sperisen, B.

    2006-12-15

    The question whether the center vortex picture of the strongly interacting vacuum can encompass the infrared dynamics of both SU(2) as well as Sp(2) Yang-Mills theory is addressed. These two theories contain the same center vortex degrees of freedom, and yet exhibit deconfinement phase transitions of different order. This is argued to be caused by the effective action governing the vortices being different in the two cases. To buttress this argument, a random vortex world-surface model is constructed which reproduces available lattice data characterizing Sp(2) Yang-Mills confinement properties. A new effective action term which can be interpreted in terms of a vortex stickiness serves to realize a first-order deconfinement phase transition, as found in Sp(2) Yang-Mills theory. Predictions are given for the behavior of the spatial string tension at finite temperatures.

  3. Point vortex model for prediction of sound generated by a wing with flap interacting with a passing vortex.

    PubMed

    Manela, A; Huang, L

    2013-04-01

    Acoustic signature of a rigid wing, equipped with a movable downstream flap and interacting with a line vortex, is studied in a two-dimensional low-Mach number flow. The flap is attached to the airfoil via a torsion spring, and the coupled fluid-structure interaction problem is analyzed using thin-airfoil methodology and application of the emended Brown and Michael equation. It is found that incident vortex passage above the airfoil excites flap motion at the system natural frequency, amplified above all other frequencies contained in the forcing vortex. Far-field radiation is analyzed using Powell-Howe analogy, yielding the leading order dipole-type signature of the system. It is shown that direct flap motion has a negligible effect on total sound radiation. The characteristic acoustic signature of the system is dominated by vortex sound, consisting of relatively strong leading and trailing edge interactions of the airfoil with the incident vortex, together with late-time wake sound resulting from induced flap motion. In comparison with the counterpart rigid (non-flapped) configuration, it is found that the flap may act as sound amplifier or absorber, depending on the value of flap-fluid natural frequency. The study complements existing analyses examining sound radiation in static- and detached-flap configurations. PMID:23556563

  4. High-resolution numerical modeling of mesoscale island wakes and sensitivity to static topographic relief data

    NASA Astrophysics Data System (ADS)

    Nunalee, C. G.; Horváth, Á.; Basu, S.

    2015-08-01

    Recent decades have witnessed a drastic increase in the fidelity of numerical weather prediction (NWP) modeling. Currently, both research-grade and operational NWP models regularly perform simulations with horizontal grid spacings as fine as 1 km. This migration towards higher resolution potentially improves NWP model solutions by increasing the resolvability of mesoscale processes and reducing dependency on empirical physics parameterizations. However, at the same time, the accuracy of high-resolution simulations, particularly in the atmospheric boundary layer (ABL), is also sensitive to orographic forcing which can have significant variability on the same spatial scale as, or smaller than, NWP model grids. Despite this sensitivity, many high-resolution atmospheric simulations do not consider uncertainty with respect to selection of static terrain height data set. In this paper, we use the Weather Research and Forecasting (WRF) model to simulate realistic cases of lower tropospheric flow over and downstream of mountainous islands using the default global 30 s United States Geographic Survey terrain height data set (GTOPO30), the Shuttle Radar Topography Mission (SRTM), and the Global Multi-resolution Terrain Elevation Data set (GMTED2010) terrain height data sets. While the differences between the SRTM-based and GMTED2010-based simulations are extremely small, the GTOPO30-based simulations differ significantly. Our results demonstrate cases where the differences between the source terrain data sets are significant enough to produce entirely different orographic wake mechanics, such as vortex shedding vs. no vortex shedding. These results are also compared to MODIS visible satellite imagery and ASCAT near-surface wind retrievals. Collectively, these results highlight the importance of utilizing accurate static orographic boundary conditions when running high-resolution mesoscale models.

  5. Geometries of Karman Vortex Street

    NASA Astrophysics Data System (ADS)

    Roushan, Pedram; Wu, X. L.

    2004-03-01

    The Bénard-von Kármán vortex street is studied in a flowing soap film channel. The two-dimensional fluid flow in the film allows stable vortex streets to be generated and investigated over a broad range of Reynolds numbers, 10wake region, the current study focuses on the entire near-wake using imaging analysis. The envelop of the Karman vortex street is analyzed for different diameter rods, which span more than two orders of magnitude in their diameters. The parameters that characterize the envelop of the vortex street, such as the growth rate and the saturation amplitude, are measured for different Reynolds numbers. It is found that all of the curves representing the envelope can be collapsed onto a single master curve, suggesting that the shape of Karman vortex streets is universal, independent of Re. We construct a simple model that takes into account the energy transfer into vortices by periodic oscillations of transverse velocity fluctuations beneath the rod. This simple model not only explains the near wake shape of the street, but also allows other useful information such as the kinetic energy injected into the fluid and the drag coefficient CD to be extracted.

  6. Wind flow characteristics in the wakes of large wind turbines. Volume 1: Analytical model development

    NASA Technical Reports Server (NTRS)

    Eberle, W. R.

    1981-01-01

    A computer program to calculate the wake downwind of a wind turbine was developed. Turbine wake characteristics are useful for determining optimum arrays for wind turbine farms. The analytical model is based on the characteristics of a turbulent coflowing jet with modification for the effects of atmospheric turbulence. The program calculates overall wake characteristics, wind profiles, and power recovery for a wind turbine directly in the wake of another turbine, as functions of distance downwind of the turbine. The calculation procedure is described in detail, and sample results are presented to illustrate the general behavior of the wake and the effects of principal input parameters.

  7. Infrared imaging simulation and detection of ship wake

    NASA Astrophysics Data System (ADS)

    Yang, Li; Chen, Xuan; Chang, Shizheng; Xu, Enchi; Wang, Xingyu; Wang, Ye; Zhao, Xiaolong; Du, Yongchen; Kou, Wei; Fan, Chunli

    2015-10-01

    The thermal wake would be formed owing to the cooling water or exhaust heat discharged by ship, and the cold wake could be formed by the cool water in the lower part of sea stirred up by the ship propeller or vortexes. Owing to the difference of surface temperature and emissivity between the ship wake and the surrounding ocean the ship wake will be easily detected by the infrared detecting system. The wave of wake also could be detected by the difference of reflected radiance between the background and the Kelvin wake of ship. In this paper the simulating models of infrared imaging of ship wake are developed based on the selfradiation of wake, the reflected radiance of the sky and sun and the transmitted radiance of atmosphere, and the infrared imaging signatures of ship wake are investigated. The results show that the infrared imaging signatures of ship wake can be really simulated by the models proposed in this paper. The effects of the detecting height, the angle of view, the NETD of detector and the temperature of wake on the infrared imaging signatures of ship wake are studied. The temperature difference between the ship wake and surrounding ocean is a main fact which effects on the detecting distance. The infrared imaging signatures of ship wake in 8-14μm wave band is stronger than that in 2-5μm wave band whenever the temperature of ship wake is warmer or cooler than the surrounding ocean. Further, the infrared imaging of thermal wake is investigated in the homogenous water and temperature stratified water at different speed of a ship and different flow rate and depth of the discharged water in a water tank. The spreading and decaying laws of infrared signature of ship wake are obtained experimentally. The results obtained in this paper have an important application in the infrared remote sensing of ship wake.

  8. The development of a prescribed wake model for performance prediction in steady yawed flow

    SciTech Connect

    Robison, D.J.; Coton, F.N.; Galbraith, R.A.M.; Vezza, M.

    1995-09-01

    A new prescribed wake model for horizontal axis wind turbines (HAWTs) is presented. The model`s wake geometry is derived from simple prescriptive functions, based on momentum theory, defining the three-dimensional wake development from the near to the far field. The work described herein considers the analysis of both steady axial and yawed flow conditions. The detailed modelling of the yawed case is still in the initial stages, it is envisaged that this will eventually include fully unsteady aerodynamic effects. Model validation is by comparison with both experimental data and results from a free wake model.

  9. Information Requirements for Supervisory Air Traffic Controllers in Support of a Mid-Term Wake Vortex Departure System

    NASA Technical Reports Server (NTRS)

    Lohr, Gary W.; Williams, Daniel M.; Trujillo, Anna C.; Johnson, Edward J.; Domino, David A.

    2008-01-01

    A concept focusing on wind dependent departure operations has been developed the current version of this concept is called the Wake Turbulence Mitigation for Departures (WTMD). This concept takes advantage the fact that cross winds of sufficient velocity blow wakes generated by "heavy" and B757 category aircraft on the downwind runway away from the upwind runway. Supervisory Air Traffic Controllers would be responsible for authorization of the Procedure. An investigation of the information requirements necessary to for Supervisors to approve monitor and terminate the Procedure was conducted. Results clearly indicated that the requisite information is currently available in air traffic control towers and that additional information was not required.

  10. Investigation of Some Wake Vortex Characteristics of an Inclined Ogive-Cylinder Body at Mach Number 2

    NASA Technical Reports Server (NTRS)

    Jorgensen, Leland H; Perkins, Edward W

    1958-01-01

    For a body consisting of a fineness-ratio-3 ogival nose tangent to a cylindrical afterbody 7.3 diameters long, pitot-pressure distributions in the flow field, pressure distributions over the body, and downwash distributions along a line through the vortex centers have been measured for angles of attack to 20 degrees. The Reynolds numbers, based on body diameter, were 0.15 x 10 to the 6th power and 0.44 x 10 to the 6th power. Comparisons of computed and measured vortex paths and downwash distributions are made. (author)

  11. Wake Development of a Model Vertical Axis Wind Turbine

    NASA Astrophysics Data System (ADS)

    Kadum, Hawwa; Friedman, Sasha; Camp, Elizabeth; Cal, Rau'l.

    2015-11-01

    At the Portland State University wind tunnel facility, an experiment is conducted to observe the downstream development of the wake past a model vertical axis wind turbine (VAWT). The flow domain is composed of streamwise-spanwise planes at mid-height of the VAWT rotor and data is obtained via particle image velocimetry (PIV). The flow field is assessed by analyzing contours of mean velocities and the full Reynolds stress tensor. Furthermore, profiles of the aforementioned quantities and flow parameters are discussed in the context of downstream evolution/flow development.

  12. Implications of MAVEN Mars near-wake measurements and models

    NASA Astrophysics Data System (ADS)

    Luhmann, J. G.; Dong, Chuanfei; Ma, Yingjuan; Curry, S. M.; Mitchell, D.; Espley, J.; Connerney, J.; Halekas, J.; Brain, D. A.; Jakosky, B. M.; Mazelle, C.

    2015-11-01

    Mars is typically viewed as a member of the category of weakly magnetized planets, with a largely induced magnetosphere and magnetotail produced by the draped fields of the solar wind interaction. However, selected Mars Atmosphere and Volatile EvolutioN Mission (MAVEN) suprathermal electron and magnetic field observations in the near wake, sampled along its elliptical orbit during the early prime mission at altitudes ranging from its ~150 km periapsis to the tail magnetosheath, reinforce a picture seen in an MHD model where magnetic fields are rooted in the planet throughout much of the Martian magnetotail.

  13. Measuring wind turbine wakes and unsteady loading in a micro wind farm model

    NASA Astrophysics Data System (ADS)

    Bossuyt, Juliaan; Meneveau, Charles; Meyers, Johan

    2014-11-01

    Very large wind farms, approximating the ``infinite'' asymptotic limit, are often studied with LES using periodic boundary conditions. In order to create an experimental realization of such large wind-turbine arrays in a wind tunnel experiment including over 100 turbines, a very small-scale turbine model based on a 3 cm diameter porous disk is designed. The porous disc matches a realistic thrust coefficient between 0.75--0.85, and the far wake flow characteristics of a rotating wind turbine. As a first step, we characterize the properties of a single model turbine. Hot-wire measurements are performed for uniform inflow conditions with different background turbulence intensity levels. Strain gage measurements are used to measure the mean value and power spectra of the thrust force, power output and wind velocity in front of the turbine. The dynamics of the wind turbine are modeled making it possible to measure force spectra at least up to the natural frequency of the model. This is shown by reproducing the -5/3 spectrum from the incoming flow and the vortex shedding signatures of an upstream obstruction. An array with a large number of these instrumented model turbines is placed in JHU's Corrsin wind tunnel, to study effects of farm layout on total power output and turbine loading. Work supported by ERC (ActiveWindFarms, Grant No: 306471), and by NSF (CBET-113380 and IIA-1243482).

  14. Transition and Turbulence Modeling for Blunt-Body Wake Flows

    NASA Technical Reports Server (NTRS)

    Nance, Robert P.; Horvath, Thomas J.; Hassan, H. A.

    1997-01-01

    This study attempts t o improve the modeling and computational prediction of high- speed transitional wake flows. The recently developed kappa - zeta (Enstrophy) turbulence model is coupled with a newly developed transition prediction method and implemented in an implicit flow solver well-suited to hypersonic flows. In this model, transition onset is determined as part of the solution. Results obtained using the new model for a 70- deg blunted cone/sting geometry demonstrate better agreement with experimental heat- transfer measurements when compared to laminar calculations as well as solutions using the kappa - omega model. Results are also presented for the situation where transition onset is preselected. It is shown that, in this case, results are quite sensitive to location of the transition point.

  15. Development of test methods for scale model simulation of aerial applications in the NASA Langley Vortex Research Facility. [agricultural aircraft

    NASA Technical Reports Server (NTRS)

    Jordan, F. L., Jr.

    1980-01-01

    As part of basic research to improve aerial applications technology, methods were developed at the Langley Vortex Research Facility to simulate and measure deposition patterns of aerially-applied sprays and granular materials by means of tests with small-scale models of agricultural aircraft and dynamically-scaled test particles. Interactions between the aircraft wake and the dispersed particles are being studied with the objective of modifying wake characteristics and dispersal techniques to increase swath width, improve deposition pattern uniformity, and minimize drift. The particle scaling analysis, test methods for particle dispersal from the model aircraft, visualization of particle trajectories, and measurement and computer analysis of test deposition patterns are described. An experimental validation of the scaling analysis and test results that indicate improved control of chemical drift by use of winglets are presented to demonstrate test methods.

  16. Wake structure of a deformable Joukowski airfoil

    NASA Astrophysics Data System (ADS)

    Ysasi, Adam; Kanso, Eva; Newton, Paul K.

    2011-10-01

    We examine the vortical wake structure shed from a deformable Joukowski airfoil in an unbounded volume of inviscid and incompressible fluid. The deformable airfoil is considered to model a flapping fish. The vortex shedding is accounted for using an unsteady point vortex model commonly referred to as the Brown-Michael model. The airfoil’s deformations and rotations are prescribed in terms of a Jacobi elliptic function which exhibits, depending on a dimensionless parameter m, a range of periodic behaviors from sinusoidal to a more impulsive type flapping. Depending on the parameter m and the Strouhal number, one can identify five distinct wake structures, ranging from arrays of isolated point vortices to vortex dipoles and tripoles shed into the wake with every half-cycle of the airfoil flapping motion. We describe these regimes in the context of other published works which categorize wake topologies, and speculate on the importance of these wake structures in terms of periodic swimming and transient maneuvers of fish.

  17. Effects of cylinder Reynolds number on the turbulent horseshoe vortex system and near wake of a surface-mounted circular cylinder

    NASA Astrophysics Data System (ADS)

    Kirkil, Gokhan; Constantinescu, George

    2015-07-01

    The turbulent horseshoe vortex (HV) system and the near-wake flow past a circular cylinder mounted on a flat bed in an open channel are investigated based on the results of eddy-resolving simulations and supporting flow visualizations. Of particular interest are the changes in the mean flow and turbulence statistics within the HV region as the necklace vortices wrap around the cylinder's base and the variation of the mean flow and turbulence statistics in the near wake, in between the channel bed and the free surface. While it is well known that the drag crisis induces important changes in the flow past infinitely long circular cylinders, the changes are less understood and more complex for the case of flow past a surface-mounted cylinder. This is because even at very high cylinder Reynolds numbers, ReD, the flow regime remains subcritical in the vicinity of the bed surface due to the reduction of the incoming flow velocity within the bottom boundary layer. The paper provides a detailed discussion of the changes in the flow physics between cylinder Reynolds numbers at which the flow in the upstream part of the separated shear layers (SSLs) is laminar (ReD = 16 000, subcritical flow regime) and Reynolds numbers at which the transition occurs inside the attached boundary layers away from the bed and the flow within the SSLs is turbulent (ReD = 5 ∗ 105, supercritical flow regime). The changes between the two regimes in the dynamics and level of coherence of the large-scale coherent structures (necklace vortices, vortex tubes shed in the SSLs and roller vortices shed in the wake) and their capacity to induce high-magnitude bed friction velocities in the mean and instantaneous flow fields and to amplify the near-bed turbulence are analyzed. Being able to quantitatively and qualitatively describe these changes is critical to understand Reynolds-number-induced scale effects on sediment erosion mechanisms around cylinders mounted on a loose bed, which is a problem of

  18. Microburst Simulation via Vortex-Ring and Turbulent Jet Models.

    NASA Astrophysics Data System (ADS)

    Wan, Tung

    Microbursts, suggested as primary causes of many aircraft fatal crashes, are the subject of this research. A microburst, or low-level intense wind shear, is generated by a thunderstorm or a small rain cloud, and presents hazardous conditions for aircraft during take-off and landing maneuvers. Recently released data show that a microburst resembles a transient vortex ring. Three microburst models have been constructed in this study. First, the turbulent jet model encompasses a free jet at high altitude and a wall jet near the ground surface. Second, the vortex ring model is a combination of a primary and an image vortex ring, with an inviscid -viscous interaction at the central axial and surface regions. An unsteady version of this model is also provided by solving the trajectory equation with the Direct Formal Integration (DFI) method or with the Runge-Kutta method. Third and finally, the complete unsteady microburst model equations (conservation of mass, momentum, and energy), or what has been referred to as the Navier-Stokes model formulation, are solved by the successive over relaxation method. Results show that the microburst can be simulated accurately by impulsive turbulent jet at high altitude and a transient vortex ring in mid-air and near the ground surface. In addition to improved understanding of the physical nature of microbursts, the models presented here can also be used for flight simulation and the pilot training purposes.

  19. Impacts of Wake Effect and Time Delay on the Dynamic Analysis of Wind Farms Models

    ERIC Educational Resources Information Center

    El-Fouly, Tarek H. M.; El-Saadany, Ehab F.; Salama, Magdy M. A.

    2008-01-01

    This article investigates the impacts of proper modeling of the wake effects and wind speed delays, between different wind turbines' rows, on the dynamic performance accuracy of the wind farms models. Three different modeling scenarios were compared to highlight the impacts of wake effects and wind speed time-delay models. In the first scenario,…

  20. An extension of the local momentum theory to a distorted wake model of a hovering rotor

    NASA Technical Reports Server (NTRS)

    Kawachi, K.

    1981-01-01

    The local momentum theory is based on the instantaneous balance between the fluid momentum and the blade elemental lift at a local station in the rotor rotational plane. Therefore, the theory has the capability of evaluating time wise variations of air loading and induced velocity distributions along a helicopter blade span. Unlike a complex vortex theory, this theory was developed to analyze the instantaneous induced velocity distribution effectively. The boundaries of this theory and a computer program using this theory are discussed. A concept introduced into the theory is the effect of the rotor wake contraction in hovering flight. A comparison of this extended local momentum theory with a prescribed wake vortex theory is also presented. The results indicate that the extended local momentum theory has the capability of achieving a level of accuracy similar to that of the prescribed wake vortex theory over wide range variations of rotor geometrical parameters. It is also shown that the analytical results obtained using either theory are in reasonable agreement with experimental data.

  1. Network-theoretic approach to model vortex interactions

    NASA Astrophysics Data System (ADS)

    Nair, Aditya; Taira, Kunihiko

    2014-11-01

    We present a network-theoretic approach to describe a system of point vortices in two-dimensional flow. By considering the point vortices as nodes, a complete graph is constructed with edges connecting each vortex to every other vortex. The interactions between the vortices are captured by the graph edge weights. We employ sparsification techniques on these graph representations based on spectral theory to construct sparsified models of the overall vortical interactions. The edge weights are redistributed through spectral sparsification of the graph such that the sum of the interactions associated with each vortex is maintained constant. In addition, sparse configurations maintain similar spectral properties as the original setup. Through the reduction in the number of interactions, key vortex interactions can be highlighted. Identification of vortex structures based on graph sparsification is demonstrated with an example of clusters of point vortices. We also evaluate the computational performance of sparsification for large collection of point vortices. Work supported by US Army Research Office (W911NF-14-1-0386) and US Air Force Office of Scientific Research (YIP: FA9550-13-1-0183).

  2. High-resolution dynamical modelling of the Antarctic stratospheric vortex

    NASA Technical Reports Server (NTRS)

    Haynes, P. H.

    1988-01-01

    Progress is reported on the high-resolution three-dimensional numerical simulation of flows characteristic of the Antarctic wintertime stratosphere. The numerical model is a modified version of the Reading University sigma-coordinate used previously for tropospheric studies. Physical parameterizations are kept to a minimum in order to concentrate as much computing power as possible on simulating details of the dynamical processes. The major question addressed is whether the features observed in recent high-resolution two-dimensional simulations - namely: (1) the formation of a sharp edge to the vortex (seen in the potential vorticity field), (2) the survival of the polar vortex in a material entity, and (3) the formation of small-scale eddies rough the break-up of tongues of high potential vorticity drawn out from the polar vortex - are realized in three-dimensional simulations.

  3. Vortex dynamics and scalar transport in the wake of a bluff body driven through a steady recirculating flow

    NASA Astrophysics Data System (ADS)

    Poussou, Stephane B.; Plesniak, Michael W.

    2012-09-01

    The air ventilation system in wide-body aircraft cabins provides passengers with a healthy breathing environment. In recent years, the increase in global air traffic has amplified contamination risks by airborne flu-like diseases and terrorist threats involving the onboard release of noxious materials. In particular, passengers moving through a ventilated cabin may transport infectious pathogens in their wake. This paper presents an experimental investigation of the wake produced by a bluff body driven through a steady recirculating flow. Data were obtained in a water facility using particle image velocimetry and planar laser induced fluorescence. Ventilation attenuated the downward convection of counter-rotating vortices produced near the free-end corners of the body and decoupled the downwash mechanism from forward entrainment, creating stagnant contaminant regions.

  4. Model for Vortex Ring State Influence on Rotorcraft Flight Dynamics

    NASA Technical Reports Server (NTRS)

    Johnson, Wayne

    2005-01-01

    The influence of vortex ring state (VRS) on rotorcraft flight dynamics is investigated, specifically the vertical velocity drop of helicopters and the roll-off of tiltrotors encountering VRS. The available wind tunnel and flight test data for rotors in vortex ring state are reviewed. Test data for axial flow, non-axial flow, two rotors, unsteadiness, and vortex ring state boundaries are described and discussed. Based on the available measured data, a VRS model is developed. The VRS model is a parametric extension of momentum theory for calculation of the mean inflow of a rotor, hence suitable for simple calculations and real-time simulations. This inflow model is primarily defined in terms of the stability boundary of the aircraft motion. Calculations of helicopter response during VRS encounter were performed, and good correlation is shown with the vertical velocity drop measured in flight tests. Calculations of tiltrotor response during VRS encounter were performed, showing the roll-off behavior characteristic of tiltrotors. Hence it is possible, using a model of the mean inflow of an isolated rotor, to explain the basic behavior of both helicopters and tiltrotors in vortex ring state.

  5. Model for Vortex Ring State Influence on Rotorcraft Flight Dynamics

    NASA Technical Reports Server (NTRS)

    Johnson, Wayne

    2004-01-01

    The influence of vortex ring state (VRS) on rotorcraft flight dynamics is investigated, specifically the vertical velocity drop of helicopters and the roll-off of tiltrotors encountering VRS. The available wind tunnel and flight test data for rotors in vortex ring state are reviewed. Test data for axial flow, nonaxial flow, two rotors, unsteadiness, and vortex ring state boundaries are described and discussed. Based on the available measured data, a VRS model is developed. The VRS model is a parametric extension of momentum theory for calculation of the mean inflow of a rotor, hence suitable for simple calculations and real-time simulations. This inflow model is primarily defined in terms of the stability boundary of the aircraft motion. Calculations of helicopter response during VRS encounter were performed, and good correlation is shown with the vertical velocity drop measured in flight tests. Calculations of tiltrotor response during VRS encounter were performed, showing the roll-off behavior characteristic of tiltrotors. Hence it is possible, using a model of the mean inflow of an isolated rotor, to explain the basic behavior of both helicopters and tiltrotors in vortex ring state.

  6. NASA Aircraft Vortex Spacing System Development Status

    NASA Technical Reports Server (NTRS)

    Hinton, David A.; Charnock, James K.; Bagwell, Donald R.; Grigsby, Donner

    1999-01-01

    The National Aeronautics and Space Administration (NASA) is addressing airport capacity enhancements during instrument meteorological conditions through the Terminal Area Productivity (TAP) program. Within TAP, the Reduced Spacing Operations (RSO) subelement at the NASA Langley Research Center is developing an Aircraft VOrtex Spacing System (AVOSS). AVOSS will integrate the output of several systems to produce weather dependent, dynamic wake vortex spacing criteria. These systems provide current and predicted weather conditions, models of wake vortex transport and decay in these weather conditions, and real-time feedback of wake vortex behavior from sensors. The goal of the NASA program is to provide the research and development to demonstrate an engineering model AVOSS in real-time operation at a major airport. The demonstration is only of concept feasibility, and additional effort is required to deploy an operational system for actual aircraft spacing reduction. This paper describes the AVOSS system architecture, a wake vortex facility established at the Dallas-Fort Worth International Airport (DFW), initial operational experience with the AVOSS system, and emerging considerations for subsystem requirements. Results of the initial system operation suggest a significant potential for reduced spacing.

  7. Tornadolike gravity-driven vortex model

    NASA Technical Reports Server (NTRS)

    Deissler, R. G.; Boldman, D. R.

    1974-01-01

    The buoyancy-induced vorticity concentration produced as the fluid in a vortex accelerates vertically was studied. The boiloff from liquid nitrogen, to which a small amount of initial vorticity was added, provided a source of cool, heavy gas in which a concentration of vorticity took place. Condensation streamers made the flow visible. It is shown that the presence of a surface boundary layer is not necessary for the effective concentration of vorticity. A simple theoretical analysis of the phenomenon was also made. A radial contraction of the flow with vertical position and a characteristic hook shape in the top view of the streamlines were observed in both theory and experiment. The vorticity concentration observed may be similar to that which occurs in tornadoes.

  8. Modelling on cavitation in a diffuser with vortex generator

    NASA Astrophysics Data System (ADS)

    Jablonská, J.

    2013-04-01

    Based on cavitation modelling in Laval nozzle results and experience, problem with the diffuser with vortex generator was defined. The problem describes unsteady multiphase flow of water. Different cavitation models were used when modelling in Fluent, flow condition is inlet and pressure condition is outlet. Boundary conditions were specified by Energy Institute, Victor Kaplan's Department of Fluid Engineering, Faculty of Mechanical Engineering, Brno University of Technology. Numerical modelling is compared with experiment.

  9. A nonlinear vortex induced vibration model of marine risers

    NASA Astrophysics Data System (ADS)

    Liu, Juan; Huang, Weiping

    2013-03-01

    With the exploitation of oil and gas in deep water, the traditional vortex induced vibration (VIV) theory is challenged by the unprecedented flexibility of risers. A nonlinear time-dependent VIV model is developed in this paper based on a VIV lift force model and the Morison equation. Both the inline vibration induced by the flow due to vortex shedding and the fluid-structure interaction in the transverse direction are included in the model. One of the characteristics of the model is the response-dependent lift force with nonlinear damping, which is different from other VIV models. The calculations show that the model can well describe the VIV of deepwater risers with the results agreeing with those calculated by other models.

  10. A prescribed wake rotor inflow and flow field prediction analysis, user's manual and technical approach

    NASA Technical Reports Server (NTRS)

    Egolf, T. A.; Landgrebe, A. J.

    1982-01-01

    A user's manual is provided which includes the technical approach for the Prescribed Wake Rotor Inflow and Flow Field Prediction Analysis. The analysis is used to provide the rotor wake induced velocities at the rotor blades for use in blade airloads and response analyses and to provide induced velocities at arbitrary field points such as at a tail surface. This analysis calculates the distribution of rotor wake induced velocities based on a prescribed wake model. Section operating conditions are prescribed from blade motion and controls determined by a separate blade response analysis. The analysis represents each blade by a segmented lifting line, and the rotor wake by discrete segmented trailing vortex filaments. Blade loading and circulation distributions are calculated based on blade element strip theory including the local induced velocity predicted by the numerical integration of the Biot-Savart Law applied to the vortex wake model.

  11. Modeling and simulation of high-speed wake flows

    NASA Astrophysics Data System (ADS)

    Barnhardt, Michael Daniel

    High-speed, unsteady flows represent a unique challenge in computational hypersonics research. They are found in nearly all applications of interest, including the wakes of reentry vehicles, RCS jet interactions, and scramjet combustors. In each of these examples, accurate modeling of the flow dynamics plays a critical role in design performance. Nevertheless, literature surveys reveal that very little modern research effort has been made toward understanding these problems. The objective of this work is to synthesize current computational methods for high-speed flows with ideas commonly used to model low-speed, turbulent flows in order to create a framework by which we may reliably predict unsteady, hypersonic flows. In particular, we wish to validate the new methodology for the case of a turbulent wake flow at reentry conditions. Currently, heat shield designs incur significant mass penalties due to the large margins applied to vehicle afterbodies in lieu of a thorough understanding of the wake aerothermodynamics. Comprehensive validation studies are required to accurately quantify these modeling uncertainties. To this end, we select three candidate experiments against which we evaluate the accuracy of our methodology. The first set of experiments concern the Mars Science Laboratory (MSL) parachute system and serve to demonstrate that our implementation produces results consistent with prior studies at supersonic conditions. Second, we use the Reentry-F flight test to expand the application envelope to realistic flight conditions. Finally, in the last set of experiments, we examine a spherical capsule wind tunnel configuration in order to perform a more detailed analysis of a realistic flight geometry. In each case, we find that current 1st order in time, 2nd order in space upwind numerical methods are sufficiently accurate to predict statistical measurements: mean, RMS, standard deviation, and so forth. Further potential gains in numerical accuracy are

  12. Identifying optimal vortex spacing for swimming and flying animals

    NASA Astrophysics Data System (ADS)

    Dewey, Peter A.; Moored, Keith W.; Quinn, Daniel B.; Smits, Alexander J.

    2011-11-01

    Swimming and flying animals generate thrust by creating an unsteady vortex wake through the oscillation of their appendages. To determine the vortex spacing that maximizes propulsive efficiency, a finite core vortex array model was developed to compute the unsteady velocity field generated by vortex streets representative of bio- inspired propulsion. The model systematically varies the streamwise and transverse spacing between vortex cores to determine the time averaged velocity field induced by a reverse von Karman vortex street and a uniform freestream velocity. Experimental particle image velocimetry was conducted in the wake of a rigid pitching panel to determine the size and strength of the vortex cores to input to the model. Viscosity is accounted for by assuming a Gaussian vorticity distribution around the vortex core. A linear spatial stability analysis was performed on the computed velocity profiles to determine which vortex configuration leads to efficient propulsion. Here it is assumed that efficient propulsion proceeds when the driving frequency of the vortex street matches the resonant frequency of velocity jet. Supported by ONR MURI Grant N00014-08-1-0642.

  13. Prediction of two-dimensional momentumless wake by k- epsilon - gamma model

    NASA Astrophysics Data System (ADS)

    Ahn, Jong Woo; Sung, Hyung Jin

    1995-04-01

    The k-epsilon-gamma model performance is extended to resolve the jet/wake anomaly, which is encountered in calculating free shear flows by the standard k-epsilon model. In the k-epsilon-gamma model, the relation between the rate of dissipation epsilon and the level of intermittency gamma is well incorporated. The model is run to predict the two-dimensional momentumless wake where a jet and a wake coexist. The predictions of the k-epsilon-gamma model are compared with those of the k-epsilon model as well as the experiment. It is shown that the model performance is generally satisfactory.

  14. Effect of nacelle on wake meandering in a laboratory scale wind turbine using LES

    NASA Astrophysics Data System (ADS)

    Foti, Daniel; Yang, Xiaolei; Guala, Michele; Sotiropoulos, Fotis

    2015-11-01

    Wake meandering, large scale motion in the wind turbine wakes, has considerable effects on the velocity deficit and turbulence intensity in the turbine wake from the laboratory scale to utility scale wind turbines. In the dynamic wake meandering model, the wake meandering is assumed to be caused by large-scale atmospheric turbulence. On the other hand, Kang et al. (J. Fluid Mech., 2014) demonstrated that the nacelle geometry has a significant effect on the wake meandering of a hydrokinetic turbine, through the interaction of the inner wake of the nacelle vortex with the outer wake of the tip vortices. In this work, the significance of the nacelle on the wake meandering of a miniature wind turbine previously used in experiments (Howard et al., Phys. Fluid, 2015) is demonstrated with large eddy simulations (LES) using immersed boundary method with fine enough grids to resolve the turbine geometric characteristics. The three dimensionality of the wake meandering is analyzed in detail through turbulent spectra and meander reconstruction. The computed flow fields exhibit wake dynamics similar to those observed in the wind tunnel experiments and are analyzed to shed new light into the role of the energetic nacelle vortex on wake meandering. This work was supported by Department of Energy DOE (DE-EE0002980, DE-EE0005482 and DE-AC04-94AL85000), and Sandia National Laboratories. Computational resources were provided by Sandia National Laboratories and the University of Minnesota Supercomputing.

  15. PREFACE: Wake Conference 2015

    NASA Astrophysics Data System (ADS)

    Barney, Andrew; Nørkær Sørensen, Jens; Ivanell, Stefan

    2015-06-01

    at scientists and PhD students working in the field of wake dynamics. The conference covers the following subject areas: Wake and vortex dynamics, instabilities in trailing vortices and wakes, simulation and measurements of wakes, analytical approaches for modeling wakes, wake interaction and other wind farm investigations. Many people have been involved in producing the 2015 Wake Conference proceedings. The work by the more than 60 reviewers ensuring the quality of the papers is greatly appreciated. The timely evaluation and coordination of the reviews would not have been possible without the work of the section editors: Christian Masson, ÉTS, Fernando Porté-Agel, EPFL, Gerard Schepers, ECN Wind Energy, Gijs Van Kuik, Delft University, Gunner Larsen, DTU Wind Energy, Jakob Mann, DTU Wind Energy, Javier Sanz Rodrigo, CENER, Johan Meyers, KU Leuven, Rebecca Barthelmie, Cornell University, Sandrine Aubrun-Sanches, Université d'Orléans and Thomas Leweke, IRPHE-CNRS. We are also immensely indebted to the very responsive support from the editorial team at IOP Publishing, especially Sarah Toms, during the review process of these proceedings. Visby, Sweden, June 2015 Andrew Barney, Jens Nørkær Sørensen and Stefan Ivanell Uppsala University - Campus Gotland

  16. Numerical Analysis of Tip Cavitation on Marine Propeller with Wake Alignment Using a Simple Surface Panel Method “SQCM”

    NASA Astrophysics Data System (ADS)

    Kanemaru, T.; Ando, J.

    2015-12-01

    This paper presents the calculation method of tip cavitation with wake alignment. Tip cavitation consists of tip vortex cavitation and tip super cavitation which means the undeveloped and local super cavitation around blade tip. The feature of this study is that the method applies the wake alignment model in order to express the realistic phenomena of tip cavitation and predict the pressure fluctuation more accurately. In the present method, the wake sheet is deformed according to the induced velocity vector on the vortex lines. The singularity of the potential vortex can be removed by using the Rankine Vortex model. This paper shows the calculated results regarding cavitation pattern, pressure fluctuation etc. comparing with published experimental data and calculated results without wake alignment.

  17. Rotor Vortex Filaments: Living on the Slipstream's Edge

    NASA Technical Reports Server (NTRS)

    Young, Larry A.

    1997-01-01

    The purpose of this paper is to gain a better understanding of rotor wake evolution in hover and axial flow by deriving an analytical solution for the time dependent behavior of vortex filament circulation and core size. This solution is applicable only for vortex filaments in the rotor far-wake. A primarily inviscid vortex/shear layer interaction (where the slipstream boundary is modeled as a shear layer) has been identified in this analytical treatment. This vortex/shear layer interaction results in decreasing, vortex filament circulation and core size with time. The inviscid vortex/shear layer interaction is shown, in a first-order treatment, to be of greater magnitude than viscous diffusion effects. The rate of contraction, and ultimate collapse, of the vortex filament core is found to be directly proportional to the rotor inflow velocity. This new insight into vortex filament decay promises to help reconcile several disparate observations made in the literature and will, hopefully, promote new advances in theoretical modeling of rotor wakes.

  18. Phase front analysis of vortex streets

    NASA Astrophysics Data System (ADS)

    Lefrançois, Marcel; Ahlborn, Boye

    1994-06-01

    The continuous formation and development of a laminar vortex street behind a circular cylinder of radius D in a flow of velocity U∞ has been modeled as a Huygens-type wave process, where the transverse velocity Uy and the vorticity ω in the near wake oscillate at the vortex shedding frequency f. Starting from the Biot-Savart law for fluids a phase front propagation integral is derived. This formalism is used to calculate for each point along the span the phase of vortex shedding as a function of the phase of the previously shed vortex generation and the shedding frequency. The amplitude is determined by a simple renormalization calculation. In good agreement with experiments, the model predicts the propagation of spanwise phase perturbations into subsequent vortex generations for two-dimensional (2-D) flow geometries and the cell formation in three-dimensional flows around tapered cylinders.

  19. Simulating microinjection experiments in a novel model of the rat sleep-wake regulatory network.

    PubMed

    Diniz Behn, Cecilia G; Booth, Victoria

    2010-04-01

    This study presents a novel mathematical modeling framework that is uniquely suited to investigating the structure and dynamics of the sleep-wake regulatory network in the brain stem and hypothalamus. It is based on a population firing rate model formalism that is modified to explicitly include concentration levels of neurotransmitters released to postsynaptic populations. Using this framework, interactions among primary brain stem and hypothalamic neuronal nuclei involved in rat sleep-wake regulation are modeled. The model network captures realistic rat polyphasic sleep-wake behavior consisting of wake, rapid eye movement (REM) sleep, and non-REM (NREM) sleep states. Network dynamics include a cyclic pattern of NREM sleep, REM sleep, and wake states that is disrupted by simulated variability of neurotransmitter release and external noise to the network. Explicit modeling of neurotransmitter concentrations allows for simulations of microinjections of neurotransmitter agonists and antagonists into a key wake-promoting population, the locus coeruleus (LC). Effects of these simulated microinjections on sleep-wake states are tracked and compared with experimental observations. Agonist/antagonist pairs, which are presumed to have opposing effects on LC activity, do not generally induce opposing effects on sleep-wake patterning because of multiple mechanisms for LC activation in the network. Also, different agents, which are presumed to have parallel effects on LC activity, do not induce parallel effects on sleep-wake patterning because of differences in the state dependence or independence of agonist and antagonist action. These simulation results highlight the utility of formal mathematical modeling for constraining conceptual models of the sleep-wake regulatory network. PMID:20107121

  20. Wake Turbulence Mitigation for Arrivals (WTMA)

    NASA Technical Reports Server (NTRS)

    Williams, Daniel M.; Lohr, Gary W.; Trujillo, Anna C.

    2008-01-01

    The preliminary Wake Turbulence Mitigation for Arrivals (WTMA) concept of operations is described in this paper. The WTMA concept provides further detail to work initiated by the Wake Vortex Avoidance System Concept Evaluation Team and is an evolution of the Wake Turbulence Mitigation for Departure concept. Anticipated benefits about reducing wake turbulence separation standards in crosswind conditions, and candidate WTMA system considerations are discussed.

  1. Remote measurement utilizing NASA's scanning laser Doppler systems. Volume 1. Laser Doppler wake vortex tracking at Kennedy Airport

    NASA Technical Reports Server (NTRS)

    Krause, M. C.; Wilson, D. J.; Howle, R. E.; Edwards, B. B.; Craven, C. E.; Jetton, J. L.

    1976-01-01

    Test operations of the Scanning Laser Doppler System (SLDS) at Kennedy International Airport (KIA) during August 1974 through June 1975 are reported. A total of 1,619 data runs was recorded with a totally operational system during normal landing operations at KIA. In addition, 53 data runs were made during cooperative flybys with the C880 for a grand total of 1672 recorded vortex tracks. Test crews were in attendance at KIA for 31 weeks, of which 25 weeks were considered operational and the other six were packing, unpacking, setup and check out. Although average activity equates to 67 recorded landing operations per week, two periods of complete runway inactivity spanned 20 days and 13 days, respectively. The operation frequency therefore averaged about 88 operations per week.

  2. Fractional vortex molecules and vortex polygons in a baby Skyrme model

    NASA Astrophysics Data System (ADS)

    Kobayashi, Michikazu; Nitta, Muneto

    2013-06-01

    We construct a molecule of fractional vortices with fractional topological lump charges as a baby Skyrmion with the unit topological lump charge in the antiferromagnetic (or XY) baby Skyrme model, that is, an O(3) sigma model with a four-derivative term and an antiferromagnetic or XY-type potential term quadratic in fields. We further construct configurations with topological lump charges Q≤7 and find that bound states of vortex molecules constitute regular polygons with 2Q vertices as vortices, where the rotational symmetry SO(2) in real space is spontaneously broken into a discrete subgroup ZQ. We also find metastable and arrayed bound states of fractional vortices for Q=5, 6. On the other hand, we find for Q=7 that the regular polygon is metastable and the arrayed bound state is stable. We calculate binding energies of all configurations.

  3. Contrail Formation in Aircraft Wakes Using Large-Eddy Simulations

    NASA Technical Reports Server (NTRS)

    Paoli, R.; Helie, J.; Poinsot, T. J.; Ghosal, S.

    2002-01-01

    In this work we analyze the issue of the formation of condensation trails ("contrails") in the near-field of an aircraft wake. The basic configuration consists in an exhaust engine jet interacting with a wing-tip training vortex. The procedure adopted relies on a mixed Eulerian/Lagrangian two-phase flow approach; a simple micro-physics model for ice growth has been used to couple ice and vapor phases. Large eddy simulations have carried out at a realistic flight Reynolds number to evaluate the effects of turbulent mixing and wake vortex dynamics on ice-growth characteristics and vapor thermodynamic properties.

  4. Homogeneous vortex model for liquid slosh in spinning spherical tanks

    NASA Technical Reports Server (NTRS)

    El-Raheb, M.; Wagner, P.

    1979-01-01

    The problem of forced fluid sloshing in a partially filled spinning spherical tank is solved numerically using the finite element method. The governing equations include Coriolis acceleration, empirical fluid damping and spatially homogeneous vorticity first introduced by Pfeiffer. An exponential instability similar to flutter is detected in the present simulation for fill ratios below 50 percent. This instability appears in the model as a result of the homogeneous vortex assumption since the free slosh equations are neutrally stable in the Liapunov sense.

  5. LCS analysis of a biologically inspired wake

    NASA Astrophysics Data System (ADS)

    Green, Melissa; Smits, Alexander

    2008-11-01

    Particle Image Velocimetry (PIV) was used to investigate the wakes of rigid pitching panels with a trapezoidal panel geometry, chosen to model idealized fish caudal fins. Experiments were performed for Strouhal numbers from 0.23 to 0.65. The three dimensional flow field around the panel is reconstructed by integrating two-dimensional PIV results across the volume surrounding the panel. A Lagrangian coherent structure (LCS) analysis is employed to investigate the formation and evolution of the panel wake. A classic reverse von Kármán vortex street pattern was observed along the mid-span of the near wake, but the complexity and three-dimensionality of the wake increases away from the mid-span as streamwise vortices interact with the swept edges of the panel.

  6. A model of the ion wake of Mars

    NASA Technical Reports Server (NTRS)

    Luhmann, J. G.

    1990-01-01

    Observations from the Phobos spacecraft suggest that, for the most part, the Martian magnetotail is induced instead of intrinsic. Test particle techniques are used to determine how the associated ion wake might appear to detectors behind Mars if it is produced primarily by planetary ions picked up by the solar wind in the dayside exosphere. The results suggest that low energy pickup ions populate the inner wake, while a more energetic component is present in the outer magnetosheath and adjacent solar wind.

  7. The Vortex Lattice Method for the Rotor-Vortex Interaction Problem

    NASA Technical Reports Server (NTRS)

    Padakannaya, R.

    1974-01-01

    The rotor blade-vortex interaction problem and the resulting impulsive airloads which generate undesirable noise levels are discussed. A numerical lifting surface method to predict unsteady aerodynamic forces induced on a finite aspect ratio rectangular wing by a straight, free vortex placed at an arbitrary angle in a subsonic incompressible free stream is developed first. Using a rigid wake assumption, the wake vortices are assumed to move downsteam with the free steam velocity. Unsteady load distributions are obtained which compare favorably with the results of planar lifting surface theory. The vortex lattice method has been extended to a single bladed rotor operating at high advance ratios and encountering a free vortex from a fixed wing upstream of the rotor. The predicted unsteady load distributions on the model rotor blade are generally in agreement with the experimental results. This method has also been extended to full scale rotor flight cases in which vortex induced loads near the tip of a rotor blade were indicated. In both the model and the full scale rotor blade airload calculations a flat planar wake was assumed which is a good approximation at large advance ratios because the downwash is small in comparison to the free stream at large advance ratios. The large fluctuations in the measured airloads near the tip of the rotor blade on the advance side is predicted closely by the vortex lattice method.

  8. Site Suitability Assessment with Dynamic Wake Meandering Model. A Certification Point of View.

    NASA Astrophysics Data System (ADS)

    Tomas Bayo, Ricard; Parro, Gema

    2015-04-01

    Establishment of large wind farms requires enormous investments putting steadily greater emphasis on optimal topology design and control of these. This requires not only an optimization of the power output, but also the development of strategies to cope with the higher loading expected. The cornerstone of such strategies is a realistic characterization and modelling of the wake flow field inside the wind farm, beyond Frandsen's equivalent turbulence method. Whereas Frandsen model has been mostly considered in the industry so far, it has not proved completely satisfactory when facing current problems such as wake effects on turbines placed at short distances or consequences of half wake for turbine loading. The objective of the present work is to address these questions from a certification point of view within the framework of Risoe's Dynamic Wake Meandering (DWM) model. The DWM model is based on the combination of three parts: modeling of quasi-steady wake deficits, a stochastic model of the downwind wake meandering and an added or self-generated wake turbulence. The analysis carried out is two-fold: First, a comparative study of the wake effects generated in Frandsen model as well as in various realizations of the DWM model is performed. For this purpose wake-induced loads are calculated using two different aeroelastic codes: HAWC2 and Bladed. Second, the applicability of DWM for the assessment of wind turbines under site-specific conditions is discussed and the conclusions summarized in a Recommended Practice. Clear prescriptions are thereby provided for the use of DWMM for site suitability assessments, including the aforementioned extreme situations, along with the interpretation of the future version of the IEC 61400-1 standards.

  9. Vortex Dynamics of Accelerated Inhomogeneous Flows: Visiometrics and Modeling

    NASA Astrophysics Data System (ADS)

    Zabusky, Norman

    1998-11-01

    Rayleigh-Taylor and Richtmyer-Meshkov instabilities arise in several high-energy fluid enviroments, including: supersonic combustion; laser (inertial confinement) fusion and supernova astrophysics. We use the ``vortex paradigm'' to guide our understanding and modeling of early-to-intermediate time phenomena at perturbed interfaces and bubbles, including reshock and reacceleration processes. We show the emergence of ``vortex projectiles" or VPs ( dipolar or ring-like coherent structures) and comment on their ubiquity. Acknowlegemets: Since 1989 I have benefited from collaborations with : J. Hawley, X. Yang, R. Samtaney, J. Ray, A. Kotelnikov and D. G. Dritschel. The work has been supported by DOE Grant No. DE-FG0293ER25179 under Drs. Daniel Hitchcock and Fred Howes. Computations were done on the C90 and T3E at Pittsburgh Supercomputing Center and the SP2 at Cornell Theory Center. We also acknowledge the support of CAIP, Rutgers University.

  10. Analysis of Tip Vortices Identified in the Instantaneous Wake of a Horizontal-Axis Model Wind Turbine Placed in a Turbulent Boundary Layer

    NASA Astrophysics Data System (ADS)

    Jain, Akash; Mehdi, Faraz; Sheng, Jian

    2014-11-01

    The near-wake field, a short region characterized by the physical specifications of a turbine, is of particular interest for flow-structure interactions responsible for asymmetric loadings, premature structural breakdown, noise generation etc. Helical tip vortices constitute a distinctive feature of this region and are dependent not only on the turbine geometry but also on the incoming flow profile. High-spatial resolution PIV measurements are made in the wake of a horizontal-axis model wind turbine embedded in a neutrally stratified turbulent boundary layer. The data is acquired over consecutive locations up to 10 diameters downstream of the turbine but the focus here is on the tip vortices identified in the instantaneous fields. Contrary to previous studies, both top and bottom tip vortices are clearly distinguishable in either ensemble fields or instantaneous realizations. The streamwise extent of these vortices stretches from the turbine till they merge into the expanding mid-span wake. The similarities and differences in the top and bottom tip vortices are explored through the evolution of their statistics. In particular, the distributions of the loci of vortex cores and their circulations are compared. The information will improve our understanding of near wake vortical dynamics, provide data for model validation, and aid in the devise of flow control strategies.

  11. Dynamic parameters in models of atmospheric vortex structures

    NASA Astrophysics Data System (ADS)

    Dobryshman, E. M.; Kochina, V. G.; Letunova, T. A.

    2013-09-01

    Vortex simulation and the computation of fields of dynamic parameters of vortex structures (velocity, rotor velocity, and helicity) are carried out with the use of exact hydrodynamic equations in a cylindrical coordinate system. Components of centripetal and Coriolis accelerations are taken into account in the initial equations. Internal and external solutions are defined. Internal solutions ignore the disturbances of the pressure field, but they are considered in external solutions. The simulation is carried out so that the effect of accounting for spatial coordinates on the structure of the above fields is pronounced. It is shown that the initial kinetic energy of rotating motion transforms into the kinetic energy of radial and vertical velocity components in models with centripetal acceleration. In models with Coriolis acceleration, the Rossby effect is clearly pronounced. The method of an "inverse problem" is used for finding external solutions, i.e., reconstruction of the pressure field at specified velocity components. Computations have shown that tangential components mainly contribute to the velocity and helicity vortex moduli at the initial stage.

  12. Data-driven Reduced Order Model for prediction of wind turbine wakes

    NASA Astrophysics Data System (ADS)

    Iungo, G. V.; Santoni-Ortiz, C.; Abkar, M.; Porté-Agel, F.; Rotea, M. A.; Leonardi, S.

    2015-06-01

    In this paper a new paradigm for prediction of wind turbine wakes is proposed, which is based on a reduced order model (ROM) embedded in a Kalman filter. The ROM is evaluated by means of dynamic mode decomposition performed on high fidelity LES numerical simulations of wind turbines operating under different operational regimes. The ROM enables to capture the main physical processes underpinning the downstream evolution and dynamics of wind turbine wakes. The ROM is then embedded within a Kalman filter in order to produce a time-marching algorithm for prediction of wind turbine wake flows. This data-driven algorithm enables data assimilation of new measurements simultaneously to the wake prediction, which leads to an improved accuracy and a dynamic update of the ROM in presence of emerging coherent wake dynamics observed from new available data. Thanks to its low computational cost, this numerical tool is particularly suitable for real-time applications, control and optimization of large wind farms.

  13. Modeling for Airframe Noise Prediction Using Vortex Methods

    NASA Astrophysics Data System (ADS)

    Zheng, Z. Charlie

    2002-12-01

    Various components of the airframe are known to be a significant source of noise. With the advent of technology in quieting modern engines, airframe generated noise competes and, in certain instances, surpasses the engine noise. Airframe noise is most pronounced during aircraft approach when the engines are operating at reduced thrust, and airframe components such as high-lift devices and landing gears are in deployed conditions. Recent experimental studies have reaffirmed that the most significant sources of high-lift noise are from the leading-edge slat and the side edges of flaps. Studies of flow field around these structures have consistently shown that there are complicated unsteady vortical flows such as vortex shedding, secondary vortices and vortex breakdown, which are susceptible to far-field radiated sound. The near-field CFD computational data have been used to calculate the far-field acoustics by employing Ffowcs-Williams/Hawkings equation using Lighthill's analogy. However, because of the limit of current computing capacity, it is very time consuming to generate unsteady Navier-Stokes (N-S) computational data for aeroacoustics. Although the N-S simulations are probably necessary to reveal many complex flow phenomena that are unsteady and fully nonlinear, these simulations are not feasible to be used for parametric design. purposes. The objective of this study is thus to develop theoretical models for airframe noise predictions which have quick turn-around computing time. Since it is known that vorticity is a major mechanism responsible for noise generation on high-lift devices, vortex methods have been chosen as modeling tools. Vortex methods are much faster in comparison with other numerical methods, yet they are able to incorporate nonlinear interactions between vortices. Obviously, as with any theoretical model, assumptions have to be made and justified when such models are used in complex flow. The merit and applicability of the models for

  14. The wake of hovering flight in bats.

    PubMed

    Håkansson, Jonas; Hedenström, Anders; Winter, York; Johansson, L Christoffer

    2015-08-01

    Hovering means stationary flight at zero net forward speed, which can be achieved by animals through muscle powered flapping flight. Small bats capable of hovering typically do so with a downstroke in an inclined stroke plane, and with an aerodynamically active outer wing during the upstroke. The magnitude and time history of aerodynamic forces should be reflected by vorticity shed into the wake. We thus expect hovering bats to generate a characteristic wake, but this has until now never been studied. Here we trained nectar-feeding bats, Leptonycteris yerbabuenae, to hover at a feeder and using time-resolved stereoscopic particle image velocimetry in conjunction with high-speed kinematic analysis we show that hovering nectar-feeding bats produce a series of bilateral stacked vortex loops. Vortex visualizations suggest that the downstroke produces the majority of the weight support, but that the upstroke contributes positively to the lift production. However, the relative contributions from downstroke and upstroke could not be determined on the basis of the wake, because wake elements from down- and upstroke mix and interact. We also use a modified actuator disc model to estimate lift force, power and flap efficiency. Based on our quantitative wake-induced velocities, the model accounts for weight support well (108%). Estimates of aerodynamic efficiency suggest hovering flight is less efficient than forward flapping flight, while the overall energy conversion efficiency (mechanical power output/metabolic power) was estimated at 13%. PMID:26179990

  15. Direct numerical simulations and modeling of a spatially-evolving turbulent wake

    NASA Technical Reports Server (NTRS)

    Cimbala, John M.

    1994-01-01

    Understanding of turbulent free shear flows (wakes, jets, and mixing layers) is important, not only for scientific interest, but also because of their appearance in numerous practical applications. Turbulent wakes, in particular, have recently received increased attention by researchers at NASA Langley. The turbulent wake generated by a two-dimensional airfoil has been selected as the test-case for detailed high-resolution particle image velocimetry (PIV) experiments. This same wake has also been chosen to enhance NASA's turbulence modeling efforts. Over the past year, the author has completed several wake computations, while visiting NASA through the 1993 and 1994 ASEE summer programs, and also while on sabbatical leave during the 1993-94 academic year. These calculations have included two-equation (K-omega and K-epsilon) models, algebraic stress models (ASM), full Reynolds stress closure models, and direct numerical simulations (DNS). Recently, there has been mutually beneficial collaboration of the experimental and computational efforts. In fact, these projects have been chosen for joint presentation at the NASA Turbulence Peer Review, scheduled for September 1994. DNS calculations are presently underway for a turbulent wake at Re(sub theta) = 1000 and at a Mach number of 0.20. (Theta is the momentum thickness, which remains constant in the wake of a two dimensional body.) These calculations utilize a compressible DNS code written by M. M. Rai of NASA Ames, and modified for the wake by J. Cimbala. The code employs fifth-order accurate upwind-biased finite differencing for the convective terms, fourth-order accurate central differencing for the viscous terms, and an iterative-implicit time-integration scheme. The computational domain for these calculations starts at x/theta = 10, and extends to x/theta = 610. Fully developed turbulent wake profiles, obtained from experimental data from several wake generators, are supplied at the computational inlet, along with

  16. Direct numerical simulations and modeling of a spatially-evolving turbulent wake

    NASA Astrophysics Data System (ADS)

    Cimbala, John M.

    1994-12-01

    Understanding of turbulent free shear flows (wakes, jets, and mixing layers) is important, not only for scientific interest, but also because of their appearance in numerous practical applications. Turbulent wakes, in particular, have recently received increased attention by researchers at NASA Langley. The turbulent wake generated by a two-dimensional airfoil has been selected as the test-case for detailed high-resolution particle image velocimetry (PIV) experiments. This same wake has also been chosen to enhance NASA's turbulence modeling efforts. Over the past year, the author has completed several wake computations, while visiting NASA through the 1993 and 1994 ASEE summer programs, and also while on sabbatical leave during the 1993-94 academic year. These calculations have included two-equation (K-omega and K-epsilon) models, algebraic stress models (ASM), full Reynolds stress closure models, and direct numerical simulations (DNS). Recently, there has been mutually beneficial collaboration of the experimental and computational efforts. In fact, these projects have been chosen for joint presentation at the NASA Turbulence Peer Review, scheduled for September 1994. DNS calculations are presently underway for a turbulent wake at Re(sub theta) = 1000 and at a Mach number of 0.20. (Theta is the momentum thickness, which remains constant in the wake of a two dimensional body.) These calculations utilize a compressible DNS code written by M. M. Rai of NASA Ames, and modified for the wake by J. Cimbala. The code employs fifth-order accurate upwind-biased finite differencing for the convective terms, fourth-order accurate central differencing for the viscous terms, and an iterative-implicit time-integration scheme. The computational domain for these calculations starts at x/theta = 10, and extends to x/theta = 610. Fully developed turbulent wake profiles, obtained from experimental data from several wake generators, are supplied at the computational inlet, along with

  17. Harbor seal whiskers synchronize with upstream wake over a range of distances

    NASA Astrophysics Data System (ADS)

    Beem, Heather; Triantafyllou, Michael

    2014-11-01

    Harbor seal whiskers have been shown to exhibit unique vibration properties as they encounter vortex wakes. Seals may use this information to detect hydrodynamic trails left by fish prey. A scaled model, which captures the undulatory morphology of the harbor seal whisker and is designed to freely vibrate, is tested here to explore these properties in more detail. This model is towed downstream of a larger cylinder, which generates a vortex wake. Effects of downstream distance, lateral distance, and diameter ratio between the two objects are explored. Frequency measurements are collected simultaneously through use of a pressure sensor placed in the wake. Cross-correlation of the whisker motion and cylinder wake pressure provides evidence that frequency synchronization holds for a range of separation distances and wake generator sizes.

  18. Three-dimensional wake of a biologically-inspired propulsor

    NASA Astrophysics Data System (ADS)

    Green, Melissa; Rowley, Clarence; Smits, Alexander

    2009-11-01

    Digital Particle Image Velocimetry (DPIV) was used to investigate the wakes of rigid pitching panels with a trapezoidal planform geometry, chosen to model idealized fish caudal fins. Experiments were performed for Strouhal numbers of 0.17 and 0.23. The three-dimensional unsteady vortex wake downstream of the panel trailing edge was visualized using spatially- and temporally-resolved two-component data. A Lagrangian Coherent Structure (LCS) analysis was employed in addition to Eulerian vortex identification criteria to investigate the generation and evolution of the wake. A reverse von K'arm'an vortex street pattern was observed near the mid-span immediately downstream of the panel trailing edge, but the complexity and three-dimensionality of the wake increases away from the mid-span as streamwise vortices interact with the swept edges of the panel. Farther downstream of the trailing edge, the wake was observed to shrink in the spanwise direction at both Strouhal numbers. In addition, a quantitative bifurcation in the LCS coincided with a qualitative transition of the wake structure observed with increasing Strouhal number.

  19. A Discretized Method for Deriving Vortex Impulse from Volumetric Datasets

    NASA Astrophysics Data System (ADS)

    Buckman, Noam; Mendelson, Leah; Techet, Alexandra

    2015-11-01

    Many biological and mechanical systems transfer momentum through a fluid by creating vortical structures. To study this mechanism, we derive a method for extracting impulse and its time derivative from flow fields observed in experiments and simulations. We begin by discretizing a thin-cored vortex filament, and extend the model to account for finite vortex core thickness and asymmetric distributions of vorticity. By solely using velocity fields to extract vortex cores and calculate circulation, this method is applicable to 3D PIV datasets, even with low spatial resolution flow fields and measurement noise. To assess the performance of this analysis method, we simulate vortex rings and arbitrary vortex structures using OpenFOAM computational fluid dynamics software and analyze the wake momentum using this model in order to validate this method. We further examine a piston-vortex experiment, using 3D synthetic particle image velocimetry (SAPIV) to capture velocity fields. Strengths, limitations, and improvements to the framework are discussed.

  20. Numerical Study of Tip Vortex Flows

    NASA Technical Reports Server (NTRS)

    Dacles-Mariani, Jennifer; Hafez, Mohamed

    1998-01-01

    This paper presents an overview and summary of the many different research work related to tip vortex flows and wake/trailing vortices as applied to practical engineering problems. As a literature survey paper, it outlines relevant analytical, theoretical, experimental and computational study found in literature. It also discusses in brief some of the fundamental aspects of the physics and its complexities. An appendix is also included. The topics included in this paper are: 1) Analytical Vortices; 2) Experimental Studies; 3) Computational Studies; 4) Wake Vortex Control and Management; 5) Wake Modeling; 6) High-Lift Systems; 7) Issues in Numerical Studies; 8) Instabilities; 9) Related Topics; 10) Visualization Tools for Vertical Flows; 11) Further Work Needed; 12) Acknowledgements; 13) References; and 14) Appendix.

  1. On vortex bursting

    NASA Technical Reports Server (NTRS)

    Werle, H.

    1984-01-01

    Vortex bursting is studied by means of visualization. The physical behavior of the phenomenon is emphasized, and its similarity with boundary layer separation or wake bursting becomes apparent. The essential influence of an increasing pressure gradient on the initiation, the position and the type of bursting is clearly confirmed. The evolution of the phenomena as a function of several parameters is analyzed in the case of delta wings, alone or installed on aircraft models, and compared with the results of similar wind tunnel or flight tests.

  2. Aerodynamic interaction between vortical wakes and lifting two-dimensional bodies

    NASA Technical Reports Server (NTRS)

    Stremel, Paul M.

    1989-01-01

    Unsteady rotor wake interactions with the empennage, tail boom, and other aerodynamic surfaces of a helicopter have a significant influence on its aerodynamic performance, the ride quality, and vibration. A numerical method for computing the aerodynamic interaction between an interacting vortex wake and the viscous flow about arbitrary two-dimensional bodies was developed to address this helicopter problem. The method solves for the flow field velocities on a body-fitted computational mesh using finite-difference techniques. The interacting vortex wake is represented by an array of discrete vortices which, in turn, are represented by a finite-core model. The evolution of the interacting vortex wake is calculated by Lagrangian techniques. The viscous flow field of the two-dimensional body is calculated on an Eulerian grid. The flow around circular and elliptic cylinders in the absence of an interacting vortex wake was calculated. These results compare very well with other numerical results and with results obtained from experiment and thereby demonstrate the accuracy of the viscous solution. The interaction of a rotor wake with the flow about a 4 to 1 elliptic cylinder at 45 degree incidence was calculated for a Reynolds number of 3000. The results demonstrate the significant variations in the lift and drag on the elliptic cylinder in the presence of the interacting rotor wake.

  3. Vortex Flow Aerodynamics, volume 1

    NASA Technical Reports Server (NTRS)

    Campbell, J. F. (Editor); Osborn, R. F. (Editor); Foughner, J. T., Jr. (Editor)

    1986-01-01

    Vortex modeling techniques and experimental studies of research configurations utilizing vortex flows are discussed. Also discussed are vortex flap investigations using generic and airplane research models and vortex flap theoretical analysis and design studies.

  4. Vortex Flow Aerodynamics, volume 1

    SciTech Connect

    Campbell, J.F.; Osborn, R.F.; Foughner, J.T. Jr.

    1986-07-01

    Vortex modeling techniques and experimental studies of research configurations utilizing vortex flows are discussed. Also discussed are vortex flap investigations using generic and airplane research models and vortex flap theoretical analysis and design studies.

  5. Calculations of axisymmetric vortex sheet roll-up using a panel and a filament model

    NASA Technical Reports Server (NTRS)

    Kantelis, J. P.; Widnall, S. E.

    1986-01-01

    A method for calculating the self-induced motion of a vortex sheet using discrete vortex elements is presented. Vortex panels and vortex filaments are used to simulate two-dimensional and axisymmetric vortex sheet roll-up. A straight forward application using vortex elements to simulate the motion of a disk of vorticity with an elliptic circulation distribution yields unsatisfactroy results where the vortex elements move in a chaotic manner. The difficulty is assumed to be due to the inability of a finite number of discrete vortex elements to model the singularity at the sheet edge and due to large velocity calculation errors which result from uneven sheet stretching. A model of the inner portion of the spiral is introduced to eliminate the difficulty with the sheet edge singularity. The model replaces the outermost portion of the sheet with a single vortex of equivalent circulation and a number of higher order terms which account for the asymmetry of the spiral. The resulting discrete vortex model is applied to both two-dimensional and axisymmetric sheets. The two-dimensional roll-up is compared to the solution for a semi-infinite sheet with good results.

  6. Calculation of symmetric and asymmetric vortex seperation on cones and tangent ogives based on discrete vortex models

    NASA Technical Reports Server (NTRS)

    Chin, S.; Lan, C. Edward

    1988-01-01

    An inviscid discrete vortex model, with newly derived expressions for the tangential velocity imposed at the separation points, is used to investigate the symmetric and asymmetric vortex separation on cones and tangent ogives. The circumferential locations of separation are taken from experimental data. Based on a slender body theory, the resulting simultaneous nonlinear algebraic equations in a cross-flow plane are solved with Broyden's modified Newton-Raphson method. Total force coefficients are obtained through momentum principle with new expressions for nonconical flow. It is shown through the method of function deflation that multiple solutions exist at large enough angles of attack, even with symmetric separation points. These additional solutions are asymmetric in vortex separation and produce side force coefficients which agree well with data for cones and tangent ogives.

  7. Dynamics of wake structure in clapping propulsion

    NASA Astrophysics Data System (ADS)

    Kim, Daegyoum; Gharib, Morteza

    2009-11-01

    Some animals such as insects and frogs use a pair of symmetric flaps for locomotion. In some cases, these flappers operate in close proximity or even touch each other. In order to understand the underlying physics of these kinds of motion, we have studied the wake structures induced by clapping and their associated thrust performance. A simple mechanical model with two acrylic plates was used to simulate the power stroke of the clapping motion and three-dimensional flow fields were obtained using defocusing digital particle image velocimetry. Our studies show that the process of vortex connection plays a critical role in forming a downstream closed vortex loop. Under some kinematic conditions, this vortex loop changes its shape dynamically, which is analogous to the process of an elliptical vortex ring switching its minor and major axis. As the length of the plate along the rotating shaft decreases to change an aspect ratio, the downstream motion of the vortex is retarded due to the outward motion of side edge vortices and less propulsive force is generated per the surface area of the plate. The impact of compliance and stroke angle of the plate on wake structures and thrust magnitudes are also presented.

  8. An Empirical Model for Vane-Type Vortex Generators in a Navier-Stokes Code

    NASA Technical Reports Server (NTRS)

    Dudek, Julianne C.

    2005-01-01

    An empirical model which simulates the effects of vane-type vortex generators in ducts was incorporated into the Wind-US Navier-Stokes computational fluid dynamics code. The model enables the effects of the vortex generators to be simulated without defining the details of the geometry within the grid, and makes it practical for researchers to evaluate multiple combinations of vortex generator arrangements. The model determines the strength of each vortex based on the generator geometry and the local flow conditions. Validation results are presented for flow in a straight pipe with a counter-rotating vortex generator arrangement, and the results are compared with experimental data and computational simulations using a gridded vane generator. Results are also presented for vortex generator arrays in two S-duct diffusers, along with accompanying experimental data. The effects of grid resolution and turbulence model are also examined.

  9. Analysis of Wake VAS Benefits Using ACES Build 3.2.1: VAMS Type 1 Assessment

    NASA Technical Reports Server (NTRS)

    Smith, Jeremy C.

    2005-01-01

    The FAA and NASA are currently engaged in a Wake Turbulence Research Program to revise wake turbulence separation standards, procedures, and criteria to increase airport capacity while maintaining or increasing safety. The research program is divided into three phases: Phase I near term procedural enhancements; Phase II wind dependent Wake Vortex Advisory System (WakeVAS) Concepts of Operations (ConOps); and Phase III farther term ConOps based on wake prediction and sensing. The Phase III Wake VAS ConOps is one element of the Virtual Airspace Modelling and Simulation (VAMS) program blended concepts for enhancing the total system wide capacity of the National Airspace System (NAS). This report contains a VAMS Program Type 1 (stand-alone) assessment of the expected capacity benefits of Wake VAS at the 35 FAA Benchmark Airports and determines the consequent reduction in delay using the Airspace Concepts Evaluation System (ACES) Build 3.2.1 simulator.

  10. Design of an Aircraft Vortex Spacing System for Airport Capacity Improvement

    NASA Technical Reports Server (NTRS)

    Hinton, David A.; Charnock, James K.; Bagwell, Donald R.

    2000-01-01

    The National Aeronautics and Space Administration (NASA) is addressing airport capacity enhancements through the Terminal Area Productivity (TAP) program. Within TAP, the Reduced Spacing Operations element at the NASA Langley Research Center is developing an Aircraft VOrtex Spacing System (AVOSS). AVOSS will integrate the output of several systems to produce weather dependent, dynamic wake vortex spacing criteria. These systems provide current and predicted weather conditions, models of wake vortex transport and decay in these weather conditions, and real-time feedback of wake vortex behavior from sensors. The goal of the NASA program is to provide the research and development to demonstrate an engineering model AVOSS, in real-time operation, at a major airport. A wake vortex system test facility was established at the Dallas-Fort Worth International Airport (DFW) in 1997 and tested in 1998. Results from operation of the initial AVOSS system, plus advances in wake vortex prediction and near-term weather forecast models, "nowcast", have been integrated into a second-generation system. This AVOSS version is undergoing final checkout in preparation for a system demonstration in 2000. This paper describes the revised AVOSS system architecture, subsystem enhancements, and initial results with AVOSS version 2 from a deployment at DFW in the fall of 1999.

  11. Venusian Polar Vortex reproduced in an Atmospheric General Circulation Model

    NASA Astrophysics Data System (ADS)

    Ando, Hiroki; Imamura, Takeshi; Takagi, Masahiro; Sugimoto, Norihiko; Kashimura, Hiroki

    The Venus atmosphere has a polar vortex rotating in the retrograde direction with a period of about three days. The vortex has a warm feature surrounded by a cold collar (e.g., Taylor et al. 1980; Piccioni et al. 2006). Although the Venusian polar vortex has been reported by many observations, its mechanism is still unknown. Elson (1982, 1989) examined the structure of the polar vortex by linear calculations. However, the background zonal wind assumed in the calculations was much stronger or weaker than those retrieved in the previous measurements (e.g., Peralta et al. 2008; Kouyama et al. 2012). Lee et al. (2010) and Yamamoto and Takahashi (2012) performed numerical simulations with general circulation models (GCMs) of the Venus atmosphere and obtained vertical structure in the polar region. However, the models included artificial forcing of Kelvin and/or Rossby waves. We have developed a new Venusian GCM by modifying the Atmospheric GCM For the Earth Simulator (Sugimoto et al. 2012; 2013). The basic equations of the GCM are primitive ones in the sigma coordinate on a sphere without topography. The model resolution is T42 (i.e., about 2.8 deg x 2.8 deg grids) and L60 (Deltaz is about 2 km). Rayleigh friction (sponge layer) in the upper layer (>80 km) is applied to prevent the reflection of waves, whose effect increases gradually with height. In the model, the atmosphere is dry and forced by the solar heating and Newtonian cooling. The vertical profile of the solar heating is based on Crisp (1986), and zonally averaged distribution is used. In addition diurnal component of the solar heating, which excites the diurnal and semi-diurnal tides, is also included. Newtonian cooling relaxes the temperature to the zonally uniform basic temperature which has a virtual static stability of Venus with almost neutral layers, and its coefficient is based on Crisp (1986). To prevent numerical instability, the biharmonic hyper-diffusion is included with 0.8 days of e-folding time

  12. An Aeroelastic Perspective of Floating Offshore Wind Turbine Wake Formation and Instability

    NASA Astrophysics Data System (ADS)

    Rodriguez, Steven N.; Jaworski, Justin W.

    2015-11-01

    The wake formation and wake stability of floating offshore wind turbines are investigated from an aeroelastic perspective. The aeroelastic model is composed of the Sebastian-Lackner free-vortex wake aerodynamic model coupled to the nonlinear Hodges-Dowell beam equations, which are extended to include the effects of blade profile asymmetry, higher-order torsional effects, and kinetic energy components associated with periodic rigid-body motions of floating platforms. Rigid-body platform motions are also assigned to the aerodynamic model as varying inflow conditions to emulate operational rotor-wake interactions. Careful attention is given to the wake formation within operational states where the ratio of inflow velocity to induced velocity is over 50%. These states are most susceptible to aerodynamic instabilities, and provide a range of states about which a wake stability analysis can be performed. In addition, the stability analysis used for the numerical framework is implemented into a standalone free-vortex wake aerodynamic model. Both aeroelastic and standalone aerodynamic results are compared to evaluate the level of impact that flexible blades have on the wake formation and wake stability.

  13. Wind tunnel investigation of helicopter-rotor wake effects on three helicopter fuselage models

    NASA Technical Reports Server (NTRS)

    Wilson, J. C.; Mineck, R. E.

    1975-01-01

    The effects of rotor wake on helicopter fuselage aerodynamic characteristics were investigated in the Langley V/STOL tunnel. Force, moment, and pressure data were obtained on three fuselage models at various combinations of windspeed, sideslip angle, and pitch angle. The data show that the influence of rotor wake on the helicopter fuselage yawing moment imposes a significant additional thrust requirement on the tail rotor of a single-rotor helicopter at high sideslip angles.

  14. Vortex and gap generation in gauge models of graphene

    SciTech Connect

    Oliveira, O.; Cordeiro, C.E.; Delfino, A.; Paula, W. de; Frederico, T.

    2011-04-15

    Effective quantum field theoretical continuum models for graphene are investigated. The models include a complex scalar field and a vector gauge field. Different gauge theories are considered and their gap patterns for the scalar, vector, and fermion excitations are investigated. Different gauge groups lead to different relations between the gaps, which can be used to experimentally distinguish the gauge theories. In this class of models the fermionic gap is a dynamic quantity. The finite-energy vortex solutions of the gauge models have the flux of the ''magnetic field'' quantized, making the Bohm-Aharonov effect active even when external electromagnetic fields are absent. The flux comes proportional to the scalar field angular momentum quantum number. The zero modes of the Dirac equation show that the gauge models considered here are compatible with fractionalization.

  15. A non-geometrically similar model for predicting the wake field of full-scale ships

    NASA Astrophysics Data System (ADS)

    Guo, Chunyu; Zhang, Qi; Shen, Yu

    2015-07-01

    The scale effect leads to large discrepancies between the wake fields of model-scale and actual ships, and causes differences in cavitation performance and exciting forces tests in predicting the performance of actual ships. Therefore, when test data from ship models are directly applied to predict the performance of actual ships, test results must be subjected to empirical corrections. This study proposes a method for the reverse design of the hull model. Compared to a geometrically similar hull model, the wake field generated by the modified model is closer to that of an actual ship. A non- geometrically similar model of a Korean Research Institute of Ship and Ocean Engineering (KRISO)'s container ship (KCS) was designed. Numerical simulations were performed using this model, and its results were compared with full-scale calculation results. The deformation method of getting the wake field of full-scale ships by the non-geometrically similar model is applied to the KCS successfully.

  16. Numerical Simulation of Wake Vortices Measured During the Idaho Falls and Memphis Field Programs

    NASA Technical Reports Server (NTRS)

    Proctor, Fred H.

    1996-01-01

    A numerical large-eddy simulation model is under modification and testing for application to aircraft wake vortices. The model, having a meteorological framework, permits the interaction of wake vortices with environments characterized by crosswind shear, stratification, and humidity. As part of the validation process, model results are compared with measured field data from the 1990 Idaho Falls and the 1994-1995 Memphis field experiments. Cases are selected that represent different aircraft and a cross section of meteorological environments. Also included is one case with wake vortex generation in ground effect. The model simulations are initialized with the appropriate meteorological conditions and a post roll-up vortex system. No ambient turbulence is assumed in our initial set of experiments, although turbulence can be self generated by the interaction of the model wakes with the ground and environment.

  17. Preliminary study of the three-dimensional deformation of the vortex in Karman vortex street

    NASA Astrophysics Data System (ADS)

    Ling, Guocan; Guo, Liang; Wu, Zuobin; Ma, Huiyang

    1992-03-01

    The mechanism for 3D evolution of the isolated Karman vortex and the thin-vortex filament in a circular cylinder wake is studied numerically using the LIA method. The results show that the vortex motion is unstable for small 3D disturbances in the separated wake of a circular cylinder. Karman vortex in the time-averaged wake flowfield wolves into a horseshoe-spoon-like 3D structure. The thin vortex filament deforms three-dimensionally in the braid and generates streamwise vortex structures which incline to the region maximum-deformation direction of the flowfield.

  18. Demonstration of rapid-scan two-dimensional laser velocimetry in the Langley Vortex Research Facility for research in aerial applications

    NASA Technical Reports Server (NTRS)

    Gartrell, L. R.; Jordan, F. L., Jr.

    1977-01-01

    Tests were conducted to demonstrate a rapid scan two dimensional laser velocimeter (LV) measurement technique for aerial applications research. The LV system is capable of simultaneously measuring both vertical and axial flow velocity components in a near or far field vortex system. Velocity profiles were successfully measured in the wake vortex of a representative agricultural aircraft model, with the vortex system rapidly transporting in ground effect. Results indicate that the laser velocimetry technique can provide quantitative information of wake vortex characteristics in ground effect.

  19. Numerical study on wake characteristics of high-speed trains

    NASA Astrophysics Data System (ADS)

    Yao, Shuan-Bao; Sun, Zhen-Xu; Guo, Di-Long; Chen, Da-Wei; Yang, Guo-Wei

    2013-11-01

    Intensive turbulence exists in the wakes of high speed trains, and the aerodynamic performance of the trailing car could deteriorate rapidly due to complicated features of the vortices in the wake zone. As a result, the safety and amenity of high speed trains would face a great challenge. This paper considers mainly the mechanism of vortex formation and evolution in the train flow field. A real CRH2 model is studied, with a leading car, a middle car and a trailing car included. Different running speeds and cross wind conditions are considered, and the approaches of unsteady Reynold-averaged Navier-Stokes (URANS) and detached eddy simulation (DES) are utilized, respectively. Results reveal that DES has better capability of capturing small eddies compared to URANS. However, for large eddies, the effects of two approaches are almost the same. In conditions without cross winds, two large vortex streets stretch from the train nose and interact strongly with each other in the wake zone. With the reinforcement of the ground, a complicated wake vortex system generates and becomes strengthened as the running speed increases. However, the locations of flow separations on the train surface and the separation mechanism keep unchanged. In conditions with cross winds, three large vortices develop along the leeward side of the train, among which the weakest one has no obvious influence on the wake flow while the other two stretch to the tail of the train and combine with the helical vortices in the train wake. Thus, optimization of the aerodynamic performance of the trailing car should be aiming at reducing the intensity of the wake vortex system.

  20. Numerical study on wake characteristics of high-speed trains

    NASA Astrophysics Data System (ADS)

    Yao, Shuan-Bao; Sun, Zhen-Xu; Guo, Di-Long; Chen, Da-Wei; Yang, Guo-Wei

    2013-12-01

    Intensive turbulence exists in the wakes of high speed trains, and the aerodynamic performance of the trailing car could deteriorate rapidly due to complicated features of the vortices in the wake zone. As a result, the safety and amenity of high speed trains would face a great challenge. This paper considers mainly the mechanism of vortex formation and evolution in the train flow field. A real CRH2 model is studied, with a leading car, a middle car and a trailing car included. Different running speeds and cross wind conditions are considered, and the approaches of unsteady Reynold-averaged Navier-Stokes (URANS) and detached eddy simulation (DES) are utilized, respectively. Results reveal that DES has better capability of capturing small eddies compared to URANS. However, for large eddies, the effects of two approaches are almost the same. In conditions without cross winds, two large vortex streets stretch from the train nose and interact strongly with each other in the wake zone. With the reinforcement of the ground, a complicated wake vortex system generates and becomes strengthened as the running speed increases. However, the locations of flow separations on the train surface and the separation mechanism keep unchanged. In conditions with cross winds, three large vortices develop along the leeward side of the train, among which the weakest one has no obvious influence on the wake flow while the other two stretch to the tail of the train and combine with the helical vortices in the train wake. Thus, optimization of the aerodynamic performance of the trailing car should be aiming at reducing the intensity of the wake vortex system.

  1. Island Wake Dynamics and Wake Influence on the Evaporation Duct and Radar Propagation.

    NASA Astrophysics Data System (ADS)

    Burk, S. D.; Haack, T.; Rogers, L. T.; Wagner, L. J.

    2003-03-01

    The conditions under which atmospheric island wakes form leeward of Kauai, Hawaii, are investigated using idealized numerical simulations and real data forecasts from the U.S. Navy's Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS). Nondimensional mountain height is varied in a series of idealized simulations by altering the island's terrain height; with increasing , the wake configuration varies from two small counterrotating vortices to a straight wake to a meandering wake to a von Kármán vortex street. In both the idealized and real data forecasts, stability changes across the wake alter the surface layer temperature and moisture profiles, thereby modifying the refractivity and evaporation duct height (EDH) fields. An electromagnetic (EM) propagation model and a radar clutter model are used to demonstrate that the alterations to the refractivity field created by the wake are capable of strongly affecting near-surface EM propagation. Substantial azimuthal variability in radar sea clutter was observed during radar performance tests conducted by the USS O'Kane leeward of Kauai in December of 1999; these anomalies were postulated to result from an island wake. Results from the linkage of COAMPS output with the two EM codes are compared with the radar returns collected aboard the O'Kane, and metrics are developed for comparing COAMPS forecast EDH values with those calculated directly from the shipboard observations.

  2. Peristaltic modes of a single vortex in the Abelian Higgs model

    SciTech Connect

    Kojo, Toru; Suganuma, Hideo; Tsumura, Kyosuke

    2007-05-15

    Using the Abelian Higgs model, we study the radial excitations of single vortex and their propagation modes along the vortex line. We call such beyond-stringy modes peristaltic modes of single vortex. With the profile of the static vortex, we derive the vortex-induced potential, i.e., single-particle potential for the Higgs and the photon field fluctuations around the static vortex, and investigate the coherently propagating fluctuations which correspond to the vibration of the vortex. We derive, analyze, and numerically solve the field equations of the Higgs and the photon field fluctuations around the static vortex with various Ginzburg-Landau parameter {kappa} and topological charge n. Around the Bogomol'nyi-Prasad-Sommerfield value or critical coupling {kappa}{sup 2}=1/2, there appears a significant correlation between the Higgs and the photon field fluctuations mediated by the static vortex. As a result, for {kappa}{sup 2}=1/2, we find the characteristic new-type discrete pole of the peristaltic mode corresponding to the quasibound state of coherently fluctuating fields and the static vortex. We investigate its excitation energy, correlation energy of coherent fluctuations, spatial distributions, and the resulting magnetic flux behavior in detail. Our investigation covers not only usual type-II vortices with n=1 but also type-I and type-II vortices with n set-membership sign Z for the application to various general systems where the vortexlike objects behave as the essential degrees of freedom.

  3. Numerical Simulation and Wake Modeling of Wind Turbine Rotor as AN Actuator Disk

    NASA Astrophysics Data System (ADS)

    Shen, Xiang; Wang, Tongguang; Zhong, Wei

    Numerical simulations of flow fields around the wind turbine rotor simplified as an actuator disk (AD) with zero thickness have been made to investigate the flow structure and wake development in different operation states. A N-S solver has been used and the energy extracted by the rotor is represented by a discontinuous pressure jump through the actuator disk. Axial pressure and velocity development from far upstream to far downstream is fully described by the simulations, which could never be obtained by the momentum theory. It is showed that there are significant differences in wake development between inviscid and viscous conditions. In inviscid simulations, the axial velocity keeps decreasing along the oncoming flow direction, which is consistent with the momentum theory. In viscous simulations, however, the axial velocity first decreases but then gradually recovers approaching to the undisturbed velocity, due to momentum transport from outer flow to wake flow by viscous shear effect. Based on the numerical analysis, the work of this paper is also focused on wake modeling. A new two-dimensional models based on nonlinear wake development has been developed, which is capable to describe the far wake more accurately.

  4. Instability of a two-step Rankine vortex in a reduced gravity QG model

    NASA Astrophysics Data System (ADS)

    Perrot, Xavier; Carton, Xavier

    2014-06-01

    We investigate the stability of a steplike Rankine vortex in a one-active-layer, reduced gravity, quasi-geostrophic model. After calculating the linear stability with a normal mode analysis, the singular modes are determined as a function of the vortex shape to investigate short-time stability. Finally we determine the position of the critical layer and show its influence when it lies inside the vortex.

  5. A numerical investigation of flow around octopus-like arms: near-wake vortex patterns and force development.

    PubMed

    Kazakidi, A; Vavourakis, V; Tsakiris, D P; Ekaterinaris, J A

    2015-01-01

    The fluid dynamics of cephalopods has so far received little attention in the literature, due to their complexity in structure and locomotion. The flow around octopuses, in particular, can be complicated due to their agile and dexterous arms, which frequently display some of the most diverse mechanisms of motion. The study of this flow amounts to a specific instance of the hydrodynamics problem for rough tapered cylinder geometries. The outstanding manipulative and locomotor skills of octopuses could inspire the development of advanced robotic arms, able to operate in fluid environments. Our primary aim was to study the hydrodynamic characteristics of such bio-inspired robotic models and to derive the hydrodynamic force coefficients as a concise description of the vortical flow effects. Utilizing computational fluid dynamic methods, the coefficients were computed on realistic morphologies of octopus-like arm models undergoing prescribed solid-body movements; such motions occur in nature for short durations in time, e.g. during reaching movements and exploratory behaviors. Numerical simulations were performed on translating, impulsively rotating, and maneuvering arms, around which the flow field structures were investigated. The results reveal in detail the generation of complex vortical flow structures around the moving arms. Hydrodynamic forces acting on a translating arm depend on the angle of incidence; forces generated during impulsive rotations of the arms are independent of their exact morphology and the angle of rotation; periodic motions based on a slow recovery and a fast power stroke are able to produce considerable propulsive thrust while harmonic motions are not. Parts of these results have been employed in bio-inspired models of underwater robotic mechanisms. This investigation may further assist elucidating the hydrodynamics underlying aspects of octopus locomotion and exploratory behaviors. PMID:24730546

  6. Numerical modelling of the impulsive orthogonal cutting of a trailing vortex

    NASA Astrophysics Data System (ADS)

    Yildirim, E.; Hillier, R.

    2013-07-01

    This paper presents inviscid compressible simulations for the impulsive blocking of a vortex, with non-zero axial velocity along its core, by a flat plate orthogonal to the vortex axis. This is a simplified model of the blade-vortex interaction between the tail rotor of a helicopter and the trailing vortex system formed by the main rotor system. There are two important elements to this phenomenon. One is the vortex response, including a physical description for the evolution of complex vortical structures near the plate surface, and the second is the resultant pressure wave structure and the manner of its propagation away from the plate surface. This paper focusses more on the vortex structure, and how this is affected by compressibility and the initial transient shock structures that form at the plate surface.

  7. Wake interaction and power production of variable height model wind farms

    NASA Astrophysics Data System (ADS)

    Vested, M. H.; Hamilton, N.; Sørensen, J. N.; Cal, R. B.

    2014-06-01

    Understanding wake dynamics is an ongoing research topic in wind energy, since wakes have considerable effects on the power production when wind turbines are placed in a wind farm. Wind tunnel experiments have been conducted to study the wake to wake interaction in a model wind farm in tandem with measurements of the extracted power. The aim is to investigate how alternating mast height influences the interaction of the wakes and the power production. Via the use of stereo-particle image velocimetry, the flow field was obtained in the first and last rows of the wind turbine array as a basis of comparison. It was found that downstream of the exit row wind turbine, the power was increased by 25% in the case of a staggered height configuration. This is partly due to the fact that the taller turbines reach into a flow area with a softened velocity gradient. Another aspect is that the wake downstream of a tall wind turbine to some extent passes above the standard height wind turbine. Overall the experiments show that the velocity field downstream of the exit row changes considerably when the mast height is alternating.

  8. Wind Speed Estimation and Wake model Re-calibration for Downregulated Offshore Wind Farms

    NASA Astrophysics Data System (ADS)

    Göçmen Bozkurt, Tuhfe; Giebel, Gregor; Kjølstad Poulsen, Niels; Réthoré, Pierre-Elouan; Mirzaei, Mahmood

    2014-05-01

    In recent years, the wind farm sizes have increased tremendously and with increasing installed capacity, the wind farms are requested to downregulate from their maximum possible power more frequently, especially in the offshore environment. Determination of the possible (or available) power is crucial not only because the reserve power has considerable market value but also for wind farm developers to be properly compensated for the loss during downregulation. While the available power calculation is straightforward for a single turbine, it gets rather complicated for the whole wind farm due to the change in the wake characteristics. In fact, the wake losses generated by the upstream turbine(s) decrease during downregulation and the downstream turbines therefore see more wind compared to the normal operation case. Currently, the Transmission System Operators (TSOs) have no real way to determine exactly the available power of a whole wind farm which is downregulated. Therefore, the PossPOW project aims to develop a verified and internationally accepted way to determine the possible power of a down-regulated offshore wind farm. The first phase of the project is to estimate the rotor effective wind speed. Since the nacelle anemometers are not readily available and are known to have reliability issues, the proposed method is to use power, pitch angle and rotational speed as inputs and combine it with a generic Cp model to estimate the wind speed. The performance of the model has been evaluated for both normal operation and downregulation periods using two different case studies: Horns Rev-I wind farm and NREL 5MW single turbine. During downregulation, the wake losses are not as severe and the velocity deficits at the downstream turbines are smaller as if also the wake is "downregulated". On the other hand, in order to calculate the available power, the wakes that would have been produced normally (if the turbines were not curtailed) are of importance, not the

  9. Fixed-wake analysis of the Darrieus rotor

    SciTech Connect

    Wilson, R.E.; Walker, S.N.

    1981-07-01

    Development and validation of a Darrieus wind turbine aerodynamic performance prediction model is described. Using a fixed-wake approach, the model combines some of the more desirable features of vortex/lifting line and conservation of momentum/streamtube approaches. The model thus accounts for up- and downwind differences that are predicted by vortex approaches while retaining the short computer run times found with streamtube models. The model treats the effects of stall, curved blades, blade pitch, and blade attachment location. Results agree with those obtained with Sandia National Laboratories' 17-m-diameter Darrieus VAWT.

  10. Inviscid Interactions Between Wake Vortices and Shear Layers

    NASA Technical Reports Server (NTRS)

    Zheng, Z. C.; Baek, K.

    1998-01-01

    Aircraft trailing vortices can be influenced significantly by atmospheric conditions such as crosswind, turbulence, and stratification. According to the NASA 1994 and 1995 field measurement program in Memphis, Tennessee, the descending aircraft wake vortices could stall or be deflected at the top of low-level temperature inversions that usually produce pronounced shear zones. Numerical simulations of vortex/shear interactions with ground effects have been performed by several groups. Burnham used a series of evenly spaced line vortices at a particular altitude to model the ground shear layer of the cross- wind. He found that the wind shear was swept up around the downwind vortex and caused the downwind vortex to move upward, and claimed that the effect was actually produced by the vertical gradient in the wind shear rather than by the wind shear directly, because uniformly distributed wind-shear vortices would have no effect on the trailing vortex vertical motion. Recently, Proctor et al. numerically tested the effects of narrow shear zones on the behavior of the vortex pair, motivated by the observation of the Memphis field data. The shear-layer sensitivity tests indicated that the downwind vortex was more sensitive and deflected to a higher altitude than its upwind counterpart. The downstream vortex contained vorticity of opposite sign to that of the shear. There was no detectable preference for the downwind vortex (or upwind vortex) to weaken (or strengthen) at a greater rate.

  11. Wake Numerical Simulation Based on the Park-Gauss Model and Considering Atmospheric Stability

    NASA Astrophysics Data System (ADS)

    Yang, Xiangsheng; Zhao, Ning; Tian, Linlin; Zhu, Jun

    2016-06-01

    In this paper, a new Park-Gauss model based on the assumption of the Park model and the Eddy-viscosity model is investigated to conduct the wake numerical simulation for solving a single wind turbine problem. The initial wake radius has been modified to improve the model’s numerical accuracy. Then the impact of the atmospheric stability based on the Park-Gauss model has been studied in the wake region. By the comparisons and the analyses of the test results, it turns out that the new Park-Gauss model could achieve better effects of the wind velocity simulation in the wake region. The wind velocity in the wake region recovers quickly under the unstable atmospheric condition provided the wind velocity is closest to the test result, and recovers slowly under stable atmospheric condition in case of the wind velocity is lower than the test result. Meanwhile, the wind velocity recovery falls in between the unstable and stable neutral atmospheric conditions.

  12. Recent Developments on Airborne Forward Looking Interferometer for the Detection of Wake Vortices

    NASA Technical Reports Server (NTRS)

    Daniels, Taumi S.; Smith, William L.; Kirev, Stanislav

    2012-01-01

    A goal of these studies was development of the measurement methods and algorithms necessary to detect wake vortex hazards in real time from either an aircraft or ground-based hyperspectral Fourier Transform Spectrometer (FTS). This paper provides an update on research to model FTS detection of wake vortices. The Terminal Area Simulation System (TASS) was used to generate wake vortex fields of 3-D winds, temperature, and absolute humidity. These fields were input to the Line by Line Radiative Transfer Model (LBLRTM), a hyperspectral radiance model in the infrared, employed for the FTS numerical modeling. An initial set of cases has been analyzed to identify a wake vortex IR signature and signature sensitivities to various state variables. Results from the numerical modeling case studies will be presented. Preliminary results indicated that an imaging IR instrument sensitive to six narrow bands within the 670 to 3150 per centimeter spectral region would be sufficient for wake vortex detection. Noise floor estimates for a recommended instrument are a current research topic.

  13. Wind tunnel study of wake downwash behind A 6% scale model B1-B aircraft

    SciTech Connect

    Strickland, J.H.; Tadios, E.L.; Powers, D.A.

    1990-05-01

    Parachute system performance issues such a turnover and wake recontact may be strongly influenced by velocities induced by the wake of the delivering aircraft, especially if the aircraft is maneuvering at the time of parachute deployment. The effect of the aircraft on the parachute system is a function of the aircraft size, weight, and flight path. In order to provide experimental data for validation of a computer code to predict aircraft wake velocities, a test was conducted in the NASA 14 {times} 22 ft wind tunnel using a 5.78% model of the B-1B strategic bomber. The model was strut mounted through the top of its fuselage by a mechanism which was capable of pitching the model at moderate rates. In this series of tests, the aircraft was pitched at 10{degree}/sec from a cruise angle of attack of 5.3{degree} to an angle of attack of 11{degree} in order to simulate a 2.2g pullup. Data were also taken for the subsequent pitch down sequence back to the cruise angle of attack. Instantaneous streamwise and vertical velocities were measured in the wake at a number of points using a hot wire anemometer. These data have been reduced to the form of downwash coefficients which are a function of the aircraft angle of attack time-history. Unsteady effects are accounted for by use of a wake convection lag-time correlation. 12 refs., 59 figs., 4 tabs.

  14. Mode Transition and Symmetry-Breaking in the Wake of a Flapping Foil

    NASA Astrophysics Data System (ADS)

    He, G. Y.; Zhang, X.; Zhang, S. G.; Wang, Q.

    2011-09-01

    A numerical model for two-dimensional flows around a pitching foil in a viscous flow is presented. The model is numerically solved using the immersed boundary method and used to investigate the flow patterns of the foil pitching sinusoidally over a range of frequencies and amplitudes. A transition from the Karman vortex streets to the reverse Karman vortex streets are found, as the amplitudes of pitching motions increase. In the transition, the vortex streets undergo symmetry-breaking to the central lines of vortex streets. Those observations are in agreement with the previous experiment (Phys. Rev. E. 77 016308 2008). Furthermore, we examine the wake of the foils pitching with different frequencies. The transition from the Karman vortex streets to the reverse Karman vortex streets is also observed. An explanation is presented to the mechanism of the transition.

  15. Dynamic analysis of marine risers with vortex excitation

    SciTech Connect

    Nordgren, R.P.

    1982-03-01

    The basic equations for nonplanar transverse vibrations of marine risers are derived from the theory of elastic rods. A numerical method is developed for solution of the equations by time integration. Spatial discretization is accomplished by a hybrid finite element method. Vortex excitation is modeled by the coupled wake oscillator proposed by Iwan and Blevins. The vortex oscillator equations are integrated numerically in time along with the riser equations. By way of example, several typical riser problems are analyzed including forced vibration and vortex-induced vibration.

  16. Rotor Wake Development During the First Revolution

    NASA Technical Reports Server (NTRS)

    McAlister, Kenneth W.

    2003-01-01

    The wake behind a two-bladed model rotor in light climb was measured using particle image velocimetry, with particular emphasis on the development of the trailing vortex during the first revolution of the rotor. The distribution of vorticity was distinguished from the slightly elliptical swirl pattern. Peculiar dynamics within the void region may explain why the peak vorticity appeared to shift away from the center as the vortex aged, suggesting the onset of instability. The swirl and axial velocities (which reached 44 and 12 percent of the rotor-tip speed, respectively) were found to be asymmetric relative to the vortex center. In particular, the axial flow was composed of two concentrated zones moving in opposite directions. The radial distribution of the circulation rapidly increased in magnitude until reaching a point just beyond the core radius, after which the rate of growth decreased significantly. The core-radius circulation increased slightly with wake age, but the large-radius circulation appeared to remain relatively constant. The radial distributions of swirl velocity and vorticity exhibit self-similar behaviors, especially within the core. The diameter of the vortex core was initially about 10 percent of the rotor-blade chord, but more than doubled its size after one revolution of the rotor. According to vortex models that approximate the measured data, the core-radius circulation was about 79 percent of the large-radius circulation, and the large-radius circulation was about 67 percent of the maximum bound circulation on the rotor blade. On average, about 53 percent of the maximum bound circulation resides within the vortex core during the first revolution of the rotor.

  17. Regimes of flow past a vortex generator

    NASA Astrophysics Data System (ADS)

    Velte, C. M.; Okulov, V. L.; Naumov, I. V.

    2012-04-01

    A complete parametric investigation of the development of multi-vortex regimes in a wake past simple vortex generator has been carried out. It is established that the vortex structure in the wake is much more complicated than a simple monopole tip vortex. The vortices were studied by stereoscopic particle image velocimetry (SPIV). Based on the obtained SPIV data, a map of the regimes of flow past the vortex generator has been constructed. One region with a developed stable multivortex system on this map reaches the vicinity of the optimum angle of attack of the vortex generator.

  18. A comparison of wake characteristics of model and prototype buildings in transverse winds

    NASA Technical Reports Server (NTRS)

    Logan, E., Jr.; Phataraphruk, P.; Chang, J.

    1978-01-01

    Previously measured mean velocity and turbulence intensity profiles in the wake of a 26.8-m long building 3.2 m high and transverse to the wind direction in an atmospheric boundary layer several hundred meters thick were compared with profiles at corresponding stations downstream of a 1/50-scale model on the floor of a large meteorological wind tunnel in a boundary layer 0.61 m in thickness. The validity of using model wake data to predict full scale data was determined. Preliminary results are presented which indicate that disparities result from differences in relative depth of logarithmic layers, surface roughness, and the proximity of upstream obstacles.

  19. Computation of rotor aerodynamic loads in forward flight using a full-span free wake analysis

    NASA Technical Reports Server (NTRS)

    Quackenbush, Todd R.; Bliss, Donald B.; Wachspress, Daniel A.; Boschitsch, Alexander H.; Chua, Kiat

    1990-01-01

    The development of an advanced computational analysis of unsteady aerodynamic loads on isolated helicopter rotors in forward flight is described. The primary technical focus of the development was the implementation of a freely distorting filamentary wake model composed of curved vortex elements laid out along contours of constant vortex sheet strength in the wake. This model captures the wake generated by the full span of each rotor blade and makes possible a unified treatment of the shed and trailed vorticity in the wake. This wake model was coupled to a modal analysis of the rotor blade dynamics and a vortex lattice treatment of the aerodynamic loads to produce a comprehensive model for rotor performance and air loads in forward flight dubbed RotorCRAFT (Computation of Rotor Aerodynamics in Forward Flight). The technical background on the major components of this analysis are discussed and the correlation of predictions of performance, trim, and unsteady air loads with experimental data from several representative rotor configurations is examined. The primary conclusions of this study are that the RotorCRAFT analysis correlates well with measured loads on a variety of configurations and that application of the full span free wake model is required to capture several important features of the vibratory loading on rotor blades in forward flight.

  20. A Hybrid Vortex Method for Two-Dimensional Flow Over Tube Bundles

    SciTech Connect

    Strickland, J.H.; Wolfe, W.P.

    1998-11-13

    A hybrid vortex method is presented for computing flows about objects that accurately resolves the boundary layer details while keeping the number of free vortices at a reasonable level. The method uses a wall layer model close to the body surface and discrete vortex blobs in the free wake. Details of the wall layer implementation are presented, and results of sample calculations are compared with known analytical solutions and with calculations from other vortex codes. These results show that the computed boundary layer details are accurate to approximately 0.3 percent of analytical solutions while using three orders of magnitude fewer vortices than other vortex simulations.

  1. Transition and Turbulence Modeling for Blunt-Body Wake Flows

    NASA Technical Reports Server (NTRS)

    Nance, Robert P.; Horvath, Thomas J.; Hassan, H. A.

    1997-01-01

    Aerobraking has been proposed as an efficient means of decelerating spacecraft for planetary missions. Most current aerobrake designs feature a blunt forebody shielding the payload from the intense heat generated during atmospheric entry. Although this forebody will absorb the largest portion of the heat pulse, accurate prediction of heating in the near wake is of great importance, since large local heating values can occur at points of shear-layer impingement. In order to address the various issues associated with these blunt-body wake flowfields, the Advisory Group for Aerospace Research and Development (AGARD) formed Working Group 18 in 1992. One of the objectives of this activity was to examine real-gas effects in high-speed flow fields around a 70 deg. blunted cone. To date, many researchers have conducted experiments using this geometry in various facilities, such as the Large Energy National Shock (LENS) tunnel at Cubric/Calspan and the HEG shock tunnel at DLR-Goettingen. Several computational studies have also been conducted in concert with these tests. Many of the experimental results have indicated the possible presence of a transitional shear layer through a large increase in heat transfer downstream of the reattachment point. The presence of transition could in fact lead to much higher peak heating than if the separated flow is entirely laminar or turbulent. In the shock-tunnel tests, however, it is difficult to separate such viscous-flow phenomena from real-gas effects. In order to help make this distinction, Horvath et al. recently conducted a set of experiments in the NASA Langley 20-Inch Mach 6 Tunnel, and compared the results to laminar Navier-Stokes calculations. They found heat-transfer distributions similar to those obtained in the high-enthalpy facilities, with the measured peak heating along the sting support markedly greater than that predicted by the laminar computations. These trends point to the need to find transitional and turbulent

  2. IEA-Task 31 WAKEBENCH: Towards a protocol for wind farm flow model evaluation. Part 2: Wind farm wake models

    NASA Astrophysics Data System (ADS)

    Moriarty, Patrick; Sanz Rodrigo, Javier; Gancarski, Pawel; Chuchfield, Matthew; Naughton, Jonathan W.; Hansen, Kurt S.; Machefaux, Ewan; Maguire, Eoghan; Castellani, Francesco; Terzi, Ludovico; Breton, Simon-Philippe; Ueda, Yuko

    2014-06-01

    Researchers within the International Energy Agency (IEA) Task 31: Wakebench have created a framework for the evaluation of wind farm flow models operating at the microscale level. The framework consists of a model evaluation protocol integrated with a web-based portal for model benchmarking (www.windbench.net). This paper provides an overview of the building-block validation approach applied to wind farm wake models, including best practices for the benchmarking and data processing procedures for validation datasets from wind farm SCADA and meteorological databases. A hierarchy of test cases has been proposed for wake model evaluation, from similarity theory of the axisymmetric wake and idealized infinite wind farm, to single-wake wind tunnel (UMN-EPFL) and field experiments (Sexbierum), to wind farm arrays in offshore (Horns Rev, Lillgrund) and complex terrain conditions (San Gregorio). A summary of results from the axisymmetric wake, Sexbierum, Horns Rev and Lillgrund benchmarks are used to discuss the state-of-the-art of wake model validation and highlight the most relevant issues for future development.

  3. A Drosophila model for age-associated changes in sleep:wake cycles.

    PubMed

    Koh, Kyunghee; Evans, Joshua M; Hendricks, Joan C; Sehgal, Amita

    2006-09-12

    One of the most consistent behavioral changes that occurs with age in humans is the loss of sleep consolidation. This can be quite disruptive and yet little is known about its underlying basis. To better understand the effects of aging on sleep:wake cycles, we sought to study this problem in Drosophila melanogaster, a powerful system for research on aging and behavior. By assaying flies of different ages as well as monitoring individual flies constantly over the course of their lifetime, we found that the strength of sleep:wake cycles decreased and that sleep became more fragmented with age in Drosophila. These changes in sleep:wake cycles became faster or slower with manipulations of ambient temperature that decreased or increased lifespan, respectively, demonstrating that they are a function of physiological rather than chronological age. The effect of temperature on lifespan was not mediated by changes in overall activity level or sleep amount. Flies treated with the oxidative stress-producing reagent paraquat showed a breakdown of sleep:wake cycles similar to that seen with aging, leading us to propose that the accumulation of oxidative damage with age contributes to the changes in rhythm and sleep. Together, these findings establish Drosophila as a valuable model for studying age-associated sleep fragmentation and breakdown of rhythm strength, and indicate that these changes in sleep:wake cycles are an integral part of the physiological aging process. PMID:16938867

  4. Simulations of tip vortex cavitation flows with nonlinear k-ε model

    NASA Astrophysics Data System (ADS)

    Wang, Benlong; Liu, Zhihui; Peng, Xiaoxing; Liu, Dengcheng

    2015-12-01

    Effects of turbulence models on the simulations of tip vortex wetted flows and cavitating flows are studied. Two types RANS turbulence models, with and beyond the Boussinesq turbulent-viscosity hypothesis, are investigated by examining experimental results regarding strain rate and Reynolds shear stress distributions in the vortex region. The numerical results imply that the spatial phase shift between the mean strain rate and Reynolds stresses can be accurately modeled by the nonlinear k-ε turbulence model; the tip vortex cavitation region can only be predicted using the nonlinear turbulence model. The mechanism of the over-dissipation due to the turbulence model is analyzed in terms of the turbulence production, which is one of the dominant source terms in the transport equations of energy. The numerical results imply that the nonlinear k-ε model is a promising candidate for predicting tip vortex cavitation flows in practical applications at a reasonable computational cost.

  5. A Mathematical Model towards Understanding the Mechanism of Neuronal Regulation of Wake-NREMS-REMS States

    PubMed Central

    Kumar, Rupesh; Bose, Amitabha; Mallick, Birendra Nath

    2012-01-01

    In this study we have constructed a mathematical model of a recently proposed functional model known to be responsible for inducing waking, NREMS and REMS. Simulation studies using this model reproduced sleep-wake patterns as reported in normal animals. The model helps to explain neural mechanism(s) that underlie the transitions between wake, NREMS and REMS as well as how both the homeostatic sleep-drive and the circadian rhythm shape the duration of each of these episodes. In particular, this mathematical model demonstrates and confirms that an underlying mechanism for REMS generation is pre-synaptic inhibition from substantia nigra onto the REM-off terminals that project on REM-on neurons, as has been recently proposed. The importance of orexinergic neurons in stabilizing the wake-sleep cycle is demonstrated by showing how even small changes in inputs to or from those neurons can have a large impact on the ensuing dynamics. The results from this model allow us to make predictions of the neural mechanisms of regulation and patho-physiology of REMS. PMID:22905114

  6. Vortex modeling for rotor aerodynamics - The 1991 Alexander A. Nikolsky Lecture

    NASA Technical Reports Server (NTRS)

    Gray, Robin B.

    1992-01-01

    The efforts toward realistic vortex modeling for rotary wings which began under the guidance of professor A. A. Nikolsky of Princeton University in 1955-1956 are discussed. Attention is given to Nikolsky's flow-visualization studies and major theoretical considerations for vortex modeling. More recent efforts by other researchers have led to models of increasing complexity. The neglect of compressibility and viscous effects in the classical approach is noted to be a major limiting factor in full-scale rotor applications of the classical vortex theory; it has nevertheless been valuable for the delineation of problem areas and the guiding of both experimental and theoretical investigations.

  7. Transverse forces on a vortex in lattice models of superfluids

    NASA Astrophysics Data System (ADS)

    Sonin, E. B.

    2013-12-01

    The paper derives the transverse forces (the Magnus and the Lorentz forces) in the lattice models of superfluids in the continuous approximation. The continuous approximation restores translational invariance absent in the original lattice model, but the theory is not Galilean invariant. As a result, calculation of the two transverse forces on the vortex, Magnus force and Lorentz force, requires the analysis of two balances, for the true momentum of particles in the lattice (Magnus force) and for the quasimomentum (Lorentz force) known from the Bloch theory of particles in the periodic potential. While the developed theory yields the same Lorentz force, which was well known before, a new general expression for the Magnus force was obtained. The theory demonstrates how a small Magnus force emerges in the Josephson-junction array if the particle-hole symmetry is broken. The continuous approximation for the Bose-Hubbard model close to the superfluid-insulator transition was developed, which was used for calculation of the Magnus force. The theory shows that there is an area in the phase diagram for the Bose-Hubbard model, where the Magnus force has an inverse sign with respect to that which is expected from the sign of velocity circulation.

  8. Wing-vortex interaction: unraveling the flowfield of a hovering rotor

    NASA Astrophysics Data System (ADS)

    Bhagwat, Mahendra J.; Caradonna, Francis X.; Ramasamy, Manikandan

    2015-01-01

    This paper focuses on one of the most prominent flow features of the hovering rotor wake, the close interaction of the tip vortex with a following blade. Such vortex interactions are fundamental determinants of rotor performance, loads, and noise. Yet, they are not completely understood, largely due to the lack of sufficiently comprehensive experimental data. The present study aims to perform such comprehensive measurements, not on hovering helicopter rotors (which hugely magnifies test complexity) but using fixed-wing models in controlled wind tunnel tests. The experiments were designed to measure, in considerable detail, the aerodynamic loading resulting from a vortex interacting with a semi-span wing, as well as the wake resulting from that interaction. The goal of the present study is to answer fundamental questions such as (a) the influence of a vortex passing below a wing on the lift, drag, tip vortex, and the wake of that wing and (b) the strength of the forming tip vortex and its relation to the wing loading and/or the tip loading. This paper presents detailed wing surface pressure measurements that result from the interaction of the wing with an interacting vortex trailing from an upstream wing. The data show large lift distribution changes for a range of wing-vortex interactions including the effects of close encounter with the vortex core. Significant asymmetry in the vortex-induced lift loading was observed, with the increase in wing sectional lift outboard of the interacting vortex (closer to the tip) being much smaller than the corresponding decrease inboard of the vortex.

  9. On the evolution of the wake structure produced by a low-aspect-ratio pitching panel

    PubMed Central

    BUCHHOLZ, JAMES H. J.; SMITS, ALEXANDER J.

    2009-01-01

    Flow visualization is used to interrogate the wake structure produced by a rigid flat panel of aspect ratio (span/chord) 0.54 pitching in a free stream at a Strouhal number of 0.23. At such a low aspect ratio, the streamwise vorticity generated by the plate tends to dominate the formation of the wake. Nevertheless, the wake has the appearance of a three-dimensional von Kármán vortex street, as observed in a wide range of other experiments, and consists of horseshoe vortices of alternating sign shed twice per flapping cycle. The legs of each horseshoe interact with the two subsequent horseshoes in an opposite-sign, then like-sign interaction in which they become entrained. A detailed vortex skeleton model is proposed for the wake formation. PMID:19746198

  10. Vortex-Vortex Interactions Behind an Oscillating Plate

    NASA Astrophysics Data System (ADS)

    Unal, M. F.; Rockwell, D.

    1996-11-01

    A blunt-based flat plate in a uniform stream is subjected to periodic pitching oscillations at multiples of the natural shedding frequency over a range of dime nsionless amplitudes. The near wake is characterized by dye and hydrogen bubble visualization. At low amplitudes of oscillation, the nature of the vortex-vortex interaction in the near-wake is such that, irrespective of oscillation frequency , the downstream wake remarkably recovers to the classical vortex street. For hi gh amplitudes, at frequencies higher than the natural shedding frequency, the vo rtex street gives way to complex vortex configurations. These features are relat ed to several interesting phenomena in the base region, including pronounced she dding of vorticity from the base and existence of a very small-scale vortex stre et along the plane of symmetry.

  11. Vortex shedding from struts in an annular exhaust diffuser

    SciTech Connect

    Fric, T.F.; Villarreal, R.; Auer, R.O.; James, M.L.; Ozgur, D.; Staley, T.K.

    1998-01-01

    Results from scale-model experiments and industrial gas turbine tests show that strut vortex shedding in an annular exhaust diffuser can effectively be modified by adding tapered chord to the struts. The struts are bluff bodies at full-speed, no-load conditions, when inlet swirl is close to 60 deg. Data from wind tunnel tests show that wake Strouhal number is 0.47, larger than that expected for an isolated cylinder wake. This value of Strouhal number agrees with those measured in full-scale exhaust diffusers. Wind tunnel tests showed that a strut with tapered chord most effectively reduced wake amplitudes and shifted shedding frequency. The tapered strut was also effective in reducing shedding amplitude in a scale-model diffuser. Finally, gas turbine tests employing a tapered strut showed significant reductions in unsteady pressure and noise. A major benefit of strut taper is a reduction of noise by uncoupling of vortex shedding from acoustic resonant response.

  12. Turbulence structures in wind turbine wake: Effects of atmospheric stratification

    NASA Astrophysics Data System (ADS)

    Bhaganagar, Kiran

    2014-11-01

    Turbulence structure in the wake behind full-scale horizontal-axis WT under the influence of realistic atmospheric turbulent flow conditions has been investigated using actuator-line-model based large-eddy-simulations. Wind turbine simulations have revealed that, in addition to wind shear and ABL turbulence, height-varying wind angle and low-level jets are ABL metrics that influence the structure of turbine wake. Turbulent mixing layer forms downstream of the WT, the strength and size of which decreases with increasing stability. Height dependent wind angle and turbulence are the ABL metrics influencing the lateral wake expansion. Further, ABL metrics strongly impact the evolution of tip and root vortices formed behind the rotor. Two factors play an important role in wake meandering: tip vortex merging due to the mutual inductance form of instability and the corresponding instability of the turbulent mixing layer. NSF CBET Energy for Sustainability.

  13. PRELIMINARY STUDIES OF VIDEO IMAGES OF SMOKE DISPERSION IN THE NEAR WAKE OF A MODEL BUILDING

    EPA Science Inventory

    A scary of analyses of video images of smoke in a wind tunnel study of dispersion in the near wake of a model building is presented. The analyses provide information on both the instantaneous and the time- average patterns of dispersion. ince the images represent vertically-integ...

  14. A Simple Analytical Model for Batoid Wake topology and Propulsive Forces

    NASA Astrophysics Data System (ADS)

    Valdivia Y Alvarado, Pablo; Srivatsa, Karthik

    2013-11-01

    Batoids swim by forcing waves along their large pectoral fins. These waves determine the topology of the shed wakes and the resulting propulsive forces. An understanding of the relation between fin kinematics and wake topology is essential to control vehicles that use batoid-like fin propulsion. Simulations of the fluid-structure interactions during fin motions provide information of the changes in wake topology and the propulsive forces that result with variations in fin kinematics. However, simulations require computing power usually not available in mobile robots and cannot be used for real time control. An alternative is to develop simple qualitative models whose errors can be compensated by closed loop feedback controllers. Here we describe an analytical model that can be used to predict wake geometry and resulting propulsive forces in batoid-like fins. The model incorporates important fin kinematic parameters such as wave number, amplitude envelope, and flapping frequency. Dye flow visualization and particle image velocimetry along with force measurements confirm the model applicability to batoid-like fin propulsion. This work was funded in whole or in part by the Singapore National Research Foundation (NRF) through the Singapore-MIT Alliance for Research and Technology (SMART).

  15. Estimation of the circulation distribution on a rotor blade from detailed near wake velocities

    NASA Astrophysics Data System (ADS)

    Mast, E. H. M.; Vermeer, L. J.; van Bussel, G. J. W.

    2004-07-01

    The circulation distribution over a blade of a wind turbine model is estimated by use of a vortex model, which is matched with measured wake properties. With near wake velocities and the Biot-Savart law an optimization scheme is constructed to estimate the circulation distribution over the blade using a polynomial function series to approximate the circulation distribution. The velocities resulting from the calculated distribution are compared with the measured data, and deviations are discussed and explained. The vortex model offers insight into how the measured velocities can be separated into induced velocities of the different parts of the vortex system, such as the influence of the tip vortex. The sensitivity of the vortex model to its most uncertain parameters is tested. Finally the circulation distribution obtained with the vortex model is compared with the circulation distribution obtained through application of a blade element momentum (BEM) code. The BEM results show an underestimation of the circulation near the root and an overestimation of the circulation near the tip with respect to the vortex model results. Copyright

  16. Source Term Model for Vortex Generator Vanes in a Navier-Stokes Computer Code

    NASA Technical Reports Server (NTRS)

    Waithe, Kenrick A.

    2004-01-01

    A source term model for an array of vortex generators was implemented into a non-proprietary Navier-Stokes computer code, OVERFLOW. The source term models the side force created by a vortex generator vane. The model is obtained by introducing a side force to the momentum and energy equations that can adjust its strength automatically based on the local flow. The model was tested and calibrated by comparing data from numerical simulations and experiments of a single low profile vortex generator vane on a flat plate. In addition, the model was compared to experimental data of an S-duct with 22 co-rotating, low profile vortex generators. The source term model allowed a grid reduction of about seventy percent when compared with the numerical simulations performed on a fully gridded vortex generator on a flat plate without adversely affecting the development and capture of the vortex created. The source term model was able to predict the shape and size of the stream-wise vorticity and velocity contours very well when compared with both numerical simulations and experimental data. The peak vorticity and its location were also predicted very well when compared to numerical simulations and experimental data. The circulation predicted by the source term model matches the prediction of the numerical simulation. The source term model predicted the engine fan face distortion and total pressure recovery of the S-duct with 22 co-rotating vortex generators very well. The source term model allows a researcher to quickly investigate different locations of individual or a row of vortex generators. The researcher is able to conduct a preliminary investigation with minimal grid generation and computational time.

  17. Wake visualization behind multiple VAWTs in a wind tunnel using sPIV

    NASA Astrophysics Data System (ADS)

    Parker, Colin; Leftwich, Megan C.

    2014-11-01

    This work visualizes the wake behind multiple vertical axis wind turbines (VAWTs). The flow is visualized in a wind tunnel behind scaled model VAWTs driven at constant rotational velocity. The wake is visualized using stereo particle imaging velocimetry (sPIV) at the mid-plane downstream of the turbines. Syncing the sPIV system with the rotation of the turbine allows images to be taken at known phase angles. These images are then averaged to see the phase-averaged wake behind the VAWTs. Moving downstream, the averaged wake structure can be tracked by phase matching. Initially, data was taken in the near wake behind a single VAWT. As the blade turns normal to, and then back towards the free-stream, a vortex structure is shed into the wake and moves downstream. The out-of-plane velocity corresponding to this vortex pair shows the structures to be highly three-dimensional. Phase averaged wakes show distinct structures behind the turbine that move downstream with the free stream. Next, we measured the wake interactions behind a two turbine system. In this setup, a pair of counter rotating VAWTs is placed in the wind tunnel. We can vary the spacing and orientation between the counter rotating pair to compare changes in the downstream wind profile.

  18. Mathematical Models for Sleep-Wake Dynamics: Comparison of the Two-Process Model and a Mutual Inhibition Neuronal Model

    PubMed Central

    Skeldon, Anne C.; Dijk, Derk-Jan; Derks, Gianne

    2014-01-01

    Sleep is essential for the maintenance of the brain and the body, yet many features of sleep are poorly understood and mathematical models are an important tool for probing proposed biological mechanisms. The most well-known mathematical model of sleep regulation, the two-process model, models the sleep-wake cycle by two oscillators: a circadian oscillator and a homeostatic oscillator. An alternative, more recent, model considers the mutual inhibition of sleep promoting neurons and the ascending arousal system regulated by homeostatic and circadian processes. Here we show there are fundamental similarities between these two models. The implications are illustrated with two important sleep-wake phenomena. Firstly, we show that in the two-process model, transitions between different numbers of daily sleep episodes can be classified as grazing bifurcations. This provides the theoretical underpinning for numerical results showing that the sleep patterns of many mammals can be explained by the mutual inhibition model. Secondly, we show that when sleep deprivation disrupts the sleep-wake cycle, ostensibly different measures of sleepiness in the two models are closely related. The demonstration of the mathematical similarities of the two models is valuable because not only does it allow some features of the two-process model to be interpreted physiologically but it also means that knowledge gained from study of the two-process model can be used to inform understanding of the behaviour of the mutual inhibition model. This is important because the mutual inhibition model and its extensions are increasingly being used as a tool to understand a diverse range of sleep-wake phenomena such as the design of optimal shift-patterns, yet the values it uses for parameters associated with the circadian and homeostatic processes are very different from those that have been experimentally measured in the context of the two-process model. PMID:25084361

  19. The interaction of helical tip and root vortices in a wind turbine wake

    NASA Astrophysics Data System (ADS)

    Sherry, Michael; Nemes, András; Lo Jacono, David; Blackburn, Hugh M.; Sheridan, John

    2013-11-01

    Analysis of the helical vortices measured behind a model wind turbine in a water channel are reported. Phase-locked measurements using planar particle image velocimetry are taken behind a Glauert rotor to investigate the evolution and breakdown of the helical vortex structures. Existing linear stability theory predicts helical vortex filaments to be susceptible to three unstable modes. The current work presents tip and root vortex evolution in the wake for varying tip speed ratio and shows a breaking of the helical symmetry and merging of the vortices due to mutual inductance between the vortical filaments. The merging of the vortices is shown to be steady with rotor phase, however, small-scale non-periodic meander of the vortex positions is also observed. The generation of the helical wake is demonstrated to be closely coupled with the blade aerodynamics, strongly influencing the vortex properties which are shown to agree with theoretical predictions of the circulation shed into the wake by the blades. The mutual inductance of the helices is shown to occur at the same non-dimensional wake distance.

  20. A vortex shedding model of a flapping membrane

    NASA Astrophysics Data System (ADS)

    Michelin, Sebastien; Smith, Stefan G. Llewellyn

    2008-11-01

    The behavior of a two-dimensional flexible membrane in an imposed axial high-Re flow is investigated. The coupling of the internal solid dynamics and the fluid dynamics makes the direct numerical simulation of this situation a computationally expensive and challenging problem. A reduced-order representation of the flow around the solid is used here to study the coupled dynamics. The vortical wake is accounted for by the shedding of point vortices with monotonically-varying intensity (Brown--Michael vortices) from the trailing edge. This model is used to investigate the flapping flag instability that arises from the competition of the destabilizing pressure difference created by the flag deflection, its bending rigidity and its inertia. The stability of the flag state of rest and the structure of the flapping modes are studied and compared to the results of the linear stability analysis. Finally, a study of the kinematic and dynamic waves traveling along the flag in the flapping regime is presented.

  1. Calculations of longitudinal and transverse velocity structure functions using a vortex model of isotropic turbulence

    SciTech Connect

    He, G.; Doolen, G.D.; Chen, S.

    1999-12-01

    The longitudinal structure function (LSF) and the transverse structure function (TSF) in isotropic turbulence are calculated using a vortex model. The vortex model is composed of the Rankine and Burgers vortices which have the exponential distributions in the vortex Reynolds number and vortex radii. This model exhibits a power law in the inertial range and satisfies the minimal condition of isotropy that the second-order exponent of the LSF in the inertial range is equal to that of the TSF. Also observed are differences between longitudinal and transverse structure functions caused by intermittency. These differences are related to their scaling differences which have been previously observed in experiments and numerical simulations. {copyright} {ital 1999 American Institute of Physics.}

  2. Arvicanthis ansorgei, a Novel Model for the Study of Sleep and Waking in Diurnal Rodents

    PubMed Central

    Hubbard, Jeffrey; Ruppert, Elisabeth; Calvel, Laurent; Robin-Choteau, Ludivine; Gropp, Claire-Marie; Allemann, Caroline; Reibel, Sophie; Sage-Ciocca, Dominique; Bourgin, Patrice

    2015-01-01

    Study Objectives: Sleep neurobiology studies use nocturnal species, mainly rats and mice. However, because their daily sleep/wake organization is inverted as compared to humans, a diurnal model for sleep studies is needed. To fill this gap, we phenotyped sleep and waking in Arvicanthis ansorgei, a diurnal rodent widely used for the study of circadian rhythms. Design: Video-electroencephalogram (EEG), electromyogram (EMG), and electrooculogram (EOG) recordings. Setting: Rodent sleep laboratory. Participants: Fourteen male Arvicanthis ansorgei, aged 3 mo. Interventions: 12 h light (L):12 h dark (D) baseline condition, 24-h constant darkness, 6-h sleep deprivation. Measurements and Results: Wake and rapid eye movement (REM) sleep showed similar electrophysiological characteristics as nocturnal rodents. On average, animals spent 12.9 h ± 0.4 awake per 24-h cycle, of which 6.88 h ± 0.3 was during the light period. NREM sleep accounted for 9.63 h ± 0.4, which of 5.13 h ± 0.2 during dark period, and REM sleep for 89.9 min ± 6.7, which of 52.8 min ± 4.4 during dark period. The time-course of sleep and waking across the 12 h light:12 h dark was overall inverted to that observed in rats or mice, though with larger amounts of crepuscular activity at light and dark transitions. A dominant crepuscular regulation of sleep and waking persisted under constant darkness, showing the lack of a strong circadian drive in the absence of clock reinforcement by external cues, such as a running wheel. Conservation of the homeostatic regulation was confirmed with the observation of higher delta power following sustained waking periods and a 6-h sleep deprivation, with subsequent decrease during recovery sleep. Conclusions: Arvicanthis ansorgei is a valid diurnal rodent model for studying the regulatory mechanisms of sleep and so represents a valuable tool for further understanding the nocturnality/diurnality switch. Citation: Hubbard J, Ruppert E, Calvel L, Robin-Choteau L, Gropp CM

  3. Low-order phenomenological modeling of leading-edge vortex formation

    NASA Astrophysics Data System (ADS)

    Wang, Chengjie; Eldredge, Jeff D.

    2013-09-01

    A low-order point vortex model for the two-dimensional unsteady aerodynamics of a flat plate wing section is developed. A vortex is released from both the trailing and leading edges of the flat plate, and the strength of each is determined by enforcing the Kutta condition at the edges. The strength of a vortex is frozen when it reaches an extremum, and a new vortex is released from the corresponding edge. The motion of variable-strength vortices is computed in one of two ways. In the first approach, the Brown-Michael equation is used in order to ensure that no spurious force is generated by the branch cut associated with each vortex. In the second approach, we propose a new evolution equation for a vortex by equating the rate of change of its impulse with that of an equivalent surrogate vortex with identical properties but constant strength. This impulse matching approach leads to a model that admits more general criteria for shedding, since the variable-strength vortex can be exchanged for its constant-strength surrogate at any instant. We show that the results of the new model, when applied to a pitching or perching plate, agree better with experiments and high-fidelity simulations than the Brown-Michael model, using fewer than ten degrees of freedom. We also assess the model performance on the impulsive start of a flat plate at various angles of attack. Current limitations of the model and extensions to more general unsteady aerodynamic problems are discussed.

  4. Singularity formation and nonlinear evolution of a viscous vortex sheet model

    NASA Astrophysics Data System (ADS)

    Sohn, Sung-Ik

    2013-01-01

    We study Dhanak's model [J. Fluid Mech. 269, 265 (1994)], 10.1017/S0022112094001552 of a viscous vortex sheet in the sharp limit, to investigate singularity formations and present nonlinear evolutions of the sheets. The finite-time singularity does not disappear by giving viscosity to the vortex sheet, but is delayed. The singularity in the sharp viscous vortex sheet is found to be different from that of the inviscid sheet in several features. A discontinuity in the curvature is formed in the viscous sheet, similarly as the inviscid sheet, but a cusp in the vortex sheet strength is less sharpened by viscosity. Exponential decay of the Fourier amplitudes is lost by the formation of the singularity, and the amplitudes of high wavenumbers exhibit an algebraic decay, while in the inviscid vortex sheet, the algebraic decay of the Fourier amplitudes is valid from fairly small wavenumbers. The algebraic decay rate of the viscous vortex sheet is approximately -2.5, independent of viscosity, which is the same rate as the asymptotic analysis of the inviscid sheet. Results for evolutions of the regularized vortex sheets show that the roll-up is weakened by viscosity, and the regularization parameter has more significant effects on the fine-structure of the core than does viscosity.

  5. Reconstruction of three-dimensional coherent structures in turbulent wakes using planar measurements

    NASA Astrophysics Data System (ADS)

    Yarusevych, Serhiy; Morton, Chris

    2014-11-01

    The present study is focused on reconstructing the dynamics of dominant three-dimensional coherent structures in turbulent wakes of complex cylindrical geometries using time-resolved, planar Particle-Image-Velocimetry data. As a test case, the turbulent wake of a low aspect ratio dual step cylinder model is considered. The model consists of a large diameter cylinder (D) of low aspect ratio (L / D) attached to the mid-span of a small diameter cylinder (d) . Experiments are performed in a water flume facility for ReD = 2100, D / d = 2, and L / D = 1. The investigated model produces cellular vortex shedding, with distinct variations in the average shedding frequency along the span of the model, and the associated complex vortex interactions. Time-resolved velocity measurements are acquired simultaneously in two mutually orthogonal planes at multiple planes along the span of the model. The technique involves conditional averaging of the planar results to produce three-dimensional reconstructions of wake topology for a given planar alignment of the dominant spanwise vortex filaments. This is achieved by identifying velocity fields matching a given flow-based template. The results demonstrate that the proposed technique can successfully reconstruct the dominant wake vortex interactions and can be extended to other flows where traditional phase-averaging approaches are not applicable. The authors gratefully acknowledge the Natural Sciences and Engineering Research Council of Canada (NSERC) for funding of this work.

  6. Sound signature of propeller tip vortex cavitation

    NASA Astrophysics Data System (ADS)

    Pennings, Pepijn; Westerweel, Jerry; van Terwisga, Tom

    2015-12-01

    The design of an efficient propeller is limited by the harmful effects of cavitation. The insufficient understanding of the role of vortex cavitation in noise and vibration reduces the maximum efficiency by a necessary safety margin. The aim in the present study is to directly relate propeller cavitation sound to tip vortex cavity dynamics. This is achieved by a dedicated experiment in a cavitation tunnel on a specially designed two-bladed propeller using a high-speed video camera and a hydrophone. The sound signature of a tip vortex cavity is not evidently present in the sound spectrum above the tunnel background. The addition of a simulated wake inflow results in a high amplitude broadband sound. With a decrease in the free-stream pressure the centre frequency of this sound decreases as a result of a larger vortex cavity diameter. In the near future each blade passage in the high-speed video will be analyzed in detail. The frequency content of the cavity dynamics can then be directly related to the measured sound. An analytic model for vortex cavity dynamics resulting in a cavity eigenfrequency using a vortex velocity model can finally be evaluated as a design instrument for estimation of broadband sound from propeller cavitation.

  7. Supersonic shock wave/vortex interaction

    NASA Technical Reports Server (NTRS)

    Settles, G. S.; Cattafesta, L.

    1993-01-01

    Although shock wave/vortex interaction is a basic and important fluid dynamics problem, very little research has been conducted on this topic. Therefore, a detailed experimental study of the interaction between a supersonic streamwise turbulent vortex and a shock wave was carried out at the Penn State Gas Dynamics Laboratory. A vortex is produced by replaceable swirl vanes located upstream of the throat of various converging-diverging nozzles. The supersonic vortex is then injected into either a coflowing supersonic stream or ambient air. The structure of the isolated vortex is investigated in a supersonic wind tunnel using miniature, fast-response, five-hole and total temperature probes and in a free jet using laser Doppler velocimetry. The cases tested have unit Reynolds numbers in excess of 25 million per meter, axial Mach numbers ranging from 2.5 to 4.0, and peak tangential Mach numbers from 0 (i.e., a pure jet) to about 0.7. The results show that the typical supersonic wake-like vortex consists of a non-isentropic, rotational core, where the reduced circulation distribution is self similar, and an outer isentropic, irrotational region. The vortex core is also a region of significant turbulent fluctuations. Radial profiles of turbulent kinetic energy and axial-tangential Reynolds stress are presented. The interactions between the vortex and both oblique and normal shock waves are investigated using nonintrusive optical diagnostics (i.e. schlieren, planar laser scattering, and laser Doppler velocimetry). Of the various types, two Mach 2.5 overexpanded-nozzle Mach disc interactions are examined in detail. Below a certain vortex strength, a 'weak' interaction exists in which the normal shock is perturbed locally into an unsteady 'bubble' shock near the vortex axis, but vortex breakdown (i.e., a stagnation point) does not occur. For stronger vortices, a random unsteady 'strong' interaction results that causes vortex breakdown. The vortex core reforms downstream of

  8. Euler solutions for self-generated rotor blade-vortex interactions

    NASA Technical Reports Server (NTRS)

    Hassan, A. A.; Tung, C.; Sankar, L. N.

    1990-01-01

    A finite-difference procedure was developed, on the basis of the conservation form of the unsteady three-dimensional Euler equations, for the prediction of rotor blade-vortex interactions (BVIs). Numerical solution procedures were obtained for the analysis of the model parallel BVIs and the more realistic helicopter self-generated-rotor BVIs. It was found that, for self-generated subcritical interactions, the accuracy of the predicted leading edge pressures relied heavily on the user-specified vortex core radius and on the CAMRAD-code-predicted geometry of the interaction vortex elements and their relative orientation with respect to the blade. It was also found that the free-wake model used in CAMRAD to predict the tip vortex trajectory for use in the Euler solution yields lower streamwise and higher axial wake convective velocities than those inferred from the experimental data.

  9. Experimental study on influence of pitch motion on the wake of a floating wind turbine model

    NASA Astrophysics Data System (ADS)

    Rockel, Stanislav; Cal, Raul Bayoan; Peinke, Joachim; Hoelling, Michael

    2013-11-01

    Wind energy has become a major contributor to energy from renewable sources and is still demanded to increase its portion to the overall energy supply. Offshore wind energy was found to have the highest potential to fulfill these demands, due to better and steadier wind conditions found on seas. Offshore wind turbines which have been installed lately use monopiles as foundations and are feasible in shallow water up to a depth of 50m. Such shallow areas are rare and often exploited, so floating support structures for offshore wind turbines in deep water are possible solutions. The additional degrees of freedom of a floating support structure will influence the aerodynamics at the rotor and its wake. Wind tunnel experiments were performed using a classical fixed turbine model and a streamwise oscillating turbine in free pitch motion. For both cases the turbines were operated under same inflow conditions and wakes up to 7 rotor diameters were measured using 2D-3C stereographic particle image velocimetry (SPIV). The obtained data was statistically analyzed and a direct comparison of the wake of the fixed and oscillating turbine was performed. Our results show that inclinations and oscillations of the turbine have a strong impact on the structure of the wake and its development.

  10. Experimental Study on the Effects of Winglets on the Wake of a Model Wind Turbine

    NASA Astrophysics Data System (ADS)

    Tobin, Nicolas; Hamed, Ali M.; Chamorro, Leonardo P.

    2015-11-01

    Wind tunnel particle image velocimetry was used to investigate the effects of winglets on the wake dynamics of a model wind turbine. The behavior of a turbine with downstream-facing winglets was compared with a turbine without winglets. The turbines were placed in a turbulent boundary layer that reached up to the hub height, allowing for investigation of behavior in both turbulent and uniform flow. The winglets did not significantly change the strength of the tip vortices in the region of uniform incoming flow. The tip vortices in the more turbulent region, however, decayed much faster, diminishing to near-zero within the first ~1.5 rotor diameters, whereas the upper tip vortices persisted potentially up to ~4 rotor diameters. The winglets also increased the power coefficient by 7.5 %, while increasing the coefficient of thrust by 10.0 %. The higher coefficient of thrust created a region of enhanced mean shear in the outer portion of the wake, leading to increased turbulence statistics in the far wake. The wingletted turbine had a similar wake deficit at 5 rotor diameters as the base turbine did at 1.5 rotor diameters, with potential implications for using wingletted turbines in wind farms.

  11. Assessment of the Breakup of the Antarctic Polar Vortex in Two New Chemistry-Climate Models

    NASA Technical Reports Server (NTRS)

    Hurwitz, M. M.; Newman, P. A.; Oman, L. D.; Li, F.; Morgenstern, O.; Braesicke, P.; Pyle, J. A.

    2010-01-01

    Successful simulation of the breakup of the Antarctic polar vortex depends on the representation of tropospheric stationary waves at Southern Hemisphere middle latitudes. This paper assesses the vortex breakup in two new chemistry-climate models (CCMs). The stratospheric version of the UK Chemistry and Aerosols model is able to reproduce the observed timing of the vortex breakup. Version 2 of the Goddard Earth Observing System (GEOS V2) model is typical of CCMs in that the Antarctic polar vortex breaks up too late; at 10 hPa, the mean transition to easterlies at 60 S is delayed by 12-13 days as compared with the ERA-40 and National Centers for Environmental Prediction reanalyses. The two models' skill in simulating planetary wave driving during the October-November period accounts for differences in their simulation of the vortex breakup, with GEOS V2 unable to simulate the magnitude and tilt of geopotential height anomalies in the troposphere and thus underestimating the wave driving. In the GEOS V2 CCM the delayed breakup of the Antarctic vortex biases polar temperatures and trace gas distributions in the upper stratosphere in November and December.

  12. SAR observation and numerical modeling of tidal current wakes at the East China Sea offshore wind farm

    NASA Astrophysics Data System (ADS)

    Li, XiaoMing; Chi, Lequan; Chen, Xueen; Ren, YongZheng; Lehner, Susanne

    2014-08-01

    A TerraSAR-X (TS-X) Synthetic Aperture Radar (SAR) image acquired at the East China Sea offshore wind farm presents distinct wakes at a kilometer scale on the lee of the wind turbines. The presumption was that these wakes were caused by wind movement around turbine blades. However, wind analysis using spaceborne radiometer data, numerical weather prediction, and in situ measurements suggest that the prevailing wind direction did not align with the wakes. By analyzing measurement at the tidal gauge station and modeling of the tidal current field, these trailing wakes are interpreted to have formed when a strong tidal current impinged on the cylindrical monopiles of the wind turbines. A numerical simulation was further conducted to reproduce the tidal current wake under such conditions. Comparison of the simulated surface velocity in the wake region with the TS-X sea surface backscatter intensity shows a similar trend. Consequently, turbulence intensity (T.I.) of the tidal current wakes over multiple piles is studied using the TS-X observation. It is found that the T.I. has a logarithmic relation with distance. Furthermore, another case study showing wakes due to wind movement around turbine blades is presented to discuss the differences in the tidal current wakes and wind turbine wakes. The conclusion is drawn that small-scale wakes formed by interaction of the tidal current and the turbine piles could be also imaged by SAR when certain conditions are satisfied. The study is anticipated to draw more attentions to the impacts of offshore wind foundations on local hydrodynamic field.

  13. VIDEO IMAGES OF SMOKE DISPERSION IN THE NEAR WAKE OF A BUILDING PART I. TEMPORAL AND SPATIAL SCALES OF VORTEX SHEDDING

    EPA Science Inventory

    In a wind-tunnel study, recorded video images of smoke dispersion in the wake of a rectangular-shaped building web analyzed. ontinuous source of smoke was emitted at floor level, midway along the leeward side of the building. moke was observed to build up within a region adjacent...

  14. Effects of incoming surface wind conditions on the wake characteristics and dynamic wind loads acting on a wind turbine model

    NASA Astrophysics Data System (ADS)

    Tian, Wei; Ozbay, Ahmet; Hu, Hui

    2014-12-01

    An experimental investigation was conducted to examine the effects of incoming surface wind conditions on the wake characteristics and dynamic wind loads acting on a wind turbine model. The experimental study was performed in a large-scale wind tunnel with a scaled three-blade Horizontal Axial Wind Turbine model placed in two different types of Atmospheric Boundary Layer (ABL) winds with distinct mean and turbulence characteristics. In addition to measuring dynamic wind loads acting on the model turbine by using a force-moment sensor, a high-resolution Particle Image Velocimetry system was used to achieve detailed flow field measurements to characterize the turbulent wake flows behind the model turbine. The measurement results reveal clearly that the discrepancies in the incoming surface winds would affect the wake characteristics and dynamic wind loads acting on the model turbine dramatically. The dynamic wind loads acting on the model turbine were found to fluctuate much more significantly, thereby, much larger fatigue loads, for the case with the wind turbine model sited in the incoming ABL wind with higher turbulence intensity levels. The turbulent kinetic energy and Reynolds stress levels in the wake behind the model turbine were also found to be significantly higher for the high turbulence inflow case, in comparison to those of the low turbulence inflow case. The flow characteristics in the turbine wake were found to be dominated by the formation, shedding, and breakdown of various unsteady wake vortices. In comparison with the case with relatively low turbulence intensities in the incoming ABL wind, much more turbulent and randomly shedding, faster dissipation, and earlier breakdown of the wake vortices were observed for the high turbulence inflow case, which would promote the vertical transport of kinetic energy by entraining more high-speed airflow from above to re-charge the wake flow and result in a much faster recovery of the velocity deficits in the

  15. Mean kinetic energy budget of wakes within an array of model wind turbines and porous discs

    NASA Astrophysics Data System (ADS)

    Cal, Raúl Bayoán; Camp, Elizabeth

    2015-11-01

    Wind turbines are often modeled as porous actuator discs within computational studies. In this wind tunnel study, stereo particle image velocimetry (SPIV) is used to characterize the wakes within a 4 ×3 model wind turbine array and an analogous array of porous disks. The SPIV measurements are performed upstream between - 2 . 9 <= x / D <= - 0 . 3 and downstream between 0 . 7 <= x / D <= 5 . 6 of the center turbine in the fourth row. To provide context, the similarities and differences in the flow fields as well as the mean and turbulent stresses are found. The primary analysis revolves around the mean kinetic energy budget in the wakes for both cases, model turbines and discs, obtained by the computation of mean kinetic energy, production of turbulence and flux of kinetic energy as these are equivalent to a measure of extracted power.

  16. Application of a stochastic vehicular wake erosion model to determine PM2.5 exposure

    NASA Astrophysics Data System (ADS)

    Jazcilevich, Aron; Wellens, Ann; Siebe, Christina; Rosas, Irma; Bornstein, Robert D.; Riojas-Rodríguez, Horacio

    2012-06-01

    A stochastic model based on empirical probability distribution functions has been applied to estimate human exposure to emissions from the resuspension of road dust due to isolated wakes from moving vehicles. The model incorporates the turbulent nature of resuspension due to vehicular wake erosion phenomena, and is tested by in situ measurements. It statistically estimates exposure as a function of ambient temperature, traffic activity, human height, and breathe intake rates as a function of age and activity. The model is applied to evaluate whether communities in the Molango region in Mexico are affected by vehicular resuspension of Manganese (Mn) contaminated soil from on-road activities related to mining. Results showed that six and 10 year old children are at higher risk to vehicular resuspended dust exposure than adults, due to their lower height and higher respiratory intake rates during periods of light and moderate activity.

  17. A Numerical Simulation Study to Develop an Acceptable Wake Encounter Boundary for a B737-100 Airplane

    NASA Technical Reports Server (NTRS)

    Vicroy, Dan D.; Nguyen, Truc

    1993-01-01

    The National Aeronautics and Space Administration (NASA) is conducting research with the goal of enabling safe improvements in the capacity of the nation's air transportation system. The wake-vortex upset hazard is an important factor in establishing the minimum safe spacing between aircraft during landing and take-off operations, thus impacting airport capacity. A batch simulation study was conducted to assess the sensitivity of various safe landing criteria in the development of an acceptable wake encounter boundary. A baseline six-degree-of-freedom simulation of a B737-100 airplane was modified to include a wake model and the vortex-induced forces and moments. The guidance and control input for the airplane was provided by an auto-land system. The wake strength and encounter geometry were varied. A sensitivity study was also conducted to assess the effects of encounter modeling methods and accuracy.

  18. Prescribed wake methodologies for wind turbine design codes

    SciTech Connect

    Galbraith, R.A.M.; Coton, F.N.; Robison, D.J.

    1995-12-31

    Prescribed wake performance assessment models have been developed successfully for both vertical (VAWT) and horizontal (HAWT) axis wind turbines. In the case of the VAWT model the Beddoes and Leishman dynamic stall model has been incorporated. This has resulted in a fully unsteady 3-D code, establishing extremely accurate performance prediction across a wide range of operating conditions. Comparison of performance estimates from the prescribed wake model with those from free wake models have shown excellent correlation. To date, the HAWT model has been developed for the consideration of steady axial and yawed inflows. In the axial flow case comparisons of predicted power output with field data and free wake predictions have shown excellent agreement. Full validation of the yawed flow model is currently underway, with very encouraging initial results. The capabilities of the HAWT model are currently being extended by the inclusion of the Beddoes and Leishman dynamic stall model. Consideration of the significant unsteady aerodynamic influences acting on HAWTs while operating in yaw will significantly improve the models performance. The power of this modelling technique is the significant reduction in the computational overhead it offers. The prescribed wake models offer performance estimates of comparable detail and accuracy to those from free vortex analyses in minutes rather than hours. As such these models are highly suited to design assessment, with particular application to fatigue load analysis.

  19. An Initial Study of the Sensitivity of Aircraft Vortex Spacing System (AVOSS) Spacing Sensitivity to Weather and Configuration Input Parameters

    NASA Technical Reports Server (NTRS)

    Riddick, Stephen E.; Hinton, David A.

    2000-01-01

    A study has been performed on a computer code modeling an aircraft wake vortex spacing system during final approach. This code represents an initial engineering model of a system to calculate reduced approach separation criteria needed to increase airport productivity. This report evaluates model sensitivity toward various weather conditions (crosswind, crosswind variance, turbulent kinetic energy, and thermal gradient), code configurations (approach corridor option, and wake demise definition), and post-processing techniques (rounding of provided spacing values, and controller time variance).

  20. Determination of Wind Turbine Near-Wake Length Based on Stability Analysis

    NASA Astrophysics Data System (ADS)

    Sørensen, Jens N.; Mikkelsen, Robert; Sarmast, Sasan; Ivanell, Stefan; Henningson, Dan

    2014-06-01

    A numerical study on the wake behind a wind turbine is carried out focusing on determining the length of the near-wake based on the instability onset of the trailing tip vortices shed from the turbine blades. The numerical model is based on large-eddy simulations (LES) of the Navier-Stokes equations using the actuator line (ACL) method. The wake is perturbed by applying stochastic or harmonic excitations in the neighborhood of the tips of the blades. The flow field is then analyzed to obtain the stability properties of the tip vortices in the wake of the wind turbine. As a main outcome of the study it is found that the amplification of specific waves (traveling structures) along the tip vortex spirals is responsible for triggering the instability leading to wake breakdown. The presence of unstable modes in the wake is related to the mutual inductance (vortex pairing) instability where there is an out-of-phase displacement of successive helix turns. Furthermore, using the non-dimensional growth rate, it is found that the pairing instability has a universal growth rate equal to π/2. Using this relationship, and the assumption that breakdown to turbulence occurs once a vortex has experienced sufficient growth, we provide an analytical relationship between the turbulence intensity and the stable wake length. The analysis leads to a simple expression for determining the length of the near wake. This expression shows that the near wake length is inversely proportional to thrust, tip speed ratio and the logarithmic of the turbulence intensity.

  1. Efficient Prediction of Helicopter BVI Noise under Different Conditions of Wake and Blade Deformation

    NASA Astrophysics Data System (ADS)

    Inada, Yoshinobu; Yang, Choongmo; Iwanaga, Noriki; Aoyama, Takashi

    Predictions of helicopter BVI noise using three-dimensional Euler code with a single blade grid are conducted under three different conditions: BVI noise caused by (1) interaction between rotating blades and vortex shed from fixed wing vortex generator, (2) interaction between rotating blades and tip vortices shed from preceding blades, and (3) interaction between rotating blades with elastic deformation and shed tip vortices. In the CFD calculation, the Field Velocity Approach (FVA) and Scully’s vortex model are used to import the wake information into the calculation grid and to determine the induced velocity made by tip vortices, respectively (cases 1 3). Beddoes generalized wake model is used to prescribe the tip vortices position in the wake (cases 2 and 3). Information about blade elastic deformation is imported from HART II project experimental data into the calculation (case 3). Acoustic analyses based on Ffowcs-Williams and Hawkings (FW-H) equation are conducted subsequently in each case. The results from the calculations show good agreement with experiments in all three cases, indicating that application of FVA, Scully’s model, and Beddoes generalized wake model is effective for BVI noise prediction in this study, which is intended for low calculation cost using a single blade grid. Also, use of blade elastic deformation data in the calculation shows marked improvement in calculation precision. Consequently, the method used in this study can predict BVI noise under various conditions of wake or blade deformation with acceptable precision and low calculation cost.

  2. Evaluation of a vortex model of turbulent cavity flow. [for computing noise generation of fluid flow

    NASA Technical Reports Server (NTRS)

    Hardin, J. C.; Block, P. J. W.

    1979-01-01

    A two dimensional discrete vortex model is applied to turbulent flow over a cavity at a Reynolds number based on cavity half length of approximately 500,000. These model predictions are compared with experimental data on a time average and on a spectral basis. The comparisons indicate that the vortex model reproduces the mean velocity profiles of this complex flow, while the turbulent intensity and Reynolds stress profiles are overpredicted in magnitude. Spectral analyses show that the vortex model introduces unrealistic low frequency power which becomes less dominant as the model becomes more disordered. The spectral power distribution of the model in this state is nearly in agreement with that of the data, somewhat too low at the higher frequencies and too high at the lower frequencies. The model is shown to be capable of reproducing the cavity feedback oscillation phenomenon.

  3. A Unified Model of Performance: Validation of its Predictions across Different Sleep/Wake Schedules

    PubMed Central

    Ramakrishnan, Sridhar; Wesensten, Nancy J.; Balkin, Thomas J.; Reifman, Jaques

    2016-01-01

    Study Objectives: Historically, mathematical models of human neurobehavioral performance developed on data from one sleep study were limited to predicting performance in similar studies, restricting their practical utility. We recently developed a unified model of performance (UMP) to predict the effects of the continuum of sleep loss—from chronic sleep restriction (CSR) to total sleep deprivation (TSD) challenges—and validated it using data from two studies of one laboratory. Here, we significantly extended this effort by validating the UMP predictions across a wide range of sleep/wake schedules from different studies and laboratories. Methods: We developed the UMP on psychomotor vigilance task (PVT) lapse data from one study encompassing four different CSR conditions (7 d of 3, 5, 7, and 9 h of sleep/night), and predicted performance in five other studies (from four laboratories), including different combinations of TSD (40 to 88 h), CSR (2 to 6 h of sleep/night), control (8 to 10 h of sleep/night), and nap (nocturnal and diurnal) schedules. Results: The UMP accurately predicted PVT performance trends across 14 different sleep/wake conditions, yielding average prediction errors between 7% and 36%, with the predictions lying within 2 standard errors of the measured data 87% of the time. In addition, the UMP accurately predicted performance impairment (average error of 15%) for schedules (TSD and naps) not used in model development. Conclusions: The unified model of performance can be used as a tool to help design sleep/wake schedules to optimize the extent and duration of neurobehavioral performance and to accelerate recovery after sleep loss. Citation: Ramakrishnan S, Wesensten NJ, Balkin TJ, Reifman J. A unified model of performance: validation of its predictions across different sleep/wake schedules. SLEEP 2016;39(1):249–262. PMID:26518594

  4. Slow-wave oscillations in a corticothalamic model of sleep and wake.

    PubMed

    Zhao, X; Kim, J W; Robinson, P A

    2015-04-01

    A physiologically-based corticothalamic neural field model is used to study slow wave oscillations including cortical UP and DOWN states in deep sleep by extending it to incorporate bursting dynamics of neurons in the thalamic reticular nucleus. The interplay of local bursting dynamics and network interactions produces the cortical UP and DOWN states of slow wave sleep while preserving previously verified model predictions in the wake state. Results show that EEG spectral features in wake and sleep are reproduced. The bursting is subthreshold but acts to intensify the amplitude of oscillations in slow wave sleep with deep UP/DOWN oscillations on the cortex emerging naturally. Furthermore, there is a continuous cycle between the two regimes, rather than a flip-flop between discrete states. PMID:25659479

  5. Trailing Vortex-Induced Loads During Close Encounters in Cruise

    NASA Technical Reports Server (NTRS)

    Mendenhall, Michael R.; Lesieutre, Daniel J; Kelly, Michael J.

    2015-01-01

    The trailing vortex induced aerodynamic loads on a Falcon 20G business jet flying in the wake of a DC-8 are predicted to provide a preflight estimate of safe trail distances during flight test measurements in the wake. Static and dynamic loads on the airframe flying in the near wake are shown at a matrix of locations, and the dynamic motion of the Falcon 20G during traverses of the DC-8 primary trailing vortex is simulated. Safe trailing distances for the test flights are determined, and optimum vortex traverse schemes are identified to moderate the motion of the trailing aircraft during close encounters with the vortex wake.

  6. Study of the Mutual Interaction Between a Wing Wake and an Encountering Airplane

    NASA Technical Reports Server (NTRS)

    Walden, A. B.; vanDam, C. P.

    1996-01-01

    In an effort to increase airport productivity, several wind-tunnel and flight-test programs are currently underway to determine safe reductions in separation standards between aircraft. These programs are designed to study numerous concepts from the characteristics and detection of wake vortices to the wake-vortex encounter phenomenon. As part of this latter effort, computational tools are being developed and utilized as a means of modeling and verifying wake-vortex hazard encounters. The objective of this study is to assess the ability of PMARC, a low-order potential-flow panel method, to predict the forces and moments imposed on a following business-jet configuration by a vortex interaction. Other issues addressed include the investigation of several wake models and their ability to predict wake shape and trajectory, the validity of the velocity field imposed on the following configuration, modeling techniques and the effect of the high-lift system and the empennage. Comparisons with wind-tunnel data reveal that PMARC predicts the characteristics for the clean wing-body following configuration fairly well. Non-linear effects produced by the addition of the high-lift system and empennage, however, are not so well predicted.

  7. Numerical simulation and validation of helicopter blade-vortex interaction using coupled CFD/CSD and three levels of aerodynamic modeling

    NASA Astrophysics Data System (ADS)

    Amiraux, Mathieu

    Rotorcraft Blade-Vortex Interaction (BVI) remains one of the most challenging flow phenomenon to simulate numerically. Over the past decade, the HART-II rotor test and its extensive experimental dataset has been a major database for validation of CFD codes. Its strong BVI signature, with high levels of intrusive noise and vibrations, makes it a difficult test for computational methods. The main challenge is to accurately capture and preserve the vortices which interact with the rotor, while predicting correct blade deformations and loading. This doctoral dissertation presents the application of a coupled CFD/CSD methodology to the problem of helicopter BVI and compares three levels of fidelity for aerodynamic modeling: a hybrid lifting-line/free-wake (wake coupling) method, with modified compressible unsteady model; a hybrid URANS/free-wake method; and a URANS-based wake capturing method, using multiple overset meshes to capture the entire flow field. To further increase numerical correlation, three helicopter fuselage models are implemented in the framework. The first is a high resolution 3D GPU panel code; the second is an immersed boundary based method, with 3D elliptic grid adaption; the last one uses a body-fitted, curvilinear fuselage mesh. The main contribution of this work is the implementation and systematic comparison of multiple numerical methods to perform BVI modeling. The trade-offs between solution accuracy and computational cost are highlighted for the different approaches. Various improvements have been made to each code to enhance physical fidelity, while advanced technologies, such as GPU computing, have been employed to increase efficiency. The resulting numerical setup covers all aspects of the simulation creating a truly multi-fidelity and multi-physics framework. Overall, the wake capturing approach showed the best BVI phasing correlation and good blade deflection predictions, with slightly under-predicted aerodynamic loading magnitudes

  8. Artifacts in the Wake: Leadership via an Oriented Compass Model

    ERIC Educational Resources Information Center

    Fallon, Paul D.

    2013-01-01

    Although inextricable, the act of leading, the leader, and outcome of leadership are unique entities. Lack of such differentiation may ensnare novice leaders in broad suppositions. This conceptual article introduces a tool for analyzing leadership. Leaders can leverage the model to evaluate the act of leading, in route, via a measurable trajectory…

  9. Effective dipole moment for the mode coupling instability: Mapping of self-consistent wake models

    SciTech Connect

    Roecker, T. B.; Zhdanov, S. K.; Ivlev, A. V.; Morfill, G. E.; Lampe, M.; Joyce, G.

    2012-07-15

    The theory of the mode coupling instability operating in two-dimensional plasma crystals is generalized, by employing the linear plasma response formalism to describe the interparticle interactions self-consistently. In this approach, the underlying ion distribution function is calculated from first principles. Subthermal and suprathermal regimes of the ion flow are considered. A mapping procedure is proposed, which relates the self-consistent coupling coefficients to the effective dipole moment of the wake-the parameter which characterizes the mode coupling in the framework of the conventionally used Yukawa/point-wake model. The importance of the self-consistent approach is demonstrated by comparing the theoretically obtained dipole moments with the values deduced from experiments.

  10. Data-driven reduced order model for prediction of wind turbine wake dynamics

    NASA Astrophysics Data System (ADS)

    Debnath, Mithu; Santoni, Christian; Rotea, Mario A.; Leonardi, Stefano; Iungo, Giacomo Valerio

    2015-11-01

    Wind turbine wakes are highly turbulent flows for which coherent vorticity structures lead to complex dynamics and instabilities. In this study, high-fidelity large eddy simulations (LES) data of a utility-scale wind turbine is analyzed through proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) in order to detect the main dynamic contributions to the temporal and spatial evolution of a wind turbine wake. Eigenmodes obtained from modal decomposition are clustered as a function of their physical origin, energy, spectral contribution and growth rate. A subset of the eigenmodes is then selected accordingly to a customized objective function in order to represent an optimal blend of the different dynamic contributions. The selected eigenmodes are embedded in a time-marching algorithm enabling the prediction of the wake velocity field and loads on downstream turbines. This reduced order model is characterized by a relatively low rank compared to the dimension of the physical space of the original LES data, thus by a low computational cost. The reduced order model is then embedded within a Kalman filter in order to perform data assimilation of new available observations in order to maximize agreement between the forecast and observations.

  11. The Explicit Wake Parametrisation V1.0: a wind farm parametrisation in the mesoscale model WRF

    NASA Astrophysics Data System (ADS)

    Volker, P. J. H.; Badger, J.; Hahmann, A. N.; Ott, S.

    2015-11-01

    We describe the theoretical basis, implementation, and validation of a new parametrisation that accounts for the effect of large offshore wind farms on the atmosphere and can be used in mesoscale and large-scale atmospheric models. This new parametrisation, referred to as the Explicit Wake Parametrisation (EWP), uses classical wake theory to describe the unresolved wake expansion. The EWP scheme is validated for a neutral atmospheric boundary layer against filtered in situ measurements from two meteorological masts situated a few kilometres away from the Danish offshore wind farm Horns Rev I. The simulated velocity deficit in the wake of the wind farm compares well to that observed in the measurements, and the velocity profile is qualitatively similar to that simulated with large eddy simulation models and from wind tunnel studies. At the same time, the validation process highlights the challenges in verifying such models with real observations.

  12. The Explicit Wake Parametrisation V1.0: a wind farm parametrisation in the mesoscale model WRF

    NASA Astrophysics Data System (ADS)

    Volker, P. J. H.; Badger, J.; Hahmann, A. N.; Ott, S.

    2015-04-01

    We describe the theoretical basis, implementation and validation of a new parametrisation that accounts for the effect of large offshore wind farms on the atmosphere and can be used in mesoscale and large-scale atmospheric models. This new parametrisation, referred to as the Explicit Wake Parametrisation (EWP), uses classical wake theory to describe the unresolved wake expansion. The EWP scheme is validated against filtered in situ measurements from two meteorological masts situated a few kilometres away from the Danish offshore wind farm Horns Rev I. The simulated velocity deficit in the wake of the wind farm compares well to that observed in the measurements and the velocity profile is qualitatively similar to that simulated with large eddy simulation models and from wind tunnel studies. At the same time, the validation process highlights the challenges in verifying such models with real observations.

  13. A vortex model for Richtmyer-Meshkov instability accounting for finite Atwood number

    NASA Astrophysics Data System (ADS)

    Likhachev, Oleg A.; Jacobs, Jeffrey W.

    2005-03-01

    The vortex model developed by Jacobs and Sheeley ["Experimental study of incompressible Richtmyer-Meshkov instability," Phys. Fluids 8, 405 (1996)] is essentially a solution to the governing equations for the case of a uniform density fluid. Thus, this model strictly speaking only applies to the case of vanishing small Atwood number. A modification to this model for small to finite Atwood number is proposed in which the vortex row utilized is perturbed such that the vortex spacing is smaller across the spikes and larger across the bubbles, a fact readily observed in experimental images. It is shown that this modification more effectively captures the behavior of experimental amplitude measurements, especially when compared with separate bubble and spike data. In addition, it is shown that this modification will cause the amplitude to deviate from the logarithmic result given by the heuristic models at late time.

  14. Wake shield

    NASA Technical Reports Server (NTRS)

    Bannister, Tommy; Karr, Gerald R.

    1987-01-01

    Progress on the modeling of the flow field around a wake shield using a recently obtained code based on the Monte Carlo method is discussed. The direct simulation Monte Carlo method is a method for solving the Boltzman Equation using an approximation to the collision integral term. The collision integrand is evaluated for randomly selected values of its arguments and the summation will approach the integral for large enough samples. The collision effects may be modeled for either hard sphere or various power law potentials. The convective side of the Boltzman equation is approximated over a time step using a simple trajectory calculation of molecules as they travel through the domain of interest.

  15. An Actuator Curve Embedding Method to Model Wind Turbine Wakes

    NASA Astrophysics Data System (ADS)

    Jha, Pankaj; Schmitz, Sven

    2013-11-01

    The Actuator Line Method (ALM) is widely used in the wind energy community to model the complex interactions within large wind farms in large-eddy simulation (LES) of the atmospheric boundary layer (ABL) at various stability states. The state-of-the-art in ALM modeling is rooted in the work of Sorensen and Shen (2002). The major weakness of the ALM still remains in having the actuator line discretized as a superposition of individual spherically-spread body forces. The associated overlap of adjacent spherical force fields leads to a large sensitivity of computed blade loads to the way in which the spherical spreading radius is altered along the actuator line (Jha et al. 2013). An Actuator Curve Embedding (ACE) method is developed that considers a general actuator line in 3-D space where the force distribution along the actuator curve is embedded continuously onto the background mesh and without overlap. The ACE method thus is expected to show improved body-force discretization for wind turbine blades, in particular those subject to aeroelastic deformations. Some preliminary results contrasting the ALM and ACE methods are discussed. Support: DOE. Graduate Research Assistant, Aerospace Engineering.

  16. Laser Doppler velocimeter system simulation for sensing aircraft wake vortices

    NASA Technical Reports Server (NTRS)

    Thomson, J. A. L.; Meng, J. C. S.

    1974-01-01

    A hydrodynamic model of aircraft vortex wakes in an irregular wind shear field near the ground is developed and used as a basis for modeling the characteristics of a laser Doppler detection and vortex location system. The trailing vortex sheet and the wind shear are represented by discrete free vortices distributed over a two-dimensional grid. The time dependent hydrodynamic equations are solved by direct numerical integration in the Boussinesq approximation. The ground boundary is simulated by images, and fast Fourier Transform techniques are used to evaluate the vorticity stream function. The atmospheric turbulence was simulated by constructing specific realizations at time equal to zero, assuming that Kolmogoroff's law applies, and that the dissipation rate is constant throughout the flow field. The response of a simulated laser Doppler velocimeter is analyzed by simulating the signal return from the flow field as sensed by a simulation of the optical/electronic system.

  17. Mean velocity and moments of turbulent velocity fluctuations in the wake of a model ship propulsor

    NASA Astrophysics Data System (ADS)

    Pêgo, J. P.; Lienhart, H.; Durst, F.

    2007-08-01

    Pod drives are modern outboard ship propulsion systems with a motor encapsulated in a watertight pod, whose shaft is connected directly to one or two propellers. The whole unit hangs from the stern of the ship and rotates azimuthally, thus providing thrust and steering without the need of a rudder. Force/momentum and phase-resolved laser Doppler anemometry (LDA) measurements were performed for in line co-rotating and contra-rotating propellers pod drive models. The measurements permitted to characterize these ship propulsion systems in terms of their hydrodynamic characteristics. The torque delivered to the propellers and the thrust of the system were measured for different operation conditions of the propellers. These measurements lead to the hydrodynamic optimization of the ship propulsion system. The parameters under focus revealed the influence of distance between propeller planes, propeller frequency of rotation ratio and type of propellers (co- or contra-rotating) on the overall efficiency of the system. Two of the ship propulsion systems under consideration were chosen, based on their hydrodynamic characteristics, for a detailed study of the swirling wake flow by means of laser Doppler anemometry. A two-component laser Doppler system was employed for the velocity measurements. A light barrier mounted on the axle of the rear propeller motor supplied a TTL signal to mark the beginning of each period, thus providing angle information for the LDA measurements. Measurements were conducted for four axial positions in the slipstream of the pod drive models. The results show that the wake of contra-rotating propeller is more homogeneous than when they co-rotate. In agreement with the results of the force/momentum measurements and with hypotheses put forward in the literature (see e.g. Poehls in Entwurfsgrundlagen für Schraubenpropeller, 1984; Schneekluth in Hydromechanik zum Schiffsentwurf, 1988; Breslin and Andersen in Hydrodynamics of ship propellers, 1996

  18. The Baldwin-Lomax model for separated and wake flows using the entropy envelope concept

    NASA Technical Reports Server (NTRS)

    Brock, J. S.; Ng, W. F.

    1992-01-01

    Implementation of the Baldwin-Lomax algebraic turbulence model is difficult and ambiguous within flows characterized by strong viscous-inviscid interactions and flow separations. A new method of implementation is proposed which uses an entropy envelope concept and is demonstrated to ensure the proper evaluation of modeling parameters. The method is simple, computationally fast, and applicable to both wake and boundary layer flows. The method is general, making it applicable to any turbulence model which requires the automated determination of the proper maxima of a vorticity-based function. The new method is evalulated within two test cases involving strong viscous-inviscid interaction.

  19. New Vortex Shedding Criteria for Low Order Models of Unsteady Plate Motion

    NASA Astrophysics Data System (ADS)

    Manar, Field; Jones, Anya

    2015-11-01

    A complex potential flow model with a small number of point vortices of time-varying strength is developed to evaluate the flow around an infinitely thin flat plate undergoing arbitrary unsteady motion. Vortex strengths are determined using the Kutta condition, and vortex convection takes place according to an impulse-matching scheme. Previous work has had only limited success due to vortices not being properly shed from the plate and acquiring too much circulation. In this work, a new vortex shedding criterion based on the dynamics of the shear layer is investigated. This criterion seeks to approximate the occurrence of vortex pinch off by observing the tangential velocities in the shear layer. The effect of the new vortex-shedding criteria on the evolution of the flow are evaluated with respect to previous shedding criteria and experimental PIV results. One motivation for the development of this model is to predict the unsteady forces on a wing quickly, and at low computational cost. Given the velocity field computed via the complex potential model, the forces on the plate are computed by taking the time derivative of the total flow momentum, and are evaluated with respect to experimental measurements.

  20. Modeling of pulverized coal combustion processes in a vortex furnace of improved design. Part 1: Flow aerodynamics in a vortex furnace

    NASA Astrophysics Data System (ADS)

    Krasinsky, D. V.; Salomatov, V. V.; Anufriev, I. S.; Sharypov, O. V.; Shadrin, E. Yu.; Anikin, Yu. A.

    2015-02-01

    Some results of the complex experimental and numerical study of aerodynamics and transfer processes in a vortex furnace, whose design was improved via the distributed tangential injection of fuel-air flows through the upper and lower burners, were presented. The experimental study of the aerodynamic characteristics of a spatial turbulent flow was performed on the isothermal laboratory model (at a scale of 1 : 20) of an improved vortex furnace using a laser Doppler measurement system. The comparison of experimental data with the results of the numerical modeling of an isothermal flow for the same laboratory furnace model demonstrated their agreement to be acceptable for engineering practice.

  1. Random Vortex-Street Model for a Self-Similar Plane Turbulent Jet

    NASA Astrophysics Data System (ADS)

    L'Vov, Victor S.; Pomyalov, Anna; Procaccia, Itamar; Govindarajan, Rama

    2008-08-01

    We ask what determines the (small) angle of turbulent jets. To answer this question we first construct a deterministic vortex-street model representing the large-scale structure in a self-similar plane turbulent jet. Without adjustable parameters the model reproduces the mean velocity profiles and the transverse positions of the large-scale structures, including their mean sweeping velocities, in a quantitative agreement with experiments. Nevertheless, the exact self-similar arrangement of the vortices (or any other deterministic model) necessarily leads to a collapse of the jet angle. The observed (small) angle results from a competition between vortex sweeping tending to strongly collapse the jet and randomness in the vortex structure, with the latter resulting in a weak spreading of the jet.

  2. The onset of chaos in vortex sheet flow

    NASA Astrophysics Data System (ADS)

    Krasny, Robert; Nitsche, Monika

    2002-03-01

    Regularized point-vortex simulations are presented for vortex sheet motion in planar and axisymmetric flow. The sheet forms a vortex pair in the planar case and a vortex ring in the axisymmetric case. Initially the sheet rolls up into a smooth spiral, but irregular small-scale features develop later in time: gaps and folds appear in the spiral core and a thin wake is shed behind the vortex ring. These features are due to the onset of chaos in the vortex sheet flow. Numerical evidence and qualitative theoretical arguments are presented to support this conclusion. Past the initial transient the flow enters a quasi-steady state in which the vortex core undergoes a small-amplitude oscillation about a steady mean. The oscillation is a time-dependent variation in the elliptic deformation of the core vorticity contours; it is nearly time-periodic, but over long times it exhibits period-doubling and transitions between rotation and nutation. A spectral analysis is performed to determine the fundamental oscillation frequency and this is used to construct a Poincaré section of the vortex sheet flow. The resulting section displays the generic features of a chaotic Hamiltonian system, resonance bands and a heteroclinic tangle, and these features are well-correlated with the irregular features in the shape of the vortex sheet. The Poincaré section also has KAM curves bounding regions of integrable dynamics in which the sheet rolls up smoothly. The chaos seen here is induced by a self-sustained oscillation in the vortex core rather than external forcing. Several well-known vortex models are cited to justify and interpret the results.

  3. Harbor seal whiskers synchronize with frequency of upstream wake

    NASA Astrophysics Data System (ADS)

    Beem, Heather; Triantafyllou, Michael

    2013-11-01

    Harbor seals are able to use their whiskers to track minute water movements, such as those left in the wake of a fish. The current study is a simple representation of what the whiskers experience as the seal chases a fish. A scaled whisker model (average cross-flow diameter: dw) is first tested in a towing tank by itself and then towed behind a larger cylinder (dc = 2 . 5dw), which serves as a wake generator. A flexing plate attached to the model base allows the whisker to freely vibrate in response to the flow. Measurements from strain gages on the plate are calibrated to tip deflections. While in the cylinder wake, the whisker vibrates with an amplitude up to ten times higher than it does on its own (A /dw = 0 . 15). Also, the whisker synchronizes with the vortex shedding frequency (fs =0/. 2 U dc) of the upstream cylinder over the range of reduced velocities tested, whereas on its own, the whisker oscillates around its own natural frequency in water. Seals may use the difference in vibration amplitude and frequency between these two cases to help detect the presence of a vortex wake.

  4. Identification of secondary instabilities in the near wake of a blunt trailing edge profiled body

    NASA Astrophysics Data System (ADS)

    Cruikshank, Ross; Zhao, Wenyi; Lavoie, Philippe

    2015-11-01

    Aerodynamic research into blunt trailing edge (BTE) airfoils is driven by their structural and aerodynamic advantages over sharp trailing edge airfoils. However, the wake of BTE airfoils is dominated by a vortex street, which causes increased drag. One method to reduce the spanwise coherence of the vortex street is to generate streamwise vorticity in the wake. Recent evidence suggests that the efficiency of this control method can be improved by forcing at the same wavelength as a secondary instability (SI) of the vortex street, present at Reynolds numbers (based on airfoil thickness, d) above 470. The objective of the present study was to investigate the variation of the SI wavelength at 2000 < Red < 35 , 000 , and to examine the effect of forcing on the wake topology. The velocity field in the wake of a BTE profiled model was measured using particle image velocimetry, and proper orthogonal decomposition was applied as a filter for measurement noise. It was found that, for a laminar boundary layer, the SI wavelength decreased as Red increased. Following boundary layer transition to turbulence, the SI wavelength was insensitive to Red . This study will also examine the effect of forcing at different wavelengths on the dominant spanwise wavelength of the wake velocity field. The authors gratefully acknowledge the support of the Natural Sciences and Engineering Research Council of Canada.

  5. Large Eddy Simulation of Wake Vortices in the Convective Boundary Layer

    NASA Technical Reports Server (NTRS)

    Lin, Yuh-Lang; Han, Jongil; Zhang, Jing; Ding, Feng; Arya, S. Pal; Proctor, Fred H.

    2000-01-01

    The behavior of wake vortices in a convective boundary layer is investigated using a validated large eddy simulation model. Our results show that the vortices are largely deformed due to strong turbulent eddy motion while a sinusoidal Crow instability develops. Vortex rising is found to be caused by the updrafts (thermals) during daytime convective conditions and increases with increasing nondimensional turbulence intensity eta. In the downdraft region of the convective boundary layer, vortex sinking is found to be accelerated proportional to increasing eta, with faster speed than that in an ideal line vortex pair in an inviscid fluid. Wake vortices are also shown to be laterally transported over a significant distance due to large turbulent eddy motion. On the other hand, the decay rate of the, vortices in the convective boundary layer that increases with increasing eta, is larger in the updraft region than in the downdraft region because of stronger turbulence in the updraft region.

  6. Comparison of model helicopter rotor primary and secondary blade/vortex interaction blade slap

    NASA Astrophysics Data System (ADS)

    Hubbard, J. E., Jr.; Leighton, K. P.

    1984-05-01

    A study of the relative importance of blade/vortex interactions which occur on the retreating side of a model helicopter rotor disk is described. Some of the salient characteristics of this phenomenon are presented and discussed. It is shown that the resulting Secondary blade slap may be of equal or greater intensity than the advancing side (Primary) blade slap. Instrumented model helicopter rotor data is presented which reveals the nature of the retreating blade/vortex interaction. The importance of Secondary blade slap as it applies to predictive techniques or approaches is discussed. When Secondary blade slap occurs it acts to enlarge the window of operating conditions for which blade slap exists.

  7. A comparison of model helicopter rotor Primary and Secondary blade/vortex interaction blade slap

    NASA Technical Reports Server (NTRS)

    Hubbard, J. E., Jr.; Leighton, K. P.

    1983-01-01

    A study of the relative importance of blade/vortex interactions which occur on the retreating side of a model helicopter rotor disk is described. Some of the salient characteristics of this phenomenon are presented and discussed. It is shown that the resulting Secondary blade slap may be of equal or greater intensity than the advancing side (Primary) blade slap. Instrumented model helicopter rotor data is presented which reveals the nature of the retreating blade/vortex interaction. The importance of Secondary blade slap as it applies to predictive techniques or approaches is discussed. When Secondary blade slap occurs it acts to enlarge the window of operating conditions for which blade slap exists.

  8. Using vortex corelines to analyze the hemodynamics of patient specific cerebral aneurysm models

    NASA Astrophysics Data System (ADS)

    Byrne, Greg; Mut, Fernando; Cebral, Juan

    2012-02-01

    We construct one-dimensional sets known as vortex corelines for computational fluid dynamic (CFD) simulations of blood flow in patient specific cerebral aneurysm models. These sets identify centers of swirling blood flow that may play an important role in the biological mechanisms causing aneurysm growth, rupture, and thrombosis. We highlight three specific applications in which vortex corelines are used to assess flow complexity and stability in cerebral aneurysms, validate numerical models against PIV-based experimental data, and analyze the effects of flow diverting devices used to treat intracranial aneurysms.

  9. Assessment of stretched vortex subgrid-scale models for LES of incompressible inhomogeneous turbulent flow.

    PubMed

    Shetty, Dinesh A; Frankel, Steven H

    2013-09-20

    The physical space version of the stretched vortex subgrid scale model [Phys. Fluids 12, 1810 (2000)] is tested in large eddy simulations (LES) of the turbulent lid driven cubic cavity flow. LES is carried out using a higher order finite-difference method [J. Comput. Phys. 229, 8802 (2010)]. The effects of different vortex orientation models and subgrid turbulence spectrums are assessed through comparisons of the LES predictions against direct numerical simulations (DNS) [Phys. Fluids 12, 1363 (2000)]. Three Reynolds numbers 12000, 18000, and 22000 are studied. Good agreement with the DNS data for the mean and fluctuating quantities is observed. PMID:24187423

  10. Analytical model of the structureborne interior noise induced by a propeller wake

    NASA Astrophysics Data System (ADS)

    Junger, M. C.; Garrelick, J. M.; Martinez, R.; Cole, J. E., III

    1984-05-01

    The structure-borne contribution to the interior noise that is induced by the propeller wake acting on the wing was studied. Analytical models were developed to describe each aspect of this path including the excitation loads, the wing and fuselage structures, and the interior acoustic space. The emphasis is on examining a variety of parameters, and as a result different models were developed to examine specific parameters. The excitation loading on the wing by the propeller wake is modeled by a distribution of rotating potential vortices whose strength is related to the thrust per blade. The response of the wing to this loading is examined using beam models. A model of a beam structurally connected to a cylindrical shell with an internal acoustic fluid was developed to examine the coupling of energy from the wing to the interior space. The model of the acoustic space allows for arbitrary end conditions (e.g., rigid or vibrating end caps). Calculations are presented using these models to compare with a laboratory test configuration as well as for parameters of a prop-fan aircraft.

  11. Analytical model of the structureborne interior noise induced by a propeller wake

    NASA Technical Reports Server (NTRS)

    Junger, M. C.; Garrelick, J. M.; Martinez, R.; Cole, J. E., III

    1984-01-01

    The structure-borne contribution to the interior noise that is induced by the propeller wake acting on the wing was studied. Analytical models were developed to describe each aspect of this path including the excitation loads, the wing and fuselage structures, and the interior acoustic space. The emphasis is on examining a variety of parameters, and as a result different models were developed to examine specific parameters. The excitation loading on the wing by the propeller wake is modeled by a distribution of rotating potential vortices whose strength is related to the thrust per blade. The response of the wing to this loading is examined using beam models. A model of a beam structurally connected to a cylindrical shell with an internal acoustic fluid was developed to examine the coupling of energy from the wing to the interior space. The model of the acoustic space allows for arbitrary end conditions (e.g., rigid or vibrating end caps). Calculations are presented using these models to compare with a laboratory test configuration as well as for parameters of a prop-fan aircraft.

  12. Simple point vortex model for the relaxation of 2D superfluid turbulence in a Bose-Einstein condensate

    NASA Astrophysics Data System (ADS)

    Kim, Joon Hyun; Kwon, Woo Jin; Shin, Yong-Il

    2016-05-01

    In a recent experiment, it was found that the dissipative evolution of a corotating vortex pair in a trapped Bose-Einstein condensate is well described by a point vortex model with longitudinal friction on the vortex motion and the thermal friction coefficient was determined as a function of sample temperature. In this poster, we present a numerical study on the relaxation of 2D superfluid turbulence based on the dissipative point vortex model. We consider a homogeneous system in a cylindrical trap having randomly distributed vortices and implement the vortex-antivortex pair annihilation by removing a pair when its separation becomes smaller than a certain threshold value. We characterize the relaxation of the turbulent vortex states with the decay time required for the vortex number to be reduced to a quarter of initial number. We find the vortex decay time is inversely proportional to the thermal friction coefficient. In particular, we observe the decay times obtained from this work show good quantitative agreement with the experimental results in, indicating that in spite of its simplicity, the point vortex model reasonably captures the physics in the relaxation dynamics of the real system.

  13. Vortex Tilting and the Enhancement of Spanwise Flow in Flapping Flight

    NASA Astrophysics Data System (ADS)

    Frank, Spencer; Barbera, Giovanni; Cheng, Bo; Deng, Xinyan

    2011-11-01

    The leading edge vortex is key in lift generation on flapping wings. Its stability depends on the transport of the entrained vorticity into the wake via spanwise flow. This study investigates the generation and enhancement of spanwise flow based on the chordwise vorticity that results from the tilting of the leading edge vortex and trailing edge vortex. Two dynamically scaled robotic model wings, one rectangular and one insect wing shaped based on Drosophila melanogaster (fruit fly), are submerged in a tank of mineral oil and actuated into flapping motion. The overall flow structure was visualized and measured by a Volumetric 3-component Velocimetry (V3V) system (TSI, Inc.). From the three dimensional flow measurements obtained, the chordwise vorticity resulting from the vortex tilting is shown. The distribution of the resulting spanwise flow induced by the vortex tilting is shown using isosurfaces and on a planar cross section downstream of the leading edge. It is observed that the largest spanwise flow is located in the area between the tilted leading edge vortex and the tilted trailing edge vortex, supporting our hypothesis that the vortex tilting enhances the spanwise flow. This vortex tilting mechanisms helps to explain the overall flow structure and the stability of the leading edge vortex.

  14. A point vortex model for the formation of ocean eddies by flow separation

    NASA Astrophysics Data System (ADS)

    Southwick, O. R.; Johnson, E. R.; McDonald, N. R.

    2015-01-01

    A simple model for the formation of ocean eddies by flow separation from sharply curved horizontal boundary topography is developed. This is based on the Brown-Michael model for two-dimensional vortex shedding, which is adapted to more realistically model mesoscale oceanic flow by including a deforming free surface. With a free surface, the streamfunction for the flow is not harmonic so the conformal mapping methods used in the standard Brown-Michael approach cannot be used and the problem must be solved numerically. A numerical scheme is developed based on a Chebyshev spectral method for the streamfunction partial differential equation and a second order implicit timestepping scheme for the vortex position ordinary differntial equations. This method is used to compute shed vortex trajectories for three background flows: (A) a steady flow around a semi-infinite plate, (B) a free vortex moving around a semi-infinite plate, and (C) a free vortex moving around a right-angled wedge. In (A), the inclusion of surface deformation dramatically slows the vortex and changes its trajectory from a straight path to a curved one. In (B) and (C), without the inclusion of flow separation, free vortices traverse fully around the tip along symmetrical trajectories. With the effects of flow separation included, very different trajectories are found: for all values of the model parameter—the Rossby radius—the free and shed vortices pair up and move off to infinity without passing around the tip. Their final propagation angle depends strongly and monotonically on the Rossby radius.

  15. Using the coupled wake boundary layer model to evaluate the effect of turbulence intensity on wind farm performance

    NASA Astrophysics Data System (ADS)

    Stevens, Richard J. A. M.; Gayme, Dennice; Meneveau, Charles

    2015-06-01

    We use the recently introduced coupled wake boundary layer (CWBL) model to predict the effect of turbulence intensity on the performance of a wind farm. The CWBL model combines a standard wake model with a “top-down” approach to get improved predictions for the power output compared to a stand-alone wake model. Here we compare the CWBL model results for different turbulence intensities with the Horns Rev field measurements by Hansen et al., Wind Energy 15, 183196 (2012). We show that the main trends as function of the turbulence intensity are captured very well by the model and discuss differences between the field measurements and model results based on comparisons with LES results from Wu and Porté-Agel, Renewable Energy 75, 945-955 (2015).

  16. Symmetry plane model for turbulent flows with vortex generators

    NASA Technical Reports Server (NTRS)

    Arnaud, Gilles L.; Russell, David A.

    1991-01-01

    An approximate procedure is proposed for predicting the performance of counterrotating vortex-generator installations in incompressible flow. An inviscid calculation that includes the motion of the vortices is used to obtain crossflow velocities at the boundary-layer edge as a function of initial position, spacing, and strength of the vortices, and local values of the spanwise gradient are then folded into an integral turbulent-boundary layer procedure applied in the plane of symmetry. Special attention is paid to the consistency of the approximations and equations used. The two-dimensional aerodynamics of vortex generator installations on a NACA 0016 airfoil at angle-of-attack are estimated in this manner, and the results compared with experiments carried out with a 30-cm chord wing mounted in a 2.4 x 3.6-m cross-section wind tunnel and tested at chord Reynolds numbers of 0.7 and 1.4 x 10 to the 6th. Agreement in the separation location is found for these complex flows for a range of conditions.

  17. Forebay Computational Fluid Dynamics Modeling for The Dalles Dam to Support Vortex Suppress Device Studies

    SciTech Connect

    Rakowski, Cynthia L.; Richmond, Marshall C.; Serkowski, John A.

    2006-12-01

    A computational fluid dynamics (CFD) model was used in an investigation into the suppression of a surface vortex that forms and the south-most spilling bay at The Dalles Project. The CFD work complemented work at the prototype and the reduced-scale physical models. The CFD model was based on a model developed for other work in the forebay but had additional resolution added near the spillway. Vortex suppression devices (VSDs) were to placed between pier noses and/or in the bulkhead slot of the spillway bays. The simulations in this study showed that placing VSD structures or a combination of structures to suppress the vortex would still result in near-surface flows to be entrained in a vortex near the downstream spillwall. These results were supported by physical model and prototype studies. However, there was a consensus of the fish biologists at the physical model that the fish would most likely move north and if the fish went under the VSD it would immediately exit the forebay through the tainter gate and not get trapped between VSDs or the VSDs and the tainter gate if the VSDs were deep enough.

  18. Experimental investigation of the wake behind a solid disk

    SciTech Connect

    Balligand, H.; Higuchi, Hiroshi

    1993-12-01

    The flow past a solid circular disk placed in time-dependent approaching stream velocity was investigated experimentally. The model was near-impulsively started from rest and moved at a constant speed. The wake behind the disk remained axisymmetric when the disk was traversed for a short distance. The scaling effect of varying the acceleration rate and the subsequent constant velocity on the wake evolution was investigated by detailed flow visualizations. The drag measurement indicated an initial maximum force dependent on the acceleration rate before it decreased toward the quasi-steady value. The model was subsequently decelerated at various rates, either to rest or to a second constant velocity. The wake overtook the disk in most cases depending of the values of both deceleration rate and velocity ratio. The force measurement showed that the drag acting on the disk became negative shortly after the onset of deceleration and reached its most negative value approximately at the end of the deceleration. The peak negative drag correlated with the deceleration rate. During the deceleration to a second velocity the drag became negative even when the vortex structure remained downstream of the disk. When the disk was subjected to constant speeds for a prolonged time, onset of asymmetry of the vortex structure occurred, eventually leading to a three-dimensional wake. Finally, the wake behind the disk was compared with the two-dimensional counterpart, using a rectangular flat plate. One of the prime motivations for studying the wake behind bluff bodies during acceleration and deceleration phases is to achieve a better understanding of the unsteady flow phenomena associated with the opening and early phase of deceleration of a parachute.

  19. Increased fragmentation of sleep-wake cycles in the 5XFAD mouse model of Alzheimer's disease.

    PubMed

    Sethi, M; Joshi, S S; Webb, R L; Beckett, T L; Donohue, K D; Murphy, M P; O'Hara, B F; Duncan, M J

    2015-04-01

    Sleep perturbations including fragmented sleep with frequent night-time awakenings and daytime naps are common in patients with Alzheimer's disease (AD), and these daily disruptions are a major factor for institutionalization. The objective of this study was to investigate if sleep-wake patterns are altered in 5XFAD mice, a well-characterized double transgenic mouse model of AD which exhibits an early onset of robust AD pathology and memory deficits. These mice have five distinct human mutations in two genes, the amyloid precursor protein (APP) and Presenilin1 (PS1) engineered into two transgenes driven by a neuron-specific promoter (Thy1), and thus develop severe amyloid deposition by 4 months of age. Age-matched (4-6.5 months old) male and female 5XFAD mice were monitored and compared to wild-type littermate controls for multiple sleep traits using a non-invasive, high throughput, automated piezoelectric system which detects breathing and gross body movements to characterize sleep and wake. Sleep-wake patterns were recorded continuously under baseline conditions (undisturbed) for 3 days and after sleep deprivation of 4h, which in mice produces a significant sleep debt and challenge to sleep homeostasis. Under baseline conditions, 5XFAD mice exhibited shorter bout lengths (14% lower values for males and 26% for females) as compared to controls (p<0.001). In females, the 5XFAD mice also showed 12% less total sleep than WT (p<0.01). Bout length reductions were greater during the night (the active phase for mice) than during the day, which does not model the human condition of disrupted sleep at night (the inactive period). However, the overall decrease in bout length suggests increased fragmentation and disruption in sleep consolidation that may be relevant to human sleep. The 5XFAD mice may serve as a useful model for testing therapeutic strategies to improve sleep consolidation in AD patients. PMID:25637807

  20. Vortex-Surface Collisions^

    NASA Astrophysics Data System (ADS)

    Conlisk, A. T.

    1998-11-01

    The interaction of vortices with solid surfaces occurs in many different situations including, but not limited to tornadoes, propeller wakes, flows over swept wings and missile forebodies, turbomachinery flows, blade-vortex interactions and tip vortex-surface interactions on helicopters. Often, parts of a system must operate within such flows and thus encounter these vortices. In the present paper we discuss the nature of a particular subset of interactions called ``collisions''. A ``collision'' is characterized by the fact that the core of the vortex is permanently altered; usually the core is locally destroyed. The focus is on fully three-dimensional collisions although two-dimensional collisions are discussed as well. Examples of collisions in helicopter aerodynamics and turbomachinery flows are discussed and the dynamics of the vortex core during a collision process are illustrated for a 90^o collision. ^Supported by the US Army Research Office

  1. Experimental characterization of rotating flow field in a model vortex burner

    SciTech Connect

    Shtork, S.I.; Cala, C.E.; Fernandes, E.C.

    2007-07-15

    Acoustic techniques, high speed filming and LDA were employed to characterize swirling jet flow in a model vortex burner. The isothermal flow conditions studied correspond to Re = 16,000 and swirl number S = 1, resulting in onset of the swirling jet breakdown. The breakdown zone exhibited distinct flow unsteadiness in the form of a precessing vortex core (PVC). Phase-averaged analysis of the LDA data was used to reveal an ''instantaneous'' flow field spatial distribution and to determine the precessing vortex characteristics. These results were compared against the time mean data to reveal the PVC's footprint in the time-averaged flow structure. In particular, this approach was shown to provide access to the precessing structure parameters making use of conventional flow field diagnostics. (author)

  2. Active twist rotor blade modelling using particle-wake aerodynamics and geometrically exact beam structural dynamics

    NASA Astrophysics Data System (ADS)

    Cesnik, C. E. S.; Opoku, D. G.; Nitzsche, F.; Cheng, T.

    2004-06-01

    An active aeroelastic and aeroacoustic analysis of helicopter rotor systems is presented in this paper. It is a tightly coupled computational aeroelastic code that interfaces a particle-wake panel method code with an active nonlinear mixed variational intrinsic beam element code. In addition, a Ffowcs-Williams-Hawkings equation-based acoustic component is incorporated to complete the numerical implementation. The theory behind each component is summarized here as well as the method for coupling the aerodynamic and structural components. Sample acoustic and aeroelastic results are given for different model-scale rotors. Comparisons with available (passive) results show very good agreement. Preliminary study with an active twist rotor is also shown.

  3. Vortex model for airfoil stall prediction using an interactive boundary-layer method

    SciTech Connect

    Dini, P.; Coiro, D.P.; Bertolucci, S.

    1995-09-01

    An interactive boundary-layer method is developed that is able to predict the aerodynamic performance of airfoils throughout the stall region. This has been achieved by taking into account the net vorticity of the flow in the turbulent separated region on the suction surface. This vorticity is modelled as an inviscid counterclockwise vortex located above the trailing edge, whose direction of rotation is justified by global conservation of angular momentum. An empirical law for the intensity of the vortex as a function of a dimensionless parameter based on flow conditions is presented. Excellent comparisons with measured lift and moment curves and pressure distributions are then presented and discussed.

  4. Evaluation of Wind Turbine Wake Interaction Models in a RANS Framework

    NASA Astrophysics Data System (ADS)

    Wilson, Jordan; Venayagamoorthy, Karan

    2012-11-01

    Wind energy produced from horizontal axis wind turbines (HAWTs) remains the most cost effective source of renewable energy production. Computational fluid dynamics (CFD) model studies are widely used as an a priori means to study wind farm environments for adequacy of wind resources and optimal configurations. This body of research explores the velocity deficit effect and flow fluctuations created by turbine wakes in a RANS framework for National Renewable Energy Laboratory (NREL) 5MW reference turbines. Various turbine models are explored to determine the most computationally efficient model that accurately captures the physics of interest. While only neutral ABL conditions are simulated in this study, consideration is also given to future work looking at the stable ABL and a full diurnal cycle when selecting a closure model. The objective of this current research is to further understand the development and resolution of turbine wakes for power optimization in neutral ABL conditions with a mind toward fatigue load minimization. Funded by the Clean Energy Supercluster, CSU.

  5. Radar Reflectivity in Wingtip-Generated Wake Vortices

    NASA Technical Reports Server (NTRS)

    Marshall, Robert E.; Mudukutore, Ashok; Wissel, Vicki

    1997-01-01

    This report documents new predictive models of radar reflectivity, with meter-scale resolution, for aircraft wakes in clear air and fog. The models result from a radar design program to locate and quantify wake vortices from commercial aircraft in support of the NASA Aircraft Vortex Spacing System (AVOSS). The radar reflectivity model for clear air assumes: 1) turbulent eddies in the wake produce small discontinuities in radar refractive index; and 2) these turbulent eddies are in the 'inertial subrange' of turbulence. From these assumptions, the maximum radar frequency for detecting a particular aircraft wake, as well as the refractive index structure constant and radar volume reflectivity in the wake can be obtained from the NASA Terminal Area Simulation System (TASS) output. For fog conditions, an empirical relationship is used to calculate radar reflectivity factor from TASS output of bulk liquid water. Currently, two models exist: 1) Atlas-based on observations of liquid water and radar reflectivity factor in clouds; and 2) de Wolf- specifically tailored to a specific measured dataset (1992 Vandenberg Air Force Base).

  6. Non-Vortex Topological Solitons of the [InlineMediaObject not available: see fulltext.] Gauge Model

    NASA Astrophysics Data System (ADS)

    Afanas'ev, K. V.; Gauzshtein, V. V.; Loginov, A. Yu.

    2016-06-01

    A (2+1)-dimensional [InlineMediaObject not available: see fulltext.] gauge model is investigated. The presence of additional local U(1) symmetry, not associated with a physical gauge field, leads to the existence in the given model of two-dimensional non-vortex topological solitons carrying unquantized magnetic flux. Topological solitons of the given type were found numerically for fixed values of the model parameters. Analytical calculations of some properties of non-vortex topological solitons were performed. Universal dependences of the energy and magnetic flux of a non-vortex topological soliton on a dimensionless combination of parameters of the [InlineMediaObject not available: see fulltext.] gauge model were obtained numerically. A comparative analysis of the properties of a non-vortex topological soliton and an Abrikosov-Nielsen-Olesen classical vortex is provided.

  7. Wind Plant Power Optimization through Yaw Control using a Parametric Model for Wake Effects -- A CFD Simulation Study

    SciTech Connect

    Gebraad, P. M. O.; Teeuwisse, F. W.; van Wingerden, J. W.; Fleming, Paul A.; Ruben, S. D.; Marden, J. R.; Pao, L. Y.

    2016-01-01

    This article presents a wind plant control strategy that optimizes the yaw settings of wind turbines for improved energy production of the whole wind plant by taking into account wake effects. The optimization controller is based on a novel internal parametric model for wake effects, called the FLOw Redirection and Induction in Steady-state (FLORIS) model. The FLORIS model predicts the steady-state wake locations and the effective flow velocities at each turbine, and the resulting turbine electrical energy production levels, as a function of the axial induction and the yaw angle of the different rotors. The FLORIS model has a limited number of parameters that are estimated based on turbine electrical power production data. In high-fidelity computational fluid dynamics simulations of a small wind plant, we demonstrate that the optimization control based on the FLORIS model increases the energy production of the wind plant, with a reduction of loads on the turbines as an additional effect.

  8. Tornadic Vortex Signature (TVS) Produced by Constrained Pulsing Inertial Oscillation (PIO) Model

    NASA Technical Reports Server (NTRS)

    Costen, R. C.

    1997-01-01

    The TVS on Doppler radar indicates a midtropospheric vortex of Rossby number Ro 1000 that develops in a supercell storm shortly before a tornado descends. This paper shows how the PIO model, which was first described at the 1991 AGU Spring Meeting, could produce a TVS.

  9. A full potential flow analysis with realistic wake influence for helicopter rotor airload prediction

    NASA Technical Reports Server (NTRS)

    Egolf, T. Alan; Sparks, S. Patrick

    1987-01-01

    A 3-D, quasi-steady, full potential flow solver was adapted to include realistic wake influence for the aerodynamic analysis of helicopter rotors. The method is based on a finite difference solution of the full potential equation, using an inner and outer domain procedure for the blade flowfield to accommodate wake effects. The nonlinear flow is computed in the inner domain region using a finite difference solution method. The wake is modeled by a vortex lattice using prescribed geometry techniques to allow for the inclusion of realistic rotor wakes. The key feature of the analysis is that vortices contained within the finite difference mesh (inner domain) were treated with a vortex embedding technique while the influence of the remaining portion of the wake (in the outer domain) is impressed as a boundary condition on the outer surface of the finite difference mesh. The solution procedure couples the wake influence with the inner domain solution in a consistent and efficient solution process. The method has been applied to both hover and forward flight conditions. Correlation with subsonic and transonic hover airload data is shown which demonstrates the merits of the approach.

  10. Model of coarsening and vortex formation in vibrated granular rods.

    SciTech Connect

    Aranson, I. S.; Tsimring, L. S.; Materials Science Division; Univ. of California at San Diego

    2003-02-01

    Neicu et al. observed experimentally spontaneous formation of the long-range orientational order and large-scale vortices in a system of vibrated macroscopic rods. We propose a phenomenological theory of this phenomenon based on a coupled system of equations for local rods density and tilt. The density evolution is described by the modified Cahn-Hilliard equation, while the tilt is described by the Ginzburg-Landau type equation. Our analysis shows that, in accordance with the Cahn-Hilliard dynamics, islands of the ordered phase appear spontaneously and grow due to coarsening. The generic vortex solutions of the Ginzburg-Landau equation for the tilt correspond to the vortical motion of the rods around the cores which are located near the centers of the islands.

  11. A Simplified model of mutually inhibitory sleep-active and wake-active neuronal populations employing a noise-based switching mechanism.

    PubMed

    Patel, Mainak

    2016-04-01

    Infant rats switch randomly between the sleeping and waking states; during early infancy (up to postnatal day 8), sleep and wake bouts are random, brief (with means on the order of several seconds) and exponentially distributed, with the length of a particular bout independent of the length of prior bouts. As the rat ages during this early period, mean sleep and wake bout lengths gradually increase, though sleep and wake bouts remain exponentially distributed. Additionally, sleep and wake bouts are regulated independently of each other - alterations in the development of sleep (wake) bouts has no impact on the regulation wake (sleep) bouts. Sleep and wake bout behavior is associated with the activity of mutually inhibitory sleep-active and wake-active brainstem populations. In this work, I employ a simplified biophysical model of two mutually inhibitory populations consisting of ten integrate-and-fire neurons each and a noise-based switching mechanism. I show that such a noise-based switching mechanism naturally accounts for the experimentally observed features of sleep-wake switching during early infancy - random alternating activity bouts occur as a consequence of noise (provided inhibition is strong relative to excitation), bout durations are exponential (due to a lack of memory within the system), and cross-population inhibition or intrapopulation excitatory coupling provide mechanisms for changing and independently regulated sleep and wake bout means. PMID:26802484

  12. A Family of Vortices to Study Axisymmetric Vortex Breakdown and Reconnection

    NASA Technical Reports Server (NTRS)

    Young, Larry A.

    2007-01-01

    A new analytic model describing a family of vortices has been developed to study some of the axisymmetric vortex breakdown and reconnection fluid dynamic processes underlying body-vortex interactions that are frequently manifested in rotorcraft and propeller-driven fixed-wing aircraft wakes. The family of vortices incorporates a wide range of prescribed initial vorticity distributions -- including single or dual-core vorticity distributions. The result is analytical solutions for the vorticity and velocities for each member of the family of vortices. This model is of sufficient generality to further illustrate the dependence of vortex reconnection and breakdown on initial vorticity distribution as was suggested by earlier analytical work. This family of vortices, though laminar in nature, is anticipated to provide valuable insight into the vortical evolution of large-scale rotor and propeller wakes.

  13. Investigation of Model Wake Blockage Effects at High Angles of Attack in Low-Speed Wind Tunnel

    NASA Astrophysics Data System (ADS)

    Shyu, Lih-Shyng; Chuang, Shu-Hao

    To improve the fidelity of measured aerodynamic characteristics at high angle of attack for modern jet fighters, this paper examines the model wake blockage effect. The wake blockage effect in a 2.2×3.1 m low-speed wind tunnel is investigated by analyzing drag and wall pressure measurements. Circular flat plates of different sizes are used to simulate a test model at high angles of attack. The present analysis results in simple formulas for corrections of model wake blockage effect. To verify the present correction formula, the NASA TP-1803 model is force-tested in the tunnel. The corrected test data agree well with the NASA TP-1803 data.

  14. 3D Reconstruction of the Vortex in a Human Right Ventricle Model using High Speed PIV

    NASA Astrophysics Data System (ADS)

    Kheradvar, Arash; Falahatpisheh, Ahmad

    2011-11-01

    This work aims to characterize the formation process and translation of the vortex, which forms along with the trans-tricuspid jet in a realistic model of a human right ventricle (RV). A clear model of the RV made of silicone rubber was carefully casted in real size from echocardiographic data of an adult human heart. The RV model was used in our heart pulsed-flow simulator at KLAB at UCI to perform experiments. Bioprosthetic heart valves in appropriate sizes were used at tricuspid and pulmonary positions. Multi-planar high-speed PIV was performed to capture and reconstruct the 3D flow field with a 1-millisecond time gap between each two velocity frames. λ2 iso-surfaces were used to illustrate the evolution of vortex cores. The highly asymmetric shape of the RV chamber results in a complex 3D trans-tricuspid vortex that forms and translates toward right ventricular outflow tract, and finally departs RV from pulmonary valve. Through this study, -for the first time- the formation, evolution and pathway of the RV vortex have been characterized in vitro.

  15. Control of submersible vortex flows

    NASA Technical Reports Server (NTRS)

    Bushnell, D. M.; Donaldson, C. D.

    1990-01-01

    Vortex flows produced by submersibles typically unfavorably influence key figures of merit such as acoustic and nonacoustic stealth, control effectiveness/maneuverability, and propulsor efficiency/body drag. Sources of such organized, primarily longitudinal, vorticity include the basic body (nose and sides) and appendages (both base/intersection and tip regions) such as the fairwater, dive planes, rear control surfaces, and propulsor stators/tips. Two fundamentally different vortex control approaches are available: (1) deintensification of the amplitude and/or organization of the vortex during its initiation process; and (2) downstream vortex disablement. Vortex control techniques applicable to the initiation region (deintensification approach) include transverse pressure gradient minimization via altered body cross section, appendage dillets, fillets, and sweep, and various appendage tip and spanload treatment along with the use of active controls to minimize control surface size and motions. Vortex disablement can be accomplished either via use of control vortices (which can also be used to steer the vortices off-board), direct unwinding, inducement of vortex bursting, or segmentation/tailoring for enhanced dissipation. Submersible-applicable vortex control technology is also included derived from various aeronautical applications such as mitigation of the wing wake vortex hazard and flight aircraft maneuverability at high angle of attack as well as the status of vortex effects upon, and mitigation of, nonlinear control forces on submersibles. Specific suggestions for submersible-applicable vortex control techniques are presented.

  16. Experimental and Numerical Study of Unsteady Wakes Behind an Oscillating Car Model

    NASA Astrophysics Data System (ADS)

    Guilmineau, E.; Chometon, F.

    This research focuses on the analysis of the instability of passenger vehicles associated with transient crosswind gusts. A new vehicle model, created to analyze the behavior of unsteady wakes on bluff bodies, is proposed. This test model called Willy is designed using the following criteria: the geometry is realistic compared to a real vehicle, the model's plane under-body surface is parallel to the ground, and the separations are limited to the region of the base for a moderated yaw angle. In the present paper, the tests are performed on the model animated by an oscillating yaw angle at a frequency of 2 Hz in a steady wind. Experiments are carried out at Reynolds number of 0.9 × 106 at the Conservatoire National des Arts et Métiers and computations are performed at the Ecole Centrale de Nantes. The numerical results are compared with experimental data.

  17. Wake Measurement Downstream of a Hybrid Wing Body Model with Blown Flaps

    NASA Technical Reports Server (NTRS)

    Lin, John C.; Jones, Gregory S.; Allan, Brian G.; Westra, Bryan W.; Collins, Scott W.; Zeune, Cale H.

    2010-01-01

    Flow-field measurements were obtained in the wake of a full-span Hybrid Wing Body model with internally blown flaps. The test was performed at the NASA Langley 14 x 22 Foot Subsonic Tunnel at low speeds. Off-body measurements were obtained with a 7-hole probe rake survey system. Three model configurations were investigated. At 0deg angle of attack the surveys were completed with 0deg and 60deg flap deflections. At 10deg angle of attack the wake surveys were completed with a slat and a 60deg flap deflection. The 7-hole probe results further quantified two known swirling regions (downstream of the outboard flap edge and the inboard/outboard flap juncture) for the 60deg flap cases with blowing. Flowfield results and the general trends are very similar for the two blowing cases at nozzle pressure ratios of 1.37 and 1.56. High downwash velocities correlated with the enhanced lift for the 60deg flap cases with blowing. Jet-induced effects are the largest at the most inboard station for all (three) velocity components due in part to the larger inboard slot height. The experimental data are being used to improve computational tools for high-lift wings with integrated powered-lift technologies.

  18. Turbulence Measurements in the Near Field of a Wingtip Vortex

    NASA Technical Reports Server (NTRS)

    Chow, Jim; Zilliac, Greg; Bradshaw, Peter

    1997-01-01

    The roll-up of a wingtip vortex, at Reynolds number based on chord of 4.6 million was studied with an emphasis on suction side and near wake measurements. The research was conducted in a 32 in. x 48 in. low-speed wind tunnel. The half-wing model had a semi-span of 36 in. a chord of 48 in. and a rounded tip. Seven-hole pressure probe measurements of the velocity field surrounding the wingtip showed that a large axial velocity of up to 1.77 U(sub infinity) developed in the vortex core. This level of axial velocity has not been previously measured. Triple-wire probes have been used to measure all components of the Reynolds stress tensor. It was determined from correlation measurements that meandering of the vortex was small and did not appreciably contribute to the turbulence measurements. The flow was found to be turbulent in the near-field (as high as 24 percent RMS w - velocity on the edge of the core) and the turbulence decayed quickly with streamwise distance because of the nearly solid body rotation of the vortex core mean flow. A streamwise variation of the location of peak levels of turbulence, relative to the core centerline, was also found. Close to the trailing edge of the wing, the peak shear stress levels were found at the edge of the vortex core, whereas in the most downstream wake planes they occurred at a radius roughly equal to one-third of the vortex core radius. The Reynolds shear stresses were not aligned with the mean strain rate, indicating that an isotropic-eddy-viscosity based prediction method cannot accurately model the turbulence in the cortex. In cylindrical coordinates, with the origin at the vortex centerline, the radial normal stress was found to be larger than the circumferential.

  19. Spectral coherence in windturbine wakes

    SciTech Connect

    Hojstrup, J.

    1996-12-31

    This paper describes an experiment at a Danish wind farm to investigate the lateral and vertical coherences in the nonequilibrium turbulence of a wind turbine wake. Two meteorological masts were instrumented for measuring profiles of mean speed, turbulence, and temperature. Results are provided graphically for turbulence intensities, velocity spectra, lateral coherence, and vertical coherence. The turbulence was somewhat influenced by the wake, or possibly from aggregated wakes further upstream, even at 14.5 diameters. Lateral coherence (separation 5m) seemed to be unaffected by the wake at 7.5 diameters, but the flow was less coherent in the near wake. The wake appeared to have little influence on vertical coherence (separation 13m). Simple, conventional models for coherence appeared to be adequate descriptions for wake turbulence except for the near wake situation. 3 refs., 7 figs., 1 tab.

  20. Unsteady wake of a rotating tire

    NASA Astrophysics Data System (ADS)

    Lombard, Jean-Eloi; Moxey, Dave; Xu, Hui; Sherwin, Spencer; Sherwin Lab Team

    2015-11-01

    For open wheel race-cars, such as IndyCar and Formula One, the wheels are responsible for 40% of the total drag. For road cars drag associated to the wheels and under-carriage can represent 60% of total drag at highway cruise speeds. Experimental observations have reported two or three pairs of counter rotating vortices, the relative importance of which still remains an open question, that interact to form a complex wake. Traditional RANS based methods are typically not well equipped to deal with such highly unsteady flows which motivates research into more physical, unsteady models. Leveraging a high-fidelity spectral/hp element based method a Large Eddy Simulation is performed to give further insight into unsteady characteristics of the wake. In particular the unsteady nature of both the jetting and top vortex pair is reported as well as the time and length scales associated with the vortex core trajectories. Correlation with experimentally obtained particle image velocimetry is presented. The authors acknowledge support from the United Kingdom Turbulence Consortium (UKTC) as well as from the Engineering and Physical Sciences Research Council (EPSRC) for access to ARCHER UK National Supercomputing Service.